- Tips on machining 2017/05/09 UP
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Tips on machining vol.9
How to make good use of water-miscible coolant
－Water-miscible coolant is a living creature－
- Tag
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- Coolant
With a recent trend in the shop floor towards faster machining for costs reduction, coolant is required to have a cooling capability in addition to a lubricating property. Before, water-miscible coolant, which boasts a good cooling capability, was inferior to oil-based coolant in lubricating property. However, the use of water-miscible coolant is on the rise due to its improved lubricating property achieved with additives and its lower fire risk than the oil-based type.
Water-miscible coolant is a living creature. Its deterioration causes many problems including lower cutting performance; rust on a product/machine tool; shorter tool life; unusual odor caused by decomposition; and health damage. So, many of you may find it difficult to handle and manage water-miscible coolant. Actually, we are often asked for advice about coolant handling, and there was a case where coolant in the tank foamed, which increased its volume and caused overflow into the factory floor.
The undiluted solution of water-miscible coolant contains oil as a main component and many additives such as a surfactant for dilution with water, antioxidant, anticorrosive, antiseptic, antifoam and extreme-pressure additive. Thus the most important thing for water-miscible coolant is the amount and proportion of each additive. Unbalanced additive amount and proportion decreases the performance of the water-miscible coolant. Therefore, proper handling and management of water-miscible coolant is the key to full utilization of the coolant while maintaining its performance.
First, we discuss how to manage water-miscible coolant. The coolant management can be divided into two parts: one is management of concentration and the other is management of pH (Hydrogen-ion concentration index). As the water in the water-miscible coolant evaporates, the coolant concentration increases in proportion to the duration of the use of the additives. The adhesion of the coolant to cutting chips also causes the imbalance between the amount and proportion of additives and decrease in pH, which makes rust more likely to form. So, it is recommended that you should periodically check the concentration and pH with a concentration meter and litmus paper. Moreover, the hardness of water may affect coolant conditions, causing foaming or unstable conditions. We cannot adjust or control water hardness because it varies depending on the area (the source of water). However, it is important to understand the controllable range of coolant.
When the concentration is high, you can maintain the concentration of the solution as well as the amount and proportion of additives by supplying highly diluted water-miscible coolant of the same type instead of adding only water.
If only water is added, the concentration will become weak, but the amount and proportion of additives will become imbalanced, resulting in the poor performance of the coolant.
Additionally, frequent coolant supply ensures a more stable coolant condition than one-time supply (e.g. supplying 15L twice a day is better than supplying 30L once a day). The pH of new water-miscible coolant is alkaline, but it becomes acid when the coolant is deteriorated. So the pH level can be very helpful to detect the performance deterioration of coolant.
Next is how to handle water-miscible coolant. Cutting chips and dust and particles in the air inevitably enter the coolant that has been used for a long period of time. As mentioned earlier, some coolant ingredients will be lost as they are carried away adhering to the surface of cutting chips, causing the imbalance in coolant ingredients. However, completely blocking the entry of these substances into the coolant is extremely difficult. Instead, it is important to take appropriate measures against the substances that have entered the coolant. We would recommend using a filtration device to eliminate chips, dust and particles. A filtration device separates foreign substances from coolant and returns cleaned coolant to the tank. As for removal of oil floating on a coolant surface such as lubricating oil, a device called oil skimmer can be used.
Oil skimmer
If a machine is not in operation for a long period of time due to a long vacation, etc., the coolant is also dormant under the condition where the temperature is likely to rise. This causes the bacteria to grow and the coolant to be decomposed. In another case, bacteria adhering to the operator’s body entered the coolant and multiplied due to a high temperature. To prevent such situations from occurring, you can take measures for controlling the temperature (e.g. by attaching curtains to the windows if machines are located close to them), or add a preservative to the coolant.
The useful life of water-miscible coolant depends on how well it is managed and handled. In other words, proper management/handling extends their life while improper management/handling shortens the life. Actually there are factories that have been using water-miscibl coolant for five years without replacement. The taste of ramen noodles served at a franchise ramen restaurant could be different from its franchise counterparts if the restaurant owner fails to manage their ramen soup.
For a company with multiple production sites operating in several locations, it is also important to pay attention to the hardness of water.
Please contact us by clicking the button below if you would like to consult with our engineers about coolant.
The responsibility for the wording of this article: DMG MORI CO., LTD.
Figures quoted from: Technical Report by YUSHIRO CHEMICAL INDUSTRY CO., LTD.
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