Lubezine Volume 8 * NOVEMBER 2013 - JANUARY 2014 | Page 26

TECHNOLOGY

FEATURE

mixture and water vapour and settles for
about half an hour. The grease mixture is
recycled continuously from the bottom of
the dehydration zone with the pressure up
to 10-200 psi. Base oil is added in the grease
mixture at lower temperature to enhance
cooling, after which it may be packaged.

Grease Trends
There are several trends which are affecting grease market. Years ago, we had a
slight shift from soda-based grease to calcium.Today, the majority of grease in use is
Lithium based. The market is, however, witnessing a shift to calcium sulphonate due
to global scarcity of lithium and the good
performance of this calcium sulphonate
soap. Shift to polymer and synthetic base
oils are also taking place across the world.
In additives, there is a slight movement
toward such novel metals as bismuth,
which are more environment-friendly than
Zinc ,with better synergy with Sulphur type
additive especially for EP grease. On market
side, the market is unfortunately suffering
from lack of knowledge and information
transfer as well as price sensitivity. These
are the main drivers for selecting grease
which have also influenced an increase in
circulation of cheap grease made by non
suitable soap , besides recycled base oils
into the market. This compromised quality
greases are corrosive and non suitable for
machineries.
One other trend is the growing acceptance of transparent type of grease which
is now available in the market. Whilst
transparency does not imply any premium
quality, the grease can have equal performance with general grease, if manufactured
the right way, with its advantage being high
aesthetic value.

.

LUBRICANT PROPERTIES

Conversations
on Viscometrics
O
ne of the
resource
persons
at a training I
attended a while
ago observed that
perhaps the best
way to explain
something is to
By Samuel
start by stating
Macharia
what it is not. I
agree with him to some extent.
But alive to the difficulty that may be
involved in starting from describing what
viscosity is not, without getting into a
conundrum, I will start by saying what
it is. Considering the basic elements that
explain viscosity, the most basic definition of viscosity is the measure of a fluid’s
resistance to flow.
And so on viscosity, including all the
derivatives that come from that word, at
the back of your mind I would want you to
have a mental perception of viscosity as
resistance to flow. Or – to put it in another
way – a liquid’s resistance capacity to flow.
Viscosity is arguably the most important property of a lubricant, holding many
other factors constant, and depending on
the perspective from which you look at it.
In a discussion I initiated within a group
on Linked In , there was a wide range of
views on what viscosity is – and what it is
not. Contributing to the discussion, Toby
Taylor described viscosity as a physical
feature that sadly does not describe what
the oil is used for.

Excessive Technicality
While Taylor’s assertion is true, it also
highlights a fundamental lubricant-user
information gap, based on the standard
descriptions used by oil companies worldwide to describe lubricant application purposes. Understanding viscosity would go a
long way to aid the public’s understanding
of lubricant applications, away from oil
24

marketers’ intricate descriptions by use of
excessive technicality with an aim limited
to marketing lubrication products.
Viscosity at the point of lubrication is
the most important of the specifications
but not the only consideration. You
cannot isolate this one important factor
and ignore the rest, because a lubricant
will interact with a dynamic environment.
Earlier, I mentioned the term Viscometry which is the Science of measuring
viscosity. In other words, of or relating
to the measurement of viscosity. Viscosity can be measured in terms of Absolute
Viscosity (Centripoise cPs), resistance to
flow and shear or by Kinematic viscosity
(Centistoke cSt) resistance to flow by shear
forces of gravity.

Viscosity with Temperature
This brings me to the next viscosity
derivative: Viscosity Index, a measure of a
lubricant’s change in viscosity with temperature. Normally, viscosity decreases
with increase in temperature and viceversa. Don McNeil stated in the Linked
In discussion, that this behaviour is
defined as an arbitrary number assigned
as a measure of the constancy of the
viscosity of lubricating oil with change
of temperature, with higher numbers
indicating viscosities that change little
with temperature.
It is simply a scale to indicate the viscosity change of oils relative to temperature.

The most basic
definition of viscosity
is the measure of a
fluid’s resistance to
flow

LUBEZINE MAGAZINE | November 2013-January 2014