Sprue bushings

Locating Ring Sprue Bushing Front Clamping Plate Clamp Slot... 

The diameter of the sprue bushing should be at least 1.6 mm larger than the diameter of the main runner and slightly larger than the nozzle orifice. A standard taper of 4-6 mm/m is a good rule-of-thumb choice. 

The molding compound flowing from the nozzle enters the mold and is distributed into the cavities. This is the task of the sprue- and numer system (see Figure 4-1). It consists of several sections, that may differ in design, subject to requirement. As the melt leaves the nozzle, it passes through the sprue bush and into the runner, which connects to the gates of the cavities. 

Moving the injection unit up against the mold s sprue-bush, as well as moving it away again (sprue-break or complete retraction)... 

The plasticating unit moves up to the mold s sprue bush. The nozzle is opened, and the material located in the screw s ante-chamber is injected into the mold by the forward movement of the screw. 

At the start of the injection process, the molten, homogenized material is poised in the injection chamber. The nozzle is closed, so that no material can escape. As soon as the plasticating unit has been moved against the mold s sprue bush, the nozzle can be opened to allow the melt free passage into the mold. 

That part of the injection molding tool, against which the nozzle pushes during the injection process to inject the melt. The bore of the sprue bush is cone-shaped and with many single impression molds connects directly into the cavity... 

The sprue is the metal attached to the nmner that solidifies in the sprue bush. The overflow is a recess with entry from the die cavity, to assist in the production of sound castings and ensure complete filling of the cavity. 

Nozzle opening at least 4.75 mm and usually 7.9 mm and 0.8 mm smaller than the orifice dimension of the sprue bushing land length < 4.75 mm and nozzle... 

Shear heating of melt] injection rate too fast/injection pressure too high/gates too small/nozzle orifice too small < 0.8 of sprue bushing/nozzle dirty/sharp corners/injection rate too fast/shutoff nozzle used instead of a general purpose nozzle/improperly designed or defective non-return valve. 

A nozzle insert of internal diameter equal to that of the sprue bush is fitted. Use of too small a nozzle is a common cause of light components due to a decrease in pressure in the runner, or in extreme cases scorch with attendant problems. 

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