1. Corrosion:
A high pH provides corrosion protection for ferrous metals. The closer the pH is to 14, the less ferrous metals rust. Non-ferrous metals are amphoteric, meaning that the potential for corrosion increases with increasing or decreasing pH from 7. Aluminum is not susceptible to corrosion at pH levels between 6.5 and 8.5. The exception is magnesium (Mg), which is not susceptible to corrosion at high pH values. The pH response of other materials, such as nickel (Ni), chromium (Cr), and cobalt (Co), is highly dependent on the specific alloy type.
2. Metal Solubility:
The dissolution of metals into working fluids follows the same principles as corrosion (rust). Alkalinity strictly controls the amount of metal dissolved into the working fluid. While alkalinity is important, it must be tailored to the working fluid and its specific pH.
3. Emulsion Stability:
For traditional emulsions, increasing the pH of the working fluid results in smaller emulsion particles. Lowering the pH increases the size of the emulsion particles, which can lead to delamination. Smaller emulsion particles provide improved wettability and reduce the amount of carryover. Large-particle emulsions can improve the lubrication performance of mechanical fluids, but they also increase daily carryover. Adjusting the pH of the machining fluid, depending on the presence of contaminants in the fluid tank, can alter the fluid's ability to resist contaminants or its emulsification capacity.
4. Dermatitis:
The further the machining fluid's pH deviates from 7.0, the more likely it is to cause dermatitis. Generally, a pH <9.5 is recommended for machining fluids during operation. When skin is exposed to alkaline environments, the alkali in the fluid saponifies the oils on the skin's surface, causing dryness and even cracking.
5. Bacterial and fungal growth:
Bacteria and fungi can grow at any pH and in any environment. When the pH of a metalworking fluid increases, bacterial growth slows. Therefore, increasing the pH can reduce bacterial growth. However, fungi in metalworking fluids grow faster in highly alkaline conditions.
6. Compatibility with machine tools:
Extreme pH values, whether highly alkaline or acidic, can cause corrosion of machine tool components. Contact between dissimilar metals (aluminum or copper with steel or cast iron) can cause corrosion. At extreme pH values, elastomers (such as seals) lose their flexibility. Plastic windows can become brittle.
When using different types of metalworking fluids to process different metals, we recommend maintaining different pH values in the fluid bath to ensure optimal performance, maximize bath life, ensure adequate tool lubrication, and achieve excellent surface roughness on the workpiece.
