TECHNOLOGY FOCUS

SMALL SHOP MAINTENANCE OF METALWORKING FLUIDS
PART I

by Dom Ruggeri

July 2000:

In early May, I attended a seminar at the on Condition Monitoring. This Seminar was offered at the Society of Tribiologists and Lubrication Engineers (STLE) national meeting in Nashville TN. This particular seminar focused on the lubricating oils used in engines. Although each presenter said the same things one point was stated in every presentation, "The Lubricating Oil is the Life Blood of the Engine. Maintain the Lubricant Change as Needed and the Engine will Last."

Well, if oil is the lifeblood of an engine, it stands to reason the metalworking fluid is the lifeblood of the metalworking operation.  If the metalworking fluid is maintained properly, fluid related problems should be minimized.  How do you make this statement a reality?

Machine shops come in all sizes, from the huge automotive machining centers, to the small job shops.  The expertise in fluid control generally varies proportionally with the size of the shop. The large shop will have people and equipment dedicated to fluid maintenance, while the small shop may have only essential equipment, i.e. a pH meter and a refractometer, and only one person to control and maintain the metalworking fluids and that may not be his only job.

The Small Shop

 If the small machine shop has only a refractometer and a pH meter, how do we control the metalworking fluid using the above instruments?  The hand-held refractometer uses light passing through a sample of coolant and a prism to measure the concentration of the coolant.  The higher the concentration of coolant in the sample, the higher the refractometer reading.  Your metalworking fluid supplier should be able to supply a concentration vs. refractometer reading graph however, be sure that your supplier is using the same model refractometer you have, since different models yield different charts. Further, tramp oil will interfere and give you a high refractometer reading, resulting in a low concentration of other metalworking fluid components essential for optimum performance.

pH is a scale ranging from 1 to 14, 1 being very acidic and 14 being very caustic.  This concept applies to water solutions and emulsions only. The pH of the average water extendable metalworking fluid solution/emulsion should be no lower then 8.5 and no higher then 9.5.  Why? Microorganisms will grow and proliferate in a metalworking fluid if the pH is below 8.5, however if the pH is at least 8.5 or higher this environment does not promote microbiological growth.  If the pH is higher than 9.5 you will run the risk of dermatitis. The ideal pH range for a fresh coolant charge is around 9.5, and after recirculation for about a day, to level off between 8.7 and 9.0.

Record Keeping; I can not stress this enough, good records will give you good control, good control will help spot potential problems before these problems cause your metalworking fluid to fail. One central system feeding many machines means one set of records,-- easy.  Many single sump machines means more record keeping and more paper work, but it is necessary, perhaps more so then with one central system.  The reason is that every machine is different and each machine will have a different set of potential problems.

Now I have presented a lot of theory, let's put this theory to some good use in a typical study:

A maintenance mechanic in a small machine shop made the following measurements:

Machine 26

Most savvy metalworking people can see what is happening here but for the sake of this article we will analyze these data beginning with the refractometer readings.

1. The refractometer readings are increasing. Why?     A. Causes
          1. Tramp oil in the system
          2. Evaporation of water and drag-out of coolant
    B. Effects
        1. Incorrect high concentration reading concentration is read as a function of refractometer reading
        2. High concentration

2. The pH is dropping why?
    A. Causes
         1. Low concentration of alkaline materials in coolant mixture
         2. Microbiological contamination
    B. Effects
         1. Rust of ferrous parts and fixtures
         2. Potential for dermatitis breakout

Two potential problems, either one will cause a major headache; notice I did not mention odors. Let's analyze:

1. Although the pH is low, it can still provide some microbiological control.  However, it may need an addition of fresh coolant.

2. The concentration is climbing steadily. Check the coolant addition records. No additions, logical.

3. Check hydraulic fluid levels. Most small shops do not keep records of these additions.

We need to determine if the system is contaminated with tramp oil. This can be done with a clean four-ounce jar (or larger).

1. Fill the jar with coolant and using a ruler measure the total coolant height in the jar (about 4 to 5 inches).

2. Let the jar stand undisturbed overnight. An oil layer or a cream layer should separate. Using the same ruler measure the cream layer (say it is one half inch)

3. Divide the inches of oil by the inches of coolant you got yesterday.
       For example:    0.5 inch cream layer / 5 inches total coolant height in jar = 0.1
                            multiply by 100
                             0.1x100= 10%
   That will give you the approximate amount of tramp oil.

4. Take a sample from below the tramp oil layer and take a refractometer reading for concentration.  Say it is 2.5%

5. Shut down that machine and let the tramp oil rise to the surface.  Skim it off and add enough new coolant to bring the concentration back to 5%

Easy, right?  On paper it always is but without good fluid control and records this could have been a much bigger problem. To conclude I will leave you with these words:
    1. Test the metalworking fluid as often as you can, daily if possible.
    2. Keep good records and review your records often
    3. Report problems

I hope this helps.  In future articles I will explore other methods to control coolants including such topics as microbiological contamination and selective depletion. Comments and questions are always welcome so till next month, good luck.

Dom Ruggeri