epoxy foam

We are making a number of the components of the ROCAT by moulding a polyurethane foam blank/core, covering it in carbon braid, and infusing epoxy inside a closed mould.

The more I use it, the less happy I am with the properties, and durability of the PU foam, and would like to find out about other hard foams that can be moulded.

I am especially interested in epoxy foam and would like to hear from anybody who has got experience with this material.

atb ... Christopher

www.rocat.co.uk

 

Not what you are asking about, but:

A few days ago I used a soft foam brush to spread some epoxy. Thru it on the floor. The next day, after beating int with hammer to unstick it I wondered if this could be used as a core material.

Perhaps the weight is too much.

 

That's a very interesting idea ... the things one gets from the observation of accidents!

One could cut the polyether foam roughly to shape; stuff it in a closed mould, and infuse it with resin. Weight would certainly be an issue, as would exotherm. I'll try some and post the result.

Christopher

 

I kinda think the foam should be soaked and then rolled once to squeeze the excess out. Exotherm it will. From what I gather epoxy that has exothermed is not as strong ... but it is still strong.

 

Squeezing out the resin makes sense, I guess it depends on the proportion of polyether to air in a block of the foam ... the more the air, the more the resin.

Exotherm depends on the mass of resin; in my experience, once epoxy has run riot, it's only good for the bin (if it hasn't set the workshop on fire first ).

Christopher

 

Everytime I use the EPON 828 Thick Laminating Resin from uscomposites.com, the leftover resin in the pot exotherms. The spreadout coating of the resin doesn't exotherm.

The yellowish white block in the partially melted cup is quite hard. I haven't smacked with a hammer to see how it breaks tho. Perhaps the foam brush soaked in resin hasn't truely exothermed, because it did not melt.

Also, I am using a fast hardner. When it kicks it heats up fast. Maybe a slow hardner would be more appropriate.

I think the foam brush expands as it cures from the heat.

The most interesting thing about using a soft foam as a core would be the illimination of scorelines and voids. Didn't someone write in that this was a problem with the foam cored boats damaged by the hurricane in Florida?

 

As we are moulding our foam, scorelines and voids are not a problem. The soft foam is an interesting idea but, although I haven't tried it yet, I supect it's not a production solution.

But is nobody out there using epoxy foam in a production situation?

Christopher

 

Given that you have modelled your boat accurately,would it be possible to machine your foam to the required shape?It might necessitate going to a tougher foam than PU but you are prepared do do this and you will not face the cost of a mould for the foam.It gets a bit more complicated if the shape requires a fixture for a second operation.

 

This would indeed be possible but, in a production situation, it would be an order of magnitude too expensive.

We have made several foam moulds now, though, and have not found them too onerous.

Christopher

 

Cristopher,

I've been meaning to reply to your question for a while, if you though you could avoid having to endure my aimless ramblings, your luck just ran out.

There is an epoxy foam made by Ciba-Geigy, I haven't used it myself, but a friend of mine built a rudder with it, after having the rudder sit in the sun for a while the foam softened and the skin popped loose.

A few months ago I was researching the possibility of using a foaming-agent with a soft epoxy to make a foam with high toughness without the downsides of Airex, but my epoxy supplier didn't think it would be very strong at low densities.

Recently I've pondered using carbon chop with the above recipe, I'm hoping the carbon filaments will be fine enough to to stay in the cell-walls and reinforce them while leave the bubbles empty. By the way, all this is just in the musing stage, I haven't done any experimenting yet.

A thought for you; if you have a molded part and a loose-fitting foam core for it, could you inject a syntactic (epoxy and Q-cel) "foam" between them? A length of soft vinyl hose and a rolling pin comes to mind as a low-pressure pump. Or, perhaps try using a couple of millimeters that Lantor core-mat to thicken the walls and forgo the urethane core altogether?

Yoke.

 

Yoke

Thanks for the pointer to Ciba-Geigy – I expected they would make an epoxy foam, but could no mention of it on their (difficult to navigate) site. Very interesting to hear about your freind's experience of it, though.

I have been trying a Sicomin product, which would appear to be extremely good. However, it's crucial to post cure it properly to get the ultimate strength – when you do get it right, it has very high compressive strength and is incredibly tough.

Your latter suggestions wouldn't fit my requirements, because I am using the foam blanks to make the shapes inside the carbon braid, inside a closed mould – I then infuse the resin between the foam and the mould.

Considering its properties, I am really surprised that 1) so few manufacturers are making epoxy foam, and 2) so few people seem to be using it.

atb ... Christopher

 

Epoxy foams--I dream of the day!!I can't imagine anyone really enjoys using the poly pour-in-place,,knowing that it's really only a matter of time before moisture creaps in!
I'll check-out ciba-geigy-is this a german company -I've heard there's something there,but they don't import to NA.
.....once had a small leftover batch of fast-cure 5:1 at cleanup--for some reason I dropped some of the clean-up acetone in--came back the next day and it had foamed-up ~2 1/2X!!....never manadged to duplicate it though!

......any further clues to epoxy pour-in-place foams or foaming agents would be MUCH appreciated!