Wet Lay Carbon Monocoque Motorcycle Subframe, No Autoclave - Resin?

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#1

I have just learnt about Thorsten Durbahn, a German man who has been making composite motorcycle products since about 1997. The really interesting thing is that he uses wet layup for his structural monocoque, also he does not use an autoclave (he can’t justify the expense given how well he can produce parts currently)!

This got me seriously thinking about starting my own monocoque subframe…

What kind of resin do you think he would use? His website says that it is “high quality”, but do you think it’s any kind of special resin, or just a regular quality resin?

Previously I had never even considered making my own structural parts, I always thought an autoclave would be needed to create the best quality part, or at least post-curing. (Maybe he does actually post-cure his parts, I’m not sure…) I suppose the reason I always thought that was because of my own lack of knowledge on the subject of composites.

Does anyone know of others who’ve made similar parts using wet layup (and even without a post-cure)? And what do you think is the most you could do with composites using wet layup and without an autoclave or post-cure?

#2

This guy can justify his prices,probably the lightest parts available and he knows moreThan any one I’ve ever seen in composites,what I no off him his method’s to some are old school,but using software is not always the way to go,this guy is on par with John Britten in my eyes.a clever guy.

#3

post cure is only necessary if both the resin system & your application need it to sustain the operating temp/physical operating properties. Again autoclave may be needed to attain the physical/op temp range. It is application specific.

#4

He is definately NOT using regular quality resin, but HIGH quality resin… :slight_smile:

Anyhow, given the dynamic loading, I presume he is using for instance Momentive LR235 or 935, which is readily available over there. These are meant to be used in rotor blades, and can be postcured to give ultimate properties and Tg.

In your area I would ask your suppliers for a resin (regardless of brand) which can be used for dynamic loading, and has a (postcured) Tg of 100C or more. Perhaps more if the exhaust is near the frame.

#5

Cheers for the info.

Thorsten definitely knows his stuff, I found a copy of a scanned article from a Performance Bikes 2009 issue. Some people would probably wonder how such parts could emerge from his workshop (it looks like a bomb hit it, and it seems like everything is coated in dust). Can’t help but respect and admire the man after learning just a bit about what he does.

Thinking more about this I realised that using wet/hand layup methods for structural parts is probably nothing new? I’m sure plenty of people have produced spoilers/airfoils like this, and when in use they’re definitely structural?

Well I consider myself a little bit more educated now. Composites really do offer some amazing possibilities!

#6

Hand layups can produce fantastic parts. I use MGS 285 for most of my stuff. It is an structural aircraft certified epoxy.

I often do hand layups over infusion because I can do them faster and at a lower cost. I’ve tested quite a few prepreg autoclave parts that were rather junky and porous. I also worked with some AoA prepregs and quite because the hand layups were testing better.

Infusion and prepregs really come into their own when the project is large. An F1 chassis takes several weeks to layup with crews working around the clock.

The challenge with any process is to insure that the fabric is fully saturated. When I first started compression molding (silicons) I had weave intersection voids. I could do an identical layup with only a hand layup and have it come out cosmetically perfect. I would do the exact same thing but add the silicone and get voids at the weave intersections. No vacuum or wicking was involved. I concluded that air was getting trapped in the tows of the carbon. When the pressure was applied the air in the tow would migrate to the place of least resistance: the weave intersections. The solution was to work the resin into the fibers. I used a stippling action with brush to eliminate the problem.

#7

Now that is a very interesting point… It seems like most people with a new interest in composites want to jump right into infusion and vacuum methods (at least that’s how it seems to me, and I’ll say that I probably would have jumped in and bought a vacuum pump and all the associated gear if I had the money). Possibly before they fully explore the potential of hand layups… It helps to keep it all in perspective!

#8

It’s also true that with vacuum you can use heavier fabrics, especially into the edges.Resin infusion or prepreg have the advantage you can glue fabric in the right place… Having say that, no doubt for many users the results reached by wet layup are great

#9

I need to practice wet layup someday. I started out with hand lamination, then a varied method of lamination with bagging, and now just do infusion. It would be nice to get some hand layup in there too since sometimes infusion is overboard for some of the parts

#10

Hi… New here but when I saw Durbahn mentioned I thought I would add a little too… I have had one of his seat units… it was black gel coated and although it was quite strong it was not as light as it could have been if it were Pre-preg. He does add extra material for a good margin of overkill… Understandable to be honest… The finished parts quality was OK but not amazing. It works and saves weight which is all that is really important to him…
I have made my own monocoque seat and combined fuel tank which it fully structural. I would make one it wet lay but it would be possibly be double the weight of mine which is pre-preg but NOT autoclaved… The only down side is if you are after a good cosmetic finish I would expect to have a number of attempts at getting it right or even acceptable. I know Pedro has made some amazing stuff but as he admits it was not an overnight sucess and he has found a method that works for him. Most of my wet lay parts are just polyester resins as they are not structural. But my more structural parts are either pre-preg or epoxy wet lay for the fuel tank base. But I will be the first to admit I have not tried to make the epoxy wet lay part cosmetically perfect as it is out of sight and only has to be strong and resistant to the ethanol now found in fuel…

Here is my wet lay carbon. This is just a frame protector… Nothing too large…

Here is my monocoque seat/fuel tank unit… Sorry for the sytlised photo…

Close up of the actual finish on the surface…


Here is the inside of the tank and the base… The inside has to be coated with an ethanol resistant epoxy due to the ethanol now in road fuels…


I would tell you how I bond the tank base in and the adhesive used but I made my own adhesive and had to work out my own special method with a pressurised bladder system as well as the clamps to get it in place and tight enough to push the base into the adhesive well enough to bond fully.

The guy who has been helping with the mould and my first lay up has said the finish is not as good as he would have got but the two you see here are my first attempts…

#11

That’s interesting, thanks for your comments on the Durbahn unit. Maybe all that extra material he uses is why his monocoques can crash so well. Haha. :stuck_out_tongue:

All the photos of your finished parts there look fairly spectacular to me. I’d be well pleased to make some parts that look like that!

With your prepreg you would have just done a post-cure, right? I remember reading something about an oven on your Facebook page… Also did you use any core materials in your monocoque or is it all just CF? (And just curious if anyone knows if Durbahn uses core materials or just straight CF as well?)

#12

Durbahn seats, they dont crash too badly… although I had smashed one to bits. He doesnt seem to use a core. I have not used a core in mine. I had planned on but the guy who has been helping me just said it will be more than strong enough with his lay up and a core will create dry areas on the surface as it will pull some resin off the surface. The Pre-preg is only 42% epoxy to Carbon ratio where wet is 100% usually. Not done a post cure on the part. The mould had to be post cured obviously. I have access to a huge oven which is what I am building at the moment. Without help from Vic I would have possibly had either sub standard moulds OR a set of moulds that I would not know what to do with. I had 3 customers pay my original supplier directly the full quoted price and he just dropped it when the three he made were worse than the pattern parts…Hmm… So I had to pick up as much info as possible and have sort of become a composites info sponge now…

The parts are good in my opinion but my “tutor” is a perfectionist and keeps pushing me to do better and better parts… I understand him to be honest but the down side is I can only get the best finish with one material that is at least 50% more expensive than the other stuff out there. Luckily this is the same for everyone who is going out of autoclave parts. There really is only one material that works well and gives a pin hole free finish.

#13

great looking parts. what do you use for the mold surface as a release? You are getting some nice cosmetic looking surface finish there.

#14

Cheers… i used Marbocote mould sealer and either fastcote or Marbocote 227cee relase. I dont use wax now as I have got used to semi permanent release and I can use it for wet lay and prepreg. I cant really use wax for pre-preg so it keeps release agents consistant.

#15

Take a look at this thread, there are some nice pictures of a carbon monocoque.

http://www.compositescentral.com/showthread.php?t=7867