Overview of Common Cutting Fluid Problems Caused by Water Quality
The importance of water quality to the application of metalworking fluids goes without saying. Based on past experience, the impact of water quality on the application effects of metalworking fluids mainly manifests in the following areas:
(1) The dilutions of micro-emulsions and fully synthetic fluids are originally supposed to be in a transparent or semi-transparent state. However, due to water quality issues, their appearance turns into a milky white, turbid state. Obvious soap floats to the surface, forming lumps and clumps. These adhere to machine tools, fixtures, and workpiece surfaces. Some mix with oil, making them extremely difficult to clean.
(2) As the usage time of the emulsion extends, tramp oil appears on the surface. In severe cases, oil-water separation even occurs.
(3) Even without the intrusion of external oils, such as equipment lubricating oil, there is still an un-cleanable layer of tramp oil on the fluid surface.
(4) When using various brands of metalworking fluids—whether imported or domestically produced, from large manufacturers or small workshops—rusting phenomena easily occur on-site.
(5) The fluid frequently needs to be replaced due to spoilage and rancidity, even when on-site management is relatively standardized.
(6) Foam easily becomes out of control. Even frequent additions of defoamers cannot solve the problem.
(7) Operators’ skin easily becomes rough or even develops allergic dermatitis.
How to Choose Dilution Water for Water-Based Cutting Fluids
All these problems can, to a certain extent, be attributed to “water.” When problems arise on-site, the influence of water quality must never be ignored. Even if these issues can be resolved by enhancing certain properties of the metalworking fluid products, it only treats the symptoms, not the root cause, and simply increases costs.
Therefore, on-site control of water quality is absolutely necessary! The emphasis on dilution water for water-based metalworking fluids is driven by practical, real-world needs. Poor water quality can cause problems like rusting and spoilage, preventing the metalworking fluid from fully exerting its functions.
Generally, the following types of water sources can be used for dilution:
(1) Tap water near the machine tool’s fluid sump.
(2) Treated well water, river, lake, or pond water.
(3) Recycled water from the waste fluid treatment process.
Various indicators of water quality will fluctuate with seasonal changes, water intake locations, and other conditions. Different water qualities may cause problems such as soap precipitation, spoilage, and rusting. Therefore, water quality must be tested regularly.
Ideal water quality conditions are shown in the table below:
| Item | Ideal Indicator Range | Description | Troubles Caused by Exceeding Standards |
|---|---|---|---|
| pH Value | 6.5~7.5 | Indicates the acidity and alkalinity of the water quality. | Acidic water: causes poor emulsion stability, corrosion, etc.
Excessively alkaline: causes instability, water stains, soap formation, etc. |
| Total Hardness | 30~100ppm | Measurement of calcium and magnesium ions in hard water. | Too low: foaming, skin roughening.
Too high: soap precipitation, rusting, spoilage. |
| Chloride Ion | < 30ppm | Generally comes from tap water disinfection products. | Too high: spoilage, rusting. |
| Sulfate Ion | As low as possible | Comes from atmospheric pollution like acid rain, etc. | Too high: spoilage, rusting. |
| Phosphate Ion | As low as possible | Widely sourced. | Too high: spoilage. |
| Ash Content | < 200ppm | White/brown scale left after water evaporates. | Too high: water stain residue, corrosion. |
