Joining bronze to stainless?

Tim Over the years I have used epoxy resins, with varying characteristics, from a Swansea company called Rotafix Resins. Their tech man was (about 1998) a Guy called Dave Smedley, their storeman "Gareth" was also extremely helpful. It sounds to me like a product called CB10T might be what you need. It's a two part product which, after mixing, can be packed into an empty standard 400mm cartridge (which they can supply- I also have a couple which I could let you have, together with sealing ends etc)) and can then be pumped into the cavity by means of a simple, readily- available builder's skeleton gun. The 'T' stands for thixotropic....a consistency rather like toothpaste which will stay where its put, unless displaced by pressure or mechanical means.

Alternatively, if you wanted a longer time before setting, CB10EP would seem to be appropriate. It takes the EP about 24 hours to set, if I remember correctly. If you wanted a very thin material which will really find its way into every little corner, like very thin treacle, before solidifying, then ask the about TG6 timber grout. I have used a lot of this over the last 20 years, its used for the repair of damaged timbers, typically in historic buildings.

The cost of a 400cc pack of CB10t was £14.50 in 1996 (my last price list)

Rotafix's number is 01639 730481, fax 01639 730858. I have just checked...the world has moved on! They now have a web-site, see

Let me know if I can be of any further help.

Regards

--

Chris Edwards (in deepest Dorset) ..."There must be an easier way...!"

Most of the big stern tube bearings we come across are cast iron tubes lined with any one of a variety of whitemetals. The cast iron is just a convenient way of holding the whitemetal and I can see that a whitemetal cylinder set in concrete would work - but would have more tendency to overheat due to poor heat transfer. Unlikely to be a problem except in unusual operating conditions.

If you join Bronze to Stainless & put it underwater, are you going to have an electrolytic corrosion problem? Not my area so I honestly only know enough to ask the question, not give the answer. I can tell you that the Navy's spec for whitemetal stern tubes has 30% zinc to protect the steel shaft by letting the stern bush be a sacrificial anode.

My main concern would be using bronze bushing on an unhardened prop shaft. You say the whitemetal was fairly hard, but the normal whitemetals for stern bushes are only about 20 to 25 Brinell. The best are about 27 to

30, and the hardest whitemetals (used in rock crushers etc., not stern bearings) are up to 35 Brinell max. At 35 Brinell or less, you don't wear a steel shaft. With Bronze you do wear steel unless it is hardened.

The other point is that over a 4 ft. bearing you have to allow for some flexing of the prop shaft. The relatively soft whitemetal does that - the bronze may not like it.

A 2 inch bore by 48 inch lonch stern tube bearing sounds weird. Even with whitemetal's tolerance of being water lubricated I would have expected trouble.

How will you lubricate steel running in bronze of those dimensions?

Phil

Hello Tim

FWIW... I have done a small amount of silver soldering stainless to stainless, It's difficult, the fluxes are very aggressive, and the results for me have not always been good. What the flux you need for stainless will do to the bronze I dread to think.

Silver solder requires a fairly high temperature... you might be close to melting the bronze by the time it melts.

I will be interested to know if this bronze to stainless soldering actually can be done.

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

Wot no Lignum Vitae?

What is the context in which you come across such things?

That was one of my implied questions (Manganese) bronze propellors fitted to stainless shaft are the norm, though.

The original had grease lubrication to the centre of the tube. I suspect from the characteristics of the material (it doesn't cut all that easily, for instance) its composition was arranged to give a compromise between being a good bearing material, and having a fair degree of mechanical strength. Maybe at one time it was marketed as stock tube for situations just such as this? Accepted 'traditional' UK canal practice was, for a 2" shaft, a bearing around a foot long which could be cast iron, white metal or bronze. Running clearances need to be generous on the assumption that water is the main lubricant - if there's a bit of grease to help it along, so much the better. The older commercial installations often also had maybe 6" of graphited packing which gave a fair bit of additional support. Current practice for new pleasure boats with 1 1/2 or 1 1/4" shafts is a bearing (probably often manganese bronze or brass) of only about 6", and an inch of packing at the most.

Shafts were usually mild steel or EN8, nowadays a 'proper' shaft will be 316, more commonly for the mass produced stuff mentioned above 304 or ?305?.

I've seen *one* chrome plated shaft in 30+ years of this sort of work, and never a hardened shaft.

The shaft which I took out of this particular vessel appears to be something like EN8, though in the 60 years or whatever it has probably gone through four or five shafts. I'll probably end up making a new shaft from 316 for it, as the one which came out is probably not worth salvageing.

The new bearing will be limited in length by how much of the old white metal I can realistically remove, I'm aiming for a minimum 6" within the structure plus about 4" outside. There had been a previous nasty bodge with a 4" brass/mag bronze outrigger held on with 2 bolts, and no locating spigot. This had inevitably both worn badly and come loose & was doing no good at all after a while. The 'running clearance' at the outer end of the original white metal bearing measured at about 4mm!

Cheers Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

Many thanks for that

Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

I'll let you know!

Silver soldering bronze is no problem at all, either as regards temperatures or normal (borax) flux. With ordinary Brazing it does start to get a bit nervous as regards temperatures.

Cheers Tim

Stainless steel silver solders fine, use Tenacity No 5 flux. I've done it to brass and bronze, just keep the torch on the stainless side of the joint ;)

-- Steve Blackmore

A few years ago we actually had an enquiry for lignum vitae! Couldn't believe it. But you can get staves of resin fibre as replacements (like the Railko & Orcot stern bush materials).

Our own involvement is that we make the whitemetals & sell it around the world. Most goes into marine diesel engines, but in big drydocks such as in the middle and far east, they use it for remetalling stern bushings of the supertankers & bulk carriers.

In the UK our own bearing works occasionally gets stern bushes of 4 or

6 inch bore to remetal, and much more rarely a big one. I think the biggest (which we centrifugally lined) was about 36 inch bore by 70 inches long.

Phil