Improved Fifteen Ton Crane 312 1a
Improved Fifteen Ton Crane 312 1b

The machine illustrated on first page has been constructed for Port Alfred Harbor, this being one of several harbors now being made by Sir J. Coode in South Africa. The pier for the construction of which the crane will be employed will consist of concrete blocks laid on what is known as the "overend system." The blocks, being brought on trucks direct from the block yard to within the sweep of the machine, are raised by it, swung round, and accurately set, the machine being continually traveled forward as the work advances. The bottom blocks are laid on bags of concrete previously deposited by the crane out of boxes with flap bottoms.

The present machine has been specially designed throughout, and represents the most complete development which block-setting plant has yet attained.

The most striking features of the crane are, the great range of all the motions, the large radius, and the method of providing for the latter by a horizontal jib suspended from a king-post. It was at first intended to have a straight inclined jib, and to alter the radius by pivoting this round its lower end, as is commonly done; it occurred, however, to Mr. Matthews, M.I.C.E., representing Sir J. Coode, that the plan eventually adopted would be in many ways preferable; the crane was therefore constructed by Messrs. Stothert & Pitt with this modification, and as far as can be judged from the trial with proof load, the arrangements can hardly be surpassed for quick and accurate block-setting. In cranes with "derricking" jibs it is necessary to connect the derrick and hoisting gears in such a manner that a variation of the radius may not affect the level of the load; this plan answers sufficiently well for ordinary purposes, but for block-setting it is requisite to have extreme accuracy in all the movements and great quickness in changing from one to another; the arrangements adopted in foundry cranes, in which all the motions are entirely independent of one another, seems therefore more suited for this kind of work. Other not inconsiderable advantages are also secured by the adoption of the foundry crane type, the amount of clear headway under the jib being much increased, and the difficulty avoided of making a jib sixty feet long sufficiently stiff without undue weight.

The principal dimensions of the crane are, total height of lift 46 feet, radius variable from 25 feet minimum to 45 feet maximum, height from rail to underside of jib 22 feet 2¾ inches, radius of tail to center of boiler 22 feet, working load 15 tons, proof load 19 tons.

The general arrangement consists of a truck on which is fixed a post, round which the crane revolves; the jib is supported midway by an inclined strut, above which is placed the king-post; the strut is curved round at the bottom and forms one piece with the side frames, which are carried right back as a tail to support the boiler and balance weight.

The hoisting gear consists of a double system of chains 13/16 in. in diameter placed side by side; each chain is anchored by an adjustable screw to the end of the jib, and, passing round the traveling carriage and down to the falling block, is taken along the jib over a sliding pulley which leads it on to the grooved barrel, 3 ft. 9 in. in diameter. In front of the barrel is placed an automatic winder which insures a proper coiling of the chain in the grooves. The motive power is derived from two cylinders 10 in. in diameter and 16 in. stroke, one being bolted to each side frame; these cylinders, which are provided with link motion and reversing gear, drive a steel crank shaft 2¾ in. in diameter; on this shaft is a steel sliding pinion which drives the barrel by a double purchase.

In the center of the crank-shaft is a large reversing friction clutch, which drives, through miter gear, a vertical shaft placed just in front of the post; from the latter the slewing, racking, and traveling motions are obtained.

The crane can be turned through a complete circle by a pinion gearing into a machine-moulded toothed ring bolted to the top of the truck; this ring is 11 ft. 4-7/8 in. in diameter, and contains 172 teeth 2½ in pitch. The slewing pinion is driven by intermediate gearing from the bottom of the vertical shaft mentioned above. For the turning motion two distinct sets of rollers are provided; these are carried by cross-girders placed between the side frames; one set runs against a cast-iron roller path bolted round the bottom of the post, and the other on the large horizontal roller path seen in the engraving. The latter is 14 ft. in diameter; it is built up of two deep curved channel irons with top and bottom plates forming a circular box girder, on the top of which a heavy flat rail is riveted, and the whole turned up in the lathe. The racking and traveling motions are driven from the top end of the vertical shaft; the racking gear consists of wire ropes attached to each side of the traveling carriage and coiled round a large barrel, the outer rope being brought over a pulley at the end of the jib. The rails for the carriage rest on rolled joints bolted to the underside of jib. This arrangement involves the use of an overhung traveling carriage, but enables the jib to be of a stiff box section, the side stiffness being further secured by wind ties.

The traveling motion is worked by a second vertical shaft, which passes down the center of the post, and by means of a cross shaft is geared to the front axle, from which four of the ground wheels are driven.

The post is octagonal, built up of plates ¾ in. thick; at the bottom end it is secured to the girders of the truck, and at the top is shrunk on to a large gudgeon 12 in. in diameter, which enters a casting fixed in the back end of the jib; on the top of the gudgeon are two steel disks on which an adjustable cap rests; by means of this and the ties to the tail and the lower end of the strut a proportion of the weight can be brought on to the post so as to relieve the roller path to any desired extent, and enable the crane to be revolved easily.

The truck is 24 ft. long and 16 ft. 4½ in. wide; it is constructed of longitudinal and transverse box girders 2 ft. 8 in. deep, and rests on two axles 6 in. in diameter; round these axles swivel the cast-iron bogie frames which carry the ground wheels. This arrangement was adopted because the crane has to travel up a gradient of 1 in 30, and the bogies enable it to take the incline better; they also distribute the weight more evenly on the wheels. The gauge of the rails is 15 ft, the wheels are 2 ft. 6 in. in diameter, and have heavy steel tires. The weight on each of the front wheels when running with the ballast, but no load, is about 16 tons. A powerful brake is applied to the wheels when descending the incline.

All the clutch levers, break treadle, and handles are brought together, so that one man has the crane under his entire control. An iron house, of which the framing only is shown, extends from the gearing right back to the boiler, forming a most spacious engine room and stokehole. A separate donkey engine is provided for feeding the boiler. The truck is furnished with legs under which packings can be wedged so as to relieve the load on the wheels when block-setting. The slings seen under the boiler are for hanging a concrete balance weight; this will weigh about 20 tons. The weight of the crane itself without load or ballast is about 80 tons. The crane was tested under steam with a load of 19 tons with the most satisfactory results; the whole machine appeared to be very rigid, an end often very difficult to obtain with portable wrought-iron structures and live loads. The result in the present case is probably greatly due to the careful workmanship, and to the fact that the sides and ends of the plates are planed throughout, so that the webs of the girders get a fair bearing on the top and bottom plates.

The crane showed itself to be very handy and quick in working, the speeds with 19 tons load, as actually timed at the trial, are: lifting 16 ft. per minute, racking motion 46 ft. per minute, slewing through a complete circle 90 ft. diameter, four minutes, equivalent to a speed at load of 60 ft. per minute. The crane was constructed by Messrs. Stothert & Pitt, of Bath, to the order of the Crown agents for the colonies, and we understand that the design and construction have given complete satisfaction to Sir J. Coode, the engineer to the harbor works, under whose supervision the crane was constructed. - Engineering.