Shanghai Daoqin Plastics Co., Ltd.

        1. internal stress

        (1) internal stress generate

         in injection molding products in, local force is different, products deformation degree will 决定于应 force distribution. if products in cooling 时, in temperature degree degree, this category of force development, therefore this category of force is “ molding force ”.

         injection molding products internal stress 包括两 types: types is injection molding products molding force, types is temperature degree force. melt temperature degree relatively low mold 时, mold cavity melt speed cooling solid 化, is separation 子链段 by “冻结”.

         due to solid polymer 层, thermally conductive property very 差, in products thick degree direction upper will generate relatively large temperature degree degree, products 心部却凝 solid versus slow, 以致于当 gate 封闭时, melt mono also solid, if injection molding machine also for cooling shrinkage 进行补 material 时, due to products internal shrinkage function and hard function direction is versus 反, 则心部会处于静态 tensile table/sheet 层则处于静态 pressure shrink.

         in melt flow 时, remove has shrinkage 效应引起 应 force outer, also has runner, gate export 膨胀效应而引起 应 force; front types 效应引起 应 force and melt flow direction has 关, rear due to export 膨胀效应 will 引起垂直于 flow direction force function.

         for/regarding semi crystallization type polymer also need attention/notes another types 效应, ultra- 玻璃化 temperature degree 时, crystallization mono between 保留 一 non crystallization versus separation 子链段 will active 动, by crystallization versus 限位, retardant tensile 链 返回, is formed internal stress. for crystallization type polymer, also has types 形变-诱导应 force;当 to crystallization type high poly material melt add force ultra- elastic property 形变极限时, will sliding flow, generate property 形变 位移, 而取代 一部 separation elastic property deformation.

         in 总形变不变 应 force conditions lower, force decline to and other certain most low value, this value is “形变-诱导”. for/regarding this type of understanding also can crystallization type polymer has types crystallization type, crystallization process in formed 堆积式位移, make in sliding upper 进一步堆积发生困 difficult, is generate reaction force, its large small and other maintain 晶格位移 structure 需 应 force, but also this type of 晶格位移 structure is in has force non balanced lower formed. this is for “形变-诱导 internal stress ”位移 mechanism understanding 释, it suitable non crystallization polymer.

        (2) internal stress and products quality 关系

         products in internal stress in heavy effect/influence products force property and use property can; due to products internal stress in and distribution 不均, products in use process in cracks, in 玻璃化 temperature degree below/following use use 时, 常发生不规则 deformation or warpage, also 会引起 products surface “泛白”, 浑浊, optical property can bad.

         internal stress reduce products for light, hot and 腐蚀介质 抵 resistant can force, in ring function lower, 发生应 force cracking or 出现“ crazing ”, therefore, decrease small or products internal stress tool has important 意义. internal stress has can utilizing 一面, can utilizing orientation internal stress generate toward property force features, make in force direction upper generate relatively high strong/high degree, in application in has selection use products, production tensile film and weaving belt/tape and other. for injection molding products internal stress small uniform distribution.

         reduce gate temperature degree, increase cold time, has improvement products in force 不均 状况, make mechanical properties 均一. for crystallization type polymer, tensile strength performance toward property features.

         melt temperature degree improve/increase, for crystallization type also is non crystallization type polymer 都会导致 tensile strength reduce, 但二者 mechanism 却不一样: front is due to crystallization degree reduce effect/influence; rear is through orientation function effect/influence.

        2. impact strong/high degree

         injection molding products impact strong/high degree performance more 突出 各 toward property. impact strong/high degree remove and polymer separation structure and injection molding process conditions has outer, also and products structure 形状, gate and 位置, 数目, distribution and 排列形式 has 关. this is is impact strong/high degree, main/primary polymer processing process formed internal stress (orientation force, temperature degree force, 形变-诱导应 force) 决定.

        3. products shrinkage

        (1) shrinkage process

         injection molding products in molding process shrinkage can separation 3 stage/phase.

        第一 stage/phase is in gate solid front holding pressure stage/phase. products shrinkage very large degree upper 取决于 melt 补偿程 degree. due to mold temperature degree low, melt temperature degree in decline, melt density and degree in improve/increase. therefore, this melt can force main/primary 取决于 holding pressure pressure large small and toward inner time.

        第二 stage/phase is from gate solid 开始至 demolding cooling stage/phase. this stage/phase again melt mold cavity inner, products weight again 改变, products density or ratio will 发生变化.

        第三 stage/phase is from demolding 开始至 use stage/phase shrinkage. this is belongs to shrinkage.

        (2) shrinkage rate control

        ① injection molding process 方面

        a. mold temperature degree need high. for polyoxymethylene (POM) products. mold temperature degree 80℃ 40℃时, shrinkage rate is 5%.

        b. material temperature degree need high. polyoxymethylene (POM) products, melt temperature degree is 190℃ 10℃时, shrinkage rate is 2.5%.

        c. injection pressure can improve/increase. 例如, for polyoxymethylene (POM) products, injection pressure is 78Mpa 9.8Mpa时, shrinkage rate is 5%.

        d.适当 improve/increase injection speed rate.

        e. holding pressure time need setting long.

        f.适当 increase cooling time.

        g. control mold cooling speed degree.

        ②材 material 方面

        a. selection pellets uniform material material, make material hot uniform, temperature degree 一致, make cooling speed degree 均一.

        b. need selection molecular weight large small and melt 指数适宜, molecular weight distribution uniform material, make process conditions easy control, flow stability, has decrease/reduce shrinkage.

        c. for/regarding crystallization type polymer provide decrease/reduce crystallization degree and stability crystallization degree conditions, for non crystallization type polymer need decrease/reduce understanding orientation factors.

        d. selection wet property small polymer, through drying, reduce water separation, can decrease/reduce shrinkage.

        e. selection flow property good, melt low polymer.

        f. selection has reinforcement filler composite/compounding material, can decrease/reduce shrinkage.

        ③ in mold 方面

        a. according to mold shrinkage rate, mold type dimensions design combined 理, selection 膨胀系数 small mold material.

        b. gate 截面积适当 add large, has decrease/reduce shrinkage.

        c. shrink short inner runner, decrease/reduce long ratio, has 利于补 shrink.