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Injection molding machine factory to parse the cause of non-uniform shrinkage molded parts

by:Hisson     2020-07-02
What is a contraction in the injection molding processing? => The shrinkage can be viewed as the geometry size of workpiece. Then by the injection molding machine factory to parse the cause of non-uniform shrinkage molded parts. Can be divided into the following plastic shrinkage of form: 1. Uniform shrinkage will not change its shape deformation of workpiece, just become smaller. 2. Shrinkage is not the average artifacts will produce deformation and change its shape, not only becomes smaller. What is a warping? When the internal stress ( Because of the uneven contraction of)> Material stiffness = & gt; Produce warping in case of differential shrinkage of plastic parts often cause internal stress ( 内部压力) Uneven distribution. If the stress more than plastic stiffness ( 刚度) , will cause plastic parts warp ( 弯曲) And the deformation ( 变形) , plastic parts dimension stability ( 尺寸稳定性) 。 Injection molding machine factory teach you uneven contraction of the four reasons: 1. Melt glue temperature difference: rubber high temperature shrinkage big 2. Different cooling rate ( Crystalline materials) ( 非对称收缩) Reason: fast cooling & lt; Slow cooling rate ( Reason: cooling speed ManZhe molecules have the time to arrange, so big shrinkage) 3. Melt glue flowing 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 flow distribution to the differences caused by the shrinkage phenomenon often cause buckling deformation of plastic parts. So if you can break up ligands to sex will help shrink uniformity, reduce buckling deformation caused by the four direction of contraction. Different sizes ( 差热应变) : simply size supplied by a massive shrinkage due to design become warped 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 meat thickness 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) Problem of 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. In general, the indentation size is also affected by the plastic shrinkage characteristics, below the consideration of strength stiffness, if can use empty ( 核心) Way to reduce the plastic pieces of meat thick, helps to reduce shrinkage. Molding conditions and deformation as related to the deformation is must pay special attention to the condition of injection and holding time, cooling time, injection speed, mold temperature. 1. Injection and injection pressure maintaining time and the sum of the holding time to design longer than gate close time. If than the gate closed time is short, sometimes deformation increase. 2. In general, prolong cooling cooling time will reduce the deformation. 3. Injection speed depending on the shape of the moulded part, injection speed, small deformation, sometimes opposite, small deformation of the injection speed is slow. In the actual forming, by changing the injection speed to find the minimum deformation conditions. 4. Mold temperature low mold temperature deformation of FRP products. However, if the use of FRP products after high temperature, can sometimes produce contraction deformation or size change. Mold temperature it will be decided according to the comprehensive considering these factors.
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