CNC coolant tramp-oil removal is essential for maintaining coolant performance and extending fluid service life.
Keeping coolant free of tramp oil helps avoid premature replacement and preserves the required machining properties—not only in CNC machine tools.
Metalworking coolants in CNC milling machines and lathes are often subjected to high loads. The effectiveness of an oil skimmer depends on the operating conditions and selecting a suitable model.
Coolant-tank dimensions and the available installation space vary considerably between CNC machines, so both must be considered during equipment selection.
CNC milling machines differ widely in design, so there is no single oil skimmer that is best for every installation. The actual operating conditions should be understood as accurately as possible before selecting a model.
In general, the exposed liquid-surface area of the coolant tank is the most important selection criterion. Belt skimmers often work well on small tanks, but can be less effective on larger surfaces. The internal arrangement of the CNC machine must also be considered.
For a belt skimmer to work effectively, the exposed liquid surface should be relatively small so that the belt’s drawing effect can bring the oil film to the collection point. This limited effective range is a common constraint of belt skimmers.
Above a certain tank size, the continuous movement of the oil film towards the belt breaks down. A vertically immersed belt influences only a limited surrounding area; inaccessible dead zones remain and the oil film is removed only partially.
In these dead zones, weak fluid circulation, a persistent oil film and limited oxygen exchange encourage bacterial growth. This leads to more frequent and costly coolant replacement and may increase health risks for employees.
Small CNC milling machines usually have compact coolant tanks. Depending on the tank layout—chip conveyors, pumps, level sensors and pipework—even a larger tank may provide only enough free space for a belt skimmer.
In these situations, belt skimmers may also be used on larger CNC systems. Several units can be installed to cover more of the exposed liquid surface when this is the only practical way to achieve the required treatment result.
Advantages
Belt skimmers remain practical where the tank design provides only limited installation space and a small accessible collection area.
When chip conveyors, pumps or other components prevent a tube skimmer from covering a large surface, a belt skimmer is often the more suitable option.
Limitations
The oil film is collected only within a limited area around the immersed belt. Inclined belt designs extend the effective range, but do not eliminate this limitation completely.
Where the exposed surface is large and a tube skimmer cannot be installed, several belt skimmers may be required to achieve sufficient removal performance.
An effective oil skimmer for CNC coolant should cover the liquid surface as widely as possible, collect a high proportion of floating tramp oil while carrying away very little coolant, and continue to operate reliably despite fluctuations in liquid level.
Above a certain tank size, tube oil skimmers are usually the preferred solution.
Limitations
The oil film is collected only within a limited area around the immersed belt. Inclined belt designs extend the effective range, but do not eliminate this limitation completely.
Where the exposed surface is large and a tube skimmer cannot be installed, several belt skimmers may be required to achieve sufficient removal performance.
An effective oil skimmer for CNC coolant should cover the liquid surface as widely as possible, collect a high proportion of floating tramp oil while carrying away very little coolant, and continue to operate reliably despite fluctuations in liquid level.
Above a certain tank size, tube oil skimmers are usually the preferred solution.
W40 model — suitable for tanks of many sizes with widths above 800 mm
W20 model — suitable for narrower tanks approximately 500–1,000 mm wide
Every installation should be assessed individually to ensure the desired treatment result. We will be pleased to introduce the relevant FRIESS oil skimmers and help you optimise tramp-oil removal from CNC milling-machine and lathe coolant systems.
The shared objective is to extend the service life of costly coolant and improve operating economics. By significantly increasing coolant life, a FRIESS oil skimmer can often achieve a short payback period while reducing both fresh-fluid purchasing and waste-fluid disposal costs.
Limitations
Chip conveyors, pumps or similar tank components can restrict the layout of the collection tube and prevent it from sweeping a large surface area.
In compact CNC machine enclosures, coolant tanks are often integrated into the lower machine structure, leaving too little freedom to route the tube. These installations require a solution tailored to the actual site conditions.
