to glue your aluminum sandwitches together, drill them full of holes. The glue will squeeze thru the holes and bond with glue on the other side and create a stronger joint. ----- Original Message ----- From: "Steve Jacobs" <st...@johnmartin.co.za> To: "KRnet" <kr...@mylist.net> Sent: Wednesday, August 23, 2006 7:03 AM Subject: KR> Urethane glue
> I stated in my original post that this application will probably squeeze > most of the glue out from between the plys. > > ++++++++++++++++++++++ > Scott > > I honestly believe that this glue has a place in building airplanes, so I > will risk getting flamed here. > > A similar discussion on another interest group site some months ago provoked > me to do a fair amount of research and tests with Urethane glue - the > up-side to this adhesive was very compelling. If I can find the links, I > will pass on some of the stuff, in particular a well written report from > Forest Products, they tested several brands. > > The short story is that Urethane adhesives are more than adequate and have > some nice plusses provided you understand HOW and WHEN to use them. My > initial tests had me believing pretty much what Mark L believes, but the > potential benefits gave me the incentive to look deeper. I am glad I did. > > All my ply scarf joints are now done with this adhesive - the break test > results are more consistent than any other adhesive - zero failure - in > fact, I have not been able to separate a joint yet (birch ply). On the > other hand, I will not use Urethane unless I am sure that I can get to and > clamp every square inch to a flush fit - NO GAPS. I mostly use it where the > glue area is large (relative). Typically, not on a block gusset, but Ok for > a ply plate gusset. When I get to doing what you are doing, laminating the > wing tip, HS and VS bows, I will not consider anything else. This adhesive > will tolerate an extended open time - may be a plus for laminating long > bits. I have not tested this, but FP says that opening and closing the > joint several times before final clamping had no ill effects on the joint > > We sometimes tend to consider the strength of the glue (psi) in isolation, > but how well the adhesive bonds to any given material is also a factor. I > have seen epoxy joints fail many times during my RC flying years, with the > bulk of the epoxy remaining (in tact) on one side of the failed joint and > what resembles a finger print of the joint on the other side. The fact that > I could probably drill and tap a hole in the epoxy did not help matters, the > joint (not the glue) had failed. Agreed, this was 5 minute epoxy, not T-88 > but I mention this to make the point - even an incredibly strong glue must > actually sticks to the host material - urethane does this better than > anything else (except cyno). > > I will not use Urethane in a cluster joint - I believe that actual strength > of the glue now becomes more significant due to a reduced adhesive contact > area - and the intrinsic strength of epoxy (psi) comes into play. > > For what it is worth, in some of my tests, even a 10mm staple (thru 4mm ply) > on a 30mm (1.3"?) spacing was not enough to keep the surfaces tight when the > glue started fizzing. I guess this pressure may force glue into the fibres > if the joint is well clamped. > > Steve J > Port Elizabeth > South Africa > > > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html
