There's no question; people who want to create perfect surfaces in metal processing need clean cooling lubricant. Yet in order to be able to act successfully on the market, the economic side of cooling lubricant cleaning must also be considered. The MicroPur^® superfine filter from KNOLL Maschinenbau scores many plus points for cleaning grinding oils. It achieves filter fineness of less than 3 µm and works without filter consumables, which makes it especially economical and environmentally friendly.

For a long time, precoat filters were second to none for grinding oil cleaning in hard metal, HSS and cast material processing. But the expensive filter systems that rely on auxiliary filter materials such as diatomite and cellulose have a serious disadvantage: the large quantities of consumables, disposal of these consumables, and the transport of oil result in high costs.

An alternative that can score points with regard to economy and environmental friendliness are superfine filter systems that work without filter aids and consume significantly less energy thanks to soft filtration. The best example is the MicroPur^® filter from KNOLL Maschinenbau, Bad Saulgau. It contains backflushable filter cartridges like the ones used in other areas of oil filtration. This allows it to reach a nominal filter fineness of 1 to 3 µm, which fulfills the strictest requirements. In combination with an integrated sludge concentrator, for carbide metal, the MicroPur^® can reduce residual moisture to four percent in the sludge. These types of dry chips can generally be sold as recyclables. At least there are no disposal costs.

"Purely for economic reasons, backflushable superfine systems like the MicroPur^® will be our future," ensures Karl-Rudolf Vogel, Team Manager Product Development at KNOLL. "Because they also provide process-technical strengths, backflushable superfine filters have already overtaken and largely replaced precoat filters for grinding carbide metal. For HSS grinding and various steel types, many customers are already using the MicroPur^® with two-stage filtration. For cast materials, it is even used with pre-separation and spares us expensive magnetic technology." Layer filters for grinding solutions have been replaced with MicroPur^® technology for three years already; they omit the time-consuming preparation and disposal of quartz sand, which is tainted with environmentally harmful heavy metals.

Time for a system change

This is due essentially to these filters' economic efficiency. Even acquiring a filter system that operates based on the precoat principle is more expensive than acquiring one with backflushable filter cartridges. For the handling of diatomite and cellulose requires additional peripheral equipment. But the incidental costs are what truly make a precoat filter expensive. This is because the auxiliary medium has to be changed up to several times each day. The procurement and disposal costs add up; and in addition, the oil transported has to be replaced.

By contrast, MicroPur^® scores points with its filter cartridges. Due to their star-shaped folding, these special elements have an especially large filter area with a cleaning output of approximately 60 l/min per cartridge. Generally, the cartridges are installed in a housing in pairs. Therefore, in the MicroPur^® 480 standard filter, there are four housings, which are double-fitted. The filter cartridges can be flushed individually with cleaning oil without interrupting the filter process – a central feature of this filter. In order to achieve as effective a backflushing as possible, KNOLL uses a special flushing pump.

Filter systems in all sizes

KNOLL offers the MicroPur^® superfine filter in different performance classes and as central systems in freely-scalable sizes. The smallest model is the MicroPur^® Mini. It is a mobile filter column, which can be moved from machine to machine for mobile cleaning in order to satisfy cleaning requirements. The current standard models of the MicroPur^® begin with the MicroPur^® 60, which has a backflushable filter cartridge. Accordingly, sizes 120, 240, 480 contain additional filter cartridges. The numbers correspond to the cleaning output in liters per minute. Starting at 480 l/min and above, a clever modular system is used. Frequently, the KNOLL MicroPur^® filter is used in individually-configured, central filter systems for entire production areas. The largest current system is designed for a cleaning output of nearly 26,000 liters per minute.

KNOLL's MicroPur^® sets standards:

• Intelligent filter control system for fulfilling the toughest requirements in microparticle separation
• A filter housing designed to create a swirling effect ensures uniform filter cake accumulation and separation of coarse particles
• Effective filtered fluid backflushing with low energy consumption and small backflushing volumes without aerosol formation
• Consumption-dependent filtration, switching of additional filter capacity in 120 liter steps
• Each housing has differential pressure monitoring, and thus optimal visualization and state reporting from each filter. Faults and wear can be located immediately.
• Change of the filter cartridges is possible quickly and drip-free, even during operation
• Temperature stability of ± 0.1°C and less is permanently possible
• Flexible, modular filter system. Filter can be installed in narrow spaces
• High-performance sludge treatment with < 4% of residual moisture in any container system, for large systems with switchable double container filling