Title of Invention

"AN IMPROVED COUNTER GRAVITY CASTING APPARATUS"

Abstract

In the present invention there is provided an improved counter gravity casting apparatus useful for producing near net shaped (NNS) components. The improved counter gravity casting apparatus consists of a vacuum box with a vacuum connection. Inside the vacuum box is an air permeable mold cavity formed by a combination of upper mold and lower mold. The bottom of the lower mold is connected to the top end of the crown of a modified tubular fill tube (MTFT) having novel constructional features, to reach a molten metal bath. In this casting apparatus of the present invention, the molten metal container has been suitably separated by the modified tubular fill tube (MTFT) from the mold having the mold cavity, thus bringing about flexibility in relative positioning between the point of filling and the source of the molten metal and also solving the problem of contamination.

Full Text

The present invention relates to an improved counter gravity casting apparatus. The present invention particularly relates to an improved counter gravity (suction-filling) casting apparatus provided with a Modified Tubular Fill Tube (MTFT). Main usage of this counter gravity casting apparatus and process is for casting of air melting ferrous and non-ferrous alloys. Counter gravity low pressure air melted casting is one of the advanced manufacturing technologies being used to produce near net shaped (NNS) components. Thin walled and net-shaped casting of product through this counter gravity (suction-filling) method is one of the advanced technologies. In this method one can avoid the surface impurities of the molten bath in the finished castings by dipping the fill tube into the clean section of molten metal bath. In this process of counter gravity casting, the sand mould is placed in a sealed chamber with an open snout or fill tube facing down. The chamber is lowered up to a precise distance to dip the fill tube into the melt. Vacuum is applied to siphon the metal up through the fill tube to enable filling every section of a mould cavity instantaneously. In the drawings accompanying this specification figure 1 represents the schematic of a basic mechanism of a vacuum assisted counter gravity casting process, wherein the sand mold, consisting of a porous, gas permeable upper mold (2) and a lower mold (4) member are sealingly engaged in the parting line and the mold assembly is placed inside a vacuum box (1). The top/upper mold (2) is exposed to vacuum line while the under side of the lower/bottom mold (4) is immersed in the liquid metal (6). On application of vacuum, the molten metal (6) is siphoned up from the underlying molten metal bath (6) through in-gates (5) of lower mould (4). As a result the molten metal moves inside the mold cavity (3) without disturbing the molten bath, at a temperature much lower than the temperature of the molten metal currently being used for gravity casting. By this process near net shaped casting (NNS) is possible due to the use of calculated amount of molten metal to fill up the casting cavity. rior art search reference may be made to US patent no. 5,088,546, titled : Vacuum assisted counter gravity casting apparatus with valve to prevent flow of melt from mold. Figure 2 of the drawings accompanying this specification depicts this apparatus, wherein the different parts are: Vacuum box (7), Valve (8), Upper mold (9), Lower mold (10), Inlet (11), Molten metal bath (12) and Mold cavity (13). This casting apparatus for the vacuum-assisted, counter gravity casting of a melt comprises a porous, gas permeable casting mold including a mold cavity and a melt inlet communicating the mold cavity to a lower mold portion adapted to engage an underlying source of melt and a vacuum box defining a vacuum chamber confronting the casting mold for evacuating the mold cavity when the lower mold portion and the underlying source of the melt are engaged. A valve member is disposed on the mold in an open position relative to the melt inlet to permit the melt to be drawn upwardly there through into the mold cavity when the lower mold portion and the source are engaged with the mold cavity evacuated and is movable to a closed position relative to the melt inlet after the mold cavity is filled with the melt to close off the melt inlet to prevent the melt from flowing out of the mold cavity when the lower mold portion and the source are subsequently disengaged. The valve member is movable from the open position to the closed position by a valve moving mechanism carried on the vacuum box. The mold is engaged with the melt source only long enough to fill the mold cavity with the melt to thereby provide a significant reduction in the overall casting cycle time. In the above referred US patent no.5,088,546, regulated amount of molten metal through a valve mechanism is permitted inside the mold cavity. In this method molten metal is contaminated when the lower mold is dipped into the molten metal and the entrapped sand particles reaches into the products as an impurity during subsequent casting. Otherwise also this apparatus has dimensional restrictions to be accommodated in the limited space of a holding furnace. In order to activate the movable parts like plugs, hydraulic or pneumatic actuator has to be placed inside the vacuum box. It restricts the effective utilization of the space available inside the box. Reference may be made to US patent no.5,035,277, titled : Counter gravity casting apparatus. Figure 3 of the drawings accompanying this specification depicts this apparatus, wherein the different parts are: Vacuum box (14), Pick-up member (15), Upper mold (16), Mold cavity (17) and Inlet (18). This casting apparatus comprises a vacuum box having a pair of laterally spaced side walls sealingly engaged to a pair of pick-up members disposed along laterally spaced apart sides of a casting mold. The vacuum box also comprises a pair of spaced end walls sealingly engaged to the casting mold. Sealing engagement of the laterally spaced vacuum box side walls to the pick-up members, rather than to the mold, permits a substantial reduction in the lateral dimension of the mold, thereby substantially reducing the amount of costly mold material (e.g., resin-bonded sand) needed to fabricate the mold for casting and to be disposed of after casting. In the above referred US patent no. 5,035,277, the lower mold is immersed into the molten metal, resulting in the possibility of contamination of liquid bath from erosion of the sand surface. Reference may be made to US patent no. 4,932461, titled : Counter gravity casting apparatus. Figure 4 of the drawings accompanying this specification depicts this apparatus, wherein the different parts are: Vacuum box (19), Mold anchoring (20), Upper mold (21), Lower mold (22), Molten metal bath (23). This patent discloses an apparatus for the vacuum, counter gravity casting of metal in shell molds including a gas permeable shell mold secured to the mouth of a vacuum box by a plurality of keepers on the ends of rotatable shafts reciprocably slidable through the ceiling of the vacuum box, which keepers are adapted for insertion into and rotation within an anchoring cavity in the mold such that the keeper engages a portion of the mold overhanging the cavity to secure the mold to the box. In the above referred US patent no. 4,932461, the special arrangement of the suspension system of the mold box is by a complex mechanical and rotating mechanism. Further, there remains the common problem of possibility of contamination of the molten metal when the lower mold box is dipped into it. The prior art search clearly indicates a common technical problem, that of possibility of contamination. In the hitherto known prior art the possibility of contamination of the molten metal when the lower mold box is dipped into it has been observed. This occurs because the lower mold erodes when it comes in contact with the molten metal volume which results in contamination of the molten metal. Another technical point comes as a hindrance, that is the low flexibility in the possibility of accommodating the molten metal container, say inside a holding furnace due to the rigidness of the mold itself, in size. The main object of the present invention is to provide an improved counter gravity casting apparatus, which obviates the drawbacks of the hitherto known prior art as detailed above. Another object of the present invention is to check the contamination in the molten bath. Still another object of the present invention is that the mold assembly can be used with any type or size of furnace that is with more flexibility of the size of the mold. Yet another object of the present invention is the possibility of interchangeability of the intermediate tubular device connecting the mold to the melt. In the present invention there is provided an improved counter gravity casting apparatus useful for producing near net shaped (NNS) components. The improved counter gravity casting apparatus consists of a vacuum box with a vacuum connection. Inside the vacuum box is an air permeable mold cavity formed by a combination of upper mold and lower mold. The bottom of the lower mold is connected to the top end of the crown of a modified tubular fill tube (MTFT) having novel constructional features, to reach a molten metal bath. In this casting apparatus of the present invention, the molten metal container has been suitably separated by the modified tubular fill tube (MTFT) from the wold having the mold cavity, thus bringing about flexibility in relative positioning between the point of filling and the source of the molten metal and also solving the problem of contamination. In the drawings accompanying this specification the invention has been described and disclosed in figures 5 and 6. Figure 5 represents the assembly of the improved counter gravity casting apparatus of the present invention along with the modified tubular fill tube (MTFT) and figure 6 shows the geometry of the modified tubular fill tube (MTFT) having novel constructional features. The improved counter gravity casting apparatus of the present invention is provided with a vacuum box (25) with a vacuum connection (24). The vacuum connection (24) is through the top cover of the vacuum box (25). Inside the vacuum box (25) is the combination of upper mold (30) and the lower mold (26) forming a mold cavity (31). The bottom of the lower mold (26) is connected with a modified tubular fill tube (MTFT) (27) via Crown (29) which is a specially shaped top portion of the MTFT (27) having novel constructional features. The MTFT (27) reaches the molten metal bath (28). Accordingly the present invention provides an improved counter gravity casting apparatus, which comprises a vacuum box (25) having a vacuum connection (24) through removably fixed top cover of the vacuum box (25), the said vacuum box (25) being provided with a combination of upper mold (30) and lower mold (26) to form an air permeable mold cavity (31), characterized in that the bottom of the said lower mold (26) being connected to a modified tubular fill tube (MTFT) (27) through crown (29) of the MTFT (27) to reach a molten metal bath (28). In an embodiment of the present invention, the upper mold (30) is more permeable to air than the lower mold (26). another embodiment of the present invention, the upper mold (30) is removably fixed on the lower mold (26) and the combination of upper and lower mold is placed inside the vacuum box (25). In yet another embodiment of the present invention, the modified tubular fill tube (MTFT) (27) having an upper portion or a crown (29) is made of shell sand. In still another embodiment of the present invention, the crown (29) portion of the MTFT (27) is embedded in the bottom of the lower mold (26), wherein the immediate vicinity of the lower mold (26) adjacent to the crown (29) is gas impermeable or permeable. In still yet another embodiment of the present invention, the geometry of the internal cross section of the crown (29) of the modified tubular fill tube (MTFT) (27) is different at bottom, middle and upper portions along its height. In a further embodiment of the present invention, the internal cross section of the modified tubular fill tube (MTFT) (27) at the bottom side of the crown portion (29) is circular (AA), gradually changing to elliptical shape (BB) in the middle portion and at the upper portion near the top end of the MTFT (27) is of thin-rectangular (CC) shape. The method of casting using the improved counter gravity casting apparatus of the present invention is described below with reference to figures 5 and 6 of the drawings accompanying this specification. In the present invention sand is used for the upper mold (30) is more permeable to air than that of the lower mold (26). The upper mold (30) is fixed on the lower mold (26) with the help of glue and kept inside the vacuum box (25) The lower mold (26) is fitted with modified tubular fill tube (MTFT) (27) at its bottom. Crown portion (29) of the MTFT (27) is made of shell sand. Geometry of the internal cross section of the crown portion (29) are different at various location along its height. Internal cross section at the bottom side of the crown (29) is circular as shown in the section AA. It gradually changes to an olliptical shape at section BB. The geometry of the in-gate near the top end of the modified tubular fill tube (MTFT) (27) is thin-rectangular in shape as shown in the section CC. Complex geometry of the MTFT (27) ensures smooth entry of metal inside the mold cavity (31). More over the thin-rectangular cross section near the top end of the crown (29) ensures instantaneous chilling of the liquid metal at the end of complete fill up of the mold cavity (31), preventing any back flow of metal from mold. However on the release of vacuum the liquid metal below section AA returns to the molten metal bath (28), resulting in higher yield. The molten metal bath (28) is prepared with the alloy to be used for casting, by heating, and then the MTFT (27) is dipped inside the molten metal bath. Vacuum connection (24) is connected with the vacuum plant, the mold cavity (31) is evacuated through the permeable sand body of the upper mold and this causes the molten metal to reach the mold cavity (31) through the crown (29) of MTFT (27). After a brief holding time the vacuum pump system is discontinued and the MTFT is taken out of the molten metal. Time is allowed for solidification of the molten metal inside the mold cavity (31) and then the product is taken out. The novelty of the improved counter gravity casting apparatus of the present invention lies in the separation of the molten metal container, suitably, from the mold having the mold cavity, bringing about flexibility in the relative positioning between the point of filling and the source of the molten metal. The novel features being elimination of contamination of molten bath due to mold erosion, flexibility in size of the mold assembly with respect to the kind of furnace, ease in casting near-net shaped product for both non-ferrous and ferrous alloys. The novelty of the improved counter gravity casting apparatus of the present invention has been realized by the non-obvious inventive step of providing a modified tubular fill tube (MTFT) having a characteristic internal geometry of cross section of crown portion of the MTFT being different at various location along its height. The internal cross section at the bottom side of the crown is circular. It gradually changes to an elliptical snape and near the top end of the MTFT the geometry is a thin-rectangular cross-section. The thin rectangular cross-section near the top end of the crown of MTFT ensures instantaneous chilling of the liquid metal at the end of complete fill up of the mold cavities. It prevents any back flow of metal from mold. The following examples are given by way of illustration of the improved counter gravity casting apparatus of the present invention in actual practice and should not be construed to limit the scope of the present invention. Example -1 Around 3 kg. of Zinc-alloy having composition: 3.5/4.3 % Al, 0.75 /1.25% Cu, density : 6.76 gm / cc , Volume shrinkage : 1.17% .Melting temperature : 380 ° C , was melted in a crucible. The molten metal was poured in a molten metal bath and placed just below the mold assembly. The fill tube of the mold assembly was dipped to a predetermined height inside the molten metal bath. Then the isolation valve of the vacuum pump was opened to reach at a vacuum level of 466mm of Hg. Within 5 seconds the mold cavity was filled up, as measured by a time-temperature recorder. The volume of the mold cavity was 240 cc. The fill tube was kept inside the molten bath upto 30secs for solidification of the molten metal of the in-gate. After 45 sees the fill tube was taken out from the molten metal bath and vacuum valve was closed down. Excess metal from the fill tube went back to the molten bath. The vacuum box was dismantled and after cooling the mold assembly, it was broken. The weight of the finished casting was 1.675 kg- Example - 2 Approximately 3 kg. of Al-alloy having composition: 12.0% Si, predetermined height inside the molten metal bath. Then the isolation valve of the vacuum pump was opened to reach at a vacuum level of 500 mm of Hg. Within 5 seconds the mold cavity (31) got filled up, as measured by a time-temperature recorder. The volume of the mold cavity (31) was 300 cc. The fill tube was kept inside the molten bath upto 30secs for solidification of the molten metal of the in-gate. After 45 sees the fill tube was taken out from the molten metal bath and vacuum valve was closed down . Excess metal from the fill tube went back to the molten bath. The vacuum box was dismantled and after cooling the mold assembly, it was broken. The weight of the finished casting was 820 grams. The main advantages of the improved counter gravity casting apparatus of the present invention are: 1. Elimination of contamination of molten bath due to mold erosion. 2. Flexibility in size of the mold assembly with respect to the kind of furnace. 3. Near-net shaped product. 4. Ease in casting. 5. Both non-ferrous & ferrous alloys can be used for casting. 6. Automation of process is possible. We claim: 1. An improved counter gravity casting apparatus, which comprises a vacuum box (25) having a vacuum connection (24) through removably fixed top cover of the vacuum box (25), the said vacuum box (25) being provided with a combination of upper mold (30) and lower mold (26) to form an air permeable mold cavity (31), characterized in that the bottom of the said lower mold (26) being connected to a modified tubular fill tube (MTFT) (27) through crown (29) of the MTFT (27) to reach a molten metal bath (28). 2. An improved counter gravity casting apparatus, as claimed in claim 1, wherein the upper mold (30) is more permeable to air than the lower mold (26). 3. An improved counter gravity casting apparatus, as claimed in claim 1-2, wherein the upper mold (30) is removably fixed on the lower mold (26) and the combination of upper and lower mold is placed inside the vacuum box (25). 4. An improved counter gravity casting apparatus, as claimed in claim 1-3, wherein the modified tubular fill tube (MTFT) (27) having an upper portion or a crown (29) is made of shell sand. 5. An improved counter gravity casting apparatus, as claimed in claim 1-4, wherein the crown (29) portion of the MTFT (27) is embedded in the bottom of the lower mold (26), wherein the immediate vicinity of the lower mold (26) adjacent to the crown (29) is gas impermeable or permeable. 6. An improved counter gravity casting apparatus, as claimed in claim 1-5, wherein the geometry of the internal cross section of the crown (29) of the modified tubular fill tube (MTFT) (27) is different at bottom, middle and upper portions along its height. 7. An improved counter gravity casting apparatus, as claimed in claim 1-6, wherein the internal cross section of the modified tubular fill tube (MTFT) (27) at the bottom side of the crown portion (29) is circular (AA), gradually changing to elliptical shape (BB) in the middle portion and at the upper portion near the top end of the MTFT (27) is of thin-rectangular (CC) shape.

Documents:

2089-del-2005-Abstract-(03-10-2012).pdf

2089-del-2005-abstract.pdf

2089-del-2005-Claims-(03-10-2012).pdf

2089-del-2005-claims.pdf

2089-del-2005-Correspondence-Others-(03-10-2012).pdf

2089-del-2005-correspondence-others.pdf

2089-del-2005-description (complete).pdf

2089-del-2005-drawings.pdf

2089-del-2005-form-1.pdf

2089-del-2005-form-18.pdf

2089-del-2005-form-2.pdf

2089-del-2005-Form-3-(03-10-2012).pdf

2089-del-2005-form-3.pdf

2089-del-2005-form-5.pdf