Welding cast iron with silicon bronze?

[T. Cotten]

I am neither a professional welder, nor a metallurgist, so I turn to the
collective knowledge of this Forum:

My most trusted TIG welder passed on years ago, but to the best of my memory, silicon bronze was most often his choice for a machineable repair upon cast iron, such as for fin replacement.
Also to the best of my memory, his successor also TIG'd silicon bronze
filler on many repairs for my customers back into the last century.
A third welder, whose service and skills have have been my first choice for
the last several years, has successfully built-up fins on early Chief heads for
me in the past, with great results using silicon bronze.

However, another Chief head of nearly identical vintage has presented problems, in that the silicon bronze falls off to reveal porosities as if it really never clads to the cast iron. The third welder gave up, so I resorted back to the second, who had a superior oven, clamping fixtures and the like. But he
refused to apply silicon bronze, adamant that it is never used with cast iron.

(Since he is a dear old friend, and a vinegary curmudgeon who is always
ready to argue, I just let it slide,... as long as the head got fixed....)

So my question is:
Is silicon bronze filler really the problem, or should we suspect that this
particular head is unusual?

Thanks in advance,
.....Cotten
PS: Nickel takes FOREVER to carve.

[Kojack]

That's an interesting question. I've never used anything but plain old brazing rod or silver solder and my experience with cast iron is limited. I looked at a popular manufacturer of brazing materials and they seem to recommend other materials for cast iron so I'd be inclined to say that your latest welder is correct.
http://www.brazing.com/products/Weld_copper/

[swall]

I suspect that there was somthing amiss with the head. Perhaps there was a non metallic inclusion (i.e. some non metal junk) present in the casting and that is why it broke in the first place. Or maybe someone had previously tried to repair the head and the repair messed up the base metal content such that the new repair would not take. I looked up silicon bronze and found that it is used to gas weld copper to itself. In this application, it tends to self flux. I also found that it is used for car body sheet steel applications, both with TIG and MIG. Main advantage is that it flows readily and has good fluidity. Didn't find any references for using it to repair cast iron, but I don't see any reason why it wouldn't work. The good flowability might be an advantage with cast iron to help wet the surface. Myself--I've always used plain old brass brazing rod with oxy acetylene. I always sand blast the surface of the casting before brazing.

[Kojack]

One other thing that comes to mind that would cause the problem you mentioned is that the cast iron was overheated to the point of melting. You'd end up with a sort of mischmetal with no strength at all. It's not likely that an experienced welder would do this. However, a TIG can melt things fast if you're not careful.
From the same Aufhauser site, here's a pretty good guide for joining cast iron.
http://www.brazing.com/techguide/pro.../cast_iron.asp

[swall]

Good point, Kojack. On one or two occaisions, I have been faced with doing a weld repair on sheet steel where it had been previously brazed. I used nitric acid to remove all of the braze alloy--don't try this at home, kids. Then I ground the joint as an extra precauation. It can be a real bear to properly fix a weld or braze job that some amateur has screwed up.

[T. Cotten]

One more time folks: The two welders I referred to are anything but amateurs. They both have decades of experience, both are skilled artisans, and both have successfully built up fins upon cast iron for me in the past.

One is just older and crankier than the other, and he assured me that the remaining silicon bronze fins that appeared intact would also fall off,... and upon carving, one did.
In the attachment it is obvious that there was tremendous porosity.

The casting does not show any penetration. The cast iron color of the fin does suggest admixture.

(Isn't "mischmetal" the stuff that lighter flints are made of?)

Since this last fin was on the opposite side of the casting, I must suspect that the entire casting has some unfriendly properties.
And the appearance of the nickel welds suggest that the welder had trouble with it as well.


...Cotten

[Kojack]

Right you are, Cotton, admixture was the term I was looking for. Mischmetal is commonly used to refer to lighter flint although the strict translation is simply “mixed metal”.
Several things seem to be coming into play here. Brazing and bronze welding are terms that are often used interchangeably, even by the material suppliers. Welder number one may not have actually been using silicon bronze rod. Actual content of the filler rod could have made a big difference. Welder number three may have overheated the filler rod. I’ve seen (created) porosity like that by “boiling” the filler rod during the process. I’m no great welder but my dad was a welder for 35 years. I hated to braze anything when he was around. He’d constantly complained that I was using too much heat. He was right of course. I was using an oxy-acetylene torch. A TIG is a great tool but it sure puts out a lot of heat in a hurry. Accidentally feeding the filler rod into the arc will boil the material instantly. I know your man is experienced but anyone can screw up now and then, especially when a job is being unfriendly. I found an article that suggests that silicon bronze can be used on cast iron although it involves MIG, not TIG. It also suggests a certain gas mixture and that may be one of the issues. Check out the section under “Gas Metal Arc Welding” in particular.
http://www.key-to-steel.com/default....Article&NM=185

Cranky the Welder seems to have the right idea. Let us know how he makes out.

[T. Cotten]

Kojak!

I never used the word "brazed".

Welder #1 was most certainly using silicon bronze.
As I posted, his fin replacements worked admirably previously, on heads of the exact same vintage ('30-'31 Chief)

There was no welder #3 on this head.

My question was a request to verify that silicon bronze was applicable for cast iron, and I have had this confirmed.

I have personally barnyard-torched great looking fins from not only brass, but old piston rings for filler rod. That has no bearing upon my question.

Cranky welder #2 "made out' poorly.

Either he has lost his touch, as the nickel looks like cheese, or the casting took it poorly. My conclusion is that this particular casting is unusually un-friendly, for reasons unknown.

....Cotten

[Tom Wilcock]

welding fins

I am certainly not a welder but I have repaired broken fins using an acetylene torch and 1/16" steel rod. The first couple of passes require concentration but after that it is easy. I don't know how strong it is but it seems to stand up to the rigors of grinding and filing to finish it smooth. I have built up fins right up from the base with this method. Maybe this is not the correct way to repair fins but it seems to work. I have also tried arc welding in pieces of cast using nickel rod with limited sucess. This is OK for an outside fin but impossible for an inner one.

[billpedalino]

Brazed Fin Repair

I am certainly not a professional welder, but have have done a fair share of fin repair on my own stuff over the years. While probably quite sophomoric compared to what has been discussed above, my technique is as follows:

Clean up the broken fin surface by grinding and abrasive blast.
Using cardboard, fashion the shape of the fin piece to be replaced.
Take a broken cylinder and carve out a replacement piece of fin material and hand-shape to match your cardboard template.
Bevel the attachment edges on the replacement piece and the parent material.
Break out the low-tech Victor Oxy-Acetylene rig and braze away - plain old brass rod.
After short term cooling, Heat helps shape excess brass along the joint although hand grinding with a dremel or die grinder will most likely be necesary.
The O.D. of your installed repair fin will most likely stick out a little, so I shape it on a belt sander.

From an engineering perspective - this is near no-stress application, aside from fatigue stress from vibration only. These are inertial stresses and very low-inertia stresses, given the mass of the repair piece. No lateral loading and no combined stresses to the brazed joint. Brass is weel suited for this repair.

Quite amature, I know. But I've repaired fins on Harley Cast Iron Heads and cylinders over 30 years ago they are still running and show no signs of failure or distress.

Bill Pedalino

[T. Cotten]

To repeat what I posted earlier:

>I have personally barnyard-torched great looking fins from not only brass, but old piston rings for filler rod. That has no bearing upon my question.<

The bottom line is that there is a great variance in the metal of different aged castings. It shall always be a roll of the dice for anyone who attempts it. This is an inherent obstacle of vintage motorcycle restoration as a whole.
(Example: The potmetal of '30 to '40 Schebler carburetors ranges from "impossible" to "anybody with a TIG" by advancing vintage.)

I have a set of 741 cases that two first-rate professional welders could not deal with.
One demanded freon for a degreaser.

The set of heads in the original question finished out at great expense to all parties involved.

....Cotten