The generation of injection pressure of plastic processing equipment should be treated with caution

When plastic processing equipment processes plastic products, it will gradually produce some pressure in the workflow, such as the pressure caused by injection molding, or the pressure caused by mold locking, back pressure and nozzle. When the pressure is generated, you must pay attention not to operate the plastic processing equipment rashly, because the pressure will bring danger. If you take the risk to force the plastic processing equipment to do some operations, there may be accidents.

◆ injection pressure

This is the pressure that causes plastic flow and can be measured with sensors on the nozzle or hydraulic line. It has no fixed value, and the more difficult it is to fill the mold, the injection pressure of plastic processing equipment also increases. The injection line pressure is directly related to the injection pressure.

During the filling phase of the injection cycle, high injection pressure may be required to maintain the injection speed at the required level. After the mold is filled, high pressure is no longer required. However, when some semi crystalline thermoplastics (such as PA and POM) are injected, the structure will deteriorate due to the sudden change of pressure, so it is sometimes unnecessary to use the secondary pressure.

◆ clamping pressure

In order to resist the injection pressure, the mold locking pressure must be used. Do not automatically select a larger value for use, but consider the projection area and calculate a suitable value. The projected area of injection molded parts is a large area seen from the application direction of clamping force.

For most injection molding cases, it is about 2 tons per square inch, or 31 trillion Newtons per square meter. However, this is only a low value and should be taken as a rough empirical value, because once the injection molded part has any depth, the side wall must be considered.

◆ back pressure

This is the pressure to be generated and exceeded before the screw retreats. Although the use of high back pressure is conducive to the uniform dispersion of pigment and the melting of plastic, it also prolongs the return time of the middle screw, reduces the length of the fiber contained in the filled plastic, and increases the stress of the plastic processing equipment; Therefore, the lower the back pressure, the better. Under no circumstances can it exceed 20% of the injection pressure (higher quota) of plastic processing equipment.

◆ nozzle pressure

Nozzle pressure is the pressure inside the nozzle. It’s about the pressure that causes the plastic to flow. It has no fixed value, but increases with the difficulty of mold filling. There is a direct relationship between nozzle pressure, linear pressure and injection pressure. In plastic processing equipment, the nozzle pressure is about 10% less than the injection pressure.

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