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I Forge Iron

A gentler quenchant

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Hi. As I promised, I will post an idea for saving oil. Unfortunately, a doggie ate my longer post last night, so I will just post the outline:(

Recently, when quenching some handled top tools in oil (to protect the eye), I experienced a fire :o . The stench was also disgusting.

I decided to try a polymer quench:

o did not want to buy the minimum quantity of Dow UCON A
o try to find an easier to source alternative
o do not use antifreeze: this is ethylene glycol, not PAG, and it is toxic
o ideas: CMC, psyllium seed powder (Metamucil), snails and slugs, shampoo
o settled on used disposable diapers from the local baby (cheap or free)
o each diaper contains about 12 grams of sodium polyacrylate ladder copolymer, with excess sodium ions
o MW is in the MD range, so only a small amount is required to boost viscosity
o slows down quench in the critical convection dominated martensite region
o enhancement must be at least an order of magnitude because oil is 10X and heat cap x density of water is about 3 x.
o simple experiment at a few ppt by weight shows promise

I am always reminded that anything I ever thought of has been discovered by another earlier blacksmith. Any experiences ;) ? I checked De Re Metallica (Hoovers translation) but came up with nothing. There is some controversy, however with the interpretation.

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Here I show my ignorance:
Here is what I think I know, but would not mind correction on.
A harder quench, as in cold water, shocks to very hard, but is can be quite brittle and may fracture some metals. A softer quench such as warm oil is less likely to warp or fracture the metal in quench. Some alloys produce more desirable crystals in one or another quench. Air would we the gentlest quench unless you include cooling in ash or pearlite as a quench.

Wouldn't placing the slab of metal in question in a big solid vise be a reasonable way to produce another gentle if not perfectly even quench? You could even warm the vise and fairly well calculate the final temperature if you weigh the metal and the vise.


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I have "quenched" a multitude of small items with a blast of compressed air. Colder than ambient air blown over the top of an item will cool it pretty quickly and of course, it's not as harsh as a fluid. In fact, this is the way I condition leaf springs when I have to rebuild a post vise. I forge the spring from a car spring, let it normalize, then reheat to critical temp and quench with compressed air - no temper.

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Bob, often evenness is more important than speed. That is why some people favor brine over plain water. Brine is faster, but more uniform.

The compressed air quench sounds interesting. I have waved pieces of air-hardening steel and gotten good hard quenches, even in fairly thick sections. I would be a little scared of using a blowgun, since it might just quench one spot well.

Thanks, Bruce, the suggestion of the oil floating on water sounds like it would save oil, but there still would be the stench and the fire risk. One would think that the diaper quench would smell bad, but it doesn't. The amount of diaper filler dissolved in a liter of water is fairly small. About 1 gram each of fluffed cellulose and sodium polyacrylate or polyacrylic acid and 20 or so grams of baby waste product. It is not even slightly tinged yellow, but I try not to touch it.

Thomas, I did a search on Smith's text that you referred to. Saw some posts on a "rainworm quench" but no diaper quench. It was actually something like this rainworm quench which gave me the inspiration. A bunch of snails and slugs got into my quench bucket. The effect on moderating the quenching vapor film was remarkable. I did not realize at the time whether it was surface tension alteration or viscosity, but after some reading, it is due to high temperature precipitation of the polymer. Snail and slug slime, and I would guess, chopped rainworm, would have some pretty high molecular weight components with interesting properties. I suspect that the ancient smiths did not realize what was going on.

The interesting thing about the diaper quench is that it does not harden plain high carbon steel completely. It does not even cause the scale to blast off. I can't wait to try it on something more discriminating, like 5160 or deep hardening 4140, or even D-2.

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This has helped fill in a lot of blanks in my data. I knew brine was faster, but not that it was more even. Makes sense though, better conductivity, higher thermal mass and an elevated boiling point.

So are you looking for a less conductive quench with an elevated thermal mass and an elevated boiling point? My wild crazy guess would be that lecithin might do just what you want. It is available in most health food stores and is a nice lipid that will combine with and even thicken water. Use about one part lecithin to 16 or more parts water if you want them to mix well.

A low sodium/electrolyte protein drink quench might also have the qualities you are looking for. The right carbohydrate might work too. In general, the more different stuff you mix in, the greater the thermal mass and the higher the boiling point.


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Hi Bruce. Thanks for that tip on the light sheen. It worked. I gave the oil,water quench a try with about a 1/16" layer of oil. No fire, but stench and mess. The scale did not blast off leaving a silvery finish as it did for the plain water quench. The steel was harder than with the diaper quench, but slightly softer than plain water. A file would scratch but not cut. So still pretty hard. Quenching time was comparable to the diaper quench.

Lecithin might work. It is more of a surfactant and viscosity modifier than a builder. It may be good in combination with food starches to help them blend with water. But, I am staying away from these because of the prep requirement (starches don't really thicken unless they are cooked) and the microbial degradation, which can also lead to stench. I just found a reference by Houghton on sodium polyacrylate quenchants. Less film formation during the vapor blanket phase, and more convection suppression during the convective phase. Exactly what is needed for crack sensitive steels. They don't seem to sell small quantities of the polyacrylate to backyard blacksmiths. So, back to the diapers.

One polymer that is very visibly absent from the literature is the polysulfonates such as ammonium laureth sulfate. These are very inexpensive. Cheap shampoo can be had for $1 per bottle at the dollar store. These concoctions have very high viscosity, but the problem is uncontrollable foaming :). Foam suppression is possible with ionic salts and small amounts of oil to form an emulsion. This could be a more friendly version of Bruce's oil quench. Animal/vegetable fats + laureth sulfate + salt may make an interesting biodegradable combination polymer oil quenchant with similar performance.

Bob, the reason why the brine is a more rapid quench is that the salt crystals that form with boiling destabilize the vapor film by producing nucleation sites. If you try it in a glass bottle while looking closely, you will see exactly what they are talking about.

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Hi Joseff. It looks like olive oil would be a pretty good quenchant, except for the price.:( There was an article yesterday in the food section of the paper in the Food 101 section by Robert Wolke, professor emeritus of chemistry from the University of Pittsburgh. It talked about the smoke point of food oils, saying this is the point at which the oils degrade and release toxic chemicals. Olive oil, as long as it is the clear extra refined stuff (light) is pretty good. But not the deep colored extra virgin oilve oil.

Here are the numbers: canola 400F, cott 420, sunflower 440, corn 450, peanut 450, extra light olive 468, saf 510. I am not quite sure of these numbers since my notes were scrawled down, but the point of the article was that olive oil was OK for deep frying if you use the light. He went on to say that oils which have been taken up to their smoke point are not really edible and should be discarded.

Hi Tek. The baby waste product is not really all that bad. At 2% or so by weight, it is not even offensive. Also, it is safe to dump this on your lawn. Our county has laws against grey water (bath water containing skin particles). This cannot be dumped on the lawn due to the risk of generating airborne disease containing particles. Olive oil is also safe to dump on your lawn, since it is biodegradable, and the bugs will eat it up fast.

If you don't like baby waste product, you can bypass the baby. Mega packs of diapers from Costco cost about 20 cents per piece. A single diaper should be enough to make about 10 liters of quenchant. If you buy small packs at the local grocery, they are about 50 cents each. I am cheap :D and go to the local baby. These are free. Do not select the ones with solid waste product. Not only are they very offensive, they are actually dangerous, from a pathogenic standpoint.

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  • 2 months later...
  • 2 weeks later...
just wandering but would the hardness of the water make a difference in a quench?

Yes. Tap water is usually no good. Don't get me wrong, I'll use tap water to quench a center punch or a cold chisel, but I would not use it for something like an ax or hammer. Use distilled water or rain water.
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  • 4 weeks later...

A while back, a neighbor I've known most of my life,came to my shop one day and wanted me to "beat out" the edge of his old , blunt mattock.

He meant draw out and taper,but that's how older folk around here would phrase it.

I must also point out that the man is 74, able bodied, and was eager to help.

After a minute or so , we(actually he) decided that he would do 'the holding"......and I would do the 'hitting.

That's not my usual way of working, but I've known this guy a long time.

After a couple of heats and some hammering on my part, he said "good enough".

All this while he had been telling me how he used to help his Grandpa in the blacksmith shop more than 60 years ago.

While he was telling me these things, I was thinking about how to quench this thing.

Well, I never got the chance to quench in oil as I had planned.

At the last hammer blow, he promptly took the quite hot mattock outside the shop and slammed the cutting edge into the damp ground in front of the shop.(It had rained the day before).

That was a real surprise for me......I had never seen anything like that before!

I asked him why he did that......and he said "that's the way Grandpa always done it"! 'Cools stuff slow so it don't crack"

certainly not a scientific method of quenching.....if it's a 'quench' at all!

Has anyone else ever heard of this?


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Weygers mentions a south east asian smith quenching a knife in a melon that matched the curve of the blade to produce a hard edge soft back. Theophilus mentions quenching engraving tools in a hunk of wax; all variations on the above method.

Note that all of these methods are duplex ones where the hardening and tempering are done together.


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Several old smiths around here that I knew did the same. They always referred to it as ground temper. Never tried it myself though, as it seems to me that the water content of the soil would vary so much as to give inconsistent results.

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