APPARATUS FOR MANUFACTURING PLASTIC PRODUCTS

Abstract: A method for manufacturing a plastic product comprising the steps of placing a wax model in a flask, pouring plaster into the flask, heating the flask to melt the wax model, flowing out the melted wax, injecting plastic material and taking out a plastic product when the plastic material has become solid. This method is particularly advantageous in manufacturing an industrial proto-type model, artificial teeth, and the like which have to be made precisely and economically. An apparatus for carrying out the method is also disclosed.

Description: METHOD AND APPARATUS FOR MANUFACTURING PLASTIC PRODUCTS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for manufacturing a plastic product, such as industrial prototype models and false teeth. 2. Prior Art In general, a plastic product to be prepared individually such as an industrial proto-type model and a piece of artificial teeth has been manufactured by means of a metal molding. More specifically upper and lower moldings conforming to the shape of the product to be manufactured have to be prepared.. These moldings are pressed together to yield a desired hsape to the plastic material injected therebetween. However, these tnoldings are limited in terms of their expensiveness, impreciseness, or difficulty of modification. For example, metal-moldings are known to be very expensive; and both of them are not easy to modify the shape once they are shaped. Therefore, simple and precise substitute for such prior art molding has been wanted for a long time. SUMMARY OF THE INVENTION Accordingly, it is the primary object of this invention to provide a method for manufacturing plastic product economically and precisely. It is another object of this invention to provide a method for manufacturing a plastic product by using a wax model which allows any modification on the shape very easily. It is still another object of this invention to provide an apparatus which is specifically designed to be used in the method of this invention. It is still another object of this.invention to provide an apparatus having a temperature controlling equipment which substantially saves the time to be involved in.the manufacturing process. -- - - The method and apparatus of this invention may be used for a variety of purposes including industrial proto-type models, artificial teeth, table wares, trays and the like. In keeping with the principles of this invention, the objects are accomplished by a unique process comprising the step of placing a model made of wax in a flask, pouring plaster into the flask, heating the model after the plaster having coagulated until the model is melted, removing the melted wax out of the flask, injecting plastic material into the .space formed by the removal of the melted wax, cooling off the plastic material until it becomes solid. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 shows a persepctive view of a plastic product to be manufactured by this invention; FIGURE 2 shows a perspective view of a flask of an embodiment of the apparatus of this invention; FIGURE 3 shows a cross-section view of a lower portion. of the flask of the embodiment with a wax model mounted therein FIGURE 4 through 7 show a vertical cross-sectional view of the apparatus for the illustration of the process of this invention; FIGURE 8 shows a plan view of a lower portion of a flask with a wax model mounted therein of a second embodiment o this invention; FIGURE 9 shows a perspective view of the apparatus put all together of the second embodiment; and FIGURE 10 shows an exploded view of the apparatus of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION First, referring to Figures 1 though 3, which show. the basic structure of an apparatus of an embodiment of this invention, a wax model 1 having an identical size and shape to a plastic product a to be manufactured and a flask 2 comprising upper and lower portions 2a and 2b are prepared. The flask 2 may be disassembled into top and bottom lids 11 and side frames 12. These parts are to be fastened together into an integral unit by means of fasteners8, typically, bolts 13 and nuts 14. Plastic injection ports 4 are formed in the side frames 12, thereby allowing melted wax to flow out through the ports 4. There is no restriction upon the number of ports 4 formed. However, in cases where there are two or more ports 4, all ports 4 except the-one used for injection of the plastic have to-be tightly sealed by means of plugs I S during injection of the plastic. Openings 9 for in-jecting plaster are formed in the top of the upper flask portion 2a. Plugs 16 are removably installed in these openings 9. The wax model 1 is fixed in place on the inside bottom- surface of the lowpr flask portion 2b.. Plastic injection gates 5 are formed-with wax extending from the wax model 1 to the plastic injection ports 4. A cooling pipe 6 is accommodated inside the lower flask portion 2b so that both ends of said pipe 6 connect with openings 7 provided in the side of the flask 2. The upper flask portion 2a is set on top of the lower flask portion 2b, and the two portions 2a and 2b are fastened together by means of fasteners 8 as shown in Figure 2. The wax model 1 is to be fixed in place by having its lower end embedded in superhard plaster bed 3 disposed on the inside bottom surface of the lower portion .2b (see Figure 4). The wax model 1 can also be made of a -mixture of wax and soft plastic. The flask 2 is formed by setting the upper portion 2a on top of the lower portion 2b and fastening the two portions together by means of fasteners 8 as shown in Figure 2 in such a manner that the flask 2 is pressure resistant. Now specifically referring to Figure 3 showing the wax model 1 mounted in the lower portion falsk 2b, plastic injection gates 5 are formed with wax,- said gates 5 extending from the wax model 1 to plastic injection ports 4 provided in the side frames 12 of the flask 2. A cooling pipe 6, both ends of which are open to the air through apertures 7 at the upper edge of the frame 12 of the lower portion flask 2b, is equipped inside the flask 2 (also- see Figure 4). The cooling pipe 6 is so made as to be pressure and heat resistant. - It is of course possible to have two or more cooling pipes in the flask 2. Now referring to Figures 4- through 7, which are for the illustration of the method of this invention, the steps used in the method are visually shown. First, the wax model 1 is placed in the flask 2 and the flask 2 is fastened tightly as mentioned above. Plaster is poured into the flask 2 through openings 9 to fill up inside of the flask 2 whereby the wax model 1, cooling pipe 6 and gates 5 are enclosed in the plaster 10 as shown in Figure 5. When the plaster 10 has hardened,-the flask 2 is heated so that the wax inside thereof is melted. This stage is shown in Figure 6. Then the melted wax is allowed to flow out through the ports 4 and is washed out of the flask 2 with hot water. The flask 2 may be heated by circulating hot water or steam thru the cooling pipe 6. The flask is then cooled by circulating cold water through the cooling pipe 6. Referring to Figure 7, one of the two plastic injection ports is tightly sealed and the flask 2 is turned on its side such that the open port 4 is at the top. Then softened plastic material such as acrylic resin, polycarbonate, polyamid resin, styrene resin, polycerethane resin and polyacetol resin is injected through such open port 4 with an injector. In this step, it is advisable to apply some plastic releasing agent into the flask before the softened plastic material is injected -thereby expediting the process of taking out.the plastic product 1 out of the plaster 10. When the plastic material has become solid to form the plastic product a, the flask 2 is disassembled and the product 1 is obtained by removing the plaster 10. Such product is to be polished by a known method.. referring to Figures 8 through 10,-showing a second embodiment of this invention, a full-denture is to be manufactured according to the concept of this invention. A wax model 21 of a full denture is mounted in a lower flask 22 comprising a bottom plate 22a and a lower collar 22b. The wax model 21 is provided with an injection gate 26 extending therefrom to an injection port 24 and a discharging gate 27 extending therefrom to a discharging port 25 as shown in Figure 8; both gates 26 and 27 are made of wax. Further, an upper flask 23 comprising an upper collar 23b and a top plate 23a are put into place such that the upper and lower flask form a complete flask, which is tightly fastened together by means of fasteners 28 as shown in Figures 9 and 10. Such flask is preferably designed 2 to have a pressure resistance of 1000 - 1500 kg/cm . The upper and lower collars 23b and 22b are provided with indents therein so that an injection port 24 and a discharging port 27 in the opposite side. At the discharging port 27, there is equipped a seal 31 which is to hold plastic material to be in jected into the flask. The seal 31 is preferably provided with an a escape 32, whereby any remaining air in the flask can be re moved therethrough. When the flask is fastened together, plaster is poured into the flask through openings 29. The openings 29 are there rafter sealed with a stopper 30. The plaster may be poured to fill up the flask by using a vacuum sucking method or a vibration.method or any ordinary manner. The plaster thus poured into the flask is left for hardening. After the plaster has become solid, the flask is heated until the wax model 21 is melted. The melted wax is removed through the discharging gate 27 by pouring hot water into the injection gate 26. The, a plastic releasing agent is injected into the injection port 24 to fully cover the inside surface of the plaster so-that a plastic product to be manu factured-in the plaster molding may be taken out easily. Before injecting plastic material, the flask is turned over its side such that the injection port 24 is positioned at the top and the discharging port 25 with the seal 31 at the bottom. Then, softened plastic material is injected into the flask. The plastic material is preferably injected at a speed about 0.01 - 10/sec., under inside pressure of 30 - 1200 keg/ 2', with holding pressure of 0.05 - 60/sec. Further, the size of the injection gate 26 is preferably 0.5. - 20 0 mm and the size of the air escape is 0.1 - 5 mm. When the plastic material has become solid, a plastic product is ready to be taken out of the plaster.

Claims: 1. A method for manufacturing aplastic product comrpising the steps of: (a) preparing a model made of a material selected from the group consisting of wax, soft plastic and the combinatic thereof, said model having a shape identical to thàt of the product, (b) placing the model in a flask, (c) pouring plaster into the flask such that the model is totally embedded in the plaster, (d) heating the flask after the plaster has hardened until the model is- melted and causing the melted model to flow out of the flask, (e) injecting plastic material into the space previously occupied by the model, and (f) taking out a plastic product from the plaster after the plastic material has become solid. 2. A method for manufacturing a plastic product according to Claim 1, further comprising between the steps of (d) and (e), the step of cooling the flask. 3. A method for manufacturing a plastic product according to Claim 1, further comprising, between the steps of (d) and (e), the step of applying a plastic releasing agent inter the flask 4. A method for manufacturing a plastic product according to Claim 1, wherein the step (d) of causing the melte model to flow out of the flask is carried out by flushing hot water into the flask. 5. An apparatus for manufacturing a plastic product comprising a flask, wherein: said flask has an upper portion and a lower portion separable from each other, said upper and lower portions are provided with at least one opening for injecting.plastic material, said upper portion is provided with at least one opening for pouring plaster, and said upper and lower portions are equipped with means for tightly fastening said portions together. 6. An apparatus for manufacturing a plastic material according to Claim 4, wherein: said upper and lower portions are further divided into a plate and a collar respectively such that said plates constitute a top and bottom cover and said collars constitute a side frame. 7. An apparatus for manufacturing a plastic product according to Claim 4, wherein: said flask is provided with a pipe for circulating temperature controlling substance.

Inventors: KOGURE, YAMATO
Applicants: KOGURE, YAMATO
Application year: 1978
Main classification: B29C1
IPC codes: B29C45, B29C33, B29C41, B29B13, A61C13, B22C9, B22C23