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What are the preparations for the injection molding machine before injection molding?

TIME:2020-12-28 Share

What are the preparations for the injection molding machine before injection molding?

1. Pretreatment of raw materials
According to the characteristics of the plastic and the supply of materials, the general injection molding machine should test the appearance and process performance of the raw materials before injection molding. If the plastic used is in powder form, such as polyvinyl chloride (PVC), it should also be batched and dry blended; if the plastic part has color requirements, you can add an appropriate amount of colorant or color masterbatch; the supplied pellets often contain different The degree of moisture, solvents and other volatile low-molecular-weight substances, especially some plastics with a tendency to absorb moisture, always exceed the allowable limit for processing. Therefore, it must be dried before processing and the water content must be measured. The moisture content of polycarbonate (PC), which is sensitive to water at high temperatures, is required to be below 0.2%, even 0.03%-0.05%, so vacuum drying ovens are often used for drying. The dried plastic must be properly sealed and stored to prevent the plastic from absorbing moisture from the air and losing the drying effect. For this reason, the use of a dry hopper can continuously provide dry hot materials for the injection molding machine, which is useful for simplifying operations, maintaining cleanliness, and improving quality. It is beneficial to increase the injection rate. The filling amount of the drying hopper is generally 2.5 times the hourly consumption of the injection molding machine.

2. Preheating of the insert
In order to meet the requirements of assembly and strength of injection molded products, metal inserts need to be embedded in the plastic parts. During injection molding, when the cold metal insert placed in the cavity of the injection molding machine and the hot plastic melt are cooled together, due to the significant difference in shrinkage of metal and plastic, large internal stresses are often generated around the insert (especially like PS and other rigid chain polymers are more prominent). The existence of this kind of internal stress will cause cracks around the insert, which will greatly reduce the performance of the plastic part. This can be achieved by selecting metals with large thermal expansion coefficients (aluminum, steel, etc.) as inserts, and preheating the inserts (especially large metal inserts). At the same time, when designing plastic parts, adopt measures such as larger wall thickness around the insert.

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3. Cleaning of the barrel
Before the newly purchased injection molding machine is used for the first time, or when it is necessary to change the type of plastic, change the raw material, the color, or find that there is decomposition in the plastic during the injection molding production, the injection molding machine barrel needs to be cleaned or removed
The cleaning barrel generally adopts heating barrel cleaning method. Cleaning materials generally use plastic raw materials (or plastic recycled materials). For the storage of heat-sensitive plastics, such as polyvinyl chloride, low-density polyethylene, polystyrene, etc. can be used for transitional cleaning, and then the transitional cleaning can be replaced with new processed materials.

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

The above is the knowledge about injection molding machine introduced by LISONG Machinery. For more professional knowledge of injection molding machine, please leave a message online or email us: kevin@lisonginc.com

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