Lab Injection Molding Machine

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injection molding machine

Pretreatment of raw material

According to the characteristics of plastics and material supply, the appearance and process performance of raw materials should be tested before molding. If the plastic used is a powder, such as polyvinyl chloride (PVC)? Proportioning and dry blending shall also be carried out; if the plastic part has color requirements, a proper amount of colorant or color masterbatch can be added; the supplied granules often contain different degrees of moisture, solvents and other volatile low molecular substances, especially the moisture content of some plastics with moisture absorption tendency always exceeds the allowable limit for processing. Therefore, the drying treatment must be carried out before processing, and the water content must be measured.

Polycarbonate (PC), which is sensitive to water at high temperatures, is required to have a moisture content of 0.Less than 2%, even 0.03% -0.05%, so it is usually dried by vacuum drying oven. The dried plastics must be properly sealed and stored to prevent the plastics from absorbing moisture from the air and losing the drying effect. Therefore, the use of a dryable hopper can continuously provide dry hot materials for the injection molding machine, which is beneficial to simplifying the operation, keeping clean, improving the quality and increasing the injection rate. The loading capacity of the drying hopper is generally 2.5 times of the hourly loading capacity of the injection molding machine.

injection molding machine

Preheating of the insert

In order to meet the assembly and strength requirements of injection molding products, metal inserts need to be embedded in the plastic parts. During injection molding, when the cold metal insert placed in the mold cavity is cooled together with the hot plastic melt, large internal stresses are often generated around the insert due to the significant difference in shrinkage rate between metal and plastic (especially for rigid chain polymers such as PS).

The existence of this internal stress will cause cracks around the insert, which will greatly reduce the performance of the plastic parts.This can be done by selecting a metal with a high coefficient of thermal expansion (aluminum, steel, etc.) For the insert and preheating the insert, especially the large metal insert. At the same time, when designing plastic parts, measures such as larger wall thickness are adopted around the insert.

Cleaning of the barrel

Before the newly purchased injection molding machine is used for the first time, or when the plastic variety needs to be changed, the raw material and color need to be replaced, or the decomposition phenomenon is found in the plastic in the injection molding production, the barrel of the injection molding machine needs to be cleaned or disassembled. The heating barrel cleaning method is generally used to clean the barrel. Plastic raw materials (or plastic recycled materials) are generally used as cleaning materials. For heat-sensitive plastics, such as the stock of polyvinyl chloride, low density polyethylene, polystyrene, etc. Can be used for transition cleaning, and then the new material processed can be used to replace the transition cleaning material.

Selection of release agent

Release agent is a substance that can make plastic products easy to release. Zinc stearate is suitable for general plastics except polyamide; liquid paraffin is better for polyamide plastics; silicone oil is expensive and troublesome to use, so it is seldom used. The use of release agent should be controlled in an appropriate amount, as little as possible or not. Excessive spraying will affect the appearance of plastic parts, and will also have a negative impact on the decoration of plastic parts.