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On New Applications:
1. Calculate
the required torque
2. Select
the Posi-Lok Bushing® with the proper torque rating
using the Performance
Chart.
3. Check
suitability of shaft and hub
using the Dimensions
Chart.
On Existing
Applications:
1. Select
the Posi-Lok Bushing® for the required shaft size
using
the Dimensions
Chart.
2. Check
the required torque transmission rating against
your choice using the Performance
Chart.
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Torque Calculations:
Given the horsepower
rating of the prime mover and the shaft rpm, the torque transmitted
is:
Calculating
the Required "Tr"
The required
torque transmission rating "Tr" is equal to the calculated
torque multiplied by service factor "a" which will account
for high starting torques, transient overloads, shock loads, pulsating
loads and alternating loads.
Certain types
of electric motors have starting torques as high as 2 to 2.5 times
rated torque which must be taken into consideration when selecting
the Posi-Lok Bushing®. Recommended service factors
for various types of applications are shown in the following table:
| Service
Factors |
|
Driver
|
Electric
Motor
|
Internal
Combustion Eng.
|
| Type
Load |
Constant |
Pulsating |
Alternating |
Constant |
Pulsating |
Alternating |
| Fans |
1.0 |
- |
- |
1.5 |
- |
- |
| Rotary
Pumps |
1.0 |
1.5 |
- |
1.5 |
2.5 |
- |
| Generators |
1.0 |
1.5 |
- |
1.5 |
2.5 |
- |
| Centrifuges |
- |
1.5 |
- |
- |
2.5 |
- |
| Chain
Drives |
- |
1.5 |
- |
- |
2.5 |
- |
| Reciprocating
Compressors |
- |
- |
2.0 |
- |
- |
3.0 |
| Piston
Pumps |
- |
- |
2.0 |
- |
- |
3.0 |
| Conveyors
(belt) |
- |
- |
2.0 |
- |
- |
3.0 |
| Crushers |
- |
- |
2.0 |
- |
- |
3.0 |
| Rollings
Mills |
- |
- |
2.0 |
- |
- |
3.0 |
Example:
A piston
engine powered compressor (a = 3) with torque of 100 lb. ft. will
require a Posi-Lok Bushing® with a torque rating
of 300 lb. ft.
The formula
is: Required Tr = Tc x a
- Where: Tr
= torque rating of Posi-Lok®
- Tc = calculating
torque
- a = service
factor
Shaft and
Hub Tolerances
Posi-Lok Bushings®
(inch series) are designed for the following tolerances:
Shaft tolerance h8, Hub Bore tolerance H7
Note: If the
Posi-Lok Bushing® is used in an application where
tolerances lie outside the recommended range, torque transmission
(Tr) will be reduced. The torque values in the tables of sizes are
based on these tolerances.
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Stress in
Hub and Shaft
The stress is
a function of surface pressure and material thickness. At constant
surface pressure, increases with diminishing material thickness.
This applies both to hubs and hollow shafts. The table below shows
recommended OD/ID ratios for hubs made of different materials.
| Material |
OD/ID |
Steel
(high grade)
Steel (normal grade)
Cast Iron
Aluminum |
1.4
1.5
2.0
2.5 |
OD
= outside diameter of hub
ID = inside diameter of hub |
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Call factory
with any questions you may have.
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