Checking and maintaining water-miscible cooling lubricants

For a long service life of your emulsion and solution!

According to the Technical Rule for Hazardous Substances, TRGS 611, the user is obliged to periodically check the coolant (cooling lubricant), including its documentation. It is recommended to check and, if necessary, adjust the parameters defined in the Technical Rules for Hazardous Substances on a weekly basis.

Examination according to TRGS 611

  • pH value
  • Nitrite content and
  • Concentration

Measuring the pH value
The pH value should be measured weekly using pH test strips. If the pH value is too high, the concentration of the cooling lubricant is often too high and can be adjusted to the correct value by dilution. A pH value that is too high can also be a sign of the contamination with alkaline foreign substances such as machine cleaners.

A low pH value is often noticeable by a strong odor. If the pH-value is too low, the mixing ratio is not optimal and therefore the concentration is too low; if the concentration is increased, the pH-value increases. Additional reasons for a low pH value can also be acid mixing in the water, such as entry of acid foreign materials (e.g. lemon cleaner) or a microbial infestation.

Measure nitrite content
High nitrite content in cooling lubricants, in combination with other ingredients, can lead to health risks. Weekly monitoring is recommended (TRGS 611).

Measure concentration
The concentration of the cooling lubricant solution or emulsion can be measured with the use of a hand held refractometer for cooling lubricants.

Steps for measuring the concentration of the cooling lubricant:

  1. Calibrate the refractometer by placing a drop of tap water on the prism and then adjusting the screw if necessary until it shows a Brix value of 0
  2. Apply a drop of cooling lubricant to the refractometer prism
  3. Read the Brix scale (refractive index) through the refractometer eyepiece
  4. Multiply the reading by the refractometer factor of that specific cooling lubricant

Calculation of cooling lubricant concentration:
Brix X refractometer factor of the cooling lubricant*
*each cooling lubricant has an individual factor, which can be found in the product information

In addition, a sensory inspection of the cooling lubricant is advisable, including documenting the results of the inspection. This is the simplest type of inspection, as no technical equipment is required. Changes can be detected at an early stage and counteracted if necessary. Modifications in the machining process, the machine and/or its environment, and the processed material can have a significant influence on the solution or emulsion in use.

Visual inspection

  • Change of color
  • A film on top of the cooling lubricant (e.g. foreign oil, emulsion separation)
  • Residue formation in the machine (e.g. processing residues, biomass)
  • Foam formation
  • Cooling lubricant dispersion and flow behavior

If the cooling lubricant has an unusual odor (e.g. pungent), this may be an indication of bacterial contamination.

The determination of the total hardness by using test strips (if possible) could also be a tool for the condition analysis of the water-miscible cooling lubricant, especially solutions. However, this value can be influenced by various disturbing factors.

It is recommended to create a machine-specific measuring protocol for water-miscible cooling lubricants, which is available on site and will be updated after each inspection. The measurements taken and any maintenance measures performed on the cooling lubricant should be documented here. It is also recommended to record any other changes.

With these actions, the service life of a water-miscible cooling lubricant can be significantly extended under normal circumstances.

Measuring water hardness
Water hardness should be measured weekly using test strips. A low water hardness is the result of foam formation in your machine and filter tank. If the water hardness is too high, the corrosion protection of the parts to be machined and the machine will be negatively affected.

Measuring the bacterial count (bacteria and fungi)
The bacterial count of the cooling lubricant is measured in our laboratory and expressed in colony-forming units. This test provides information on further actions required, such as further use or preservation or the replacement of the emulsion.

Measure nitrate content
The nitrate content should only be measured in the water used for preparation. Make sure that the water used for the preparation of cooling lubricant emulsions and solutions or for refilling does not exceed a nitrate content of 50 mg/l. A low nitrate content should be the desired result. The nitrate content of the preparation or refill water must be checked from time to time or requested from the responsible water plant.

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