Cutting Oils And Metal Working Fluids - | Oil Analysis : Swansea Tribology Services

Cutting Oils and Metal Working Fluids are used to lubricate and cool machining tools and the components being machined. The fluid also helps to remove debris from the machined surface and to protect from corrosion.

There are many different types and formulations of cutting fluids, including oils, oil-water emulsions, etc. The use of a suitable cutting fluid will improve the quality of the machined surface and extend tool life.

With cutting fluids being an essential component of the machining operation it is vital that the condition of the cutting fluid is monitored and maintained. Especially so due to the health and safety implications from operator exposure to the cutting fluid.

Cutting fluids, especially oil-water emulsions, are subjected to challenging environmental conditions and are a perfect breeding ground for bacteria, yeasts and moulds. Regular monitoring and control of biological growth is essential to maintaining operator safety and fluid condition. More on metalworking fluid biological contamination and safety can be found at the HSE website.

At the same time, as oil-water emulsions are designed for use at specific concentration levels it is important to monitor their concentration to ensure that optimal performance is maintained.

Routine monitoring of oil-water emulsions

Regular monitoring of cutting oil condition allows for precise control of fluid concentration and biological contamination levels, making the fluid effective and safe.

Biological Contamination Monitoring

Cutting fluids, especially oil-water emulsions, are a perfect breeding ground for microbes. Ready access to water, oil and elevated temperatures, as well as exposure to the surrounding environment create the perfect conditions for rapid biological growth.

Biological contamination can be in the form of bacteria, yeasts, moulds or fungi and is most likely to happen where water contamination is present, although it doesn't necessarily take that much water - 500ppm may be sufficient. These microbes consume organic material from the oil and particularly enjoy warm temperatures, stagnant/low flow areas, an oxygen supply for accelerated growth and suspended particles to use as initial colonisation sites. These colonies can produce blockages, degrade oil quality and performance and produce corrosive by-products. They can block filters and pose a significant health risk to operators who may come into contact with contaminated cutting fluid.

We can check your samples for evidence of biological contamination. Water is used to extract potential contaminants from the oil sample (although oil-water mixtures may be analysed as received). This is then deposited onto a dip slide with growth medium. The slides are incubated for a week and checked for colonies of bacteria, yeasts and moulds. Each sample is run in duplicate to avoid false positives and a clean water blank is tested to ensure no water-borne contamination is introduced.

If biological contamination is discovered, you will need to consider adding a suitable biocide to control growth. Monitoring and controling oil concentration and pH levels is also important in management and prevention of biological contamination.

Fluid Concentration

For optimal performance the concentration of the cutting fluid must be kept at the recommended level. If the concentration is too high it will produce more mess, increase the risk of skin problems and increase the cutting fluid consumption. Insufficient concentration will result in microbial contamination, corrosion and poor lubrication, reducing the useful life of the tools and the fluid.

Concentration of the oil-water cutting fluid mixture can be monitored my measuring its refractive index.

The refractometer value is multiplied by the formulation specific factor, or, where this is not available, an in-house calibration curve may be re-created.

pH Level

The pH level of a metalworking fluid is a key indicator of the fluid's health. Many metalworking fluids have a typical working range of pH between 8.5 and 10.5, making the fluid alkaline. The pH of the fluid affects such properties as:

Corrosion - having the pH in an alkaline range protects ferrous metals from corrosion.

Metal solubility - the pH and reserve alkalinity of the fluid control the amount of metal solubility.

Emulsion stability - the pH has an effect on how tight (higher pH) or coarse (lower pH) the emulsion is, affecting the stability of the emulsion and such properties as wetting and lubricity.

Dermatitis - when pH gets too high the risk of dermatitis increases as the alkalinity can "saponify" the oil in the skin, causing it to dry out.

Bacterial and fungal growth - while not able to prevent the growth of biological contamination the pH does affect the growth rate, with bacterial growth reducing at higher pH levels and fungus preferring highly alkaline solutions.

Machine tool compatibility - extremese of pH can cause damage to machine tools, elastomers (seals) and plastic components (embrittlement).

By monitoring the pH of your metalworking fluid you can keep it in the optimal level for the system, reducing the negative impacts, improving safety and prolonging the life of the fluid and the machine tools.