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by Dom Ruggeri

March 2004:

At one time or another, all of us have been on a central system charge-up.  You know; those field trips we hope for something interesting to happen.  Yet we pray nothing happens.  A paradox?  Not really.  Provided everyone has done their homework, all charge ups should be boring.

Back in the late eighties, I was working for a large formulating house.  To familiarize me with the product line and to introduce me to various system configurations, I was sent on many charge ups.  I arrived at a major heavy equipment manufacturer to supervise the dump and recharging of one of our twenty percent active semi-synthetic materials.  I must admit I was in awe at the size of these machines, and the parts they produced.

The central system feeding coolant to these machines was 260,000 gallons.  I figured that to be enough coolant to fill a small lake.  I met with the plant superintendent and expressed my awe at the shear size of this facility.  He chuckled and advised that this was a small facility in comparison to the others the company owned. 

The dump and cleanout was uneventful, as they knew how to maintain their systems.  I wondered who taught them.  I paid close attention to whatever the coolant maintenance supervisor said; it would come in handy later.  The charge up began and everything was normal.  The coolant and water mixed well, no pump problems, and no foam.  You normally expect a small amount of foam until the system get a bit dirty but not this time all was well I thought.

Since there were no problems that first night my confidence was building, but as is always the case, just when you think you have it all under control something comes along and bites you.  The next morning we had foam out the wazzo.  Why and where it came from I hadn’t a clue.  My only goal was to kill it before it became uncontrollable.  Fortunately, we always had a supply of defoamer on-site for just such an emergency.  The foam was quickly brought under control and all was well. 

Killing the foam was not enough.  I had to determine what caused the foam.  A full system survey revealed that at one point the coolant fluid flow hit a wall and made a ninety-degree turn.  This sharp turn caused the coolant to flow back on itself as it made the turn, thus aerating the system and causing foam.  This problem was systemic, not coolant related, so we had to develop a program of antifoam additions to control this unusual problem.

The words defoamer and antifoam have been around our industry for quite some time. 
Both words are used interchangeably and because of this, we lose the meaning of both words.  Therefore, let me define both words as follows:

Defoamer - A mixture designed to quickly eliminate and/or control foam.

Antifoam - A mixture designed to not only eliminate and/or control foam but to prevent it from building up.

Sounds easy and in reality it is.  We are all familiar with the bis-stearamide wax type defoamer.  This is a true defoamer.  The hydrophobic wax particle attacks the bubble surface causing it to rupture and the bubble breaks.  This material works quickly to destroy foam.  However, as this defoamer circulates through the system the filters can remove it from the coolant and the problem comes back.  Therefore, one must add this defoamer on a schedule to control the foam.  A hydrophobic precipitated silica dispersion functions by the same mechanism, and hence this defoamer must also be added continuously the control foam. 

Now let’s say the system has a 100-micron filter.  This will catch many of the most common and problematic coolant contaminates, including coffee cups, cigar butts, lunch boxes, micrometers, hardhats, and the like, but not a 2-micron defoamer particle.  A particle that size will pass through a 100-micron filter like a Heisman candidate through a calculus class.  Hence, it should last forever right?  Not so.  Although the particles are hydrophobic and float on the surface of the fluid, they will not remain there indefinitely.

The silica particle has a coating baked on, thus changing the surface chemistry from hydrophilic to hydrophobic.  This hydrophobic coating will react with the emulsifier package in the coolant converting the surface of the silica particle back to hydrophilic.  When this happens, the particle will drop like a rock and be useless as a defoamer.

The wax particle on the other hand, is hydrophobic naturally.  So it should last longer, right?  Wrong.  The wax surface becomes coated with the surfactants in the coolant, thus altering the surface chemistry of the wax particle from hydrophobic to hydrophilic.  Once again, the particle drops like a rock and is rendered useless.

One last point for the formulator when working with this class of defoamers; over time, you will see a precipitate in your neat product.  Now you know why.  It takes a bit longer in a neat product due to the lack of mechanical energy provided by the pumps in the central system but the defoamer will deactivate nonetheless. 

As always, should you have any questions please feel free to e-mail me in care of the magazine.  Till next month,