Mold making pre release, Help?

We've been having no end of troubles with pre release building molds.

On the plugs..
3 - 4 coats of wax
PVA
tooling gelcoat 2 coats to build up a layer than can take some wear.
Print blocker, and I don't remember what kind.
Skin coat of 1 oz mat & resin.

Typically by this time its popped off the plug. Today we made it through 7 layers of 1oz mat & Opti-plus tooling resin before it popped off while curing.

We are kinda' at our wit's end. What are the common causes of pre release? There has to be something we're doing wrong.

Ideas? Anyone?

Many thanks in advance!

-jim lee

 

what is it a mold of?
what are you using for resin?

 

I have two suspects in mind - heat and vibration.

Your gelcoat should be 18 mils, applied in three passes in one operation. Don't apply a second "coat". And don't move the plug (vibration). Moving the plug after the gelcoat has cured is inviting prerelease.

When the gelcoat has cured, apply the skin layer and let it cure. Then maybe a layer of 3-oz instead of three layers of 1-oz. The idea is to have the glass cure, but not in thick layers that will create excessive temperatures. Keep the layouts thin, and apply the next layer with 24 hours. (Make sure you're not overwetting the 'glass, too.) OptiPLUS appears to be a polyester resin, so the surface will be tacky at full cure, awaiting the next application.

Control your shop environment to avoid temperature swings.

If you've applied gelcoat and 'glass to the plug a couple of times, you're okay to leave out the PVA step now. Sticking molds (unless there has been really poor mold prep) occur on the first part when they do occur. Sounds like your first few parts are in the dumpster. I have no idea what really damp ambient conditions may do to PVA, but I can come up with no pleasant scenarios.

 

We control the temp of the room 70-ish

As for the temps, the optiPlus stuff needs to get to a certain temp to work. It uses temp to counteract the normal shrink.

Vibration might be the culprit.. At least for this go around. But the rudder molds that pre released didn't have any vibration issues.

Tooling gelcoat - Polycor tooling gelcoat #965YJO71 HP40
Barriercoat resin - Donno', can't find the paper on that one.
Skincoat resin - CCP - Amorstar - VE
Then its Opti Plus resin for the bulk of the material.

Its always something you never suspect. Pre release? This one came out of the blue.

Here's the story and some pix : http://www.leftcoast.biz/iWeb/Left_...8/8/12_Going_nowhere_at_great_expense....html

Thanks milliions for the help.

-jim lee

 

how much "shrinkage" are you getting?
how hot is everything getting while its "kickin"?

 

How would I measure shrinkage?

As for heat, the skincoat was around 90 - 120 deg

Opti plus 180 - 220 deg

Here's another bit I just found out. The Gelcoat we're using for tooling gelcoat is vinyl ester resin. I wonder if that could be causing problems?

-jim lee

 

what kind of resin are you using for your "part"?
to measure shrinkage,,,put your part back on your plug,, and see if its a tight fit,,,or if you have to "press" the part on with difficulty,,,,,,,,, on my next piece i would mark your piece to a certain place on the plug,,,,and if it happens again,, see if the marks line up,,,,,sometimes over catalyzing causes more shrinkage then usual,, and the piece will "pop" off the plug or mold.
im just "stabbing" at this....it could be 1 of 1000 things,, or a combination of any of them ,,, but sometimes having an "idiot" ask stupid questions helps,,hehe

 

Well, in this case the "part" is the mold. And what I listed was the layup of the mold we're making.

I haven't measured the mold to the plug, but I'd be really surprised if there was much shrinkage. Mostly because all this fancy opti plus stuff we're using is designed specially to stop shrinkage.

-jim lee

 

i just read a LITTLE on the opti stuff,,,,,man,,, looks complicated,,hehe,,,,ya know,,,sounds stupid,,,but maybe no shrinkage isnt good,,hehe
have you looked ( im sure you have,,, but every once in a while we get lucky ) is everything from your plug, compatible with everything your mold is being made with?
your using all that fancy stuff hehe i never got a chance,,,print blocker,,, thats called,, " you better get that gel thick nuff jim!",,hehe
and this part just "pops" off the plug all by itself?,, or does it just pre-release in spots?.....

psssst,, you need bigger pics on your site,,,i see as good as i type,,,haha

 

I've sprayed a lot of vinyl ester gelcoat, but never thought to accuse it of causing prerelease. My only reservation about it was that it was reputed to not polish as shiny as polyester.

That high temp (220) kinda worries me. Is that a result of thick multiple layers? That might be the problem.

Ohhh - just checked your pics. Is it prereleasing near a "joint"? If you have thinner gelcoat on a vertical surface adjacent to overly thick gelcoat on a horizontal surface, the difference in temps as they cure can sometimes cause prerelease. You want 18 mils EVERYWHERE.

 

It pre released right in the middle of the fin.

The Opti stuff is kinda' complicated. The idea is that you can build it up pretty quickly. Its designed to kick hot like that.

Right now, MikeS (The guy at the shop with the brains) is about ready to can it all and go back to they we he used to do this 20+ years ago. Like he says, it ain't fancy, but at least they got results and it all worked. The other option is to infuse the mold.

I do have some questions about compatibility of the plug materials. Our first failed mold attempt we used some rattle can spray paint primer to speed things up. I swear that stuff melted, outgassed and caused the gelcoat to pop off. Now, when this last mold popped off, we noticed that you could see the ribs on the bulb plug. This plug was glued together using west system epoxy. I know epoxy doesn't like heat, maybe its reacting? This and there looked like there was some blistering. Possibly the Bondo underneath is reacting? Everything is coated in Duratec. The hope was that the Duratec would seal everything up.

Wait a sec.. Maybe its water coming out of the wooden plugs with all the heat? That would blow off any cover/coating we put on there. It would also explain why after a couple tries, everything suddenly works.

Well see..

Thanks a lot for the tips and questions. Somehow this'll get solved.

-jim lee

 

What's probably happening is the plug made with epoxy, wood, bondo, primer, gelcoat and other items is changing shape. all of those materials cure and react differently to heat, so when you use the plug the first time the materials shrink and change shape, that's why you see the ribs and other shapes in it. Most fillers, and Bondo in particular, are very susceptible to heat and moisture, so the first time the plug get's warm it changes shape slightly resulting in pre-release. There was a section in the tooling class discussing soft fillers in plugs and what can happen (shape change) when using them. Bondo is also effected by styrene and other solvents even after it's cured, so any solvents still in the plug materials can be released by the heat will soften it.

The idea behind Optiplus is to get as complete of a cure as possible right away with as little residual cure left as possible, so there is less post cure of the laminate. The traditional method of mold building can make good tools, but what you run into with multiple layers of thin laminates is a tool that looks good when first made, but can suffer from a great deal of post cure after the first few parts and then again whenever it gets subjected to heat.

When I re-read the first post you said it was the gel coat pre-releasing before or during lamination, the main reason for gel coat pre-release is uneven cure, this is mostly due to uneven thickness and would have nothing to do with the resin used.

If you plan to make another mold let me know and I can be there, we should be able to get it done in about half a day.

 

Well every thing's fixed, braced and recoated. Mike is due back from the east coast Monday. We'll probably be doing a mold shot Monday or Tuesday.

Another bit we gleaned.. Grounding the mold flange and the spray gun before shooting the gelcoat. I can't se how this helps. But, from what I hear, some people do this to help stop pre-release.

ondarvr, what's your "real" name? Have we met?

-jim lee

 

i think their whole thing with the grounding is to stop static,,,,,but i dont see how that actually works,,, since you need it NOT grounded to stop static.just 1 of those "old wives tales" hehe
but,,,,,, dont take my word for it,,, i havent really had someone explain it to me.

 

Jim

Yes we know each other, Bob Sage may have already talked to you, I told him about this post so we could help.