ABS, commonly known as acrylonitrile butadiene styrene, is a copolymerization of three monomers of acrylonitrile-butadiene-styrene. Due to the different proportions of the three monomers, they can have different properties and melting temperatures, and if the ABS with flow properties is blended with other plastics or additives, it can be expanded to ABS with different uses and properties, such as impact grade, heat resistance grade, flame retardant grade, transparent grade, reinforced grade, electroplating grade, etc.
The fluidity of ABS is between PS and PC, and its fluidity is related to injection temperature and pressure, of which the influence of injection pressure is slightly greater, so higher injection pressure is often used in molding to reduce melt viscosity and improve mold filling performance.
1. Treatment of plastics
The water absorption rate of ABS is about 0.2%-0.8%, for general grade ABS, bake with an oven at 80-85°C for 2-4 hours or dry hopper at 80°C for 1-2 hours before processing. For heat-resistant grade ABS containing PC components, the drying temperature is appropriately adjusted to 100 °C, and the specific drying time can be determined by air extrusion.
The proportion of recycled material cannot exceed 30%, and electroplating grade ABS cannot use recycled material.
2. The injection molding machine can choose Ramada standard injection molding machine (screw length-diameter ratio 20:1, compression ratio greater than 2, injection pressure greater than 1500bar). If masterbatches or products with high appearance requirements are used, screws with a small diameter can be selected. The clamping force is determined according to 4700-6200t/m2, which needs to be determined according to the plastic grade and product requirements.
3. Mold and gate design mold temperature can be set to 60-65°C. The runner diameter is 6-8mm. The gate width is about 3mm, the thickness is the same as the product, and the gate length is less than 1mm. The exhaust hole is 4-6mm wide and 0.025-0.05mm thick.
4. The melting temperature can be accurately determined by the empty injection method. Different grades, the melting temperature is also different, it is recommended to set as follows: impact grade: 220°C-260°C, 250°C is the best plating grade: 250°C-275°C, 270°C is the best heat-resistant grade: 240°C-280°C, 265°C-270°C is the best flame retardant grade: 200°C-240°C, 220°C-230°C is the best transparent grade: 230°C-260°C, 245°C is the best glass fiber reinforced grade: 230°C-270°C
For products with high surface requirements, higher melting temperature and mold temperature are used.
5. The injection speed should be slow for the fireproof grade and fast for the heat-resistant grade. If the surface requirements of the product are high, the rate of fire control of high-speed and multi-stage injection molding should be used.
6. Back pressure is generally the lower the back pressure, the better, the commonly used back pressure is 5bar, and the dyeing material needs to use higher back pressure to make the color mixing uniform.
7. At a temperature of 265 °C, the residence time of ABS in the melt cylinder should not exceed 5-6 minutes at most. The flame retardant time is shorter, if you need to shut down, you should first set the temperature as low as 100 °C, and then clean the melt cartridge with general-purpose grade ABS. The cleaned mixture should be placed in cold water to prevent further decomposition. If you need to change ABS from other plastics, you must first clean the melt cartridge with PS, PMMA or PE. Some ABS products are not a problem when they are just demolded, and they will change color after a period of time, which may be caused by overheating or the plastic staying in the melt cartridge for too long.
8. Post-treatment of products General ABS products do not need post-treatment, only electroplating grade products need to be baked (70-80 °C, 2-4 hours) to passivate the surface traces, and the products to be electroplated can not use mold release agent, the products should be packaged immediately after taking out.
9. There are several grades of ABS (especially flame retardant grade) that should be paid special attention to when molding, and the adhesion of the melt to the surface of the screw is very large after plasticization, and it will decompose after a long time. When the above situation occurs, it is necessary to pull the homogenization section of the screw and the compression out of the rubbing test, and regularly clean the screw with PS and the like
