Black Carbon Fiber Masts - Why don't they soften?

[CatBuilder]

We all know not to paint our epoxy boats black so they don't get hot and soften.

Why is it, then, that a black carbon fiber mast does not have the same problems?

[troy2000]

Because they aren't epoxy, maybe?

edit: flippant, ignorant answer. I'd delete it, but too many people have seen it already.....

These masts are usually pre-preg materials that are cured in an autoclave at fairly high temps. Between the epoxy formulations and the post cure, they can attain some pretty good tg numbers. I've read that NASA has some materials that can easily exceed 2,000 degrees! Of course , they're also playing with titanium fibers.... not exactly within the reach of the average builder.

[TeddyDiver]

With thin upright shape it's not so susceptible to heating compared to decks.. I think.. anyway it sounds right.. right?

[Herman]

We are discussing epoxy boats, and epoxy masts.

The trick is that epoxy is not just epoxy.

There are many different types of epoxy, all with their own heat resistance.

The heat resistance is given as Tg (Glass Transition Temperature). This (ultimate) Tg can range anywhere from 40 degrees C tot over 200 degrees C. Keep in mind that this Tg only develops after receiving enough heat. In general one can say that the Tg will be approx 15 degrees over the postcure temperature, of course untill the ultimate Tg is reached.

Most marine epoxy has a Tg of 45-55 degrees tops. Some (infusion) resins have a Tg of 80 or 90 degrees, which should not be of any problem in hot places.
More advanced epoxy resins, also used for prepregs, have Tgs ranging anywhere from 100-140 degrees (given a 80-120 degrees cure temp). This is what mast manufacturers use mostly.

You can even go higher in Tg, but that is out of scope here. One example is the use of high Tg resins for composite wheels for trucks. When doing an emergency stop the brakes can reach 520 degrees. The rims need to be capable of temperatures up to 185 degrees.

[CatBuilder]

Thanks, Herman. My wife and I were talking about this and I didn't have the answer to this question. Makes perfect sense now.

[Jimbo1490]

Many different resin systems (a system is a resin and its curing agent(s) and modifier(s)) can yield very good high temperature performance. DGEBPF family resins yield consistently higher Tg's than the DGEBPA family resins. Higher EEW resins of either family yield better cured-state properties, including Tg, though higher EEW means higher viscosity and poor handling properties. This is the basic reason that 'pre-preg' exists; the best resin systems in terms of cured state properties are unmanageably viscous, some even being a solid at room temperature. One of the most common systems used in commercially made pre-preg is Epon SU-3. The basic resin in this system is so viscous, it has to be heated to facilitate blending with the curing agent. Then it is mixed with MEK as a non-reactive diluent to facilitate impregnation into the cloth. A short bake cycle evaporates the MEK, then is goes to the freezer for storage.

There are a few curing agents that give really good high temperature performance with the less viscous resins, those suitable to either hand layup or infusion process. One is the Lewis Acid family (boron trichloride amine for example) and the other is the imidazoles (2-ethyl, 4-methyl imidazole, for example). Both act as true catalysts (as opposed to curing agents) and will work in any resin and have no strong stoichiometry, so can be used at a variety of very low mix ratios, typically from 1-5% by weight. Both families yield Tg much higher than cure. Lewis acids must use elevated temperature to cure, with initiation ~90C. The imidazoles are on the lower edge of ETC systems with initiation only around 50C. Both yield VERY long working life, the Lewis acids even considered latent @ ~6 months, while 3-5 days is typical for imidazole systems. Both types cure in a few hours at elevated temps. Both yield very high Tg numbers, usually something like 50C above cure (or post cure) temperature. So with an imidazole system cured at 50C you can expect a Tg of ~100C, which will make a black boat mast quite rigid in the noon day sun as a flat black surface will reach only about 70C

UV stable epoxy resin systems are also available, so you don't have to paint it either.

Jimbo

[variverrunner]

Jimbo,

Are any of the UV Stable epoxy resins you mentioned available thin enough to use for infusion?

Thanks in advance.

Allan

[Waddie]

this thread is more about the nature of composites than specific to boats, so I'll wander a little off topic here and throw out a couple of concerns a friend of mine has about the new composites being used in commercial aviation. He is an airline pilot with about 15 years experience.
1. how well will these composites hold up to prolonged UV at 30,000 ft?
2. how do you identify composite fatigue, or I should say will the average maintenance tech know it when he sees it? (lots of maint. done overseas).
3. the plane he currently flies is all computer operated, there is NO control yoke. How will these circuits handle lightning strikes over time? (usually the lightning travels down the aluminum fuselage, but more and more of the plane is being built of composites).
he's just wondering, discussed over a brew or two, not trying to alarm anyone.
waddie

[Herman]

1. Paint. You see Volvo Ocean Racers with fancy transparent paint on fancy prepreg layups. (if Susho is reading this, can you post the nice picture you posted before?)
Most airplanes are white. And for a reason. Racing boats don't sink because of some low-level UV degradation. But up there in the sky UV can be a nasty thing.

2. You can do some analysis with equipment. On the eye it is very hard to determine. Except for the obvious faults, of course.

3. No idea about planes, but windmills (also prone to lightning strikes) are protected by extensive ground plates in the tips. (windmills are glass, in general, and not conductive). Planes are carbon, which is conductive, so that at least should help maintaining a faraday cage. I guess (I hope...) some engineering went into that part of flying...

Anyhow, lightning strikes can do a lot of damage, and I guess (again) that strikes are being reported and/or detected and recorded. No matter if the plane is aluminium, carbon or anything else.

Top Gear did an item on lightning strikes. (600.000 volts) http://www.topgear.com/uk/videos/car-lightning

[susho]

yes I'm reading this (it has carbon fibre in the title, haha) here it is, follow the red arrow. I guess they've used awlgrip or similar.
I've painted masts with double cout from "de ijssel" wet lay up as well as a prepreg mast.

so that at least should help maintaining a faraday cage

They use a copper mesh in parts

[Herman]

Originally Posted by susho

They use a copper mesh in parts

Airplanes as well? Probably yes.

[susho]

from what I've heard, yes!