Industrial Lubricants are always a vast and interesting subject to discuss and share. Broadly Industrial Lubricants can be discussed in two verticals – one is, of course, Factory, Plant & Machinery [ FPM ] products like Hydraulics, Gear Oils, Compressor Oils, etc. Another is Lubricants used in processing. One of the most sensitive portfolios in the later segment is water extendable cutting coolants used in metal processing industries. Many technical publications and in-depth experiences are shared for the maintenance of cutting coolants. However, today’s effort is to address the maintenance basics of Soluble cutting coolants, either mineral-based conventional high oil content products or new generation semi-synthetic products.
Before going into maintenance, practices let us have a quick look at the composition and chemistry of Cutting coolants. New generation cutting oils are a complex combination of Lubricity components blended with Emulsifiers, Co-emulsifiers, Corrosion Inhibitors, Special Anti-wear chemistry to enhance tool life, and Biocides to prevent microbial manifestations in the coolant. So its power-packed chemistry is made stable by the formulator intended to be used as an Oil in Water Emulsion, typically in the range of 4 to 8% concentration depending on application type.
If we recall the maintenance issues, those are typically associated with Component Finish, Corrosion, pH drop, Bacterial Growth, etc. Let’s talk about the right maintenance practices in these contexts.
Its starts with water quality. For extendable water products on an average 95% in water content in the coolant. So the water quality in coolant has paramount importance, and we often forget this as we focus on product attributes.
Water used for making and top-up in coolant must have few basics
- Hardness below 50 ppm [ too soft water leads to foaming ].
- Chlorides and Sulphates should be below 20 ppm. These ions are the primary reasons for corrosion on metal parts.
- Should not have a bacterial load of more than 102 CFU. A higher level of bacterial load in water will make the emulsion prone to the accelerated growth of micro-organisms in case of contamination or abuse during the use.
- Last but never the least, coolant to be made with proper mixing facilities where Oil to be added slowly into water [ never the other way round ] to have a uniform dispersion of Oil in water.
Once water parameters are ensured, it would be critical to maintaining in-process controls during use.
Following are the salient points for good control of coolant and extended sump life
- The most important parameter of in-process control is Concentration which a handheld refractometer can easily check. The right Concentration would maintain the right alkalinity, i.e., pH of the coolant. The right pH level [ above 8.5 ] ensures the right level of corrosion protection, and it would also ensure that Microbiological manifestations do not occur in the coolant. A lower pH environment is conducive for the growth of Bacteria or Fungi. So just by maintaining the right concentration level recommended by Oil manufacturer, the user not only achieves the machining properties of lubrication but also ensures the health of the emulsion for an extended period of use.
- Apart from Concentration, tramp oil is another critical factor. The key to keeping the sump healthy is the timely and periodic removal of tramp oil floating on the surface of the emulsion. A skimmer or manual removal is important so that the floating tramp oil layer does not hinder the aeration of coolant in circulation. Else it cuts off the air to go into the coolant, resulting in Bacteria’s anaerobic growth. Machine shop identifies this growth as a bad odor coming from coolant, typically after a shutdown day called “Monday morning smell.” To prevent this, it’s important to keep the coolant free from floating tram oil typically comes from hydraulic or sideway lubricants, and keep the circulation on to avoid liquid stagnation.
These are some of the basics of coolant control, and I trust you could find these simple practices useful. I look forward to hearing about your experience, and please share your thoughts to enrich our learning curve.