Sprue bushing injection molding is connecting between nozzle of injection machine and injection molding. It is same a part of the runner, which allows the molten plastic material to be injected into the mold through the nozzle of an injection machine.
I. Construction of sprue bushing injection molding.
+ Sprue bush can design follow your calculation or you can buy it from other supplier. You can refer some Sprue bushing construction of Misumi factory.
This is 3D construction od sprue bush.
Sprue with 2 bolts use for small mold, It can use for injection machine that smaller than 350 ton.
Sprue with 4 bolts use for large mold, It can use for injection machine that bigger than 200 ton.
+ Fixing sprue bush.
II. Sprue bush design.
+ We usually use SKD61 to make sprue bush, sometimes, we can use chipper material as 2311, S55C.
+ When you design or select sprue bush you have to note that ball radius of sprue must larger than radius of nozzle. It it is smaller then radius of nozzle, will has gap between sprue and nozzle, resin can over and pressure of injection machine will be lost.
+ Hole diameter inner must be larger than hole diameter of nozzle. If it is smaller than hole diameter of nozzle, it will prevent moving of the molten plastic material. Diameter of nozzle usually is about 2~5mm. When you select the sprue, note check injection machine catalog and select it is larger than 0.5 m or bigger.
+ The angle of hole inner usually is about 2~6 degree. For best choose, you can select about 3~5 degree.
+ Check the dimension of mold plate, the length of sprue must be fit with the plate thickness.
III. Sprue bush cooling design.
If diameter of sprue is large, some times sprue bush need cooling to reduce the cycle time of injection process. we can make the cooling layout for sprue bush as picture below.