Mold clamping device

A mold clamping device comprising:

• a clamping cylinder slidably fitted with a clamping ram in a front end thereof, a front end of the clamping ram being connected to a movable board of a mold;
• a rear high pressure chamber and a front oil chamber of said clamping cylinder being divided by a piston section of said clamping ram;
• a first oil path for supplying oil to the rear high pressure chamber of said clamping cylinder;
• a connecting path passing through the piston section of said clamping ram to connect the front oil chamber and the rear high pressure chamber of said clamping cylinder;
• a first open-close valve being fitted on the rear end section of said clamping ram at the back of the piston section of said clamping ram, said first open-close valve opens said connecting path during mold opening and closing, and closes said connecting path during tight mold clamping;
• a high-speed piston for opening and closing said mold, said high speed piston being slidably fitted in said clamping ram from a rear end thereof, said high speed piston having a base section fixed on an inner rear wall of said clamping cylinder;
• a rear pressure chamber for mold opening and a front air chamber connected to atmosphere, said clamping ram being divided by a large-diameter piston section of said high-speed piston;
• an oil chamber for mold closure being formed in said high speed piston by a piston rod which extends from the inner wall of the air chamber to slidably fit in said high speed piston from a front side thereof;
• a second oil path for supplying oil to said oil chamber in said high speed piston for high speed mold closing;
• a third oil path for supplying oil to the rear pressure chamber in said clamping ram for high speed mold opening;
• an oil chamber for valve opening being formed at a position where said first open-close valve is slidably fitted on said clamping ram;
• a through-hole passing through said clamping ram to connect said rear pressure chamber for valve opening to said oil chamber for mold opening of said clamping ram;
• a charge tank being provided alongside of said clamping cylinder, said charge tank being connected to the front oil chamber of said clamping cylinder and having a capacity larger than a capacity difference between the front oil chamber and the rear high pressure chamber of said clamping cylinder;
• and
• a second open-close valve for connecting and disconnecting the front oil chamber of said clamping cylinder and said charge tank.