Process conditions of PBT injection molding
Process conditions of PBT injection molding
1) PBT has less
hygroscopicity, but it is sensitive to water at high temperature. During the
molding process, PBT molecules will be degraded, the color will be darker, and
the surface will produce spots, so it should be dried.
2) PBT melt has excellent fluidity, so it is easy to form thin-walled and
complex products, but pay attention to die overflow and nozzle salivation.
3) PBT has an obvious melting point. When the temperature rises above the
melting point, the fluidity of PBT will increase sharply, especially attention
should be paid.
4) PBT is suitable for rapid injection because of its narrow processing range,
fast crystallization and good fluidity.
5) PBT has a large shrinkage and its shrinkage range, and the shrinkage
difference in different directions is more obvious than other plastics.
6) PBT is very sensitive to the response of notches and sharp corners. In these
locations, stress concentration is easy to occur, which makes the bearing
capacity greatly reduced, and it is easy to crack when subjected to force or
impact. Therefore, attention should be paid to this point in the design of
plastic parts. Circular arc transition should be adopted at all corners,
especially the internal corners.
7) The elongation of pure PBT can reach 200%, so the products with small
depression can be forced to demould from the mold. However, after filling with
glass fiber or filler, its elongation is greatly reduced. If there is a
depression in the products, forced demoulding cannot be carried out.
8) When possible, the channel of PBT die is shorter and thicker, and the effect
of circular channel is the best. General modified and unmodified PBT can be
used in common flow channel, but glass fiber reinforced PBT can be used in hot
flow channel molding.
9) Point gate and latent gate have great shear effect, which can reduce the
apparent viscosity of PBT melt, and is beneficial to molding. They are often
used gates, and the gate diameter should be larger.
10) The gate is preferably facing the core cavity or core, so as to avoid
spraying and minimize the replenishment when the molten material flows in the
cavity. Otherwise, the product is easy to produce surface defects, and
performance degradation.
Main injection
molding conditions of PBT
1) Barrel temperature. The selection of barrel temperature is very important
for PBT molding, such as low temperature and poor plasticization, which will
result in material shortage, depression, uneven shrinkage and lusterless. If
the temperature is too high, the nozzle will salivate seriously, overflow the
edge, darken the color and even degrade. Generally, the barrel temperature is
controlled at 240-280 ℃, and the glass fiber-reinforced PBT is
controlled at 230-260 ℃. The temperature of the nozzle should be
controlled at 5 ~ 10 ℃ lower than that of the front section of
the barrel.
2) Mold temperature. Mold temperature is directly related to dimensional
stability, warpage, molding cycle and crystallinity of products. PBT is easy to
crystallize, even at room temperature, it also crystallizes quickly, so the
mold temperature does not need to be too high, usually 40 ~ 60 ℃, while the mold temperature of glass
fiber reinforced PBT is slightly higher, usually 60 ~ 80 ℃.
3) Injection pressure. The melt viscosity of PBT is low and its fluidity is
good. Medium injection pressure can be used, generally 60-90mpa, 80-100mpa for
glass fiber reinforced PBT. Generally, the injection pressure increases with
the increase of the thickness of the plastic part, but not more than 100MPa,
otherwise it will make the demoulding difficult.
