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werner
12-07-2003, 05:25 PM
HI,
The lead keel has a very rough surface on top ,and looks as being repaired many times.Some trim weights were cut out.There is even a layer of red/pink cristals in one place under a thin layer of lead ((leadoxide salts ?I presume)will remove with care; don't think this is healty stuff).
Is there a proven method of preparing the surface to get a "grip" when pouring molten lead on? The earlier repairs do not look so succesfull.
regards,
werner

Ed Harrow
12-08-2003, 09:10 AM
Bump.

Werner, sorry I can't advise you on this, but I suspect you'll need to resort to mechanical fasterners. I'm guessing that you wish to add lead to rather "flat" surfaces, like on the sides of the ballast.

To smooth the roughness, you can use a plane, and work the lead as for wood. Obviously, sanding it presents some serious concerns.

Bob Cleek
12-08-2003, 03:13 PM
A picture would have been worth a thousand words. I'm not sure what you are describing, but it sounds like the top of a lead keel casting. If so, what you are describing is not particularly unusual, except that the picture you describe sounds like the top of the keel was never properly finished off, nor, perhaps, properly poured.

Unless all the dross is fully skimmed before the pour (or the pour is off the bottom of the pot), the top of a casting will be very rough, with all the dross that floats to the top hardened up and stuck in the hardened lead. Even with a "clean" pour, you will get dross, particularly if the sides of the wooden mold char and so forth.

Properly done, the casting is made and the lead poured higher than what is needed for the finished product. This allows for shrinkage in cooling, which should be allowed for in lofting the pattern or mould in any event. The top edge of the casting is then planed flat, removing the dross and leveling the top of the casting. This may be done with a wood plane (laborious) or these days may be done with a router. (Make the pattern edge level and then mount the router in a "sled" and run it back and forth across the top of the mould with the bit set to the depth you want.)

Any casting of any size will shrink, particularly at the top of a keel casting. This often produces a large "dimple" in the top of the casting. If the lead is not hot enough when poured, or temperatures are uneven in the pour, shrinkage can be uneven, resulting in pockets forming in the casting where the metal pulls apart, leaving voids with a crystaline surface, much like a geode does with crystals. (Not a good thing, but generally no big deal, since you never see them, as they are encapsulated in the casting, unless you cut the keel up.)

There is NO way to pour lead on top of a casting and obtain any really effective bond between the original and the added lead will never really stick sufficiently. From your description, it may be that somebody tried to fill up voids in the top of the casting already. If the voids are small, you CAN try to fill them with lead by first heating the surface as much as possible. You will not be able to melt the surface so as to form a puddle, as with welding, since the mass of the casting is so great it will absorb tremendous amounts of heat before melting, and will, indeed, not melt much at the top until the whole keel is almost ready to melt, which would not be a good thing.

If you are only filling the surface of the top of the keel, adding but a fraction of the depth of the keel bolts, which should set well into the original casting, I doubt that the poor ("cold") bond between what you fill in and the top of the original casting will make any structural difference. DO NOT, however, trust an "overpour" to hold on to the rest of the keel!

Hope that answers your questions.

werner
12-09-2003, 05:22 AM
Thanks,
I realise it would be very difficult
to melt lead locally ( keel 1500kg 4meters long).I hoped it would somehow be possible to weld it on using some kind of flux.
So the only way will be to scrape or plane the top as straight as possible and fill with epoxy resin to get an even contact area with the wooden keel? For the trimming parts wich were cut out recast them and glue them in with epoxy?

kind regards ,
Werner

Carfunkel
12-09-2003, 10:23 AM
If the areas that you need to build up are large enough to warrant it, you might try drilling small holes at random angles, to insure a mechanical bond and then filling with thickened epoxy filled with lead shot. If it is simply a matter of fairing the keel rather than replacing or maintaining weight, then just epoxy.

Lead is an excellent conductor of heat. As a result of this, the entire mass of lead would have to be very close to the melting temperature before any one part of it would actually melt. Thus if you try to cast new lead into the keel, you could end up with a very large, hot, heavy puddle where your keel used to be.