1、拉丝 Stringiness（1） 何谓拉丝（外观 What is stringiness ? (appearance)）拉丝是指主流道前端没有断开而伸展成丝状的一种现象。最大的问题是有时会发生成形品因拉丝而无法脱落，最大的问题是有时会发生成形品因拉丝而无法脱落，被模具夹住，从而导致无法连续成形树脂的纺丝性（在熔融状态下拉伸时可伸长成丝状的性质）越好，拉丝就越严重。因此与改性材料相比，非强化的材料更易引起拉丝 Stringiness is a phenomenon that the sprue tip does not cut but extends stringy. The largest
2、problem is a case that a molded piece does not fall by stringiness but comes between molds. Then continuous molding is stopped。图 1. 拉丝的样子 Figure.1 Stringiness拉丝的生成原因 Causes of Stringiness 2-1) 主流道前端尚未固化- Sprue tip is not solidified yet.注射后，经过冷却工序，主流道会与产品一起固化，但由于其前端与机筒喷嘴相接，从而保持着一定的温度，因此有时芯部并未完全固化。如果此
3、时打开模具，纺丝性（拉伸时会伸展成丝状且不会断开）好的材料便容易在主流道前端产生拉丝 After injection the sprue is solidified with the product through the cooling process, but sometimes the sprue core has not been solidified yet for the temperature kept at a certain level from contacting the cylinder nozzle. At that time, when the mold is op
4、ened, a material of good spinnability (When a material is drawn, it extends to form a string without cutting.) tends to generate stringiness at the sprue tip.。从成型条件来说，如果树脂温度（特别是喷嘴温度）或模具温度偏高，则容易引起拉丝。As molding conditions, stringiness is liable to occur when resin temperature is high (in particular, n
5、ozzle temperature) or when mold temperature is high.图 2. 主流道内部尚未固化时容易产生拉丝 Figure.2 Inner melting resin extends stringy2-2) 材料和等级固有的问题 Problem proper to material or grade大家知道，液晶聚合物以及使用过某种弹性体的耐冲击性等级比其他材料更容易引起拉丝。这是因为这些材料的纺丝性很好。此外，就同一种材料而言，粘度越低就越容易拉丝。A shock resistant grade using a kind of elastomer and
6、 a liquid crystal polymer are known to be more liable to cause stringiness than the other materials. This comes from good spinnability of these materials. When the same material is used, as viscosity increases, stringiness is more liable to occur.拉丝的对策 Countermeasures against stringiness3-1) 使主流道前端固
7、化 To solidify sprue tip具体来说，可更改下列成型条件 Specifically, molding conditions are modified as follows:降低机筒温度 To lower cylinder temperature,降低喷嘴温度 To lower nozzle temperature,降低模具温度? To lower mold temperature.? ?3-2) 加快开模速度，增大开模量 To increase mold opening speed, and increase mold opening distance加快开模速度并增大开模量
8、有时也可在一定程度上减少拉丝 Sometimes stringiness can be suppressed by increasing the mold opening speed and by the mold opening distance.。 Figure.3 Cutting by mold opening3-3) 更改喷嘴 To change nozzle更改喷嘴形状可减少拉丝。具体对策就是减少喷嘴和减小闭式喷嘴的孔径。有些成型机生产商有时也备有防拉丝喷嘴。如果仅靠调整成型条件无法解决拉丝问题，则应与成型机生产商联系并商讨改进措施。Stringiness can be suppre
9、ssed by changing the nozzle shape. Specifically, the countermeasures include use of a shut-off nozzle or reduction of the nozzle hole diameter. Some molding machine manufacturers have special nozzles for stringiness prevention. If stringiness can not be mended by molding conditions only, please consult the molding machine manufacturer for nozzle change.此外，如果在流动性方面还有余地，则改用粘度更高的材料也是一种好方法。If you have some reserve in flowability, switching to a grade of higher viscosity may be another way for solving stringiness.
