View Full Version : Cast Iron Repair

11-13-2014, 02:29 PM
I have been asked to fix a part for an old cast iron bank. The part is about 1.25" in diameter. Below are pictures of how it looks now and how it is suppose to look when repaired. The only welding capability I have is oxy-acetylene. Can the broke part be brazed back in place? What preparations are needed to ensure a solid joint? Appreciate any suggestions as I have not brazed before! I do have some supplies for brazing but they may not be the right ones.

http://i163.photobucket.com/albums/t308/i422twains/DSCN0852_zps7cf17543.jpg (http://s163.photobucket.com/user/i422twains/media/DSCN0852_zps7cf17543.jpg.html)

http://i163.photobucket.com/albums/t308/i422twains/DSCN0853_zps6b0ce360.jpg (http://s163.photobucket.com/user/i422twains/media/DSCN0853_zps6b0ce360.jpg.html)

Alistair Hosie
11-13-2014, 03:04 PM
I would remake in steel with welded tags.Alistair

Forrest Addy
11-13-2014, 03:17 PM
The part looks like it sees little strain in use. The break is clean and will self-key into position and stay put once assembled and wired to hold it.

My suggestion is to silver braze it. Grind a little pocket in the center of the fracture face just large and deep enough to accept a short length of 1/16' silver brazing wire. Wire brush to clean up but do not stop there. The parts have to be surgically clean and free of oil and rust. Bead blasting is the way to go. It also blows off the surface carbon and silica dust so a maximum of clean metal is exposed.

Bead blast the whole surface of both parts with clean media immediately before brazing. Slobber liberally with flux, place the silver braze wire, assemble, and wire into place with steel stove wire. Heat gently so the water sizzles out of the flux dabbing on more flux to the bare seeming places. Keep heating until the flux goes from white to a clear syrup appearance.

Watch the edges of the fracture. As the part approaches dull red visible in dim light (1300 degrees F) you should see glimmers of bright silver peeking out. Apply more silver as needed but not enough to blob. When it comes time to stop, stop. Resist the temptation to monkey with it. Allow to cool. If you did the job right you will see a bere thread of silver around the fracture.

Boil in water for about 20 miutes to remove the flux. Lightly blast and paint to suit. A good silver braze repair is a boon for restorers of broken antique castings and the repair, if well done, requires no dressig or fettling, is strong as the parent casting, and it holds its strength into the 700 degrees range - safe enough for everything but stop tops.

This is not a job the learn on. Bust the handle off an old frying pan or an ear off a water pump casting and fix it. When you get a little practice move on to your project.

Harris makes the fluxes and silver brazing alloys you need. You may find them blister packed in the welding section of your local big box store. I recall paying $26 or so. It aint cheap: the wire is half silver.


Use the reccommended flux.

Here's the Airgas offering for the Harris 56 kit. The price of the kit may be a deal killer bit consider the value of having a silver braze capability in your shop making carbide scraper, assembling complex "brazements" of elemental shapes to take the place of castings, etc. The price of silver solder follows market volatility. Silver was nearly $80 per Troy oz in Dec 2012 and $20 last summer. Now it's about $40. There's less than 1/4 troy oz in the kit linked below. YMMV, take it from there. Personally, I buy when the market is down.


Sliding stove damper door right? A less elegant fix would be to drill and tap from the back side to attach with countersunk screws. The shape of the fracture is nearly perfect to socket the broken part in place for drilling. There might be room for two #8 FHMS if I eyeball the size of the part correctly.

11-13-2014, 04:16 PM
I'll 2nd everything that Forrest said - especially this part This is not a job the learn on.

11-13-2014, 04:27 PM
Considering the effort Forrest put into his post and the obvious position of knowledge from which he speaks.
You just gotta do what he said.

I sure would - and not the screwfix, do the silver brazing, after the practicing.

loose nut
11-13-2014, 05:13 PM
Build up the area of the missing bit by brazing and machine/file to shape.

11-13-2014, 05:59 PM
I'd give it a good preheat, should braze easily once hot enough, check the other ear too,may already be cracked

11-13-2014, 06:00 PM
If you are concerned about messing up this ear/weld it's a small piece , just take it to a weldor, can't cost much to do a nice job on that.

11-13-2014, 06:21 PM
I don't know why it work, but i had good results with fluxcore mig wire. I recently weld many frozen crack on the water hopper of a Novo gaz engine. Went out reel nice

11-14-2014, 04:45 AM
I would find something similar to practice on , if you have not done much or any brazing.

Brazing is a good way to repair cast iron and as most of the original is still there this should be easy , clean , preheat and braze , wrap it in a heat resistant blanket when finished and check it next day .

Light wire wheeling should clean the flux off , as the repair is mostly hidden I would not be too concerned about the braze not being visually perfect..

If you dont try you will never learn or become confident .


11-14-2014, 07:19 AM
Forrest's advice is very good.

I would add that piece is so small and thin you are going to need to be careful when you add the heat. The silver is going to have a fairly small temperature window and the part will heat up fast.
Plus whatever on the practice on something else first, that flame is going to need to be quite gentle or you are going to blow that little ear/tab away with the force of the flame unless its pinned down. This is far closer to working with jewelry in terms of size than anything else. {Which is who I would take it to once cleaned if you don't feel confident.}

As well, I would also check the other surface of the bank that this piece moves/slides/rotates on (the surface) and clean that was well. Nothing to do with the brazing but rather I suspect the reason the little tab/ear broke off was wanting to rotate it and there being rust (?) or sliding surface irregularity and force too great for that ear being used.

loose nut
11-14-2014, 10:22 AM
I don't know why it work, but i had good results with fluxcore mig wire. I recently weld many frozen crack on the water hopper of a Novo gaz engine. Went out reel nice

If you welded up cast with steel wire then it may work OK for now but it won't last. Steel on cast has no strength. SS may work better but I an not aware of a cast flux core wire or regular mig wire.

John Buffum
11-16-2014, 01:24 PM
Just two additions.

www.gossonline.com - incredible selection of torches in all heat ranges.
www.sra-solder.com - incredible selection of solders, solder masks, fluxes, and tools for soldering.
www.brownells.com - Search on solder. If you are concerned about temperature damaging the workpiece, check out Hi-Force and Hi-Temp-Hi-Force solders.

That having been said, a word of advice from a tool junkie. If you don't want to acquire a solder infrastructure, complete with three or four kinds of solder, an array of those fine Goss torches, and a whole shelf full of fluxes, as well as having to acquire a bead blaster, for just one job, then the first suggestion, about kludging together one out of mild steel is a great idea. Using files you already have, you can come to a very close approximation. Using your plumbing propane torch, you can age the steel. A little permitted rust, a little gun bluing. With the mild steel, you NEVER have to worry about it breaking again.

Alistair Hosie
11-16-2014, 03:21 PM
In my opinion if you decide to silver solder you will need to clean it up first.IMHO of course .I did a lot of silver solderring over the years but it always required flux and that is on new stuff I E Clean from scratch.Alistair

11-16-2014, 03:49 PM
Some cast brazes (brass)well while some try your patience I've never tried to silver solder it or cast arc rods