Any experiences with structural bonding ally to steel?
I've seen reccommendations for PU type adhesives but they are very flexible compared to steel or ally and I doubt they add significant stiffness
to the frame. They may stop water penetration and stop the rivets working loose but I'm looking for more than that
On the other hand I imagine epoxy, which is stiffer, would tend to crack and peel.
Car is used for sprinting and steel is too heavy (and the seam rusts), penetration isn't a problem but I need the diagonal bracing effect of a
securely attached panel.
Going by manufacturers litrature epoxy is the bees knees but then they don't always make the disadvantages clear do they?
I got some info from a company the makes aluminium sandwich panel for my project. Their panels are bonded using a PU adhesive, and its what they
recommend to stick it together with, even in structural applications.
Another company uses epoxy based adehesives in the panels and recommends...yep you guessed it epoxy adhesive for structural joints.
PU has a peel strength of around 5 times that of epoxy. But its more prone to temperature change and chemical attack. PU is also easier to use...
David
I think that epoxy resin attacks aluminium. I know that there are problems when ali is attached to carbon fibre, but maybe the galvanic corrosion only occurs between carbon and ali.
David,
Why can't life be simple? I had half guessed that there wouldn't be a clear answer
Cheers
David
PU may be rubber but it sticks well; just try peeling something off that is stuck with it.
A small piece of PU may aclt like rubber but a 2 metre seam will be prety rigid due to the shape.
Remember also that the rivets will add some structural strength. I would be surprised if an aly panel boneded and riveted to a steel frame
didn't add stiffness.
The structural adhesives used in aerospace tend to be epoxy based, try a search for Hysol, or look on the 3M's site.
Hammerhead, your correct, it's galvanic action that affects CF / AA joints. (As it will the rivets used to hold on CF panels hence composite
structural panels are usually bonded to the structure)
Mick
I know of a commercial body builder who uses PU adhesive for bonding the panels to the chassis of 40 foot lorries! So it cant be that bad can it?
I know of a commercial body builder who uses PU adhesive for bonding the panels to the chassis of 40 foot lorries! So it cant be that bad can it?
Razman are you in this trade?
Thanks guys got the info on Locktite site seems to be the busness - just to find out the cost!!!
Try EvoStick Liquid metal....Sh1t name superb product....dries silver...
The easiest stuff to use is a proper structural double sided tape - sometines called helicopter tape.
Don't think of the stuff you put mirrors up with. This is very thin, with a network of fibres in a very sticky adhesive. If you stick a GRP or
ally panel to a frame, the only way you get it off is by damaging the panel. I will try to find a data sheet on the product I have experience with.
Cheers
Fred WB
The easiest stuff to use is a proper structural double sided tape - sometines called helicopter tape.
Don't think of the stuff you put mirrors up with. This is very thin, with a network of fibres in a very sticky adhesive. If you stick a GRP or
ally panel to a frame, the only way you get it off is by damaging the panel. I will try to find a data sheet on the product I have experience with.
Cheers
Fred WB
We use sikaflex in the shipyards, when some brackets and mountings had been put in the wrong place, we removed the bolts just leaving a couple of
square inches of sikaflex holding it, we could not get any of the brackets off without totally destroying them, they were 6mm thick plate brackets
which were completely mashed before we eventually could get them off using a sledgehammer and a crowbar
PS it's also totally resistant to salt, oils, etc
Cheers
David
[Edited on 15/3/06 by Minicooper]
quote:
Originally posted by Fred W B
The easiest stuff to use is a proper structural double sided tape - sometines called helicopter tape.
devcon epoxy products are good, i have used them and have excellent results. they are availble from industrial supplies dealers where i live, canada.
not nearly as expensive as hysol.
hysol, formely made by dexter, then loctite and now henkel, are aerospace grade products. i have used 9309,934,956. 934 would be best suited for your
application. it is very expensive though. 300cdn for a quart.
these products are all useless without the proper preparation. surface must be clean and free from grease and dirt. they should be mechanically
abbraded to promote adhesion. degrease with MEK, and a final wipe with acetone. MEK contains silicone and other byproducts that can compromise
bonding.
aluminum should be chemically converted. or alodined. alodining is simmilar to anodizing. it converts the surface layer into a hard oxide film. this
promotes adhesion.
a note on epoxy resins. they must be mixed accurately by either weight or volume specified by the manufacturer.
unlike polyester resins, epoxy resins contain very little by-products compared to polyesters and PVA's( ie one part adhesives) when cured.
there pot life cannot be altered by adding more hardener, unlike a polyester resin. read and obey the instructions to the t. you will get maximum
performance from the product if you do.
as for corrosion. epoxies typically do not do the corroding, as they are a plastic and non conductive. it is the reinforcing material that does.
carbon is higher on the nobility scale that aluminum. it pulls electrons from the aluminum and the corrosion process begins.
and a final note. epoxies are extremely toxic. wear gloves and a respirator.
funnily enough, was reading about some steel/aluminium that is explosively welded together. You can weld ali onto one side and steel to the other.
Would need to find the info but it sounds like it won't be locost.
I used PU sealant when I fixed my ali back panel to the chassis. When I tried to remove the panel because I'd cocked it up, the ali had to be
torn off and destroyed. Also had use an old (sharp) woodworking chisel to get the remains of the PU of the chassis...
I reckon a PU-glued floor with an appropriate number of rivets would be more than strong enough.
I've tried using epoxy on aluminium - I think it suffers the same problems as paint, in that you're only gluing to the oxide surface instead
of the metal itself, so the glue just cracks off. Don't know if some form of etching would help.
Any road up, PU cetainly doesn't crack off - sticks like the proverbial to a blanket.
David
Another vote for double sided sticky tape from me. 3M VHB (very high bond) tape is the proper name and it's awesome stuff. Used to stick busses
and trains together among other things.
The adhesive is acrylic based and the tape has a thin foam carrier which isolates the two metals as well as providing fantastic sound deadening - no
vibrating panels. Comes in handy inch wide rolls too. A 5" test bond between a piece of rhs and some ally panel was strong enough to easily
hold my weight, and there is about 35 times that bond area on my floor. Even so I intend to use a few rivets in the corners to resist peel. Heck of
a lot easier than drilling millions of holes and rivetting and squirting goop on...
Liam
Rescued attachment 2005_0528_155221AA.JPG
I like the idea of VHB tape. Where do you get it from? As I have never seen it anywhere. I know its a bit pricey...
David
FYI
----
http://www.m-source.com/portal/tapeselections.html
and one supplier in uk
http://www.vikingtapes.co.uk/tape6.htm
[Edited on 16/3/06 by Taz Surfleet]
I think I got mine from viking...
HERE
I used tape number 4611 (general purpose and relatively cheap) but in 1" width (had to phone em). Worked out to £35 for a 33m roll which was
enough for my floor, footwells, sides, and rear bulkhead. I'm sure I would have spent at least this on rivets, pu and drill bits, not to mention
a significant portion of my life!
Oh yeah i had to get 2 rolls minimum but was OK as my mate wanted one too. Even if you have to get two you can just have fun sticking anything
imaginable together with the spare!!
A bonus feature of tape 4611 is that it can withstand powder coat curing temperatures - so you could panel an unpainted chassis with it then get the
whole lot powder coated. Mine was already painted though...
Liam
quote:
Originally posted by airframefixer MEK contains silicone and other byproducts that can compromise bonding.
the difference in Pu adhesive /sealants is quite marked. Ordinary builders PU is fine for most things but where you are loooking for absolute strength
and rigidity you are better to use one of the Sikaflex high modulus fast curing types which the Yacht Chandler sells to Locost Builders of the
stockbroker type. I think if somethings going to flex then allow for it to flex rather than have it break.
Alex
VHB tape is available from RS stock No. 458-7365
but make sure your sitting down before you look at the price!
I've ordered some.
Or rather my company has.
Well I've got some of this VHB tape now and I have to say that so far I'm less than impressed!!!
Does it have a "cure time"?
So far the tests that I have done show it to be similar bond strength to standard "Bostic Outdoor Sticky Pads" available from most hardware
stores!
Brian, the VHB tape requires a thorough degreasing of the bonding surfaces to be effective - it is also pressure sensitive and bond strength improves
over a few hours. Ambient temperature is a factor too