Jan. 06, 2025
This is the third installment in a weekly 3-part series on flexible vs rigid couplings running through December. Here, Ruland's Bobby Watkins shares his insight into the best options for different coupling applications. This excerpt was taken from Watkins' presentation during the Design World Webinar, Flexible vs Rigid Couplings.
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Ruland Manufacturing specializes in various coupling types, including rigid couplings, servo insert couplings, bellows, metal bellows, metal disc, Oldham types, and beams, ensuring we provide a comprehensive range of motion control couplings.
Previously, we examined different types of misalignment. Rigid couplings, in particular, are often misapplied and misunderstood. They cannot accommodate any form of misalignment, yet they serve a specific purpose and are very effective when used correctly.
Misalignment is a significant concern. When your coupling fails to address misalignment, it can lead to severe issues such as broken couplings or bearing failures. In systems with misalignment, a flexible coupling is often necessary to resolve these concerns. It's crucial to consider backlash, windup, and bearing load. Certain types of motion control couplings, such as servo insert and beam couplings, have windup and vibration absorption features that are vital in applications that do not require high torsional stiffness. Conversely, bellows and disc types provide high torsional stiffness, with rigid couplings being the ultimate in this regard.
Misusing the wrong coupling can result in bearing load problems, particularly with rigid couplings. If a rigid coupling is used where misalignment exists, problems can escalate rapidly. It's vital to account for bearing load during design phases. Managing misalignment is paramount; many types of couplings, particularly bellows couplings, can fail if not installed correctly, whether compressed or extended, which is a common issue we encounter.
Rigid couplings offer excellent torque transmission capabilities, almost zero windup, and are the most precise couplings available, essentially welding your shafts together. They are suitable for shaft support in push-pull applications and are relatively low cost. However, they lack any misalignment capabilities and cannot accommodate thermal expansion. Even perfectly aligned shafts must consider the thermal expansion of high-speed motors; failing to do so can lead to bearing failure.
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Aligning rigid couplings can be challenging unless there’s a proper design in place to facilitate alignment. One effective method involves using clearance holes on your motor bracket flange during assembly, allowing the coupling to align the motor with the shaft before securing everything. This approach works exceptionally well and is commonly applied in actuator setups.
In our experiences as manufacturers, we often receive calls from customers who have tried multiple coupling types without success. They sometimes believe that switching to a rigid coupling will solve their issues, usually stemming from alignment problems causing failure of flexible couplings. We advise our customers to assess their alignment before opting for rigid couplings, as these can be effective if used correctly.
Oldham couplings provide a good compromise for applications without requiring high torsional stiffness. Their forgiving nature makes them popular in stepper and servo drive systems. On the other hand, beam couplings are ideal for lighter-duty applications, though excessive torque can introduce positioning errors.
Bellows couplings, known for high torsional stiffness, are favored for high-speed applications exceeding 5,000 RPM. The servo jaw coupling allows for shock load absorption, which is critical in systems with aggressive movement profiles. Similarly, disc couplings share comparable qualities with bellows, providing high performance while being slightly less popular.
Choosing the right coupling requires careful consideration of application requirements. Multiple solutions are available, and understanding each type's strengths and weaknesses is essential for optimal performance.
Ruland
www.ruland.com
Rigid couplings are straightforward and cost-effective, comprising two flanges, hubs, or sleeves that fasten around shaft ends. They provide a firm connection without any relative motion, making them ideal for applications with properly aligned shafts and consistent loads. Rigid couplings offer various advantages, including easy installation, compactness, reliability, and durability. However, they cannot handle misalignment, nor can they absorb shock or torque loads, leading to potential damage in shafts and connected equipment.
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