Ken Lincoln, the boat building whiz at the former Olympic Boat in Port Townsend used to complain that every time I went to a composites seminar, his workload increased. I think he was talking about in the late 80s when I learned at a MACM conference that post curing room temperature epoxy improves it’s properties, just like it improves those of exotic epoxies. One more job for him to do. Ken would also grumble about the best seminar at the last IBEX. More to do.
The best seminar at IBEX 2013 was the one on bonding to infused parts. The speakers were, and I think this is a hot link….
|Mark Cooper, Tom Cudmore, Jean-Pascal Schroeder, Bret Thomas|
It had an armload of information that changed the way I do laminating. First, infused parts are harder to bond to as the degree of cure is greater.
One change for me was the solvent cleaning of the part. Typically I have used a solvent dampened cloth to remove the sanding dust, and clean at the same time. Two for one.
Bad idea as the solvent can force contaminants into the sanding grooves or even the fibers. Solvent clean before sanding. One more job.
Also, the best solvents don’t flash off immediately as JB Carrell (right spelling? I forgot to get his card) of MAS epoxy reminded me. He has a Green Clean product that cleans better and flashes off much later. I will find that link when I get back to office.
Next, I always assumed that grinding or sanding the part was a one-time thing. You do it and it’s done. I was wrong.
One of the speakers anthropomorphized it something like this. “Imagine the electrons in the part are like kids at a rock concert. If you stir them up, they will raise their hands up. The electrons get excited by recent sanding and bond better, but will lose interest after a few days.” I knew that grinding would give a mechanical bond, but grinding or sanding just before secondary bonding also gives a chemical bond. That is a much better bond. Sorry Ken. That might mean grinding or sanding twice.
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When I worked at Goetz, Eric claimed that the process of prepping epoxy for secondary bonding was better served by use of a Scotchbrite pad on a die grinder rather than the typical sandpaper. He claimed the molecules were excited by the heat and produced a better bond. The PATTI tests I was involved with seemed to bear this theory out. Although I have heard contrary argument from voices I trust.