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  1. #1
    Mr. Dopolina Bob Dopolina's Avatar
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    Carbon Clincher Rim Manufacturing Primer; Taiwanese vs Chinese Methods

    The purpose of this thread is to shed a little light on some of the principal differences between how Carbon Clincher rims are produced in Chinese factories vs Taiwanese factories.

    A few caveats:

    1. There will be some generalities here because it would be impossible to know how EVERY factory does what they do and it would be false to claim otherwise.

    2. There will be some omissions because some information is not mine to discuss and if I did so I would have to close up shop and sell fruit by the side of the road.

    A few other facts:

    1. What I am describing I have seen in person and held in my hands. This is 100% first hand knowledge and this is what I do to feed my family and buy my beer.

    2. Cats don't always land on their feet.

    To start:

    Carbon rims are made in a mold that has a top half and a bottom half. Carbon prepreg is wrapped around a bladder much like paper machete is wrapped around a balloon. In most cases the rims are made in one piece but not always. The rim is then placed in the bottom of the steel mold.

    Here is where things can diverge:

    The issue becomes how to make the shape that will be the part of the rim where the clincher tire attaches to the rim. There are some VERY specific dimensions set by ETRTO that need to be followed to ensure tires will mount (and stay mounted) on the rims. See: DRAWING A


    DRAWING A: The ETRTO specifications for a clincher rim

    The Taiwanese method:

    Taiwanese mold makers (in any industry) have a solid reputation around the world for being good mold makers. And it is not just enough the be able to make a good mold, the mold must also interface with the machines that will inject stuff into it, whether it is a gas, plastic on anything else or any other piece of equipment that comes into play during the manufacturing process.

    Chinese mold makers...not so much...but they are cheaper.

    With molds it is basically a cavity inside a machined steel box. Some of the cavity is cut into the box and some of it must be achieved by pieces that are slid into place usually after the mold is closed called, funnily enough, "sliders". Sliders are also machined from specialty steels.

    This is the method used in Taiwan (I can't show a picture of a rim mold).

    The advantage of using sliders is tolerance and pressure. I will come to that in a bit.

    The Chinese method is a bit different. See: DRAWING B


    DRAWING B: Sliderless Clincher rim production

    The Chinese method is to make a cavity in the mold but NOT to use sliders. Instead a silicone rubber section is inserted in the top of the rim and a layer of carbon is placed over top.

    Both methods then inflate the bladders to pressure and bake until golden brown. Rims then cool and are removed from the molds.

    Removing the rims too early (to speed up production) can result in rims that look ok but are not completely straight. When building these rims it is tough to get good spoke tension balance and they will often go out of true over time.

    The Chinese rims then undergo an additional step where the carbon layer and silicone filler are MACHINE out of the rim.

    Which is better and why?

    Using a mold with a slider is much more expensive for the factory but the advantages are tolerances that never change (as the pressures involved will not impact the steels) and less voids in the rim specifically in the rim bed and brake track areas because, unlike steel, silicone rubber will compress under pressure.

    The end result is that rims manufactured in molds with sliders will be stronger due to better compaction and less voids that those produced using the insert method.

    Stay tuned for:

    Prepreg choices: Is T-700 right for you?

    10 signs your polyester resin in cheating on you.
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  2. #2
    Senior Member datlas's Avatar
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    Very interesting.

    Thanks for the post!
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  3. #3
    Senior Member Steve90068's Avatar
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    great read. thanks for posting, Bob
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  4. #4
    Senior Member Nachoman's Avatar
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    How would a lay person ever know if sliders were or were not used in the construction of their inexpensive carbon wheels?
    .
    .

    Two wheels good. Four wheels bad.

  5. #5
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by Nachoman View Post
    How would a lay person ever know if sliders were or were not used in the construction of their inexpensive carbon wheels?
    You can't.

    I can't either unless I see a rim that was warrantied due to failure or failed QC because of a problem in the machining step.

    Someone posted a new Chinese wheel purchase a while ago that included a photo that clearly showed that these rims had failed QC horribly and that the factory had them slathered on some 3k in the rim bread to cover the worst of the damage.

    Glaringly obvious.
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  6. #6
    Senior Member abstractform20's Avatar
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    OP, what kind of fruit will you be selling, and do you stock anything other than Hammer? everytime i use hamer, i drop it.

  7. #7
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    I thought it was 'drope the hamer'.

  8. #8
    Senior Member ericm979's Avatar
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    Here's some additional diagrams from Far Sports (CN) web site:



    There are two different methods for the core mold. Most rims use an inflatable bladder which is removed later. Some use a foam core which is left in. Generally speaking you want to be able to put more pressure on the composite before its cured to squeeze out more expoxy. It's stronger and lighter that way. Also my understanding is that more pressure results in fewer voids in the epoxy.
    Attached Images Attached Images

  9. #9
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by abstractform20 View Post
    OP, what kind of fruit will you be selling, and do you stock anything other than Hammer? everytime i use hamer, i drop it.
    Luckily I live near the Mango capitol of Taiwan so I have good access. I can wheel a cart from the field to a highway on ramp without too much trouble.
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  10. #10
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by ericm979 View Post
    Here's some additional diagrams from Far Sports (CN) web site:



    There are two different methods for the core mold. Most rims use an inflatable bladder which is removed later. Some use a foam core which is left in. Generally speaking you want to be able to put more pressure on the composite before its cured to squeeze out more expoxy. It's stronger and lighter that way. Also my understanding is that more pressure results in fewer voids in the epoxy.
    Foam core is even less desirable for the reasons you've already mentioned.
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  11. #11
    Senior Member abstractform20's Avatar
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    Quote Originally Posted by Bob Dopolina View Post
    Luckily I live near the Mango capitol of Taiwan so I have good access. I can wheel a cart from the field to a highway on ramp without too much trouble.
    you should have a freebie code on your website. BF members (not the members of boyfriends, but bikeforum members) type in the code on an order, and receive a free mango (carbon if possible)

  12. #12
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    It has been some years, but I worked in an aerospace company that was making significant inroads into composite propeller and spinner construction.

    All layups were with elevated temp, epoxy prepreg cloth. Mostly carbon, but also some kevlar for impact issues. All layups followed a prescribed schedule, were a given number of layers, of very specific shapes of impregnated cloth were arranged in a specific manner; not unlike making a garment. Prepreg material has a specific balance between fiber and resin. I don't remember exact details, but I seem to remember or cloth was ~60% of total weight, while the resin was ~40%. Unlike wet layup methods, the goal is NOT to squeeze any more than a minor amount of resin out of the layup, just enough to ensure all layers are fully bonded without air pockets. Generally, wet layups end up a bit resin rich, which isn't optimal from a strength for a given weight.

    When we were first working out a layup schedule, we had a blue 'witness film' that was applied as the outer layer. In a good layup, the final product would have an even, semi-transparent blue tone over the entire surface. Too much pressure, and there would be just the black of the prepreg, and too little, or a void, and the blue would be opaque. There is a good bit of skill, expense and hair tearing in getting a layup schedule right. Closed molds, as illustrated above, and as used for propeller blades, are more difficult than open molds with a vacuum bag, like we used for spinners and fairings.

    Some initial temporary molds were made from aluminum filled epoxy resigns. All final molds were steel and cast iron.

  13. #13
    Senior Member himespau's Avatar
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    Quote Originally Posted by Bob Dopolina View Post
    Glaringly obvious.
    to you anyway. not to all of us. hope you pointed it out.
    Punctuation is important. It's the difference between "I helped my uncle, Jack, off a horse" and "I helped my uncle Jack off a horse"


  14. #14
    Senior Member Nick Bain's Avatar
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    do they make carbon wheels with a bonded non-structural metal braking surface?

  15. #15
    Mostly Harmless rjones28's Avatar
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    Quote Originally Posted by Bob Dopolina View Post
    2. Cats don't always land on their feet.
    No WAY!

    I enjoyed the primer.
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    getting banned from trollheim. does that mean you win?

  16. #16
    Senior Member ericm979's Avatar
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    Lightweights use a foam core (see http://weightweenies.starbike.com/fo...69488&start=15).
    Do they actually suck or is it more complex than "foam core construction bad"?

    Does the foam core add impact strength? Does it absorb energy, adding to rolling resistance?

    Nick, I don't know of any cf rims that have aluminium brake tracks. There are aluminium rims with cf fairings (mavic, and hed I think), aluminium rims with more substantial cf making a deep section (zipp), and madfiber's clinchers which have an aluminium rim that's little more than bead hooks and enough material to hold them together. The cf wraps both sides so the brake surface is still cf but with aluminium backing it to (theoretically) conduct heat away from the CF and keep the beads from spreading apart due to braking heat.

  17. #17
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    I am curious, how many factories are there in Taiwan that make Carbon Clinchers. Also how many in China.

    My guess, based on the rims I see available on the internet is that in Taiwan there is Gigantex and maybe one other and in China, there two maybe three at most.

    Thanks

  18. #18
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by Staggerwing View Post
    All layups were with elevated temp, epoxy prepreg cloth. Mostly carbon, but also some kevlar for impact issues. All layups followed a prescribed schedule, were a given number of layers, of very specific shapes of impregnated cloth were arranged in a specific manner; not unlike making a garment.
    This brings up another point. All fabrics have a bias which is like grain in wood and runs 45 deg to the edge of the fabric. A good suit will have all the pieces cut with the bias running in a favourable direction. The problem is that this leaves a lot of wasted material and so adds to the cost.

    You can save money by laying out and cutting all the pieces so as to leave the least amount of wasted material but most pieces will not be cut with a favourable bias and will not produce the optimal product with the given materials.

    Quote Originally Posted by Staggerwing View Post
    When we were first working out a layup schedule, we had a blue 'witness film' that was applied as the outer layer. In a good layup, the final product would have an even, semi-transparent blue tone over the entire surface. Too much pressure, and there would be just the black of the prepreg, and too little, or a void, and the blue would be opaque. There is a good bit of skill, expense and hair tearing in getting a layup schedule right. Closed molds, as illustrated above, and as used for propeller blades, are more difficult than open molds with a vacuum bag, like we used for spinners and fairings.
    Interesting. Thanks.

    I don't know if this applies to current production or not. I think this is something I will try to find out in the future although finding a factory willing to share might be tough.

    Quote Originally Posted by Staggerwing View Post
    Some initial temporary molds were made from aluminum filled epoxy resigns. All final molds were steel and cast iron.
    I've heard that some factories will use temporary molds to really cheap out but I've never seen it and have no idea if it is true or not.
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  19. #19
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by Nick Bain View Post
    do they make carbon wheels with a bonded non-structural metal braking surface?
    Yes, sort of.

    There are a few brands now using a ceramic coating on the braking surface to address the heat issue which have a thin metal layer under this coating.

    This sounds like a really good idea but there seem to be some wear issues and it has yes to take off.
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  20. #20
    Senior Member I <3 Robots's Avatar
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    Quote Originally Posted by ericm979 View Post
    Lightweights use a foam core (see http://weightweenies.starbike.com/fo...69488&start=15).
    Do they actually suck or is it more complex than "foam core construction bad"?

    Does the foam core add impact strength? Does it absorb energy, adding to rolling resistance?

    Nick, I don't know of any cf rims that have aluminium brake tracks. There are aluminium rims with cf fairings (mavic, and hed I think), aluminium rims with more substantial cf making a deep section (zipp), and madfiber's clinchers which have an aluminium rim that's little more than bead hooks and enough material to hold them together. The cf wraps both sides so the brake surface is still cf but with aluminium backing it to (theoretically) conduct heat away from the CF and keep the beads from spreading apart due to braking heat.
    I saw the same post on WW. If foam cores are bad...why is Lightweight using them? AFAIK...LW is the Holy Grail of wheels. I've seen them in person...they sure are bling...are they really all that? I doubt I'll ever get a chance to ride a set to see for myself. I've never seen data of any kind on them. There has to be something to them...
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  21. #21
    Mr. Dopolina Bob Dopolina's Avatar
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    Quote Originally Posted by ericm979 View Post
    Lightweights use a foam core (see http://weightweenies.starbike.com/fo...69488&start=15).
    Do they actually suck or is it more complex than "foam core construction bad"?
    Yeah, it is more complicated than that. I wish it wasn't.

    There are a lot of holes in my knowledge and understanding and what makes a good foam core rim vs most of the crappy ones I've seen falls into one of those holes.

    I don't know.

    Part of the motivation for this thread was to draw out others who lurk on this forum who do know about things like this. I'm certainly not the voice of authority on all things carbon. There's more I'd like to know, too and I am eager to do so.
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  22. #22
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    Back in the late-80's, we used urethane foam as the core blank for the aforementioned propeller blades. It was cast oversized, and machined to final dimensions, which were pretty tight. Sorry, can't supply an actual tolerance number.

    Basically, the foam core, was cast onto an aluminum blade root/stub. The stub component was less than 12" long, and provided a flange for the blade bearings (constant speed aircraft propellers rotate around their primary axis). The layup proceeded over the foam core and extended onto the aluminum stub. Then the whole setup went into the heated steel mold, which was in a giant press (over 10 ton), for final cure. After the cure cycle, the blade was pulled for initial cleanup around the parting lines. Next, pre-preg kevlar fiber was filament wound around the blade root, where the layup extended over the stub. This became a retention ring, to prevent the structural layup from being pulled away from the aluminum root under flight stress.

    The foam core really wasn't structural, although it had to be made to a very particular size. The idea being that the combination of core and layup would overfill the cavity by some specified percentage, yielding proper compression to the fiber layers during the cure cycle. Too big, and finished part would be resin starved, and weaker. Too small, and there would be voids between fabric layers, which is and even bigger structural issue. A bladder, if you can get it in place, is more straight forward, but in some situations, unworkable.

    Foam cores can also let you do some other interesting things. For example, on propellers/airfoils, you can split it down the middle, insert, or layup, a supporting spar in the split, put them back together, and wrap with your overlayers. Of course, the more complex the layup schedule, the more chance for things to go wrong.

    About the best publicly info you will find on structural composite construction is from the home building aviation community. The Experimental Aircraft Association is the keeper of the flame on that front. However, they don't deal much with closed mold stuff. They have invented other interesting techniques though. Seem to remember that the main spar or boom for one of the early, record breaking, human powered aircraft was filament wound over a section of aluminum irrigation pipe. After cure, the unneeded mandrel was dissolved away with acid.

    Most places that are good at this kind of thing don't make their techniques public.

  23. #23
    HMF
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    SkinnyStrong HMF's Avatar
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    Bob, why are you so good to us? Maybe I won't buy those china carbon tubies after all

  24. #24
    Blissketeer HokuLoa's Avatar
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    Thanks for the primer Bob. Real interesting for carbon neophytes like myself!

    BTW, about the mango sales and Tainan, boy do I miss that access... and the fish isn't bad either! You are one lucky 老外!

  25. #25
    Senior Member Quel's Avatar
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    Quote Originally Posted by HMF View Post
    Bob, why are you so good to us? Maybe I won't buy those china carbon tubies after all
    I'm sure it's a total coincidence that the thread was started by a guy who sells wheels out of Taiwan.

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