TECHNOLOGY FOCUS

SMALL SHOP MAINTENANCE OF METALWORKING FLUIDS
PART IV - FOAM

by Dom Ruggeri

October 2000:

          Back in the early 1990’s I was asked to formulate a metalworking coolant for a new machine center.  This machining center was designed to hold 120,000 gallons of coolant, with 60,000 gallons in three 20,000-gallon tanks and 60,000 gallons circulating in the headers.  In other words this system had to run twenty-four hours a day seven days per week.  Why?  Should this system ever be powered down, 60,000 gallons of coolant would flow back to the holding tanks flooding the basement.  Not a pleasant thought, further owing to the above the coolant must not foam.  “Impossible!  Those engineers have lost their minds,” I thought.  To add to the challenge, the coolant had to be kept at 50 degrees F because if the coolant was warmer then 60 degrees Fahrenheit tool life would be non-existent.

           Our formulating efforts were successful.  I found out later that the new machining center was manufacturing the Cadillac North Star Engine.  As is always the case, the coolant needed to be fine-tuned, and this project was eventually handed over to another chemist since I had moved on to other projects.  Things were going well, and about a month passes.  Then I get an angry call from the North Star engineer:  “The coolant is foaming all over the floor you better get out here and fix it now!”  Needless to say, the product manager and I were on the next plane.  When we arrived at the shop they had foam everywhere.  This was not right.  I couldn’t make that product foam, what happened?  Further, the salesman and his regional manager were there ahead of us.  I began to look around, listen to pumps, hoping to find a reason for the foam other then the product.  All the while the salesman is whining in my ear about this problem, but I kept my composure.  Eventually all four of us began to analyze the situation.  As we looked into the foamy tanks the salesman looked at me and whined, “You mean that foam does not scare you?”  My answer was quick, “When that foam grows arms and legs and begins grabbing people then I will be scared and not a second before.”  We decided to begin treating the system with a combination of defoamer and antifoam.  We managed to kill the foam and devise an antifoam addition program to keep the foam down. 

Foam is a dispersion of gas in a liquid medium, in this case air in the coolant.  It can come from many sources:

Pump Cavitation
Machine or System Design
Contamination
          a.  Floor Soap
          b.  Machine Cleaner
The Coolant

Any of these factors will produce copious quantities of foam.  Not only will this foam present a housekeeping nightmare; it will cause loss of cooling resulting in higher tool costs and increased scrap parts.  How? Well in order for your machines to make parts within specification, the appropriate volume of coolant must flow to the workpiece.  When the coolant is foamy there is entrained air in the liquid.  This entrained air reduces the volume of coolant coming in contact with the work piece, and the heat transfer capacity of air is far less than that of the coolant.  The result is not enough coolant to adequately remove the heat generated at the tool part interface.  Further, foam overflowing onto the floor presents a safety hazard.

How can the small shop solve a foaming problem? The first step is to investigate, assuming your shop is using the same coolant in every machine, ask if the problem is all over the shop? If the answer is yes, it is the coolant, and you should contact your coolant supplier.  Should the answer be no, then begin checking the machines that are foaming.  Normally the foam is mechanically generated and a simple adjustment is the answer.  Check the coolant concentration in that machine, if the coolant is too rich foam could develop in even the low foam coolant formulations. 

None of the above seem to solve the problem consider adding a chemical defoamer.  Many small shops have their own defoamer, some effective brew they make up onsite.  Other shops use mineral seal oil, kerosene, and various solvents.  These may or may not be effective.  Today’s metalworking coolant formulations are designed to meet many regulations.  This yields a very complex formulation, and introducing the above antifoams may effect coolant performance and quite possibly invert the system.  Contact your coolant supplier before introducing any chemical defoamer.

Antifoam vs. Defoamer, Yes There is a Difference.

I have always been amazed at how many people use these terms interchangeably to describe the same material.  Lets clear this up; a defoamer is designed to quickly knock down foam.  These are normally either wax or chemically treated silica particles dispersed in a carrier.  The solid particle attacks the foam bubble causing a rupture in the bubble surface and the bubble breaks.  However, these types of defoaming materials are not designed to keep foam away. 

Antifoam is designed to both knock down foam and keep it from coming back.  This is accomplished by using silicone polymers that have been chemically reacted with surface-active agents.  These antifoams will knock down foam at the surface and attack the entrained air under the fluid’s surface.  Further, antifoams will form a barrier on the coolant surface.  This silicone barrier prevents the foam from forming again.  However, as your fluid circulates in your machine the mechanical action will eventually emulsify the antifoam so you need to add more antifoam to keep the foam away. 

In conclusion if you’re having a foam problem:

Is the foam throughout the plant?
          Yes: call your coolant supplier
          No:   check for:
                   Contamination
                   Mechanical Causes
                   Coolant Concentration

As always when using any additive your coolant supplier will know how much you should add and how often.  As always it is pleasure writing these articles if I can be of any help please e-mail me at the magazine.

Good Luck,

Dom