模具专业英语 教学课件 作者 王浩钢 14456第15章.pptVIP

Lesson 15  Runnerless Moulds Nozzle types 　　The purpose of the nozzle is to provide a flow path for the plastic melted from the machine’s cylinder to the mould. In the simplest design the nozzle butts on to the sprue bush of the mould. 　　There are two standard designs in common use and they differ only with respect to the form of seating that is made with the sprue bush. 　　One design incorporates a hemispherical end and the other design is flat-ended. 　　The small length of reverse taper in the bore at the front end of the nozzle is such that the sprue is broken just inside the nozzle①. 　　This helps to keep the nozzle face clean and assists in maintaining a leak-free sealing face. The nozzle types are as follows: 　　extended nozzle (Figure 15-1), barb nozzle, antechamber design, internally heated sprue bush (Figure 15-2), internally heated extension nozzle, multi-nozzle manifold. 　　This is the name given to a mould which contains a heated runner manifold block within its structure. 　　The block, suitably insulated from the rest of the mould, is maintained at a closely controlled elevated temperature to keep the runner permanently as a melt. 　　The polymer material can thereby be directed to the mould extremities without loss of the heat and without the pressure loss associated with temperature variations②. 　　The hot-runner unit (see Figure 15-3) is mounted adjacent to the cavity plate and accommodated in a suitably design grid. 　　The polymer material enters via a centrally positioned sprue bush, passes through the flow-way and leaves the unit via a secondary nozzle in line with the impression③. 　　When the mould is opened the molding is pulled from the cavity, and the sprue is broken at the small diameter end. 　　The remainder of the feed system remains heated within the unit, ready for the next shot. 　　An insulated runner mould (Figure 15-4) is one in which the melt flows through a large-diameter runner machined in the butting surfaces of th