Elevator Traction Sheave
Elevator Traction Sheave
The elevator traction sheave, and the steel wire ropes that it drives, are critical to the safe operation of elevators. A damaged sheave or rope can cause an out-of-control car movement.
Elevator traction sheaves are sized between 0.6 and 1.2 meters (2-4 ft) in diameter. They rotate at a rate of 50 to 200 revolutions per minute in a traditional gearless system.
Drive Sheave
An elevator’s drive sheave, also called a traction sheave, moves a hoist rope to control the mechanical movement of an elevator car. Sheaves are a vital part of any elevator system, whether geared or gearless.
Elevator sheaves are either forged from cast iron or steel, depending on the machine being used. They can be large or small in diameter, but they all need to meet safety codes for maximum traction and durability.
Sheaves have a groove on their outer surface to help transmit the tension of the hoist rope over them. Sheaves should be regularly inspected to ensure the tension on the ropes is balanced and that they still fit the sheave grooves properly.
The sheave also needs to be able to withstand the pressure of the hoist rope over it. A common problem with sheaves is that they are prone to sheave wear and tear over time.
This can occur if the sheave is not properly maintained and inspected. Sheave wear can cause sheave grooves to become damaged and loosen. Sheave wear can also lead to deterioration in the sheave material and may result in poorer traction.
Moreover, sheave wear can cause the sheave to be in danger of fracturing due to the sheave’s bending radius. Sheave wear is a serious issue and should be addressed as soon as possible.
In addition, sheave wear can result in a shortened service life of the sheave. This can be caused by several factors, including a poor sheave Elevator Traction Sheave design or the sheave’s failure to develop adequate tractive force.
As a result, sheaves should be inspected and maintained by an experienced elevator technician. If sheave wear is found, the sheave can be replaced with a new sheave to prevent future damage.
Another way to prevent sheave wear is by ensuring that the ropes are properly sewed together and the tension is properly balanced between them. Sheave tension can change significantly during the run, which is why sheave inspections are so important.
Sheave wear is a common problem with elevators, and it should be addressed as soon as possible. A professional elevator technician can regroove your sheave or recommend that it be replaced if it is damaged or worn out.
Counterweight
The elevator counterweight balances the weight of the car and reduces the amount of energy the motor needs to lift the car. This reduces energy consumption, saves money, and minimizes maintenance.
Since 1900, traction elevators have used the same mechanism for balancing their cars: a sheave. The sheave is a large, grooved pulley that rolls steel ropes over to move the elevator cab up and down.
To maintain a stable, smooth operation, the ropes must have adequate traction, and that can only be achieved with an effective counterweight. A counterweight frame is a rectangular component that provides the necessary traction between the traction sheave and the suspension ropes, resulting in a smoother and safer operation.
A typical traction sheave elevator is driven by an electric motor that must be capable of turning the drive sheave at a rate of 50-200 revolutions per minute. To ensure that the electric motor turns the drive sheave smoothly, a counterweight frame is required to provide adequate traction between the hoisting ropes and the traction sheave.
In the traditional gearless traction sheave system, the hoisting ropes 3 run upward from the anchorage 13 to the diverting pulley 9 rotatably mounted on the counterweight 2. From there, the hoisting ropes 3 pass over a traction sheave 7 of the drive machine 6 that rotates along the rope grooves.
The hoisting ropes can be arranged in different ways to suit the basic layout of the elevator. Generally, three or more ropes are combined side by side to form a set of hoisting ropes 3.
If the number of hoisting ropes in an elevator is reduced, the traction sheave can be adapted by changing the direction of deflection of the hoisting ropes. In addition, the traction sheave can be changed by means of diverting pulleys provided with different rope grooves.
When the traction sheave reaches a certain torque value, the hoisting ropes may slip or “equalize.” As the ropes slide past the traction sheave, they grind (saw) the sheave material. This can cause the sheave to break, which is why equalizing must be done periodically.
Cables
In an elevator, there are many cables that work together to get the elevator car up and down. There are traction cables, hoisting ropes, and counterweights. Depending on the type of elevator, these Elevator Traction Sheave cables all work to move the cab up and down the shaft.
Cables are important for an elevator to operate properly and safely. They transmit information to the control system and help to make sure the elevator is running smoothly and efficiently.
Elevator wire ropes are typically designed with parallel strand construction, which helps to reduce the number of abrasions caused by the wires. Generally, they have higher fatigue bending life and less wear to the running sheaves than ropes with a cross lay construction.
However, there are some problems that can arise with the use of a rope based elevator drive system. These include the possibility of vibrations, uneven rope tension, and sheave groove damage.
Uneven rope tension can lead to a variety of problems, including the potential for uneven sheave groove wear, sheave material grinding, and the ability for the elevator to fail if a rope is broken. A special type of rope tension measuring device allows the elevator operator to set the tensile force to an even level, which can prevent a variety of problems from occurring.
Sheave groove damage can be caused by a variety of factors, including the use of unequally tensioned wire ropes, maladjustment of fastening points, and the loss of material in the sheave groove due to the elevator’s turning motion. If these problems are not corrected, they can lead to the need for expensive repairs or replacements.
The tensile strength of wire ropes is a very important factor in determining their service life. This is why wire ropes are available in a range of strengths. The higher the tensile strength, the longer the service life of the wire ropes. This is especially true for elevator ropes.
Motor
The motor of an elevator, which is typically housed in a machine room above the shaft, turns the traction sheave to lift and lower the elevator. In a gearless elevator, the traction sheave is rotated directly by the motor; in a geared elevator, the traction sheave is turned by a worm-and-gear-type reduction unit.
The traction sheave is made from stainless steel or carbon steel and is usually a small diameter to reduce friction between the ropes and the traction sheave. It can also be made from other materials.
A traction sheave is the most important piece of the elevator system because it turns the hoisting ropes, which are connected to the elevator car and the counterweight. The traction sheave is driven by an electric motor that is either AC or DC powered.
Besides the traction sheave, an elevator may also have other diverting pulleys that help with the suspension of the elevator car and/or counterweight. These pulleys are mainly used for the suspension ratio but can also be positioned in order to guide the passage of the hoisting ropes, if desired.
As with all other parts of an elevator, the traction sheave is inspected for wear and tear. This is done in order to maintain a safe and efficient operation of the elevator.
It is important to check the sheave groove depth and the steel wire rope diameter regularly. This can be done using a straightedge or feeler gauges. The sheave groove depth is a good indicator of whether the ropes are equally tensioned.
When the steel wire ropes are unequally tensioned, they will have different lengths and will travel differently in the traction sheave groove. This will cause the groove to wear out.
For this reason, it is essential to ensure that the ropes are properly fastened and the traction sheave is not damaged. It is recommended to check the traction sheave every year for damage and re-tighten the steel wire ropes.
If an elevator has a damaged sheave groove or a damaged rope, it can be difficult to correct this problem. It is best to take care of these issues early in the life of an elevator.
