Elevator Traction Sheave

There are two common types of elevator traction sheave: gearless and geared.

In the geared system, a worm-and-gear reduction unit drives the hoisting sheave. These machines operate at a slower rate than gearless sheaves but provide much faster lift rates than the traditional direct-drive sheave.

The traction sheave is an important component of any elevator, and is subject to wear due to the rope’s contact with it. Fortunately, there is an innovative solution to this problem.

Rope Grooves

In traction drive elevators, the ropes used to pull the elevator car up or down are inserted into rope grooves on the sheave of the drive machine. These grooves are designed to provide the best possible surface pressure on the rope and to help maintain its cross-sectional shape as it passes around the sheave and deflects.

The strand construction of the elevator rope plays an important role in the way it is operated, and a wide variety of strand constructions are available to choose from. Some ropes are made with filler wires, which improve their flexibility. Others are made with thin outer strand layers, which reduce the overall flexural stress in use.

There are two types of strand construction that are commonly encountered: Seale and Warrington. Both strands offer superior fatigue bending properties in rope grooves, and their service life is often twice as long as elevator ropes with thicker outer wires.

These strands are often used in traction elevators, where they are particularly well suited for high shaft heights and for traction drive elevators with large numbers of deflection sheaves. They also have the advantage of being able to withstand higher levels of flexural stress, especially in the case of ropes with a large diameter.

One of the most popular elevator rope strands is a 19-wire Seale strand (1-6-6+6), which is particularly effective for round grooves and offers good resilience against external wear in use. These strands can be used in both double wrap drives and in roped hydraulic elevators, and they are included in the current elevator standards for all major countries.

A further common strand construction for elevator ropes is the 9-strand construction with steel wire core. This strand provides excellent abrasion resistance and is the most suitable solution for traction elevators with large number of deflection sheaves.

The 9-strand construction also has the benefit of being the least prone to lateral spreading during compression, and this is a particular concern in the case of elevators with high shaft heights. The special arrangement of the wires in the strand and the strand itself, which helps to prevent the wires from crossing each other, reduces this danger.

Rope Tension

Rope tension is a crucial factor in the traction of an elevator. Uneven rope tensions can lead to uneven wear in the traction sheave groove, as well as different degrees of contact pressure between the rope and the traction sheave. The difference in tension can also cause the traction sheave to over- rotate, which may cause damage to the elevator.

The traction sheave is driven by the drive machine to move the set of hoisting ropes, which are then guided through the traction sheave groove and eventually to the elevator car. Each rope in the set of Elevator Traction Sheave hoisting ropes is guided separately, and a traction sheave groove is provided for each rope.

During the running of the elevator, the wire ropes pass over the traction sheave and are thus subjected to high stress factors. These factors include tension, flexural stress and torsion. These stresses lead to material fatigue and abrasion.

As a result, over long service periods, the diameter of wire ropes is reduced. This can be especially pronounced in ropes with fibre cores, where abrasion can accelerate the wearing process.

This can be particularly damaging to the traction sheave groove, because it means that damaged wire ropes travel less than the rest of the ropes, which leads to more friction between the ropes and the sheave groove. The resulting damage in the groove and the ropes can lead to premature rope breakage.

To prevent this, it is essential to make sure that the traction sheave grooves are not damaged and the elevator is properly maintained with annual verification of rope tensions. It is also important to make sure that the steel wire ropes are properly fastened.

Rope Length

Traction sheave elevators typically use five to eight lengths of wire cable, known as hoisting ropes, wrapped around the drive sheave in special grooves. The combined weight of the elevator car and counterweight presses the hoisting ropes into the grooves as the sheave turns, providing traction for the sheave.

The material used to make the hoisting ropes is a critical factor in their performance. In addition to their tensile strength, the ropes should also have good fatigue bending properties.

This is because the hoisting ropes must be capable of flexing in response to changing conditions such as the weight of the elevator car, counterweight and hoisting machine. They should be able to do this in a relatively smooth manner, ensuring that the elevator’s occupants are not subjected to excessive force or injury.

For this reason, the material used for the hoisting ropes should be selected carefully. This is particularly the case if the elevator’s occupants will be exposed to heavy loads during operation.

Ideally, the materials used should be a high-quality galvanized or stainless steel. These materials can be corrosion-resistant and are also available at reasonable prices.

Another consideration is the quality of the rope’s strand construction. Typical rope constructions include Seale, Warrington and Filler strands.

In a Seale rope, the outer strands are made from one wire type while the inner strands are made from two different types. This allows for higher strength levels, but also requires a more complicated strand construction.

This makes Seale ropes ideal for applications with large rope diameters, such as those found in traction sheave elevators.

The strands in these ropes are usually made from steel wire. However, they can be made from other wires as well.

When choosing the strands for a suspension rope, it is important to take into account their bending characteristics and the end-of-service life (discard age) of the rope. A good, low-elongation rope that does not require frequent relubrication should be chosen.

In most cases, the strands are made from a wire type that is easy to mount and does not require frequent relubrication. In addition, the ropes are able to be mounted at a lower cost than those made from Lang lay ropes.

Maintenance

The Elevator Traction Sheave is the main component of the traction system that moves the elevator car. It uses a geared or gearless motor that is powerful enough to move the elevator at a rate of 50-200 revolutions per minute. The motor is connected to the traction sheave by two large, grooved pulleys, commonly called sheaves in the industry.

The grooved sheaves are made of a hardened steel or alloy, such as bronze or aluminum. The grooves are deep and wide, about 0.6 to 1.2 meters (2-4 ft) in diameter, and are designed to fit the ropes perfectly as they are pulled up over the sheave. The traction sheave must be strong enough to hold the load of the elevator and its counterweight, which balances the weight as the elevator car rises and descends.

In many cases, the traction sheave is remachined when the ropes are changed in order to reduce friction and minimize abrasion between the rope and sheave. However, it has been proven that abrasion or rope impressions can also occur at a significantly higher rate after remachining than when the sheave is originally installed.

Fortunately, there are ways to detect Elevator Traction Sheave sheave degradation and determine whether it needs to be corrected before it leads to mandatory sheave replacement. The first step is to perform a thorough inspection of the sheave.

A visual examination of the sheave can identify groove wear that is causing damage to the traction ropes. This could result in reduced traction and uncontrolled car movement. If you find sheave groove wear, you should immediately regroove the sheave or replace the sheave, depending on the severity of the damage.

Once regrooved, it is critical to inspect the sheave to make sure that the ropes still fit properly. Any uneven or significant sheave wear should be reinspected and may signal other issues that require attention, such as the elevator’s motor or cab.

Sheave wear is a major problem that should be addressed to avoid the need for sheave replacement in the future. The traction sheave must be regrooved regularly to ensure that the tension between the elevator’s ropes is balanced and the grooves are still in proper alignment with the elevator’s cables.