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Basic Knowledge About Injection Molding Mold

1.  Injection molding mold Nozzle 

Generally speaking, the melt can flow from one nozzle into another. However,  in some molds the nozzle can be used as part of the mold since the nozzle extends to the bottom of the mold.  It has two main nozzles: open nozzles and closed nozzles.  In injection molding production, open nozzles should be used more, as they are cheaper and less likely to hold. If the injection mold is equipped with a decompression device, this nozzle can be used even for lower viscosity melts. Sometimes a closed nozzle must be used, because this nozzle acts as a stop valve and can block the plastic in the injection cylinder. To ensure that the nozzle fits into the sprue sleeve correctly, the top hole is slightly smaller than the sprue sleeve, which allows the sprue to be withdrawn from the mold more easily.

2. Filter and combined nozzle of injection molding mold

Plastic impurities can be removed by the filter of the extendable nozzle, that is, the molten and plastic flow through a channel, which is divided into narrow spaces by inserts. These narrows and gaps remove impurities and improve mixing of the plastic. Therefore, extended, fixed mixer can be used to achieve better mixing effect. These devices can be installed between the shot tank and the nozzle to separate and remix the melt to allow the melt to flow through the stainless steel channels.

3. Exhaust of injection molding mold

Some plastics need to be vented in the injection cylinder during China custom plastic injection molding, so that the gas can be discharged. Most of the time these gases are just air, but it could also be moisture or monomolecular gases released from melting. If these gases cannot be released, they are compressed by the melt and carried into the injection mold, where they will form bubbles in the product. If the gas is to be expelled before it reaches the nozzle or die, it is sufficient to reduce the screw root diameter.

In China plastic injection mold factory, the gas can be exhausted from the holes in the shot cylinder. Then the diameter of the screw root is increased, and the melted glue of volatiles is adapted to the nozzle. An injection molding machine equipped with this facility is called a vented injection mold tooling machine. There should be a smoke exhauster with good catalytic gas effect above the exhaust injection molding machine to remove potentially harmful gases.

4. The effect of increasing the back pressure of the injection molding mold

To get a high-quality melt, the plastic is heated or melted consistently and mixed well. Proper melting and mixing is achieved with the correct screw and sufficient pressure (or back pressure) in the shot cylinder to achieve mixing and thermal consistency. By increasing the resistance to oil return, back pressure can be created in the firing cylinder. But the screw takes longer to reset, so there is more wear and consumption in the injection moulding drive system. Keeping back pressure as much as possible and isolate it from air also requires consistent melt temperature and mixing degree.

5. Check valve of injection molding mold

No matter which screw is used, the tip is usually equipped with a stop valve to prevent the plastic from flowing out of the nozzle, and also equipped with a decompression (reverse cable) device or a special shooting nozzle. it must be checked regularly, if you use the stopper for supply and marketing, because it is an important part of the shooting material tank. At present, switch-type nozzles are not commonly used, because the nozzle equipment is prone to leakage and decomposition of plastic. Each plastic is now listed with the appropriate nozzle type.

6. Rotation speed of injection molding mold screw

The rotational speed of the screw affects the stability of the injection moulding process step by step and the amount of heat acting on the plastic. The faster the screw turns, the higher the temperature. When the screw rotates at high speed, the frictional (shear) energy transmitted to the plastic improves the plasticizing efficiency, but also increases the non-uniformity of the melt temperature. Due to the importance of screw surface speed, the screw rotation speed of a large injection molding machine should be less than that of a smaller injection molding machine. Because at the same rotational speed, the shear heat energy generated by the large screw is much higher than that of the small screw. the speed at which the screw rotates is also different because of the different plastics.

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