The grinding wheels made by this Saxony-based specialty manufacturer are made to customer orders and are able to effortlessly meet a variety of requirements. The particularly rough manufacturing environment heavily relies on presses and separating machines. In order to significantly increase their service-life, metallic bushings were replaced with robust linear round-guides with quickly measurable results. Self-lubricating and maintenance-free, they demonstrate their capabilities in everyday use.
"Every day, we produce about 150,000 grinding tools with a variety of diameters and shapes", explains Kersten Müller, Technical Manager at the grinding tool manufacturer Rottluff GmbH in Chemnitz. Business for this nearly 100 year old company has been strong for years. Everything for the nearly 150 employees is centered on wheels in three shift operations for five days a week. The business supplies end-customers and large-scale users. The cutting, grinding and flap discs are characterized by long service-lives and short cutting times. Their design is tailored with respect to grain, binder, structure, shape and structure. These are supplemented by the most up to date manufacturing technologies, therefore providing a comprehensive product range.
As a member of the association of grinding tool manufacturers and OSA - the organization for grinding tool safety, the specialist is actively contributing to user safety. For instance, hand guided wheels are operated at grinding speeds of 80 and up to 100 m/s, which can result in enormous thermal and mechanical loads on the tools. "At these speeds, even the high-tech materials on a Formula 1 race-car are approaching their limits", Kersten Müller observes.
Grinding disks primarily consist of a reinforcement material, a press mass, the binder (generally fiberglass weave) and a label with a shaft ring. The press mass contains the various grinding filler agents to improve the cutting properties "These grinding agents are extremely abrasive and cause considerable wear on our machines and lines", the Technical Manager explains. For instance, when hard silicone-carbide is used for the stone industry, considerable amounts of dust are generated that increases wear further. "And since we work in a three-shift operation, maintenance and repairs can only performed in regularly scheduled intervals. " “
For a number of years, highly wear-resistant linear round-guides of type drylin® R from igus® GmbH, Cologne, have been replacing ball linings, which had repeatedly resulted in sudden machine failures. "I learned about the technical advantages of the maintenance and lubricant-free linear guides while reading a technical paper", the Technical Manager recalls. "I quickly realized that they would also prove themselves in our difficult environmental conditions." “
Ordered and installed as incidental materials, they have since provided the required machine uptime. Up to ten linear bearings are in use in the centerpiece of the grinding tool machinery, the hydraulic press and separation lines. The press machines work under the roughest conditions; they ensure consistent thickness and density of the products. The cutting and grinding wheels are then processed in curing furnaces. In order to guarantee consistently good quality, they must first be placed between steel plates, which are removed again after the curing process. This is in turn performed by customized separation machines, which are used to disassemble the stacks.
drylin® R linear plain bearings are based on extremely wear-resistant polymers specially developed for the linear technology. Their dimensions are compatible with standard linear ball bearings. They use round shafts as counter partners and are able to work with various shaft materials. Rottluff has proven the steel shafts, which have demonstrated their ability to withstand the environmental conditions. The special guide geometry also ensures high reliability under all application conditions. Since the bearing surface is composed of individual glide pads with seams, dirt buildup is not an issue. Even when wet dirt collects on the shaft, it is wiped away from the individual glide tracks and pushed back into the contact-free area. The pads of the bearing surfaces then glide on the dirt-free track.
The linear guides are 100 percent lubricant-free. Easily replaced standard liners made from iglidur® J ensure good gliding friction values. "With reference to the environmental conditions, it could hardly be more abrasive. The bearings must be able to hold up over the long-term to the material we use in grinding wheel production", the Technical Manager reiterates.
These linear guides are also subject to wear. But generally, only the liner needs to be replaced in a worst case scenario. Although the application conditions on the machine change, i.e. the press mass, a point of note is that their service-lives have significantly increased when compared to the previously used metallic bushings. And the durability of the steel shafts has increased four-fold, therefore not only highlighting the technical advantages of lubricant-free linear guides, but also making an investment into the consumables a good financial proposition.
"As an additional benefit, the wear limit is reached with advance notice. It is no longer reached abruptly", explains Kersten Müller. This allows us to schedule an exchange during the next maintenance interval. "The linear guides not only demonstrate their capabilities in the press and separating machinery, but also in the shrink-wrap packaging line. "Here as well, we replaced the manufacturer installed ball linings as part of our maintenance efforts. Akin to the manufacturing process, a large volume of abrasive material is released during the packaging process, which had impacted the running performance of the line in the past. Today, the line works trouble-free. “
As part of the required incidental material purchases, the linear round-guides not only replace metallic bushings, but the machines and lines were also partially retrofitted with plastic flange bearings. In addition, plastic energy chains from igus® ensure that lines are guided reliably in continuous use under the rough operating conditions.
"We are always open to new approaches", Kersten Müller summarizes. "Our machinery must work smoothly. We cannot accept unnecessary downtime. The robust linear guides have played a key role in providing a reliable service for this over the last years!"
Linear round-guides in press machinery. They must stand up to highly abrasive loads.
Linear round-guides in separating machinery. They ensure high machine availability.
Linear round-guides in use on separating machinery. These replace metallic bushings, whose grease nipples (right side of image) are still clearly visible.
Linear round-guides in the shrink-wrap packaging line. It now works completely trouble-free.
As part of retrofit activities, energy supply systems made by igus® are also in use on the machinery and lines.
The operating principle of drylin® linear bushings: The runners on the liner push the dirt aside, which then only runs on the clean part of the shaft.
Kersten Müller (left), Thomas Sommerweiß in the exhibit room of the grinding tool manufacturer Rottluff GmbH in Chemnitz.