To reduce the stress in the product is the key to heat-resistant ABS injection molding.In this paper, the author summarizes the processing points of the heat-resistant ABS resin molding from five aspects of mold design, material drying, molding temperature, packing pressure and time, mold temperature.
Ordinary ABS heat resistance is not good enough, and now by adding ɑ-methyl styrene copolymer and N-phenyl maleimide copolymer heat-resistant agent developed a series of heat-resistant ABS resin, heat distortion temperature (HDT ) Is 90-120 ° C.
As the heat-resistant ABS molecular structure contains high rigidity of the benzene ring and N-phenyl group, improve heat resistance, but also increase the steric hindrance effect of the molecular chain, the relaxation rate of molecular chains to reduce, easy to make products There is a large internal stress, resulting in product stress cracking, stress whitening, product brittle hair and other defects.Therefore, to reduce the product stress is the key to heat ABS injection molding.
Product mold design
Thickness requirements of the product uniform, ABS products, wall thickness difference should be controlled within 25%, to prevent excessive wall thickness caused by local stress concentration.Weak pillar at the root of the need to increase the R angle or additional ribs to prevent the column fracture.
Buckle design, buckle root need to reverse R angle, R angle depends on the size of the product wall thickness, R angle and wall thickness ratio should be above 0.3, with this ratio increases, the internal stress gradually reduced, but also Consider the problem of shrinkage of the product surface.The design of the mold cooling water channel should ensure the uniformity of cooling and avoid the internal stress caused by uneven cooling and shrinkage.
Material is dry
Usually, heat-resistant ABS resin will absorb the moisture in the air during storage and transportation. The water absorption varies with the air humidity, generally between 0.2% and 0.4%. Therefore, the material must be fully dried to reduce the moisture content of the material 0.05% or less, preferably 0.02% or less, otherwise it may appear on the surface of water, silver, etc. Heat ABS resin drying temperature is higher than ordinary ABS, usually 80-95 ℃, drying time 3-4 hours.
Molding temperature
Molding temperature is heat ABS processing requires special attention to a parameter, which is set to ensure heat-resistant ABS is fully plasticized as a benchmark, we should try to use the supplier of the middle of the molding temperature of the upper temperature range, the molding temperature Increase will significantly reduce heat-resistant ABS viscosity, increase resin flow, the flow distance longer, to ensure that the material has sufficient filling capacity.
Holding pressure and time
For heat-resistant ABS, packing pressure and time setting is reasonable, a direct impact on the size of the workpiece stress. Increasing the packing pressure will make the molecular gap smaller, the range of activities of the chain decreases, the volume of the melt Shrinking, increasing density, increasing the force between molecules can improve the product shrinkage and internal quality, but will lead to greater internal stress, therefore, to ensure the appearance of the quality of the product under the premise of try to choose a lower holding pressure.
Dwell time is set according to the gate with the cooling to complete its curing, the screw is no longer re-push the molded product pressure is applied to the time. Dwell time is too long, easy to fill too much material, the molecular gap smaller, within The stress becomes larger, the dwell time is too short, the product tends to shrink, the size is unstable, and the dwell time should be set as the best dwell time with the shortest time when the product weight no longer changes.
Mold temperature
The use of mold temperature control in the molding heat ABS mold temperature control, the proposed mold temperature is 60-80 ° C. Higher mold temperature, tend to produce good flow, higher weld line strength, smaller products Stress, but the molding cycle will be extended.
If the mold temperature is lower than the recommended one, it will lead to excessive stress in the product, which will reduce the performance of the product. There may be some defects such as brittle crack, screw hole cracking or paint cracking.