Sand Pot, could it be a salt replacement.

Natlek said:
I did not really understand what you exactly mean without drawing , but what do you think about this? I need to drill a few more bricks to get about 18 inches in height, the hole is 4 inches now ...... 2.5 inch stainless steel tube would be enough for small knive ?
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There are some full sentences not in that quote. Not sure what happened???
I will have to look at it and edit them back in.

For a salt pot, 2.5" would be fine. My concern in a small diameter tube filled with sand is that fluidization may not work as well. I'll have to read up more on the process and size parameters.
 
Another thing that I don't think has been mentioned in this thread is the volume change when you heat up a gas. Taking a given gas (argon, nitrogen, air...) from 75* F to 1650* F will increase the volume by a multiplier of (about) 4. You will need to use about 4 times less gas when up to temperature than when you are cold to have the same amount of gas running through the sand.

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Ok guys update time. I was able to pick up a 50lb box of 70grit (80grit) aluminum oxide. I just got what harbor fright had and with a 20% off coupon it was $39 for 50lbs. It's black aluminum oxide and what thy call 70grit. But knowing how harbor fright operates I was wagering a bet that it was much finer then 70grit. Thy are not going to spend extra money screening out all the fines. So when I opened it I was presently surprised that it was indeed much finer then thy claimed. Yes there is grit in it that I would say is 70grit but most of it is much finer. The first thing I noticed was the weight. It's amazing how heavy this stuff is. It's much much heavier then the silica dioxide I was using. I don't think there will be any problem with this stuff floating out with the gas. To give you a idea to the weight the box is only 10"x9"x8" and weighs 50lbs. That's over 1oz per cubic inch which means a 5"x20" sand pot would hold over 27lbs of this stuff. I will be playing with it tomarow and seeing how much better this works. I'm very optimist about the possibilities.

Studying the book one chart caught my eye and it's a chart showing flow rate for .004 size grains and a range of temps. What's very apparent is the drastic flow rate reduction as the temp goes up. At 1500° the flow rate is 10 times less then when the temp is 32° (0°C) this is a much larger drop then the expansion the gas undergoes when heating. According to my math the gas will expand by a factor of just over 3.5x going from 0°C to 800°C so this does not explain the factor of 10 drop needed for minimum fluidization. All I can assume is as the grains heat up the air resistance also goes up as well which would require less flow velocity to creat a levitating environment.

Here is a picture of the aluminum oxide.
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I spread if out on a white paper to inspect the grains and most of it looks much finer then 70 grit.
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Here is the charts was talking about.
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Do you think the additional weight of the SC compared to SiO2 will be an issue in fluidization? Will it take a higher gas flow rate to move heavier objects?
 
Hmm. Hope that works. The book I was reading mentioned that particles above about a 100 grit size don't allow effective fluidization... too heavy perhaps. I will be interested to see what happens. Man I want to build one of these.
It seems like the most attractive thing about this is as an alternative to a hi temp salt pot. No need to quench into those, and all of the pros remain the same but with the cons of volcano danger and corrosive salt etc. eliminated. Then you could quench into low temp salt, or oil and then temper in lo temp sand pot. You could use your hi temp sand pot as a tempering pot too, depending on the situation.
Must build one.
 
I think the extra weight will actually help the situation. I'm thinking it will allow the pressure to be increased which should help reduce how sensitive it is to pressure fluctuations. I'm also thinking it will reduce the chugging affect, this is where the whole sand surface raises and drops over and over. In the book thy state optimum bed density as 80-100lbs/ft^3 which is right in the range of aluminum oxide. If you go denser then that thy say it can affect heat transfer and require more power for fluidization. Thy also say optimum flow rate is 2 to 3 times the minimum fluididization velocity. This is to get the most heat transfer and even temp out of the sand.

The only reason I got the 70g stuff was because it was cheep-ish and it's a starting point. Also if I can get it to work good with this cheep harbor fright aluminum oxide then it makes sourcing sand pot media a lot easier for other people. I'm heading out to the shop right now to give it a try but one thing I'm instantly churning over in my head is pot construction and forge construction to handle the extra weight.
 
Ok I did a little testing and have mixed results. The testing befor heating went amazing, nice and fluid at a low flow rate. Then I started heating and holly crap this aluminum oxide was releasing some noxious fumes. About choked me out when I went to look inside the pot. Had to step out of the shop till it was burned off what ever it was. It was not pleasant at all, but after it got up to temp it was all gone and ok. So let that be a warning to you guys. I don't know what could be burning but I'm guessing it's some impurities from manufacturing. When I got choked out I shut off the air to the sand and stepped out side. This was a mistake I think because the sand kinda clumped up in the bottom and messed up my fludizing effect. Also the grains look clumped together. I had a wad of kowool in the bottom and the sand clumped onto it because the air was not flowing. So I am letting it cool down and I'm going to start over and keep it circulating the entire time it burns off. I could tell I had a problem because when it was at temp it was not mixing and it was chugging bad when I would turn it up to increase the flow. This told me one of 2 things. 1- I have a plugged bottom and air is forming a large bubble or 2- the heavier sand needs a larger diamater pot to reduce the chugging. The air was flowing along and up the side of the pot. So I'm guessing there was a hole in the clump at the bottom at the side of the pipe. So once it's cold I will reset and start over.
 
Clean SC should not smell bad when heated. Crappy pulverized coal ash sold as SC blast grit would smell like sulfur and suck the air out of your lungs. If it is fusing together when hot, I suspect it isn't pure SC.

I could be wrong, but I think you should have stayed with the SiO2 grit.
 
JTknives said:
Funny you bring that up. I was thinking the exzact same thing. This will make for an easyer build and hole-less pot. Would only work on a proper larger diameter pot. I tried out wool defuser and at least in the small diameter pot I did not notice much if any difference. The only real difference was I was able to insert a steel bar all the way to the bottom and touch the wool where with just the pipe it would stop a few inches from the bottom. But I did video record it and also did a quench test because Salem asked so nicely lol. Once I have wifi I will upload the video.
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I've been thinking about this ..................What if we make a double bottom like on sketch ? As I understand it , it is important that the air evenly mixed sand ? This way, size hole is not that important ? I do not see a problem if sand filled the lower part below the hole ? Since the air enter under pressure will find the way to evenly spread in each hole ? What you think ?

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The cheep harbour fright aluminium oxide grit is crap. It has a strong smell of what smells like fireworks/black powder. And once you heat it it clumps together making the grains like 3-10 times larger. This really impedes the fluidizing effect and causes chugging which can be reduced by reducing air flow but it also does not mix well at all which does not create the even temp we are needing. So back to the drawing board.
 
JT, I want to thank you for sharing the results of all of your testing. It's a great help, and you are saving us time and money by letting us know what doesn't work.
 
Hey guys, the sandpot seems very interesting to me. Thank you all for the experimentation and good luck with further testing!

Is there perhaps already an estimate available for nitrogen consumption?
 
oh, and what about the aluminum oxide being an abrasive? How does the swirling 120 grit stuff attack sharp edges and the surface finish of the inserted blade?
 
This is for HT, so there are no edges and the surface will be abraded a lot more in the post HT sanding. The blades should come out more or less looking like they were sandblasted clean. That is a big plus over normal forge/oven HTed blades covered with scale and decarb.
 
That stuff looks real good Salem. I think we will just have to deal with there being fine particles mixed in. This stuff gets more and more expensive when we start screening it more and more. I'm just about done with the designing of the first sand pot. Been thinking it over for awhile and gathering ideas from your comments. I will post the model when it's done.
 
What size pot are we thinking would be good. I'm drawing it at 5" as that seams like a good user size. Also the larger the diamater the less the sand will rise when we put stuff in it.
 
Ok guys this is what I have silently been working on all this time in the background. The design is rather simple but I feel will work really well for what we need. In my testing the first thing I noticed was the. Sand will come out guerenteed and if there is an opening to the forge the sand will fall down inside and get shot out as super hot flying grit. So the forge top will be welded to the tube and then a 10" guard tube will be welded to it to keep the sand on the lid. The lid has tabs that transfers the weight to the forge body which allows the sand pot to mostly hang. This will remove the need for having a really thick wall tube to support all the weight of the lid and sand. Still planning on using sch40 316 because this will provide years and years of wory free operation. Next up you will notice the gas tube comes out the bottom of the pot and forge. This serves 2 purposes, first it keeps everything centered in the middle. And second keeps the gas tube away from the hot burner and out of the sand which could cause a weird effect with the fluidizing. You might be wondering how we keep the sand from going into the tube. After much research and conversation with a high temp expert and salesman I think we have solved the issue. First a "ZIRCONIA METAL FILTER" will go into the pot and set on the bottom. This will defuse the gas and act as a support base for the next layer. Then a tight fitting disk of kaowool paper will be pressed down onto the zirconia disk. The zirconia is rated to operate at 2000°C so no problem there. The kaowool paper is a felt of sorts that's very dense and used in high temp filters. The kaowool fibers are interwoven and trapped so very little if any will escape. The paper is 1/4" thick so it is rather tough and should be easly punched into round circles. the forge is designed to have 2 inches of insulation on the top, bottom and side(s). It has a 5" Diamater sand pot that is 24" deep which should allow for most things and the over flow ring is 3" high with will catch over flow sand when using it for bulkier items that your forging. So that's about it for now, I'm sure your chomping at the bit to see the pictures. So with out further adue here you go.
Oh and please let me know if you see any problems with this or you have any ideas to make it better.

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Hey JTknives,

Great! Very nice design. I'm glad you found the right air filter.

About the design, the following came to my mind; it is about ease of construction, right now the "air born particle collector tube" is 10" while the forge body tube is slightly larger. This requires ordering two different tubes, while ordering one tube and sawing a small piece off for the collector is easier. I suppose the diameter difference won't be a big problem.

It might also be easier if the top plate diameter would have the same dimensions as the forge body tube outside diameter. You wouldn't need the three lids for support. The collector tube could be welded to this plate on the top. What lasts is something that mates the plate concentric with the body tube, but if the plate will be tack welded to the forge body tube it wouldn't be necessary.

Do you line the kaowool with refractory? I wonder about the size of the combustion area, maybe slightly larger will be better? I suppose the flame of the burner needs some 'room' for proper combustion, but it is hard to tell since I don't know your burner capacity.

Besides this, great work! Thank you very much!
 
That's a great idea, plus that got me thinking about increasing the volume of the catch area to hold all the sand that's in the tube. If you turn up the gas high enough all the sand will come pushing out of the pot. By increasing the fence to 12" I only needed to make it 5" tall. This provides more then enough room for all the sand in the event of an eruption. Let me adjust the drawing.
 
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