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by Dom Ruggeri


Back in the early nineties a large automotive manufacturer was building a new machining center.  I was lucky I was assigned to the team charged with developing a coolant for this state of the art system.  I was eventually named team leader and we set about the work of developing a machine tool coolant of a quality to match the machining center.

I must admit I marveled at this new completely computerized system.  Using the latest tooling and technology they were able to control every move the machines made, thus insuring each cut, grind, and turn would meet specification every time.  The tooling was so new that the coolant had to be delivered to the work site at a temperature not exceeding 60°F.  If the coolant were delivered at a higher temperature it would cause excessive tool wear.  Therefore, this new coolant had to provide exceptional lubrication at 60° F, run very clean, have a stable emulsion, reject tramp oil, last for at least a year, and never foam.  Hey, if it were easy everyone would be doing it.

During the development process we had our share of miscues and really bad formulations.  When one of our special formulations was chilled to 60°F, a substance floated to the surface and quite a few jokes were made about its appearance.  As with all projects of this type, eventually the team was able to meet the customer’s needs.  Also, as with all high technology materials, this one carried a high technology price tag.

The customer was happy and the coolant performed as we promised.  Since this was such a large account, one member of the team went out to the site each week for the first three months just to make sure all was well.  It was my turn to go out, and as was the procedure I was to meet with the salesman and regional manager prior to entering the account.  I was informed that the head of purchasing was taking a tour of the facility today, if he asked me any questions I was to refer his questions to the salesman.  A wise choice.  After all, the account belonged to the salesman; any miscue on my part, he pays the freight.

My luck held for most of the day as the tour was heading south I was going north.  I actually felt I would dodge this bullet, but no such luck.  I was running a test at the far end of the system when I saw the salesman and the head of purchasing coming toward me.  We exchanged the usual pleasantries, before the purchasing manager proceeded to question me about the development process for this particular coolant.  Normally I would have been happy to answer any of his questions, however, he wanted proprietary information.  I dodged the questions as best I could.  When he pressed, I deferred to the salesman.  He flatly rejected the invitation to get the information from the salesman, calling him a “fool.”  Now I was mad.  That was also proprietary information!  Finally he got up in my face and said he could run this system using a soluble oil costing about $3.00/ gallon.  I was fuming but I could not let him know he got to me.  I told him, well, then you should do it.  The salesman was livid.  Not about being identified, but I just cost him this very important central system.  I caught real grief when I got back to the office.  I explained that with the requirements of this system, the soluble oil he described would give them so much trouble that the engineers would make him come back to us.  I was told I had better be right.  Four weeks and eight recharges later, the purchasing manager called the salesman and invited him in to discuss recharging the new system with our coolant.  The price went up $0.50/gallon and they gladly paid the increase.

I have yet to meet a coolant salesman that does not tout he has the universal coolant.  A coolant so good that it will do every job in the shop no matter how difficult at a concentration of 20:1 and leave no after taste.  I am sure there are coolants that can do every job in the shop, but it has always been my experience that the concentration is a critical parameter.  Another critical parameter is the coolant type.  Each type Soluble Oil, Semi-Synthetic, Synthetic, and Solution Synthetic is designed to do a specific type of job and the systems must be prepared.

The editor and I have been having this discussion for about 2 years now.  His feeling is that standard ASTM tests should be used to evaluate coolants.  I agree with him but only this far the ASTM procedures will determine which coolant is better than another, but only as far as that particular test goes.  In my experience, these tests will not predict how a coolant will perform in a central system.

So how do we match coolants to the job?

1.  Know the cost of a change over:

If a system is using a soluble oil and you want to change to a synthetic solution, there is a bit more involved then just changing the coolant, such as seals for example.  So there should be more involved then just a simple dump and recharge.

2.  Do a break-even analysis:

The new coolant may cost more but as you use it you will save money in the long run, with longer tool life, longer coolant life, and less system additives.  Each of these to name a few cost money Know when your savings will justify the higher price.

3.  After the coolant passes the ASTM screening do a shop test:

There is an old saying among coolant suppliers: “Does the customer want a coolant to pass the tests, or to work in the system?”  Answer both.  A coolant may look great in the screening but get it on the shop floor and it falls flat.  A shop test will yield valuable insight thus complimenting the laboratory testing.

4.  If it is not broke, don’t fix it:

The machine is running well with a semi-synthetic and you want to change coolant suppliers for whatever reason, by all means do so, but keep the coolant type constant.

Now what if you’re changing to a different much harder alloy? Then you may have to change coolant types.  Should you choose this route then be sure you are aware of all the system changes you will have to complete before the changeover takes place.  This practice will save you many headaches and downtime. 

This is a very broad-brush presentation to coolant selection but it gives you a feel for the things that must be considered before a changeover is attempted.

--It is hard to believe that it has been two years since my first article.  My thanks to you the many readers of Metalworking Fluid Magazine for all your support and good wishes, since it is you that enable and challenge us to move forward.  As always, if I can be of any help please feel free to email me at the magazine.

Good Luck & Thank You.