Handling and maintenance of cutting fluids/systems

During Christmas or summer stoppages, pump the oil off and remove swarf and any other residues at the bottom of the tank. Clean the conveyor, tank and machine, and then filter the oil back into the system. You generally only need to fill with a small amount of new oil.

The system cleaner is normally added 1-2 days before the fluid is to be changed. However, you can also use a higher concentration of cleaner over a shorter period of about 6-8 hours, as long as there are no operators working inside the machine. The approach you choose depends on the circumstances in production when the fluid is due for a change.

Next the system is emptied (including swarf and other impurities) and rinsed with water. Use a system cleaner only in conjunction with an emulsion change.

Use a disposal method that has as low an impact on the environment as possible. Used emulsion can either be evaporated or splitted using acid. The emulsion should be evaporated to approximately 10% before being sent for disposal. When emulsion is splitted using acid, the oil phase is sent for disposal. The water phase is cleaned up and reused, or neutralised and sent to a treatment works if this is approved by the local authorities.

The best results are always achieved using a mixer. To ensure a stable emulsion, concentrate must always be added into the water, rather than the other way around. This ensures the emulsification process is successful and the resulting emulsion is stable. If you add water into the concentrate there is a risk that the emulsion becomes inverted, which means there are water drops in oil rather than oil drops in water, and the emulsion will not work as intended.

The concentration of the emulsion must be kept at the right level if the emulsion is to work optimally.

• If the concentration is too high it will produce more mess, increase the risk of skin problems and also increase cutting fluid consumption.
• Too low a concentration results in bacteria, fungal infestations, corrosion, poor lubrication, and a reduced life span on the tools and system.

It is therefore important to regularly measure the concentration, ideally daily but at least once or twice a week.

The concentration is measured either using a refractometer, which is easiest, or by titration.

The tramp oil content can be measured as follows: 
Concentration (refractometer) – Concentration (titration) = Tramp oil content
Tramp oil is most easily removed using a skimmer or an oil separator.

Adjust the concentration as required after measurement. A weaker concentration of approximately 1–2% should normally be used for topping up the system.

It’s important to keep an eye on the pH value in the system. If the pH decreases, you either have too low a concentration or a bacterial problem. In most cutting fluids, the pH should be at least 9.0. pH can either be checked using a pH meter or a pH stick.

pH-scale

Most cutting fluids have a pH of 9–9.6 but there are also products that have a lower pH during use.

The problem with bacteria is that they eat the cutting fluid’s components and secrete acidic substances, which leads to a drop in pH and then to corrosion problems and bad odours. Bacteria breed quickly if they are able to infect the system, so it is important to measure the bacteria levels once a week.

Bacteria is most easily measured using a dip slide. Bear in mind the results could take up to two days for bacteria, and up to four days for mould and fungi. More advanced equipment can be used to also measure the amount of bactericide in the system.

Contact us or follow the standard maintenance procedure if the pH falls below the recommended value, or if the bacteria content cannot be kept below 106 per ml.

Support products are used to maintain the performance of the cutting fluids and to rectify various kinds of problems.

A system cleaner is a water-soluble cleaner and dispersant for emulsions and solutions. System cleaners are only used in connection with a change of emulsion, rather than for regular emulsion maintenance. System cleaners kill bacterial and fungal growth, and also loosen microbiological slime and sludge.

Biocides are used to prevent uncontrolled bacterial and fungal growth.

Advantages and drawbacks of biocides
Biocides are added to kill fungi and bacteria. This has a positive impact, but incorrect handling could lead to side effects, usually in the form of allergic reactions in operators and service engineers. The risk increases if you add biocides on site and fail to dose or handle the chemicals in exactly the right way. Choosing a cutting fluid that contains biocide from the start and following the product’s handling instructions properly minimises the risk of side effects.

Here at FUCHS, we have developed different types of water-miscible cutting fluid for minimising the risk of side effects, bacterial and fungal problems in different ways.

Metalworking fluids do not normally produce any problems with foam. If foam does form, it is either due to a mechanical problem (e.g. the pump is sucking in air), or because the metalworking fluid has been contaminated with another liquid. Causes of foam problems could be soft water, too high an emulsion pressure, incorrect nozzles or system tanks that are too small.

Anti-foaming agents can be added to the cutting fluid in small amounts as a temporary measure, but it is important to identify and remedy the underlying cause of the foam. Otherwise the problem will soon reoccur.

Used to raise the pH of an emulsion. The pH should always be adjusted in connection with a production stoppage, and before using biocides.