Exotherm and low exotherm resin!!

General Discussion
1

Prior to installing some FCS plugs in an EPS board I thought I’d buy some reccommended resin. Low exotherm Epoxy with Ultra slow hardener. According to datasheet it peaks at 38C. This peaked at 150C after about 25 minutes! Have a look at pictures DSCF 1219 & 1220 at link below

http://www.photobox.co.uk/album/5725078

Now, nobody in their right mind would cast structural resin like this, too big volume, too much insulation so this is really an unfair test. I have subsequently used this resin filled with Microfibres, Colloidal silica and glass bubbles (not all together!) and filled volumes about 100mm x 5mm x 20mm and had no trouble, but that was in both GRP and wood, so a little less insulation.

However it is interesting to see how EPS breaks down to almost nothing with some heat. Anyone seen what PU does?

2

good stuff… that’s the kind of info we need here on Sways…

I always add pigment and microbubbles to RR and use fast hardener and have never had a meltdown. I also always us cold, wet cloths under the deck, and make sure I have a clean ring of exposed glass there. It does no good to try to cool down kicking resin without making sure that head can escape through the deck glass. Leaving any foam insulates the heat from the cooling cloths and is asking for trouble.

I forget who said it, but the truth is: shade, cool temps, wet cloths, pigment, filler… all slow down the kick and decrease exotherm into the foam.

3

If you burn eps it actually releases roughly the same amount of harmfull gasses as a peice of wood of the same size. Weight for weight however the eps is far more nasty.

try pouring acetone on some scrap eps to see it vanish pretty quickly… or any other solvent with styrene in it…

rif.

4

Hey Rikds,

Have you tried the low exotherm epoxy yet?

What is it called?

I’m having the same problems.

Thanks

Rick.

5

Hi rickrickrick.

That experiment WAS with the low exotherm stuff. I’ve not done the PU test yet, no scrap lying around at the moment.

Another odd thing about that test was that there was no sign from the top as to what was going on below. I had a thermocouple embedded in the resin to check temp. At one stage a couple of bubbles appeared on the surface and that was it.

However the epoxy plug in the photos is massively hard and has not yellowed like other over cooked epoxies. My gut feeling is that with the relatively small volumes when fitting plugs, this would work well.

The epoxy is made by a French company called Sicomin SR 5550. It’s designed for use with wood but it a great adhesive. I’ve used Sicomin resins on Carbon race boats and they’re great stuff. They do a super gloss version specifically for boards which I’ve not used.

6

Now, this got me kinda interested,being as I have seen a couple burnt boards over the years…well,decades…

Polystyrene( PS ) is a thermoplastic: It can be heated,melted, reformed and recycled,so that the melting temperature ( circa 240 °C ) causes it to become a liquid, taking up a lot less room than as a foam and demonstrating that kind of ‘wet bread’ look as in http://www.photobox.co.uk/shared/photo.html?c_photo=1324431554

Okay, this is indeed interesting, as it’s indicating that a temperature > 240°C may have been reached in a few spots.This has some implications for use with Polyurethane ( PU ) foams.

Polyurethane is a thermosetting plastic. That is,it doesn’t melt,it burns, given sufficient heat and asupply of oxidiser. And, according to http://www3.interscience.wiley.com/cgi-bin/abstract/113507128/ABSTRACT

Quote:
Abstract[/url]:    Oxidation and ignition of flexible polyurethane foams have been investigated by observing the effects of internal and external heating. <span style="font-weight:bold">External temperatures of some 190°C are required to induce combustion</span>. <span style="font-weight:bold">Internal temperatures of 250 -350°C initiate a self-propagating internal reaction which results in foam ignition when the reaction reaches the foam surface</span>. The stability of a polyurethane foam to such heating increases with the age of the foam.

Boldface added for clarity-

Basicly, if you get it hot enough, urethane foam will catch fire.And if you heat it up enough, it’ll burst into flame when it gets some oxidiser,like,oh, for instance, air.

This in turn raises a couple of questions;

Can you set fire to a board by using too hot a batch of resin for a large fding repair/filler?

Yes, you can. It’s not just a surfing urban legend.

How does one slow down the reaction?

In addition to using less catalyst,plasticisers ( like cabosil and q-cell) ,pigments, etc in polyester resins, you can also do it in a cool,shaded place. Also,chilling the resin might help, as the original temperature of the resin should have quite an effect on how fast it initially goes off,the rate of heat generation by the resin should be slower and the ability of the resin to lose heat fast enough to keep it from ‘overreacting’ might be preserved.

It might be useful to run a fan over the spot too, but if it does catch fire, well, the term ‘fanning the flames’ comes immediately to mind.

Adding less catalyst ( hardener) isn’t an option with epoxies, but plasticisers, pigments and such can’t hurt, along with chilling the resin components. That has also been shown to add to pot life and working time without damaging the ability of the epoxy to harden. I wouldn’t go putting the stuff in the freezer, but in a regular refrigerator at around 42° F ( 10° C) could help a lot

Hope that’s of use

doc…

7

Hi Doc,

I’d go with all you’ve said. Trouble is when you cool the resin it becomes more viscous and wont flow into all those wee gaps and crannies that would be nice to fill up.

WHAT? You mean there are people out there who don’t get any gaps and crannies? That’s amazing!

I’m toying with using a pond water recirculating pump and a bucket of cold water beneath the shaping rack and a load of rags taped to the deck with a pipe into the bucket. Bucket catches the waste and so it goes.

OK, OK it’s going a bit overboard and I’ve not done it but it would work!!

8

Hi Rik

Well, yeah, though I haven’t had great luck with dampconditions around resins.Though if you circulated cooled water through something like a hot water bottle set on top of the thing you were glassing/casting, that might work…

Say,something like this:

I might wax the outside of the thing,just so nothing sticks that shouldn’t.

doc…

9

Hey Rikds,

I just did a probox set in #2 EPS and RR epoxy with fast hardener last night. Larry (from probox) suggested pouring the resin in 1/3’s. Pour 1/3 wait till it kicks and starts to cool. Pour another 1/3 wait till it kicks and starts to cool. Pour last 1/3. Whole process of pouring resin took about hour and 20 min. And was actually alot cleaner than pour all at the same time.

http://swaylocks.com/forum/gforum.cgi?post=last-323346;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;

Here’s my post.

Seemed to work out.

I didn’t use any was of cooling what so ever. Pour in 1/3’s allows heat to ecsape which wouldn’t in pour all at once.

And watch the room temp! I was at 75 degree F

Rick

10

i think your approaching from the wrong angle

the simplest solution is to use dyvincell inserts

not that i have any problems with exotherm on finboxes

just use a resin that doesnt heat up

though these types usually benefit from low temp post cure

anyway

it takes 5 minutes to route in some inserts

11

Do you have a link to these inserts. Never seen or heard of them.

Thanks

Rick

12

http://www.swaylocks.com/forum/gforum.cgi?do=post_view_flat;post=295419