Patent ID: 7425123

Claim:
A hydraulic mold clamping unit, comprising: a fixed lower platen; an upper platen defined by a weight force; an open-close mechanism for moving the upper platen in a vertical direction in relation to the fixed platen, said open-close mechanism including at least one hydraulic cylinder of a first type having a double-acting piston, wherein the hydraulic cylinder of first type has one side constructed for holding part of the weight force of the upper platen, and at least one hydraulic cylinder of a second type including a single-acting piston and having one side constructed for holding another part of the weight force of the upper platen; a hydraulic pump system constructed for operative connection to both sides of the hydraulic cylinder of first type; a pressure accumulator operatively connected to the one side of the hydraulic cylinder of second type; and a valve disposed in the pump system for modifying a back pressure in the hydraulic cylinder of first type, when clamping the lower and upper platens.