Bellows couplings are single-piece , flexible shaft connectors used to connect drive and driving shafts of mechanical power transmission units. Flexible shaft couplings are utilized to prevent the inevitable misalignment between the shafts that are connected and, in certain cases they are used to absorb shock.
Coupling design
Trailer coupling bellows are made of pleated, thin tubes made of metal connected by shaft connectors on their ends. It is rotationally strong which makes it an ideal device for demanding instrumentation and motion control applications. It can also be used in a few industrial applications in which its capacity to handle the axial growth of thermal is a benefit for installation with high temperature swings. There are heavy-duty models available with shaft diameters ranging from many inches. The design is extremely low in energy, which means it places a little impact on the performance of a combination of drive and driven equipment.
To create the bellows nickel is electrodeposited on an amandrel. The mandrel is dissolves leaving behind a thin, flexible component. This method produces bellows that are extremely thin, but with extremely controlled thicknesses, which makes for a responsive, sensitive coupling, even though they have a less torque than those of bellows produced through other methods. The more rigid versions are produced from stainless steel as well as compatible versions of bronze typically through hydroforming. Aluminum is typically used for the ends, to limit inertia. Other metals are employed in this process too. The assemblies can be welded or joined using adhesives. The majority of bellows couplings are connected to shafts using integrated clamps, but other connecting methods, such as taper-lock bushings are available. Couplers can often include keys, however it is typically not advised over the more popular shaft-clamping techniques that are readily accessible.
In smaller systems for motion controls, the inertia of couplings can constitute a significant portion of system inertia. this hollow bellows coupling can make steps towards lessening it, especially in comparison with other couplings for servo-systems like Oldham, beam, and the zero-backlash jaw.
Failure of bellows couplings result mostly due to fatigue of the metal resulting from the deformation and relaxation of the convolutions in the metal to adjust for shaft misalignment, particularly when the bellows are located closest towards the connectors. A peak torque applied will usually break the material. If a problem does develop it is when the torque transfer to the drive machine typically ceases, and the coupling needs to be replaced completely. If misalignment is not too severe the bellows couplings will endure many, many cycles without fatigue. Certain manufacturers say that they’ll last for years.
Applications
Bellows couplings typically allow for angular misalignment as low as 1-2 degrees and parallel misalignment of 0.01 up to 0.02 in. The design permits an axial expansion and expansion. A little less tolerant of alignment issues than other designs of couplings bellows couplings provide only a small amount of restorative force on the coupling equipment, but remain rigid along the axis of rotation and flexible in the parallel, angular and the axial planes.
When determining a bellows coupling to be used in applications using servos, the best procedure is to measure the maximum torque for the drive. calculate its amplification by any gearing, and then apply the safety factor 1.5. The chosen coupling must have at least that capacity as the value calculated. For frequent torque reversals as well as stop/starts the acceleration torques are taken into consideration in addition to moments of inertia as well as the shock load factor in order to determine a recommended torque for couplings. Couplers can also be sized by torsional deflection or, in some cases it is based on resonance frequency. Many manufacturers offer Sizing software to guide users through the selection process.
The majority of bellows couplings available can operate at speeds of up to 10,000 rpm. And if the hubs are balanced dynamically more than that, the speed can be much higher. Some manufacturers provide double-bellow models that can be used in industries that have heavy use.
Specifications and Attributes
Bellows specifications for couplings include these parameters as well as attributes
Bore diameter or size The diameter of the bore that connects to the shaft. Bore sizes can be the same or differ on either part of the coupling dependent on the type of coupling.
Overall length – the length from end to end 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 inner face that connects to the bellow.
Hub material – the substance of which the hub is made.
Bellow material is the material of which the bellow is built.
Hub diameter – the total dimension of hubs in the section that makes up the coupling.
Bellow diameter is the total dimension of the bellow section in the coupling.
Maximum torque rated – the maximum capacity of the coupling that can handle the maximum torque load.
Lateral offset, also known as parallel misalignment – is the maximum distance tolerable for shaft misalignment on the axial dimension which can be taken care of through the coupling.
An angular offset, sometimes referred to as an angular misalignment, is the maximum angle deviation of shaft misalignment on the radial dimension which can be taken care of via the coupling.
Shaft coupling fastening technique is the method by which the coupling connects to the shaft that drives it usually clamped or through the set screw.
Things to Consider
Since many bellows couplings are utilized as precision motor systems that are zero-backlash devices, they’re not very flexible to misalignment in comparison to other designs of couplings. When installing such couplings it is essential to align the driven and driving equipment as precisely as you can to ensure the longevity that the coupling.
Another thing to consider is that the coupling could be the cheapest component in the system and is the most likely 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 They are immune to the extreme maximum forces caused by non-symmetrical couplings which makes them a good choice for applications that require delicate motion control. Their torsional rigidity lets them handle rapid speed and high-speed motion that is the hallmarks of numerous motion systems. They can withstand high speeds and thermal expansion. The only downside is a slightly less tolerance to the misalignment.
Like any coupling the bellows couplings that are exposed must be secured to avoid injuries.
The majority of shaft couplings are able to take care of shaft misalignment, but to some degree or even more dependent on the coupling’s type. It is common for misalignment to occur in an angular and parallel form. Parallel misalignment refers to shafts with axes that are parallel, but not collinear. An angle misalignment is defined as shafts whose axes cross but with an angle that is less than 180 degrees. The coupling manufacturer will release each of these limitations on their product. The methods for aligning machine train differ from the manual rule-and-feeler-gage method to the utilization of shaft-mounted dial indicators and laser-based methods. Installation of rotating equipment is a common practice. shaft alignment services using different methods.
Summary
This article offered a brief overview of bellows couplings comprising applications, attributes, specifications, as well as considerations for selection.
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