I have the following part that I am trying to repair. I have tacked it together for alignment. I have read that I need to use a high nickel rod and use an arc welder. I plan to notch out the break and weld one side, then then notch out the other side and weld it.
Sounds good you just need to preheat, peen with a punch after every pass and let it cool very slowly. Being that small of a piece I would wait til the wife isn't around and preheat in the oven and put it back in the oven after you are finished and slowly bring the temp back down.
Ni rod is pretty easy to run just dont let the part cool down way to fast. ive also had really good success with tig welding cast with aluminum bronze filler wire. just dont forget grind all the gunk out thats possible and peen it after welding and keep fingers crossed it doesnt crack someplace else. welding cast is a luck of the draw type deal
A2 bronze will work for tig welding cast but you won't have the tensile strength that you would have with arc welding. You can also braze it but once again you don't have the strength. Welding cast is not difficult but you need to spend time prepping everything properly.
The metal is brittle and any added tension can cause cracks as it cools. You peen it when it is hot to de-stress the weld so it isn't as prone to cracks.
Brazing is the easiest and best way to repair cast iron when high heat during use isn't an issue. Pretty much zero chance of it cracking. No preheat. No postheat. No short welds. No peening. It just works.
The lack of tensile strength is not an issue most of the time. Only when the parent material is very high strength (not all "cast iron" is created equal) and actually sees that type of load in use.
So many people think that brazing is not as strong as steel. One of our many assignments I did in school was to braze steel parts together then put them through a guided bend tests and tensile pull tests. If the brazing and prep were done correctly, the steel fractured and the brazed filler material held. I'm not saying that will be the case with high strength alloys, but with mild steel it is.
I would agree with you in many instances but personally I would weld this part as long as you are a competent welder. It is very easy to preheat and roll around while welding. Afterwards the slow cool down is easy as well. With arc welding and peening if done properly it will look like it was never repaired. It also depends on quality of the cast. Some of the old tracker parts that I have repaired have been a very very high quality that has welded very easily. If is is very dirt, pourus sp? Metal I would agree with the brazing. If I brazed it I would cut the fit back apart and drill and tap both sides and put a piece of threaded rod in to assist in lineup. That way you added a little strength and you can bend it before you start brazing while it is mocked up to make it fit together like it is supposed to. I would also sharpen the ends like a pencil like knaffie described.
With those pictures you have shown, the first thing I would do is grind all that weld out of there completely. Tacking them together was not smart. Then grind the parts so they either meet like two chisels or two center punches. This will give you the most surface area for the filler metal to adhere to.
I've successfully welded cast iron using er70s-6 wire. I always preheat to at least 600 degrees and I only weld and inch or so at a time. I immediately take a center punch to my weld and stress relieve it (all while maintaining the 600 degree minimum). My next bead is dropped at the opposite end of the part that I had just welded and I slowly work my ends together. After welding and stress relieving, I cool the part slowly over a period of hours.
Rolling the dice using that wire. That might work sometimes, and won't work others. Material is the biggest you variable that you don't know and can't control.
Clearly I am in over my head with this. While I have welded a bit, mostly sheet metal and grader blades to loader buckets.
When I tacked it together, It took quite a while as I only welded for a few seconds at a time, and it didn't get very warm.
I don't see this part getting much load or heat. It's a clutch pedal. It broke once before when a piece of firewood got between the ground and the pedal. I had someone weld it, but don't know how he did it, and he is no longer in the area, but I think he arc welded it and built up a donut around the break with very little penetration into the break.
It broke again pushing firewood, (this time once fixed I'll add a skid plate).
I like the idea of drilling and tapping (or maybe even pining) the two parts together. and then welding or brazing it.
I can't give any technical advice but I have this observation. I have been in stamping plants where large cast stamping press frames have cracked. Like machines rated at 1000 tons. The repair............ brazing.
That's all I got.
With that said I am with knaffie on brazing it. The fact that it was hack welded once already means that there could be a bunch of stress cracks. Braze would be the safer bet in my opinion.
That's because its nearly impossible to properly preheat, weld, and postheat something as large as a press frame. Not to mention the potential replacement cost and downtime if it were to crack after the repair and ruin the whole frame. Brazing is pretty much fool proof as long as your technique is solid.
This is how I have always welded cast. I have never Brazed before.
Grind the area to be welded
Get the part to a dark cherry color (not bright red) all around the area to be welded
Use High Nickle rod
Run a small bead on one side then the opposite side
Place in Kitty liter until it cools 1.5 to 2 hours for a part this size or until you can touch it without feeling a difference in temp.
Repeat until part is welded fully
If it was a easy to find part I would probably just replace it. I had a clutch pedal break before sitting at a light. Broke just under the factory upper welds having the entire arm fall onto the floor and required a tow.
I ended up grinding it down to 25% of the original diameter, heated, arc welded with high nickel rod, peened it, let it cool, repeat until I built it back up. I then cut a piece of 1" angle iron and headed and nickel welded that over the repair.
I should have ground them smooth. I was having a hell of a time with the nickel rod on the mild steel.
-tim
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