epoxie questions....

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rockaukum
Posts: 558
Joined: Fri Nov 03, 2006 9:23 am
Location: Placerville area

epoxie questions....

Post by rockaukum »

Okay here goes....
I spent the other day with a friend of mind. We built a prostethic for a guy who returned from Irac (lost lower leg). My friend works for the VA. WOW this is very cool stuff! Unfortunate as it may be. He is also a BC tele skier to boot.
He invited me to his shop to see how he does the layup process. All the computer stuff was done prior to me being there. In a nutshell: Computer takes pics of the leg, He puts a foam block into the CNC machine and it carves out an exact replica of the leg. We set the machined foam up on the vacumme apparatus and begin to wrap the various layers of material around it. He uses PVA bags inside and on the outside of the layup. For this persons devise he did not want carbon fiber so we used triaxel (i think) glass. Then misxed up the resin and poured in from the top. The vacumme pulled the resin (between the two PVA bags) from the top of the mold to the bottom.
Thats a long story just to get to my question. He used a resin that generated a significant amuont of heat as it set. It seems from what I have read on this site that you use a resin that does not generate alot of heat. (We pulled the mould out of the press in about 25 munites and it was done, ready for test fit and minor alterations.) Is there a reason for this other than a longer time to get things set up? Any insight would be great! My friend and offered to help with the layup when I'm ready, so I'm sure I'll work around his schedule. The resin he used is "eco-lam acrylic" (I think).
Again, any imput would be great and thank you all for this site and information!
rockaukum
Thomas
Posts: 3
Joined: Mon Dec 04, 2006 8:39 am
Location: 19067

Post by Thomas »

OK. All epoxy generates heat, but the faster curing epoxys will generate more. Another factor in heat generation is the size of the surface area that the epoxy is spread out over. A cup of mixed epoxy will generate more heat (and cure faster) than that same cup spread-out over a large area. You are correct, epoxy that cures that fast will be difficult to work with. Typically used epoxys will take any where from 9-12 hrs to be dry to the touch, and can take up to a week to reach most of its maximum strength (epoxy will continue to cure for months).
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