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A Tale of Two Castings

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vtsteam:
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:

vtsteam:
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:

awemawson:
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 !

vtsteam:
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:

awemawson:
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.

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