New lining for the iron furnace

[vtsteam]

Mathew is your present furnace used for iron? Or do you plan to use the future one for iron?

[vtsteam]

I think the first casting I'd like to pour will just be a 2" solid cylinder of cast iron. That would come in handy for making pistons in the sizes I'm interested in. I'm thinking it may work to just pour that vertically with an open top. In which case it also doesn't need much of a flask -- I've done that before in a stainless kitchen canister with just some greensand packed around the pattern.

I did much the same thing with the Tee slot bars for the carriage on my new lathe.

[mattinker]

Mathew is your present furnace used for iron? Or do you plan to use the future one for iron?

The kiln I referred to is a ceramics kiln on which I used the sodium silicate, I was running it at up to 1100°C , the sodium silicate easily resisted those temperatures. I have bought the Zirconium silicate and the Kaolin which I intend using on a cast iron foundry. the kaolin which is porcelain clay fires at 1300° plus, I don't know how it will react with the Zirconium, but I think it's worth a try!

Cheers, Matthew

[vtsteam]

Mathew, that should be really interesting. 

I spread out a new tarp in front of our home woodstove (with permission!) and have been drying the greensand that way, but it is still very slow going!

[awemawson]

Keep the cat off it 

[vtsteam]

No cat!

Cat's and foundries don't mix.......

[vtsteam]

I cleared up the tarp and sand by evening.

When I first started drying, I did a moisture check by heating a 100 gram sample of the greensand in our toaster oven, spread out on a scrap of aluminum foil. I brought the whole above 100C for 15 minutes. Weight loss was 10 grams to start.

At the end of the drying session, a second heated sample showed a 7 gram loss, so after a full day we went from 10% moisture content down to 7%. 

To cast iron, I need to drop it to 4%. To me the sand still feels quite wet in the hand.

[awemawson]

Can you put it in a container and pull a vacuum to remove the moisture? I have an Edwards vacuum pump that I used to use for lost wax degassing, and once used this trick on my last remaining bit of core sand that had absorbed too much water.  It was surprisingly quick.

[vtsteam]

Nope, no vacuum pump, Andrew.

Spread it out today for another few hours, turning it every once in awhile. Down to 6% now. Starting to feel a little better in the hand, but still too damp, yet.

I did some physical measurements, out of curiosity with a micrometer of various sands I have. The first was my aluminum and zinc molding sand -- which I've used for many years. I did several samples and averaged them -- surprisingly they were all quite close. This measures the largest average grain size -- it isn't a uniform sand. I rinsed all clay (hawthorn fireclay) off to do the measurements. It worked out to .012" or a #50 screen.

I then measured my ceramic grade quartz sand, which seems very uniform, also rinsing off the clay (bentonite) and it worked out to .010" or #60. Which confirms what the bag it came in said.

Finally I measured some "Fine" masonry sand purchased bagged at a local building supply store. It also tested out at #60. No idea how refractory it is as I've never tried it or mixed it with clay. But I'd like to try it with fireclay and see how it compares with my old aluminum greensand.

Interesting to find that my aluminum sand was so coarse. I thought it was up closer to #100 (.006") Several casting book authorities talk about #100 - #120 sieve for aluminum sand. Yet, my aluminum castings have always seemed to come out quite satisfactory, and better looking than most I see online. I did once try a bagged #120 blasting sand, but it had poor permeability, tended to short pour, and I ended up only using it for facing sand sometimes.

Anyway it was all something to do on a January day, indoors. High temps for the days will be well below freezing for the next week or so, and nghts around 0F with winds, so no casting yet.

[awemawson]

Casting sand grain sizes are not logical I’m afraid when you compare the surface finishes on the castings. Certainly with iron quite coarse sands can give a surprisingly smooth finish due to the gas layer formed from the crushed coal.

There’s quite a bit to it, permeability, refractory quality, surface finish, cohesiveness, ability to release the pattern and of course availability!

Artificially chemically bonded sands such as the phenolics and sodium silicate raise a whole new set of variables but are more predictable ( but have the disadvantage of not being reusable)

Towards the end of my foundry playing about I went over practically exclusively to sodium silicate. The sand when the carbon dioxide has done its bit is very stable, and intricate patterns can be pulled with little chance of it all falling out when inverted. For that to happen with a greensand mould is very disheartening!

[vtsteam]

One of the facts I like about casting is that there are a huge number of variables...and so, a seemingly infinite number of  problems and approaches. And so, it tends toward creating a personal style for the person casting. What I like about it is, it's still an art. And an art based on personal experience.

[vtsteam]

The sand has finally dried to a good molding feel. It's been 2 weeks in a low indoor humidity of 30%!

What's even more surprising to me is that I dried 100 grams of it in the oven, and it looks like it's now at a moisture of 2%.
That's amazing. Unless I'm doing something wrong, but yes 2% and it has very good feel, compacts in the hand nicely without sticking, and a squeezed clump of it breaks clean. That's just how I like it. But 2% seems numerically, at least, very low. I was expecting 4% to be about right, but it was too wet at that level.

Well, not complaining -- that's actually really good in terms of casting without steam gassing problems.

Getting closer every day to trying an iron melt. I've got cores, steel flasks, furnace relined, burner tested, crucibles, tools rounded up, found my ferrosilicon and plumbago, sand at proper temper, I need to make a pattern, and I need the weather to get better.

Major 13F 20mph winds blizzard predicted for tomorrow. Wednesday the opposite, 47F, but it will rain, which will be a mess with the snow, for sure. Well, pattern making for now........

Cylinders for a Rider Stirling of 2-1/2" bore.

[PekkaNF]

Sounds good.

Any chance of some educational pictures on paternmaking?

I sympathize with the weather. Here it is has been few days nice. Some snow, but not more than I can shovel of the driveway. This morning temp is -8C. Fine, but weekend is pretty much only time I have a chance of changing some old AC ducting in the crawl space between ceiling and roof. For evening and tomorrow weather forecast  predicts blizzard and 30-40 cm of snow. Almost tempted to postpone. Maybe I just carry some firewood inside for oven and sauna to weather the storm. But it is hard not to what I have set to my mind.

[vtsteam]

Sure, Pekka, here:

https://www.madmodder.net/index.php/topic,13467

[PekkaNF]

Sweet!

You describe reasoning and thought process, that is something I enjoy following and I learn there way more than from traditional "how to" instructions.

Thank you very much,
Pekka

[RotarySMP]

My first foundry was an A5 with Kaowool, and the Mullite hard face to the recipe of the Alloy avenue moderator Anon (A name which hasnt aged well  )

I used a little normally aspirated bunsen burner from 1/2" water pipe, a reducer  and a mig nozzle, and managed an iron pour (although the mould broke). It took nearly 2 hours for the melt though.

Amazing how little energy you have to shove in, if you have good enough insulation to not have it all fall straight out again.
Mark

[vtsteam]

The day was predicted to reach 40F and was clear with little wind so I decided to try to cast the new piston pattern in iron. i got most everything set up. It seemed like there was just a huge amount of gear to collect together for an iron melt -- mainly because I haven't done one in several years. Tongs, shanks, skimmer, flasks, leather protective gear, face shield, molding tools, oil fuel, vacuum cleaner, hoses, iron, greensand, ferrosilicon, riddle, ingot mold, plumbago, paring dust, and.....wait a minute, where's my compressor? Oh yeah, next town over, half an hour away......and a half hour back at my in law's garage. 

I Did the drive, well that killed things until after 2;30, with only a couple hours of good light left, but tomorrow was predicted to snow/rain, so I thought I'd give it a try. I set an A6 crucible with 5-1/2 lbs of iron in the furnace. Hooked up vacuum, compressor, diesel oil fuel, set comp pressure at 60 psi, soaked a small piece of rag in fuel, stuck it in the furnace, lit it with a torch, and then cracked open the oil valve. Whoosh! That familiar big yellow flare up on oil start. Always gets the adrenalin up. The outside temp was now 38F, but that didn't seem to stop the atomized oil from an instant startup. This furnace does not need propane to warm the walls before feeding oil.

I started the vacuum cleaner and then she roared - a little sooty smoky, so I eased the oil valve down until the smoke just disappeared. The furnace walls lit up almost immediately. That's the reflective face of the compound at work. It's a very fast heat up. So fast I started to wonder if I'd have time to make up a mold -- I used to have an hour and a half, more or less, but within 5 minutes the iron and crucible were now bright orange.

Unfortunately I was seeing some black smoke and soot flowing back around the burner pipe where it was attached. That meant the seal wasn't good around the burner pipe, and the pressure of the vacuum cleaner was apparently blowing some air fuel mix back out. The last lining was solid firebrick and clay ganister, so the burner was effectively cemented in for a 4" thickness. Now with this new blanket insulation, it's much easier to have a leak. The hot face coating has absolutely no strength -- It's like a thick paint layer over a cotton ball, so it doesn't hold tight to anything. I probably had just not pushed in enough insulation blanket around the burner hole when I installed it.

I kept going for a couple more minutes, but I started to see small flames licking out around the burner, so I reluctantly made the decision to abort. I shut off the fuel, the blast and the compressor. With everything shut down, the furnace was still brilliant orange hot, as were the crucible and the iron pieces. It took about a half hour to get the furnace unloaded and cool enough to patch more blanket in around the burner. I sealed it with hot face compound.

So no metal poured, but I was very pleased with the performance of the new lining so far, and I do have everything now collected for a melt as soon as the weather cooperates. I hope that can happen this weekend. 

[tom osselton]

It’s almost amazing how fast it heats up with the blanket.

[vtsteam]

Sure is, Tom. I just hope the lining holds up to the amount of heat I'm pumping in. That Kwiky burner really puts it out. I was running the vacuum cleaner blower full power without a waste gate or a variable supply.

I've got an old HF router speed controller, which I'll hook up next time to the vac, and maybe turn it down a little to start with and see how fast she heats up. I still feel like that hot face coating is fragile. It's pretty expensive, and the blanket under is not rated for iron temps, or the violence of a direct oil blast, so I might back off a little next time and see what kind of heating rate we get.

[awemawson]

Can you set the burner in a block of fireclay to give it strength to the furnace outer shell. If it’s not too large the heat loss of not being Kaowool at that point will be minimal.

[vtsteam]

That's Plan C. 

I might do a furnace run-up to check for leaks today if precipitation holds off.

[vtsteam]

I made up some new small molding boxes to do a piston casting. Smaller boxes are easier to roll, and use less sand, so I can mold two at once from the same pattern with the 50 pounds of sand I have.

[vtsteam]

Wooden flasks don't last long when pouring iron. Generally it happens when there's an overflow from the sprue basin that reaches an edge, or a spill at the edge, or often just touching the crucible to the edge of the flask while pouring. Generally the rest of the box suffers less. It's mainly the top edge where the crucible is being poured from.

I do have some steel flasks that I built years ago. They are heavy and, as in this case, they aren't always ideal for the shape of the pattern you want to pour. So it's easy to quickly put some wooden boxes togetherfor a special need, but it would be nice if they lasted longer. Their light weight makes molding easier, particularly if the pattern is tall or large and you have to roll a few times.

I've thought about keeping the lightt weight of wood but adding more heat resistance by inlaying a flat metal edge. Better would be a channel shape, Though that would need to be flush with the wood on all three edges. So, it's impractical.

Then this morning I thought, why does the metal protector have to be attached to the flask? Just use a piece of heavy  angle iron,cut to size and lay it on top of the pouring edge after the mold is made up. That will protect the edge the side, and also stop any sprue overflow. Adds weight, too when it's needed, Simple!! 

And that's just what I did.

btw. poured iron today........

[tom osselton]

I was going to mention that to protect the wood. I’ve never painted my boxes but do have places on the sides to bolt both sides together in case of separation on larger pours.

[vtsteam]

I did a third iron melt in a week today. I timed it at 15 minutes from start to melting 6 lbs of iron in an A6 crucible, and with slagging and ferrosilicon addition, plus bringing it up to pouring heat, it was 21 minutes total from lighting the furnace.to pouring iron.

I used about a gallon of diesel fuel for that, now in winter, when heavier oils would not flow or atomize as well. I'm guessing there's enough heat  in the furnace after to probably do a zinc melt with no more fuel, or an aluminum or brass melt within a few minutes of lighting up again. I imagine a second iron melt might be 10 minutes more.

This same furnace and same burner, with 4" of firebrick and ganister insulation took 1-1/2 to 2 hours to pour iron 9 years ago, and those were borderline hot enough sometimes.

The only problem I've had so far is that a small piece of the lid blanket, (which was pieced together from leftovers of the main furnace lining), has come loose twice. That didn't happen during a melt, but after cooling. The blanket tends to shrink a litlle after an initial melt, and where once it was packed in place at the edges, it loosens. I did cement all edges with sodium silicate, per Ironman's video, and covered the joints with the hot face compound, but the blanket still shrank and loosened.

Today I put positive retaining in by screwing with self tapping metal roofing screws from the sides of the lid into the looser blanket pieces. I hope that holds better.