Coolant mixing and water quality
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The concentrate of water-soluble coolants for metalworking is miscible with water in most cases at a concentration of 4 to 12%. Manufacturers usually indicate the recommended concentration for different cutting operations and materials for each brand of emulsion in product information data sheets. For example, for EASYCUT UNI301 coolant, we recommend maintaining a concentration of 6–10% for turning and milling operations and 4–6% for grinding.
We must always remember that the main component (by volume) in the ready emulsion is water! Therefore, in a tank of 1000 liters at an 8% concentration, we will have only 80 liters of coolant concentrate and 920 liters of water. Accordingly, water quality has a significant impact on the quality of the finished emulsion, the lifetime of the coolant, the safety of equipment, and even human health.
The main parameters for water are:
Water hardness (salt content, including calcium carbonate)
The use of soft water (less than 8° dH) can lead to strong foaming.
The use of hard water (more than 20° dH) can lead to the formation of residues (lime soap), a decrease in corrosion protection, and degradation in the stability of the emulsion, resulting in a shorter service life for the coolant.
On one hand, the hardness of water depends directly on its source, but on the other hand, we can adjust the hardness in both directions.
To increase hardness, calcium acetate can be added to the working emulsion.
To reduce hardness, reverse osmosis or deionization is most often used to remove all salts and obtain distilled water.
For the preparation of the EASYCUT UNI I emulsion, we recommend using ordinary tap water (dH up to 30°). However, for daily (depending on consumption) top-ups, it is advisable to use prepared soft or distilled water.
The ideal scenario is described above; however, if it is not possible to use prepared water for coolant top-ups, EASYCUT UNI I is able to work with hard water, including for tank refills. We do not recommend exceeding the hardness of the emulsion above 60° dH.
Note: The salts contained in the water always remain in the machine's tank, as they do not evaporate like water. When using tap water (containing salts), we always experience a cumulative hardness effect. Additionally, in rare cases, rigidity may increase in the tank when processing aluminum alloys containing magnesium due to its leaching.
Another important quality parameter is the concentration of chlorides, which should not exceed 25 mg/l. A high concentration of chlorides can lead to corrosion of machine parts and workpieces, as well as a loss of emulsion stability (reverse decomposition into water and oil). Reverse osmosis or deionization can also be used to remove chlorides from water.
Cleanliness (presence of impurities, rust, or dirt)
Ways to check water quality:
Water hardness and chloride concentration can be measured in the shop using test strips. In many cities and regions, information on water quality is also available on the websites of municipal services responsible for water supply.
Proper preparation (mixing) of the emulsion:
In addition to choosing the right coolant and providing the workshop with quality water, it is essential to organize the correct mixing process. With proper mixing, we obtain a stable emulsion with fine droplet size.
The recommended mixing option — Automatic:
Automatic preparation involves using a mixer that can be mounted on a canister or drum/TOTE containing coolant concentrate. Water is supplied to the device (water supply, pump from intermediate container, etc.). After applying water pressure, the concentrate is sucked in and mixed with the water stream inside the mixer using the principle of the Venturi nozzle. The finished emulsion is then fed into the working area of the machine or container through the drain hose.
The mixers have an approximate concentration adjustment, which should be accurately set after installation by checking the real values with a refractometer.
Acceptable mixing option — Manual:
To prepare the emulsion manually, use an intermediate container and add the CONCENTRATE to the water during the mixing process (but not vice versa!).
With manual mixing, the concentration is adjusted during the process by periodically measuring with a refractometer.
To simplify the process, it is recommended to mark the intermediate container and add the concentrate through the measuring container.
For example, make a mark of 20 liters on the inside of the bucket and prepare a measuring container for the concentrate. By pouring 20 liters of water and 1.5 liters of coolant concentrate into a bucket, we obtain 21.5 liters of ready emulsion with a fairly accurate concentration value of 7%.
The concentrate must only be poured into the machine after it has been mixed in an emulsion.
Invalid mixing options (common mistakes 😭):
- Adding water to the container in which the concentrate has already been poured.
- Adding concentrate to the working area of the machine or directly to the coolant tank.
In both cases, there is a high probability that the concentrate will not be able to mix completely with water; it will partially remain on the walls of the container, tank, elements of the working area of the machine, or in the machine's filtration system.
At a minimum, this will lead to increased consumption, and at a maximum, it will result in increased droplet size (not visible to the eye) inside the emulsion, which will affect the effectiveness and durability of the coolant.
** Always multiply the values obtained on the refractometer by the refractive index indicated on the PIDS. For EASYCUT UNI301, the refractive index is 1.3.
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