Sand Pot, could it be a salt replacement.

Thank you for sharing, and you've got it working GREAT!!! As you said, add a TC for temp control..... and using N2 I'd expect scale to be no problem.

I wonder if the temperature could be increased to 1950ºF range to work with SS? With Nitrogen perhaps no need for foil wrapping?

Good job! Ken H>
 
Hey guys, I usually just observe on this forum, but I have to comment. This is fantastic! I will be tracking this thread with huge interest and looking for anything I can do to help. JT thank you! I really think you are on to something big here.

Dan
 
JT, what did you use for the 'diffusion plate' part, or did you just run the SS tubing in and pump air through it without a fancy plate???????
 
Also, do you have any indication about what is the best media to use for the actual sand, and where to get it?
120 grit white aluminum oxide abrasive can be found in 25 lb quantities online for pretty cheap. That's what Peters HT uses?
I notice in the notes on that stuff it states that it withstands extreme temperatures and is used in refractories...
 
Fiddleback said:
JT, what did you use for the 'diffusion plate' part, or did you just run the SS tubing in and pump air through it without a fancy plate???????
Click to expand...

That's my next question.

If you had some sort of fine diffusion and regulated the pressure, it may be less "bubbly"

Maybe something ceramic and porous like they use for fishtank bubblers
 
I have been doing some interesting reading on the subect. There is a lot of info online, including a good book on Google books- the preview covers the entire fluidized bed furnace section.

Some cool things: You could use the same pot for hardening and tempering. The media will work for both temperature ranges. Although a guy might want to have two running for this, still it could be handy. I know folks who harden in a forge and temper in salt... also, you can quench into a fluidized bed. From what I read, it can achieve the thermal transfer rates of slower quench oils. So, marquenching and austempering could be possible.

I have to read more.
 
From a book...
"The greatest heat transfer rates occur with Type B media, which include aluminum oxide. Of these media, aluminum oxide provides the best heat transfer capacity, thermal stability, and uniformity."
And:
"In general, the optimum heat transfer on heating and cooling is achieved with particles in the range of 100-125 micron. If the particle size is less than 100, the uniformity of fluidizing deteriorates,and if the particle size becomes greater than 250, the use of gas becomes uneconomical."

Looking at conversion charts, 100-120 grit equals about 122-102 micron. So, it becomes apparent why Peters would use 120 grit aluminum oxide. Seems like that's the smallest particle size that affords uniform fluidity, which should be the most economical in terms of gas consumption.
 
I think it could work at 1950° As well you would just need to pump in more btus to get the sand temp up. but I don't think temp has anything to do with it's effectiveness.

One thing is very apparent that I relized after I woke up thismorning. That is I need a larger diameter tube. If you watch the sand you will see the entire sand lift and then kinda burp. I think this is becaus of the small diameter of pipe uses. I think it's building up one big bubble that lifts the sand. If the sand pot was larger in diameter I believe it would work much better in the boiling effect.

I did not diffuse the gas I just put inserted the stainless tubing into the base of the tube so it was about half way inside the sand pot. I don't know if a dufusing screen or thing is needed. The sand is not water where a bubble will flote to the top. The air is being forced in and only rises becaus the sand is falling into the bubble space so I think the sand it self will defuse the gas.

I need to find a better sand media, this silica gel "silicon dioxide" is problematic becaus of the water issues. And becaus of how fine it is it it just comes out of the tube. It's all over the shop and now I got a big mess to clean up besides my normal shop mess which after looking at the video is quite messy lol. But I think proper grit size will be the ticket in getting this even better. I was looking and harbour fright has aluminium oxide blast media in 50lb and 25lb bags for a good price. Thy have 70grit black aluminium oxide which might be perfect. Black might absorb the heat better any ways as it will catch more radiant heat I would think. 70grit is sized at a average of around .008 with a range of .003 to .013 grain size. The stuff I'm using is so fine it feels like powder in the hand. When I go back out into the shop I will mesure it with the callipers. One sec I will go do it right now lol

Well I'm back, my measurement says like .002-.0005 which for a calaper means about nothing lol. But then I looked on the side of the drum and it has the size right on it facepalm. Says from .063mm to .200mm and also 70-230 mesh ASTM.
So it looks like thy clam .0025 to .0079 particle size which I find hard to believe as it seams finer then that but maybe it's because it is very light weight.

Another thing that came to my mind was thermal conductivity.
Aluminium oxide has a much greater thermal conductivity then the silicon dioxide.
Silicon dioxide is between 1 and 2W/m°K where aluminium oxide is from 18 to 35W/m°K. This means much greater efficiency in absorbing heat from the tube/forge.

Next thing to look at is density. We need a little more density then the silicon dioxide but not to much more because we want it to flow.
Silicon dioxide is 135-165lbs/ft^3
Aluminium oxide is 230-240lbs/ft^3

This means each grain will be a bit heavier which should reduce the stuff flying in the air.

Last thing to look at is Specific Heat, this is the heat energy needed to raise the material by x deg. Higher the better because when we insert steel we are absorbing that heat into the steel. And a higher Specific Heat material will have more Energy to donate to the steel before it looses temp.
Silicon dioxide is 162BTU/lbF°
And aluminium oxide is 210BTU/lbF°

Aluminium oxide takes more energy to increase the temp but that's good because the total energy in the tube us much higher with aluminium oxide.
But aluminium oxide has a higher density by a factor of 1.45 to 1.70 so this greatly affects the total energy in the tube as well because a tube of aluminium oxide will weigh more then silicon dioxide and specific heat is a function of BTUs per pound to rise it 1° f. This means you can multiply the 210btu for aluminium oxide by 1.45-1.7 to get a true comparison between silicon and aluminium oxide for the volume the tube holds. This number is 304.5 to 357btu/lbF° so much greater energy density with aluminium oxide. Take this number and devide by the specific heat of silicone dioxide we get about a average of double for aluminium oxide. Which means a sand pot full of aluminium oxide holds twice the energy of a pot full of silicone dioxide. This means it will take longer to heat up but will hold the heat longer and not drop in temp as greatly when steel is inserted. But aluminium oxide also conducts heat much faster then silicone dioxide by a factor of about 20 so you never know it could heat much faster as long as the forge puts out the btus faster then the tube and sand sucks up the heat.

The last key point to look at is melting temp. Higher temp is a good thing in this case.
Silicone dioxide is 2912°
Aluminium oxide is 3762°

So peters is right on the money for using aluminium oxide. Plus it's cheep which is good.


Wow sorry for the rambling on like that, but it's my way of processing data and comparing things.
 
Wow I did all the math and calculating and I could have just found the info if I had stronger Google-foo like Salem lol
 
Just ordered that book "Heat Treatment in Fluidized Bed Furnaces" and it will be here on the 10th. Should have everything we need to know in it.
 
JT, (that was my Uncle's name - JT. Nothing else, just "JT") - you sure did some thinking 'n figuring and it all makes sense. It looks like your tube is around 2" ID? Do you think 4" pipe will work good? Larger? Wouldn't a ceramic pipe be good? Just wrap it with heating coils and much easier to build than a electric oven - I think anyway.

Looking good.
 
I think the electric could work but not sure, as the incoming air does cool the sand, not much but it does. I think a larger tube will work a lot better. I'm currently on the hunt for for a larger tube. I have some thick wall well casing but I would love stainless as I don't know how the well pipe would hold up. The well pipe is actually the business end of the drill pipe that's hardened steel.
 
From my research, 120 grit white aluminium oxide basting media would be the thing to use. Get the 99.5% pure grade.

The higher percentage of 120 grit, the better. Most blasting grits are "XXX and finer", with the grade grit being only 40-50% ( thus 120 grit would be 40-50% 120 grit and the rest finer particles). Ask for a 75% or higher accurate size grade. You will pay more, but you aren't going to be throwing it away in use like you would in sand blasting.


I think the grit grade tolerance will be a factor in getting the fluidizing effect. If there is too much smaller grit, the small particles will either get blown out the top, or pack between the larger grains and impede the fluidized process.
 
That's the problem I think I have, the fines just blow out and settle all over the shop. Launching a mortar tube of hot sand all over did not help either. But I'm wondering if we would need that thick of a stainless tube. You can get thin wall stainless tube for cheep at around $25- $30 a foot for 4" diameter exhaust tubing. The only problem would be structural support but if you hung the tube from the top then I think it would be ok.
 
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Perfect timing. I was going to build a salt pot in the near future, and was going to go order steel for my press and salt pot next week.
 
I just ordered the book. This is totally doable from what I've read.
 
Looks like 5" diameter .065 wall stainless tube is available from any place that sells muffler stuff. And it's cheep, but I wonder how well the thin wall would hold up to the heat and if it would support the sand.
 
Found a 13 page PDFs that talks about it and it's not as detailed as the book will be but it talks about some great stuff. On thing is how uniform the heat is. Thy say becaus of the particles moving from bottom to top it's almost perfect in heat spread. Normal fluid bed heat treating furnaces are within +/- 3°c through out the entire bed. Thy use fluid beds to calibrate thermal couples and thy hold +/- 0.14° C wow.
 
I would look for a tube around 8".

6" would work, but the larger the tube the more it can be fluidized.
 
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