ABS resin is a terpolymer developed on the basis of modification of polystyrene resin. Where a represents acrylonitrile, B represents butadiene, and s represents styrene. ABS resin has comprehensive properties of three components. A can improve oil resistance and chemical corrosion resistance, so it has a certain surface hardness; B Make ABS present rubber like toughness and improve impact toughness; S makes ABS plastics have better fluidity, good thermoplastic molding and processing properties.

ABS plastic is mainly used in manufacturing the shells of instruments, household appliances, telephones, televisions and electroplating ABS plastic in China to make it have metallic luster and replace metal. Injection molding is the main molding method of ABS plastics, and its molding mainly depends on six conditions.

Drying of ABS plastics

ABS plastic has good hygroscopicity and sensitivity to water. Processing Plastic water storage tank Before fully drying and preheating, it can not only eliminate the pyrotechnic bubble band and silver wire caused by water vapor on the surface of the part, but also help to plasticize the plastic and reduce the color spots and clouds on the surface of the part. The moisture content of ABS raw materials should be controlled below 013%.

The drying conditions before injection molding are: the drying period is below 75~80 ℃ in winter, 2~3H, and 80~90 ℃ in summer and rainy season, 4~8h. If the parts need to obtain special excellent gloss, or the parts themselves are complex, the drying time is long, up to 8~16h. Due to the existence of trace water vapor, the fog spots on the surface of parts are often ignored.

Injection temperature

The relationship between temperature and melt viscosity of ABS plastics is different from that of other amorphous plastics. When the melting temperature rises, the melting is practically not reduced. However, once the plasticizing temperature (suitable for processing temperature range, such as 220~250 ℃) is reached, if the temperature continues to rise blindly, it will lead to thermal degradation of ABS with low heat resistance, but it will increase the melt viscosity, make injection molding more difficult, and reduce the mechanical properties of parts. Therefore, although the injection temperature of ABS is higher than that of polystyrene and other plastics, it cannot have a relatively loose heating range like the latter.

The greater the temperature changes, the defects such as welding, poor gloss, flash, mold sticking and discoloration will occur.

Injection pressure

The viscosity of ABS melt is higher than that of polystyrene or modified polystyrene, so higher injection pressure is used in the injection process. Of course, not all ABS components require high pressure. For small parts with simple structure and large thickness, lower injection pressure can be used. In the injection molding process, the pressure in the mold cavity when the gate is closed often determines the surface quality of the workpiece and the degree of silver wire defects. If the pressure is too small, the plastic will shrink significantly, and there is a great chance of disengagement from the cavity surface, and the part surface will be atomized. If the pressure is too high, the friction between the plastic and the cavity surface is very strong, which can easily lead to die sticking.

Injection speed

ABS material with medium injection speed has better effect. When the injection speed is too fast, the plastic is easy to be burnt or decomposed and gasified, resulting in defects such as fusion, poor gloss and red plastic near the gate. However, in the production of thin-walled complex parts, it is still necessary to ensure a sufficiently high injection speed, otherwise it is difficult to fill.

Mold temperature

The molding temperature of ABS is relatively high, and the mold temperature is also relatively high. The mold temperature is generally adjusted to 75~85 ℃. When producing parts with large projection area, the temperature of fixed mold is required to be 70~80 ℃, and the temperature of mobile mold is required to be 50~60 ℃. When injecting large, complex and thin-walled parts, special heating of the mold should be considered. In order to shorten the production cycle and keep the mold temperature relatively stable, after taking out the parts, you can use cold water bath, hot water bath or other mechanical setting methods to compensate for the original cold fixing time in the mold cavity.

Material quantity control

When the injection volume of each injection molding machine reaches 75% of the standard value, the injection volume of each injection molding machine reaches the standard value. In order to improve the quality and dimensional stability of parts, as well as the uniformity of surface gloss and hue, the injection volume is required to be 50% of the calibrated injection volume.