weld fracture

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Hi all, need some help with a fracturing problem,I am repairing a cement mixer with 29/9 rods,I did a spark test and have come to the conclusion that the steel is actually cast steel,too many sparks for cast iron not enough for mild steel so I ran 2.5mm 29/9 for dissimilar metals at 85amps label on box said 75-85 amps.any way the weld cracked like broken ice.sorry no pics as only had my phone with me and picture is not good enough.any help will be greately accepted,regards Martin.
Reply:Define " cement mixer". Are you talking about the small tow behind units or a large drum on a truck?Considering how abrasive concrete and "cement" is, ( simply pouring 10 yards will polish the rust off the chutes on Monday morning)  it would not at all surprise me if the steel in a drum on a truck is Abrasion Resistant steel..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Likely you are dealing with an abrasion resisting steel or maybe Corten in a commercial mixing drum,?  European designations are different than AWS.  You likely will require preheating and/or low hydrogen electrodes.  Try preheating to 200 C run a short fillet weld  on a scrap piece  to the drum wall then snap it off.  If it breaks immediately then increase preheat and try again until the weld bends before snapping.
Reply:D.S.W thanks for the quick reply,its an old tow around 8 barrow cement mixer built in the uk in 1972;its not the bowl im welding its the frame that the bowl axle is mounted in.
Reply:It likely is grey cast iron, maleable iron or the most expensive and unlikely cast steel.  Preheat is your friend.
Reply:Pre-heating is correct......if it is cast iron, you must use nickel based electrodes NiCad or Castaloy type. Only weld short beads then tap off the slag with a chipping hammer which actually is just peening the weld (relieving residual stresses) if you weld to much to fast it will crack as soon as you pull the arc back. Slower, shorter beads say no more than 1" at a time.A young green pipe welder asked an old salt one day...How can I make the weld on the bottom of the pipe look like the top.......The old salt replied....Screw up the top......
Reply:never posted a pic before so if it works you'll see the mixer and the repair site,phone pics so closeups aren't very good.
Reply:Pre heat and lots of it. I'd get a good grind and make sure there is no concrete dust or concrete anywhere near the weld zone. That stuff is murder.I like Super Missile Weld or 309 stainless for these type of repairs if you can get it clean enough. Make sure to keep your weld zone and surrounding area hot enough to make your skin smoke if you touch it.Do a little post heat to butter the stress away from the repair and you should be good to go.Last edited by Shiftace; 01-15-2012 at 05:53 PM.Reason: corekting pore spellin.
Reply:If it's cast iron be sure to not grind "V" grooves but "U" grooves. I like UTP rods and the 85FN would be my choice for this. The first welds you make will be full of pin holes. Just grind out the weld and weld in another and only inch at a time and peening the flux off. Good luck.
Reply:To determine if it's cast iron or steel................Drill a hole in it.If the shavings are powdery and granular, it's cast ironIf you get chips, it's steel"Any day above ground is a good day"http://www.farmersamm.com/
Reply:thanks for the help guys,pretty sure its cast steel sam but I will try the drill test first chance I get had to put it one side for moment wheel bearings need to be done on a small 8x4 plant trailer first.thanks again will keep you up to speed as I go.regards Martin.