
在生产过程中,由于PVC是热敏性材料,即使加入热稳定剂也只能是提高分解温度,延长稳定时间而不可能不出现分解,这就要求PVC的成型加工温度应严格控制。特别是RPVC,因其加工温度与分解温度很接近,往往因为温度控制不当造成分解现象。因此,挤出温度应根据配方、挤出机特性、机头结构、螺杆转速、测温点位置、测温仪器的误差及测温点深度等因素确定。
1、温度的控制
温度的控制是挤出操作中重要的控制因素。挤出成型所需的控制因素的温度是机筒温度、机径温度、口模温度。温度过低,塑化不良,管材外观无光泽,力学性能差,产品质量达不到要求:温度过高,物料会发生分解,产品变色等现象出现。
2、螺杆转速
螺杆转速提高,挤出量增加,从而可提高产量,但容易产生塑化不良的现象,造成管材内壁毛糙,强度下降,这时应调节机头压力,使产量、质量到达更佳。螺杆的温度控制影响到物料输送率、物料的塑化、熔融质量等。挤出管材需要通冷却水,降低螺杆温度,有利于提高塑化质量,螺杆通冷却水温度在50~70左右。
3、牵引速度
在挤出操作中牵引速度的调节很重要,物料经挤出熔融塑化,从机头连续挤出后被牵引,从而进入定型装置、冷却装置、牵引装置等,牵引速度应与挤出速度相匹配。一般在正常生产时,牵引速度应比管材的挤出速度快1%~10%左右。
4、压缩空气和压力
压缩空气能够将管材管材吹胀,使管材保持一定的圆度。要求压力应大小适当。压力过小,管材不圆,压力过大,芯模被冷却,管材内壁出现裂口,不光滑,管材质量下降。同时压力要求稳定,如压力忽大忽小,管材容易产生竹节现状。
5、定径装置、冷却装置的温度
挤出不同的塑料产品,采用不同的定径方式和冷却方式,冷却的介质可以是空气、水或其他类液体,需要控制温度,其温度主要与生产效率、产品内应力等有关。
以上五点就是一般厂家在生产pvc管材的时候都需要注意的地方,只要做好以上五点,相信做出来的PVC管材一定能让质量得到更好的保障。详情也可以咨询洁尔康建材。
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