Epoxy hulls, and sunlight / heat? - Aging behavior

[robse]

Hi.

Having allmost completed my hull, I've got to thinkking... I have during the work noticed that the glassfiber / resin hull gets soft, if heated my eg. a cutting disk or heavy sanding using a power tool. And so what, you might ask.. well..

Imagine your black sub sails around the pond in a surfaced condition, or rests along the shore. The sub's black, and ths sun is shining bright. Is there a risk that the resin will start to sack, or sink, over time from the heat exposure?
And what about the UV radiation from the sun as well?

If any of the two is a "yes", then what can be done about it? I know a guy who builds fancy "hot-rod" cars, and he calims that the bigger parts in glassfiber sometimes sink a bit after a while, but then again.. a car is in the sun all the time, and I'd imagine that the physical stress on the parts are higher too...

Anyone?

[anonymous]

when the hull is in

when the hull is in the water, the heat is disapated by the water. I have had and seen numerous boats on the shore and in direct sun light with no effect on them. Hoope this helps you...

[sam reichart]

ask Matt Thor about heat

ask Matt Thor about heat and epoxy hulls. a few years back he shipped me a huge box of hulls that we brought for him to sell at the Regatta. whatever was left was sent back to him by UPS. UPS decided to go on strike while his hulls sat in the back of a hot UPS truck for weeks...
all that was left was a pile of epoxy slag when he finally received the box.

Bill's correct about the water dissipating some of the heat. but don't leave you epoxy or fiberglass black submarine baking out in the sun...it may have a detrimental effect on the hull, and on the propel cooking away inside your WTC...

[thordesign]

http://www.subcommittee.com/forum/icon_eek.gif

[rkc]

Just to try and back

Just to try and back up what Matt said.

What is important is the Epoxy resin is not allowed to reach its Tg. This is the Glass Transition Temperature, and will vary from one Epoxy to another. If the Tg is reached (probably not difficult on a matt black sub on a sunny day) the Epoxy will soften and any residual stress will relieve and the hull will distort.

The Tg can be pushed up from the normal room temperature cure Tg by post curing, where the ramp rate or rate of heating is very important.

sorry to jump in like this as a newbie, but this is the first post where i consider i may be of some help.

I have been trawling the forum for some months, and learnt so much, that i felt it was time to try and give something back.

Look forward to learning more and contributing if i can .

rich

[robse]

Thanks guys!

I'm really glad I

Thanks guys!

I'm really glad I asked, and will use UV resistant paint, and experiment with the post-cureing thing, as you describe, Matt. THX. (And most important, NOT leave the sub in the car while driving some where, if parked in the sun.)

I use West Systems Resin 105, and hardener 206 (the slow one), and have during some sanding using power tools noticed the softening of the otherwise hardened resin.. maybe one could even use HOT water to shape any items which are not perfect.. hmm.. gave me an idea there..

-and welcome to the new menber! Allways nice with more people here.

[rkc]

Robse

Thanks for the welcome.

I will

Robse

Thanks for the welcome.

I will try to find out what the post cure schedule is, but dont get too hung up on it. Its essential you keep the post cure curve just ahead of the temperature gradient otherwise you will do more harm than good. (read deformed mess)

If you do want to play, you will need an oven with a good controller where you can set ramp rates of 1/2 a degree or less per minute. (Degrees C, sorry im british)

With some room temperature cure resins its not possible to increase the Tg by much so unless every ounce of resin performance is needed, its often best to leave well alone.

rich

[adriaticsea]

Hi everyone,

I've been following this

Hi everyone,

I've been following this topic for a while and found it very interesting...I've a couple of question regarding epoxy, because I'd like to learn a bit more about it for a future project.

1. A well known italian manufacturer of epoxy resins and heli blades (probably you know it...SAB Composites) recommends curing its longest cure epoxy resin(120 min working time) at 40 C° for 10 hours in a oven in order to obtain max resin performance...that is its ability to resist 120 C° of heat without destortion. Is this process of hot temperature curing called post cure or I'm wrong? And if I'm wrong, what is post curing?

2.Are there any directions (books, websites) to build a small but capable oven for composites curing? Ok I know it would be better to use autoclaves like the big ones I've seen at Ferrari but I think it would be a bit too expensive

3.What is used to raise the temperature in the oven? I've heard that simple 100 Watt light bulbs will do the job, but maybe there's a better way.

I'm asking this because here in Italy summer is usually quite hot and the pond is quite far from my home...I wouldn't like to see the hull of my future scratchbuilt submarine distorted by heat.
And anyway, regarding Robse's post, I've noticed that, when cutting with the Dremel on my ThorDesign 1/96 Uss Permit, no softening of the manufact happens...really professional epoxy glass work!!

Thanks for the reply, and keep posting!
BEST REGARDS MAURO

[rkc]

Hi Mauro

Dont know the resin

Hi Mauro

Dont know the resin system, but this is a similar profile to one of the resins we work with. You dont say if it is a room temp cure resin, followed by 40 dgrees C for 10 hours. If it is then yes the 40 degrees C is the post cure. That is an impressive Tg for such a low cure temp resin.

Autoclaves are really for use with pre-pregs, used by F1 teams and aerospace. This is a system where the fabric is already impregnated with part cured resin (pre-pregs need to be kept at about -18C to prevent full cure at room temp over a long period of time.). This is where an autoclave comes in, to provide high pressure consolidation (up to 14 BAR on ours), and the temp required (up to 200C) for cure. You can cure pre-pregs in ovens but its not as benneficial. (cost, ours was £85,000 in 1985, was an ex demo and is only 3 cubic meters capacity)

Dont know of any books on making an oven but yes its possible to use light bulbs or many other forms of heating, in an improvised oven. The main thing is that the temp is even all around the job, otherwise stresses will be introduced into the structure that may not manifest themselves until later.

A little note that may be useful later. When working with epoxies in the mixed but uncured state, for every 10C rise in temp, the viscosity will be roughly half.

If you have any specific questions Mauro e-mail me. In fact that goes for anybody.

I suppose i should come clean, i work for the composites department at the university of plymouth, so if i dont know the answer i can usually find someone who does.

rich

[Guest]

Nice to hear some views

Nice to hear some views and opinions from the experts in these fields. There does seem to be a bias against Polyester resin though. Why? It's inexpensive and does the job.

All of OTW's hulls are cast in polyester. So are Sheerline and Darnell nee Metcalf Mouldings. Most of Engels range is cast in Polyester too, I believe.

Epoxy seems more popular in the States, where it is a lot less expensive.

I've found that movement in the resin is a problem, but only if the hull halves aren't 'pegged' together in some way.

I was told, by Steve Warner (OTW chief modelmaker) that much of the problems with hull warpage are more to do with poor layup than the material itself.

He always recommended using a roller when consolidating the resin with the cloth, as opposed to just stippling with a brush.

This results in a more even resin/cloth consistency and I would guess, a more even curing.

Andy

[rkc]

Hi andy

I suppose your right,

Hi andy

I suppose your right, there does seem to be a drive to use epoxies instead of polyesters. This has a lot to do with the enhanced properties of epoxy, but in the main these probably don't concern modellers.

Polyester does shrink and no amount of clamping will stop this, but serious deformation can be limited by leaving the resin to fully cure, not popping the item out of the mould whilst the resin is still GREEN (not its colour, its state i.e. slightly soft to the touch.)

Using a consolidation roller in hand layup is essential whatever system you use, as this will force most of the trapped air out. But i must admit i don't often hand layup as my speciality is infusion (RIFT, SCRIMP in the US), which is a method of sucking the resin in to the fibre stack under vacuum. This gives a far superior result, but perhaps overkill for a model. What steve says about layup is partially correct, but cloth layup is a complex subject. If you are using a simple chopped strand mat then you are completely at the mercy of the resin shrinkage, but a woven fabric will allow you to control how the finished product will behave to a degree. Polyester shrinks, typically about 4%, whereas epoxy is somewhat less tha 1%,so you can see why this can be a problem when designing your layup.

I suppose one other boring factor worth mentioning is that all fibres, Glass, Carbon etc have a surface treatment to aid bonding of the matrix (resin) to the fibres. Typically with glass this is tailored to polyester, with carbon being streated for epoxy, however fibres can be produced with sizing for either. This means that the typical chopped strand matt most people see is treated for polyester, and the thermoplastic binder that holds all those fibres together only breaks down with styrene, so CSM does not generally work well with epoxy.

Hope this kind of helps, but composites is a minefield and not worth getting too involved with, if you dont need to.

rich

[adriaticsea]

Hi Rich,

thanks very much for

Hi Rich,

thanks very much for the answer, I'll see what the resin system is but on SAB website they only say that, in order to get a good cure of the resin, it must be heated to 40 C° for ten hours, otherwise the manufact will remain soft and won't cure completely, therefore not reaching its full mechanical properties until complete cure (heating) happens.
I'm interested in composites also for reasons not strictly related to submarine modelling, because I find this kind of materials and tecnology really interesting.
I checked the web and found some infos on autoclaves...there are really BIG ones used in the aerospace and marine race industries ...now I know how they cure America's Cup sailboats epoxy hulls!! I guess your autoclave was manufactured by LBBC, correct?
Regarding Andy's post, I think another reason not to use polyester is that its catalyzer, MEKP, is HIGHLY toxic, and I heard somewhere on the web (not sure about this though) that if MEKP gets in contact with your eye one will lose almost immediately ability to view from that eye.
It would be useful to know if this is true or not, because if the answer is yes then for the modeller with limited number of hulls to layup it would be MUCH better to use epoxy instead of poyester, considering that epoxy uses hardeners (wich is different from catalyzer I guess) less hazardous than polyester.
Thanks for the replies!
BEST REGARDS MAURO

[rkc]

Hi Mauro

No our autoclave is

Hi Mauro

No our autoclave is by Aeroform (Airbus 40m one!).

Not heard about instant loss of sight, but will try to find out.

Now trust me on this, DO NOT (not shouting) think epoxies are safer, they are not. In fact they are full of some real nasties, and you can become sensitised to them. In a worst case scenario this could lead to hospitalisation or worse (not trying to scare anyone, just trying to make us all aware of the risks). Yes catalysers and hardeners are very different, but to stop filling the forum up with composites info email me and i will put you on to some useful sites for general composites knowledge.

Hope this helps.

regards
rich

[tmsmalley]

For fiberglass newbies - if

For fiberglass newbies - if you are working indoors at home and not in a detached garage or professional workshop with a heavy duty fume exhaust system, keep in mind that polyester resin REALLY stinks up the place.

Your wife will thank you for using a low smell factor product like West Systems epoxy.



Edited By TMSmalley on 1102370803

[rkc]

Good advice Tim, but i

Good advice Tim, but i must admit i prefer the smell of styrene to epoxy.

Mind you your right, i've used some west system stuff lately and it doesnt smell anywhere near as bad as some of the epoxies out there.