What Does a Coolant Filter Do?

A coolant filter takes dirt out of the coolant as it circulates round a machine. The coolant goes back to the cutting area clean, so it can do its job.

What does coolant do?

Coolant is sprayed onto the tool and the workpiece while the machine cuts or grinds. It does three jobs:

• It carries heat away from the cutting area.
• It lubricates the tool as it cuts.
• It washes chips and swarf away from the work.

After that, the coolant runs back to a tank, often called the sump. A pump sends it round again. The same coolant can circulate for months.

What gets into the coolant?

Every pass through the machine adds dirt:

• fine metal particles from grinding, honing and cutting
• small chips that the chip conveyor misses
• wear particles from the machine itself
• sludge, a mix of fine metal, broken-down coolant and dirt
• tramp oil that leaks from slideways and hydraulic systems

On machines that work steel or cast iron, most of the solid dirt is ferrous. Much of it is very fine.

What happens if the coolant is dirty?

Dirt in the coolant goes back to the cutting area on the next pass. There it causes damage:

• Particles scratch the surface of the part and spoil the finish.
• Parts can move out of tolerance, and more parts are rejected.
• The tool and the grinding wheel wear faster.
• Nozzles and small coolant lines block.
• Pumps, seals and slideways wear.
• Sludge builds up in the sump and bacteria grow in it. The coolant starts to smell and breaks down sooner.

Dirty coolant also cools less well. The tool runs hotter and wears faster.

What does a filter change?

A coolant filter removes the dirt before the coolant goes back to the machine. The results are simple:

• The finish on the part is better and more even.
• Fewer parts are rejected.
• Tools and wheels last longer.
• The machine has fewer breakdowns and repairs.
• The coolant lasts longer, so it is changed less often and less is thrown away.

Clean coolant also flows at a steady rate and keeps a steady temperature. That helps close tolerance work such as grinding and deep hole drilling.

Which filter?

There are several kinds of coolant filter. Bag, paper and cartridge filters hold back particles larger than their pores. Centrifuges spin the dirt out. Magnetic filters pull iron and steel out of the flow. The guide to types of filtration for CNC machines explains each one.

On machines that work steel or cast iron, a magnetic filter is a good first stage. It holds very fine ferrous particles, it does not block, and it has no filter element to replace. Where there is also aluminium, brass or other non-magnetic dirt, a barrier filter after the magnet catches the rest. For a side-by-side view, see magnetic filters compared with other filters.

The right system depends on the particle size, the type of coolant, the flow rate and the amount of work the machine does.

Where are coolant filters used?

• Grinding. Grinding makes very fine steel particles. They are the main cause of a poor finish.
• Bearing and precision part making. Tight tolerances need clean coolant on every pass.
• Machining centres and lathes. Fine swarf blocks nozzles and wears pumps.
• Honing and lapping. The finish depends on the coolant or oil being clean.
• Wire cut machines. The fluid needs to stay clean for a steady cut.
• Parts washers. Iron in the wash liquid settles back onto the next batch of parts.

The SMAG range

Santosh Magnetic Works builds the magnetic coolant filter for water based coolants, neat oils, hydraulic oil and wash solutions. Each unit is built to order in Mumbai to suit the connection size and flow rate. See the filtration range or contact us with the machine, the fluid and the flow rate.