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Ask the Expert Question-and-Answer Archive by Ron Joseph July, 2007 Curing of MIL-DTL-64159 Polyurethane in Fluid Line Q: We now mix MIL-DTL-64159 Type II Green 34094 in a Cyclomax mixing system, our activator V93V502 causes problems through blockages. Is a solvent available which will keep the activator diluted when the Cyclomax is not in use? We now use Zylene but the activator will still go hard after a number of days within the system. We wish to use the solvent as a flushing product and leave in the system over the weekend, so we need a product that will not deteriorate the machine, the majority is stainless steel. A: MIL-DTL-64159 water-dispersible (WD) CARC is a two-component waterborne coating. I’m surprised that the curing agent (activator) is hardening in the fluid hose, because frankly you should be able to leave it in the line without it hardening. Of-course, once it is mixed with the base, Component A, it will harden within 4-8 hours unless you flush out the mixed coating with water. My guess is that your fluid hose is not airtight and that atmospheric moisture is getting into the line. Component B, the curing agent (activator) is very sensitive to moisture. Assuming that xylene is the correct solvent for Component B, it MUST, I repeat MUST be moisture free. Most solvents contain trace amounts of water and unless you purchase a pure grade, this could well be the cause of your problem. It is OK to use a commercial lower grade solvent to flush out the fluid hose after painting, but if you intend to leave the solvent in the fluid line over a weekend, it must be moisture free. In summary, I suggest that you check all the connections from the original container (5- gallon paint, 55-gallon drum or whatever you purchase) all the way to the Cyclomax mixer. There must be no air leaks. If necessary, use stainless steel tubing and airtight fittings, even if they are expensive. If you do this right you will not need to flush out the system at the beginning of the weekend. Also, consider using a nitrogen blanket or a desiccant over the headspace of the curing agent in the holding container. Sherwin-Williams or your equipment supplier should be able to assist you with this. Regards, Ron Joseph |