Machining grey cast-iron components produces coarse chips together with fine graphite and iron particles. These contaminants form a black sludge layer on the coolant surface.
Combined with lubricating and hydraulic oils entering through minor leaks, the material forms a sticky floating layer that is difficult to remove.
An automotive supplier installed a new central coolant system with a capacity of approximately 30 m³. A floating-phase extractor was intended to remove tramp oil and sludge.
A feed pump transferred the mixture of emulsion, oil and dirt particles into a separator. The cleaned emulsion was expected to return to the clean tank, while the oil phase flowed to a waste-oil container.
Because the floating layer contained a very high concentration of fine particles, a sticky deposit quickly formed on the extractor. It eventually became so heavy that it sank into the emulsion.
With the plant running continuously in three shifts, the required regular cleaning could not be carried out. The operator therefore needed trouble-free continuous operation without routine maintenance.
The customer needed a system that could reliably and fully automatically remove the floating layer of lubricating oil, hydraulic oil, graphite and metal wear at regular intervals—without routine cleaning.
A FRIESS W40 oil skimmer with a freely floating collection tube was installed to remove the floating phase across a large surface area. The tube follows the liquid level automatically and attracts the oil phase from the coolant surface.
Because solid and graphite particles were also floating on the emulsion, magnets were fitted to the collection tube. They retain the particles even when the oil content is very low, while ceramic scrapers remove the adhered material from the tube inside the skimmer.
While the coolant system is running, a thin layer of oil and solids forms on the tank surface within approximately 5–10 minutes. Two rotations of the collection tube are sufficient for the integrated magnets and oleophilic surface to remove this layer.
The exact operating cycle was established during commissioning. When the emulsion is at rest—especially at weekends—most of the incoming oil rises to the surface and is removed during the next skimming cycle.
Tube movement is monitored continuously. If the tube stops moving while the skimmer is running, or if mechanical damage removes it from the collector, the system issues a warning.
The skimmer controls can be connected to the plant PLC or central control room for higher-level monitoring and operation.
After several months of operation, the contamination and tramp-oil content of the coolant had fallen substantially. Apart from emptying the collected oil-and-solids mixture, the skimmer required no additional maintenance. The maintenance savings produced a payback period of approximately 13 months.
