Welding Repair,... Cast Iron?

Robo_Pi

Robo_Pi

Registered
Registered
Joined
Feb 18, 2016
Messages
451
I didn't see a forum section on welding. But I know a lot of machinists also weld. I'm wondering if anyone can give me some hints on how to repair an old vice. I'm guessing this is cast iron?

Here are some photos of the vice and a nasty crack in the casting.

Top view: (actually I guess this is really the bottom of the vice jaw).

The crack starts at the lower left corner of the rectangular cut out on the round shaft. And continues all the way around to about the midpoint on the other side (see side view photo)

vice (4).JPG

Side view:

vice (2).JPG

I have no experience welding cast iron. But I do have experience welding steel to steel.

I have 3 methods to weld.

1. Oxy-Acetylene torches and lots of flux-coated brazing rod.
2. An old AC/DC stick welder
3. A brand new TIG welder.

I would like to TIG weld it if possible. But I'm not sure what I need to do that.

Are their special rods I'll need to get for welding cast iron?

Two more Question on pre-welding preparation:

1. I'm thinking I'll need to grind a V-groove all the way down the crack. But I thought I'd double check here whether that's actually needed? I didn't want to hack into this thing with a grinder until I get some feedback. :grin:

2. I've always heard that cast iron needs to be preheated before welding lest it might crack while welding it due to extreme temperature changes. If that's true what does it take to heat it up? Should I just heat it up with the oxy-acet torch for a while before welding it? And if so, how hot does it need to be.

Thanks for reading and for any suggestions or guidance you have to offer..
 
Cast iron HATES to be welded.
That said, yes pre heat by torch to about 500F.
Yes, VEE it out.
Most guys stick weld using a nickel alloy rod.
Some guys like to post weld cover to slow cooling.
Likely lots of different opinions will be expressed.
Pay your money and take your chance.
Expect to be disappointed but what the Hell......................Bob
 
Deep V groove, complete grinding until clean metal showing everywhere. Lots of the proper flux for brazing, and appropriate brazing rod. Slowly heat the entire piece, flux, then heat crack area until the brazing rod flows into the V groove and fills it all, add a bit extra to make sure it is filled completely and the braze bonding to all the crack surfaces. Insulate the work well so it can cool down very slowly. Fire proof blankets or deep ashes all around the part work well. Let it sit until it cools completely.

TIG can be used, but as it often done it does not heat the entire piece enough to equalize the stresses in the entire part. It is more difficult to do without proper training, the biggest problems being cold joints that fail and stress cracks from uneven heating.
 
Thanks for the awesome quick advice fellows.

Based on the feedback thus far I think I'll go with trying to braze it just using the oxy-acet torch. Come to think of it I'm pretty sure I have repaired cast iron things in the past using brazing. I know they can be welded nowadays, But as has been pointed out welding cast iron probably takes far more experience and proper tools than I have available,. So brass it will be.

By the way, this vice isn't an expensive item. I picked it up at a yard sale. I took it apart to restore it just for myself. But when I took it apart I saw this nasty crack. Apparently it was last used as-is with this crack in it. I mean, it's actually usable as-is. But clearly it could break at any moment. I thought I should try to do something with this crack before reassembling it.

It's not like anyone will need to depend on this to get them to Mars. :grin:

I'd just like to do something with this crack before putting it back together and trying to use it. It's a pretty nice sized vice that I could put to good use. I'll try to avoid putting heavy metal pieces in it and beating on them with a sledge. :grin:

So thanks for the feedback. I just braze it up then. I think I can handle that. Nice big deep vee groove with a drilled hole at the end of the crack.

That's what I'll try to do.

Dag blast it. I just bought that TIG torch and the darn thing is useless. :grin: Better off with the old-fashioned oxy-acetlyene and some brazing rod.

Should I get special brazing rod?

I just bought a ton of this General Purpose brazing rod.

I hope I can use this stuff:

I got it at Amazon:

Blue Demon Gas brazing Rod
I actually used this rod last fall to repair my outdoor wood boiler stove. I was welding on very old rusty corroded steel and this stuff flowed onto it really well. Of course, I ground it down the best I could, but even grinding it down didn't clean it perfectly. Yet this brass rod seemed to find a way to flow and stick even over rusty pitted areas. I was impressed.

I hope it will work for this vice repair. Like I say I bought a ton of it, (well, actually only 10 lbs. :grin: ), but that's a ton of brass rod.

I'll try brazing it with this stuff. Like I say, I'm not going to Mars with this vice, so if it fails, so be it. It won't be the end of the world. At least I'll still be on my home planet. :grin:
 
I have done both. I depends on how much stress the part sees in service. As thin as the part is stick welding would be at real chore with an AC welder. Getting the heat right presents an undercutting problem. Brazing is much easier. I would follow the prep, preheat and cool down advice above for ether process. I don't think a hole at the end of the crack will help in this case.
 
One added suggestion, after veeing the crack out, feather the edges of the vee at a slight angle so the braze can flow out a bit, maybe just 1/8" or so, then butter up the whole thing with silver solder flux so that torch heat will not blacken the surface to be brazed and make it difficult to get the braze to adhere; this I do always when brazing cast iron. I usually "tin" the surfaces with braze, then go back and fill to finished level with additional braze metal. Try to not overheat the iron, just barely red is plenty hot, just hot enough for the braze to flow without boiling it, causing porosity.
 
pontiac428 said:
Preheat and TIG with silicon bronze. Easy and you'll be glad you did. Let it cool slow.
Click to expand...

I didn't even know that you could braze with TIG until I saw Tony do it on a "This Old Tony" video. That kind of got me interested in trying to use the TIG torch for this repair. After all I just bought the TIG welder last year and would like to use it. :grin:

But then I'd need to buy the special silicon bronze rod right?

I guess if I just go with the old-fashioned oxy-acetylene I can use the brazing rod I already have. I'm probably over-thinking this one too much. It's just an old vice repair. I only paid $25 for this vice, which would have been a great deal had it not been broken.. I didn't see the crack until I got it home and took it apart. I'd really like to restore this vice to some level of use. It doesn't need to be super strong.

I'll probably just go with the oxy-acetylene brazing rod I already have. Save the TIG torch for other projects. Lord knows I have enough other projects that I will be able to use the TIG torch on. So it's really no big deal if I don't use the TIG for this one job.
 
James
Yes there is a welding forum and I have gotten replies there to my questions.

With that new TIG you're itching to use I would braze it with aluminum/bronze (1st choice) or silicon/bronze. Do what others have said with cleaning, Veeing, SLOWLY preheating, and cooling very slowly. You don't want to get it hot enough to melt the base metal. That will make it brittle. sometimes use an electric frypan with cover for pre and post heating. Bring temp up slowly and after brazing use heat and turn down gradually.

Here is a good video on doing just what you're trying.

welding tips and tricks brazing cast iron - Search Videos

www.bing.com www.bing.com

Good luck
Aaron
 
You must log in or register to reply here.
Back
Top