Veneer machine: Plastic plain bearings master extreme loads and high temperatures

Wood dust, high pressure and high temperatures: The environmental conditions for the plain bearings of machines that assemble wood veneers are anything but ideal. Plastic plain bearings from igus® prove themselves under these extreme conditions. Heinrich Kuper GmbH, the only manufacturer worldwide to cover the entire spectrum of veneer assembly technologies, uses split igus® plain bearings made of the material iglidur® G in a new generation of machines at a particularly critical point - the pressure beam bearing.

When it comes to woodworking, German mechanical engineering has a strong position internationally. This may be due in large part to the fact that the material and manufacturing processes place very high demands on the machines and the engineering expertise of the designers. Take veneer production, for example: individual veneer strips are assembled into so-called carpets using high pressing forces and high temperatures.

Profile

What was needed: Slide bearings in the veneer machines, more precisely on the pressure beam bearing for turning and swivelling movements
Requirements: Resistance to high temperatures, dirt, dust and pressure
Sector: Wood industry
Success for the customer: iglidur® plain bearings are less expensive to purchase than conventional bearings, meet the technical requirements of the customer and minimise the service effort, thus guaranteeing a long service life.

Veneer machine with control panel and multiple workpiece holders.

Problem

Heavy dirt and dust loads in combination with high temperatures make the conditions for bushings in this application more difficult. Heinrich Kuper GmbH also wanted a maintenance- and lubrication-free solution for the bearing points of the veneering machine that would enable long downtimes.

Solution

Plastic plain bearings made of iglidur® G offer a lubrication-free solution that is very insensitive to dust and dirt. The occurring loads are absorbed by the pressure-resistant material iglidur® G. Furthermore, the coefficient of friction remains low even under the difficult conditions of the veneer machine and enables a very good solution for continuous use.

"The use of the iglidur® G bearing is also the first choice for us in this case due to its corrosion resistance and insensitivity to the abundant wood dust."

Michael von Mutius

Deputy Design Manager at Heinrich Kuper GmbH

The centrepiece: Bonding pressure beam

Heinrich Kuper GmbH in Rietberg is one of the market leaders in this highly specialised area of mechanical engineering. With the "ACR-Superquick" veneer cross-cutting machine, the company has had a globally successful series in its programme for years - the requirements and expectations were correspondingly high when Kuper began developing the successor series "ACR-Speedstar".

The centrepiece of a veneering machine is the gluing beam. It joins the veneer strips together with the help of gluing elements. Pressing forces of up to 20,000 N and temperatures of up to 220 oC are achieved in the joining area. As the veneer strips can be very long, the pressure beam is not exactly small either: it reaches a length of around 3500 mm and weighs around 500 kg.

The fact that the designers and, subsequently, the users of the machine place very high demands on the bearing of the beam is due to the ambient conditions. After all, in addition to its own weight, the beam must also be able to withstand the high pressing forces of up to 20,000 N. One of the reasons why this requirement is not easy to fulfil is that the pressure causes the beam to deflect. One of the tasks of the bearing points is to compensate for these deflections.

Component of a veneering machine with protective housing and drive unit inside.

Beams must remain flexible

In addition, the high temperatures that occur lead to thermal expansion, which must also be compensated for by the bearings. Further requirements relate to the ease of servicing and the availability of the bearing and therefore the entire machine: as access to the gluing elements is required for cleaning purposes, the bearing should allow this access - in other words, the beam must be able to move when servicing is required. In addition, the bearings should be largely maintenance-free and wear-free. Last but not least, the costs of the bearings also play a role.

For the ACR - Superquick, Kuper had still provided a translatory pressure beam bearing with ball bushing guides. Michael von Mutius, deputy design manager and project engineer at Heinrich Kuper GmbH responsible for the design of the ACR - Speedstar: "However, this bearing was not maintenance-free and was also relatively expensive. Accessibility to the adhesive elements was also not ideal."

Maintenance-free bearing

To ensure this accessibility, Kuper designed the new machine with a rotating movement: The pressure beam can move 90o towards the operator. And a new approach was also chosen for the bearing of the pressure beam: plastic plain bearings are used here, more precisely iglidur® G-bearing of type GFM 90-95-100, which were split and shortened to a length of 60 mm.

This solution has proven itself in practice: The rotary movement swivels the adhesive elements directly towards the operator and is easily accessible for cleaning and maintenance purposes. Due to the pitch of the bearing, the assembly and disassembly of the pressure beam is very simple, and the bearing clearance of the iglidur® bearings very effectively compensates for thermal expansion and deflection of the pressure beam. The bearing and the bearing material do not even reach their load limit: The use of the iglidur®-bearing still leaves room for manoeuvre upwards, so that larger working widths of up to 4000 mm and 25,000 N load are also possible.

Inside a machine assembly with motor, gearbox and cables in a veneer machine.

Corrosion-free and dust-proof

The usual ambient conditions in woodworking also speak in favour of the use of plastic plain bearings. Michael von Mutius: "The use of the iglidur® G bearing is also the first choice for us in this case because of its corrosion resistance and insensitivity to the abundant wood dust."

This is why Kuper is by no means the only manufacturer of woodworking machines that relies on iglidur® materials for innovative bearing solutions. The fact that iglidur® G is used very frequently is due to the fact that this material is considered the "all-rounder" in the extensive iglidur® programme. iglidur® G is very well suited for swivel and rotary movements at low to medium speeds, even at extremely high loads (temperature, dirt, pressure...) and under adverse environmental conditions - precisely for the application profile for which the Kuper engineers were looking for a solution. And since igus® keeps the iglidur® G bearing in stock in a variety of dimensions from stock, Kuper was able to choose an "off-the-shelf" solution that is always available.

Technical drawing of a veneer machine component with multiple views and roller conveyor.

Long-term applications with constant coefficients of friction

At surface pressures of up to 100 MPa, only negligible plastic deformation is measured with iglidur® G bearings. This high compressive strength was also one of the requirements that Kuper placed on the pressure beam bearing. The bearing is also suitable for accommodating high pressures because the coefficient of friction decreases with increasing load. load but not least, not only the technical but also the economic data are right: iglidur® bearings are significantly more cost-effective compared to commercially available metallic rolled bearings, and of course even more so compared to ball roller bearings. At the same time, the service effort is minimised because the bearings are maintenance-free and have a very long service life: Even at high loads, long-term use with constant friction values is achieved.

Kuper broke new ground with the innovative pressure beam bearing of the ACR-Speedstar and sees this detailed design solution as further confirmation that innovation strengthens competitiveness: The plastic slide bearing has proven itself in practice, and the new generation of machines has already been honoured with the "Challenge Award" at the wood trade fair in Atlanta, USA.

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