Get To Know Your H2O

Water represents more than 90 percent of a metalworking fluid solution. This makes water one of the critical components in any machining process.

CIM—Canadian Industrial Machinery asked metalworking fluid expert David Foster, Master Chemical Corp., to discuss the important role water plays in a shop’s MWF. Here is what he had to say.

Foster: Corrosion, residue, rancidity, foam, and almost any metalworking fluid performance problem can be caused by the quality of the water used in making the mix.

Untreated water always contains impurities, and the quality varies with the source. It may or may not contain dissolved minerals, dissolved gases, organic matter, microorganisms, or combinations of these that can cause deterioration of metalworking fluids.

CIM: What types of water can be found in a shop?

Foster: Seven types of water can be used in the mixing process. They are:

• Raw: Water that has not been processed to alter its hardness or dissolved solids content.
• Soft: Water with low calcium/magnesium content (less than 3.5 grains per gallon).
• Hard: Water with high calcium/magnesium content (more than 7 grains per gallon).
• Softened: Water that has been processed to alter its hardness. The calcium/magnesium ions have been removed and replaced with sodium ions, but there has been no reduction in the amount of dissolved solids.
• Deionized: All dissolved solids have been removed by ion exchange.
• Reverse osmosis (RO): Low-pressure “filtration” in which water is passed through a membrane to remove dissolved solids. Only about 93 percent of these solids will get trapped.
• Distilled: Water that has been evaporated, leaving solids behind.

CIM: What is good water from a metalworking point of view?

Foster: Good water has low levels of bacterial contamination. Tap water from a typical municipal treatment plant typically has between 10² and 10⁴ bacteria. Industrial well or ground water can have many times these numbers.

Good water is free of suspended particles. It is not unusual for suspended materials to be in water sources. We frequently find sand and other contaminants in well water and rust flakes in city water after fire hydrants have been flushed.

It also will have few, if any, dissolved minerals or other chemicals. The dissolved minerals (cations) can generate all types of problems chemically in the MWF.

CIM: Does the “charge” of the water affect the fluid?

Foster: Yes. Much of the performance-critical chemistry in MWF concentrates is anionic (has a negative charge). When these come into contact with cationic ions, they cause a reaction. Typical examples of anionic chemicals found in metalworking fluids are surfactants, emulsifiers, corrosion inhibitors, antioxidents, and extreme-pressure (EP) additives.

While there are many sources of cations in the machine shop, the single largest source typically is the water that is mixed with the metalworking fluid. Typical city water contains some amount of dissolved calcium and magnesium, and it is not uncommon to find a variety of metals, such as iron, zinc, and copper.

The reaction is most easily observed in soluble oils. Once the cations react with the anionic emulsifiers, the emulsion can become unstable and will tend to split. This can cause very high concentrate usage and poor product performance.

CIM: What affect do dissolved minerals have?

Foster: The amount of dissolved minerals depends on whether the source is near mineral deposits. Typically, lake water is of consistent quality, while river water varies with weather conditions.

Well water (ground water), since it seeps through minerals in the earth, tends to contain more dissolved minerals than either lake or river water. Surface water, however, is likely to contain a higher number of microorganisms (bacteria and mold) and thus may need treatment.

Some manufacturing plants will water supplied by a municipal water works, which maintains weekly and/or daily analysis of the water.

CIM: What should a shop test for in its water?

Foster: To estimate the effect of water on a metalworking fluid mix, a shop should measure the water’s total hardness, alkalinity, calcium content, chlorides, phosphates, sulfates, and pH.

In water analysis total hardness has the greatest effect on metalworking fluid because this hardness comes from dissolved minerals, usually calcium and magnesium ions.

CIM: What can hard water do to the machine?

Foster: When combined with some water-soluble metalworking fluids, hard water (higher than 7 grains per gallon) promotes the formation of insoluble soaps. The dissolved minerals in the water combine with anionic emulsifiers to form scum in the mixture. This can coat the inside of machines with sticky residues and clog reservoirs, pipes, and filters.

CIM: How does hardness affect the different types of metalworking fluid?

Foster: Soluble oils typically have the least hard water stability, therefore hard water has a more detrimental effect on them. Separation of the mix can happen quickly and reveals itself as an oil layer raising to the top of a fresh coolant mix.

Semisynthetics and full synthetics may not be visibly affected by hard water as they may be formulated with good hard water tolerance. Dissolved minerals can, however, react with ingredients other than emulsifiers, resulting in a change in the fluid’s performance.

CIM: How can a shop purify its water?

Foster: There are a few options for pure water.

• Water softening. Water passes through a zeolite softener. The softener exchanges calcium and magnesium ions (positively charged ions responsible for water hardness) for sodium ions. Basically, water that was rich in calcium and magnesium ions becomes rich in sodium ions.

  The total amount of dissolved minerals has not decreased, but sodium ions do not promote the formation of hard water soaps. Corrosive, aggressive negative ions are not removed by the zeolite and can continue to build up in the fluid mix and lead to corrosion problems or salty deposits.

  The use of softened water is not recommended for water-soluble fluids.

• Demineralization. A deionizer is used to demineralize water by removing dissolved minerals. This can be done selectively or completely depending on the type and number of resin beds through which the water passes. A two-bed resin deionizer process produces water of a sufficient quality for metalworking fluids as opposed to a more expensive mixed-bed deionizer. One hundred percent of dissolved solids are removed by ion exchange.

• Reverse osmosis also removes dissolved minerals by forcing water through a semipermeable membrane under high pressure. This process typically removes 90 to 95 percent of dissolved metals.

www.masterchemical.com