Problems with resin casting

Ytierian · Post by **Ytierian** » Fri Aug 03, 2007 5:16 pm

Ok, I'm trying to cast my own Bussard Domes for the AMT-E

I'm using Alumilite Water Clear.

Here's my problem; this is with new cans of resin and catalyst.

1st cast, adding transparent red dye; mix 50/50 by weight (yes, I have a gram scale) according to instructions; mold is pre-heated; pour went fine; wait 2 hours (more than the 30-60 minute de-mold time they recommend) pull apart the mold.... it's still gooey and flowing

Toss that cast

2nd cast; no dye this time; preheat mold; mix; pour went fine; wait 27 hours; pull mold apart.... it's STILL gooey and flowing

What the heck is going on? Should I toss the Alumilite and try something else?

Basement sits at 75 degrees (24c) and 40% relative humidity

HELP!!!

Ytierian

macfrank · Post by **macfrank** » Fri Aug 03, 2007 6:58 pm

The clear Alumilite that I have sets very quickly. The molds have to be pretty warm; 120F or so.

What are you using for a mold? I used their RTV mold material and it worked well, but sucked for other clear resins (like Envirotex). Try demolding as soon as it hardens.

Frank

Ytierian · Post by **Ytierian** » Fri Aug 03, 2007 7:11 pm

Yes, I'm using their RTV with release, and I'm warming the mold in a 130 oven for 10 minutes

Problem is, it NEVER hardens..... the second cast is still down there, flowing all over the scrap cardboard I put it on.

DX-SFX · Post by **DX-SFX** » Fri Aug 03, 2007 7:27 pm

Epoxy.

Treadhead · Post by **Treadhead** » Fri Aug 03, 2007 7:56 pm

Are you covering up the mold opening? I understand this can cause problems by not letting heat escape. Condesation or something happens that doesn't let it cure completely.

Also it is possible you might have some contaminant in the mold. I'd wash it out completely.

The other possibility is that you have a bad batch of resin.

Ytierian · Post by **Ytierian** » Fri Aug 03, 2007 8:08 pm

>Are you covering up the mold opening? I understand this can cause problems by not letting heat escape. Condesation or something happens that doesn't let it cure completely.

Nope, leaving the pour and overflow holes open for expansion and bubble release (if needed)

>Also it is possible you might have some contaminant in the mold. I'd wash it out completely.

Did that after the first failure - IPA wash, pat/air dry

>The other possibility is that you have a bad batch of resin.

That was my (regretable) opinion, but was hoping it was something else

Ytierian

macfrank · Post by **macfrank** » Sat Aug 04, 2007 12:13 am

I'll go with the bad resin batch. I tried the Alumilite in a "cold" mold and it took longer than usual to fully cure (the exterior stayed tacky for a while) but it did cure solid within hours.

Have you tried it in a warm mold without their release agent?

Chacal · Post by **Chacal** » Sat Aug 04, 2007 1:18 pm

Heve you tried pouring a (little) bit of resin into a test mold (like a shallow cup made out of aluminum foil)? That'll tell you if the problem is with the mold or with the resin itself: if the resin hardens (don't worry/care if it doesn't come off the "mold" -- you want to see if it hardens), the problem is with the mold/release agent/temperature... If the resin DOES NOT cure, it is a bad batch.

DX-SFX · Post by **DX-SFX** » Sat Aug 04, 2007 1:19 pm

Epoxy.

Ytierian · Post by **Ytierian** » Sat Aug 04, 2007 8:22 pm

>If the resin DOES NOT cure, it is a bad batch.

Well, there was some left in my mix-pour cup that I left on the work table.... it's been 54 hours now and even THAT is still gooey.

I've given up on the Alumilite - I can't even find specs on it anywhere - ordered some Smooth On.... we'll see how that works

Ytierian

macfrank · Post by **macfrank** » Sun Aug 05, 2007 12:27 am

Ytierian wrote: I've given up on the Alumilite - I can't even find specs on it anywhere - ordered some Smooth On.... we'll see how that works

Ytierian

I hope you've seen this thread with my experiences in clear cast resins. Envirotex will work in Smooth-On oomoo molds, but will stay very tacky in the Alumilite RTV molds unless you age the molds by baking them.

Envirotex has the advantage of being fairly cheap and easy to use, and it takes a while to set up, so air bubbles have plenty of time to rise to the surface.

If you're making a thin clear shell, you may want to consider clear acrylic. You can buy it as a fake fingernail repair kit in almost any drugstore. the stuff is expensive and one of the components stinks, but with a little polishing, it can be made glass clear.

Frank

Shinnentai · Post by **Shinnentai** » Mon Aug 20, 2007 5:10 am

Hola. Thought I'd pop back in to mention this: I've found an easy alternative solution to the EnviroTex/Alumilite problem. It was one of those "why didn't I think of that waaaay back then" head slapper things (I'll bet it's occured to others before me).

Give the inside of the mold a coat of Future before pouring.

The acrlyic acts as a barrier, preventing whatever's in the Alumilite from adversely effecting the EnviroTex (and protecting the mold from the resin too. Nifty!). This also eliminates the need for a mold release, even with old rubber: the acrylic is apparently very easy on the rubber, and finished castings prepped this way literally fall right out of the mold.

Morty Seinfeld · Post by **Morty Seinfeld** » Thu Sep 06, 2007 7:46 am

Shinnentai wrote:Hola. Thought I'd pop back in to mention this: I've found an easy alternative solution to the EnviroTex/Alumilite problem. It was one of those "why didn't I think of that waaaay back then" head slapper things (I'll bet it's occured to others before me).

Give the inside of the mold a coat of Future before pouring.

The acrlyic acts as a barrier, preventing whatever's in the Alumilite from adversely effecting the EnviroTex (and protecting the mold from the resin too. Nifty!). This also eliminates the need for a mold release, even with old rubber: the acrylic is apparently very easy on the rubber, and finished castings prepped this way literally fall right out of the mold.

Thanks for that suggestion, I'm going to give that a try.

Is there anything that Future can't do?

Balok · Post by **Balok** » Tue Sep 18, 2007 6:14 pm

I bought $50 bucks worth of casting stuff at Tap plastics a couple months ago. The RTV that was supposed to set up in an hour became unworkable in 5 minutes. Took it back and they gave me a different lot of similarly defective product. Exasperating as hell. I tried casting with their Crystal Clear casting resin. This stuff shrinks in the mold and stays gooey on the surface so all the surface detail is destroyed. Whatta waste of time and energy. So guys, does the Alumilite and or the Envirotex shrink in the mold?
I'm fed up with casting until I get some decent product, I simply do not trust Tap plastics any longer.

Blappy · Post by **Blappy** » Tue Sep 18, 2007 7:56 pm

Did you shake both bottles of resin before you poured out the measured amounts? The one half can separate over time and need to be shook well. Smooth-On resin is notorious for this.

Shinnentai · Post by **Shinnentai** » Tue Sep 18, 2007 8:07 pm

Envirotex shrinks a little, but no more than you'd expect from most other resins. It has a very long pot life: 45 minutes to three hours, depending on how hot your climate is. This makes it very easy to work with, but on the other hand, total turnaround tends to be measured in days rather than hours. On the plus side, this long cure time spreads out the heat produced: I've cast parts using over 1/4 a cup of resin without it ever rising above room temperature (I have had heat troubles with other finishing epoxies though, so this should only be taken to apply to Envirotex).

Properly degassed it is nicely clear; not optically clear, but nearly water clear. It's on the viscous side for casting resins, but that can be greatly reduced by adding a few drops of alcohol to the mix. It can be tinted or colored with regular model paints, both acrylic and enamel, and this can have a similar effect on its viscosity.

IMO its extreme ease of use makes it very well suited to amature benchtop casting, but because of it's long cure time it is not well suited to production casting.

I haven't tried Alumilite's clear resin. Their regular stuff though I didn't like: 90 second pot life makes pouring and degassing very very frustrating unless you've got a pro casting setup; produces a frightening amount of heat, even in very small amounts; degree of shrinkadge varies unpredictably from one mixing to the next.

Balok · Post by **Balok** » Tue Sep 18, 2007 8:25 pm

This crystal clear Tap stuff has an MEKP activator. You put in the number of drops recommended. I'm going to try the heated mold. I tried casting with epoxy glue, it worked well except for the bubbles and the yellowness. I'm a newbie at this in the head bashing against the wall mode. I guess one needs to be careful in heating the mold as the vapors from the curing resin are likely flammable or even explosive when confined.

I'm searching for the mystery product that works every time as advertised, has no major downside, and does not expire in 6 months. I may be a dreamer, but you can join me. ... how does that song go? ... um, I'm hammered after a hard day. While we're at mystery products, I want a drink lite and effervescent that has properties of both alcohol and cocaine. Not addictive of course, and no inconvenient hang overs. Neelix my man, a pan-galactic-gargleblaster, hold the side effects, and slide it down the ally.

Course I'm still dreaming. Reality then. Who know how to safely heat the mold?

Balok · Post by **Balok** » Tue Sep 18, 2007 8:39 pm

Thanks Shinnentai. What I'm looking to do is, GULP, recast the individual engine parts on the FMMF. I want to produce a small number engines with 20 or so LED's, in either blue or white, for sale. I know one guy produces these engine segments in clear resin, but I'm loathe to ask him how as I want to include them myself with my engine. Wonder how he does it? Not with my products, its a safe bet.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Tue Sep 18, 2007 9:37 pm

Balok wrote:I bought $50 bucks worth of casting stuff at Tap plastics a couple months ago. The RTV that was supposed to set up in an hour became unworkable in 5 minutes. Took it back and they gave me a different lot of similarly defective product. Exasperating as hell. I tried casting with their Crystal Clear casting resin. This stuff shrinks in the mold and stays gooey on the surface so all the surface detail is destroyed. Whatta waste of time and energy. So guys, does the Alumilite and or the Envirotex shrink in the mold?
I'm fed up with casting until I get some decent product, I simply do not trust Tap plastics any longer.

The Tap Plastics Clear casting resin is awful.
And it will not cure in a silicone mold. It might work in their Latex mold, but after a few attempts in different years, I talked at length with my local Tap representitive, and she said that the Clear cast is an "air inhibited cure. How it gets "air exposure" inside that silcone mold, is beyond me.
Probably due to the huge amount of shrinkage that occurs.

I gave up on Tap Plastics after they messed up their quick cast.
and changed their mold material. They might still be a good starter kit, but
I wont have anything to do with their casting products any more.

Balok · Post by **Balok** » Tue Sep 18, 2007 9:55 pm

Thanks Umi for that confirmation. Tap sucks. I'll move on to better products. Sounds like that high priced Allumilite is next. I've used the Alumillite resin before, not the clear, and found it pretty reasonable, Though it does set up quick.

macfrank · Post by **macfrank** » Tue Sep 18, 2007 10:24 pm

Nate,

Like Shinnentai mentioned, Envirotex is pretty easy to work with. Just remember the issues with RTV molds and the workarounds. One drawback of Envirotex is the tackiness/softness (it never gets really hard).

The Alumilite clear is great stuff, but it cures far too quickly and it requires that the molds be heated.

Clear acrylic powder (the kind used in fake fingernail repair kits) is great for relatively small objects, but too expensive for large casts, and it also sets fairly quickly. It polishes out very nicely, though.

Frank

Balok · Post by **Balok** » Tue Sep 18, 2007 11:37 pm

Thanks Frank,

I'll give the Alumilite a shot making small pieces first. I'm burned on tackiness for now. Is there a retardant for Alumilite? I'll go look this up for myself.

USS Atlantis · Post by **USS Atlantis** » Wed Sep 19, 2007 6:58 am

I've had good luck with Castin' Crafts clear resin

Takes transparent colors well and sets up nice and hard after a quick (2hr) bake at 150f

Mix is around 8 drops catalyst to 1 oz resin

Can get it at just about any craft store (Michaels, Dick Blick, etc)

Atlantis

Balok · Post by **Balok** » Wed Sep 19, 2007 2:38 pm

Thanks Atlantis, I'll look into that as well.

USS Atlantis · Post by **USS Atlantis** » Wed Sep 19, 2007 5:41 pm

Note that the 'bake' is after it's room-temp curing - which is about 8-10 hours... comes out of my molds a little 'sticky', but the bake takes care of that.

Also, if you vary the catalyst amount, you can get results from a softer, toolable cast - close to ABS or Styrene; all the way up to a VERY brittle cast - almost like clear Acrylic or Acetate

Atlantis

macfrank · Post by **macfrank** » Wed Sep 19, 2007 7:46 pm

Balok wrote:Thanks Frank,

I'll give the Alumilite a shot making small pieces first. I'm burned on tackiness for now. Is there a retardant for Alumilite? I'll go look this up for myself.

I don't think there is; even varying the ratio of the two components only affects the setting time only slightly (but can really screw up the final hardness). The setting time is the main problem with the Alumilite clear; unless you degas it (or pressure cast) you'll end up with bubbles. I don't think you have enough time to pressure cast the stuff before it sets. The mold has to be pretty warm as well.

Blappy · Post by **Blappy** » Wed Sep 19, 2007 10:22 pm

Did you even try the "shaking" solution?

macfrank · Post by **macfrank** » Thu Sep 20, 2007 8:39 am

Blappy wrote:Did you even try the "shaking" solution?

I tried shaking and tapping the mold, even as far as putting it on top of my old compressor and have it vibrate the bubbles out. It works for the larger bubbles, but the Alumilite clear sets so quickly that some bubbles (mostly tiny ones) still get trapped.

Balok · Post by **Balok** » Thu Sep 20, 2007 2:19 pm

SCC-7107 USS Atlantis wrote:Note that the 'bake' is after it's room-temp curing - which is about 8-10 hours... comes out of my molds a little 'sticky', but the bake takes care of that.

Also, if you vary the catalyst amount, you can get results from a softer, toolable cast - close to ABS or Styrene; all the way up to a VERY brittle cast - almost like clear Acrylic or Acetate

Atlantis

Are you baking it out of the mold, or in the mold? I can experiment, I went by Michael's and got a small container to practice with.

USS Atlantis · Post by **USS Atlantis** » Thu Sep 20, 2007 6:09 pm

I'm doing the bake after de-molding it

So the sequence would be

Cast
Allow to set for 8-10 hours
De-mold
Bake at 150f for 2 hours

Atlantis