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Welding cast iron, preheat temp ?

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  • Welding cast iron, preheat temp ?

    Can anyone tell me to what temp should the castiron be preheated ? I had this crazy idea today to just leave the thingamajig out in the hot Texas sun all day....Ken...
    KenCO " Uccahay "

  • #2
    temp for cast iron

    KEN, I'M REALLY NOT SURE ABOUT THE EXACT TEMP CAST IRON SHOULD BE HEATED FOR OPT. WELDING BUT IRON MELTS AT ABOUT 2780 AND MY GUESS WOULD BE TO TRY TO GET IT TO ITS OPERATING TEMP OF THAT PART,I HEAT EXAUST MANIFOLDS TO ABOUT 600 OR 700 AND THEY SEEM TO BE JUST FINE. I'M SURE HAWK,ROCK OR ONE OF THOSE GUYS OUT THERE IN WELDING LAND WILL GIVE US THE STRIGHT DOPE. I'M INTRESTED TO KNOW TOO!!!! PISTOL8

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    • #3
      Preheating For Cast Iron

      Ken,
      The Texas sun certainly has not hurt your casting. However, I don't think it is hot enough. The whole premise behind preheating and post heating is to relieve as much stress as possible to prevent the weld area from cracking as the casting cools. If you weld without preheating you are "cold arc welding" and quickly applying heat to the "cold" casting causing all types of stress because the thinner areas heat and cool quicker than the thicker areas. The welded area is being pulled in lots of opposing directions likely causing it to crack on cooling.

      I'm thinking cast iron melts around 2300 give or take depending on carbon content, etc. PISTOL8 may be closer at the 2780 mark. The trick,(if there is one),is to uniformly heat the entire casting if possible. Be careful not to go too hot too fast! Let your casting,
      at least the large portion around the area to be welded, have plenty
      of time to absorb the heat. Once heated you can weld the prepped area. Prior to preheating, v out the cracks and drill holes at each end of the crack to prevent spreading. I have drilled holes about every inch along the crack and at both ends if it was severe enough.
      It is also a good idea to lightly grind, rope brush will probably work, to each side of the crack. This will help prevent flaming and spitting from the impurities while heating.

      NOW THE ANSWER: DEPENDS-IF YOU CAN GO THROUGH ALL THIS HOOPLA WITHOUT LOSING SANITY THEN HERE WE GO.

      SMALL OBJECTS: CAST IRON SKILLETS, SEWING MACHINE PEDALS, SMALL ORNAMENTAL ITEMS-TRY 300-400

      I THINK PISTOL8 IS ON THE MONEY WITH 700 ON MANIFOLDS AND CASTINGS IN THAT SIZE RANGE.

      FOR THE REALLY BIG STUFF- PROBABLY NO LESS THAN 1000-1200

      ALL TEMPERATURES ARE IN DEGREES F

      I've welded a lot of small to medium cast iron pieces with little or no preheating with success. Just remember the hotter you go, the more care to take in the cooling process. Once welded you will probably want to postheat back up to temperature prior to weld process and then begin the cooling process-24 hours or so.

      IF YOUR WELD DOES NOT CRACK DURING THE COOLING PROCESS, THEN IT SHOULD BE THERE UNTIL "THE COWS COME HOME".

      A large rose bud #10 or bigger will help the heating process along. Hope you have lots of oxygen and acetylene. In general you'll burn 2-2-1/2 times the oxygen to one acetylene.

      I am no expert at cast welding, but I think I experience has taught me a lot. Good luck.

      IF YOU ARE REALLY SERIOUS ABOUT CAST WELDING AND WANT TO BE RIGHT FOR SURE-DITCH THE ARC WELDING AND BRAZE IT WITH A BRONZE ROD. NOW THERE'S ANOTHER STORY.

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      • #4
        cool down boys

        HAWK MY FINE FRIEND THE WORDS ROLL OFF YOUR GAS TORCH TANED LIPS LIKE SILVER THEAD TO CLEOPATRA HEART. IFOUND YOUR ANSWERS TO BE PERFECTLY IN LINE WITH THE EXPLANATION'THE LONGER THE PIECE IS HOT AND WELDED LET MOTHER NATURE DO THE COOLING OVERNIGHT IF POSSIBLE'
        IF IT CRACKS BEFORE YOUR FINISHED THERES NOT ENOUGHT HEAT GOING IN. COLD BASE METAL AND HI-TEMP WELD IS LIKE TOSSING DRY-ICE IN A POT O BOILING WATER NOT MUCH IS GOING TO STICK

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        • #5
          Pre Heating Cast Iron

          PISTOL8,

          I know. It's too wordy. Hopefully informative. Thanks for the reality check.

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          • #6
            I would say the hotter the better and the longer the cool down time the better, but be careful with too hot a pre/post heat or you might cause the casting to sag. I've read where 1,400 is the max recommended and I'd probably only use 1,200 to save gas. I doubt something like a grill will get that hot.

            Sean

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            • #7
              A friend of mine said that after welding cast iron, you can tap the metal with a ballpeen hammer to relieve stress. Anyone ever heard of this ?.....Ken
              KenCO " Uccahay "

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              • #8
                Pre Heating Cast Iron

                Ken,

                I've heard of it and know welders that do it. The only time I saw it done was on a small crack in a manifold lightly preheated to roughly 200 degrees F with a torch. The guy told me it would help relieve the stress during the initial cooling process. He was doing it just after welding each small section prior to welding the next section. I DON'T PEEN AND HAVE NOT HAD BAD LUCK YET-MAY HAVE SPOKEN TOO SOON!

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                • #9
                  A bunch of good answers!
                  Here's a good preheat structure. You don't need a ton of preheat. This will harden the surface of the cast.

                  100-200deg for malleable irons
                  300-500deg for grey irons
                  400-600deg for ductile irons
                  above 600deg for white iron

                  these numbers can be increased with large or thick or complex castings, but with manifolds and typical castings, most of these are less than 1/2 inch thick.

                  Also, the longer it cools, the better. Place the welded unit in a dry sand box or wrap it in a thermo blanket to keep the heat in the unit as long as possible.

                  Andy

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                  • #10
                    Peening Cast

                    Originally posted by Ken Wickliff
                    A friend of mine said that after welding cast iron, you can tap the metal with a ballpeen hammer to relieve stress. Anyone ever heard of this ?.....Ken
                    Hey Ken,

                    I got stuck on a job last night with a cast iron stove that had cracked out the back side. It was for a first time client and inside his house. I burned a pound of 99% nickel one inch at time from oppossing ends and peened with a small hammer. It worked and I had no choice but to NOT preheat. No torch in the living room. Just thought you might like to know. May be the process, may be luck!

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                    • #11
                      The real test will be after a few heat cycles with the oven.

                      I usually find that once cast cracks or breaks, any welding is only a bandaide and usually breaks sometime doen the road. I guess you can call that "repeat business"

                      A-

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                      • #12
                        About 6 years ago, I took a cast iron exhaust manifold off of a diesel tractor to my cousin to have a 1.5" sch 40 length of pipe welded into the exhaust port. The engine is very old, and a replacement part manifold is very hard to find, and quite expensive when you do find one. The old exhaust pipe was rotten and had broken off inside the manifold.

                        I cleaned out the old pipe remains (which was threaded originally) and bored the cast opening to the appropriate size of 1.90" to accept the new pipe. I then prepped the area to be welded on both the pipe and the manifold.

                        Although hesitant at first, my cousin agreed to try it after I told him that he would not be responsible if it ruined the manifold. I wanted a pipe welded in.... Period...

                        He used a rosebud and preheated the cast slowly up to 700 deg.F., removing the torch every so often to allow the cast to absorb the heat. He used a stick welder (sorry, I can't remember the rod he used) and ran a thin root pass around the pipe. He checked it, knocked the slag off and made a final pass. After he completed the weld, he heated it back up to 700 deg. F and wrapped the whole manifold and pipe tightly in a piece of ceramic fiber blanket he kept in his shop for slow cooling.

                        The weld came out great and is still holding like new on the old Tractor......

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                        • #13
                          CAST & OLD TRACTORS

                          HEY MOE DON'T YOU JUST LOVE FIXING THE PARTS DEPARTMENTS PRICING PROBLEMS. GREAT TO HEAR ITS WORKING. PISTOL8

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