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A MOBILE CRANE •

27th August 1929, Page 62
27th August 1929
Page 62
Page 63
Page 62, 27th August 1929 — A MOBILE CRANE •
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Which of the following most accurately describes the problem?

for 6-ton Loads

A Remarkable F.W.D. Machine with Herbert Morris Fixed Jib and a Hook Clearance of 10 ft. from the Ground and 4 ft. from the Chassis.

FOR many classes of industrial work and transport the employment of some form of mobile crane is almost an essential if the highest efficiency is to be attained. The design of a self-propelled crane of large capacity is, however, not an easy matter. Its chassis must be of exceptional strength, and this applies particularly to the rear axle, upon which is imposed a concentrated load much greater than that which it would have to take if the heaviest weight to be lifted were instead to be carried in the ordinary man ner. A considerable weight must also be concentrated at the front of the machine, otherwise the load, instead of being lifted, will remain on the ground whilst the front of the chassis will be forced upwards. This• is even more likely to happen when the vehicle is operated on an incline with its front axle -pointing up the slope.

Provision must also be made for preventing undue stressing of the springs, and the crane gear must be very easily controllable, for the lowering of a heavy article at too great a speed might easily cause considerable damage; likewise, -with a powerful crane it is advisable to have some safety

device to prevent over-lifting, which 'would probably damage the jib or the winding gear and its drive from the gearbox.

Alt these features, as well as many others of interest, are to be found in the new 6-:ton mobile jib-crane produced c40 by the Four Wheel Drive Lorry Co., Ltd., 46, Charing Cross, London, S.W.1.

The chassis of this machine, in its main particulars, closely resembles the standard F.W.D. product, in that it has four-wheel drive, a central differential and forward controls with the driver's seat over the engine, but an unusual feature is the provision of epicyclic reduction gearing in the wheel hubs, this being of a similar type to that which was recently described in connection with the six-wheeler. The reason for utilizing this gear requires some explanation. It is not only that it provides a lower ratio, but because When under conditions of maximum stress the rear-axle load is almost 12 tons, and although the machine is so designed that the front-axle load is then slightly more than one ton, yet practically the whole of the drive is bound to be taken through the rear wheels, and if it were not ' for the reduction gear in the hubs, the propeller shaft, axle, differential and driving shafts would all have to be of much greater strength ; as it is, they can be comparatively

This vehicle is, we believe, the first to be equipped with twin 44in. by 10-in, high-pressure pneumatic tyres, which are, of course, on the rear wheels only.

The actual machine forms a repeat order for the Burmah Oil Co., Ltd., the previous crane being one of four tons capacity with a hook affording 3 ft. clearance from the frame.

Reference to our illustrations will show the general layout of the parts, which include S a fixed jib

made by Herbert Morris, Ltd., of Loughborough.

Two horizontal drums are mounted across the frame at approximately amidships and are driven from a power take-off on the gearbox, this being so arranged that by sliding a dog clutch either drum may be engaged. The forward drum operates the crane through a snatch block, whilst that at the rear carries 400 ft. of I-in.-diameter steel-wire rope and is fitted with a laying-on gear similar to that used on the six-wheel-drive F.W.D. Each drum has a hand brake for lowering the load or payingout the cable, and ratchet sprags are provided on -the drums to hold the load where required, interlocking arrangements preventing paying-out of the rope when its sprag is engaged. All the controls for the crane and winch are (5) The winch carries

400 yds. of On. steel-wire rope and has a special laying-on gear.

mounted on a platform at the back of the driver's cab and provided with a seat. They consist of a forward-and reverse lever, two levers for engaging the drums, a brake lever for each drum and another for the sprags ; there are also separate clutch and accelerator pedals.

The headlights are mounted on swivelling brackets so that they can be turned to the rear when the vehicle is operated at night ; a searchlight is also mounted on the driver's cab.

The engine has four T-headed cylinders and develops 73 b.h.p. A HeleShaw clutch takes the drive to a constant-mesh gearbox giving ratios as follow :—Top, direct ; second, 2 to 1; first, 4 to 1. The drive from the main shaft of this box is taken by means of a silent chain to a central differential, the chain ratio being 2.06 to 1. The bevel ratios of the two axles are 4,3 to 1 and the hub-reduction ratio 2.33 to 1. The over-all gearing and the corresponding road speeds at 1,300 r.p.m. are :Top, 20.7 to 1 (8.2 m.p.h.); second, 41.4 to 1 (4.1 m.p.h.) ; first, 82.8 to 1 (2.0 m.p.h.).

When the snatch block reaches the top of its travel and any further movement might be dangerous, the engine is automatically switched off.

At the front of the machine is a castiron cross-member 3 ft. wide, 1 ft. 1 in. broad and 5 ins, deep, this being supplemented by three heavy cast-iron blocks bolted below it, the whole weighing about 15 cwt. Thts assists in preventing lifting of the front of the machine. Steering is effected by ti Merles cam and-roller gear, and, as showing the attention which has been paid to detail, the exhaust pipe and silencer are carried vertically behind the cab so that the exhaust is discharged high into the air, thus gassing of the man operating the crane is avoided.

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People: Herbert Morris
Locations: London

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