HYDRODYNAMIC LUBRICATION
The design of oil is to produce a film of oil between two mating
surfaces which gives
you the best protection against wear. As the image below shows,
oil flows, and creates a
hydraulic pressure (elasto-hydrodynamic lubrication,EHL) between the
two surfaces.
Now under perfect conditions this type of lubrication will not allow
wear. But in reality,
this is not always the case.This takes us to the next state of lubrication.
(magnified surfaces show mating sides are not smooth)
MIXED FILM LUBRICATION
This is where lubrication is marginal. Under load conditions
oil is squeezed under pressure. For example, during accelleration of an
engine, you step on the gas and the engine dumps fuel, in turn the force
is increased against the rod bearings, pushing (or squeezing) on the hydrodynamic
oil creating a marginal lubrication condition. This is under normal use.
But what happens to oil when it is under extreme pressure created by abuse
or just a heavy foot? Follow me to the next state of lubrication.
(magnified surfaces show mating sides are not smooth)
BOUNDARY LUBRICATION
This is where lubrication is dependant on antiwear additives.
What happens here, is lubrication can be put under so much pressure, and
is momentarily squeezed out to such a point that if oil didn't have any
antiwear additives, you would be metal to metal. This is the last line
of defense for lubrication to protect your equipment. A common place where
you see a lot of high levels of barrier lubricant is in gear lubes. Ever
wonder what that rotten smell was? Yep, high levels of zinc, and phosphorus.
These are the two most used antiwear wear additives used in oils today.
(magnified surfaces show mating sides are not smooth)
A lot of aftermarket additives use zinc and phosphorus for extra protection.
The problem is, when you overload an oil with this type of additive, your
oxidation levels tend to increase, causing an attack on the base oil, which
in turn can cause an increase of viscosity, (thicken the oil) .This is
why it is important not to play home chemist and blend in aftermarket additives
that are not designed to be in the oil to start with.
So, as you can see, viscosity of the oil isn't the only important factor.
Like building a house, you want a good foundation or base. Then you would
use a quality product to build with. In this case, a good base oil is a
start, then with good additives you achieve a good lubricant. Is zinc and
phosphorus the only barrier additives available? No, there are more. Follow
me to a barrier lubricant that has been around for a long time and has
proven out for many years..
