If you want to know more about the plastic industry, please go to Jicui Plastic Network - the most popular e-commerce platform in the plastic industry. ABS, commonly known as acrylonitrile butadiene styrene, is made of three monomers: acrylonitrile-butadiene-styrene. Due to the different proportions of the three monomers, different properties and melting temperatures can be achieved. If ABS with flow properties is mixed with other plastics or additives, it can be expanded to ABS with different uses and properties, such as impact grade, anti-impact grade, etc. Thermal grade, flame retardant grade, transparent grade, reinforced grade, electroplating grade, etc.
The fluidity of ABS is between PS and PC. Its fluidity is related to the injection temperature and pressure. The injection pressure has a slightly greater impact. Therefore, higher injection pressure is often used during molding to reduce Melt viscosity improves mold filling performance.
1. Plastic processing
The water absorption rate of ABS is about 0.2%-0.8%. For general-grade ABS, bake it in an oven at 80-85℃ for 2-4 days before processing. hours or use a drying hopper to bake at 80°C for 1-2 hours. For heat-resistant ABS containing PC components, the drying temperature should be appropriately increased to 100°C, and the specific drying time can be determined by extruding it into the air.
The proportion of recycled materials cannot exceed 30%, and recycled materials cannot be used in electroplating grade ABS.
2. Selection of injection molding machine
You can choose Ramada's standard injection molding machine (screw length-to-diameter ratio 20:1, compression ratio greater than 2, injection pressure greater than 1500bar). If masterbatch is used or the appearance of the product requires high material, a screw with a smaller diameter can be selected. The clamping force is determined according to 4700-6200t/m2, which depends on the plastic grade and product requirements.
3. Mold and gate design
The mold temperature can be set to 60-65°C. The flow channel diameter is 6-8mm. The gate width is about 3mm, the thickness is the same as the product, and the gate length should be less than 1mm. The exhaust hole is 4-6mm wide and 0.025-0.05mm thick.
4. Melt temperature
can be accurately determined by the air injection method. Different grades have different melt temperatures. The recommended settings are as follows:
Impact grade: 220℃-260℃, preferably 250℃
Electroplating grade: 250℃-275 ℃, preferably 270℃
Heat-resistant grade: 240℃-280℃, preferably 265℃-270℃
Flame-retardant grade: 200℃-240℃, preferably 220℃-230℃ is better
Transparent grade: 230℃-260℃, 245℃ is better
Glass fiber reinforced grade: 230℃-270℃
< p>For products with high surface requirements, use higher melt temperature and mold temperature.5. Injection speed
Slow speed should be used for fire-proof grade, and fast speed should be used for heat-resistant grade. If the product surface requirements are high, high-speed and multi-stage injection molding injection rate control should be used.
6. Back pressure
Generally, the lower the back pressure, the better. The commonly used back pressure is 5bar. Dyeing materials need higher back pressure to make the color mixture even.
7. Residence time
At a temperature of 265°C, the residence time of ABS in the melt barrel cannot exceed 5-6 minutes at most. The flame retardant time is shorter. If the machine needs to be shut down, the set temperature should be lowered to 100°C first, and then the melt barrel should be cleaned with general-grade ABS. The cleaned mixture should be placed in cold water to prevent further decomposition. If you need to change from other plastics to ABS materials, you must first clean the melt barrel with PS, PMMA or PE. Some ABS products have no problem when they are first demoulded, but will change color after a period of time. This may be caused by overheating or the plastic staying in the melt barrel for too long.
8. Post-processing of products
Generally, ABS products do not require post-processing. Only electroplating-grade products need to be baked (70-80°C, 2-4 hours) to passivate. Release agents cannot be used for products that have surface traces and require electroplating, and the products must be packaged immediately after being taken out.
9. Things to pay special attention to when molding
There are several grades of ABS (especially flame retardant grade). After plasticization, the adhesion of the melt to the screw surface It's very large and will break down over time. When the above situation occurs, it is necessary to pull out and wipe the homogenizing section and compression of the screw, and clean the screw regularly with PS, etc.