The Case for a Rubber-Element Coupling
Not every coupling problem needs more steel. When a drive transmits shock loads — a crusher hitting rock, a compressor hammering on pressure spikes, a conveyor starting under full load — a rigid or chain coupling passes those impulses straight into the gearbox and driven machine. A rubber-element coupling like the Martin-Flex series deliberately flexes, absorbing torsional shock and damping vibration before it reaches the equipment. For many plants, that one change extends the life of gearboxes, bearings, and driven shafts.
What Martin-Flex Brings to the Drive
The Martin-Flex coupling is a flanged coupling with a rubber element between the two flanges. The element is the replaceable wear part — no lubrication, no metal-to-metal contact, and no need to move the machine when the element wears out. The catalog lists the key service data for each size: maximum RPM, horsepower at 100 RPM at a 1.0 service factor, torque rating, and average static torsional stiffness. Sizes run from the compact size 5 (1 in. max bore, 4,500 RPM, about 1 HP at 100 RPM) up through size 12 and beyond, where bores reach 2-7/8 in. and torque ratings climb into the thousands of lb-in.
Each size uses a specific QD bushing (JA, SH, SDS, SK, SF, or E pattern), which means the same bushing family already in stock for sheaves and sprockets fits the coupling. The rubber elements themselves are color- or number-coded by size (E5 through E12 and up), so reordering the wear part is a one-line part number.
Sizing and Selection
Selection follows the same service-factor logic as other couplings: multiply the motor HP by the service factor for the driven unit, then pick the size whose horsepower rating at your operating speed meets or exceeds the adjusted figure. Because Martin-Flex carries a 1.0 service factor rating on its published tables, applying the correct factor from the drive classification automatically builds in the shock-load margin.
Installation Notes
The catalog calls out a few practical details. Shaft ends are normally M or N apart and may project beyond the bushings — allow space for end float and misalignment. Flange assemblies use Grade 8 capscrews torqued to the values in the table (from 125 in-lb on the size 5 up to 900 in-lb on the size 12). When it is time to remove the coupling, the pull-up capscrews double as jackscrews. The rubber element can be inspected with a simple visual check — cracks, chunks missing, or permanent set mean replacement.
RBC Industrial stocks Martin-Flex couplings, elements, and QD bushings. Call (915) 845-8188 or visit www.rbc-industrial.com for sizing help and same-day quotes.