Positioning equipment (l) - Hoist

The first positioning equipment we are going to touch on is hoist.

What is hoist?

A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium.

Advantages of hoist

• It can be placed in tight spaces such as between benches
• Flexible
  

Disadvantage of hoist

• There is a need take the weight usage into consideration. For example, package hoist is most suitable for light to moderate usage. When handling with heavy usage, we must use built-up hoist. (It will be covered in later part of this post) There is also a need to minimise ratio of dead-weight to payload of the handling equipment.
  

It usually consists of a block and tackle—a combination of one or more fixed pulleys, a moving pulley with a hook or other similar means of attaching loads, and a rope (or cable) between them.

Characteristic of hoist

The basic hoist has two important characteristics to define it: Lifting medium and power type.

• The lifting medium is either wire rope, wrapped around a drum, or load-chain, raised by a pulley with a special profile to engage the chain. Both the wire rope hoist and chain hoist have been in common use since the 1800s.
• The power type can be either electric motor or air motor.

It must be noted that a hoist can be built as one integral-package unit, designed for cost-effective purchasing and moderate use, or it can be built as a built-up custom unit, designed for durability and performance.

Package Hoist:
The term “package” refers to the fact that the hoist is an “integrated package”. In other words, the hoist is made up of a series of “proprietary” parts, designed specifically for the purpose of that hoist and all electric chain hoist and most wire rope hoists are “package type” hoists.

Therefore, package hoist is most suitable for light to moderate usage, standard speed and normal lifting lengths. If any service that does not have the norms listed, there would be increase in down time, higher maintenance cost and a drastically reduced service life. The farther out of the norms, the worse the performance. Package hoist is normally being used is in a machine shop or fabricating shop.

Built- up Hoist:

When the needs exceed the norms listed above (package hoist), it would be most suitable to use a built- up hoist. It should be noted that built up hoists can be as low as 3 ton capacity, when special speeds, duty cycles or long lifts are required, but normally heavy usage applications, high production, maintenance intensive applications. Even though built-up hoist is more expensive, it is easier to repair and more durable. Built-up hoist on the other hand is used for heavy to sever service like Steel Mill or NASA due to its durability, performance, and reparability requirements.

Hoist Safety

Only qualified and licensed individual can operate both cranes and hoists, and there is a list of safety rules and responsibilities whereby all personnel which came in contact with the equipment must obey to maintain a safe workplace for all personnel.

The following PDF file shows a list of safety rules when handling hoist:www.state.ar.us/labor/pdf/program_crane_safety.pdf

Types of hoist

When deciding which type of hoist should be used, so as to provide extended service and efficiently matches the requirements of the job; we should also ask questions like:

• Is a manual or power hoist needed?
• Is power hoist which is an electric or pneumatic (compressed air) type the better choice?
• What load capacity is required?
• How fast and how high must the hoist work?
• Is a chain or wire rope required?
• What headroom is available for hanging the hoist?
• Manual or Power?

Construction hoist:
Although there are many types of hoist, construction hoist is what most of us haven seen before as it is part of our daily life.

It known as a Man-Lift, or construction elevator, this type of hoist is commonly used on large scale construction projects, such as high-rise buildings or major hospitals.

The purpose being is to carry personnel and materials quickly between the ground and higher floors, or between upper floors.

The construction hoist is made up of either one or two metallic cages which travel vertically along stacked mast tower sections. For controlled travel along the mast sections, most modern construction hoists utilize a motorized rack-and-pinion system mounted onto the mast sections, while some older hoists still utilize a system of counterweights.