Shanghai Daoqin Plastics Co., Ltd.

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 also is “ molding force ”. 善德宸信 small is large and:

injection molding products internal stress 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 generate relatively large temperature degree degree. products 心部凝 solid versus slow, 以致于当 gate 封闭时, products in melt mono also solid, this injection molding machine also method for cooling shrinkage 进行补 material. this products internal shrinkage function and hard function direction is versus 反; 心部处于静态 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 in 垂直于 flow direction force function.

                                     
 

2. effect/influence force process factors

（1） toward force effect/influence in speed cold conditions lower, orientation 会导致 polymer internal stress formed. due to polymer melt viscosity high, internal stress can very fast 松驰, effect/influence products physical properties and dimensional stability.

各 parameters for orientation force effect/influence

a melt temperature degree, melt temperature degree high, viscosity low, 剪切应 force reduce orientation degree decrease small; 另一方面 due to melt temperature degree high make force add fast, make understanding orientation can force add strong/high. can is in 不改变 injection molding machine pressure lower, mold cavity pressure increase large, strong/high function also orientation force improve/increase.

b in nozzle 封闭以 front, long holding pressure time, 会导致 orientation force increase.

c improve/increase injection pressure or holding pressure pressure, increase large orientation force.

d mold temperature degree high can ensure products slow cooling, to understanding orientation function.

e increase products thick degree make orientation force reduce, is thick products cooling slow, viscosity improve/increase slow, force process time long, therefore orientation force small.

（2） for temperature degree force effect/influence

如 upper due to in 充模时 melt and type between temperature degree degree very large, solid outer melt need rear solid inner melt shrinkage, in outer generate pressure force （ shrinkage force ）, inner generate force （ orientation force ）.

if rear also in holding pressure pressure function lower relatively long time, polymer melt also mold cavity in, make mold cavity pressure improve/increase, pressure 会改变 due to temperature degree 不均而 generate internal stress. in holding pressure time short, mold cavity pressure also relatively low lower, products internal still maintain cooling 时 应 force 状态.

if in products cooling mold cavity pressure 不足时, products outer 层会因凝 solid shrinkage formed 凹陷; if in products already formed cold hard rear mold cavity pressure 不足时, products inner 层会因 shrinkage separation 离, or formed 空穴; if in gate front mold cavity pressure, has improve/increase products density, remove cooling temperature degree force, is in gate 附近会 generate relatively large force in.

由此看 thermoplastic property polymer in molding 时, inner pressure large holding pressure time long, has temperature degree generate shrinkage force decrease small 反之会 make pressure shrink force increase large.

3. 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 会发生 cracks. in 玻璃化 temperature degree below/following use 时, 常发生不规则 deformation or warpage, also 会引起 products surface “泛白”, 浑浊, optical property bad.

设 method reduce gate temperature degree, increase cold time, has improvement products force 不均, make products mechanical properties 均一.

不 tube/pipe for crystallization type polymer also is non crystallization type polymer, tensile strength performance toward toward features. for non crystallization type polymer tensile strength gate 们置而异; gate and direction 一致时, tensile strength melt temperature degree improve/increase reduce; gate and direction 垂直时, tensile strength melt temperature degree improve/increase increase.

due to melt temperature degree improve/increase understanding orientation function add strong/high, orientation function decrease low make tensile strength reduce. gate 方位会 through effect/influence material direction effect/influence orientation, also due to non crystallization type polymer ratio crystallization type polymer toward property performance strong/high 烈, therefore in 垂直于 flow direction upper tensile strength front ratio rear large. low temperature injection ratio high temperature injection has more large force toward property, injection temperature degree high 时, direction and flow direction strong/high degree ratio is 1.7, injection temperature degree low is 2.

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