Review WIP Fluidized Sand Pot

G

Gting

Joined
Feb 12, 2014
Messages
52
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Hey folks Steel Pig Forge here,

Its been a long time since I have been on blade forums, but since I got the inspiration from here I thought I would give back a little bit.

Here is my fluidized sand pot build. Ill add pictures and descriptions and a parts list. Here is my warning though. This is serious stuff. Not to be played around with. I in no way am responsible for any injury or property damage that may come from someone attempting to replicate this build.

With that said, Ill be happy to answer any and all questions you have. Lord knows I had plenty during my build and owe quite a few people a big thanks.

Gonna toss a couple pictures of another upgrade we did in the shop. We made a low temp slat pot for temping and mar-quenching. Its awesome. Very accurate and straightening blades after the quench is easy now. I have used it to mar-quench 52100 and the added toughness is slightly noticeable.

So lets begin... Here is all the goods in their natural state. Before being put together.
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List of items used-
1- 30 gallon air bubble
1- 24" 304SS pipe with professionally welded 304SS end cap and 304 air pipe.
1- ITT Asco 120V ,3/8" NPT 15 PSI Solenoid Valve
1- PID controller w/25amp SSR
1- Inconel Thermocouple
1- 16" thermo well
1- Dayton blower (build burner body at Menards)
1- 50lb bag of grit 120 mesh AO blast Media
1- 20lb box of santanite
1- 10sqft roll of 2" kaowool
1- 1/2 ITC-100
6- soft 3" firebrick
2- 1sqft insoboard
1- 0-50psi air regulator

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Begin by cutting up the 30 gallon air tank but and putting burner hole in.

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Cut the top and bottom off. My inner tube is 24" tall and the tank was much longer than that. I had 5" from the bottom of the shell that the sand tube would sit on. so overall length of my outer shell is 28". That would leave 1" coming out the top that a ring would go around. The flat plate would end up being the top. Leaving 1" of the sand tube exposed. More on this later.

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Here I begin putting the Kaowool fabric liner in. This is 2" thick used in full width. As you can see I have 5" of space on the bottom where the base of the tube will sit.*Note, I had to clean the inner tube extensively ass there was about 2" of sludge and rust in the bottom. I used kerosene to clean it and only cut my self once and had to get stitches. ALWAYS DE-BUR AFTER CUTTING STEEL. Had my arm down in it and the top of the shell took a 5/32" chunk out of my arm.

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Mock up of how it would look. At this point I was thinking I would use the cut end of the tank as the top. I would end up cutting a ring and using a flat top.

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Early base that would slide inside the bottom of the shell. Where the sand tube would sit. Sprayed with rigidizer. I scraped this idea on first dry run. The sand tube was 22lbs of 304 Stainless steel tube and would end up getting another 20+ lbs of sand added. The wool alone would not support that amount of weight. I ended using fire bricks and an insoboard for the base. No pictures of that modification as there was a lot of cussing and beverage intake.

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First coat of santanite applied after letting the rigidizer dry for 8 hours. I applied it at about 1/8' layer at a time. attempting to smooth it out as I went.

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Here is the electronics.... I love electronics as you can see. This is what will precisely control the temp of the sand pot. A thermocouple (electric temp gauge) will be placed in the sand and connected to the PID. The PID will be connected to a gas solenoid. It will turn the gas on and off controlling the temp of the chamber.

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Here's a mock-up of the burner. 134 CFM blower choked down with the 1.5" ball valve, propane injected through the cap on the left. I drilled a hole and placed a 1/4" pipe nipple in there. Then welded it tight. it is all 1.5" pipe. So this is a big burner. I thought I would need it as there is only one to heat the entire pot. Later I found out that It was more than enough. I had to turn it way down.

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The sand tube. Its 1/4" 304SS pipe. With a 1/2" base TIG welded in. Triple passes to make sure it lasts forever. 1/4" wide 10" long 304SS pipe nipple also triple pass TIG'ed on. This will be the inlet tube for the air that will fluidize the sand.

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Initial mock up of the outer shell.

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The sand..... not actually sand. Its 120 grit Aluminum Oxide blast media. I ordered this from Mcmaster Car. It worked great. I was advised to screen and sift the media to get out all the bigger particles and very fine particles. This leaves you with a very uniform size that will work better for fluidization. Otherwise the very fine will blow out the top and become aerosolized which is not good for your health and the large will sink to the bottom and plug the diffuser.

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This is what we used for a diffuser. 3.5" soft fire brick. Cut to the exact size of the pipe. The air comes in the bottom through the pipe nipple, gets diffused by the soft brick and that goes into the sand, making it like quick sand.
 
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This is the simple hook up for the air in the bottom of the sand pot. It clear plastic hose from the 0-50 psi air regulator to the SS pipe nipple on the bottom of the sand pot tube. It's all ran from a 33 gallon air compressor. The regulator is turned all the way down and next to no air is used to fluidize the sand.

*note. Some will ask why i'm not using an inert gas to fluidize the sand. Well first of all its expensive even with the little amount that is used. In the future I plan to set up a nitrogen purge to use only when the knives are in the pot. At this point I'm just coating the blades to protect against the added decarb from running straight compressed air through it.

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The first dry run of the fluidization. When I made this first diffuser I attempted to draw the circle then cut to size and slide in. Well I was unable to get a perfect circle when I cut it so there was a gap. In this GIF you can see that it is only bubbling on that one side, that is because the air found the path of least resistance and is coming up through that gap. Well to alleviate this I cut to a slightly larger diameter and twisted and worked the brick down into the tube. the tube cut away the brick to the exact diameter. Much more even distribution now.

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First run of the burner to cure the santanite. Run it for 5 minutes. then shut off. I did this 3 times then did a 15 minute burn. Then a 30 minute. I wanted to make sure it was totally cured and slowly release the moisture. As you can see I angled the burner to flow along the side and up. This swirl creates a very consistent heat around the sand tube. If you build any sort of forge especially a vertical this is what you want in your forge. It eliminates hot spots.

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Here's the exhaust pipe at the top of the pot. Pretty blue flame! Running rich but getting hot.

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Got the sand pot all installed and initial run. This is where I realized that the domed lid was a no go. It was too tall to have the pipe come out. Also the insulation I attempted to glue to to dome did not hold.

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Here is the 1/4" thick mild that I had the guys at the metal shop munch out a circle for the pot to come through. I then used a flap wheel on a angle grinder to smooth everything out. I was able to make it about a 1/4" around the pipe.

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The flat plate on top installed. also you can see the 3" inch ring I welded on top of the shell. This encapsulated the top of the insulation that was sticking out that was to go into the domed lid. It created a 1" lip that I then used a custom made Insoboard to fill and go just around the pipe. Keeping the heat contained inside of the chamber.

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At this point it was apparent that I needed a better welder. I was using flux core and it was just garbage. I picked this Hobart up off amazon. It was like night and day better.

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Since I enjoy electronics so much.... not. I had my dad set up all the gizmo's as I helped explain the plan. He's an engineer so it was a cake walk for him. He put is all together in this nice box. The fan has a switch, the solenoid as well, emergency shut off valve for the gas. I'm running a 0-30 regulator from high temp tools. It runs off about 1.5 psi.

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Here's a shot of the regulator attached to the gas line and also the electronics box.

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We used pipe nipples as a way to give stand-off from the sand pot to prevent over heating. It has seemed to work great so far. Haven't gotten over 75 in the box.
So after all of that we had to play with the PID to get everything to run correctly. We found out that we were running way too hot with too much air and furl. We installed a needle valve on the fuel line to help regulate that, and backed the air way off to about 50%. This helped the heat rise much slower. At the beginning of the calibration we were over shooting our temp by 200+ degrees then swing way low and wasn't able to ever hold a constant temp. backing the temp down made it run correctly. It will hold a constant temp within 2 degrees. It heats up from 40 degrees to 1650 in less than 30 minutes. Switching temps only takes 4 or 5 minutes then another 3 or 4 to stabilize.

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Here is a shot of it running. Its got a couple knives in there doing it's thing.
*Little something on the safety of a sand pot. With a sand pot the sand cools extremely fast when it leaves the tube. with in 1 foot it is cool enough that it wont burn you. unlike a salt pot. Another added plus is it wont turn into a 1500 degree volcano shotgun if there is some moisture on a blade when put inside. One more added plus is being able to use clay on a blade to create a hamon. With salts you can us clay. It must be 100% dry and will eventually ruin your salts.
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On to the low temp salt tempering pot. This is an old kiln we acquired that has a 11"x11" heating chamber. It was rated up 2300 degrees. We replaced the coils and added a PID controller to modernize it. This is what we used to heat treat our blades before the sand pot.

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Here it is. Nothing special.

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The top is just a 4.5" square hole in the top of the kiln. The pipe is 4" square tube and hold 12lbs of low temp salts. They melt at 275 degrees and can go up to 1100. It tends to work really great. Once the knives are all done, just pull them out and let them hang cool. Wash them all off with warm water afterwards and your finished.

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Here is a little dama skinner I did in there at 415. After the quench I knocked the scale off with a 220 grit belt then into the tempering salts. Talk about a nice straw color.

Well I hope everyone has enjoyed this journey as much as I have. Please feel free to ask any questions you have!
Garrett Elting
Steel Pig Forge
 
I’m glad to see someone actualy take my idea/prototype and try it out themselves. Looks like a solid build. In the first prototype I have my sand tube resting on a fire brick floor. This brick has a hole through it that the gas supply tube runs through. This brick supports the weight of the sand pot and shealds the supply tube from the flame. It’s funny that you used a fire brick for the defuser. I had wondered if a fire brick would work for this. My plan was to seal the brick to the edges of the tube with furnace cement. The tricky part is using something that will not get eaten away by the turbulent sand. As to the sand your using I think its not quite corect. This is the tricky part that took me quite a bit of research to figure out. The particle size has to be controlled. I spent so much time going over grit size standard charts and looking at the percentages of mix in different sizes grits. The more uniform the grit size the better performance you will have. The smaller the grit is the less air you use to fluidise the bed. I found a company that will supply the required size and control percentages of screened practices.

All that said it looks good. For anyone wondering here is the origanial thread on this topic. This is where all brain storming happend for this concept.
https://www.bladeforums.com/threads/sand-pot-could-it-be-a-salt-replacement.1417680/
 
Thanks JT for the comment I hoped you would comment quickly. Your original post was the precursor to all of this. If you could please send me the information for the sand supplier that would be great. I sieved this sand through 2 mesh sizes 100 and 140 mesh. This is the goods from the middle. so it should be pretty similar in particle size. Let me know what you think. I'm using firebrick to support the weight of the sand tube now. I abandoned the Kaowool idea quickly after I put all the pieces together. Again i would like to say thank you, without your original prototype, this would have been a more difficult build.
 
Gting said:
Cut the top and bottom off. My inner tube is 24" tall and the tank was much longer than that.
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Why you not put the upper lid upside down ? That would reduce the length of tank and will have good shape to collects sand beck inside tube ? I like what you done :thumbsup: I work on mine almost two years ...electric one ;)

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Natlek said:
Why you not put the upper lid upside down ? That would reduce the length of tank and will have good shape to collects sand beck inside tube ? I like what you done :thumbsup: I work on mine almost two years ...electric one ;)

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If I did that it would expose too much of the sand tube. Leaving approximately 5" out of the chamber. Too much Heat loss.
 
Nice build. Good to see one of these owner built sand pots up and running. Find this a lot more appealing than a high temp salt pot - seems to have all the benefits and less of the dangers.

Is your build capable of the 1800 - 2000 degree F. temps many stainless steels require?

J

JDWARE KNIVES
 
JDWARE said:
Nice build. Good to see one of these owner built sand pots up and running. Find this a lot more appealing than a high temp salt pot - seems to have all the benefits and less of the dangers.

Is your build capable of the 1800 - 2000 degree F. temps many stainless steels require?

J

JDWARE KNIVES
Click to expand...


We'll see, I've been interested in these as well, but I've yet to see anybody pulling perfectly clean steel out of them. Let alone test proving the elimination of any decarb. The OP says he's not going to use a shielding gas either, but compressed air instead. To me the only advantage of this is even heat, but a good HT oven will give you more than acceptable evenness of heat also.

With high temp salts, the molten salt actually forms a protective layer over the steel, preventing scale, decarb, or any other issues, which allows you to functionally "finish" the work, pre-austenizing. This is extremely advantageous for certain things, that interest me, such as engraving or inlay, which can be exceedingly more difficult under other circumstances. There's also marquenching, is this possible with sand pots?

Is going from a high temp sand pot, to a low temp salt pot safe? Can you build a low temp sand pot for marquenching?


Lots of unanswered questions to me, but I'll be curious to see what actually works out. Seen a few people building these, however, information seems to cease after they show them running, I'd like to see some real use feedback, from someone that's actually utilizing them heavily, and for a reason other than they being cool and new (no offense to anybody, not saying this is what the OP is doing).
 
javand said:
We'll see, I've been interested in these as well, but I've yet to see anybody pulling perfectly clean steel out of them. Let alone test proving the elimination of any decarb. The OP says he's not going to use a shielding gas either, but compressed air instead. To me the only advantage of this is even heat, but a good HT oven will give you more than acceptable evenness of heat also.

With high temp salts, the molten salt actually forms a protective layer over the steel, preventing scale, decarb, or any other issues, which allows you to functionally "finish" the work, pre-austenizing. This is extremely advantageous for certain things, that interest me, such as engraving or inlay, which can be exceedingly more difficult under other circumstances. There's also marquenching, is this possible with sand pots?

Is going from a high temp sand pot, to a low temp salt pot safe? Can you build a low temp sand pot for marquenching?


Lots of unanswered questions to me, but I'll be curious to see what actually works out. Seen a few people building these, however, information seems to cease after they show them running, I'd like to see some real use feedback, from someone that's actually utilizing them heavily, and for a reason other than they being cool and new (no offense to anybody, not saying this is what the OP is doing).
Click to expand...


What questions would you like answered?

I have been heat treating 5-9 blades a week for about a month thus far in this guy. I have been using a protective coating on all my blades to prevent de-carb so far. I don't personally have a reason to spend the money on an inert gas set-up at this point as I do my finish grind post quench.

As for high temp sand to low temp salt of course its safe. Not sure why it wouldn't be? I have done this with 52100 and had fantastic results. I wrote a little on this towards the end of my post about the low temp salt pot I built as well. I almost think sand may be a little more most advantageous than people going from high temp SALT to low temp SALT. As the two different types of salt have different melting temps and are completely different chemically. They do this over at Winkler Knives with their medium and slower quench high carbon steels with great results. I'm sure you could make a low temp sand pot, but I don't see the advantage of this though. It wouldn't cool the blade fast enough even for medium speed steels.

Please feel free to ask away though this build is an open book.
 
JDWARE said:
Nice build. Good to see one of these owner built sand pots up and running. Find this a lot more appealing than a high temp salt pot - seems to have all the benefits and less of the dangers.

Is your build capable of the 1800 - 2000 degree F. temps many stainless steels require?

J

JDWARE KNIVES
Click to expand...


To answer your question yes it can reach these temps, but the only down fall is at higher temps that SS requires the sand tube expands and breaks your diffuser in the bottom and you get uneven fluidization. And you would have to replace it after just that heat.
 
javand said:
We'll see, I've been interested in these as well, but I've yet to see anybody pulling perfectly clean steel out of them. Let alone test proving the elimination of any decarb. The OP says he's not going to use a shielding gas either, but compressed air instead. To me the only advantage of this is even heat, but a good HT oven will give you more than acceptable evenness of heat also.

With high temp salts, the molten salt actually forms a protective layer over the steel, preventing scale, decarb, or any other issues, which allows you to functionally "finish" the work, pre-austenizing. This is extremely advantageous for certain things, that interest me, such as engraving or inlay, which can be exceedingly more difficult under other circumstances. There's also marquenching, is this possible with sand pots?

Is going from a high temp sand pot, to a low temp salt pot safe? Can you build a low temp sand pot for marquenching?


Lots of unanswered questions to me, but I'll be curious to see what actually works out. Seen a few people building these, however, information seems to cease after they show them running, I'd like to see some real use feedback, from someone that's actually utilizing them heavily, and for a reason other than they being cool and new (no offense to anybody, not saying this is what the OP is doing).
Click to expand...

For me, Javan, it's not a question of new or cool (my tools and methods are all pretty simple, old school) The fluidized bed technology seems to have the advantages of salt pots while being much safer to operate. From at least one paper I've read, with high purity nitrogen as a shielding gas, they are capable of results (neutral hardening with minimal oxidation and decarb) comparable to salt baths (although not quite as good as vacuum furnaces). Given that I expect to do some fine grinding after heat treatment, that would work for me.

I'd be happy stop using coatings on oil hardening steels and foil wraps on stainless (I've read that fluidized beds are used at temps of up to 1200C). Maybe JT has found a diffuser that will hold up better than the OP's soft fire brick.

Would also like to hear more from others, including JT's experiences.

J
JDWARE KNIVES
 
There is another smith on instagram that built one both me. He wanted to use it for Stainless steels in those ranges. He was going to have a Inconel plate that would be laser drilled smaller than the particle size so it wouldn't just fill it. I think he gave that up when he found out it would cost $1500 plus for the plate. ouch. I also would need to find a fine controlled regulator for the gas purge. Once I can do that at a reasonable price I would consider using an inert gas purge.

As for the safety. I would consider it much more safe. You would have to try to get burns. When pulling blades with pliers the hot sand bouncing up at you feels similar to turning bacon in a pan.
 
No offense intended to either of you, of course, JD, I know your situation, and fwiw, I'm as enthusiastic as you about the possibility of this tool, I'm just trying to offer some "objectively critical questions", and hope, not to detract anybody, rather, foster honest discussion.

I've had to be really critical lately of ribbon burners, since everyone is jumping in on building forges with these, and I am one of the very few people that I'm aware of that's run one for hundreds, if not thousands of hours, in our field. They have both advantages and disadvantages, like everything, but nobody seems to want to be honest about both, and simply hype up the purported advantages.



I've gotta say though, in the OP's case, without using shielding gas as opposed to air, what real advantage do you see here over a standard HT oven? I think I'm missing it. Without shielding gas, personally, I don't see it as comparable to a salt pot at all, what am I missing? Even a gas HT furnace would offer better shielding with a reducing atmosphere (to my mind), than an air pumped fluid bed. Honestly, so even would a standard electric HT oven, since at least you've a fixed volume of oxygen. My concern here, is that not only do you not have anything to mitigate decarb or oxide formation, you're actually fueling it, by pumping a steady supply of air into it.


Honestly, I'm asking, not to chastise, but contribute, and I hope it's taken as such.

Also, from the numbers I've seen, it doesn't seem to me at all like it would be very expensive on the argon side to run this with shielding gas, have you come up with numbers to the contrary?
 
Thanks for replies I honestly appriecate that.

My main reason for building this was to create a HT'ing apparatus that would last a good long while, was up gradable, and could run on a simple 110v circuit. I am currently restricted to using not using 220v unless I wanted to run a long (50'ft) extension cord from my dryer outlet to the garage and leave the door open while doing so. No room in the box for more breakers, and maxed power service so they would have to pull new lines from the terminal to the house. It was gonna be a couple grand to get more power. So we have moved everything to 110v, the hydraulic press, grinder, mill, welder. So I guess that is my entire reason behind the build.

My old kiln which is now my low temp salt pot took 10 minutes to get to 1000 degrees, but another 2 hours to warm to 1600. It used up all 20 amps on its own circuit. So we needed an upgrade. So far this is an upgrade.
 
Gting said:
Thanks for replies I honestly appriecate that.

My main reason for building this was to create a HT'ing apparatus that would last a good long while, was up gradable, and could run on a simple 110v circuit. I am currently restricted to using not using 220v unless I wanted to run a long (50'ft) extension cord from my dryer outlet to the garage and leave the door open while doing so. No room in the box for more breakers, and maxed power service so they would have to pull new lines from the terminal to the house. It was gonna be a couple grand to get more power. So we have moved everything to 110v, the hydraulic press, grinder, mill, welder. So I guess that is my entire reason behind the build.

My old kiln which is now my low temp salt pot took 10 minutes to get to 1000 degrees, but another 2 hours to warm to 1600. It used up all 20 amps on its own circuit. So we needed an upgrade. So far this is an upgrade.
Click to expand...


Good info to have about this build bro.

I'd still like to hear more about why you're not using shielding gas?

Also, did you consider a propane HT furnace build instead? I've used many, and done correctly, they're excellent, very economical, and mitigates some of the concerns I mentioned above. Either way, I'm following this build, and I hope you'll do us the favor of outlining the disadvantages you discover, along with the advantages, once it's done. Trust me when I say, we'll all respect you more for your honesty, regardless of how successful it turns out.
 
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