Mobile crane

A Liebherr LTM 1200-5.1 Crane

Defination

Mobile Crane A cable-controlled crane mounted on crawlers or rubber-tired carriers. A hydraulic-powered crane with a telescoping boom mounted on truck-type carriers or as self-propelled models. .^[1]

History

Truck-mounted crane at bridge constructing.

Before 1870 Cranes were fixed to a selected position except the one which were fixed on railway track which also gave some restricted movement. Steam Power cranes were shown by appleby brothers at Paris in 1867 Vinnea in 1873.Henry Coles (Manager Of Appleby Corp.) in 1922 began producing Truck mounted cranes which cracked the market under the name "The Petrol Electric Lorry Crane".In 1939 the Coles had been acquired by Steel and Co. Ltd. of Sunderland. Major Steps In Development- 1-Adopton of IC engine 1922 2-Invention of telescopic jibs Before 1960 cranes carried additional booms with them to increase height. Which Increased the opreating cost. In 1959 R.H.Neal (Crane Expert) F.Taylor (Hydraulics specialist)And Design Director Bob Lester Intigrated all the three and modernized cranes . Coles Hydra Speedcrane:Appeared in 1962 It further modified with the 10ton fully telescopic hydraulic boom in 1966 followed by the 1968s 30ton military versions with four wheel drive named as Husky. 1972, Steels as a company were suffering from a variety of problems forced to merge with the Acrow Group.Because of this there three most Talanted personalities left them.Lan Hassel, Johnny Johnson who started a new manufacturing processes plant.With backing from the British Crane Hire Corporation they acquired small factory unit and ordered every single element of their product from subcontracted suppliers. In 1976 the Cosmos team had created a 25 ton crane which brought together several state of the art developments. 1977- 25 Ton Crane Appared.

Mobile cranes generally operate a boom from which end a hook is suspended 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.

A mobile crane's advantage is its ease of transportation and its flexibility in handling different types of load or cargo quickly.

The history of mobile cranes in Great Britain

Prior to 1870 cranes were likely to be fixed in position, either on the side of a dock, on the deck of a ship, or mounted on a railway wagon that allowed some movement but only where the railway lines had been constructed.

Appleby Brothers had begun to develop their steam powered railway cranes in the 1860s and displayed them at the Paris exhibition of 1867 and in Vienna 1873.

Henry Coles, general manager of Appleby's later set up his own business which he eventually relocated to Derby, producing improved steam cranes until his death in 1905.

In 1922 the company founded by Henry Coles began producing truck mounted cranes for both the home market and for export, some going as far as Japan and Karachi. The first model was sold under the title of "The Petrol Electric Lorry Crane".

In the 1930 the Coles company, like most British firms, suffered as a result of the world depression, but the re-armament programme on the eve of the Second World War brought the opportunity for expansion, starting with a order in 1937 for 82 of their two-ton cranes, at a price of £750 each, for the RAF.

By 1939 the Coles brand had been acquired by Steel and Co. Ltd. of Sunderland. During the war years production took place in both Derby and on Wearside, but in the post war period was consolidated at Crown Works in the Pallion District of Sunderland.

If the adoption of the internal combustion engine in 1922 had been the first great step forward for mobile cranes, the next was the invention of telescopic jibs. Prior to 1960 it was necessary for the cranes to be accompanied by a truck carrying spare boom sections which could be bolted on to increase the reach of the crane. This called for not only the additional vehicle but also an additional driver, increasing the costs to crane hire companies who hired out the vehicles on a daily basis. In 1959 Steels acquired two new subsidiaries, R. H. Neal, another cranemaker with significant experience in diesel engines, and F. Taylor and Sons of Manchester, a hydraulics specialist. Design Director Bob Lester recognised the importance of bringing together these modern technologies in order to modernise the aging Coles Designs. He was fortunate in being able to promote one of his own team to be manager of the drawing office, John (Johnny) Johnson, who was destined to revolutionise the industry over the next 15 years.

Between 1960 and 1966 Johnson and his co-workers produced a range of exciting new designs.

The Coles Hydra Speedcrane first appeared in 1962, but in May 1966 the ten ton version appeared with a fully telescopic hydraulic boom, generating over 200 immediate orders. By 1968 a 30 ton version was produced for military use. There were also rough terrain versions with 4 wheel drive, referred to as the Husky, as opposed to the Hydra.

In 1972, Steels as a company were suffering from a variety of problems, aging plant, a lack of investment, mindless levels of union militancy and a lack of vision on the board. The company was forced to merge with the Acrow Group, whose most noteworthy product was a metal bar used to hold up partly build structures. It was an excruciating humiliation for the company and a sad reflection on the state of British Industry at that time. Coles Cranes entered into a slow and painful decline.

In response to the takeover of the company three of the more talented members of the management team chose to leave Coles in order to continue to make innovations. Don Hassel, as managing director, and his financial director Ken Dunlop managed to persuade Johnny Johnson (now works manager at Coles) to go with them. Rather than joining a rival firm they decided to take the brave and difficult step of starting a new manufacturing company from scratch. Considering the size and cost of their product this would seem almost impossible to achieve without the support of a multinational parent company or huge financial backer. Johnson's supreme grasp of manufacturing processes offered them an alternative.

With relatively modest backing from the British Crane Hire Corporation they acquired a remarkably small factory unit in a new business park at Alfreton in Derbyshire and ordered every single element of their product from subcontracted suppliers. Everything from chassis and engine down to the last nut and bolt came in on a delivery truck and went out just days later as a finished product. A workforce of a few dozen men were able to produce as much as the thousands employed at Coles Cranes. Rivals attempted to throttle the newly formed company which was forced to defend a number of spurious legal actions, and at one point had to change it's name from Crown Cranes to Cosmos Cranes (Crown Works being the site of the Coles Cranes factory in Sunderland).

The true potential of the new company was reflected in Johnson's innovative designs, which now provided the third great step forward in the history of the truck mounted mobile crane. Having spent his entire career in the field (aside from military service) he had an intuitive grasp of what was needed and what could be done. By 1976 the Cosmos team had created a 25 ton crane which brought together several state of the art developments.

A fluid flywheel clutch assembly enable the vehicles to travel at motorway speeds, as compared to the 20 mph of their predecessors, which enabled them to travel to a job and complete it in a day, rather than incurring two days of travel with overnight hotel stops for the driver.

The stabilising legs were no longer cranked up by hand but shot out under the power of hydraulic cylinders, a system first developed for fire engines. These allowed the crane to begin work immediately on arrival on site, but more importantly, it made it possible to move the crane again and again during the working day without any great loss of working time.

The positioning of the fulcrum and the general design of the chassis permitted a 360° arc of lift, where earlier cranes could not lift over their own rear for fear of overbalancing. Up to date electronic alarm systems warned the driver when his lift was near capacity and in true 1970s style there was a cassette tape player with a relaxing female voice taking the operator through the basics of the controls.

A popular campaign of the time aimed to encourage greater support for British Industry with the slogan "I'm Backing Britain" and Johnny Johnson took this to heart, insisting that every crane left the factory with a union flag sticker on the steering column looking out on the road ahead.

The 25 ton crane was the greatest design of its generation and was recognised by the Design Council, receiving The Queen's Award to Industry for the best design in 1977.

A 75 ton model was soon produced with the same futuristic features and the company seemed destined for success until currency fluctuations led to the collapse of their financial backers.

Cosmos Cranes ceased trading as a company and Johnson's innovative designs were bought up by his former employers, Acrow. The innovations he had implemented became standard in designs throughout the world and 35 years later they remain the basis of all mobile crane designs.^[2]

Types of Mobile Cranes

Threre are various types of Mobile cranes Some of them are listed below. The most basic type of mobile crane consists of a truss or telescopic boom mounted on a mobile platform - be it on road, rail or water. Common terminology is conventional and hydraulic cranes respectively.

Truck-mounted crane

A truck carrier provides the mobility for this type of crane. This crane has two parts: there carrier, often referred to as the Lower, and the lifting component which includes the boom, referred to as the Upper. These are mated together through a turntable allowing the upper to swing from side to side. These modern hydraulic truck cranes are usually single-engine machines, with the same engine powering the undercarriage and the crane. the upper is usually powered via hydraulics run through the turntable from the pump mounted on the lower. In older model designs of hydraulic truck cranes there were 2 engines. One in the lower pulled the crane down the road and ran a hydraulic pump for the outriggers and jacks. The one in the upper ran the upper through a hydraulic pump of it's own. Many older operaters favor the 2 engine system due to leaking seals in the turntable of aging newer design cranes.

Generally, these cranes are able to travel on highways, eliminating the need for special equipment to transport the crane unless weight or other size constrictions are in place such as local laws. If this is the case most larger cranes are equipped with either special trailers to help spread the load over more axles or are able to disassemble to meet requirements. An example is counterweights. Often a crane will be followed by another truck hauling the counterweights that are removed for travel. In addition some cranes are able to remove the entire upper. However, this is usually only an issue in a large crane and mostly done with a conventional crane such as a link-belt HC-238. When working on the jobsite, outriggers are extended horizontally from the chassis then vertically to level and stabilize the crane while stationary and hoisting. Many truck cranes have slow-travelling capability (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 anti-tipping stability then lies in the stiffness of the chassis suspension. Most cranes of this type also have moving counterweights for stabilization beyond that provided by the outriggers. Loads suspended directly aft are the most stable, since most of the weight of the crane acts as a counterweight. Factory-calculated charts (or electronic safeguards) are used by crane operators to determine the maximum safe loads for stationary (outriggered) work as well as (on-rubber) loads and travelling speeds.

Truck cranes range in lifting capacity from about 14.5 short tons (12.9 long tons; 13.2 t) to about 1,300 short tons (1,161 long tons; 1,179 t).

A sidelifter crane is a road-going truck or semi-trailer, able to hoist and transport ISO standard containers. Container lift is done with parallel crane-like hoists, which can lift a container from the ground or from a railway vehicle.

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 are used to level and stabilize the crane for hoisting.

These telescopic cranes are single-engine machines, with the same engine powering the undercarriage and the crane, similar to a crawler crane. In a rough terrain crane, the engine is usually mounted in the undercarriage rather than in the upper, as with crawler crane. Most have 4 wheel drive and 4 wheel steering which allows them to traverse tighter and slicker terrain than a standard truck crane with less site prep. In addition, there are rough terrain cranes with the operating cab mounted on the lower as opposed to the P&H in the above image.

A mobile crane with the necessary equipment to travel at speed on public roads, and on rough terrain at the job site using all-wheel and crab steering. AT‘s combine the roadability of Truck-mounted Cranes and the manoeuvrability of Rough Terrain Cranes.

AT’s have 2-9 axles and are designed for lifting loads up to 1,200 tonnes (1,323 short tons; 1,181 long tons).[32]

A Pick and Carry Crane is similar to a mobile crane in that is designed to travel on public roads, however Pick and Carry cranes have no stabiliser legs or outriggers and are designed to lift the load and carry it to its destination, within a small radius, then be able to drive to the next job. Pick and Carry cranes are popular in Australia where large distances are encountered between job sites. One popular manufacturer in Australia was Franna, who have since been bought by Terex, and now all pick and carry cranes are commonly referred to as "Frannas" even though they may be made by other manufacturers . Nearly every medium and large sized crane company in Australia has at least one and many companies have fleets of these cranes. The capacity range is usually ten to twenty tonnes maximum lift, although this is much less at the tip of the boom. Pick and Carry cranes have displaced the work usually completed by smaller truck cranes as the set up time is much quicker. Many steel fabrication yards also use pick and carry cranes as they can "walk" with fabricated steel sections and place these where required with relative ease.

A carry deck crane is a small 4 wheel crane with a 360 degree rotating boom placed right in the centre and an operators cab located at one end under this boom. The rear section houses the engine and the area above the wheels is a flat deck. Very Much an American invention the Carry deck can hoist a load in a confined space and then load it on the deck space around the cab or engine and subsequently move to another site. The Carry Deck principle is the American version of the pick and carry crane and both allow the load to be moved by the crane over short distances.

Telescopic Handlers are like forklift trucks that have a telescoping extendable boom like a crane. Early telescopic handlers only lifted in one direction and did not rotate, however, several of the manufacturers have designed telescopic handlers that rotate 360 degrees through a turntable and these machines look almost identical to the Rough Terrain Crane. These new 360 degree telescopic handler/crane models have outriggers or stabiliser legs that must be lowered before lifting, however their design has been simplified so that they can be more quickly deployed. These machines are often used to handle pallets of bricks and install frame trusses on many new building sites and they have eroded much of the work for small telescopic truck cranes. Many of the worlds Armed forces have purchased telescopic handlers and some of these are the much more expensive fully rotating types. Their off road capability and their on site versatility to unload pallets using forks, or lift like a crane makes them a valuable piece of machinery.

A crawler is a crane mounted on an undercarriage with a set of tracks (also called crawlers) that provide stability and mobility. Crawler cranes range in lifting capacity from about 40 to 3,500 short tons (35.7 to 3,125.0 long tons; 36.3 to 3,175.1 t).

Crawler cranes have both advantages and disadvantages depending on their use. Their main advantage is that they can move around on site and perform each lift with little set-up.

References

1. ^ McGraw-Hill Dictionary of Scientific & Technical Terms. McGraw-Hill. 1999. 
2. ^ Coles 100 years by Martyn Wilson and Karen Spink

• Mobile cranes database at www.portvision.eu (Retrieved June 2006)