Bonding metal to grp

Kelpie

Kelpie

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I'm wondering what is the best way of bonding a fibreglass tube inside a copper pipe.
The respective tube sizes I am consdering are 19.6mm ID for the copper, and 19mm OD for the grp, so a pretty snug fit. Total length is about 2m, so plenty of surface area. About half of this length will be below waterline level.
First thought is to use epoxy, but I wonder how much the copper will expand/contract with temperature and possibly cause the epoxy to detach?
Second thought is to use a PU glue which may retain some flexibility, but as this foams up on application I wonder if it might distort the copper. I also wonder about water seeping into the glue over time.
Third idea would be sika or similar, which I expect would be too thick and would just get scraped off as I pushed the grp tube inside the copper.
 
It is a very similar situation to fitting a Vesconite bearing into a stern tube, but much longer! The recommendation is to use epoxy. It is not so much to provide adhesion as to provide a firm base in order that the bearing cannot move. I think that for your application this is just what is needed.
 
Thanks Vyv! Thought I'd throw it out to the forum as I'd taken up enough of your time already :)
Epoxy it is then.
 
I think that your biggest problem would be to cover the inside of the copper pipe over the entire 2-metre length and to keep the inside tube centred within the copper.
What about the ends, where they enter or exit (presumably) the hull?
 
PuffTheMagicDragon said:
I think that your biggest problem would be to cover the inside of the copper pipe over the entire 2-metre length and to keep the inside tube centred within the copper.
What about the ends, where they enter or exit (presumably) the hull?
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Right.

Unless the two tubes are dead straight, which is very unlikely, and accurately held in position while the adhesive sets, some kind of spacing collars will have to be used to maintain the clearance (0.3mm = 0.0118") between the tubes.
 
Actually I don't think that should be a problem, as all that is going through this tube is a wire that lifts the keel up, so the two tubes don't have to be exactly concentric.

Will that rubber stuff really be thin enough to flow 2m down a 0.3mm gap??
 
Nothing sticky will flow down that gap, but it is a good gap size for Epoxy.

Over that distance you'll need to give it a helping hand. I would suggest that you warm the copper tube as this will help to lower the viscosity of the resin and increase the clearance between the two tubes. Paint the resin on the GRP tube and slide the two together. Probably a good idea to chamfer & plug the leading end on the GRP, and add some resin inside the copper tube.

It might help to spin the grp tube as you slide it in. This may also help to lower the viscosity of the resin (note this is resin dependent, it doesn't work with all resins)
 
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We used to do similar jobs in a lab I worked in using a water-activated glue. You coated the parts, assembled them and then sprayed a mist of water on the visible bits. That started a reaction (catalytic?) which set the glue off throughout the join. It's a long time ago, and I can't remember what theh stuff was, I'm afraid. It stank to high heaven.
 
Heat the copper and the epoxy will flow down OK. Use a hot air gun, e.g. Black and Decker.

TBH if the application is what I understand, I would look for stainless tube to avoid the copper wearing through?
Epoxy generally sticks well to copper, stainless a bit less so. Degrease and abrade it should be OK unless the join is highly stressed?
 
Firstly clean the inside of the copper tube,( a 12 gauge bronze shotgun brush will do the job ) and the outside of the GRP tube with acetone. Make a plug with a conical end fit to inside the end of the GRP tube, fill the inside of the copper tube for a distance of approx 200mm with CT1. Push the GRP tube inside the copper tube from the filled end rotating the pipe as you insert it. The conical plug will spread the adhesive around the copper tube as you insert the GRP tube in to the copper tube.
 
PuffTheMagicDragon said:
Pardon my ignorance but are you certain that the exposed wire will still be aligned with the tube when its attachment point to the keel will be swinging in an arc?
Click to expand...

Should be- the centreboard has a curved trailing edge to accommodate the wire, so it works out in the same place throughout the board's travel.
The boat will be 46yrs old next year so I think the design does work...
 
BERT T said:
Firstly clean the inside of the copper tube,( a 12 gauge bronze shotgun brush will do the job ) and the outside of the GRP tube with acetone. Make a plug with a conical end fit to inside the end of the GRP tube, fill the inside of the copper tube for a distance of approx 200mm with CT1. Push the GRP tube inside the copper tube from the filled end rotating the pipe as you insert it. The conical plug will spread the adhesive around the copper tube as you insert the GRP tube in to the copper tube.
Click to expand...

That could work quite well, but my worry would be that over a 2m length I might get stuck before I've managed to push the grp all the way into the copper. Epoxy, being runnier, sounds a bit easier.
At the end of the day there shouldn't be much of a load on this so it's just something to locate the grp tube and stop it falling out (the tube ps will be vertical).
 
What was the original arrangement installed by the builder and what's wrong with repairing/restoring that? I'm sure he would have gone for the simplest solution.
 
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