No announcement yet.

Welding Cast Iron

  • Filter
  • Time
  • Show
Clear All
new posts

  • Welding Cast Iron

    How many times must I remind myself? When welding cast iron, BUY THE DARN RODS. Expensive as heck, and worth every cent. There just ain't no shortcut. Yeah yeah yeah, you can use stainless rods too. Works only half the time, cracks half the time, if you even get a bite into the cast iron. You spend twice the time grinding & redoing. Cast iron rods? Nooo prob, man.

    Duly noted, I have achieved some success using the TIG torch and Copper/Phosphor brazing wire. Kind of a welding/brazing hybrid. Holds together anyway; never have strength-tested it. Tip: go loooow on the amps. Might save someone in a jam, anyway.

  • #2
    Years ago, I had to weld a cracked exhaust manifold. It was a quick and dirty job using regular welding rod. I remember heating up the manifold in the gas barbecue for an hour, and then stick welding the crack (I did notch the crack). The car had to last another year so it wasn't worth putting too much effort. Surprising, the car is still on the road and the weld is holding.

    Rob, I agree with you that you shouldn't even attempt a job unless you have the proper tools, but welding is one area where I have been successful many times at improvising.



    • #3
      The neat trick these days in the automotive end is spray welding.I think it is an old process that has been updated.The torch looks like a cutting torch with a hopper controled by the lever to mix the powder in with the flame.You have to keep the core temp of the part about 700 degrees if I remember right.It has to be cooled slowly or it will crack.Tig welding with nickle filler works good as does plain old brass brazing on some parts.Welding cracks without preheating will almost always cause a crack with any arc welding style.Brazing works as you have to preheat just to get a weld.Spraw welding won't stick on a cold part.Good luck as cast welding is one of those arts that are fading away.Robert.


      • #4
        I repair a lot of cast iron gears, and sometimes machinery parts. I have been doing this process for many, many years. All of the welding has to be machined and strong, for instance making a new tooth. The only rods that i use are 7018 arc welding rods, but i must stress that the prep and the pre-heat of the part are as critical as the cooldown period after the weld. To pre-heat a part i use a kitchen oven to bake the part for 2 hours at 500 degrees, and use the oven for a slow bake down after welding.One critical point when welding cast is to use your torch to heat the spot before each weld bead then only weld 1/2"long beads and not next to each other, and use the torch to heat each bead after each weld. You don't get much welding time then the part needs to be re-heated. what cracks the welds is the rapid cooldown. If you are doing a buildup then heat the bead till it starts to get red and using a pointed hammer start pecking the weld to knit the weld to the cast during the first layer of a build up. A steel rod works because steel is iron that has various other elements in chemical combination, basically cast iron and steel are Ferrous metals both having carbin in them. Nickel rods i guess have their role but get very hard and not easily machined. I have yet to have a tooth break. One other nice feature of the 7018 rod is that after machining the weld is practically invisible ,unlike nikel that shines and really shows where cast stops and weld starts. Just for info a tooth weld up could take a whole day.


        • #5
          I have welded many old manifolds by heating the whole assembly in a forge to red heat and either gas welding with piston rings or arc welding with 7018 both work well so long as you take time to aneal evenly.
          I just need one more tool,just one!


          • #6
            When you weld manifolds if they are in two pieces you can bolt them to an old head and it will help keep warpage down to a point it may not need to be resurfaced.Don't bolt it too tightly so it can slide.That is the reason the bolt holes are larger on the end holes.They really move a lot back and forth.That is why most iron heads don't use a gasket.Aluminum heads need one to protect the head from the manifold.Robert.


            • #7
              Speaking of Manifolds moving: My motor home has a 455 olds, front wheel drive. Purchased 2nd hand. Log book showed leaking exhausht manifold at about 40K miles, and every 5K miles there after. Seller used local dealer for repairs. Several dealers confirmed that when those manifolds give trouble, the trouble is prepetual.

              The factory manual says: used no gaskets, said torque to 25 inch pounds, use a dual washer with a tongue to lock bolts.

              Tried to purchase the washer from dealer, I got all the washers the dealer had, the washers the other dealer had (this same system is used on caddies and olds and buick). Stripped the ware house supply. Finally got all FOUR washers needed (in other words the stock level was ONE per seller, and the stock did not tirun over fast).

              Put the manifold up per factory manual, no more leaks. I think secret, not known to dealers (or used by them) is that the bolts must be loose enough to "float"- as said above, the holes are large for that reason.
              The "tab" washers are need to prevent the bolts backing out.

              This thing has pulled most every steep grade in the west, towing a light car. well over 100K miles since the "fix" (I did not do it right several times- I did it like the dealers. Did it so many times that I just carried spare gaskets and did the repair while wife cooked supper. I was FAST for that job anyway )

              I suspect many manifold problems are traceable to expansion and over torque.


              • #8
                Nobody wants to use the method I prefer because it's too much work. On the other hand the welded part comes out melallurgically consistant, stable, and machinable and the repair almost invisible.

                Yeah, I know buy this rod or that rod and you don't need all that grief. But it works best for the most sensitive and delicate repaairs.

                A couple of months ago two buddies and I welded together a broken Cincinnatti milling machine that was nearly 10 feet long and we kept it straight within 0.003" overall. Yes it was a 100% weld that repaired a complete fracture at a slight diagonal across the table about 1/3 along the leength.

                All you need is a 12" car bottom furnace, a couple of bales of ceramic fiber insulation, ... brace the work with insulated water cooled machined steel box tubes ... coat with a ceramic barrier wash ... erect a ... preheat to ... do this ... do that ... cover every variable. We had a three page check list.

                Anyway it was a huge evolution prohibitive in cost if it wasn't for all the volunteer talent and free use of the furnace. We used over $600 in consumables alone. I forgot just how hot a guy can get welding large preheated parts even when well protected with aluminized welding gear and with the work buried under a drift of ceramic fiber.

                A while in the furnace to stress relieve it, a while in the sharp room of a cold storage outfit to stabilize it, and onto the planer. Chomp off the blobby weld. Release the clamps and dial it in and Lo! Pretty dang straight: about a 0.003" kink in each direction.

                Plane it and scrape it. Re-cut the table slots 0.030 oversize. Took only a 0.010" shim behind the gib to make it fit and we had to elongate a couple of holes in the lead screw brackets - twice. Somebody best left nameless cut 'em the wrong direction the first time. That's AWAY from the table surface and TOWARDS the gib. Not the other way around.

                Took a three day weekend of 24's in a borrowed commercial shop but a great old milling machine was saved. The only fly in the ointment was the owner of the shop we borrowed kept visitng and spinning us yarns. Problem was he was a great story teller. We could have done the job in two days but we wasted all that time listening and laughing.

                I still haven't heard the last of Barbara's zinging me about "male bonding". Naw! It was a bunch a guys working their butts off to help another.

                [This message has been edited by Forrest Addy (edited 05-08-2003).]