The application was designed together with FFE Minerals.
A South African deep level gold mine has a double drum winder.
The two drums are joined through a "silent block clutch assembly" to ensure that the shock loads transmitted are
The completed assembly.
The original assembly had rubber metallistic bushes (two steel sleeves with rubber in the cavity in between the
sleeves). After years of operation the clutch needed to be refurbished but the original special high duty
silent block bush assemblies were not available.
Vescoflex elastomer with its excellent fatigue strength properties was proposed as an alternative for the coupling
There are 16 coupling bush assemblies at a PCD of 2000 mm.
The maximum dynamic torque to be transmitted through the bushes is 1909 kNm.
This translates to a maximum load per bush assembly of 106 kN.
The bush size is 178 x 140 – 150 mm length in total.
This translates to a maximum loading of 5.9 Mpa.
Silent block assemblies, showing the steel sleeves and the Vescoflex before installation.
In addition to the loading on the bush the deflection within the bush also needed to be limited in order to
maintain alignment within the clutch.
Vescoflex is an elastomer material with excellent fatigue strength. It was tested at 5 Mpa for 2.5 million
cycles without material degradation.
An unconstrained test sample of Vescoflex can be loaded to above 10 Mpa and still return to its original size.
Vescoflex has a compressive modulus of approximately 50 Mpa.
The ability of Vescoflex to flex under load and the ability to withstand a moderate compressive load make it
ideal for the application.
The silent block bush assembly was designed to accommodate axial thrusts and to allow for a pre-compression of
the Vescoflex to ensure a tight fit within the housing.