Cast Iron Repair Nightmare

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So, if you are playing along at home, I had asked about how to repair a tight cast iron crack in the cast iron motor cover pictured in this thread.  The only reason for the repair was to prevent the crack from showing through the new paint, the part is not structural.  http://weldingweb.com/vbb/showthread.php?t=23192What I finally decided to do, was heat the casting up to around 100 degrees and run a 1/2" long weld with NI 99 rod to stabilize the crack.  I had 1/8" rod and ran 90 amps DC.  I figured since the crack was tight and I was going to do a really short weld I should be fine.I beveled the crack, drilled the end, and made the weld.  As it was cooling off, Immediately I heard two "pings" and sure enough another crack formed 3" away from the original crack.  Luckily it did not crack all the way though.  Best I can figure, was this cover was dropped on a hard surface and there was more than the 1 crack that I saw.  Everything was stable so I ground down the weld flat with a carbide bur and just painted and installed it.rants:  Why was I able to do a dozen practice welds on cast iron of similar thickness with no issues?  UGHAt the last minute I was going to go for a Oxy/Acetylene braze, but on my test piece I could not get the CI hot enough to wet with my #2 tip.I also had no luck with the TIG brazing, but I thought the stick would be less intrusive since it was faster.Just posted as an FYI.  I am going to place the next piece of CI in my gas grill before welding!Chris
Reply:Originally Posted by *chris*  I am going to place the next piece of CI in my gas grill before welding!Chris
Reply:I repair cast iron front end parts on my tractors, and build out bearings on my disc.  All cast iron parts.What's worked for me is a really good preheat.  Water will sizzle when you drop some on it.  High nickel rod at a reccomended amperage.  I usually use 135amps for 1/8 rod.  Then I whack it with a ball peen hammer a few times as it's cooling.  Peening relieves some of the stress I believe.From what I understand, most cracking is due to the base metal cooling at a different rate than the weld.  The preheat slows down the cooling.  Some people put the part in sand to cool, in order to hold the heat in.  Obviously ya can't do that with a block.I wonder if you need to preheat to a higher temp., and over a wider area.  My bearings are pretty large, and I heat the whole thing evenly as possible with a rosebud, then go to town on it.  Might just have to heat farther out from the crack you're trying to repair.Man that's the pits.  I'd be sick."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammMan that's the pits.  I'd be sick.
Reply:Ran out in the yard to get a pic of a high use, high stress part repaired like I am used to doing.  It seems to work.  The steering arm has been service 4 yrs. since the repair.  The shiny part is the repair.  Total bevel to a needle point, then built out.THE OTHER WELD AIN'T MINEI'll bet higher preheat, and peening will work.Good luck."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Cast iron preheat is the ticket.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Forgot to upload the pic Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Interesting. I just did some repairs on a very badly cracked cast iron exhaust manifold:http://weldingweb.com/vbb/showthread.php?t=23555I used TIG with NI99 rod at around 100amps, I used NO preheat. I ran about 1" of weld and waited until it was cool to the touch before welding another 1". Absolutely did not try to re-crack once. Better quality casting maybe...
Reply:Cast welding is a totally different animal compared with Mig, Tig, etc. I have to weld cast frequently, so the following is from experience....take it for what it's worth to you.Since prep work is key to any good welding, cleaning and grinding a "V" into the crack is critical....from this point, cast has to be treated differently.If you attempt to weld any cast without pre-heating/post-heating, you are only asking for trouble. I "always" pre-heat to 1100F -  1200F (yes, that is correct) and use a O/A RCI cast rod as my filler. Then I post-heat. Since wood ashes are a fantastic insulator, I post-heat in an open fire, covering the material up with ashes, thus keeping the heat in. I then leave it for a couple of days to cool very, very slowly to avoid the cracking you mentioned. I do nearly the same for Ni55 or Ni99 electrodes, but I only arc weld cast when it involves building up. I only lower the pre-heat to around 700F, but the post-heat remains the same. It has always worked for me.Last edited by kepe; 09-03-2008 at 06:13 PM.
Reply:I was told by a very old gentleman to put a piece of 2X4 (yes wood) in the cast piece.  Preheat till the wood starts to char and weld.  I have had pretty good success with a minimum preheat of 400 and manifolds I heat red before welding.  Brazing works, so does tig welding with Ni99 flux cleaned off.  I tried using 309, but it cracked.  You can't miss that sound when it does crack.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Some types of cast iron are not weldable.
Reply:I look at the cast material as it is heating...if it's not a deep red color, I don't touch it, period! I will give some examples of a few upcoming cast welding projects and try to explain how I will do the job.This drill press table will be put into a rather large wood fire, heated until it is deep red, then I will be using O/A RCI filler, then post-heating (stick it back into the fire), cover with ashes and let cool for 2 days:Since this flywheel will have no stress on it, it will be done the same way as the table (above):This is where things change just a bit. This next piece is the table lift gear from the same drill press. 3 of the gears are broken (1 isn't visible in the pic), and it will be under stress during use. I will be heating it to about 700F, using a Ni55 electrode as my "build-up" filler, so I can rebuild the gear lugs. After welding, it will be post-heated to around 1100F, covered with ashes for a couple of days, then ground into lugs.This drill press is over 100 years old, so there is no replacement....it must be done correctly the first time because there is no second attempts. I am totally confident that it will weld up just fine with the procedures I typically use. Hope this helps Last edited by kepe; 09-03-2008 at 06:38 PM.
Reply:Originally Posted by kepeI look at the cast material as it is heating...if it's not a deep red color, I don't touch it, period! I will give some examples of a few upcoming cast welding projects and try to explain how I will do the job.This drill press table will be put into a rather large wood fire, heated until it is deep red, then I will be using O/A RCI filler, then post-heating (stick it back into the fire), cover with ashes and let cool for 2 days:Since this flywheel will have no stress on it, it will be done the same way as the table (above):This is where things change just a bit. This next piece is the table lift gear from the same drill press. 3 of the gears are broken (1 isn't visible in the pic), and it will be under stress during use. I will be heating it to about 700F, using a Ni55 electrode as my "build-up" filler, so I can rebuild the gear lugs. After welding, it will be post-heated to around 1100F, covered with ashes for a couple of days, then ground into lugs.This drill press is over 100 years old, so there is no replacement....it must be done correctly the first time because there is no second attempts. I am totally confident that it will weld up just fine with the procedures I typically use. Hope this helps
Reply:It is also better to grind a rounded groove instead of a v-groove as suggested by United Technology Products. For 400 degrees preheat just use a torch with just acetylene flame and blacken ther metal. Heat until the black burns off and it will be right at 400 degrees. I use nothing but UTP rods and methods for cast iron and have had no failures in the last 20 years.
Reply:Chris did you peen the weld as it came off the red??  Also I read somewhere that the curving spokes on wheels is not for ornamentation as it is to allow the spokes to bend as they are cooling.  With straight spokes and a cooling new casting.  The result will be the spokes snapping from tension.
Reply:*Chris*,Nice saw!That old cheap gray iron, (more like white really) is almost impossible to weld without taking every precaution in the book.  I say cheap not to knock it, but because it typically was never used on anything structural, mostly caps or ornaments. If compared to a typical car casting from the same era, say a transmission or clutch housing; the auto stuff would show a much higher grade of cast.Newer castings seem easier to repair because of the metallurgy. I suppose maybe more and more steel scrap is entering today's cast pour.Compare the density Kepes's two castings for an idea of the difference in grades. Farmersamm's steering arm would have to be more ductile yet, that's probably actually cast steel.The really weak imported vises of about 20 years ago seemed to be poured from the old fragile white blend, -and sand! You mentioned not being tooled for it; but really I think brazing would have been a more practical, if not the only way to make this nightmare a sweet dream..But, try try again.Thanks for the pics.
Reply:Originally Posted by denrep*Chris*,Nice saw!That old cheap gray iron, (more like white really) is almost impossible to weld without taking every precaution in the book.  I say cheap not to knock it, but because it typically was never used on anything structural, mostly caps or ornaments. If compared to a typical car casting from the same era, say a transmission or clutch housing; the auto stuff would show a much higher grade of cast.Newer castings seem easier to repair because of the metallurgy. I suppose maybe more and more steel scrap is entering today's cast pour.Compare the density Kepes's two castings for an idea of the difference in grades. Farmersamm's steering arm would have to be more ductile yet, that's probably actually cast steel.The really weak imported vises of about 20 years ago seemed to be poured from the old fragile white blend, -and sand! You mentioned not being tooled for it; but really I think brazing would have been a more practical, if not the only way to make this nightmare a sweet dream..But, try try again.Thanks for the pics.
Reply:The weldment needs to be preheated slowly in a oven - then weld.But the MOST important part is SLOW cool down.After welding immediately bury the weldment in DRY sand overnight.Still there are no guarantees. Not your fault.AWS certified welding inspectorAWS certified welder
Reply:You say this is strictly cosmetic?  Why not just bevel the crack out and fill it with epoxy.  The stuff works great for this type of repair.