In the middle of nowhere - Wyoming

Discussion in 'New member introductions' started by Smoking Shoe, Oct 12, 2021 at 12:45 PM.

  1. Smoking Shoe

    Smoking Shoe Copper

    I'm a semi retired grumpy old guy that hasn't cast anything in well over a decade. I have a couple of projects (too many) that will require some aluminum castings and I'm too cheap to sublet the work. That means resurrecting my casting hobby and upgrading significantly the hardware and my knowledge base.

    This desire lead to this forum. Been lurking for a while now and have learned a lot. :cool:
    The pics below is of the few patterns left from those days and some of the castings from the recycle bin. These were done using charcoal and a large flower pot setting in a 5 gallon paint bucket of sand. I did eventually get usable parts.
    I had collected all the hardware to build a nice propane fired unit but life took a turn and it all got put on hold. I still have most of that hardware but...........
    The parts I want to make are quite a bit more complex than I have ever done and are better suited to lost wax than sand and the quality of the final product needs to be pretty good. Also my work area has changed quite a bit over the years and clean electric heat seems to be a better fit today.

    I was pointed to this thread today: Muses about a low mass electric furnace
    More ideas to assimilate. :oops:
    Low mass was one of my design parameters and I had planed to cast my own light weight refractory. From my days working in a Halliburton lab* I know how to make 6#/ft^3 cement with a 500 PSI strength and had thought about using the same method, but with refractory. I'm rethinking that pending tests of my original plan.
    Attached below is the spread sheet I worked up to design the coils for my planned 6kW unit. I decided on 4 coils to reduce the gauge of the Kanthal thinking it would be easier to wind using my 3D printed (untested) winding tool. Change the file type from *.txt to *.xlsx to open

    Cast 1.jpg Cast 2.jpg
    Cast 3.jpg




    * No I couldn't find a source of bentone back then even with my Halliburton contacts. I bought Petrobond.
     

    Attached Files:

    Last edited: Oct 12, 2021 at 12:51 PM
  2. Petee716

    Petee716 Gold Banner Member

    Welcome Smoking Shoe. This is a great group as you’ve probably already found, and I’m sure you’ll get some good direction here.
    Pete
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Couldn't get that file to open, so maybe you did same, but I followed the Kanthal recommendations from page 12 their handbook.

    https://www.kanthal.com/globalasset...-elements/resistance-alloys_s-ka041-b-eng.pdf

    I actually went the other way and designed the coil to use the largest gauge wire possible because it is more durable and longer life. I made a simple winder. Takes a couple minutes to wind a 14 ga coil.



    The coil design is really just a matter of the simple resistance calculation, and checking the maximum coil and furnace surface loading have not been exceeded, and assuming a round coil, applying a 3x-5x stretch to solid wound length.

    For me, on a 10" bore furnace that turned out to be two 13.5 ohm, 14ga Kanthal A1 coils (in parallel), that were 63ft long, and wound into a 1/2" OD coil and stretched a little more than 3x to make three trips around the furnace bore.

    So that turned out to be 4kw for each coil which worked out well for my available 240vac power circuit at about 32amps. I arranged the two coils in a nested helix like a double lead screw but like in kilns, separate elements on shelves connected in combinations of series and parallel offer a lot of options.

    That would be interesting. There have been several visitors here that indicated they had made their own insulating fire brick, but never came back to explain. I think it would be very useful to be able to cast IFB shapes.
    • My first electric furnace liner used 2300F IFB and it was medium mass, and a fair trade of mass and durability.
    • I cast a dense refractory liner, and though it was/is indestructible, it was more than twice the mass of the IFB and took more than 2x time to come to temperature.
    • The latest version was the low mass moldable ceramic fiber in that linked thread in your post above. It's by far the highest performer in time to temp but it may not stand up to tool contact very well. Since I have a lift off furnace that is not a problem for me.

    Though I have a PiD controller, the first two versions never hit the 1800F set point on the first melt, because the melt always came to temp before the furnace mass was heated. Subsequent melts would. My low mass furnace does bounce off the temp set point before the charge melts. Nothing magical about 1800F, but it's just fine for aluminum and coil life is indefinite at that temp. It will melt an A20 of aluminum in 30-40 minutes from cold start.

    Best,
    Kelly
     
  4. Smoking Shoe

    Smoking Shoe Copper

    Ditto.
    I'm a bit of a frustrated engineer so the spread sheet was/is probably more complicated* than needed. It was set up more for 'what if' than to solve a particular set of parameters.

    I plan to have a lift off like your setup so I too am not too worried about tool contact damage. One less tool to make too. Just grab the crucible and go pour.

    Excellent data point! I was kind of wondering about thermal lag and the position of the thermocouple. If I can melt an A10 full of aluminum in an hour I'll be satisfied. PID is going to be a big change from my old way of determining temp. Figured out how long it took to get to melt point and then mentally calculate how much longer to leave the crucible to get to the desired temp. As can be seen by the pictures in my first post that isn't the most reliable way!

    I'll try to report back with my progress - which WILL be slow. I have 3 bags** of refractory and some wool left from my last planed upgrade that I bought from Budget Casting Supply back when they had a more robust inventory and I can get more 2300F locally.


    * K factor for coil diameter/spring back - allowance for double wrap on lead in - cold start amp surge etc. ...........
    ** 2 1/3 now after a raccoon got trapped in my old shop and trashed the interior.
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That really is the biggest benefit of a lift-off. The other is you can get by with smaller clearance to accommodate a bigger crucible for a given bore because you don't need as much clearance for tools or in the case of an electric, combustion. I have less than an inch at the spout on an A20 in the 10" bore but an A10 is by far the most often used crucible. Using open ring shanks for grab and go is great. No moving pieces need, but.....I added a top clamp for insurance.

    Here's a thread I started a long time ago. Might be some ideas you can use. There are several styles that can accommodate snatch and pour shanks. Take a look at the tilting body furnace.

    http://forums.thehomefoundry.org/index.php?threads/the-furnace-thread.276/

    For fuel fired furnaces, I've seen several casters take a small trash can, cut a vent hole in the bottom, line it with ceramic fiber, and it is so light, it can just be lifted off with one hand. The Tuyere and burner are fixed in the base.

    I've seen people just attach the coils on the surface of the interior furnace wall, but I wouldn't do it. For a resistive electric, you need to give some thought to the shelves to retain the coils because the tend to grow out of the grooves in the heating cycle. Also, making the cold junction from the resistive wire(s) to the electrical conductor, and managing the moving conductor cable as it will need to attach to the moving/lifting body.

    I've molded the shelves out of various materials, but perhaps the most practical is to just cut IFBs so you have a 6 or 8 side bore, and cut the coil shelves into each layer of brick. If you fit them well to the exterior shell. It can be done (outdoors) with a hand or table saw. I wouldn't even glue the bricks together, that way they can be repaired and the coils easily serviced/replaced.

    For the cold junction, double or triple the resistance wire lead. This reduces the resistance and thus temperature. If you run that lead to a ventilated box external to the furnace insulation, it will be cold enough to connect to ordinary cooper conductor or appliance wire. If you don't, it will be too hot, alloy with the conductor, melt and fail.

    Also make sure you have a high integrity/redundant (maybe even automated) way to de-energize the coils before opening the furnace to add stock, skim, or take melt temperature or you'll have built a high power defibrillator.

    You'll like the electric.

    Best,
    Kelly
     
  6. Smoking Shoe

    Smoking Shoe Copper

    Automation is my biggest decision right now. Balance between what I want and what is needed to actually do some work seems to be constant challenge. Adding a switch to the lift mechanism to cut off the SSRs should be simple enough......probably be able to use the lower limit switch for that function as well.
    Had not considered a CGFI but since I have not yet purchased the circuit breaker for the chicken coop wiring I may consider that option. Not required by code but probably prudent. $100+ cost delta really pokes my 'cheap' button.

    I grew up around electric ceramic kilns. Simple and clean.
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You might get by with CGFI since it is purely resistive load, but controller and SSRs might cause some fits. Though I do have a limit which for the lift actuator, I don't use it to de-energize coils. I have low power toggle switches in series with the SSRs, but, I only have two SSRs that open the high side of each (of the two) coils and in US 240vac, that still leaves the low side at 120vac to ground. If I didn't want to be able to operate the two coils independently, I could do the deed with two SSRs but as opposed to adding two more SSRs, I just added a conventional contactor to open both legs of the incoming power (except control circuit) and that is what I use. I also have lamps to give visual indication of coil power status.

    Even though I strive to be very deliberate in procedure, there have been several times over the last 5yrs that I have forgotten to de-energize or more commonly reapply power.....without incident.

    Best,
    Kelly
     
  8. metallab

    metallab Silver

    Electric furnaces are also nice. However, if you want to cast iron, an electric resistance (Kanthal) furnace does not suffice, it reaches at most 2300 F and cast iron requires 2600 F. I have built a Kanthal furnace for smaller amounts of copper alloys, but for larger amounts (A4 crucible or larger) I use my roaring propane furnace. For cast iron I have a smaller propane furnace which reaches 2700 F.
    With the electric furnace: be sure to de-energize it before putting any metal parts, such as crucible tongs or shanks inside, otherwise you risk electric shock or even death !
     
  9. Smoking Shoe

    Smoking Shoe Copper

    No iron in my immediate future but I have been saving all of the brass from my VW/auto rebuild days/plumbing and where ever else I found some for free.

    I'd like to cast a large (1 meter or larger) sundial for the garden someday. This has been a 20+ year want and the sole reason to collect the brass. When I get to that project I'll assemble the diesel/oil burner parts I have and build a larger furnace. Then I'll think about iron.........
     
  10. metallab

    metallab Silver

    A sundial of one meter ? That requires lots (10-20 kilos) of brass, which requires a 2-3 liter (more than half a gallon == A20?) crucible. and a BIG BIG furnace which roars like a jetliner nearby. Or you can make the sundial from parts which you cast separately and then assembles the sundial.
     
  11. Smoking Shoe

    Smoking Shoe Copper

    Solidworks says, in round numbers, about 200 to 225 pounds (90 to 100 Kg) 700 in^3 (12L ).
    That includes a hefty gnomon.
    With a very thin base, relieved on the back side, the single pour would be in the 100 pound (5.5L) range.

    I might need some help?!?
     

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