what am I doing wrong....resin

[rsxse240]

So I'm trying to get some wheels cast using micro mark CR600 resin and alumilite RTV mold. I know I mixed the resin correctly, and the mold is just like the other 10 molds I've made (10:1 ratio firm and flexible). I can mix 1 ounce of resin and pour it into all of my molds at one time and all the molds turn out perfectly cast parts and the resin sets up and cures as expected except one mold. the resin in that mold won't fully harden and is really sticky, leaving residue on my fingers.

so any clues as to what's happening here? any of you other casters have this problem, and what did/do you do to fix it?

all of the molds have come from the same batch of RTV which is only about 3 months old, and the resin is only about 1 month old.

[rsxse240]

hello?

well I have taken it upon myself to just make a new mold...AGAIN!!! this wheel project I'm working on is a pain in the @$$!!! but it will be worth it. at least it better be.

thanks for all the replies....pffft

[p9o1r1sche]

Okay, it wasnt mixed good, or in the right proportion. If all the other pourings came out okay, what else could it have been?

[D_LaMz]

Same thing happened to me a couple of times, I think it's the mixing.

[rsxse240]

well the master part is sitting in fresh RTV, so hopefully it will come out better this time.

one thing I did notice is that I didn't have as much clear fluid on top of the white part (alumilite). if this turns out the same way, I'll be getting some from micro mark and trashing the rest of this alumilite junk.

I must say, alumilite sucks compared to the quality and quantity that you get from micro mark products.

[white97ex]

I use alumilite RTV and vagabond (i think) resin. I've had those flexibility bad casting issues, I found that I got those when the quantity of resin I mixed was small. But it would happen in all of my castings, not just one. I assume you are casting all of the parts from the same batch of resin? I would doubt that it is an issue with the RTV mold. You may try heating the mold before you pour. It sounds like the resin just isn't curing properly

[klutz_100]

When mixing resins, the proportions are actually critical and have little tolerances.

If you don't have the correct proportions of the 2 parts, the polymers will not have "partners" (I haven't got a clue about the actual chemistry involved) and therefore will not harden. This is particularly noticable when mixing small quantities. Are you measuring with scales or "by eye"?

Also, a thorough shaking of the 2 parts prior to mixing is important - this gets all the sediment well mixed in. After shaking lt it stand for a little while to let it relase trapped air.

[rsxse240]

I appreciate your advice guys, I am still quite new at this whole casting bit, but I do thoroughly enjoy it. haha, I actually have piles of parts just laying there for no reason other than practice.

Now about my resin. I have had absolutely no issues with the CR600 resin. every time I have cast (using those little 1 ounce graduated measuring cups) the parts have come out perfect, except for this one mold. I think I'll try heating it in some boiling water to see what will happen. it's been like a week since I made the mold, so I'm sure if it were going to cure at room temp it would have by now, but it is still not rendering usable parts. I have some water on the stove heating up as we speak.

cross your fingers!

and thanks for the suggestion!

[white97ex]

I would not use boiling water. Even if you held the mold in the steam you are going to get moisture build up from the steam condensing back to water. I would simply pop it in the microwave for a few minutes.

[tigeraid]

Thanks for helping him out guys, my customer's anxiously awaiting these so I can finish his project!

[foto_choppa]

microwave is best way to heat the moulds, faster than oven

[rsxse240]

yeah, I found that out the hard way. so I set the molds aside until today. I'll try the micro wave.

I also have some quick dry RTV coming from micro-mark, should be here this week. and if their RTV is as good as their resin, I'll be completely satisfied.

thanks again for the assistance, guys.

[kaho]

I thought microwaves only heat up objects with H2O within?

[rsxse240]

nope, what they do is aggitate the molecules in an object and the friction between the molecules creates heat. water heats up faster because the molecules are not as densely packed. metal reflects the micro waves, and creates a sort of feedback, that's why you see lighting bolts and crazy light shows when you put tin foil in there.

oh and btw, thanks for the micro wave tip, I saved the mold, and it works great now. I guess the heat cured the rest of the RTV or something, because the mold feels a bit more firm now. I tried pouring some more resin in using a much larger amount (1oz:1oz) and it hardened much more quickly, has a MUCH better feel to it, and is REALLY bright white, where as before when I was mixing 1/4:1/4 or 1/2:1/2 it would turn out slightly creamy looking, not so vivid white. the down side to the proper mix is that the resin is a lot more brittle.

thanks for the advice! John, I'll have your parts in the mail by monday I PROMISE!!! I'll throw in a few extras as a show of good faith, since I took so freakin long on these wheels. I am SO SORRY about that man.

[white97ex]

How thin is the part that you are molding? One thing I also noticed was that thinner parts don't cure as fast and have a tendency to stay gooey