014chapter 13 drum hoists.pdf

8/17/2019 014chapter 13 drum hoists.pdf

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Drum Hoists

Hard Rock Miner’s Handbook

Chapter

13


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H A R D R O C K M I N E R ’ S H A N D B O O K

©©©©McIntosh Redpath Engineering McIntosh Redpath Engineering McIntosh Redpath Engineering McIntosh Redpath Engineering 160160160160

13131313 Drum HoistsDrum HoistsDrum HoistsDrum Hoists

13.1 Introduction

Drum hoists are employed in mines on tuggers, slushers, stage winches, cranes, rope tensioners, andeven for long plumb line winches. Chapter 13 is mainly devoted to drum hoists that serve as minehoists (winders). These machines are the most significant hoists in a mine, used for hoisting the oreand waste rock as well as moving personnel, equipment, and materials into and out of the mine.

Single-drum mine hoists are satisfactory for limited application; however, most are manufactureddouble drum to facilitate balanced hoisting of two conveyances in the shaft. Balanced hoisting canbe accomplished with a single-drum hoist for shallow applications that require a single layer of ropeon the drum. In this case, the rope being wound is wrapped in the same grooves that are vacated bythe other rope being unwound. Single-drum hoists have been built with a divider flange and even with the drums of different diameter on either side of the flange (“split-differential”) to accomplish

balanced hoisting – these designs are no longer manufactured. This chapter is largely devoted to thedouble-drum mine hoist because it is by far the most common type employed.

All mine hoists manufactured today are driven electrically by motors that have an independent ventilation source. Having an independent source reduces the horsepower requirements by moreefficient cooling of the windings especially during slow-speed operations and permits filtering of theair that reaches the motor.

Until recently, DC drives with solid-state converters (thyristors) were almost exclusively employed.Lately, larger mine hoists have been manufactured with AC drives that are frequency controlled(cyclo-converter).

Typically, the larger double drum hoists are direct driven with overhung armatures, while double

helical open gears drive those of medium size. Small or very slow mine hoists may employ agearbox for speed reduction.

For mine applications, drum hoists compete with friction hoists (refer to Chapter 14). The decisionconcerning which one is best employed for a particular application is discussed as an example of aside study in Chapter 6 – Feasibility Studies. Some hoisting parameters explained in this chapter(e.g. hoist cycle time) have equal application to friction hoists.

For historical reasons, drum hoists (unlike friction hoists) are still thought of in terms of Imperialrather than metric units. To describe the size of a drum hoist, miners will say “a 10-foot hoist”rather than “a 3m hoist.” For this reason, the explanations and calculations that follow are mainlyperformed in Imperial units.

The Blair multi-rope (BMR) hoist (a variation of the double-drum hoist) employed for extremelydeep shafts is not discussed in this Chapter.


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13.2 Rules of Thumb

Hoist Speed

• The maximum desirable speed for a double-drum hoist with fixed steel guides in the shaft is18m/s (3,600 fpm). Source : Peter Collins

• The maximum desirable speed for a drum hoist with wood guides in the shaft is 12m/s (2,400fpm). Source : Don Purdie

• An analysis of the theory developed by ASEA (now ABB) leads to the conclusion that theoptimum speed is a direct function of the square root of the hoisting distance. Applying theguideline of 50% and assuming reasonable values for acceleration and retardation leads to thefollowing rule of thumb equation for the optimum economic speed for drum hoists, in which His the hoisting distance.

Optimum Speed (fpm) = 44H

½

, where H is in feetOr, Optimum Speed (m/s) = 0.405 H½ , where H is in metres

Source: Larry Cooper

• Assuming reasonable values for acceleration gives the following rule of thumb equations for thedesign 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

Source: Ingersoll-Rand

• The hoist wheel rotation at full speed should not exceed 75 revolutions per minute (RPM) for ageared drive, nor 100-RPM for a direct drive. Source : Ingersoll-Rand

Hoist Availability

• With proper maintenance planning, a drum hoist should be available 19 hours per day for asurface installation, 18 for an internal shaft (winze). Source: Alex Cameron

• A drum hoist is available for production for 120 hours per week. This assumes the hoist ismanned 24 hours per day, 7 days per week, and that muck is available for hoisting. Source : JackMorris

• The total operating time scheduled during planning stages should not exceed 70% of the totaloperating time available, that is 16.8 hours per day of twenty-four hours. Source: Tom Harvey

• In certain exceptionally well-organized shafts, utilization factors as high as 92% have beenreported, but a more reasonable figure of 70% should be adopted. With multi-purpose(skipping and caging) hoists, the availability will be much lower. Source: Fred Edwards


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Rope Pull

• The manufacturer’s certified rope pull rating for a drum hoist assumes the rope flight angle is 25degrees or more from the horizontal. The rope pull rating should be reduced by 10% for aninstallation where the ropes run horizontally between the hoist and the head sheave. Source:

Ingersoll-Rand

Hoist Drums

• The hoist drum should be designed to coil rope for the hoisting distance plus an allowance equalin length to 10 dead wraps on the drum. Source: John Stephenson

• The hoist drum should be designed to coil sufficient rope for the hoisting distance plus anallowance of 500 feet, for most applications. Very deep shafts may need 600 feet of allowance.Source: Jack de la Vergne

• The hoist drum should be designed to coil sufficient rope for the hoisting distance plus thestatutory three dead wraps, the allowance for rope cuts and drum pull-ins for the life of theropes plus at least 200 feet of spare rope. (At least 250 feet of spare rope is desirable for deepshafts.) Source: 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. Source: 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 aninch. Source: Ingersoll Rand

• The pitch distance between rope grooves on the drum face may be calculated at the ropediameter plus 4% for ropes of any diameter. Source: Larry Cooper

• The maximum allowable hoop stress for drum shells is 25,000 psi; the maximum allowablebending stress for drum shells is 15,000 psi. Source: Julius Butty

• The flanges on hoist drums must project either twice the rope diameter or 2 inches (whichever isgreater) beyond the last layer of rope. Source: Construction Safety Association of Ontario

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. Source: 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).Source: Hamilton’s Gear book

• The width of a key should be ¼ the shaft diameter. Source : Jack de la Vergne


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Shafts and Gearing (continued)

• For geared drives, pinion gears should have a minimum number of 12 teeth and preferably notless 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 thetooth). Source: Hamilton’s Gear book

• For geared drive drum hoists, pinion gears should have a minimum number of 14 teeth. Source:Ingersoll Rand

Overwind and Underwind

• The overwind distance required for a drum hoist is one foot for every hundred fpm of hoist linespeed. Source: Tad Barton

• The overwind distance required for a high-speed drum hoist is 7m. Source: Peter Collins

• The underwind distance required is normally equal to ½ the overwind distance. Source: Jack dela Vergne

Hoist Inertia

• The residual inertia of a double-drum hoist (including the head sheaves and motor drive, but notropes and conveyances), reduced to rope centre, is approximately equal to the weight of10,300m (33,800 feet) of the hoist rope. For example, the approximate inertia (WR 2 ) 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.

Source: Tom Harvey

• The inertia of a single-drum hoist may be assumed to be 2/3 that of a double drum hoist of thesame diameter. Source: Ingersoll-Rand

• The inertia (in Lbs-feet2 ) of the rotor of a direct current (DC) geared drive hoist motor isapproximately equal to 1,800 times the horsepower of the motor divided by its speed (RPM) tothe power of 1.5:

WR 2 = 1800 [HP/RPM] 1.5

Source: 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) tothe power of 1.35:

WR 2 = 850 [HP/RPM] 1.35 .

Source: Khoa Mai


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Root Mean Square Power

• Power consumption (energy portion of utility billing) of a drum hoist is approximately 75% ofroot mean square (RMS) power equivalent. Source: Unknown

• In calculating the RMS horsepower requirements of a drum hoist, it is not important todetermine a precise value for the inertia. A 10% error in inertia results in a 2% error in the RMShorsepower. Source: Tom Harvey

Peak Power

• For a DC hoist motor, the peak power should not exceed 2.1 times the RMS power for goodcommutation. Source: 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. Source: LarryGill

Delivery

• The delivery time for a new drum hoist is approximately 1 month per foot of diameter (i.e. for a12-foot double drum hoist, the delivery time is approximately 12 months). Source: Dick Roach

• The delivery time for new wire ropes for mine hoists is approximately 4 months for typicalrequirements. For special ropes manufactured overseas, delivery is near 6 months. Source: KhoaMai

13.3 Tricks of the Trade

• The easy way to design a drum hoist is to first determine the required hoisting speed andpayload, then determine the rope that is needed to meet the safety factor (SF). The hoistparameters can then all be determined only considering the hoist rope and line speed. Source: Tom Harvey

• For purposes of initial design, the hoist line speed should be 40% of the highest speed that istheoretically obtainable over the hoisting distance. This value leaves room to increase the speedat some future date to as high as 60% without seriously compromising power costs. Source: ASEA

• The statutory minimum drum diameter to rope diameter ratios have been deleted from MSHAregulations; however, the ratios remain intact in the ANSI guidelines and these should beincorporated into the specifications for a proposed drum hoist installation at normal hoistingspeeds. Source: Julian Fisher

• Where guidelines indicate an 80:1 drum to rope ratio, it may be reduced to 72:1 at hoistingspeeds up to 2,000 fpm (10m/s) without significant loss of rope life when employing stranded wire ropes on drum hoists. For speeds exceeding 3,000 fpm (15m/s), the minimum drumdiameter to rope diameter ratio is 96:1. At this minimum, the head sheave diameter to rope


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diameter ratio may be increased to 120:1 as an inexpensive means to help maintain good ropelife. Source: Largo Albert

• The overwind distance is normally first calculated for the minimum statutory requirement andthen increased if required to meet good engineering practice. Source : Jack de la Vergne

•For deep shafts, the overwind distance calculated must include an allowance for less turns of thehoist drum that result from hoisting an empty conveyance. Hoist controllers don’t know wherethe conveyance is; they precisely track the revolutions of the hoist drum. Source: Largo Albert

• The inertia of the drive motor rotor must be multiplied by the square of the gear ratio for theeffect at drum radius. Source: John Maude

• An easy way to obtain an accurate value for the RMS horsepower of a counterweight hoistingsystem (round trip) from a computer program designed for balanced skip hoisting (one-way trip)is by making two runs. The first run hoists the full payload and the second hoists thecounterweight while lowering the empty conveyance. The RMS horsepower for the round tripmay then be obtained from averaging the heating values:

RMS HP = [(HP12 + HP22 )/2] ½

Source : Jack de la Vergne

• An easy way to obtain a value for the RMS horsepower of a double-drum sinking hoist from acomputer program designed for balanced skip hoisting is to substitute the sums of the stop andcreep times in the sinking cycle for those of the skipping cycle. Source: Jack de la Vergne

• The RMS horsepower calculation is not always the criteria for selecting the drive for a drumhoist installation. When hoisting single from a deep horizon (or balanced hoisting from greatdepths), if the peak horsepower exceeds the RMS by a wide margin, the peak horsepower maybe the basis for selecting the size of the hoist drive. Source: Jack de la Vergne

• For drum hoists, fleet angles of 1 in 45 (10 16’) or 1 in 50 (10 9’) are desirable. Source: HenryBroughton

• The fleet angle for drum hoists should not exceed 10 30’. Source: Ingersoll Rand

• In mine-shaft hoisting, the fleet angle should be as close as possible to 10 20’. Excessive drum wear and poor spooling will result if this angle is exceeded. Source: Wire Rope Industries

• Ideally, the fleet angle should not exceed 10 15’. Some line scrubbing will occur in the zone

between this angle and 10 30’, but at a wider angle the rope may pull away from the flange orjump at high speed. Source: Lebus International

• In practice, the maximum acceptable fleet angle depends upon the rope line speed. For speedsof 5m/s (1,000 fpm) 10 45’ may be satisfactory as may 10 30’ at 10m/s (2,000 fpm) and 10 15’ at15m/s (3,000 fpm). Source : Jack de la Vergne

• A minimum fleet angle of 30’ for a drum hoist will ensure that the rope will cross back and starta new layer without piling. Source: Fred Edwards


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• Ideally, the minimum fleet angle should not be less than 15’. In the zone between this angle andzero, there may be trouble to kick or turn the rope back for the next layer. Source: LebusInternational

• You have only to consider a tower mounted auxiliary drum hoist over a deep shaft (that operates without an intermediary sheave) to realize that the minimum acceptable fleet angle is zero.

Source: Cass Atkinson• In practice, the minimum fleet angle must never be negative, but it may be near to zero at slow

hoisting speeds. Source : Jack de la Vergne

• Optimization of fleet angle geometry is obtained when the axes of the head sheaves are alignedto aim the sheave flight at the center of the face of the hoist drums rather than have the flightsexactly parallel. Source: Largo Albert

13.4 Hoist Cycle Time “T”

One of the important aspects of hoisting is determining the cycle time. For an existing installation,

it may be measured with a stopwatch or determined with a portable hoist trip recorder. The cycletime must be determined to design and specify a proposed hoist and, for this purpose, a simulatedhoist cycle is calculated. The simulated cycle enables prediction of the hoist production and thecapacity of the drive motor(s).

The hoist cycle time is the time taken for one complete trip. It is usually measured in seconds. Thecycle is different for skipping, caging, or shaft sinking. For balanced hoisting (i.e. two skips), it is aone-way trip. For single hoisting or counterweight hoisting, the cycle is a round trip (up and down).

The cycle consists of the following components.

• Creep speed – typically 2 feet/second, except for cage hoists that creep at 1 foot/second.

• Acceleration – rate typically varies with line speed.• Full speed – maximum rated or controlled line speed of hoist.

• Retardation – rate typically varies with line speed.

• Rest – Stop: 10-15 seconds for skip, 30-45 seconds for cage.

For hoisting skips or sinking buckets in balance, the cycle time, T (in seconds), can be accuratelysimplified to the following formula.

T = H/V + V/a + stops + creep times

In which

− H is the hoisting distance in meters (or feet)

− V is the full line speed in meters/second (or feet per second)

− a is the average of acceleration and retard rates in m/s/s (or feet per second/second)

Stops are rest periods at the pocket, dump, or hanging mark (in seconds), and creep times are thesum of the duration of travel at creep speed (in seconds).


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The acceleration and retard rates may be adjusted for a particular installation. For purposes ofgeneral cycle calculations, it can be assumed that they are equal and proportional to the hoist speed.

a = V/15

In which

− a is feet/second/second (or m/s/s)

− V is feet per second (or m/s)

This permits a further simplification that is satisfactory to determine the hoist cycle for balancedhoisting.

T = H/V + 15 + stops + creep times

Stops

The stops for balanced hoisting with skips include simultaneous loading and dumping. This istraditionally assumed to be 10 or 12 seconds but ought to be increased to 15 seconds or more whenautomatic hoisting is employed. The extra time is required for PLC proving before and after the

skip is loaded. The stop time for cage hoisting is taken at 30 seconds for a small cage and 45seconds for a large one. The sum of the stop times for double-drum shaft sinking may be taken as45 seconds.

Creep Times

The creep times for skip hoisting applications is usually taken as equal to 5 seconds at the beginningand 5 seconds at the end of the wind (“creep out” and “creep in”). For deep shafts, the creep outcan be omitted, but the creep in is typically increased to 15 or even 20 seconds for high-speedhoisting from deep shafts, to provide an extra safety margin. For cage hoisting, the creep out can beomitted, but the creep in may be increased to 10 seconds to allow for spotting the deck. The sum ofthe creep in times for shaft sinking in North America with a double-drum hoist may be taken as 65

seconds, and for creep out it totals about 40 seconds. With these considerations, formulas for the hoisting cycles (in seconds) of different drum hoistingapplications (valid for use with either metric or Imperial units) can be derived as follows.

Typical shaft skip hoisting in balance

T = H/V + 35 (manual)

Typical shaft skip hoisting in balance

T = H/V + 40 (automatic)

Deep shaft skip hoisting in balance

T = H/V + 45 (automatic)

Shaft sinking in balance

T = H/V + 165 (North America)

Shaft sinking in balance

T = H/V + 135 (South Africa*)


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Small cage and counterweight hoisting

T = 2H/V + 100 (round trip)

Large cage and counterweight hoisting

T = 2H/V + 130 (round trip)

Single drum shaft sinking (North America) T = 2H/V + 215 (round trip)

* South African shaft sinkers employ a creep speed higher than 2 feet/second.

Note

At installations where skips are hoisted on rope guides, the cycle time may have to bemodified to account for slow down at the ends of travel required for the transition fromrope guides to fixed guides. An entry speed of 300 fpm (1.5m/s) is considered desirablealthough there are installations that have been carefully engineered to permit a fastertransition speed (as high as 1,100 fpm).

13.5 Maximum Line Speeds for Drum Hoists

The speed selected for a proposed drum hoist installation is first selected on the basis of economics. This speed is determined with sufficient accuracy by applying a rule of thumb formula (Cooper orIngersoll Rand formulas provided above). A practical limit exists to the hoisting speed that may beemployed. This maximum speed may be determined by rule of thumb and by investigating themaximum speeds employed at existing operations elsewhere.

Case Histories

Tables 13-1 and 13-2 show case histories on hoisting speeds on wood and fixed guides.

Table 13-1 Hoisting Speeds on Wood Guides – Exceeding 10m/s (2,000 fpm) Skip Hoisting Hoisting Guide

Mine Shaft Capacity Speed Speed Type

INCO-Copper Cliff North 15.00 tons 15.2 m/s 3,000 fpm Wood

INCO-Levack 2 12.00 tons 14.2 m/s 2,800 fpm Wood

INCO- Garson 2 10.00 tons 11.2 m/s 2,205 fpm Wood

INCO- Frood 3 12.00 tons 12.2 m/s 2,400 fpm Wood

Teck Corona David Bell 7.00 tons 11.4 m/s 2,250 fpm Wood

Macassa No.3 11.2 m/s 2,200 fpm Wood

Pamour 14 5.00 tons 12.2 m/s 2,400 fpm Wood

Rio Algom Stanleigh 15.00 tons 14.6 m/s 2,880 fpm Wood

Lac Dufault Corbet 10.00 tons 13.2 m/s 2,600 fpm Wood


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Table 13-2 Hoisting Speeds on Fixed Guides (Steel), Exceeding 15m/s (3,000 fpm)

Skip Hoisting Hoisting Guide

Mine Shaft Capacity Speed Speed Type

INCO-Creighton No.9 16.00 tons 16.8 m/s 3,300 fpm HSS

INCO-Copper Cliff South 17.00 tons 16.8 m/s 3,300 fpm HSS

Falco - Onaping Craig 18.3 m/s 3,600 fpm HSSBuffelsfontein East Primary 13.10 tons 18.3 m/s 3,600 fpm Top Hat

West Driefontein 4 9.00 tons 16.0 m/s 3,150 fpm Top Hat

West Driefontein 6 10.00 tons 16.0 m/s 3,150 fpm Top Hat

East Driefontein 2 17.20 tons 18.3 m/s 3,600 fpm Top Hat

East Driefontein 1 13.60 tons 18.0 m/s 3,550 fpm Top Hat

Deelkraal 1 21.00 tons 18.3 m/s 3,600 fpm Top Hat

Elandsrand Rock Vent 12.50 tons 16.0 m/s 3,150 fpm Top Hat

Western Holdings Saaiplaas 2 11.80 tons 17.8 m/s 3,500 fpm Channel

Western Holdings Saaiplaas 3 21.00 tons 16.0 m/s 3,150 fpm Top Hat

President Brand 3 9.10 tons 16.0 m/s 3,150 fpm Top Hat

Vaal Reefs 7 9.25 tons 16.0 m/s 3,150 fpm Top Hat

South Deep man/mat 27.00 tons 18.0 m/s 3,550 fpm Top Hat

13.6 Production Availability

Confusion and controversy exists in the mining industry when defining the word “availability” asapplied to mine hoists. For hoist maintenance personnel, it may mean the percent of the time thepiece of equipment is available to work compared with the total time available. On the other hand,those engaged in selecting and evaluating hoists for mine service must consider the availability of thetotal hoist system, taking not only maintenance downtime into account, but also downtime due toshaft repairs, power outages, rope dressing, skip change-out, etc. This chapter is concerned with the

availability of the total system, and for this purpose, it is described as “production availability.” To determine the production availability of a double drum hoist for purpose of estimating hoistingcapacity per day, a detailed calculation should be made for each case, taking into account the totalhoisting system. This will include allowances for empty loading pocket, full bin, hoisting spill, etc.It will usually be equivalent to approximately 16 hours of hoisting per day (67%), for a seven day per week operation. For a five or six day per week operation, it may be 18 hours per day (75%) becausesome maintenance work can be performed on the weekend.

Example

Facts: 1. Estimate is based on a seven-day workweek

2. Automatic hoisting is assumed.

3. No cage service is required

4. 12-day annual shutdown is assumed

Solution:

Hoist plant availability is shown in Table 13-3.


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Table 13-3 Hoist Plant Availability – Double Drum Hoist (Seven Days per Week Operation)

Activity SkippingContinued?

Frequency Duration(hours)

Factor EquivalentHrs/Week

Remarks

Work in Shaft

Shaft Inspection no weekly 8 1.000 8.00

Manway Inspection N/A monthly N/A 0.000 Duringinspection

Hoist from spill pocket yes N/A N/A 1.000 No spill pocket

Hoist spill from spill ramp yes weekly 0.9 1.000 0.90 ½% spill

Skip Hoisting

Shift change yes daily N/A 0.000 Automatic hoist

Lunch time yes daily 1.5 0.000 Automatic hoist

21st shift in the week no weekly 8 1.000 8.00

Change from ore to rock no daily 0.5 7.000 3.50

Change back to orehoisting

no (in above)

Electrical/Mechanical

Daily mechanical hoistinspection

no daily 1 7.000 7.00

Inspection of skips andattachments

no daily (included above)

Inspection of ropes no daily (included above)

Weekly mech. runningtests

no weekly 1 1.000 1.00

Weekly electricalinspection

no weekly 4 1.000 4.00

Grease both ropes no monthly 2 0.231 0.46

Replace scroll wearplates

no annually During AnnualShutdown

EM Test of the ropes no quarterly 2 0.077 0.15

Cage Drop Test no quarterly 2 0.077 0.15Recap hoist ropes no semi-annual 12 0.038 0.46

Major Hoist Electrical no annually During AnnualShutdown

Major Drive Electrical no annually During AnnualShutdown

Major Hoist Mechanical no annually During AnnualShutdown

Change skip @ 500,000tons

no 500,000 tons 12 0.098 1.17

Change-out cage no 5 years During AnnualShutdown

Change Counterweight no 5 years During Annual

Shutdown Annual maintenanceallowance for shaftsignals


Headframe AnnualInspection maintenance



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Table 13-3 (continued)

Electrical/Mechanical (continued)

Inspect & adjust headsheaves for 2 skip ropes


Change one skip rope &

groove head sheaves

no 36 months During Annual

ShutdownChange other skip rope &groove head sheaves

no 36 months During AnnualShutdown

Change cage rope no 4 years During AnnualShutdown

Change counterweightrope

no 4 years During AnnualShutdown

NDT on hoist brakes,pins, shafts, etc.


Delays

Load-out delays, Ore Binfull

no per week 2 1.000 2.00

Repairs to underground

ore handling

no per month 4 0.231 0.92

Loading Pocket delays no per week 6 1.000 6.00

Loading Pocketmaintenance and repair


PLC proving bugs no per week 4 1.000 4.00

Fault Finding no per week 2 1.000 2.00

Repairs to surfaceconveyors, bins, etc.


Delays for slinging no per week 0 1.000 0.00 use cage hoist

No muck - system empty no per month 4 0.231 0.92

Power outages no per month 3 0.231 0.69

Shaft bottom pumpsrepair

no weekly 0 1.000 0.00

Shaft bottom clean-up no quarterly 8 0.077 0.62

Misc. delays(unidentified)

no weekly 4 1.000 4.00

Total Weekly Downtime (hours) 59 hours

Total Hours in a Week (7 days x 24 hours) 168 hours

Remaining Time to Skip (hours/week) 109 hours

PRODUCTION AVAILABILITY 65.0%


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Example

Determine the skip capacity required for a double-drum hoist.

Facts: 1. Production Availability = 65%

2. Production capacity required = 4,500 tpd (ore and rock)

3. Hoisting distance (lift), H = 2,025 feet4. Fully automatic hoisting

5. 24 hours per day operation

Solution: 1. Optimum line speed, V = 44 x √2025 =1,980 fpm = 33FPS

2. Cycle Time, T = H/V + 40 = 2025/33 + 40 ≈ 100 seconds

3. Trips per hour = 3,600/100 = 36

4. Trips per day = 36 x 24 x 65% = 562

5. Skip capacity = 4,500/562 = 8 tons

Note

Refer to Chapter 15 of this handbook to determine the hoist rope required for a skipcapacity of 8 tons and subsequent determination of drum hoist design parameters for thisexample.

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