Method and mold clamping press for injection molding machines

A locking device for locking a tie-rod to a mold supporting platen of a press, comprising:

• a displaceable tie-rod extending through the platen of the press, said tie-rod having an outer threaded portion thereon;
• a locking bush rotatably supported by the platen, said locking bush having an inner threaded portion engageable and disengageable with the outer threaded portion of the tie-rod;
• the threaded portions of the tie-rod and the locking bush being constructed and arranged to provide an axial clearance allowing a relative axial displacement between them;
• an annular shoulder on the locking bush to be urged against a shoulder surface of the platen;
• guide means rotatably engaging the locking bush to maintain the threaded portion of the same bush, disengaged from the threaded portion of the tie-rod, upon rotation of the bush and during displacement of the platen;
• and
• control means to provide an axial displacement between the threaded portions of tie-rod and the bush, and to urge said annular shoulder against said shoulder surface at the clamping of the mold.

Press for the injection molding of plastic materials, comprising:

• a stationary platen for supporting a first half mold;
• a movable platen for supporting a second half mold, said platen being slidingly movable along a longitudinal axis of the press;
• a plurality of peripheral tie-rods parallelly extending between the platens of the press, each of said tie-rods having a threaded portion at one end;
• first control means being provided to displace the movable platen towards and away from the stationary one;
• and
• second control means for the tie-rods and threaded bushes having threaded portions operatively engageable with threaded portions of the tie-rods to generate a clamping the force for tightly close the mold;
• the tie-rods being movably supported in the axial direction by the platens of the press, through locking bushes rotatively supported by one of the platens of the press;
• the threaded portions of each locking bush and the respective tie-rod having an axial clearance between them, to allow a relative axial movement of the tie-rod in respect to the locking bush;
• each locking bush comprising an annular shoulder to engage a shoulder surface of a platen, by a short axial movement of the same bush;
• and
• means for providing a synchronized rotation of the locking bushes correlated to the sliding displacement of the movable platen of the press, and to maintain the threaded portion of the bush disengaged from the threaded portion of the corresponding tie-rod;
• said second control means provided for selectively causing a first sliding movement of the tie-rods with respect to the locking bushes, along said axial clearance to bring the screw threaded portions into contact with each other, respectively a second sliding movement of the tie-rods and the locking bushes to bring the annular shoulders of the bushes into engagement with the shoulder surfaces of a platen, and to tightly clamp the two half molds.