High and Low Temp Saltpots

[B. Norris]

I am getting ready to take the plunge into heat treating with salts and wish to benefit from someone else's experience. The part that baffles me is the electronics. K type thermocouple? 16 Pin DIN Controller? Any of you good folks care to walk me through it?

 

~Bruce~

[Aldo]

Chuck,

 

Was at the NY show this past weekend and spoke to Pete of Peter's Heat Treat. He uses Aluminum Oxide sand and runs Nitrogen through it to void the O2. He says it's much safer than Salts. Said if it spills over you just sweep it up and throw it back in. If any dust or dirt gets in it burns off and he also said you can pour water into it and it just evaporates. The system is liquidless!! Just seems safer to me all around and you don't need to do to much modification. You should also have no problem using regular Schedule 40 pipe instead of Stainless because the Alum.Ox. is not corrosive.

 

Something to think about,

 

Aldo

[guarnera]

Chuck,

 

Was at the NY show this past weekend and spoke to Pete of Peter's Heat Treat. He uses Aluminum Oxide sand and runs Nitrogen through it to void the O2. He says it's much safer than Salts. Said if it spills over you just sweep it up and throw it back in. If any dust or dirt gets in it burns off and he also said you can pour water into it and it just evaporates. The system is liquidless!! Just seems safer to me all around and you don't need to do to much modification. You should also have no problem using regular Schedule 40 pipe instead of Stainless because the Alum.Ox. is not corrosive.

 

Something to think about,

 

Aldo

 

Aldo,

First off, thanks for Mr.Eggerlings #. Second, more info on Aluminum Oxide sand, never heard of it. Sounds pomising.

 

Tony G

[Sam Salvati]

Chuck,

 

Was at the NY show this past weekend and spoke to Pete of Peter's Heat Treat. He uses Aluminum Oxide sand and runs Nitrogen through it to void the O2. He says it's much safer than Salts. Said if it spills over you just sweep it up and throw it back in. If any dust or dirt gets in it burns off and he also said you can pour water into it and it just evaporates. The system is liquidless!! Just seems safer to me all around and you don't need to do to much modification. You should also have no problem using regular Schedule 40 pipe instead of Stainless because the Alum.Ox. is not corrosive.

 

Something to think about,

 

Aldo

 

 

NO FRIGGIN WAY!!!! I had the tube full of sand idea a few weeks back....... not the nitrogen part though.....

Edited February 27, 2008 by Sam Salvati

[B. Norris]

Some questions come to mind.

 

How even is the temperature of the sand vs. salt? I suppose once it gets up to temp. it is probably fairly even because of the thermal mass of the sand. My mental picture is of a vertical tube setup, like the salts, just filled with sand, and having an inlet at the bottom for nitrogen gas. Would the addition of nitrogen gas make a cold spot in the tank or is it pretty much hot by the time it gets there? I suppose it depends on how much nitrogen it takes. Speaking of that, how are the operating costs on this setup? I bet you could put some kind of lid on the tube and cut down on the quantity of nitrogen needed and get the sand up to temperature faster. I definitely can see the safety appeal of doing it this way. IMHO the only thing the salts have going for them is the eveness of temperature they provide. If the sands can provide the same thing then I think they are a winner.

 

Neat idea. I would like to know more about it. Do you have contact information for Pete?

[dsloan]

Hey Bruce,

 

Good question. I excited to get more details too. I can answer the question about nitrogen though. The only cold spot would be right at the tank. Nitrogen turns to a gas very quickly. We use some here at work or an inert gas.

 

Dave from Diller

[Aldo]

The way Pete explained it to me was that the sand acts very much like a liquid. Said it look like it's boiling at times. And I imagine you wouldn't need the Nitrogen until the sand was at temp it should void the O2 in no time.

 

I have Peter's Ph# and will give him a call and get more info. Would hate to have him slammed with calls from Smiths trying to get info that yields him less customers. I'll get the name of the system and we'll be able to look all over the web for interesting facts and photos and figure out how to rig one of these suckers the old fashion Bladesmith Way. (CHEAP!!)

 

Aldo

Edited February 28, 2008 by Aldo

[J.Arthur Loose]

Only problem I can think of is scale developing during normalizing, when one heats the blade up to crit and lets it air cool. With salts you get a nice coating that prevents any scale from forming.

[B. Norris]

Only problem I can think of is scale developing during normalizing, when one heats the blade up to crit and lets it air cool. With salts you get a nice coating that prevents any scale from forming.

 

Ah yes. I wonder... Could you just turn the pot off and leave the blade in it with a bit of Nitrogen going to purge any oxygen?

 

~Bruce~

[Mike Lambiase]

now that would be some annealing....

 

I dont know about the sand, but my low temp salts take at least 9 hours to get down to a temp that I can call cool.

 

I think that this sand would be perfect for annealing, because after it is cool, it wont have surrounded your blade and hardened.

 

these sands really sound like a great idea.

[Kevin H]

The description sounds to me like what's called in industry a fluidized bed furnace. The media usually isn't sand, but rather alumina or zirconia (think of it as fancy, high temp resistant sand) I suspect that regular silica should be OK at lower temperatures. If you have a boiling/bubbling motion you have to have enough nitrogen flow to overcome gravity's affect on the individual particles of sand so that the flow lits and separates them. The nitrogen will minimize oxide formation - we used to spheroidize anneal 52100 bar stock uing a straight nitrogen atmosphere in a roller hearth furnace - that was enough to minimize additional oxide formation. I suspect that the addition of a little bit of natural gas or propane into the nitrogen stream (4% or less by volume) would promote a scale fee surface by acting as a preferential oxide scavenger - I'd keep it as low as possible - the goal would be to dilute the hydrocarbon so that the mixed gas is below the flammibility limit. Much safer that way.

[kb0fhp]

Kevin - I believe you are right - it sounds a lot like a fluidized bed furnace. It has the same basic fast heat transfer as a salt bath, but few of the negatives. It is not as fast as a salt bath - but it does work quickly. One issue is static buildup on the sand, making it clump. You can also add a small bit of natural gas - about 1% to provide a reducing atmosphere to reduce decarb and scaling.

 

Kevin - that sounds like one of my customers down south...the used to sperodize anneal 52100 using nitrogen and a small amount of natural gas. Does the name Harry Walton ring a bell?

[Aldo]

Spoke to the people at Peters' Heat Treating. The units he has are very similar to the salt pot setup. Go to this link http://www.rapidheattreat.com/technology.html, you'll find a simple diagram and some info.The units that he has were from a company in Canada and,as anything dealing with hi-temp always is, they're expensive as hell, but damn it seems simple enough. Just gotta get real close to one with a camera and a ruler

[B. Norris]

Did some googling of "fluidized bed furnace" and found it quite interesting. They have many different uses. Nitriding can be done in them as well as carburizing steel. One site indicated that hardening could be carried out in them and that the rate of cooling was similar to that of oils. I assume this was a low temp setup and that one would have a high temp / low temp setup like that of salts. It is also possible to create a closed system where the nitrogen atmosphere recirculates. I do not know if this will be possible in a system built in my garage but, it is something to think about.

 

In the fluidized bed furnace, gas is passed up through a bed of dry, finely divided

particles, typically aluminum oxide. The turbulent motion and rapid circulation of the

particles in the furnace provide heat transfer rates comparable to those of conventional

salt bath equipment. The parts to be treated are submerged in a bed of fine solid particles

held in suspension by an upward flow of gas. Heat input to a fluidized bed can be

achieved using:

• Internal resistance heated beds. The particles and gas are heated by sheathed internal

resistance heated elements.

• External resistance heated beds. A fluidized bed contained in a heat resisting pot is

heated by external resistance elements.

• Direct resistance heated beds. Electrically conducting material, such as carbon

powder or silicon carbide, is employed as the bed material.

• Internal combustion gas fired beds. An air/gas mixture is used for fluidization and

ignited in the bed, generating heat by internal combustion.

• External combustion heated beds. A fluidized bed, contained in a heat resisting pot,

is heated by external gas firing.

• Submerged combustion fluidized beds. Combustion products pass directly through

the mass to be heated.

2Pays

 

Steel (carbon, alloy, tool, and stainless), aluminum, titanium, and other metal can be heat treated economically in a fluidized bed furnace. All heat treatments except controlled rate cooling rate annealing are viable. Since gases are used to fluidize a bed of powder, any gaseous atmosphere can be used, and simply by turning a few valves, an atmosphere can be completely changed over in 2 minutes or less. This feature allows multiple heat treating operations to be done in the same furnace without cool down, switching furnaces, and reheating which is standard in commercial shops. Fluidized bed heat treating is economical, safer, and almost emission free.

STInet

 

The hardening ability of a fluidized bed is the same as that of oil.

Springerlink

[Aldo]

So it sounds like you're gonna go for it. I was thinking that the internal combustion might be the way to go The same gas you use as an O2 barrier is heating the bed as well. That leaves the Nitrogen out of the picture.

Edited March 2, 2008 by Aldo

[Mike Krall]

You should also have no problem using regular Schedule 40 pipe instead of Stainless because the Alum.Ox. is not corrosive.

 

I read this here a couple of nights ago... Using black pipe for salt pots??

 

Mike Krall

Edited March 2, 2008 by Mike Krall

[kb0fhp]

So it sounds like you're gonna go for it. I was thinking that the internal combustion might be the way to go The same gas you use as an O2 barrier is heating the bed as well. That leaves the Nitrogen out of the picture.

 

 

You can also quench in fluidized beds - it gives similar quenching performance as quenching in molten salt. You have to watch how you design the nozzle plate to direct the fluidizing gas for any design of fluidizing beds. Typically they use small nozzles - say 3/8" diameter drill holes in a circular pattern.

 

As you increase the the flow of gas, the bed will expand. Gradually up to a point it will keep expanding. There is a point where the bed will become "fluidized" and there is rapid bubbling or rolling of the bed. Increase this gas flow rate further, and you start blowing the sand out of the bed. I have installed and operated larger (36" diameter beds) and they work very well with limitations. Probably the biggest limitation is the static charge build up when dry nitrogen is used. The sand starts to clump and fluidization is difficult or impossible to achieve.

[Mire Blades & Tools]

I am impressed.

 

http://gateway.metalcasting.govtools.us/re...d%5FFurnace.pdf

 

there ahs been an offical study back in 97' on it and there saying it works to the degree that what i interpet as .... it will work for swords knives and the like for what ever metalurgy range you want in the crystaline structure.

 

you tube has some nice commercial vidieo of it

 

http://www.youtube.com/results?search_quer...mp;search_type=

 

and here's a comany that uses it regualy i suppose with some nice explinations of how it works.

 

 

hummm.... sand blast and heat tre all in one.... say round the 600 grit...... yea i like the sounds of that!

[Mire Blades & Tools]

I am impressed.

 

http://gateway.metalcasting.govtools.us/re...d%5FFurnace.pdf

 

there ahs been an offical study back in 97' on it and there saying it works to the degree that what i interpet as .... it will work for swords knives and the like for what ever metalurgy range you want in the crystaline structure.

 

you tube has some nice commercial vidieo of it

 

http://www.youtube.com/results?search_quer...mp;search_type=

 

and here's a comany that uses it regualy i suppose with some nice explinations of how it works.

 

 

hummm.... sand blast and heat tre all in one.... say round the 600 grit...... yea i like the sounds of that!

 

 

oops

 

http://www.rapidheattreat.com/technology.html

[B. Norris]

So it sounds like you're gonna go for it. I was thinking that the internal combustion might be the way to go The same gas you use as an O2 barrier is heating the bed as well. That leaves the Nitrogen out of the picture.

 

Using the combustion gases to fluidize the bed is almost the same as an atmospheric forge. I suspect there would still be some scaling. Incidentaly, I have heard that this technology is being used for blacksmith forges in Europe. I guess there is not much difference between a firepot in a coal or charcoal forge and an internal combustion fluidized bed. Using nitrogen could give performance closer to that of salts (as far as protecting from scaling) but, the static build up sounds like a pain in the keister. An internal combustion fluidized bed used to heat up a piece of steel for hardening, lets say a sword blade, would have to be long and deep. Probably a tube 8" in diameter by 40" long. I do not know if the temperature would be consistent throughout the tube. It seems to me that an external heat source (to the tube) might produce more even heating. Then again, there may be enough agitation in the sand that it is not an issue. Another thought would be to lay the thing on its side and create a trough. It would take more nozzles and might use more gas to keep the bed fluidized. If using internal combustion to fluidize the bed, will that limit the operating temperature of the fluidized bed because turning the gas down to lower the temperature will de-fluidize the bed and turning it up will start to blow the sand out? Using an external heat source would be a way around this. The only way to really find out is to try and that will take a fair amount of time and money.

 

You can also quench in fluidized beds - it gives similar quenching performance as quenching in molten salt. You have to watch how you design the nozzle plate to direct the fluidizing gas for any design of fluidizing beds. Typically they use small nozzles - say 3/8" diameter drill holes in a circular pattern.

 

As you increase the the flow of gas, the bed will expand. Gradually up to a point it will keep expanding. There is a point where the bed will become "fluidized" and there is rapid bubbling or rolling of the bed. Increase this gas flow rate further, and you start blowing the sand out of the bed. I have installed and operated larger (36" diameter beds) and they work very well with limitations. Probably the biggest limitation is the static charge build up when dry nitrogen is used. The sand starts to clump and fluidization is difficult or impossible to achieve.

 

I do not understand what you are saying about the nozzles. Do you mean 3/8" diameter aperatures for the gas or a series of smaller holes, in a circular pattern, on the end of a 3/8" nozzle? My thinking is that the aperature should be smaller than the grain size of the sand, otherwise the sand could plug up the aperature. Maybe there is no getting around the sand infiltrating the nozzle and it is not a big deal, the gas will just flow around the particles. I suppose the more evenly the gas is introduced to the floor of the bed, the better the fluidization? What would be an optimal way to direct the gas to fluidize the bed? A ring of aperatures around the outside of the tube creating an upflow at the walls and a downflow in the center? What about the opposite, apperatures clustered in the center and downflow along the walls? That might be a better way to go if the heat source is external. The media could pick up heat as it flows downward along the tube walls before heating up the nitrogen and rising up again in the center. Then again, it could just as easily pick up heat as it flows upward along the walls and then heats up the workpiece while flowing down the center.

 

What methods are there to prevent static build up when nitrogen is used? Introduce water in the gas flow? Just dump some water into the bed from time to time?

 

It seems to me that the fluidized beds have some real promise but, I want to hear from people who have hands on experience with them. I'm not wanting to reinvent the wheel and all! I still may just build a salt pot as it seems there are fewer engineering hurdles than the fluidized beds, they definitely protect against oxidation of the workpiece. However, they scare the willies out of me. My brain is quick to latch onto all the destructive potential they posses!

 

~Bruce~

[kb0fhp]

The sand will circulate on its own. You set up nozzles at the bottom - about 3/8" in diameter in a circular pattern - think lots and lots of nozzles. Set them up on a series of circles inside one another. There are two type internally heated and externally heated. Check out Technomics and Procedyne - they make commercial fluidized beds. You may also want to check out some transport phenomena books to get the physics behind it. But you generally have the right idea. Just one set on nozzles at the bottom is adequate. You may want to go for a higher velocity using smaller nozzles, but more of them.

 

Regarding clumping and static buildup, probably the best idea is not to use extremely dry nitrogen. Because it is so dry, static electricity can build up. Add a small amount of natural gas or propane so you are below the flammability limit. That should help the amount of static electrictiy build up and provide a small measure of scaling protection.

[Mike Krall]

If the heat transfer in a fluidized bed system follows the principles of transferring heat (hot water source) to air, as in a heat exchanger, counter-flow transfers more efficiently.

 

Mike Krall