Safe working load (SWL) is the load that a lifting device such as a crane, a cherry picker, or a lifting arrangement can safely lift, suspend or lower. Other synonyms include
working load limit (WLL), which is the maximum working load designed by the manufacturer. The load represents a mass or force that is much less than that required to make the lifting equipment fail or yield. The SWL is calculated using a given safety factor (SF) which for lifting slings could be given for example 5:1. The failing load is also known as minimum breaking load (MBL).
Factor of safety (FoS), also known as safety factor (SF), is a term describing the structural capacity of a system beyond the expected loads or actual loads. Essentially, how much stronger the system is than it usually needs to be for an intended load. Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure's ability to carry load must be determined to a reasonable accuracy.
Many systems are purposefully built much stronger than needed for normal usage to allow for emergency situations, unexpected loads, misuse, or degradation.
Ultimate load, strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). With respect to aircraft structure and design, ultimate load is the amount of load applied to a component beyond which the component will fail.
A chain is a series of connected links which are typically made of metal. A chain may consist of two or more links.
Chains are usually made in one of two styles, according to their intended use:
Those designed for lifting, such as when used with a hoist; for pulling; or for securing, such as with a bicycle lock, have links that are torus shaped, which makes the chain flexible in two dimensions (The fixed third dimension being a chain's length.)
Those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, and are flexible in only one dimension. They are known as Roller chains, though there are also non-roller chains such as block chain.
Wire rope is a type of rope which consists of several strands of metal wire laid (or 'twisted') into a helix. Initially wrought iron wires were used, but today steel is the main material used for wire ropes.
Historically wire rope evolved from steel chains which had a record of mechanical failure. While flaws in chain links or solid steel bars can lead to catastrophic failure, flaws in the wires making up a steel cable are less critical as the other wires easily take up the load. Friction between the individual wires and strands, as a consequence of their twist, further compensates for any flaws.
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 can be provided by different means. Common means are hydraulics, electrical and air driven motors. Both the wire rope hoist and chain hoist have been in common use since the 1800s. however; Mass production of an electric hoist did not start until the early 1900's and was first adapted by Germany. 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 where once regarded as being designed for light to moderate usage, but since the 60's this has changed. Built-up units are designed for heavy to severe service, but over the years that market has decreased in size since the advent of the more durable packaged hoist. 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 durability, performance, and repairability requirements.
A hoist is a suspended machinery unit that is used for lifting or lowering a freely suspended (unguided) load. It may be manually operated, electrically operated or pneumatically driven and may use chain or wire rope as its lifting medium.
An electric hoist is a suspended (overhead) hoist that is powered by electrically driven motors and is used to lift or lower a freely suspended (unguided) load. It generally uses chain or wire rope as its lifting medium
A manual hoist is a suspended machinery unit that, by use of manual operation, is used for the lifting and lowering of a freely suspended (unguided) load. A manual hoist generally uses chain (roller or link) as its lifting medium.
Manual hoists have a wide range of lifting capacities and can be used either for vertical lifting and lowering or for horizontal pulling.
A manual hoist is operated by hand. An operator will pull down on one of the chain loops on one side of the chain. This will turn a pulley mechanism inside the chain hoist housing. When this pulley turns, it will lift up the end of the other chain which usually has a hook on the end. By pulling down on one chain, the manual hoist is actually able to increase the mechanical work that is being done. This is caused by the gear ratio inside the manual chain hoist.
Generally, a chain hoist is any hoist which utilizes link or roller chain as its lifting medium. Chain hoists can be manually operated (hand or lever), pneumatically driven or electrically driven
A lever hoist is a manual device used to lift, lower, or pull a load and to apply or release tension. It utilizes a ratchet and pawl mechanical configuration to incrementally raise or lower a load or to apply or release tension.
Lever hoists and pullers have the advantage of being easy to transport, require minimum set-up, and are a practical option in confined spaces. They are suitable for different applications ranging from heavy-duty construction work to day-to-day maintenance and repair jobs.
A ratchet lever hoist or "ratchet hoist" is a lever operated manual device used to lift, lower, or pull a load and to apply or release tension. It utilizes a ratchet and pawl mechanical configuration to incrementally raise or lower a load or to apply or release tension.
The ratchet lever hoist is a versatile tool used in a wide variety of applications, both in industry and in the private sector. Its versatility allows it to be used in confined spaces, and also allows for heavy loads to be maneuvered and positioned safely and efficiently。
A trolley hoist is a hoist suspended from a trolley. A hoist can be connected to a trolley by hook or clevis, or a hoist can be integral with the trolley.
Trolley Hoists are available with varying spans and capacities. Trolley Hoists feature adjustable I-beams and heights for optimal use. Trolley Hoists are weather and moisture proof. Trolley Hoists need only one operator and are capable of heavy-duty lifting.
A trolley is a wheeled carriage, cage or basket that is suspended from and travels on an overhead track.
A monorail is a single run of overhead track on which carriers (trolleys) travel
A single girder crane is an overhead travelling crane that utilizes a single bridge beam attached to the two runway/end trucks. This bridge beam or single girder supports a lifting mechanism or hoist that "runs" on the bottom flange of the bridge beam.
A double girder crane is an overhead traveling bridge crane that utilizes two bridge beams set atop the runway (end) trucks. Generally this type of crane utilizes a top running trolley hoist, which moves along the top of the two bridge beams on its own set of trucks/trolley wheels. The hook from the hoist "falls" between the two bridge beams. Headroom under the crane is increased by utilizing this hoist/crane configuration
An overhead crane is a crane with a single or multiple girder (bridge girder) bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure.
An overhead crane, also known as a bridge crane, is a type of crane where the hook-and-line mechanism runs along a horizontal beam that itself runs along two widely separated rails. Often it is in a long factory building and runs along rails along the building's two long walls. It is similar to a gantry crane. Overhead cranes typically consist of a hoist to lift the items, the bridge, which spans the area covered by the crane, and a trolley to move along the bridge.
A crane (also known as a bridge crane or overhead crane) is a type of machine used for lifting, generally equipped with a hoist) (also called a wire rope drum), wire ropes or chains and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines like a hoist to create mechanical advantage and thus move loads beyond the normal capability of a human. Cranes are commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment.
The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human treadwheels, permitting the lifting of heavier weights. In the High Middle Ages, harbour cranes were introduced to load and unload ships and assist with their construction – some were built into stone towers for extra strength and stability. The earliest cranes were constructed from wood, but cast iron and steel took over with the coming of the Industrial Revolution.
For many centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first 'mechanical' power was provided by steam engines, the earliest steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Modern cranes usually use internal combustion engines or electric motors and hydraulic systems to provide a much greater lifting capability than was previously possible, although manual cranes are still utilised where the provision of power would be uneconomic.
Cranes exist in an enormous variety of forms – each tailored to a specific use. Sometimes sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings. For a while, mini - cranes are also used for constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships.
This article also covers lifting machines that do not strictly fit the above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes.
A top running crane is an electric overhead traveling crane having the end trucks supported on rails attached to the top of the crane runways
An overhead traveling crane is a crane with a single or multiple girder (bridge girder) bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure
A runway is an assembly of rails, beams, girders, brackets and framework on which a crane or trolley travels
An I-beam crane is an overhead traveling bridge crane that utilizes standard I-beams (S beams) as the bridge girder and at times, also utilizes I-beams as the runway beams. Cranes that utilize H-beams (structural beams) as girders and runways are sometimes referred to as I-beam cranes as opposed to patented track cranes
A box girder crane is an overhead travelling crane that utilizes a "box" configuration in fabricating the bridge girder. This box girder design incorporates a four-sided box with a running surface plate for the hoist trolley attached to the bottom of the box. The advantage of the box girder is that it possesses greater loading capabilities and is able to span greater bridge distances. The crane is generally utilized in pairs with the hoisting mechanism operating on rails attached to the top of each box girder
A jib crane is a stationary or fixed crane that utilizes a cantilevered bridge (girder) supported from a stationary vertical support. A jib crane consists of a hoist attached to a rotating arm that functions as a manipulator. The arm can rotate 360 degrees and is mounted on a wall or attached to a floor-mounted support.
Jib cranes can have varying boom styles, including some that articulate or pivot. Jib cranes may also mount to walls, ceilings or floors, or may be portable.
The bottom block is the device at the bottom of a hoist's lifting medium (chain/wire rope) through which the medium is reeved and supports the hook and/or an attachment. It may be stationary or rotating depending upon the requirements for the piece of lifting equipment
Material handling is the movement, storage, control and protection of materials, goods and products throughout the process of manufacturing, distribution, consumption and disposal. The focus is on the methods, mechanical equipment, systems and related controls used to achieve these functions. See also, supply chain, supply chain management, logistics and third party logistics. Note that all of referenced terms are highly interrelated and their definitions are frequently intermingled.