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COUPLINGS


3.0 Types of Flexible Couplings


Most small to medium size couplings are basically one of three types.

3.1 Universal Joints


A universal joint is a linkage consisting of two yokes, one on each shaft, connected by spider as shown on Figure 2. Since universal joints are frequently used, and thee r analysis is complex, a separate section is devoted to them following this section.

Spider and Yoke Construction

By substituting an elastomeric member in place of the conventional spider and yoke construction Such as in the design shown in Figure 3 backlash is eliminated. Lubrication is no longer a consideration because there are no moving parts and a fairly large amount of lateral misalignment can be accommodated. The Illustrated coupling is available in the product section of the catalog. Please refer to Figures 4 and 5 for specific design data for this type of Coupling.

Torque Capacity

3.2 Oldham Coupling


Oldham couplings consist of three members. A floating member is trapped by 90 displaced grooves between the two outer members which connect to the drive shafts as shown in Figure6.

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 Coupling 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:
  • 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:
Speed Formula

Flexible shafting for power transmission is wound for maximum efficiency when rotating in only one direction – the direction which tends to tighten the outer layer of wires on the shaft. Direction of rotation is identified from the power source end of the shaft. Torque capacity in the opposite direction is approximately 60% of the "wind" direction. Therefore if the power drive shaft must be operated in both directions, the reduced torque capacity will require a larger shaft than would normally be selected for operation in the wind direction.

Because flexible shafts were developed primarily as a means of transmitting power where Solid Shafts cannot be used, most applications involve curves. Each shaft has a recommended minimum operating radius which is determined by the shaft diameter and type. As the radius of curvature Is decreased, the torque capacity also decreases and tends to shorten shaft life.
Shaft Coupling

Lastly, service conditions such as temperature present no special problems to flexible shafts when operating in the -65 to +250°F range. Plastic casing coverings are able to cover this temperature range and provide additional protection from physical abrasion as well as being oil and water tight. Sometimes it is desirable if not essential that a flexible shaft coupling be as short as possible and still retain most of the features previosly described. Figure 7 illustrates such a coupling, available in the Product Section of the catalog.

The "flexible Shaft" center section consists of three separately would square wire springs. Individual spring layers are opposingly wound to provide maximum absorption of vibration, load shock and backlash. The hubs are brazed to the springs for maximum strength. Design data is available in Figure 8 as well as in the Uni-Flex catalog page in this catalog.

Figure 8 - Uni-Flex Couplings Selection Data
Series
Number
Max.
Torque
Lb.in.
H.P. Capacity* At Varying Speeds (R.P.M.)
100  300  600 900  1200  1500 1800  2400   3000 3600
18
25
37
50
18
34
39
82
.03
.05
.06
.13
.09
.15
.18
.39
.18
.30
.36
.78
.27
.45
.54
1.2
.36
.60
.70
1.5
.45
.75
.90
2
.5
.9
1
2.3
.7
1.2
1.4
3
.9
1.5
1.8
3.9
1
1.8
2
4.6
*Based on service factor of one only


    Service Factors:
  • Light, even load – 1
  • Irregular load without shock, rare reversals of direction – 1.5
  • Shock loads, frequent reversals – 2
    Unflex Selection Procedure:
  • Select the service factor according to the application.
  • Multiply the horsepower or torque to be transmitted by the service factor to obtain rating.
  • Select the coupling With an equivalent or slightly greater horsepower or torque than shown in the table.


3.4 Miscellaneous Couplings


Jaw Type CouplingThis group of couplings incorporate design features which are frequently unique, approximations or combinations of universal, Oldham and flexible shaft couplings. Two widely used couplings in this category are the Jaw and Sleeve types, both of which are available in the Product Section of our catalog.

Jaw type couplings Consist of two metal hubs which are fastened to the input and output shafts. Trapped between the hubs is a Urethane spider" whose legs are confined between alternating metal projections from the adjacent hubs. The spider is the wearing member and can be readliy replaced without dismantling adjacent equipment. The coupling is capable of operating without lubrication and is unaffected by oil, grease, dirt or moisture. Select the proper size for your application from the table in Figure 10 and the selection instructions.

Figure 10 - Jaw Type Couplings Selection Data
Coupling
Series
No.
Rated
Torque
in Lbs.
Service
Factor
Horsepower capacity at Varying Speeds (R.P.M.)
100 300 400 900 1200 1500 1800 2400 3000 3600
035 3.5 1.0
1.5
2.0
.0056
.0037
.0028
.017
.011
.009
.034
.023
.017
.05
.033
.25
.067
.045
.033
.084
.056
.043
.13
.087
.065
.10
.067
.05
.17
.113
.025
2
.13
.10
050 25.2 1.0
1.5
2.0
.04
.03
.02
.12
.08
.06
.24
.16
.12
.36
.24
.18
.48
.32
.24
.60
.40
.30
.72
.48
.36
.96
.64
.42
1.2
.80
.60
1.44
.96
.70
070
37.8
37.8
1.0
1.5
2.0
.06
.04
.03
.18
.12
.09
.36
.24
.12
.54
.36
.27
.72
.48
.36
.90
.60
.45
1.08
.72
.54
1.44
.96
.72
1.8
1.2
.90
2.16
1.44
1.08
075 75.6 1.0
1.5
2.0
.12
.08
.06
.36
.24
.18
.72
.48
.36
1.08
.72
.54
1.44
.96
.72
1.80
1.20
.90
2.16
1.44
1.08
2.88
1.92
1.44
3.6
2.4
1.8
4.34
2.88
2.10
090 126. 1.0
1.5
2.0
.20
.13
.10
.60
.40
.30
1.2
.20
.60
1.8
1.2
.90
2.4
1.6
1.2
3.0
2.0
1.5
3.6
2.4
1.8
4.8
3.2
2.4
6.0
4.0
3.0
7.2
4.8
3.6
Service Factors
1.0 _______ Even Load No Shock infrequent Reversing with Low Starling Torque
1.5 _______ Uneven Load Moderate Shock Frequent Reversing with LOW Start Torque
2.0 _______ Uneven Load Heavy Shock Hi Peak Loads Frequent Reversals with High Start Torque

Sleeve Type Coupling
    Jaw Type Coupling Selection Procedure:
  • Select the service factor according to the application.
  • Multiply the horsepower or torque to be transmitted by the service factor to obtain rating.
  • Select the coupling with an equivalent or slightly greater horsepower or torque than shown in the table.
  • Turn to the Product Section page illustrating the same coupling and make your specific selection in that number series.
A sleeve type Coupling consists of two splined hubs with a mating intermediate member of molded neoprene. Because of its construction features, it is capable of normal operation with angular shaft misallgnments up to 7.112.

Lubrication is not required. All parts are replaceable without disturbing adjacent equipment provided sufficient shaft length is allowed by slide coupling hubs clear of the sleeve member during disassembly. Select the proper size for your application from table In Figure 12 and follow the selection instructions.

    Sleeve Type Coupling Selection Procedure:
  • Determine motor characteristic.
  • Determine service conditions.
  • Select the series coupling with an equivalent or slightly greater horsepower than shown in the table.
  • Turn to Powergrlp couplings in the Product Section and select the specific assembly or individual components in that number series.


Other types of couplings are also available and are fully described along with technical specifications in this catalog.

Sleeve Type Couplings Selection Data

SERVICE CONDITIONS
    Normal Duty
  • speed not exceeding 3600 rpm
  • operation less than 10 hours per day
  • infrequent stops and starts
  • no heavy, pulsating load
  • no mechanical or electric clutch
    Severe Duty
  • speeds from 3600 to 5000 rpm
  • operation more than 10 hours per day
  • frequent starts and stops
  • heavy, pulsating load
  • mechanical or electric clutch
page 3 - Universal Joints
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