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Understanding Bellows Couplings

Bellows couplings are single-piece , flexible shaft connectors utilized to join drives and driven shafts of mechanical power transmission systems. Flexible shaft couplings can be used to prevent the inevitable misalignment between the shafts that are connected and, in certain cases they can absorb shock.

Coupling design

Bellows couplings comprise of pleated, thin tubes made of metal connected by shaft connectors on their ends. This coupling can be described as torsionally stiff which makes it an ideal device for demanding instrumentation and motion control applications. It is also utilized in certain industrial processes, because its capacity to accommodate an axial temperature increase is a benefit for installation with high temperature swings. The designs can be heavy-duty for shaft diameters up many inches. This design has a very low energy, which means it places a little impact on the performance of a drive/driven combination.

To create the bellows nickel is electrodeposited on an amandrel. The mandrel is will dissolve leaving behind a thin, flexible component. This method produces bellows that are extremely thin, but with precisely controlled thicknesses that allow an extremely responsive and sensitive coupling, despite having a smaller torque capacity than those of bellows produced through other methods. These bellows are more rigid using stainless steel, as well as compliant bronze versions generally through hydroforming. Aluminum is usually used at the ends in order to reduce inertia. Other metals are utilized in this manner too. The assemblies can be welded or joined using adhesives. The majority of bellows couplings are connected to shafts using clamps that are integral, however other connection methods like taper-lock bushings are available. Some couplings include keys however using a keyway is typically not advised over the most popular shaft clamping methods accessible.

In smaller systems for motion controls, coupling inertia could be a significant part of system inertia. it is the bellows-like coupling that can make efforts to reduce it, especially in comparison with other couplings for servo-systems like Oldham, beam, and the zero-backlash jaw.

The failure of bellows couplings results mostly due to fatigue of the metal resulting from the deformation and relaxation of the convolutions of metal as they adjust for shaft misalignment, particularly in the areas where the bellows are close towards the connectors. A peak torque applied can break the steel. If a problem does develop and the machine is affected, the transfer of torque to the drive machine typically stops and the coupling has to be replaced completely. If misalignment is not too severe the bellows couplings will be able to endure many, many times without fatigue. Certain manufacturers say that they can run for a long time.


Trailer coupling bellows typically allow for angular misalignment as low as 1-2 degrees and parallel misalignment of 0.01 and 0.02 in. The design is flexible enough to allow an axial expansion too. A little less tolerant of alignment issues than other designs of couplings Bellows couplings exert very little force to restrain the equipment that is coupled, while remaining rigid along the axis of rotation and flexible in the angular, parallel and the axial planes.

When determining a bellows coupling that is suitable for applications using servos, the best procedure is to measure the maximum torque that the motor produces, calculate the amplification of any gearing, and then apply the safety factor 1.5. The chosen coupling must be at or near that capacity as the value calculated. In the case of frequent torque reversals as well as stop/starts the acceleration torques are taken into consideration along with moments of inertia as well as the impact of shock on in order to determine a recommended torque for couplings. The couplings could also be measured according to torsional deflection or, in some cases it is based on resonance frequency. The majority of manufacturers will provide the sizing application to help specifiers through the selection procedure.

A majority of bellows couplings that are standard can run at speeds as high as 10,000 rpm. And if the hubs are balanced dynamically more than that, the speed can be much higher. Certain manufacturers offer double-bellows models that can be used in industries that have heavy use.

Specifications and Attributes

Bellows specifications for couplings comprise some of the attributes and parameters listed below:

Bore diameter or size The diameter of the bore that is used to connect the shaft. The sizes of the bore may be identical or differ on either part of the coupling according to the model.
Overall length is the entire distance of the coupling determined from the two ends sides on the coupling.
Hub width is the size of the hub, measured from the face that ends at the inside face which connects to the bellow.
Hub material is the material that the hub is made.
Bellow material – the substance that the bellow is made.
Hub diameter is the overall size of the hub of the coupling.
Bellow diameter is the total size of the bellow section in the coupling.
Maximum torque rated – the maximum torque rating of the coupling to handle maximum torque load.
Lateral offset, also referred to as parallel misalignment – is the longest distance that can be tolerated by shaft misalignment on the axial dimensions that can be taken care of through the coupling.
An angular offset, also known as an angular misalignment, is the maximum angle deviation of shaft misalignment in the radial dimensions that can be taken care of via the coupling.
Shaft coupling fastening technique The method through which the coupling is fastened to the drive shaft or the driven shaft generally clamped or with the set screw.

Things to Consider

Since many bellows couplings are employed as precision motor systems, such as zero-backlash devices, they’re not intolerant of misalignment when contrasted with other designs of couplings. When installing such couplings it is essential to align the driven and driving equipment as precisely as is possible to ensure the longevity of the device.

Another factor to consider is that the coupling could be the least expensive component in the system and could be the source of failure in overload. There are designs that limit torque which can also serve this purpose.

Bellows couplings provide high stiffness and, as the bellows is symmetric throughout its construction and is symmetrical throughout its construction, they are able to avoid the high force that non-symmetrical couplings may produce and are therefore a great choice for applications that require delicate motion control. Their torsional stiffness lets them handle rapid velocity and dynamic movements that have become characteristic of various motion systems. They can withstand high speeds and thermal expansion. Their only disadvantage is a slightly less tolerance to the misalignment.

As with all couplings the bellows couplings that are exposed must be secured to avoid injuries.

Most shaft couplings are equipped to handle shaft misalignment, but to an extent or more according to the coupling’s type. It is common for misalignment to occur in an angular and parallel form. Parallel misalignment can be defined as shafts with axes that are parallel, but not collinear. An angle misalignment is defined as shafts that intersect but with an angle that is less than 180 degrees. Manufacturers of couplings will announce each of these limitations on their product. Methods to align machine trains differ from the manual rule-and-feeler-gage method to the utilization of shaft-mounted dial indicators and laser-based strategies. Installation of rotating equipment is a common practice. shaft alignment services using the various techniques.


This article offered a brief overview of bellows couplings including their applications, attributes and specifications, as well as considerations for selection.