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-------------------------------||C R A N E S||------------------------------
A crane is a mechanical lifting device equipped with a winder, wire ropes and sheaves that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines 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.
----------------------------------------||Overview||-------------------------------------
The first 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 tread wheels, 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 stonne 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 utilized where the provision of power would be uneconomic.
Cranes exist in an enormous variety of forms – each tailored to a specific use. Sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings, and the largest floating cranes, used to build oil rigs and salvage sunken ships.
------------------------------------||History of cranes||------------------------------
The cranes have found many uses since the beginning of the history, and the history of cranes has come across since then. The Greek were the first people to use cranes for doing the lifting jobs. After this many other peoples like the Roman, the Chinese etc used the cranes and made many changes to the existing design of that time.
||Ancient Greek cranes||
The crane for lifting heavy loads was invented by the ancient Greeks in the late 6th century BC.[1] The archaeological record shows that no later than c.515 BC distinctive cuttings for both lifting tongs and Lewis irons begin to appear on stonne blocks of Greek temples. Since these holes point at the use of a lifting device, and since they are to be found either above the centre of gravity of the block, or in pairs equidistant from a point over the centre of gravity, they are regarded by archaeologists as the positive evidence required for the existence of the crane.[1]
The introduction of the winch and pulley hoist soon led to a widespread replacement of ramps as the main means of vertical motion. For the next two hundred years, Greek building sites witnessed a sharp drop in the weights handled, as the new lifting technique made the use of several smaller stonnes more practical than of fewer larger ones. In contrast to the archaic period with its tendency to ever-increasing block sizes, Greek temples of the classical age like the Parthenon invariably featured stonne blocks weighing less than 15-20 tons. Also, the practice of erecting large monolithic columns was practically abandoned in favour of using several column drums.
Although the exact circumstances of the shift from the ramp to the crane technology remain unclear, it has been argued that the volatile social and political conditions of Greece were more suitable to the employment of small, professional construction teams than of large bodies of unskilled labour, making the crane more preferable to the Greek polis than the more labour-intensive ramp which had been the norm in the autocratic societies of Egypt or Assyria.[2]
The first unequivocal literary evidence for the existence of the compound pulley system appears in the Mechanical Problems (Mech. 18, 853a32-853b13) attributed to Aristotle (384-322 BC), but perhaps composed at a slightly later date. Around the same time, block sizes at Greek temples began to match their archaic predecessors again, indicating that the more sophisticated compound pulley must have found its way to Greek construction sites by then.
||Ancient Roman cranes||
The heyday of crane in ancient times came under the Roman Empire, when construction activity soared and buildings reached enormous dimensions. The Romans adopted the Greek crane and developed it further. We are relatively well informed about their lifting techniques thanks to rather lengthy accounts by the engineers Vitruvius (De Architectura 10.2, 1-10) and Heron of Alexandria (Mechanica 3.2-5). There are also two surviving reliefs of Roman tread wheel cranes offering pictorial evidence, with the Haterii tombstonne from the late first century AD being particularly detailed.
The simplest Roman crane, the Trispastos, consisted of a single-beam jib, a winch, a rope, and a block containing three pulleys. Having thus a mechanical advantage of 3:1, it has been calculated that a single man working the winch could raise 150 kg (3 pulleys x 50 kg = 150), assuming that 50 kg represent the maximum effort a man can exert over a longer time period. Heavier crane types featured five pulleys (Pentaspastos) or, in case of the largest one, a set of three by five pulleys (Polyspastos) and came with two, three or four masts, depending on the maximum load. The Polyspastos, when worked by four men at both sides of the winch, could already lift 3000 kg (3 ropes x 5 pulleys x 4 men x 50 kg = 3000 kg).
In case the winch was replaced by a treadwheel, the maximum load even doubled to 6000 kg at only half the crew, since the treadwheel possesses a much bigger mechanical advantage due to its larger diameter. This meant that, in comparison to the construction of the Egyptian Pyramids, where about 50 men were needed to move a 2.5 ton stonne block up the ramp (50 kg per person), the lifting capability of the Roman Polyspastos proved to be 60 times higher (3000 kg per person).
However, numerous extant Roman buildings which feature much heavier stonne blocks than those handled by the Polyspastos indicate that the overall lifting capability of the Romans went far beyond that of any single crane. At the temple of Jupiter at Baalbek, for incidence, the architraves blocks weigh up to 60 tons each, and the corner cornices blocks even over 100 tons, all of them raised to a height of ca. 19 m above the ground. In Rome, the capital block of Trajan's Column weighs 53.3 tons which had to be lifted at a height of ca. 34 m.
It is assumed that Roman engineers accomplished lifting these extraordinary weights by two measures: First, as suggested by Heron, a lifting tower was set up, whose four masts were arranged in the shape of a quadrangle with parallel sides, not unlike a siege tower, but with the column in the middle of the structure (Mechanica 3.5). Second, a multitude of capstans were placed on the ground around the tower, for, although having a lower leverage ratio than treadwheels, capstans could be set up in higher numbers and run by more men (and, moreover, by draught animals).[7] This use of multiple capstans is also described by Ammianus Marcellinus (17.4.15) in connection with the lifting of the Lateranense obelisk in the Circus Maximus (ca. 357 AD). The maximum lifting capability of a single capstan can be established by the number of lewis iron holes bored into the monolith. In case of the Baalbek architrave blocks, which weigh between 55 and 60 tons, eight extant holes suggest an allowance of 7.5 ton per lewis iron, that is per capstan. Lifting such heavy weights in a concerted action required a great amount of coordination between the work groups applying the force to the capstans.
||Mechanics and operation||
In contrast to modern cranes, medieval cranes and hoists - much like their counterparts in Greece and Rome- were primarily capable of a vertical lift, and not used to move loads for a considerable distance horizontally as well. Accordingly, lifting work was organized at the workplace in a different way than today. In building construction, for example, it is assumed that the crane lifted the stonne blocks either from the bottom directly into place,[or from a place opposite the centre of the wall from where it could deliver the blocks for two teams working at each end of the wall.
Additionally, the crane master who usually gave orders at the treadwheel workers from outside the crane was able to manipulate the movement laterally by a small rope attached to the load. Slewing cranes which allowed a rotation of the load and were thus particularly suited for dockside work appeared as early as 1340.While ashlar blocks were directly lifted by sling, lewis or devil's clamp (German Teufelskralle), other objects were placed before in containers like pallets, baskets, wooden boxes or barrels.
It is noteworthy that medieval cranes rarely featured ratchets or brakes to forestall the load from running backward. This curious absence is explained by the high friction force exercised by medieval treadwheels which normally prevented the wheel from accelerating beyond control.
||Harbor cranes||
Beyond the modern warship stands a crane constructed in 1742, used for mounting masts to largesailing vessels.
According to the “present state of knowledge” unknown in antiquity, stationary harbor cranes are considered a new development of the Middle Ages. The typical harbor crane was a pivoting structure equipped with double treadwheels. These cranes were placed docksides for the loading and unloading of cargo where they replaced or complemented older lifting methods like see-saws, winches and yards.
Two different types of harbor cranes can be identified with a varying geographical distribution: While gantry cranes which pivoted on a central vertical axle were commonly found at the Flemish and Dutch coastside, German sea and inland harbors typically featured tower cranes where the windlass and treadwheels were situated in a solid tower with only jib arm and roof rotating. Interestingly, dockside cranes were not adopted in the Mediterranean region and the highly developed Italian ports where authorities continued to rely on the more labor-intensive method of unloading goods by ramps beyond the middle Ages.
Unlike construction cranes where the work speed was determined by the relatively slow progress of the masons, harbor cranes usually featured double treadwheels to speed up loading. The two treadwheels whose diameter is estimated to be 4 m or larger were attached to each side of the axle and rotated together.[11] Today, according to one survey, fifteen treadwheel harbor cranes from pre-industrial times are still extant throughout Europe.]Beside these stationary cranes, floating cranes which could be flexibly deployed in the whole port basin came into use by the 14th century.
||Mechanical principles||
There are two major considerations that are taken into account in the design of cranes. The first is that the crane must be able to lift a load of a specified weight and the second is that the crane must remain stable and not topple over when the load is lifted and moved to another location.
Lifting capacity
Cranes illustrate the use of one or more simple machines to create mechanical advantage.
THE LEVER. A balance crane contains a horizontal beam (the lever) pivoted about a point called the fulcrum. The principle of the lever allows a heavy load attached to the shorter end of the beam to be lifted by a smaller force applied in the opposite direction to the longer end of the beam. The ratio of the load's weight to the applied force is equal to the ratio of the lengths of the longer arm and the shorter arm, and is called the mechanical advantage.
THE PULLEY. A jib crane contains a tilted strut (the jib) that supports a fixed pulley block. Cables are wrapped multiple times round the fixed block and round another block attached to the load. When the free end of the cable is pulled by hand or by a winding machine, the pulley system delivers a force to the load that is equal to the applied force multiplied by the number of lengths of cable passing between the two blocks. This number is the mechanical advantage.
THE HYDRAULIC CYLINDER. This can be used directly to lift the load (as with a HIAB), or indirectly to move the jib or beam that carries another lifting device.
Cranes, like all machines, obey the principle of conservation of energy. This means that the energy delivered to the load cannot exceed the energy put into the machine. For example, if a pulley system multiplies the applied force by ten, then the load moves only one tenth as far as the applied force. Since energy is proportional to force multiplied by distance, the output energy is kept roughly equal to the input energy (in practice slightly less, because some energy is lost to friction and other inefficiencies).
||Stability of crane||
In order for a crane to be stable, the sum of all moments about any point such as the base of the crane must equate to zero. In practice, the magnitude of load that is permitted to be lifted (called the "rated load" in the US) is some value less than the load that will cause the crane to tip. Under US standards for mobile cranes, the stability-limited rated load for a crawler crane is 75% of the tipping load. The stability-limited rated load for a mobile crane supported on outriggers is 85% of the tipping load.
----------------------------------||Types Of Cranes||-------------------------------
||Railroad cranes||
A railroad crane is a crane with flanged wheels, used by railroads. The simplest form is just a crane mounted on a railroad car or on a flatcar. More capable devices are purpose-built.
Different types of crane are used for maintenances work, recovery operations and freight loading in goods yards.
||Mobile crane||
The most basic type of mobile crane consists of a steel truss or telescopic boom mounted on a mobile platform, which may be rail, wheeled (including "truck" carriers) or caterpillar tracks. The boom is hinged at the bottom, and can be raised and lowered by cables or by hydraulic cylinders. A hook is suspended from the top of the boom by wire rope and sheaves. The wire ropes are operated by whatever prime movers the designers have available, operating through a variety of transmissions. Steam engines, electric motors and internal combustion engines (IC) have all been used. Older cranes' transmissions tended to be clutches. This was later modified when using IC engines to match the steam engines "max torque at zero speed" characteristic by the addition of a hydrokinetic element culminating in controlled torque converters. The operational advantages of this arrangement can now be achieved by electronic control of hydrostatic drives, which for size and other considerations is becoming standard. Some examples of this type of crane can be converted to a demolition crane by adding a demolition ball, or to an earthmover by adding a clamshell bucket or a dragline and scoop, although design details can limit their effectiveness.To increase the horizontal reach of the hoist, the boom may be extended by adding a jib to the top. The jib can be fixed or, in more complex cranes, luffing (that is, able to be raised and lowered).
||Telescopic crane||
A telescopic crane has a boom that consists of a number of tubes fitted one inside the other. A hydraulic or other powered mechanism extends or retracts the tubes to increase or decrease the total length of the boom. These types of booms are often used for short term construction projects, rescue jobs, lifting boats in and out of the water, etc. The relative compactness of telescopic booms makes them adaptable for many mobile applications.
||Tower crane||
The tower crane is a modern form of balance crane. Fixed to the ground (or "jacked up" and supported by the structure as the structure is being built), tower cranes often give the best combination of height and lifting capacity and are used in the construction of tall buildings. To save space and to provide stability the vertical part of the crane is often braced onto the completed structure which is normally the concrete lift shaft in the center of the building. A horizontal boom is balanced asymmetrically across the top of the tower. Its short arm carries a counterweight of concrete blocks, and its long arm carries the lifting gear. The crane operator either sits in a cabin at the top of the tower or controls the crane by radio remote control from the ground, usually standing near the load. In the first case the operator's cabin is located at the top of the tower just below the horizontal boom. The boom is mounted on a slewing bearing and is rotated by means of a slewing motor. The lifting hook is operated by a system of sheaves.
A tower crane is usually assembled by a telescopic crane of smaller lifting capacity but greater height and in the case of tower cranes that have risen while constructing very tall skyscrapers, a smaller crane (or derrick) will sometimes be lifted to the roof of the completed tower to dismantle the tower crane afterwards. A self-assembling tower crane lifts itself off the ground using jacks, allowing the next section of the tower to be inserted at ground level.
||Hammerhead crane||
The hammerhead, or giant cantilever, crane is a fixed-jib crane consisting of a steel-braced tower on which revolves a large, horizontal, double cantilever; the forward part of this cantilever or jib carries the lifting trolley, the jib is extended backwards in order to form a support for the machinery and counter-balancing weight. In addition to the motions of lifting and revolving, there is provided a so-called "racking " motion, by which the lifting trolley, with the load suspended, can be moved in and out along the jib without altering the level of the load. Such horizontal movement of the load is a marked feature of later crane design. Hammerhead cranes are generally constructed in large sizes, up to 350 tons.
The design evolved first in Germany around the turn of the 19th century and was adopted for use in British shipyards to support the battleship construction program from 1904-1914. The ability of the hammerhead crane to lift heavy weights was useful for installing large pieces of battleships such as armour plate and gun barrels. Hammerhead cranes were also installed in naval shipyards in Japan and in the USA. The British Government also installed a hammerhead crane at the Singapore Naval Base (1938) and later a copy of the crane was installed at Garden Island Naval Dockyard in Sydney (1951). These cranes provided repair support for the battle fleet operating far from Great Britain.
The principal engineering firm for hammerhead cranes in the British empire was Sir William Arrol & Co Ltd
||Truck-mounted cranes||
A crane mounted on a truck carrier provides the mobility for this type of crane.
Generally, these cranes are designed to be able to travel on streets and highways, eliminating the need for special equipment to transport a crane to the jobsite. When working on the jobsite, outriggers are extended horizontally from the chassis then down vertically to level and stabilize the crane while stationary and hoisting. Many truck cranes possess limited slow-travelling capability (just a few miles per hour) while suspending a load. Great care must be taken not to swing the load sideways from the direction of travel, as most of the anti-tipping stability then lies in the strength and stiffness of the chassis suspension. Most cranes of this type also have moving counterweights for stabilization beyond that of the outriggers. Loads suspended directly over the rear remain more stable, as most of the weight of the truck crane itself then acts as a counterweight to the load. Factory-calculated charts (or electronic safeguards) are used by the crane operator to determine the maximum safe loads for stationary (outriggered) work as well as (on-rubber) loads and travelling speeds.
Truck cranes range in size from about 14.5 US Tons to about 120 US tons.
||Rough terrain crane||
A crane mounted on an undercarriage with four rubber tires that is designed for pick-and-carry operations and for off-road and "rough terrain" applications. Outriggers that extend horizontally and vertically are used to level and stabilize the crane for hoisting. These telescopic cranes are single-engine machines where the same engine is used for powering the undercarriage as is used for powering the crane, similar to a crawler crane. However, in a rough terrain crane, the engine is usually mounted in the undercarriage rather than in the upper, like the crawler crane. HAC Cranes is one of the top leading dealers in the nation.
||Crawler crane||
A crawler is a crane mounted on an undercarriage with a set of tracks that provide for the stability and mobility of the crane. Crawler cranes have both advantages and disadvantages depending on their intended use. The main advantage of a crawler is that they can move on site and perform lifts with very little set-up, as the crane is stable on its tracks with no outriggers. In addition, a crawler crane is capable of traveling with a load. The main disadvantage of a crawler crane is that they are very heavy, and cannot easily be moved from one job site to the next without significant expense. Typically, a large crawler must be disassembled and moved by trucks, rail cars or ships to be transported to its next location.
||Gantry crane||
Portainer gantry cranes at the Hamburg Harbour
A gantry crane has a hoist in a trolley which runs horizontally along gantry rails, usually fitted underneath a beam spanning between uprights which themselves have wheels so that the whole crane can move at right angles to the direction of the gantry rails. These cranes come in all sizes, and some can move very heavy loads, particularly the extremely large examples used in shipyards or industrial installations . A special version is the container crane (or "Portainer" crane, named after the first manufacturer), designed for loading and unloading ship-borne containers at a port.
||Overhead crane||
Also known as a "suspended crane", this type of crane works in the same way as a gantry crane but without uprights. The hoist is on a trolley which moves in one direction along one or two beams, which move at right angles to that direction along elevated tracks, often mounted along the side walls of an assembly area in a factory. Some of them can lift very heavy loads.
||Floating crane||
Floating cranes are used mainly in bridge building and port construction, but they are also used for occasional loading and unloading of especially heavy or awkward loads on and off ships. Some floating cranes are mounted on a pontoon, others are specialized crane barges with a lifting capacity exceeding 10,000 tons and have been used to transport entire bridge sections. Floating cranes have also been used to salvage sunken ships.
Crane vessels are often used in offshore construction. The largest revolving cranes can be found on SSCV Thialf, which has two cranes with a capacity of 7,100 metric tons each.
||Vessel (Deck) crane||
Located on the ships and used for cargo operations which allows to reduce costs by avoiding usage of the shore cranes. Also vital in small seaports where no shore cranes available. Mostly are electric, hydraulic, electro-hydraulic driven.
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|Aerial crane||
Aerial cranes usually extend from helicopters to lift large loads. Helicopters are able to travel to and lift in areas that are more difficult to reach by a conventional crane. Aerial helicopter cranes are most commonly used to lift units/loads onto shopping centers, multi-story buildings, highrises, etc. However, they can lift basically anything within their lifting capacity, (i.e. cars, boats, swimming pools, etc.). They also work as disaster relief after natural disasters for clean-up, and during wild-fires they are able to carry huge buckets of water over fires to put them out.
Examples include:
Sikorsky S-64 Skycrane/Erickson Air Crane - civilian version
CH-54 Tarhe - military version
Mi-26 - Russian flying crane helicopter
||Jib crane||
A Jib crane is a type of crane where a horizontal member (jib or boom), supporting a moveable hoist, is fixed to a wall or to a floor-mounted pillar. Jib cranes are used in industrial premises and on military vehicles
The jib may swing through an arc, to give additional lateral movement, or be fixed. Similar cranes, often known simply as hoists, were fitted on the top floor of warehouse buildings to enable goods to be lifted to all floors.
||Crane-like machines||
The generally-accepted definition of a crane is a machine for lifting and moving heavy objects by means of ropes or cables suspended from a movable arm. As such, a lifting machine that does not use cables, or else provides only vertical and not horizontal movement, cannot strictly be called a 'crane'.
Types of crane-like lifting machine include:
Block and tackle
Capstan (nautical)
Hoist (device)
Winch
Windlass
More technically-advanced types of such lifting machines are often known as 'cranes', regardless of the official definition of the term. Some notable examples follow:
||Loader crane||
A loader crane offloading aerated concrete bricks at a building site
A loader crane (also called a knuckle-boom crane) is a hydraulically-powered articulated arm fitted to a truck or trailer, and is used for loading/unloading the vehicle. The numerous jointed sections can be folded into a small space when the crane is not in use. One or more of the sections may be telescopic. Often the crane will have a degree of automation and be able to unload or stow itself without an operator's instruction.Unlike most cranes, the operator must move around the vehicle to be able to view his load; hence modern cranes may be fitted with a portable cabled or radio-linked control system to supplement the crane-mounted hydraulic control levers.
In the UK, this type of crane is almost invariably known colloquially as a "Hiab", partly because this manufacturer invented the loader crane and was first into the UK market, and partly because the distinctive name was displayed prominently on the boom arm.
||Rolloader crane||
This is a loader crane mounted on a chassis with wheels. This chassis can ride on the trailer. Because the crane can move on the trailer, it can be a light crane, so the trailer is allowed to transport more goods. Manufacturer of rolloader cranes include the Dutch Kennis and the Finnish company Hiab (Hydrauliska Industry AB).
||Stacker crane||
A crane with a forklift type mechanism used in automated (computer controlled) warehouses (known as an automated storage and retrieval system (AS/RS)). The crane moves on a track in an aisle of the warehouse. The fork can be raised or lowered to any of the levels of a storage rack and can be extended into the rack to store and retrieve product. The product can in some cases be as large as an automobile. Stacker cranes are often used in the large freezer warehouses of frozen food manufacturers.
----------------------||OVER VIEW OF EOT CRANES||-------------------
An overhead crane typically consists of three important parts:
The hoist providing up/down motion of the load item.
The trolley, providing left/right for the hoist and the load.
The bridge providing the back/forward motion of the hoist, trolley and the load.
A EOT crane is permanently installed in a factory, shop or ware house to move the items which cannot be moved by human beings.
||Use of overhead cranes||
Single grinder cranes find applications in Steel plants, Induction Furnaces, Paper mills, Cold Rolling mills, Arc Furnace, Pipe mills, Power plants, Hydro Power plant, Heavy Engineering industries, Container Handling, Dyeing Plants/Woolen mills, Chemical & Pharmaceutical units, Petrochemical industry.
Double girder cranes find application in Induction Furnace, Arc Furnace,Cold Rolling Mills, Paper Mills, Pipe Mills and Heavy Engineering Industry.
---------||HOISTS||---------
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 you are using them in different places, you still need the tracks in place to enable them to work at all the places you require. 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.
-----------------||SOME RELATED TERMS WITH CRANES||-----------------
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. The load is attached to the hoist by means of a lifting hook.
SIMPLE MACHINE: In physics, a simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance. The amount of work required to achieve a set objective is constant; however the force required can be reduced provided the lesser force is applied over a longer distance. The ratio between the two forces is the mechanical advantage.
MECHANICAL ADVANTAGES: In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it.The ratio A:B is called mechanical advantage.
HYDRAULICS: Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion.
LIFTING HOOK: A lifting hook is a device for grabbing and lifting loads by means of a device such as a hoist or crane. Lifting hooks are usually equipped with a safety latch to prevent the disengagement of the lifting wire rope sling, chain or rope to which the load is attached. Hook may have one or more built - in pulleys to amplify the lifting force.
WIRE ROPE: Wire rope consists of several strands laid (or 'twisted') together like a helix. Each strand is likewise made of metal wires laid together like a helix. Initially wrought iron wires were used, but today steel is the main material used for wire ropes.
||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 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
----||SIMPLER HOIST DESIGN REDUCES COSTS||-----
In brief, the hoist has a drive that is formed with an integral decelerator and brake flanged on one side of the main frame. The drive decelerator and brake are formed as a single body and the traveler can be detached from its mounting simply. This is said to make installation and exchange easy, reducing maintenance costs. This is operated together with the wire-rope drum by a drive motor mounted on the opposite side of the flange.
A traveler unit connected below the main frame has wheels coupled to bearings on both sides of the unit through a bored space. Each wheel has an involutes spine gear groove on its centre bore matching a groove gear on the drive shaft. This design reduces the weight and volume of the main frame compared to previous designs, thereby making production costs lower. Other claims include reduced transports costs and simpler installation.
Existing art problems
According to the earlier laws, one type of conventional electric hoist has an intermediate shaft, connected to the traction motor, and extending through the inside of the wire-rope drum to a decelerator and electromagnetic brake. This makes it comparatively long, causing a loss in power. Any widening of the wire-rope drum also means that the intermediate shaft has to be lengthened, but the wire-rope drum cannot be increased over a predetermined width. The conventional design also means that the extended intermediate shaft rotates with the lifting operation of the hoist.
It is claimed that a high speed in the intermediate shaft causes vibration, which can damage the object being lifted. Avoiding this problem by rotating the intermediate shaft at a predetermined speed limits the speed and capacity of the traction motor, and thus limits the weight of the object that can be conveyed by the hoist.
An existing design of hoist, adapted to carry heavier objects, uses a motor rotating at high speed. In this a decelerator, hoisting traction motor and brake are mounted at one side of the drum with a horizontal arrangement on the upper portion of a main frame, also carrying the wire-rope drum. Four wheels on the corners of the frame each have a travelling decelerator, travelling motor and brake formed at one side of each to operate in cooperation. This arrangement of horizontal fixing means that each part occupies a relatively large space, resulting in a bulky structure. The large weight increases installation and production costs.
The design employs a sheave to support the wire-rope drum at its centre and perpendicular to it. This gives an angular differential to the object being transported, necessitating a capacity of hoist traction motor greater than the weight of object being carried, again increasing production costs.
The decelerator is housed in a gearbox with upper and lower portions containing lubricating oil. This may result in oil leakage through connections over a long period of time. In addition, the couplings of the decelerator, traction motor and wire-rope drum are force fittings that cause difficulties in assembly, disassembly, maintenance and repair.
The travelling wheels, driven in cooperation with each other, are integral with the main frame of the hoist, causing higher conveyance costs and high installation costs for high-capacity hoists.
An Idea
The invention tackles these problems with a winding sheave at the lower part of the winding drum connected to a driving sheave with a lifting hook to operate in parallel with each other. All the parts can be packaged separately for transport to the installation site, to make installation work easy and reduce transport costs. The travelling section is detachably mounted to the lower part of the main frame. Each of the parts can be exchanged in accordance with the load and size of the object, helping to standardize the product’s components, and improves power efficiency through connecting the parts in series.
The previously mentioned spline gear couplings on each of the travelling wheels and drive shafts makes the assembly process easier and increases the rotational efficiency of the couplings between the gears.
------||LOAD HOIST ARRANGEMENT||--------
There are load hoist arrangements that enable a manually-guided load moving in three dimensions to be driven by sensing the lateral movement of a lifting cable. These designs often have a problem with self-induced vibrations or excessive swinging. The changes in acceleration and direction, induced manually by the operator to the load-carrying device often make it start to swing. Once it has started to swing, it is difficult to stop, especially if the load is heavy, decreasing the system's maneuverability and increasing the risk of accidents.
A load hoist arrangement consists of a traversing device with traveling bridge and carriage. Two motors on the support structure drive cables that pull the traveling bridge in either direction.
But the design has some drawbacks. There is a need for a load hoist arrangement that supports motions in both lateral directions and not only along a line. By positioning the motors on the support structure, the design makes a relatively stable working environment. However, there are a lot of cables connecting static components with moving parts. These cables often connect to sensitive connections and couplings that will be prone to wear in this dynamic environment, risking less accurate motion control and increasing the need for maintenance. There is also a need for a load hoist arrangement that is easy and quick to install.
The invention is designed to overcome these issues and be capable of handling manually-induced accelerations, maintaining stability in the load hoist arrangement even when handling heavy goods.
A control device is arranged along a lifting cable between a traverse device and load-carrying device. This load-carrying device is manually guidable in a three-dimensional space. A driving device controls the lateral movement of the load carrying device.
The vertical motion is not part of this patent. An industry-standard electronically-controlled balancer controls the vertical motion of the load-carrying device. A transmitter in the control device that tells the hoist to compensate for any load, so that an operator guiding the crane manually will experience a fraction of the total resistance of the load.
The driving device comprises two motors secured to carriage. The ends of two drag cables and are secured to opposite ends of the supporting rails and cross at traveling bridge. The drag cables cross each other at the carriage so that a driving wheel unit of one motor works in contact with one drags element
The axle unit has two separate grooves, one for each drag cable. The combination of the two drag cable paths, each working in a different direction, locks the axle unit, providing the driving device with increased stability. The drag elements are arranged to turn in a 90 degree angle around a pulley from their anchor point to the carriage. With this arrangement, possible imperfections will be almost automatically corrected because the two drag cables working in opposition to each other.
The friction between the drag element and possible guide wheels axle units and driving wheel units together with the drag cable path will prevent the drag cable from sliding when the driving device is in operation.
The carriage is moved by actuation of the two motors and hence the load carrying device will follow. The motors are capable of clockwise and counter-clockwise motion.
The motors are actuated by the movement of the load. The angle of a load-carrying element is used as reference of force impact for guiding and controlling the driving device, and thus the load carrying device in a lateral direction. The traverse device moves in proportion to the force manually applied by the operator. This allows a controlled movement of the load carrying device relieving the operator from bearing the actual weight of the load while still being able to lift and move them.
The invented driving device is easy to manufacture and install since the carriage can be made in a standardized manner and the support structure together with the drag elements are simple to adapt to suit the location in question. Furthermore, the need for control data transmission cables is limited to a zone near the carriage. This design reduces the need for cable racks interconnecting motors and sensors.
Since it is a dynamic system, often covering a large working area, and frequently used, the risk for play in the interconnections of the control system, e.g. motors, transmitters and recording sensors,may lead to downtime and reduced productivity
THE DESIGN
We are concerned with the design of the hoisting arrangement of 2 tonne capacity of EOT crane ,which will lift the load up to a distance of 8 meters
1.DESIGN OF HOOK
Selection of section : The section is trapezoidal
Selection of material : Mild steel
Load to lift : 2 tonne
Considering 50 % over loading.
So the design load = 2 tonne+50% of 2 tonne = 3tonne
Taking the help of (IS 3815-1969) for selection of material for 8 dimensions of crane hook.In IS 3815-1969 the nearest selection for 3.3 tonne is 3.2 tonne.
For load 3.2, proof load (P) is 6.4 tonne.
So C = 26.73√P = 26.73 x √6.4
= 67.62
≈ 68 mm
A = 2.75 C = 2.75 x 68 ≈ 187 mm
B = 1.31 C = 1.31 x 68 ≈ 89mm
D = 1.44 x C = 1.44 x 68 ≈ 98mm
E = 1.25C = 1.25 x 68 ≈ 85mm
F = C = 68mm
G = 35mm
G1 = M33, Pitch = 6mm (Coarse series)
H = 0.93 x C = 0.93 x 68 ≈ 63mm
J = 0.75 x C = 0.75 x 68 ≈ 51mm
K = 0.92 x C = 63mm
L = 0.7 x C = 0.7 x 68 ≈ 48mm
M = 0.6 x C = 0.6 x 68 ≈ 41mm
N = 1.2 x C = 82mm
P = 0.5 x C = 34mm ≈ 34mm
R = 0.5 x C = 0.5 x 68 ≈
U = 0.33 x C = 0.3 x 68≈20 mm
Checking for strength Area of the section = ½ x 63 x (41+8) = 1543.5 mm2
Centroid from ‘a’
= (.05 x 8 x 65) 63/3+(.5 x 41 x 63) x (2 x 63)/3
½ x 68 x (41+8)
= 38.571mm
= 38.6 mm= h2
So centroid from b = 63-38.6=24.4mm =h1
0 = 34 +24.4 = 58.4mm
r0 = A/(dA/u)
dA/u = [b2+r2/h (b1-b2)] ln r2/r1 – (b1-b2)
=28.65mm
r0 = A/(dA/u) = 1543.5 = 53.87 53.9 mm.
28.65
e= 0-r0 = 58.4 - 53.9 = 4.5mm
Moment
M = -P x 0
= -3 x 58.4
= - 175.2 (tonne x mm)
Stress due to bending is given by
b = M X 4
Ae r0-y
For point a
Y = -(e+h2)
= -(4.5+38.6)
= - 43.1 mm
For point b
Y = r0-r1
= 53.9 – 3.4
= 19.9 mm
Stress due to direct loading = P/A
= 3/1543.5
= 1.9436 x 10-3 Tonne/mm3
Stress due to curvature of ‘a’
ba = - (-175.2) x -43.1
1543.5 x 4.5 {53.99 – (-43.1)}
= 0.0112
So total tress at a
= - 0.0112 + 1.9436 x 10-3
= - 9.2642 x 10-3 Tonne/mm2
= - 9.2642 kg/mm2 -90.85 Mp
Stress due to curvature at b
bb = -(-175.2) x . 19.99 .
1543.5x 4.5 (53.9 – 19.9)
= 0.014763
So total stress at b
=bb + 1.9436 x10-3
=0.014763 + 1.9436 x 10-3
=0.0167 tonne/mm2
= 16.7 Kg/mm2 163.84 MPa
Let the material be class 4 carbon steel ( 55C 8)
Ultimate tensil strength I 710MPa
Design strength = Ultimate tensil strength
Factor of safety
= 710/4
= 177.5 MPa
163.84 > 177.5
So design is safe
Determination of length of threaded portion
Pitch = 6mm
Nominal dia of thread = 33 mm (G1) = d
Considering the screw and thread are of single safest & square mean diameter of screw =
dm = d- (p/2)
= 33 – (6/2)
= 30
tan = 1/dm = 6/( x 30)
tan = tan-1 { 6/( x 30)} = 3.640
Let the co-efficient of fraction be 0.15
So = tan = 0.15
= 8.530
Torque required to resist the load
T = W x dm* tan ( + )
2
Where w is the weight of load is 3 tonne and the load of the hook itself.
The maximum weight of the hook is 50kg (from the use of the soft ware ‘Pro-Engineer’)
So
T = 3050x 30 x tan (3.61+ 8.53)
2
=9866.42 Kgmm
Stress induced in the screw
Direct tensible stress (allowable or design)
=4w/ d02
d0 = core diameter of the screw.
dc = d-p = 33-6 = 27 mm
1 = 4x 3050
272
= 5.326 kg/mm2 52.24MR
Torssional shear stress
= 16T = 16x9866.42
de3 x 273
= 2.5529 Kg/mm2 = 25MP
Maximum shear stress in the screw
max = ½ (2 + 4 2)
= ½ √ (52.242 + 4 x 252)
= max = 36.15Mpa
Height of the nut
a)Considering bearing action between the thread in engagement.
Let ‘n’ is no of thread in engagement with screw.
Considering bearing action between nut & screw.
Let the permissible bearing pressure =pi= 6 MR.
We know
Pi = 4W
(d2-dc2) x n
So 6 = 4x3050 x 9.8
(332-272) x n
N = 4 x 3050 x 9.8
(332-272) x 6
1.27 x 9.8
12.5
So the height of the nut is = 2 x 12.5 = 25mm.
b) Considering shear failure of thread across root
Shear stress induced
= . W .
dc(0.5xP) xn
= . 3050 x 9.8 .
x 27 x (0.5 x 6) x n
= 117.46
n
= 0.5 x 177.5 = 117.46
n n
= 117.46
177.5 x0.5
= 1.32 = 2
So height is n x p = 2 x 6 =12mm
Tacking the highest value 25mm
Design of pin which will carry the dead load & the load of hook.
We have to determine the dimension of ‘t’.
n = M x Y
I
= M x (24)
I 2
Where “I” is moment of inertial about bh3 t x 243 x 2
12 12
Maximum bending moment for = M = ¼ x W x L
Let L = 70 mm
So M = ¼ x 3050 x 70 = 2 x 26687.5 Kgmm.
= 2 x 261.715 x 103 N-mm
= 2x 261.715 x 103 x 24
1 t x 243 2
177.5 = 1363 x 2
t
t = 1363 x 2 = 7.8 x 2 15.2 MM
177.5
16 mm
Taking 20 m for additional safety
Diameter of the projected portion
The projected position is undergo only shearing failure.
Design shear stress = 0.5 x design tensive stress.
Force action on each side i.e. projected portion is
3050/2 =1525 kg 14.95 x 103
15 KN
So the minimum value of the height of the projected portion is 15mm, taking n= 40mm for screwing arrangement.
= 15 x 103
/4 x dk2
= 177.5 x 0.5 = 15 x 103
(/4) dk2
= dk2 = 15 x 103 x 4
177.5 x 0.5 x
= dk2 = 15 x 103 x 4
177.5 x 0.5 x
= 215.19
= 14.66
15mm
Taking 20 mm for additional safety purpose.
So that it can be turned to thread in size ‘m20’.
Height of the projected portion
P * x * dk = w/2
Where p = bearing pressure or crushing stress.
Let p = 210 MPx
Allow crushing stress =210/4 =
210/4 x x x 20 = 3050 x 9.8
2
x = 3050 x 9.8 x 5
2 x 20 x 210
= 3.56 mm x 4
= 14.024 =15 mm
So the minimum value of the height of the projected portion is 15 mm, taking x = 40 mm for
screwing arrangement.
Design of link and the cover plate
[caption id="attachment_78" align="aligncenter" width="300" caption="coverplate"]
[/caption]Thickness of link and cover plate should not be minimum.
Let the material be (55C8).
a)Hole fopr placing the pin which will carry the hook will be ‘dk’ i.e. 20 mm.
zchecking for the failure of link & cover plate combindely(as they are of same material and undergone same condition of failure).
Mode of failure
Tearing of cover plate & link at the edge.
Crushing of cover plate and link.
Breaking at the lowest cross section.
i).Considering tearing of cover plate & link at the edge
Experiments from the riveted joints have shown that if the distance between the centre of rivet
and the edge is 1.5 times the diameter of the rivet.The element will not undergo the failure of tearing at the edge.
The same condition is also applicable in our case.
But for more safety reasons taking the distance between the centre of the projected element and the edge of the cover plate & linkis 2 times the dia of the projected element.
So Z = 2 x dk
= 2 x 20 = 40 mm
Considering tensile failure at the lower cross section
So σd = w/2
A
177.5 = 3050 x 9.8/2
2 x x x 30
x = 3050 x 9.8/2
2 x 30 x 177.5
= 28/2 mm ≈ 1.4 mm
Considering crushing failure
Force = σcrushing(d) x projected area
3050 x 9.8 = σcrushing(d) x (20 x x)
FOS
= 3050 x 9.8 x 4 = 14.24 mm ≈ 15 mm
2 x 210 x 20
So taking maximum of x i.e 15 mm, So x = 15 mm
[caption id="attachment_74" align="aligncenter" width="300" caption="cover-plate-auto-cad"]
[/caption]AutoCAD drawing Of Cover plate
[caption id="attachment_75" align="aligncenter" width="300" caption="auto_link Auto CAD"]
[/caption]AutoCAD Drawing Of Link
Design of shaft carrying the pulley
[caption id="attachment_79" align="aligncenter" width="300" caption="shaft to carry pully"]
[/caption][caption id="attachment_80" align="aligncenter" width="243" caption="Pulley"]
[/caption]The weight of each cover plate is 2.5 kg.
Weights of each link weigh 2 kg.
So weight of 2 covers plate & 2 link
Is 2 x 2.5 + 2 x 2 = 9 kg.
So the total weight which the shafts carry is 3050 + 9 = 3059 ≈ 3060
Each Side subjected to a load of 3060/2 = 1530 kg.
The shaft is only subjected to
Crushing failure (at the cover plate and link).
Shear failure.
Crushing failure (at the pulley)
Considering shear failure
= f/a
= allowable shear stress
= 0.5 x 177.5 = 0 .5 x 177.5 = 22.2 MR
FOS 4
Stress induced = 1530 x 9.8 = 150042
π/4 x 302 π/4 x 302
= 21.22 MPa
As induced stress is less than that allowable stress, the design is safe
Considering crushing failure at the cover plate
Crushing stress = Force/Protected area
Allowable stress = 240/4 = 60MPa
Induced Crushing stress = Force
Projected area
= 3060 x 9.8
70 x 40
As allowable induced stress 60.86 KN. The selection is feasible.
Design of Sheave
[caption id="attachment_76" align="aligncenter" width="273" caption="sheave"]
[/caption]a = 40mm
b = 30mm
c = 7mm
d = 18mm
e = 1mm
l = 10mm
r = 12mm
r4 = 8mm
h = 25mm
r1 = 4mm
r2 = 3mm
r3 = 12mm
Material is caste iron
Let dia of the sheave = 20 x d
= 20 x 14
= 240mm
The reference is made from Rudenko,N.’Materials Handling Equipment ‘,Mir Publishers, Moscow(1969).
P .86,Table 16.
Drum design
Drum grove size
Referring to Redenko,N “Materials Handing Equipment”,Mir publishers,Moscow (1969),P.No.90 table 17.
Considering standard groove of drum, for, diameter of wire 15 mm as it is nearest to 14mm.
Drum diameter = sheeve diameter = 240 mm.
r 1 = 0.53 x d (d ≈15) = 9mm
s1 = 1.15d = 17mm
C1 = 0.25 d = 5mm
No. of turn on each side of drum
Z = (hi/πd) + 2 =
Where
H = Lifting Height.
I = Ratio of the pulley system.
D = Drum diameter ≈ 45 x 14 = 630
So Z = ( 8.00 x 2) + 2
Π x63
Z = 10
Full lenth of drum for one rope.
L = (2HI + 7)Si (I = 2 assumed)
πD
=(2 x 800 x 2 + 7)1.5
=34.75
≈35 cm
The drum is made up of IS grade = SG 80/2
With stress = 480Mpa
W = 0.02 x 630 = 10
= 22.6
≈ 23 mm
Outside dia of the drum Do = D + 6d
= 630 + 6 x 14 = 714mm
Inside dia of the drum = Di = D – 2W
= 630 – 2 x 25
= 584 mm
Checking of strength
Bending Stress in drum
σbend = 8WLD
π(D4 – Di4)
= 8 x 6200 x 9.8 x 35 x 630
Π x (6304 - 5844)
= 0.0828MP
Maximun Torque
Tmax = W (D + d)
2
= 6200 x 9.8 (630 + 14)
2
= 19.564 x 106
Maximum Shear Stress
= 16 Tmax D
π(D4 – Di4)
= 16 x 19.56 x 106 x 630
π x (6304 - 5844)
≈ 1.523 MPx
Direct Compressive Stress
= W = σc
wSi
= 6200 x 9.8
23 x 17
= 155.4MPx
Maximum Stress in the Drum
σ = √σbend2 + σc2 + 4max2
= (0.08282 +155.42 = 4 x 1.5232)1/2
σ < 480 MPx, S the Design is safe.
Fastening Of Rope With The Drum
For 14 mm dia
Locating Dimension
Pitch of screw = 53 mm
T = 43 mm
Screw size
Lo = 18 mm
L = 50 mm
Plate
C = 7 mm
No. of fastenings = 1
Selection of Motor
W = 3100 kg x 9.8 m/s2
V = 0.2m/sec
So power required = 3100 x 9.8 x 0.2
= 6080.123Nm/sec
= 6.08 Kwatt
Taking 11 Kwatt 3 phase induction motor (flange type) of 11 KW (nearest to 6.08KW)
Frame No. 132 M
Flange designation F265B
The speed is 1000 RPM
By using gear box the speed can be reduced to 300 RPM
GearBox Calculation
Gearbox ratio = (Input RPM x π x rope drum dia)
(speed x no. of falls /2)
= ( 980 x π x .714) = 183.54
(3.00 x 4 )
Brake calculation
Required Brake Torque = 1.5 x 716.2 x mech H.P.
Motor RPM
= 1.5 x 716.2 x 50.12
300
= 53.84 Nm
Design of wormset
Power = P = 6.08 Kwatt
RPM of Worm = Nw = V x 60
πd
= 0.2 x 60
π x 0.63
RPM of Worm Gear NG = 300 RPM
So R = NG
Nw
= 300
6
Let Ф = 14.5o
Let the centre distance = C = 300 mm =0.3m
Pitch circle diameter of the worm
Dw = C.8750 = 3Pc
3.48
Dw = 3.8750 = 0.10020m
3.48
≈ 100mm
Dw = 3Pc = 3Pa = 3 x π x ma
So ma = Dw/3π = 100.2/3π
= 10.63 mm ≈ 11mm
Pitch circle dia of the gear Dg = 2C - Dw = 2x 300 – 100 = 500 mm
Velocity ratio = Ng/Nw = 50
Ng/Nw = Dg /(ma x Nw)
50 = Dg/(11 x Nw)
Dg = 50 x 11 x Nw
Taking Ng = 1 , because Dw is closer to the calculated.
So, Dg = 550
Dw = 2C - Dg
= 2 x 300 -500
= 50mm
Face width of the gear
b = 0.73 x Dw
= 0.73 x 50
= 36.5
= 40 mm
Static strength of Bronze
σd = 90MPa
In worm drive irrespective of materials of worm and worm ger,the gear is weak.
So design should be based on gear.
Tangential load on the gear :
Ft = σ π mn y b
= (σd x Cv)π mn y b
Velocity factor Cv = 6 .
6 + Vg
Vg = π x Dg x Ng
60
= 8.69
Cv = 6 = 0.41
6 + 8.69
Form factor
Y = 0.124 – 0.684
Ng
= 0.11132
Tan λ = m x Nw
Dw
= 11 x 1
50
λ = tan-1 (.22) = 12.4o
Nominal Module = m (ma) x cos λ
= 11 x cos 12.4
= 10.743 mm
Ft = 90 x .41 x π x 1o.743 x .11132 x 40
= 5545.47 N
= 5.55 KN
Power Capacity = P1 = Ft x Vg
= 5.55 x 103 x 8.69
= 48.19 K watt
Which is greater than capacity so the design is safe.
Powe capacity of drive from wear point of view
P2 = Dg x b x W x Vg
= 550 x 40 x W x 8.64
W = .550 = Material combination factor.
For worm and worm gear made up of hardened steel and phosphor bronze
So, P2 = (550 / 1000) x 40 x .55 x 8.64
= 104.4 Kwatt
Power capacityof the drive, from the heat dissipation point of view is given by :
P3 = 3650 x C17
R + 5
= 3650 x 300 17
50 + 5
= 361.99K watt
So The safe power capacity is minimum i.e P1 = 48.19 Kw
CONCLUSION : The design of the hoist of EOT crane is done Numerically .We can implement the design practically in industries for various lifting jobs.
