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Physical Properties
Speed vs. Load - P/V Factor
Material Max P/V
Wall Thickness
Shaft Diameter
& Recommended Wall Thickness
Installed Bearing
Clearances
Press Fits
Close-In
Grain Direction
Lubrication
Installation
Application Information
| Physical Properties |
|
| Lubricant content by weight |
41-47% |
| Tensile Strength |
1150 psi |
| Compression permanent
deformation |
(psi, for .005" set) 7500 |
| Specific Gravity |
1.3 |
| Coefficient of thermal expansion
per ºF |
4.3 x 10^-6 |
| Temperature range |
-50 - 160ºF |
| Coefficient of friction |
.07 to .115 |
| Weight per cubic inch, lbs. |
.039 |
| Wear rate factor |
<0.1 x 10^-10 |
| Max P/V Factor |
12,000 PIA-SFM |
| Max P |
2,000 PIA |
| Max V |
2,000 SFM |
Speed vs. Load - P/V Factor
All bearings have a P/V rating (Pressure/Velocity) based
on empirical testing. The rating is a mathematical expression
of Pressure (PIA = pounds per inch of projected area)
times Velocity (SFM = surface feet per minute). The
expressed P/V value of a material is the maximum load-speed
that a bearing can withstand. This value is further
refined by the maximum PIA and SFM that the material
can withstand regardless of the total P/V value. The
recommended P/V factor for WOODEX® is 12,000, with
a maximum PIA and SFM of 2,000 each.
As a comparison, the following are operating characteristics
of a variety of bearing materials:
| Material |
Max
P/V |
Max
P |
Max
V |
Inj. Molded Nylon
101
|
3,000 |
380 |
475 |
Delrin
|
3,000 |
1,000 |
100 |
UHMW-PE
|
4,000 |
1,200 |
50 |
WOODEX
|
12,000 |
2,000 |
2,000 |
Babbitt (10% tin)
|
18,000 |
1,300 |
1,400 |
Oilite Bronze
|
50,000 |
2,000 |
1,200 |
| Cast Bronze SAE
660 |
75,000 |
3,000 |
750 |
WOODEX is unusual in that it has
the capability to handle both high speeds and loads,
a quality that enhances its flexibility. As an example,
in a dry, ambient condition a 2" long WOODEX bearing
supporting a 1" shaft can support a shaft load of up
to 1,800 pounds, while the shaft is rotating at 50 rpm.
Conversely, the bearing can tolerate a shaft RPM of
up to 1,800, while the shaft load is 50 pounds.
To calculate the P/V for any given application, use
the following formulas:
PIA and SFM must each equal 2,000 or less. Multiply PIA
times SFM: the product (P/V) must be 12,000 or less. If
true for all three values, WOODEX may be right for your
application.
NOTE: Add appropriate safety factors to both
load and speed before calculating.)
Wall Thickness
It is important that the wall thickness of the bearing
meet minimum standards. Proper wall thickness will guarantee
a sufficient supply of lubricant to last the life of
the bearing. Shaft size can rarely be reduced, but housing
size may be increased to satisfy this requirement.
| Shaft
Diameter |
Recommended
Wall Thickness* |
| up to 1/2" |
1/16" to 1/8" |
1/2" to 1"
|
1/8" to 3/16" |
1" to 1 1/2"
|
3/16" to 5/16" |
1 1/2" to 2"
|
5/16" to 3/8" |
2" to 2 1/2"
|
3/8" to 1/2" |
| 2 1/2" to 4" |
1/2" to 5/8" |
* Thinner bearing wall may produce reasonable service
life under certain conditions.
Clearances
An oil-lubricated bearing must have sufficient clearance
to allow the lubricant to penetrate and form a lubricating
film. Insufficient clearance will inhibit this lubricating
film and excessive clearance will allow excessive movement
between parts. Either condition will result in premature
bearing failure. The inside diameters of all WOODEX bearings
are machined oversize to provide the required clearance.
Designs that require tighter tolerances can be met by
supplying bearings without built-in clearance and calling
for reaming at installation. Reaming will not restruct
the self-metering lubrication qualities of the bearing.
| Installed
Bearing Clearances |
|
|
|
|
| Shaft Diameter |
Operating Condition |
Roll-end Operating Condition |
|
|
Dry
|
Wet
|
Dry
|
Wet |
up to 1/2"
|
.002"-.010" |
.020"-.028" |
.015"-.024" |
.030"-.035" |
1/2" to 1"
|
.004"-.016"
|
.024"-.032"
|
.024"-.028"
|
.035"-.042" |
1" to 1 1/2"
|
.007"-.019" |
.038"-.046" |
.024"-.030"
|
.038"-.050" |
1 1/2" to 3"
|
.010"-.025"
|
.045"-.060"
|
|
|
| 3" & up |
.015"-.031" |
.050"-.066" |
|
|
Press Fits
A WOODEX bearing remains stationary in its housing because
it has been furnished with an oversized outside diameter
to ensure firm retention. Sleeve, flange and roll-end
bearings are all machined to include this press fit. Oil
impregnated maple bearings have greater press fit dimensions
than metal, since they are much more compressible.
Close-In
The compressibility of oil-impregnated rock maple means
that approximately 70% of the press fit on a WOODEX bearing
will be reflected in close-in of the inside diameter.
WOODEX bearings are normally furnished with an oversized
inside diameter. This provides a correct running clearance
once the bearing has been pressed in place and the close-in
effected.
| Press
Fit - Close-In |
|
|
| Nominal O.D. |
Press Fits |
Close-In Factor |
| up
to 1/2" |
.003"-.006" |
.003" |
| 1/2" to 1 1/2" |
.004"-.008" |
.004" |
| 1 1/2" to 3" |
.005"-.010" |
.005" |
| 3" & up |
.006"-.012" |
.006" |
Grain Direction
In a lubricated bearing, the oil must be delivered to
the load carrying area of the interface. In order to do
this, a wood bearing must have its bore at right angles
to the grain of the wood. Aligned in this cross-grain
fashion, the cell structure meters the lubricant to the
interface.
Lubrication
WOODEX bearings self-lubricate in three modes:
- boundary lubrication
- full film (hydrodynamic) lubrication
- mixed film lubrication
These modes indicate the effectiveness of bearing lubrication
in reducing friction.
Under full-film lubrication, the shaft is completely
separated from contact with the bearing by a thick film
of lubricant. Without shaft to bearing contact, bearing
service life is nearly infinite. This condition is rarely - if ever - achieved with a wood plane bearing.
Boundary lubrication permits bearing-shaft contact
in the presence of an extremely thin lubricating film.
Bearing wear is proportional to load and speed.
Mixed film lubrication combines both other modes.
Pools of self-pressurized lubricant accept part of the
load while very thin films take the rest.
WOODEX bearings are charged with a lifetime lubricant
supply. Outside lubricants should not be used, as they
will impair the natural action of the WOODEX lubricant.
Installation
An arbor press should be used to press a WOODEX bearing
into place. A slight chamfer is furnished on one end of
the bearing as an aid in starting the fit into the housing.
The inside of the housing also should be slightly rounded
or relieved to make sure there is no burr on the edge
of the housing to cut the bearing as it is pressed into
place.
Application Information
When inquiring about custom WOODEX bearings, please be
sure to include the following information:
- Nominal Housing Dimensions
- Bearing Length
- Shaft diameter
- Shaft Speed
- Shaft Load
- Temperature, and
- Operating Condition (wet, dry or partially-wetted)
We will be pleased to answer any questions and consult
on any application. If we cannot help you, we will direct
you to someone who can.
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