Distance travelled by skip in accelerating period


Question 1

a) For the following winding conditions determine if a rope with a minimum breaking force of 10 MN gives a satisfactory factor of safety for the winding of ore?

Depth of wind = 775m

Mass of skip and attachments = 10 tonne

Mass of ore wound per wind = 20 tonne

Height of sheaves above skip top when skip unloading at shaft top = 20m

Mass of rope/100m = 750 kg/100m

Note for ore hoisting using a drum winder minimum factor of safety = 7.0

b) If the maximum winding speed for the wind described in part (b) is 18 m/s and acceleration = deceleration = 0.6 m/s2 (assume linear change of speed during acceleration and deceleration) determine:

• Accelerating period

• Decelerating period

• Distance travelled by skip in accelerating period

• Distance travelled by skip during decelerating period

• Time travelling at maximum speed

• Distance travelled at maximum speed.

• Total cycle time assuming a 10 s rest period between winds

• Number of cycles per hour

• Capacity of the system per hour

Plot a speed-time graph for this situation.

c) The system described in parts (a) and (b) are for an unbalanced hoisting system employing a drum winding system. Determine variation of the tractive force at the circumference of the drum and the total torque required at the drum to drive the system. Rope diameter is 50mm, minimum drum diameter = 100 x rope diameter, diameter of sheaves = 5 m. Skip hoisting system, so k = 1.15. Friction resistance between skip and guides, air resistance, bending resistance etc. = k x mass of loaded skip.

d) Determine the variation of the power at the drive shaft for this system assuming a constant radius of coiling of the rope on the drum (hint do this for each element within the cycle and plot on a torque/power time graph)

e) Determine the rms torque and power for this system.

Question 2

Estimate the cycle time and production of a 72 tonne GVW off highway truck with 41 tonnes on its rear wheels when loaded to its rated capacity, operating on a level haul road of 1500m length. The road is a rutted dirt roadway with no maintenance and no stabilisation, tyre penetration is 4cm. The following can be assumed;

a) Loading time 1.4 min

b) Manoeuvre and dump time 0.8 min

c) Truck hauls 40 tonnes of ore each trip

d) Job efficiency of 0.8

question 3

Two 5 tonne shuttle cars operate at an average speed of 1.1 m/s during the development phase of a panel. The loading machine has a rate of 2.5 tonnes/min. loader/ change out distance is 30m. If each shuttle car incurs a wait at the change out point of 0.5 min and the shuttle car discharge time is 1.2 min what is the haul distance from the change out point to the dumping point?

Question 4

A Caterpillar D30D articulated dump truck has the rim pull curve in figure 1. (Gross weight 21.9 t empty, 49.117 t loaded). If the truck ascends an 8% grade with a rolling resistance of 40 kg/t, find the following:

a) Total resistance (kg)

b) The required rim pull (kg) when loaded

c) The maximum speed of the truck when loaded (km/h)

A Caterpillar 631 E tractor scraper has the following characteristics:

Maximum heaped volume = 19.6 Bm3

Maximum payload = 34,000 kg

The material hauled is earth with a density of 1825 kg/Bm3

Rolling resistance is 60 kg/t and operating conditions are average with a job efficiency of 50 min/hour.

The haul route comprises of the following sections:

Section 1 (100m) level-loading zone

Section 2 (900m) 5% down grade

Section 3 (100m) level dumping zone

Section 4 (900m) 5% up grade

Section 5 (80m) level turnaround area.

Estimate the machines production under these conditions.


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