Welding cast iron forge help

[Walker's Forge]

Hi everyone,

 

Got my hands on an old forge this weekend. The guy was 75 and he and his dad used the forge to make horse shoes back in the day when they broke in horses. I am guessing it is cast iron based on age however I will be doing a spark test to confirm. The forge came with an excellent hand cranked blower too.

 

The forge is fed air from the underneath. There is a T section of pipe (ignore the words in the picture):

 

 

 

Where this T section joins the forge are three rusted out bolts that were at sometime welded to the forge. I would like to weld the T section completely to the forge so it becomes one solid piece. My question for you guys and gals is what is the best way to weld cast iron? I have access to a MIG and an Arc welder. I have heard that heating the forge up first and welding while hot and then allowing to cool slowly is the best way.

 

If the forge turns out to be cast steel will there be much difference for welding?

 

Any help you can provide would be much appreciated.

 

Giles

[Francis Trez Cole]

a real picture of the forge would help to direct you in the right direction.

[DSW]

Cast steel vs cast iron will make a huge difference. There are a number of ways to weld cast iron. However cast iron doesn't always weld well for a number of reasons. Biggest issue is that cast iron has a bad tendency to crack as your weld cools.

 

One way is to heat the whole thing up, weld with correct filler, then slowly cool the whole piece. Another way is to weld very small sections with high nickel filler and wait until it's cooled before welding some more. The high nickel filler is more ductile and the low heat input helps reduce the chance of cracking. Peening the welds as they cool to help relieve stresses also can help. When I've done this I usually tig the welds and wait until I can touch the previous weld with my bare hands before doing the next. I'll also jump around to reduce heat even farther. I know some guys who have had luck doing something similar with stainless mig running very short beads to keep things cold. Brazing is another option for medium to low heat areas.

 

Personally I'd leave it alone.

[jeremy k]

Bolt if possible!

[Walker's Forge]

Thanks for the replies everyone, I will try and load some pictures this weekend.

 

Thanks for the info DSW - from what I have read you hit the mark that it is a very difficult thing to do, and even if you follow the correct procedures you still run the risk of it not working or cracking the whole thing.

 

I think I may have to drill some holes and bolt the thing together. At least this way I dont have to worry about damaging the forge.

 

Giles

[VaughnT]

The existing bolts probably rusted into place.  My old forge was exactly the same way, looking like a solid mass, but when I drilled out the old bolts, the heads popped free at the last second.

 

Definitely recommend you drill some new holes and install stainless steel bolts to join the two pieces.  Last nearly forever and you can separate the two if needed.

[wpearson]

I think I may have to drill some holes and bolt the thing together. At least this way I dont have to worry about damaging the forge.
 Giles

+1     wes

[David Einhorn]

Welding the tuyer to the forge is not something I would do.  If the tuyer, when heated, expands and contracts at a different rate than the forge area it is attached to, something will eventually break.  Also, as folks already mentioned, future repairs would be much more difficult if the two parts were welded together.  Please consider drilling and bolting instead. 

[Dodge]

I agree with NOT welding. Having welded professionllyfor most of my "other life", I learned that even if you have the right equipment and experience in welding cast, there are so many reasons, including the ones mentioned here, not to. The first one that came to my mind was material contamination. Cast is far more pourous than other metals and absorbs crud from coal as well as oxidatioon (rust) etc. You can buff the heck out of it and it will look clean but as soon as you start welding (or brazing), all the bad welding gremlins come out of the "woodwork" and really make a mess with things. The other best reason I saw was that the tuyere is a different shape and size than the pot and it will react differently to the heat and probably break again right away. What's worse is that the weld probably won't break (especially if you are experienced at welding cast); It will probably break around the weld making a worse problem than before. Far to many welds have been made by folks that weld stuff because they can without first making an informed decision on whether they should.

 

Sorry, I sort of did the soapbox thing there ;)

Scott

[ThorsHammer82]

DSW Knows his stuff when it comes to welding and the advice to not weld should be strongly considered as you run a higher risk of destroying the forge than you do of actually fixing it to your liking.

[David Gaddis]

RE-machining the bottom for new bolts is a very good idea. But I am not in to the stainless bolt replacement. If I am ever going to replace those bolts I want them to be of the softess grade possible to be easily re-drilled and tapped.

 

But here I differ with the other ideas as I am not opposed to brazing a new ring and mount to the bottom of the fire pot. This is not a newbee type project by any means. Look around and there should be some old time welders from the past that had experience in doing such a repair. WARNING: This is a very hot project like you may never again see and the casting must be brought up to operational welding temp evenly without a whisper of wind or breeze. A slight wind stir will render this project useless quickly and a tinging sound will show a great crack! When through welding another person should apply a weed burner to the project to evenly heat the remainder of the piece right nicely and place in hydrated lime or vermiculite until tomorrow afternoon! Then you can drill the bronze or brass easily and apply neverseize to the screw threads. I would bet on a 95 plus percent success rate.

 

BTW cast iron can be married to many other products with the use of brazing.

 

In the past we used real cast iron rods...triangular in shape...and almost extinct today.

 

Carry on

[ThomasPowers]

If it's cast it's cast iron!  Cast steel would have been excessively expensive for such a task.

 

I want to second David Einhorn's mention of allowing for temperature expansion and contraction!

[Walker's Forge]

Thanks everyone for all your answers. I am going to cut off the little spikes where the old bolts were and re-drill bolts holes. I don't want to risk ruining the forge and like many of you have said even if done properly things can still go astray and the forge could crack.

 

I will hopefully get to it this weekend unless the wife goes into labour (only week and a half left until baby is due). Once it is done though I will post some pictures. I did mange to make a stand for the blower that came with it though. Cleaned it out over the weekend, there was about 20 years of caked on grease and dirt to clean off, it purrs now though.