What Is a Sheave?
A sheave is a wheel or pulley through which a rope or wire rope is threaded.
Sheaves typically serve as blocks attached to either the end or the middle of the boom (arm) of a crane. The rope or wire rope is threaded along the groove of the sheave, enabling the crane load to be lifted or lowered by pulling on the rope.
They also provide high strength and durability and are an important factor in the crane’s precise operation. Depending on the type of crane and its application, there are a variety of types, from single grooves to those with numerous grooves.
Uses for Sheaves
The following are some examples of uses for Sheaves:
1. Lifting and Lowering Loads
Sheaves function as blocks attached to the boom of a crane to lift and lower loads through a rope or wire rope. By using Sheaves, the load lifting force is evenly distributed and the load can be efficiently maneuvered.
2. Moving and Placing Loads
The use of sheaves on cranes allows loads to be moved and placed precisely at specific locations. Sheaves facilitate the transportation and placement of loads, especially when handling heavy or large loads.
3. Working at Heights
The crane’s boom can be extended to reach objects at great heights. Sheaves can be attached to the end of the boom to help lift loads from heights or position loads in high places.
4. Assisting in Lifting Operations
Sheaves are useful in performing complex lifting operations with multiple ropes or wire ropes. Multiple Sheaves can be used in combination to lift higher loads.
Principle of Sheave
The principle of Sheave is based on the principle of the pulley. The pulley principle is a mechanism that amplifies force by changing the direction of the force. By using a sheave, the force required to lift an object can be reduced.
This is because Sheaves can disperse the force by wrapping around a rope or wire rope multiple times.
1. Simple Pulley
When a sheave consists of a single wheel, the incoming force (pulling force) and the outgoing force (lifting force) are in the same direction. No force amplification takes place, but the crane operation is facilitated by changing the direction of the rope.
2. Multiple Pulleys
When a sheave consists of multiple wheels, the rope is wound around the sheave multiple times. In this case, the tension in the rope is distributed, reducing the pulling force required to lift the same load. This effect allows heavy loads to be lifted with less force.
The principle of the pulley allows Sheaves to improve the efficiency of the crane and increase its ability to lift large loads.
Types of Sheaves
The following are common types of sheaves:
1. Single Sheave
The most basic type of sheave consists of a single wheel. The load is lifted by passing a rope through the sheave and wrapping the rope around the wheel. The force is not amplified, but the crane can be operated by changing the direction of the rope.
2. Double Sheave
This is a sheave with two wheels mounted side by side. The rope wraps around the Sheave twice, thus reducing the pulling force required to lift the load. Double Sheaves are suitable for lifting larger loads than single Sheaves.
3. Triple Sheave
This sheave has three wheels mounted side by side. A rope can wrap around the Sheave three times, further amplifying its power and allowing it to lift large loads. Triple sheaves are used when very heavy loads need to be lifted.
4. Block Sheave
This is a one-piece sheave with multiple wheels built in. They are usually double block (two wheels) or triple block (three wheels). Block sheaves are compact and easy to operate while having the ability to lift high loads.
5. Height Sheave
This is a specially shaped sheave in which the rope wraps around the outside of the sheave. The high sheave is attached to the end of the crane’s boom and is suitable for lifting work at high elevations or in curved locations.
These are common types of crane sheaves, but customized sheaves are sometimes used for specific cranes or applications.