Water used as coolant in CNC machines benefits from treatment to remove chlorine, dissolved gasses and inorganic mineral contaminations. A typical coolant contains 10% refrigerants and 90% diluting water. Water taken directly from the mains or a natural water source contains a variety of compounds ranging from sand and stone sediment to agricultural run-off and microorganisms. The composition of mains water varies from place to place and even at different times of the year, so it is important to know exactly what is going into your coolant water before you use it in a machine.

Waterborne compounds can cause severe damage to CNC equipment over time by inducing a build-up of rust. Therefore, we strongly recommend implementing a regular regime of tests throughout the year, alongside a water treatment system to remove common contaminants from the feed water.

Contaminants To Watch Out For

The following contaminants are the most harmful to CNC equipment. Keep a close eye on their levels in the feed water and take the appropriate action to limit their build-up.

Sulphate & Sulphur

Sulphate and sulphur levels above 40 ppm are enough to induce rust in industrial equipment.

Chloride & Chlorine

Chloride is ubiquitous in mains water due to its use as a purification agent. In general, levels of chloride above 20 ppm can cause rust when mixed with coolant, although some varieties of coolant are less tolerant to chloride. Check with your coolant supplier if in doubt.

Water-Soluble Minerals

Mixing coolant with water invariably causes some water evaporation to occur. This evaporation increases the concentration levels of many water-soluble minerals, including sodium, calcium and magnesium. At concentrations above 100 ppm, these common minerals have an abrasive effect on machinery, eventually leading to damage and reducing the machine’s working life.

How Clean Is Too Clean?

Can coolant mixing water be too clean? Yes it can, or rather it can be too soft. When too many soluble minerals are removed from water its pH level becomes more acidic. This can make the water corrosive and risk damaging your equipment. Furthermore, soft water can have an emulsifying effect when mixed with coolant, foaming and causing the coolant and mixing water to separate. To avoid these problems, try and keep your water hardness level between 100 ppm and 200 ppm.

Water Treatment Systems

The most popular water treatment systems for industrial plant are deionisation and reverse osmosis. Both can be used to treat water destined for mixing coolant in CNC machines. The system you use depends on the purity of water you require in the sector you operate in. For the food, food packaging, medical and pharmaceutical industries, we recommend deionisation for most processes, as this can potentially produce 100% pure water. However, for CNC coolant, completely pure water is neither desirable nor necessary, for the reasons we have discussed.