Forming and processing properties of PBT
1) The moisture absorption of PBT is small, but it is sensitive to moisture at high temperature. During molding, PBT molecules will be degraded, the color will become darker, and the surface will produce
Mark, so it should be dried normally.
2) PBT molten material has excellent fluidity, so it is easy to form thin-walled and complex shaped products, but pay attention to mold overflow and nozzle salivation
Phenomenon.
3) PBT has an obvious melting point. When the temperature rises above the melting point, the liquidity will increase sharply, which should be noted.
4) PBT molding processing range is narrow, cooling crystallization is fast, coupled with good liquidity, especially suitable for rapid injection.
5) PBT has a large shrinkage rate and its shrinkage range, and the difference of shrinkage rate in different directions is more obvious than other plastics.
6) PBT is very sensitive to notch and sharp corner. Stress concentration is easy to occur at these positions, which greatly reduces the bearing capacity
It is easy to crack when striking, so attention should be paid to this point when designing plastic parts. All corners, especially internal corners, should be rounded as far as possible
Du.
7) The elongation of pure PBT can reach 200%, so the products with small depressions can be forced to demould from the mold. But filled with glass fiber or filler
After that, its elongation is greatly reduced, and forced demoulding cannot be carried out in case of any depression in the products.
8) When possible, the runner of PBT mold should be short and thick, and the round runner is the best- Ordinary modified and unmodified PBT can be used
However, glass fiber reinforced PBT can only have a good effect by hot runner molding.
9) The shearing effect of the point gate and the latent gate is large, which can reduce the apparent viscosity of the PBT melt, and is conducive to forming. They are frequently used gates
The mouth diameter should be larger.
10) It is better to face the core cavity or core directly with the gate, so as to avoid spraying and minimize the back filling when the molten material flows in the cavity. Otherwise, the product capacity
It is easy to produce surface defects and degrade the performance.
Main injection molding conditions of PBT
1) Barrel temperature. The selection of barrel temperature is very important for the forming of PBT. If the temperature is too low and the plasticization is poor, the products will be short of material and concave
Collapse, uneven shrinkage and tarnish. If the temperature is too high, the nozzle will salivate seriously, overflow, darken the color, and even degrade. through
Normally, the barrel temperature is controlled at 240~280 ° C, and the glass fiber reinforced PBT is controlled at 230~260 ° C. The nozzle temperature shall be controlled below the temperature in the front of the barrel
Degree 5~10 ° C.
2) Mold temperature. Mold temperature is directly related to the dimensional stability, warpage, molding cycle and crystallinity of products. PBT is easy to crystallize, i.e
The mold temperature does not need to be too high, usually 40~60 ° C, because the mold temperature of glass fiber reinforced PBT is slightly higher, usually
60~80°C。
3) Injection pressure. PBT melt has low viscosity and good fluidity. Medium injection pressure can be used, generally 60~90MPa, and glass fiber reinforced
The PBT is 80~100MPa. Generally, the injection pressure increases with the increase of the thickness of the plastic part, but it should not exceed 100MPa, otherwise it will be difficult to demould.
