What are the advantages of thermosetting plastic injection molding?

The thermosetting plastics are mainly formed by compression and injection molding. These two methods have complex process operation, long forming cycle, low production efficiency, high labor intensity, easy damage to the mold, and unstable forming quality. The injection molding of thermosetting plastic parts can be said to be a major reform of thermosetting plastic molding technology. It has the advantages of simplifying the operation process, shortening the molding cycle, improving production efficiency (5~20 times), reducing labor intensity, improving product quality, and longer mold service life (about 100000~300000 times). However, this molding process has high requirements for materials. At present, the most commonly used are phenolic plastics filled with wood flour or cellulose, in addition to amino plastics, unsaturated polyester and epoxy resin.
What are the characteristics of thermosetting plastic injection mold?
1. Pouring system design
Because thermosetting plastics are not heated to enough temperature in the material barrel (to prevent early curing) during molding, it is hoped that the sectional area of the main runner will be smaller to increase friction. Generally, the cone angle of the main runner is 2 °~4 °. In order to improve the surface area of the splitter to facilitate heat transfer, the splitter with circular or trapezoidal cross-section is generally used, and the depth of the splitter can be appropriately smaller under the same cross-sectional area. The selection principle of gate type and location is basically the same as that of thermoplastic injection mold, that is, the size of the point gate should not be too small, generally not less than 1.2 mm, and the depth of the side gate should be selected within 0.8~3 mm to prevent the melt temperature from rising too much, accelerate the chemical crosslinking reaction, make the viscosity rise, and make it difficult to fill the mold.
2. Push-out mechanism
Because the melting temperature of thermosetting plastics is lower than the curing temperature, the material fluidity is good under certain molding conditions, and it can flow into small gaps and become flash. Therefore, during manufacturing, the mold closing accuracy should be improved, the push plate push mechanism should be avoided, and the splicing parts should be minimized.
3. Cavity position layout
Due to the high injection pressure of thermosetting plastics, more overflow and flash will be produced between the parting surfaces when the mold is under unbalanced stress. Therefore, when the cavity position is arranged, the center of the projected area on the parting surface should coincide with the center of the injection machine's clamping force as much as possible. The upper and lower positions of the thermosetting plastic injection mold cavity have a great influence on the temperature distribution of different cavities or different parts of the same cavity. This is because of the effect of the movement of the hot air from the bottom to the top during natural convection. The actual measurement shows that the heat absorbed by the upper part can differ by two times from the lower part. Therefore, in order to improve this situation, the distance between the upper and lower cavities should be minimized when arranging multiple cavities.
4. Mold material
The molding parts (cavity and core) of thermosetting plastic injection mold need to be made of materials with good wear resistance and low surface roughness due to the scouring effect of the filler in the plastic. The molding parts should be chrome plated to prevent corrosion.
How about the pressure holding pressure and time of thermosetting plastics?
The holding pressure and holding time of thermosetting plastics directly affect the mold cavity pressure, as well as the filling and density of plastic parts. The pressure holding pressure of commonly used thermosetting plastics can be slightly lower than the injection pressure, and the pressure holding time can also be slightly shorter than that of thermoplastic injection, usually 5~20s.
What is the molding cycle of thermosetting plastics?
In the injection molding cycle of thermosetting plastics, the most important is the injection time and hardening setting time, in addition to the pressure holding time and mold opening and taking time. The injection time of domestic thermosetting injection materials is 2~10s, the pressure holding time is about 5~20s, the hardening setting time is selected within 15~100s, and the molding cycle is about 45~120s. The hardening setting time of thermosetting plastics should not only consider the structural shape, complexity and wall thickness of the plastic parts, but also pay attention to the quality of the materials, especially when determining the hardening time according to the maximum wall thickness of the plastic parts. Generally, the hardening time of domestic injection materials after mold filling can be calculated according to the maximum wall thickness of plastic parts and the hardening rate of 8~12s/mm.