TECHNOLOGY FOCUS

METALWORKING FLUID FORMULATION

PART 3 -  SEMI OR SYNTHETIC?

by Dom Ruggeri

February  2001:

My wife came in to help me move into a new office recently.  We were amazed at how much paper one collects in three years. She was happy to help and during the move she mentioned she knew what to get me for Christmas.

Weird Science
Christmas Morning arrives and I find a dartboard under the tree.  The card read “For your new office.”  I roared with laughter.  Back in the late eighties while working for a large metalworking formulator we elected to have an extended, beverage-enhanced lunch; someone’s birthday as I recall.  Under the escort of a designated driver, we returned to the lab late, about three sheets to the wind.  Anticipating a productive afternoon, we returned to our respective work areas.  A colleague who sat directly across from me had a dartboard mounted in the area.  Considering it unsafe to operate a computer in our present state, we decided to formulate a product by playing darts.  We actually managed to formulate a decent semi-synthetic fluid.  This formulating masterpiece passed all the standardized tests and for a brief moment looked like it would be a huge seller.  However, we never sold a drop of the proposed formulation.

Semi-Synthetic Basics
When I was still a novice in this business, I was taught that a semi-synthetic was a formulation that contained between thirty to fifty percent active ingredients and the balance water.  This made perfect sense however, today this is not the case since the term synthetic has taken on quite a few different meanings.  For example a semi-synthetic can be a mixture of mineral oil and some oil soluble fatty ester, or it can be a fluid containing a mixture of water, polyalpha olefin (PAO) with a fatty ester.  Confused yet? I hope not but I will admit that it can get quite confusing and if your not careful you could choose the wrong fluid for the job.

Let’s get back to basics and to do this I will formulate a simple semi-synthetic metalworking fluid: 

        Oil: Either Parafinic or Napthenic
        Emulsifier: Petroleum Sulfonate
        Emulsifier: Fatty Acid Soap
        Co-emulsifier: Surfactant HLB=8
        Coupler: Glycol ether
        Bactericide
        Fungicide
        Water (deionized or city water)


Semi-Synthetic Properties
Sometime back in the first article of this series, I mentioned that the raw materials could be similar and only the amounts would be different.  As you can see, I listed water as a major component.  The reason is that when you use a semi-synthetic the fluid is already an emulsion.  This micro emulsion has a particle size of less then one-micron.  Further, when this class of materials is diluted with water, the traditional milky white emulsion is not formed.  Instead you could get a transparent to translucent emulsion that will cloud as the working fluid is recirculated in your system.  Also in a previous article, I mentioned a concept called pH leveling.  This is when the pH of the working fluid drops as the solution recirculates in a central system.  This phenomenon is more pronounced with semi-synthetics.  As a class of metalworking fluids, they are also more likely to emulsify tramp oil, due to the increased amount of emulsifier needed to form a micro-emulsion in the neat fluid.  The above formulation is basic.  Depending on your needs and your fluid supplier’s formulation philosophy, the formulation will look different.  However, the above components will be there in one form or another.
                                                
Suppose we replaced the mineral oil with an ester or a PAO or a vegetable oil. Would this base stock replacement make our semi-synthetic a true synthetic formulation?  That answer lies with your fluid supplier and their product definitions, but a word to the wise: Question all products that claim to be “synthetic.”

This is a broad-brush approach to semi-synthetics designed to give you, the reader the flavor of what composes these materials. Any specific needs you may have should be addressed to your fluid supplier. They are the experts and will know how to meet your specific needs, as always if I can be of any help please feel free to e-mail me through the Magazine good luck to all in 2001.

Dom