Forming instead of a cutting ring: Walform, EO2-FORM and the LT-KF42 machine
How to assemble a 24° cone tube joint without cutting rings: the machine forms the tube end for the nut and an elastomer seal. We explain the technology, compare the forming systems — and show that all of them are produced on one machine.
Rigid hydraulic piping in Europe, Russia and Asia has traditionally been assembled with 24° cone fittings to DIN 2353 (ISO 8434-1). The classic way to fix a tube in such a fitting is a cutting ring: when the nut is tightened, its hardened edges cut into the outer surface of the tube. The technology has been proven for decades, but it has structural drawbacks. Tube end forming was developed to eliminate them.
The classic: the cutting ring and its limits
What is built into this design:
- A cut in the tube. The ring edges cut the surface — a stress concentrator appears in the zone of maximum vibration stress. Under pressure pulsation and vibration, fatigue cracks start exactly there.
- Dependence on the fitter. If the nut is under-tightened, the ring has not bitten: the joint leaks and under load the tube may be pulled out. If over-tightened, the ring has crushed the tube. The instruction "one and a half turns after contact" is interpreted differently by every fitter in practice.
- Metal-to-metal. A seal without an elastomer is sensitive to surface micro-relief and temperature cycles; micro-leaks on vibrating machinery are a typical complaint.
- Limited re-assembly. Every disassembly weakens the ring's grip.
Tube end forming: how it works
The idea of forming systems is to move the "difficult" operation from the installation site into a machine. The tube end is cold-formed once: a special tool upsets the end, raising an annular bearing shoulder and a seating surface for the seal. The wall is not cut — the metal is redistributed and the fibres remain continuous.
Assembly after that is simple: an elastomer seal is placed on the formed end, the tube is inserted into a standard 24° cone fitting body, and the nut is tightened down to a rigid stop on the shoulder. No cutting rings are used, and the result of tightening does not depend on the fitter's skill.
What forming gives: the advantages
- The tube is not weakened. No cut means no stress concentrator: the fatigue strength of the joint under vibration and pressure pulsation is significantly higher than with a cutting ring.
- Elastomer sealing. An FKM/NBR ring in the cone withstands high pressure, temperature cycles and micro-vibration — no periodic re-tightening.
- Assembly does not depend on the fitter's experience. The nut is tightened to a rigid shoulder stop: over-tightening is physically difficult and under-tightening is visible at once.
- Faster and cheaper to assemble. One part fewer in the joint — no cutting ring — and with it the pre-assembly operation disappears. The forming cycle on the machine takes 15–20 seconds.
- Repeated re-assembly. The shoulder is formed permanently — the joint can be disassembled and reassembled many times; only the elastomer seal is replaced.
- Standard fitting bodies. A formed tube fits ordinary DIN 2353 24° bodies — You can switch to the technology gradually, changing only nuts and seals.
Walform, WALFORMplus, EO2-FORM, VOSS Form: what is the difference
Several proprietary systems develop the forming idea. The principle is the same for all — cold forming of the tube end for a 24° cone; they differ in contour geometry and in the design of the nut and the sealing element:
| System | Nut | Seal | Feature |
|---|---|---|---|
| Walform | standard DIN | elastomer ring (FKM, H-NBR, NBR, EPDM — per medium) | the first mass-produced forming system; body and nut are ordinary DIN 2353 parts |
| WALFORMplus | standard DIN | elastomer (FKM) | development of WALFORM for highly dynamic duty — pressure pulsation and vibration |
| EO2-FORM | standard, EO2 system | functional ring with elastomer | contour for the EO2 sealing element — forming integrates into that fitting range |
| VOSS Form SQR | SQR functional nut with integrated clamping ring | metal-to-metal + additional soft FKM ring | the tube end seats deep, to the bottom of the body, with a bevelled bearing face — unlike the straight end of DIN systems; the clamping ring grips the tube radially and damps vibration before the sealing zone |
| 24° metal-to-metal forming | standard DIN | no elastomer | the end is formed into a sealing cone — an option for media where an elastomer is undesirable |
A little history. The pioneer of forming is the German company Walterscheid: its WALFORM system appeared in the 1990s and was the first to prove that a cutting ring could be replaced by a contour on the tube itself. Later the tube-connection division of Walterscheid became part of the Eaton group, which is why the system is known today as Eaton Walterscheid WALFORMplus. VOSS entered the market with its SQR system in the early 2000s and concentrated on vibration protection: thanks to the clamping ring in the nut, the system is certified for shipbuilding and offshore platforms among others.
LT-KF42: one machine for all contours
LT-KF42 is a tube end forming machine with a 650 bar hydraulic drive. The tube is clamped by dies (sets from D6 to D42), the punch upsets the end into the contour of the installed die. Modes — manual and automatic; tooling is stored in the machine's own cabinet.
| Parameter | Value |
|---|---|
| Forming, steel ST 37.4 | 6×1 – 38×6 mm, up to 42×4 mm |
| Forming, stainless steel 1.4571 | 6×1 – 38×5 mm, up to 42×3 mm |
| Hydraulic pressure | 650 bar |
| Power / supply | 3 kW · 380/400 V |
| Dimensions / weight | 630×750×1150 mm · 251 kg |
The ranges cover the whole DIN 2353 size series — from the light 6×1 to the heavy 38×6, including stainless piping for shipbuilding and food industries.