Abstract: Mold clamping forces are provided by mounting the mold halves between spaced crossheads connected by elastically deformable rods of tensile steel. The crossheads are pulled slightly apart by hydraulic cylinders to expand and tension the rods, and the prepared molds are then inserted together with appropriately dimensioned wedges or shims to occupy the expansion space. When the hydraulic pressure is released the elastic restoration or spring forces of the stretched rods serve to clamp the assembled molds tightly together to enable injection, curing, etc. A plurality of such mold assemblies may be circumferentially spaced around a rotatable turntable, and the various opening and closing movements may be controlled by rollers on the mold components running in stationary cam tracks around the turntable. C-shaped mold clamps may also be used instead of the crosshead and rod configurations.