"It could hardly be more abrasive" - wear-resistant linear guides ensure 50 per cent longer service life in grinding tool machinery

Profile

• What was needed: robust linear round guides
• Requirements: thermal and mechanical load of the tools
• Industry: Mechanical engineering
• Success for the customer: significant increase in tool life

Schleifscheibenfabrik Rottluff GmbH in Chemnitz produces around 150,000 grinding tools per day in a wide variety of diameters and shapes. Business has been going well for the 100-year-old company for years. For the approximately 150 employees, everything revolves around the disc in three-shift operation five days a week. The company supplies end customers and bulk consumers.

The cut-off, roughing and flap discs are characterised by high trade show resistance and short cutting times. Their design is customised in terms of grain, bond, structure, shape and composition. In addition, they are manufactured using the latest trade show state of the art technology, enabling a comprehensive range of products. As a member of the Association of Abrasive Manufacturers and the oSa, the organisation for the safety of abrasive tools, the specialist makes an active contribution to user safety. After all, the processing speeds of hand-held discs, for example, are 80 or up to 100 m/s, which can lead to enormous thermal and mechanical loads on the tools. Grinding wheels essentially consist of a reinforcing material, a pressing compound, the bond (usually glass fibre fabric) and a label with a bore ring. The moulding compound contains a wide variety of abrasive fillers to improve the release properties. These abrasives are extremely abrasive and cause a high level of wear on our machines and systems. If, for example, hard silicon carbide is pressed into discs for use in the stone industry, an extremely large amount of dust is produced, which further increases wear. And because we work in three shifts, maintenance and repairs can only be carried out at regular intervals. In terms of environmental conditions, it could hardly be more abrasive. The bearing must be able to withstand the various materials used in grinding wheel production over the long term.

The automatic presses work under the harshest conditions; they guarantee consistent thickness and compaction of the products. The cutting and grinding discs are then sent to the hardening ovens. In order to guarantee consistently good quality, they are placed between steel plates beforehand, which have to be removed again after the hardening process. This is done using customised automatic separators, which are used for the necessary destacking.

The grinding wheels are manufactured to customer specifications and effortlessly withstand the most diverse requirements of the trade show. Pressing and separating machines play a key role in the extremely harsh production process. In order to significantly increase their service life, metal bushings have been replaced with robust linear round guides with quickly measurable success. Self-lubricating and maintenance-free, they prove their suitability for everyday use right from the start. Ordered and installed as an operating resource requirement, the linear guides ensure the necessary machine availability. Up to ten linear bearings are used in the centrepiece of the grinding tool machinery, the hydraulic pressing and separating systems.

drylin® R linear bearings are based on highly wear-resistant polymers specially developed for linear technology. Their dimensions are compatible with standard linear ball bushings. They use round shafts as mating partners and accept a wide variety of shaft materials. At Rottluff, steel shafts have proven to be excellent at withstanding harsh environmental conditions. The special geometry of the guidance guarantees a high level of safety under all operating conditions. As the bearing surface is made up of individual raceways with interruptions, contamination is not a problem. Even if damp dirt hits the shaft, it is wiped off the individual tracks and pushed back into the non-contact tracks. The crossbar of the bearing running surfaces then glide along the track free of dirt. The linear guides are 100 per cent lubrication-free. Easily replaceable standard sliding foils made of the material iglidur® J ensure good sliding friction values.

Although the operating conditions, i.e. the pressing masses, change on the machines, it can still be stated that their service life is significantly longer than with the previously used metallic bushings. And the durability of the steel shafts has at least quadrupled, so that not only the technical advantages speak in favour of the linear guide, but the investment in this equipment also pays off economically. What's more, the wear limit is now approaching. It is not reached abruptly, so a corresponding replacement can be initiated as planned at the next maintenance interval. The linear guides prove their efficiency not only in the pressing and separating machines, but also in a shrink-wrapping machine.