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Figure-eight agitation in liquid quenchant?


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In 1976, I was able to visit Bethlehem's home plant when they were in full swing. I took with me on the field trip a class from Peters Valley. In the heat treatment department, there were three good ol' boys, and one of them found out I was a smith. He said, "Do you figure-eight 'em when you quench 'em?" When we claimed ignorance, he repeated that you gotta' figure-eight 'em [meaning work pieces]. The other two guys nodded affirmation.

Apparently, agitation by the figure-eight allows the quenchant to hit the submerged piece from all angles. Ever hear of that? Any comments?

http://www.turleyforge.com Granddaddy of Blacksmith Schools

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That is how I was taught and it requires even more aggressive agitation when you`re talking about water/brine rather than oil.
I was told that you need to be more aggressive with water/brine in order to break up the steam barrier that forms between the quenchant and the work.Sounded reasonable so that`s what I continued to do.
The old timer`s instructions were backed by every machinist and heat treater I talked to who regularly did that scale of work.I even find myself doing this on the rare occasion I use an air blast as a quenchant,old habits etc.

I`ve always wondered at the knife/sword makers who advocate quenching in a rather small diameter pipe full of oil and why they seem to discount the need for agitation and how it effects the heat treatment process.Many I`ve worked with don`t see the need for it,they dump it in the tank and go on to something else.

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Everything I did in class was dump it in the basket in the oil, fish it out by lifting the basket after the boiling stopped, or all the parts were in.

I see the value of agitation to improve the evenness of hardening, but if the quench is fast enough without agitation, then it maters not right? The value of process control testing, both destructive and non-destructive would have to come into play to determine the adequateness of a quenching method, agitation method, and quenchant used.

The parts I have hardened recently have been in 1 quart of canola oil, and have been small. I did use agitation, and I felt that the container was rather smallish for the job. I got good consistent results from a file test, and did not crack any parts (I have had bad luck with cracking in the past. My class projects were near 100% failure on the first try, and 100% success on the repeat.)

Phil

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I work in a machine shop from dawn to dusk and 'smith the rest of the time. We make beaucoup small parts that are sent out for heat treatment and I have been fortunate enough to visit both of our H/T suppliers. Their big tanks are about 10-12 feet in diameter and 20 feet deep; they have pumps to agitate the oil and break the vapor blanket so the parts remain stationary in the basket while the oil swirls around them. I don't think the pattern is magic but I do think that some amount of agitation is important, whether you trace an 8, a circle, a triangle or a dodecagon... :P

Some years ago, I watched a toolmaker make some long thin shafts that needed H/T. He had to suspend them vertically in the oven so they would not bend under their own weight at critical temp then he quickly dipped them in a black iron pipe filled with quench oil, all the while plunging them up and down. We didn't discuss his technique at the time but I expect any type of side to side action would have warped the parts.

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When you take in to consideration the viscosity of your quechant, the amount of quechant, and the type of steel and it's required drop in temp speed needed for proper hardening, the main factor that determines the need for aggitation of the part comes down to the crossectional thickness of your workpiece because it will determine how long a piece needs the vapor barrier disrupted. Back and forth, up and down, figure eight,, they all expose the part disapating heat to fresh quechant so the temp continues an uninterupted drop and solidifies the grain in the steel.Very thin parts will naturally have all the temp drop need almost immedeiately, but the thicker your part, the longer that time difference is, and the need for breaking up that barrier. Wes

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  • 1 month later...

Quenchant agitation is standard practice in commercial heat treating, as I understand it. I've been thinking for a while about ways to agitate my quenchant with minimal muss and fuss, because agitating the work piece seems like just begging it to warp. (Not a big problem with hammer heads, maybe, but I tend to make long, thin stuff.) I considered strapping an angle grinder (minus disk) to the outside of the quench tank (stainless steel soda-acid fire extinguisher tank) and letting it run when I quench. But I haven't tried it yet. If that's not enough, I thought about a small, asymmetrical steel slug that could mount on the grinder. There's nothing like an unbalanced load to cause vibration, although at 12,000 RPM I'd be a little afraid of things getting out of hand.

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But I haven't tried it yet. If that's not enough, I thought about a small, asymmetrical steel slug that could mount on the grinder. There's nothing like an unbalanced load to cause vibration, although at 12,000 RPM I'd be a little afraid of things getting out of hand.


Instead of a slug, make a disk of metal and notch the edge. It will be easier to control very small amounts of eccentricity that way.
Phil
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How about hanging long thin bits vertical, and move them up and down (Like large bore gun barrel HT)


If you have enough tank to keep the while piece submerged while you move it, that'd probably be fine. If you pulled it part-way out of the quenchant during the process, I think you'd be setting yourself up for problems.
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Good Morning All

Frank et all -what is your recommendation for production quench oil for black smith heat treating? Most established Smiths have a five gallon bucket they have had for so long the oil is no-longer produced. Frank's name comes up in some of these discussions, something about a 55 gallon barrel outside under a shade tree. I resurrected a post about a Shell product, Voluta, hoping to build a consensus, even their oil has three versions and multiple viscosities in each version. I'll keep the 55 gallon drum under the shade tree if we can determine what we want.

PS -Frank, I do "figure eight it" however I learned from someone who probably learned it from you.

-grant

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  • 1 month later...

Grant & All,

I'm a professional, but if you earn a nickel from your work, you're a professional. Furthermore, nobody knows 10% of anything.

With that said, years ago I purchased from a Texaco distributor a 55 gallon drum of quenching oil. If memory serves, they had two grades available, Quenchtex A and Quenchtex B. I was told that the "A" was a little slower that "B". "A" was the one I chose. It's appearance is not unlike motor oil, although I have seen another quenching oil that was a dark color. As I understand it, the quenching oil is treated to abstract heat at the proper rate and to have a higher flash point than motor oil. If the oil is warmed with say, a hot bar of iron, the viscosity changes and you can get a slightly quicker quench than at ambient temperature.

For my small work, I normally quench in a five gallon bucket. It has a multiple holed, steel basket in the bottom (with bail), so that if I drop something by mistake, I can retrieve it. I keep a lid on it always when not in use to keep shop dust and fly ash out. Dirty oil and crankcase oil slow the quench too much for my liking.

As far as "under the shedding sprussnut tree," I'm in Santa Fe, and our yard trees are pretty small. So the big drum sits in the sun and rain and snow. I have sold a lot of the oil, so there is probably only 15 gallons remaining.

I'm fairly certain that the HT pros will determine how to quench based on the shape of the object, whether it has holes in it or sharp corners, whether it's delicate or chunky, etc. Therefore, the figure-eight idea is not engraved in stone. I think those ole Bethlehem heat treaters were kind of hoorawin'* us steel mill visitors, and at the same time, they were testing us.

*Cowboy palaver for "teasing."

http://www.turleyforge.com Granddaddy of Blacksmith Schools

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  • 6 months later...

I don't know about quenching other kinds and shapes of steel, but for quenching knife blades it's my understanding that you want to use a very straight slicing motion, knife-edge-first or dipping the blade tip-first, pulling it out and then dipping it again. And you do not want to figure eight or any other motion would cause problems with one part of the metal cooling quicker than the other parts as the S-wave of austenite turning into martensite goes through the steel faster on one part than another. What you want in the quench is as smooth an S-wave as possible going through the metal. The problems could include things like the blade cracking visibly during the quench or the first time you use it. I used a figure-eight motion while quenching a chisel and the first time I used it, the entire tip fell off.

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S-wave? Not heard of that one before. Where can I go learn more about the S-wave?

Sorry to hear about your chisel. Do you know what kind of steel it was and what temperature it was at? (And what temperatures it was forged at?) The lion's share of quench cracks are from overheated steel.

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You just need to move it around a bit so as to keep it in cool oil and stop it from vapourising around the job, figure of 8 back and forth it does'nt really matter. When we quench 200kg or up you cant really do much with it but go up and down with the hoist in the quench tub. Even to turn on the pump all that does is pump the quenching medium through a cooling tower and back to the tank. Them good ole boys, were like the old fella who told a bloke that came to see me that bellows leathers were elephant skin, the nubie believed him. I can just imagine back in the 40s a telegraph comes in from a sawmill up the coast, to an industrial supplier in the big city, "yeh Briggsvale sawmill wants us to send a new elephant skin for their blacksmith shop bellow" "oh OK no probs, do you know if they need an indian elephant or an african elephant skin" "nah I don't i'll have to telegraph them again". Bet that old fella is still laughing on the verandah of the nursing home for that one.

Phil

Phil

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  • 3 weeks later...

S-wave? Not heard of that one before. Where can I go learn more about the S-wave?

Sorry to hear about your chisel. Do you know what kind of steel it was and what temperature it was at? (And what temperatures it was forged at?) The lion's share of quench cracks are from overheated steel.


I'd like to answer your questions about the chisel I ruined, but when I did that particularly masterful bit of work, the only thing I knew was, "Heat it real hot with a torch, then shove it into some oil and you'll never have to sharpen it again." Which has turned out to be true, because I put the chisel on a shelf and only take it out to admire it once in a while, and then I return it to the shelf...

I think quenching blades is like lots of subjects, where in order to truly understand it, you might want to approach it from a multidisciplinary viewpoint. When I couldn't find the depth of information I wanted about quenching (admittedly, I didn't buy the expensive ASM books or correspond with the old masters of knifemaking...), I turned to wikipedia, physics books, and other sources, and read that there are two types of waves that earthquakes produce: Primary waves, and Secondary waves, or P waves and S waves. Then I did a search for waves and quenching, and found that S waves also occur during quenching- that the cooling effect of the quenching process moves through the steel in an S wave that forces the hot, austenitic steel to cool so quickly that it bypasses the next step in cooling and locks the steel into the martensitic stage. I think of the S wave as a shock wave because quenching certainly comes as a shock to the steel, and as the S wave moves through the steel, if it encounters a sharp edge such as a deep scratch, a sharpened blade edge, or a sudden change of dimension such as an un-radiused 90 degree angle between the blade and the tang, the sharp edge cools much faster than the surrounding metal, which induces a stress line in the steel.

So, in preparing a blade for heat treat, you sand out all of the deep sanding marks and gouges, round all of the edges, round all of the sharp transitions in blade shape, and leave a 1/16" or so radius on the sharp edge rather than fully sharpening it, all of which helps prevent a thin part of the blade from getting hit with a very fast S wave that then slows down drastically when it hits a significantly and suddenly thicker part of the blade. It's that slowing down of the S wave that creates stress lines that even tempering might not be able to get out of the blade, because when the S wave moves fast and then slow, the metal crystalizes at different rates and therefore forms a physically weak boundary line between the faster-quenched part and the slower-quenched part.

The other aspect of avoiding stress lines during quenching is to use a slicing, edge-first quenching motion through a big enough quench container so you can get the blade cool enough with one swipe through it, or a plunging the tip straight down, pulling it up, and plunging it straight down motion. These motions allow for a consistent vapor barrier breakdown. The speed of the vapor barrier breakdown controls how quickly heat is transferred from the blade to the quenchant. If you use a figure-eight motion on a blade, you can get an uneven breakdown of the vapor barrier and thus an uneven transfer of heat out of the knife, and thus an uneven movement of the S wave through the metal. But after studying this stuff for years, one thing has become clear: there are a lot of unknowns about metal and about heat treating. Sometimes the slightest little difference in whatever, can create a better blade or a worse blade.

I don't know if those guys at the factory were kidding about figure-eighting their quench motion, but I've heard some knife makers say that some of the heat-treating methods used for massive pieces of metal in industrial applications, don't work so well for the very slight mass and the shape of a knife blade.

My wife says I ramble too much and that I don't know nearly as much as I think I do. She's probably right...
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