Title of Invention	A DEVICE TO PRODUCE SHAPED CASTINGS AND A METHOD FOR PRODUCING SHAPED CASTINGS USING THE DEVICE
Abstract	A device to produce shaped castings and a method for producing shaped castings using the device A device to produce shaped castings and a method for producing shaped castings using the device by a hollow refractory container, housing a refractory mould at one of its ends, the mould having cavity resembling the shape of the desired casting to be produced at one end of the said refractory container such that the passages provided in the mould for the flow of molten material are open to the hollow space of the refractory container, the refractory container being closed at this end by a refractory plate, the container being filled with a thermit mixture, the refractory container along with the mould, thermit mixture and refractory plate being encapsulated in a metal pipe, the metal pipe being closed nearer the end housing the mould by a metal plate and the whole assembly being capable of rotation about an external axis (0).

Title of Invention

A DEVICE TO PRODUCE SHAPED CASTINGS AND A METHOD FOR PRODUCING SHAPED CASTINGS USING THE DEVICE

Abstract

A device to produce shaped castings and a method for producing shaped castings using the device A device to produce shaped castings and a method for producing shaped castings using the device by a hollow refractory container, housing a refractory mould at one of its ends, the mould having cavity resembling the shape of the desired casting to be produced at one end of the said refractory container such that the passages provided in the mould for the flow of molten material are open to the hollow space of the refractory container, the refractory container being closed at this end by a refractory plate, the container being filled with a thermit mixture, the refractory container along with the mould, thermit mixture and refractory plate being encapsulated in a metal pipe, the metal pipe being closed nearer the end housing the mould by a metal plate and the whole assembly being capable of rotation about an external axis (0).

Full Text	The present invention relates to a device to produce shaped castings by thermit reactions using cen trifugal force and a method for producing shaped castings using the device. The present invention provides particularly an improved device for producing shaped castings from metals, alloys, ceramics and their combinations and a method for producing shaped castings using the device. The shaped castings so produced are useful for many engineering applications. Many commercially adopted casting methods, such as sand casting, investment casting, die casting and centrifugal casting, are useful to produce shaped castings. These methods require a suitable furnace to produce molten material which is subsequently poured or forced into the cavity of a metal or refrectory mould to produce a shaped casting. Thus, these methods consume more power and require separate steps of melting and casting. A.G. Merzhanov et.al. (U.K. patent 1497025, 1978) developed a method to synthesize molten refractory inorganic materials, namely carbides, bo-rides, nitrides and silicides of metals as well as hard alloys, and cast them insitu to produce cylindrical castings in one step without employing a furnace by using thermit reactions. To prevent porosity in the products and to accelerate separation of the products, the method was preferably carried out under conditions of steady rotation and pressurised gaseous medium. 0. Odawara (U.S. Patent 4363832, 1982) developed a method for forming a ceramic, lining layer on the inward surface of a hollow body, such as a pipe, by carrying out thermit reaction under the influence of centrifugal force. Similar method was adopted by O.Odawara and J.Ikeuchi (J.Amer.Ceram.Soc.69(4)C-80-C-81, 1986) to produce ceramic-ceramic composite pipe. Thus, none of the prior art methods is either useful to produce shaped castings in one step without the help of a furnace or intended to produce shaped castings in one step by thermit reactions using centrifugal force. The main object of the present invention is to provide a device to produce shaped castings by thermit reactions using centrifugal force which obviates the drawbacks as detailed above. Another object of the present invention is to provide a method for producing shaped castings utilising the above device. In the drawing, accompanying this specification, fig.l represents schematic illustration of the cross section of the device employed to produce shaped castings according to the present invention. Fig.2. illustrates different shaped castings of iron produced using the device and method of the present invention wherein 2(a) represents an impeller having six radial blades, a central hub and a circular plate on one side, 2 (b) represents an. impeller having six radial blades between two circular plates and attached to a central hub, 2(c) represents a pipe having eight fins on the outer surface, 2(d) represents a pipe having eight fins on the inner surface and 2(e) represents a casting which resembles the shape of a turbine or compressor blade with a solid block at one end. According to the present invention there is provided a device to produce shaped castings by thermit reactions using centrifugal force which consists of a hollow refractory container (1) housing a refractory mould (2) at one of its ends, the mould having cavity resembling the shape of the desired casting to be produced at one end of the said refractory container (1) such that the passages provided in the mould for the flow of molten material are open to the hollow space of the refractory container, the refractory container being closed at this end by a refractory plate (3), the container being filled with a thermit mixture (4), the refractory container along with the mould, thermit mixture and refractory plate being encapsulated in a metal pipe (5), the metal pipe being closed nearer the end housing the mould (2) by a metal plate (6) and the whole assembly being capable of rotation about an external axis (O) by any conventional means. According to another feature of the present invention there is provided a method for producing shaped castings by thermit reactions using centrifugal force using the device as defined above which comprises a) filling the hollow space of the refractory container (1) with the required thermit mixture containing powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts, b) rotating the refractory container (1) about an external axis so that the thermit mixture is pressed against the mould (2) by the centrifugal force in the range of 200 to 1200 G, c) igniting the thermit mixture in the refractory container at least at one point on its free surface to initiate the thermit reaction which propagates through the remaining thermit mixture in the refractory container and the strongly reductive element oxidises to molten metal oxide while the metal oxide reduces to molten metal which gets seperated from the molten metal oxide by centrifugal force and fills the cavity of the refractory mould causing the molten metal oxide to collect outside the mould in the hollow space of the refractory container, d) continuing the rotation of the refractory container for sufficient time to allow the reaction products to solidify and cool by loosing heat to the sourroundings, e) removing the mould, containing the shaped casting, and the solidified metal oxide from the refractory container, fj separating the solidified metal oxide from the shaped casting and refractory mould by conventional method and g) releasing the shaped casting by carefully destroying the refractory mould. In an embodiment of the present invention, a self propagating thermit reaction is carried out by igniting a small portion of a stoichiometric thermit mixture in a refractory container, having a refractory mould at one end, while the refractory container is being rotated about an external axis so that the products of the reaction, which are molten due to the large amount of heat released by the thermit reaction, experience centrifugal force of magnitude sufficient to cause their seperation due to the difference in their densities and to force the denser molten product into the cavity of the refractory mould to fill the mould completely, resulting in the production of a shaped casting after solidification and cooling. In another embodiment of the present invention, one of the products of the thermit reaction is added to the stoichiometric thermit mixture as an inert diluent to lower the temperature of the thermit reaction. In yet another embodiment of the present invention, the stoichiometric thermit mixture is mixed with other elements to produce a casting from other materials such as an alloy. The detailed description of the process steps required to produce shaped castings by the present method is given below. A thermit mixture is prepared by uniformly blending the powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts together with any other material, if desired, in powder form. This is done by mixing the powders in a mechanical mixer, preferably sealed, for 12 to 24 hours. The powders used are preferably of size -325 mesh or finer and baked at about 120 deg.C for 12 to 24 hours. The strongly reductive element can be selected from aluminium, magnesium, zirconium and silicon. However, aluminium is the most prefered reducing element due to lower ignition temperature (approx. 1200 deg. C), easiness in controlling the thermit reaction and easy availability. The reducible metal oxide can be chosen from the oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc and manganese. Any thermit mixture, consisting of a strongly reductive element and a reducible metal oxide, may be used in the present method depending on the material from which the shaped casting is to be produced. However, the heat released by the thermit reaction should be sufficient for the self propagation of the reaction and to raise the products of the reaction to a temperature (called adiabatic temperature) well above their melting points so that the denser product is separated by centrifugal force and cast to desired shape by the present method. If the heat released by the thermit reaction is inadequate to meet the above requirements of the present method, prior heating of the thermit mixture to a suitable temperature is required. Alternatively, thermal boosters such as sodium chlorate and potassium nitrate may be added to the thermit mixture to meet the requirements. If the heat released by the thermit reaction is large so that the adiabatic temperature is equal to or higher than the boiling point of the metallic product of the reaction, the metallic product will be lost by vaporization. This results in the lower yield of the matallic product. In such cases, inert diluents can be added to the thermit mixture to lower the adiabatic temperature so as to minimise or overcome the vaporization loss of the metallic product. However, the quantity of inert diluent added should be such that the adiabatic temperature is lowered below the boiling point of the metallic product, the self propagation of the thermit reaction is retained and the products of the reaction are produced in molten state. One of the products of the thermit reaction can be used as an inert diluent to lower the adiabatic temperature. For example, the effect of addition of an inert diluent, iron or aluminium oxide, to the stoichiometric thermit mixture of iron oxide (Fe203) and aluminium on the adiabatic temperature and self propagation of the reaction is shown in table 1 where the adiabatic temperature is calculated from the principles of thermodynamics. It can be seen that the addition of an inert diluent, iron upto 2.0 moles or aluminium oxide upto 0.6 moles, lowers the adiabatic temperature below the boiling point of the product iron, retains the self propagation of the thermit reaction and the products, namely iron and aluminium oxide, are produced in molten state. Also, when the denser product of the thermit reaction is used as an inert diluent, more quantity of that product is produced in molten state per unit quantity of the thermit mixture having diluent. This helps in the production of a casting larger than the one produced by using the same quantity of the stoichiometric thermit mixture. If, on the other hand, the adiabatic temperature is higher than the boiling or sublimation temperature of the reducible metal oxide of a thermit mixture, the metal oxide will be lost by evaporation or sublimation, respectively, during the thermit reaction. In such cases, the present method should be carried out under high inert gas pressure. In the next step, a refractory mould, having cavity resembling the shape of the desired casting, is fitted closely inside the refractory container at its one end such that the passages, provided in the mould for the flow of molten material, are open to the hollow space of the refractory container. Alternatively, if the mould cannot be accommodated inside the refractory container, it can be fitted to the end of the refractory container by suitable arrangements. The refractory mould and container are prepared from a material, such as graphite, which can withstand high temperature attained in thermit reaction and provide sufficient thermal insulation to the adjoining metal parts to prevent them from overheating before the heat produced by the thermit reaction is lost to the surroundings. It is further required that the material is stable and inert at the temperature attained in the thermit reaction. The refractory mould and container can be prepared by machining or from a suitable refractory by sintering. The moulds can also be prepared from a suitable refractory by lost wax process using procedures developed for investment casting. The refractory container, having the refractory mould, is filled with the prepared thermit mixture. The quantity of thermit mixture accommodated in the hollow space of the refractory container should be sufficient to produce enough quantity of the desired molten product to fill the mould completely. The refractory container is closed at the end, where the refractory mould is located, by a refractory plate and inserted in a suitable metal pipe as shown in fig. 1. The metal pipe is closed by a metal plate at the end, where the refractory plate is located, to support the refractory container and its components during rotation. The metal pipe and plate, should have sufficient strength to withstand the stresses induced in them by the cetrifugal force developed while carrying out the present method. Suitable metals for the pipe and plate include iron, nickel and chromium as well as their alloys. The metal pipe, with the components assembled as above, is rotated at high speed about an external axis so that the thermit mixture is pressed against the mould by the centrifugal force. The speed of rotation should be selected such that the molten products of the thermit reaction experience centrifugal force of magnitude sufficient to cause their separation and force the denser product of the thermit reaction into the cavity of the refractory mould to fill the mould completely. Centrifugal force of from 200 to 1200 G near the mould may be adequate in most of the cases. The thermit reaction is initiated by locally heating the thermit mixture in the refractory container atleast at one point on the free surface of the thermit mixture to or above the ignition temperature. This may be carried out, for example, by bringing an arc, struck between two steel electrodes, in contact with the free surface of the thermit mixture in the refractory container while it is rotating. The reaction, thus initiated, rapidly self propagates through the remaining thermit mixture in the refractory container due to the heat released by the thermit reaction and the reducible metal oxide is reduced to molten metal while the strongly reductive element is oxidised to molten oxide. As the reaction propagates, the molten metal and the molten oxide get separated by the centrifugal force due to the difference in their densities and the molten metal, having higher density, is pushed towards the mould more than the molten oxide. Finally, when the reaction of the thermit mixture in the refractory container is completed, the molten metal fills the cavity of the mould and the molten oxide collects outside the mould in the hollow space of the refractory container. It is desirable to hold the reaction products at a temperature higher than their melting points for a few seconds after the completion of the reaction to ensure complete separation of the products. Usually, the air trapped in the mould and the gases produced during the reaction escape to the atmosphere before the onset of solidification of the reaction products. However, it is desirable to provide small vent holes at appropriate places of the mould for easy escape of the air trapped in the mould. It may also be advantageous to carry out the present method in vacuum to accellarate the removal of gases produced during the reaction. After the completion of the reaction, the rotation of the assembly is continued for sufficient time to allow the reaction products to solidify and cool by loosing heat to the surroundings. The refractory mould, having the shaped casting, and the solidified metal oxide are removed from the refractory container. The metal oxide is separated and the shaped casting of the metal is obtained by carefully destroying the refractory mould. As is understood from the above description, the heat released by the thermit reaction is sufficient to produce the reaction products in molten state. Thus, the present method requires no furnace to produce molten material for casting, thereby minimising the power cinsumption. Also, the desired molten material is synthesized, separated and cast insitu in one step to produce shaped castings by the present method as compared to separate steps of melting and casting required by the commercially adopted casting methods. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example 1 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphitccontainer was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron. The cylindrical iron casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron was 77 wt.% of the expected value. The iron casting was 14.9 mm in diameter and having an average thickness of 2.9 mm. The density of the iron casting was 7.21 g/cm3 which is 91.6% of the theoretical density of iron (7.87 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron. Example 2 : Iron oxide (Fe203) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 16 mm internal diameter, 24 mm outside diameter and 105 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 125 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 1040G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron. The cylindrical iron casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron was 80 wt.% of the expected value. The iron casting was 16 mm in diameter and having an average thickness of 6.7 mm. The density of the iron casting was 6.85 g/cm3 which is 87% of the theoretical density of iron (7.87 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron. Example 3 : Nickel oxide (NiO) and aluminium powders, having size of-325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing l00g of nickel oxide and 24. lg of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of nickel from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 30% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and nickel, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of nickel. The cylindrical nickel casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of nickel was 77 wt.% of the expected value. The nickel casting was 14.9 mm in diameter and having an average thickness of 6 mm. The density of the nickel casting was 6.53 g/cm3 which is 73.5% of the theoretical density of nickel (8.9 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of nickel. Example 4 : Copper oxide (CuO) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 100g of copper oxide and 22.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of copper from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 45% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and copper, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of copper. The cylindrical copper casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of copper was 13 wt.% of the expected value. The copper casting was 14.7 mm in diameter and having an average thickness of 1.6 mm. The density of the copper casting was 7.79 g/cm3 which is 87% of the theoretical density of copper (8.96 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of copper. Example 5 : Iron oxide (Fe2O3), aluminium and iron powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A mixture was prepared from these powders by mixing 50g of iron oxide, 25.4 g of aluminium and 17.5 g of iron in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron aluminide (Fe3Al) from the above mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above mixture so that the green density of the mixture in the container was about 30% of the theoretical density of the stoichiometric mixture. The graphite container, containing the mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron aluminide, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron aluminide. The cylindrical casting of iron aluminide had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron aluminide was 89 wt.% of the expected value. The iron aluminide casting was 14.6 mm in diameter and having an average thickness of 4.6mm. The density of the iron casting was 6.99 g/cm3 which is 104% of the density of iron aluminide (6.70 to 6.72 g/cm3) reported in the literature. Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron aluminide. Example 6 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 8 mm long cylindrical graphite mould, having 15 mm diameter and 5 mm length at one end and 22 mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with six 1.5 mm wide and 3 mm deep radial grooves on the circular flat surface of the end having 15 mm diameter. The grooves were equidistant on the circumference and connected to a 7.5 mm diameter and 5 mm deep axial hole made at that end. This mould was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the radial grooves and the axial hole were open to the hollow space of the graphite container. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and mould, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the mould was housed, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle AL,O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron impeller (15 mm overall diameter and 5 mm width) having six radial blades (each 1.5 mm thick and 3 mm wide), a 7.5 mm diameter central hub and a 2 mm thick circular plate on one side. This casting is shown in fig. 2a. The circular plate had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force. Example 7 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 6.5 mm long cylindrical graphite mould, having 10mm diameter and 3.5mm length at one end and 15mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with six 2 mm wide and 3 mm deep radial grooves on the circular flat surface of the end having 15 mm diameter. The grooves were equidistant on the circumference and connected to a 7.5 mm diameter and 5 mm deep axial hole made at that end. This mould was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the radial grooves and the axial hole were open to the hollow space of the graphite container and the 10 mm diameter cylindrical portion of the mould projected 3 mm from the end of the graphite conainer. The end of the graphite container, where the mould was housed, was closed by a 22 mm diameter and 3 mm thick circular graphite plate having 10 mm diameter hole at the center to accommodate the projecting portion of the mould. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and other components, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron impeller (15 mm overall diameter and 5.5 mm width) having six radial blades (each 2 mm thick and 3 mm wide) between 0.5 and 2 mm thick circular plates and attached to a 7.5 mm diameter central hub. The circular plate with 0.5 mm thickness had a 10 mm diameter central hole. This casting is shown in fig. 2b. The circular plate with 2 mm thickness had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force. Example 8 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 15 mm long cylindrical graphite mould, having 15 mm diameter and 12 mm length at one end and 22 mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with eight 0.5 mm wide and 12 mm long radial grooves on the curved surface of the cylindrical portion having 15 mm diameter. The grooves were equidistant on the curved surface and connected to a 10 mm diameter axial hole, drilled to a depth of 12 mm from the end of that cylindrical portion. The other cylindrical portion, having 22 mm diameter, was provided with a 8 mm diameter axial hole. A cylindrical graphite core, having 8 mm diameter and 15 mm length, was placed inside the mould by introducing it through this hole. The mould, along with the core, was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the annular space, between the mould and the core, and the ends of the radial grooves were open to the hollow space of the graphite container. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and mould, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the mould was housed, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron pipe (8 mm internal diameter, 1 mm thick and 11 mm long) having eight fins (each 0.5 mm thick and 2.5 mm wide) on the outer surface. This casting is shown in fig. 2c. The fins were slightly discontinuous. The pipe had curved surface at the end where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force. Example 9 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 15 mm long cylindrical graphite core, having 13 mm diameter and 11 mm length at one end and 6 mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with eight 0.5 mm wide, 11 mm long and 1.5 mm deep radial grooves on the curved surface of the cylindrical portion having 13 mm diameter. The grooves were equidistant on the curved surface. The other cylindrical portion, having 6 mm diameter, was inserted in a 6 mm diameter axial hole provided in a graphite plate having 15 mm diameter and 3 mm thickness. The graphite plate, along with the core, was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the annular space between the core and the container and the ends of the radial grooves were open to the hollow space of the graphite container. The end of the graphite container, where the graphite plate and the core were housed, was closed by a circular gaphite plate having 24 mm diamter and 3 mm thickness. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and other components, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron pipe (15 mm outside diameter, 1 mm thick and 11 mm long) having eight fins (each 0.5 mm thick and 1.5 mm wide) on the inner surface. This casting is shown in fig.2d. The fins were slightly disontinuous. The casting had curved surface at the end where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force. Example 10 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A cylindrical graphite mould, having 15 mm diameter and 10 mm length, was prepared by machining. A 12 mm wide cavity, resembling the shape of a turbine or a compressor blade, was made from one end along the axis of the mould. The cavity was made to meet a 6 mm wide and 3 mm deep groove provided on the circular flat surface of the other end along the diameter. The mould was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the groove and the cavity were open to the hollow space of the graphite container. The end of the graphite container, where the mould was housed, was closed by a circular gaphite plate having 24 mm diamter and 3 mm thickness. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and other components, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3mm thickness. The end of the mild steel tube, where the circular graphite plate was located , was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron casting (12 mm wide and 7 mm height), which resembled the shape of a turbine or compressor blade, with a solid block (6 mm wide, 15 mm long and 3 mm thick) at one end. This casting is shown in fig. 2e. The solid block of the casting had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force. The method for producing shaped castings by thermit reactions using centrifugal force has been demonstrated by these examples wherein the castings were produced from pure metals and an alloy without employing a furnace. Also, the molten materials were synthesized and cast insitu in one step. The present method can also be employed to produce different shaped castings from other metals, alloys and materials, not covered in these examples, using suitable thermit mixtures and additives. TABLE 1 (Table Removed) Tm = Melting point of A12O3 Tb = boiling point of Fe * determined by igniting compacts of powder mixtures The main advantages of the present invention are : 1. simplicity, 2.shorter processing time, 3. lower energy consumption as no furnace is required to produce molten material and 4. the molten material is synthesized and cast insitu in one step. WE CLAIM : 1. A device to produce shaped castings by thermit reactions using centrifugal force which consists of a hollow refractory container (1) housing a refractory mould (2) at one of its ends, the mould having cavity resembling the shape of the desired casting to be produced at one end of the said refracto ry container (1) such that the passages provided in the mould for the flow of molten material are open to the hollow space of the refractory container, the refractory container being closed at this end by a refractory plate (3), the container being filled with a thermit mixture (4), the refractory container along with the mould, thermit mixture and refractory plate being encapsulated, in a metal pipe (5) , the metal pipe being closed nearer the end housing the mould (2) by a metal plate (6) and the whole assembly being capable of rotation about an external axis (0). 2. A method for producing shaped castings by thermit reac tions using centrifugal force using the device as defined above which comprises a) filling the hollow space of the refractory container (1) with the required thermit mixture containing powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts, b) rotating the refractory container (1) about an external axis so that the thermit mixture is pressed against the mould (2) by the centrifugal force in the range of 200 to 1200 G, c) igniting the thermit mixture in the refractory container at least at one point on its free surface to initiate the thermit reaction which propagates through the remaining thermit mixture in the refractory container and the strongly reductive element oxidises to molten metal oxide while the metal oxide reduces to molten metal which gets separated from the molten metal oxide by centrifugal force and fills the cavity of the refractory mould causing the molten metal oxide to collect outside the mould in the hollow space of the refractory container, d) continuing the rotation of the refractory container for sufficient time to allow the reaction products to solidify and. cool by loosing heat to the sourroundings, e) removing the mould, containing the shaped casting, and the solidified metal oxide from the refractory container, f) separating the solidified metal oxide from the shaped casting and refractory mould by conventional method and g) releasing the shaped casting by ceirefully destroying the refractory mould. 3. A method as claimed in claim 2 wherein the strongly reductive element is selected from aluminium, magnesium, zirconium and silicon and the reducible metal oxide is selected from the oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc and manganese. 4. A method as claimed in claims 2 and 3 wherein the refractory container is rotated about an axis so that the thermit mixture is pressed against the mould by the centrifugal force of from 200 to 1200 G. 5. A method as claimed in claims 2 to 4 wherein the rotation of the refractory container is continued for a period in the range of 10 to 45 minutes to allow the reaction products to solidify and cool by loosing heat to the surroundings. 6. The method as claimed in claims 2 to 5 wherein an inert diluent is added to the thermit mixture in an amount such that the adiabatic temperature is lowered, the self propagation of the reaction is retained and the products of the reaction are in molten state. 7. A method as claimed in claim 5 wherein either iron or aluminium oxide, one of the products of the thermit reaction, is added in an amount upto 2.0 or 0.6 moles, respec- tively, to the thermit mixture, containing stoichiometric amounts of iron oxide and aluminium, as an inert diluent. 8. A method for producing shaped castings by thermit reactions using centrifugal force substantially as herein described with reference to the examples. 9. A device to produce shaped castings by thermit reactions using centrifugal force substantially as herein described with reference to the examples and drawing accompanying this specification.

Full Text

The present invention relates to a device to produce shaped castings by thermit reactions using cen trifugal force and a method for producing shaped castings using the device.
The present invention provides particularly an improved device for producing shaped castings from metals, alloys, ceramics and their combinations and a method for producing shaped castings using the device. The shaped castings so produced are useful for many engineering applications.
Many commercially adopted casting methods, such as sand casting, investment casting, die casting and centrifugal casting, are useful to produce shaped castings. These methods require a suitable furnace to produce molten material which is subsequently poured or forced into the cavity of a metal or refrectory mould to produce a shaped casting. Thus, these methods consume more power and require separate steps of melting and casting. A.G. Merzhanov et.al. (U.K. patent 1497025, 1978) developed a method to synthesize molten
refractory inorganic materials, namely carbides, bo-rides, nitrides and silicides of metals as well as hard alloys, and cast them insitu to produce cylindrical castings in one step without employing a furnace by using thermit reactions. To prevent porosity in the products and to accelerate separation of the products, the method was preferably carried out under conditions of steady rotation and pressurised gaseous medium. 0. Odawara (U.S. Patent 4363832, 1982) developed a method for forming a ceramic, lining layer on the inward surface of a hollow body, such as a pipe, by carrying out thermit reaction under the influence of centrifugal force. Similar method was adopted by O.Odawara and J.Ikeuchi (J.Amer.Ceram.Soc.69(4)C-80-C-81, 1986) to produce ceramic-ceramic composite pipe. Thus, none of the prior art methods is either useful to produce shaped castings in one step without the help of a furnace or intended to produce shaped castings in one step by thermit reactions using centrifugal force.
The main object of the present invention is to provide a device to produce shaped castings by thermit reactions using centrifugal force which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a method for producing shaped castings utilising the above device.
In the drawing, accompanying this specification, fig.l represents schematic illustration of the cross section of the device employed to produce shaped castings according to the present invention. Fig.2. illustrates different shaped castings of iron produced using the device and method of the present invention wherein 2(a) represents an impeller having six radial blades, a central hub and a circular plate on one side, 2 (b) represents an. impeller having six radial blades between two circular plates and attached to a central hub,
2(c) represents a pipe having eight fins on the outer surface,
2(d) represents a pipe having eight fins on the inner surface and
2(e) represents a casting which resembles the shape of a turbine or compressor blade with a solid block at one end.
According to the present invention there is provided a device to produce shaped castings by thermit reactions using centrifugal force which consists of a
hollow refractory container (1) housing a refractory mould (2) at one of its ends, the mould having cavity resembling the shape of the desired casting to be produced at one end of the said refractory container (1) such that the passages provided in the mould for the flow of molten material are open to the hollow space of the refractory container, the refractory container being closed at this end by a refractory plate (3), the container being filled with a thermit mixture (4), the refractory container along with the mould, thermit mixture and refractory plate being encapsulated in a metal pipe (5), the metal pipe being closed nearer the end housing the mould (2) by a metal plate (6) and the whole assembly being capable of rotation about an external axis (O) by any conventional means.
According to another feature of the present invention there is provided a method for producing shaped castings by thermit reactions using centrifugal force using the device as defined above which comprises
a) filling the hollow space of the refractory container (1) with the required thermit mixture containing powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts,
b) rotating the refractory container (1) about an external axis so that the thermit mixture is pressed against the mould (2) by the centrifugal force in the range of 200 to 1200 G,
c) igniting the thermit mixture in the refractory container at least at one point on its free surface to initiate the thermit reaction which propagates through the remaining thermit mixture in the refractory container and the strongly reductive element oxidises to molten metal oxide while the metal oxide reduces to molten metal which gets seperated from the molten metal oxide by centrifugal force and fills the cavity of the refractory mould causing the molten metal oxide to collect
outside the mould in the hollow space of the refractory container,
d) continuing the rotation of the refractory container for sufficient time to allow the reaction products to solidify and cool by loosing heat to the sourroundings,
e) removing the mould, containing the shaped casting, and the solidified metal oxide from the refractory container,
fj separating the solidified metal oxide from the shaped casting and refractory
mould by conventional method and g) releasing the shaped casting by carefully destroying the refractory mould.
In an embodiment of the present invention, a self propagating thermit reaction is carried out by igniting a small portion of a stoichiometric thermit mixture in a refractory container, having a refractory mould at one end, while the refractory container is being rotated about an external axis so that the products of the reaction, which are molten due to the large amount of heat released by the thermit reaction, experience centrifugal force of magnitude sufficient to cause their seperation due to the difference in their densities and to force the denser molten product into the cavity of the refractory mould to fill the mould completely, resulting in the production of a shaped casting after solidification and cooling.
In another embodiment of the present invention, one of the products of the thermit reaction is added to the stoichiometric thermit mixture as an inert diluent to lower the temperature of the thermit reaction.
In yet another embodiment of the present invention, the stoichiometric thermit mixture is mixed with other elements to produce a casting from other materials such as an alloy.
The detailed description of the process steps required to produce shaped castings by the present method is given below.
A thermit mixture is prepared by uniformly blending the powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts together with any other material, if desired, in powder form. This is done by mixing the powders in a mechanical mixer, preferably sealed, for 12 to 24 hours. The powders used are preferably of size -325 mesh or finer and baked at about 120 deg.C for 12 to 24 hours. The strongly reductive element can be selected from aluminium, magnesium, zirconium and silicon. However, aluminium is the most prefered reducing element due to lower ignition temperature (approx. 1200 deg. C), easiness in controlling the thermit reaction and easy availability. The reducible metal oxide can be chosen from the oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc and manganese.
Any thermit mixture, consisting of a strongly reductive element and a reducible metal oxide, may be used in the present method depending on the material from which the shaped casting is to be produced. However, the heat released by the thermit reaction should be sufficient for the self propagation of the reaction and to raise the products of the reaction to a temperature (called adiabatic temperature) well above their melting points so that the denser product is separated by centrifugal force and cast to desired shape by the present method. If the heat released by the thermit reaction is inadequate to meet the above requirements of the present method, prior heating of the thermit mixture to a suitable temperature is required. Alternatively, thermal boosters such as sodium chlorate and potassium nitrate may
be added to the thermit mixture to meet the requirements. If the heat released by the thermit reaction is large so that the adiabatic temperature is equal to or higher than the boiling point of the metallic product of the reaction, the metallic product will be lost by vaporization. This results in the lower yield of the matallic product. In such cases, inert diluents can be added to the thermit mixture to lower the adiabatic temperature so as to minimise or overcome the vaporization loss of the metallic product. However, the quantity of inert diluent added should be such that the adiabatic temperature is lowered below the boiling point of the metallic product, the self propagation of the thermit reaction is retained and the products of the reaction are produced in molten state. One of the products of the thermit reaction can be used as an inert diluent to lower the adiabatic temperature. For example, the effect of addition of an inert diluent, iron or aluminium oxide, to the stoichiometric thermit mixture of iron oxide (Fe203) and aluminium on the adiabatic temperature and self propagation of the reaction is shown in table 1 where the adiabatic temperature is calculated from the principles of thermodynamics. It can be seen that the addition of an inert diluent, iron upto 2.0 moles or aluminium oxide upto 0.6 moles, lowers the adiabatic temperature below the boiling point of the product iron, retains the self propagation of the thermit reaction and the products, namely iron and aluminium oxide, are produced in molten state. Also, when the denser product of the thermit reaction is used as an inert diluent, more quantity of that product is produced in molten state per unit quantity of the thermit mixture having diluent. This helps in the production of a casting larger than the one produced by using the same quantity of the stoichiometric thermit mixture. If, on the other hand, the adiabatic temperature is higher than the boiling or sublimation temperature of the reducible metal oxide of a thermit mixture, the metal oxide will be lost by evaporation or sublimation, respectively, during the thermit reaction. In such cases, the present method should
be carried out under high inert gas pressure.
In the next step, a refractory mould, having cavity resembling the shape of the desired casting, is fitted closely inside the refractory container at its one end such that the passages, provided in the mould for the flow of molten material, are open to the hollow space of the refractory container. Alternatively, if the mould cannot be accommodated inside the refractory container, it can be fitted to the end of the refractory container by suitable arrangements. The refractory mould and container are prepared from a material, such as graphite, which can withstand high temperature attained in thermit reaction and provide sufficient thermal insulation to the adjoining metal parts to prevent them from overheating before the heat produced by the thermit reaction is lost to the surroundings. It is further required that the material is stable and inert at the temperature attained in the thermit reaction. The refractory mould and container can be prepared by machining or from a suitable refractory by sintering. The moulds can also be prepared from a suitable refractory by lost wax process using procedures developed for investment casting.
The refractory container, having the refractory mould, is filled with the prepared thermit mixture. The quantity of thermit mixture accommodated in the hollow space of the refractory container should be sufficient to produce enough quantity of the desired molten product to fill the mould completely.
The refractory container is closed at the end, where the refractory mould is located, by a refractory plate and inserted in a suitable metal pipe as shown in fig. 1. The metal pipe is closed by a metal plate at the end, where the refractory plate is located,
to support the refractory container and its components during rotation. The metal pipe and plate, should have sufficient strength to withstand the stresses induced in them by the cetrifugal force developed while carrying out the present method. Suitable metals for the pipe and plate include iron, nickel and chromium as well as their alloys.
The metal pipe, with the components assembled as above, is rotated at high speed about an external axis so that the thermit mixture is pressed against the mould by the centrifugal force. The speed of rotation should be selected such that the molten products of the thermit reaction experience centrifugal force of magnitude sufficient to cause their separation and force the denser product of the thermit reaction into the cavity of the refractory mould to fill the mould completely. Centrifugal force of from 200 to 1200 G near the mould may be adequate in most of the cases.
The thermit reaction is initiated by locally heating the thermit mixture in the refractory container atleast at one point on the free surface of the thermit mixture to or above the ignition temperature. This may be carried out, for example, by bringing an arc, struck between two steel electrodes, in contact with the free surface of the thermit mixture in the refractory container while it is rotating. The reaction, thus initiated, rapidly self propagates through the remaining thermit mixture in the refractory container due to the heat released by the thermit reaction and the reducible metal oxide is reduced to molten metal while the strongly reductive element is oxidised to molten oxide. As the reaction propagates, the molten metal and the molten oxide get separated by the centrifugal force due to the difference in their densities and the molten metal, having higher density, is pushed towards the mould more than the
molten oxide. Finally, when the reaction of the thermit mixture in the refractory container is completed, the molten metal fills the cavity of the mould and the molten oxide collects outside the mould in the hollow space of the refractory container. It is desirable to hold the reaction products at a temperature higher than their melting points for a few seconds after the completion of the reaction to ensure complete separation of the products. Usually, the air trapped in the mould and the gases produced during the reaction escape to the atmosphere before the onset of solidification of the reaction products. However, it is desirable to provide small vent holes at appropriate places of the mould for easy escape of the air trapped in the mould. It may also be advantageous to carry out the present method in vacuum to accellarate the removal of gases produced during the reaction.
After the completion of the reaction, the rotation of the assembly is continued for sufficient time to allow the reaction products to solidify and cool by loosing heat to the surroundings. The refractory mould, having the shaped casting, and the solidified metal oxide are removed from the refractory container. The metal oxide is separated and the shaped casting of the metal is obtained by carefully destroying the refractory mould.
As is understood from the above description, the heat released by the thermit reaction is sufficient to produce the reaction products in molten state. Thus, the present method requires no furnace to produce molten material for casting, thereby minimising the power cinsumption. Also, the desired molten material is synthesized, separated and cast insitu in one step to produce shaped castings by the present method as compared to separate steps of melting and casting required by the commercially adopted casting methods.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example 1 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to
allow the products of the reaction to solidify and cool. The graphitccontainer was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron. The cylindrical iron casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron was 77 wt.% of the expected value. The iron casting was 14.9 mm in diameter and having an average thickness of 2.9 mm. The density of the iron casting was 7.21 g/cm3 which is 91.6% of the theoretical density of iron (7.87 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron.
Example 2 : Iron oxide (Fe203) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 16 mm internal diameter, 24 mm outside diameter and 105 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 125 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel
tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 1040G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron. The cylindrical iron casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron was 80 wt.% of the expected value. The iron casting was 16 mm in diameter and having an average thickness of 6.7 mm. The density of the iron casting was 6.85 g/cm3 which is 87% of the theoretical density of iron (7.87 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron.
Example 3 : Nickel oxide (NiO) and aluminium powders, having size of-325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing l00g of nickel oxide and 24. lg of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately
stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of nickel from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 30% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and nickel, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of nickel. The cylindrical nickel casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of nickel was 77 wt.% of the
expected value. The nickel casting was 14.9 mm in diameter and having an average thickness of 6 mm. The density of the nickel casting was 6.53 g/cm3 which is 73.5% of the theoretical density of nickel (8.9 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of nickel.
Example 4 : Copper oxide (CuO) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 100g of copper oxide and 22.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of copper from the above thermit mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 45% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the
remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and copper, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of copper. The cylindrical copper casting had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of copper was 13 wt.% of the expected value. The copper casting was 14.7 mm in diameter and having an average thickness of 1.6 mm. The density of the copper casting was 7.79 g/cm3 which is 87% of the theoretical density of copper (8.96 g/cm3). Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of copper.
Example 5 : Iron oxide (Fe2O3), aluminium and iron powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A mixture was prepared from these powders by mixing 50g of iron oxide, 25.4 g of aluminium and 17.5 g of iron in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A hollow cylindrical graphite container, having 15 mm internal diameter, 24 mm outside diameter and 40 mm length, itself was used as a refractory mould to produce a cylindrical casting of iron aluminide (Fe3Al) from the above mixture. One end of the graphite container was closed using 24 mm diameter and 3 mm thick circular graphite plate. The graphite container was filled with the above mixture so that the green density of the mixture in the container was about
30% of the theoretical density of the stoichiometric mixture. The graphite container,
containing the mixture, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3mm thickness. The end of the mild steel tube, where the circular graphite plate of the refractory container was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 15 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of cylindrical castings of A12O3 and iron aluminide, attached to each other. The brittle A12O3 casting was separated to obtain the desired cylindrical casting of iron aluminide. The cylindrical casting of iron aluminide had curved surface at the end where it was attached to the oxide co-product. The curved surface represents the interface between the molten products separated by the centrifugal force. The yield of iron aluminide was 89 wt.% of the expected value. The iron aluminide casting was 14.6 mm in diameter and having an average thickness of 4.6mm. The density of the iron casting was 6.99 g/cm3 which is 104% of the density of iron aluminide (6.70 to 6.72 g/cm3) reported in the literature. Microscopic observation revealed porosity in the casting. X-ray analysis showed that the desired casting was made of iron aluminide. Example 6 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was
prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 8 mm long cylindrical graphite mould, having 15 mm diameter and 5 mm length at one end and 22 mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with six 1.5 mm wide and 3 mm deep radial grooves on the circular flat surface of the end having 15 mm diameter. The grooves were equidistant on the circumference and connected to a 7.5 mm diameter and 5 mm deep axial hole made at that end. This mould was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the radial grooves and the axial hole were open to the hollow space of the graphite container. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and mould, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the mould was housed, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the
products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle AL,O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron impeller (15 mm overall diameter and 5 mm width) having six radial blades (each 1.5 mm thick and 3 mm wide), a 7.5 mm diameter central hub and a 2 mm thick circular plate on one side. This casting is shown in fig. 2a. The circular plate had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force.
Example 7 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A 6.5 mm long cylindrical graphite mould, having 10mm diameter and 3.5mm length at one end and 15mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with six 2 mm wide and 3 mm deep radial grooves on the circular flat surface of the end having 15 mm diameter. The grooves were equidistant on the circumference and connected to a 7.5 mm diameter and 5 mm deep axial hole made at that end. This mould was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the radial grooves and the axial hole were open to the hollow space of the graphite container and the 10 mm diameter cylindrical portion of the mould projected 3 mm from the end of the graphite conainer. The end of the
graphite container, where the mould was housed, was closed by a 22 mm diameter
and 3 mm thick circular graphite plate having 10 mm diameter hole at the center to
accommodate the projecting portion of the mould. The hollow space of the graphite
container was filled with the above thermit mixture so that the green density of the
thermit mixture in the container was about 25% of the theoretical density of the
stoichiometric thermit mixture. The graphite container, containing the thermit
mixture and other components, was placed inside a 50 mm long mild steel tube
having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel
tube, where the circular graphite plate of the refractory container was located, was
closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild
steel tube. The mild steel tube, with other components thus assembled, was rotated
at 2840 rpm about an external axis so that the closed end of the graphite container
experienced a centrifugal force of 425G. The thermit reaction was initiated by
bringing the free surface of the thermit mixture in the graphite container in contact
with an electric arc, struck between two mild steel electrodes. The reaction, thus
initiated, propagated itself rapidly through the remaining thermit mixture in the
graphite container and was completed in two to three seconds. The rotation of the
assembly was continued for 20 more minutes to allow the products of the reaction
to solidify and cool. The graphite container was removed from the steel tube and the
products were released from the graphite container. The products consisted of a
cylindrical casting of A12O3 and a shaped casting of iron, attached to each other.
The brittle A12O3 casting was separated and the desired shaped casting of iron was
obtained by carefully destroying the graphite mould. The shaped casting produced
was an iron impeller (15 mm overall diameter and 5.5 mm width) having six radial
blades (each 2 mm thick and 3 mm wide) between 0.5 and 2 mm thick circular
plates and attached to a 7.5 mm diameter central hub. The circular plate with 0.5
mm thickness had a 10 mm diameter central hole. This casting is shown in fig. 2b.
The circular plate with 2 mm thickness had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force.
Example 8 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh,
were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was
prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium
in a sealed double cone blender for 12 hours. The mixing ratio was approximately
stoichiometric. A 15 mm long cylindrical graphite mould, having 15 mm diameter
and 12 mm length at one end and 22 mm diameter and 3 mm length at the other
end, was prepared by machining. It was provided with eight 0.5 mm wide and 12
mm long radial grooves on the curved surface of the cylindrical portion having 15
mm diameter. The grooves were equidistant on the curved surface and connected
to a 10 mm diameter axial hole, drilled to a depth of 12 mm from the end of that
cylindrical portion. The other cylindrical portion, having 22 mm diameter, was
provided with a 8 mm diameter axial hole. A cylindrical graphite core, having 8 mm
diameter and 15 mm length, was placed inside the mould by introducing it through
this hole. The mould, along with the core, was inserted at one end of a graphite
container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length,
such that the annular space, between the mould and the core, and the ends of the
radial grooves were open to the hollow space of the graphite container. The hollow
space of the graphite container was filled with the above thermit mixture so that the
green density of the thermit mixture in the container was about 25% of the theoretical
density of the stoichiometric thermit mixture. The graphite container, containing
the thermit mixture and mould, was placed inside a 50 mm long mild steel tube
having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel
tube, where the mould was housed, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron pipe (8 mm internal diameter, 1 mm thick and 11 mm long) having eight fins (each 0.5 mm thick and 2.5 mm wide) on the outer surface. This casting is shown in fig. 2c. The fins were slightly discontinuous. The pipe had curved surface at the end where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force.
Example 9 : Iron oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture was prepared from these powders by mixing 200g of iron oxide and 67.6g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately
stoichiometric. A 15 mm long cylindrical graphite core, having 13 mm diameter
and 11 mm length at one end and 6 mm diameter and 3 mm length at the other end, was prepared by machining. It was provided with eight 0.5 mm wide, 11 mm long and 1.5 mm deep radial grooves on the curved surface of the cylindrical portion having 13 mm diameter. The grooves were equidistant on the curved surface. The other cylindrical portion, having 6 mm diameter, was inserted in a 6 mm diameter axial hole provided in a graphite plate having 15 mm diameter and 3 mm thickness. The graphite plate, along with the core, was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm outer diameter and 40 mm length, such that the annular space between the core and the container and the ends of the radial grooves were open to the hollow space of the graphite container. The end of the graphite container, where the graphite plate and the core were housed, was closed by a circular gaphite plate having 24 mm diamter and 3 mm thickness. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and other components, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3 mm thickness. The end of the mild steel tube, where the circular graphite plate was located, was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the
assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron pipe (15 mm outside diameter, 1 mm thick and 11 mm long) having eight fins (each 0.5 mm thick and 1.5 mm wide) on the inner surface. This casting is shown in fig.2d. The fins were slightly disontinuous. The casting had curved surface at the end where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force.
Example 10 : Iron oxide (Fe2O3) and aluminium powders, having size of -325
mesh, were dried in an electric oven at 120 deg.C for 24 hours. A thermit mixture
was prepared from these powders by mixing 200g of iron oxide and 67.6g of
aluminium in a sealed double cone blender for 12 hours. The mixing ratio was
approximately stoichiometric. A cylindrical graphite mould, having 15 mm diameter
and 10 mm length, was prepared by machining. A 12 mm wide cavity, resembling
the shape of a turbine or a compressor blade, was made from one end along the axis
of the mould. The cavity was made to meet a 6 mm wide and 3 mm deep groove
provided on the circular flat surface of the other end along the diameter. The mould
was inserted at one end of a graphite container, having 15 mm inner diameter, 24 mm
outer diameter and 40 mm length, such that the groove and the cavity were open to
the hollow space of the graphite container. The end of the graphite container, where
the mould was housed, was closed by a circular gaphite plate having 24 mm diamter
and 3 mm thickness. The hollow space of the graphite container was filled with the above thermit mixture so that the green density of the thermit mixture in the container was about 25% of the theoretical density of the stoichiometric thermit mixture. The graphite container, containing the thermit mixture and other components, was placed inside a 50 mm long mild steel tube having 24.5 mm inside diameter and 3mm thickness. The end of the mild steel tube, where the circular graphite plate was located , was closed by fixing a 24 mm diameter and 12 mm thick mild steel plate inside the mild steel tube. The mild steel tube, with other components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of 425G. The thermit reaction was initiated by bringing the free surface of the thermit mixture in the graphite container in contact with an electric arc, struck between two mild steel electrodes. The reaction, thus initiated, propagated itself rapidly through the remaining thermit mixture in the graphite container and was completed in two to three seconds. The rotation of the assembly was continued for 20 more minutes to allow the products of the reaction to solidify and cool. The graphite container was removed from the steel tube and the products were released from the graphite container. The products consisted of a cylindrical casting of A12O3 and a shaped casting of iron, attached to each other. The brittle A12O3 casting was separated and the desired shaped casting of iron was obtained by carefully destroying the graphite mould. The shaped casting produced was an iron casting (12 mm wide and 7 mm height), which resembled the shape of a turbine or compressor blade, with a solid block (6 mm wide, 15 mm long and 3 mm thick) at one end. This casting is shown in fig. 2e. The solid block of the casting had curved surface at the place where it was attached to the oxide coproduct. The curved surface represents the interface between the molten products separated by the centrifugal force.
The method for producing shaped castings by thermit reactions using centrifugal force has been demonstrated by these examples wherein the castings were produced from pure metals and an alloy without employing a furnace. Also, the molten materials were synthesized and cast insitu in one step. The present method can also be employed to produce different shaped castings from other metals, alloys and materials, not covered in these examples, using suitable thermit mixtures and additives.
TABLE 1
(Table Removed)
Tm = Melting point of A12O3 Tb = boiling point of Fe * determined by igniting compacts of powder mixtures
The main advantages of the present invention are : 1. simplicity, 2.shorter processing time, 3. lower energy consumption as no furnace is required to produce molten material and 4. the molten material is synthesized and cast insitu in one step.

WE CLAIM :
1. A device to produce shaped castings by thermit reactions
using centrifugal force which consists of a hollow refractory
container (1) housing a refractory mould (2) at one of its
ends, the mould having cavity resembling the shape of the
desired casting to be produced at one end of the said refracto
ry container (1) such that the passages provided in the mould
for the flow of molten material are open to the hollow space of
the refractory container, the refractory container being closed
at this end by a refractory plate (3), the container being
filled with a thermit mixture (4), the refractory container
along with the mould, thermit mixture and refractory plate
being encapsulated, in a metal pipe (5) , the metal pipe being
closed nearer the end housing the mould (2) by a metal plate
(6) and the whole assembly being capable of rotation about an
external axis (0).
2. A method for producing shaped castings by thermit reac
tions using centrifugal force using the device as defined
above which comprises
a) filling the hollow space of the refractory container (1) with the required thermit mixture containing powders of a strongly reductive element and a reducible metal oxide in stoichiometric amounts,
b) rotating the refractory container (1) about an external
axis so that the thermit mixture is pressed against the
mould (2) by the centrifugal force in the range of 200 to
1200 G,
c) igniting the thermit mixture in the refractory container
at least at one point on its free surface to initiate the
thermit reaction which propagates through the remaining
thermit mixture in the refractory container and the strongly
reductive element oxidises to molten metal oxide while the
metal oxide reduces to molten metal which gets separated
from the molten metal oxide by centrifugal force and fills
the cavity of the refractory mould causing the molten metal
oxide to collect outside the mould in the hollow space of
the refractory container,
d) continuing the rotation of the refractory container for sufficient time to allow the reaction products to solidify and. cool by loosing heat to the sourroundings,
e) removing the mould, containing the shaped casting, and the solidified metal oxide from the refractory container,
f) separating the solidified metal oxide from the shaped casting and refractory mould by conventional method and
g) releasing the shaped casting by ceirefully destroying the
refractory mould.
3. A method as claimed in claim 2 wherein the strongly
reductive element is selected from aluminium, magnesium,
zirconium and silicon and the reducible metal oxide is
selected from the oxides of iron, nickel, copper, tungsten,
titanium, molybdenum, vanadium, chromium, niobium, zinc and
manganese.
4. A method as claimed in claims 2 and 3 wherein the refractory container is rotated about an axis so that the thermit mixture is pressed against the mould by the centrifugal force of from 200 to 1200 G.
5. A method as claimed in claims 2 to 4 wherein the rotation of the refractory container is continued for a period in the range of 10 to 45 minutes to allow the reaction products to solidify and cool by loosing heat to the surroundings.

6. The method as claimed in claims 2 to 5 wherein an inert diluent is added to the thermit mixture in an amount such that the adiabatic temperature is lowered, the self propagation of the reaction is retained and the products of the reaction are in molten state.
7. A method as claimed in claim 5 wherein either iron or aluminium oxide, one of the products of the thermit reaction, is added in an amount upto 2.0 or 0.6 moles, respec-
tively, to the thermit mixture, containing stoichiometric amounts of iron oxide and aluminium, as an inert diluent.
8. A method for producing shaped castings by thermit reactions using centrifugal force substantially as herein described with reference to the examples.
9. A device to produce shaped castings by thermit reactions using centrifugal force substantially as herein described with reference to the examples and drawing accompanying this specification.

Documents:

1869-del-1997-abstract.pdf

1869-del-1997-claims.pdf

1869-del-1997-complete specification (granted).pdf

1869-del-1997-correspondence-others.pdf

1869-del-1997-correspondence-po.pdf

1869-del-1997-description (complete).pdf

1869-del-1997-drawings.pdf

1869-del-1997-form-1.pdf

1869-del-1997-form-19.pdf

1869-del-1997-form-2.pdf

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Patent Number

237418

Indian Patent Application Number

1869/DEL/1997

PG Journal Number

01/2010

Publication Date

01-Jan-2010

Grant Date

21-Dec-2009

Date of Filing

04-Jul-1997

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	RAJAIYENGAR SESHADRI	NATIONAL AEROSPACE LABORATORIES, KODIHALLI, BANGALORE-560 017,INDIA.

PCT International Classification Number

B22D 13/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA