Small Kiln Auxillary Melting Furnace.

Discussion in 'Furnaces and their construction' started by Melterskelter, Jan 30, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Here are a couple posts about the winder when I did my dense refractory furnace.

    http://forums.thehomefoundry.org/index.php?threads/furnace-fail-reconstruction.209/page-3#post-3660

    http://forums.thehomefoundry.org/index.php?threads/furnace-fail-reconstruction.209/page-3#post-3670

    ….and some more here about the coils when I did my low mass furnace.

    http://forums.thehomefoundry.org/in...w-mass-electric-furnace.607/page-4#post-16069

    There are some other useful tidbits in the links above but it’s devilishly simple. Here’s a sketch of what works best.

    8 Winder Sketch.JPG

    ……and here it is in action, but before I was smart enough to position my phone correctly for video :):



    When you make the simple winder, cut a 12” piece of your wire and do a test wind or two.

    When you’re ready to make the actual coil:
    1. You’ll want to premeasure the desired wire length and add and mark straight leads on each end.
    2. Whatever length you need for your external connections increase it 50% because when you double or triple with a twisted wire to reduce the resistance the length will shrink. This reduces the wire temp so it won’t alloy at the electrical conductor outside the kiln.
    3. Try not to nick or gouge the wire with pliers because it can produce higher resistance hot spots. You’ll probably need to make a small clamp and T-handle to twist up the leads. With 12ga, they will be stiff.
    4. I’m assuming you already have and will want 4 separate coils that are connected in series outside the furnace, so the active coil length without leads is ¼ your total length/resistance. This will help winding because my arm was barely long enough to reach the drill because my solid length was long. You should have no problem.
    5. When you go to stretch them, anchor one end/lead and hold the other end tight and stretch the whole coil until it is the desired length after it relaxes. This will give you a nice uniform coil spacing throughout the length of your coil. I just held a tape measure alongside the coil as I stretched it.
    6. Then double or triple up the leads and they’re ready to install.
    7. For the stretched length, calculate Pi times the centerline diameter of your groove/shelf. Sometimes using the OD works better. Try centerline on your first coil, test for fit, and stretch further if needed. Having the coil slightly over length so it is compressed in the groove can help it stay put in use.
    Happy winding!

    Best,
    Kelly
     
  2. dennis

    dennis Silver

    I have heard/read about using a lathe for winding coils.
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'm sure a lathe can work, but the winder in my diagram can be made from two blocks of wood. Takes 5 or 10 minutes to make a jig that winds perfect coils. In those links, I discuss when I started, winding on a 3/8-16 threaded rod, and I thought I was being clever because the wire diameter (.063") matched the pitch of the 3/8-16 thread so I thought the wire would lay down nicely in the root of the thread. It did but every two inches or so of solid length it would bind and jump a wound diameter or a thread. If you use a smooth rod and feed at the tangent point of the rod against the surface where the rod emerges, the wire radius lays down on the side of the previous coil and naturally advances the winding rod. So this method will work for any diameter wire and winding rod as long as the winding ID is >3x the wire diameter.

    On my initial winder I also had a spring loaded block to vary the resistance on the wire feed. It worked.....sort of, but controlling it with your own grip worked better so I don't use that feature.

    You could do it on a lathe, set the carriage advance as desired like threading, but you'd still need to make something to clamp the wire on the rod and feed/tension the wire tangent to the rod. You might also experience rod wip or deflection without a steady/follow rest.

    That coil I wound in the video was 63ft of 14ga wire wound to a close-wound length of about 31".....that's almost 500 revolutions/coils in a minute or so. If you have many feet of wire, it does help to put the premeasured length on a tensioned spool. I was stopping and starting the wind in that video because the coil was unwinding on the bobbin on the floor and then tangling ahead of the winder.:mad:

    Best,
    Kelly
     
  4. dennis

    dennis Silver

    Nothing near that complex, but I wasn't winding thick evil KanThal wire, either. If I need to wind resistance wire in the future, it will probably be thinner than 12-14 gauge. I'm guessing 18 gauge, as the oven will be both smaller and (probably) a good deal less warm - probably no more than 500 degrees for the larger, and the 1600 degree one - for heat-treating - is likely to be very small...

    Also, 220 takes real doing to access here.
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    I'll be copying your design for the winder, Kelly. the way it self-feeds is really slick. To tension wire for making springs on the lathe I have used a lever with two pegs that cause the wire to experience some drag depending on the angle of the lever. I think I'll do that here as well. I do not know how long it will take for Euclids to ship my wire. But, I am anxious to get it into the furnace.

    Thanks for the post above.

    Denis
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Just a little follow up. Euclids advised me today that the order has shipped. This is 8 days after the order was placed. No tracking information given. I guess I am spoiled by the various online sources that usually get an order out in a day or so at most and provide tracking info. Oh well, today I am recovering from my 2nd Moderna vaccination and don't have tons of energy anyhow. Fever and aches last night, mild fever and some ache today. Well worth it though in my opinion.

    Denis
     
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  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    As I recall the comms weren't great but I always had the order within 8 days......might be someone (kiln pottery supply house) a little closer to home for you, but you gotta beat the bushes for someone that'll just sell you what you want buy the lb.
    Good for you on getting it....hope the side affects subside quickly. If it's any consequence, my 24 year old daughter is a health care professional and also felt poorly for a day after her second, but after that no issues......oh to be young.

    Best,
    Kelly
     
    dennis likes this.
  8. Melterskelter

    Melterskelter Gold Banner Member


    And, just like a switch was thrown, I started to feel normal about 24 hours after the vaccination. And this morning I am rarin’ to go after packing a mold yesterday afternoon. Total duration of mild symptoms was about 16 hours—-nothing compared to the potentially fatal or long-term damage from Covid. And, once again, so glad for the opportunity to be vaccinated.

    Hope to be pouring iron in just about 4 hours.

    Denis
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    My 12 ga Kanthal A1 came yesterday. I have 63 feet and need 55 feet of resistance wire to hit my 8kW goal. So, no room for screwup considering the need for doubling up the connecting ends.

    With respect to coupling the mains to the coils, what are preferred connectors? I was thinking of using short sections of appropriate-sized stainless tubing crushed using standard compression pliers for crimped connectors.

    I did try a short test coil and found that coiling it over .250 round bar results in a coil that will just slip into the existing slots.

    Denis
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Measure twice, cut once!
    I've used ceramic wire nuts, home made stainless lugs, and just stainless screw-washers-nuts, in all cases wrapping the conductor around the doubled Kanthal lead so the lug wasn't really conducting, just binding contact.
    I use high temp wire appliance wire and buy from these guys. Nickel plated copper MG wire has much higher ampacity than normal wire and very high service temp.

    Industrial Cable - Hi Temp (125C-538C) - Page 1 - Pro Wire and Cable

    McMaster also has it and several lower grades and will give you some indication of current rating at temp. The also have ceramic wire nuts but too small gauge, and frankly, they don't work well with hard doubled Kanthal.

    https://www.mcmaster.com/high-temperature-wire

    Just curious, what how was your kiln originally set up? Usually they just have a twisted pair run some length out to a well ventilated enclosure and lug in a ceramic body. The combination of the twisted pair and in-air length drops the temp of the resistive wire, and that might result in low enough temps where nothing special is required. I bought some lugs from Euclids and they looked like ordinary copper to me. I'd just recommend you use something that is reconnectable. I did have a failure wear the MG wire conductor alloyed and melted, but it was a single lead of Kanthal and not routed in open air. Tripling the Kanthal lead and it has caused me no trouble since, but you might want to give yourself enough external lead that you could snip off and reconnect if needed.
    Good deal. Time to get all wound up.

    Best,
    Kelly
     
  11. Melterskelter

    Melterskelter Gold Banner Member

    I wound my first coil this morning. It went well. I did it on my lathe. Its coiled length was 14.5inches though I expected 16. The coiled wire length was 13.75 feet. The resistance measure 1.7 ohms with my simple multimeter and that was the target. It it currently stretched to 44” with an expected need for 48”. That puts the ratio of wire cross-sectional diameter to peak-to-peak distance just a little more than 3.5 which I take to be in the target range.

    In other words, so far so good. 3 more coils to do. Who knows how tricky bending it to fit into the grooves, particularly the corners, ay be.

    One safety handling note: I would strongly suggest folks wear a face shield when stretching it. It takes maybe 30 to 40 pounds of pull. If the far end comes loose, this 12 ga wire or even smaller wire could do some serious damage, particularly to an eye. I think it could also make a deep stab into the chest if it struck just right.
    Denis
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'd rely on the ohms/ft figure they provided with the wire as opposed to measured resistance. The resistance in the probes of inexpensive multimeters can be significant, but either way it's a good reference.
    You're in good shape being on the low end of stretch.
    I'm sure 12ga on that small diameter is stiff. You'll probably want to be stretched pretty close to the nominal installed length....only slight overstretch/compression. Fit them up well. They get more brittle after multiple heat cycles.
    Good advice. I figured 12ga on that small diameter would be a stiff bugger......but I would think it will make a durable element for you.
    Best,
    Kelly
     
  13. Melterskelter

    Melterskelter Gold Banner Member

    Actually, I did carefully measure the length to be coiled and marked it out with Sharpie. But, it is nice to see that crude measurement at least agrees with calculated target. Something like measure twice, cut, and measure again.:)

    Denis
     
  14. Melterskelter

    Melterskelter Gold Banner Member

    An observation or two on coiling 12 ga Kanthal A1.

    I was concerned as to how much torque it might take to wind a coil and whether a 1/4" mandrel would be stiff enough to not itself wind up into some sort of bird's nest. My conclusion is that Kanthal is moderately stiff, but not a lot stiffer than copper of a similar guage. The 1/4" mandrel never tended to twist into a kink. I will qualify that saying my setup on the lathe supported the manderl pretty well and I kept a close eye on it as I wound the coil at a few RPM. A length of 13.5 feet of 12 ga wire wound onto a .250 mandrel resulted in an unstretched coil length of 14.5 inches.



    Making doubled-up ends is necessary but at first was not easy. I found that starting with a nice tight bend on the folded-back wire was a help and made for a smaller bundle that needed to be joing to the power supply. Making that bend is tough if bending cold wire. But if you get the wire bent back on itself fairly well and then, using a Mapp or propane torch, heat the tip and finish the bend while hot works slick. Kanthal softens a lot when heated to a dull red. Once the wire was bent back on itself tightly, clamping the base of the loop in a vise with aluminum or copper soft jaws and grabbing the tip with a Vise Grip was the way to go. By at the same time putting traction on the loop and twisting the loop a nice neat doubled end could be quickly made. It took a few clumsy tries to figure this out. I would think that lighter guage wire would not need the heating. But the 12 will break if bent sharply when cold---like hammering the tip loop shut.

    Doubled Tip.JPG

    Also a caution on using heat to straighten Kanthal. The wire will draw out if heated to red and will stretch and thin like taffy.

    Kanthal does not spring back "very much." I need to actually measure this. But after winding it on a .250 mandrel, the coil still fit inside a .422 recess in the winder tool I made. The wire is about .80 diameter, so two thicknesses of it plus the mandrel would be .410. So, springback was very mild.

    The stretched coil can be compressed a bit or lengthened a bit by either squeezing adjacent loops together a skosh using needle-nosed plier and similarly can be lengthened using a needle-nose with a couple small notches I ground (old plier) on the outside of the jaws. The notches prevented the plier from slipping off the loops. You can easily feel the wire yield when you compress or stretch it past its elasticity (spring back) limit.

    More tomorrow. I expect to fire it up in the morning. But I still need to connect the elements in series and fit and connect a couple elements.

    Denis
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    When I saw you winding it on the lathe I thought you were advancing the carriage under power feed but it was just self advancing through the winding lead....correct?
    Ya-know, I'm not sure can't remember comparing my actual solid wound length to the calculated length. If you assumed all the deformation was stretch and calculated off the your mandrel diameter, I get 16.7" solid wound length. If you assume no stretch and all compression at the mandrel OD I get 10.4". Obviously you get some of both but since it would be 12.6" at the wire center line. With your 14.5" observed solid length more wire stretch near than OD occurs which makes sense, but it can affect your min/max stretch targets.
    I haven't had to heat it to work it but that is using one of Kanthal's liabilities to advantage......it has poor hot strength.

    Best,
    Kelly
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    Today I actually hooked the furnace up to see if there was a Fouth-of-July fireworks display. Nope. All seemed good. I measured its current draw on 240 and it read 33.3 amps ons tart up---right on target. After a few moments the draw decreased to 32 as the resistance of the wire increases as it gets hot. I only ran it ofr a few minutes and did not time it but it did heat to over 1000 degrees F in just a few mins. This was far far faster than prior to changing out the original coils for the 12ga coils. Interestingly the original coils were quite fine wirw and barely stretched. So there was barely a wore sidth of space between adjoing loops. That coupled with the fact that they sdat well back in grooves had to reduce their efficiency. It looked like they were probably factory originals.

    I am very anxious to put some aluminum in it tomorrow and try a melt and pour.
    That loss of hot strength may be a problem when it comes time to make my heat treat (for iron not al) oven. Does anyone have guidelines as to spacing of supports for a given guage of wire. Or does it have to be continuously supported in the way it would be if draped in a tray or skewered by a ceramic bar?

    Denis

    Denis
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Good deal. Hope it's a good performer for you.

    Seems strange for an OE kiln coil. Too close of coil spacing causes higher localized element temps and reduced life. In any case, your better off and souped up now.

    If it's just heat treating, you don't really need the upper temp limit of Kanthal and might better off with NiCr 80/20. It does have better hot strength albeit at lower temps but I'm not sure it changes the how to package the element much. The Kanthal handbook shows three examples of wire elements. Coils in grove, coils on rod, and draped/corrugated wire elements. That is listed from lowest to highest as far a loading with a corrugated wire in free space being best in that regard.

    The problem is the wire doesn't easily train into straight sections with 1/4" radius u-bends. You probably noticed it has circular memory coming off the spool. If you stretch/tension level it might but I'd tell you the stuff will move all over the place through heat cycles if it is not constrained. I've seen a couple home made electric furnaces that have straight loops on the furnace wall and they work for a while but usually end up a total mess.

    Other than coils on rods or grooves, we previously discussed forced air. You could wrap a coil around a large diameter ceramic tube and force air through it. What is the highest operating temp required for your heat treating?

    Best,
    Kelly
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    I see I neglected to answer a prior question regarding self-advance of the lathe carriage vs power feed. No power feed was used. I just let the carriage move of its own accord.

    And I did measure the spring back. It was only 10 thousandths on my 1/4" mandrel. I was expecting more before I began winding.

    Since I intend to line my heat treat oven with wool, I am wondering just how to suport the wire. Lots of thoughts whirling around.

    My max heat would be annealing temp of 1750F.

    Denis
     
  19. Melterskelter

    Melterskelter Gold Banner Member

    BTW, this is a pic of the heating element I removed: Original element now removed.jpg

    The wire measures .045". So it looks like it is 25 ga.

    Denis
     
  20. Zapins

    Zapins Gold

    I love that loop back melterskelter, I cut a piece and wound it up by hand but bending it back and twisting would have been way better. Next time I'll do that!
     
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