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What products are made by injection molding?

TIME:2021-01-07 Share

Injection molding is an injection molding machine used to manufacture many things, such as wire spools, packaging, bottle caps, automotive parts and components, toys, pocket combs, one-piece chairs and small tables, storage containers, mechanical parts and most other plastic products.

What is the principle of injection molding process?
Injection molding: refers to a model with a certain shape. The molten colloid is injected into the mold cavity by pressure. The process principle is: the solid plastic is melted at a certain melting point and injected at a certain speed through the pressure of the injection machine In the mold, the mold is cooled by a water channel to solidify the plastic to obtain the same product as the designed cavity. It is mainly used for the molding of thermoplastics, but also for the molding of thermoset plastics.

What are the factors that affect the injection result?
1. Material temperature:
The processing temperature of the plastic is controlled by the barrel of the injection machine. The correct selection of the barrel temperature is related to the plasticization quality of the plastic. The principle is to ensure smooth injection molding without causing partial degradation of the plastic. Generally, the maximum temperature at the end of the barrel should be higher than the flow temperature (or melting temperature) of the plastic, but lower than the decomposition temperature of the plastic.

In addition to strictly controlling the maximum temperature of the injection machine barrel during production, the residence time of the plastic melt in the barrel should also be controlled. When determining the barrel temperature, the structural characteristics of the product and mold should also be considered. When forming thin-walled or complex-shaped products, the flow resistance is large, and increasing the barrel temperature helps to improve the fluidity of the melt.
The maximum temperature of the nozzle is usually controlled to be slightly lower than the maximum temperature of the barrel to prevent the melt from casting at the nozzle mouth.

2. Mold temperature:
In the injection molding process, the mold temperature is controlled by the cooling medium (usually water), which determines the cooling rate of the plastic melt. The lower the mold temperature, the faster the cooling rate, and the faster the melt temperature decreases, resulting in an increase in melt viscosity and injection pressure loss, which may even cause insufficient mold filling in severe cases. As the mold temperature increases, the melt fluidity increases, the required filling pressure decreases, and the surface quality of the product improves; but due to the increase in cooling time, the productivity of the product decreases and the molding shrinkage rate of the product increases.

Injection molding process
For crystalline plastics, since higher temperatures are conducive to crystallization, increasing the mold temperature can increase the density or structural crystallinity of the product. At higher mold temperatures, the polymer macromolecules in the product relax faster, and the molecular orientation and internal stress will be reduced.

The time required to complete one injection molding is called the injection molding cycle, which includes feeding, heating, filling, holding pressure, cooling time, as well as time for mold opening, demolding, mold closing, and auxiliary operations. In the entire injection molding cycle, the injection speed and cooling time have a decisive influence on the performance of the product.


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