Elevator Wire Rope
The elevator wire rope is a suspension or tensioned balance rope that can be used to connect the drive sheaves of traction elevators. It is mainly used for shaft heights of between 50 and 100 m.
The most frequently used strand constructions for these suspension ropes are Seale, Warrington and Filler strands. Usually, these are produced in sizes of around 200 mm diameter.
Elevator wire ropes are exposed to a complex combination of stress factors during operation. These include tension, flexural stress and torsion as well as the effects of friction between the wires. These factors result in material fatigue. Abrasion is also a significant factor.
Depending on the application, different types of elevator wire rope can be used. These vary in terms of their core materials, strand construction and elongation behaviour.
The fibre core of an elevator wire rope has a considerable influence on the life expectancy of the suspension rope. It is crucial to ensure that the core remains dimensionally stable for as long as possible, since this will help to keep a good connection between the outer strands and the fibre core.
A fibre core can be made of natural fibres, polypropylene (PP) or synthetic fibres such as glass or polyester. Synthetic fibres are more expensive than natural fibres and thus have an impact on the price of a rope. However, they can be used for ropes with diameters of 7 mm and below, as long as they are manufactured to an adequate degree of diameter accuracy.
Ropes with a fibre core are especially suited for use in traction drive elevators. elevator wire rope They are subject to a high level of flexural stress, so they need thicker outer strand layers than ordinary ropes.
Another benefit of ropes with a fibre core is that they are resistant to changes in humidity in the shaft. This is important in cases where the elevator is in a construction phase, or if it is operating during monsoon climatic conditions.
An 8 x 19 Seale or 8 x 19 Warrington rope construction with a fibre core is the most commonly used type of elevator wire rope internationally, and it has a wide following due to its superior fatigue bending properties.
Despite their many advantages, fibre cores can be damaged by excessive elongation. They should therefore always be re-lubricated from the outside in such a way that lubricant also penetrates the fibre core.
In addition, the rope termination should be secured against rotation to prevent structure changes taking place. This is particularly important when the rope is installed in longer shaft heights.
The hardness of elevator wire rope is an important factor when it comes to the safe operation of elevators. The hardness of the traction sheave and deflection points depends on the wire nominal tensile strength as well as on the material used for the sheave.
The main strand construction for elevator wire ropes is the Seale strand, which consists of 19 thick outer wires (strand structure 1-9-9). This type of construction offers an excellent degree of resistance against external wear during operation when running over the traction sheave and the deflection points.
This makes the strand structure ideal for use in elevator drive systems with numerous sheaves arranged closely with one behind the other, and for reverse bending. It also reduces the risk of sheave damage.
In most cases, the strand construction of an elevator rope is selected based on the required breaking strength of the wire. Nevertheless, the nominal tensile strength of the sheave also plays an important role when it comes to choosing the strand construction.
Depending on the application and the requirements, steel wire cores are often incorporated in elevator ropes as a means of reducing elastic rope elongation. This is because the inner strands of the steel wire core are not as long as those of the outer strands.
With this, the rope cross-section becomes much larger, and the elastic rope elongation is reduced. In addition, the breaking strengths of these ropes are significantly higher.
Ropes with a steel wire core are therefore suitable for use in elevators, where the demands placed on ride comfort and the need for high rope breaking strengths are of paramount importance.
However, there are drawbacks to the design of elevator ropes with a steel wire core. The large metal-lic cross-section means that they have very low elasticity and permanent elongation.
This is an important disadvantage for many elevator users. It is therefore preferable to replace these ropes with a more dimensionally stable full steel rope.
When replacing elevator ropes with a steel wire core, it is recommended to perform regular checks of the sheaves and the traction sheave and to change the traction sheave when necessary. This can be done by using special inspection devices for rope tension. The rope should be inspected after 4 to 6 weeks, for example. This inspection enables the traction sheave and the rope to be inspected for any signs of damage.
Elongation is a major factor in the operation of elevators. The elongation of ropes is influenced by many different factors and has to be monitored over the course of operation.
The elongation of ropes is affected by the load conditions in which they are used, their geometry (shaft height) and their age. It is therefore essential that they are selected carefully to avoid unnecessary deterioration of their service life.
This is especially true of the steel wire cores used in elevator ropes. This type of core enables the outer strands to be produced with less tensile stress and, in turn, reduces the amount elevator wire rope of elongation. The steel wire cores can be manufactured independently in a work step or in a joint work step with the outer strands and, if necessary, are reinforced by fibres in order to increase their tensile strength.
Elevator ropes with a steel wire core have proven to be extremely reliable in the past and are therefore recommended for all elevator installations where large shaft heights are involved. In particular, they are suitable for all traction drive elevators with a number of deflection sheaves and for the suspension of lift shafts.
When elevator ropes are stored for a long time before installation, they are usually protected against corrosion. This protection can be achieved using light lubricant coatings on the wires. This protection should be renewed periodically, preferably before the rope is subjected to any load cycles.
The lubrication is important to keep the ropes supple. It is also necessary to ensure that the lubricant penetrates all of the rope’s elements and that the strands do not come into contact with any dirt or dust.
To ensure this, the lubricant should be applied to the entire rope surface, which means that it should cover both the wires and the strands. In addition, the lubricant should be re-applied every few months, depending on the environment in which the elevator is located.
It is also essential to check the elongation of the ropes when changing them. If they are untwisted, this could be due to an incorrect installation or a lack of securing against rotation.
Elevator wire ropes are customarily made from bright, low-corrosion wires and coated with a light lubricant. They should be stored in a dry, frost-free and dust-free environment. In particular, the use of water-resistant lubricants is recommended for long-term storage and in lift shafts operating in damp or humid climates or in aggressive environments.
Wires in elevator ropes have a helical structure (Fig. 1). This structure makes it possible to achieve a very high degree of redundancy.
During installation, the outer strands of the elevator rope are bent over the drive sheave while the inner strands lie at a slightly different length on the sheave. The length compensation is achieved by moving the strands on each side of the sheave a small distance.
In this way, the strands are prevented from moving together when running over the sheave, thereby preventing damage to the sheave. This is particularly important in double wrap drives where the drive sheave can move in opposite directions during operation and the strands of the elevator rope should be able to compensate for this.
The helix formation in elevator ropes has another, less important benefit: it means that the wires can be replaced without having to remove the sheave from the shaft. In this way, ropes can be changed more frequently and a larger number of wires can be installed.
As an added bonus, the helix structure of elevator wire rope also prevents the wires from wearing out in the same places, because each individual wire is not contacting another wire. This is a very important factor in fatigue bending tests.
However, a helix construction can only be used for so long before it begins to sag under its own weight, which may happen especially when the rope is hung freely in the shaft. For this reason, the elevator rope should be secured against rotation during installation, even for longer shaft heights.
During service, elevator ropes are exposed to a large variety of stress factors including flexure, tension and compression but also abrasion between the wires as well as between the rope and the sheave due to slip. The combination of these factors creates a complex stress profile which, in the absence of a suitable strand construction, would lead to premature failure of the elevator rope.