Coupling for tripartite injection or compression mold

Claim 1

In a tripartite mold comprising a first outer plate, a second outer plate and an intermediate plate sandwiched between said outer plates, said plates having contact surfaces perpendicular to a direction of relative motion, the combination therewith of coupling means for enabling two-stage separation of said plates from one another after the molding of a workpiece in a mold-closed position in which said plates are in mutual contact, said coupling means comprising: a control bar rigid with said first outer plate extending transversely to said contact surfaces toward said second outer plate; a locking bar rigid with said second outer plate extending parallel to said control bar toward said first outer plate; a transverse guide block on said intermediate plate with a channel forming a track parallel to said contact surfaces, said channel intersecting two parallel passages in said guide block that are traversed by said bars with limited lateral play in said mold-closed position; a generally U-shaped detent member slidable in said channel transversely to said direction of motion, said detent member having a first and a second leg straddling said locking bar, said first leg being provided with a beveled face confronting said second outer plate, said control bar having a camming face paralleling said beveled face, said second leg having an angular cross-section and being positively engageable by a transverse shoulder of said locking bar whose width exceeds said play and which faces away from said first outer plate, said shoulder being coplanar with a transverse face of said second leg in said mold-closed position, said control bar extending past said detent member in said mold-closed position with said camming face spaced from said beveled face by a certain distance in the direction of said second outer plate; and spring means effective in said mold-closed position to urge said detent member into latching engagement of said transverse face with said shoulder for preventing separation of said intermediate plate from said second outer plate, with said beveled face lying in the path of said camming face whereby relative displacement of said outer plates away from each other by said certain distance causes said camming face to repress said detent member through said beveled face against the force of said spring means with resulting disengagement of said second leg from said locking bar and separation of said intermediate plate from said second outer plate upon further relative displacement of said outer plates.