When an equipment manufacturer needed roller assemblies for a freshwater wire rope catenary system—some submerged, some operating above water—they came to us for help validating the design. The goal was straightforward: select materials that could run maintenance-free in a mixed environment while protecting both the 2¾" galvanized wire rope and the roller assembly itself.
A PV Calculation That Raised Eyebrows—Until We Looked Closer
The customer’s PV calculation looked impossible: over 500,000 psi·ft/min at peak load. But the duty cycle mattered—peaks lasted only 30 milliseconds with significant dwell time, and published PV limits generally assume continuous operation. With intermittent duty and thermal recovery between cycles, correction factors change the result; their dwell-to-run ratio yielded a corrected PV near 65,000 psi·ft/min.
The split environment added complexity: submerged rollers get water cooling, while above-water units rely on the duty cycle and material properties for heat management. We validated whether self-lubricating bearings could handle the intermittent loading and specified materials to manage heat, wear, and rope interface performance.
Why a Single-Material Roller Wasn’t the Best Answer
The customer initially considered a full Ultracomp UC300AX roller, reasoning that a polymer surface would be gentler on the wire rope. Sound logic, but with a wrap angle under 5° and a 6x41 galvanized rope construction, the contact area is concentrated enough that groove wear would outpace expectations.
We recommended a different approach: optimize each component for its specific job rather than search for one material to do everything.
A Multi-Material Assembly Built Around the Duty Cycle
The final assembly combined three TriStar materials. Nylon rollers provide proven wear resistance against galvanized wire rope with a machined groove profile sized for the 2¾" diameter. CJ composite bearings handle the high radial loads and intermittent duty cycle—exactly the application where wound composites excel. Ultracomp thrust washers manage axial loads and spacing within the 7" weldment width. The assembly runs on a 1.5" diameter 17-4 PH stainless pin (Rc 35 min, 16 RMS finish) for corrosion resistance in the freshwater environment.
The result: 16 rollers across 8 assemblies, maintenance-free, no external lubrication, and material choices matched to function rather than compromise.
Sheave and Roller Applications—We Can Help
Wire rope interface design, high-PV intermittent loads, and dual-environment operation are exactly the kinds of problems our engineering team works through daily. If you're facing a similar challenge—or just want a second opinion on material selection—contact our experts to start the conversation.
