成型不良----流延.doc

成型不良 － 流涎 Injection Molding Trouble - Drooling 1）何谓流涎（外观） 1) What is Drooling ? (appearance) 是指树脂从成型机喷嘴漏出的一种现象。 This phenomenon is that melting resin is leaked from nozzle of cylinder.一般的注射成型机的喷嘴前端的树脂并没有完全固化，当机筒内压偏高，或树脂粘度偏低时，已熔化的树脂就会漏出。Generally, resin in the nozzle is not solidified. Then, the melting resin is leaked when inner pressure of cylinder is high or viscosity of melt resin is much low.树脂粘度偏低或成型机机筒的内压偏高时就会出现流涎。（2） 流涎的生成原因 (2) Causes of Drooling Generation 2-1) 树脂粘度偏低(2-1) Low resin viscosity大部分注射成型机都采用开式喷嘴，并通过条件调节来防止外流。但是，如果分子量因分解而降低，或把机筒的设定温度设得很高，树脂就会因粘度降低而流出Most injection machines adopt open nozzle, and normally resin does not flow out for the viscosity of the resin. However, when the molecular weight decreases by degradation or when cylinder temperature is set high, the resin viscosity is lowered and the resin flows out. 图2. 分子量降低时容易引起流涎(2-2) High inner pressure in cylinder(2-2) 机筒内压偏高对机筒内的树脂施加一定压力的原因有2点：一个是气体的膨胀，另一个是计量时的背压。气体膨胀的原因是树脂的分解气体和粒料中的水分。它们气化并膨胀后，无处可去的压力就会流向喷嘴的前端，从而形成流涎。另一方面，就背压而言，由于计量时需要用它来防止空气卷入，因此必须施加一定程度的背压。但如果施加过度，树脂就会被压缩成紧缩状态，从而导致内压升高和流涎。另外，空气也会因加热而膨胀起来，因此如果计量时卷入了大量空气，流涎就会越发严重。A constant pressure is applied to resin in the cylinder by two factors. One is gas expansion and the other is back pressure in metering.In gas expansion, the causing substances are decomposed gas of resin and moisture in pellet. When they are vaporized and expanded, the pressure which has no discharge outlet goes toward the nozzle tip to cause drooling.As for back pressure, a definite back pressure is needed to prevent air catching in metering. But if the pressure is too high, the resin is compressed and the internal pressure is increased to cause drooling.Since air in the cylinder is also expanded by heating, too much air catching in metering aggravates drooling. 图3. 机筒内部的压力Figure.3 Pressures in a cylinder（3） 流涎的对策(3) Countermeasures against Drooling(3-1) 提高树脂粘度3-1) To increase resin viscosity把机筒温度、特别是喷嘴温度设得略低一些。设得过低则会影响流动性并产生冷料（混入熔化不足的树脂）等，进而造成外观不良