First mold thoughts

General Composites Discussions Composites Talk
#1

So, I popped out my first plug the other day. I had sprayed the plug with Fiberglast orange tooling on a beautiful 75 degree day with an ES cup gun. It looked pretty good and even. I had spent a long time on the plug sanding and polishing to get a great finish. Plug release prep was done with a few coats of Frekote 700NC. Here’s how thing’s went…

  • The Frekote comes with no instructions and the only video I could find was about a water based release, but I followed the same wiping instructions. the video showed how tape was unable to stick to the prepped surface, but tape was sticking very well to my prepped plug. The frekote also left residue that I could see, as if you had wiped your car down with a wet paper towel and then left it to dry like that.

  • Note to self: Try to get at least a 5CFM compressor if you’re going to use a cup gun.

  • The plug was a flat piece but gel coat still got underneath it when spraying. Chalk it up to a learning process. Next time I’ll use some clay. is that the easiest fix?

  • After sanding down where the gel coat had gone under the plug so it wasn’t locked in anymore. I attempted to get it out. I’m not sure the Frekote did anything or if that was even the right thing to use. I was saved by the fact that the plug was a resin covered solid piece of wood, so I could bend the mold itself to pop out the plug. I didn’t over-reinforce the mold just for this very reason.

  • The gloss had not transferred to the mold. It was smooth, but a dull finish. I could also see the residue marks from the Frekote left on the plug. By the way, at what grit would you start with to go after the gel coat finish at this point?

Anyway, any comments or feedback about anything above is welcomed. Thanks!

#2

When I do plugs with a polyurethane paint the moulds also come out with a flatter finish but still release just fine.

I have been told by others that this is a small sign of materials cross linking between the plug paint and the new gelcoat. Apparently the paints can take a while to fully cure. The longer you leave the paint to cure the better and safer your job will be.

The gel coat will still polish up great with cutting compound.

I also use Frekote sealer, frekote 700 and wax. I always get streaks with Frekote too but this wipes away if you are also waxing the pattern/mould.

#3

I imagine your biggest problem was not sealing the plug first with Frekote sealer. If tape was sticking after release, something wasn’t done right. The Frekote release is pretty simple. Wipe on and as it starts to dry wipe with a dry rag. Good luck.

#4

Plug - coating with resin is not the same as coating with a product designed for the job. Duratec has a line of products made for patttern making. More than likely why you have a dull finish. Try buffing first and if that doesn’t work go to a fine wetsand, maybe 1000 grit.

Release - You didn’t apply the right product, in the right sequence, in the right manner. Sealer first, then release. Most polymer release systems follow the same pattern, i.e. a sealer and a top coat.

Most of the sealers I’ve used are wipe-on wipe-off. The sealer should be applied with a damp rag applying only enough to wet the surface. Immediately follow with a dry rag to pick up excess. Don’t buff it off, just get rid of the really wet streaks. The object is to leave behind the thinnest of films. I use 5 coats on patterns.

Top coats come in a variety of application styles - wipe-on wipe-off, wipe-on leave-on, spray-on leave-on. For me the wipe-on leave-on, or wolo for short, seems to work best for ease of application and economy. 2 coats and then tape test. The tape should stick slightly but come away with little resistance. Add more coats as needed.

Mold - to each his own but I prefer a well constructed and reinforced mold. I know that, barring some unforeseen circumstance, each molded part will be a reflection of the mold. A flexible mold could distort differently with each molding.

Compressor - 5cfm is pretty short in the air delivery department. You might find yourself waiting for the compressor to pump back up while you are spraying. Hot gelcoat in a cup and waiting for air are a recipe for failure.

#5

Thanks for the feedback everyone. So I made a new plug and redid the mold this week, and it turned out much better. One of the problems was, I used Lexan for the top(sort of like Acrylic, except it doesn’t shatter when you cut it) since the top was flat and I wanted a perfect finish. This backfired, as the Lexan had a bad reaction as the Lexan lost it’s finish after being gel coated. I noticed the sides of the mold where I had just used resin were nice and clear. So this time, I just used resin for the whole thing, spent a ton of effort sanding and polishing, and it came out great.

Again I only reinforced the mold a bit so I could bend it to pop the plug out. This was because I still couldn’t get the Frekote to pass the tape test. I went through the whole process of mold cleaner, seal, and release, but the tape still stuck pretty well. No idea there. Either I’m just doing something terribly wrong, or I’ll try a different manufacturer’s system next time.

I’ve never seen “Don’t cut corners” and “Do it the right way” apply to something as much as it does to composites. It’s been a great learning experience. After popping the plug, I continued reinforcing and the mold is going to sit out in the sun this week, and then it’s time for parts this weekend. Thanks everyone!

#6

Maybe some sort of reaction with the Lexan and the solvents in the Frekote system??

Yeah, you really need to be sure of your process so that time and money is not lost. If you you did not already know that the Lexan was ok then you should have a done a small test sample to check it before committing with the job.

These guys are infusing/moulding parts off clear material mould of ?? Someone suggested to me that it was Poly-carbonate?? Anybody know what it might be??

https://www.youtube.com/watch?v=OnkY8kcUe68

#7

Probley a urathane, or transparent aluminum:)

#8

Hyrdo flex use acrylic sheets. They have come along way on a short period of time , brilliant work and great guys.

#9

ive made a few acrylic moulds, really kewl to watch the epoxy move around in em … some guys have had problems with release , especially if its a fragile part … so be sure to do some tests