Hi all. I made a CF hood for my car a couple years ago but have never been completely happy with the pin holed results. I would like to try another using infusion with epoxy resin vs. the wet layup vacuum bagged VE I used the first time. I originally used VE because of its higher TG but from all my searching I can't find any mention of people using high temp resins for their hood creations. Is a 180-200F TG high enough for a hood? I could always make an oven for post curing a high temp epoxy but that just adds extra work and cost. What have others been using as an epoxy resin choice and how have they held up? Thanks for any help.

> from all my searching I can't find any mention of people using high temp resins for their hood creations.

Sure, people have even used West System epoxy, but I doubt many of them report back and admit their mistake when the hoods starts to soften during summer and the weave starts to print through or the hood deforms.

> Is a 180-200F TG high enough for a hood?

Depends on where you live. What temperature does your hood develop on a windless summer afternoon? Carbon parts in the interior of a car can reach 100°C/over 200F.
It's a start and certainly better than using resin systems that are proven to soften and turn rubbery slightly above room temperature. The cost of a hood is quite high, why take any chances and try to save 10 bucks on resin? Makes no sense to me.
I don't consider 90°C/200F Tg very high temp resin, that's a Tg range many resins are able to reach (except certain sub-standard boat building resins). But they require post-curing, whether you want to let the sun do your post curing or you want to do it yourself under controlled conditions is up to you. I 'd choose the former.

> I could always make an oven for post curing a high temp epoxy but that just adds extra work and cost.

My simplest curing oven was build in 3 minutes, consisted of a corner of the room, three sheets of styrofoam and a light bulb. Then again I didn't use it to cure car hoods

> What have others been using as an epoxy resin choice and how have they held up?

Resins with Tg in the 90-120°C range. Can't give you any brand names since they aren't available in your corner of the world.

Ideally you need a to find a resin that can be initially post cured at a lowish temperature (50/60/80degC) but also one that can be post cured off the mould so it will cure in service without distorting. There are a number of resins that will do that but you have to hunt them down

Thanks for the replies. From my previous research I had come to the conclusion that high temp was needed, it just struck my curiosity that I didn't see anyone mentioning it in their hood/bonnet threads. I can get a PTM&W high temp infusion epoxy in Canada but only in 5gal/20l kit quantities so I will probably end up using it for everything regardless of whether it needs it or not. Only my hood and dash really need it IMHO. It is a bit high on the viscosity side but I think it should infuse OK (says the guy who has never infused before ) The PTM&W can be final cured out of mold but I still think I would feel more comfortable making an oven and doing it in a controlled environment. 

As a general rule of thumb the achievable Tg is determined by the hardener. If you look at a certain resin it will produce different Tg with different hardeners. If you take another resin brand and use the same hardeners with it the ranking will be the same. And slower hardeners will often (not always) produce a higher Tg.

Also look at the MSDS of different hardeners. If you find one which for example consists of isophorone diamine ( http://www.chemspider.com/Chemical-Structure.16867.html ) and nothing else it will produce a Tg of up to 120°C and has a pot life of roughly 90 minutes. Hexane diamine is another good material with a little shorter pot life.

These are pretty common materials but very often you can't get them pure, many of these "resin systems" contain horrible mixtures. "Resin systems", where you have to buy both resin and hardener from the same source are a big lie anyway. You can use resin from manufacturer A with hardener from manufacturer B and tailor the results to suit your needs. You just need to calculate the proper ratio, which isn't too difficult if you can get a real datasheet for the components.

So what I'm trying to say here is you can buy a resin and then use it with the hardener of your choice to achieve the same or better results for less money than many commercially available epoxy "systems" will produce. Or you can copy epoxies that are locally unavailable.

[edit:]
Just had a look at your link. Without having seen the MSDS I am pretty sure that pt5712 stuff contains isophorone diamine...

I think you guys are overestimating how hot your bonnet gets a little bit. 

I don't think so. I live somewhere in the middle of Europe, our summers here are pretty lame compared to yours.
When I park my car in the sun I sometimes can't touch my steering wheel without hurting myself, and I certainly couldn't touch the roof of my car during holidays somewhere in southern Europe. The colour isn't black, btw.

You have to build such parts for the worst case, which means real world Tg being less than the one in the datasheet, car parked with three walls around it, no wind whatsoever and the sun shining directly on it. The thread starter seems to live in the US and not in Scandinavia, can get pretty hot there.
There have been tests made of car parts like dashboards, and they indeed can get very hot. Same has been done for aircraft. There's a reason why almost all of them are painted white. If I find these tests again I will post them here.

Well interior parts are another matter, they sit inside the car like an oven. I know it can get extremely hot in there, and I would consider it necessary to use a high Tg resin there. 

I am doing another bonnet/hood for my race car here in Australia (I trashed the first one in a double rollover) and I was selecting a new resin for the infusion.  I was worried about the temperature that a black (naked carbon) bonnet/hood would get to and matching the TG/HDT to that.  I stressed for a long time!

Then I went and got my $30 eBay laser/infrared thermometer and went around a car park in the middle of the day in summer!  The dark blue and black cars sitting for hours in full sun on a 30oC day reached ~65oC.  I tested all different colors, metallic, non-metallic paint, steel and alloy, etc.  I used my own cars as control cars, etc.  It was pretty thorough with the only exception I can think of being that the cars did not have engines running - but then again they also did not have passing air cooling them either.

I would suggest that everyone gets a laser/infrared thermometer anyway because they are invaluable for checking very accurate temp ranges on post curing parts.  Finding hot/cold spots in a curing part is important, as well as the temp of molds when infusing, etc is all very good.

As everyone knows, consistency in conditions produces consistency in results - so get a laser/infrared thermometer!

But I digress.  Check the temperature of the corresponding part in the same conditions as the proposed part.  And if you are doing it with your hand, 60oC is bearable to hold your hand on, and at 65oC you will want to take your hand off as the heat soaks in ... or get a laser/infrared thermometer!

In the end I am using Kinetix infusion resins (by ATL composites who also do the West System resins). There are 2 I am using, one of which requires post cure to cure for higher temps (92oC HDT), but the room temp cure resin (helped with a 60oC post cure) raises the HDT to 68oC.  And with these resins I have heard/read that further post curing increases these results as well (that is not confirmed!).

Yes I did the same thing with very similar results to you. Good to see someone else in Australia getting the same results as me.