卫生法律法规医博士试题及答案.doc

This trial version can use only a part of item.
Runner System
In this chapter, you will learn about the functions, characteristics, and shapes of the sprue, runner, and gate.
The molten plastic injected from the injector nozzle will go through a sprue (sprue bush), a runner, and a gate and fill up in the cavity.
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.
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 sprue, the runner, and the gate will be discarded after a part plete. However, the runner and the gate are important items that affect the quality or the cost of parts.
Gate
The gate is categorized into restrictive gate, which narrows the entrance, and nonrestrictive gate, which does not narrow the entrance.
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.
Restrictive Gate
A restrictive gate has a narrow entrance to the cavity to restrict the amount of molten plastic in order to improve filling in the cavity.
The restrictive gate has the following characteristics.
Generates shear heat by going through the narrow gate, raising the temperature of molten plastic and improving the filling in the cavity.
Reduces residual stress, and thus reduces part defect such as warp.
As the cooling solidification time is shortened, molding cycle is also shor