Uncompromising HSS filtering

With the StingR ultra-fine filter technology, Lehmann-UMT has developed a pneumatic-hydraulic backflushing process that offers the user a number of advantages. For Gesau-Werkzeuge, one of them is paramount: mastering a particularly difficult filtration process when grinding gear cutting tools.

Cooling lubricants are a crucial component in the machining process, often making it possible to solve a machining task in the first place. Cooling lubricant preparation is therefore also an indispensable part of the process, as the cooling lubricant supply must be maintained at the required purity and the necessary volume flow. For its part, the degree of purity of the cooling lubricant has a significant influence on process stability, but also on the machining result and the wear of the cooling lubricant components.
However, the right technology can only be selected and designed with a precise analysis of the machining process and its requirements. Gesau-Werkzeuge Fabrikations- und Service GmbH has consistently followed this path. The tool specialist from Glauchau-Gesau has completed the final stage of a metamorphosis of coolant preparation that has been driven forward over the years with Lehmann-UMT.

Manufacturing and reconditioning special tools

The fact that the company had to take this path can be seen directly from the range of services offered by the tool specialist. founded in 1980 as a workshop for regrinding cutting tools, the company focused on tools for metalworking from the 1990s onwards and developed from a craft business into an industrial service provider. Today, Kerstin Milenkov, daughter of the company founder, and Ulf Köhler are the owner-managers of the 35-strong company.

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Production in Glauchau-Gesau concentrates on rotating, monolithic shank tools, preferably made of carbide and HSS, but also Cermet or CBN. Milling and drilling tools are just as much a part of the portfolio as semi-finished products and precision parts. "Among other things, we have specialized in filigree tools with high aspect ratios," reports Köhler. Gesau-Werkzeuge also manufactures custom-made products from CBN and Cermet. The company's second area of activity is tool grinding as a service.

"In this segment, we have specialized in gear cutting tools with geometrically defined cutting edges and repair all tools that work on the tooth flank," says the Managing Director. Hob cutters, for example, are ground in all dimensions and designs up to grade AAA. In addition to accuracy, another challenge when resharpening is the dimension of the tools. "In the case of broaching tools, our largest tools are 3 m long and weigh up to 500 kg."

The challenge of corundum chip abrasion

This is also where Lehmann-UMT's filter technology comes into play when reconditioning gear cutting tools. Why? Because it is a particularly delicate process: some of the HSS tools have to be ground with dressable wheels, which produces a high proportion of abrasive abrasion. Together with this corundum, the abrasion from HSS, which unlike carbide is a long-chipping material, forms a tough mass that places high demands on the filter technology. "That's why we set out to find a supplier whose filter technology could cope with these types of abrasion or contamination," says Köhler.

By this time, coolant preparation at Gesau-Werkzeuge had already undergone several stages of metamorphosis. Years earlier, the company had invested in a centrifuge system. With this centralized system, however, the company was restricted to one type of cooling lubricant and only had a limited technological field of application available. The process ran reliably, but there was a lack of flexibility. From 2015, the tool specialist therefore began to decentralize again. A second circuit with a gap filter system was put into operation, which now filtered the cooling lubricant from carbide grinding. "We immediately made a big leap in this area: in terms of quality, throughput and process reliability," reports Production Manager Frank Enderlein.
The problem with the corundum HSS compound remained. "We have four CNC machines here that use dressable grinding wheels. We wanted another island for this, a third circuit that could handle this abrasion," says Köhler. "Today, we have reached the goal of our metamorphosis and use three coolant circuits: the large system with centrifuge technology, which handles the mixing operation, the candle gap filter system, which is designed for carbide machining, and the StingR system from Lehmann-UMT for the critical corundum-HSS sludge."

Multi-stage filter technology

The ultra-fine filter system from Pöhl, which Gesau-Werkzeuge uses today, can be equipped with a magnetic separator, compact filter, scraper discharge system, lamella separator and 5-stage filtration. This provides a high degree of flexibility that enables applications in machine tool, mechanical engineering and environmental plant engineering as well as in the chemical industry or water treatment.

At Gesau-Werkzeuge, the StingR works in the first stage with a lifting station, from which the fluid from the four machines is collected and lifted to the filter system via a dirt pump. "The first filter stage involves a magnetic separator that removes all magnetic substances, but also binds some non-magnetic substances in the filter cake," explains Marcus Ludwig from Lehmann-UMT's field sales team. "The magnetic separator uses a counter-rotating pressure roller, which ensures a dry filter cake and that the oil remains in the process."

After the magnetic separator, the fluid passes through a baffle plate into an intermediate tank two cubic meters in size. Inclined plates have the function of calming the fluid and preventing the formation of foam, so that the particles fall out on the bottom of the tank. The bottom is scraped with a chain conveyor that discharges into the same drum as the magnetic separator. The fluid is then pumped from the intermediate tank into several filter domes. "The process used here works with filter cartridges that are periodically flushed from the inside to the outside using a fluid column. A patented process that - unlike the competition - does not take fluid from the clean tank for backwashing. This can quickly add up to 60 liters of fluid, which is then missing for the machine supply," says Ludwig. With the StingR, the cleaned medium then goes into an approx. 2 m3 clean tank, from which a pump supplies the four grinding machines. The recleaned medium is finally discharged with a belt filter, which is timed by level or time.

Customized, flexible, adaptable

The ultra-fine filter system was put into operation at the turn of the year 2019/2020. As the project manager, Ludwig was also the contact person and interface between the two companies from the very first inquiry. " The space available at Gesau was a major challenge, so we consulted three or four times," he says, giving an example. Today, the plant runs largely unmanned. A service employee comes to the company twice a year to ensure machine availability. In addition to on-site maintenance, the machine is also equipped for remote maintenance so that a technician can quickly connect to the system and rectify any faults. "We guarantee that the machine is available almost 100 percent of the time," says Ludwig, summarizing this point.

The StingR is designed for a flow rate of 500 l/min at an oil viscosity of around 15 cSt. Two different types of filter cartridges are installed. The first nominally filters down to 15 µm, the second to 3 to 5 µm. "This means that we now have the grinding of HSS with dressable wheels safely under control," emphasizes Köhler. There are hardly any drag-out losses and the grinding result is better. "Because we filter across several stages, the user can implement their specific requirements," emphasizes Ludwig. "If they want to run 70% HSS and 30% carbide, for example, that's no problem for the StingR." Köhler also confirms this advantage: "First of all, it handles the difficult medium safely, but then above all it also offers a high degree of flexibility. What's more, we can now select cooling lubricants that may be better suited to our processes individually for our three systems."
Finally, Ludwig brings a decisive point about flexibility into play: "If a production process changes in such a way that a second or third machine is required, we can expand the filter system accordingly." It is also possible to combine the StingR with other filtration processes to increase their purity levels. "If a user has a large tank, for example, we can use a bypass to increase the previous filtration level." In addition to the multi-stage filter technology of the StingR system and its adaptability to the respective process, this gives the user additional degrees of freedom to react to process changes or new requirements. For Gesau tools, this could be interesting in terms of throughput in the future: "We want to further expand the repair of gear cutting tools in the future," says Köhler. Of course, this would be a modification, but not a metamorphosis.

The StingR technology

The StingR is a sophisticated filter system for maintaining technological equilibrium. The patented process can be used for oil, emulsions or aqueous solutions in the machining of HSS, hard metals and even mixed machining. The filter system can be used for grinding, honing and lapping as well as for eroding. Filter finenesses of up to one micrometer can be achieved. The StingR impresses with its long service life of the filter elements, high system availability and low energy costs. The system combines short amortization times for the investment with high liter capacities in a small installation space.

Uncompromising HSS filtering

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