Audit of chairlift system

4. Horizontal transportation

4.8 Chairlifts

4.8.1 Audit of chairlift system

4.7.2.5 Cost implications

An approximate installation cost for a single personnel riding belt of ± 1 800 m in length would be in the order of R9 000 000. This cost includes the cost of all steelwork, head drives, tail and take-up pulleys and all safety devices associated with personnel riding needs. This cost breaks down into a cost of R5 000 per running metre for the belt, supports, emergency stop and communication systems, and lighting and warning signs. The additional costs over a standard rock carrying belt due to personnel riding safety requirements, boarding and alighting platforms, control cubicle, brakes and safety devices are R2 000 000.

4.8.1.2 Capacity

The carrying capacity of the chairlift is a function of the rope speed, spacing of the chairs and the distance between supports. The distance between supports and the allowable tension on the rope determine the spacing allowed between chair, however a minimum distance of 5 m is required to allow for the safe boarding and alighting of personnel. Sagging between supports must be kept to a minimum, with 200 mm sag being acceptable.

Speeds of the chairlift are little more than walking speed, with 1,25 m/s being the norm. At this speed, a chairlift system with a chair spacing of 7,5 m would be able to transport 600 persons per hour. It is possible to increase the speed up to 2 m/s, which would increase the capacity to 960 persons per hour.

The use of detachable chairs could allo~increased speeds of up to 5 m/s, but this is at the expense of flexibility and such systems prevent the use of intermediate boarding stations. Special boarding and alighting stations must be provided to allow for the chairs to match the rope speed.

4.8.1.3 Limits on length

Chairlifts with lengths of up to 3000 m have been installed and it is possible to install systems in excess of this length, particularly where detachable chairs are used. Drive units with power ratings of up to 132 kW producing pulling forces of 32 kN are available that can handle these lengths.

4.8.1.4 Environmental compatibility

Electric or electro-hydraulic drive motors are used to power the chairlift. These motors are efficient and produce no environmental contaminants. Chairlifts are sensitive to changes in horizontal and vertical alignment due to ground movement, but the impact of this can be reduced by the use of adjustable supports. Supports can be rigid supports either grouted into the footwall, or can be suspended from the hangingwall by means of slings or chains.

4.8.1.5 Powering systems

Electric or electro-hydraulic motors are the standard power sources for the drive units of the rope pulleys. Drive units are static motors usually placed directly in line with the chair lift system with power transmitted to the rope pulleys through a

gearbox or hydraulic couplings. Tension is maintained on the rope pulleys by means of hydraulic pistons on the drive wheels, or via a tensioning tower at the return station.

Drive and return wheels correspond to the system gauge, which can range from 900 mm to 1835 mm. The drive units are placed at the head of the system in the case of an incline chairlift (Figure 4-54), or else at the shaft station on a level, where only one drive unit is used per system.

Drive station Embarking/disembarking station

Figure 4-54: Drive source and embarking station (Nehrling, 2002)

4.8.1.6 Boarding and alighting

Chairlift systems with a maximum speed of up to 2m/s do not require any special boarding or alighting arrangements. Persons simply walk behind the chair and climb on at the boarding stations, and similarly at the alighting stations they slip off the rear of the chair. Fixed chairs used on these systems have pre-set distances and gaps are maintained automatically. No attendant is necessary, but care must be taken when boarding not to produce any sideways motion in the chair, as this could cause the rope to slip off the intermediate support wheels and derail the system. Boarding stations are required to be level, and are typically 10 m to 20 m long.

Higher speed chairlifts make use of detachable chairs. At boarding stations, these chairs are placed on a special boarding rail, and released by means of a manual trigger. The chairs are then led down a set of small rollers to the end of the rail1

by which time they have reached the operating speed of the system. The chairs are then held onto the rope by the friction between the rope and the support element. The manual trigger can only release the next chair when the previous

chair has travelled a minimum distance of three times the travelling speed. At alighting stations, the reverse occurs, with the chairs being lifted off the rope onto a rail and slowed to a stop. The chairs are then simply lifted off the rail and placed in a depository.

As indicated in section 4.8.1.2, the fixed chair system, intermediate boarding and alighting stations can be provided at any point on the system. The removable chair system, however, only allows for a station at either end of the system.

4.8.1.7

Maintenance

The drive and return wheels, as well as the wheels of the intermediate supports are designed with replaceable polyurethane inserts to minimise wear on the rope.

Consequently, these require regular monitoring and replacement in order to ensure that they do not wear to a point where the rope could be damaged. The rope itself requires replacement on an annual basis, although, with regular inspection, this could be extended.

Horizontal alignment of the intermediate supports is critical as even minor misalignments could lead to derailments of the rope. Any misalignments caused by ground movement must be attended to immediately. For this reason, the supports are designed to be adjustable to allow for quick realignments. Drive and tensioning units require maintenance on a regular basis. Loss of tension in the system could allow the sag between the supports to cause chairs to bottom out on the footwall.

4.8.1.8

Installation considerations

Chairlift systems can be designed to accommodate any mine layout. Horizontal curves of up to 120° and 4 m diameter can be accommodated by the fixed chair system, and gradients of up to 45° are possible. High-speed removable chair systems can operate on inclines of up to 18°. Curves are accommodated by means of special curve stations. However, the curves may require a larger radius than 4 m as the chairs are taken off the rope and guided around the curve on tubes.

4.8.1.9 Compatibility with other systems

Chairlifts are designed for the transport of personnel, but any material that can be carried in a handbag (elephant bag) is permissible. In emergencies, it is possible to attach a stretcher unit to the rope. The chairlift can be designed to have a narrow operational width of 900 mm, which allows for the installation of a parallel rail or conveyor system for the transport of rock.

Alternative system

A variation on the chairlift system is the "Men Assisted Walking System". This type of system is commonly installed in steep or long inclines where labour is assisted to negotiate the inGline. This system consists of a motor at one end driving an endless wire rope through a pulley, or set of pulleys. Each person using the system is issued with a handgrip, which is placed over the rope in such a way, that it "grips" the rope, enabling the person to be pulled up the incline. For safety considerations, low speeds must be adopted to prevent persons from being pUlled off their feet and injured, particularly in a steep incline where the consequences of a person falling could be fatal. Safety trip wires are therefore included in any system.