Needing reliable hydraulic connections for its new range of front end loaders, Wilhelm Stoll Maschinenfabrik selected the WALFORMplus tube fitting from Eaton Corporation
From bases in Lengede near Hannover and in Poland, Wilhelm Stoll Maschinenfabrik manufactures front loaders for tractors, including pallet lifts, bail forks and buckets, and offers different product lines for tractors with outputs of 25 to 300 HP.
One example is the company’s new ProfiLine FZ/FS front loaders. Offering high performance and extremely robust design, these are often used in continuous operation and under extreme conditions. Not only are these faced with vibration caused by the drive and uneven ground, but if the driver fits the front loader with a shovel, for example, and then drives at speed into a pile of sand, the entire implement is exposed to high mechanical forces.
When designing the new product line, the engineers at Stoll also wanted to optimise the interfaces in the hydraulic system – with the aim of achieving maximum leakproofness, process and assembly reliability. The specifications required that the ProfiLine be equipped with hydraulic lines made of steel tubing, which offer higher quality and durability.
In contrast to flexible hoses, however, steel line connection calls for absolute process reliability during manufacturing – from cutting, deburring and shaping of the contour, all the way to bending. Consequently, the process has to be optimised accordingly, and it is only logical to consider the use of a new connection system when they are developed.
In the past, the company used the WALPRO cutting ring at this critical interface. Konrad Willenborg, head of quality management, said: “The ‘human factor’ in the assembly process always has to be taken into account when using cutting rings – there’s no such thing as absolute, reproducible process and assembly reliability.”
Moreover, cutting rings do not offer maximum leakproofness if the connection is exposed to extreme dynamic stresses, such as pressure fluctuations, compressive and tensile forces, transverse forces and torsion, and those are precisely the stresses that can occur on the ProfiLine front loaders.
Having examined the tube reshaping systems of several suppliers, Stoll decided in favour of the WALFORMplus system. Uwe Ockert, design engineer, said: “The system’s machine technology met the prerequisites for maximum process reliability in our just-in-time tube production operations. Also, we can remain flexible and continue to use the 24° system to DIN 2353 and DIN EN ISO 8434-1 that’s familiar from the WALPRO fitting.”
The WALFORMplus tube fitting system consists of just three components: the mechanically reshaped tube end is positively connected by a conventional DIN body with 24° cone and a DIN nut. The only possible leakage path is sealed off by a captive elastomer ring that optimally fills the chamber between the tube and the 24° cone. The patented WALFORM ‘nose’ provides additional metal-to-metal sealing.
The end face of the tube, which is shaped by an electronically controlled reshaping machine, has a shoulderthat is inserted into the 24° cone of the body. This design detail greatly improves the assembly behaviour: since the operator can clearly feel the end of assembly, there is far less risk of excessive or insufficient tightening than with other tube fittings.
An additional benefit to the WALFORMplus user is the reliable, positive fit of the tubes, even when subjected to extreme stresses. This also reduces the assembly time, which was particularly important at Stoll because the installation space of some tube fittings is so confined that repeat assembly would entail a major effort.
The introduction of WALFORMplus at Stoll necessitated only a few changes to the process. The bending and reshaping process steps merely had to be switched: when using the system, the tube is first reshaped before being bent.
Willenborg commented: “We achieve maximum reliability in the field, and complete reliability in assembly.”
The steel tubes are safely accommodated in the loading arms of the front loaders, and practical experience shows that maximum leakproofness really is achieved. The high-performance, functionally reliable system has proved its worth, even when subjected to severe stresses and operating under very tough environmental conditions.