Fast, straight, precise: This is how the requirements in sheet metal processing can be summarised. Sophisticated straightening technology makes all this possible. Friction and wear-optimised plastic plain bearings help to improve machines and plants technically and economically. They are rated high for being maintenance-free and resistant to dirt even in extremely harsh environments.
"Whether pre-cut blanks in millimetre thickness, plates for clutch construction or cut parts up to 50 mm thick - we serve all markets with reliable machines. They meet the highest standards and are extremely precise in their results," says Dipl.-Kfm. Helmut Kunz, Head of Materials Management and Vice President of Kohler Maschinenbau GmbH in Friesenheim. "Since the company was founded in 1963, we have developed into a major manufacturer of straightening machines and equipment for the sheet metal processing industry." Today, around 130 employees generate a turnover of around 25 million euros per year.
With the construction of the first straightening machine for punching workpieces in 1966, the product range was constantly expanded. In the 80's the development and construction of large straightening machines and plant technology for the steel and automotive industry was added. In addition, systems for long parts production and transfer systems, which serve to transport parts within the press, were manufactured. "With over 5,000 straightening machines built worldwide, we have an enormous wealth of experience in the areas of straightening technology and coil handling," says Helmut Kunz.
In sheet metal processing, one encounters a variety of problems as the production processes pass through various stations. However, the highest demands on the machine elements are made by cinder particles and the ubiquitous rolling and drawing oil . The operating temperatures for the plain bearings range from 45°C to -20°C, plus an air humidity of up to 95%, which is created by the straightening of -80°C cold sheet metal. In combination with the rough conditions, rollers made of wear-resistant materials are required.
With the extensive product range from the product areas igubal spherical bearings, iglidur plain bearings and drylin linear plain bearings, the various requirements of the application are fulfilled. The freedom from maintenance and lubrication of the igus products, as well as the low coefficient of friction, ensure that the maintenance intervals could be reduced to an absolute minimum. Their functionality also does not become restricted under extreme temperature conditions.
Various trends in sheet metal processing ensure that straightening technology is becoming increasingly important. On the one hand, there are narrower tolerance limits in production, since processors are placing increasingly stringent demands on the straightening machine manufacturers in terms of surface flatness. On the other hand, the increasing use of high-strength steels requires precisely designed machines. Another aspect is that the quality of the raw material is getting worse and worse.
"Due to these specifications, the demands on machine technology are becoming ever greater," reports Günter Keller, Product Manager Special Systems. "Our focus is also on the cost aspect, of course without compromising on quality. " This applies both to standard machines, which are increasingly assembled in a modular system, and to special mechanical engineering. "In day-to-day business we need more freedom in order to be able to concentrate even better on our strength, special mechanical engineering," Günter Keller sums up. "We must always achieve a healthy economic mix between standard and special machine construction. “
Straightening machines for sheet metal processing can be used to eliminate almost all stresses in the sheet metal arising during forming or punching, so that the quality of the products is appropriate for their further processing. Tribo-optimised plastic plain bearings help to solve the many technical challenges. Machine elements from igus have been used in the Kohler Maschinenbau product range for many years. "From plain bearings and linear technology to plastic rollers - we are finding more and more applications for the lubrication-free and corrosion-resistant components," reports Günter Keller.
"With our machines, the most important thing is maximum reliability," says the design engineer Lothar Hug. "When the system is on site at the customer's premises, it must run in continuous operation without problems. " Three and four shifts of operation seven days a week are the norm here. The environmental conditions that the plastic components withstand are quite different. "In a current project from the aviation industry we are straightening -80°C cold sheets. As a result, we get a lot of condensed water on the machine. Another example concerns special alloys that can only be straightened after cooling to 900°C," says the designer.
Added to this are the most varied climatic conditions. At ambient temperatures of 40 to 45°C and a humidity of 95 percent, the machines must run just as reliably as at -20°C. However, the highest demands on the machine elements are made by cinder particles and the ubiquitous rolling and drawing oil. "The igus polymer bearings prove their worth even under these rough environmental conditions," Günter Keller reports from his everyday life. "Their long runtimes, ease of maintenance and resistance to dirt have paid for themselves from the very beginning. “
Design engineer Lothar Hug can also only confirm this: "Since some of our plants are located in very confined spaces, the topics of maintenance and servicing play an increasingly important role for our customers, especially from the automotive industry. Since the polymer bearings are lubrication-free and also insensitive to dirt, possible maintenance intervals are reduced to an absolute minimum. Of course we are able to impress our customers with this!"
A plant with an overall length of only 13.50 m was recently constructed for an automobile manufacturer. Since it is located in a very confined space, its ease of maintenance was one of the key customer requirements, which was achieved by using plastic plain bearings.
"Contamination of the lateral guide is often a very hot topic for us," says Günter Keller. Oil drips everywhere, the belt is partly damp. In this aggressive environment, for example, eight drylin R linear plain bearings with supported shafts serve as guide systems. They are based on extremely wear-resistant polymers specially developed for the linear technology. The dimensions are compatible with standard ball bearings. Their special geometry guarantees robustness even in extreme environments. Added to this are the high loads. "Here we also demand a great deal of flexibility from our suppliers.
The design input is particularly high for lateral guidance. Added to this is the high vertical range of manufacture. "For standard machines we intensify our collaboration with igus. We receive the lateral guide as a complete system, which is then just flanged on. This eliminates the design work, parts production and assembly for us. The technical and economic advantages are around 50 percent," calculates Lothar Hug. "This is worthwhile for us in every respect. “
There is a series of processing steps from the beginning to the end of the belt. Around 1,400 iglidur rollers are used as smooth-running transport rollers for the complete guidance. Several technical advantages speak for themselves. "The belt is partly coated and oiled. Since the special plastic is insensitive, there is no wear and tear or damage due to scratches or other quality impairments. The surfaces present themselves in perfect condition," Günter Keller sums up.
Furthermore, iglidur G plain bearings and igubal pillow block bearings for various adjustment tasks are used in the straightening plant. They also prove themselves in their respective tasks and ensure safety and high functionality.
There are still a number of different approaches for using polymer bearings in straightening machines. As a first step, the coil is placed on the reel with an insertion aid. "This is where the highest loads occur, making enormous demands on technology," reports Lothar Hug. "Our ready-to-install slewing ring bearings up to 15 tons, for example, are ideal for these positions," says Dominik Hartmann, technical sales consultant at igus. They are robust and can withstand the high loads without any problems." Initial discussions are already being held. Because, "particularly in special mechanical engineering, we are dependent on the know-how of our suppliers in order to present the best solution to our customers," Günter Keller is well aware.