Apparatus for injection molding a tamper-proof plastic cap

Mold for manufacturing a plastic closure comprising an external skirt formed with internal ribs corresponding to the ring portion and grooves of the neck of the container to be stopped, and bounding a guaranty strip partially tearable due to circular thinning grooves formed on the inner surface of said skirt, said mold comprising a compensation plate, a fixed base plate overlying said compensation plate, a sliding plate above said fixed plate, a resilient pusher between said base plate and said sliding plate, a cylindrical ejection ring solid with said sliding plate, a cylindrical core solid with said base plate, a shaped sleeve adapted to slide freely on said core and guided by an integral heel portion, said ejection ring being movable through a height equal to that of said notch formed in said base plate, a fixed plate disposed above said supporting plate and comprising holes for guiding said sleeve and ejection ring, an impression plate disposed above said fixed plate and formed with holes corresponding to the holes of said fixed plate, a push member secured to said impression plate and adapted to be actuated by said compensation plate, and a chamber defined between said impression plate and said sliding sleeve above said ejection ring and into which the plastic material is adapted to be injected.