What you need to keep in mind when using water-miscible coolants

The quality of the water you use has a considerable influence on the functionality of your coolants. This is hardly surprising, as the proportion of water in emulsions is often over 90% and in solutions even in excess of 95%. But what are the main factors to consider?

The pH factor

One important parameter when using mixing water is the pH-value. A value of 7 is optimal, as the water will then have a neutral effect, but pH values of up to around 9 are still permissible as long as there are no other reasons not to use this mixing water. However, water with a pH value of < 6 is unacceptable. Water with such a low pH could in turn lower the pH value of the coolant emulsion, even when freshly mixed — with far-reaching consequences including reduced corrosion protection.

A pH value of 7 is optimal

The total hardness factor

Total hardness is also a crucial factor when it comes to ensuring optimal mixing water. It is one of the most important application parameters and has a considerable influence on quality. But why is this? If the water is too hard, this may cause the hardness components it contains to react with anionic emulsifiers to form poorly soluble compounds — known as lime soaps. This can result in clogged filters and deposits on workpieces and tools and in machines. Mixing water that is too soft is also detrimental to emulsions, as it encourages the formation of foam.

A hardness range between 5 and 20°d is optimal

How can you change unsuitable water hardness levels?

There are specific measures that can help, depending on the situation (either freshly mixed or after mixing).

Freshly mixed:

If your mixing water is too soft (< 5°d), we have a special additive you can use: Adding a hardener containing Ca2+ will change the alkaline earth content of the water. This measure is usually only required with freshly mixed preparations, as the total hardness of emulsions increases over time.

After mixing:

If the mixing water has a relatively high total hardness, replenishing the volume losses after mixing with demineralised or deionised water is the key to success.

Chloride and germs as additional influencing factors

You should also ensure that the mixing water has a low chloride content. Too high a value primarily has a negative impact on the corrosion protection behaviour of water-mixed coolants. Furthermore, the mixing water should not be contaminated with microbes. In this respect the requirements are the same as those for drinking water quality.

An overview of our guidelines for best results

Our tip: Ensuring that the composition of the mixing water meets specific minimum requirements will help you to achieve the best results. Our overview shows you the key data for machining at a glance:

Water components Metal machining
pH value approx. 7
Conductivity [µS/cm] max. 1.000-1.500
Total hardness [°d] 5-20
Nitrite (ppm) max. 5
Nitrate (ppm) max. 50
Chloride (ppm) max. 250
Germ count [cfu/ml] max. 10²

Daniele Kleinmann
Leiterin Produktmanagement

Telefon +49 2161 5869-45

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