Small Kiln Auxillary Melting Furnace.

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

  1. Melterskelter

    Melterskelter Gold Banner Member

    I tried it out yesterday in a cobbled-together configuration just to test its performance prior to making proper enclosures for electrical connections. It did not disappoint. I melted 12 pounds of aluminum in an A20 in just one hour and actually overheated it to 1450 as the metal temp rose faster at the end than expected. So, I am satisfied the basic configuration is good. Now to safely enclose those HOT coil terminations and and at the same time allow adequate cooling ventilation within the enclosure. I’m open to suggestions.

    I didn’t not have a PID in the circuit yesterday and noted that the measured air temperature inside the kiln did not exceed 1550. Direct radiated heat from the coil to the crucible must be the major player in this setup. I intend to put a PID into the circuit. But it looks like it won’t be very active. I suppose it might play more of a role if I add metal to the crucible so that there are longer melt times. Then the air temp may exceed 1800 which I think Kelly recommended as an upper limit.

    Denis
     
  2. Melterskelter

    Melterskelter Gold Banner Member

    By the way, I needed some high temperature insulating rings for the kiln to guard the lugs where the mains were connected to the two coil leads exiting the kiln. With the original Kanthal coils mullite cylinders were placed to prevent shorting between the lead and the metal skin of the kiln. But the fact that the new leads were much thicker than the originals prevented reuse of the mullite insulators. What to do? Getting apperopriately-sized insulators would have meant a special order taking at the least a week or two if I could even find the right size.

    To the rescue: ceramic wool and Sodium Silicate. I simply used a sharpened 1" ID tube to cookie cutter a few discs of 1" wool and a 1/4" leather punch to punch out the center. Then I mixed a couple ounces of NaSilicate and Propanyl Carbonate kicker and saturated the wool discs with the NaSilicate. I popped them into the oven at 175 for a couple hours and they come out hard as a rock and will put up with much higher temps than needed. Practically free and immediately available. I have no worries about them standing up tot he task.

    Just passing it along. I think I will be wrapping my copper jumpers that span from one winding to the next with the same insulating material . I think it will be more durable than mica wire and again---available in 8 ga.

    Insulatoirs for Kiln.JPG

    Denis
     
  3. rocco

    rocco Silver

    Mullite or high temperature ceramic cylinders like you mention are available in a few different sizes from pottery supply places. For example, this particular one from a place near me has an i.d. of 3/16".

    Click on the pic.
    [​IMG]
     
    Last edited: Mar 6, 2021
  4. If the resultant cured sodium silicate is hydroscopic, you may trigger the earth leakage breaker until they dry out a bit....that's assuming they suck up any water. This can even be a problem with normal stove elements if not used for a while.
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    I don't think uptake of water should be a problem. My somewhat limited experience with cured (and no-sugar added) sodium silicat is that it turns to "stone." I accidentally forgot to add weakening sugar to a core I used in a iron a year or two ago. It became so hard and inert that I could not soften or remove it with boiling water, various acids or bases. It simply could not even be chipped out. I ended up scrapping the casting. I'll provide follow up if this is ever a problem.

    Thanks, I did some searching to find easily available commercial products. I spent a lot more time surfing the web and eventually finding nothing suitable than I did making just what I needed in a total time of fifteen minutes. No doubt there is something out there somewhere...

    The one you pictured is from Euclids. It is the only size they show. My leadout connections require a 1/4" hole and theirs is 3/16." In addition, my experience with Euclids has been that they are slow to fill and slow to ship with no tracking provided. My prior order took ten days. So, wanting to fire up again in a day or so, I just made what I needed in the size I needed and am ready to go, now.

    I'll keep an eye on this part. Should it fail it will cause a short to the grounded skin of the kiln which should be announced by a definite pop and puff of smoke and a tripped breaker. But most likely it will prevent that problem.

    Denis
     
  6. Once the kiln is operational, you'd be able to make whatever you want out of fired clay if needed.
     
  7. Melterskelter

    Melterskelter Gold Banner Member

    True enough. Porcelain insulators have a well-proven history.

    Denis
     
  8. rocco

    rocco Silver

    Also available from Euclids and others are what they call thermocouple protection tubes most of the ones I've seem are mullite 12" long, 3/8 or 5/8 i.d, they're sealed on one end so you'd need to cut one end.
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    Sounds like a possible solution. What is like cutting mullite?
    Diamond wet saw?

    Denis
     
  10. rocco

    rocco Silver

    Good question, I'm really not sure. You've already got some mullite tubes that are too small for you to use, experiment on them, a diamond wet saw sounds like good place to start.
     
  11. Melterskelter

    Melterskelter Gold Banner Member

    Might be interesting to try but I am afraid there are other fish to fry... I have a working solution for now, at least.

    Denis
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    I am finishing the rather cobbled-together test build of my small kiln. One item, mentioned earlier, that I needed was insulators for the transition of the coil wire as it exits the fire brick of the kiln. I needed 1/4" diameter holes in insulating plugs. Smaller Mullite plugs, made for the purpose, exist but not in 1/4" ID, so far as I could tell. There were several options to consider. I could have purchased some stoneware clay and molded and fired it. I think that would have been a very good option, but would have involved some time driving around to pottery places trying to find the stuff I needed and I would have had to learn how to properly bisque it and fire it.. So, I elected, instead, to use BluRam refractory which I had on hand and with which I was familiar.

    The results seem very satisfactory. Once fired to 1750, BluRam is very hard and very resistant to breakage. Here is a pic of one of the 10 pieces I molded and fired.

    Insulator1.jpg Insulator2.jpg
    You can see the parting line of the mold in this one.
    Insulator3.jpg

    So, now I will bore 1" holes in the brick and slide these in. I am debatring whether to mortar them in place, use wool as stuffing to hold them in place, or (less likely) just slide them into holes and lead the wire out through them.

    Denis
     
    dennis likes this.
  13. dennis

    dennis Silver

    Would this stuff make good plinths?

    Would it cope well with direct flame?
     
  14. Melterskelter

    Melterskelter Gold Banner Member

    The most durable plinth I’ve made to date and am still using is made of BluRam. It has significantly outperformed Kastolite and dense castable plinths I made in the past.

    Denis
     
    Billy Elmore likes this.
  15. Billy Elmore

    Billy Elmore Silver

    I agree. The one I made out of it has been bullet proof. Think we may need to throw some more of it out soon if shelf life is gone....may need to go look at the dates and see if it is free to me yet.LOL
     
    dennis likes this.
  16. dennis

    dennis Silver

    Perhaps make plinths for sale?

    (I might be able to make molds...)

    Chief issue for most is sourcing BluRam...)
     
  17. Melterskelter

    Melterskelter Gold Banner Member

    That outdating of BluRam is interesting. Since it is a moist product in a poly bag, the manufacturer must figure it very slowly looses moisture. The outdate must be a conservative guess as to when too much drying could occur. I’ve found that if a partial package seems be getting dry, just putting a tablespoon or two of water into the bag reconstitutes the mass of refractory. I don’t bother to mix. Just letting it sit for a few days to a week seems to result in uniform distribution through diffusion. So, if I notice a bag seeming a bit drier than I like, as I finish what I am doing, I toss in the water and twist the bag shut. A few days or week later that water is well distributed.

    My (currently) favored plinth design is a hollow truncated cone shape with walls about an inch or inch and a half thick. It has held up well. I’ve been using it for a year or so and looks like hell. But it is holding up the crucible.

    Denis
     
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  18. Billy Elmore

    Billy Elmore Silver

    I think they only put an expiration date on it to sell more. I dont have any issues using the old stuff! I like the old refractory we throw out as well!
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Maybe Petee will chime in. IIRC he had a stash of BluRam that was many years out of date and seemed to perform fine.

    Best,
    Kelly
     
  20. Melterskelter

    Melterskelter Gold Banner Member

    Just a couple more notes on things I am learning as I build out this kiln:

    I did manage to break off the twisted pigtail on one of my coils. My own fault for horsing the wire when installing the leadout tubes shown above. I though it might be possible to tig a piece or the pigtail itself to the coil. Well, you can, sort of. I was able to join two practice pieces without too much trouble with my tig using a scrap of wire as filler. But where the intact wire meets the join seems to be a weak spot prone to cracking after the weld cools. I tried annealing the area without much success. So, my conclusion for now is that tigging does not seem to be a solution. If someone knows how to do it, I'd love to know.

    This seems pretty obvious, but heating the wire definitely aids in twisting it and seems to reduce/eliminate a tendency for the wire to work-harden and break in the twisted area. The wire comes 3/4 hard. But using a propane or MAPP torch to heat it to a medium (not bright) red and allowing it to air cool does make it noticeably softer for a while. More bending hardens it. So, I found heating a segment to medium red and twisting it a few turns followed by more heating and more twisting seemed like a good way to go. I will not say I know that is the BEST way to go. But it does seem like a good method. Again, comments from those with other or better experience would be appreciated.

    Just posting this for the benefit of "the next guy" trying to sort this all out.

    Denis
     
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