| Title of Invention | IMPROVED PROCESS FOR THE PRODUCTION OF METAL CASTINGS |
|---|---|
| Abstract | An improved process for production of metal castings, id process comprising: (a) placing in a casting mold of shell sand core having the pattern of the metal casting to be produced; (b) introducing molten metal into the casting mold; (c) allowing the molten metal to cool to form the metal casting; and (d) removing the metal casting from the casting mold; characterized by: (i)cutting out portions of the shell sand core corresponding to the portions of the casting having defects, to form shell sand core portions; (ii) dressing each shell sand core portion to the shape of a chill to be produced; (iii) positioning a said shell sand core portion in a casting mold and pouring molten metal into the mold to produce a chill mold; (iv) pouring molten metal into the chill mold to produce a chill; (v) repeating steps (iii) and (iv) for each shell sand core portion to produce chills; (vi) shot blasting the chills by methods known per se to make the surfaces thereof rough; (vii) preheating the chills to about 100 to 150°C; (viii) positioning the chills of step (vii) at appropriate positions in a shell sand core mold mounted in a shell core shooting machine; (ix) injecting resin-sand mixture into the shell sand core mold and curing the mixture to produce a chill core comprising a shell sand core embodying said chills; (x)placing the chill core in said casting mold and thereafter pouring molten metal into the casting mold to produce said metal casting. |
| Full Text | The present invention provides an improved process for production of metal castings such as intake manifold castings. The present practice in foundries is to use a shell sand core for casting. Sand core is a poor conductor of heat. As a result, when molten metal is introduced into the sand core, heat dissipation through the walls of the sand core is very slow. Therefore, molten metal in heavy and isolated casting areas remains hotter for a longer time than in other areas of the casting. This results in shrinkage/porosity problem. In order to solve this problem, the casting area in which shrinkage occurs has to be fed with molten metal from additional feeders, or this area has to be cooled faster. In many cases, it is not possible to use additional feeders or risers. So, in prior art faster cooling, called 'chilling' was adopted. It is also known in the prior art to provide an aluminium paint coating on sand cores where porosity is likely to appear. But this has not been found to be satisfactory. Further, in the case of heavy castings where the section is very heavy, such a method does not solve the problem of porosity. The object of the present invention is to provide a process for production of metal castings which eliminates the occurrence of shrinkage/porosity, especially in heavy- castings. The present invention envisages to eliminate, or at least minimize shrinkage problems in complicate castings in permanent gravity/tilting gravity molds using shell sand cores. Accordingly, the present invention provides an improved process for production of metal castings, said process comprising: (a) placing in a casting mold a shell sand core having the pattern of the metal casting to be produced; (b) introducing molten metal into the casting mold; (c) allowing the molten metal to cool to form the metal casting; and (d) removing the metal casting from the casting mold; characterized by: (i) cutting out portions of the shell sand core corresponding to the portions of the casting having defects, to form shell sand core portions; (ii) dressing each shell sand core portion to the shape of a chill to be produced; (iii) positioning a said shell sand core portion in a casting mold and pouring molten metal into the mold to produce a chill mold; (iv) pouring molten metal into the chill mold to produce a chill; (v) repeating steps (iii) and (iv) for each shell sand core portion to produce chills; (vi) shot blasting the chills by methods known per se to make the surfaces thereof rough; (vii) preheating the chills to about 100 to 150°C; (viii) positioning the chills ofstep (vii) at appropriate positions in a shell core mold mounted in a shell core shooting machine; (ix) injecting resin-sand mixture into the shellsand core mold and curing the mixtureto produce a chill core comprising a shell sand core embodying said chills; (x)placing thechillcore insaid casting mold and thereafter pouring molten metal into the casting mold to produce said metal casting. It is preferableto makethechillsofaluminium, instead of cast iron or steel for the following reasons: (a) Molten aluminium is readily available in the foundry and hence economical; (b) Latent heat of aluminium is 93 cal/g, as compared to latent heat of 63.7 cal/g of iron; so, aluminium chills formed can absorb more heat than iron; (c) Thermal conductivity of Al is 0.5 cal/cm /cm2/S/cc), which is 3 times more than that of iron; so, chilling effect of aluminium chill is three times faster than that of iron chill; (d) The chills can be produced by mass production, with the help of simple molds which are prepared using the casting portion itself as the pattern; The invention will now be described by way of illustration with reference to the accompanying drawings, wherein: Fig. l shows an intake manifold casting with prior art process; Fig. 2 shows shrinkage porosity observed in the casting of Fig. 1; Figs. 3 and 4show close-up view of the shrinkage porosity and air leak in the casting of Fig. 1; Fig. 5 showsa casting having a chillin the area of shrinkage porosity according toafirstembodiment of the present invention; Fig. 6 shows a close-up view of the casting produced by the first embodiment of the present invention; Fig. 7 showsa graph of air leak in a casting without chills and a casting with chills according to the present invention; Fig. 8 shows an intake manifold casting produced by a second embodiment of the method of the present invention; Figs. 9 and 10 show a close-up view of a casting of prior art surrounded by sand core on three sides; Figs. 11 and 12 show close-up views of a casting produced by the second embodiment of Fig. 8; Fig. 13 shows graph ofairleak withoutchills and with chills. Fig. 1 shows an intake manifold produced by known processes. In this case, molten metal is fed from a main riser 1 into a casting mould 2 filled with sand core 3. When the casting is removed from the mould 2, it is observed that there is shrinkage 4.Fig. 2 shows the shrinkage 4 in a greater detail. It is known to apply aluminium paint 5 (Fig. 3) on the sand core at places where the casting is likely to have shrinkage. Even when such aluminium paint is used, in the case of heavy castings or castings of complicated shapes, the shrinkage cannot be eliminated. It is seen from Fig. 4 that when drilling is carried out, air leak (6) is observed. In order to overcome this problem, the present invention proposes use of chills embodied in the shell sand core. First of all a casting is produced by the known processes. Then, the areas of shrinkage porosity in the casting are identified. Thereafter, the shell core portion corresponding to these areas are cut from the shell sand core. Thus, the shell sand core 3 itself is used as the pattern. Each shell core portion is dressed and shaped to the desired shape of the chill to be produced. Each shell core portion should preferably be of a size at least twice the size of the defective area, (preferably two to three times the size of the defective area), so that the chill does not get melted by the molten metal during casting. A shell core portion is placed in a casting mold and metal is poured into the mold. After cooling, the metal solidifies to form a chill mold. The cavity in the chill mold is preferably coated with dycote. Metal is poured into the chill mold and allowed to cool and solidify to form a chill. During pouring, the temperature of the molten metal is preferably kept below 700°C. The chill is removed from the casting mold. Burrs and fleshes on the chill are removed by methods well known in the art. Thereafter, the chill is shotblast by- methods known per se. These steps are repeated for each shell core portion. The chills are then preheated to about 100 to 150°C and placed at appropriate positions in a shell sand core mold of a shell core shooting machine. Resin-sand mixture is injected into the shell core mold and cured to form a chill core comprising shell sand core embodying the chills. The chill core is positioned in the casting mold. Thereafter the molten metal is introduced into the casting mold. After cooling the metal casting is taken out. When the sand is knocked out of the casting mold, the chills also drop out and can be re-used. Figs. 5 and 6, it can be seen that chill core comprises shell sand core 3 with sand core portions 7 corresponding to the identified defective area encast therewith. From Fig. 6, it can be seen that the casting 8 produced does not have any porosity even after drilling operation is carried out. For checking air leak, tapped holes were drilled in the castings produced by known process and the process according to the present invention. From the graph shown in Fig. 7, in the case of a casting made without the use of chill core, it can be seen that the air leak was quite high. But when chill core was used according to the present invention, there was a dramatic elimination of air leak, indicating that the casting had no shrinkage porosity. Fig. 8 shows an intake manifold casting produced with shell sand core 3 on three sides. When no chill core was used, an area 4 having shrinkage porosity was identified. The shrinkage was observed in the casting area formed by sand cores from three sides. This was due to poor conductivity of the sand cores. This caused shrinkage / porosity in the identified area. In Fig. 9, the aluminium casting portion 9 has a central sand core 31 and also sand cores 32, 33 and 34. From Fig. 10, it can be seen that a portion 91 of the casting is surrounded by sand cores 32, 33, 34. Due to poor conductivity of the sand cores, area 4 of shrinkage porosity is formed. This cannot be eliminated even by application of aluminium paint, especially in the case of heavy castings. In order to overcome this problem, chills 7 made as earlier described are encast with the sand cores at the places where porosity is observed. This is shown in Fig. 11. From Fig. 12 is can be seen that porosity is almost eliminated. Air leak tests were carried out on castings produced by known method and castings produced by the method of the present invention. As can be seen from Fig. 13, air leak was high in castings produced by known methods, whereas there was very little air leak in castings produced with chill cores according to the present invention. The present invention is very usefulin producing aluminium castings having complicatedshapeswithno shrinkage or the least shrinkage. In the prior art, shrinkage was a problem. Although use of aluminium paint can be adopted, it cannot fully eliminate the problem of shrinkage porosity. Further use of aluminium paint with alcohol entails higher cost of production. Also, when air-cleaning the mould, aluminium paint particles fly around and form a pollution hazard around the foundry. Further, use of aluminium paint does not solve the problem of shrinkage in heavier castings and castings having complicated shapes. In the present invention, chill cores are used. These have high heat conduction property. As a result, fine grain size is obtained in the castings. In heavier castings, shrinkage can be minimized to a great extent. Also, this eliminates the use of additional feeders or risers and thus greatly reduces the cost of production. Further in certain cases, it may not be possible to provide such additional feeders or risers. In addition, chill cores can be made in the same foundry where the castings are made. Thus the process according to the invention is very economical. In addition, the chills can be taken out of the shell sand core after casting and re-used. Although the chills can be made of any metal having a good thermal conductivity, aluminium chills are preferred. The present invention is very economical for production of aluminium castings of heavy sections or complicated shapes. CLAIM: An improvedprocess forproduction of metal castings, said process comprising: (a) placing in a casting mold of shell sand core having the pattern of the metal casting to be produced; (b) introducing molten metal into the casting mold; (c) allowing the molten metal to cool to form the metal casting; and (d) removing the metal casting from the casting mold; characterized by: (i)cutting out portionsof the shellsand core corresponding to the portionsofthe casting having defects, to form shell sand core portions; (ii) dressing each shell sand core portion to the shape of a chill to be produced; (iii) positioning a said shell sand core portion in a casting mold and pouring molten metal into the mold to produce a chill mold; (iv) pouring molten metal into the chill mold to produce a chill; (v) repeating steps (iii) and (iv) for each shell sand core portion to produce chills; (vi) shot blasting the chills by methods known per se to make the surfaces thereof rough; (vii) preheating the chills to about 100 to 150°C; (viii) positioning thechillsof step (vii)at appropriate positions in a shell sand core mold mounted in a shell core shooting machine; (ix) injecting resin-sand mixture into the shell sand core mold and curing the mixture to produce a chill core comprising a shell sand core embodying said chills; (x)placing the chill core in said casting mold and thereafter pouring molten metal into the casting mold to produce said metal casting. 2. A process as claimed in claim 1, wherein said chills are made of aluminium. 3. A process as claimed in claim 1 or 2, wherein in step (ii), the chills are formed to have a size at least twice, preferably two to three times, the size of the area which is prone to shrinkage porosity. 4. A process as claimedin any ofclaims1to 3, wherein instep (iv), prior to pouring metalintothe chill mold,thecavity in the moldiscoated with dycote. 5. A process as claimed in any of claims 1 to 4, wherein in step (iv), the temperature of the molten metal is maintained below 700°C. 6. A process for the production of metal castings substantially as herein described, particularly with reference to the accompanying drawings. An improved process for production of metal castings, id process comprising: (a) placing in a casting mold of shell sand core having the pattern of the metal casting to be produced; (b) introducing molten metal into the casting mold; (c) allowing the molten metal to cool to form the metal casting; and (d) removing the metal casting from the casting mold; characterized by: (i)cutting out portions of the shell sand core corresponding to the portions of the casting having defects, to form shell sand core portions; (ii) dressing each shell sand core portion to the shape of a chill to be produced; (iii) positioning a said shell sand core portion in a casting mold and pouring molten metal into the mold to produce a chill mold; (iv) pouring molten metal into the chill mold to produce a chill; (v) repeating steps (iii) and (iv) for each shell sand core portion to produce chills; (vi) shot blasting the chills by methods known per se to make the surfaces thereof rough; (vii) preheating the chills to about 100 to 150°C; (viii) positioning the chills of step (vii) at appropriate positions in a shell sand core mold mounted in a shell core shooting machine; (ix) injecting resin-sand mixture into the shell sand core mold and curing the mixture to produce a chill core comprising a shell sand core embodying said chills; (x)placing the chill core in said casting mold and thereafter pouring molten metal into the casting mold to produce said metal casting. |
|---|
| Patent Number | 272502 | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Indian Patent Application Number | 75/CAL/2000 | ||||||||
| PG Journal Number | 15/2016 | ||||||||
| Publication Date | 08-Apr-2016 | ||||||||
| Grant Date | 05-Apr-2016 | ||||||||
| Date of Filing | 14-Feb-2000 | ||||||||
| Name of Patentee | DYNAMATIC TECHNOLOGIES LIMITED | ||||||||
| Applicant Address | 79/7-B, ACHARYA JAGADISH CHANDRA BOSE ROAD, CALCUTTA 700014 | ||||||||
Inventors:
|
|||||||||
| PCT International Classification Number | B22D 15/00 | ||||||||
| PCT International Application Number | N/A | ||||||||
| PCT International Filing date | |||||||||
PCT Conventions:
|
|||||||||