We have a very old shear, which broke a tooth on the driven gear. I'm reasonably certain that its cast iron. I can't believe that getting a spare part will be easy, so we'd like to take a shot at welding it. We have good welders but none have work cast iron before.
Am I correct that the work should be pre-heated? How hot?
What type of filler metal is recommended?
Is there anyone in Cleveland who' has done this type of work before?
Cast iron welding applies for repairing purposes, not structural. By repairing, I mean to fill up a crack or hole, for example, i.e., a weld that will not be subject to stress. In your case, the weld would be a structural one, because the tooth will have to withstand a stress. If I were you, I would try to fasten the broken tooth to the original shear by screwing it.
Drill a couple of holes (or as many as you think) through the tooth, with a diameter, say, 0.5 millimeters larger than the screw that will pass inside them. Then, drill the same number of holes on the shear, in the same position of the other ones, but with the necessary diameter to tap a female thread on them.
Once you have chosen the screw diameter, based on your good judgement, any mechanical engineering handbook will tell you the diameter of the holes to be drilled on the shear, i.e., the ones on which you will tap the female thread.
Then, fasten the teeth to the shear by means of the screws.
If you follow my opinion, I would like how you got along
Giovanni S. Crisi
Sao Paulo - Brazil
Mr. Crisi's reply makes good sense as welding cast iron is very tricky, and may be a waste of your time.
However, if there is a lot of stress on this gear tooth, you may consider a couple of tacks to increase or back up the shear strength on the screws.
There is some general cast iron welding info in the "Technical" topic under the post titled " Need help with cast iron welding".
Good Luck!
Hmc,
Your are corrrect on preheating. Call your welding supplier and procure some Messer MG systems MG289 Cast Iron Rod.
Preheat is 400 F for heavy sections V bevel and drill cracks at ends for stops...
Short stringers on root portion short to medium arc length. Peen lightly after slag removal.
Back up to fill crater when breaking arc....
Weaving 2X rod diam is ok for cover on multipass....
buildup section as needed once complete allow for slow cool (insulate)
Messers Toll Free Number is 1-800-558-8524 They have an outstanding tech service. If you have trouble finding Messer products I can hook you up with my supplier here in Cincinnati.
Good luck,
Steve Dodd
Dodd Welding Services
Newtonsville, OH
Email Doddwelds@aol.com
Dear HMC,
what Weldmedic says is new for me, for I've always understood that cast iron welds are just repair ones, not structural, i.e., capable of withstanding stresses. I suggest you to proceed as he recommends and after a few days, when you've seen the results, post an advise on this site telling what they (the results) were. If they were good, I'll surely change my opinion.
Giovanni S. Crisi
Forum
