A Snake Spring Coupling, also known as a helical or wound spring coupling, is a distinct category of flexible shaft coupling renowned for its high torque capacity, resilience, and ability to absorb substantial shock loads. Its name derives from its unique flexible element: a series of flat spring steel strips, typically arranged in a multi-start helical pattern, that resemble a snake or coil when assembled. This spring pack is housed within precisely machined grooves in two aluminum or steel alloy hubs. The fundamental operating principle is the transmission of torque through the elastic deflection (primarily in bending and torsion) of these prestressed spring strips. As torque is applied, the springs wind up slightly, storing energy, and unwind to deliver smooth, cushioned power transmission. This design inherently accommodates shaft misalignment—angular, parallel, and axial—through the flexing of the spring pack, while simultaneously damping torsional vibrations and shock.
The coupling consists of three primary components. First, the two coupling hubs are mounted on the driver and driven shafts. These hubs feature external teeth or lobes, often with a curved profile, that engage the spring pack. The hubs are typically lightweight aluminum for general industrial use or steel for high-torque, high-integrity applications. Second, and most critical, is the flexible element: the "snake spring" pack. This is not a single spring but a set of parallel, flat spring steel strips. They are heat-treated to achieve an optimal balance of strength and flexibility, and are often coated for corrosion resistance. The springs are assembled in a continuous, multi-start helical arrangement within the coupling, with each end of each spring strip anchored in the hubs. This creates a grid-like flexible structure. Third, a cover or shroud, often made of neoprene or polyurethane, encloses the entire assembly. This cover serves vital functions: it retains lubricating grease (usually a high-quality, high-tack lithium-based grease), excludes dirt, dust, and moisture, and provides a safety guard to contain the springs in the unlikely event of a failure.
The coupling operates through a combination of mechanical actions. For torque transmission, rotational force from the driver hub is transferred to the curved lobes, which apply a load to the prestressed spring strips. The springs deflect, storing energy, and this deflection propagates through the helical arrangement to drive the output hub. This wind-up provides inherent torsional flexibility, which is the coupling's primary method for damping shocks and smoothing out pulsations from engines or compressors. For misalignment compensation, angular and parallel offsets cause the spring strips to bend and flex in their planes. The prestress in the springs ensures they maintain positive contact with the hub teeth even under no-load conditions, eliminating backlash. Axial movement is accommodated by the springs sliding slightly within the hub grooves or through their axial compressibility.
