Considering Using Firebrick For Making Molds For Steel - Ideas?

[SolarInput]

Greetings Artists and Engineers!

 

I'm up against a tough hurdle. If you check my first patent "Dual Nature Puzzle Pieces" from the 70's you will know I can hardly be discouraged. For that project I learned everything from scratch, built several injection molds and a two-color injection molder. I had no help in my twenties, except for Mom. That was a very difficult project to see through and now I have another where I am in over my head from the start. Mom is no longer with us. But life should hold adventure and also deliver it. My good results here will benefit many, many people.

 

The stumbling block for now, I need to get steel into special shapes, the larger is about 60 pounds or more, the smaller maybe about 25 pounds. Twelve of each are needed. The machining time to fabricate these is A LOT. The trouble is A LOT. The cost to go to an outside shop for casting is prohibitive. So I keep imagining ways to do this on my own where I succeed to keep the expense within reason. I can get the steel at almost no expense but it is not in the final shape.

 

I'm thinking now that I can get regular fire bricks and machine them with cutting blades as I desire, and arrive at a reasonable mold when they are assembled and trapped in a sandbox. The brick has to go to the molten steel temperature without having problems. Hopefully it can. It is possible to do sand casting, yes, but I am intrigued about the firebrick approach. Sand molds are not ridgid, the surfaces can slump out prematurely, etc.

 

So, I imagine having a firebrick crucible, bricks tightly bundled  in a circle or square, locked in a sandbox perhaps, and some means of getting the steel up to temperature. The temperature reached by a fresnel lens from an old projection TV will melt a rock, so maybe with solar input I can get close for free, then switch to induction or something effective. I have to wonder if straight electricity can do it, if you have the ideal electrodes and a great relationship with the power company.

 

The mold itself could work as the crucible, perhaps, and the step of valving molten steel through a passage is skipped. I like the sound of that. Whatever works and works best, within my ability at home, that is what I need to find. The parts have to be structurally sound, they are suspension parts for a new kind of RV I designed for my retirement. My suspension provides a huge amount of travel so off-road becomes practical. The power sourcing is based foremostly in conversion of organic materials into methane, hydrogen, and CO, going with electric motors. It is a great project and I intend to finish. There is room for help with this potential big industry. I am located I Austin, Texas but I am hoping to get a bit east for bigger trees, shade, and rain. You can send technical email to MountainSteamship at hushmail dot com if you prefer.

 

I ran across a discussion by a member who used some high temperature mesh and filled it with some high temperature repair putty, to get a much better repair on a broken kiln block. Doc somebody, wish I could remember. Hmmm , Weldon? Could have been... Suppose a combination of materials such as in that innovative repair would make a re-useable mold for steel? With one master to pull the molds from, my machining time is kept under control maybe and I can make dozens of sets in production instead of one set for one prototype. So, does anyone see the proper choices of materials and innovative approach here? It takes the heat, no distortion, not very costly? The brick is already fired and stable, somebody has done this I bet... if you know someone who has some experience with these materials, please let me know. Thanks!

 

[Mark C.]

Doc was talking about soft bricks which can be carved easy for shapes. You will want K 28s as they can go to 2800. K 25s may spall at your temps.They are sold in k23oo-k2400 K25 and k26 and k28s-they get more grainy as you get higher numbers except the made in china ones that are always more grainy. Steel melts at 2500 to 2750 best as I could read up on.Soft brick are just that soft so they will need good support. If you are using hard brick no worries  as most are fired very much hotter than any temps you may reach. They do not carve well and diamond tools are all you really can use with any progress.

You could use a high temp castable refractory but you will need to know its limits.

Usually steel is melted in a cast crucible and is melted with a massive amount of electricity with electrodes. I doubt your old TV lens will do the trick. I think you could set this up under one of those massive electric towers like Godzilla likes to play with and tap into that power before any  large monsters or power cops show up.

Let us know how this turns out.

Mark

[SolarInput]

Perhaps my next question in solving my furnace heat is to know electrodes, copper might work if it takes the heat, I think it can.

 

Tonight I reviewed some interesting induction demonstrations on youtube, and I saw a guy re-wire a transformer output winding to get hundreds of amps at low voltage, melted nails in no time.  The copper did not melt near the nail, nor at all.  This was simple resistance heating, not induction.

 

Maybe I can create a long trough in firebricks to hold 75 pounds of steel, and somehow get the energy into it.  If it is enclosed in insulator bricks and blanket, it will hold the heat better.  Oil heat gets up to temperature, I see people do it on YouTube.  For solar input I could attempt a trough reflector, and it is useful if the hard bricks conduct the solar through to the metal, which they do somewhat well.  Locally there are bricks of the darker red color, they reflect less light.  Who knows, I will be giving it a lot of thought.  If solar brings it close for free, and the welder current brings it the rest of the way, that is nice.  It means I build a fixed furnace, safely supported such that the support won't melt, and maybe it can be on a large cart so I can follow the sun better.  The reflector trough can follow the sun for a few hours, that part goes easy I imagine, probably alongside the brick trough, not under it.  Then the worry is how to gate the flow if I have my molds next to the furnace.  I suppose the brick trough can be made to tip incrementally.  Yikes.  This is tough.

 

So, my hard bricks should take the heat of molten steel.  Hope so!  I wonder how many cycles.  Of course I can also bring the molds up to high temperature if that helps.

 

If I put mirror material on my ten foot diameter antenna dish I can get 3000 degrees at the focus, not a tight focus either.  The trough approach keeps me lower to the ground, I like that better, sheets of aluminum are easy to come by and work into trough reflectors...

 

If this would give good production parts, economically, I should find out and have it at my usage.

[justanassembler]

its not just the heat that the brick has to take, steel and other materials become corrosive when molten, my guess is that you are going to need something much higher in alumina than a standard high or even superduty brick.

[SolarInput]

Thanks for replies, my knowledge has increased a bit in the past week, every bit helps.  My test of local firebrick (heavy 9x4x2.5 I think) showed me that the steel melt will bite into the brick about a third of a mm and the composition there seems to become different. The surface of a crucible must do something similar, or take on a layer of slag. When I search for large crucibles, so far I find none, the small ones are expensive.  But I did find 24" wide blanket, 50 square feet, 1 inch thick, 2600 degree rating, for about $80 and I will probably use it for the lid on my trough smelter.

 

I bought a 50 pound bag of powder to mix with water, for bonding firebricks, and I can check this material to see what the slagbite is like when steel is molten against it.  The sales people say the mix is good for the heat I am after... they say the bricks are good for maybe 3000 degress.  Well, I don't know.  Heavy firebrick, blond or red.  The bottom surface of my trough has to be a material that can handle the melt temperature over and over.  I don't want to rebuild it each pour.

 

Maybe there is alumina in this powder-water mix that helps control the corrosion effect of molten steel.  I envision pouring the steel from one end of a six foot long trough, the slagbite layer will stay behind and remain thin, hopefully.  My smelter concept so far starts with a structural steel tube perhaps wider than 12", split lengthwise to receive a bed of sand under mortared firebricks held together in compression by way of screws mounted at the ends of the tube.  The bricks are cut or assembled to provide the long trough volume, the cover can be high temp blanket, maybe with a layer of mix bonded into it to arch and stiffen it.  The cover will be light weight but effective.

 

Initial heat can be gas, I need to get a large pyrolysis unit going anyway as part of this entire project.  If my insulation factor is good enough I can get up to some good heat on little fuel, given an hour or two.  Then I can turn on the electric boost.  Here is where I need a little advice... I am thinking the electrode choice is important, maybe copper can work but I'm not sure.  Carbon can work.  I think the resistance heating is best, no arc is wanted at all.  The arc will cut copper instantly, as the arc itself is something like 10,000 degrees.

 

I would guess rather cluelessly today that with 30 amps (maybe/hopefully less) going through 100 pounds of steel already under gas heating, I can melt this volume inside my smelter in a couple minutes and keep bringing it up to admirable liquid state ready to pour.  Someone may have some practical experience here, watching steel take this much or more direct electric heating.  My structural tube will be a teeter-totter with a lift screw at one end for smooth control.  The target for the melt is most likely sand molds, and when the steel contracts it will start destroying the mold - a firebrick mold is not easy to save each time, even if I find the proper surface treatment for it.  I have read that the sand can put silica into the air when the steel hits it and then the air is harmful for breathing.  So that is another problem to deal with.  I wonder if I painted my positive with the mix and stuck it in the sand quickly, maybe the mold would have a better surface material.  I could spray the positive with wax release, paint it with mix, pack the sand to it quickly... heat it up, pull away the positive... nice! ...? Maybe?... What is the best mix to make these shells anyway?  If I make half shells and glue them together I can put them in the sand like that.  Maybe I can use the cheapest sand around such shells.  This is sounding possible, really possible and practical.  My molds won't blow out from pressure, and I don't use pounds and pounds of wax all day long trying to get good results.  All I need is a parting agent on the positive.

 

Now, with my lack of experience, I am guessing that when I tip the trough there is slag floating and it will drop out the spout of my trough and try to plug the mold entry.  I am thinking there is a way to shape the spout to help capture the slag.  Maybe the spout can be tubular and the slag floats so high during the pour that it won't go out until last.  As well, the mold entry can be shaped to float the slag while the good melt fills the cavity.  Sounds like you develop a feel for these things.  I think I need to taper the spout into a tall slot, if not make it a tube.  The slag will catch there and the heavy melt passes beneath.  I need to fill the mold so fast that the entry remains full of melt and keeps the slag floating.

 

So, this is the point I am at, more to report in a week or so.  Your helpful thoughts are encouraged. - Dave

[Bob Coyle]

Your hybrid gas/electric furnace sounds too complicated. and the current requirements and estimated time to melt are way low.  An arc welder pulling 30 amps will just puddle 3/16 rod on 1/2 inch plate. no way is it going to do anything with 50 or 100 lbs of metal.

 

The metal you pour must be uniformly hot. It is unrealistic to think of melting it as you go, if that is what you are thinking. It cools amazingly fast once it hits the mold and you will get what they call a "Cold shut" where the metal reaches it's freezing point before the whole mold is filled.

 

Forget the fire brick mold. You can form a durable sand mold that can be manipulated buy using commercially available resins that polymerize the sand while still allowing it to breath. I also heard you could do this by spraying the sand with sodium silicate, making your mold, and then placing it in a CO2 atmosphere until it cures out.

 

Remember, all those old steel engine blocks were made this way. If there was some simpler or cheaper way to do it they would have.

[SolarInput]

In the near future I'll be testing my dry powder mix as a crucible with arc melt to load it up with melt toward failure of whatever kind - or success.  I'm going to put sand around the alumina shell to see what happens in this test.  My earlier test on a brick indicated I could maintain a surprisingly large puddle with an average welder.  The melt left a troublesome slagbite in the surface of the brick.

 

With the powder mix crucible test I am going to wipe graphite powder into the surface on half of it to see what benefit I get.  Maybe I will come up with another powder for the other half in this same test, maybe aluminum oxide?  My melt will hit 2800 F no doubt.  The powder mix crucible is said to take such heat.  Maybe tomorrow my heat blanket will arrive (2600 F) and I can make quick lids for these tests.  I guess any high fired pottery lid would work.

 

As for crucible innovations, I am hopeful about the powder-water mix.  If I get the p-w crucible to carry a good load of melt, and the release powders work, the steel will come loose when cool.  This will imply that my molds can work about as well or better than this if I use the mix to make shells to be the receiving surfaces inside my sand molds.  There is a large transverse core in my cast part, so the sand cast is not simple.  The shell approach seems helpful to this end.  Of course, shrinkage of the steel is going to destroy my shells each time.

 

If my volume of cast part is about 210 cubic inches (good estimate for now) then the weight is about 70 pounds and I see there are some graphite crucibles available that will hold this much.  The big one holds about 750 cubic inches, my cost is about $500 delivered.  It seems the graphite goes to 5000 F reliably, but transfers heat quickly, so I have to decide if it is OK to try to insulate it.  Maybe it can be held in a box of sand.  Maybe the inner surface life can be prolonged by putting a suface coat on it?  Of what?  Maybe alumina powders will expand and break the graphite...

 

Today I have the idea that I can build a large chamber or trough for melt scrap, positioned above the crucible.  I can use bricks, powder mix, and a box with sand to build the chamber.  Within the chamber I arc the scrap, the melt constantly rolls into the crucible where it is kept hot because I'll put another pair of electrodes in there to keep it hot.  This method lets me work through the scrap by hand until it is melted.  Obviously I need a thousand amps at hand to do this quickly.  But the heat is conserved if the scrap melts fast under the arc and fills the crucible.  Maybe the shock waves are bad for the crucible?   If the powder mix does not hold up to the heat and the bricks don't hold up, then I have to rely on the graphite crucible to get me through these casting days.

 

The large graphite crucible has a 10 inch ID.  Most of my scrap can be made to fit in this crucible.  Maybe I can arc in there without ruining my $500 crucible.  If it can take a coating of the powder mix, maybe someone knows about doing it correctly.  Insulating the outside is desireable as well.  The blanket could do that nicely.  I like the idea of holding the crucible in a sand box, the whole box tilts when it is time to pour and it is built to retain all sand and crucible accordingly with planned success.  It gets a spout added so it pours well.

 

So, has anyone used electrodes to produce this much melt, and how did it go?  Thanks - Dave

[Mark C.]

My guess is a metal smithing forum would yield you better info than a clay forum on steel making.

mark

 

Like this yahoo group

http://finance.groups.yahoo.com/group/STEEL/

[SolarInput]

The steel group looks useful, thanks Marc!  Today I picked up some talc to use as a parting agent on my powder mix molds.  The melting temperature for talc will be about the same for steel.  So I'm looking for carbon black or graphite powder in bulk to also try at the high heat.  Locally there are welding supply houses where I can get carbon electrodes, they are low cost but the box holds 100.

 

What refractory material will work best at the steel temperature, it is not known to me!.  I expect the hard brick holds up, but not the blanket.  I expect the powder mix will hold up for awhile, or a shell of it will work to line a sand casting and somehow I get the transverse core set up in there as well without going to lost wax method.

 

Given some good current limiting device, I can probably use line voltage with these heavy electrodes I found and I don't need to buy a $4000 welder.  The scrap can be layed out in a trough of firebrick lined with the powder mix.  I can build a window into this furnace, maybe pyrex will work, maybe nothing at all is better.  I think the blanket will be OK to cover this arc furnace.  If the heat retains well, the scrap will come up to heat and melt, all 100 pounds.  It might take 30 minutes, or 60 or more, like baking a turkey except the duty cycle is 100% and the metal in the oven gets "involved" before its over.  Once in a while things like this happen and the meal is burned away to carbon long before discovery.  I just need great insulation for my furnace and 5000 watts, maybe 10,000 watts, a good current limiting device, and I believe the desired melt is within reach.  Maybe, just maybe, I won't need the graphite crucible to go forward from there. 

[Mark C.]

I would stick to a crucible .

I would hate to pay the power bill on that line voltage of 10,000 watts while 100# of scrap melts

 

I suggest talking about this on the steel group as they have done this a time or two and will have some great ideas on how to get that 100# of scrap melted without blowing out the power grid in your town.

Mark

[SolarInput]

So with a graphite crucible, the heat is transferring through at a higher rate, I suppose the density and strength are also higher.  I've seen ceramic bonded to the outside of a small induction crucible, to slow the heat loss I believe.  Heat loss is huge with gas heating, the guys doing it on YouTube complain how much propane they go through. Maybe 30 or 40 bucks worth, I don't know.  None of them that  I've seen are melting 100 pounds of steel.  The exhaust gases carry away most of the energy, by a factor of at least ten.  The Co2 is good though.  Induction heating may not be as wasteful as it appears, but the tubing holds water and the water boils, for small steel melts.

 

My three generators from home depot total 10kw, but they are over-rated of course.  Maybe I need six of them so I can stay off the grid while putting 10kw into my scrap.  The fuel consumption is small.

 

The 2600 F blanket got here yesterday.  I'm going to weld on top of a piece of it, the arc will cut right through it I suppose but the steel may puddle and not burn through it... just to see the limit...

 

I wonder if I can cure my powder mix refractory crucible inside a b-b-q grill over charcoal with a piece of blanket over it to raise temperature?  Should work...  Once cured I can load it with small scrap and a couple of electrodes, given a good power source that won't trip off.  Maybe my eight cubic inch crucible will load with melt in a few minutes...  If I insulate it in some blanket and simply arc inside it, how much melt will I get in there to stay red hot?  It might puddle an inch thick, wouldn't that be something?  If I can make my own alumina crucibles to carry 100 pounds, and hold up to the abuse, we have made seriously good progress here.

 

This is a great forum structure, very user friendly and accessible.  Your knowledge has benefited me.  Thank you.  Keep the ideas coming, though, you are pitted against the steel guys now, they may not be looking for the same shortcuts that I am so I won't give up yet on potters who discover new tricks each week! - Dave

[SolarInput]

Here is a trick I should mention for those who are following:  With a neon sign transformer you can pull one inch long arcs over the surface of materials.  The arc remains as tight as .005 inch in places and etches the material surface because of the high local arc heat.  Some materials such as granite will melt and reform like glass.  You can use thin metal wire to get involved in the melt and change color or create bubbles.  With stronger transformers and bigger spark, these melts will become wider on your surfaces.  I never tried a plasma gun this way but it probably does much the same and it is safer to work with.  The neon voltage is in thousands of volts, yes, I know what that does to your day.  Ouch.

[oldlady]

if you solve all these problems and are successful in making something, what in the world will be the result of all this?

[SolarInput]

To Oldlady - We could say a new world of economic and green technology freedom is born.  Seriously.  I admit that I now hate my car for its inherent problems and expenses.  I hate the new electronic ignition, fuel injectors that set your loved one's car on fire so fast you can hardly exit alive, and the cost of gasoline or diesel.  Also I admit I hate the standard mortgage for the clauses that allow foreclosure, I hate the extra 200% typically paid in interest getting past the banker's whims, I hate the inferior design and construction that often makes a built home a liability during one's own lifetime.  Then there is the period of adjustment to foreclosure, where does one turn?   When I acquired an MCI bus, I realised what it was to find superior construction and benefit owning a reliable motorhome.  There were some limits there still that needed to be overcome to be really happy.  The monster MCI RV will not drive back roads, cross pastures or travel dirt roads in rainy season  These buses can not be worked on easily, the costs are astronomical.  Even my car is trouble, the engine is too proprietary and the suspension is out of reach for me to self service.  My ranch is so rugged I can't get an MCI bus back in there.  The new design will go almost anywhere, without petroleum expense ever.  Without engine work that kills you financially.  Without stranding you due to powertrain breakage (redundancy works best).  Imagine owning such a machine and not fearing about losing your job ever again.  Imagine having several owned in the family.  Imagine getting some farmland and having everything you really need, right then and there.  Superior design and function.  Agricultural exemption and no insanely repeating property tax on your rolling homes.  Transportation that can not fail to transport because the systems are designed to fully overcome their own failures.

 

You expected to hear something good I hope.  Your question seemed hopeful.  I, too, am hopeful, as the project testifies.  The mere conception has been worth it.  The industry awaits us.