Re: Sulphur Oil on Electronic Parts



Charlie Gary wrote:
I'm searching for a cutting oil to replenish a dwindling supply, and
in my searching I ran across a couple of comments about not using
sulphur compounds on electrical parts. I haven't found any
information saying why it's bad, just that it is. I need more info
than that. Can somebody clue me in?

Charlie:

I found these, they aren't specifically about sulfur containing cutting oils, but they do indicate that sulfur is corrosive to copper and it's alloys:

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http://www.hghouston.com/coppers/copperog.htm

Copper and its alloys are susceptible to rapid attack in oxidizing acids, oxidizing heavy-metal salts, and sulfur and ammonia and their compounds.
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http://www.faqs.org/patents/app/20080251424

[0002]Insulating oils are used in power transformers, distribution transformers and reactors. These oils often contain traces of reactive sulfur compounds, especially thiols (a.k.a. mercaptans). The reactive sulfur compounds may react with copper, forming copper mercaptides. The copper mercaptides can decompose further, leading to the formation of copper(I)sulfide, Cu2S. The net reactions could be as shown below:

Cu2O+2RSH=>2 CuSR+H2O

2CuSR=>Cu2S+RSR

where --SH is a thiol group (or mercaptan), --R is an alkyl group.

[0003]Other sulfurorganics, especially sulfides, can also be active, either by direct reaction with copper or via conversion to thiols.

[0004]Cu2S is insoluble in oil and may form deposits, especially on surfaces of cellulose material. Once deposition of Cu2S has started the process is believed to be self-catalytic. The surface selectively adsorbs the reactants and intermediates, and also catalyzes the decomposition of intermediates to Cu2S.
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http://tdworld.com/test_monitor_control/highlights/Doble-corrosive-sulfur/

The problem occurs because the corrosive sulfur reacts with copper conductors and silver contacts to form metal sulfides that contaminate the insulating paper.
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I'd call you local coolant distributor, if you've been using water soluble cutting oil, you might be disappointed at the cooling ability of straight oil.

--
BottleBob
http://home.earthlink.net/~bottlbob

.

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