Key points of molding and processing of the hottes

2022-08-05
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Key points of heat-resistant ABS resin molding

reducing the internal stress of products is the key to heat-resistant ABS injection molding. In this paper, the author shared the key points of heat-resistant ABS resin molding from five aspects: mold design, material drying, molding temperature, holding pressure and time, mold temperature, etc

the heat resistance of ordinary ABS is not good enough. Now, teknor apex can develop softer or stronger compounds for specific use ɑ- A series of heat-resistant ABS resins have been developed by heat-resistant agents such as methyl styrene copolymer and N-phenyl maleimide copolymer. The heat deformation temperature (HDT) is ℃. For example, Shanghai Jinhu Rili's economic&easy series heat-resistant ABS resin can meet the heat-resistant demand of different degrees, and can be widely used in small household appliances such as microwave ovens, rice cookers, electric heaters and hair dryers; There are a series of products with higher heat resistance, which can be heat resistant

because the molecular structure of heat-resistant ABS contains highly rigid benzene ring and N-phenyl group, the heat resistance is improved. At the same time, the steric hindrance effect of the molecular chain is increased, and the relaxation speed of the molecular chain is reduced. It is easy to cause large internal stress in the products, resulting in defects such as stress cracking, stress whitening and product embrittlement. Therefore, reducing the internal stress of products is the key to heat-resistant ABS injection molding

product mold design

the product wall thickness shall be uniform. The wall thickness difference of ABS products shall be controlled within 25% to prevent local stress concentration caused by excessive wall thickness difference. R angle or reinforcing bar shall be added at the root of column with weak strength to prevent column fracture. For buckle design, the root of the buckle needs an inverted R angle. The size of the R angle depends on the wall thickness of the product. The ratio of R angle to wall thickness should be more than 0.3. With the increase of this ratio, the internal stress will gradually decrease. However, it should also be considered that all samples between the two clamps will get different degrees of tensile deformation surface shrinkage. The cooling water channel of the die shall be designed to ensure the uniformity of cooling and avoid the internal stress caused by uneven cooling and shrinkage

material drying

generally, heat-resistant ABS resin will absorb moisture in the air during storage and transportation, and the water absorption rate will change with the air humidity, generally between 0.2~0.4%. Therefore, the material must be fully dried to reduce the moisture content of the material to less than 0.05%, preferably less than 0.02%, otherwise there may be surface defects such as water spray and silver wire. The drying temperature of heat-resistant ABS resin is higher than that of ordinary ABS, which is usually ℃, and the drying time is hours

forming temperature

the forming temperature is a parameter that needs special attention during the processing of heat-resistant ABS. Its setting is based on ensuring that the heat-resistant ABS is fully plasticized. Try to use the temperature area higher than the middle value of the forming temperature recommended by the supplier. An increase in the forming temperature will significantly reduce the viscosity of the heat-resistant ABS, increase the fluidity of the resin, and lengthen the flow distance, so as to ensure that the material has sufficient filling capacity. For example, Jinhu Rili's heat-resistant ABS hu600 suggests a molding temperature of ℃. In principle, when using the upper limit of the recommended forming temperature, the retention time of the melt shall be as short as possible. The hydraulic pump shall be a variable axial piston pump to avoid high-temperature degradation of the material

holding pressure and time

for heat-resistant ABS, whether the setting of holding pressure and time is reasonable directly affects the internal stress of the workpiece. The increase of packing pressure will reduce the molecular gap, reduce the range of chain segment activity, reduce the volume of melt, increase the density, and increase the force between molecules, which can improve the shrinkage and internal quality of products, but will lead to the increase of internal stress. Therefore, the packing pressure should be as low as possible on the premise of ensuring the appearance quality of products. This makes the software go beyond the laboratory level of domestic peers. The setting of pressure holding time is based on the time when the gate solidifies with cooling and the screw is no longer pressed on the molded product. If the holding time is too long, the material will be filled too much, the molecular gap will become smaller and the internal stress will become larger; If the holding time is too short, the product is easy to shrink and the size is unstable. The pressure holding time shall be set to the shortest time when the weight of the product does not change as the best pressure holding time

mold temperature

the author suggests using a mold temperature machine to control the mold temperature when forming heat-resistant ABS. The recommended mold temperature is ℃. Higher mold temperature will often produce good flow, higher weld line strength and smaller product internal stress, but the forming cycle will be appropriately prolonged. If the mold temperature is lower than the recommended value, the internal stress of the product will be too high, which will reduce the performance of the product, and the product embrittlement, screw hole cracking or paint cracking may occur

finally, all forming process elements should be considered comprehensively and coordinated with each other. (end)

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