The modern facilities employ some 60 employees in the manufacture of high-quality fireproof fireclay products. The product spectrum encompasses fireclay elements for tiled stoves, fireclay linings for house chimneys and fireclay casings for heating elements. The company’s own clay deposits provide a reliable source of raw materials and the basis for high-quality products. The company operates in one shift. Its main customers are builders of tiled ovens, wholesalers, industrial customers, and interest groups and cooperatives from all over Europe. And because the Wolfshöher Tonwerke are also committed to protecting the environment, they fuel their tunnel kilns with biogas from a nearby compost dump.

Cost-effective automation

Economic considerations are of primary importance, of course. “We have been investing in automation for years, wherever it makes economic sense”, explains Dipl.-Ing. Georg Wolf, Managing Director of the Wolfshöher Tonwerke. “For example, fireclay chimney pipes which have tongue and groove joints have been transported automatically for some time now. Previously this was done using linear units at a factory which has since been decommissioned.”

In September 2002, the order for three jointed-arm robots for handling of fireclay chimney pipes was placed with KUKA Roboter GmbH of Augsburg, Germany. These robots are part of the production line which the pipe blanks are transferred to when they come out of the worm extruder. This system, supplied by FREYMATIC AG of Felsberg, Switzerland, integrates a KR 180 PA four-axis palletizing robot with a passive fifth axis, and two six-axis KR 45s. The robots’ end-effectors are vacuum suction grippers which can be adjusted for various pipe diameters. Factors in favor of KUKA were good references and geographical proximity. The robot types were selected based on the layout of the system. The KR 180 PA was chosen above all due to its long reach.

The KUKA KR 180 PA palletizing robot comes with an application-specific, FEM-optimized kinematic system. Its arm is made of carbon fiber composite material (CRP), which thanks to its smaller mass moment of inertia has truly remarkable acceleration rates. Despite its lightweight construction, the arm demonstrates extremely high stiffness characteristics, allowing the KR 180 PA to stack loads weighing up to 180 kilograms to heights of up to 3000 millimeters. The robot can do this at rates as high as 1800 cycles per hour. Moreover, as a four-axis robot it is less expensive to manufacture than a six-axis machine.

Output increased significantly

“This conversion has resulted in a significant increase in output”, notes Axel Wolf, son of the managing director and plant manager of the Wolfshöher Tonwerke. “The area where we use the robots now operates more than 50 percent faster than before. Furthermore, we now require much fewer employees there.”

The current production rate of 16 fireclay chimney pipes per minute is achieved thanks to the short cycle times of the robots, and due to the fact that the connecting pieces are provided with their tongue and groove not sequentially, as before, but in pairs at two parallel stations.

In addition, the user obtains better quality because of the robots’ high repeatability and their extremely gentle handling of the blanks, as a result of which the breakage rate has dropped considerably. Another advantage of the robots is their flexibility. This is demonstrated, for example, by the way they can handle the five most common pipe sizes at the Wolfshöher Tonwerke, with diameters ranging from 120 to 200 millimeters. Pipes with less popular diameters are produced at a different factory operated by the company.

Sensitive handling accurate to the millimeter

After leaving the worm extruder, the fireclay blanks are automatically cut to lengths of 330 or 660 millimeters. A group of four 330 millimeter long pipes and a short stacking ring make up a unit, which is later stacked into a tower by the KR 45s. When 660 millimeter long pipes are produced, two connecting pieces and a stacking ring make up a unit.

After cutting, they are transferred to the transport troughs of the pipe production system. The system operator uses the control panel display to select the program corresponding to the length and diameter of the blanks. With regard to the robot, the operator uses the KUKA Control Panel of the PC-based KR C2 robot controller, whose familiar Windows interface makes program selection easier.

In the case of 330 millimeter long pipes, two blanks are placed in each trough, alternating between pairs of pipes with and without a stacking ring. The system cuts the groove in the stacking ring even before it reaches the pickup position of the KR 180 PA; the stacking ring is then placed directly on the pipe conveyor and transported onwards. The connecting pieces, on the other hand, are lifted out of the transport trough by the KR 180 PA and placed in the troughs of the transverse pipe conveyor. This simultaneously feeds one blank each to the tongue and groove cutting stations on the left and right sides. After the cutting process, the conveyor system brings the pipes to the KR 45s. These two six-axis robots pick up the blanks and stack them vertically one on top of the other on the stacking ring which is already located on the pipe conveyor.

Since the stacking ring is mechanically located in a defined position, the KR 45s can stack the pipes with accuracy to the millimeter. In this process, the robot controller uses a laser sensor integrated into the gripper to monitor the remaining distance continuously. This information makes it possible to position the blank with great sensitivity. Once a pipe tower is complete, the conveyor advances it to a pipe pickup unit. This picks up the tower and transfers it to the furnace carriage, thus replacing the manual handling which was previously used in this area as well.

For 660 millimeter pipes, the user only needs one KR 45 and one transverse pipe conveyor. Moreover, in this case the remaining six-axis robot always picks up only one blank, and the KR 180 PA adds a stacking ring in every second cycle.

Fewer errors and lower personnel requirements

Since three KUKA robots now “set the pace” at the Wolfshöher Tonwerke, the corresponding manual operations and various transfer tasks are no longer required. “In this respect we benefit not only from increased productivity and higher quality, but also from reduced personnel requirements, a minimized error rate and shorter transfer distances. Moreover, we have noticed a reduction in damage,” says Georg Wolf. “In addition to the pipe production system, we have also been able to optimize our downstream processes. For example, today we use a smaller furnace than in the old factory, whose significantly greater capacity was not being utilized;  this way we save on energy costs.”

Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany