CF accessories are very popular amongst motorcycle riders, especially exhaust/muffler silencer cans. It’s not uncommon to pay up to a $1000 for one muffler. And manufacturers are sometimes reluctant to include a warranty. Somewhere along the line these CF mufflers crack open or “explode”. This is due to the heat and high RPM’s. 4 cylinder motorcycles tend to have more mercy on CF mufflers but 2 cylinder v-twin engines eat them up. I have 4 different makes here, all cracked open. The manufactures claim its “seamless”, but all of them crack open in a straight line, then you can see a clear seam. Sometimes these tubes consist out of two halves bonded or flanged together, but the naked eye can’t see it. Done very well though. One manufacturer uses a flat piece of carbon about 1.3mm thick and then roll it in a tube and bond the two edges, these designs last only a few thousand miles.
Is it really possible to create a seamless tube, I guess it is, but I don’t know how to.
About a year ago a local motorcycle muffler builder asked me to start experiment with CF mufflers. The demand is sky high and people can’t pay brand name prices.
That is how I ended up trying to build a tube the “wrong?” way. But to our surprise it worked. We made two mufflers and decided to do some very harsh testing on it. We fitted it to a track racing superbike that participated in competitive racing. For almost a year these mufflers were hammered and raced at 15 000RPM around a track. And no trouble what so ever.
Here is my how I did it. I used an oval mandrel and covered it with 1 layer of sheet plastic. (To ensure it doesn’t bond to the mandrel) Then I simply rolled 200grm twill weave carbon over it while wetting it out. The same way as toilet paper is rolled onto a tube. But as I roll it onto the mandrel I wet it out with epoxy resin. When dry I knock out the mandrel in the centre and there you go. You end up with an epoxy soaked ugly looking tube. Then the sanding process starts. This takes a lot of effort, blood sweat and swearing, but after a while it’s flat and smooth (and dull). Two layers of clear coat spray paint and it look very sweet!
The clear coat doesn’t last; the heat makes it tacky and snotty. But the tube last!
Questions:
1.Im aware this is not the way to make a seamless tube, but for some reason it works. Is there an easier way to obtain a smoother CF finish and look that requires less sanding and no clear coat paint?
2. Is it necessary to bag and suck up excess resin to get a better carbon resin ratio?
3. What is the right way to manufacture a seamless tube, with the tools found in a domestic garage?
hi is there a way you can post a pic?
thanks
1: Carbon braided sleeve, or filament wound. It would be very seamless. You can also do more than one layer, overlapping the fabric edge. You can do this on a male mold, or female mold halves with a bladder. (actually, even a tube vac bag would work.) Bonding 2 halves together is just stupid, but many companies are only around to make money.
2: To directly answer that question. Yes. However, you can do VARTM, or prepreg to get a consistent fvf.
3: Besides using the exact shape aluminum mandrel, you can do a split mold (with plastic on the mandrel to cover the gap), and then you can release the mold halves and pop the tube off. Even weekend warriors of composites have done a split female mold and make their own pressure bladder (latex, silicone, etc). You can do wet layup, or prepreg that way.
If you want a pristine finish out of the mold then it becomes difficult to do it without seams of some sort. If you wrap a firm bladder with a sleeve and then inflate in a female mold you will end-up with pinholes on the surface almost every time. Little bits of air get trapped between mold wall and the layup during bladder inflation. That air just gets trapped there.
To get a pristine finish with a male wound/wrapped tool will require a lot of labor.
To have a tough stable structure you almost always need fibers going in more than two orientation. This requires seams of some sort.
I make a lot of tubes in female molds with bladders but they all seams. The advantage is that the seam overlap can be large and the seam can be co-cured which is much stronger and lighter than a secondary bond. With a roomy diameter like a muffler you could have the overlaps be 2" or more and staggered to eliminate any stress risers. During destruction/spec testing these parts do not fail along the seam.
Would you mind to post some pics of the construction process? my biggest downlfall is that i make thing too complicated in my head, and then i tend to say :“i dont know how”. I came across a How 2 guide on tubes, but its not going to be strong enough for muffler construction…
The first photos shows how the fabric would be oriented in the mold. The second photo shows how the mold would be joined. The seaming flap and staggers could be done much larger than the illustration shows.
This video briefly shows how to make a bladder and the bladder assisted process. Here is a video of the part being demolded.
Here is a video of some destruction of the above 40 gram part.
You need a beefy mold to handle the pressures. The more the surface area the stronger the mold has to be. The end opposite the bladder entry need to be rounded to support the bladder. The entry needs to be tapered to transition the bladder from the entry port to the portion where the part will start. See the third photo of this transition. You can see that the conic shape in the mold exists just to transition the bladder. The line/edge in the mold is where the part would begin.
The forth photo is what a carbon seam can look like immediately after demold.
I would think you could use braided sleeves, of various nominal diameters. The small the nominal diameter, you’d have something like +/- 30, correct nominal diameter +/- 45, and a larger nominal diameter could be +/- 60 or something. I’ve not experimented with this, but I know that braids are designed to have +/-45 degree orientation when applied at their nominal diameter, and that orientation will change based on the actual diameter the braid is conformed to.
You undoubtedly can but trying to “swell” them inside a female mold to get a pin-hole free surface and keep the fibers aligned takes luck. Putting them over a male tool is no problem but then you have a lot of finish work to do. The advantage to working with cuts is that you can position them and work them to insure that there is no air between the mold surface and the layup.
It is quite possible to infuse tubes in a female mold. If the tube is larger enough you could get your hands into a closed two piece female mold to position the fabric, peel-ply and flow media. The mold is closed on one end with a vacuum port and the other end is open. The whole closed mold gets put into an envelope bag that is a little more than twice the length of the mold. A vacuum line goes through the bag and into the vacuum port in the mold. A second line goes through the bag to a spiral ring that circles the open end. Vacuum gets applied and the long evelope bag gets sucked right into the open end of the tube mold. You can infuse through the spiral tube line towards the vacuum line.
I could do a muffler sized tube faster with a hand layup and bladder than I could rigging and doing the infusion.
Thank you very much! The video answers a lot of questions. Im very tempted to try out your technique. The way you constructed this part makes me think you are a brain surgeon by day? The precision and accuracy are perfect! However, Im also tempted to play around with braids, but its so much more expensive.
You guys gave me an idea now. Forgive me for the explicitness of the thought…lol. construct a 2 piece split female mold, get some braid, wet it out, and use a bladder something in the line of a condom? and cover the condom with the braid, insert in mold an inflate??? I recon a condom is stronger than a tube party baloon… but would i get a smooth surface finish?
That technique will end up with oodles of pinholes all over the surface. As the bladder inflates it will trap air at every weave intersection between the carbon the mold surface. If you get it wet enough…we are talking puddles here…you can sometimes get a near perfect part. It’s luck in my opinion.
The key for bladder molded parts that have pristine finished is to insure that there is no air between the layup and the mold when the bladder gets inflated. If there is air in there the bladder will just lock it into position. The only time that air moves is if the resin moves. I crack the mold about .003" during the first 20 minutes after bladder inflation. This lets the excess resin out as the layup gets compacted. Some air will move with it but far from all of it. The key is to not have any air in there to begin with.
BTW, I’m not brain surgeon. I’ve just done bladder molded parts 5 days a week for 5 years. 
Avoid using ribbed pleasure ones or You end up with funny inside finish… :laugh:
Joke aside, condom is not the best solution unless if You can get them prior to being lubricated. I tried using them and it was a mess. Then I made a bladder out of inside tire and used it many times to produce this:
Qualatex twisty balloons can work ok. They come in varying diameters and lengths. The first number in the sizing code is the inflated diameter and the second number is the inflated length. A 160 would be 1" in diameter and 60" long. They come in 160, 260, 350, and 646. They key is inflating them before hand for about an hour before using. This takes the stretch out and allows them to inflate more predictably. Bladders that stretch can be problematic. Often you need a stem to stretch the length out so they don’t try and grow in length inside the mold. This can distort and slide the fabric around.
Other things that can work are bicycle and car innertubes, silicone tubing, molded silicons/latex/dragon skin, heat welded Stretchlon 800, and heat welded plastics like in the video I posted.
If you have a more complex shape then you need a shaped bladder that won’t stretch.
Ever tried Release Bag 375, or 460 if you need to go higher in temperature?
I personally have not tried them.
Wyowindworks, those fuses look really good!
Any chance you could explain a little more about that sprayed clear coat and what’s exactly? Does it helps with pin holes finishing or is just the pressure which gives such a nice finish?
Cheers,
Jordi
On this lightweight hobby part the clear-coat is just a single component lacquer. On parts that can afford a heavier in mold coating I shoot 2K urethane into the mold. I use a clear-coat in the mold because it:
- Makes the release easier
- Makes the mold easier to clean-up and no little bits get left behind
- Eliminates resin beading on the Frekote mold release. This helps the hand layup go a little smoother.
- #1 #2 combined increase the life of the tool. The tool in the video has now produced 78 parts and still going strong.
- I can hit the part with a swirl remover and 1 minute of hand rubbing to clean up the part and make it shine before it is packaged.
I don’t use a clear-coat to eliminate pinholes. If you have pinholes between the clear and the layup they will still show up. I do the layup so no pinholes exist. I hate doing post mold painting so all my painting is done in the mold. If the mold finish is stellar the part finish is stellar. It’s also much lighter. I do the same thing on contracted UAV parts.
The nice finish comes from have a really good mold surface, stable well fitting molds, and leaving no air in the layup before bladder inflation.
I found a motorcycle exhaust can yesterday to study how its made. Its one of the most expensive CF mufflers you can buy for your Italian bike and is also made in italy, not going to mention names. It wil set you back $2500 for a new one. The spesific one I obtained is 12 years old and still perfect. I was shocked to see how its constructed. Its made exactly like mine and is even thinner. 90% of the thickness is obtained by wovan glass, and the last 10% 200grm 2by2 twill CF. You can see clearly the start line of the glass, and the end line of the CF. So its also made with a male mold in the same way. I highly doubt if its pre preg, but rather a wet lay up. The surface finish is not shiney at all, its dull and raw CF with a very rough uneven surface. But there are very prominent tooling marks on it. It looks as if it was worked down on a lathe. But I think its the aftermath of the shrink tape. I worked out they must have used at least 25 meters of shrink tape. Besides the horrible high price of shrink tape, it requires tools to heat up the tape that i dont have.
So my question. I like all the input and suggestions i recieved from you guys. But I want to stay with this technique.
How can I get an acceptable surface finish with a male mold, without using any shrink tape, female mold or automotive clear coat?