From the ICMMESA Archive
A detailed discussion of the passenger carrying mono-cable ropeway at Milner Park Showgrounds, Johannesburg, built in 1964.
Bronze wire ropes were used at Pompeii, but it was not until the nineteenth century that drawn steel wire ropes were made and used by mines in the Harz Mountains, Germany. Subsequently, mono-cable aerial ropeways were constructed in England and America using steel ropes. These were followed by bi-cable ropeways in Germany, Austria and Russia. These earlier ropeways were designed for the transportation of goods, but passenger carrying ropeways were soon developed and by the end of the nineteenth century, ropeways were in use throughout the world.
We distinguish between two types of aerial ropeway: continuously operating and intermittently operating ropeways.
Continuously operating
Mono-cable
The mono-cable ropeway is generally made with a single rope running continuously with cars fixed to the rope permanently, or so that they can be detached at the stations.
Fig. 1: Rope supports made
of precast concrete.
Fixed grips
Mono-cable ropeways employing the fixed grip principle are usually used for ski-lifts where loading and unloading can be undertaken with the car in motion. The fixed grip is clamped securely onto the rope in such a way that it can be tightened from time to time to allow for decrease in rope diameter.
Detaching grips
A mono-cable system with a detachable grip is used where a car must come to a standstill for loading or off-loading. This grip falls into three general categories: spring loaded, gravity loaded and hook-cm type. The spring and gravity loaded grips are made with jaws which clamp onto the rope and are held in position by the load of a spring or by the weight of the car. The hook-on type grip hooks onto either a hanger fixed permanently to the rope, or onto the rope itself.
The detaching grip is automatically detached from the rope as the car enters the station to allow the car to slow down and stop for loading. With loading completed, the car is accelerated to rope speed when the grip automatically engages with the rope and the car proceeds to its destination.
Fig. 2: Profile of the Milner Park ropeway.
Examples of this type of ropeway are found at the Milner Park Showgrounds in Johannesburg; at the Klip River Power Station, Vereeniging, and at the Pretoria Portland Cement Company at Loerie, in the Cape Province.
Bi-cable
The bi-cable ropeway consists of two sets of rope, one comprising the stationary track rope and the other the moving hauling rope. The car hanger is fitted with grooved wheels which run along the fixed track rope while a detachable type grip is used to connect the car to the hauling rope. As with mono-cable ropeways, the detachable grip is either spring loaded or gravity loaded.
Intermittently operating
Mono-cable
This type of ropeway has the car fixed permanently to the single moveable rope through a hanger and clamps. The whole system is stopped when a car enters the station. These ropeways are usually used in conjunction with a fairly large car accommodating a number of persons at a time.
Bi-cable
Intermittently operating bi-cable ropeways fall into two categories: single track and double track rope type.
Fig. 3: The balancing wheels assembly.
The single track rope type consists of a track rope supporting a carriage, a hauling rope which moves the carriage and the crane rope which passes over pulleys on the carriage to a hook.
This type of ropeway, more commonly known as the cable crane, has been used on the Storms River Bridge, as well as the Klaver and Vaal River bridges, the Kyle Dam in Rhodesia and the Kat River Dam in the Eastern Province.
The double track ropeway is mainly for passengers and consists of two track ropes, each carrying one car. The cars run in opposite directions and are attached to hauling ropes driven by a double drum winding engine at the higher terminal station. The engine can be dispensed with where the requirement is to transport ore down from the higher station. The heavier car raises the empty car by gravity and the speed is controlled by a brake.
Ropeway transport
Ropeway transport is generally feasible where more conventional means are hampered by inaccessibility. The ropeway can operate directly from one point to another, which means that, in mountainous country, the distance traversed is reduced considerably, the necessity for a good road is obviated and the human element is reduced to a minimum.
Fig. 4: Diagram of the dispatch section.
The Milner Park mono-cable ropeway
The passenger carrying mono-cable ropeway at Milner Park Showgrounds, Johannesburg, was constructed at the beginning of 1964 by a consortium of Johannesburg industrialists. The ropeway has now operated successfully for two seasons during which time
185 000 persons have been transported. The system, which covers a distance of 1700 ft between stations and which has seven intermediate support points, cost around R100 000.
End stations and supports
South Station
This end station was built onto the existing Tower of Light and the platform is 26 ft above ground level. The station has two decks, the upper containing the return sheave, accelerating and retarding rollers and the fixed track rails, while the lower deck forms a platform for passengers to board and alight.
North Station
The north end terminal, which is 110 ft lower than the south terminal, consists again of two platforms built onto and around a tower containing the drive, tensioning gear and the control room. The accelerating and retarding rollers and fixed track rails are supported on the upper platform which is 40 ft above ground level.
Intermediate supports
The rope supports were constructed of precast reinforced concrete for aesthetic effect and are spaced roughly 220 ft apart. They are in the form of arches, each arch having been made in two sections on the ground and then raised into position on foundation pads (see Fig. 1).
Fig. 5: The cast steel grip consists of eight parts.
Midway between the two terminals, the existing Everite tower was used to attach a seventh rope support. The profile of the system is such that the rope rises fairly steeply from the north or lower station to the first portal or arch, and then continues to rise but at a much less acute angle until it reaches the upper portal where it enters the south station almost horizontally (see Fig. 2). The two ropes are supported at 12 ft centres on sets of four balancing wheels arranged in pairs so that they can articulate vertically in line with the rope (see Fig. 3).
Each balancing wheel is made of two steel discs, the outer periphery of which form flanges. A special rubber tread is clamped between the discs. The groove of the wheel is machined into the rubber so that the rope is supported on the rubber and never touches the steel flanges.
Midway between the balancing wheels is a spindle passing through bearings in the side plates and connected to the outer ends of the equalising arms, which are pivoted centrally on bearings supported by a box section hanger supported on trunnion bearings in a fabricated steel plate frame attached to the concrete portal. The balancing wheels are therefore free to form whatever profile is necessary in a vertical plane.
Fig. 6: A grip entering the spear.
General method of operation
The rope has a diameter of 1 in, is 3400 ft long and is of a 6 x 19 (9/9/1) construction. It has only one splice. It is driven by an 8 ft diameter drive wheel round which it laps for 180 degrees. The rope runs at a speed of 420 ft/min and, under normal circumstances, is never stopped. It goes from the drive wheel over a pair of deflecting sheaves near the top of the north station tower and then rises to grip level. It is gripped by one of the detachable grips on the car, rides under a hold-down roller at the extremity of the station and takes the car with it up and over the balancing wheels at intermediate portals, eventually entering the south station.
Here, the rope is deflected back to the horizontal line over a single pair of balancing wheels, the grip on the car is released and the rope is deflected down and away from the grip. The rope then passes around the return sheave and up slightly to meet an outgoing grip. It is gripped by another car and passes from the station through the various portals and carries the car on the return journey to the north station where the grip is again released and the rope deflected down slightly away from the grip, around the two sheaves in the north tower and back to the drive wheel.
An important aspect of this operation is the gripping and releasing of the rope at the appropriate moment. This has to be done with the grip travelling at exactly the same velocity as the rope. A simple way to achieve this this is by using gravity to accelerate the car and the grip. The gripping action is then accomplished by using the mass of the car.
This system has one serious drawback in that the inclined rail is set for the full speed of the rope. If it is required to run the rope at some other speed, the car is caused to sway uncomfortably at contact and the action of grip on the rope produces severe abrasion (see Fig. 2).
Fig. 7: The dispatch section showing the grip profile trip
Accelerating and retarding devices
The acceleration and retardation of the grip is done by means of a bank of 10 inch diameter rubber-tyred rollers set at 10 ½ inch centres. The drive for the rollers is taken from the hold down rollers at the north station and from the return sheave at the south station by means of a chain to the middle roller of the bank. There are 20 in each bank at the north station and at the receiving side at the south station, and 15 rollers in the despatch bank at the south station, each roller being coupled to the adjacent roller by means of individual chain drives. Each roller therefore has two sprockets of such a size as to make it run slightly faster than the roller preceding it. The rollers are individually spring loaded vertically and set so that they will bear down on the top of the grip, causing it to move and accelerate or retard at the required rate. Because the rollers are driven off the rope, their speeds are always proportional to rope speed, so obviating any difficulty caused by variation of the speed of operation (see Fig. 4).
The grips
The grip is made of cast steel, is spring loaded and consists of eight parts, namely the fixed-grip and body; movable jaw; helical springs; grip actuating rollers; fixed roller; track rollers; overlock and the grip lever system (see Fig. 5).
As a car enters the path of the accelerating rollers, it is suspended by the track rollers on a square section which runs below and parallel to the rope (see Figs. 4 and 5).
The accelerating rollers make contact with the top of the body of the grip and move it forward to engage with a linear cam or spear which enters the grip between the fixed and moving rollers. At the same time, another cam engages the overlock roller unlocking it. As the grip is moved forward, the spear forces the moving rollers inwards against the pressure of the two springs, causing the movable jaw to move inwards, away from the fixed jaw, so opening the grip.
At this stage, the rope is deflected upwards to enter between the fixed and movable jaws. By this time, the accelerating rollers have brought the car up to rope speed and the spear begins to taper back to zero. The springs close the movable jaw and the grip is attached to the rope.
As this happens, the overlock cam loses contact with the overlock roller, allowing it to snap into the locked position. With the overlock down, the grip cannot be opened even though the springs break.
The grip now passes through a series of safety flaps which ensure that the grip has closed properly and is lying in the correct position relative to the rope, and that the overlock lever is in the correct position (see Fig. 6).
The grip then runs for a further 8 ft on the steel track, now propelled by the rope directly. Over this section it may still be stopped if one of the safety flaps indicates incorrect attachment to the rope. Having passed the flaps satisfactorily, the grip leaves the rail and the station and proceeds. The gripping force of the springs is designed to allow no slip between rope and grip at a pull of 800 lb measured parallel to the rope axis.
All pivot points in the grip have sealed bearings of the roller or needle type. The track rollers have grease points. Two sets of linkages, one near the grip end and one at the roller end ensure that the faces between the fixed and the movable jaws are always parallel. These links, with the same radial movement, constrain the movable jaw without sliding friction and yet provide the required parallel action. The ends of both the fixed and the movable jaws are belled to prevent sharp bends in the rope when the grip and car are passing points of maximum deflection such as at mid-span and on approaching the portals.
The spears
The spear, which is actually a linear cam, forces the grip open and allows it to close at the appropriate moment. It is the length of the accelerating or retarding roller bank and is tapered on the inside from zero to 24 in and back to zero. The outside of the spear is straight and is parallel to the fixed track rail. The lower face of the spear is also straight and is horizontal, acting as a location for the outer end of the grip. The spear is made from high tensile steel plate (see Fig. 7).
Drive and counterweight
The drive and counterweight assembly is located in the tower at the north end and are suspended on the rope. The total weight of the assembly is 15 tonnes, twice the tension in the rope. All pivot points in the grip have roller or needle sealed bearings. The track rollers have grease points.
Two sets of linkages, one near the grip end and one at the roller end, ensure that the faces between the fixed and the movable jaws are always parallel. These links, which have the same radial movement, constrain the movable jaw without sliding friction and yet provide the required parallel action. The ends of both fixed and movable jaws are belled to prevent sharp bends in the rope when the grip and car pass points of maximum deflection such as at mid span and on approaching the portals.
Because there was not sufficient space available at the south end for either the drive or the take-up mechanism, these devices were combined and positioned at the north end.
This was achieved by a dead-weight made of concrete blocks held in a steel box below a platform on which is supported the motor and gearbox driving the main friction wheel through a spur wheel and pinion. This arrangement can move up or down and is guided by steel rollers on two steel boxed columns running vertically from floor to sheaves.
The main drive a 25 hp, 3-phase slipring motor through the gearbox. An auxiliary petrol engine can be connected by means of a chain coupling, for power failures. It is not usual to drive a cableway from the lowest point because, by doing so, the effective pull due to the weight of the rope and car is not used at the friction sheave. The loss in the effective pull is negligible because the difference in level between the upper and lower station is not great.
The motor speed is 1420 rev/min, which is reduced by a worm gearbox to 117 rev/min. The speed is further reduced through an open pinion and spur wheel to 17 rev/min, which is the speed of the friction wheel.
Two sets of brakes are supplied, one of which acts at the coupling of the motor and is used as the “normal brake”. The other set acts on a 4 ft brake race attached directly to the friction wheel. Both sets of brakes are spring loaded. Nitrogen under pressure from a portable gas container is used to release the brakes. The material used on the tread of the friction wheel is PVC and it has been found to withstand wear and pressure satisfactorily to date.
The gondolas
Each gondola or car accommodates three persons, and has a tubular framework with a seat, sides and roof made of fibre glass. The construction is lightweight yet robust. The car has one door which opens outwards and which when closed, is locked with two catches for safety. The car is suspended from a central point in the roof by means of a curved fabricated box section member which is connected to the grip by a bushed pin, allowing the car an unrestricted swing through an angle of 110 degrees in the plane of travel.
Conclusion
The Milner Park prototype has indicated that this type of ropeway can be successful provided that cognisance is taken of the experience to date with this installation. Any saving made in the capital cost of installation is usually only a fraction of the cost of breakdown and of maintenance.
References
[1] WE Hipkins: “The wire rope and its applications”.
[2] Z Schneigert: “Aerial ropeways and funicular railways”.
[3] J Flucher: “Notes on the operation and maintenance of an aerial ropeway”.
Contact Mariana Jacobs, ICMEESA, Tel 011 425-0585, icmeesa@icmeesa.org.za
