Elevator Traction Sheave

In a traditional gearless system, the drive sheave is quite large, from 0.6 to 1.2 meters (2-4 ft) in diameter. A powerful electric motor turns this sheave at 50-200 revolutions per minute to move the elevator at its desired rate.

Traction sheaves typically have undercut or V-shaped rope grooves which increase friction between the traction sheave and the hoisting rope. This causes a strain on the hoisting rope and thus more wear of the hoisting rope than with traction sheaves with an advantageous semi-circular cross-sectional form.

Control Devices

The Elevator Traction Sheave is a key component of the drive system for an elevator. It holds the hoisting ropes in place and is also responsible for the traction of the ropes as they are lifted up. Over time, this sheave can wear out and can result in a decrease in traction or other problems with the lift.

To reduce the wear of the sheave, it is common for traction elevators to have their sheaves regrooved by a specialized company that is experienced in this type of work. This process involves grinding the sheave grooves so that they fit the hoisting ropes properly. Once this is done, the elevator sheaves can again be used.

It is important to note that a sheave can only be regrooved so many times before it becomes too damaged to be safely used. This is due to the fact that the sheave grooves are designed to hold the elevator ropes in place while they are being raised and lowered. If a sheave is regrooved too many times, the ropes will start to rub against it and this can cause significant wear.

In order to minimize the wear on the sheave, it is advisable to have a professional elevator technician inspect the sheaves regularly to check for uneven or major wear. Depending on the findings, your technician will either suggest regrooving or replacement of the sheave.

A number of different control devices are used to control the elevator. These include a switch for the motor, an emergency stop button, a safety button, and a direction button. These can be placed on the sheave or on a cylinder mounted on the bottom of the car.

The most common device used to control the traction sheave is the direction button, which allows the operator to either pull or push in order to raise and lower the elevator. In addition, the direction button can be used to select the desired floor to be climbed or lowered.

The traction sheave is also able to vibrate and produce harmonics. This can be a problem when the sheave is not isolated from the building structure, as this vibration can be transferred through the elevator hoisting ropes to the machine beams and the perimeter steel of the building. This can lead to structural noise that can be heard in living spaces and on the floors below.

Motors

The traction sheave used in this type of elevator is a large, 0.6 to 1.2 meter (2-4 ft) diameter grooved sheave, which must be driven by a motor capable of turning the sheave at 50-200 revolutions per minute. In addition, a gear reducer is often added to this system to limit the load on the motor as the elevator car rises.

The hoisting ropes connecting the elevator car and counterweight run over a traction sheave and at least one diverting pulley, usually attached to a bed that is placed in the elevator shaft. The traction sheave and the diverting pulleys are mounted on a machine bed in a machine room above the elevator shaft.

It is important that the continuous contact angle between the traction sheave and the hoisting ropes is in the range of 200deg to 270deg. If the contact angle is below this value, the ropes may slip out of the sheave grooves and become loose or otherwise unattached from the traction sheave. This can lead to excessive distances between the wheels, which would result in fast rope wear, compromising the travel comfort of passengers using the elevator.

This problem is solved by adjusting the wheelwork, so that the traction sheave and diverting pulleys are at different heights, thereby allowing the hoisting ropes to be adjusted Elevator Traction Sheave in a manner that achieves a narrower rope distance while retaining the same size and mutual distances of the traction sheave and the diverting sheave. In addition, the wheelwork can be tilted in order to adjust the distance of the hoisting ropes.

It is also possible to reduce the bending force of the traction sheave by installing a bearing solution in the sheave that is specially designed to support bending forces. This solution can be particularly beneficial in applications with a high bending speed, such as those found in tall buildings. It is a simple and inexpensive way to prevent the loss of sheave material.

Ropes

The ropes in an elevator traction sheave system are a significant part of the overall design. They must not only provide the needed traction force for the cab to move up and Elevator Traction Sheave down, but also must be strong enough to resist wear during operation.

Ropes are made up of strands and wires, which must be able to bend around the drive sheave and pulleys. The strands must also be capable of bending and straightening repeatedly under high speeds without breaking (e.g., at the valleys or crowns of the sheave).

A number of different types of rope structures are used in elevator applications. Two major arrangements are Seale and Warrington-Seale, both of which typically have 19 pieces of wire arranged on one strand.

These ropes must be lubricated properly so that they do not break when rubbing against each other or the grooves on the drive sheave. Alternatively, a coating may be applied to the traction sheave or diverting sheave so that the surface of the wires does not rub against the ribbed steel grooves on the sheave.

The ribbed grooves on the traction sheave are designed to pinch the ropes with varying degrees of pressure. This pinching action provides a large frictional effect that promotes the use of the elevator. However, it can reduce the service life of the ropes and traction sheave because of the abrasion that occurs when the rope comes into contact with the grooves.

To avoid this problem, the diameter ratio of the traction sheave to the steel wire rope must be kept as low as possible while still meeting performance and cost requirements. Smaller sheave diameters permit smaller guide sheaves and drive units that produce a lower (cost-determining) output torque.

For this reason, the traction sheave and the sheaves on the diverting pulleys should be of comparable sizes. This will ensure that the traction sheave is strong enough to support the weight of the elevator car and counterweight.

This will also ensure that the traction sheave has the proper strength to maintain its position when the elevator reaches a stall or stops. A strong traction sheave and sheaves on the diverting pulleys will also help to prevent the car from slipping down the shaft or falling into a void.

Counterweight

The traction sheave is a type of sheave used in elevators that are powered by a motor. The traction sheave is used to lift an elevator car in and out of the shaft of the elevator. The traction sheave is also used to control the rotation of the ropes that move the elevator car up and down.

In a typical gearless traction elevator, five to eight hoisting ropes pass around a drive sheave in special grooves on the sheave. As the elevator car moves up and down, it presses the hoisting ropes into the grooves on the drive sheave to give the elevator traction.

To enhance the traction of the hoisting ropes, the traction sheave is provided with a coating. The coating is adhesively bonded to the sheave and contains the rope grooves on the sheave. The coating is thinner in the edge areas of the rope groove than at the bottom of the rope groove, thereby decreasing the roughness of the surface area of the rope running in the rope groove.

This reduction in the roughness of the surface area of the traction sheave reduces the wear of the hoisting ropes and the need for the hoisting rope to have thicker surface wires. In addition, this coating is less likely to deteriorate due to grinding or other wear and tear of the rope groove material as the hoisting ropes are passed around the traction sheave.

Generally, the traction sheave is designed for hoisting ropes of substantially round cross-section. The ropes are twisted from steel wires to make them load-bearing, and the sheave is fitted with the hoisting ropes through a sheave mounting.

A counterweight is often attached to the sheave. The counterweight is matched with the weight of the elevator car and half the elevator load, so as the cab moves up or down, the counterweight is able to balance the weight.

To reduce the amount of frictional resistance caused by the counterweight, the sheave is designed to have a lower diameter than the elevator car. This design is ideal for high-speed traction elevators. The counterweight is a significant part of the power consumption in a traction elevator, so reducing the amount of power required can be a good way to increase energy efficiency.