Mining Rule of Thumb

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.

Field: Drum Hoists

Area: Delivery

• The delivery time for a new drum hoist is approximately 1 month per foot of diameter (i.e. for a 12-foot double drum hoist, the delivery time is approximately 12 months). Dick Roach
• The delivery time for new wire ropes for mine hoists is approximately 4 months for typical requirements. For special ropes manufactured overseas, delivery is near 6 months. Khoa Mai

Area: Hoist Availability

• With proper maintenance planning, a drum hoist should be available 19 hours per day for a surface installation, 18 for an internal shaft (winze). Alex Cameron
• A drum hoist is available for production for 120 hours per week. This assumes the hoist is manned 24 hours per day, 7 days per week, and that muck is available for hoisting. Jack Morris
• The total operating time scheduled during planning stages should not exceed 70% of the total operating time available, that is 16.8 hours per day of twenty-four hours. Tom Harvey
• In certain exceptionally well-organized shafts, utilization factors as high as 92% have been reported, but a more reasonable figure of 70% should be adopted. With multi-purpose (skipping and caging) hoists, the availability will be much lower. Fred Edwards

Area: Hoist Drums

• The hoist drum should be designed to coil rope for the hoisting distance plus an allowance equal in length to 10 dead wraps on the drum. John Stephenson
• The hoist drum should be designed to coil sufficient rope for the hoisting distance plus an allowance of 500 feet, for most applications. Very deep shafts may need 600 feet of allowance. Jack de la Vergne
• The hoist drum should be designed to coil sufficient rope for the hoisting distance plus the statutory three dead wraps, the allowance for rope cuts and drum pull-ins for the life of the ropes plus at least 200 feet of spare rope. (At least 250 feet of spare rope is desirable for deep shafts.) Largo Albert
• The pitch distance between rope grooves on the drum face is the rope diameter plus one-sixteenth of an inch for ropes up to 2½ inches diameter. Henry Broughton
• The pitch distance between rope grooves on the drum face is the rope diameter plus one-sixteenth of an inch for ropes up to 1¾ inches diameter, then it increases to one-eighth of an inch. Ingersoll Rand
• The pitch distance between rope grooves on the drum face may be calculated at the rope diameter plus 4% for ropes of any diameter. Larry Cooper
• The maximum allowable hoop stress for drum shells is 25,000 psi; the maximum allowable bending stress for drum shells is 15,000 psi. Julius Butty
• The flanges on hoist drums must project either twice the rope diameter or 2 inches (whichever is greater) beyond the last layer of rope. Construction Safety Association of Ontario

Area: Hoist Inertia

• The residual inertia of a double-drum hoist (including the head sheaves and motor drive, but not ropes and conveyances), reduced to rope centre, is approximately equal to the weight of 10,300m (33,800 feet) of the hoist rope. For example, the approximate inertia (WR²) of a 10-foot double drum hoist designed for 1½ inch diameter stranded ropes weighing 4 Lbs. per foot, will be:
  5 x 5 x 4 x 33,800 = 3,380,000 Lbs-feet².
  Tom Harvey
• The inertia of a single-drum hoist may be assumed to be 2/3 that of a double drum hoist of the same diameter. Ingersoll-Rand
• The inertia (in Lbs-feet²) of the rotor of a direct current (DC) geared drive hoist motor is approximately equal to 1,800 times the horsepower of the motor divided by its speed (RPM) to the power of 1.5:
  WR² = 1,800 [HP/RPM] ^1.5
  Khoa Mai
• The inertia (in Lbs-feet²) of the rotor of a direct current (DC) direct drive hoist motor is approximately equal to 850 times the horsepower of the motor divided by its speed (RPM) to the power of 1.35.
  WR² = 850 [HP/RPM] ^1.35
  Khoa Mai

Area: Hoist Speed

• The maximum desirable speed for a double-drum hoist with fixed steel guides in the shaft is 18m/s (3,600 fpm). Peter Collins
• The maximum desirable speed for a drum hoist with wood guides in the shaft is 12m/s (2,400 fpm). Don Purdie
• An analysis of the theory developed by ASEA (now ABB) leads to the conclusion that the optimum speed is a direct function of the square root of the hoisting distance. Applying the guideline of 50% and assuming reasonable values for acceleration and retardation leads to the following rule of thumb equation for the optimum economic speed for drum hoists, in which H is the hoisting distance.
  Optimum Speed (fpm) = 44H½ , where H is in feet
  Or, Optimum Speed (m/s) = 0.405 H½ , where H is in metres
  Larry Cooper
• Assuming reasonable values for acceleration gives the following rule of thumb equations for the design speed of drum hoists, in which H is the hoisting distance (feet).
  Design Speed (fpm) = 34 H½ , hoisting distance less than 1,500 feet
  Design Speed (fpm) = 47 H½ , hoisting distance more than 1,500 feet
  Ingersoll-Rand
• The hoist wheel rotation at full speed should not exceed 75 revolutions per minute (RPM) for a geared drive, nor 100-RPM for a direct drive. Ingersoll-Rand

Area: Overwind and Underwind

• The overwind distance required for a drum hoist is one foot for every hundred fpm of hoist line speed. Tad Barton
• The overwind distance required for a high-speed drum hoist is 7m. Peter Collins
• The underwind distance required is normally equal to ½ the overwind distance. Jack de la Vergne

Area: Peak Power

• For a DC hoist motor, the peak power should not exceed 2.1 times the RMS power for good commutation. Tom Harvey
• A typical AC induction hoist motor is supplied with a 250% breakdown torque. In application, this means that the peak horsepower should not exceed 1.8 times the RMS power. Larry Gill

Area: Root Mean Square Power

• Power consumption (energy portion of utility billing) of a drum hoist is approximately 75% of root mean square (RMS) power equivalent. Unknown
• In calculating the RMS horsepower requirements of a drum hoist, it is not important to determine a precise value for the inertia. A 10% error in inertia results in a 2% error in the RMS horsepower. Tom Harvey

Area: Rope Pull

• The manufacturer's certified rope pull rating for a drum hoist assumes the rope flight angle is 25 degrees or more from the horizontal. The rope pull rating should be reduced by 10% for an installation where the ropes run horizontally between the hoist and the head sheave. Ingersoll-Rand

Area: Shafts and Gearing

• At installation, the allowable out of level tolerance for the main shaft of a drum hoist is one-thousandths of an inch per foot of length. Gary Wilmott
• Square keys are recommended for shafts up to 165 mm (6½ inches) diameter. Rectangular keys are recommended for larger shafts. Standard taper on taper keys is 1:100 (1/8 inch per foot). Hamilton's Gear book
• The width of a key should be ¼ the shaft diameter. Jack de la Vergne
• For geared drives, pinion gears should have a minimum number of 12 teeth and preferably not less than 17. If the pinion has less than 17 teeth, undercutting may occur and the teeth should be cut long addendum ("addendum" is the distance between the pitch line and the crown of the tooth). Hamilton's Gear book
• For geared drive drum hoists, pinion gears should have a minimum number of 14 teeth. Ingersoll Rand