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PC材料內應力産生的機理和分類

今天靈科超聲波帶大家了解一下PC材料內應力産生的機理和分類。

一、內應力産生的機理

內應力是指在塑料熔融加工過程中由于受到大分子鏈的取向和冷卻收縮等因素而産生的一種內在應力。

內應力的本質爲大分子鏈在熔融加工過程中形成的不平衡構象，這種不平衡構象在冷卻固化時不能立刻恢複到與環境條件相適應的平衡構象,這種不均衡構象的實質爲一種可逆的彈形變，而凍結的高彈形變平時以位能形式儲存在塑料制品中，在適宜的條件下,這種被迫的不穩定的構象將向自由的穩定的構象轉化，位能改變爲動能而釋放。

當大分子鏈間的作用力和相互纏結力承受不住這種動能時，內應力平衡即遭到破壞，塑料制品就會産生應力開裂及翹曲變形等現象，特別在高溫和有機溶劑等外因誘導下，破壞程度更是明顯增加，當使用超聲波塑料焊接機時就要注意這個問題。

二、內應力的分類

1、取向應力。塑料熔體在充模過程中由于受到剪切作用會使大分子鏈伸展,形變,沿流動方向發生取向,在冷卻過程中若幹大分子來不及恢複就被凍結下來,就産生了取向應力。取向應力主要集中在進膠口側和制品表層,薄壁制品表現更爲嚴重。

2、体积温度应力。塑料注塑时,熔体温度与模具温度之间温差很大,靠近模壁的熔体冷却较快,中心层较慢,使産品表层形成凝固壳层,阻碍了内层继续收缩时的自由收缩形成了拉伸应力,而外部产生了压缩压力。体积温度应力主要是由收缩不均造成的,産品结构厚薄差异大的制品表现明显。

3、脱模应力。与脱模时産品的变形有关的应力。

4、結晶內應力。與結晶結構有關的應力(PC材料是無定型材料,PBT/PC材料是微結晶材料）。結晶聚合物結晶區與非結晶區界面産生的內應力;結晶度不同,收縮不一致産生的內應力。

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靈科超聲波致力于高性能的超聲波塑焊設備研發、制造，爲客戶供應珠海超聲波、中山超聲波焊接機、江门超声波塑焊机、宁波超音波设备清洗机等、根据厂家需求定制非标设备。靈科超聲波産品广泛用于各个领域：汽车塑料零件的超声波焊接，打印耗材塑料焊接，电子电讯超声波焊接，无纺布超声波焊接等。

靈科超聲波焊接机急停按钮的作用

关于对靈科超聲波焊接机一些常见问题的调试（二）

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