26-07-2012, 11:21 AM
The Science of SelfLubrication
The-Science-of-Self-Lubrication.pdf (Size: 402.57 KB / Downloads: 141)
Introduction
Bearing and linear guide manufacturers’ misuse of performance buzzwords such as “self‐lubrication”,
“maintenance free”, and “lubed for life” has led to a broad misunderstanding of what these terms actually
mean. This confusion can lead to misapplication of products resulting in failures, downtime, and bottom
line losses in productivity and dollars.
felt wicks may extend the life of a bearing system, they cannot be classified as “self‐lubricating”. They
require maintenance attention to oil levels that dissipate, age, and become ineffective over time.
True “lube for life” requires that the lubrication be an integral element of the original bearing material. To
be truly self‐lubricating, the lubrication cannot be an add‐on, does not break down, and remains a part of
the bearings makeup for its entire life without the need for outside maintenance.
What is SelfLubricating?
Self‐lubrication is characterized by the bearings ability to transfer microscopic amounts of material to the
mating surface. This transfer process creates a film that provides lubrication and reduces friction over the
length of the rail or shaft.
Transfer Process
The transfer process is an ongoing dynamic function of the self‐lubricating
bearing that will continue throughout its operational life.
The first and most critical step in the process is the break‐in period. This is
when the initial transfer of material to the mating surface takes place. The
amount of bearing material affected during the transfer is dependent upon
multiple factors including the speed, load, and length of stroke, etc. for the
application. Typically the initial transfer process will be accomplished in
50‐100 strokes of continuous operation.
The secondary and ongoing phase of the transfer is where the selflubrication
is most effective.
The transfer process deposits a microscopic
film on the shaft and in the valleys of the
mating surface creating a true selflubricating
condition.
Common Misconceptions
Clever advertising gimmicks and inaccurate training materials are claiming “self‐lubricating” or “lubed for
life” capabilities for systems or components that do not fit the definition of the lubrication being an integral
element of the bearing material. Below is a description of some of these types of systems.
Types of Non SelfLubricating Systems
Rolling Element Systems
These include rotary (ball and roller) bearings, round‐way linear ball
bearings, and rolling element profile type monorail designs. All of
these systems require some kind of external lubrication to operate.
The metal‐to‐metal contact of the rolling element against the
raceway necessitates that there be grease or oil present at all times.
If this external lubricant is not present, the ball or roller will begin to
make direct contact with the shaft or rail material resulting in galling
and brinelling damage. Many manufacturers attempt to overcome
this weakness in the design by adding oil‐impregnated seals to the
ends of the bearing or housing. This approach can result in some
benefit to the life a rolling
Oil impregnated bronze
These bronze bearings are very porous and have lightweight oil
soaked into the material. Under the optimum conditions, this oil is
drawn to the bearing surface creating a lubricated layer between the
bearing and the shaft.
Graphite plugged bronze
Graphite is a good solid lubricant that is normally added to a bronze type bearing. Solid plugs of graphite
are usually inserted into holes in the base bronze.
Teflon coated materials
PTFE can be used to coat bearing surfaces in several ways. It can be applied as either a part of a powder
simply dusting the bearing. It can be a sprayed mixture that adheres to the bearing surface. Or it can be
part of a liquid or grease compound applied to the bearing. Any of these methods results in a very thin
layer of actual lubricant that is quickly worn away and becomes ineffective.
Oil impregnated plastic
Here again, lightweight oil is added to the base material to aid in bearing lubrication. The result is
decreased friction initially, but lubricant aging and dissipation quickly reduce its effectiveness.
What makes a system selflubricating?
1. The lubrication is an integral component of the bearing material.
2. The oil or grease is NOT added to the original bearing design.
3. The oil or grease will NOT breakdown and be ineffective over time (lubricant ageing or aging).
4. The oil or grease is consistently applied to the shaft surface.
5. Additional components do not add cost to the overall system.
shaft or bearing damage and reduce system life. (Double edge sword of rolling element bearings)
To truly be selflubricating,
a bearing system must do exactly
what the name implies. It must provide its own lubrication
throughout the life of the system and not have some external
source facilitating lubrication for a period of time. It must be
designed and manufactured into the bearing material from the
beginning. One example of this is PBC Linear’s Simplicity® selflubricating
liner.
The Advantages of Simplicity Frelon® Liner
• No metal‐to‐metal contact
• No galling or brinelling
• No added lubricants to attract additional contaminants
• Dampens vibration for smooth and quiet operation
• Actual “maintenance free” operation
Proven Success in PBC Linear™ Products
• Simplicity Linear Plane Bearings
• Uni‐Guide™ Modular Guides & System
• Mini‐Rail® Miniature Linear guide