[Hammarlund] More on Graphite and other lubricants

Sat, 14 Dec 2002 20:04:26 -0500

Let me begin by saying I appreciate the number of people who
have commented on this topic.  I'll try to address  few issues
brought up and how they might relate to restoring old radios
and to keeping engines running longer.

Bruce Martin's, K1XR, and Kim Herron's, W8ZV, replies about
automobile engines provide insight.  Actually graphite is a
very common oil additive; it is certainly nothing new.  It has
been used as an additive to motor oils for at least 75 or more
years.  But motor oil is really a very complicated mixture of
a number of materials, each with their own special purpose.

One problem with adding significant amounts of graphite to
motor oil, especially if the particles are not fine enough, is
clogging of the oil filter.  This becomes really significant
with additive concentrates where the graphite may not mix
properly and disperse well enough.  Another problem is the
interaction between the graphite and detergents in oils.
Graphite is oleophyllic - it likes oil and mixes well with
oil.  The reference I listed in my earlier post even refers to
it as oilioscopic meaning that it attracts oil.  [As opposed
to hydroscopic, attracting water.]  But at the same time it is
hydrophobic - it does not mix with liquid water.  Detergents
in many motor oils are not particularly compatible with
graphite because they allow the water and oil to mix.  Again
that same reference notes that most dry film lubricants,
including graphite, do not tolerate detergents well.  Also as
Kim notes, the oxidation products of most oils and gasoline
tend to be acidic.  Most oils have additives to help
neutralize the acidity but "not all oils are created equal,"
so some oils do better than others in neutralization.  It is
even possible for engines to run properly with several brands
of oils used individually, but to suffer problems when these
oils are mixed.  At one time it was common practice to add
sulfur to oil.  The sulfur would react with the iron
components in contact with the oil to produce sulfide and
sulfate films that would protect the surface of the metal from
wear.  But sulfur is a bane to modern catalytic converters and
even gasoline is now blended to reduce the sulfur content.
With the elimination of tetraethyl lead in gasoline, different
companies have developed different anti-knock additives.  Some
of the calcium additives were not as compatible with engine
oil and engine components as were many of the other
additives such as methyl tertiary butyl ether (MTBE).  Teflon�
(PTFE) and the other fluorocarbon additives are pretty inert
up to several hundred degrees, but at higher temperatures they
can decompose into some extremely corrosive products.

So engine wear is related to many, many things.  Switching to
a high graphite oil and having the engine wear out may - or
may not - have anything to do with the graphite itself.  It
could have been clogged filters, or the oil used previously,
or harsh service, or ...

In very large, fixed service engines and motors, it is
becoming more and more common to take periodic samples of the
lubricants and send them to a laboratory for chemical
analysis.  One of my former employers, Eastman Chemical
Company (formerly part of Kodak), did this routinely and found
that trace metal analysis could foresee problems long before
they became apparent to performance degradation.  As an
instrumentation engineer, I was intrigued by the use of the
online measurement of dielectric constants of oils.  One of
the industry/university cooperative research centers Eastman
belonged to found that subtle changes here could accurately
predict future problems quite early, well before the
lubrication failed.

[Preventive maintenance was a big improvement over "wait 'til
it breaks" but predictive maintenance is gaining ground.
Preventive maintenance uses statistics to determine a
frequency of maintenance that prevents most failures.
Predictive maintenance uses measurements to predict when
failures are imminent.  It can often provide big cost savings
over preventative maintenance if the predictive measures are
accurate.]

But to bring the issue of lubrication back to our old radios,
Barry Hauser's statement "it depends" is a good one.  No one
lubricant is suitable for every application.  Plastic gears,
as he notes, are generally considered self-lubricating
(especially Nylon).  Adding organic lubricants can often
destroy such gears.  Many plastics swell in oils and that is
NOT what you want gears to do.  Remember too that I said that
around high voltages and electronics, it is generally best to
avoid graphite and molybdenum disulfide as they are
conductive.

Hauser is correct about most lubricants filling in microvoids
on surfaces allowing them to slide easier.  This applies to
all classes of lubricants, not just the dry film ones.

A good example is to take two concrete blocks and try to slide
one over the other.  The rough surface provides peaks and
valleys that touch and bind.  The technical term for these is
asperities.  Rub some paraffin wax on the blocks to fill the
pits and coat the peaks and you have a simple dry film
lubricant that makes sliding much easier.

With a non-porous surface, such as a metal where the
asperities are much smaller, you might use an oil as a fluid
film lubricant.  The oil film is typically thicker than the
height of the asperities.  When the surfaces slide over each
other, the oil flows and provides a method of keeping the high
points of the surfaces from touching.  How well the oil
lubricates is extremely dependent on the properties of the
oil.  A thick grease will certainly work but the high
viscosity of the grease takes considerable energy to make the
grease flow.  So you might consider using a much thinner oil.
But here the viscosity may be too low, so while the oil flows
readily, it also flows away from the aspherites and does not
develop enough backpressure to bear the load.  Also as most
oils are non-Newtonian fluids, the actual viscosity of the oil
is dependent on how fast the surfaces are moving.  So the
selection of the proper oil with the proper viscosity over the
range of expected operation becomes a compromise.

[Most oils are dilatant fluids, meaning that they thin with
increasing shear.  A material which thickens with increasing
shear is called thixotropic.  A thick paste of cornstarch in
water is a good example.  Rapid stirring turns the liquid
almost solid.]

The burnishing process that Hauser describes is applicable to
most dry film lubricants.  In his case, he used a molybdenum
disulfide filled grease, but the powder can be applied
similarly.  Simply sprinkling on graphite or other dry film
products is not the way to use these lubricants properly.
Squirting powdered graphite into a bearing with no way to hold
it in place is not correct either.

The lubrication of electronic connectors and switches is even
more specialized that general lubrication.  Many electrical
contacts are gold or silver plated, not just for conductivity,
but for lubrication as well as both of these metals are soft
and easily deformed.  Most electronic lubricants for
connectors and switches these days are based on polyphenyl
ethers.  If you wish to read an article on this, check the
following.  It specifically discusses connectors in a high
radiation environment that fortunately we normally do not have
to deal with.  But the basic concepts still apply in our radio
gear.

  http://www.chemassociates.com/products/findett/PPEs_Radiation2.pdf

To conclude, lubrication is a very complex issue and we have
only touched on it here.  The previously suggested reference
on dry film lubricants is an excellent one.  I'll list it
again for convenience.

  http://www.dynamiccoatingsinc.com/technical.htm

Finally, if you have some time to read through it, and decent
speed for Internet downloads, look at the following document.

  http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1424/

This is a U.S. Army Corps of Engineers engineering manual.
It's title is: "Engineering and Design - Lubricants and
Hydraulic Fluids" and it is written on a relatively basic
level, although it is quite complete in its scope.  You can
download the full document, or just chapters.  The second
chapter, "Lubrication Principles" is especially useful.  The
sixth chapter is "Nonfluid Lubrication", and it covers such
lubricants as graphite and molybdenum disulfide.  I have not
read this full document yet myself, but the selections I did
read were excellent.

I hope this note has filled in even more details about
lubrication.  It is a fascinating subject, and one with
extreme importance.

        73,  Dr. Barry L. Ornitz     WA4VZQ     [email protected]