Europaisches Patentamt J European Patent Office 0 Publication number: 0 677 346 A2 Office europeen des brevets

EUROPEAN PATENT APPLICATION

0 Application number: 95104952.7 int. Ci.6; B22D 17/24, B22D 29/00, B22C 9/10 0 Date of filing: 03.04.95

0 Priority: 13.04.94 JP 74995/94 0 Applicant: Masaru, Nemoto 12.05.94 JP 98556/94 1867-1, Showa-cho 09.06.94 JP 127669/94 Isesaki-shi, 22.07.94 JP 171181/94 Gunma-ken (JP) 05.12.94 JP 300951/94 05.12.94 JP 301126/94 0 Inventor: Masaru, Nemoto 1867-1, Showa-cho 0 Date of publication of application: Isesaki-shi, 18.10.95 Bulletin 95/42 Gunma-ken (JP)

0 Designated Contracting States: AT BE CH DE DK ES FR GB GR IE IT LI LU MC 0 Representative: Muller-Bore & Partner NL PT SE Patentanwalte Grafinger Strasse 2 D-81671 Munchen (DE)

0 Casting method using core made of synthetic , core made of synthetic resin, and cast product.

0 A core 10 made of a synthetic resin is set in dies, and the dies are filled with a molten metal. The molten metal is cooled by the dies, whereby a cast product 12 including the synthetic resin core 10 is obtained. Totally heating the cast product 12, a projecting portion 10a of the synthetic resin core 10 is caught and pulled, whereby the synthetic resin core 10 is drawn in a semi-molten state out of the cast product 12. F I G. I

CM < CO 00

CO

Rank Xerox (UK) Business Services (3. 10/3.09/3.3.4) 1 EP 0 677 346 A2 2

The present invention relates to a casting ing the cast product and the synthetic resin core to method using a core made of a synthetic resin, the draw the synthetic resin core in a semi-molten core made of a synthetic resin, and a cast product, state out of the cast product, and thereby forming and more particularly to a casting method by which an inner space in the cast product. a cast product of a complicated shape can be 5 A second feature of the present invention is a formed easily and precisely, the core made of a casting method using a synthetic resin core, which synthetic resin, and the cast product. comprises: In casting for forming a cast product, a non- a step of placing the synthetic resin core in collapsible core or a collapsible core is used to dies; form an inner space and an undercut portion. In io a step of filling the dies in which the synthetic this case, a metal core is used as a non-collapsible resin core is placed, with a molten metal; core, but it cannot be used in applications other a step of cooling the molten metal by the dies than those which allow direct draw or deformation to form a cast product; and draw. Therefore, its application range is limited to a step of taking the cast product and the specific shapes. 75 synthetic resin core out of the dies, and thereafter On the other hand, a sand core has generally heating the cast product and the synthetic resin been used as a collapsible core, which had various core in a furnace to melt the synthetic resin core problems that molding was difficult, that handling then to remove the synthetic resin core out of the was difficult because it was easily collapsed, and cast product. that it was difficult to satisfy reciprocal conditions 20 A third feature of the present invention is a between pressure resistance in casting and col- casting method using a synthetic resin core, which lapsibility after cast. comprises: Then, there is a recent suggestion that a spe- a step of placing the synthetic resin core in cial coating is applied to the surface of sand core, dies; but it has a big problem that the coating ingredient 25 a step of filling the dies in which the synthetic permeates a cast product to cause negative effects resin core is placed, with a molten metal; such as porosities in the cast product, which is a step of cooling the molten metal by the dies likely to be defective. to form a cast product; and As described above, the application range of a step of taking the cast product and synthetic metal core is limited to specific shapes, while the 30 resin core out of the dies and thereafter immersing sand core is apt to be collapsed and handling the cast product and the synthetic resin core in a thereof is thus difficult. Further, where the sand solvent to dissolve the synthetic resin core out of core is coated with a coating, there are problems the cast product. that the coating ingredient permeates the cast A fourth feature of the present invention is a product to produce porosities in the cast product 35 core made of a synthetic resin. and that it is difficult to remove the coating and A fifth feature of the present invention is a core sand core ingredients from the cast product after made of a synthetic resin, which comprises a core cast. body made of a heat-resistant synthetic resin and The present invention has been accomplished having a space inside thereof. taking the above points into account, and an object 40 A sixth feature of the present invention is a of the invention is to provide a casting method core for forming a die cast product, to be set in a using a core made of a synthetic resin, by which a cavity in die casting dies, wherein the core for die cast product of a complicated shape can be ac- casting comprises: curately formed and by which the core can be a synthetic resin portion extending in the cavity drawn in a smooth manner from the cast product 45 of the dies; and after cast, the core made of a synthetic resin, and a metal portion connected to the synthetic res- the cast product. in portion, provided at an end portion in the cavity A first feature of the present invention is a of the dies and at a position corresponding to an casting method using a synthetic resin core, which end thick portion of the cast product, and projec- comprises: 50 ting outwardly from the cavity. a step of placing the synthetic resin core in A seventh feature of the present invention is a dies; core for forming a die cast product, to be set in a a step of filling the dies in which the synthetic cavity in die casting dies, wherein the core for die resin core is placed, with a molten metal; casting has a synthetic resin portion arranged to a step of cooling the molten metal by the dies 55 extend in the cavity of the dies, wherein a metal to form a cast product; and buried portion is buried at a position in the syn- a step of taking the cast product and the thetic resin portion, corresponding to an inside synthetic resin core out of the dies, thereafter heat- thick portion of the cast product.

2 3 EP 0 677 346 A2 4

An eighth feature of the present invention is a Fig. 1 is a partial, sectional view to show a core cast product having an inner space, which is cast made of a synthetic resin and a cast product to by the method as set forth in Claim 1 . represent a first embodiment of the present inven- According to the first feature, the cast product tion. can be accurately formed using the synthetic resin 5 Fig. 2 is a plan view to show the core made of core and after cast, the core can be removed out of the synthetic resin and the cast product shown in the cast product without having scraps of core in Fig. 1. the cast product, simply by heating the cast prod- Fig. 3 is a plan view to show a core drawing uct and drawing the synthetic resin core in the apparatus for the core made of the synthetic resin. semi-molten state. io Fig. 4 is a schematic drawing to show an According to the second feature, the synthetic aluminum die casting apparatus. resin core is melted in the furnace to be removed Fig. 5 is a sectional view to show the place- out of the cast product. ment of the synthetic resin core and the cast According to the third feature, the synthetic product in a stationary die and a movable die. resin core can be dissolved out of the cast product is Fig. 6 is a drawing to show a modification of in a solvent. the core. According to the fourth feature, the core can be Fig. 7 is a drawing to show a modification of removed out of the cast product without leaving the core. scraps of core in the cast product, simply by Fig. 8 is a drawing to show a modification of heating the cast product after cast and drawing the 20 the core. synthetic core in the semi-molten state. Fig. 9 is a partial, sectional view to show a core According to the fifth feature, the cast product made of a synthetic resin and a cast product to can be accurately formed by using the synthetic represent a second embodiment of the present resin core consisting of the core body made of the invention. heat-resistant synthetic resin and having a space 25 Fig. 1 0A is a sectional view to show the place- inside, and the core can be removed out of the ment of a synthetic resin core and a cast product cast product without leaving scraps of core in the in a stationary die and a movable die. cast product, simply by heating the cast product Fig. 1 0B is a sectional view to show the place- after cast and drawing the synthetic resin core in ment of a synthetic resin core and a cast product the semi-molten state. Since the core body made 30 in a stationary die and a movable die. of the synthetic resin has a space inside, the Fig. 11A is a partial, sectional view of the material costs can be reduced. synthetic resin core. According to the sixth feature, the core is set in Fig. 1 1 B is a partial, sectional view of the the cavity and is filled with the molten metal. Since synthetic resin core. the metal portion is provided at the cavity end 35 Fig. 12 is a partial, sectional view of a die portion and at the position corresponding to the casting apparatus and a core made of a synthetic end thick portion of the cast product, there is no resin to represent a third embodiment of the imbalance between an amount of heat conduction present invention. from the molten metal to the dies and an amount of Fig. 13 is a sectional view to show a die cast heat conduction from the molten metal to the metal 40 product and a core made of a synthetic resin. portion of core at the position corresponding to the Fig. 14 is a perspective view to show a die cast end thick portion, thereby preventing shrinkage at product and a core made of a synthetic resin to the end thick portion of the cast product. show another embodiment of the present invention. According to the seventh feature, the core is Fig. 15 is a sectional view of the die cast set in the cavity and is filled with the molten metal. 45 product and the synthetic resin core shown in Fig. Since the metal buried portion is buried at the 14. position corresponding to the inside thick portion of Fig. 16 is a partial, sectional view to show a the synthetic resin portion, there is no imbalance core made of a synthetic resin and a cast product between an amount of heat conduction from the to represent a fourth embodiment of the present molten metal to the dies and an amount of heat 50 invention. conduction from the molten metal to the metal Fig. 17 is a plan view to show the synthetic buried portion of core at the position corresponding resin core and the cast product shown in Fig. 16. to the inside thick portion, thereby preventing Fig. 18 is a plan view to show a core drawing shrinkage at the inside thick portion of the cast apparatus for synthetic resin core. product. 55 Fig. 19 is a sectional view to show the place- According to the eighth feature, casting can be ment of a synthetic resin core and a cast product done without leaving scraps of core in the inner in a stationary die and a movable die. space.

3 5 EP 0 677 346 A2 6

Fig. 20 is a drawing to show a method for of it, the polycarbonate core 10 could be melted removing a residual part of core remaining in an near the thick portion 12a. Therefore, the coating of internal space of a cast product by shot blast. the silicone rubber 1 1 can prevent melting of poly- Fig. 21 is a drawing to show a method for carbonate core 10. removing a residual part of core remaining in an 5 A core drawing apparatus is next described internal space in a cast product by high-tempera- referring to Fig. 3. As shown in Fig. 3, the core ture and high-pressure steam. drawing apparatus has a locking device 20 for Fig. 22 is a drawing to show a method for locking the cast product 12 after cast, and a burner removing a residual part of core remaining in an 27 for heating the cast product 12 locked by the internal space in a cast product by a solvent. io locking device 20. An engagement pin 21 to be Fig. 23 is a drawing to show a state in which a engaged with a hollow portion 12b of cast product cast product and a core made of a synthetic resin 12 (Fig. 1 and Fig. 2) is fixed in the locking device are set in a furnace. 20. Also, as shown in Fig. 3, a clamp device 30 for First Embodiment is clamping and pulling the projecting portion 10a of core 10 projecting from the cast product 12 is The first embodiment of the present invention provided beside the locking device 20. This clamp will be described with reference to the drawings. device 30 has a pair of holding pawls 22, 22 Fig. 1 to Fig. 5 are drawings to show an arranged as rockable through rocking shafts 23, 23 embodiment of the present invention. First, the 20 on a frame 28, and this pair of holding pawls 22, 22 scheme of an aluminum die casting apparatus is hold the projecting portion 10a of core. Namely, the described referring to Fig. 4. As shown in Fig. 4, pair of holding pawls 22, 22 are connected to each the aluminum die casting apparatus is provided other through a connecting shaft 25, and are ac- with a steel, stationary die 41 fixed to a stationary tuated to be closed when a pneumatic cylinder not platen 40 and a steel, movable die 43 fixed to a 25 shown pulls the connecting shaft 25 in the direction movable platen 42, and is so arranged that when of arrow L in Fig. 3. the stationary die 41 and movable die 43 are The frame 28 is arranged to be moved in the brought into close fit, a cavity 45 is formed be- horizontal directions in Fig. 3 through a drive shaft tween the two dies. 31 driven by a hydraulic cylinder not shown, and A cylinder 50 is provided on the opposite side 30 the horizontal movement of the frame 28 is guided to the stationary die 41 in the stationary platen 40, by a pair of guides 32, 32. and a piston 51 is slidably arranged in the cylinder The operation of the present embodiment in 50. The cylinder 50 is provided with an input port the above arrangement is next described. First, in 53 through which molten aluminum is put into the Fig. 4, the synthetic resin core 10 is set at a cylinder. 35 predetermined position in the stationary die 41 , and The inside of cylinder 50 communicates thereafter the movable platen 42 and movable die through a sprue 48 with the cavity 45 formed 43 are moved toward the stationary platen 40 and between the stationary die 41 and the movable die stationary die 41 to make the movable die 43 43, and a gate 46 is provided at an exit of sprue 48 closely fit with the stationary die 41. In this case, on the cavity 45 side. 40 the cavity 45 is formed between the stationary die A synthetic resin core 10 is set in the cavity 45 41 and the movable die 43 whereby the core 10 is formed between the stationary die 41 and the mov- set in the cavity 45. able die 43, and an aluminum cast product 12 is Next, molten aluminum 55 at about 680 °C is formed with this synthetic resin core 10 (Fig. 1 and put into the cylinder 50 through the input port 53 Fig. 2). 45 thereof and then the molten aluminum 55 is push- The synthetic resin core 10 is next described ed toward the sprue 48 by the piston 51. The referring to Fig. 1 and Fig. 2. In Fig. 1 and Fig. 2, molten aluminum 55 entering the sprue 48 is in- the synthetic resin core 10 is made of a synthetic jected through the gate 46 into the cavity 45 to fill resin, for example of heat-resistant polycarbonate, a space formed by the stationary die 41, movable and the synthetic resin core 10 has a projecting 50 die 43, and core 10 (Fig. 5). The molten aluminum portion 10a which slightly projects from the cast 55 flowing from the gate 46 into the cavity 45 is product 12 after cast. sprayed, and the temperature thereof becomes Out of the surface of the synthetic resin core about 600 ° C. 10, a portion corresponding to (or in contact with) a Next, the molten aluminum 55 filled in the thick portion 12a of the cast product 12 is coated 55 cavity 45 is rapidly cooled by the stationary die 41 with silicone rubber 11 having strong heat resis- and movable die 43 to form the aluminum cast tance. The thick portion 12a of cast product 12 is a product 12. portion where an escape of heat is slow. Because

4 7 EP 0 677 346 A2 8

During this period, heat transfer occurs also another core. from the molten aluminum 55 to the synthetic resin As described above, according to the present core 10 of polycarbonate. However, because the embodiment, the aluminum cast product 12 can be thermal conductivity of the synthetic resin core 10 formed easily and accurately by using the syn- is normally far smaller than that of the steel station- 5 thetic resin core 10 of polycarbonate. The core 10 ary die 41 and movable die 43 (for example, the can be removed from the cast product 12 without thermal conductivity of polycarbonate is 4.6 x 10_+ any residual scraps of core in the cast product 12 cal/s«cm°C while the thermal conductivity of iron simply by heating the cast product 12 after cast is 0.18 cal/s«cm°C), an amount of heat transfer and drawing the synthetic resin core 10 in the from the molten aluminum 55 to the synthetic resin io semi-molten state. core 10 becomes extremely small. Thus, the syn- Modifications of the present invention will be thetic resin core 10 is not melted during casting, described in the following. and the cast product 12 excellent in accuracy of The above embodiment showed an example in shape can be formed accordingly. which the silicone rubber was applied to the sur- The synthetic resin core 10 will not be melted 15 face of polycarbonate core 10 located near the even with slow escape of heat from the thick por- thick portion 12a of cast product 12, but the sili- tion 12a, because the surface of the synthetic resin cone rubber may be replaced by a thermosetting core 10 near the thick portion 12a of cast product resin selected for example from melamine , 12 is coated with very-high-temperature-resistant phenol resins, urea resins, resins, silicon silicone rubber 1 1 . 20 resins, resins, etc. Next, the movable die 43 is separated from the Also, the above embodiment showed an exam- stationary die 41, and the aluminum cast product ple in which the synthetic resin core 10 was the 12 and synthetic resin core 10 are taken together polycarbonate core, but, without a need to be limit- out of the cavity 45 formed between the stationary ed to it, the synthetic resin core 10 may be one die 41 and the movable die 43 (Fig. 1 and Fig. 2). 25 consisting of a thermoplastic inner resin 56a and a Next, the cast product 12 and synthetic resin heat-resistant resin 56b covering the entire surface core 10 are set on the locking device 20 shown in of the inner resin 56a, as shown in Fig. 6. Fig. 3. In this case, the hollow portion 12a of cast In this case, the thermoplastic inner resin 56a product 12 is engaged with the engagement pin 21 may be selected from fluororesins (poly- of locking device 20 to be fixed there. 30 fluoroethylene resins) such as ethylene Then the cast product 12 is totally heated by tetrafluoride, polyimide resins, polyamideimide res- the burner 27 to heat the synthetic resin core 10 of ins, polysulfone resins, vinyl chloride resins, polycarbonate up to about 280 to 350 °C. Since polyamide resins (nylon resins), polypropylene res- the softening point of polycarbonate is 160 °C and ins, polyethylene resins, polyester resins (Tetron the melting point thereof is 380 to 400 °C, the 35 resins), or polysulfonic acid resins. whole of core 10 turns into a semi-molten state The heat resistant resin 56b covering the entire when the synthetic resin core 10 is heated up to surface of the inner resin 56a may be the silicone about 280 to 350 °C. Out of the synthetic resin rubber as described previously, or a silicon resin. core 10, the projecting portion 10a is not heated so Further, the synthetic resin core 10 may be much so as to be kept in a hard state. 40 made of a material obtained by mixing particles Then the frame 28 of clamp device 30 is totally 57a of a thermoplastic resin such as a poly- moved toward the cast product 12 and thereafter propylene resin with particles 57b of a heat-resis- the pair of holding pawls 22, 22 hold the projecting tant resin such as a silicon resin, as shown in Fig. portion 10a of the synthetic resin core 10. In this 7, and baking the mixture to harden. Also, the state the entire frame 28 is moved away from the 45 synthetic resin core 10 may be made of a material cast product 12 by the drive shaft 31. In this case, obtained by mixing the polypropylene resin par- the synthetic resin core 10 inside the cast product ticles with either calcium carbonate particles, cal- 12, being semi-molten, is integrally drawn rightward cium sulfate particles, or calcium silicate particles, in Fig. 3 from the cast product 12. and baking the mixture to harden. After that, the cast product 12 is taken out of 50 Further, a biodegradable plastic may be used the locking device 20. Since the synthetic resin for the synthetic resin core 10. Here, the biodeg- core 10 is integrally drawn in the semi-molten state radable plastic means a plastic which is decom- from the cast product 12, no scraps of core will posed into low-molecular-weight compounds giving remain in the inner space 18 of cast product 12 no negative effects to the environment, in nature in (Fig. 22). Accordingly, the cast product 12 can be 55 connection with microorganisms. shipped as a final product as it is. On the other The biodegradable plastic can be classified hand, the synthetic resin core 10 drawn from the into the complete degradation type and partial deg- cast product 12 is collected for reuse to form radation type. The complete degradation type plas-

5 9 EP 0 677 346 A2 10 tic may include plastics of naturally-occurring poly- The cylinder 50 is provided on the opposite mers consisting of a complex of starch and modi- side to the stationary die 41 in the stationary platen fied polyvinyl alcohol, starch and polycaprolactone, 40, and the piston 51 is slidably arranged in the or chitosan and cellulose; fermentation product cylinder 50. The cylinder 50 is provided with the plastics consisting of a microorganism-produced 5 input port 53 through which molten aluminum is put polyester or a microorganism-derived cellulose; into the cylinder. and synthetic plastics consisting of an aliphatic The inside of cylinder 50 communicates polyester. The partial degradation type plastic may through the sprue 48 with the cavity 45 formed include plastics of a mixture of starch in polyethyl- between the stationary die 41 and the movable die ene, and alloys of polycaprolactone and a general- io 43, and the gate 46 is provided at an exit of sprue purpose plastic. 48 on the cavity 45 side. When the biodegradable plastic core is used, The synthetic resin core 10 as described below the core can be readily discarded after cast. is set in the cavity 45 formed between the station- In another modification, as shown in Fig. 8, the ary die 41 and the movable die 43, and the alu- synthetic resin core 10 may be composed of a first 15 minum cast product 12 is formed with this syn- member 60a and a second member 60b removably thetic resin core 10 (Fig. 9). attached to the first member 60. In this case, the The synthetic resin core 10 is next described synthetic resin core 10 is assembled by inserting a referring to Fig. 9, Fig. 10, and Figs. 11A and 11B. projection 61 of the second member 60b into an In Fig. 9, the synthetic resin core 10 consists of a insert hole formed in the first member 60a. As in 20 core body 70 in which a space 71 is formed. The this modification, a cast product 12 with a com- core body 70 is made of a synthetic resin, for plicated shape can be readily formed by assem- example of impact-resistant and heat-resistant bling the core 10 with the first member 60a and polycarbonate, and the synthetic resin core 10 has second member 60b. the projecting portion 10a which slightly projects In the above embodiment the aluminum die 25 from the cast product 12 after cast. casting method was described as a die casting Out of the surface of the synthetic resin core method, but the casting method of the present body 70, a portion corresponding to (or in contact invention can be applied to any other die casting with) the thick portion 12a of the cast product 12 is methods, such as the gravity die casting method, coated with silicone rubber 11 having strong heat the low pressure die casting method, and the preci- 30 resistance. The thick portion 12a of cast product 12 sion die casting method. Further, the cast product is a portion where an escape of heat is slow. may be not only of aluminum, but also of lead, Because of it, the polycarbonate core body 70 zinc, magnesium, manganese or an alloy thereof. could be melted near the thick portion 12a. There- As described above, according to the present fore, the coating of the silicone rubber 11 can invention, the cast product can be formed with high 35 prevent melting of polycarbonate core body 70. accuracy using the synthetic resin core and the The synthetic resin core 10 is further described core can be readily removed from the cast product below referring to Fig. 10A and Fig. 11 A. As shown without remaining scraps of core in the cast prod- in Fig. 10A and Fig. 11 A, the synthetic resin core uct after cast. Therefore, the cast product excellent 10 consists of the polycarbonate core body 70 in in accuracy of shape can be quickly formed. 40 which the space 71 is formed, and the core body 70 has a predetermined thickness so as to have a Second Embodiment strength sufficient to stand injection of molten alu- minum as detailed later. The second embodiment of the present inven- As shown in Fig. 10A and Fig. 11 A, an amount tion will be described with reference to the draw- 45 of the expensive polycarbonate material can be ings. reduced by making the synthetic resin core 10 of Fig. 9 to Figs. 11A and 1 1 B are drawings to the polycarbonate core body 70 with the space 71 show the second embodiment of the present inven- formed therein. tion. Same portions as those in the first embodi- As shown in Fig. 3, the core drawing apparatus ment are described with the same reference nu- 50 has the locking device 20 for locking the cast merals. As shown in Fig. 4, the aluminum die product 12 after cast, and the burner 27 for heating casting apparatus is provided with the steel, sta- the cast product 12 locked by the locking device tionary die 41 fixed to the stationary platen 40 and 20. The engagement pin 21 to be engaged with the the steel, movable die 43 fixed to the movable hollow portion 12b of cast product 12 (Fig. 9) is platen 42, and is so arranged that when the station- 55 fixed in the locking device 20. ary die 41 and movable die 43 are brought into Also, as shown in Fig. 3, the clamp device 30 close fit, the cavity 45 is formed between the two for clamping and pulling the projecting portion 10a dies, similarly as in the first embodiment. of core 10 projecting from the cast product 12 is

6 11 EP 0 677 346 A2 12 provided beside the locking device 20. This clamp tion 12a, because the surface of the synthetic resin device 30 has a pair of holding pawls 22, 22 core 10 near the thick portion 12a of cast product arranged as rockable through the rocking shafts 23, 12 is coated with very-high-temperature-resistant 23 on the frame 28, and this pair of holding pawls silicone rubber 1 1 . 22, 22 hold the projecting portion 10a of core. 5 Next, the movable die 43 is separated from the Namely, the pair of holding pawls 22, 22 are con- stationary die 41, and the aluminum cast product nected to each other through the connecting shaft 12 and synthetic resin core 10 are taken together 25, and are actuated to be closed when a pneu- out of the cavity 45 formed between the stationary matic cylinder not shown pulls the connecting shaft die 41 and the movable die 43 (Fig. 9). 25 in the direction of arrow L in Fig. 3. io Next, the cast product 12 and synthetic resin The frame 28 is arranged to be moved in the core 10 are set on the locking device 20 shown in horizontal directions in Fig. 3 through the drive Fig. 3. In this case, the hollow portion 12b of cast shaft 31 driven by a hydraulic cylinder not shown, product 12 is engaged with the engagement pin 21 and the horizontal movement of frame 28 is guided of locking device 20 to be fixed there. by the pair of guides 32, 32. is Then the cast product 12 is totally heated by The operation of the present embodiment in the burner 27 to heat the synthetic resin core 10 the above arrangement is next described. First, in consisting of the polycarbonate core body 60 up to Fig. 4, the synthetic resin core 10 is set at a about 280 to 350 °C. Since the softening point of predetermined position in the stationary die 41 , and polycarbonate is 160 °C and the melting point thereafter the movable platen 42 and movable die 20 thereof is 380 to 400 °C, the whole of core body 43 are moved toward the stationary platen 40 and 70 turns into a semi-molten state when the core stationary die 41 to make the movable die 43 body 60 is heated up to about 280 to 350 ° C. Out closely fit with the stationary die 41. In this case, of the synthetic resin core 10, the projecting por- the cavity 45 is formed between the stationary die tion 10a is not heated so much so as to be kept in 41 and the movable die 43 whereby the core 10 is 25 a hard state. set in the cavity 45. Then the frame 28 of clamp device 30 is totally Next, molten aluminum 55 at about 680 °C is moved toward the cast product 12 and thereafter put into the cylinder 50 through the input port 53 the pair of holding pawls 22, 22 hold the projecting thereof and then the molten aluminum 55 is push- portion 10a of the synthetic resin core 10. In this ed toward the sprue 48 by the piston 51. The 30 state the entire frame 28 is moved away from the molten aluminum 55 entering the sprue 48 is in- cast product 12 by the drive shaft 31. In this case, jected through the gate 46 into the cavity 45 to fill the synthetic resin core 10 consisting of the poly- a space formed by the stationary die 41, movable carbonate core body 70 inside the cast product 12, die 43, and core 10 (Fig. 10A and Fig. 10B). The being semi-molten, is integrally drawn rightward in molten aluminum 55 flowing from the gate 46 into 35 Fig. 3 from the cast product 12. the cavity 45 is sprayed, and the temperature After that, the cast product 12 is taken out of thereof becomes about 600 ° C. the locking device 20. Since the synthetic resin Next, the molten aluminum 55 filled in the core 10 consisting of the polycarbonate core body cavity 45 is rapidly cooled by the stationary die 41 70 is integrally drawn in the semi-molten state from and movable die 43 to form the aluminum cast 40 the cast product 12, no scraps of core will remain product 12. inside the cast product 12. Accordingly, the cast During this period, heat transfer occurs also product 12 can be shipped as a final product as it from the molten aluminum 55 to the synthetic resin is. On the other hand, the synthetic resin core 10 core 10 consisting of the polycarbonate core body drawn from the cast product is collected for reuse 70. However, because the thermal conductivity of 45 to form another core. the synthetic resin core 10 is normally far smaller The aluminum die cast product 12 thus ob- than that of the steel stationary die 41 and movable tained is the cast product 12 having the inner die 43 (for example, the thermal conductivity of space 18 (Fig. 20) corresponding to the core 10. polycarbonate is 4.6 x 10_+ cal/s«cm°C while the As well as the die cast product 12 having the inner thermal conductivity of iron is 0.18 cal/s«cm°C), 50 space 18, another die cast product 12 having an an amount of heat transfer from the molten alu- undercut portion can also be obtained using the minum 55 to the synthetic resin core 10 becomes core 10. extremely small. Thus, the synthetic resin core 10 As described above, according to the present is not melted during casting, and the cast product embodiment, the aluminum cast product 12 can be 12 excellent in accuracy of shape can be formed 55 formed easily and accurately by using the syn- accordingly. thetic resin core 10 consisting of the polycarbonate The synthetic resin core 10 will not be melted core body 70. The core 10 can be removed from even with slow escape of heat from the thick por- the cast product 12 without any residual scraps of

7 13 EP 0 677 346 A2 14 core in the cast product 12 simply by heating the 45 is formed between the two dies, similarly as in cast product 12 after cast and drawing the syn- the first embodiment. thetic resin core 10 in the semi-molten state. Also, The cylinder 50 is provided on the opposite the core 10 can be produced at low cost, because side to the stationary die 41 in the stationary platen the synthetic resin core 10 consists of the polycar- 5 40, and the piston 51 is slidably arranged in the bonate core body 70 having the space 71 . cylinder 50. The cylinder 50 is provided with the Modifications of the present invention will be input port 53 through which molten aluminum is put described in the following. into the cylinder. The above embodiment showed an example in The inside of cylinder 50 communicates which the silicone rubber was applied to the sur- io through the sprue 48 with the cavity 45 formed face of polycarbonate core body 70 located near between the stationary die 41 and the movable die the thick portion 12a of cast product 12, but the 43, and the inlet gate 46 is provided at an exit of silicone rubber may be replaced by a thermoset- sprue 48 on the cavity 45 side. ting resin selected for example from melamine As shown in Fig. 12 and Fig. 13, the synthetic resins, phenol resins, urea resins, epoxy resins, is resin core 10 is set in the cavity 45 formed be- silicon resins, polyurethane resins, etc. tween the stationary die 41 and the movable die The above embodiment showed an example in 43, and the synthetic resin core 10 is arranged to which the synthetic resin core 10 consisted of the form the aluminum die cast product 12 (Fig. 13). polycarbonate core body 70 having the space 71, The die cast product 12 is of an elongated shape but, without a need to be limited to it, the space 71 20 and a plurality of injection gates 46a, 46b commu- in the polycarbonate core body 70 may be filled nicating with the inlet gate 42 are provided in the with a filling of synthetic resin center body 72 stationary die 41 along the longitudinal direction of made of a cheaper material than polycarbonate, for cavity 45. example of or urethane rubber As shown in Fig. 12 and Fig. 13, the synthetic etc., in order to increase the strength of synthetic 25 resin core 10 is composed of a synthetic resin resin core 10. portion 110b made of a synthetic resin, for exam- This center body 72 may be made of grains of ple of heat-resistant polycarbonate, and a metal a synthetic resin or of an integral body of a syn- portion 110a of steel connected to the synthetic thetic resin. resin portion 110b. Among them, the metal portion As described above, according to the present 30 110a is located at the end portion in the cavity 45 invention, the cast product can be formed with high and at a position corresponding to a flange portion accuracy using the synthetic resin core consisting (thick portion on the end side) 12a of cast product of the heat-resistant synthetic resin core body hav- 12, projecting outward from inside the cavity 45. ing the space and the core can be readily removed On the other hand, the synthetic resin portion 110b from the cast product without remaining scraps of 35 extends from the metal portion 110a through the core in the cast product after cast. Therefore, the inside of cavity 45. cast product excellent in accuracy of shape can be Next described is a casting method using the quickly formed. Material costs can be reduced be- synthetic resin core. First, in Fig. 4, the synthetic cause the core body of synthetic resin has the resin core 10 is set at a predetermined position in space inside. 40 the stationary die 41, and thereafter the movable Further, a die cast product having an undercut platen 42 and movable die 43 are moved toward portion or a hollow portion can be obtained on a the stationary platen 40 and stationary die 41 to sure basis. make the movable die 43 closely fit with the sta- tionary die 41 . In this case, the cavity 45 is formed Third Embodiment 45 between the stationary die 41 and the movable die 43 whereby the synthetic resin core 10 is set in the The third embodiment of the present invention cavity 45. will be described with reference to the drawings. Next, as shown in Fig. 4, molten aluminum 55 Fig. 12 to Fig. 15 are drawings to show the at about 680 ° C is put into the cylinder 50 through third embodiment of the present invention. Same 50 the input port 53 thereof and then the molten portions as those in the first embodiment are de- aluminum 55 thus put thereinto is pushed toward scribed with the same reference numerals. As the sprue 48 by the piston 51. The molten alu- shown in Fig. 4, the aluminum die casting appara- minum 55 entering the sprue 48 is injected from tus is provided with the steel, stationary die 41 the inlet gate 46 through the injection gates 46a, fixed to the stationary platen 40 and the steel, 55 46b into the cavity 45 to fill the cavity 45 (Fig. 12). movable die 43 fixed to the movable platen 42, and The molten aluminum 55 flowing from the injection is so arranged that when the stationary die 41 and gates 46a, 46b into the cavity 45 is sprayed, and movable die 43 are brought into close fit, the cavity the temperature thereof becomes about 600 ° C.

8 15 EP 0 677 346 A2 16

The injection of molten aluminum is described thermal conductivity of polycarbonate is 4.6 x 10_+ in more detail referring to Fig. 12. As shown in Fig. cal/s«cm°C while the thermal conductivity of iron 12, the stationary die 41 has the injection gates is 0.18 cal/s«cm°C), an amount of heat transfer 46a, 46b provided at the left end portion and at the from the molten aluminum 55 to the synthetic resin center portion of cavity 45 and the molten alu- 5 portion 10b becomes extremely small. Thus, the minum 55 is first injected through the injection synthetic resin portion 110b is not melted during gates 46a, 46b into the cavity 45 (first injection casting, and the cast product 12 excellent in accu- step). In this case, the injection pressure of molten racy of shape can be formed accordingly. aluminum 55 is about 300 to 400 kg/cm2 in alu- The thick portion 12a on the end side of the minum die casting apparatus of a relatively low io cast product 12 is a portion where an escape of pressure, for example of about 500 t. The molten heat becomes slower. Therefore, if the synthetic aluminum 55 injected through the injection gate resin portion 110b were arranged at the portion 46a advances rightward inside the cavity 45, while corresponding to the end thick portion 12a, an the molten aluminum 55 injected through the injec- imbalance would occur between an amount of heat tion gate 46b advances both rightward and left- is conduction from the molten aluminum 55 to the ward. stationary die 41 and movable die 43 and an When the molten aluminum 55 fills the almost amount of heat conduction to the core 10, which all region inside the cavity 45 as described, the would cause shrinkage in the end thick portion 12a. injection pressure of molten aluminum 55 is in- In contrast with it, when the metal portion 110a is creased up to about 2000 kg/cm2 (second injection 20 placed at the position corresponding to the end step). Various kinds of gases including air mixed in thick portion 12a, a difference is made smaller the molten aluminum 55 remain in the cavity 45, between the amount of heat conduction from the but by increasing the injection pressure of molten molten aluminum 55 to the stationary die 41 and aluminum 55, the remaining gases in cavity 45 can movable die 43 and the amount of heat conduction be discharged from inside the cavity 45 for exam- 25 from the molten aluminum 55 to the core 10, ple through a clearance 112 between the stationary whereby shrinkage can be prevented from appear- die 41 and movable die 43, and the synthetic resin ing in the end thick portion 12a. core 10 to the outside. Next, the movable die 43 is separated from the As described, the molten aluminum 55 is in- stationary die 41, and the aluminum cast product jected in a relatively low pressure before the al- 30 12 and synthetic resin core 10 are taken together most entire region is filled in the cavity 45, where- out of the cavity 45 formed between the stationary by a load on the synthetic resin core 10 can be die 41 and the movable die 43. suppressed in a low level. In addition, the injection Then the cast product 12 is totally heated by pressure of molten aluminum 55 is increased after the burner 27 to heat the synthetic resin core 10, the almost entire region in cavity 45 is filled with 35 particularly the synthetic resin portion 110b of poly- the molten aluminum 55, whereby the remaining carbonate, up to about 280 to 350 °C. Since the gases can be discharged from inside the cavity 45 softening point of polycarbonate is 160 °C and the to the outside. By this, the core 10 can be pre- melting point thereof is 380 to 400 °C, the syn- vented from being deformed during casting or thetic resin portion 110b turns into a semi-molten porosities can be prevented from being produced. 40 state when the synthetic resin portion 110b is heat- Since the injection gates 46a, 46b are provided ed up to about 280 to 350 ° C. Out of the synthetic at the left end portion and at the center portion of resin core 10, the metal portion 110a is not heated cavity 45 in the stationary die 41, the molten alu- so much. minum 55 can be uniformly filled in the cavity 45 Next, the metal portion 110a of the synthetic and the molten aluminum 55 can be fully put 45 resin core 10 is held by a clamp device 120. In this throughout the cavity 45 even under a low injection state the clamp device 120 is moved away from pressure. the cast product 12, whereby the synthetic resin The molten aluminum 55 filled in the cavity 45 portion 110b of the synthetic resin core 10 set in is rapidly cooled by the stationary die 41 and the cast product 12 is drawn in the semi-molten movable die 43 to form the aluminum cast product 50 state leftward in Fig. 13 from the cast product 12. 12. Another embodiment of the present invention is During this period, heat transfer occurs also next described referring to Fig. 14 and Fig. 15. In from the molten aluminum 55 to the synthetic resin the embodiment shown in Fig. 14 and Fig. 15, the core 10, particularly to the synthetic resin portion aluminum cast product 12 has an inside thick por- 110b of polycarbonate. However, because the ther- 55 tion 113 nearly at the central portion in the longitu- mal conductivity of the synthetic resin portion 110b dinal direction in addition to the end thick portion is normally far smaller than that of the steel station- 12a and a metal buried portion 111 is buried at a ary die 41 and movable die 43 (for example, the position corresponding to the inside thick portion

9 17 EP 0 677 346 A2 18

113 in the synthetic resin portion 110b of core 10. Fourth Embodiment Other parts are substantially the same as those in the embodiment shown in Fig. 12 to Fig. 14. The fourth embodiment of the present inven- As shown in Fig. 14 and Fig. 15, in the syn- tion will be described with reference to the draw- thetic resin portion 110b of core, the metal buried 5 ings. portion 111 of aluminum is buried as exposed at Fig. 16 to Fig. 23 are drawings to show an the position corresponding to the inside thick por- embodiment of the present invention. Same por- tion 113 in the surface of synthetic resin portion tions as those in the first embodiment are de- 110b. Because of this arrangement, where the core scribed with the same reference numerals. As shown in Fig. 14 and Fig. 15 is set in the cavity 45 io shown in Fig. 4, the aluminum die casting appara- (Fig. 12) between the stationary die 41 and the tus is provided with the steel, stationary die 41 movable die 43 and thereafter the molten alu- fixed to the stationary platen 40 and the steel, minum 55 is introduced into the cavity 45, there is movable die 43 fixed to the movable platen 42, and no shrinkage caused in the inside thick portion 113 is so arranged that when the stationary die 41 and of the cast product 12. is movable die 43 are brought into close fit, the cavity Namely, though the inside thick portion 110 is 45 is formed between the two dies, similarly as in a portion where an escape of heat becomes slower, the first embodiment. the arrangement where the metal buried portion The cylinder 50 is provided on the opposite 111 of aluminum is buried at the position cor- side to the stationary die 41 in the stationary platen responding to the inside thick portion 113 in the 20 40, and the piston 51 is slidably arranged in the synthetic resin portion 110b can reduce a differ- cylinder 50. The cylinder 50 is provided with the ence between an amount of heat conduction from input port 53 through which molten aluminum is put the molten aluminum 55 to the stationary die 41 into the cylinder. and movable die 43 and an amount of heat con- The inside of cylinder 50 communicates duction from the molten aluminum 55 to the metal 25 through the sprue 48 with the cavity 45 formed buried portion 111, whereby no shrinkage occurs in between the stationary die 41 and the movable die the inside thick portion 113. 43, and the gate 46 is provided at an exit of sprue Then the aluminum cast product 12 is taken 48 on the cavity 45 side. together with the synthetic resin core 10 out of the The synthetic resin core 10 is set in the cavity cavity 45 between the stationary die 41 and the 30 45 formed between the stationary die 41 and the movable die. After that, the cast product 12 is movable die 43, and the aluminum cast product 12 totally heated to turn the synthetic resin core 10, having the inner space 18 (Fig. 20) is formed with particularly the synthetic resin portion 110b of poly- this synthetic resin core 10 (Fig. 16 and Fig. 17). carbonate, into the semi-molten state and it is Also, a decreased-diameter 16 projected into the drawn from the cast product 12. 35 inner space 18 is formed in the nearly central The above embodiments showed examples us- portion of cast product 12. ing the die casting core 10 for the aluminum die The synthetic resin core 10 is next described casting method, but the material is not limited to referring to Fig. 16 and Fig. 17. In Fig. 16 and Fig. aluminum. For example, the material may be lead, 17, the synthetic resin core 10 is made of a syn- zinc, magnesium, manganese, or an alloy thereof. 40 thetic resin, for example of heat-resistant polycar- According to the present invention, there is no bonate, and the synthetic resin core 10 has the imbalance between the amount of heat conduction projecting portion 10a which slightly projects from from the molten metal to the dies and the amount the cast product 12 after cast. of heat conduction from the molten metal to the Out of the surface of the synthetic resin core metal portion of core at the position corresponding 45 10, a portion corresponding to (or in contact with) to the end thick portion, thereby preventing shrink- the thick portion 12a of the cast product 12 is age at the end thick portion of cast product. Fur- coated with a silicone rubber 1 1 having strong heat ther, there is no imbalance between the amount of resistance. The thick portion 12a of cast product 12 heat conduction from the molten metal to the dies is a portion where an escape of heat is slow. and the amount of heat conduction from the molten 50 Because of it, the polycarbonate core 10 could be metal to the metal buried portion of core at the melted near the thick portion 12a. Therefore, the position corresponding to the inside thick portion, coating of the silicone rubber 1 1 can prevent melt- thereby preventing shrinkage at the inside thick ing of polycarbonate core 10. Furthermore, the portion of metal product. synthetic resin core 10 has a center member inside 55 as shown in Fig. 16, for example a compression spring 15 of steel. This compression spring 15 functions to reinforce the core 10 upon drawing of core so as to draw it together without any separa-

10 19 EP 0 677 346 A2 20 tion of core 10, as described later. ary die 41 and movable die 43 (for example, the The core drawing apparatus is next described thermal conductivity of polycarbonate is 4.6 x 10_+ referring to Fig. 18. As shown in Fig. 18, the core cal/s«cm°C while the thermal conductivity of iron drawing apparatus has the locking device 20 for is 0.18 cal/s«cm°C), an amount of heat transfer locking the cast product 12 after cast, and the 5 from the molten aluminum 55 to the synthetic resin burner 27 for heating the cast product 12 locked by core 10 becomes extremely small. Thus, the syn- the locking device 20. The engagement pin 21 to thetic resin core 10 is not melted during casting, be engaged with the hollow portion 12b of cast and the cast product 12 excellent in accuracy of product 12 (Fig. 16 and Fig. 17) is fixed in the shape can be formed accordingly. locking device 20. io The synthetic resin core 10 will not be melted Also, as shown in Fig. 18, the clamp device 30 even with slow escape of heat from the thick por- for clamping and pulling the projecting portion 10a tion 12a, because the surface of the synthetic resin of core 10 projecting from the cast product 12 is core 10 near the thick portion 12a of cast product provided beside the lacking device 20. This clamp 12 is coated with very-high-temperature-resistant device 30 has a pair of holding pawls 22, 22 is silicone rubber 1 1 . arranged as rockable through rocking shafts 23, 23 Next, the movable die 43 is separated from the on the frame 28, and this pair of holding pawls 22, stationary die 41, and the aluminum cast product 22 hold the projecting portion 10a of core. Namely, 12 and synthetic resin core 10 are taken together the pair of holding pawls 22, 22 are connected to out of the cavity 45 formed between the stationary each other through the connecting shaft 25, and 20 die 41 and the movable die 43 (Fig. 16 and Fig. are actuated to be closed when the pneumatic 17). cylinder not shown pulls the connecting shaft 25 in Next, the cast product 12 and synthetic resin the direction of arrow L in Fig. 18. core 10 are set on the locking device 20 shown in The frame 28 is arranged to be moved in the Fig. 18. In this case, the hollow portion 12a of cast horizontal directions in Fig. 18 through a drive shaft 25 product 12 is engaged with the engagement pin 21 31 driven by a hydraulic cylinder not shown, and of locking device 20 to be fixed there. the horizontal movement of frame 28 is guided by Then the cast product 12 is totally heated by the pair of guides 32, 32. the burner 27 to heat the synthetic resin core 10 of Next described is the casting method using the polycarbonate up to about 280 to 350 °C. Since synthetic resin core. First, in Fig. 4, the synthetic 30 the softening point of polycarbonate is 160 °C and resin core 10 is set at a predetermined position in the melting point thereof is 380 to 400 °C, the the stationary die 41, and thereafter the movable whole of core 10 turns into a semi-molten state platen 42 and movable die 43 are moved toward when the synthetic resin core 10 is heated up to the stationary platen 40 and stationary die 41 to about 280 to 350 °C. Out of the synthetic resin make the movable die 43 closely fit with the sta- 35 core 10, the projecting portion 10a is not heated so tionary die 41 . In this case, the cavity 45 is formed much so as to be kept in a hard state. between the stationary die 41 and the movable die Then the frame 28 of clamp device 30 is totally 43 whereby the core 10 is set in the cavity 45. moved toward the cast product 12 and thereafter Next, molten aluminum 55 at about 680 °C is the pair of holding pawls 22, 22 hold the projecting put into the cylinder 50 through the input port 53 40 portion 10a of the synthetic resin core 10. In this thereof and then the molten aluminum 55 is push- state the entire frame 28 is moved away from the ed toward the sprue 48 by the piston 51. The cast product 12 by the drive shaft 31. By this, the molten aluminum 55 entering the sprue 48 is in- synthetic resin core 10 inside the cast product 12, jected through the gate 46 into the cavity 45 to fill being semi-molten, is integrally drawn rightward in a casting space formed by the stationary die 41, 45 Fig. 3 from the cast product 12. movable die 43, and core 10 (Fig. 19). The molten In this case, because the synthetic resin core aluminum 55 flowing from the gate 46 into the 10 has the compression spring 15 inside, the core cavity 45 is sprayed, and the temperature thereof 10 is reinforced by the compression spring 15. By becomes about 600 ° C. this arrangement the core 10 can be drawn to- Next, the molten aluminum 55 filled in the 50 gether out of the cast product 12 without any cavity 45 is rapidly cooled by the stationary die 41 separation. and movable die 43 to form the aluminum cast As described, the cast product 12 having the product 12. inner space 18 is obtained and thereafter the cast During this period, heat transfer occurs also product 12 is taken out of the locking device 20. As from the molten aluminum 55 to the synthetic resin 55 described previously, the decreased-diameter por- core 10 of polycarbonate. However, because the tion 16 projecting into the inner space 18 is formed thermal conductivity of the synthetic resin core 10 in the nearly central portion of cast product 12, so is normally far smaller than that of the steel station- that a residue of core 10 could remain deposited

11 21 EP 0 677 346 A2 22 on the inner surface of the inner space 18 near the following hydrocarbon solvents. decreased-diameter portion 16. Namely, when the Methylene chloride (dichloromethane or synthetic resin core 10 is drawn in the semi-molten methylene chloride), NMP (N-methyl-2-olefin), DMP state out of the cast product 12, a part of core 10 is (NN-dimethylformamide), MFK (methyl ethyl ke- caught by the decreased-diameter portion 16 pro- 5 tone), and ethyl acetate (). jecting into the inner space 18, thereby remaining Further, an ultrasonic generator 100 is set in as a residue. In this case, the residual core remain- the solvent 101, so that ultrasonic waves are gen- ing in the inner space 18 needs to be removed. erated in the solvent 101 by the ultrasonic gener- Methods for removing the residual core are next ator 100, thereby quickly dissolving and removing described. io the polycarbonate residual core remaining on the First described referring to Fig. 20 is a method inner surface of inner space 18. for peeling off the residual core by shot blast. As described above, according to the present As shown in Fig. 20, a shot blast apparatus 91 embodiment, the aluminum cast product 12 can be having a nozzle 92 is brought near an opening 90a formed easily and precisely using the synthetic of cast product 12 and a lot of shots 93 are ejected is resin core 10 of polycarbonate. After cast, the core (or blasted) into the inner space 18 of the cast 10 can be removed from the cast product 12 product 12 through the nozzle 92. Then the ejected simply by heating the cast product 12 and drawing shots 93 peel off the residual core of polycarbonate the synthetic resin core 10 in the semi-molten remaining in the inner space 18, particularly on the state. Also, the residual core remaining on the inner inner surface near the decreased-diameter portion 20 surface of inner space 18 in the cast product 12 16. The residual core peeled off from the inner can be easily and simply removed using the shot surface of inner space 18 is then discharged to- blast, high-temperature and high-pressure steam, gether with the shots 93 through the other opening or solvent. 90b. Another embodiment of the present invention is During the shot blast operation with the above 25 next described referring to Fig. 23. The embodi- shot blast apparatus 91, the cast product 12 may ment shown in Fig. 23 is substantially the same as be heated up to about 200 ° C, whereby the peel- the embodiment shown in Fig. 16 to Fig. 22 except ing-off removal of the residual core becomes that the synthetic resin core 10 is a polycarbonate easier. The shots 93 may be aluminum powder, core without a compression spring and that the glass powder, silica powder, graphite powder, salt 30 aluminum cast product 12 and synthetic resin core powder, or other anti-rust metal powder. 10 are taken out of the cavity between the station- Next described is a method for peeling off and ary die 41 and the movable die 43 and the cast removing the residual core by high-temperature product 12 and synthetic resin core 10 thus taken and high-pressure steam. out are heated in a furnace. As shown in Fig. 21, a steam spraying appara- 35 As shown in Fig. 23, the synthetic resin core tus 95 is set close to one opening 90a of the cast 10 is a polycarbonate core without a compression product 12 and then high-temperature and high- spring, casting is carried out while setting the core pressure steam 97 (for example steam at 300 °C 10 in the cavity (Fig. 4) between the stationary die to 500 °C) is sprayed through a nozzle 96. The 41 and movable die 43, and thereafter the alu- thus sprayed steam 97 peels off and removes the 40 minum cast product 12 and synthetic resin core 10 polycarbonate residual core remaining on the inner are taken out of the cavity between the stationary surface of inner space 18 near the decreased- die 41 and the movable die 43. Then the aluminum diameter portion 16. The residual core peeled off cast product 12 and synthetic resin core 10 are set from the inner surface of inner space 18 is then on a receptacle 81 in the furnace 80, and then they discharged together with steam 97 from the other 45 are heated in the furnace 80 up to a temperature of opening 90b. the melting point of polycarbonate (380 to 400 ° C) Next described referring to Fig. 22 is a method to 600 ° C. for peeling off and removing the residual core with Generally, shrinkage would occur inside the a solvent. aluminum cast product 12 when heated up to about As shown in Fig. 22, a solvent 101 is poured 50 600 °C, but using nonporous aluminum cast prod- into a receptacle 98 and the cast product 12 is uct 12, it can fully stand the temperature of about immersed in the solvent 101. In this case, the 600 ° C without shrinkage. polycarbonate residual core remaining on the inner With heating in the furnace 80, the synthetic surface of inner space 18 in the cast product 12 resin core 10 is melted to flow out of the aluminum can be washed out with the solvent 101 to be 55 cast product 12, so that the polycarbonate ingre- dissolved and removed. dient in the synthetic resin core 10 is collected in The solvent for dissolving to remove the poly- the receptacle 81 . carbonate residual core is one selected from the

12 23 EP 0 677 346 A2 24

Another possible arrangement is such that after of 250 to 350 ° C out thereof. the aluminum cast product 12 and synthetic resin core 10 are taken out of the cavity between the 3. The casting method using a synthetic resin stationary die 41 and the movable die 43, the core according to Claim 1 , further comprising aluminum cast product 12 and synthetic resin core 5 a step of peeling off and removing a resid- 10 are immersed in the solvent 101 (Fig. 22) in- ual core remaining in the inner space in the stead of being heated in the furnace, whereby the cast product by shot blast. synthetic resin core 10 is dissolved out of the aluminum cast product 12. 4. The casting method using a synthetic resin In the above embodiment the aluminum die io core according to Claim 3, wherein casting method was described as a die casting the cast product is heated upon peeling off method, but the casting method of the present and removing the residual core by shot blast. invention can be applied to any other die casting methods, such as the gravity die casting method, 5. The casting method using a synthetic resin the low pressure die casting method, and the preci- is core according to Claim 1 , further comprising sion die casting method. Further, the cast product a step of blowing off and removing a resid- may be not only of aluminum, but also of lead, ual core remaining in the inner space in the zinc, magnesium, manganese or an alloy thereof. cast product by high-temperature and high- As described above, according to the present pressure steam. invention, the residual core remaining in the inner 20 space of cast product can be easily and simply 6. The casting method using a synthetic resin removed. Therefore, a cast product can be ob- core according to Claim 5, wherein tained with clean inner surface having no residual the synthetic resin core is a polycarbonate core. Also, the synthetic resin core can be re- core and the high-temperature and high-pres- moved as melted out of the cast product in the 25 sure steam is steam of 300 ° C to 500 ° C. furnace. By this, a cast product can also be ob- tained with clean inner surface. Further, the syn- 7. The casting method using a synthetic resin thetic resin core can be dissolved in the solvent out core according to Claim 1 , further comprising of the cast product. This can also provide a cast a step of immersing the cast product in a product with clean inner surface. The core can be 30 solvent and thereby washing out to remove a integrally drawn without separation out of the cast residual core remaining in the inner space in product. Thus, an amount of the residual core the cast product. remaining in the inner space of cast product can be suppressed to a minimum level. 8. The casting method using a synthetic resin 35 core according to Claim 7, wherein Claims upon washing out to remove the residual core with the solvent, ultrasonic waves are 1. A casting method using a synthetic resin core, generated in the solvent to wash out to remove comprising: the residual core. a step of placing the synthetic resin core 40 in dies; 9. A casting method using a synthetic resin core, a step of filling the dies in which the syn- comprising: thetic resin core is placed, with a molten metal; a step of placing the synthetic resin core a step of cooling the molten metal by the in dies; dies to form a cast product; and 45 a step of filling the dies in which the syn- a step of taking the cast product and the thetic resin core is placed, with a molten metal; synthetic resin core out of the dies, thereafter a step of cooling the molten metal by the heating the cast product and the synthetic res- dies to form a cast product; and in core to draw the synthetic resin core in a a step of taking the cast product and the semi-molten state out of the cast product, and 50 synthetic resin core out of the dies, and there- thereby forming an inner space in the cast after heating the cast product and the synthetic product. resin core in a furnace to melt the synthetic resin core then to remove the synthetic resin 2. The casting method using a synthetic resin core out of the cast product. core according to Claim 1 , wherein 55 the synthetic resin core is a polycarbonate 10. A casting method using a synthetic resin core, core and the cast product is heated to draw comprising: the synthetic resin core in a semi-molten state a step of placing the synthetic resin core

13 25 EP 0 677 346 A2 26

in dies; 21. The core made of a synthetic resin according a step of filling the dies in which the syn- to Claim 20, wherein thetic resin core is placed, with a molten metal; said inner space is filled with a filling. a step of cooling the molten metal by the dies to form a cast product; and 5 22. The core made of a synthetic resin according a step of taking the cast product and syn- to Claim 21 , wherein thetic resin core out of the dies and thereafter said filling comprises grains of a synthetic immersing the cast product and the synthetic resin. resin core in a solvent to dissolve the synthetic resin core out of the cast product. io 23. The core made of a synthetic resin according to Claim 21 , wherein 11. A core made of a synthetic resin. said filling is an integral body made of a synthetic resin. 12. The core made of a synthetic resin according to Claim 1 1 , wherein is 24. In a core for forming a die cast product, to be said core is a core made of polycarbonate. set in a cavity in die casting dies, the core for die casting comprises: 13. The core made of a synthetic resin according a synthetic resin portion extending in the to Claim 12, wherein cavity of the dies; and a silicone rubber is deposited at a position 20 a metal portion connected to the synthetic corresponding to a thick portion of a cast prod- resin portion, provided at an end portion in the uct. cavity of the dies and at a position correspond- ing to an end thick portion of the cast product, 14. The core made of a synthetic resin according and projecting outwardly from the cavity. to Claim 1 1 , wherein 25 said core comprises a thermoplastic inside 25. In a core for forming a die cast product, to be resin and a heat-resistant resin covering a sur- set in a cavity in die casting dies, the core for face of the inside resin. die casting has a synthetic resin portion ar- ranged to extend in the cavity of the dies, 15. The core made of a synthetic resin according 30 wherein to Claim 1 1 , wherein a metal buried portion is buried at a posi- said core can be divided into a plurality of tion in the synthetic resin portion, correspond- portions. ing to an inside thick portion of the cast prod- uct. 16. The core made of a synthetic resin according 35 to Claim 1 1 , wherein 26. The core for die casting according to Claim 25, said core is a core made of a biodeg- wherein radable plastic. the metal buried portion is made of alu- minum. 17. The core made of a synthetic resin according 40 to Claim 1 1 , wherein 27. The core for die casting according to Claim 25, said core is a core made by mixing par- further comprising ticles of a thermoplastic resin with particles of a metal portion connected to the synthetic a heat-resistant resin and baking them to har- resin portion, provided at an end portion in the den. 45 cavity of the dies and at a position correspond- ing to an end thick portion of the cast product, 18. The core made of a synthetic resin according and projecting outwardly from the cavity. to Claim 1 1 , wherein said core has a center member inside. 28. A cast product having an inner space, cast by 50 the method as set forth in Claim 1 . 19. The core made of a synthetic resin according to Claim 18, wherein said center member is a coil spring.

20. The core made of a synthetic resin, comprising a core body made of a heat-resistant synthetic resin and having a space inside thereof.

14 EP 0 677 346 A2

F I G. I

F I 6. 2

15 EP 0 677 346 A2

16 EP 0 677 346 A2

F I 6. 4

17 EP 0 677 346 A2

F I G. 6 F I G. 7

60a

18 P 0 677 346 A2 EP 0 677 346 A2

20

EP 0 677 346 A2 IP 0 677 346 A2

26 EP 0 677 346 A2

43

FIG. 19

12b

F I G. 20

12b

24 EP 0 677 346 A2

FIG. 22

25