|Servo & Standard & Variable Pump
all electric injection molding machines,
plastic products making machine
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 become darker 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 a distinct 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 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 makes the load-bearing capacity greatly reduced, and it is liable 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 the internal corners.
7) The elongation of pure PBT can reach 200%, so products with smaller depressions can be demoulded by force from the die. However, after filling with glass fibers or fillers, the elongation decreases greatly. If there are holes in the products, forced demoulding can not be carried out.
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.
(2) Main Injection Molding Conditions of PBT
1) barrel temperature. The selection of barrel temperature is very important for the forming of PBT. For example, too low temperature and poor plasticization will result in material shortage, depression, uneven shrinkage and gloss. The temperature is too high, will cause serious nozzle salivation, overflow, darker color, and even degradation. Usually, the barrel temperature is controlled at 240-280 C, and the glass fiber reinforced PBT is controlled at 230-260 C. The temperature of the nozzle should be controlled below 5 - 10 C in the front section of the barrel.
2) Mould temperature. Mold temperature is directly related to dimensional stability, warping deformation, forming period and crystallinity of products. PBT is easy to crystallize, even at room temperature, it crystallizes very quickly, so the mould temperature does not need to be too high, usually 40-60 C, while the glass fiber reinforced PBT is slightly higher, usually 60-80 C.
3) Injection pressure. PBT melt has low viscosity and good fluidity. It can use medium injection pressure, generally 60-90 MPa, glass fiber reinforced PBT 80-100 MPa. Usually injection pressure increases with the increase of the thickness of plastic parts, but not more than 100 MPa. Otherwise, it will make demoulding difficult.
Contact Person: Mr. Michael