Hydraulic clamping frame for heavy weldments: block cylinders on a portal that hold a welded machine base in place

01

From 10 kN on a 16 mm piston to 1,570 kN on a 200 mm piston: push and pull force of 500 bar block cylinders

Römheld's data sheet B 1.5094 covers double-acting block cylinders in 11 sizes, piston diameters 16 to 200 mm and strokes 8 to 200 mm, for a maximum operating pressure of 500 bar. [1] Römheld states that double action generates force in both axial directions, push and pull, with exactly calculable and repeatable stroke times. [1]

Editorial calculation: push force is pressure times piston area. A 63 mm piston has an area of 31.2 cm², and at 500 bar (50 N/mm²) that gives 156 kN, matching the table. The pull figures are lower because the rod takes up part of the area on the return side: 93.0 kN on the 63 mm size is 60% of its push force.

AMF's block cylinder 63461 is single-acting with spring return: maximum operating pressure 500 bar, maximum clamping force 98 kN, stroke 20 mm and weight 5,670 g. [2] Editorial note: a spring-return cylinder retracts only with its spring force, so where a clamp has to pull free under load the double-acting type in the table above is the one to specify.

For each clamp point give the force needed, the direction (push down, push sideways), the stroke to clear the part when loading, and the supply pressure available; ask whether each cylinder is single- or double-acting.

02

Every kilonewton comes back into the frame: screws, side support and the crushing zone

A cylinder pushing on the part pushes equally on the column or beam it is bolted to, and both cylinder makers put the load path on the fixture builder. [1] [2]

Editorial calculation: four 100 mm cylinders pushing down from a top beam at 500 bar put 4 × 392 kN = 1,568 kN, about 160 tonnes-force, into that beam and its columns; the beam must carry it with deflection small enough that the part is still held where intended. The figure is an illustration of scale, not a design load for a particular frame.

Ask the frame supplier for the design clamp load per beam and column, the beam deflection at that load, the screw grade and the guarding around each cylinder.

03

NBR seals to 100 °C, FKM to 200 °C: cylinders working next to the weld

Römheld lists NBR seals and wipers for −25 to +100 °C and FKM for −15 to +200 °C, PTFE glide and back-up rings for −45 to +200 °C, and special versions to +250 °C on request; with FKM seals the cylinders are rated to operate up to 200 °C. [1] The housing is high-alloy steel, black oxide (larger sizes lacquered), and the piston rod case-hardened. [1]

Editorial note: on a clamping frame the cylinders nearest the joint see radiant heat and spatter; specify the seal material from the temperature measured at the cylinder, not from the room.

State the distance from each cylinder to the nearest weld, the welding process, preheat temperature if any, and whether spatter shields are wanted.

04

Three times fewer restraint points, 6–8% less distortion: what a 10 m welded steel plate study found

Mróz and co-authors (Rzeszów University of Technology, Naftoremont-Naftobudowa and the Łukasiewicz Centre of Welding) simulated and then welded a 10,000 mm storage tank bottom of 6 mm S235JR plate by MAG, with two layouts of wedge restraints. [3]

The aim was to tighten flatness from 0.25% × D = 25 mm, the tolerance met under EN 14015 by the previous technology, to 0.2% × D = 20 mm. The second fixture layout used three times fewer fixture points than the first; in the SYSWELD simulation the first layout's distortion was 6% higher before release from the fixtures and 8% higher after release. [3]

The authors caution that both layouts must be judged with the clamping force: with fewer clamps and less force the total may be too low, changing the restraint and the distortion. They also note that the stiffness and clamping method are hard to reproduce in a model and that small changes in clamping conditions can shift distortion substantially. [3] In the physical welding test with the second layout, Z-axis distortion ranged from −19 to +12 mm on one measurement line and −4 to +16 mm on the other, and the authors write that the 20 mm condition was met on the second line but not "for the majority of the points on line L1". [3]

Editorial note: this is a thin, wide plate, not a stiff machine base, so the percentages do not transfer; what does transfer is the method of comparing restraint layouts by simulation before the frame is built and measuring after release, not only while clamped.

Send the part drawing with weld sequence, the flatness or position tolerances after release, and ask the supplier how clamp positions and forces were chosen.

05

What to send for a hydraulic clamping frame

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Part: [drawing; mass; envelope; material]
Process: [welding / straightening / machining; weld sequence]
Clamp points: [number; force; direction; stroke]
Cylinders: [single or double acting; seal material; supply pressure]
Frame: [design load; deflection limit; floor or bed plate interface]
Tolerances: [after release]
Safety: [guarding; pressure monitoring]

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