ABS treatment for plastic injection molding
Known as acrylonitrile butadiene styrene, ABS is an acrylonitrile – styrene copolymer of the monomers from – butadiene. ABS fluidity is between PS and PC, its fluidity could be effected by the injection pressure and temperature ,while the injection pressure is slightly more important , thus a higher injection pressure is often used to reduce the melt viscosity and improve the filling performance.
1,plastic pre-treatment for abs injection molding
ABS water absorption ratio is about 0.2% -0.8%. for the normal ABS before molding ,its drying time in oven is for 2-4 hours at 80-85 ℃ ,or in hopper 80 ℃ at 1-2 hours. if PC material mixed with heat-resistant grade ABS, its drying temperature should be increased to 100 ℃. The proportion of the recycled ABS materials can not exceed 30%, electroplating grade ABS can not be used again at plastic injection moulding manufacturer facilities.
2, mold and gate design
The mold for abs injection temperature can be set to 60-65 ℃. Runner diameter is 6-8mm. Gate width is 3mm, if the thickness of the article should be same as gate, the gate length is less than 1mm. Vent width 4-6mm, and its thickness 0.025-0.05mm.
Melt temperature could be decided by Air injection . Different grades of ABS means that their melt temperatures are also different, we recommend the following settings for plastic injection moulding manufacturer:
Impact resistance grade: 220 ℃ -260 ℃, 250 ℃ better
Plating grade: 250 ℃ -275 ℃, 270 ℃ better
Heat-resistance grade: 240 ℃ -280 ℃, 265 ℃ -270 ℃ better
Flame Retardant grade: 200 ℃ -240 ℃, 220 ℃ -230 ℃ better
Transparent grade: 230 ℃ -260 ℃, 245 ℃ better
Glass fiber reinforced grade: 230 ℃ -270 ℃
High requirements for products surface is, the higher melt temperature and mold temperature should be.
4, the injection speed
Flame Retardant grade with slow speed, Heat-resistance grade with quick speed. abs injection molding products with high surface requirements should take use of high-speed and multi-stage injection rate .
5, back pressure
Back pressure should be as low as possible under normal circumstances, the normal back pressure is 5 bar.
6, residence time in barrel
At a temperature of 265 ℃, maximum of 5-6 minutes residence time in the barrel . Flame Retardant grade ABS is even shorter.For the downtime, it should set the temperature as low as 100 ℃, and then clean up barrel with the melting common grade ABS . after cleaning up,the mixture should be put into cold water to prevent further decomposition. if ABS need to replace the other material used, it firstly need clean up barrel with PS, PMMA or PE. Some ABS products is without any problems after releasing from the mold , but over a period of time, they could be discolored,for it may be overheating or melting plastic staying too long in barrel.
7, the ABS plastic molding after-treatment
ABS injection moulding products generally do not need the further treatment, only plating grade products should be subject to heat (70-80 ℃ ,2-4 hours) to remove the surface traces.Electroplated products could not use release agents, and products should be packaged immediately after removing from the mold .
8, other issues
There are several grades of ABS (especially flame retardant grade), after the plasticizing , its adhesion force is large on the screw, after long time it will decompose. When that happens, we need to pull, wipe and clean up the screw regularly with PS and other plastic material.