模具专业英语 教学课件 作者 王浩钢 14456第4章.pptVIP

Lesson 4 Feed System 　　It is necessary to provide a flow-way in the injection mould to connect the nozzle (of the injection machine) to each impression. 　　This flow-way is termed the feed system. Normally the feed system comprises a sprue, runner and gate. 　　These terms apply equally to the flow-way itself, and to the molded material which is removed from the flow-way itself in the process of extracting the molding. 　　A typical feed system for a four-impression, two plate-type mould is shown in Figure 4.1. It is seen that the material passes through the sprue, main runner, branch runners and gate before entering the impression. 　 　　As the temperature of molten plastic is lowered while going through the sprue and runner, the viscosity will rise; therefore, the viscosity is lowered by shear heat generated when going through the gate to fill the cavity①. 　　 　　It is desirable to keep the distance that the material has to travel down to a minimum to reduce pressure and heat losses. 　　It is for this reason that careful consideration must be given to the impression layout and gate’s design. Sprue 　　A sprue is a channel through which to transfer molten plastic injected from the nozzle of the injector into the mold. It is a part of sprue bush, which is a separate part from the mold. Runner 　　A runner is a channel that guides molten plastic into the cavity of a mold. Gate  　　A gate is an entrance through which molten plastic enters the cavity. 　　The gate has the following functions: restricts the flow and the direction of molten plastic; simplifies cutting of a runner and moldings to simplify finishing of parts; quickly cools and solidifies to avoid backflow after molten plastic has filled up in the cavity. Cold slug well 　　The purpose of the cold slug well, shown opposite the sprue, is theoretically to receive the material that has chilled at the front of the nozzle during the cooling and ejection phase②. 　　Perhaps of greater importance is the fact that