Coupling variations complement specific machine dynamics and meet specific application criteria. Rigid coupling designs handle drive components already in alignment and flexible couplings compensate for post-installation misalignments. Misalignment potential, temperature, mechanical resonance and other factors make some couplings better suited for given applications. Here are some different coupling types and their most common applications.
Rigid couplings are torsionally stiff and used when shafts are already in alignment. However, parallel shaft misalignment exceeding one thousandth of an inch will cause failure. These couplings cannot run at high speeds are also susceptible to vibration.
Compression or clamp couplings offer high torsional strength. The two-piece design lets engineers quickly remove the couplings for maintenance purposes. Designers select rigid couplings for servo systems requiring moderate speed, high torque capacity, and reduced cost.
Some engineers see flexible couplings as one of the most manageable mechanical motion system elements. This trait is why torsional stiffness is paramount for maintaining positional control. Designs often require a driving element to stop and start several times per second. This dynamic requirement mandates torsional stiffness to decrease settling time between cycles. Regardless, flexible couplings often prevail because of their torque capacity. Flexible couplings damp vibrations in both continuous-motion and intermittent applications.
Prevalent in motion applications that need precision control and misalignment compensation, flexible bellows couplings have three pieces: two hubs and a metal bellows. As the first hub attaches to the driving element; the second hub attaches to the driven element. The two hubs connect with the bellows. This configuration accounts for the three types of potential misalignment. As such, bellows couplings work well in many applications. Engineers select bellows couplings CNC machine, robotics and encoders applications.
Jaw couplings have twin hubs sandwiching an elastomer spider insert. They’re less stiff than other couplings, so flexible-jaw couplings work best in constant motion applications—in oil and gas, construction and aerospace, for example.
Engineers frequently choose Oldham couplings as opposed to straight jaw couplings for industrial equipment like valves, pumps, conveyors, and gearboxes. They offer versatility and prolonged reliability, even in designs that exhibit significant misalignment. Their three-piece design—two hubs and a torque-transmitting center—makes them easy to install and disassemble.
Manufacturers use a variety of materials for Oldham couplings. This diversity helps satisfy a multitude of demands—vibration reduction or zero backlash, to name a few. They also handle parallel misalignment and axial motion restriction.
Disc couplings are a common choice for demanding applications and servomotors because of their high torque transmission capabilities, high or changing speed adjustments capabilities, and misalignments compensation.
Regardless of subtype or material, beam couplings are easy to maintain because of their one piece design. These couplings are also zero backlash with spiral cuts transmitting torque over spaces with parallel, angular, or axial misalignment. Beam couplings appear in motion control applications for attaching servomotors to leadscrews, robotics, and for attaching shafts to encoders.
Offset couplings need less space for offset shaft connection in larger systems. With these couplings, motion system designers can make machines smaller and more efficient.
Offset couplings can mount to shaft hubs or directly to machine flanges. The offset couplings are for shaft displacements from 0.156 to 17.29-in. and torque capacities from 50 to 460,000 in.-lb.
One option is to combine zero-maintenance bearings with couplings to bolster uptimes and decrease lubrication needs. Sealed bearings like this do not have lube fittings—streamlining coupling setup. Offset couplings work in presses, embossing systems, paper production equipment and pharmaceutical machinery.
Diaphragm coupling helps polymer resin pumps
When a global petrochemical company had a coupling failure on a polymer pump in one of its larger resin processing facilities, the problem caused expensive, time-consuming production line shutdowns.
Ameridrives was called in to solve the problem and guarantee it would be the last time. Initially, gear couplings were on all polymer pumps between the gearboxes and pumps for this low-speed, (50 RPM) high-torque, application. Maintenance crews did their best but keeping pricey gear couplings lubricated globally proved to be a tough challenge.
After review, the engineering team suggested swapping the gear couplings for diaphragm couplings for a continuous running solution requiring no maintenance or lubrication (unlike the gear couplings’ six-month maintenance intervals).
The Ameridrives team collaborated with industry professionals to create custom diaphragm couplings that met resin pump requirements. The custom components were delivered in several sizes and arrangements with torque ranges reaching 1,100,000 Nm (10,000,000 in. lbs.). One example was a 10-ft long, 23-in. diameter coupling featuring split retaining rings on the gearbox end hubs, the pump, multiple convoluted diaphragm pack flex elements at each end, and more. An integral indexing/timing device also aligned the coupling with the mixing blades of the polymer pump.