Patent ID: 7311517

Claim:
A mold clamping device comprising: a stationary platen that supports a stationary mold; a movable platen that supports a movable mold; a plurality of tie bars with ends that are detachably connected to the stationary platen and other ends that extend through the movable platen; mold opening and closing means that moves the movable platen toward and away from the stationary platen so that the movable mold opens from and closes on the stationary mold; tie bar connecting means that detachably connects each of the plurality of tie bars to the movable platen by having a split nut engaged with an engagement portion formed in each of the tie bars; and a mold clamping cylinder that is provided around a tie bar insertion through hole in the movable platen and propels the movable platen toward the stationary platen side, using the split nut in the tie bar connecting means as a reaction point, so as to generate a mold clamping force, wherein the mold clamping cylinder includes a secondary piston that defines, out of two chambers in front and in rear defined by a primary piston that abuts against the split nut, the chamber positioned on the stationary platen side into a front chamber and a rear chamber, and the secondary piston integrally operates with the primary piston at a time of a mold contact and a mold clamping, but makes a movement relative to the primary piston at a time of a mold release.