Fog Quenching

JTknives

JTknives

Joined
Jun 11, 2006
Messages
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With the upcoming tomahawk batch I have been looking at solving the quenching problem. My quench tanks would quickly overheat if I was doing more then a handful of these big blades. I looked at cooling the oil with heat exchangers and radiators. Also considered a water jacket around the tank or water cooling tubing in the tank. In my research I came across something called fog or spray quenching. I did a bit of digging and was quite interested in what I found.

In a nut shell water is forced through a misting nozzle. There is nozzles on both sides that face each other. The quenching speed is adjusted by how much water is sprayed or misted onto the steel. The graphs I looked at showed very impressive control on quench speed. The industry uses air powered mist/jets. Thy can adjust the air and water independently and really tweak the cooling curve.

just thought I would toss this out there. I’m working on putting together a simple setup to see how well it works for blades.
 
That's pretty cool. Following too.

How would one effectively monitor the cooling curve though?

Just good results?
 
I think it would take a few tests to tweak it in. But you would know real quick if you where to fast. To slow and you would be lacking hardness. I have a flow meter that will tell me what my flow is doing so it’s repeatable once numbers aren’t discovered.
 
Intriguing. If I understand correctly, you could "slow down" the water quench to accommodate oil hardening steels? I wonder how well it works on a shallow hardening steel, especially thick stock.
 
That is interesting JT - you're always coming up with new stuff that makes me want to follow along to learn. Keep up the GREAT work.
 
JTknives said:
You can speed up the quench speed faster then water as well because it does not develop a vapor jacket.
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I'm not sure that is an accurate statement. You may be able to speed the quench because of flow rate, volume, and other dynamics, but it isn't about no vapor jacket.
 
There are all kinds of water soluble quenchants. I wonder if this fog quenching utilizes these. Think "superquench."
 
It sounds like this is more of a "pressurized mist" rather than a true "fog". Wouldn't a pressurized mist help keep the vapor jacket broken up? When I think "fog" I think of a static fog that's not moving, like a foggy road?
 
tkroenlein said:
There are all kinds of water soluble quenchants. I wonder if this fog quenching utilizes these. Think "superquench."
Click to expand...
Mix of water and air

The cooling fog consists in a mixture of fine dispersed or sprayed water and compressed air. The procedure, known as "fog quenching", becomes applicable only on specialized cooling equipments.The main difference between fog quenching and the other techniques (immersion quenching, film quenching, cooling in air), is the potential to close control over a wide range of heat transfer rates. The controlled cooling rates offered by fog quenching are often required to obtain the hardness uniformity; the distinction on each zone for the hardness by leading the cooling; the lack of deformation during the cooling process.The cooling in fog ensures simultaneous to effects: cooling in forced convection regime and cooling by vaporization of water droplets in suspension inside the air. The degree of cooling from any nozzle is primarily determined by the water flux incident on the cooled surface. Other factors such as droplet size and droplet velocity can modify the cooling rates and heat transfer of the fog.The pressures modification and consequently of the water and air flows enables the modification of the cooling capacity of the heterogeneous fog type medium in a large domain of values. Therefore knowledge of the various factors affecting "fog heat transfer" is important. To this effect, this chapter describes some techniques used to characterize spray nozzles and air-mist nozzles, as well as an application on 70VMoCr28 rolling mill.The experimental fog type cooling medium consists in water-air mixture (water droplets spraying by means of pressurized air jets). The water spraying is being done by-means of nozzles, the mixture compressed air-water being achieved either inside the nozzle, in the mixing chamber ("Internal Mix"), either outside the nozzle ("External Mix").As a general conclusion one can say that the heat transfer coefficient can be modified in a very large scale of values, to fit every specific application. It can obtain some dynamical programmable cooling cycles through jet regulation and "fog" adjustment.
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That was my point, the vapor jacket is constantly broken up, not exactly "no vapor jacket". The transfer of heat is based on the rate of flow of the coolant material. The amount and pressure of air/water will allow very precise control. I am not sure it is suitable for blades, though. IIRC, it is used in industry for continuous quenching of things like band saw blades, long bars, sheets, RR track, etc..
 
Increase your oil volume with a secondary tank and a pump... kinda like a blood transfusion. You have a consistent protocol with your current set up. Don't jeopardize your system, unless you are willing to start from scratch again.
 
I just meant that with millions of tiny droplets impacting the steel incredibly fast the vapor jacket does not have a chance to Form like it does it water quenching.
 
That is correct, but I think it is too violent for a thin knife blade .. unless you like corkscrew blades.

Make a 20 gallon ( or larger) quench tank with a circulation pump and radiator/fan. It will cool the oil nicely.
 
I think Rick is right, you’re risking a lot doing something like that. Especially with what’s on the line.
 
It was just somthing that came up in my searching and I wanted to try it. I would never use it on customers blades unless it was 100% proven and known to be perfect. I just found the concept interesting.

right now I’m just 5 gallons of parks 50 and AAA. At this point I do t use AAA much any more and quench just about everything in the parks. It is such a nice oil to use. Wonder if I could get a discount on a drum of it.
 
JT, I think you should go for it. If you've got the tone and resources to do it, why not?

If you can come up with a system that can accurately track how much air and water you are using per quench, you'll have a real, measurable piece of data that you can compare to traditional methods...

I think it's worth looking at.
 
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