Coolant maintenance / metalworking fluid maintenance: major factors
Most machine shop operators think of metalworking fluids (MWF, or coolant) as a necessary nuisance, something that blows chips off the part. In fact, the most important jobs for all MWF are keeping the tool cool so it lasts longer, and lubricating the tool edge so that it makes a faster and cleaner cut.
Today's MWF are a sophisticated soup of chemicals that all try to do the same thing, blend the best properties of oil into the best properties of water. Along the way the compounders who make these MWF try for other goals as well: rust inhibition, tolerance of a wide range of water hardness, ability to work with many metals, and even environmental safety.
Three major forces are making us take better care of our MWF. First, coolants are becoming more expensive. Second, the increasing cost of labor means they are more expensive to take care of. Third and finally, the cost of disposal keeps increasing. In order to keep our coolants working properly for years we have to understand how they work, and why they go bad. The rest of these basics will cover the hows and whys behind MWF maintenance. Once you understand what is going on, you can expect to use a coolant sump for over a year before it will need changing or major maintenance.
Chemistry is where it all starts. MWF are a complex blend of many chemicals, whether organic or fully synthetic. The basic function of these chemicals is to allow oil to emulsify into water, but they also must be able to resist corrosion of steel, not alter the surface of aluminum, to maintain pH stability around 9 to 10, and to resist breakdown from the extreme heat of the tool tip.
Biology is where it all ends, because microbes are the real enemy of all MWF. Whether you fight infections with an antibiotic, or enjoy beer with your cheese, you have dealt with a microbe in some form. Given the right conditions and a little bit of time, your pristine sump can go from having only a few hundred microbes in every milliliter (about ten drops) to over a million.
Mechanics is what makes the MWF work, and what keeps them working. The pump forces fluids through pipes and onto the workpiece. The fluids then splash down into the collection sump. Oils from the ways, leaking seals, and from other sources ends up in the sump as well, eventually floating on top of the MWF. Chips and dirt from the machine also find their way into the sump, and this collection of fluids and particles presents a very different problem of coolant maintenance for every sump.
The following pages will cover these major factors in more detail. For even more information, we suggest the metalworking fluid papers and reports listed on this site.