I had a go at making a degassing lance this weekend. I decided to try to cast it from refractory. I made the mold from XPS polystyrene board and then used 3lb test monofilament fishing line and a needle to sew the string array into the foam. I dabbed hot melt glue on where each line pierced the exterior of the foam mold so if I broke one line packing the refractory I wouldn’t lose them all. There are two arrays at the two stepped diameters. The monofilament is about .005” in diameter, the idea being the fishing line will burn out and leave an array of fine holes for the gas. I glued the XPS plug in the center to manifold monofilament arrays together and connected it to the delivery tube which is a piece of 5/16” OD 1/8” ID stainless tube I fished out of the scrap bin at work. I ground some grooves in the end of the stainless rod to anchor it in the refractory but I applied a layer of packing tape to the rest of the tube so it would also burn out and hopefully allow the rest of the refractory to float on the stainless tube so the difference in thermal expansion would not break the refractory…..that’s the plan any way. I made a funnel and clamped the vibrator onto the vice. I should have sifted the aggregate out of the refractory applied to the string array area as the aggregate was too big to fit between the strands and inhibited refractory flow but I fished out the chunks and it fill and settled out ok. The OD of the refractory tube is 1” and the OD of the biggest gassing disc is 3”. The refractory portion of the tube is 18” long, just enough to get the stainless out of the furnace. Here it is demolded. You can see some of the remnants of the monofilament. There are 48, .005” holes in the large array and 24 in the smaller array. Hopefully they will generate some small frothy bubbles in the molten aluminum. Here it is going into the furnace. I fired it today and at 1200F furnace temp the end of the stainless tube was just warm to the touch and at that temp I could just begin to blow through the tube so it appears to have burnt out and is still in tact. I continued to fire it up to 1800F. I hope to use it this week. I'll position it above the melt to bring it to temperature to minimize thermal shock before immersing in the melt and applying Argon. We'll see how it goes. Best, Kelly
Very nice concept. I am trying to get my head around did you have to burn out the foam as well as the wire?
Yes, the .005" nylon string and small polystyrene manifold plug that were cast internal to the refractory were burned out. I removed the external foam and clear plastic tube before firing it as shown laying on the bench. I suppose it all could have been burned off the exterior mold too but since it's winter here and I was doing it inside, I wanted to minimize the odor so I made a few cuts and peeled off the exterior portions of the mold by hand. Best, Kelly
Maybe but even dense Refractory is a poor conductor so heat may conduct away up the probe faster than through a refractory sheath. K
Not likely.... Even the carbon gouging rods take a minute to come up to temp.... But i like the way your thinking.
I'm following this Kelly. I watched Oldfoundryman's UTube explanation of the Argon degassing and the reduction in number of passages in his cast iron head. That is a slick way to protect the submerged portion of the lance.
ESC, yes Oldfoundryman's (OFM) lance was the inspiration for this. The trick to such a lance is figuring out how to produce .005" holes, let alone in something that can take the heat and metal contact. OFM machined steel and essentially scratched the vents into the disc halves, then coated with Boron Nitride. I figured it was easier to machine foam than steel and the refractory would do at least as well in molten metal contact and of coarse age well in aluminum service temps. I can tell I'm getting decent gas flow through it but I cant tell if all the holes are clear and flowing and after firing it to 1800F at 100F/hr, so I don't want to stick it in a water bucket to watch the bubbles. Even though it easily fit in the furnace, long term I'm going to need to modify my furnace lid lift so I can position the lance height above or in the melt because the 1" refractory tube wont clear the present hardware. One very pleasant surprise was how cold the stainless tube remained even when the refrctory portion inside the furnace was soaked at 1800F. I could easily touch all of the exposed tube and the packing tape had only melted away from the stainless tube about 1/2" up from the refractory, the rest was in tact on the exposed tube. So the dense refractory and also the stainless steel are poor conductors....which is good (but unfortunately not good at all for making a pyrometer sheath Negative3)! I could actually deliver the a Argon with a plastic or rubber hose. Yesterday I poured 13 cups for 20 lost foam castings and by the end of the day was feeling a bit tired. Did I mention it was 0 degrees F! I positioned my furnace by my shop overhead door, melted metal in my electric furnace, prepared the molds inside, then moved the molds outside, lifted the door and walked the crucibles a short distance outside to pour. We'll see what today brings. Best, Kelly
I think he used cast iron and by seperating the head he could scratch the passages with the cross slide. An angle on the compound rest would yield a tapered slot that could be reduced by facing the piece. The cast iron should hold up pretty well submerged in aluminum. I have used the same little 5 lb cast iron pot in my resistance furnace for twenty years. I wouldn't think a short test in water would hurt your head, it isn't water soluable after it is fired. You might even discover some porosity which might be a good thing.
I hooked a hose to the end of the stainless tube and applied compressed air, wet my lip and rotated the lance. I could clearly feel the little jets of air on my lip all the way around the perimeter of both arrays of the lance so it appears the lost string method indeed did burn out and worked well. However, now I have another problem with my electric furnace and I'm going to have to do a rebuild before I can test the lance. I'll start a thread in the furnaces and construction forum about the mishap that led to this. Best, Kelly
I don't know what is in suspend slurry but I suspect it's a poor conductor, but still, it could be applied thin which would help. The two challenges with any coating are the difference in thermal expansion of almost any metal and ceramic, and surviving metal contact and thermal shock. Before you commit a thermocouple to the experiment, you might try experimenting with a rod the same diameter as your thermocouple, coat it, fire it, see if it cracks or crazes, and if it survives firing, and dip it a few times in molten metal. I think the commercial contact pyrometers have silicon carbide coatings. SiC is conductive and high refractory but I don't now what they suspend and bind it with. Sodium Silicate is another coating that comes to mind. It would have sufficient refractory but I don't know how it does with metal contact and thermal shock. It would be pretty easy to put fillers like graphite in it though. Best, Kelly
Sorry about your furnace failure. I suppose you're going to have to put up the lance for awhile. Will you be putting everything in a box and setting it on the 'projects on hold' shelf?
Nope! I'm going to fix the furnace and get right back in the saddle. New build commences today.... I suppose technically the IFB refractory didn't actually fail in use. If I didn't have to disassemble due to coil failure from my carelessness, it may have chugged along for a long time.....but it was supposed to be rebuildable. The IFB wall was only 1 1/4" thick and it had a 5/8" deep groove cut into that...so only 5/8" minimum wall thickness of IFB. But the thick flanges were also fractured. I can remember being pretty pleased with it all when I built it. Best, Kelly
Well, when the moment of truth came, and I saw the lance glowing red hot, I decided plunging a pressurized untested piece of refractory into a crucible of molten metal, indoors, wasn’t a very good plan……So a little bench testing was in order. Here is a room temperature test with compressed air in water. Since aluminum is 2.7x denser than aluminum, I tested a depth 3x of the molten metal. I didn’t think .6psi would make much difference until I started testing but it turns out it’s only is going to take a 3-4psi delivery pressure which is great news. Looks like it gives pretty good dispersion and gassing action in low single digit psi. Here’s a short video. So with that, I applied 30psig as room temperature proof pressure. The air hums pretty good at that pressure but structurally all seems well. Here’s a video of 30 psig. So now it’s on to 1800F. Here’s a couple pictures Here’s a video and you can see what a refractory wand at 1800F looks like and why I decided to do a little more testing before I jammed that in a crucible full of molten aluminum. Well, seemed to handle 35psig at 1800F. Though even a 3psi lance failure could still splatter things pretty good, I’m really encouraged by this and having proofed at 7x-10x the intended hot operating pressure, I’m ready to have a go with Argon and aluminum this weekend. Best, Kelly
It looks to me that the lance is good to go. If the head was to pop off, what kind of bubbling action would there be with 5 psi squirting out the tube?
