Furnace Fail & Reconstruction

Think I gott’er whipped boys.

I made a couple simple forming bucks and beat some shape into a cap for the furnace lid



There’s a little tab at the rear of the lid that allows it some motion for the lid to seat but not flop around.



To make them a little more durable, I put a thin coat of mortar on the IFB holders for the degassing lance, pyrometer, and the lid plug, and made a rack to hold them.




Here’s the plug and Pyrometer in place



…..and here’s the degassing lance.



Think I’ll melt some metal tomorrow and see how that degassing lance works.

Best,
Kelly

 

Thanks for the comments guys. During the reconstructi0n I tried to add some features that operating experience over the past year suggested could be beneficial. Seems to look the part......now it just needs to work as planned. The maiden voyage heat seemed to go well. It's only 5F outside this morning with some wind so likely an indoor melt and mold prep followed by outdoor pour. I have 6 small foam patterns I can cast for a trial run that should provide an opportunity to test the degassing lance. I think using the lance should be fairly straight forward but in use video may take some doing.

PatJ, the stainless is a great choice for the skin but as you mentioned, there's a big difference between working it and pushing around some thin gauge mild steel sheet but it should do very well in service.

Besides testing the lance, I'll be interested to see how the shell temps on the furnace compare to the previous IFB liner. I still have some other improvements to add to my rig but they can wait for another day. I'll report back tonight.

Best,
Kelly

 

I had a small casting session today and have a few pictures and a handful of videos. I should have looked at my Argon bottle regulator a little closer because it was not easy for me to tap it for the degassing lance but I did kluge something together. I preheated the lance in the furnace and it came out of the furnace red hot. However, I kept blowing the hose off as I was feeding it Argon. My Argon regulator is the style that the second stage feeds an orifice and doesn’t display pressure, but instead indicates flow. I decided I had better put a gauge on it and when I did, I was up to 10-15 psig before I could detect any appreciable flow out of the fine array of lance holes. I decided I wasn’t comfortable putting higher pressures to red hot refractory and then stuffing it into a crucible full of molten metal indoors. If the head came off the lance the expanding gas would shower me and my shop in molten metal. Sorry boys but I need to do some more bench testing.

I did proceed to cast some parts for the maiden voyage of the rebuilt furnace. It worked well. I have some videos of the day’s events for those of you that like those.

Here’s walk-around description of my rig along with some of the new features since the rebuild.



Here’s the lost foam patterns for the today’s session. Six thermostat housings paired up on three pouring cups.



Here’s everything staged and ready to pour. Flasks are vibrated and packed with patterns and cups in place, and furnace has a charged crucible and is on its way.



Here’s the pour. It started snowing outside and I had to move the flasks out of view because the wind would have blown it all back in my shop.



Here’s shake out and quench video



Here's a video of Tstat castings as cast



Here are the de-gated castings and a video inspection of them





Not being able to test the degassing lance was a little disappointing but if you would have seen it glowing red you too may have thought twice about twisting up the pressure and stuffing it in the molten metal…..just wasn’t worth taking a molten metal shower or burning my shop down. I’ll do some more work on that. I’m very happy with the furnace. The shell temps did seem somewhat higher but not significantly so. One positive I did notice is it holds heat better. The dense refractory took a little longer to come to temperature but once that that 60lb lump got there it did the job nicely and the furnace temp recovered very quickly after being opened due to the extra mass.

Best,
Kelly

 

To be honest, the lance was bit of an impulsive on-the-fly build which is not the norm for me. I was focused on a fabrication technique for building a lance with very small holes, high refractory, and molten metal resistance. If the holes are .005" in diameter and there are 72 of them, it's the same area as about an.043 orifice. If the 72 holes are .003" diameter, it's about the same area as a single .025" orifice. I need to give some more thought to the volumetric flow of Ar this suggests. I also hadn't given much thought to the what ifs...

Everything may be just fine because the flow through each hole may be very hard to detect at only 5-10 psi but still fit for purpose. When I tested it I just pointed my blow off air nozzle at the end of it and I could feel the air around the arrays but I suppose that could have been 30-50psi if I was holding it tight against the lance inlet.

The regulator on my Argon cylinder was behaving strangely and when I shut the bottle valve down the pressure down stream would rapidly climb and blow the silicone hose which was loosely retained (which was a good thing). It seemed to slip at about 10 psi. I was going to clamp the hose when it occurred to me I didn't know what the pressure might spike to and I was about to jam an untested piece of pressurized red hot refractory into 10lbs of molten metal.....inside in a room with combustible material, tinder, and some solvents in the cabinets.

So I decided instead of the pneumatic kluge I had, I'd rather set up a known regulated source with a gage, and bench test it before I potentially had a small compressed air explosion in a crucible of molten metal......inside my shop! Popping the end of that lance at 5 psi would be one thing....but 50psi is another and yes, I want to test to 5x hot operating pressure and install a relief valve. When I pulled the lance after preheating it above the molten metal, at 1800F it was literally glowing red and that along with all of the above, helped crystalized my thoughts and focused my mind.

I'll post up more in the lance build thread.

Best,
Kelly

 

Sometimes the carbon sheath leaves a ring of carbon on the surface and this was one of those times. I usually do the final skim in the furnace but just forgot to this time. It was nearly 1600F and with the part size being so small I figured I had plenty of time or I would have stuck it back in the furnace.

I did not. The sand had been sitting in a part of my garage I keep above freezing but not much above. It was in the heated portion of my shop after packing for about an hour but I doubt it heated up much. It's actually the pouring of the thin stream through the cold air that seems to make the biggest difference and that is why I gave it another +50-75F than usual. The small parts aren't much of a challenge.

For small parts and single pours yes. I also pour on wooden flasks.

Those small parts are pretty boring. Very little foam being vaporized and not much going on with them.

If I had waited a few hours I would have had to shovel a bare spot to place the flasks!

Best,
Kelly

 

Thanks Pat. Small aluminum pours in a rig with which I have many melts and experience seem ok but familiarity can breed contempt and showering me, the shop, or even the interior of the furnace I just spent two weeks of spare time rebuilding didn't seem wise.

Yah, just not worth it under the circumstances for the reasons I mentioned. I'll be back at it after a little further thought and investigation.

Best,
Kelly

 

Explosion is a relative thing, just like aircraft landings.....it's just a matter of how hard you hit the ground. There's not much volume in the lance and if you keep the pressure low there will never be much gas to expand. If it's inside the furnace, that's probably the safest place. Also need to make sure it is redundantly isolated/protected from cylinder pressure. There isn't going to be enough gas to explode the furnace but there certainly is enough to splatter molten metal everywhere. But I'm not anxious to shower the inside of my furnace and brand new heating elements either. If its integrity is in that high of doubt, it shouldn't be used thus my decision to do a little more investigation and testing before using it.

Best,
Kelly

 

Yes. The resistive alloys are primarily Nickel and will readily alloy with Aluminum at their operating temps which will severely reduce its melt point. Once aluminum touches a red hot NiChrome coil it wont come off and it will fail locally shortly thereafter. A careless splash of Al is what started the chain of events in motion that prompted my recent rebuild.

Best,
Kelly

 

Thanks J. I have a thread started in the foundry tools section for the lance that Ill be posting progress reports.

I have 1/4"thick refractory felt gaskets on the furnace base, lid, and lid plugs so the furnace seals up reasonably tight (I plug the drain hole too). When I was melting wheel weights for the lead, the furnace would flash when I lifted the lid from all the crap melting and volatilizing off the weights so it apparent seals up tight enough that it oxygen depletes. Even so, I think it would still take quite a bit more Ar flow to inert the furnace than degass a melt and that might get a bit expensive. I was thinking more along the lines of a crucible hat that slid over the lance shaft and sat on top the crucible rim for that but getting the lance in and out of the furnace and through the lid gets a little trickier....but doable. With that small of space I'd say that definitely would provide an inert blanket to the melt but not sure it's worth the pain beyond degassing.

For heat treating small steel parts (in either this or my larger furnace), flowing the Ar through a stainless can or a stainless foil pouch with or without flow is the chosen approach.

Stay tuned.

Best,
Kelly

 

Thanks CBB. ESC suggested a water test too and though I balked at that then, tend to agree now.

I think it's going to be water first to see what sort of pressure gets results, then a dry room temp proof pressure test at 4x to 5x that pressure, then and dry 1800F test at same pressure. The high temp test should cook off any residual water. I'll just let it bake a lower temp for a while before taking it up to temp. If it survives all that it may be ready for molten metal.

Best,
Kelly