Cleaning coolant lubricants

Why do coolant lubricants need to be cleaned?

Coolant lubricant is an important part of industrial production with CNC machine tools. The coolant lubricant cools and lubricates the machining task, thereby enabling cost-efficient and reliable production. However, when the coolant lubricant is introduced directly into the machining gap to provide maximum cooling it becomes contaminated. Machining residues such as metal chips, grinding dust and tool abrasion collect in the coolant lubricant. These machining residues in the coolant lubricant damage the coolant lubricant system aggregates (such as pumps, valves, coolers or nozzles) by means of abrasive wear or clogging. Besides this, contaminated coolant lubricant may also lead to the desired machining result, such as high surface quality, not being achieved.

To free the coolant lubricant from these contaminants and attain the necessary purity, coolant lubricant filtration systems are used. If an efficient filtration system is employed in production, this reduces wear on the system components and extends the service life of the coolant lubricant. coolant lubricant filtration also has a positive effect on the reliability of the machining task. A correctly dimensioned coolant lubricant filtration system is essential for ensuring seamless production with consistent machining quality, low coolant lubricant system component wear and low production failure rate.

Challenges of coolant lubricant cleaning

The filtration of coolant lubricants brings its owns challenges with it. The most important demand placed on the filtration system is ensuring that the required volume flow is made available at the required degree of purity. The purity of a coolant lubricant is defined using NAS 1638 or ISO 4406. The difficulty with coolant lubricant filtration is guaranteeing the required purity in spite of fluctuating dirt loads, different volume flows and clogging caused by the filter material.

To fulfil these goals, the correct dimensioning of the filtration system is a basic prerequisite right from the planning stage of the production line. It is also essential to regularly monitor the cleaning performance of the lubrication filtration system in running operation.

Options for cleaning coolant lubricants

A number of different processes are available for cleaning coolant lubricants. The required coolant lubricant purity and the required volume flow (l/min) are decisive in selecting a filtration method. Some common filtration processes are briefly outlined in the following:


During sedimentation, the contaminated coolant lubricant is collected in a container in which the solid particulate contaminants settle at the bottom due to gravity. The cleaned coolant lubricant can then be removed from the surface, while the sedimented dirt is removed from the bottom of the container using a scraper-type conveyor.


During centrifugation, the contaminated coolant lubricant is supplied to a rotating drum. Here, centrifugal force separates the solid particles from the liquid coolant lubricant. Disc separators, for example, are frequently used as centrifuges for coolant lubricant cleaning.


During filtration, the contaminated coolant lubricant is led through a porous filter medium which binds the solid particulate contaminants and allows the liquid coolant lubricant to flow through. The filter medium may be designed as a belt, drum or candle. When using backwash filters, however, coolant lubricant may be discharged from the coolant lubricant system. These losses must be occasionally replaced or replenished.

Magnetic separation

During magnetic separation, the solid particulate contaminants are magnetized and separated in this way from the liquid coolant lubricant. This process can only be used if the contaminant particles are magnetic. The highly abrasive grit of the grinding wheel must likewise be filtered out of the coolant lubricant. However, this is not magnetic.

The above-mentioned filtration processes are described in more detail in our magazine article “coolant lubricant Filtration Systems (Kühlschmierstoff-Filtrationsanlagen)”.

Costs for coolant lubricant cleaning

Coolant lubricant maintenance is costly, as a number of steps are necessary in various systems in order to prepare the coolant lubricant for reuse. Besides the procurement of the lubrication filtration system, the biggest cost factors are broken down in the following:


Coolant lubricant is pumped from the filtration system to the machining unit and back via pipes. This task is carried out by efficient pumps which make the required pressure and volume flow available. These pumps are driven by electric motors which, in relation to their power, demonstrate high energy absorption. In the filtration system itself, other motors may be necessary – for instance to drive the centrifuges.

Filter aids

Filter aids are auxiliary materials which are used to achieve the desired filtration result. Filter aids are consumed and must thus be newly procured again. Filter candles, for example, need to be replaced after a certain usage time.

Maintenance and care

As with all machines, the coolant lubricant filtration system requires maintenance and care. When required, pumps, valves and other expensive components must be replaced, thereby leading to considerable costs.

Replacement, disposal and new procurement of coolant lubricant

Even with the best maintenance and filtration systems, the coolant lubricant is still subject to aging and must thus be replaced after a certain load-dependent life cycle. Besides the new procurement of coolant lubricant, costly disposal of the the old one must also be dealt with.

To reduce the above-mentioned costs, it is advisable to reduce the entire coolant lubricant throughput. In this way, the filters are subject to less load, the pumps consume less energy and a lower overall volume of coolant lubricant may be needed. There is optimization potential in almost every production environment. In the long-term, needs-based coolant lubricant supply and filtration can lead to significant cost savings.


Coolant lubricant filtration is an indispensable part of the lubrication system for maintaining coolant lubricant supply in the required purity and at the required volume flow. Various processes are available for filtration of the coolant lubricant. These must be selected and dimensioned based on the existing production requirements. coolant lubricant filtration incurs a considerable share of coolant lubricant-related costs, as energy and filter aids are consumed.

Is coolant lubricant filtration still a “black box” for you, or are you already encountering problems in your production facility? We can help you! As an experienced coolant lubricant system service provider, Grindaix GmbH brings know-how from numerous successful optimization projects to the table. Feel free to contact us – our specialists would be happy to advise you on coolant lubricant processing!

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