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The injection temperature for ABS plastic machining includes barrel temperature, nozzle temperature and mold temperature. Although the viscosity of ABS melt is less affected by the temperature than the injection pressure, it is advantageous for the mold of thin-walled products under the condition of high temperature. The decomposition temperature of ABS is theoretically as high as above 270t, but in the actual injection molding process, due to the influence of time and other process conditions, plastics often begin to change color at around 2501, and the rubber contained in ABS cannot adapt to high temperature, otherwise it will affect product performance. In terms of the molding of ABS, except plastics such as heat-resistant and electroplating grade ones which require a slightly higher temperature to lower the difficulty of melt filling or facilitate the electroplating performance, for general-purpose, flame-retardant, and impact-resistant ABS plastics, the temperature should be lowered to prevent decomposition or causing unfavorable damage to physical and mechanical properties.
The mold temperature has an important effect on the surface roughness of ABS plastic products and reducing the internal stress of the products. If the mold temperature is high, the melt is easy to fill the mold, the appearance of the product is good, the internal stress is small, and the electroplating property of the product is also improved or lifted, but there are also problems such as large product shrinkage rates, long molding cycles, and easy to deform after demolding. For products with general requirements, the mold temperature can be controlled at 40 to 50°C; for products with higher appearance and performance requirements, the mold temperature can be controlled at 60 to 70°C. Moreover, the mold temperature must be uniform, and the temperature difference between the mold cavity and the mold core should not exceed 10°C. For deep-hole products or products with more complex shapes, the mold cavity temperature is required to be slightly higher than the mold core temperature to facilitate the smooth demoulding of products.
Compared with plastics such as polyethylene, polystyrene, nylon, etc., ABS has a slightly lower fluidity, so the required injection pressure is higher. However, excessive injection pressure is likely to cause difficulty in demolding or damage to the product, and may also bring greater internal stress to the product. So in the process, the ABS plastic properties should be taken into consideration. The injection pressure of ABS plastic machining is not only related to the wall thickness of the product and the type of equipment, but also related to the grade of the resin. For thin-walled, long-flow, and small-gate products, the injection pressure required is high, as high as 130 to 150MPa. In the actual production process, the injection pressure of the screw injection machine is usually below 100MPa, while the plunger injection machine is generally above 100MPa. The holding pressure should not be too high. The screw injection machine generally uses 30 to 50MPa, while the plunger type requires 60 to 70MPa or more. If the holding pressure is too high, the internal stress of the product will increase.
The injection speed of ABS plastic machining has a certain effect on the change of the fluidity of the ABS. If the injection speed is slow, the appearance of the product will appear ripples and confront poor welding; if the injection speed is fast, the mold can be filled quickly, but it is prone to poor venting, poor apparent roughness, etc., which will also reduce the tensile strength and elongation of the product, and the adhesion of the coating will also decrease due to the excessively fast injection speed. For this reason, in the production process, a higher injection speed is only used to address the difficulty of filling the mold. Generally, medium and low speeds are appropriate.
