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Thread: Pulling carbon tubes from their mandrels

  1. #11
    To take further advantage of CTE, try Al molds and dry ice. However, if you later decide to make some dry ice bombs, don't let baja find out, or they will call the police, and you'll end up on the cover of the university paper.
    Dr. Adam Witthauer
    Iowa State University 2002-2013 alum

    Mad Scientist, Gonzo Racewerks Unincorporated, Intl.

  2. #12
    h t t p : / / w w w .acp-composites.com/home.php?cat=4663

    I normally like the DIY approach but these are too cheap to not just buy. we used the unidirectional stuff on our rear wing supports in '07. way lighter, but they are very fragile and i wouldn't recommend them for that reason. after our spectacular explosion, the track workers tried to push the car by the rear wing and they buckled.

    also, i put these on the MTS machine and they buckled when expected based on calcs, and they failed at the bond between the lugs and the carbon in tension (also about where expected based on adhesive shear strength), so they are good quality.
    Matt Brown

  3. #13
    After using PVA on a few nose cones and having to destroy a plug during my FSAE days, I tried Fibre Glast 1153 FibRelease on my roadster seat plug/mold and it popped off really easy. Plus you just wipe the FibRelease on and start laying up, no need to spray or wait for the right dry time. Pretty cool stuff. I also sanded to 1000 grit and used 3 coats of Turtle Wax.

  4. #14
    How bout aluminum mandrels. Vacuum bag and heat to 350F to cure. Obviously, this means the mandrels will need to be undersized so the CTE will bring the aluminum to the nominal size at cure temperature. When everything cools after cure, the aluminum will shrink and you should be able to just pull the composite off the mandrel.
    Shaun Kapples
    Mechanical Engineer
    Alumni, FSAE at UCF

  5. #15
    I would also try using a slide hammer instead of a come-along. The impulse helps to get things loose. It worked for some parts of ours.
    University of Illinois Urbana-Champaign - Car 3
    '09 Team Leader

  6. #16
    To echo Auerbach, we made some CFRP tubes only a couple of days ago. CFRP wrapped around a polished half-inch steel tube with release agent (12 coats) on the steel tube before CFRP was layed onto it. CFRP tube came off the steel tube by hand. Easy.
    Simon
    ----------------------------------------
    Powertrain Research Student 2010-2013

    Team Principal 2009-2010
    Engine Development 2008-2009
    Brunel Racing

  7. #17
    Echoing cjanota, some impact will go a long way.

    The other thing you could try since you've got your (scary) setup built already, is put some load on it with the tethers, and then *whap* along the outside of the part with a rubber or plastic mallet, it may pop loose that way.

    We used a slide hammer made from a piece of all-thread, some fender washers, and a failed attempt at a machined aluminum diff carrier (or something) to pull the halves of our restrictor, but that had a lot more taper than you guys did.

    Plus we had some freshies do like 8-10 coats of wax on all the AL moulds before the layup, that probably helped a lot too.

    Best,
    Drew
    _______________________________________

    Northwestern Formula Racing Alum
    Head Engineer, Frame/Suspension 2006-2009

    My '73 Saab 99 Road Race Build

  8. #18
    w w w . f o r m u l a s t u d e n t .de/public-relations/fsg-news/news-details/article/-6a9dfde268/

  9. #19
    Thank you for all the replies. After reading some of your feedback and speaking to some sponsors, we made a fixture to press the tubes off the mandrel on a hydraulic press. The presses went flawlessly. No injuries, no abrupt explosions as the press lightly pushed the tubes off the mandrels. Except for one tube in which the visqueen we were using as a release agent bunched up inside the tube and ruptured about 4 inches of perfectly good tube, the pressing process only damaged about 1 inch of each tube which we were going to trim anyway.

    After speaking to a couple sponsors, it seems we made a few critical mistakes which I figured I'd post here so future teams could benefit from this knowledge.

    Our first big error was using the visqueen as a release agent. Apparently as it heats up during the cure it sort of melts and stops being as slick as it normally is. This contributed to the insane amount of friction present in the pull.

    Additionally, we performed post-cure while the tubes were still on the mandrels which made the carbon contract further onto that mandrel and increase the force with which it was clamping onto the mandrels.

    While speaking to the folks at carbonfibertubeshop dot com who seem to be extremely experienced on the subject, they also suggested two big things that they found helped. The first is to make sure you have tight straightness and diameter tolerances on your mandrels. They said they typically grind their mandrels in house, but that McMaster's precision ground drill rod is an excellent substitute if you don't have the means to do your own grinding or get it sponsored. Lastly, the folks at tubeshop also recommended using the Chemlease 41 release agent system. They said in the past they've also had some success with products from Frekote.

    Once again, thank you for all the help. And hopefully someone can benefit from our hard-learned lessons in future seasons. As Pat Clarke clearly pointed out, going about this the wrong way is a good way to earn yourself a ticket to the local ER.

  10. #20
    I'll echo Frekote as a good release agent.
    Shaun Kapples
    Mechanical Engineer
    Alumni, FSAE at UCF

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