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Degrading RTV mold


nugundam93
04-28-2015, 02:45 PM
Short background - About 2 years ago, I've made a RTV mold for some 1/24 brake parts (sorry I don't have much info about what kind of RTV it is, except that it's RTV 524 from this one: http://polymerprod.com/main/3000/index.asp?pageid=126047&t=molding). A few weeks ago, while making my latest batch of recast brake parts, I noticed that the rubber felt rather spongy (for lack of a better word) instead of the usual firm and springy. Worse, some RTV actually easily came off and were attached to portions of the recast parts (I use 2-part epoxy and have never had RTV coming off with the recast). Oh, and weather here can get hot and humid/hot and hot (hahahaha)/cold and humid/cold and dry as expected from a country in the equator.

So my questions are:

-How long is RTV usually expected to last?
-Does "store in a cool, dry place" apply with RTV too?
-How can we prolong the life of a RTV mold?

Thanks in advance!

kitbash
04-29-2015, 10:09 AM
I do quite a bit of casting, but I mostly use GI-1000 RTV, simply because it's cheap and easy to use. I generally get 50 good pulls out of a given mold, but there's a lot of factors. Using a mold release will help, because resin will actually tend to "seep" into the surface of the mold after so many pulls, and eventually that resin will make the top layer of rubber brittle and prone to cracking and crumbling. Also, most RTV's tend to naturally break down after a certain amount of time even if you don't use them. One thing you can try is to cook a used mold in the oven at about 150 degrees for a half hour or so; sometimes that will stabilize the mold and give you a few more good pulls out of it. It also depends on what kind of resin you use; certain resins are more benign than others, and I've noticed the ones that take the longest to set up usually treat the molds the kindest. The quicker, "hotter" resins seem to attack the RTV more aggressively.

Hope all this helps

nugundam93
04-29-2015, 11:34 AM
hmmm. so RTV usually only gives that number of pulls? i guess that does explain things. while I haven't done resin in a long time, i guess the 2-part epoxy i use also degrades the RTV that much too.

thanks for the advice! :)

MPWR
04-29-2015, 08:33 PM
RTV molds certainly do degrade, both with use and just time. There are of course many variables that determine how long a mold will last, and heat/humidity could be a factor. I would certainly guess that keeping them refrigerated might increase their useful life, but I can't say from experience. Putting a ripe banana in with them also might or might not help. :dunno:

nugundam93
04-30-2015, 12:53 PM
heat and humidity. oh no, we have that in tons and even more tons. lol. :D

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