Question: With regard to the question "Painting Cast Iron Valves" sent in from P.J., there are so many unanswered questions in my mind concerning his high rework rate that he says is close to 100%. It may sound strange, but I could feel the frustration in myself in not being able to evaluate his set up and solve his problem.
With regard to the question "Painting Cast Iron Valves" sent in from P.J., there are so many unanswered questions in my mind concerning his high rework rate that he says is close to 100%. It may sound strange, but I could feel the frustration in myself in not being able to evaluate his set up and solve his problem. Since he is using a two-part epoxy system, he probably does not have to be involved with any heat or low heat and therefore would minimize out gassing. What type of primer is being applied by his casting supplier? Two-part systems can have strong solvents involved and we don’t know what effect it has on his primer.
But, if his paint supplier cannot help him, I would urge him to get another source for his paint. Any knowledgeable salesperson in the technical coatings field should be invaluable to him. Also, as we both know, there are companies that produce application equipment for two-part coatings. They, too, can steer him in the right direction for a supplier and paint system. There is absolutely no reason for P. J. to be struggling along. He is on the right track since he has written and is asking for advice. Bottom line, get tough with your current supplier or get another source. Ask a lot of questions from equipment people and other paint people. S. B.
P. J.‘s problem is more a function of his casting supplier than his paint supplier. He knew that a two-component epoxy will provide a durable finish on his products. He didn’t know about compatibility of that material with shop primers. He just learned that the hard way. This is one of the problems with outsourcing components for manufactured products. P. J must specify a shop primer for the casting supplier to apply to his castings that is compatible with his topcoat. Shop primers used to have oleoresinous vehicles. Since these dry too slowly, the supplier probably switched to a modified alkyd. P. J.’s paint supplier is as clean as a hound’s tooth (I can’t believe I said that).
Better adhesion, enhanced corrosion and blister resistance, and reduced coating-part interactions make pretreatment a must.
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