This article will discuss the processing points of heat-resistant ABS resin molding from five aspects: mold design, material drying, molding temperature, holding pressure and time, and mold temperature.
1. Product mold design
The product wall thickness requirements are uniform, and the wall thickness difference of ABS products should be controlled within 25% to prevent local stress concentration caused by excessive wall thickness difference. The root of the column with weaker strength needs to increase the R angle or additional reinforcing ribs to prevent the column from breaking. Buckle design, the root of the buckle needs to be inverted R angle, the size of the R angle depends on the wall thickness of the product, the R angle and the wall thickness ratio should be above 0.3, as the ratio increases, the internal stress gradually decreases, but also Consider the shrinkage of the product surface. The design of the mold cooling channel should ensure the uniformity of cooling and avoid the internal stress caused by uneven cooling and shrinkage.
2, the material is dry
Generally, the heat-resistant ABS resin absorbs moisture in the air during storage and transportation. The water absorption rate varies with the humidity of the air, generally between 0.2 and 0.4%, so the material must be sufficiently dried to reduce the moisture content of the material. Below 0.05%, preferably below 0.02%, otherwise surface defects such as water splash and silver wire may occur. The drying temperature of the heat-resistant ABS resin is higher than that of ordinary ABS, usually 80-95 ° C, and the drying time is 3-4 hours.
3, molding temperature
The molding temperature is a parameter that needs special attention during the processing of heat-resistant ABS. The setting is based on ensuring the full plasticization of the heat-resistant ABS. The temperature range of the molding temperature recommended by the supplier should be used as much as possible. The increase will significantly reduce the viscosity of the heat-resistant ABS, increase the fluidity of the resin, and make the flow distance longer, to ensure that the material has sufficient filling ability.
4, holding pressure and time
For heat-resistant ABS, the setting of holding pressure and time is reasonable, which directly affects the internal stress of the part. The increase of the holding pressure will make the molecular gap smaller, the range of the segment movement will be reduced, the volume of the melt will be reduced, the density will become larger, and the force between the molecules will increase, which can improve the shrinkage and internal quality of the product, but will result in internal The stress becomes large, so the lower holding pressure should be selected as much as possible under the premise of ensuring the appearance quality of the product.
The holding time is set according to the time when the gate is solidified by cooling, and the screw is pushed forward to no longer apply pressure to the molded article. If the holding time is too long, the material is easily filled excessively, the molecular gap becomes small, and the internal stress becomes large; the holding time is too short, the product is prone to shrinkage, and the size is unstable. The holding time setting should be the best holding time when the product weight does not change any more.
5, mold temperature
A mold temperature machine is used to control the mold temperature during molding of the heat-resistant ABS. The recommended mold temperature is 60-80 °C. Higher mold temperatures tend to produce good flow, higher weld line strength, and lower product internal stress, but the molding cycle is extended. If the mold temperature is lower than recommended, it will lead to excessive stress in the product, which will reduce the performance of the product, and may cause undesirable phenomena such as cracking of the product, cracking of the screw hole or cracking of the paint.
