Euroflex Coupling - A design review
Euroflex India
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Design Review

Coupling Range

Variations to Design

Coupling Selection



Principle of Torque Transmission:

The Euroflex coupling is torsionally stiff with zero backlash and torque is transmitted through pure tension in the flexing elements. Figure 1 shows holes A, C & E in the flexing elements, bolted to the driving machine flange, whilst holes B,D & F are fastened to either the spacer / driven machine flange.

Torque is transmitted from bolt C to B, E to D and A to F.
Flexibility ia achieved when flexing elements bend between the drive and driven bolts .

The principal reasons why, the Euroflex couplings, out perform others in its class is on account of the two fundamental design principles adopted by us:

It is this design feature of the flexible element which enables the Euroflex couplings to offer smaller diameters, for a given torque, than, would otherwise have been possible.

A) Flexing Element Design:

In the Euroflex design, the flexible elements have a polygonal outer profile with a circular central hole. The design ensures that, all the forces in the flexible elements are purely tensile and also provides for the maximum material at the points of bending, leading to very low bending stresses, while permitting high misalignment capacity.


B) Coupling Bolt:

The coupling bolts in the Euroflex design are manufactured out of high tensile steel and are adequately sized to transmit torque through friction rather than shear.

Coupling Bolt

The bolts are preloaded to achieve adequate bolt extension thereby inducing a large tensile load in the bolts, which is adequate to prevent both bending of the bolts as well as slip between the flexing elements. The prevention of slip is very important to prevent the flexing elements from fretting.

Misalignment Capacity:

Misalignments arise in all rotating machinery due to various reasons, like temperature variations,bearing wear, foundation settling etc.


The type of misalignments faced by rotating equipment is depicted below:

Axial Misalignment

Axial Misalignment:

Axial misalignment is the variation in axial distance
between the shafts of the driving and driven machinery.

Angular Misalignment:

Angular misalignmnet is the effective angle between the two shaft centerlines and is usually quantified by measuring the angle between the shaft centerlines as if they were extended till they intersect. If the shafts are flanged, it is simply enclosed angle between them if they were to be brought to a position of contact.

Abgular Misalignment

Radial Misalignment

Radial Misalignment:

Radial or Parallel misalignmnet is the transverse distance between the two shaft centerlines and is quantified by measuring the radial distance between the centerline of one shaft if it were to be extended to overlap the other.

The Euroflex couplings are designed to accept Axial, angular and radial misalignments and the degree of misalignment is limited by the imposed stresses in the flexing element.

Bending Moment

The axial misalignments imposes a tensile bending stress in the flexing element, which is dipicted by the bending of the beam between the anchor points(see figure), while angular or radial misalignment introduces a bending in the span of the flexing element

Thus the permitted amount of axial and radial misalignments is dependent on the number of bolts and geometry of the flexing element.

Axial and Parallel misalignments are inversely related, in other words, when one increases, the other decreases. Further this misalignment capability is determined by assessing the combined steady and fluctuating stresses experienced by the flexible elements.

The hallmark of the Euroflex design is the expertise to accurately determine the cylical stresses under all conditions of coupling operations. A proff of the same is the unmatched 1o angular misalignment capability that the Euroflex coupling offers on all 4 Bolt designs.

These stresses for the entire range of operating conditions are plotted on the modified Goodman Diagram , for evaluating the fatigue life of the flexible element material. Curve 1 is a plot of the fatigue data generated by the life cycle testing of the flexing element material(AISI 301) which shows an infinite life at a bending stress of 410 N/mm2(1011 Cycles).

The Euroflex design criterion ensures that the imposed bending stresses do not exceed 290N/mm2 and all continuous and short term conditions must necessarily have a plotted operating point falling within the area under Curve-2. Thus any point within this area has a minimum cyclic factor of safety of 2.0.

Modified GoodMan Diagram