JPH044056B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a model material for full molding. (Conventional technology) The full molding method, which uses expanded polystyrene as the model material, is a casting method in which hot water is poured into the model without removing it, unlike molding methods that use wooden molds or metal molds, which reduces the weight of the model and increases the price of wood. , it is attracting attention as a method that can cope with the decrease in the number of engineers who make complex models. In this method, a model of the product is made of expanded polystyrene, and the molten metal is poured into the mold while the model is filled in the mold.
It decomposes, oxidizes, disappears, and is replaced by molten metal, ultimately yielding a high-precision cast product that matches the model. However, the biggest drawback of this method is that it creates surface defects such as undulations caused by the carbon generated by the decomposition of the model material, which requires a great deal of effort to remove, and that it is difficult to use for complex products. This may lead to quality deterioration, and it requires a great deal of effort to remove and clean the carbon. (Problems to be Solved by the Invention) The present invention provides a model material that can reduce decomposition residues. (Means for Solving the Problems) The present invention relates to a full-mold model material made of a mixed foam of polystyrene and polypropylene, and characterized in that the polypropylene content is 5 to 95% of the total weight. It is generally well known that aromatic hydrocarbons are more likely to generate carbon during thermal decomposition than aliphatic (chain) hydrocarbons. This means that the C-C bond energy of chain hydrocarbons is 58.6 to 71 Kcal/mol.
On the other hand, we can get a glimpse of this from the fact that the C _ar - C _ar bond energy of aromatic hydrocarbons is 96 Kcal/mol and the C _ar - C _al bond energy is 80 Kcal/mol. Therefore, chain hydrocarbons can be used as raw materials for model piles, but if chain hydrocarbons are used alone, the thermal decomposition rate will be high, gas defects will occur due to generated gas, and the molten metal will blow up, making it difficult to work. Not only is this extremely dangerous, but it also makes it impossible to ensure the appropriate hardness required for the model material. Therefore, in the present invention, a mixture of polystyrene and polypropylene is used, and a model made by foaming with this mixture can reduce the above-mentioned wavyness to a negligible level. The mixing ratio of polystyrene and polypropylene is preferably such that the polypropylene content is 5 to 95% of the total weight ratio. (Example) A casting experiment was conducted as shown in FIG. In Fig. 1, 1 is a casting model formed by foam molding using a mixture of polystyrene and polypropylene shown in the composition shown in Table 1, and the molten metal 3 is poured from a sprue 4 while it is filled in a mold 2 made of sand and a hardening agent. Pour hot water. At this time, the casting model 1 in the mold 2 gradually decomposes and disappears from the bottom due to the heat of the molten metal 3, and finally the molten metal fills the area occupied by the model in the same way as the model. As soon as the product is completed,
The decomposed gas diffuses and disappears within the mold. These experiments were conducted using models in which the blending ratios of polystyrene and polypropylene were varied as shown in Table 1, and the results were as shown in Table 1. As is clear from this, for example, by mixing 50% of both model materials, the amount of gas generated could be reduced by 37.5% compared to the case of using only polypropylene as shown below. As a result, the undulations became negligible and there was no danger during the work. Gas generation reduction rate = 1 - (1.10 - 0.85) / (1.25 - 0.85) = 0.375

[Table] In Table 1, it is easily inferred that the occurrence of gas defects and the state of gas wrinkles (wavyness) on the surface of the casting differ depending on the shape of the casting and its size.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the implementation procedure in an embodiment of the present invention.

Claims (1)

[Claims] 1. A full-mode model material made of a mixed foam of polystyrene and polypropylene, characterized in that the content of polypropylene is 5 to 59% of the total weight ratio.