DISK COUPLINGS

Disk couplings contain two hubs and a thin-metallic or composite disk that transmits torque. A tight-fitting pin fastens the hubs to the disk and prevents relative play or backlash.

Single-disk couplings handle only small levels of parallel misalignment because of the complex bending that takes place on the disk. Two-disk couplings overcome this limitation. They use two disks separated by a rigid center member that attaches to a hub at each end. The two-disk style lets each disk bend in opposite directions under parallel offsets up to 5° with minimal bearing loads. The rigid center member is typically metallic, but plastic versions are available to provide electrical isolation.

A downside to disk couplings is they are extremely delicate and prone to damage when misused or installed improperly. Be sure to keep misalignment within rated levels for proper operation.

BELLOWS COUPLINGS

Bellows couplings are an assembly of two hubs and a thin-walled stainlesssteelor nickel bellows. Nickel bellows are electrodeposited onto a bellowsshaped mandrel. The mandrel is then chemically dissolved, leaving behind the finished bellows. The technique precisely controls bellows wall thickness and permits thinner walls than possible with other methods. Thin walls lower torque capacity but boost sensitivity and responsiveness, important metrics for small, precision instrumentation applications. Stainless-steel bellows are typically made by a process called hydroforming and are stronger than nickel types. Here, a thin-walled tube goes into a machine and hydraulic pressure forms the bellows convolutions around specialized tooling.

Bellows couplings impart low bearing loads that remain constant at all points of rotation — without the damaging cyclical high and low loading of some other coupler types — yet remain rigid under torsional loads. A high stiffness makes bellows couplings ideal for applications needing a high degree of accuracy and repeatability.

Bellows couplings accommodate up to 2° of angular misalignment and 0.010 to 0.020-in. parallel misalignment and axial motion. The use of stainless-steel hubs improves corrosion resistance, though the trade-off is higher mass and inertia. Couplings with aluminum hubs lower rotational inertia, important in modern, highly responsive systems. Bellows couplings can be balanced at the factory for operation to 10,000 rpm or higher.

RIGID COUPLINGS

Small, rigid couplings (especially in aluminum) excel in servo applications. They have zero backlash, high torque capacity, and virtually zero windup. However, any misalignment forces fully transmit to shafts, bearings, and the coupling itself, which can lead to premature failure of connected components. Also, avoid using rigid couplings for high-speed applications where heat buildup is an issue, because they are not good at compensating for thermal growth in shafting.