专业英语资料.ppt

容易产生竞流效应(race-tracking effect)，导致包风(air traps)和缝合线(weld lines)，在塑件表面产生瑕疵。假如厚肉区没有充足的保压，就会造成凹痕(sink marks)或气孔(voids)，(Injection molding is)A process in which granular polymer,usually thermoplastic,is fed from a hopper into a heated barrel where it is melted,after which a screw or ram forces the material into a mold.注塑是一种成型方法，它是将粒状聚合物（通常是热塑性塑料）从料斗加入到加热了的机筒中，并在机筒中将其熔融，之后在螺杆或柱塞的强迫下进入模具。Pressure is maintained until the part has hardened.The mold is opened and the part is ejected by some mechanism.It is by far the most important technique for mass production.保持压力，直到制件硬化。（然后）打开模具，并用某些机构装置将制件推出。目前为止，它是对聚合物大批量生产中最重要的技术。The major disadvantages of the process are that not all polymers can be processed(most thermosets),and the metal molds are very expansive.这种成型方法主要的缺点是不是所有的聚合物都能用这种方法成型（大多数的热固性塑料就不行），且金属模具非常昂贵。This basic process is also used for co-injection of two different polymers.There are two extrusion barrels and injection systems.这种成型也用于两种不同聚合物的共注塑。有两套挤压的机筒和注塑系统。A shot is made with one polymer,and a second shot with a second polymer can be used to surround or surface the part made in the first shot.第一次注射第一种聚合物，第二次用第二种聚合物注射，第二次注射的聚合物能用来包围或形成第一次注射成的部件的表面。Co-injection is often done to achieve a cosmetic effect or to alter use properties.共注塑经常用于得到装饰的效果或来改变使用性能。Another variation of injection molding is structural foam molding.注塑成型的另一种变形是结构发泡注塑成型.The mold is only partially filled,and injected plastic expands to fill the mold to produce a part that is light weight because of the entrapped porosity,but the skin is integral.通常部分填充模具，并使注入的塑料膨胀来填充模具，制成具有很轻重量的制品，这些轻制品是由于引发产生了孔状结构，但是制品的表皮是实心的.Foamed polymers have lower weight(and cost)over their nonfoamed counterparts,and,the mechanical properties are often comparable.发泡的聚合物比没有发泡的相应物具有更轻的重量（和成本），且通常具有相似的机械性能.This process is often used on polyphenylene oxide,olefins,vinyls,nylons,and thermoplastic elastomers.这种成型方法经常用于聚苯醚，聚烯烃类、乙烯基类、尼龙类和热塑性弹性体的加工。