JPH0155082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming hollow plastic articles such as pipes, fittings, containers, etc.

Conventionally, a core mold is formed from a heat-melting substance such as wax or paraffin, a plastic molded product is formed around the outer periphery of the core mold, and the inside of the plastic molded product is formed by heating and softening the core mold. A method of forming a plastic hollow molded article is being carried out in which the core is removed. However, according to this method, the surface hardness and strength of the core made of wax, paraffin, etc. are low, and the heat resistance is also poor.
When molding a hollow molded product using inorganic fiber-reinforced plastics (FRP) such as carbonized fiber or ceramic fiber, the inorganic fibers may bite into the core mold, making it impossible to finish the inner surface of the hollow molded product smoothly, or the resin may There were drawbacks in that the core mold was deformed and melted by the heat of curing, making it impossible to form the internal shape of the hollow molded product with high precision, and causing roughness on the inner surface of the hollow molded product.

The object of the present invention is to improve the surface hardness, strength, heat resistance, etc. of the core mold by improving the above-mentioned drawbacks, and to produce a plastic hollow molded product with a smooth inner surface and good inner shape precision. The main idea is to use a mixture of a heat-fusible substance and a filler in the core mold.

To explain the present invention with reference to an embodiment shown in the drawings, the core mold 1 is made of a heat-melting substance such as paraffin, wax, wax, sand, cement, calcium carbonate, bentonite, carbon powder, metal powder, inorganic fiber, etc. It consists of fillers such as carbon fibers and metal fibers. Core type 1
A band heater 2 is passed through the shaft core of the band heater 2. The outer periphery of core mold 1 is coated using the hand lay-up method.
An FRP molded article 3 is formed. Once the FRP layer has hardened, the band heater 2 is energized to heat the core mold 1.
The area around the band heater 2 melts, and when hot air is blown out from the nozzle 4 as shown in FIG. The entire core mold 1 is softened by heating, and the core mold 1 is taken out from the FRP molded product 3 (pipe joint). Steam instead of hot air,
Hot water, hot oil, etc. may be injected into the cavity 1A. In the core mold 1, the mixing weight ratio of the heat-fusible substance and the filler is 20:80 to 70:30. If the filler is contained below the above range, the reinforcing effect of the filler will not be noticeable, and if the filler is contained above the above range, the binding by the heat-fusible substance of the filler will be insufficient, resulting in a core-like shape. becomes brittle. The optimum mixing weight ratio of the heat-fusible substance and the filler varies within the above range depending on the types of the heat-fusible substance and the filler.
In particular, the type of filler greatly influences the optimum mixing weight ratio. For example, if a filler has a high specific gravity, the weight ratio of the filler can be increased within the above range compared to a filler with a low specific gravity.For example, for metal powder with a high specific gravity, the mixing weight ratio is 30:70 to 40. : About 60 is desirable;
For calcium carbonate, which has a small specific gravity, the mixing weight ratio is
A ratio of about 60:40 to 70:30 is desirable, or the weight ratio of fillers with small particle sizes can be increased within the above range compared to those with large particle sizes,
For example, for bentonite with a small particle size, the mixing weight ratio is preferably about 20:80 to 40:60, and for sand with a large particle size, the mixing weight ratio is preferably about 40:60 to 60:40.

Since the present invention has the above configuration, the heat-fusible substance in the core mold is reinforced by the filler, and it is possible to provide good hardness, strength, and heat resistance while maintaining heat-fusibility. It becomes possible to obtain a plastic hollow molded product with a smooth inner surface and high internal shape precision.

[Brief explanation of drawings]

The figures relate to one embodiment of the present invention; FIG. 1 is a cross-sectional view during molding, and FIG. 2 is a cross-sectional view when the core is taken out. In the figure, 1...core mold, 3... molded product.

Claims (1)

[Claims] 1. A core mold is formed from a mixture of a heat-fusible substance and a filler in a weight ratio of 20:80 to 70:30, and a plastic molding is formed around the outer periphery of the core mold, and then the core mold is heated. A method for molding a hollow plastic molded article, which comprises removing a core mold from the inside of the plastic molded article by softening it.