Author Topic: A Tale of Two Castings  (Read 6739 times)

Offline vtsteam

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A Tale of Two Castings
« on: February 14, 2022, 09:56:11 AM »
This was the first time melting iron in, yipes, 9 years. Has it really been that long? And first time with the relined furnace. Lots of casting with zinc alloys, aluminum, brass, since then, including building the new lathe, but not iron.

I was rushed for this new trial with only 2 hours until darkness. The only metal I had immediately on hand was old iron sprues from from casting experiments 9 years ago -- mostly scrap radiator iron, and that had a lot of defects. But I nevertheless hoped for the best, who knows, maybe the older finally successful experience and new furnace lining would make a difference.

Well yes and no. Results were mixed. For one thing, I did have an iron spill on damp concrete before pouring. Unfortunately the crucible had stuck to the lining and molded in plinth (ganister), so when it released from the furnace bottom, a clump of it stuck to the bottom of the crucible making it rounded so it would not stand up,when I tried to set it in the ring shank.

I replaced the crucible in the furnace (cooling all the while) then figured out that I had to use one hand to hold the tongs and the other to hold the ring shank up off of the ground to do the transfer. I did that and spilled about a pound of metal in the process. No fun, but I did have on full protective gear, so it was an annoyance, not a tragedy. (I wear welding helmet leather welder cape, leather apron, leather gloves, and leather shoe spats for iron.)

Also, because of the timing, and the metal cooling, I had to get rid of the metal fast. The spill had cleared a big hole in the slag crust in the crucible, I couldn't set the pot down to slag it properly, so I just poured through the hole in the slag. I still had enough to fill the mold, and not quite enough to pour an ingot after.

Well at least I'd melted and poured something, after all these years! It felt great!  :ddb:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #1 on: February 14, 2022, 10:16:23 AM »
The result. Considering the problems and questionable metal content It was a nearly viable casting. It did fill completely, and the greensand core worked fairly well, though there was some collapse (I think I may have hit it closing the mold).

On the negative side, finish was very rough and sandy, with two obvious flaws (see photos). I think they may have been slag inclusions, they are irregular and don't look like blowholes. Unfortunately, too deep to make the casting usable as a piston.

Also, the metal is somewhat chilled, despite the addition of (too small an amount) ferro-silicon. It was drillable with HSS (see photo) but the drill shavings were very fine, progress was slow. A first try at turning didn't cut deep with an old carbide tool (might have been dull), I tried another and it did cut better, but going was slow. The sand inclusions of the surface fnish were very hard on tools.

Surface finish was as poor as it was because I had no facing sand with coal dust (or sawdust -- see my other thread on that).

The internal sand core collapse would have made boring out the piston a real challenge. Well, nightmare, properly.

But all in all, I learned a lot. The melt actually went better and MUCH faster than prior casting sessions with this furnace almost a decade ago. And as it turned out, the lining facing which had been very fragile, did gain a lot of rigidity after this melt. Photos of the casting below:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: A Tale of Two Castings
« Reply #2 on: February 14, 2022, 10:18:01 AM »
It's all about learning and having fun and you seem to be doing both Steve.

So long as no one gets injured the experience can be added to the next session.

I resurrected my induction furnace not because I needed it, and not because I wanted to cast anything specifically, but because I wanted to - so I did ! (It had been looking at me resentfully for over a decade, unloved and deteriorating rapidly !) - now I can do a melt at the press of a button - well two actually - generator and induction furnace - in half an hour from start to finish.

. . . have I actually used it in earnest since then . . . . . er . . . .well . . . . . no . . . . BUT I CAN IF I WANT TO !



Andrew Mawson
East Sussex

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #3 on: February 14, 2022, 11:13:47 AM »
Yes sir, Andrew, there's nothing like melting metal, and in melting metal, nothing like melting iron. It definitely get's the adrenaline going for me. And the mystery of what you're going to uncover loooooong hours later in that molding box.... Will it be a disappointment, or the prize you imagined?

So, the next day, though originally predicted to be less suitable, actually was even warmer than the day before, and the precipitation predicted, turned out to be only a few flakes of snow in the morning. Then the sun came out and temps rose to 50F. A true winter thaw.

So out with the second pattern for a cylinder. I scraped off the bottom of the crucible by "sanding" it on the concrete pad. The bottom was restored to a flat surface again. (btw, I had placed cardboard under the crucible last time, but that didn't prevent the sticking.)

Where the crucible had sat in the furnace, I removed all loose material, and painted on some of the lining hot face compound. Then I dried it with a torch, and put cardboard over that, and used a quarter piece of firebrick as a new plinth. Firebrick had worked in my old furnace, though it didn't last more than a few melts in the role as plinth without cracking. But it did work, and I thought I'd give it a try again. On top of the brick, more cardboard, and then the crucible.

I did a rough calculation of the metal I'd need for the cylinder - 7-1/2 pounds, and this time charged the pot with chunks of cast iron I broke from an old cast rail. Shaped like a railroad rail, though not one obviously, since cast iron. I knew that stuff had worked well in the past. I also wire brushed it, and rinsed it in fresh water to get it clean as possible. No old sprues, this time.

In molding, I did also try a little of my first attempt at sawdust facing sand mix, but it had no bond strength and simply crumbled. I removed most of it (but a little remained at the bottom of the pattern cavity, only). So again, no facing sand.

Melting: I added a little more ferrosilicon to the melt (estimated by eye only). I also melted for a shorter time, because I think I overdid it the prior melt. After all, iron doesn't really melt in 10 minutes from cold does it? Well yes it does, in this furnace! So this time the melt took 20 minutes total, instead of 40 for the previous one. I was able to slag it part way through, in the furnace - which netted quite a big gob of the stuff (some of it no doubt left over from the day before.)

The crucible lifted easily from the new plinth, and I was able to set it down properly in the ring shank, I tried slagging it again there but didn't do a perfect job, as the slag was sticking to the tool, and the handle was overly long and clumsy for the job, out of the furnace. I'll have to make a new shorter one for that purpose.

The metal poured nicely though I saw one bit of slag run into the sprue after detaching itself from the crucible wall. Maybe it would get trapped in the sprue or gates. The metal poured perfectly down the sprue without a spill, until.......it stopped. Oh no! 

Oh yes, you miscalculated the amount needed, you idiot, and short poured!   :bang:  Well it came part way up the sprue, maybe there's hope. Fingers crossed!

Yeah, right. Afraid not.

Anyway, the concrete core worked perfectly, just like ironman's. Thank you IM for all the information you give people, all the great ideas and experience!

As for the casting, well it probably would have been good, other than the rough sandy external finish. The internal finish was quite nice (due to plumbago on the core). It would have machined reasonably. Also the metal was much nicer, when drilled producing bigger crumbly graphite laden swarf, as it should for good gray cast iron.

Interestingly the short poured top of the casting had a good finish (probably reducing gas from the small amount of sawdust. It did have rounded ridges suggesting the edges of a gas bubble under some pressure. However this would likely have dissipated though the sand if the pouring head of iron were higher in the sprue. The height of the casting surface and the sprue matched.

So, needed: new slagging tool, new sawdust facing formula, new spreadsheet calculator for common shapes (being worked on presently) for estimating metal, and ferrosilicon required. And we'll try again when the weather cooperates.

Finally, besides the learning involved in these two pours, I also had to re-think my design for the patterns and the need for subsequent machining, as well as the actual design of the engine. People may have noticed I removed the original rectangular flange from the cylinder pattern. But I've also realized these castings are just too thick and heavy for machining in a reasonable time on the equipment I have.

I think the piston pattern would work as a tapered greensand core type, but the machining would be unnecessarily time consuming. It would better be a split conventionally cored pattern, with a much thinner casting thickness. And the piston top might be a pressed in piece instead of cast in. And likewise the cylinder pattern could be reduced in thickness if not only the flange but the water jacket support rings were altered in design.

Anyway, good to be casting again, and very happy with the new furnace lining. I wish I could have afforded it a decade ago, but I used what I had on-hand and got what experience I could with that. That informs what I do today.

 :proj:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: A Tale of Two Castings
« Reply #4 on: February 14, 2022, 01:13:30 PM »
More experience gained !

Is your burner adjusted to a neutral flame? If not it might possibly be why the carbon from the cardboard didn't do it's job last time - just a thought, not based on any actual knowledge BUT it can make quite a difference to the longevity of furnace linings.
Andrew Mawson
East Sussex

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #5 on: February 14, 2022, 02:33:03 PM »
Well it can be easily, you just watch the exhaust flare and adjust. I tend favor very slightly toward rich. Not enough to smoke or soot up tools held above to pre-heat (a good idea btw, to ensure there is no moisture on them before plunging into metal). But that wouldn't affect the cardboard carbon, since it's without air under the crucible, and a slight richness in flame wouldn't oxidize it faster anyway.

But imagine: if cardboard would burn anywhere else in the furnace -- which it will instantly -- there's enough oxygen in the fireball even in a neutral flame to burn it anywhere in the furnace that's exposed. Beneath the crucible isn't exposed -- one hopes. Obviously with rough and rounded surfaces that's not a perfect seal. And the furnace bottom wasn't perfectly smooth.

I think that one of the main causes of sticking is that the pasty ceramic crucible glaze and drips of slag move down the outside and find there way to the bottom and "braze" the crucible to what it's standing on. That happens at the perimeter of the crucible bottom, which, because it is necessarily exposed, can't maintain cardboard carbon as a release agent.

Well that's my theory anyway.   :smart:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #6 on: February 17, 2022, 10:05:18 AM »
Third time's the charm!  :ddb:

This one looks free of flaws, and the sawdust facing sand worked pretty well. I drilled a hole in one of the gates and it drilled easily and produced good-looking gray iron swarf, so I'm hopeful the main casting is free of chill and machinable.

Differences: I did use my new short handled slagging tool after pulling the crucible out of the furnace, and the mold had the 2% sawdust facing sand. The facing was a little dry (I think sawdust draws moisture out of the clay binder), so I lost a little bit of definition from crumbling at the edges of the pattern - thus the small amount of finning at at the parting line. No problem to clean off with an angle grinder.

This casting is only about 7mm thick -- really pleased with how metal filled the mold completely. Surface finish is greatly improved, it looks to be sand inclusion-free -- though not quite up to the shiny casting level yet. More sawdust would undoubtedly help, but there's a tradeoff in bond strength of the facing sand  -- the finning here illustrates that.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline tom osselton

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Re: A Tale of Two Castings
« Reply #7 on: February 17, 2022, 05:07:40 PM »
That’s a beautiful casting! I wonder how long it would have to sit in order to have the sawdust and sand moisture balance out.

Offline krv3000

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Re: A Tale of Two Castings
« Reply #8 on: February 17, 2022, 05:37:07 PM »
just my bit well dune  in the uk leave any bit of steel lying abawt it will soon go rusty one of the old tips regarding small castings was to dig a hole and bury it but make sure you make where you have burred it the other methera it to put it in a bucket and pee on it and leev it to soke  i have never tried the last one but at present i have a set of castings of a Stuart turner   S50  just siting in the garden waiting for spring to cum si i can dig them up lol

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #9 on: February 17, 2022, 06:13:39 PM »
Thanks Tom! :beer: I did another iron pour this afternoon, same pattern (I need 3), I hope it came out as well -- don't know yet because I need to let it cool for 4 hours (I think that's minimum for iron of this size even though it's winter.)

Bob, why would it be good to bury a casting -- or put it in a bucket of pee? What does that do?  :scratch:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline krv3000

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Re: A Tale of Two Castings
« Reply #10 on: February 17, 2022, 07:49:40 PM »
 right it brakes dawn any hard scale by rusting the outer surface

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #11 on: February 17, 2022, 07:52:58 PM »
Oh, okay, that makes sense!  :med:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #12 on: February 17, 2022, 09:01:52 PM »
Fourth casting was a success!  :thumbup:

It's the twin of the last one, but with less finning. Surface finish is just a bit less shiny but free of sand sticking. This time I used a facing sawdust mix with spruce, instead of white pine (mainly because the pattern is spruce this time --the sawdust came from shaping it). The facing sand had a little more water in it and it had enough bond strength not to drop out at the edges, so the casting has less finning.

Photos tomorrow -- not enough light tonight.....

Tom, I don't think the sawdust absorbing water is likely to be a good thing. I think the faster it flashes to gas when the molten metal hits it, the more effective it is going to be in pushing the metal back from the sand surface. I mean it's probably only milliseconds difference between the burn time of very dry and somewhat moister sawdust, but the standard is coal dust, which has no water content and is more finely ground. I bet it flashes very fast. Well that's all guesswork on my part.

I'm thinking that maybe hardwood sawdust would be better than soft wood -- slower moisture absorption, denser, and higher energy content. I bet a higher percentage (by weight) in the sand won't decrease the bond strength -- because it is nearly twice as dense as softwood -- there is less volume of it for a given weight, and volume of wood is what will adversely affect bond strength.

I'll have to give it a try.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: A Tale of Two Castings
« Reply #13 on: February 18, 2022, 03:13:28 AM »
In the days before ‘just in time’ manufacturing one lathe maker piled his castings in the yard and apprentices were instructed to relieve themselves on them. They were left for up to a year before machining. I was told this was for the stresses from the casting process to relax. Presumably the rusting as Bob says would help get rid of any surface sand issues not that good cast iron rusts much short term.
Andrew Mawson
East Sussex

Offline PekkaNF

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Re: A Tale of Two Castings
« Reply #14 on: February 18, 2022, 03:58:29 AM »
Wet sandblasting and rusting were old ways to get rid of hard scale and aging did some stress relieving.

Fun anecdote: One mortar manufacturer had problems with tubes developing cracks after finishing or after few shots. Not ideal as you might guess. The tubes were made rotary hammer or something. There were some serious stress issues, heat treating would have been a logistical nightmare, but temporary solution was simple. They strapped full days production onto a pallet really tight and bolted that to a eccentric mass vibrator for overnight. That apparently did the trick!

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #15 on: February 18, 2022, 09:05:19 AM »
Photo of the latest casting (with sprue) and the one from the day before with fins ground off.

I'm going to attempt to get both pistons and cylinders from the same pattern. And in fact, two pistons from one of the castings. I need a third one of these, assuming all goes well, to yield two pistons and two cylinders. What could go wrong?  :lol:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline tom osselton

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Re: A Tale of Two Castings
« Reply #16 on: February 18, 2022, 05:43:50 PM »
Looks like you have this downpact.

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #17 on: February 19, 2022, 09:49:48 AM »
Thanks Tom!  :beer:

Weather's cooled off too much to want to cast for a couple days, but looking forward to reducing a backlog of things I want to do with the furnace. Just got to get the lathes capable of dealing with the output...
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #18 on: February 19, 2022, 05:59:42 PM »
I cut one of the castings into two pieces to make hot and cold pistons for the Rider engine. I turned it on my new lathe (well, the one I built, not so new, but not the Gingery. I'm going to have to name it and stop calling it the "new lathe") and it turned beautifully!!!!  :ddb:

Oh I am so happy! A furnace I built, machining an iron casting I made from a pattern I built, for an engine I'm making, using scrap iron from a broken rail I found buried in the ground, and to have it come out like this, it's just a thrill!,

My new lathe is so solid and precise feeling, it's a joy. Small but really solid and smooth to operate, it definitely is whole other world than from Gingery (which I still have a lot of affection for, however).

And the furnace is so fast! 20 minutes for eight pounds of iron. It all just finally gives me the capability I've always wanted. To imagine anything, and then be able to just make it from scratch -- that's such a feeling of independent capability in this day and age of increasingly enforced dependencies.

Okay enough jabbering. Here's the simple little piece of cast iron, roughed out on the outside to eventually become a piston. It sawed out nicely on the bandsaw before mounting on the lathe (two pistons from one tube shaped casting, and two cylinders will come from identical castings. There's enough thickness in the pattern to do all four parts.

This piece will eventually get bored out as well, and the outside turned down further to match the cylinder bore.



I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline tom osselton

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Re: A Tale of Two Castings
« Reply #19 on: February 19, 2022, 06:50:47 PM »
Looks good!

Offline PekkaNF

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Re: A Tale of Two Castings
« Reply #20 on: February 20, 2022, 05:13:45 AM »
That looks real professional quality!

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #21 on: February 21, 2022, 08:16:57 PM »
Thank you kindly, Pekka!  :beer:

Today, instead of doing the same casting a third time, I wanted to try something different as an experiment. I have a lot of old sprues and problem castings from 9 years ago when I first tried iron. I wanted to see if any of that was usable with careful slagging (it had a very difficult pasty slag back then), and also I wanted to try a smaller more complicated casting, and see whether I could get small pattern details. Also whether smaller castings could be kept soft enough to machine well.

So I tried using the old junk iron on a pattern I made a few years ago for a Westinghouse style twin cylinder steam engine block.

The slag was again horrible, and I probably should have added a little sodium carbonate to liquefy it better. I've been mostly avoiding that because it attacks the crucible. But added just before the pour minimizes the problem. Anyway, here is the result of today's pour.

Again I did lose a little definition and added finning because of the weak bond strength of the sawdust facing sand. But actually, pretty good detail definition in a small casting. I'm looking forward to trying hardwood sawdust instead of this older spruce stuff.

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline tom osselton

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Re: A Tale of Two Castings
« Reply #22 on: February 22, 2022, 06:22:09 PM »
That looks good. When you pull the dross off what do you use for a lifter?

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #23 on: February 22, 2022, 06:56:58 PM »
Tom I don't have a picture of it tonight, I'll get you one tomorrow.

I am using two, one for while the crucible is in the furnace, and a second smaller one of different shape for immediately after I've set it in the pouring shank. The bulk of the slag comes out while in the furnace with the long skimmer -- which does a crude job. The smaller skimmer gets whatever has been missed just before pouring.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #24 on: February 22, 2022, 07:15:11 PM »
Interesting point, Tom, btw, there's a relatively huge loss in casting iron compared to aluminum and zamak. I'd say 35% in general, loss of metal, comparing part, gate, sprue, weight after casting compared to weight of scrap iron put into the crucible. It's a lot easier to underestimate than other metals, I've found.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #25 on: February 23, 2022, 06:08:15 PM »
Tom, these are the tools I use for scraping out slag before pouring. The longer one is used in the furnace, the shorter one is used once the crucible has been lifted out.

The long one is made from angle iron, with the end cut and bent. The short one is just a simple rake, with the bottom curve ground to match the curve of the crucible.

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline ironman

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Re: A Tale of Two Castings
« Reply #26 on: March 04, 2022, 12:08:12 AM »
I think that one of the main causes of sticking is that the pasty ceramic crucible glaze and drips of slag move down the outside and find there way to the bottom and "braze" the crucible to what it's standing on. That happens at the perimeter of the crucible bottom, which, because it is necessarily exposed, can't maintain cardboard carbon as a release agent.

Well that's my theory anyway.   :smart:
You are sooo right because that is exactly what happens. I get that suggestion all the time on youtube by people who have never melted iron. Once the pedestal is stuck to the crucible there is no need to remove it. I use ceramic fiber instead of cardboard and if I do separate the pedestal from the crucible there is a very thin ring on the outside where the glaze makes the crucible stick to the pedestal.

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #27 on: March 04, 2022, 09:46:32 AM »
Thank you Ironman!  :beer:

Slag and spilled iron seem really tough on the the furnace lining, when using blanket and hotface insulaton. My slagging tool is a bit clumsy, and slag sticks to it sometimes even after banging it out in a bowl while hot. I'd like to reduce or avoid drips inside the furnace.

Your slagging tool seems much thinner than mine, and better at non-stick, by comparison, yet it stands up to the temperatures. As a guess, is it a thin piece of stainless steel bent and welded to a steel rod, or some other material?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: A Tale of Two Castings
« Reply #28 on: March 08, 2022, 05:58:05 PM »
Latest stuck job. And proof that it's the outside of the crucible that sticks due to drips, not the underside where the cardboard is. This happened when there were 2 layers of cardboard under the crucible.

It was released when cool by tapping a small chisel around the outside welded joint. The underside was not stuck.

Also note that the firebrick itself did not stick to the floor of the furnace. No drips there.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg