Veteran machinists and experienced manufacturers often rely on smell to know when their machine tool’s coolant needs attention. Unfortunately, by the time coolant has developed an odor, it has likely already caused a number of costly, time-wasting problems, including poor part quality, prematurely worn tooling and tool holding, wasted coolant, and undue machine component wear.
From a shop’s water quality to how clean it keeps its machines, there are several factors that come into play for keeping coolant healthy and machining operations successful. To simplify the process – and avoid the smell test – shops should follow six easy steps to ensure they’re getting the most out of their coolant.
1) Start with good quality water. Many manufacturers don’t realize the importance of water quality until after they’ve tried several different brands of coolant and still experience issues like rusting tool holders. Water must be tested to detect detrimental substances; a common culprit is chloride, which is a salt, and at elevated levels can cause corrosion and rust.
2) Mix the coolant properly. In most instances, a ratio of 10 percent coolant and 90 percent water is sufficient, and two different types/brands of coolant should never be combined and run together. The accuracy of the mixture is critical, which is why a refractometer is important – inaccurate mixture ratios, usually the result of hand mixing, can lead to significant added costs. If the mixture is running too lean, shorter tool life is often the result, but if it’s running too rich and excessive coolant is being used, it can also contribute to shorter tool life. Plus, high concentrations of coolant will create a stickier fluid that creates gasket-eroding residue in the machine and gets carried out more easily by chips instead of being properly recycled. Meanwhile, without enough water, some coolants will foam up, which keeps the coolant from actually reaching the cutting zone, thus causing shorter tool life. This proves especially detrimental in drilling operations that rely on effective coolant for not only cooling but also chip evacuation.
3) Maintain the correct mixture going forward. Once a proper coolant-to-water mixture ratio is achieved, shops must then maintain it. During the course of normal machining operations, water in the coolant evaporates and some of the coolant itself leaves on finished parts and chips. However, to bring a concentration back up to proper levels, a shop should never add straight coolant to one that is too lean or add straight water to a mixture that’s too concentrated, as this could shock the coolant. Instead of replacing one or the other when needed, shops should replenish lost coolant and water together as a mixture, but one that is either more concentrated or leaner than the original mixture ratio to bring the coolant in the machine back to the optimal 1:9 concentration ratio. This ensures a consistent and harmonized mixture.
4) Keep the sump maintained. To do so, shops must minimize tramp oil. Some coolants are actually designed to reject tramp oils and push them to the top so that they can be easily skimmed off the coolant’s surface. Studies have shown that tramp oils in a sump system begin to cause issues at just 2% concentration. This doesn’t just dramatically shorten tool life but can also provide a food source for bacteria growth. Once coolant is infected with bacteria, its stinks and can cause dermatology issues for operators. To avoid this, shops should use skimmers on individual machines’ coolant tanks to effectively and automatically remove tramp oils; for multiple machines, coalescers and portable centrifuges can make the process more efficient. And obviously, any debris will negatively impact coolant performance, so be sure to never discard cigarette butts or any other solid and/or liquid refuse into either a machine coolant tank or sump.
5) Make sure everyone has the training they need to handle coolant. Shops need to learn how to properly take care of their machine coolant – and make sure everyone on the shop floor is also trained on how to do so as well. Nine out of ten times, most individuals on a shop floor have never received formal training on proper coolant maintenance procedures. Luckily, many coolant OEMs/suppliers offer online and/or onsite training classes and presentations, so take advantage of these opportunities.
6) Keep machines clean. Shops should thoroughly clean machines, tanks and sumps on a regular basis. It is recommended that shops use special cleaners, often available through coolant suppliers, designed to be used in existing coolant while the machine runs for a period of days. This allows the machine to continue production during the cleaning cycle, after which shops pump out the coolant, thoroughly clean and wipe down the machine, flush it with a new weak coolant solution for about an hour, flush that out and refill the machine with a proper coolant mixture ratio.
Without proper and regularly performed machine tool coolant maintenance, the outcomes are costly and can range from wasted coolant and significantly shorter cutter and tool holder lives to hazardous conditions for operators and long-term machine tool damage. All of this can be avoided when shops follow the simple steps for maintaining their machine tool coolant and coolant systems.