Hoist (device)
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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. The load is attached to the hoist by means of a lifting hook.
Hoists are powered lifting assistants. They can be used to lift a heavy item or even a person. Hoists are usually placed overhead and attached to the ceiling, and may have a power supply. They use a suspension system, sling, and power supply cable. There are many different types of hoist, and it is important to be aware of how they function before you begin using them.
There are two main types of powered hoist. Portable battery operated hoists have advantages and disadvantages. These are lightweight, and can be easily detached and moved to enable work on different tracks. However, if used in different places, one still needs the tracks in place to enable them to work at all places one requires. These are particularly popular in nursing homes for moving elderly people who may need assistance.
A permanently attached ceiling track hoist is fixed to a ceiling track in one place. It has a powered lifting mechanism that you can operate continually. These are used in large warehouses or any place where lifting is performed routinely. Unlike the portable hoist, this type of hoist cannot be moved and hence does not require constant dismantling.
The main power supply for these hoists comes through the main electricity supply. However, if the hoist fails to operate, there is sometimes the option of a backup battery supply. If the hoist does not have this option, then you should be able to operate it manually to lower the heavy item.Another factor to consider is the type of tracks and suspension for your hoist. You can choose from a straight or angled track. These basically hoist things in the direction they are set. With angled track hoists, you can move things around corners and bends. There are also turntable hoists that can swivel weights completely around.
An X-Y tracking hoist uses two parallel tracks on each side of the room, either on the ceiling or opposite walls. Hoists of this type can move the weight anywhere in the room as needed. Gantry and free standing hoists have floor-standing frames. They are particularly useful for people who do not have much space to maneuver and are sometimes used when moving elderly people in and out of bed. Different hoists have different lifting capabilities. Hoists with a powered lifting mechanism take all the strain of the item and place none on the person operating it. Also remember to check that a hoist has the lifting capacity you require to move your items. The lifting height range will also vary between hoists; each has its own maximum height and can usually not be extended.
The hoist's safety aspects are another important factor. Does it have an automatic cut off switch? This will enable quick power cut off if there is an emergency. Is there a battery back-up supply or wind down option, in case of power failure? All of these factors should be checked be before buying or operating a hoist.
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[edit] Types 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. The power type can be either electric motor or air motor. Both the wire rope hoist and chain hoist have been in common use since the 1800s. 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. The built-up hoist will be much more expensive, but will also be easier to repair and more durable. Package units are designed for light to moderate usage, while built-up units are designed for heavy to severe service. A machine shop or fabricating shop will use an integral-package hoist, while a Steel Mill or NASA would use a built-up unit to meet durabilty, performance, and repairability requirements.
[edit] Construction hoists
Also known as a Man-Lift, Buckhoist, temporary elevator 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 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 cars (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 hoists have been predominantly produced the United States and Europe, China is emerging as a leading manufacturer of hoists.
In the US, General Contractors rent or lease hoists for a specific project. Rental companies provide erection, dismantling, and repair services to their hoists to provide General Contractors with turnkey services.
[edit] Mine hoists
These are, effectively, elevators built in mine shafts. Human, animal and water power were used to power the mine hoists documented in Agricola's De Re Metallica. Stationary steam engines were commonly used to power mine hoists through the 19th century and into the 20th, as at the Quincy Mine. Modern mine hoists are usually electric powered.[1]
[edit] Chain or wire rope
Common small portable hoists are of two main types, the chain hoist or chain block and the wire rope or cable type. Chain hoists may have a lever to actuate the hoist or have a loop of operating chain that one pulls through the block which then activates the block to take up the main lifting chain.
A hand powered hoist with a ratchet wheel is known as a "ratchet lever hoist" or, colloquially, a "Come-A-Long". The original hoist of this type was developed by Abraham Maasdam of Deep Creek, Colorado about 1919, and later commercialized by his son, Felber Maasdam, about 1946. It has been copied by many manufacturers in recent decades.
Ratchet lever hoists have the advantage that they can usually be operated in any orientation, for pulling, lifting or binding. Chain block type hoists are usually suitable only for vertical lifting.
For a given rated load wire rope is lighter in weight per unit length but overall length is limited by the drum diameter that the cable must be wound onto. The lift chain of a chain hoist is far larger than the liftwheel over which chain may function. Therefore, a high-performance chain hoist may be of significantly smaller physical size than a wire rope hoist rated at the same working load.
Both systems fail over time through fatigue fractures if operated repeatedly at loads more than a small percentage of their tensile breaking strength. Hoists are often designed with internal clutches to limit operating loads below this threshold. Within such limits wire rope rusts from the inside outward while chain links are markedly reduced in cross section through wear on the inner surfaces. Regular lubrication of both tensile systems is recommended to reduce frequency of replacement. High speed lifting, greater than about 60 feet per minute (20 m/min), requires wire rope wound on a drum, because chain over a pocket wheel generates fatigue-inducing resonance for long lifts.
The unloaded wire rope of small hand powered hoists often exhibits a snarled "set", making the use of a chain hoist in this application less frustrating, but heavier. In addition, if the wire in a wire hoist fails, it can whip and cause injury, while a chain will simply break.
[edit] Chainfall
A chainfall is another example of a hoisting device consisting of a chain suspended from or laid over a fixed structure such as a beam, or on well built saw horses resting on well supported joists used to lift heavy objects, such as steel beams, microlaminated structural beams, vehicle engines etc. Depending on the situation there are many other temporary rigs that can be improvised for lifting heavy objects with the tool. This principle is very similar to a block and tackle.
||Design & Constructional Features of "LIFT UP" Electric Wire Rope Hoists||
DESIGN: "" Hoists are designed as per standards(IS 3938 Class II) duty operations and repetitive use under most severe operating conditions. Hoists specially designed for higher lifts, faster hoisting & cross travel speeds & moveable on curved .
MOTORS: Hoist & crane duty Vz hour rated squirrel cage induction motors, confirming to IS 325 with comparatively higher H.P. and higher starting torque to reduce handling time. It is flange mounted to suit the design and provided with suitable insulation . ROPE DRUM : The rope drum should be made of seamless pipe machined & grooved accurately, to ensure proper seating of wire rope in a proper layer. The drum should be fitted with two heavy duty Ball / Roller bearings of reputed make for smooth operation & longer life.
ROPE GUIDE: The rope guide should be made of special close grain castings & is specially designed and accurately machined to suit the grooves of the rope drum & prevents the rope from overriding & loosening. It also operates the limit switches provided as a safety feature to limit the over hoisting & over lowering of the hook. The guide is so designed to ensure proper tensioning of the rope.
GEAR BOX: Totally enclosed oil splash lubricated & dust free gear box should be provided for smooth, trouble free & longer life. All gears are helical type and cut from alloy steel / low carbon steel on hobbing machines for achieving higher precision & a special process of gear toughening ensures smooth, silent, trouble free running of drive system. The pinions and gears are supported on anti-friction bearings on both ends.
MODULAR : The design is of modular construction and its maintenance is easy as each component
CONSTRUCTION: brake, motors, gear box & Control panel are independent units and are accessible easily. The complete hoist can be easily maintained by keeping it in its installed position, thus saving on precious labour as well as down time maintenance time.
BEARINGS: Heavy duty deep groove ball / roller bearings of reputed make i.e. FAG / NACHI or equivalent make are used on all rotating parts and are grease packed for longer bearing life.
TROLLEY: Push-pull, Hand Geared or Motorized Trolleys are of adjustable type and fitted with ball bearings to suit recommended size of I-Beams.
HOOKS: Heavy duty high tensile steel forged hooks are used & fitted in such a manner that they rotate and swivel freely.
BRAKES: Heavy duty 3 phase AC fail safe electromagnetic disc type brakes are provided on hoisting motion held closely to sustain the full load when current supply is switched off either accidentally or intentionally. It is mounted on the rear end of the motor for easy maintenance.
TESTING: The hoist components should be subjected to strict quality control procedures. And the hoist should be finally tested to 25% overload to prevent any accidents
[edit] See also
[edit] External links
- Using a two-post hoist (automotive) Free video content from CDX eTextbook
- Hoist Configuration Basics Sketches of Hoists mounted to Cranes
- [2] HMI Hoist Duty Classifications
