Basics of Locking Elements
This Handbook provides some of the basic and detailed information which designers should bear in mind when considering locking elements on conveyors.
a) Functional description
Locking elements are components manufactured to high precision tolerances and are used on shafts, to transmit torque to- or from- the shaft in a number of different ways, depending on the application.
Locking elements are essentially an alternative to keyways and keys and offer the benefit of smaller shaft diameters for a given torque rating as well as a simplified shaft and coupling manufacturing process.
A number of suppliers offer locking elements to the industry and different vendors' products usually offer different features and different specifications.
The principle of the design of a locking element is to apply a substantial radial force to two interfacing, machined surfaces and to use the resulting frictional resistance to transmit an tangential force and, in some cases, withstand an axial force along the shaft.
b) Anatomy of a locking element
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The adjacent sketch (click thumbnail for larger image) indicates a cross-section through a typical 'Ringfedder'-type locking element used on a conveyor pulley hub / diaphragm plate.
The locking element comprises two different tapered halves (1) joined together by means of a series of bolts (2) and split at one point in their circumference for contraction.
On their internal diameter, both halves have parallel surfaces to suit the shaft (3). The shaft diameter is selected to suit the nearest standard locking elements' inner diameter. |
The outer sleeve (4) of the locking element is also tapered on its inside surfaces to allow the two halves of the locking element to slide along their respective surfaces when the bolts are tightened. Like the two halves of the locking element, the outer sleeve is split to allow expansion of the sleeve when the bolts are tightened.
The outer circumference is flat to engage the pulley hub (5).
As the bolts are tightened in a specific sequence and to a specific torque setting, the pressure between the shaft and locking element increases as the internal diameter of the locking element decreases.
Similarly, the outer flat surface of the locking element sleeve expands and applies radial pressure to the pulley hub (in this example).
In so doing, the locking element accomplishes the following :-
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The locking element is secured to the shaft.
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The locking element is secured to the pulley via its hub.
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The shaft is secured to the pulley via the locking element.
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The shaft and pulley are both centered relative to each other along the shaft centerline.
Depending on the locking element selected, both a rotational torque and an axial load can be accommodated by the locking element. These loads are specified for each locking element in the relevant tables.
There are different types and designs of locking elements and variations to the above example are common, although the basic principle remains unchanged.
c) Applications for locking elements
Applications for locking elements on conveyors includes the following examples :-
i. Pulley hub / shaft assemblies
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As explained above, locking elements are used to connect pulley shells to their shafts, via their hubs as depicted in the adjacent diagram.
There are a number of different hub designs for pulleys however, when locking elements are used the hubs are the landings for the locking elements. |
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The locking element indicated is a RINGFEDER-Type _____.
An alternative RINGFEDER locking element used on pulleys is the RfN 7013.1 shown below, with a single taper.
ii. Rigid flange couplings with keyless shafts
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Where two rigid shafts are to be connected together, two suitable locking elements shown here could be employed in conjunction with the rigid flange couplings.
The locking elements shown are double-tapered RfN 3012 self-centering locking elements and this assembly would typically be used to connect the output shaft of a reducer to the drive pulley shaft. |
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In this example the self-centering feature is a fundamental requirement in this application.
iii. Stuwe-type flanged coupling for torque and bending applications
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For applications where the shaft may be subjected to bending as well as torque transmission, this rigid flange coupling employs a locking element on the outer radius of the coupling, to allow bending in the coupling while maintaining a firm lock on the shaft.
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