COOLANTS help remove swarf, and cool and lubricate workpieces during machining. In optimum conditions, coolant is an asset to operations, but if the fluid’s condition deteriorates, the consequences can be costly and potentially dangerous.
“At the cutting interface where the tool engages with the work there are very high temperatures. What you are relying on is a consistent stream of coolant that has the same concentration and basically the same chemical make up,” Dimac Tooling general manager, Paul Fowler told Manufacturers’ Monthly.
“The moment you introduce something different into that process [such as a contaminant], the process changes and variations lead to inconsistent results...That can lead to premature tool failure. It can lead to changes in workpiece finish.”
Contamination also promotes bacteria growth, causing foul smells and posing a risk of dermatitis to workers who come into contact with the fluid, Fowler added.
ITW Polymer technical manager, Geoff Mahoney told Manufacturers’ Monthly the main contaminant was fugitive oil. “That’s oil from the gearbox on the machine, hydraulic oil from the hydraulics, or oil imported into the sump by way of some sort of corrosion preventative oil on the parts being machined. But there are also other contaminants, there is dust, dirt and debris that one would find around the workshop,” he said.
The first step to keeping coolants clean, Mahoney says, is to ensure residual pollutants are removed from the system before new fluid is added.
“We recommend the use of a biocide cleaner which is added to the old fluid for one shift prior to dumping...that helps clean out all the build up inside the sump and kills the bacteria so that one starts off with a fluid that is very low in bacteria levels, as low as possible, and the sump has been fully cleaned,” he said.
According to Mahoney, coolant type and quality also has a major effect on the fluid’s lifespan.
Coolants may be synthetic or oil-based. They may be biocide protected or bio-stable to resist bacterial growth. Biodegradable coolants are also under development by some fluid manufacturers.
Mahoney claims oil-based coolants are typically better than synthetics, which have been associated with problems such as rubber swelling, seal incompatibility and paint stripping.
He also claims bio-stable products, which have a natural resistance to bacteria and fungi growth, have a longer sump life than biocide protected fluids. “Generally, when the biocide has been depleted, bacteria begins to grow, the sump begins to smell and the machine coolant life is at its end,” he explained.
Fowler says regular maintenance is essential to maximising coolant life, but its frequency depends on the nature of the process. Some manufacturer get as little as six months from their coolants, while others may achieve two or even three years, he claims.
“For instance, some customers are using their CNCs 24 hours a day, seven days a week. Others might use them for half a day to a day, five days a week. Then there are different materials they’re cutting.”
Aluminium and cast iron are hard on coolants, giving off fine powders when cut. Cast iron also leaves sediment at the bottom of the coolant tank. By contrast, steel ships are much larger and off-cuts tend to be removed on the chip conveyor.
Fowler claims the interval between coolant changes can also be extended by using equipment such as oil skimmers and oxygenation units.
Fugitive oils float on the coolant’s surface, forming a blanket which prevents oxygen entering the coolant. This promotes bacteria growth and degrades performance. Oil skimmers drag the layer of oil off the coolant and out of the machine.
Oil skimmers are not new, but Fowler says new features allow oil to be separated more effectively from the coolant. “Previously these units would pull out a fair amount of coolant as well as oil from the machine. For environmental reasons, you don’t want to be throwing out coolant, and for cost reasons as well. These units now prevent that from happening.”
Oxygenation units are also becoming more popular, Fowler claims. These small pumps draw in air from the atmosphere and pump it through the coolant, aerating it and helping reduce bacteria growth.
Fowler has also noticed a move towards coolant processing systems. These portable units can be wheeled up behind coolant tanks and plugged in. A line dropped into the tank then pumps the dirty coolant out of the machine, filtering and aerating the fluid, then returning cleaned coolant to the tank.
Despite these advances, Fowler sees coolants ultimately being eliminated from machining operations. “There’s a trend to actually taking the coolant out of the machine and using another technology called MQL (minimum quantity lubrication). This is basically a very fine mist of vegetable oil and air to lubricate the workpiece...It has some limitation and there are some places where coolant is still necessary, but when you talk about the future of coolant, I think there will come a day when there won’t be coolants in the machine,” Fowler said.