Volume of quench tank...

[MLenaghan]

Hi guys, I was wondering if someone can enlighten me on some things I've never seen talked about much. Now I dont claim to know what I'm talking about so sorry if this is a little cunfusing or over thought

 

Now we all heard about all the different types of things to quench into like Fast oils, slow oils, veggie and what not then there is water and brine and how they all have there place. But now I've never seen much talked about the volume of quench tanks... for a long time I was getting mixed results with my hardening, but I was using a small 3 inch pipe with oil in it. With swords the half towards the tangs would some times not fully harden or devolpe auto hamons. For a long time I thought about buying a faster Oil like parks 50 but it's hard to find around here and shipping always sucks so after a while I started thinking that maybe it wasn't the oil alone but also that there wasn't enough oil to pull all the heat away without also heating its self to a point where it's not a efficient at pulling the heat away.

 

This won't be a perfect example but it's what I've noticed... (also I'm using a kiln so the temps the same, and weights of blades are very similar)

 

My old set up was a 3 inch by 36 thick walled tube, for the most part preheated to 130 F. and after the quench would be over 400 f with all kinds of bubbling and fire

Volume 4 liters of oil

 

New tube I got is a 6 inch by 40 thin SS same thing preheated to 130 F and after the quench 190 F with only a small flame and very little turbulance in the oil

Volume is about 18 liters

 

So having 4 times the volume worked out to less then half the temp after all the heats been exchanged. Would this in anyway mean that it would be any faster of a quench? or more even of a quench with more space for the heat to transfer into? This would also have affect more at smaller amounts or else people would be using bath tubes...

 

There is a good chance I'm over thinking this or maybe my tank befor was just to small for what I'm using it for. Either way I'd love to hear some peoples thoughts or experiences since this is a topic that doesn't seem to get brought up much.

[Raymond Jewell]

i personally believe volume does indeed play a key role in your quench efficiency. I cannot give any scientific specifics on actual volume to steel size ratios, but I find that the more quenchant you have, the better your quench efficiency is (within reason, of course).

[B. Norris]

The tank needs to be able to hold a large enough volume of quenchant to extract enough heat, quickly enough, to get below the nose on the graph. My experiences, similar to your own, have led me to believe that a small diameter tube is not ideal for swords! Another thing that plays a big role is agitation of the quench. As you noticed, heat rises in a liquid, and the part of the sword at the top of the quench sometimes did not harden successfully. Another point, that a MS made to me once, that really got me thinking, is that having a larger surface area is ideal. His point was that all that heat, that rises, in a narrow tube, will easily heat the oil at the top to the point where it flashes. A quench tank with a larger surface area will be less likely to do so because, the heat is distributed over a larger area. Having the oil flash is very bad, especially if it is something expensive like Parks, because, the oil degrades faster and it affects the rate of heat extraction of the oil. Of course agitation would play a big part in preventing this.

 

~Bruce~

[B. Norris]

Here is a link to a topic on BladeForums Recommendation? Pump for a quench tank. There are lots of links to other sources of information.

 

~Bruce~

[B. Norris]

Whoops! Sorry, went through the topic and none of the links were working. You could probably access them with the Wayback Machine, if you wanted.

 

~Bruce~

[Matt Todd]

Just a thought, but have you thought of going with a tub type design? If it works for the Japanese swordsmith, it seems like the way to go. Obviously this would require more volume of oil, but if it gets the job done.....

[C Craft]

Ha Ha, that is funny Norris that is my old post.

 

I use to be and still am, on that forum Dixieblade57. It was a name I picked when I first got interested in knife making. After I got serious I changed my screen name to the same as my makers mark, C Craft! They have a charge for name change on that forum so it was never changed on that site.

I rarely even go there anymore, as I had a disagreement with one of the moderators and then the owner of the site. Basically I felt they were too centered around money when I know of at least three other forums that I continue to be an active member of at this time, that focus on knife making and not how much they can charge you for this and that!

 

Anyway back to the subject the design still remains the same on the quench tank. I have everything in hand to build the quench tank. However at this time it has not been built any questions I might be able to help with feel free to ask. I am a part timer and have two grandchildren that I am helping with M-F, as well as a girl that is almost 2 yr.s of age. My wife also is very sick and so I stay real busy and the knife making often has to take a back shelf.

 

OK I just went back and re-read your post. I think it may be a case of over thinking but in case I am missing your train of thought, here goes.

 

The oil and it depends heavily on what quench oil are using as to the speed of the quench. The idea behind the quench tank is that if you are quenching more that one item in a short period of time the temperature of the oil will begin to increase.

 

The thought behind the tank design was that it would preheat the oil to a desired temp and the pump would constantly circulate from the bottom to the top to maintain an equal temperature throughout the quench oil container! That came from great discussion with Kevin Cashen on another forum as to whether the effect of the quench could and will vary from the tip of the blade to the ricasso area considering how the knife is plunged into the quench oil. By preheating and circulating the oil, you can help to take some of the variables out of the equation.

 

It also tends to make an equal oil atmosphere whether your tube is long enough to quench a sword or only long enough to quench say a bowie!

 

In short what I am trying to say is volume really only plays a part when the temperature of the quench oil is not not correct. If it is not hot enough for the low optimum heat range of the quench oil you are using, or as well if the temperature begins to get too hot ( when more than one item is quenched) pushing the temp beyond the optimum high heat range, temperature for the particular quench oil! IMHO

 

That is what the quench tank I was discussing on that post was supposed to do. The heating element would preheat the temp of the quench oil to its low range, as well the pump would continue to circulate the oil so that temp would be consistent throughout the tank. The heating element is set on a thermostat so once it achieves that low range temp, the heating element will kick out. It will cycle back only when the temp drops below the desired low range.

There will be a warning light that is thermostatically controlled on the tank that monitors the high heat range and once it is hit the warning light will come on and flash. At this point you will have to allow the quench to cool to at least the high heat range desired. This will keep you from overheating the oil, and thus shortening its life

 

!If I can help in any way give me a holler!

Edited February 24, 2014 by C Craft

[R.H.Graham]

Fwiw in water quenching swords I did not find i was happy till I was up into the gallon per inch range, about 32-34 gallons is what I had in the quench tank.

For salts and oil both I used tubes 40 inch tall and 8 diameter, was going to switch to 12 inch but never got to it, but it seemed to be enough oil, just, for the swords I was doing.

For salts it was fine.

 

For the knife and tool quench tank I had 5'gallons in that usually, a big stock pot, found I had enough convection to keep the oil even enough for tempering and quenching low alloy.

 

If possible, more is always better for quenching I think. Especially water. The bigger the tank, the smoother the currents, and the less warping issues I had.

[Jeppe]

ok, here is the science version (yes, I am a geek and chemistry/physics is my professional line of work).

It is all a matter of how much energy is stored in the steel object you want to quench compared to how much energy the quench media can take.

This can be calculated using what is know as specific heat of a material.

For carbon steel, this is 0.49 KJ/(Kg*degree) - that is it takes 0.49 KJ of energy to raise the temperature of 1Kg by one degree Celcius.

 

Lets take an example of a Viking sword blade of 1Kg heat treated to 1000 degrees C and quenched to 100 degrees C - temperature difference is 900 degrees.

900 degrees is equal to 441KJ of energy that we have to remove (900*0.49).

If we use just 1 litre of water (1Kg) the temperature of the water will go up by 105 degrees C (441/4.2).

Assuming the water was at room temperature it would all have boiled off!

You want a water bath that only goes up a couple of degrees in the process (say 10 degrees),

so we need 441/(4.2*10) = 10.5 litres

 

all oils have less specific heat that water and we will need more.

Linseed oil is 1.84 KJ/Kg*degree so we would need 441/(1.84*10) = 24 litres for the same process.

 

Here is a link about quench oils

http://www.globalspec.com/learnmore/materials_chemicals_adhesives/industrial_oils_fluids/quenching_oils_heat_treatment_fluids

 

Here is link about the quench process (steel microstructure)

http://www.keytometals.com/Articles/Art12.htm

 

[Raymond Jewell]

and that is why I loved my science teachers... they always explained things in laymans terms

[Jeppe]

Regarding the shape of the tank, if you have a cylinder then more energy will be deposited in the top where the blade enters than in the botton. In some cases (if the tank is too small or only just the right volume) this will result in a less efficient (slower) quench in the top region.

The result is a hardness gradient from the tip of the blade towards the guard. For a sword this may be desireble giving a hard penetrating/cutting tip and a softer more flexible region sust above the handle so the tang doesn't snap off so easily.

For a uniform quench a bathtub design is better, so a pipe cut in half lengthwise and the ends sealed.

[Jerrod Miller]

To add to all that:

The specific heat is variable based on temperature. Since we are dealing with a very large temperature range (relatively for both the metal and the quenchant) it is wise to put in a good factor of safety above the basic calculated amount.

Think about what is happening during the quench besides heat rising: As the blade enters the quenchant the top bit of the oil is taking energy (heat) from the blade tip blade tip and every bit behind it as the metal passes through the quenchant. That is likely the single greatest factor in temperature gradients during the quenching of a blade.

The bathtub design is better uniformity for the quenchant, but not the blade. That is why they are more prone to warping, especially with double edged blades. When the metal is cooling down it is shrinking and getting stronger. When using the bathtub design one side of your blade is shrinking and getting stronger in that shrunken state than the other side (first side into the quenchant versus the top edge). This isn't as big of a deal for single edge blades, and plays into the bending of Japanese style blades (along with the clay, both effect cooling rates through the cross section).

[Jeppe]

To add to all that:

The specific heat is variable based on temperature. Since we are dealing with a very large temperature range (relatively for both the metal and the quenchant) it is wise to put in a good factor of safety above the basic calculated amount.

 

Which is why I only allowed the quenchant to heat up 10 degrees C in the example, in that case the room temperature value is ok.

For the steel I only had the room temperature value, and that would be different at 1000 degrees C. Another factor I have not taken into account is that extra energy is involved when crossing phase boundaries (for example water turing into steam). So yes, you should add a safety factor.

Also, Jerrod, thank you for explaining the difference between a tube and a bathtub quench better than I was able to.

[R.H.Graham]

Never found a gradient in hardness in the tubes, when they were too small it would be hard and then go to soft coarse pearlite across a fairly small zone, perhaps a few centimetres.

Quenched dozens of sword blades successfully in an 8 inch by 40 inch tube with peanut oil, although it was right on the edge of not being enough. 10 or 12 inch diameter tube would be more than enough for swords I think.

 

No science on my end, just from observations over quite a few large blades.

 

Tub for double edged swords? Forget it, don't even bother. Disastrous warpage pretty much every time.

[Jeppe]

Actually Randal, you are right on target. 8 inch by 40 inch is 20 litres, and the specific heat for peanut oil is around 2.2

If these values are used in my example above, it coresponds exactly to the energy stored in the blade.

[R.H.Graham]

Cool, makes me happy to hear that :0)

I started with 6 inch way back, very quickly realized it was not enough, went to 8 inch and it was pretty good, occasionally had issues with really big sword blades , so 10 would have been the next step for me.

 

With low temp salts 8 seemed to be sufficient for everything I needed to cover.

[Dave Stephens]

Jeppe --

 

This is awesome. Thanks for the technical explanation of a phenomenon I've not fully understood until now. Amazingly, my quench tank seems to conform to your formula, but it's very nice to know that the science behind it is sound.

 

Thanks again for your contribution.

 

Dave

[Jerrod Miller]

I didn't make it too clear in my first point, but it is definitely best to use the "simple" equations then add the safety factor. It certainly is not worth all the effort to come up with the equation that solves for variable heat capacities and heat of transformations (the energy used for phase change - as noted in re/decalescence).

 

Here is a rough Cp verses temperature, including phase changes worked in. Notice that the far left value is about equal to Jeppe's 0.49 kJ/(kgK).

 

It doesn't take a whole lot to miss beating the nose of the curve on a TTT, so if your quenchant gets to the point where it cannot take the heat away from the metal fast enough you are pretty hosed. Plunging tip first as fast as possible helps even things out, and agitate the quenchant (stir) as much as possible to keep the temperature (and therefore heat transfer rate) as even as possible.

[R.H.Graham]

I have a whole big problem with this stir/agitation advice, particularly if you are talking about heated oil.

 

Speaking from my own in-practice observation;

 

Anything much longer than a dagger will be warped in a heavily agitated quench, often badly.

I've quenched double and single edged sword blades mostly past 26 inches and out to 40 inches, of my own, and as many again for other people, and everything I tried as far as flow or agitation goes made for much higher warpage rates.

 

However, at the same time I learned that the oil in my tubes, heated at the bottom with a simple stovepipe jacket around them, usually had no more than a 5 degree spread in temp top to bottom, had very minimal warpage, and never had trouble fully hardening anything, accept for a few very exceptionally low harden-ability steels, 1086M and a particular w-1 melt.

As I said before though, I was also left with the impression that a larger tank would have been better. If I did not do my part correctly then occasionally I would have to re-do a heat treat, and once in a while twice even.

 

So definitely not perfect. But I can say for sure it was a much more acceptable circumstance for me, as opposed to dealing with a much more severe warpage percentage.

 

This would have been the 8x40 i had mentioned before.

 

I think volume is more important, and in big blades I kept seeing agitation in the tubes was more harm than good.

 

That being said, I have seen flow rigs on tub/horizontal quench set-ups that seemed to work very well indeed.

 

Again, not arguing at all, sharing personal observation.

[MLenaghan]

Thanks alot guys for all sharing your info with me, I got alot to think about now...

 

and like Dave said I'm happy science should be on my side, most blades I do are double edged, thin cross section and for the most part well under the 1 kg mark when quenched. As R.H.Graham said bigger would most likely be better, but honestly it's taken me a long time to find a 6 inch tube so I'm gonna have to use this one for a while anyways. There's always moving to a faster Oil option if need too.

 

atleast it's better then a 3 inch tube and now I have some idea why...

[Alan Longmire]

I've run into the agitation issue on long double-edged blades as well. About all you can do it pump 'em up and down in the tube, and even that will sometimes cause warp issues. You sure as heck don't want to move them edgewise or heaven forbid flat-wise. Now, if one could build a setup with perfect laminar flow from bottom to top, recirculating the oil, I can see that working well. I just don't know how to do that since everything I can think of ends up causing turbulent flow, which warps sword blades without even trying.

 

I have heard of vibrating the tank to help break up the vapor phase, everything from a small electric buzzer to hanging a (running) drill chucked with an L-shaped rod off the tank, but I've never seen a test of it on long double edged blades.

 

Any thoughts, science guys?

[R.H.Graham]

Thanks alot guys for all sharing your info with me, I got alot to think about now...

 

and like Dave said I'm happy science should be on my side, most blades I do are double edged, thin cross section and for the most part well under the 1 kg mark when quenched. As R.H.Graham said bigger would most likely be better, but honestly it's taken me a long time to find a 6 inch tube so I'm gonna have to use this one for a while anyways. There's always moving to a faster Oil option if need too.

 

atleast it's better then a 3 inch tube and now I have some idea why...

If you are quenching low alloy like 5160, something with high harden-ability, the 6 inch will get you by I think.

It'll be dicey with the 10xx stuff sometimes.

[Jerrod Miller]

Any thoughts, science guys?

 

Just a gut feeling, but I would guess you are splitting hairs here. And if you were going to vibrate anything to break up the vapor jacket, vibrate the part. Have fun with that!

 

The goal with the agitation is to ensure even distribution of temperature. If you stir with your blade either edge-wise or with a flat then you are exposing the leading edge/face to better cooling, which gives the same problem as the tub style quench. This is also true for stirring during the quench with something other than the blade. I am very glad this was brought up as that could easily be overlooked by the beginner. I would stir just prior to quench to ensure uniformity at the beginning, and if you have a helper and you are doing an interrupted quench stirring during the interruption would be good. If you really wanted to have constant agitation I would think along the lines of a pump pushing quenchant up from the bottom of the tank straight up the middle, or even better uniformly across the area using a baffle. This sounds like a lot of extra work with potentially little (if any) gain. I would recommend using the biggest tank you can and just moving the blade vertically.

[R.H.Graham]

I always put them straight in, quickly, and hold them still.

 

I found natural convection kept the temps in both salts and oil more than acceptably even, as far as I could tell.

[J.Arthur Loose]

I agree with Randal. If you're working with a decent oil at its proper working temperature, for a long, double-edged blade, plunging straight in and holding- convection will move the oil quickly enough and symmetrically, reducing warpage. Agitating or stirring will increase the possibility of warpage.