Oldham
couplings can accommodate lateral shaft misalignments up to 10% of nominal shaft diameters
and up to 3 angular misalignments.
Lubrication is a problem but can in most
applications be overcome by choosing a coupling that uses a wear resistant plastic or an
elastomer in place of steel or bronze floating members.
|
Oldham couplings have the
following advantages: a. No velocity variation as with universal joints b. High lateral misalignments possible c. High torque capacity d. Ease of dismantling Disadvantages: a. Limited angular displacement of shafts b. Need for periodic lubrication due to relative sliding motion unless nylon or rubber construction is employed c. Possible loss of loose members during disassembly |
3.3 Flexible Shafts
Flexible shafts are stiff in torsion and very compliant in bending and lateral
misalignments. A good example of this is in their use on automotive speedometer drives.
| Flexible shafts Consist of: | |
a. |
Shaft — the rotating
element consisting of a center wire With several wire layers wrapped around it in
alternating directions. Casing — the sleeve made from metal or non•metals to guide and protect the shaft and retain lubricants. Case End Fitting — connects the casing to the housing of the driver and driven equipment. Shaft End Fitting — connects the shaft to the driving and driven members. |
Flexible shafts are also supplied without a
casing when used for hand operated controls or intermittent powered appiications.
Flexible shafts as shown in the product section of
the catalog are often substituted in place of more expensive gear trains and universal
joints in applications where the toad must be moved in many directions.
They are extremely useful where the load Is located
in a remote position requiring many gear and shafting combinations.
The basic design considerations are torque capacity,
speed, direction of rotation, bend radii and service conditions.
Torque capacity is a
function of the shaft size. Operating conditions must be considered in power drive
applications such as starting torque, reversing shocks, and fluctuating loads. These
conditions constitute overloads on the shaft. If they are substantially greater than the
normal torque load, a larger shaft must be selected. Since in power applications torque is
inversely proportional to speed, it is beneficial to keep the torque down thereby reducing
shaft size and cost. Ordinarily speeds of 1750 to 3600 RPM are recommended. However there
are applications in which shafts are operating successfully from 600 to 12,000 RPM. The
general formula for determining maximum shaft speed is:
|
N = 7200 pd |
where |
N = R.P.M. d = shaft dia. in inches |
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