Hydraulic Press Centering Cylinder

The Smallest Cylinder.
The First Thing That
Must Be Right.

The master cylinder delivers 80 MN. The clamping cylinder grips with 9,621 KN. The centering cylinder produces just 441 KN — the lowest thrust of any press cylinder. But if this cylinder fails, the billet is gripped off-centre, forged off-centre, and every dimension on the finished part shifts with it. Alignment is not optional.

The centering cylinder is typically a double-acting cylinder mounted on the manipulator frame, connected to the clamp head carriage via a direct rod connection or a lever linkage. When both ports are pressurised equally (or a dedicated centering valve is activated), the cylinder pushes the clamp head to a mechanical mid-stroke position — defined by equal oil volume on both sides of the piston, or by a mechanical stop at the centre of travel.

The centering force (up to 441 KN) needs only to overcome the friction and inertia of the clamp head carriage — not to resist forging forces. Once centred, the clamp head is held in position by the centering cylinder's hydraulic lock while the clamping cylinder grips the billet. After gripping, the billet's position is fixed by the clamping force, and the centering cylinder can be depressurised without affecting the billet alignment.

On manipulators that handle multiple billet sizes, the centering cylinder can also function as a jaw-width adjustment actuator — positioning the clamp head at a specific offset (not centre) to accommodate billets of different diameters. This dual-purpose capability eliminates the need for a separate adjustment cylinder on some manipulator designs.

Perspective — The Smallest Cylinder in a System of Giants

The centering cylinder is the smallest actuator on the manipulator and in the entire press cylinder system. But its output — precise billet alignment — feeds directly into the quality of every downstream operation. Here is how it compares to its neighbours:

The centering cylinder's 441 KN is 0.55% of the master cylinder's 80 MN — but a centering error propagates through every single press stroke that the 80 MN master delivers. The cost-to-impact ratio of the centering cylinder is the highest of any actuator in the system. Contact the hydraulic cylinder engineering team for manipulator cylinder sets.

The centering cylinder is physically smaller than the clamping, tilt, or return cylinder — but the machining precision is identical. The bore is honed to the same Ra 0.2–0.4 µm finish, the rod is chrome plated to the same thickness and ground to the same surface standard, and the seal grooves are machined to the same tolerances. A centering cylinder that sticks, chatters, or creeps at low speed defeats its purpose — the clamp head must move smoothly and stop precisely at the centre position.

Because the centering cylinder is mounted on the manipulator arm — in the same harsh forging environment as the tilt and clamping cylinders — it receives the same environmental protection: high-temperature seals (FKM), heavy-duty wiper seals to exclude scale, and chrome plating thickness appropriate for forge-spray exposure. Korea Ever-Power manufactures centering cylinders as part of the manipulator cylinder set, alongside the clamping and tilt cylinders, using the same batch of materials and seals for consistency.

Every centering cylinder is hydrostatic tested at 1.5× working pressure. For position-critical applications, the cylinder is also tested for mid-stroke positioning accuracy — verifying that the centring position is repeatable within ±1 mm across multiple cycles.