Question about brazing bronze with O/A

admin

Hi, I've got a rudder stuffing box from a boat I'm restoring that has some cracks in the lower area.  There is really not a lot of stress on this area as the contact point is at the top where the packing nut attaches.  It is also further supported by a bracket higher up in the boat. Anyway, to my question, I have an O/A set (no gas bottles yet, but set up my account at Airgas) and some flux coated bronze brazing rods.  It seems a good fix would be to run a hack saw blade through the crack and maybe give it a small chamfer, then build back up with braze, then clean up.  Of course, buying a new one is also a possibility and I'll leave it up to the customer. As a new guy to O/A, I'm just curious I've got the right idea and am looking forward to using my torch to its full capability.  Any comments or ideas would be appreciated. Thanks.  Here are some pics... Attached Images
Reply:Wouldn't it be easier and cleaner just to get a new bronze bushing, cut the old part off and braze the new bushing bushing on at the base to the plate?
Reply:I'd run a little brass on it. Build up some on the outside for a bit of reinforcement and let it go.Lincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:With a rotary burr, excavate a groove along the crack, about half the thickness of the bushing.............on the inside. When cool, do the same procedure on the outside, excavating into the previous repair. Clean up the bore, and your part should last a good while longer.Bgbkwndo.Last edited by Bgbkwndo; 07-22-2012 at 10:54 PM.Reason: I,ve omiited a step that needs mentioning.
Reply:Originally Posted by BgbkwndoWith a rotary burr, excavate a groove along the crack, about half the thickness of the bushing.............on the inside. When cool, do the same procedure on the outside, excavating into the previous repair. Clean up the bore, and your part should last a good while longer.Bgbkwndo.
Reply:I'll have to get another picture of the whole unit. It isn't a bushing. The other side of the unit has threads on it to accept a packing nut and a lock nut. These are usually cast and then machined.  As far as the filler being the same as the parent metal, the unit is bronze and the brazing rod I have is bronze. Whether silicon bronze or tobin bronze or whatever, I am not sure.
Reply:Originally Posted by hobohiltonI'd run a little brass on it. Build up some on the outside for a bit of reinforcement and let it go.
Reply:Would it be possible to press/shrink a stainless sleeve over the whole stub for support,and then it maybe does not need brazing at allLincoln SP-170 MigHypertherm powermax 45Lorch T220 AC/DC TigButters FM 215 synergic MigKemppi 180 adaptive mig RULES ARE FOR THE OBEDIENCE OF FOOLS AND THE  GUIDANCE OF WISE MEN.
Reply:Thanks for the replies... I got a pic of the whole unit. The smooth side actually passes down through the keel of the boat.  The threaded side is up and a packing nut with flax in it tightens down on the rudder shaft like a collet and makes it watertight. Brass vs. Bronze.  I don't use brass on boats unless is something ornamental. Although there is a little room in the fitting of the rudder post and the hole in the keel for bedding material, there shouldn't be any extra material on the post such as a metal band.  What I'm looking for is whether my thoughts on the fix are correct.  It seems like prep of the joint is a good idea as you'd want clean metal to work with, correct?   Thanks! Attached Images
Reply:Have a ~50 year old O/A welding handbook, and I looked up bronze welding for you (since you most likely would be welding it, not brazing - unless the rods you got melt way before the piece you are repairing). Please have oversight with my translation of the highlights, after all, english is my second language.Problem: Tin in bronze evaporates when hot, like zink in brass does, making a porous weak joint. The rod should contain additives preventing the tin from evaporating.Brass also gets very weak when hot, so anything that can be distorted or break under its own weight must be supported (don't think you need to worry about that).Flux: Use the same as for brass.Joint type: Thicker than 3mm should be V:ed out, thinner should not. For the non metric among you, that is just under 1/8" - you really should learn metric anyway. Flame setting: use reducing or if needed oxidizing flame (surplus oxygen). Tip size generally the same as for steel welding.Preheat to 450 degrees celcius (842 Farenheit). Pack in insulation and let cool slowly after welding.Hope that helps!
Reply:Several months back I repaired a broken rudder support bearing.  Took several attempts to get things right.Found that tig with silicon bronze filler (and lots of preheat) gave the best results.  Weld in short spurts and peen the weld throughly.When welding was complete, I allowed the part to cool in a bucket of dry sand.PS.  Think you'll find that Lincoln's Procedure Handbook of Arc Welding (The Bible), has an excellent section on welding copper based alloys.Here, it appears that you're more interested in "filling the crack" than you are in obtaining strength.  You may be able to V out the crack and fill with silicon bronze filler using O/A, but my choice would be to tig it.  If you're not "very experienced" with O/A, I'm afraid you're going to get a lot of distortion in heating the part.Last edited by SundownIII; 07-23-2012 at 11:54 AM.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:brazing involves a very thin gap , such as you have, providing capillary action  to wick the liquid metal from the rod, which melts much lower, into the crack..i see no reason to prep the joint if you intend to braze..to weld ,such as tig with silicon bronze, much hotter than braze, ,yes veeit out..
Reply:Hmm, just read the part about not being able to use a sleeve.I use bronze brazing alloy to repair cracks all of the time on ferrous materials but the last time I tried to actually weld or braze bronze (may have been red brass) I spent the rest of the day chasing spiderwebs.  I gave up on using bronze and repaired the cracks with 50N silver brazing alloy.  I would have saved a lot of money on silver (about half and oz) has I skipped the bronze and just started with silver.Last edited by 76GMC1500; 07-24-2012 at 12:47 AM.
Reply:Thanks for all of the replies. The customer wants to put back it back in without brazing. Its backed up by the wooden keel and shouldnt see any stress. We will inspect it later in the year. I am a novice at O/A so I doubt I would do the fix anyway. Its good to know the procedures though and I look forwarding to practicing this.I read the brazing rod sleeve and it said copper based alloy, not bronze specifically.Thats good to know about the silver solder. I remember an article now about making little marine fittings with bronze and silver solder.Thanks again. If anyone is interested, this is the boat. Sorry, no welding as I work in woodhttp://www.villageboatshop.com/1956century.html
Reply:FWIW, in any event, you might want to stop drill the crack so it doesn't continue to run. Pardon if this was mentioned and I missed it.PaulLast edited by ciscotex; 08-04-2012 at 06:44 PM.