[SEL] sulfur and sulfurized lubricants for cutting metal

[peter ogborne]

Thank you Richard ...............very thorough explanation.
----- Original Message ----- 
From: "Richard Allen" <linstrum55 at yahoo.com>
To: "Stationary Engine List" <sel at lists.stationary-engine.com>
Sent: Thursday, March 03, 2005 4:44 AM
Subject: [SEL] sulfur and sulfurized lubricants for cutting metal


> The way sulfur works as a metal cutting lubricant is that it melts at a
> fairly low temperature to make a thick oily liquid that is very
> slippery.
>
> Sulfur is peculiar because it melts twice. Just above the boiling point
> of water at about 106° C (223° F) it melts, but when the temperature is
> raised slightly it freezes again, then at about 115°C (239° F) it melts
> again. Either molten phase works well as a cutting lubricant, but
> because most machining operations create cutter point-of-contact
> temperatures above the second melting point, it is in that form when
> working.
>
> The reason why sulfur is mixed with oil, grease, and lard is for
> several reasons. At room temperature, sulfur is a solid a lot like hard
> rosin (which is also a very good cutting lubricant but expensive), so
> it has to be powdered and mixed with a liquid other than water to get
> it into the cut. Sulfur by itself catches on fire at the temperatures
> generated during cutting, so mixing it with oils and greases prevents
> this. Sulfur is also very active chemically and it reacts directly with
> the copper and zinc of brass, and when wet it rapidly attacks iron.
> When heated in contact with air it forms sulfuric acid. All this is
> very bad for the parts being made and the cutting machinery, so the
> oils and greases are used to neutralize sulfur's bad properties.
> Because sulfur is very reactive chemically it forms several different
> kinds of compounds with the oil and grease molecules, and those in turn
> are also extremely good cutting lubricants. What actually goes on at
> the point of contact is not fully understood, but apparently the
> sulfur-oil compound molecules break apart at higher temperatures and
> release the sulfur as minute or colloidal particles, which help push
> the metal out of contact with the cutting tool.
>
> The 250-year old unbeatable standard cutting lubricant for drilling and
> lathe work, as well as taps and dies, is sulfurized lard. I don't know
> how it is made, but because it was around 250 years ago it can't be too
> difficult. I have always used plain de-salted bacon fat or lard for
> cutting steel because I can't tell the difference between it and
> sulfurized lard when using a torque wrench to determine how much force
> is needed to turn a tap. Mice and rats eat lard but usually won't touch
> sulfurized lard, though, and more than a few times my dog got the can
> of bacon fat off the lathe and ate it along with all the metal chips in
> it, and the brush, too. Like I say, work and play safely, and that
> includes your pets.
>
> Free machining stainless steels and steels have sulfur, selenium, or
> lead introduced into the metal when being alloyed. When these alloys
> are cut, the free sulfur, selenium (selenium is very much like sulfur
> but EXTREMELY poisonous), or lead act as cutter lubricants, but the
> down side is that free machining alloys are rather weak and have
> limited usefulness, plus they don't weld very well. Lead is also used
> in some armor piercing bullets as a lubricant, and does an excellent
> job judging from the holes I have seen all the way through 6-inches of
> hot-rolled mild steel that were made using an ordinary hunting rifle.
>
> Work and play safely,
>
> Richard Allen
>
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