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Mining Rule of Thumb

Mining Rules of Thumb have been gathered over 30 years of hard rock mining service provided by Stantec / Mining and predecessor firms.

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About the rules

The primary usage of Rules of Thumb should be in the development of conceptual designs and feasibility studies or, when a quick decision is required in the solution of an operating problem. Although an approximated answer, derived from a Rule of Thumb may solve an immediate problem, Rules of Thumb are not a substitute for the application of sound engineering and design methodologies. Although we firmly believe that the presented Rules of Thumb provide great continuing value to our industry, McIntosh Engineering does not guarantee their validity, nor do we (or the referenced individual sources) accept responsibility for application of the Rules of Thumb by others. Where possible, direct quotes have been provided from individual references; however, it is possible that referenced sources may not have directly stated the Rule of Thumb for which they are assigned credit. Although we have endeavored to accurately quote all individual references contained in the Rules of Thumb compilation, we apologize in advance for any misquotes that may be attributed to individual sources. We will provide updates to the Rules of Thumb compilation, as we become aware of corrections that may be necessary.

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Field: Koepe/Friction Hoists

Area: Hoist Speed

  • Where the hoist line speed exceeds 15m/s (3,000 fpm), the static load range of the head ropes should not be more than 11.5% of their combined rope breaking strength. The (ratio of) hoist wheel diameter to rope (stranded or lock coil) diameter should not be less than 100:1, and the deflection sheave diameter to rope diameter should not be less than 120:1. E J Wainright
  • The maximum desirable speed for a friction hoist is 18m/s (3,600 fpm). Jack Morris
  • The maximum attainable speed for a friction hoist that can be safely obtained with today's (1999) technology is 19m/s (3,800 fpm). Gus Suchard
  • In North America, the desirable speed for cage service is approximately 2/3 of the optimum speed calculated for a skip hoist for the same hoisting distance. Jack de la Vergne

Area: Hoist Wheel Rotation

  • The total number of friction hoist wheel revolutions for one trip should be less than 100 for skip hoists, but may be as high as 140 for cage hoists. Wire Rope Industries and others
  • The hoist wheel rotation at full speed should not exceed 75 RPM for a geared drive, or 100-RPM for a direct drive. Ingersoll-Rand

Area: Hoist Wheel Specifications

  • The hoist wheel diameter to rope (lock coil) diameter should not be less than 100:1 for ropes up to 1-inch diameter, 110:1 for ropes to 1½ inches diameter, and 120:1 for ropes to 2 inches diameter. Glen McGregor
  • A ratio of 100:1 (wheel diameter to lock coil rope diameter) is adequate for ropes of 25-35 mm diameter. This should increase to 125:1 for ropes of 50-60 mm diameter. Jack Morris
  • Rope tread liners on the hoist wheel should be grooved to a depth equal to one-third (1/3) of the rope diameter when originally installed or replaced. The replacement (discard) criterion is wear to the point that there is only 10 mm (3/8 inch) of tread material remaining, measured at the root of the rope groove. ASEA (now ABB)
  • On most fiction hoist installations, the maximum tolerable groove discrepancy is 0.004 inches, as measured from collar to collar. Largo Albert

Area: Hoisting Distance

  • A friction hoist with two skips in balance is normally suitable for hoisting from only one loading pocket horizon and for a hoisting distance exceeding 600m (2,000 feet). Otherwise, a counter-balanced friction hoist (conveyance and counterweight) is usually employed (for multi-level, shallow lifts, or cage hoisting). Ingersoll-Rand
  • The practical operating depth limit for a friction hoist is 1,700m (5,600 feet) for balanced hoisting and 2,000m (6,600 feet) for counterweight hoisting. Beyond these depths, rope life may be an expensive problem. Jack de la Vergne
  • The hoisting ropes (head ropes) for a friction hoist are not required to be non-rotating for depths of hoisting less than 800m (2,600 feet) provided right hand and left hand lays are employed to cancel rope torque effect. Tail ropes must always be non-rotating construction and connected with swivels at each end. Various

Area: Position

  • The distance between the hoist wheel and the highest position of the conveyance in the headframe should not be less than 1.5% of the distance from the hoist wheel to the conveyance at the lowest point of travel. Largo Albert
  • At full speed, a time increment of at least ½ a second should exist as any one section of rope leaves the hoist wheel before experiencing the reverse bend at the deflector sheave. George Delorme
  • The clearance between the bottom of the conveyance, at the lowest normal stopping destination in the shaft, and the top of the shaft bottom arrester (first obstruction) is usually 5 feet. This arrangement ensures that the weight of the descending conveyance is removed from the hoist ropes. Largo Albert
  • The tail rope loop dividers are generally placed below the arrester. The bottoms of the tail rope loops are then positioned 10 to 15 feet below the dividers. Beneath this, a clearance of about 10 feet will allow for rope stretch, etc. Largo Albert

Area: Production Availability

  • A friction hoist is available for production for 108 hours per week. This assumes the hoist is manned 24 hours per day, seven days per week, and that muck is available for hoisting. Jack Morris
  • With proper maintenance planning, a friction hoist should be available 126 hours per week (18 hours per day). Largo Albert

Area: Spacing

  • The minimum distance (design clearance) between a rope and bunton or divider is 5 to 6 inches. This is mainly because the hoist rope vibration is normally 2 to 3 inches off centre; 4 inches is considered excessive. Humphrey Dean
  • The spacing between head ropes should be 1 inch for each foot diameter of the hoist wheel to get an adequate boss for the deflection sheave. Gerald Tiley

Area: Static Tension Ratio

  • For a tower mounted skip hoist, the calculated static tension ratio (T1/T2) should not exceed 1:1.42, but 1:1.40 is preferable. For a ground mounted skip hoist, the calculated static tension ratio should not exceed 1:1.44 but 1:1.42 is preferable. For a cage hoist installation, these values may be exceeded for occasional heavy payloads of material or equipment transported at reduced speed. Various

Area: Tail Ropes

  • The natural loop diameter of the tail ropes should be equal to or slightly smaller than the compartment centres. George Delorme

Area: Tread Pressure

  • Tread pressure should not exceed 17.5 kg/cm2 (250 psi) for stranded ropes and 28 kg/cm2 (400 psi) for locked coil ropes. A.G. Gent
  • For lock coil hoist ropes, the tread pressure calculated for skip hoists should not exceed 2,400 kPa (350 psi), or 2,750 kPa (400 psi) for a cage hoist when considering occasional heavy payloads of material or equipment. Jack de la Vergne
  • For stranded hoist ropes, the tread pressure calculated for skip hoists should not exceed 1,700 kPa (250 psi) or 2,000kPa (275 psi) for a cage hoist when considering occasional heavy payloads of material or equipment. Largo Albert