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I'm ready to acquire some oil for my first oil quench tank. I'm going to make the tank out of an old fire extinguisher that is ~ 8" round and 22" tall. I will cut the top off and weld a hinged lid on it. Should be a bit over 4 gallons of quenchant.

I would like to harden mostly spring steel and 4140 for things like top tools, chisels, punches and spring fullers for the PH. I would also like to try my hand at some blades.

What would everybody recommend for the oil. I like the idea of vegetable oils because of the ease of getting them and the less toxic nature of the fumes and disposal, but have heard that certain kinds go rancid. How often does veggie oil need to be changed? Can you add something to make it not go rancid? What about used aft or motor oil? Open to all suggestions.

thanks for the advice.

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All food safe oils will go rancid. You can extend the life of them by adding lemon juice or viniger, but then you have water in them and that is dagerouse when you add heat. 22" tall makes for a lot of oil on top of the water and if it get to the boiling point it will be under pressure. The best bet is to heat the oil often and add some rosemary sprigs to it, and to change it out when it goes really bad.

There are some peanut oils designed specifically for deep fat fryers, and they have additives to them to extend thier life and reduce foaming. They come in 5 gallon buckets and are availible from any good restaurnt supply company.

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I'm trying to remember how many years my veggie oil has been in the tank---it doesn't stink---yet. Been a couple at least. Keeping a lid on it helps---less oxidation and keeps the critters out of it. Climate may make a difference too.

I'm using a very similar set up to what you describe, tank bottom, one thing I did to make it "safer" was to build a wooden holder for it. Scrap 2x6, two lengths on their sides and then two cross sections on top of that cut to fit around the tank---makes it much more stable and makes most of the dripping or boil over caught by the easily replaceable wood instead of the hard to clean floor.

Make up a pre-heater too, simple slab of steel with a heavy steel wire with a hook on the end attached to it. Heat in forge, drop in tank with the hook holding the rim and getting the heat to transfer in the bottom of the tank rather than just the top. Due to a student who didn't realize that heating the quenchant hotter than the draw temperature for the alloy would be a bad idea I have also picked up a thermometer to measure the oil temp.

If you are really worried about it turning get used fry oil from a fast food place and switch it out often.

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For the steels you mention, in not-too-large cross-sections, a medium speed oil would probably be a good choice. The McMaster-Carr 11 second oil or Brownells Tough Quench (Houghto Quench G) both come to mind as options that are readily available. (The 11 second stuff is a little toward the fast end, actually. McMaster also has a 28 second oil, which very well might be fast enough for 4140 and 5160. I'm not sure.) Brownells charges a serious premium on Tough Quench, but the McMaster stuff is about $80 (plus shipping) for 5 gallons. That's not cheap, but it'll last a long time if it's not abused.

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I have been quenching in 100% veterinarian grade mineral oil heated to around 140° I harden 5160, 1084, 52-100 and have made hammers out of 4140 and all have hardened no problem. The mineral oil doesn't put off fumes as bad as some oils. It will flare up but not bad. My oil is about three years old and still clear. It also doesn't leave a mess on the steel and is cheaper than regular quench oil. I get my mineral oil from my local farming co-op.

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I missed the part where you specifically asked about veggie oils.

The thing about vegetable oils is that they oxidize over time ("rancid" is another word for "oxidized"), and that changes their cooling characteristics, among other things. Some folks, like Thomas, don't seem to have much trouble with that, but it seems like many do. I'm sure environment and storage make a big difference. Mineral oils oxidize too, but not enough to matter at room temperatures -- and commercial quench oils have antioxidants added to help extend quenchant life. So they'll last a lot longer.

I have quenched in used motor oil. Aside from the fact that it's a slow quench with unpredictable characteristics, I'm really not convinced that's such a good idea from a health perspective.

Thomas, for some time now I've been thinking about some kind of immersion heater for my oil. I have used the "quench a big piece of red hot metal" method many times, but I have a feeling that that's much harder on the oil than bringing it up to temp more gently, over 15 or 20 minutes.

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Quench black heat piece of metal?

What my student has learned is that you don't want a read hot piece in the tank generally as they you have to wait till it cools down They make heaters for chemical uses that go outside the tank---but what about a simple bain marie---hot water bath? Perhaps set the quench tank in an old crockpot full of water?

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i have been using etra virgin olive oil for a about to years and as thomas said by keeping a lid on it it will last a long time. if you can find the new instruction you can make a batch of rob gunter's super quinch. i think the hammers blow or the california blacksmiths have details. or you can talk to your local oil supplier and see if the can still get chevron"s quinching oil last time i checked you could only get it in 55gal barrel.

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For breakfast this morning I had eggs cooked in small pyrex bowls sitting in a large pyrex baking pan full of water and set in the oven (as well as raisin bread french toast, ham steaks, grapefruit and tea...my wife does a *mean* spread for Breakfast and Bible Study or B & BS as our vicar calls it...)

You can see how the thought of heating something using water was on my mind...

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I looked in the yellow pages for a local lubricant place and I bought 10 gallons of quench oil from them about 12 years ago. I could use another couple to top up my tank. I cannot remember how much it was but it was cheaper than motor oil. I need to make a water bath/jacket for my quench tank to cool it rather than heating it. I have had it get pretty hot doing multiple pieces.

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John posted my suggestion, call around and buy quench oil or heat transfer oil. The guys who deliver heating oil can tell you who to call if they don't carry it. I brought home a few gallons of heat transfer oil when we changed the oil in the crack pot at work and it works really well.

Frosty the Lucky.

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use what ya got..i have used motor oil but this years flavor is non foaming hyd oil it's about a 32 vis in it's cool state so i heat it to 130+- and have used it for 4-5 years but..i have it in a 3" cut off drive shaft so it's not alot of volume so a 5 gallon can will last a long time

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