“Agricultural harvesting machines have to work smoothly for many hours every day for just a few weeks in summer; that is the high season for them” explains the design manager at FELLA-Werke GmbH, Bernhard Kohl, at the company location in Feucht. “They are then normally cleaned using the high pressure washer and wait around more or less protected for the rest of the year, before they are used again in the next warm season. “
The agricultural machine manufacturer's customers are large concerns, contractors, machinery syndicates, but also farmers who only manage a few hectares.
“As we don't know the respective issues down to the last detail, above all we must pay attention to robustness when designing our machinery, without losing sight of the manufacturing costs,” says Kohl.
“The selection of all the components used is equally important. “
Maintenance-free through hedges and bushes
What do protesting dairy farmers and agricultural machinery construction have in common? They are both under high cost pressure. The consequence of this is that investments in agricultural technology have to provide significant improvements for relatively little money. In the following example, tribologicially optimized polymer plain bearings – special bearings – on a standard component, the heart of the machine, provide a positive-fit connection. The plastic plain bearings have proven themselves in rough field work for many years.
“iglidur® G” polymer plain bearings – special bearings – are fitted to the prongs of the rotary swather.
The company FELLA has been designing work machines for tractors for over 90 years. These include mowers, hay rakes and swathers. The function of the swather is to rake together mown or already spread hay into a single swathe using eight, ten or twelve prongs. All swathers made by this supplier work exclusively with rotary technology, which among other things have the advantage of a high acreage. “The bearings on the prongs as a part of the elaborate control system is the most important function of the machine,” the design manager points out. “If these get damaged, the rotary swather stops working. And that must not happen during harvest time under any circumstances. “
Two plastic bearings are fitted to each prong. For ten years now, these have been tribo-optimized polymer plain bearings made of the special material “iglidur® G”. We are talking about economical all-round bearings, which – without lubricants and maintenance – show their strengths when it comes to simple pivoting and rotary movements, very high loads and high demands when faced with dirt. In the application described, a special bearing made of “iglidur® G” is used. “Right from the trial phase, we realized that we needed a reliable anti-twist device,” remembers the design engineer, Jürgen Riedel.
Each rotary swather has eight, ten or twelve prongs. The maintenance-free polymer plain bearings ensure that the machine runs smoothly over the course of a long service life.
CAD simulation of the rotary swather
Prong with two polymer plain bearings
“The system has worked smoothly since its serial introduction.
The anti-twist device ensures that the bushing sits completely firmly in the housing. The friction couple is right, so we expect to continue using these subassemblies for a long time to come,” says Jürgen Riedel. The benefits add up for the agricultural machinery manufacturer: the wear has reduced considerably compared with metal plain bearings, and there is less noise when being operated.
Furthermore, it is cost-effective, as there is no need to drill holes for the plain bearings in the aluminium bearing tube among other things.
The company FELLA-Werke, whose name is derived from the Egyptian word “fellache” for farmer incidentally, has stood for decades for quality and innovation in the feed harvesting technology sector. Thanks to its close contact with national and international customers, the machines are continually developed in practical terms and adapted to increasing demands. Their most important attributes are a high quality of work, safety and simple operation.
“As a partner of the farming industry with a very wide product range of mowers, hay rakes and swathers, we can always offer our customers the right machine for their business and requirements,” adds the design manager, Bernhard Kohl. “Naturally they must be at the forefront of technology in order to be able to prove themselves even in the harshest conditions. “
The external demands on the special bearings developed by igus® when used on the job in summer are extremely high. “First and foremost this involves radial forces," explains Kohl. “These normally occur by transporting the hay across the ground; but also by the prongs touching the ground or by bumping into obstacles such as bushes, hedges and stones. So that the plain bearings are not damaged in these crash situations, they must be impact-resistant and very robust. “ Then there is dust and dirt plus finally the high pressure washing. “Rough conditions and long service lives with possible corrosion on the steel parts place very high demands on the plastic bearings,” says Bernhard Kohl.
The internal stresses on the swather arm are very high, as it is continuously pressed in the cam disk. Furthermore, the technology is strained by many load changes with an oscillating motion. The single arm must be able to withstand many and also relatively fast movements. “It was our aim here to come up with a compact and affordable solution,” reports Jürgen Riedel. Whilst welded bearing tubes with inserted brass bushings used to require costly machining times when being made, there is no need at all for this now. “The plastic bearing with the conical outside was adapted to the conical shape of the locating hole, thus saving the whole machining process. That also applies to the conical fastening holes on the aluminium bearing tube, which are screwed together with the tapers on the rotary sockets. We therefore get a form-fit connection, which is very stable and proves itself excellently in rough everyday work conditions. “
The company soon realized that costs could be saved with plastic. “At the start we had plastic bushings lathed ourselves and later injected. The result was not right, however, because the choice of material didn't work,” Jürgen Riedel remembers. “As a machinery manufacturer, we preferred to look for an expert for the field of plastic. ” From the extensive igus® product range, which includes standard and special parts, the right solution was soon found. The high abrasion resistance plus the dry-operation properties of the polymer plain bearings tested thousands of times in the igus® laboratory under everyday conditions, immediately proved their worth in agricultural practice.
“System works smoothly” – design manager Bernhard Kohl (l.) and design engineer Jürgen Riedel, both from FELLA, with Dirk Lanuschni (igus®).
Investments in agricultural engineering must be well thought out. On the one hand steel prices are being continually increased at the moment. On the other hand, the customers, especially the dairy farmers, are not prepared to pay more for the machines. Nevertheless, the quality of the machines must be good. “We can only reduce the manufacturing costs,” says Bernhard Kohl, “by substituting expensive tailor-made components with standard parts or by achieving quantities that are economical to produce using modular designs. “ Quality tests are constantly carried out during assembly. The key company expertise lies in developing and assembling the machinery. “We buy all the components from the respective specialist, which include the special bearings made of plastic from igus®. The proportion of “iglidur®” polymer bearings in all the machines in our product range will increase further,” Kohl is certain. “Their stability and the cost benefits simply add up. “