Cracked Blanks ???

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woodwzrd

woodwzrd

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Joined
Oct 26, 2011
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450
Location
Baraboo WI
I cast two cholla pen blanks and one game call blank yesterday and they all came out of the tank cracked.

Here is what I did when I cast them...

1. weighed out the resin and mixed in my pearlexe pigment
2. Placed my cup of resin in a coffee cup of hot water to heat the resin as I mixed in the catalyst
3. Mixed in 10 drops of catalyst per ounce of resin (the can calls for 14 drops).
4. poured resin into the mold slowly in one spot letting it seep into the cholla.
5. Placed molds into pressure tank at 80# for 2 hours.
(It was about 95-100 degrees in my shop when I did this)

My guess is that the combination of the heated resin, high temp in the shop, and the amount of catalyst used resulted in to much heat and it cured to fast.

Any amount of input is greatly appreciated.
 
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not sure but for me that's lot of pressure for 2 hours

in this heat in Texas, my resin will gel in a few minutes in the open...and starts getting hard in 30 minutes +-

but I don't do pressure any where as much as I do vacuum
 
If it's PR, 10 drops per ounce is a whole lot. It would also create an enormous amount of heat. Even in the winter I only use 5 drops per ounce. The summer I use 3 or 4 depending on how hot it is.
 
If you used PR, that is way too much hardner IMHO. I use 3 drops per ounce to prevent my casts from cracking. Even when I previously dropped to 6 drops casting some snakeskin, it virtually jellied the skin from the heat and cracked at both ends.
 
I am casting with PR.

I stepped up my hardener to 10 drops from 5 per ounce because I had a batch of game call blanks come out kind of rubbery. They just felt a little different when I took them out of the mold and when I turned a couple, at the opening of the call the resin had quite a bit of flex to it and had a rubbery feel to it.
 
Also what type of pigment are you using? I've had that kind of rubbery feel before and it was due to using too much colorant.

10 drops is WAY too much unless your trying to cast thin sheets of resin. 3-4 drops is all you'll need. The cracking is probably due to the extreme heat added by the amount of pressure on top of it all.
 
ed4copies said:
How old is your resin and where has it been stored? (what temperature extremes)
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The resin is fairly new. It has been stored in my shop which lately has been ranging in the 90's for temp but nothing lower than 70 since I bought the resin
 
Brooks803 said:
Also what type of pigment are you using? I've had that kind of rubbery feel before and it was due to using too much colorant.

10 drops is WAY too much unless your trying to cast thin sheets of resin. 3-4 drops is all you'll need. The cracking is probably due to the extreme heat added by the amount of pressure on top of it all.
Click to expand...

I have been using pearlex pigment powder and artist oil paint for coloring. When I use the pearlex I have been using about 1/4 teaspoon per 5 ounces of resin and more like 1/2 teaspoon of the oil paint when I use it.
 
Shop heat

I think it might be the heat in your shop.

Most resin manufacturer's stat that resin should be stored at standard conditions. These are a ambient temperature of 25oC ( 77oF) and moderate humidity.
 
woodwzrd said:
Brooks803 said:
Also what type of pigment are you using? I've had that kind of rubbery feel before and it was due to using too much colorant.

10 drops is WAY too much unless your trying to cast thin sheets of resin. 3-4 drops is all you'll need. The cracking is probably due to the extreme heat added by the amount of pressure on top of it all.
Click to expand...

I have been using pearlex pigment powder and artist oil paint for coloring. When I use the pearlex I have been using about 1/4 teaspoon per 5 ounces of resin and more like 1/2 teaspoon of the oil paint when I use it.
Click to expand...


Definitely not the pearlx in this situation. My money is on the oil paints. I've used it before by different company's and they don't all work the same. If you looking for solid non pearl colors maybe try the castin craft opaque dyes or the ones from UScomposites. They're made for PR. From what I remember with oils they take a bit of mixing to really incorporate into the PR.

Edit: I should have pointed out that I think the oils is what's causing the gummy flexing problem, not the cracking. That's most likely from too much catalyst, ambient heat (which won't be a problem once you drop the amount of catalyst), and pressure. If you're just trying to avoid air bubbles you'll only need around 40lbs for that.
 
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I did a pine cone casting this week, and poured 5 drops / ounces on a PR that I have it for one year and the result was ok so far, I've drilled and the inside was dry as well, it can wait to turn it, I agree 10 drops is too much
 
I have to agree with Brooks on the oil paints as coloring agents, they are all made to different formula's. Especially artist's oil paints, they can be made to dry slowly or dry fast on the medium they were made for paper, canvas and other materials. They aren't made to color or tint resins. They could have inhibitors, retarders, levelers, dyers, flexors etc which all can effect the resins and the catalyst reaction.
With both hobby lobby and Micheal's selling the proper dyes for coloring the alumilite and PR type resins with their weekly 40% off coupons the colorant dyes will cost under $3.00 each.
It will save you dollars in time, materials, which will more than cover the cost of the proper colorant.
I have posted this before, YOU CAN NOT MIX WATER BASED POWDERED PAINT OR LIQUID with the resins. They are formulated to have water as a solvent not the solvent used in the resins. Use the proper colorants and you can cut down on the number of problems that can develop. As any search back over the last 5/6 months will show the number of problems people have had. And that just the people that will admit it.

Same as with the powder glitter, pearls and metallic's that is used in the pen blanks. Most are not what the name states. If you read the MSDS you will find they are mylar squares of assorted sizes along with colorants to give the effect they want. They also are "INERT" which generally means they will not affect the carriers(resins) or catalyst reaction. Since they are used in make up and eye shadows they have to be non reactive on the skin.

Use only the approved type colorant as they are Ph balanced for the resins.
And yes the Testor's works for most, but it still has materials that can affect the resin mix. And what they are charging now for them, and the amount you might have to use to get your effect it might be cheaper to use the correct colorant.
:clown:
 
I've had those rubbery type blanks before. Just put them in a toaster oven. It may take more time than normal, but they will eventually cure.
 
Thanks for all the replies guys. I am going to give it another try today with much less hardner.

I am also going to ditch the oil paint. I was not real happy with the way it mixed with the resin anyway.
 
Thanks again for all the advice and comments. This casting is both addicting and frustrating all at the same time but I am really loving it.

I just did two more cholla blanks and four 3/4" round blanks with 4-5 drops per ounce and it was already jelling after about 10 minutes. I will report back with the results in a few hours.
 
woodwzrd said:
Thanks again for all the advice and comments. This casting is both addicting and frustrating all at the same time but I am really loving it.

I just did two more cholla blanks and four 3/4" round blanks with 4-5 drops per ounce and it was already jelling after about 10 minutes. I will report back with the results in a few hours.
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Tonights cast was a success. I did two sets of two blanks. It is amazing how much resin that dry cholla will suck up under pressure. I will post up some pick tomorrow after I get a couple pens turned.
 
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