TECHNOLOGY FOCUS

METALWORKING FLUID FORMULATION

PART 9 -  EMULSIFICATION BY THE BOOK

by Dom Ruggeri

October  2001:

In the late eighties to early nineties I was working for one of the major metalworking formulating houses.  I must admit all was going well.  Product was moving out the door with few if any issues. I was just waiting for the next shoe to drop.  We received a call from one of our major customers telling us that the tank truck of coolant we just shipped would not emulsify.  Now a fresh made product that will not emulsify is bad enough.  Compound this by shipping it to a major customer in a tank truck and well you get the picture.  Further, the same material in his storage tank would not emulsify.

The director of research made his opinion quite clear, "fix this at the exclusion of all else."  A technician and I worked on this problem for a good week to no avail.  At the end of the week I assembled the following facts:

1.   The coolant emulsified and remained stable in distilled water
2.   The coolant emulsified and remained stable in our tap water
3.   The product met all quality specifications
4.   The product emulsified and remained stable in the customer's tap water

The above facts clearly indicate that there is no problem with the material, but as we all know when a customer has a problem they will not buy into the claim that your product was made correctly.  Another week of work examining all possible options, and still no light at the end of this tunnel.  By now the customer is getting a bit annoyed, unless your talking to the salesman in which case your about to loose all the business and his first born male child.  I dare say that at this point in time I was out of ideas, we could not determine what the problem was since there was no problem we could readily identify. 

Another Friday meeting with the Director of Research and we had no progress to report.  I was not happy.  We did all the right things in the right order and came up empty; of course the laboratory manager was wringing his hands like the sky was falling, and to add insult to injury, it was my formulation. 

Throughout the meeting we discussed many ideas and theories. None held any merit.  Finally the director said, "I am open to any ideas."  I had one, "Gentleman", I began "since we can not find what the problem is we should determine what it is not and by elimination the problem will find us."  I was greeted by blank stares until the director spoke, "Of course," he said, "…eliminate the possible and what is left, however improbable, must be the cause."  True enough, we found that the customer was using recycled water.  They were breaking the emulsion and reusing the water.  A good idea, but the water-soluble portion of the coolant remained in the water and built up until my formulation could not emulsify due to the accumulated Total Dissolved Solids.

As everyone has been keeping up with our masterpiece (tic) I find that some explanation about emulsification is appropriate, such as what emulsification system works best in what systems, and how does one choose the best system.  There are many ways to emulsify oil for instance, you can go to an additive supplier and purchase an emulsifier package; just add oil and you have a soluble oil metalworking fluid.  A good approach, but suppose you need an EP additive, or a corrosion preventative.  Will these materials be compatible with your neat product?

With a premanufactured emulsifier package, your abilities to adjust for additives are very limited at best.  Often times a customer may want a specific additive in the formulation and you find it to be incompatible with the emulsifier package.  So you determine that you will have to make your own emulsifier.  The most common starting point is medium petroleum sulfonate, mixed with fatty acid amine soap, finishing up with a surfactant co-emulsifier. 

Sounds easy and as I am fond of saying it is not really rocket science but there are some guidelines one needs to be aware of:

The amount of Sodium Sulfonate depends on the type of product your going to formulate.

Soluble oils normally require 3 to 10 percent sulfonate to obtain emulsion stability.  While semi-synthetics, due to their high water content, may only require 3 to 5 percent Sodium Sulfonate.  However, the semi-synthetic may require a co-emulsifier.

The amount of fatty acid soap will vary depending on which fatty acid you choose, and the type of emulsion you desire.

For example:

    Oleic Acid: A very clean acid on average you may need between 2 and 5 Percent.

    Tall Oil Fatty Acids: A byproduct of the paper making industry, depending on the rosin content you may need between 3 and 7 percent of this acid.

Please bare in mind you will have to add the appropriate amount of amine to neutralize the fatty acid and form the amine fatty acid soap.  Further, the amount of amine will vary with which amine you select.  One more point, you are making a soap not an amide.  An amide is a reaction product that will yield different properties to our fluid.  More on that in another article.

Co-Emulsifiers:

These can range from the nonyl-phenol surfactant products to almost any surfactant you can imagine.  They are used in the range of 0.5 to 2.5 percent to control emulsion particle size and emulsion stability.  These are not always necessary.  It all depends on the type of product your formulating.

Once again this is a very broad-brush presentation to emulsification but it should give you a feel for how these things are developed.  As always, if I can be of any help please feel free to e-mail me at the magazine, at Feedback.

Good Luck
Dom