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Thread: Oil Quenching - Potential fire hazard or not?

  1. #1
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    Oil Quenching - Potential fire hazard or not?


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    I have a newbie question about hot steel and oil.

    Not that I have any intention of performing any oil quenches in the near future, but as a rural FF for 23 years, never once did we have a call where the cause of the fire was from an oil quench, and I'm sure that there were more than a few knife making attempts in the area.

    So, when you stick the hot steel in the oil, what keeps the oil from catching fire?

    I've see posts with temps of 900, 1000, 1400, 1800 deg F among others and I'm pretty sure these temps are all way above the flash point of most oils. Obviously something is being done to prevent Class B fires in all the home shops when oil quenching is being accomplished, but what?
    "A Folding Blade is a Broken Blade" - Anonymous #465 in RyanW's 2014 GAW
    "A Folding Blade is a Bleeding Finger" - Zzyzzogeton

    Beckerhead #346

  2. #2
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    If the blade is fully submerged, there isn't enough oxygen to combust.

  3. #3
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    Quote Originally Posted by Willie71 View Post
    If the blade is fully submerged, there isn't enough oxygen to combust.
    OK, I understand that part, but I have seen statements about "partial tempering" or "edge tempering" or something similar implying that only the edge of the blade or just the blade and not the tang gets quenched? That's where I was thinking that the really hot metal and oil interface right at the surface could cause a flash-over like effect. Am I misinterpreting what is happening in those cases?
    "A Folding Blade is a Broken Blade" - Anonymous #465 in RyanW's 2014 GAW
    "A Folding Blade is a Bleeding Finger" - Zzyzzogeton

    Beckerhead #346

  4. #4
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    Plus

    Sufficient oil volume to absorb that heat and give only a moderate temp increase in the oil.

  5. #5
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    There are times when the oil right around the blade will catch fire, but if your container is large enough, it's usually brief. Edge quenching on the other hand is usually done in a large flat container and the surface can catch fire (sometimes a maker will use a flat pan as a quench tank). If the maker is using a veg oil or motor oil, the chances of a flare up increase. Commercial quench oils aren't prone to flare ups, but it can happen.



    Last edited by Mudbug007; 08-28-2013 at 12:18 AM.
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  6. #6
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    This is why there are no knife makers left after they do their first quench. only us beginners wanting to learn from people who never lived long enough to finish the first.

    But really......its okay. Its not that serious.

  7. #7
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    Thanks EB, for the explanations. Now, being dangerously armed with a little knowledge, I realize I STILL don't know enough to even think about doing my own HT yet. First, I have to build or buy a "heater", then.......
    "A Folding Blade is a Broken Blade" - Anonymous #465 in RyanW's 2014 GAW
    "A Folding Blade is a Bleeding Finger" - Zzyzzogeton

    Beckerhead #346

  8. #8
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    Edge quenching is a metallurgically stupid idea and causes flare ups because you have hot metal igniting the vaporized oil on the surface, people sometimes multiply this stupidity by using motor oil or transmission fluid. Do a full immersion quench with either manufactured quenching oil or vegetable oil and you will not have problems.

    -Page

  9. #9
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    If you feel it necessary to do a differential ht or produce a hamon either fully harden the blade and follow with a spine draw or do a clay coat

    -Page

  10. #10
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    Well, if you're in the right shop, and you have things cleared, if it catches it's no big deal. I've had it happen, and I never had a reason to panic. Granted, I've been the type to learn firebreathing and such weird things.

  11. #11
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    and have a good lid handy for the quench tank. I use Parks and have never had a flare up that didn't go right out. But, if I did I would just place the lid on the tank and smother it. Also have a big enough tank it don't slop it over the sides. I got other stuff that I feel has a lot more fire hazard potential. Just like drill presses, grinders and the like, good hazard management is the key.

  12. #12
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    Using a commercial quenchant, which has a flare up retardant in the formula, and having a tight fitting lid will take care of any worries.
    Stacy E.Apelt
    It is better to die fighting evil than to live under it.

  13. #13
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    Never gave it much thought. Many times when I plunge the blade into the oil there is a brief flame in the oil around the hot blank but it goes out by putting the lid on the bucket. I'm more concerned about getting rid of the oily fumes before they can circulate around the shop and out into the house.

  14. #14
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    I remember a while back somebody was thinking about using the plastic 5 gallon bucket the oil came in to quench, if he was to try this and he let the blade slip your beeper will probably go off.

  15. #15
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    Ya' think?
    (And I completely agree with your previous statement as well.)

    Quote Originally Posted by sunshadow View Post
    If you feel it necessary to do a differential ht or produce a hamon either fully harden the blade and follow with a spine draw or do a clay coat

    -Page

  16. #16
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    One of the dumbest things I've done in the shop involved a flash up like this.

    I was doing an interrupted quench on a very large W2 blade (11-1/2" L x 2-5/16" W x 0.350" ricasso!). I pulled the blade from the digitally monitored forge, plunged it tip first into a tall, vertical 8 gallon tank of Park50, in for a few seconds, and pulled back out for 2.... None of this so far is anything new to me, I had done it a hundred times.

    The difference, was I normally do it with the blade hanging from a wire. I had this blade held by a pair of tongs and I completely forgot to put my welding gloves on. With a pair of gauntlet style welding gloves this wouldn't have been an issue. But, I didn't have 'em on, and I got a big flare-up that wrapped itself around my hands/forearms, I dropped the tongs+blade right into the tank, warped the blade like a frigg'n banana, and didn't have any hair on my forearms for a few weeks. Luckily, the burns were only bad enough to blister my hands.

    One of those things where I got busy trying to do 5 things at once, and made a stupid mistake.

    I've never had anything happen while oil quenching that would cause fear of starting a shop fire though.
    -Nick-



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  17. #17
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    I singed some eyebrows and probably modified my hairline a bit a few years back oil quenching a bunch of 4 pound hammers. There's enough thermal mass there that even 15 seconds after submersion they're still hot enough to ignite the fumes if they break the surface while agitating. The fire ball was large enough that if I had been doing it in an unwise location it could conceivably have started a fire. There was an impressive amount of heat generated. You wouldn't want something like that around a bunch of WD-40 soaked belts and wood dust for sure.

    I was using a commercial quenchant. I wonder if something like canola oil, which doesn't really create much oil vapor, would have made a smaller flame?


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  18. #18
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    I am new to knife making and do not have and "real" quenching oil yet so I use canola oil for my 1075 steel. I was using a 1 gallon metal paint can and dipped my knife tip first and went as far down as I could, for some reason I lifted the knife and had a flare up. I stayed calm as the flame burned all my hand hairs and the flame went out as fast as it flared. It was the second largest fireball I have ever created. As my skills progress with grinding I will start upgrading my equipment including a more proper quench oil and quench tank.

  19. #19
    Since every tool we use is borrowed from industry; in big commercial settings heat treating tanks have been fitted with lids
    held open by fuseable links. The links are much like what is found in a sprinkler head, so when there is a flare up the links melt and the lid falls down by it self.

  20. #20
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    You can sure get a flare up, just be prepared.

    Here is a video, Its a "promotional" video so excuse the music, its where I work, go to right about 56 seconds. They were filming different things at the plant, the guy was using a radio controlled helicopter and got pretty close LOL

    This was a large piece, probably 4140, being quenched. The tank is about 25 feet deep, you can see the open oven in the background, fun to watch, even in person


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