SKF Lubrication Systems CZ
An important part of ensuring high quality at low cost in metalworking applications is the reliable supply of the machine tools with coolants. Various coolant pumps from Spandau Pumps are deployed for the machining process and for a modular island filter system, including chip conveyor, at the SKF Lubrication Systems CZ s.r.o. plant in the Czech city of Chodov. Supervisors have been noting lower energy and operating costs and higher system availability ever since their installation.
Progressive metering devices for lubrication systems are among the products produced at the SKF plant in Chodov. There were, however, problems in the earlier production line. Internally cooled tools kept experiencing blockages due to residual dirt and grime. On the previous, relatively slow machines, single-station solutions were used as the filter variant. SKF’s Manufacturing Technology project team, led by Steffen Siegemund, was tasked with ensuring that Chodov will produce more flexibly, with higher quality and at lower cost. They therefore decided to purchase fast single-spindle milling centers.
To clarify how chips can be efficiently handled, coolant recovered and fed back into the production process, the SKF project team and the global Purchasing department contacted Mayfran GmbH in Aachen, Germany. Together with the chip conveyor and filter systems specialist, they assessed and compared the advantages and disadvantages of the concepts for single-station and island solutions as well as centralized supply. The decision was ultimately made for a modular island system with chip conveyor. Steffen Siegemund is very satisfied: “We implemented the project successfully with Mayfran GmbH.”
The filter system serves two production lines, each with three machine tools and a single-station solution. The system handles full-flow cleaning of chips up to 25 µm in size, plus up to 5 µm using a second fine filter stage (bypass cleaning) using a paper belt filter. The system is equipped with a secondary protective container and meets the requirements of the German Federal Water Act (WHG). It also has an immersion cooler with a powerful control unit. The SKF plant is thus well prepared for increasing production counts and can bring this cooler on line if needed to keep the coolant at a constant process temperature.
Support from within
The last piece, the right pump manufacturer, was still missing. The SKF project team was able to find it among its own: Spandau Pumpen, headquartered in Berlin, has been part of the SKF Group since 2004. The company develops and builds powerful solutions for centralized supply and disposal and for processing related to machine tools. “Spandau Pumps is an independent brand within the SKF Group, so the decision to rely on in-house products was clear,” says Martin Zverina, Plant Manager in Chodov.
Spandau Pumps supplied three low-pressure and three high-pressure pumps (PS and LMP series), each with frequency converters, for the modular island solution with chip conveyor. The standard commercial motors that were used can easily be retrofitted with a frequency converter using an adapter. The pumps with converters are operated in parallel, reducing the complexity of controls and increasing the dependability. Some components are designed redundantly to avoid system failures. The cleaning process always follows the same pattern. Spandau PSH rinsing pumps feed the medium contaminated by machining from the machine tools back to the filter system. The clarified and reusable fluid is fed into a reservoir. PS pumps feed the filtered medium from this clean tank under low pressure, and the LMP screw pumps feed the finely filtered medium back again under high pressure for reuse on the machines (see Figure “Schematic illustration of the coolant flow”).
Due to parallel control of the pumps, with master function, they always operate according to demand and enable a long service life because they are loaded uniformly. The system feeds only as much coolant as required by the connected machines. The master or alternating control ensures a homogeneous running time of the individual pump units. Since not all process pumps are necessarily operational every day, a different master pump is selected every 24 hours, so all components are exposed to nearly identical levels of wear. The redundant pumps are checked regularly for proper function.
The sensors in the tubing feed the frequency converter with input on the actual state of the process pressure. The converter then controls the rotational speed of the pumps to maintain a consistent pressure level. This renders a bypass control unnecessary, as any additional energy requirement and unnecessary heat input into the coolant are avoided.
Efficient and powerful with low maintenance costs
Automatic adaptation of the speed by the frequency converter also compensates for a possible drop in performance due to wear on spindles or impellers: The desired working point continues to be controlled, and unplanned system downtime is avoided. An impending need for repair is thus detected in time, so maintenance work can be scheduled efficiently. The gentle system start-up using converter technology avoids pressure surges, protecting components such as fittings, hoses and filters and increasing the useful life of the entire system. The overall result is a notable reduction operating costs in Chodov.
The system is also especially energy-efficient. “Based on consumption measurements and machining volumes, we’ve calculated energy consumption of just 40% that of an operational single-station system,” reports Martin Zverina. And that with energy savings of 60%. Furthermore, four rinsing pumps (PSR series) for filter cleaning were incorporated into the system, as were two residual dirt pumps (PMS series) for removing residues. Two lift pumps (PSH series) each were provided for the chip conveyors with lateral pump stations. Thanks to this setup, the SKF plant is optimally equipped to meet the requirements.
The filter system has a modular design and can be expanded at any time. This can be done at a later time as needed. The island filter system is also flexible with regard to the machine application. The same system type can still be used if, for example, a grinding center or another milling machine line is added in Chodov. The only thing to change would be the filter quality. The solution from Spandau Pumps impressed the supervisors in Chodov from the start. They are pleased with the high availability when using the machines around clock and the short maintenance periods. SKF emphasized a fully automated process in Chodov. Baskets requiring manual cleaning in front of the lift pumps were not used. The components such as associated filter elements were specially developed for the purpose.