Vescoflex, an advanced, tough elastomer produced by Vesconite Bearings, was trialled as an alternative to traditional rubber-based metallistic bushings in a demanding mine winder clutch application at a South African deep-level gold mine. The application was developed in collaboration with FFE Minerals at the time and involved a double-drum winder system where the drums were joined via a silent block clutch assembly, designed to limit shock loads transmitted through the drivetrain.
The original assembly used rubber metallistic bushings, consisting of two steel sleeves with rubber in between. After years of service, the clutch required refurbishment, but the original high-duty silent block bushing assemblies were no longer available. Vescoflex elastomer was proposed as a potential replacement due to its fatigue resistance and elastic properties.
The refurbishment involved 16 coupling bushing assemblies arranged on a pitch circle diameter of 2,000 mm. The system had a maximum dynamic torque of 1,909 kNm, resulting in an estimated peak load of 106 kN per bushing assembly. Bushing dimensions were 178 mm outer diameter, 140 mm inner diameter, and 150 mm in length, corresponding to a maximum operational stress of approximately 5.9 MPa.
A critical design requirement was controlling deflection within the bushings to maintain clutch alignment. Vescoflex samples were tested at 5 MPa for 2.5 million cycles without apparent material degradation. Unconstrained samples were able to withstand loads above 10 MPa and returned to their original dimensions. The material had a compressive modulus of approximately 50 MPa, allowing it to flex under load while bearing moderate compressive forces.
The silent block bushing assemblies were designed to accommodate axial thrusts and included pre-compression to ensure a tight fit within the housing. The application illustrated how Vescoflex could perform under significant loading and cyclical stress in this type of coupling system.
Double-drum winders remained, and in many cases continue to be, a standard feature in deep-level mining operations, particularly in gold and platinum mines.
The trial of Vescoflex in this project provided insight into its mechanical performance in a heavy-duty mining environment, particularly regarding fatigue resistance, compressive strength, and elastic recovery under cyclic loading.
