Toothed gear injection molding

Injection Molding of a Plastic Toothed Gear Type and Position of Sprue. 339... 

Toothed gears for small and medium-sized watch motions and gears for automobiles and toys, in a few cases even for vehicle gears, are injection-molded or pressed out of thermoplastics and occasionally duroplastics as well. Dimensional accuracy is the key to production quality, and it must be sustained throughout the useful life of the part. 

In injection molding of semicrystalline thermoplastics, for example polyamide, polyoxymethylene, ultrahigh molecular polyethylene (very high melt viscosity), linear polyesters (PET, PBT), local variations in molecular orientation result in dimensional variations in the part (warpage, memory effect), especially if the toothed gear is exposed to a thermal stress load. 

Composite molding n. The process of molding two or more materials in the same cavity in the same shot, but a combination of transfer and compression molding. For example, in making a ring gear, a loose nylon-fiber-filled material is loaded into an open mold around the tooth circle, the mold is closed, and then molten nylon is injected by transfer molding. 

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