Cooling lubricants: selection, use and working environment
What cooling does for the cutting edge — and what the mist and oil do to your skin and lungs
The cooling lubricant, which many just call 'cooling liquid' or 'bore-grease', has three jobs at once: it cools the cutting zone, it lubricates to reduce friction, and it flushes the chips away. Used correctly, it significantly extends tool life and improves the surface. But it is also one of the chemical occupational health problems you encounter most closely in a metalworking shop, and which a skilled technician should take seriously — both for their own and colleagues' sake.
§What cooling does for the cutting edge
With chipping almost all cutting work is converted to heat. The cutting fluid removes much of that heat so the tool is not softened and the workpiece does not expand uncontrollably. Lubrication reduces friction between chip and tool and counteracts built-up edge especially in tough materials such as stainless steel and aluminium. And rinsing away chips keeps the cutting zone free so chips are not cut again. In some materials — for example cast iron — however one often runs completely dry.
§Types of coolant-lubricants
There is a rough distinction between water-mixable and non-water-mixable agents. The water-mixable ones — emulsions and microemulsions — are mixed with water and used most because water cools well. Non-water-mixable cutting oils lubricate best and are used for heavy, slow operations like thread cutting and broaching. With minimal lubrication (MQL), a very small amount of oil is sprayed as a fine mist, which results in less waste and cleaner chips. The choice depends on material, operation and machine.
| Type | Cooler | Lubricates | Typical use |
|---|---|---|---|
| Emulsion (water-based) | Good | Medium | Common turning and milling |
| Cutting oil (non-water-soluble) | Medium | Best | Threads, broaching, deep holes |
| Minimal lubrication (MQL) | A little | Good | Pure production, less waste |
§The risk to skin and airways
Cooling lubricants can affect both skin, mucous membranes and lungs — through direct contact and by inhaling mist, gases and smoke. On the skin it often shows first as mild redness or irritation that can develop into eczema, especially where work clothes soaked with the substance rub against the skin. Inhalation of oil mist can give respiratory problems and over time inflammatory reactions in lung tissue. Used water-miscible substances can also get bacterial and fungal growth if not looked after, which worsens the problems.
§Good practice with the agent
Much of the risk can be removed with ordinary discipline. Keep the machine's guard closed so the mist stays inside the machine, and make sure that exhaust and filters work. Avoid skin contact — do not use the product to wash your hands, and change contaminated clothes. Check mixing ratios and pH regularly so the emulsion does not become acidic and bacteria-ridden, and replace it when it is used up. A skin care plan with barrier cream and good hand hygiene protects against eczema.
- 01Læs sikkerhedsdatabladet, før du bruger et nyt køle-smøremiddel
- 02Keep the machine hood closed and suction running to catch the mist
- 03Avoid skin contact—change soaked clothes and use barrier cream.
- 04Check blend and pH; replace emulsion if bacteria grow
- 05Consider substitution for a less troublesome agent where possible
“The cooling saves your tool — but it's you who must take care of yourself while it does.”