What are the process conditions of PBT injection moulding?
Release date:2019-08-30 15:08
Machinability of PBT
1) PBT has less hygroscopicity, but it is sensitive to water at high temperature. When it is processed, PBT molecule will be degraded, its color will deepen and its surface will be marked. Therefore, it should be dried normally.
2) PBT melt has excellent fluidity, so it is easy to form thin-walled products with complex shapes, but attention should be paid to die spills and nozzle salivation.
3) PBT has obvious melting point. When the temperature rises above the melting point, the fluidity will increase dramatically, especially attention should be paid to it.
4) PBT is suitable for rapid injection because of its narrow processing range, fast crystallization and good fluidity.
5) PBT has a larger shrinkage rate and shrinkage range, and the difference of shrinkage rate in different directions is more obvious than other plastics.
6) PBT is sensitive to the response of notches and sharp corners. Stress concentration is easy to occur at these locations, which can greatly reduce the bearing capacity and lead to rupture when subjected to stress or impact. Therefore, this should be paid attention to in the design of plastic parts. Arc transition should be adopted at all corners, especially internal corners.
7) The elongation of pure PBT can reach 200%, so the products with smaller depression can be demoulded by force from the die. However, after filling with glass fiber or filler, the elongation decreases greatly, and forced demoulding can not be carried out if there are holes in the product.
8) The channel of PBT die is shorter and thicker when possible, and the circular channel is the best. Generally modified and unmodified PBT can be used in common runner, but glass fiber reinforced PBT can be formed by hot runner.
9) Point gate and latent gate have great shearing effect, which can reduce the apparent viscosity of PBT melt and is beneficial to forming. They are commonly used gate, and the gate diameter should be larger.
10) Gate should be directed to the core cavity or core, which can avoid spraying and minimize the filling of melt when flowing in the cavity. Otherwise, the product is prone to surface defects and deterioration of performance.