cleaner bath. Even a softer water cleaning bath can become a hard water cleaning bath over time without proper condition monitoring of the bath. Knowing your water hardness is one of the first steps in selecting the right cleaner.
Soft Water: Hardness < 100 ppm (mg/L)
Typically, a standard mild alkaline to alkaline cleaner would be recommended. Due to the softness of the water, it is also critical to avoid using a cleaner with sequestrants or chelators as these may cause foaming problems. Selecting a cleaner designed for deionised water (DI) or soft water is critical to avoid foaming issues.
Moderate Hardness “City Water”- 100-250 ppm and Hard Water- > 250 ppm
In a cleaning bath, hard water can react with the alkaline builders and surfactants and form insoluble hard water soaps “soap scum.” These soaps can leave residue on parts, reduce the cleaner effectiveness, and even clog spray nozzles or build up on heat exchangers. Selecting a cleaner with a built-in chelator or sequestrants (if waste treatment allows), milder alkalinity and hard water stable surfactants is critical. Using a cleaner designed to clean at lower temperatures will help reduce water evaporation and help extend the life of the cleaner bath. Monitoring the hardness regularly is recommended.
Conductivity
Conductivity is a measure of electrical activity of an aqueous fluid in which the total dissolved solids (TDS) are examined. The conductivity is measured via a small electronic bridge in units of either microSiemens (µS) or micromhos (µmho). One microSiemen is equivalent to one µmho. The primary ions contributing to the TDS are calcium, magnesium, chloride, sulfate, and iron. Ion-specific electrodes exist for measuring these ions. There is a Volhard procedure for determining chlorides in emulsions and solutions which is typically a lab procedure.
While these can be naturally occurring ions, chlorides and sulfates are often carried into the cleaner bath from other fluids and compounds on the soiled parts. Iron can come from the ferrous machining and grinding process of steel and cast iron. Like high hardness, high conductivity can disrupt the ability of
the cleaner to emulsify the soil from the part. High conductivity, especially from chlorides and sulfates, can also lead to increased corrosion. Unfortunately, the only way to minimise high chlorides and sulfates once in the cleaning bath is through partial dumps. If the source of the ions is in the incoming water, it is suggested to treat the water (such as with reverse osmosis or deionisation) to remove the ions and to select a low residue cleaner. This is especially critical for high-temperature cleaning of stainless steels to avoid potential stress corrosion cracking. If entering the cleaning bath through soiled parts, it is suggested to use a moderate to alkaline cleaner with increased corrosion protection to prevent flash rusting and to perform frequent condition analysis to maintain chloride and sulfate levels.
Alkalinity and pH
In general, most water sources have a pH range of about 5.7-8.0. If using pH as part of a condition analysis program, it is important to understand the pH of the cleaner in the specific water source. The cleaner may have a different in-use pH in DI water versus hard water. The pH is generally not too much of a concern, unless it has a corresponding high alkalinity.
The alkalinity of the water is attributed to carbonates in general and typically, the harder the water, the higher the alkalinity. However, the main concern about alkalinity is when it is high enough to impact an alkaline titration. Cleaner concentrations are typically maintained through an alkalinity measurement. It is critical to subtract the alkalinity of the water from the total titration to ensure the alkalinity measurements are accurate.
Microbes Microbial contamination in cleaning comes from bacteria or fungus, either in the makeup water of the cleaning bath or as carry in from a water dilutable metalworking fluid on the part. Microbes can reduce the cleaner bath life, promote corrosion, destabilise the cleaner chemistry and cause foul odors. If left untreated, biofilms may form which can cause sludge build up, potential clogging of spray lines and reduced life of the cleaning bath. If microbe contamination is high, selecting a cleaner with higher reserved alkalinity will help promote cleaning bath longevity.
quakerhoughton.com
LUBE MAGAZINE NO.193 JUNE 2026
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