See also:machines by means of which heavy bodies may be lifted, and also displaced horizontally, within certain defined limits . Strictly speaking, the name alludes to the
See also:arm or jib from which the load to be moved is suspended, but it is now used in a wider sense to include the whole mechanism by which a load is raised vertically and moved horizontally . Machines used for lifting only are not called
See also:cranes, but winches, lifts or hoists, while the
See also:term elevator or conveyor is commonly given to appliances which continuously, not in
See also:separate loads, move materials like
See also:grain or
See also:coal in a vertical,
See also:horizontal or diagonal direction (see
See also:CONVEYORS) . The use of cranes is of
See also:great antiquity, but it is only since the great
See also:industrial development of the 19th century, and the introduction of other
See also:powers than
See also:hand labour, that the
See also:crane has acquired the important and indispensable position it now occupies . In all places where finished goods are handled, or manufactured goods are made, cranes of various forms are in universal use . Cranes may be divided into two
See also:main classes—revolving and non-revolving . In the first the load can be lifted vertically, and then moved
See also:round a central
See also:pivot, so as to be deposited classlfliceat any convenient point within the range . The type of tlon . this class is the ordinary jib crane . In the second class there are, in addition to the lifting motion, two horizontal movements at right angles to one another . The type of this class is the overhead traveller . The two classes obviously represent respectively systems of polar and rectangular co-ordinates .
Jib cranes can be subdivided into fixed cranes and portable cranes; in the former the central •
See also:post or pivot is firmly fixed in a permanent position, while in the latter the whole crane is mounted on wheels, so that it may be transported from place to place . The different kinds of motive power used to actuate cranes—manual, steam,
See also:hydraulic, electric—give a further
See also:classification . Hand cranes are extremely useful where the load is not Motive excessive, and the quantities to be dealt with are not powers. great; also where
See also:speed is not important, and first cost is an essential
See also:consideration . The
See also:net effective
See also:work of lifting that can be performed by a man turning a handle may be taken, for intermittent work, as being on an
See also:average about 5000
See also:foot-lb per minute; this is
See also:equivalent to 1 ton lifted about 1 ft. per minute, so that four men can by a crane raiser ton 9 ft. in a minute or 9 tons 1 ft. per minute . It is at once evident that hand power is only suitable for cranes of moderate power, or in cases where heavy loads have to be lifted only very occasionally . This point is dwelt upon, because the speed limitations of the hand-crane are often overlooked by
See also:engineers . Steam is an extremely useful motive power for all cranes that are not worked off a central power station . The steam crane has the immense
See also:advantage of being completely self-contained . It can be moved (by its own
See also:locomotive power, if desired) long distances without requiring any complicated means of conveying power to it; and it is rapid in work, fairly economical, and can be adapted to the most varying circumstances . Where, however, there are a number of cranes all belonging to the same
See also:installation, and these are placed so as to be conveniently worked from a central power station, and where the work is rapid, heavy and continuous, as is the case at large ports, docks and railway or other warehouses, experience has shown that it is best to produce the power in a generating station and distribute it to the cranes . Down to the closing decades of the 19th century hydraulic power was practically the only
See also:system available for working cranes from a power station . The hydraulic crane is rapid in
See also:action, very smooth and silent in working, easy to handle, and not excessive in cost or upkeep,—advantages which have secured its adoption in every
See also:part of the
See also:world .
See also:Electricity as a motive power for cranes is of more
See also:recent introduction . The electric transmission of energy can be performed with an efficiency not reached by any other method, and the electric motor readily adapts itself to cranes . When they are worked from a power station the great advantage is gained that the same plant which drives them can be used for many other purposes, such as working machine tools and supplying current for
See also:lighting . For
See also:dock-side jib cranes the use of electric power is making rapid strides . For overhead travellers in workshops, and for most of the cranes which fall into our second class, electricity as a motive power has already displaced nearly every other method . Cranes driven by shafting, or by
See also:mechanical power, have been largely superseded by electric cranes, principally on account of the much greater
See also:economy of transmission . For many years the best workshop travellers were those driven by
See also:ropes; these performed admirable service, but they have given place to the more
See also:modern electric traveller . The
See also:principal motion in a crane is naturally the hoisting or lifting motion . This is effected by slinging the load to an
See also:eye or Liking
See also:hook, and elevating the hook vertically . There are three mechan- typical methods: (I) A
See also:direct pull may be applied to isms. the hook, either by screws, or by a cylinder fitted with
See also:piston and
See also:rod and actuated by direct hydraulic or other pressure, as shown diagrammatically in fig . I . These methods are used in exceptional cases, but
See also:present the obvious difficulty of giving a very
See also:short range of lift .
(2) The hook may be attached to a rope orchain, and the pulling cylinder connected with a system of pulleys around which the rope is led; by these means the lift can be very largely increased . Various arrangements are adopted; the one indicated in fig . 2 gives a lift of load four times the stroke of the cylinder . This second method forms the basis of the lifting
See also:gear in all hydraulic cranes . (3) The lifting rope or chain is led over
See also:pulley to a lifting
See also:barrel, upon which it is coiled as the barrel is rotated by the source of power (fig . 3) . Sometimes, especially in the case of overhead travelling cranes for very heavy loads, the chain is a
See also:special pitch chain, formed of
See also:flat links pinned together, and the barrel is reduced to a
See also:wheel provided with teeth, or " sprockets," which engage in the links . In this case the chain is not coiled, but simply passes over the lifting wheel, the
See also:free end
See also:hanging loose . All the methods in this third category require a rotating lifting or barrel
See also:shaft, and this is the important difference between them and the hydraulic cranes mentioned above . Cranes fitted with rotating hydraulic engines may be considered as coming under the third category . When the loads are heavy the above mechanisms are supplemented by systems of
See also:purchase blocks suspended from the jib or the traveller crab; and in barrel cranes trains of rotating gearing are interposed between the motor, or
See also:manual handle, and the barrel (fig . 3) .
When a load is lifted, work has to be done in overcoming the action of gravity and the
See also:friction of the mechanism; when it is Brakes, lowered, energy is given out . To
See also:control the speed and absorb this energy, brakes have to be provided . The hydraulic crane has a great advantage in possessing an almost ideal
See also:brake, for by simply throttling the exhaust from the lifting cylinder the speed of descent can be regulated within very wide limits and with perfect safety . Barrel cranes are usually fitted with
See also:band brakes, consisting of a brake rim with a friction band placed round it, the band being tightened as required . In ordinary cases
See also:conduction and convection suffice to dissipate the
See also:heat generated by the brake, but when a great
See also:deal of lowering has to be rapidly performed, or heavy loads have to be lowered to a great
See also:depth, special arrangements have to be provided . An excellent brake for very large cranes is
See also:Matthew's hydraulic brake, in which
See also:water is passed from end to end of cylinders fitted with reciprocating pistons, cooling jackets being provided . In electric cranes a useful method is to arrange the connexions so that the lifting motor acts as a dynamo, and, driven by the energy of the falling load, generates a current which is converted into heat by being passed through resistances . That the quantity of heat to be got rid of may become very considerable is seen when it is considered that the energy of a load of 6o tons369 descending through 50 ft. is equivalent to an amount of heat sufficient to raise nearly 6 gallons of water from 6o° F. to boiling point . Crane brakes are usually under the direct control of the
See also:driver, and they are generally arranged in one of two ways . In the first, the pressure is applied by a handle or treadle, and is removed by a
See also:spring or
See also:weight; this is called " braking on." In the second, or " braking off " method, the brake is automatically applied by a spring or weight, and is released either mechanically or, in the case of electric cranes, by the pull of a solenoid or magnet which is energized by the current passing through the motor . When the motor starts the brake is released ; when it stops, or the current ceases, the brake goes on . The first method is in general use for steam cranes; it allows for a far greater range of power in the brake, but is not automatic, as is the second .
In free-barrel cranes the lifting barrel is connected to the revolving shaft by a powerful friction clutch; this, when interlocked with the brake and controller, renders electric cranes exceedingly rapid in working, as the barrel can be detached and lowering performed at a very high speed, without waiting for the lifting motor to come to
See also:rest in
See also:order to be reversed . This method of working is very suitable for electric dock-side cranes of capacities up to about 5 or 7 tons, and for overhead travellers where the height of lift is moderate . Where high speed lowering is not required it is usual to employ a
See also:reversing motor and keep it always in gear . In steam cranes it is usual to work all the motions from one
See also:double cylinder engine . In order to enable two or more motions to be worked together, or independently as required, reversing friction cones are used for the subsidiary motions, especially the slewing motion . With the exception of a few special cranes in which friction wheels are employed, it is universally the practice, in steam cranes, to connect the engine shaft with the barrel shaft by
See also:spur toothed gearing, the gear being connected or disconnected by sliding pinions . In electric cranes the motor is connected to the barrel, either in a similar manner by spur gear or by
See also:worm gear . The toothed wheels give a slightly better efficiency, but the worm gear is somewhat smoother in its action and entirely silent; the
See also:noise of gearing can, however, be considerably reduced by careful machining of the teeth, as is now always done, and also by the use of pinions made of raw-hide
See also:leather or other non-resonant material . When quick-running
See also:metal pinions are used they are arranged to run in closed oil-
See also:baths . Leather pinions must be protected from rats, which eat them freely . Worm wheel gearing is of very high efficiency if made very quick in pitch, with properly formed teeth perfectly lubricated, and with the end thrust of the worm taken on
See also:bearings . Much
See also:attention has been paid to the improvement of the mechanical details of the lifting and other motions of cranes, and in important installations the gearing is now usually made of
See also:steel .
In revolving cranes ease of slewing can be greatly increased by the use of a live
See also:ring of conical rollers . Electric
See also:motors for barrel cranes are not essentially different from those used for other purposes, but in proportioning the sizes thv intermittent output has to be taken into consideration. powe This fact has led to the introduction of the " crane rated " reyulr red motor, with a given " load factor." This latter gives the ratio of the length of the working periods to the whole
See also:time; e.g. a motor rated for a quarter load factor means that the motor is capable of exerting its full normal
See also:horse-power for three minutes out of every twelve, the pause being nine minutes, or one minute out of every four, the pause being three minutes . The actual load factor to be chosen depends on the nature of the work and the kind of crane . A dock-side crane unloading cargo with high lifts following one another in rapid succession will require a higher load factor than a workshop traveller with a very short lift and only a very occasional maximum load; and a traveller with a very long
See also:longitudinal travel will require a higher load factor for the travelling motor than for the lifting motor . In practice, the load factor for electric crane motors varies from a to e . In steam cranes much the same principle obtains in proportioning the
See also:boiler; e.g. the engines of a 10-ton steam crane have cylinders capable of indicating about 6o horse-power when working at full speed, but it is found that, in consequence of the intermittent working, sufficient steam can be supplied with a boiler whose
See also:surface is only a to ; of that necessary for the above power, when
See also:developed continuously by a stationary engine . In well-designed, quick-running cranes the mechanical efficiency of the lifting gear may be taken as about 85 %; a
See also:good electric jib crane will give an efficiency of 72 %, i.e. when actually lifting at full speed the mechanical work of lifting represents about 72 % ci the electric energy put into the lifting motor . A very convenient
See also:rule is to allow one brake horse-power of motor for every to foot-tons of work done at the hook; this is equivalent to an efficiency of 661%, and is well on the safe side . The motor in most
See also:common use for electric cranes is the series
See also:wound, continuous current motor, which has many advantages . It has a very large starting torque, which enables it to overcome the inertia of getting the load into motion, and it lifts heavy loads at a slower speed and lighter loads at a quicker one, behaving, under the action of the controller in a somewhat similar manner to that in which the cylinders of the steam crane
See also:respond to the action of the stop-
See also:valve . Three-phase motors are also much used for crane-
See also:driving, and it is probable that improvements in single and two-phase motors will eventually largely increase their use for this class of work . Tests of the
See also:comparative efficiencies of hydraulic and electric cranes tend to show that, although they do not vary to any very considerable extent with full load, yet the efficiency of the hydraulic crane falls away very much more rapidly than that of the electric crane when working on smaller loads .
See also:drawback can be corrected to a slight extent by furnishing the hydraulic crane with more than one cylinder, and thus compounding it, but the arrangement does not give the same economical range of load as in an electric crane . In first cost the hydraulic crane has the advantage, but the power mains are much less expensive and more convenient to arrange in the electric crane . The limit of speed of lift of hand cranes has already been mentioned; for steam jib cranes average practice is represented by the Speed.
See also:formula V =3o+2oo/T, where V is the speed of lift in feet per minute, and T the load in tons . Where electric or hydraulic cranes are worked from a central station the speed is greater, and may be roughly represented by V=5+3oo/T; e.g. a 3o-cwt. crane would lift with a speed of about 200 ft. per minute, and
See also:loo-ton crane with a speed of about 8 ft. per minute, but these speeds vary with
See also:local circumstances . The lifting speed of electric travellers is generally less, because the lift is generally much shorter, and may in ordinary cases be taken as V=3+85/T . The
See also:cross-traversing speed of travellers varies from 6o to 120 ft. per minute, and the longitudinal from loo to 300 ft. per minute . The speed of these two motions depends much on the length of the span and of the longitudinal run, and on the nature of the work to be done; in certain cases, e.g. foundries, it is desirable to be able to lift, on occasions, at an extremely slow speed . In addition to the brakes on the lifting gear of cranes it is found necessary, especially in quick-running electric cranes, to provide a brake on the subsidiary motions, and also devices to stop the motor at the end of the lift or travel, so as to prevent over-running . There are many other important points of crane construction too numerous to mention here, but it may be said generally that the advent of electricity has tended to increase speeds, and in consequence great attention is paid to all details that reduce friction and
See also:wear, such as
See also:roller and ball bearings and improved methods of
See also:lubrication; and, as in all other quick-running machinery, great stress has to be laid on accuracy of workmanship . The machinery, thus being of a higher class, requires more
See also:protection, and cranes that work in the open are now fitted with elaborate crane-houses or cabins, furnished with
See also:weather-tight doors and windows, and more care is taken to provide proper platforms, hand-rails and ladders of
See also:access, and also
See also:guards for the revolving parts of gearing . Typical Forms of Cranes.—Fig . 4 is a
See also:diagram of a fixed hand revolving jib crane, of moderate
See also:size, as used in railway goods yards Fixed and similar places .
It consists of a heavy
See also:base, which is securely bolted to the foundation, and which carries the cranes. strong crane-post, or pillar, around which the crane revolves . The revolving part is made with two side frames of cast iron or steel plates, and to these the lifting gear is attached . The load is suspended from the crane jib; this jib is attached at the
See also:lower end to the side frames, and the upper end is supported by tie-rods, connected to the framework, the whole revolving together . This
See also:form of crane thus embodies the essential elements of foundation, post, framework, jib, tie-rods and gearing . Fig . 5 shows another type of fixed crane, known as a
See also:derrick crane . Here the crane-post is extended into a long
See also:mast and is furnished with pivots at the top and bottom; the mast is supported by two " back ties," and these are connected to the socket of the bottom pivot by the " sleepers." This is a very good and comparatively cheap form of crane, where a long and variable
See also:radius is required, but it cannot slew through a
See also:complete circle . Derrick cranes are made of all powers, from the
See also:timber 1-ton hand derrick to the steel 150-ton derrick used in
See also:shipbuilding yards . The derrick crane introduces a problem for which many solutions have been sought, that of preventing the load from being lifted or lowered when the jib is pivoted up or down to alter the radius . To keep the load level, there are various devices for automatically coupling the jib-raising and the load-lowering motions . Somewhat allied to the derrick are the sheer legs (fig . 6) .
Here the place of the jib is taken by two inclined legs joined togetherat the top and pivoted at the bottom; a third back-
See also:leg is connected at the top to the other two, and at the bottom is coupled to a
See also:nut which runs on a long horizontal
See also:screw . This horizontal
See also:movement of the lower end of the back leg allows the whole arrangement to assume the position shown in fig . 7, so that a load can be taken out of a vessel and deposited on a quay
See also:wall . The same effect can be produced by shortening the back leg by a screw placed in the direction of its length . Sheer legs are generally built in very large sizes, and their use is practically confined to marine work . Another type of fixed crane is the " Fairbairn " crane, shown in fig . 8 . Here the jib, superstructure and post are all
See also:united in one piece, which revolves in a foundation well, being supported at the bottom by a toe-step and near the ground level by horizontal rollers . This type of crane used to be in great favour, in consequence of the great clearance it gives under the jib, but it is expensive and requires very heavy
See also:foundations . The so-called "
See also:hammer-headed " crane (fig . 9) consists of a steel braced tower, on which revolves a large horizontal double
See also:cantilever; the forward part of this cantilever or jib carries the lifting crab, and the jib is extended backwards in order to form a support for the machinery and
See also:balance . Besides the motions of lifting and revolving, there is provided a so-called " racking " motion, by which the lifting crab, 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 cranedesign; it first became prominent in the so-called " Titan " cranes, mentioned below (fig . 14) . Hammer-headed cranes are generally constructed in large sizes, up to 200 tons . Another type of fixed revolving crane is the foundry or smithy crane (fig . 10) . It has the horizontal racking motion mentioned above, and revolves either on upper and lower pivots supported by the structure of the workshop, or on a fixed pillar secured to a heavy foundation . The type is often used in foundries, or to serve heavy hammers in a smithy, whence the name . Portable cranes are of many kinds . Obviously, nearly every kind of crane can be made portable by mounting it on a
See also:carriage, fitted with wheels; it is even not unusual to make the Scottish derrick portable by using three trucks, one under Portable the mast, and the others under the two back legs. cranes . Fig . II represents a portable steam jib crane; it contains the same elements as the fixed crane (fig . 4), but the foundation
See also:bed is mounted on a
See also:truck which is carried on railway or road wheels .
With portable cranes means must be provided to ensure the requisite stability against overturning; this is done by weighting the tail of the revolving. part with heavy weights, and in steam cranes the boiler is so placed as also to form part of the counterbalance . Where the
See also:gauge is narrow and great weight is not desired, blocking girders are provided across the under side of the truck; these are arranged so that, by means of wedges or screws, they can be made to increase the base . In connexion with the stability of portable cranes, it may be mentioned that accidents more often arise from overturning backwards than forwards . In the latter case the over- turning tendency begins as soon as the load leaves the ground, but ceases as soon as the load again touches the ground and thus relieves the crane of the extra weight, whereas overturning backwards is caused either by the reaction of a chain breaking or by excessive counterweight . When portable cranes are fitted with springs and
See also:axle-boxes, drawgear and buffers, so that they can be coupled to an ordinary railway
See also:train, they are called " break- down " or " wrecking " cranes . Dock-side jib cranes for working general cargo are almost always made portable, in order to enable them to be placed in correct position in regard to the hatchways of the vessels which they serve . Fig . 12 shows an ordinary hydraulic dock-side jib crane . This type is usually fitted with a very high jib, so as to lift goods in and out of high-sided vessels . The hydraulic lifting cylinders are placed inside the revolving steel mast or post, and the
See also:cabin for the driver is arranged high up in the front of the post, so as to give a good view of the work . The pressure is conveyed to the crane by means of jointed " walking " pipes, or flexible
See also:hose, connected to hydrants placed at
See also:regular intervals along the quay . It is often very desirable to have the quay space as little obstructed by the cranes as possible, so as not to interfere with railway
See also:traffic; this has led to the introduction of cranes mounted on high trucks or gantries, sometimes also called " portal " cranes .
Where warehouses or station buildings run parallel to the quay
See also:line, the high truck is often extended, so as to span the whole quay; on one side the " long leg " runs on a rail at the quay edge, and on the other the " short leg " runs on a runway placed on the
See also:building . Cranes of this type are called "
See also:half-portal " cranes . Fig . 13 shows an electric crane of this class . They give the minimum of interference with quay space and have rapidly come into favour . Where the
See also:face of the warehouse is sufficiently close to the water to permit of the craneropeplumbingthehatches without requiring a jib of excessive radius, it is a very convenient plan to place the whole crane on the warehouse roof . A special form of jib crane, designed to meet a particular purpose, is the " Titan " (fig . 14) largely used .in the construction of piers and breakwaters . It contains all the essential elements of the hammer-headed crane, of which it may be considered to be the
See also:parent; in fact, the only essential difference is that the Titan is portable and the hammer-
See also:head crane fixed . The Titan was the first type of large portable crane in which full use was made of a truly horizontal movement of the load; for the purpose for which the type is de-signed, viz. setting concrete blocks in courses, this motion is almost a
See also:necessity . As types of non-revolving cranes, fig . 15 shows an overhead traveller worked by hand, and fig .
16 a somewhat similar machine worked by electric power . The principal component parts of a traveller are the main cross girders forming the
See also:bridge, the two end carriages on which the bridge rests, the running wheels which enable the end carriages to travel on the longitudinal gantry girders or runway, and the crab or jenny, which carries the hoisting mechanism, and moves across the span on rails placed on the bridge girders . There are numerous and important variations of these two types, but the above contain the elements out of which most cranes of the class are built . One variation is illustrated in fig . 17, and is called a "
See also:Goliath " or " Wellington." It is practically a traveller mounted on high legs, so as to permit of its being travelled on rails placed on the ground level, instead of on an elevated gantry . Of other variations and combinations of types, fig . 18 shows a modern design of crane intended to command the maximum of yard space, and having some of the characteristics both of the Goliath and of the revolving jib crane, and fig . 19 depicts a combination of a traveller and a hanging jib crane . When the cross
See also:traverse motion of a traveller crab is suppressed, and the longitudinal travelling motion is increased in importance we come to a FIG . 19 . type of crane, the use of which is rapidly increasing; it goes by the name of " transporter." Transporters can only move the load to any point on a vertical surface (generally a
See also:plane surface); they have a lifting Trans-motion and a movement of
See also:translation . They are of two porters. kinds: (I) those in which the motive power and lifting gear are self-contained on the crab ; and (2) those in which the motive power is placed in a fixed position .
A transporter of the first class is shown in fig . 20 . From the lower flange of a suspended runway, made of a singlesection, run wheels, from the axles of which the trans-
See also:porter is suspended . The latter consists of a
See also:frame-work carrying the hoisting barrel, with its driving motor and gearing, and a travelling motor, which is geared to the running wheels in such a manner as to be able to propel the whole machine; a seat is provided for the driver who manipulates the controllers . A transporter of this kind, when fitted with a grab, is a very efficient machine for taking coal from
See also:barges and depositing it in a coal
See also:store . In the other class of transporter the load is not usually moved Non-revolving cranes . through such long distances . It consists essentially of a jib made of single I-sections, and supported by tie-rods (fig . 21), the load to be lifted being suspended from a small travelling carriage which runs on the lower flange . The lifting gear is located in any convenient fixed position . In order that only one motor may be used, and also that the load may be lifted by a single part of rope, various devices have been in-vented . The jib is usually inclined, so as to enable the travel to be performed by gravity in one direction, and the
See also:object of the transporter mechanism is to ensure that pulling in or slacking out the lifting rope shall perform the cycle of operations in the following order:—Supposing the load is ready to be lifted out of a vessel on to a quay, the pull of the lifting rope raises the load, the travelling jenny being meanwhile locked in position .
On arriving at a certain height the lift ceases and the jenny is released, and by the continued pull of the rope, it runs up the jib; on arriving at an adjustable stop, the jenny is again locked, and the load can be lowered out; the hook can then be raised, when the jenny is automatically unlocked, and on paying out the rope the jenny gravitates to its first position, when the load is lowered and the cycle repeated . The jibs of transporters are often made to slide forward, or lift up, so as to be out of the way when not in use . Transporters are largely used for dealing with general cargo between vessels and warehouses, and also for coaling vessels; they have a great advantage in not interfering with therigging of vessels . Nearly all recent advances in crane design are the result of the introduction of the electric motor . It is now possible to apply motive power exactly where it is wanted, and to do so economically, so that the crane designer has a perfectly free hand in adding, the various motions required by the special circumstances of each case . The literature which deals specially with cranes is not a large one, but there are some good German text-books on the subject, amongst which may be mentioned Die Hebezeuge by
See also:Ernst (4th ed., Berlin, 1903), and Cranes, by Anton BSttcher, translated with additions by A . Tolhausen (
See also:London, 1908) . (W .
WILLIAM HENRY CRANE (1845– )
Have you any information relative to the Pert Way Steam Crane. This was a steam crane operated on the railwys. I have a hand built 3/4" scale model of this crane but can not find any infomation regarding same. Your comments would be appreciated. Regards Mike Dickinson
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