Changing the coolant: How to correctly renew the coolant in machine tools.

How to Replace Metalworking Fluid in a Machine Tool

Metalworking fluid (MWF) gradually accumulates machining debris, tramp oil, sludge and other contaminants during operation. Under unfavorable conditions, water-miscible MWFs may also develop microbiological contamination.
A deterioration in fluid condition does not always mean that the entire charge must be replaced immediately. First, check concentration, system condition, make-up practice, tramp oil and visible contamination.
If the fluid can no longer be restored to a stable working condition, or if the system shows pronounced biological contamination, a complete drain, system cleaning and preparation of a fresh working fluid are required.

When should an MWF be replaced

A complete replacement should be considered when the working fluid shows persistent deterioration that cannot be corrected through normal operating adjustments.

• significant accumulation of chips, sludge and other contaminants;
• a large amount of tramp oil in the system;
• persistent unpleasant odor and other signs of microbiological contamination;
• noticeable instability of the working fluid;
• normal working properties do not recover after the cause of the problem has been corrected.

Do not base the decision on a single symptom. Assess the overall condition of both the MWF and the circulation system.

When a complete replacement may not be necessary

A concentration that has moved away from the target value does not, by itself, mean that the entire system must be drained. First, measure the concentration with a refractometer and, if the fluid is otherwise in acceptable condition, correct it with a properly prepared make-up solution.
Excessive foaming is also not automatically a reason for replacement. It may be caused by concentration, water quality, intensive circulation, air entrainment or other system-related factors. Identify the cause before deciding on a full fluid change.

How to replace the MWF correctly

1. Drain the old working fluid
Remove as much of the old MWF as possible from the tank, pipelines and other accessible parts of the circulation system. Do not pour fresh working fluid over a significant volume of old contaminated fluid.
2. Clean the system mechanically
After draining, remove the following from the tank and accessible system components:

• chips;
• sludge;
• sediment;
• tramp oil;
• other accumulated contamination.

Pay particular attention to dead zones and areas where deposits or old fluid residues tend to collect. Mechanical cleaning remains important even when a subsequent flushing stage is planned.
Routine replacement and biological contamination are different situations
A routine MWF replacement does not automatically require an intensive microbiological cleaning procedure.
If the system shows clear signs of biological contamination, however, simply draining the old MWF may not be sufficient. Contamination can remain on tank surfaces and within the circulation system and then affect the fresh fluid.

Cleaning a system with biological contamination

A 10% solution of Biol Lemon may be used to clean a circulation system affected by biological contamination.

1. Drain the old MWF.
2. Remove as much chip, sludge, sediment and other contamination as possible.
3. Prepare a 10% Biol Lemon solution.
4. Fill the system and ensure that the solution circulates through the circuit.
5. After cleaning, drain the Biol Lemon solution completely.
6. Flush the circulation system with a 10% Biol ECO solution.
7. Drain the flushing solution.
8. Prepare the system for filling with fresh working MWF.

Protective gloves are required when working with a 10% Biol Lemon solution.
No universal circulation time is specified for the cleaning solution; it depends on the condition of the specific system.

Prepare the water for the new MWF

For water-miscible MWFs, water quality influences working-fluid stability, foaming and operational behavior. Consider hardness, dissolved salts, mechanical impurities and the consistency of the water source. Where relevant, the microbiological condition of the water should also be checked.
Well water is not automatically unsuitable for MWF preparation, but its characteristics may vary over time, so periodic testing is especially important for this type of source.
For more detail, see the Novohim guide on water preparation for metalworking fluids.

Prepare the fresh working MWF

A water-miscible MWF should be prepared separately at the concentration required for the specific machining operation. Add the concentrate to prepared water while mixing.
The working concentration must be selected according to the recommendations for the specific MWF and the actual machining conditions. There is no single concentration that is suitable for all products, machines and operations.
After preparation, verify the concentration with a refractometer in accordance with the recommendations for the specific product.

Fill and start the system

Fill the cleaned system with the prepared working MWF and start circulation. Once the fluid has mixed and passed through the system, check:

• actual concentration;
• appearance of the working fluid;
• stable circulation;
• whether excessive foaming occurs;
• whether significant residual contamination remains.

If problems appear immediately after replacement, do not automatically increase concentration or add auxiliary products. Identify the cause first.

What to monitor after replacing the MWF

During operation, monitor concentration, general fluid condition, chip and sludge accumulation, tramp oil, foaming, and changes in odor or appearance.
For make-up, it is preferable to use a pre-prepared solution at an appropriate concentration rather than compensating for volume loss by adding water or concentrate without control.

Common mistakes when replacing MWF

Filling fresh MWF into a dirty tank. The new working fluid immediately comes into contact with old deposits, sludge and other contamination.
Only draining the fluid when biological contamination is present. Contamination may remain within the circulation circuit and on system surfaces.
Skipping chip and sediment removal before flushing. Chemical flushing does not replace mechanical cleaning.
Using unchecked water. A problem may develop immediately after the fresh MWF is introduced.
Preparing the working fluid without concentration control. A concentration that is too low or too high may impair MWF performance.
Trying to solve every problem by increasing concentration. The actual cause may be water quality, contamination, circulation, air entrainment or the condition of the system itself.

FAQ

How often should the MWF be completely replaced?
There is no universal interval. It depends on the specific MWF, operating regime, machine condition, water quality, system contamination, maintenance and other operating factors. The decision should be based on the actual condition of the fluid and the system.
Does the system need to be flushed every time the MWF is changed?
The tank and accessible system components should be cleaned of chips, sludge, sediment and other contamination. The intensified cleaning procedure using 10% Biol Lemon is intended for systems with biological contamination and should not automatically be used for every routine replacement.
Can fresh MWF simply be added to the old fluid?
Regular make-up is a normal part of operation when the fluid remains in acceptable condition. However, if a complete replacement is required because of significant contamination or fluid deterioration, simply adding fresh solution will not correct the underlying problem.
What can be used to clean a system with biological contamination?
A 10% Biol Lemon solution may be used. After cleaning, drain it completely and flush the circulation system with a 10% Biol ECO solution before preparing the fresh working MWF.
How should concentration be checked after replacement?
A refractometer is used for routine control of water-miscible MWF concentration. Readings should be interpreted in accordance with the recommendations for the specific product.
What should I do if the fresh MWF starts foaming heavily?
First check concentration, water quality, mixing procedure, circulation, delivery method and possible air entrainment. A defoamer should be considered only after the main cause of the foaming has been checked and, where possible, corrected.