Saturday, November 13, 2010

Curing disaster

It looked really promising when I left the workshop yesterday, so it was a huge disappointment to find that something had gone terribly wrong after I left.  However, it was not until the mast piece was out of the mould that I realized something was really wrong, although the vacuum meter reading one atmosphere gave suspicions.  A few dl of epoxy in the trap, and the bag seemingly in place.  However, the feeding tube was empty, leading the suspicion towards the patch mentioned in the last post:

I removed the bag and tubes, and lifted out the T-bars.  Easy release.  You can see the recess in the mast side here, and the glueing flange for the shear web.  Excess carbon extending inwards in the mast.

 The mast was released by sticking a sharp plastic spatula between the carbon and the mould, and then a thin piece of plywood.  Easy release.  As soon as the piece was lifted out of the mould, the disaster was clearly visible.  For some reason, the vacuum has disappeared after more resin was sucked out, but before reasonable curing.  The foam had straightened back to it's original shape and the outer carbon was lifted out from the mould, creating a major delamination all along the side of the mast.  The really big surprise was the considerable stiffness, taken the sandwich is obviously not functional, and the epoxy is far from a full cure.  Maybe I am seriously overbuilding?

So, this carbon monster will be brought to the dump.  Too bad.  On the bright side, the mould is still good, the release system seems to work fine, and it will definitely not be a soft stick.  Also, the trailing edge containing the boltrope track seems to be fine, and I will have this to experiment on how to cut a nice and straight slot.  You can see the saturated carbon and the "pre" bend here.

Also, the recess and flange seems to be just fine, making the joining process later more easy.  Making carbon wing masts is probably not a usual thing to do at home, and considering what they charge for these things, it is probably a reason for that.  However, I will not let this minor unfortunate incidence stop my plans for making an excellent mast.  I just have to order some more materials and pull my sleeves back up .....


Anonymous said...

Hi Tor , what a bummer , love your attitude though , sometimes things go wrong and the only thing to do is never give up ! Best of luck with the next try . I am not a fan of leaving vacuum pumps to their own devices , have had a few failures myself and now monitor them at least until resin has gelled . For a structure like your mast a simple plastic sheet draped over the top and a home type blow heater will get you to 50 degrees no problems and also give you a stronger structure . Cheers , Jim B.

framsblog said...

Hi Tor,
You wrote "I stopped the pump and the bag kept a steady vacuum, excess resin slowly filling up the suction lines. I turned the temp up to 26ºC and left trough the winter night to have a beer and write this story" I hope I understand this wrong but the pump must be kept running till the resin has cured. Another good thing just prior to the infusion is a drop test to be sure there are no leaks. Me too hates to go away while the pump is running, but lately I have to do this too as my workshop is not at home anymore. But when ever possible I try to stay at least another hour or so to be sure the bag will be fine. By the way, interesting attempt. It is still my intention too to make the carbon mast myself.

Tor Rabe said...

I'm afraid of heating too much until demoulding, I suspect it might be a struggle to get the piece out. The drop test was OK, the problem was quite certainly my rush to get the infusion going and not paying attention to an area with too small bag. I suspect the lack of bag to fold around the inlet part of the spiral tube led to the failure described above, and then probably a failure of my repair later.
I have always wanted to be in the workshop until curing/gelling, but with 20 below zero outside, open time of ten hours on the epoxy system, work and family, that is hard to manage. I'll probably bring a bed and stay over night the next time.