LM-TARBELL
ADVANCED PLAIN BEARING
SPECIALISTS
1-800-628-8332
Sintered Bronze - Cast Bronze - Cast Bronze Wear Plate

Designing & Machining: Oil Filled Bronze ●  Rulon® ● MELDIN™ ● Vespel® ● Thordon™ ● Ertalyte® ● HYDEX™ ● Delrin® ● INTECH Power-CoreTM

 

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The above picture features an Oil filled bronze bushing lubrication system. For illustration purposes, this bearing was pressurized by air via the ID. Note that the pressure applied to the ID forced oil to bubble-up on the OD of the bushing.
Thousands of capillaries remain open from ID to OD.


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.

 

 SINTERED BRONZE MACHINING TIPS


LUBRICANTS
Standard Sintered  Bronze is impregnated with
turbine oil. There are several alternative lubrication systems:

Wax Based Lubricants
Graphite
Molybdenum
PTFE

However, here are some basic rules:
1) Low viscosity oil for low temperatures,
high speeds or light loads.
2) High viscosity oil for high temperatures,
low speeds or heavy loads.
3) High viscosity index oil for wide variations in
operating temperatures.
4) Oxidation stable oils for long-period usage.
5) Oil with ‘oiliness’ additives for boundary conditions.
6) Oil of lesser ‘oiliness’ for full film
(hydrodynamic) conditions.
7) Oil with Extreme Pressure (E.P.) additives
for very heavy or shock loads.

How long does the oil last?

A Sintered Bronze Bearing 3/4" in diameter and
1-1/8' long has been run at 1800 rpm for a total of 1,321,920,000 revolutions without wear. There was
no scoring of shaft or bearing.
 
MACHINING Sintered Bronze



Machining of Sintered Bronze Bearings is
best accomplished with standard
Tungsten-Carbide tools. The cutting edges
of the tool must be dead sharp. The nose
of the tool should be broad enough to overlap
the width of the feed per revolution. Standard
practice of fine feed and shallow depth cut normal to finishing operations.

LM-TARBELL - THE SINTERED BRONZE EXPERTS
1-800-628-8332  Fax: 413-525-3735

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