A hoist is used to lift a load (usado para elevar la carga) from one place and lower it to another. The process involves the use of a chain or a rope which is wound around a lift wheel or drum. Hoists can be operated manually, pneumatically or electrically driven.
The lifting medium can be made from rope, chain or fiber. The load is connected to the hoist by a lifting hook. Hoists have predominately been manufactured in the United States and Europe; however, China has emerged as a major producer of hoists (mayor productor de polipastos) for use in Asia and around the world.
The two basic characteristics of hoists are lifting and power. The lifting medium has either a load chain which is elevated by a pulley using a special means of engaging the chain; or a wire rope that is wound around a drum. The power may be provided by electrical, hydraulic or air driven motors.
Packaged Unit And Built-Up Hoists
A hoist built as an integral packaged unit is more cost-effective and designed for moderate use, while a custom built hoist (hecha a la medida) is designed for high performance, durability and heavy service. A fabricating or machine shop will make use of an integral packaged hoist while a built up unit is more likely to be used by a steel mill. NASA, for example, would require a built-up hoist to meet their stringent requirements (satisfacer sus requisitos estrictos) for performance, durability and repairability, while the astronaut training section of NASA may utilize package-hoist cranes.
Different Types Of Electric Hoists
1. Chain Hoist or Wire Rope Hoist
Electric hoists are the most commonly used hoists in the world. There are two types: rope and chain type. Portable hoists can be either chain block or chain hoist types and use wire or cable. Chain hoists are actuated by a lever or are operated by a loop of chain (known as a chain fall) that pulls through a block activating it to take up the lifting chain. Chain or Wire Rope hoists are used in hundreds of ways, from small factories (pequeñas fábricas) to farms, to move equipment or other products from one location to another.
2. Construction Hoists
A Buckhoist or a man-lift hoist is a temporary hoist used as an elevator for construction (para construcción), building or passengers and is most commonly used for construction projects such as major complexes and high rise buildings.
A construction hoist works with cages that travel vertically up and down (arriba y abajo) sections of a stacked mast tower attached to the building structure approximately 25ft apart for added stability.
Man-lift hoists are also commonly used for medical applications (aplicaciones médicas) in hospitals or for caring for invalids at home to help move a patient from place to another. A hoist makes the task easier and prevents the strain that manual handling can cause.
3. Mine Hoists
A hoist or winder is used in underground mining to raise or lower (subir o bajar) conveyances in a mining shaft. In the past mine hoists were powered by animal, water or human power. Later steam engines were used and today modern hoists are powered by electric motors using drives with alternating current. There are three main types of hoists for mining applications: Friction or Kope Hoists, Drum Hoists or multi-rope Blair Hoists.