ABS, commonly known as "acrylonitrile butadiene styrene", is synthesized by copolymerization of acrylonitrile-butadiene-styrene monomers. The fluidity of ABS, if mixed with other plastics or additives, can be extended to ABSs of different uses and properties, such as impact resistance, heat resistance, flame retardant, transparency, reinforcement, electroplating, etc.
The fluidity of ABS is between PS and PC. The fluidity of ABS is related to the injection temperature and pressure, and the injection pressure is a little more important. Therefore, high injection pressure is often used to reduce the melt viscosity and improve the mold filling performance.
1. Treatment of plastics
The water absorption rate of ABS is about 0.2-0.8. For general grades, drying for 2-4 hours with oven at 80-85 ℃ before processing or 1-2 hours at 80 ℃ with drying hopper. For heat resistant grade ABSs containing PC components, the drying temperature is properly adjusted to 100C, The specific drying time can be determined by squeezing out the air.
Recycled materials should not be used more than 30 percent, electroplated ABS can not use recycled materials.
3. Mould and gate design
The mold temperature can be set to 60-65 ℃. The runner diameter is 6-8 mm. the gate width is about 3mm, the thickness is the same as the product, the gate length is less than 1mm. the exhaust hole width is 4-6mm, the thickness is 0.025-0.05mm.
4. Melt temperature
Accurate determination can be made by air injection. Different grades and different melting temperatures are recommended as follows:
Impact grade: 220 ℃ -260 ℃, 250 ℃ preferred
Electroplating grade: 250 ℃-275 ℃, 270 ℃ preferred
Heat resistance: 240 ℃ -280 ℃, 265 ℃ -270 ℃.
Flame retardant grade: 200 ℃ -240 ℃, 220 ℃ -230 ℃
Transparent grade: 230 ℃ -260 ℃, preferably 245 ℃
Glass fiber reinforcements: 230 ℃ -270 ℃
For products with high surface requirements, high melting temperature and mold temperature are adopted.
5. Injection speed
The fire resistance grade should be slow and the heat resistant grade should be fast. If the surface requirement of the product is high, the injection speed of high speed and multi-stage injection molding should be used.
6. Back pressure
In general, the lower the back pressure, the better, the commonly used back pressure is 5 bar. dyeing materials need to use a higher back pressure to make the mixture uniform.
7. Residence time
At a temperature of 265 ℃, the retention time of ABS in the melt cylinder shall not exceed 5-6 minutes. The flame-retardant time is even shorter. If the stop time is required, the setting temperature should be as low as 100 ℃, After cleaning, the mixture should be placed in cold water to prevent further decomposition. If it is necessary to change ABS from other plastics, it is necessary to clean the cylinder with PSG PMMA or PE. Some ABS products are not problematic when they are just unmolded. It takes some time to discolor, which may be caused by overheating or the long stay of plastic in the cladding tube.
8. Reprocessing of products
General ABS products do not need post-treatment, only electroplated products need to be baked 70-80 ℃ for 2-4 hours) to passivate surface traces, and the products to be electroplated can not use release agent, the products should be packaged immediately after taking out.
9. Matters to be paid special attention to in shaping
There are several grades of ABS (especially flame retardant grade), after plasticizing, the surface adhesion of the melt opposite injection molding machine screw is very large, and it will decompose after a long time.
When the above situation occurs, the vertical injection molding machine screw homogenization section and compression pull out rub test, and regular use of PS cleaning screw.