Casting question

[MrPinski]

Has anyone ever reinforced their polyurethane castings while still in the mold by adding fiberglass fibers to the casting resin?

I want to make thinner castings but stronger at the same time.

Any suggestions?

 

[BrundelFly]

You could.

There are other things you could add to the resin, but the harder it gets the more brittle it can be. What are you casting if I can ask?

Why not just use FIBERGLASS? Helps if i knew what you were making.

 

[MrPinski]

You could.

There are other things you could add to the resin, but the harder it gets the more brittle it can be. What are you casting if I can ask?

Why not just use FIBERGLASS? Helps if i knew what you were making.

I am making Dredd 3D shoulders. The thing I want to make strong and thin are the edges so they can be drilled and sewn to EVA without worry of cracking for any reason.

Polyester resin kills mold silicone and I'd rather my molds last a while.

Thank you!

 

[Zombie Killer]

I would go straight to an epoxy and fiberglass mat. Or even better a thin coat of something like TC-1630 urethane and then apply the epoxy and glass mat.

 

[MrPinski]

I would go straight to an epoxy and fiberglass mat. Or even better a thin coat of something like TC-1630 urethane and then apply the epoxy and glass mat.

I would be cool with that, but if I do it that way, would I have any chance of separation because I'd be layering polyurethane and polyester? Or should I not worry because I'd be sewing through the edges anyway?

 

[Zombie Killer]

I don't know about polyester resin, that is the stuff that stinks forever. I use epoxy resins. They are not the same. You can put epoxy over polyester but not polyester over epoxy. It has to do with the hardeners. Polyester mixes with a catalyst to harden and the catalyst doesn't become part of the final product where epoxy uses a polyamine based hardener that combines with the epoxy to make the final product. The MIB guns i have here are polyester over urethane and i don't see any issue other then it stinking. That is why i covered one in epoxy. I know epoxy goes over the TC urethane without issue because i use them now without any problems.

These guys are who i get my epoxy from and they have a good write up on it.

System Three: Resource Library: Published Literature

 

[Kailon]

Matt Munson has a youtube post about using a gelcoat first then once thats dried adding a layer of fiberglass, not sure if this would make it thin enough though, he was doing it for some loki gauntlets, but i'm sure there's got to be other things you couild use as a thin layer between the fiberglass and the mold.

 

[Toxx]

You can put epoxy over polyester but not polyester over epoxy.

Why?

I had put polyester based car body filler over my cured epoxy resin reinforcing my pepakura, and it worked well?!


.

 

[Zombie Killer]

I'll just qoute what they say. They are the chemists not me. I guess the polyester will not cure against the amine used in the epoxy whereas the epoxy doesn't care what it goes on. Once the polyester is cured it is cured. The amine can go over it at that point.

"Caution must be observed when using epoxy resins along with
polyester resins . Observe the general rule that epoxy resins may
be applied over cured polyesters that have been dewaxed and
well sanded but polyesters should never be used over cured epoxy
resins. Unreacted amine in the epoxy inhibits the peroxide catalyst
in the polyester causing an incomplete cure at the interface.
Sanding does not get rid of unreacted amine. The result is a poor
bond even though the surface appears cured. Debonding will be
the inevitable result."

 

[robn1]

I've done exactly that, urethane resin backed up with fiberglass. I used Smooth-Cast Onyx, slush cast in a thin coat, then applied epoxy and glass mat. The epoxy bonds well with the resin and shows no sign of delaminating.

But the Onyx may be fine on it's own. I've slush cast parts about 1/16 to 3/32in thick, they are very tough but not brittle. But glass can be as hard or harder but a bit thinner if that's what you need.

I never use polyester, as Zombie Killer said it stinks, I can't stand the stuff. I use EpoxaMite medium from Smooth-On, very good tough stuff with no odor.

Edit to add: polyester and epoxy are both very tough on silicone molds. I've tried a number of solutions but I've found that urethane resin as a "gel coat" works best. The epoxy bonds to it well, and can't get through to the rubber.

 

[animefan]

urethane backed with polyester will eventually delaminate. urethane backed with epoxy wont.

[/QUOTE]
Polyester resin kills mold silicone and I'd rather my molds last a while.

Thank you![/QUOTE]

Depends what type of silicone you use, most platinum silicone's are designed to release Polyester naturally, no mold release need and virtually unlimited amounts of casts, depending on how well its made and how you handle it. Urethane is the killer.

 

[BrundelFly]

There are two kinds of bonds.

Chemical, and mechanical. If two incompatible materials are used with each other, and the first one applies is still TACKY, the second one WILL adhere to it.
It MIGHT come loose eventually. Depends how much they physically bonded.

 

[MrPinski]

I added fiberglass mat to the edges and used casting resin instead of polyester resin and it made the edges very strong and kept them thin!

Thanks for the suggestions y'all! They pop out great now!