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Choosing the Right Filter

Maintaining clean coolants and lubricating oil is vital in ensuring efficiency and quality output on processes such as grinding, lapping, wash systems, honing, drilling and other “super-finishing” operations. There are many different types filter or filtration system available, whilst each will make distinct process improvements - closer inspection may suggest that they are not performing to the optimum levels. You may think your filtration is working but is it?

Advanced Magnetic Filtration

Our advanced magnetic filters have been developed to overcome some of the typical problems experienced when using traditional filters. They remove almost 100% of ferrous particles, including sub-micron size. As a result they extend fluid lifespan, save costs on consumable filters, minimise filter waste and improve product quality. In addition they offer 24/7 uninterrupted filtration.

Before choosing a new filtration system or upgrading an existing one its’ important to consider the positives and negatives of each:-


Barrier Filtration

(Cartridges, Socks, Bags, Paper Bands)

Basic Concept: Fluid passes through some form of barrier usually in the form of a bag, cartridge or sheet made from paper, polyester or polypropylene. The barrier allows the fluid to pass through but prevents contamination particles from circulating. When full the barrier is either cleaned or replaced.

Positives +

In applications with low levels of contamination, which don’t require an ultra-precise surface finish, barrier filters provide an adequate and effective means of filtration, and do offer some positives :-

Ease of Control – differential pressure gives the operator a clear indication when a filter is full and maintenance work is needed.

Capital Cost – barrier filters are relatively cheap to buy and install, in fact in some cases the fluid supplier may subsidise the costs. However, because of the on-going spend on consumable filters media the overall costs are high with a very long return on investment period.

Non-magnetic Contamination - barrier filters remove both magnetic and non-magnetic particles but only to a certain size.

Negatives -

Running Costs – barrier filters are usually disposable items, when they become blocked they are replaced. In medium to heavy contamination applications the costs of replacement consumable filters can be enormous. In addition there are downtime costs each time the machine is stopped to replace the filters.

Environmental Costs – using disposable filters results in disposal costs and environmental damage, as used media is sent to landfill sites. With the advent of ISO14001 and more corporate focus on environmental responsibility many companies are looking to reduce waste.

Limited Filtration Capability – in order to maintain flow, barrier filters are often limited by the media pore size. To avoid restricting flow typically the pore size maybe set at 10-20 microns which means that any contamination particles below this size continue to be circulated, damaging components, reducing surface finish quality, reducing process accuracy and reducing oil/coolant lifespan.

Downtime – in medium to high contamination applications barrier filters are susceptible to blinding or blocking which cause a drop in pressure which in turns triggers the machine to stop. In certain applications this can result in hours of downtime and maintenance time.

Settlement Tanks

Several processes still do not have distinct filtration media but rely on natural settlement to remove contamination particles.

Basic Concept: Often during the cycle fluids, such as coolants and oils, are pumped into a holding tank where larger particles fall to the bottom of the tank through natural gravity settlement. In some cases they are removed by a drag conveyor but more likely they accumulate to point where the tank has to be drained and manually cleaned.

Positives +

Filter Media Costs: The main advantage of settlement is that there is no on-going investment in disposable filters.

Primary Separation: Settlement provides adequate, cost effective means of primary separation of larger particles, typically 100 microns or larger, which does reduce the burden on secondary filters.

Negatives -

Ineffective Filtration Capability: Settlement relies on the weight of the particle and the time the fluid remains in the tank to be effective. If the particles are small, low density or pass through the tank quickly, natural settlement is largely ineffective. Generally any particles below 100 micron size continue to circulate - damaging finished product, process equipment and reducing fluid quality/lifespan.

Downtime: Manually cleaning the holding tank can be an expensive process in terms of direct man hours and resultant process stoppages.

Reduced Fluid Quality: The lifespan of coolants and oils can be significantly reduced as contamination is recirculated and gradually builds up in the fluid.

Secondary Filtration – for effective filtration an additional secondary filter will usually be needed to work in conjunction with the tank.

Cyclonic Separation

Basic Concept: Cyclonic, centrifuge or hydro-cyclonic systems are widely used. The general principle relies on the different densities of the liquid and contaminant to accelerate natural settlement. Fluid flows in a cyclonic pattern around a vessel wall, centrifugal force separates out contaminated particles which are forced downwards for collection whilst clean fluid flows out.

Positives +

Filter Media Costs: After an initial capital investment there are no consumable filter costs or disposal costs.

Negatives -

Filtration Capability: Generally cyclonic systems can only extract medium to larger contamination, low density or smaller particles pass through. In many cases anything smaller than 10 microns will continue to circulate causing on-going damage to finished parts, process equipment and reducing fluid quality.

High Maintenance: Many cyclonic systems need regular cleaning to remove contamination and prevent outlets from becoming blocked.

High Capital Investment Costs: On larger machine tool applications cyclonic systems can represent a high capital investment cost relative to other filter systems.

Flow restrictions: Due to the nature of the process cyclonic systems are often unable to handle higher flow rate applications.

Traditional Magnetic Systems

When magnetic filtration is mentioned many people think of traditional methods such as a magnetic rod or bar mounted or suspended in a holding tank or a low intensity magnetic roller such as a coolant roller. This is by far removed from the advanced magnetic filtration systems now available.

Basic Concept: Rely on magnetism to attract ferrous particles as the device comes into contact with the fluid, thereby removing it from circulation.

Postive +

Filter Media Costs: Magnetic filtration does not need any consumable items and has no on-going running costs.

Negative -

Ineffective Filtration Capability – traditional magnetic systems are possible to use as primary filters to remove large particles but if used as the sole means of filtration they are ineffective in precision finishing applications. They are often limited by magnetic strength; low intensity magnets are often used. They are also limited by design, in most cases the fluid does not flow close enough or for long enough around the magnet. Large volumes of contamination continue to circulate with the negative effects previously discussed.

Vacuum Filters

Basic Concept: These filters use vacuum or suction to draw fluid through a filter media. Clean fluid is flows into a “clean” tank and contamination is held on the filter media which is periodically cleaned.

Positives +

Automation: Such systems are often automated which reduces downtime or manual intervention for cleaning.

Higher Flow Rates – Vacuum filters are available for larger applications which handle high volumes of fluid and higher flow rates.

Negatives -

High Capital Investment: Many Vacuum filtration systems are expensive investments, whilst they are effective for some applications the return on investment is over a very long period.

Filter Media Costs - Vacuum filters rely on a filter media to capture the particles, in some cases this can be cleaned and reused, ultimately however this will need replacing with resultant cost and disposal issues.

Filtration Capability – Whilst Vacuum filtration systems generally have an improved capability than standard barrier filters they are not fully effective for high precision processes. The market leading Vacuum filters can remove particles down to 1 micron size but many other systems only operate at 5-10 microns. The issues are that smaller sub-micron particles remain in the process damaging process equipment, reducing part quality and reducing the fluid life.

For a no obligation assessment of your filtration systems please contact us.