Welding a cracked cast housing

[stephan]

Well I managed to crack the gearbox housing for my rotary cutter and am after ideas/advice on welding it. I have a 240 volt 120 amp MIG and I'm not afraid to use it ... just ... ahh not very good at using it.

I'll post a picture of the break, did I say crack?, when I get the gearbox off. The attached picture is a before shot showing the nut around which the break has occured.

 

[JimR]

Did you say cast housing? What is it made out of?

 

[Soundguy]

Cast steel will be no problem.. cast iron takes nickel? rod and a pretty savy welder..

Guess you could braze it if ti is cast iron.

One thing though... if it broke bad.. did any bearing surfaces that a shaft rides in deform?

or did you loose any cast parts in the box?

Soundguy

 

[AlanB]

I would be heasitant about doing it.

I have seen it done, succesfully, I have welded a fair amount of Cast Iron fairly successfully. But in a bush hog gearbox, I just would not be overly comfortable with it.

The problems with welding casting's are many.

Quality can vary widely, especially in "cheap" sand castings.

Base material compostition can vary widely.

Your weld will not have the same hardness and density of the surrounding materials, that leads to failures.

Proper (hot enough and even enough) preheating and controlled cooling, (both of which I think you will find difficult to achieve on that piece) is the secret to succsesful welding of cast.

All that being said,

V- Groove it down, insure that you have found the end of the cracks, stop drill, Preheat well, lay some mig wire or nickel rod or 7018 (depends on who you listen too) there are also special Cast rods available, and then make it cool slowly through the use of asbestos (well, how about flame retardent) blankets or a dry sand box.

You are trading time for money (as in all things) if it was a really valuable casting I would tell you to dissasemble it, remove all pieces of it, and I would then TIG weld (with cast filler rod) it on top of my turkey deep fat fryer to maintain an even preheat throughout, then throw it in the sandbox and cover it over and leave it till the next day, then I would suggest allowing it to age a week or more before returning it to service.

I doubt a bushog gearbox is worth the effort.

 

[Charlie_in_TX]

I agree with the others welding iron is difficult.

Another possible solution. On a side note, I am making this recomendation based on the assumption that the cutter frame is in good strong shape. There is a perminately installed stud comming up from the frame. Fab a strap that goes from the stud at the broken section over the gear box to the stud on the oposite side. The 3 remaining studs should hold it in place, the strap will hold it down.

 

[RichNJKubota]

I've brazed castings before with no problems. The braze is not nearly as strong as the original but so far I've had no problems.

Rich

 

[OkeeDon]

<font color="blue"> I've brazed castings before with no problems. The braze is not nearly as strong as the original but so far I've had no problems.
</font>

Yep. I've even tig welded some cast aluminum. But, because I agree that it's not nearly as strong, I'd only do it in select situations. Example - you have a broken cast leg on the end cap of a park bench. You weld the leg, it's always in compression, and won't come apart no matter how much weight is put on it. Or. you have a broken upright back support on the same park bench casting. You weld it, someone leans back too hard, it's in tension, it breaks.

Your gear box has stresses that put it in tension, sometimes. You can weld it and it may work forever, but it also might break again right quick. If it's a rare or very expensive housing, it's worth a try, but go into it expecting failure.

 

[theonlybull]

personally, i would braze the crack, and unlike some are saying, a properly cleaned and brazed joint will be strong enough to break the case in another spot, not the joint...

btw, i do this on a regular basis, as part of our machine/welding shop business.

 

[stephan]

I just did some grinding around the break and the sparks were bright which I think means that it is cast steel rather than high carbon iron. Would it be better to braze it than "v" out along the break then weld it? Perhaps then put a brace across the top of the break and weld that to the gearbox. Typically, the break is around the bolt holding the gearbox to the chassis so is both required and under more stress then perhaps other sections.
I think to use a strap to the chassis would be OK but would prevent me removing the gearbox in the future (I have already blown a bottom seal).
We're just going into winter so I have plenty of time to fix it and as to the "worth" of doing it? To replace it would cost a couple of hundred (AUD) bucks whereas welding wouldn't. I was also thinking that I could have a crack (pun intended) at welding it and if that doesn't work I can always replace it?

 

[OkieG]

<font color="blue"> To replace it would cost a couple of hundred (AUD) bucks whereas welding wouldn't. I was also thinking that I could have a crack (pun intended) at welding it and if that doesn't work I can always replace it? </font>

Same situation happened to me a year ago with a cast iron front axle spindle housing. I brazed. The plug brazed nicely, but a small nearly invisible crack continued to leak. So, I brazed the whole bottom of the housing. Just over a year now, and not even a drop has leaked. Beginners luck.

We were told in welding class that welding cast was a challange. I guess that scared me a little, so I went with brass. So far so good. Good luck to you, Stephan.

OkieG