How does an injection molding machine control temperature?

The temperatures that must be controlled by the injection molding machine during the injection molding process include barrel temperature, nozzle temperature and mold temperature. The first two temperatures seriously affect the plasticization and fluidity of the plastic, while the latter two temperatures seriously affect the fluidity and cooling of the plastic.

1. Injection molding machine barrel temperature

"The selection of the injection molding machine barrel temperature is related to the characteristics of the plastic, and largely depends on the flow temperature (Tf) or melting point (Tm) of the plastic.

For amorphous plastics, the high temperature at the end of the barrel should be higher than Tf, while crystalline plastics should be higher than Tm, but the temperature of the plastic should be lower than the melting temperature (Td) of the polymer. Therefore, the good temperature range of the barrel should be between Τf or Τm--Τd.

For plastics with a narrow range of Tf or Tm--Td, such as PVC, pom, etc., the barrel temperature should be controlled slightly lower, and for plastics with a wider range, such as pE, APP, etc., the barrel temperature should be controlled slightly lower and the temperature can be slightly higher. In addition, the plastic, filler and Heat resistance, content and distribution of reinforced materials, crafts and injection molds and their injection molding equipment. The barrel distribution is stable. Generally, the silo starts and stops the nozzle and gradually rises, so that the temperature of the raw materials rises evenly to achieve the purpose of plasticization and symmetry.

2. Injection molding machine nozzle temperature

Due to the different nozzles, the melt temperature will increase with the increase of cutting speed (about 103-102), so the nozzle temperature is slightly lower than the high temperature of the barrel, but if it is too low, the injection working pressure will increase, or cause the raw materials to solidify prematurely, affecting the quality of crafts.

Due to the many factors that affect the fluidity of polymers, it is generally adjusted according to "air injection" or "craft visualization analysis" before molding, which is convenient for confirming a good injection from the text Molding machine barrel temperature and nozzle temperature.

3. Injection molding machine mold temperature

Mold temperature has a considerable impact on the quality of handicrafts. Its selection is whether the polymer is crystallized, the specifications and structure of the process, and other injection standards (melt temperature, injection rate and working pressure, molding cycle), etc.

For non-crystalline polymers, mold temperature has a key influence on the viscosity (fluidity) of the solution.

If the melt viscosity of the raw material is low, such as Ps, the mold temperature can be slightly lower to increase the yield. If the melt viscosity is high (such as mPPE, PSF), choose a higher mold temperature: mPPE is 120℃~140℃, PSF is 140℃~130℃.

For crystalline polymers For materials, the crystals in the large injection molding machine mold are non-isothermal. The mold temperature of the injection molding machine should be set near or slightly lower than the temperature (Tcm) where the maximum crystallization rate occurs between Tg and Tm.

For example, the Tcm of PP is 65℃, PET is 190℃, and AS-6 is 146℃; the Tg of several polymers is -30℃, 83℃ and 46℃ respectively; the mold temperature during injection is 40℃~86℃, 160℃~180℃ and 75℃~130℃ respectively, so that the raw materials can be cooled and solidified under the maximum crystallization rate standard. If a low temperature state is caused, the grain size is very low, the rigidity of the product is insufficient, and the demolding is affected. However, for high-pressure polyethylene, even if the low temperature level is quite large, products with high grain size can be obtained.