“New results concerning ropes of tramways” (1970)

“New results concerning ropes of tramways”

The author begins his article with a review of the origins of ropeway engineering and cites the invention of the wire rope by Julius Albert (see box) as the decisive prerequisite for the introduction of ropeway systems. He briefly discusses the development of the monocable and bicable systems before turning to the subject of rope construction. Here is an excerpt from the somewhat unorthodox original English translation:

For moving ropes the following type is carrying through: six-stranded parallel lay worked out in Lang’s lay. The reason for that is that the durability is longer because of the favorable contact conditions of the wires in the strands and the way the Lang’s lay is lying in the groove of a sheave. Normally the Seale construction seems to be most suitable. In special cases the filler wire rope has proved good. In some cases the Warrington construction has led to non sufficient results.

A significant part for the construction of a rope is the core. Mostly it will be a fibre core.

The main purpose of a fibre core is to support the strands radially. For this purpose the core must have enough volume and keep this volume for the life of the rope.

So what has changed with regard to ropeway ropes? Not very much with regard to the basic principles, but although the ropes – and the thinner ropes especially – look much as they did fifty years ago, significant technological developments have taken place in line with the growing demands of the ropeway manufacturers in terms of the higher rope tension needed to cope with increases in carrier weight. While the diameter of a carrying-hauling rope used on a double chairlift would normally be 38 mm at that time, for example, the diameter of the rope of a modern 10-passenger gondola lift is now 56 mm. In terms of rope construction, they are usually Warrington-Seale ropes. (For information on rope construction, you are referred to my article titled The ropes used on ropeway installations in ISR 2/2019, p. 124). Since the mid-1980s, wire diameters for the rope cross-section have been calculated using computer programs that take into account the exact sectional shape of the wires in the rope structure. This ensures, to the best possible extent, the even distribution of pressure between the wires, which is a prerequisite for long rope life.

Other developments in moving ropes include the use of compacted ropes or strands as well as seven or eight-strand, round strand rope. Compacting flattens the outer strands of the ropes and reduces the diameter of the strands, so that rope diameter is reduced while breaking force remains the same. The “rounder” surface also makes for smoother running of the rope over the sheave trains and round the bullwheels. Seven- or eight-strand carrying-hauling ropes offer smoother running, because the valleys between the strands are less pronounced than those of six-strand, round-strand ropes. A rope construction in which the rope surface comes even closer to a cylindrical shape is the Performa rope. Six compacted round strands separated by six extruded synthetic rods are arranged around an extruded polyethylene rod that serves as the core (see Fig 1).

There have also been new developments in rope cores, but they must still meet the same requirements as those described by Müller above. One such development is the use of an elastic synthetic rod as a rope core, in which the strands are evenly embedded during stranding while it is warm. This gives the synthetic rod a star-shaped cross-section. Another rope manufacturer uses a synthetic rope core in combination with plastic inserts or support profiles between the strands to ensure even strand spacing (see Fig 2).

Returning to the article written in 1970, the author has the following to say on the subject of track rope constructions (again quoted from the original English translation):

The construction of the carrying ropes seems to depend on the borders of the different countries. In Germany and Switzerland one exclusively uses full locked coil ropes while Austria and Italy are preferring multi-strand ropes. Obviously this not a question of technical facts but a question of the composition of the supervisory boards. In Germany the use of full locked coil ropes is practically prescribed because this kind of rope has got some advantages: greater corrosion resistance by profiled wire locking, smooth surface, smaller diameter by higher degree of filling, more favorable behaviour at vibration stressing by better conditions of wire contact, better behaviour at braking, and wires of the outer layer easy to replace.

Of course the full locked coil rope has to be well fabricated. Typical manufacturing defects:

• Cork-screws caused by loosening of the outer layer. Here the outer layer is archlike propping in itself instead of exerting pressure on the core. By that a profiled wire is squeezed out of the outer layer.
• Rope twist. The reasons for it are not quite known, but maybe the reasons can be found in the different tensions of the wires at stranding and in too small pretension of the rope at the moment when it is pulled out of the stranding machine. Here, too, the rope can form like a cork-screw.
• Too little lubrication. Here, some of the hollows of the inside of the rope are not completely filled. There will be corrosion in the inner layers and disturbance of the judgement of the state of the rope when magnetic-inductive inspection is done ...

There is little to be added to these comments today, except that the author has not mentioned another advantage of full-locked track ropes: The smooth rope surface means less wear on the linings of the carriage wheels.

The problem of differences between the industry codes of the various ropeway countries depending on the personal views of the staff in their supervisory authorities is a subject I hope to come back to some time in the future. This was one of the reasons for the creation of uniform ropeway standards by Technical Committee TC 242 of the European Standards Institute (CEN). It should also be pointed out that the use of multi-strand ropes as track ropes for new ropeway installations is no longer permitted. Nobody would even think of it today!