View Full Version : What is the Magic of SULPHUR?

10-07-2006, 05:27 PM
I finally have to ask.
I keep seeing references to "Sulphur Oil", "Heavilly Sulphurised Oil" and the like. This could be regarding cutting, drilling, tapping and Heat Treatment Quenching.
The Sulphur being refered to is the Yellow Powder right??
What does it do and how?
Can you add Sulphur powder to various oils to get the magic (what ever it is) to happen? :)


P.S. I haven't even touched on the statements that go something like " I normally use Pelican Spit but have had reasonable results with Lard in an emergency" What are Reasonable results?

10-07-2006, 07:08 PM
The Sulphur in the oil is not exactly yellow, and not solid.
It is chemically involved in the hydrocarbon chain.
Don't know how many or where in the chain.

As I understand it easily reacts with the fresh surface of the metal being cut and then does a good job of acting as a solid seperator. i.e. NO gall, or at least strong gall resistance.

Hth Ag

10-07-2006, 10:51 PM
Miker ,Iam no expert on anything let alone sulphur, but it seems that sulphur adds lubricity to whatever it is contained in. Diesel fuel contains sulphur, but now has to be refined to remove sulphur, thus lowering the lubricity of the fuel , thereby creating scoring & gaulding of fuel pump & injection parts. I would guess that cutting oils containing sulphur helped with lubricating the cut, the chip flow, and affected tool life, etc. Now the sticky part is, in the good USA sulphur has become a health hazard and a contributor to air pollution . So we now have diesel fuel &cutting fluids with very little or no sulphur. Also probably causes cancer in California. JIM

A.K. Boomer
10-08-2006, 01:35 AM
Also probably causes cancer in California. JIM

Thats why i dont live there, it seems everything causes cancer in calie...

Jack Burns
10-08-2006, 05:24 AM
No magic; just well-known surface chemistry.

For a little background, all lubrication occurs under basically two regimes:

The first regime is called full Hydrodynamic Lubrication and occurs where opposing surfaces are held apart by a relatively thick liquid (e.g. oil) film, solid particles (e.g. graphite, moly sulfide, Teflon etc.) or some combination of both which prevents direct contact between moving parts. One good example of this regime is a plain journal (e.g. headstock) bearing operating within design load and velocity parameters where the shaft literally rises and floats in the journal cavity. Another would be a piston ring/cylinder wall interface at mid-stroke where a relatively thick oil film -- typically on the order of about 6 microns -- separates the respective parts due to wedging action induced by upper and lower ring bevels. In both cases the opposing asperities (high points) of both parts are sufficiently separated (after run-in) so that no appreciable metal-to-metal contact occurs and the only friction (ideally) comes from fluid shearing.

The second regime, known as Boundary Lubrication, is defined by direct contact between opposing moving surfaces and may or may not be the result of hydrodynamic failure such as over-loading or under-speeding a journal bearing, or what happens at the top and bottom dead centers of a piston stroke where all relative motion stops and all meaningful oil is squeezed out of the ring/cylinder interface, both instances resulting in metal-to-metal contact. Clearly, in these, and all such circumstances, something must be done at the surface level if catastrophic damage due to microscopic asperity welding and subsequent tearing is to be avoided and plain old mineral oil is all but useless to the task.

Enter Extreme Pressure additives

Lubrication engineers long ago discovered that various elements such as sulfur, chlorine, phosphorus, and compounds including several zinc and molybdenum derivatives as well as constituents of some animal fats (think lard oil) react with raw metal surfaces and form protective oxide layers (generally only a few molecules thick) at high local temperatures generated by asperities rubbing in-situ. While the examples mentioned above are obviously on a larger scale than you had in mind, exactly the same principle applies to cutting tools: To avoid microscopic welding of work-piece material to the cutting edge, leading to progressive build-up and surface tearing, some sort of shearable protective layer must be interposed between the two materials on a constantly regenerating basis and nothing fills the bill like just the right E.P. additive in a liquid phase of which highly sulfurized mineral oil has proved among the best.

Hope this helps.


P.S. While high sulfur and chlorinated cutting lubs work well for steel, they’ll stain the hell out of and typically corrode any copper-bearing metals such as brass and bronze unless thoroughly cleaned. Also, avoid putting any type of E.P. additive lub oil in any gearbox with copper-bearing parts such as gears and bushings; those types of additives will eat copper-bearing stuff alive in nothin’ flat!

10-08-2006, 05:54 AM
Very good explanation, Jack; you should post more often.

10-08-2006, 11:03 AM
I agree with Millman in this instance.
Very good explanation, thanks. Post more often.
I was just going to mention that sulphur & moly. are used as Extreme Pressure additives in lubricating & cutting oils. Think tread cutting lubes like Rigid pipe threading oil....
Open gear lubes use similar additives, along with tackifiers, etc.
Thanks again.

loose nut
10-08-2006, 01:45 PM
Will Extreme Preasure lubricating oils work as a cutting oil

10-08-2006, 03:40 PM
Once upon a time and many years ago I took a Materials class. One of my projects was testing cutting compounds for extreme pressure lubrication using an Almen EP testing machine. One of the best compounds was bacon fat that had been dewatered by heating, then filtered to remove the residual solids. It worked well in the tester and for turning and tapping. It was improved a lot by again heating and adding 5% by volume of flour of sulfur. Just like a kitchen recipe: heat, add, stir, and cool. Nothing to it!


Peter N
10-08-2006, 04:05 PM
Interesting post Jack, thanks.

On a related note, the sulphur content in steel can also help it machine more easily.
We make quite a few mould tool parts out of P20 steel. It's pre-toughened steel that doesn't need hardening, and used on either very large parts where having to harden another tool steel like H13 or D2 may run the risk of too much distortion, or on cores & cavities for relatively low volume parts/non-abrasive materials.

One of the several grades available, (1.2312 spec) has a greatly increased suphur content over the others in the range, and although still less than 0.1% it makes a big difference in how this stuff machines.


10-08-2006, 08:21 PM
In the early days of machining lard and sulfur mix was used. Did you know that the quenching barrel in blacksmith shops often contained water and urine and sometimes blood.

Your Old Dog
10-08-2006, 09:20 PM
I haven't read this entire thread and may be wrong but from my limited info on the matter.

Sulphur based oil is from the middle east and parafin based oil is from the Pennsylvania. For heat treat I like parafin based.

When the sludge of middle eastern oil meets with water it forms a sort of sulpuric acid and thins out valve stems wheere the sludge is. That don't happen with parafin based oils. I hope there's someone here who didn't already know that !

EDITED TO ADD: Yea, what Jack said !!

10-08-2006, 11:04 PM
Thanks for each and every answer. You have all given me a better understanding of the processes involved. Also added new thoughts for me to pursue (what do Flour and Sulphur have in common?). I also now know not to drink from the Blacksmith's barrel....:)

As always, good info freely and kindly offered. Thanks again.


10-09-2006, 12:48 AM
Thanks for each and every answer. You have all given me a better understanding of the processes involved. Also added new thoughts for me to pursue (what do Flour and Sulphur have in common?). I also now know not to drink from the Blacksmith's barrel....:)

As always, good info freely and kindly offered. Thanks again.


He meant a finely ground sulpher powder. Commonly refered to as Flour of Sulpher. Disperses thru out the oil more easily when mixing.

10-09-2006, 03:00 AM
Good catch Jim. I read flour OR sulphur instead of flour OF sulphur.


10-09-2006, 03:52 AM
Strangely, although the term "flour of sulphur" makes sense, it is incorrect. The correct term is "flower of sulphur" after the German word "Schwefelblume". Schwefelblume means "sulphur flower" and refers to the sulphur deposits found around hot springs. The scientific term is Sulphur sublimatum meaning sublimated sulphur.

10-09-2006, 10:45 AM
Yep, it's flowers of sulphur.

Flowers of sulphur is a required safety item around a weather station, at least in the Air Force. It's purpose is as a cleanup agent in the event of a mercury spill (as in mecurial barometer). It will coagulate and corral the mercury, making for easier pick up.

Or so I was told... we never spilled any mercury during my watch.

10-09-2006, 03:30 PM
Evan, thanks for the correction. Carl

10-09-2006, 05:18 PM

Rotorua New Zealand. Interesting smell in that place!:)


Doc Nickel
10-09-2006, 06:22 PM
Any use in adding sulfur to an oil- say old crankcase oil or even fresh motor oil- to make up something for the occasional heavy turn or stainless tapping job?

I know sulfurized "heavy, dark" oil is easily available, but I'm just curious. The local oil refinery has a massive pile of sulfur extracted from the crude. Every couple of years they truck it down to the docks and it gets barged off to some place to uses it for something. (Presumably vulcanizing rubber, for one.)

Anyway, like I said, I'm curious. I can get a couple pounds of pretty pure sulfur no charge (I know people at the plant, and at something like $10 a ton, it's not exactly a valuable commodity.) Would it help- or even do anything- if mixed in with a cheap oil?