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What must be done before injection molding?

What must be done before the injection molding machine is turned on
1. Check whether there is water or oil in the electrical control box. If the electrical components are damp, do not start the machine. The electrical components should be blown dry by maintenance personnel before starting the machine.
2. Check whether the power supply voltage meets the requirements, generally should not exceed 15%.
3. Check whether the emergency stop switch and front and rear safety door switches are normal. Verify that the rotation direction of the motor and the oil pump are the same. Check whether the electrical connections are loose.
4. Check whether the cooling pipes are unblocked, and pass cooling water into the oil cooler and the cooling water jacket at the end of the barrel.
5. Check whether there is lubricating oil (grease) in each movable part, and add enough lubricating oil.
6. Turn on the electric heating switch to heat each section of the barrel. When the temperature of each section reaches the requirements, keep it warm for a period of time to stabilize the temperature of the injection molding machine. The holding time varies according to the requirements of different equipment and plastic materials.
7. Add enough plastic to the hopper. According to the requirements of different plastics for injection molding, some raw materials need to be dried first.
8. The heat shield on the barrel should be covered, so as to not only save energy, but also extend the life of the electric heating coil and current contactor.

Preparation before injection molding
1. Pretreatment of raw materials
According to the characteristics of the plastic and the supply of materials, the appearance and process performance of the raw materials should be tested before 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, an appropriate amount of colorant or color masterbatch can be added; the supplied pellets often contain different The degree of moisture, solvents and other volatile low-molecular 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 commonly 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
For 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 mold cavity 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, etc.) The rigid chain polymer is more prominent). The existence of this kind of internal stress will cause cracks to appear 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, take measures such as larger wall thickness around the inserts.

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 injection production, it is necessary to clean or disassemble the barrel of the injection molding machine.
The cleaning barrel generally adopts the 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, and used 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.