Elevator Traction Sheave
The traction sheave is a key component to a cab-to-railway elevator system. It provides “traction” between the hoisting ropes and a drive sheave in order to prevent them from slipping as the cables are rolled over the sheave.
The traction sheave can be either geared or gearless. Both have their advantages and disadvantages.
Rope and Sheave
A traction sheave is the element in an elevator traction machine that turns the ropes to lift the car or counterweight. Sheaves are designed to have grooves that fit over the grooves on the ropes and provide friction between the two elements. They have a diameter of about 0.6 to 1.2 meters (2-4 ft) and can be driven by a motor with or without a gearbox.
Sheaves are usually made of steel, with finished grooves and metal shafts. They are used in both geared and gearless traction machines and can be found on elevators with a rated speed of up to 3.2 m/s or 800 ft/min.
The sheave can also be made of a nonmetallic material. This can be done to reduce the weight of the sheave and make the system more compact.
Another advantage of using a sheave that is made of metal is the sheave’s durability and resistance to wear. Sheaves can be made of stainless steel, aluminum or titanium. They are also available in different sizes.
Sheaves are primarily used for high-speed traction elevators because they allow for higher rated speeds and require less power to operate. This allows for lower energy consumption, but sheaves can also be used in lower-speed traction elevators with a higher power rating.
Since the sheave can be made of different materials, it is important to choose a type that will last. For example, the stainless steel sheave is a popular choice because it is resistant to corrosion and will not rust over time. It is also durable and has a long service life.
In addition, sheaves should be made of materials that are Elevator Traction Sheave strong enough to handle the force that is exerted on them. For example, a sheave that is made of titanium should be stronger than an aluminum sheave.
Traction sheaves are usually designed with V-grooves that are about 40 degrees out of vertical and round grooves that are about 50 degrees out of vertical. This configuration minimizes sheave wear, which reduces energy consumption and the cost of replacement.
Sheave wear can be reduced by applying a coating to the sheave. This coating should be a minimum of 1-3 times the thickness of the surface wire on the sheave. The coating will reduce the amount of friction between the sheave and the ropes, reducing wear and increasing safety.
Geared Traction Machine
Elevator traction sheave is a part of an elevator that allows for the raising and lowering of an elevator car. It is used in both geared and gearless elevators to allow for the traction of the hoisting cables.
Typically, a geared tractor traction machine is located in the rooftop machine room of an elevator. It uses an alternating current (AC) or direct current (DC) motor to drive the wheel and ropes that move the car upward and downward.
The traction sheave is usually a sheave with an undercut or grooved design to increase the friction between the sheave and the ropes. This is a more effective means of providing traction than simply wrapping the rope around the sheave. Grooving can be achieved using polyurethane, steel, and copper groove liners.
A geared traction elevator typically has a pit depth in the range of 5′-12′ (1.5-3.7 m) depending on the application. These machines are able to travel at speeds up to 500 feet per minute and have a maximum height of nearly 75 m.
Typical geared traction elevators require a penthouse machine room to store the mechanical equipment and a counterweight to balance the load placed on the machines by the car and passengers. These machines are also more prone to wear and tear than gearless machines.
They are generally more costly to install and maintain than gearless elevators. This is due to the varying size of the geared hoist motors and combined instruments required for their operation.
These geared traction elevators can also have high energy consumption. They are also susceptible to damage due to wear and tear, including heat, pitting, rumbling, and vibration.
In many cases, these geared winding drum machines are removed and replaced with new geared or gearless traction machines during a modernization of an elevator. This is a common practice as these old machines are not designed to support the increased loads of modernized controls.
Gearless Traction Machine
The most common type of elevator in commercial buildings is the traction elevator, which uses machines and cables to move a cab up and down a hoist way. These systems can be geared or gearless, and they typically use a counterweight system to help counterbalance the cab.
In geared traction elevators, an electric motor is used to power a worm gear that turns the hoisting sheave. This allows the elevator to lift cars up and down at speeds up to 500 feet per minute (2.5 m/s).
Another common traction elevator is the gearless machine, which uses a low speed (low RPM), high torque electric motor powered by AC or DC. This design also uses a drive sheave that is attached directly to the motor. These models can reach speeds up to 2,000 feet per minute (10 m/s), and they are more energy efficient than geared traction elevators.
Some traction elevators have a generator that supplies electricity for the motor and control system; this is often removed when the elevator is modernized. The generators are prone to dust buildup, which is a serious maintenance issue.
When a motor runs out of power, a brake is mounted between the motor and the drive sheave or gearbox to hold the elevator stationary at a floor. This brake is usually an external drum type that is actuated by spring force and held open electrically; a power failure will cause the brake to engage and prevent the elevator from falling (see inherent safety and safety engineering).
Finally, some traction elevators are hydraulic, which do not use overhead hoisting machinery but instead lift the cab by using a piston inside of a cylinder. Some hydraulic elevators have a sheave that extends below the elevator pit and others do not.
The main difference between a hydraulic and a traction system is that the fluid used in a hydraulic system can be changed to a non-oil-based one that helps reduce the environmental impact of an elevator. Hydraulic elevators can have a sheave or not, and some have telescoping pistons that collapse and do not require a hole in the elevator pit.
Counterweight
In an elevator traction sheave, the counterweight plays a key role in creating adequate traction. Without adequate traction between the traction sheave and the elevator car, the traction machine will simply not have enough power to pull the elevator cab up.
If the counterweight is too heavy, it will be unable to balance the weight of the elevator car which could cause damage to the traction sheave and result in an uncontrolled movement of the car (UCM). The counterweight helps Elevator Traction Sheave to balance the suspension ropes between the traction sheave and the suspended elevator car, creating an equal force to move the elevator cab up and down.
The counterweight can be made of a variety of materials, including steel, aluminum or stainless steel. It is usually welded to the traction sheave to help prevent abrasion or other damage that may occur during the traction process.
Elevator traction sheaves, like most of the other components in an elevator, are subject to wear and tear over time. They require frequent maintenance to keep them in a good condition and to ensure that they continue to function properly.
During this maintenance, it is important to check that the counterweights are not being overbalanced. This is a very common problem that can lead to a number of safety issues.
One way to determine if an elevator is overbalanced is to use a platform scale. This will allow you to weigh each counterweight block individually and then calculate the average weight of each block. Once you have this information, it is then possible to install the anti-vibration device required to reduce vibrations and make the counterweight safer to operate.
Another way to determine if an elevator is overbalanced includes measuring the height of the traction sheave. This is an easy and quick way to check that the traction sheave is not overly high or too low.
The traction sheave can be a very expensive part of an elevator to replace, so it is important that it remains in good condition. This is especially true for older and less-used elevators in residential buildings that often travel only a few times a day during non-peak hours. This type of elevator is more likely to need frequent replacement of the traction sheave as the material that is used to create it can deteriorate over time.
