成型收缩
来源:
|
作者:profed5ca94
|
发布时间: 2021-02-02
|
1400 次浏览
|
分享到:
收缩机理：熔融体填满模腔形成塑件，从熔融的液态变换转化为固态，存在热收缩、取向收缩、相变（结晶）收缩、压缩收缩（弹性可挥复）4种状态。
3.3成型收缩影响
3.3.1收缩机理：熔融体填满模腔形成塑件，从熔融的液态变换转化为固态，存在热收缩、取向收缩、相变（结晶）收缩、压缩收缩（弹性可挥复）4种状态。
① 热收缩等同其它物质的热胀冷缩规律，与相变收缩有一定的关联性；
② 取向收缩会使制件纵横方向上收缩率存在差异；
③ 相变（结晶）收缩根据塑料种类的不同可长达几个月制件尺寸都在变化。控制的方法是使塑件结晶过程快速完成，并保持晶核细小匀一，避免出现大的晶核；
④ 压缩收缩产生的影响极小，可忽略不计。
3.3.2收缩过程：收缩存在注射、保压、固化、后收缩4个主要过程，受熔体温度、模腔压力、注射速度、模具温度、浇口尺寸（横截面积、长度）等因素的影响。塑件整体收缩量的80%由注射保压量及模具温度所决定，20%由冷却速度、总循环周期引起。
3.3 Molding Shrinkage
3.3.1 contraction mechanism: the formation of cavities filled melt plastic parts, from the melting of the liquid transforms into a solid state, there is shrinking, shrinking orientation, phase change (crystallization) contraction, compression shrinkage (elastic can command complex) four kinds of state .
① shrink the same law of thermal expansion and contraction of other substances, and the contraction phase transition has some relevance;
② vertical and horizontal orientation of the direction of the workpiece will shrink shrinkage differences;
③ phase change (crystallization) of different types of contraction under the plastic workpiece size of up to several months are changing. Control method is to quickly complete the crystallization process plastic parts, and maintain a uniform small nuclei, to avoid large nuclei;
④ the impact of compression shrink small, can be neglected.
NO small nucleus large nuclei OK
Shrinking phase transition (crystal) orientation of contraction contraction
3.3.2 contraction: contraction there is injected, packing, curing, after the contraction of four main processes, affected by melt temperature, cavity pressure, injection speed, mold temperature, gate size (cross sectional area, length) and other factors impact. Plastic shrinkage of 80% of the total by the amount of injection holding pressure and mold temperature are determined by the cooling rate of 20% of the total cycle caused.
Nucleation of small nuclei big NO OK
