Title of Invention

A METHOD FOR CASTING BILLETS WITH NON DENDRITIC GLOBULAR MICROSTRUCTURE

Abstract

The present invention relates to a mould assembly. More particularly, a device for casting and reheating of metallic alloys in an electromagnetic stirrer to produce billets with non-dendrite globular microstructure comprising mould assembly consisting of; a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and an electromagnetic stirrer circumferentially surrounding the mould assembly. immure 1 and 2

Full Text

FIELD OF THE INVENTION I ‘he present invention relates to a mould assembly. More particularly, a device for casting and reheating of metallic alloys in an electromagnetic stirrer to produce billets with non-dendritic globular microstructure comprising mould assembly consisting of; a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and an electromagnetic stirrer circumfercntially surrounding the mould assembly. BACKGROUND OF THE INVENTION AND PRIOR ART In several applications of casting, dendritic microstructure is not desirable as it results in poor mechanical properties. Enhancing the fluid flow in the mushy zone by stirring (such as electromagnetic stirring) during casting is one of the means to suppress this dendritic growth. The strong fluid flow detaches the dendrites from the solid-liquid interface and carries them into the mould to form slurry. This slurry has a solid phase consisting of fragmented dendrites, instead of the conventional dendritic structure, immersed in liquid. When this slurry solidifies, the microstructure is characterized by non-dendritic primary phase particles, usually in a globular or rosetted form, separated and enclosed by a near-eutectic lower-melting secondary phase. Stirring of the alloy in the liquid state can be done by several methods, such as electromagnetic ally, mechanically or by using ultrasonic vibrations. The existing methods of producing a billet with non-dendritic microstructure can be classified into two categories, namely 'Thixocasting' and 'Recasting'. In the thixocasting operation, billets having non-dendritic microstructure are first produced through a direct chilled (DC) casting operation along with mechanical or electromagnetic stirring. The non-dendritic billet casting is similar to the conventional DC casting process in many ways. However, unlike in a conventional DC casting process, it is also subjected to a stirring (e.g. electromagnetic stirring (EMS)) in order to shear off the dendrites in the mushy zone. In most existing practices of recasting, liquid alloy with a prescribed superheat is poured into a mould, usually made of metal or refractory material. The metal in the mould is stirred until a specified temperature is reached. The resultant stirred slurry is then transferred into a separate mould/container and instantaneously cooled to form a billet. In either method described above, the billet is further reheated in a heat treatment furnace, following the standard heat treatment practice for that particular alloy. After heat treatment the resultant solid attains the desired final semisolid microstructure, which is the preferred microstructure for further processing to form light weight high performance castings. In the conventional processes described above, stirring provides the necessary forces to break the dendrites formed during solidification, which is the first step in creating a non-dendritic microstructure. However, the desired final globular microstructure is obtained only after heat treatment. OBJECTS OF THE INVENTION Fee principal object of the invention is to develop a mould assembly for casting billets with non-dendritic globular microstructure comprising; a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal. Another object of the invention is to develop the refractory tube (2a) which maximizes the effect of electromagnetic forces acting on the liquid metal. Yet another object of the invention is to develop the casing (1) which is made of any nonmagnetic material preferably, stainless steel. Still another object of the invention is to develop the casing (1) which is cooled using coolants selected from a group comprising air, water, and oil. Still another object of the invention is to develop the end cap (2d) which prevents leakage of liquid metal from the mould. Still another object of the invention is to develop the cooling arrangement (2c) having a mould cooling inlet (2c) and a mould cooling outlet (2f). Still another object of the invention is to develop a device for casting billets with non-dendrite globular microstructure comprising; a mould assembly consisting of a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported on the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and to prevent leakage of liquid metal from the mould, a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and an electromagnetic stirrer circumferentially surrounding the mould assembly. Still another object of the invention is to develop the electromagnetic stirrer selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helical electromagnetic stirrer or any other arrangement, which can simultaneously stir and heat the metal. Still another principal object of the invention is to develop a method for casting billets having non-dendritic globular microstructure, said method comprises steps of; pouring liquid metal into a mould; stirring the liquid metal electromagnetically to eliminate dendrites and to form semi-solid slurry; cooling the slurry to obtain solidified billet cast within the same mould; and heating the billet within the mould to obtain billet with globular microstructure. Still another object of the invention is to provide stirring which enables shearing of dendrites formed during the solidification process. Still another object of the invention is to provide for stirring which is performed using electromagnetic stirrer, selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helicoidal electromagnetic stirrer; or any of the combination of above electromagnetic stirrers. Still another object of the invention is to provide the stirring forces developed by exciting the electromagnetic stirrer with a predetermined current and frequency. Still another object of the invention is to provide for stirring as well as the heating of the metal are performed simultaneously by the electromagnetic stirrer. Still another object of the invention is to provide for extraction of heat from the mould in any one or all directions and the solidification advances in a direction opposite to that of heat extraction. S FATEMENT OF HIE INVENTION Accordingly the invention provides for a mould assembly for casting billets with non-dendritic globular micro structure comprising; a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the polling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; a device for casting billets with non-dendritic globular microstructure comprising; a mould assembly consisting of a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported on the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and to prevent leakage of liquid metal from the mould, a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and an electromagnetic stirrer circumferentially surrounding the mould assembly, a method for casting billets having non-dendritic globular microstructure, said method comprises steps of ; pouring liquid metal into a mould; stirring the liquid metal electromagnetically to eliminate dendrites and to form semi-solid slurry; cooling the slurry to obtain solidified billet cast within the same mould; and heating the billet within the mould to obtain billet with globular microstructure. URIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Figure 1: shows section view of mould assembly having casing (1), refractory tube (2a), cooling mould (2b), cooling arrangement (2c), end cap (2d), mould cooling water inlet (2e), mould cooling water outlet (2f). Figure 2: shows the section view of the mould showing mechanism of dendritic shear wherein convective flow (3) in the metal is created by electromagnetic stirrer (3a), braking of dendrites at the phase change interface (4), and heat extraction. Figure 3 (a): shows micrographs for solidification of A356 Alloy poured into the mould and stirrer at 680^C, with no stirring. Figure 3 (b): shows micrographs for solidification of A356 Alloy poured into the mould and stirrer at 680^C with the stirring intensity at 250 A. Figure 3 (c): shows micrographs for solidification of A356 Alloy poured into the mould and stirrer at 680**C, with the stirring intensity 450 A. DF FAILED DESCRIPTION OF THE INVENTION The present invention is in relation to a mould assembly for casting billets with non-dendritic globular micro structure comprising; a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal. In yet another embodiment of the present invention the refractory tube (2a) maximizes the effect of electromagnetic forces acting on the liquid metal. In yet another embodiment of the present invention the casing (1) is made of any nonmagnetic material preferably, stainless steel. In yet another embodiment of the present invention the casing (1) is cooled using coolants selected from a group comprising air, water, and oil. In yet another embodiment of the present invention the end cap (2d) prevents leakage of liquid metal from the mould. In yet another embodiment of the present invention the cooling arrangement (2c) has a mould cooling inlet (2e) and a mould cooling outlet (2f). The present invention is in relation to a device for casting billets with non-dendritic globular microstructure comprising; a mould assembly consisting of a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported on the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and to prevent leakage of liquid metal from the mould, a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and an electromagnetic stirrer circumferentially surrounding the mould assembly. In yet another embodiment of the present invention the refractory tube (2a) maximizes the effect of electromagnetic forces acting on the liquid metal. In yet another embodiment of the present invention the casing (1) is preferably made of a non magnetic material or stainless steel. In yet another embodiment of the present invention the casing (1) is cooled using coolants selected from a group comprising air, water, and oil. In yet another embodiment of the present invention the electromagnetic stirrer is selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helical electromagnetic stirrer or any other arrangement, which can simultaneously stir and heat the metal. In yet another embodiment of the present invention the end cap (2d) prevents leakage of liquid metal from the mould and facilitates extraction of billet. In yet another embodiment of the present invention the cooling arrangement (2c) has a mould cooling inlet (2e) and a mould cooling outlet (2f). The present invention is in relation to a method for casting billets having non-dendritic globular microstructure, said method comprises steps of; pouring liquid metal into a mould; stirring the liquid metal electromagnetically to eliminate dendrites and to form semi-solid slurry; cooling the slurry to obtain solidified billet cast within the same mould; and heating the billet within the mould to obtain billet with globular microstructure. In yet another embodiment of the present invention the stirring enables shearing of dendrites formed during the solidification process. In yet another embodiment of the present invention the stirring is performed using electromagnetic stirrer, selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helicoidally electromagnetic stirrer; or any of the combination of above electromagnetic stirrers. In yet another embodiment of the present invention exciting the electromagnetic stirrer with a predetermined current and frequency develops the stirring forces. In yet another embodiment of the present invention exciting electromagnetic stirrer with a predetermined current and frequency produces the heating in the billet. In yet another embodiment of the present invention the stirring as well as the heating of the metal are performed simultaneously by the electromagnetic stirrer. In yet another embodiment of the present invention the heat is extracted from the mould in any one or all directions and the solidification advances in a direction opposite to that of heat extraction. figure 1 illustrates the side cross section of mould assembly having casing (1), the refractory tube (2a) which maximizes the effect of electromagnetic forces acting on the liquid metal, cooling mould (2b), cooling arrangement (2c), end cap (2d) prevents leakage of liquid metal from the mould, mould cooling water inlet (2e), mould cooling water outlet (2f). figure 2 illustrates the cross section of the mould showing mechanism of dendritic shear, fhe liquid metal at a desired superheat is poured into a mould which is cooled at the bottom depending on the desired cooling rate, either air or water can be used as the cooling medium in the mould entered through mould cooling inlet (2e) and comes out through mould cooling outlet (2f). The alloy is stirred electromagnetically by employing a linear electromagnetic stirrer (LEMS) by creating convective flow (3). In the process of stirring the dendrites/solid particles formed at the interface are sheared and transported into the bulk melt inside the stirrer to form slurry. Due to the specific cooling design of the mould, heat is extracted from and the solidification front advances from the bottom of the mould to the top of the sfirrer to form solidified metal. The linear electromagnetic stirrer can simultaneously stir as well as heat the metal (by induction heating, which can be independently controlled. The same stirrer, when energized with high frequency power without any phase shift in currents, is capable of producing heat without altering average stirring forces. We may therefore excite the stirrer coil with low frequency phase displaced currents to produce the stirring forces and high frequency phase aligned currents to produce heating in the billet. Hence, this stirrer offers flexibility in controlling the cooling rate of the alloy. Stirring will stop once the solid fraction reaches a critical value, usually known as the coherency point. Further cooling of the alloy results in a solidified billet cast inside the stirrer. During solidification, the solid fraction of the slurry is also dynamically monitored by measuring the temperature using a thermocouple placed inside the melt. Even after solidification of the billet is complete as detected by the thermocouple temperature measurement, heating of the billet can be controlled by high-frequency induction heating provided by the same LEMS. Hence, for this heat treatment process, one can tune the input power supply parameters to the stirrer coils to facilitate induction heating suitable for heat treatment. An important feature of the method lies in the fact that the solidified billet can be heat treated without removing it from the mould. Hence, the method described herein is a one-step process to obtain the final micro structure, thus eliminating the need for additional heat treatment. The technology of the instant invention is further elaborated with the help of following example. However, the example should not be construed to limit the scope of the invention. Example: The equipment is tested extensively for aluminum-silicon alloys. However, the method is applicable for all metals and its alloys. Although the method is tested using a linear electromagnetic stirrer, the method is applicable to any other form of electromagnetic stirring. blxtensive laboratory tests using the mould assembly apparatus and procedure have been carried out. The tests have been carried out using A-356 alloy. Some sample results in the form of micrographs are presented in Figure 3(a-c). The case with no stirring yielded dendritic microstructure as shown in fig. 3 (a). The case with a moderate stirring current of 250 A (involving low induction heating) gave rise to reseated structure shown in fig. 3 (b). Figure 3c corresponds to high stirring current of 450 A (resulting in high induction heating as well), yielding globular microstructure Industrial Applicability The disclosed mould assembly for casting billets having non-dendritic globular microstructure comprises of a casing (1) having a cooling mould (2b) at its lower end, a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), an end cap (2d) acting as a base to provide for extraction of the billets, and a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal. The mould assembly is placed in core of the electromagnetic stirrer such that electromagnetic forces acts upon liquid metal poured inside the mould finds potential application in any metal casting process. The disclosed mould assembly finds particular applicability in casting billets. Other industrial advantages includes, eliminates the need to transfer the melt into another container for cooling after the slurry is formed, allows flexibility in terms of controlled heating as well as stirring using one equipment, additional heat treatment equipment is not required to reheat the billet to get the desired microstructure, the method adopted is a one step process of obtaining the desired globular microstructure, and the process saves time and energy. It will be apparent to those skilled in the art that various modifications and variations can be made to the mould assembly of the present disclosure. Other embodiments of the mould will be apparent to those skilled in the art from consideration of the specification of the mould assembly disclosed herein. It is intended that the specification and multiple alternatives be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. We claim: 1. A mould assembly for casting billets with non-dendrite globular microstructure comprising; a. a casing (1) having a cooling mould (2b) at its lower end, b. a refractory tube (2a) placed inside the casing (1) and supported onto the cooling mould (2b), c. an end cap (2d) acting as a base to provide for extraction of the billets, and d. a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal. 2. The mould assembly as claimed in claim 1, wherein the refractory tube (2a) maximizes the effect of electromagnetic forces acting on the liquid metal. 3. The mould assembly as claimed in claim 1, wherein the casing (1) is made of any non-magnetic material preferably, stainless steel. 4. The mould assembly as claimed in claim 1, wherein the casing (1) is cooled using coolants selected from a group comprising air, water, and oil. 5. The mould assembly as claimed in claim 1, wherein the end cap (2d) prevents leakage of liquid metal from the mould. 6. The mould assembly as claimed in claim 1, wherein the cooling arrangement (2c) has a mould cooling inlet (2e) and a mould cooling outlet (2f). 7. A device for casting billets with non-dendrite globular microstructure comprising; a. a mould assembly consisting of i. a casing (1) having a cooling mould (2b) at its lower end, ii. a refractory tube (2a) placed inside the casing (1) and supported on the cooling mould (2b), iii. an end cap (2d) acting as a base to provide for extraction of the billets, and to prevent leakage of liquid metal from the mould. iv. a cooling arrangement (2c) surrounding the cooling mould (2b) to extract heat from molten metal; and b. an electromagnetic stirrer circumferentially surrounding the mould assembly. 8. The device as claimed in claim 7, wherein the refractory tube (2a) maximizes the effect of electromagnetic forces acting on the liquid metal. 9. The device as claimed in claim 7, wherein the casing (1) is preferably made of a non magnetic material or stainless steel. 10. The device as claimed in claim 7, wherein the casing (1) is cooled using coolants selected from a group comprising air, water, and oil. 11. The device as claimed in claim 7, wherein the electromagnetic stirrer is selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helical electromagnetic stirrer or any other arrangement, which can simultaneously stir and heat the metal. 12. The device as claimed in claim 7, wherein the end cap (2d) prevents leakage of liquid metal from the mould and facilitates extraction of billet. 13. The device as claimed in claim 7, wherein the cooling arrangement (2c) has a mould cooling inlet (2e) and a mould cooling outlet (21). 14. A method for casting billets having non-dendrite globular microstructure, said method comprises steps of; a. pouring liquid metal into a mould; b. stirring the liquid metal electro magnetically to eliminate dendrites and to form semi-solid slurry; c. cooling the slurry to obtain solidified billet cast within the same mould; and d. heating the billet within the mould to obtain billet with globular microstructure. 15. The method as claimed in claim 14, wherein said stirring enables shearing of dendrites formed during the solidification process. 16. The method as claimed in claim 14, wherein the stirring is performed using electromagnetic stirrer, selected from a group comprising linear electromagnetic stirrer, rotary electromagnetic stirrer, and helicoidally electromagnetic stirrer; or any of the combination of above electromagnetic stirrers. 17. rhe method as claimed in claim 14, wherein the stirring forces are developed by exciting the electromagnetic stirrer with a predetermined current and frequency. 18. The method as claimed in claim 14, wherein the heating in the billet is produced by exciting electromagnetic stirrer with a predetermined current and frequency. 19. The method as claimed in claim 14, wherein the stirring as well as the heating of the metal are performed simultaneously by the electromagnetic stirrer. 20. The method as claimed in claim 14, wherein the heat is extracted from the mould in any one or all directions and the solidification advances in a direction opposite to that of heat extraction. 21. A mould assembly, a device, and a method for casting billets having non-dendrite globular microstructure as herein described in the description and substantiated along with drawings. A

Documents:

3136-CHE-2007 AMENDED CLAIMS 18-06-2012.pdf

3136-CHE-2007 AMENDED PAGES OF SPECIFICATION 18-06-2012.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS 21-08-2013.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS. 21-08-2013.pdf

3136-CHE-2007 EXAMINATION REPORT REPLY RECEIVED 12-10-2012.pdf

3136-CHE-2007 POWER OF ATTORNEY 21-08-2013.pdf

3136-CHE-2007 POWER OF ATTORNEY 18-06-2012.pdf

3136-CHE-2007 AMENDED CLAIMS 21-08-2013.pdf

3136-CHE-2007 AMENDED CLAIMS 06-07-2012.pdf

3136-CHE-2007 AMENDED CLAIMS 09-07-2012.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS 18-04-2013.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS 06-07-2012.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS 09-07-2012.pdf

3136-CHE-2007 CORRESPONDENCE OTHERS 11-07-2012.pdf

3136-CHE-2007 EXAMINATION REPORT REPLY RECEIVED 18-06-2012.pdf

3136-CHE-2007 FORM-1 18-06-2012.pdf

3136-CHE-2007 FORM-13 18-06-2012.pdf

3136-CHE-2007 FORM-13-1 18-06-2012.pdf

3136-che-2007-abstract.pdf

3136-che-2007-claims.pdf

3136-che-2007-correspondnece-others.pdf

3136-che-2007-description(complete).pdf

3136-che-2007-drawings.pdf

3136-che-2007-form 1.pdf

3136-che-2007-form 18.pdf

3136-che-2007-form 26.pdf

3136-che-2007-form 3.pdf

3136-che-2007-form 5.pdf