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Quenching volume of oil


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My style of blacksmithing could be classified as " Rural Circa 1850 " as apposed to "ASME Circa 2012" .

Is there a rule of thumb as to how much oil is needed to safely and effectively quench a given weight of steel.

Now I know this question may be a little vague, but I'm using junkyard leaf and/or coil springs and the parts to be quenched will be in the range of a few ounces up to a maximum of about two pounds.

I can not keep the oil at the forge so I expect to bring the oil to the forge and remove it after I use it.

I know there are oils specifically made for quenching steels, but what did blacksmiths use a hundred years ago, before these were invented.


Will used motor oil work. ? I can do the quenching outside in the open air if necessary.

Many thanks

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1 gallon quenchant per pound steel is an industry recognized guideline. You can use more without concern.

Used oils, particularly motor oil have contaminants that become areosolized during quench. Without proper and adequate ventilation this is a health hazard. With fresh clean oils the areosols are still a health hazard, so set up for proper ventilation anyways.

Special quenching oils have a known rate of cooling, with used oils you may want to run a sample before runing your item to make sure the performance is as expected.

It sounds like a 5 gallon *STEEL* bucket *WITH A LID* about 1/2 full of oil will be adequate for most of your needs, and a 1 gallon steel paint can with a lid about 1/2 full for many of your needs.

I like veggie oil. I use a 1 qt container with a lid about 2/3 full for end quenching small punches and chisels.

Phil

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Since I generally HT fairly small but long items---blades. My quench tank is the bottom of a welding tank to get dept without excessive width requiring greater amounts of oil. I use vegetable oil and have a chunk of steel on a 1/8" steel wire for preheating the oil.

In 18th and 19th century times most steels were water quenched with the highest grades being quenched in fish oil or whale oil. Brine was also used, mixed so that it "would float an egg".

In renaissance times they used a lot of various things to quench in believing they "helped" like radish juice or worm water, (see "Sources for the History of the Science of Steel" for a long list of renaissance suggestions)

And finally Theophilus in 1120 A.D. suggested quenching in the urine of a red headed boy or that of a goat fed ferns for 3 days. (such an amusing smell when hot steel hits stale urine!) He also mentions quenching the tips of small tools like gravers in candle wax.

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  • 2 weeks later...

In the 18th and 19th centuries, a good many a smith used what they called "lotions" for quenching. These were formulae containing anything from sal amoniac to yellow prussiate of potash. (Don't try this at home - it involves cyanide compounds.)

 

To get back to the original question - look at the specific heat capacity of steel and the specific heat capacity of the quenchant. This is where the gallon per pound rule of thumb originates.

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The gallon per pound rule only applies for very short runs or hobby use: if you are going to be making say 1000 mason's hammers or 5000 brick chisels a day, you will need a lot more.

 

We had a retired industrial smith give a talk at our quarterly meeting on Saturday. He went thru a dump truck full of coal every quarter, and bought steel in multi-ton lots. The kicker: most of the time he was working solo, or with one shop helper. Eye opening to say the least.

 

The best industrial shops have a big mobile metal quench tank with a tight fitting metal lid, sloping bottom and drain. The lid is a must to put out a fire if the oil overheats. Stainless steel is best, trapped moisture will not rust the bottom out and leak all over the shop. If there is any condensation, it will sink to the bottom and not evaporate, hence the drain in a lower corner. If you heat the oil above 212F (100C), the water turning to steam will cause the oil to explode upwards in a hot fountain, which may then be ignited from another source. (You have all heard the turkey fryer horror stories, right?) Water will not put out an oil fire, you need lots of dry sand, a shovel, and at least one appropriately sized dry fire extinguisher on standby.

 

Do this operation outside, away from all buildings, cars, decks, trees, etc. Many times the item coming out of the oil will have enough residual heat to ignite the oil left on it; sometimes the vaporized oil over the tank will ignite in a fireball also. Keep your head out of the fume plume, wear gloves and eye protection, keep the bar pointed slightly down or hot oil will run over your hands.

 

Done right, this is good theater. There are lots of video of this, and forge welding with borax for that captivating image.

 

Done poorly it becomes drama, or even tragedy. More than one budding blacksmith or knifemaker has suffered burns or even lost his shop this way.

 

Used motor oil may generate toxic fumes, vegetable oils go rancid. And last, if you pour the oil into a separate storage container, you either have to get metal cans and funnels, or wait until it cools. Those of you who have had experience with commercial kitchen fryers know what I am talking about. (I have had to do this often when draining portable fryers after cooking at sidewalk events.)

 

Now do you see why so many commercial folks have gone to water-based polymer quenches? I like Goddard's goop quench for demos and small items myself.

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