British Dumpers Replace Rail Trucks
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Specially Designed Eagle I2-ton Semitrailers with A.E.C. Tractors to Work in Welsh Mountain Quarry THE first of four semi-trailer HE dumpers, designed to carry a net load of 12 tons and to withstand the impact of a 5-ton piece of excavated rock falling from a considerable height, has recently been completed by the Eagle Engineering Co., Ltd., Warwick, for the Penmaenmawr and Welsh Granite Co., Ltd., Llandudno.
The dumper is of particular interest because it represents a type of equipment in the development. of which the Americans have specialized for many years, and the possibility of importing American equipment was originally contemplated by the Penmaenmawr engineers. The decision to buy a British product now appears to have been fully justified.
The amount of stone to be moved is indicated by the size of the crushing plant which has a capacity of 500 to 600 tons an hour. The site gradients are limited to 1-in-6 maximum, but will rarely exceed 1 in 10. The dumpers are to be employed in place of the present rail system at the Penmaenmawr mountain quarry, and it is expected that a considerable saving in operational costs will be achieved as a result of the change, which was planned after an American tour by the managing director of the company.
Robust construction is an outstanding feature of the dumper, but because damage may be caused by rock falls, the skip has been so designed that it can -be lifted from the chassis and replaced by a new or reconditioned body in a few minutes.
The skip, which rests on four hingepins of large diameter, is tipped by hoisting one of the outrigger lifting lugs. When fully tipped to either side, the skip comes to rest on an outer set of binge-pins, but because it will normally be tipped to the right,the end frames are extended on the off side to form two supports for the load when resting on a low wall above the crushing-plant chute. • To resist shock loading, the laminated floor and sloping sides of the body are fitted with 2-in, oak boards sandwiched between 1-in. detachable steel linings which are bolted in position. The skip is 12 ft. long and 9 ft. 6 ins, wide, the vertical ends reaching a height of 3 ft. 21 ins, above the floor and the sloping sides have a depth of approximately 1 ft. 111 ins.
The main longitudinal members are constructed of 10-in. by 3+-in, channel sections braced by 8-in, by 3+-in. channel-section cross-members spaced about 1 ft. apart. The outside longitudinal members are of box section and comprise 8-in. by 31-in, rolled-steel channel sections reinforced by 71-in, by fin. plate at the top and with 6-in. by Fin. plate at the bottom. The outer edge is reinforced with 7-in. by Fin, plate, and a full-length flitch plate is fitted diagonally across the section to support the top corner.
Massive Construction The sloping sides and ends are braced with 7-in. by 3+-in. channel members, and the bottom. plate is of Fin. mild steel sheet welded to the supporting frame work. The chassis frame is constructed of 9-in. by 31-in, rolled-steel channel members and is strongly braced with the cross-members. The four wheels, which are fitted with single 14.00 by 20 low-pressure barred tyres, are mounted in pairs on a two-unit aide of the oscillating four-in-line type. The semi-elliptic springs are located on trunnion brackets to permit sideways oscillation and to allow axle tilt on uneven ground. Girling 2-LS brakes are employed, being operated by a Clayton vacuum-servo system.
An A.HC. Matador, with a special low-ratio gearbox forms the tractor unit. The turntable is mounted on a rectangular frame bolted to the tractor chassis and locked stops are fitted to limit the lock on the right-hand side as a precaution against the chassis extensions fouling any part of the towing vehicle. A locking slide and lever fitted to the coned-top bolster blocks permit of easy disengagement of the semitrailer.