And Injection mold processing plant Relevant main plastic properties

Movability The plastic in molten form after being heated can only fill the entire cavity under pressure, which is called mobility. Generally, professional mobility test mold is used to stop the test

The mobility of plastics of the same variety and different brands is different. Plastic parts of different structures have different requirements for the mobility of plastics. The mobility of plastics is closely related to the conditions such as molding temperature and pressure

Generally, if the mobility is too large, on the one hand, the molten material will not be filled tightly, resulting in loose products and affecting the quality of goods; On the other hand, the mobility is too large, and the periphery of the injection molded parts is easy to show a flaring edge (burr), mold sticking and nozzle flow, forming a nozzle blockage. The mobility of the plastic is too small. For the plastic parts with complex structure and long process, it is difficult to move during the injection processing and production, and it is easy to show signs of glue shortage, water shrinkage, etc., and a small amount of waste products occur; Or it is necessary to use high-pressure injection molding, which is easy to cause excessive internal stress in the plastic parts. We should select plastic molding with appropriate mobility according to the commodity structure, size and thickness. The content of water absorbing volatiles in thermoplastics more or less contains water and volatiles, and excessive water has a plasticizing effect

If the water content and volatile matter in the plastic exceed a certain proportion, many achievements will be made during injection molding (such as degradation, fogging, strength reduction, etc.). In serious cases, bubbles (crazing) and rough appearance may occur. It is difficult to make precision of fine plastic parts due to bad scenes such as damage of light transmittance (turbidity) of transparent products

However, the relatively dry plastic will cause reduced mobility, brittle addition, and difficult filling during molding, which is also unusable. Pay special attention to this. Some people think that the more boring the plastic, the better. This is a wrong idea

There are three main reasons that cause more moisture and volatile matter in plastics:; A. The uniform molecular weight of plastic resin is low; B. The consumption of plastic resin has not lost its full dryness; C. The plastic with high water absorption absorbs the moisture in the surrounding air due to improper storage. Different plastics have different drying temperature and drying time rules

Expansion rate

The secondary causes of expansion rate are as follows:

A. Plastics have much greater thermal expansion than metals (an order of magnitude, about ten times greater)

B. The plastic product is not rigid after hardening, but has a certain elastic recovery after demoulding

C. When just demoulding, the pressure begins to decrease, but the plastic part still sticks to the mold wall, and the product undergoes plastic deformation

The factors that affect the expansion rate are the properties of plastics, molding conditions, mold and product design. The expansion rate of amorphous plastics is less than 1%, and the expansion rate of crystalline plastics is more than 1%. The products of crystalline plastic injection molding have a post expansion scene, and they need to stop measuring their size after cooling for 24 hours, with an accuracy of 0.02mm

Processing temperature of plastics The processing temperature of plastics is the temperature that reaches the viscous flow state, and the processing temperature is not a point but a range (from the melting point to the decomposition temperature). When hot forming of plastics is stopped, the appropriate processing temperature should be selected according to the size, complexity, thickness, insert condition, temperature tolerance of the colorant used, machine function and other factors

Why is the temperature reflected by the thermometer often changeable in injection molding consumption, and the temperature set when the same product (the same mold) is put into different machines for consumption can be different?

In practice, the hot forming temperature of plastics is fixed, which is only due to the differences in temperature measurement methods, temperature measurement point layout and the functions of temperature sensors. The temperature displayed on the temperature indicator controller is not the actual temperature of molten materials in the barrel, but the direct and partial temperature