Small Shop - Part 2


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by Dom Ruggeri

August 2000:

Coolant salesmen I know will tout how resistant their fluids are to microbiological attack.  What they don’t tell you is that once the fluid is in use how much maintenance is required to keep that bioresistance.  During my tenure in the metalworking industry I came to dread coolant microbiological problems.  Why? Because no matter what, the solution always involved dumping, cleaning and recharging the system.  A labor-intensive process resulting in overtime, loss of production, and disposal costs.  Needless to say this recommendation is a last resort made while running for the nearest exit.

Back in the eighties I was working for a major metalworking fluid supplier.  One day we received a telephone call from one of our larger customers who reported that the machine tool operators on second shift were having trouble breathing.  The next day I was at the customer’s site with the salesman in tow.  We had the typical meetings with the Industrial Hygienist, the plant superintendent, and various managers.  These meetings normally yield little insight and all they really accomplish is to assure all involved that you will investigate the problem, recommend solutions and work with the customer to find the root cause.  Having had the meetings the salesman and I set about our work.  Whenever I enter a new shop, I know that if I can taste the coolant then that shop has a serious misting problem.  Anyway, about ten minutes into our plant tour I began to feel tightness in my chest, "the mist" I thought.  I was half-right.

It has been my experience that if a shop has a problem, first shift will not notice it as much as second shift.  The reason is that the shop is at full force on first, and between maintenance and supervision, someone is always there to help solve a problem.  On the other hand second shift is not so lucky.  They had to call people in when a problem occurred and that is not always easy.  When we went back to the shop on second shift to talk to those people; we met an operator who was having trouble breathing.  Once again I felt my chest tighten up.  The operator took us to his machine where it was even more difficult to breath.  I opened the machine and found biomass hanging down everywhere.  The machines were badly infested with microbiological growth.  Further tests confirmed the coolant was destroyed.  I recommended a full dump and clean out while running for the door.

The above case could have been prevented with proper fluid maintenance and record keeping.  As we all know, most metalworking fluids are food for microorganisms.  Allowed to grow, they will cause problems such as odors, dermatitis, and rancid coolant, to name a few.  However, these all cost money to correct, and the most expensive of course, is dumping and recharging a system.  It should also be noted, that left unchecked, the potential cost is enormous, including machine damage, scrap, downtime, injured employees, lawsuits, escalating tooling costs, etc.  So how do we prevent these problems?

1.  Know your concentration and pH

2.  Test the fluid for microbiological levels.

Last month I wrote about pH and concentration control.  I said a pH 8.5 or higher will retard microbiological growth.  Further the concentration must be maintained at recommended levels so all additives can function as expected.  That is level one to reach the next level of fluid maintenance we must monitor micro levels.  There are many ways to accomplish this.  They range in cost from many thousands of dollars to fewer than thirty dollars.  Of course the cost of the instrument is not the only consideration, there's the people to collect and interpret the data, equipment maintenance, and the most costly question: "can the instrument tolerate a shop environment?"  Most high-end equipment is designed for research and is too sensitive for a shop.  What about petri dishes?  These will work but then you have to prepare a compound called agar: time consuming.

There is a product on the market called BF Indicators.  These are dip slides available from Troy Chemical Company.  These dip slides are relatively inexpensive and are accurate enough for shop floor microbiological control.  The fluid maintenance person fills the dip slide container half-full of the metalworking fluid to be tested.  Then the slide is placed in the fluid for about 10 seconds.  Dump the fluid back into the machine place the slide back into its container; store the slide at 80
° F for three days.  You can probably accomplish this by placing the container in a winter jacket pocket.  After three days compare the slide to the enclosed card and add biocide as needed.  The dip slides are already coated with agar on one side for bacteria readings and with a fungi coating on the other side so you can measure both bacteria and fungi together.  Of course you can build a box that holds an 80° F temperature or buy an incubator.  Either way it will be worth it to monitor the micro levels in your coolant.

How often should you check the microbiological levels in your metalworking fluid?  Once a week if possible.

Case Study: Machine 26



 Refractometer Reading


Fresh charge
























As you can see, there was a pH drop the machines were left idle over a weekend; further, a Monday morning order was detected.  What would you do?

1.  Add biocide and increase the pH with caustic.

2.  Add fresh coolant to raise the concentration to 5.0%

Both answers are risky, but number 1 is the more risky choice.  Ammonium is generated as microorganisms grow.  If you increase the pH above 8.5 quickly with caustic, the ammonium that is water-soluble will convert to ammonia, and you will get an undesirable ammonia release.  Option 2 will raise the concentration and slowly increase the pH.  It will give you a dose of biocide that may be enough to begin eliminating your problem.  One last point: over a weekend always let the coolant recirculate.  Stagnant coolant is the perfect breeding ground for bacteria and fungi.  Always add biocides according to your fluid supplier’s recommendation.  These materials are poisons and decisions regarding their usage are best left to the experts.  In conclusion remember: monitoring and maintaining your coolants is cost effective.

If you have any questions or comments regarding this article, please send your feedback to METALWORKING FLUID MAGAZINE and I will personally answer and help any way that I can. 

Good luck,