Sand Pot, could it be a salt replacement.

Kuraki that is most gracious offer. I might take you up on that offer if funds run tight. As some of you might have seen I did a 15n20 sale for a hardness tester. In the middle of the sale I scored a nice Rams Rockford (mini) hardness testers for $95+shipping, it needs test blocks and a diamond penetrator. I'm waiting for it to be delivered but I my thought is I will use the extra money to develop this sand pot to kinda say thinks to the forum. So let's put our heads togather and hammer out some details and I will put togather a parts list.

My thought is to make this rather deep so long items like swords could be heat treated. Thinking about setting it on the floor and doing something like 36"-42" deep. As to the width I'm with Stacy in thinking we need wider not narrower, I think 4" ID is minimum. But we are kinda limited becaus the metal filters we are using as the defuser inlet comes in certain sizes.

Next up is media, I have silica gel and it works good except the fact that it absorbs water and can clump when heating and also will actually boil as heating because the extra gas from the water being driven off. I would like to use actual aluminum oxide sand because it will be easyer and cheaper for others to acquire it.

I have a pid controller to monitor temp. My thought on this is to take a page from burt fosters book and just control the temp with a needle valve not a on-off pulse from a solenoid.

With all this being said, this build is for you guys. What do you guys want to see and what features do you think it needs.
 
I suggest a two-stage PID control. There are just too many variables for a needle valve to be suitable.
 
After thinking it over I think 4" is pushing it for size, 6" would be much nicer. Located a stick of 6.15" ID and .25 wall 316 stainless that is 47" long. It's a tad pricy but if it's the direction we want to go I will get it. Bug what length do we want to go with?
 
I think I have settled on a final design. The big issue has been the defuser and designing it properly. I have been neck deep in research papers from university's and the us government and one thing is made perfectly clear. The defuser is the key and no one is sharing there design. But what I did gather from all the research is a few things. First we need even pressure across the sand surface at the defuser. Second is that the bubbles rising to the surface is what creates the mixing effect and the super even temps. General data says the temp from top to bottom and side to side is within +-3°C. That's hard to beat right there. So when I researched deeper it looks like using tiny jets eavenly spaced to create small bubbles is the ticket. Kinda like a pot of boiling water, you have lots of small bubbles rising to the surface not one huge one.

But tiny jets can be problematic as thy can weep sand down into the manifold when there is a pressure drop after a bubble forums. So this got me thinking about a way we can kinda kill 2 birds with one stone so to speak. My thought is to do it like I had origanily planed. Using the refractory filter disk in the bottom then a disk of koawool felt/paper over it but then cut out a stainless disk that fits the tube nicely and drill tiny holes in it. We can drill as many as we want and what ever size we want. Then set this disk down on top of the felt. This serves two purposes, A. It holds down the felt and B. It directs the gas into jets where ever we want them and alows us to easly control the jet size. The problem with just using the felt is it will act like one giant jet with no control of size and also the pressure could push the felt up letting sand weep down into the refractory filter and down into the manifold. The reason for the refractory filter is it alows the gas to eavenly apply pressure to the entire underside of the jet plate. The jet plate also offers protection to the felt from pointy knives poking holes in it.
 
Are you planning an indirectly fired pot or a directly fired pot? Sorry if that's been discussed, it just seems that a directly fired pot is an elegant way of creating a neutral atmosphere.
 
Well a directly fired sand pot creates other issues in heat control. Temp is directly controlled by burner but burner also controlls the fludizing so it makes it really tricky and gives really limited temp control. It's also a bit more complacated to build.

After thinking it over I wonder if we car remove the refractory filter completely. I hate using something that is not common to find and has size limits. So I think if we removed the refractory filter and replaced it with a stainless ring that was say 1/2" tall then set a disk with say half inch holes closely spaced then the kaowool then the jet disk we would be set. The only use of the refractory filter is to support the wool filter felt and alow the gas to spread out under it. But a ring and a support disk will do that as well and be something that can be easly duplicated.
 
The size is actually controlled quite well when you buy good quality aluminum oxide grit. I think the chart I saw said 120grit was .0025 to .005. I found sintered screen that would work as a filter but I'm woried that at thoes high temps it would scale and plug up.

I will be ordering a box of 120grit in the next few days and will see how it looks. I know all the books and papers say .004 aluminum oxide is considered the best. But in what we can get we might have to step up to say 100 grit so we do t have the super fine stuff and have mostly .004-.007 size grit.
 
I will suggest it again. Sintered stainless air stones for Brewing. Micron sized pores and inexpensive.

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JT I have some surplus 4" schedule 10 304ss pipe but that's the only thing in the size range your considering. Let me know if you need some.
 
Great info here.

In the Peters video, Brad says they are using this method for oil hardening steels.. Any reasons NOT to use fluidized sand at the higher temps needed for air-hardening stainless steels like 440c, 154cm, etc?

J
 
There is no reasion you can't go higher in themp, the sand can take just about any temp you toss at it. The limiting factor is the stainless tube that holds the pipe. If you could afford an inconel pipe you would be good up to around 2000° but it's crazy pricy. There are other options like clay graphite that you can melt steel in but I don't know how thy would hold up to the sand and quick heating.
 
Well, I read to page 7, then skipped ahead to add this, so hopefully no one said it already.

Why not COMBINE vibration and an inert gas? Some people have been skeptical of the fluidizing ability of vibration, but as Stacy pointed out on page 1, vibration is actually used in MOST fluidizing baths, and this phenomenon has been observed in earthquakes. I even witnessed this phenomenon in a college class once. VIBRATION WORKS! It does NOT compact the sand. You can also see this yourself if any of you have a brass tumbler for cleaning ammo casings.

That being sorted out, why not use argon, nitrogen, or whatever to purge the tube of all the air, then seal the tube, and switch to vibration. You would have to restart the gas any time you open the tube, but it should drastically reduce the gas consumption. Awesome thread, by the way!

EDIT: You could also just reduce the flow of the gas during vibration to a bare minimum. If using Argon, which is heavier than air, even the most minute flow rate should push the oxygen out even if the top were open.
 
Sealing a tube of red hot materials has a name ... it is referred to as a bomb. Seriously, it would be very problematic to get a good seal in any simple way. However, a loosely fitting cap might help keep toss out ( grit discharge) and gas loss down.
 
An indirectly fired tube of sand heated to 1500f and fluidized by vibration only makes me wonder how much oxygen would actually remain present in the bath. It isn't like an oven where you have an open portal exchanging air each time the door opens.

You can develop vibration rather easily, when I worked in an iron foundry and we shook out castings in a big vibratory sand reclaimer it was just a large motor with an eccentric weight that created the vibration.
 
Take this with a grain of salt or sand.
Yes vibration is easy to create but creating the right kind of vibration could be quite tricky then we add in the fact that we are heating this in a verticle forge to 1500° would make it near impossible. I'm not saying it can't be done or is a bad idea I'm just saying are gole here is easy to make and simple. Another problem I can see with fluidisation from vibration that even heating could be a big problem. Yes media tumblers mix VERRY well but that's because of its shape. At on of my jobs we had a huge vibratory tumbler. Held like a 100-200 or more gallons of media. Yes the media was fluidized but differently then we need. It's use is to impact and clean the parts so the media impacts the parts and the parts MUST be alowed to move with the media. You hold a part still and it drastically affects the fluidizing effect. But using air or gas to fluidize is not dependent on part size, pot size and it's quite simple and elagent. I know some of you are concerned with gas cost but remember you can use air from your air compressor to fludize the sand. Then when you go to heat treat cut the air and run nitrogen. The steel heats so fast in sand that you won't use a lot plus when the sand is hot you use ALOT less gas to fludize.
 
Ok I just talked to the local (80miles away) and thy have all the stainless pipe in stock and at a good price. 4" sch40 is $76 for 24" and 6" is $110. I'm currently doing some testing with 4" pvc pipe to determine if it's to small or if it even matters.
 
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