FRIESS Oil Skimmer remove Tramp Oil and Dirt Particles from Coolantwhich is used for Machining Cast Iron

During machining of cast iron, metal chips and fine particles of carbon black and iron are produced. Bigger chips are removed by the filtration system, while fine carbon black and iron particles float as a black layer on the coolant. Tramp oil, especially lubrication oil and hydraulic oil, float on the surface of the coolant too and mixes with the iron and carbon black particles. The result is a sticky and ductile layer which is very difficult to remove.

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A producer of components for car engines has mounted a new central coolant tank with a volume of 30 m³. In order to remove floating oil and sludge from the surface of the coolant, the supplier installed a floating funnel. With an additional pump, the mixture of coolant, oil and dirt particle was pumped into a decanter. The cleaned coolant was guided back into the main tank, while the floating oil and sludge should float into a waste oil tank.

During machining of the cast iron parts, a lot of fine iron and carbon black particles were produced.  Together with the oil, the particles stuck to the floating skimmer. After a short time, the floating skimmer sank to the ground because of the big amount of sludge sticking on the surface. Because of production around the clock, it was not possible to clean the floating skimmer regularly. In addition, the customer asked for continuous operation without maintenance or cleaning.


The customer wanted a system which is able to remove the floating sludge, oil, carbon black and metal  particles fully automatic without cleaning.

w40 Oil Skimmer for coolant

Solution: FRIESS oil skimmer W40

Oil Skimmer W40

The customer decided to install a FRIESS oil skimmer W40 with free floating oil collector tube. Because of the free floating oil collector tube, the oily sludge can be removed from the total surface of the basin. The oil collector tube was equipped with additional magnets because many carbon black and iron particles were floating on the coolant surface.

The built in magnets are able to attract the particles. The particles will stick to the surface of the oil collector tube. The oil collector tube is able to collect these particles, even in case there is nearly no oil floating on the coolant surface.

The sludge particles and oil are removed from the surface of the oil collector tube by ceramic scrapers in the oil skimmer. The skimmed off material is not liquid and consists mostly of particles. For this reason, the standard oil collector pan of the oil skimmer W40 was replaced by an open funnel underneath the oil skimmer. The particles and the sludge falls from the scrapers through the funnel into an open collecting tank. An automatic level control in the collecting tank switches off the oil skimmer as soon as the collecting tank is filled with sludge.

The oil skimmer is equipped with a frequency converter and a timer in order to adjust the capacity of the oil skimmer to the amount of sludge floating on the coolant.

During production, it takes about 5 – 10 min. until the thin layer of oil and particles floats on the surface of the coolant. It takes approx. 2 rounds of the oil collector tube to remove the floating particles with the magnets. During the start-up-period, the exact speed and the exact times were determined.

During production stop or during weekends, the coolant rests in the tank. Most of the tramp oil in the coolant floats on the surface when the coolant rests. During this time, the oil skimmer operates continuously in order to collect the floating tramp oil.

In addition, the oil skimmer was equipped with a sensor, which checks the operation of the oil collector tube. In case that the oil collector tube does not move, although the oil skimmer is working or in case that the oil collector tube has been destroyed mechanically an alarm is shown.

The switchboard of the oil skimmer can be connected with the central control system, so that the continuous supervision is possible.


After several months of operation, the amount of particles and the amount of tramp oil in the coolant was reduced drastically. The oil skimmer did not need any maintenance. Only the collected sludge had to be removed.

  • Because of the reduced maintenance cost, the system was paid in 13 months.