PU Polyurethane resin / Epoxy alternative

[yellow_submarin]

Hi everyone

I'm currently designing my future mill (see appropriate section) which will probably made out of EG.

Maybe this topic has already been discussed, but I don't see a dedicated thread, so here I go.

I see there is only epoxy being used so far. Considering the prolific choice of polymer resins out there, I am pretty confused. I understand Polyester has a consequent shrinkage coefficient which is not suited for casting unless you don't mind warping.
Yet, Epoxy and Polyester resins are mainly used in laminating process. For casting purposes, there are specific resins such as Polyurethane.
I'm not a specialist concerning polymers, but it seems that Polyurethane has interesting properties, it seems decently rigid, and also features low shrinkage, which is the reason it's used for casting. Thus, you can find special casting Polyurethane casting resins such as this one :
Water Clear Polyurethane Casting Resin for Embedding and Rapid Prototyping - Easy Composites

There is also a fast curing one, but as the polymerization is exothermic, that's not good for us.
It seems that the price is comparable to epoxy resin, and maybe even a bit cheaper.

So what do you specialists think ?

Greetings from France

Cyril

[rowbare]

I seem to remember there was a discussion about that in the big e/g thread and the consensus was to stick to epoxy. AFAIK no one is advertising poly*/granite bases...

bob

[yellow_submarin]

I haven't seen anything about that either commercially speaking yet polyurethane seems more used in casting than epoxy. I gues I'll check in the "master thread" to see if anyone has tried yet.

[RomanLini]

Polyurethane is a lower quality result, it has much lower strength and extremely low adhesion. So in a composite like EG it will break very easily.

Also PU tends to set very quickly, which might be a benefit when casting little ornaments and statues, but would be a nightmare when trying to mix/vibrate/degass an EG composite.

It's also not much cheaper than epoxy. Add all that up and you'll see why nobody is using PU to make big expensive EG machines.

[yellow_submarin]

Well, I think I got my answer, thanks