Manual for water-soluble coolants

How to handle water-soluble products the right way?

1. System cleaning
Each time before refilling a machine that runs with an emulsion the system should be cleaned with system cleaner in order to remove dirt and bacteria. 24 hours before exchanging the old emulsion 0,5 – 2% of system cleaner are added. If the machine is filled with a fully synthetic coolant solution 1 to 2% of system cleaner are added depending on the degree of soiling. Work through another shift with this mixture, then drain it off. After flushing the system with clear water it can be filled with fresh coolant.

2. Mixing the coolant
Water-mixable coolants must be protected from frost during storage. Use tap water for mixing, never use warm water. Water containing a nitrate level of more than 50 mg/l (checked through test stripes) is also non-usable because of the risk of nitrite forming (see point 4). The water should have a hardness from 4° dH to 25 °dH ( 1). Water harder than 25° dH must be softened, soft water must be hardened (please contact us). The emulsion should not be mixed in the tank, please use clean, extra containers. Always put the concentrate into the water, never the other way around! Special mixers can be used to prepare the emulsion fast and easy.

3. Monitoring and maintenance of the coolant
When using water-mixable coolant a few checking intervals have to be taken in account: The concentration of the mixture needs to be checked by using a hand refractometer daily to weekly. Emulsions containing mineral oil can become thinner by the time which leads to a lower performance and less corrosion protection. On the other hand, the concentration of fully synthetic solutions and micro-disperse emulsions can become higher by the time which leads to oil mist and sticky residue in the machine. Emulsions must never be thinned with pure water, they will lose their stability. A very low concentrated emulsion has to be added to the used emulsion.

The pH-value is measured weekly using special test stripes. It should lie between 8,5 and 9,3. Products which are free of amines might have a pH-value down to 8,0 which is absolutely no problem. At a lower value corrosion might occur, at a higher pH-value there is a risk of skin irritation. Drastic decreasing of the pH-value could indicate a microbial contamination and therefore a biological degradation. Each month the number of germs should be checked, e.g. for bacteria, fungi or yeast. This is done either by a laboratory in the company or within a complete, standard analysis of water-mixable coolants by oelheld. A high microbial contamination not only causes bad smell, it also compromises the disposal of chips and the filtration as well as corrosion protection. The coolant can even be completely destroyed. Main reasons are ageing and not enough maintenance. For example backflow tubes must not be used for waste removal, and tramp oil has to be removed with an oil skimmer.

4. Nitrosamines
Nitrosamines are carcinogenic substances. They may occur in coolants which contain secondary amines when there are nitrite compounds. Nitrite compounds can come from, e.g. water containing nitrite or nitrate, bacteria, oxides of nitrogen in the air (combustion engine, welding etc.), even from machining nitrate hardened steel or material which was treated with corrosion protection containing nitrite. The TRGS 611 (2) prohibits working with coolants which contain secondary amines. However, since these compounds can also form during system operation a weekly analysis of the nitrite content is mandatory according to the government safety organization. If a limit of 20 mg/l (ppm) is exceeded and the coolant does not contain nitrosamine inhibitors, then a partial or complete change of the coolant is necessary or the concentration of N-nitrosodiethanolamine has to be measured. If the concentration is higher than 0,0005 % (5 ppm) the coolant needs to be changed. This does not apply when keeping the mentioned limit of nitrite or when using a coolant which contains inhibitors according to TRGS 611.

Further, the temperature of the coolant should never rise above 30 °C. It was monitored that nitrosamines were forming at higher temperatures. Also avoid decreasing of the pH-value under 8 because of the same reason (amine free coolants under 7,5).

Following amines can be found in coolants:

  • Secondary amines (e.g. diethanolamine, morpholine) are said to easily form Nitrosodiethanolamine. The TRGS 611 prohibits working with coolants which contain secondary amines.
  • Primary amines (e.g. monoethanolamine) are also nitrosable. However, they would immediately decompose as nitrogen and alcohol and do not form a stable nitrosamine. Today we know that primary amines are even able to inhibit secondary amines from forming nitrosamines.
  • Tertiary amines (e.g. triethanolamine) are nitrosable but do not form stable nitrosamines. However, under certain conditions (pH-value < 7,5) they can be reduced to secondary amines. According to TRGS 611 (4.4(3)) using a product which contains inhibitors or is free from amines is alright if the concentration of nitrite is higher than 20 ppm.

5. Metal wear – Metal ions
Due to the alkaline environment in the coolant ionic parts separate from fine particles during metal working; so the fine particles cannot be filtered anymore. This can lead to leaching of cobalt and nickel which are known to be allergenic, especially when grinding tungsten carbide. Aside from regularly checking the heavy metal contents it helps to use special products such as AquaTec 3101 (amine free). With those products heavy metal salts are bound in the grinding sludge and get neutralized.

6. Skin irritation
According to a study done by the government safety organization 95% of skin irritation when working with coolants are caused by wrong handling and 5% happen by chance. Hands must never be washed in the emulsion or solution because metal splinter, small grinding grains or even dust can cause fine injuries so that dirt or germs are able to get into the skin. Good cleaning, drying und special care are mandatory in every break and after work to repair the acid protective layer of the skin. Our product range offers the right products.

7. Disposal
Disposing old solutions and emulsions has to be done by certified waste disposal companies. As an alternative specially certified cracking systems can be used to split the emulsion into partially mineral oil and water. The mineral oil has to be disposed in accordance with the law. Everything stated above is based on today’s knowledge. Required auxiliaries for mentioned checking methods are also available at oelheld. If any further information is required please do not hesitate to contact us.

1 To convert into other units please use the following numbers as multiplier:
°e (English degree of hardness) = 1.25216338
°TH (French degree of hardness) = 1.78480457
2 Technical rule for hazardous substances

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