Is This the World's Biggest-capacity Trailer?
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Vehicle Capable of Carrying a Load of 140 Tons Has its Own Power-operated Hydraulic jacking System. A Fine Example of the Art of Fabrication by the
Welding Process
IN our issue dated January 14 last we made reference to an out-size in trailers constructed by the \yelllcnown concern of Cranes (Dereham), Ltd„ South . Green Works, East Dereham. Norfolk. This piece of equipment which is thought to have the largest carrying capacity of anything of its kind yet built, has an overall length of approximately 61 ft. and an overall height of 8 ft. 3 ins. It has a wheelbase of 44 ft. 2i ins., with an outer track of 7 ft. Two such machines have been laid down and the first has recently been delivered to Pickfords, Ltd
The trailer comprises essentially a main • frame and two swan-neck-type end members which rest on two eightwheeled bogies. At their lower ends, these members are hinged to the main girders, their upper ends being attached to the top of these girders by two hydraulic jacks or struts. Connection is made at the lower ends by pins of 5 ins diameter, whilst the eyes of the jacks have pins of 4 ins. diameter, Each' swan neck carries a petrol engine and a Towler pump, together with an emergency hand pump. Either of these pumps will deliver oil under a pressure of up to 11 tons pet sq. in. to the hydraulic frame jacks and both ends of the trailer can be operated at the same time.
Extension of the jacks will lift the frame to give a total clearance, under the girders, of 2 ft. 10 ins., whilst release of the pressure causes the frame to he lowered to the ground The lifting operation, when the power pumps are used, takes about 8 mins., the time taken when using the hand pump being about 30 ruins The jacks have a bore of 7 ins, and a stroke of 16 ins., the piston rod, which is hinged at its lower tad to a casting secured to the loading deck, • is in the form of an Acme-threaded screw. A bronze nut, working on this thread, allows each jack to be fixed at any length desired—the height of the frame above the ground can be set as required up to a maximum of GI ins. to the topof the members.
A fine example of fabrication by welding is .found in the main frame members, which are box-like in construction. The flange plates are 27 ins. wide by. 1 ins, thick and the web plates in. thick, the total depth being 27 ins. Four cross-members of like construction are employed and to ensure the maximum•degree of rigidity, two tubes of 18 ins, diameter by / in. thick are welded across the frame at each end. Danks of Netherton, .Ltd., was responsible for the swan necks and main frame consit action,
Siaran-neck Rigidity Of particular interest is the construction of the swan necks, as it will be appreciated how essential it is that these should, at all times, remain perfectly rigid, This feature is imparted to them by a crescent-Shaped crosstube measuring 3 ft. 3 ins, in diameter; it is made of Fin, plate material. To its lower side is welded a box-form cross-member.
The bogies. have -been constructed as compactly as possible, a feature which contributes towards ease of steering. Each has eight wheels equipped with 77I-mm. by 15-in, solid-rubber tyres and 'running orf taper roller bearings. The ascleS, of which there are four on each bogie, are made from 5-in. square high-tensile steel; they are supported on the Crane patent-trunnion springing gear The springs are 5 ins, wide and there are eight plates /in. thick and three 1-in, thick. Each is tested up to a load of 42 tons.
Each bogie frame is of rectangular
form, the cross-members being exceptionally massive, as may he gauged from the fact that they are capable of carrying half the gross weight of the .complete machine •at the centre of the bogie.
The 'extreme length of the trailer makes it necessary to provide for the simultaneous steering of both bogies, should the occasion arise. Although a . means for hand 'steering is provided for each bogie to meet such contingencies, there are two other methods of steering applicable to this trailer. With the rearmost bogie locked in line with the main frame there is a true trailer action which meets normal straight hauling conditions and allows fOr a turning effort of somewhat wide radius. Secondly, by using a second traitor at the rear, one of the two drawbars provided is coupled up to the rear bogie and the towing eye hitched to the front of the rear tractor.
All the wheels are equipped with brakes having hnpsf 20 ins, diameter by 4 ins. wide. These are of Crane design and, on one'side, are expanded by Lockheed :2-in, wheel cylinders, and on the other a cam action is employed This latter, in the case of half the wheels, provides an efficient parking , brake. A Bendix-Westinghouse relay system is responsible for giving simultaneous brake action cn both bogies.
Reservoirs, mounted on each bogie, supply compressed air to two Clayton Dewandre cylinders, which, in turn, operate the hydraulic master cylinders. By this arrangement brake action is not only synchronized on the two bogies but an effective compensating action is achieved.