Clamping force applying means for molding machines

Claim 1

In a molding machine, a first platen, a second platen movable towards-and-away from said first platen, a plurality of tie rods associated with one of said platens and longitudinally projecting from said one platen towards the other thereof, gripping means operatively associated with said other platen for gripping said tie rods, said gripping means for each said tie rod comprising a plurality of breech blocks located on the opposite side of said other platen from said one platen and relatively movable for gripping a therebetween said tie rod, and individual clamping force applying means operatively associated with each said tie rod for applying clamping force to a mold between said platens through the tie rod and its respective said breech blocks, each said clamping force applying means comprising means defining a plurality of cylinders aligned with its respective tie rod and on such opposite side of said other platen intermediate said other platen and the respective said breech blocks for the tie rod, the end said cylinder most adjacent to such breech blocks having its end most adjacent to the latter open thereto, a piston in each of said cylinders, said pistons being interconnected to be fluid actuatable towards-and-away from such breech blocks for conjointly applying said clamping force, said pistons being annular and containing openings aligned with the tie rod and dimensioned to permit axial movement of the tie rod through said pistons, the piston in said end cylinder being adapted to apply clamping force through said cylinder open end to such breech blocks upon fluid driving of said piston towards the latter, means for supplying pressure fluid to said cylinders for driving said pistons towards-and-away from such breech blocks, and each said clamping force applying means further comprising by-pass means for by-passing pressure fluid around all of its said pistons, except its said piston in said end cylinder, after a predetermined movement of the pistons for application of clamping force, such by-pass means comprising internal grooves in the walls defining said cylinders constructed to communicate portions of said cylinders on opposite sides of their contained pistons, said grooves being located to prevent fluid flow therethrough during the normal application of clamping force by the pistons and said grooves being at the ends of said cylinders most adjacent to said breech blocks.