Help with Brazing

[Farmall]

Ok, I have never brazed before. I got a small forge that has a cast iron gear wheel cracked in two places. I figure its time to learn how to braze. So, I've attached a picture so you know the task at hand. I figure for the outside ring crack, I'll grind from the top down almost to the bottom edge, fill it, then grind to shape. For the spoke, I was thinking of grinding towards the middle from both sides, then filling and grinding to shape. However, I don't know if I should preheat, and if so, how much, and most importantly, what brazing rod to use (and where to get it). Do I fill it with brazing material all at once or do I layer it? I appreciate any and all help. Thanks.

[Thomas Dean]

I remember this from the other day and when I suggested you brazing it I had no idea that you had no experience with brazing. May be difficult at best for you do attempt this, but here ya go... You can get the brazing rod from any welding supply store, I would get a flux coated rod and just a FYI, they were $9.00p/lb the last I bought. (a couple of sticks should do you but it won't hurt to purchase more.) You do not need to preheat as the heating of the part to braze will work. If your part ever turn red you are too hot, move the flame to somewhere else. When you grind the part for brazing you will need to grind the edges of the part to shiney, this removes the scale and brass will stick...doesn't want to stick to the scale. Once completed its would be a good idea to cover with some insulation or DRY sand til it cools, but at least keep it out of any breeze til cool.

Where are you located? If you are close to me I would be glad to show you how this is done. But there maybe someone in your area that could help. Good luck.

[Farmall]

I am in Virginia. Would love to come to Texas to learn, but it is a bit of a drive. Last time I drove to Dallas, took me 22 hours! Thanks for the advance. I do have some other pieces of cast iron I was going to practice on first to try and get the feel for things.

[Thomas Dean]

I am in Virginia. Would love to come to Texas to learn, but it is a bit of a drive. Last time I drove to Dallas, took me 22 hours! Thanks for the advance. I do have some other pieces of cast iron I was going to practice on first to try and get the feel for things.

That'd be a good idea. The flame you want is neutral. Light your torch, and add oxy until the 'whisker' just leaves the 'cone' of the flame. You don't want too much oxy or your flame 'blowing' hard.

[arftist]

Build a bed to rest the gear on. Fire brick is best, dry sand in a metal tray is good.

Since the object is close ended, preheating is a good idea, as well as slow cooling. Fiberglass works but just barely, and it stinks as it burns. An ashcan of wood ashes is best, bury it as soon as you are done brazing. If no wood ashes, dry sand is OK.

Butter the joints first, then fill. Having a big enough welding tip makes this job faster and easier.

Vee the joints, but don't overdo it, as the brass is much stronger than the cast iron.

Slow cooling is the key to success on this item.

[Farmall]

Thanks arftist. Dad still heats with wood, so I can get as many wood ashes as I want! I've got enough fire brick to make a "bed".

[brian robertson]

I have found that brazing ring gears can be problematic. If allowed to heat or cool unevenly they will crack in new places. My successful repairs were preheated using an oven set at 450 f for atleast 1 hr, support the pieces in a bolt on frame to maintain proper alignment, laid on a 2" blanket of Kao wool, brazed, returned to the oven rewrapped in kao wool and slowly allowed to cool down over 3 to 6 hrs depending on thickness. I've brazed parts for pumps, steam engines, farm impliments and tractors this way no call backs to date.

[Frosty]

Braze joints are nearly as strong as welds provided you're NOT filling deep scarfs, the thinner the braze the stronger the join. Saying that I prefer to use emery cloth and sand the joins clean as possible, I simply wedge the breaks apart enough to pass the emery and work it shoe shine manner on both faces.

Then I preheat in the oven to 450f is a good temperature, hotter is better. Bring it out, tough it with a neutral flame torch, (feathered flame as described) apply fluxed brazing rod and let it draw to the other side. Wrap and put it back in the oven to post heat and slow cool. (as described)

This can be a tricky job and if you have a welder I'd advise Welco 92 or the equivalent nickle rod, scarf, preheat and weld it up, then post heat, wrap and cool as slowly as practical.

Maintain as little fillet as possible in any case as the superheated filler rod must shrink in proportion to the thickness of the fill. The stress on the rest of the part is likely to find relief where you don't want it. (CRACK that is!)

Best of luck.

Frosty the Lucky.

[Francis Trez Cole]

also with nickle cad rod it helps to peen right after welding it relives the stress.

[pkrankow]

Braze something else first. Use cast iron or steel, and make a similar joint to practice on. It will be well worth the gas, rod and time to have a successful "dry run" or "dress rehearsal"

You can use borax before and during heating to maintain a clean joint too.

Phil

[Thomas Dean]

If you are game, I will make your repair if you will pay for shipping both directions. I have made this same repair for a friend in Illinois a few years back on the same deal, he paid shipping both directions. Looks as though it will fit in a 'flat rate' box.

[peacock]

I would take Thomas up on his offer. In addition to being a top notch welder his is a great guy.
The only way you can go wrong is to not send it to him. that stye gear has allways been a problem
to crack. The spokes are sprialed that way to help them not crack when they were cast. Then the
teeth on the inside and out side compounds the problem. The thing is notched just looking for
a place to crack.

[Thomas Dean]

So, how's the repairs coming?

[Farmall]

Thomas, if you will send me your address, I'll send it to you. I'd rather someone with more experience than I braze this. I have been working on the other bits of the forge, and keep looking at the cracks. So, I'll get them on their way to you if you would be so kind as to tell me where to send them!

Thanks.

[Thomas Dean]

I'll send it via a PM here on IFI.

[Thomas Dean]

Repairs made, ready to ship tomorrow. Didn't take any pictures...thought about it AFTER I had it packaged for shipment. Jim, you will have to post pics if he choose to do so. This casting had some real bad sand pockets in it but I ground them all out, in the repaired area, and then brazed and dressed teeth and arm. Hope it works!

[Farmall]

I'll be sure and post pics when I get it. The sand pockets may explain why it cracked....quality of the casting doesn't sound the greatest. Thank you, Thomas.

[Farmall]

Got my gear back from Thomas today! Looks great. Can't wait to get it back on the forge. Still cleaning the rest and prepping for some paint. I'll bet I've got the only Thomas Dean Autographed forge in town! (see second picture) Thanks again Thomas......

[evfreek]

Hi Thomas. Beautiful repair. Looks like a work of art. Any special preheat tricks or counter-heating for that tricky spoke?

[Thomas Dean]

Thanks, I signed it on a lark! thought Jim would get a kick out of that!

I beveled it and did a preheat that would "bounce spit" No post heat. Did the same for the gear portion. Once finished with the brazing I did cover with kaowool and did the grinding for the teeth the next day. I think I have about 2hrs in it...really didn't pay that close attention to the time since this was a freeby. I use a flux coated rod and will use Peterson's flux some, even with the fc rod.

When you braze cast you are not "shocking" the cast with an arc, and the "experts" claim that the heat of a welding arc is like 'kabunches' times hotter than the surface of the sun.... Usually by the time you have a joint hot enough to melt the brass the heat has creapt into the part that it won't crack....or should I say is less apt to crack. I sent Jim a couple of pics of a blower that I repaired a few yrs back using brass as he has some other problems that he want to tackle on his blower. Back in the '70s I used a vise that had been repaired with brass, and the repair was done in the late 50s or early 60s and held as tight as any new vise. I have also seen cast iron that was "repaired" by arc welding that failed. I just have better luck with brass, the "magic" cast iron rods don't hold up as long as a brazed weld...and I do have the proof.

[SmoothBore]

Many moons ago, I worked with a guy who was building a semi-passive solar storage system, in his basement.

( This was looooong before any "alternate energy" products were available. )

Along with a huge stainless steel tank, for storage, he was disassembling old, scrapped steam radiators, and reconfiguring the cast iron segments, so they would lay flat against the walls of his basement.

Needless to say, the poorly drained, and often frozen segments, had their fair share of cracks.

Being a gullible chump, ( with an over inflated opinion of my welding prowess, ... and a good supply of NI-FE ) it somehow fell to me, to weld up the cracked radiators.

Not knowing any better, I cleaned up one of the cracks, and laid down a lovely repair bead.

After admiring it for a minute, and congratulating myself on the nice job, I hooked up an air hose, to verify the that it was sealed up.

It held air pressure, ... and all was well with the World.

Until it went PING !

And a brand new crack appeared, ... right next to the weld.

To make a long story short, ... that was when I learned all about pre-heating cast iron, and about burying the finished castngs in a box of dry sand, to slow down the cooling.

That all occurred in the mid 1970's ... but I remember it well, and the lessons learned are still relevant.

.