Shanghai Daoqin Plastics Co., Ltd.

what is and shrink 痕(Sink MarK)?

凹陷 and shrink 痕(Sink MarK), is due to gate rear or material injection local inner shrinkage formed.

injection molding products surface generate or is micro is injection molding formed molding process in 一 老 issues. generally is due to plastics products thick increase products shrinkage rate local increase generate, it can can in external 尖角附近 or thick 突变处, 如凸起, add strong/high or base/seat rear, has 时也会出现 in 一 不 Common 部位. generate 凹痕 根本 causes is material hot cold shrink, is thermoplastic property plastics thermal expansion coefficient versus high. and shrinkage degree 取决于 many factors, its in plastics property can, most large most small temperature degree scope/range and type holding pressure pressure is most important factors, also has injection molding parts dimensions and 形状以 and cooling speed degree and uniform property and other is effect/influence factors. plastics products upper and shrink is comparison Common molding defect. 如图 示:

凹陷 and shrink 痕(Sink MarK) defect analysis and troubleshooting methods

1） molding conditions control 不当

if injection pressure low, injection and holding pressure time short, injection speed rate slow, material temperature and mold temperature high, parts cooling 不足, demolding temperature degree high, parts temperature degree low or material 不足, 都会引起塑 parts surface 出现凹陷 or 桔皮状 fine micro 凹凸不平. for 此, 应适当 improve/increase injection pressure and injection speed degree, increase material pressure shrink density, long injection and holding pressure time, melt shrinkage, increase injection amount. holding pressure can high, 否则会引起凸痕.

if and shrink 痕发生 in gate 附近时, can through long holding pressure time solution. parts in thick generate 凹陷时, 应适当延 long parts in inner cooling time.
if parts due to melt local shrinkage 引起凹陷 and shrink 痕, this main/primary is due to parts temperature degree low formed, method improve/increase parts temperature degree.
if injection molding machine nozzle small or nozzle local retardant 塞, 也会因 is injection pressure local loss large 引起凹陷 and shrink 痕. for 此, more nozzle or 进行清理.
if due to material 不足引起塑 parts surface 凹陷, increase material amount.
in addition, parts in inner cooling must separation. 一方面 can through adjustment material temperature degree, reduce material temperature degree; 另一方面, can 采取改变 mold cooling system 设置, reduce cooling water temperature degree, or in amount maintain mold surface and 各部位 uniform cooling front lower, for generate 凹陷 部位适当 strong/high cooling. 否则, parts in cooling conditions lower demolding, very easy generate shrinkage 凹陷, but also also due to hard demolding 导致塑 parts in local 凹陷.

2） mold defect

if mold runner and gate 截面太 small, retardant force large, gate 设置不 for 称, speed degree 不均衡, material 口位置设置不 combined 理, and mold gas defect effect/influence material, shrink and cooling, or mold abrasion loss 引起释 pressure, 都会导致塑 parts surface generate and shrink 痕, for 此, combined specific 情况, expand large gate and 浇道截面, gate 位置尽 amount in for 称处, material 口应设置 in parts thick 壁 部位.

if and shrink 痕发生 in gate 处, generally is due to mold structure in certain 一部位熔 material flow 不畅, pressure 传递. for 此, 应适当 expand large mold system structure dimensions, especially is for/regarding retardant material flow “ bottle 颈”处必 must increase 注道截面, most good is will 注道延伸 to generate 凹陷 部位.

for/regarding thick parts, excellent using/adopting gate. this 样, for/regarding 不适宜 will gate 直接设置 in parts upper and molding rear easy in gate generate deformation parts, can in parts upper 附设一 翼形体, again will gate in small upper, in small upper gate can using/adopting gate and gate, will parts defect to small upper, parts molding rear again will small remove.

in addition, 应经常检查 mold is in abrasion consumption pressure or gas defect, and more mold in easy consumption easy loss parts or improvement mold gas conditions.

3） raw materials combined molding requirements

if molding raw materials shrinkage rate large or flow property can 太差, and raw materials inner lubricant or raw materials wet, 都会引起塑 parts surface generate and shrink 痕. therefore, for/regarding surface requirements comparison high parts, amount selection low shrinkage rate resin grade.
if due to material flow 不畅引起欠注凹陷, can in raw materials in increase amount lubricant, improvement material flow property, or add large system structure dimensions.
if due to raw materials wet 引起塑 parts surface generate 凹陷, for raw materials 进行预 dry 处理.
4）塑 parts structure design combined 理

if parts 各处 壁 thick versus very large 时, thick 壁部位 due to pressure 不足, molding very easy generate and shrink 痕. therefore, design parts structure 时, thick amount 一致. for/regarding 特殊情况, parts thick relatively large, can through adjustment system structure parameters solution.