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 cavity.,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 gates design.,(a),Figure 4-1 Feed system: (a) typical shot of consisting of moldings with sprue, runner and gates attached; (b) section through feed portion of mould,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 phase.,Perhaps of greater importance is the fact that it provides positive means whereby the sprue can be pulled from the sprue bush for ejection purposes.,The sprue, the runner, and the gate will be discarded after a part is complete. However, the runner and the gate are important items that affect the quality or the cost of parts.,Notes, 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 cavity.,熔融塑料通过主流道和分流道时温度降低而使熔体黏度升高，然而，熔体通过浇口填充型腔时，由于剪切作用产生的热量又使黏度降低。,句中的therefore是连接前后两个句子，As the temperature of molten plastic is lowered while going through the sprue and runner是原因状语从句，修饰the viscosity will rise。, 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 phase.,冷料井正对着主流道。理论上，冷料井的作用是用来储存在（塑件）冷却和推出过程中注塑机喷嘴处所形成的熔体前锋冷料。,句中shown opposite the sprue，修饰the cold slug well，that has chilled at the front of the nozzle是定语从句修饰the material。,