newb question; oil temp

K

kennymc80

Joined
Jan 22, 2006
Messages
5
I have looked in my books and searched for a reason but cannot find an explanation. Why does the quenching oil have to be 140 degrees when oil hardening? Should or does it ever vary? :confused:


Warning: if the answer is way to technical it will probably go over my head.
 
the reason as i understand it is because contrary to what you would think, it actually speeds the quench up. the reason being is because when the oil is cold it is very viscous and it doesnt flow around the blade so the superheated oil gets stuck next to the blade. when you preheat the oil it lowers the viscosity and allows it to carry the heat away. at least thats how i got it, someone please correct me if i'm wrong
 
It's not exact but approximate 140F and it's a combination of viscocity and cooling properties that works best at that temperature.
 
I've been using olive oil at 140, but it has occurred to me, after reading many threads about metallurgy (and a big thanks to you, mete, for sharing!) that each specific quenching oil would probably have its own optimal temp to cool at the optimal speed. I've been thinking of changing to a commercial product (like tough-quench) for this reason, assuming that it comes with a optimal recommended temp. Would this really make a noticable difference in hardening?
 
Thats an interesting question Kenny.Not because I didn't know the answer,(after hanging around here for a while you just know[if you don't,you should:) ])but because the quenchant I use(Brownells Touqh Quench) specifically says on the label - " IMPORTANT : USE AT ROOM TEMPERATURE - DO NOT HEAT ! " I'm not yelling at you guys :) That is just how it's written on the label ( capitals & ! included ) Since this is an "engineered" quenchant does any one else who uses "Tough Quench" follow the directions ?? I have always been curoius about this,I have tried it both ways & now just warm it to 90*-110*.Middle of the road,can't go wrong with that now can you :D BTW - I have always had good results with this quenchant but until I purchased a "Hardness Tester" could not accurately check the results and since the purchase have not experimented with the 140* or (what is room temp,about 68*?) I am anxious for feedback on this thread that Kenny started.
 
I think 140o is a bit high, and have gotten poor results at this temp. The info on my 01 wrappers say 125o, and this works very well for me. When a red hot blade goes into cold oil, the heat vaporizes the oil that contacts it, forming a vapor barrier around the blade and not allowing acuall contact until it cools, which is often too slow to get a good hardness. The warmed oil vaporizes much less and speeds the cooling for better hardness. Using an extreme for an example, drop a piece of red hot iron in clear water and you will see a mass of tiny bubbles come off as it sinks. The same thing is happening with the oil, only to a lesser degree. The thickness of the oil also plays a large roll in this process.
 
Each particular quenchant will have its own recomended temperature to suit its specific formulation. If you lack the means to read exactly how the oil is performing with you treatment, it is probably best to just follow what the manufacturer recommends.

Most folks get all hung up on quench speed, but unless you are right on the borderline of hardenability (e.g. 3/16" or better 1095) this is one of the lesser concerns. Think about it, if quench speed was all that matters then water or brine would be all we needed. If you are working with almost anything other than 10XX or "W" series, something as fine as a few degrees temp before the blade goes in will not be a huge difference.

The problem is that the quenching process is so much more- vapor points, flash points, thermal conduction, thermal convection, oxidation and longevity of the quenchant etc...

Getting it hard is one thing, keeping it straight and in one piece is another;)
 
Kevin R. Cashen said:
Getting it hard is one thing, keeping it straight and in one piece is another;)
Click to expand...

Despite having done a lot of research (the best info I've found is from threads involving you and mete - thanks much!), I'm still learning this the hard way. Thanks for the info.

BTW, my wife, looking over my shoulder and reading your above quote, laughed out loud.:)
 
Sorry for this newbie question but if you put a red hot blade into a bucket of oil...won't the oil set on fire?
 
Not a dumb question.The fire is called flare up.If there is enough oil (at least 1 gallon,more is better) the flare up will either not happen or will be very short lived.There will not be any explosion like on TV.Have a lid for the quench tank to cover it if the flare up does not go out in a short while.Commercial quench oils often have a fire retardant added to prevent flare up.
And always have a fire extinguisher (a good ABC one,not a little kitchen job) wherever you create your knives.
 
Although Brownell's does not recommend heating its Tough Quench, I have found that using it at room temperature gives less than optimal results. I did a lot of testing using it at room temperature with O1 and Dan's JD5160. I was not getting the hardness (I have an Rc tester) I believed I should even with careful temperature controls and soak times. I have since obtained excellent results in my shop by heating the oil. For O1 I heat to 120F and for 5160, 140F. Hopefully, Bruce Bump and Rlinger will chime in here as I know they both use Tough Quench.
 
What Bladesmth said. Also we need to remember that the liquid itself does not burn, it is the vaporized oil that ignites, and this requires a special blend of O2, fuel and heat in order to happen. So if you get your entire blade below the surface, it makes it very difficult for this to happen. Unfortunately edge quenching makes a flare up almost inevatable, and that is why I do not recommend using you finest quench oil for an edge quench, unless you clay it and go entirely under the surface. I have watched a beautiful batch of #50 go from crystal clear to a sludgy black mess in less than a day from a shop full of students edge quenching:( .

I have been putting 1500F blades into oil for many years now and in my shop I have NEVER had my #50 flash yet. Never is s very strong word, and I had to think about it, but I believe I am safe in saying that.

One also wouldn't think that overheating your blade would make that much of a differnece, after all at 1475F and above what difference does a few hundred degrees make when the flash point of an oil is around 400F, but it does make a difference. If the blade is at a proper heat the quench is actually a very peaceful thing, there is a soft little purr when the blade goes into the #50 and then you can watch the colors quickly fade under the surface as you move the blade and count off the time, and then it is all over. If you heat your blade too hot there is a growl when it hits the oil and there is fire and boiling! Things get very hectic for a minute or two and this is when some often panic and get burned quite badly.

If you get a flash, forget the blade, it will be safe sitting in the oil and it is the least of your worries. Don't throw anything on the oil to put out the fire, and NEVER try to move the quench container. Even a fire extiguisher could be disastrous by sraying flaming oil everywhere. Calmly put a cover on the quench container and remove O2 from the equation and the fire will go out every time. Take a few minutes before lifting the lid since you still have fuel and heat and reintroducing O2 will only allow it to take up where it left off. For those who didn't know, this post probably gave away that I fight fires when I am not forging blades.
 
Thanks for the info...honestly it sounds totally complicated and hazardous, especially when the only place I have to work is my garage (l live in suburbia not a farm). The last thing I want is to have burning oil flying everywhere! I have a funny feeling that I will only be working on pre tempered steel and just grinding it. Still got a heap to read up on though. Thanks again.
 
Irezumi said:
Thanks for the info...honestly it sounds totally complicated and hazardous, especially when the only place I have to work is my garage (l live in suburbia not a farm). The last thing I want is to have burning oil flying everywhere! I have a funny feeling that I will only be working on pre tempered steel and just grinding it. Still got a heap to read up on though. Thanks again.
Click to expand...


I have very little experience so far but I can tell you from the few blades I have done it's not that hazardous. I do it outside of my garage and have a bucket with about 5 gallons of oil. I have so much oil, and I get such a good submersion that I only get a little smoke. It is very difficult for me to heat that much oil though, hence my original question. I am still very green to this craft.
 
I am new at it too, and was very nervous about the heat treat & quench, but it was not nearly as dramatic as I thought. I'm using olive oil (other veg oils can be used too). With smaller knives (all I've done so far) there is no flare up, and the little smoke made neither sets off smoke alarms nor smells bad (smells kinda good, in fact).
 
To heat up your quench tank,just stick the end of a 3 foot long piece of 3/4-1" round mild steel in the forge.When it gets red stick it in the quench and stir around for 10-15 seconds.Do this a number of times and the oil will heat up nicely.I realize that this won't work with a one brick forge or those using a torch to HT.
This weekend I will try to make a tutorial on building a 2 gallon,temperature controlled,recirculating quench tank.
Stacy
 
By using olive oil, I can just heat it up on the stove (I use a large roasting pan with lid in case of flareup) and carry it (carefully!) to the garage. I use a candy thermometer to check the temp. I heat it to 150 -- by the time I get the blade heated, it has dropped to 135-140 for quench.
 
Chant said:
By using olive oil, I can just heat it up on the stove (I use a large roasting pan with lid in case of flareup) and carry it (carefully!) to the garage. I use a candy thermometer to check the temp. I heat it to 150 -- by the time I get the blade heated, it has dropped to 135-140 for quench.
Click to expand...

I kept mine, when I used Veggie oil or Olive oil, to 125F, it worked very well.
as a side note..for my quench vessels
I use exht pipe with a plate welded to one end so I can use them vertically
I hate the mess of sticking anymore steel in the stuff than I have to
so I
heat the out side of the tubes with O/A working from the bottom up, you can use one of those round headed meat thermometers by setting it on top submerged in the oil, I say tubes because I have
4 different sizes to accommodate different amounts of oil I'll need for a particular size blade. I dump oil from one to the other as needed.

I should add, for Full quench or clay coating.
 
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