Hydraulic Press Clamping Cylinder

Maximum Force.
Minimum Stroke.
Never Let Go.

Every other press cylinder acts and returns. The clamping cylinder acts and holds — maintaining full grip pressure on a 1,200 °C steel billet for the entire forging sequence, through every press stroke, every manipulator rotation, every lateral shift. If the grip fails, the billet falls. There is no second chance.

Engineering Insight — The Physics of Not Dropping a 10-Tonne Billet

The clamping force is not arbitrary — it is calculated from the billet weight, the friction between the jaw faces and the billet surface, and a safety factor that accounts for the dynamic forces during forging (shock, vibration, inertia from manipulator movement).

The safety factor of 3–5 accounts for the press shock force (transmitted through the billet into the jaws), the inertial force during rapid manipulator rotation, and the possibility of reduced friction from oxide scale on the billet surface. Korea Ever-Power sizes the clamping cylinder bore to deliver the calculated grip force at the operating pressure — with the full safety margin. Contact the hydraulic cylinder engineering team for clamping force calculations.

Most hydraulic cylinders cycle: extend → work → retract → repeat. The clamping cylinder extends to close the jaws, then holds at full pressure for 5–30 minutes while the forging sequence proceeds. During this hold period, the cylinder must maintain pressure without any drop — because any pressure loss relaxes the jaw grip on the billet.

This continuous hold creates different engineering demands than cyclic operation. The seals must resist static friction (stiction) — the tendency of elastomer seals to bond to the bore surface under sustained pressure. When the jaws finally open after a long hold, the seals must break free cleanly without stick-slip. Korea Ever-Power uses low-stiction seal compounds (PTFE-bronze composite piston seals) for clamping cylinders to ensure smooth jaw opening after prolonged pressure holds.

The hydraulic circuit includes a pressure-maintaining valve (accumulator or check valve) that keeps the cylinder pressurised even if the pump is serving other cylinders on the manipulator. This guarantees uninterrupted grip regardless of what else the hydraulic system is doing — the tilt cylinder, the traverse cylinder, and the rotation cylinder can all be active without affecting the clamping pressure.

A clamping cylinder failure during forging has immediate, severe consequences. The hot billet — weighing tonnes, at temperatures that instantly ignite anything it touches — drops from the manipulator onto the press bolster, the floor, or worse. The billet is unpredictable: it may bounce, roll, or shatter if it has internal cracks from the forging process.

Prevention relies on three layers. First, the clamping force calculation includes a safety factor of 3–5×, so the actual grip far exceeds the minimum needed. Second, the hydraulic circuit includes a pilot-operated check valve on the clamp port that locks the cylinder at pressure even if the supply line loses pressure. Third, pressure sensors monitor the clamp circuit continuously — any pressure drop triggers an immediate press-stop interlock and an alarm.

Korea Ever-Power designs every clamping cylinder with the check-valve mounting face integrated into the cylinder head — not as a remote installation. This eliminates the hose segment between the cylinder and the check valve, removing the most common failure point (hose burst between cylinder and valve = instant pressure loss = instant grip loss).