Wire Ropes, Sheaves, and Conveyances

Chapter 15 - Wire Ropes, Sheaves, and Conveyances
Number	Topic	Rule of Thumb
15.01	Ropes	The actual rope stretch when a skip is loaded at the pocket is almost exactly double that calculated by statics (PL/AE) due to dynamic effect. Source: L. O. Cooper
15.02	Ropes	The rope installed on a drum hoist or winch should be pre-tensioned to 50% of the working load. Source: George Delorme
15.03	Ropes	The tension required for a guide rope is one metric tonne (9.81 kN) for each 100m of suspended rope. Source: Tréfilunion
15.04	Ropes	The tension for a guide rope should be should be a minimum of 10 kN for each 100m of suspended rope. It is recommended to increase the tension further – up to the limit as set for the required SF of the rope. Source: Sigurd Grimestad
15.05	Ropes	The size of guide rope (steel area of cross section in mm², S) required is equal to 1½ times the length of suspended rope in metres, H. (i.e. S = 1.5 H). Source: Tréfilunion
15.06	Ropes	The pitch radius of a wire rope thimble should not be less than 3.5 times the rope diameter. Source: Largo Albert
15.07	Ropes	The length of a wire rope thimble should not be less than five times the pitch radius. Source: Largo Albert
15.08	Sheaves	A change in direction of a rope (around a sheave) of 15° or more is generally accepted as constituting a complete bend. At lesser deflections, a grooved sheave should never be less diameter than one lay length (about seven times rope diameter), nor 1½ times lay length for a flat roller. Source: African Wire Ropes Limited
15.09	Sheaves	For every increase in speed of 1m/s (200 fpm), 5% should be added to the sheave or roller diameter. Source: African Wire Ropes Limited
15.10	Conveyances	Conventional practice at hard rock mines is to employ “Kimberly” skips for a payload capacity of up to 5 tonnes and “bottom dump” skips for a payload between 5 tonnes and 20 tonnes. “Arc-door” skips are usually employed for payloads over 20 tonnes. Source: Jack de la Vergne
15.11	Conveyances	Aluminum alloy is as strong as mild steel and is three times lighter but six times more expensive. Source: George Wojtaszek
15.12	Conveyances	The centre of gravity of a loaded bottom dump skip should coincide with the geo-centre of the skip bridle. Source: Coal Gold and Base Metals of South Africa
15.13	Conveyances	The old rule stating that the bridle of a bottom dump skip should have a length equal to twice the set spacing has been demonstrated to be incorrect. Source: Coal Gold and Base Metals of South Africa
15.14	Conveyances	For a fixed guidance system, the bail (bridle) of a bottom dump skip or the length of an integral skip (between guide shoes) should be of minimum length equal to 1½ times the set spacing. For shaft sinking on fixed guides, the crosshead must be of minimum length equal to 1½ times the face-to-face distance between the guides, otherwise it will chatter. On rope guides, the length of the conveyance is of no concern. Source: Jim Redpath
15.15	Conveyances	A properly designed liner system should allow a skip to hoist 30,000 trips before the conveyance is removed from service for maintenance. Source: Largo Albert
15.16	Conveyances	A properly designed liner system should allow a skip to hoist 500,000 short tons before the conveyance is removed from service for maintenance. Source: Largo Albert
15.17	Conveyances	The regular maintenance refit and repair of an aluminum skip costs approximately 35% of the price of a new skip. Source: Richard McIvor
15.18	Conveyances	A properly designed and maintained aluminum skip should have a total life of 5,000,000 tons (including refits and repairs). Source: Richard McIvor
15.19	Conveyances	The cage capacity will be between 1.6 to 1.8 times the empty cage weight. Source: Wabi Iron Works