Injection mold for plastic roller bearing cages

Claim 1

A two-part die construction for injection molding of plastic cages for a roller bearing assembly, each die part including a die block having a finished flat surface, said die blocks being adapted to have the finished surfaces cooperate to seal a molding cavity within the dies, one die block having a solid cylindrical core extending perpendicularly away from the block at the finished flat portion, said core having a plurality of similar teeth extending radially outwardly therefrom, said teeth being angularly spaced about the core at equal intervals, said teeth extending along the core length from the finished die block portion toward the core free end but stopping short a predetermined distance; said other die block having a blind cavity extending perpendicularly inwardly from its finished portion, said other die block having similar teeth extending radially inwardly from the cavity wall, the radially innermost ends of the cavity teeth lying in a cylindrical surface whose diameter is slightly larger than that of the cylindrical surface defined by the radially outermost ends of the core supported teeth, the teeth in both die parts corresponding in number and orientation, the cavity teeth extending along the cavity axis from the cavity inner end toward but short of the finished block portion, the two blocks, when in molding relation, having radially offset tooth pairs suitably shaped along the tooth sides to provide desired molding contours, the annular clear regions at the core end on the one block and on the other block adjacent the flat finished portion permitting the formation, during molding, of inner and outer cage ring portions to integrate with cage ribs created between tooth pairs, said core end and cavity bottom cooperating to provide plastic cut-off, the clearances between the radially spaced tooth pair portions providing cut-off; at least one runner and gate at the finished flat portion of the other block and an air vent for the molding cavity, said die parts cooperating to mold a bearing cage having substantially no flash except where the gate runs into the mold cavity.