Frustration

Are you anywhere near a pottery supply company? If so, get some ceramic wool and wrap the piece after heating. As to how hot in my experience if I heat cast iron to about 700 degrees it won't crack. I have had the best luck heating to a dull red heat when observed in low light, wrapping in ceramic wool, and welding. It's a pain because everything is so hot but on the other hand no peening is required and no cracking is happening. I have used this method with brazing rod, aluminum bronze rod, stainless steel rod, and nickel alloy rods. Eric

I don't have a pottery supply near , but I do have a large pile of fiberglass batts . You think they'll work at the temps you use ? The grates aren't so awkward in shape , I plan to build an enclosure with firebricks and preheat with my foundry burner . Heat 'em both up and let one soak while I weld on the other , swap as they cool .

I don't know about the fiberglass batts because I think they use some sort of glue to hold the fibers together. Tear a small chunk off and point a torch at it to see if it burns. Not too close because the tiny glass fibers may burn while in the torch flame. Your enclosure idea is a good one. Lay the grate on some more fire brick while welding so that it doesn't lose heat through conduction. You know, I bet the fiberglass would be fine if it was just used to cover the part while it was being welded. Try it. It just occurred to me that a fireplace shop may also have ceramic woll. Eric

Heh , we don't have one of those too . This is a very small (>5,000) very isolated town - the nearest freeway is a hundred miles away more or less . Those 'glass batts were salvaged fom a tearout , cost me the labor to load 'em up . Today I'm working on toy boxes for my 2 youngest grand daughters . Tomorrow I'll be setting up for the CI job , get it outta the way so I can go back to laying cement block

No, you can melt fiberglass on a kitchen stove. I don't know what the glass type is, but really low melting point.

Jon

THanks , looks like I'll be inventorying the fire bricks . I've got enough , just gotta dig 'em out of storage .

Cast Iron, I assume?

Two approaches - one is the preheat to something like 800F or more.

The other is cold welding with nickel (55 or 95 ni rod) followed by peening until cold. I was taught that in college and wrote it up on here a while ago. Lincoln briefly mentions it here:

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In either case you also need to grind the crack out to a vee, and drill the ends of the crack or it just keeps cracking.

Reposting myself from 8/27/06:

Cold welding with nickle rod: Drill the ends and V out the crack - use a narrow (60 degree) V to minimize shrinkage, and leave the back of the crack connected if possible. For this job, fixturing to hold the parts tight would probably help with either welding or brazing.

Use DC-, you should not have a crater (pulling iron into the nickle is

about every 2 inches, and then start each new short section on a tack, moving to the cast to lengthen the tacks until the whole crack is covered. Cutting and pasting my own comments from a January 2004 discussion of cast iron repair, with some slight edits:

Use 55 or 99 Ni rod and your stick welder. Weld 3/8 inch, peen the crap out of it RIGHT AWAY, weld 3/8 inch somewhere else on the crack, peen the crap out of it, repeat until done, never get the casting hot. Take a break if you're in danger of getting the casting hot. Very localised application of heat, lots of beating, very quickly, on the nickle to let the nickle move as the weld bead cools, rather than let the cooling weld bead crack the iron. Keep peening until each bead has fully cooled. I personally have only done a little bit of this in class 11 years ago. But the guy who taught me did it, and spent the summers teaching NYS DOT and town maintenance welders to do it, as part of the Ag Engineering school's mission to save the state taxpayers money by educating local maintenance workers. As he explained it, the difference between preheating and not preheating was the difference between (for instance) stripping an engine block, finding or cobbling up a furnace big enough to preheat it, welding on it, cooling it, then putting it back togther afterwards, .vs. cold-welding the crack in place, or at least without needing to fully strip the block.

Having both done it and seen it done, I do think it actually works. Welding a stich and goofing off for 15 seconds to find your hammer probably would not work. Trying to hurry the process definitely won't work.

I guess you know to heat and dry them slowly if they got damp. I keep mine in a big plastic bag (3 mil) made for collecting trash on construction sites. They can crack, and even explode, if you heat them when they're really damp or wet.

Glass wool melts at around 1,000 deg. F. If they use Johns Manville Mineral Wool for insulation in your area, that melts at around 2,000 F. Other kinds of "rock wool" and "mineral wool" vary all over the map. The old stuff was made from steel mill slag, but they make it from a variety of things today.

You shouldn't heat your iron above 1,200 F. It goes hot-short at around 1,400 F or just over, and it will crack if you look at it cross-eyed at that temperature. Lincoln Electric says to pre-heat in the range of 500 - 1,200 deg. F.

The fact it can be melted in a kitchen stove flame isn't really a good indication of its service temperature as it was exposed to the naked flame, it may well be fine to insulate your piece if placed on it after heating rather than exposing it to direct flame, you may just get some binder burning off. I don't know about fibreglass insulation but some refractory fibre material I use on occasions use starch as a binder, a bit whiffy when burning out but fairly harmless. I work with glass as an amateur glass blower and normal annealing temperature for soda lime glass is around 500C and fibreglass insulation is made from a mix of new and recycled soda lime glass. This table may give you some idea

. Regarding melting fibreglass on a kitchen stove I've melted or badly damaged woven silica cloth with a propane torch and that has a far higher melting point than glass, concentrated heat on fine fibres does the damage.

Good point on the fire brick if dense fire brick but if insulating fire brick it's so porous I can't see it being an issue as it would just vent steam when heated. If I need to make a temporary hearth I have quite a few 2300F and 2600F classification temperature IFB.

These are the porous brick , useta reside in a pottery kiln until Agnes overheated it and melted the trays that carried the heater elements . Ugly .

I have the porous bricks and I'm not sure of the rating but I know Agnes

smaller kiln and the top and bottom of a big one here - and the rest of the big one still down in Memphis . I've been planning on building a forge and a smaller foundry furnace for bronze/brass with the material so I guess I'll have to be careful how I cut it (if I cut it) .

At least being Superwool it is the safe body soluble fibre, sometimes referred to as AES fibre (alkaline earth silicate)

so not considered carcinogenic like the RCF (Refractory Ceramic Fibre) blanket like Cerachem, kaowool etc. Having used both though the safe stuff does break up much more readily and is more annoying to use than the RCF blanket, cost wise about the same. I've used Maftec blanket which is safe, takes higher temperature like 1600C, works like RCF but what fibre is does give off when worked is more annoying due to the larger fibre size, it's also much more expensive.

I was doing pretty much like your description of cold welding, but using TIG and Invar 42 . Peening was started before the helmet lens cleared ... and that wasn't working , so today I preheated it to somewhere

, I still have about half the thickness not fused , but I plan to take care of that in the morning by welding from the other side - after a suitable preheat .