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Veneering machine - plastic plain bearings master extreme loads and high temperatures

Wood dust, high pressure and high temperatures: the ambient conditions for the plain bearings of machines that assemble wood veneers are anything but ideal. Plastic plain bearings from igus prove their worth under these extreme requirements. Heinrich Kuper GmbH, the only manufacturer worldwide to cover the entire spectrum of veneer splicing techniques, uses split igus plain bearings made of the iglidur G material in a new generation of machines at a very 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 materials and manufacturing processes here place very high demands on the machines and on the engineering competence of the designers. Take the example of veneer production: Individual veneer strips are assembled into so-called carpets using high pressing forces and at high temperatures.
 

Veneering machine of Heinrich Kuper GmbH uses iglidur plain bearings  

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-free and lubrication-free solution for the bearings of the veneering machine that would allow a long service life.  

Solution

Plastic 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 veneering machines and provides a very good solution for continuous operation.    

 

"The application of iglidur G bearings is also the first choice for us in this case because of their corrosion resistance and insensitivity to the abundant wood dust.
 
Michael von Mutius, Associate Design Manager of Heinrich Kuper GmbH

The centrepiece: Bonding pressure beam

In this very specialised area of mechanical engineering, Heinrich Kuper GmbH in Rietberg is one of the market leaders. The "ACR-Superquick" veneer cross-feed splicing machine had been a globally successful series in the product range for years - the requirements and expectations were accordingly high when Kuper started developing the successor series "ACR-Speedstar".
 
The centrepiece of a veneering machine is the bonding pressure beam. It joins the veneer strips with the help of adhesive elements. Compressive forces reach up to 20,000 N and temperatures up to 220oC in the joining area. Since the veneer strips can be very long, the pressure beam is not exactly small either: it reaches a length of about 3500 mm and weighs about 500 kg.
 
The fact that the designers and, consequently, the users of the machine place very high demands on the bearing arrangement of the beam results from the environmental conditions. After all, in addition to its own weight, the beam must also withstand the high pressing forces of up to 20,000 N. One of the reasons why this requirement is not easy to meet is that the pressure causes the beam to sag. One of the tasks of the bearing points is to compensate for these deflections.

The pressure beam bearing of a veneering machine of Heinrich Kuper GmbH

The pressure beam bearing of the machine must be able to withstand high forces and compensate both deflections and temperature-related distortion.

 

Beam must remain flexible

In addition, the high temperatures that occur lead to thermal expansion, which must also be compensated by the bearings. Further requirements concern the service-friendliness and availability of the bearing arrangement and thus of the entire machine: Since access to the adhesive elements is required for cleaning purposes, the bearing arrangement should allow this access - i.e. the beam must be movable in case of service. In addition, the bearings should be maintenance-free and wear-free as far as possible. Last but not least, the costs of the bearing also play a role.
 
For the ACR - Superquick, Kuper had also planned a translatory pressure beam bearing with ball bushing guides. Michael von Mutius, Associate Design Manager  and Project Engineer in charge of design of the ACR - Speedstar at Heinrich Kuper GmbH: "However, this bearing arrangement was not maintenance-free and was also relatively expensive. In addition the accessibility to the adhesive elements was not optimal". 
 

Maintenance-free bearing

To ensure this accessibility, Kuper provided for a rotary movement in the new machine: The pressure beam can move 90o towards the operator. And for the bearing of the pressure beam, new methods were also decided upon: Plastic bearings are used here, more precisely iglidur G bearings of type GFM 90-95-100, which were split and shortened to the length of 60 mm.
 
This solution has proven itself in practice: Due to the rotational movement, the adhesive elements swivel directly towards the operator and are easily accessible for cleaning and maintenance purposes. Due to the division of the bearings, assembly or disassembly of the pressure beam is very simple, and the bearing clearance of the iglidur plain bearings very effectively compensates for thermal expansions and deflections of the pressure beam. Here the bearings or the bearing material do not even reach their load limit: The use of the iglidur bearings still leaves room for some upward leeway, so that even larger working widths up to 4000 mm and 25,000 N load are possible.
 

Drive of the pressure beam bearing of a veneering machine of Heinrich Kuper GmbH

View of the drive of the pressure beam bearing: The 500 kg pressure beam can be moved 90° towards the operator for service and cleaning purposes via an electric motor with slip-on gear.

 

Corrosion-free and dust-proof

The ambient conditions common in woodworking also speak in favour of the use of plastic plain bearings. Michael von Mutius: "The application of the iglidur G bearings is the first choice for us in this case also because of their corrosion resistance and insensitivity to the abundant wood dust.
 
Therefore Kuper is by no means not the only manufacturer of woodworking machines that relies on iglidur materials for innovative bearing solutions. The reason why iglidur G is used very frequently is that this material is regarded as the "all-rounder" in the extensive iglidur product range. The iglidur G is very well suited for pivoting and rotary movements at low to medium speeds, even under extremely high loads (temperature, dirt, pressure ...) and under adverse environmental conditions - in other words exactly the application profile for which the Kuper engineers were looking for a solution. And since igus keeps the iglidur G bearings in stock in a variety of dimensions, Kuper was able to select an "off-the-shelf" solution that is always available.
 

Drawing: Plastic plain bearing in veneering machine

Technical drawing: You can see iglidur plastic plain bearings in the veneer splicing machine

 

Long-term use with constant coefficients of friction

At surface pressures of up to 100 MPa, only negligible plastic deformation is measured in 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 absorbing high pressures because the coefficient of friction decreases with increasing load. Last but not least, not only the technical, but also the economic data are accurate: iglidur bearings are significantly more cost-effective compared to conventional metallic rolled bearings, and of course even more so compared to ball roller guides. At the same time, service costs are minimised because the bearings are maintenance-free and have very long service lives: Even under high loads, long-term operation is achieved with constant coefficients of friction.
 
Kuper broke new ground with the innovative pressure beam bearing of the ACR-Speedstar and sees this detailed design solution as confirmation  that innovations strengthen competitiveness: The plastic plain bearing has proven itself in practice, and the new generation of machines has already received the "Challenge Award" at the woodworking trade show in Atlanta, USA.
 

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