WRONG!
This sintered bronze bushing was not machined properly,
the pores have been smeared over both on
the
ID and OD. Now you have a cast bronze bearing
- they need to be lubricated. The oil has been sealed
within
the bearing and the entire purpose
of an filled bushing has been defeated. Oil filled
bushings should be machined by companies that
have extensive experience with this material. No
one has more experience than LM-Tarbell. |
RIGHT
This is an
example of proper machining. Please
note the small specs on the body of the bearing.
These specs
are evidence that the capillaries from
ID to OD remain open allowing oil to flow
( wick ) readily.
We are often called by engineers who
tell us that oil impregnated bronze bushings failed in
their application. We ask them to send us their failed
bearings and more often than not, they have failed because
they were improperly machined. |
|
UNDERSTANDING
Sintered Bronze
Sintered
Bronze - "A Metallic Sponge"
In order to
properly machine oil impregnated,
sintered
bronze bushings an understanding of the manufacturing
techniques of the raw material must
be taken into account.
Sintered bronze begins as powdered metal which is
packed into a die and
pressed under heavy tonnage to
finished blank -
near net - sizes. This material, now in a "green state"
,is then sintered in a furnace to fuse the powdered particles
into a solid form. This form remains approximately 20%
porous.
Lubricant is absorbed
and stored in countless thousands of
tiny interconnected pores -
between sintered groups of powder - by vacuum impregnation or
hours long immersion in hot oil. Capillary action holds the
oil in
the bearing and
prevents it from dripping out.
6
O'CLOCK
As the shaft begins to rotate within the bearing, it
is
in a boundary situation. At 6 O'Clock, there is
enough heat
generated to draw oil from thousands
of pores
and the shaft
is lifted on an oil film -
becoming hydrodynamic.
|
SINTERING
A
process of forming objects from a
metal powder by heating the powder at a
temperature below its melting point.
Through chemical or
mechanical procedures a
fine
powder of the metal
can be produced. When the
powder is compacted
into the
desired shape and
heated, i.e., sintered,
for up to three hours, the
particles composing the
powder
join together
- micro weld - to
form a single densified part.
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