If you think of granite and concrete, you are likely to think about buildings rather than applications in metalworking machine construction. Yet thanks to their maximum rigidity and abrasion resistance, optimum vibration damping and minimum thermal expansion, granite and high-strength concrete have optimum characteristics for use in machines and their components. The conventional machining of natural granite and high-strength concrete is extremely complex and expensive, however. Which is why automated machining processes using metalworking machines are also used for machining natural stone and concrete. Working on behalf of E. Reitz Natursteintechnik, WMZ MOTORSPINDELN has developed particularly resistant motor spindles for just such jobs.

PRÄWEMA Antriebstechnik GmbH in Eschwege is no stranger to granite, because all the high-performance honing machines of the type SynchroFine produced at the plant are fitted with a granite bed as standard. “Without granite beds, the process of high-performance honing in the micrometer precision range required today would not be possible", says Jörg Schieke, Managing Director at PRÄWEMA Antriebstechnik GmbH. He continues, “As far as rigidity, vibration damping and thermal conductivity are concerned, granite is absolutely unbeatable compared with other materials.”

Yet how is a machine bed made of granite shaped in order to meet the demanding requirements of a machine manufacturer like PRÄWEMA? Egbert Reitz, Managing Director of E. Reitz Natursteintechnik e.K., explains: “We use the common processes of milling, drilling and grinding to machine granite and high-strength concrete.” Ancient natural stone for ultra-modern machine components – this is how Reitz summarises the company’s portfolio in a nutshell. At the manufacturing centre in Asslar near Wetzlar, both natural stones like granite and blocks cast from high-strength concrete are machined completely for mechanical engineering companies like the DVS TECHNOLOGY GROUP.

“Both our machines and their spindles and tools must be designed for maximum loads. In the case of motor spindles in particular, we found that many brands are not able to cope with these challenges unfortunately", recalls Production Manager Martin Simon. The extreme development of dust during machining, the coolant mist heavily saturated with particles and the use of aggressive pure water to cool the tools can quickly cause damage to a motor spindle. Resulting in machine downtime and delays in delivery. To prevent this scenario, a particularly sturdy type of motor spindle was created in close cooperation with WMZ MOTORSPINDELN.

In order to protect the sensitive interior of the motor spindles, the design engineers at WMZ decided to make important spindle components of stainless steel. The complex labyrinth seal design with additional sealing air support is an additional shield for the front spindle bearing. The bearing system has been given an extremely robust design in order to withstand fluctuating loads long-term. The rear spindle area has a multi-layer sealing system. Due to the greatly fluctuating dimensions of granite and concrete blocks, machining requires a wide range of different cutting capacities and frequent tool change. A special tool clamp has been developed for this, which goes easy on the bearings during tool change and ensures a long period of use.

Egbert Reitz sums up as follows: “The motor spindles from WMZ MOTORSPINDELN, which were customised to our particular requirements, had us convinced after a very short time in field use.”