What are the process conditions for injection molding

Update:29-03-2019
Summary:

1. PBT has less hygroscopicity, but it is sensitive to […]

1. PBT has less hygroscopicity, but it is sensitive to moisture at high temperatures. PBT molecules are degraded during molding, the color becomes darker, and the surface is stained, so it should be dried.

2. PBT melt has excellent fluidity, so it is easy to form thin-walled, complex-shaped products, but pay attention to mold overflow, and nozzle flow phenomenon.

3. PBT has a clear melting point, when the temperature rises above the melting point, the fluidity will suddenly increase, especially to pay attention.

4. PBT molding processing range is narrow, crystallizing quickly when cooling, coupled with good fluidity, especially suitable for rapid injection.

5. PBT has a large shrinkage rate and its shrinkage range, and the difference in shrinkage in different directions is more obvious than other plastics.

6. PBT is very sensitive to the reaction of notches and sharp corners. Stress concentration tends to occur at these locations, which greatly reduces the bearing capacity and is prone to cracking when subjected to stress or impact. Therefore, attention should be paid to the design of plastic parts. All corners, especially internal corners, should use arc transitions as much as possible.

7. The elongation of pure PBT can reach 200%, so products with smaller depressions can be forced to release from the mold. However, after being filled with glass fiber or filler, the elongation thereof is greatly lowered, and forced release may not be performed if there is a depression in the product.

8. The flow path of the PBT mold is preferably short and thick under the possible conditions, and the circular flow path is the best. Generally, both modified and unmodified PBT can be used in ordinary flow channels, but glass fiber reinforced PBT can be applied to hot runner molding to have good effects.

9. the point gate and the latent gate have a large shearing effect, which can reduce the apparent viscosity of the PBT melt, which is beneficial to the molding. It is a frequently used gate, and the gate diameter should be larger.

10. The gate is preferably facing the core cavity or core so as to avoid jetting and to minimize the replenishment of the melt as it flows through the cavity. Otherwise, the article is prone to surface defects and degrades performance.