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Cause of vertical injection molding machine injection molded parts what are the cause of non-uniform shrinkage

by:Hisson     2020-09-23
Vertical injection molding machine of the uneven contraction of about a few big reasons: 1, melt glue temperature difference: melting glue temperature high shrinkage; 2, different cooling rate ( Crystalline materials) Reason: the cooling speed & lt; Slow cooling rate ( Reason: cooling speed ManZhe molecules have the time to arrange, so big shrinkage) ; 3, melt glue to different ( Amorphous materials) ( 各向异性) : Jane and the tensile stresses in the big flow, so the shrinkage. Match to the plastic due to flow in the process of filling ( 流方向) Reason, make the match to occur molecular chain. By the polymer chains in the flow direction and vertical direction flow direction by stretching ( 拉伸) Different situation, make the shrinkage behavior is also different. Systolic (called direction 定向收缩) 。 In general, the direction of flow reduction ( 在- - - - - - 流收缩) The vertical flow reduction ( 跨 flowshrinkage) For the high. This is because the flow direction of plastic polymer chain being done more serious, to return to a larger without stretching state. Due to the design of skip area: meat thick ( 壁厚) Meat thick thick to the size of the area, cooling and holding more difficult, the required cooling time is longer, the holding effect is poorer. Local high temperature remains after demoulding, continued to cool. So in local meat thick thick place, such as rib ( rib) , easy to have the plastic parts produced from local contraction dent ( 缩痕) The phenomenon occurs. So for a plastic parts, with artifacts change into the water the location selection can be beneficial to the holding in thick place, even if the workpiece in curing, still can smoothly pass the holding pressure, improve the shrinkage. Meat thick change ( 壁厚变化) : plastic pieces of thick meat will improve shrinkage. If plastic pieces of thick meat distribution, consideration should be given due to shrinkage caused by the effect of different cooling pressure difference will cause plastic parts warp distortion, and the meat thick transition region ( 壁厚过渡区域) The stress concentration caused by ( 应力集中) The problem. Meat thick transition region ( The buffer area) The internal stress concentration phenomenon can cause short-term ( 短期内) Or for a long time ( long term) Buckling problem, to reduce the plastic mechanical performance ( 机械性能) Shortcomings and so on. Plastics can introduce reinforcing rib ( 钢筋肋) To reinforcing structure strength in order to reduce shrinkage. Rib part in contact with the plastic wall thrown enough to ease the stress concentration ( 应力集中) Problem, overcome flow resistance; But also could cause the dent should be paid attention to ( 缩痕) The problem.
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