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March, 1949

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Erection of the largest drag line ever to operate in this country has just been finished.

Situate on the Ewart Hill Deep opencast coal site, about a mile to the west of Bedlington, Northumberland, it is being operated by Parkinson Strip Mining Co. Ltd., a subsidiary of Sir Lindsay Parkinson & Co. Ltd.

Our Field Editor recently had an opportunity of inspecting the machine which was still undergoing its trials. He was, however, able to form an idea of the colossal output of which the machine will be capable when in full operation.

As the site is estimated to produce in the region of 3,000,000 tons of coal with overburden running from some 30-120 ft., it warranted not only the installation of this large machine, but also of a well laid out screening plant. The drag line will work initially on glacial drift overburden, but later will be shifting pre-blasted shale and sandstone.

The machine, one of nineteen such produced in the U.S.A. we are told, was previously operating in America and was re-assembled on the Ewart Hill Deep site in something just over four months. It is a Bucyrus Erie, 1150B of the walking type, following the Monighan design, having a total working weight of some 1,200 long tons (this unit is referred to throughout the text). The bucket is of 25 cu. yd. capacity and weighs 28 tons 14 cwt. (the dimensions of the bucket are 17 ft. 4 in. long, 12 ft. 11 in. wide and 11 ft. 0 in. high). The boom is 180 ft. long and there are twin hoist ropes and twin drag ropes through twin fair-leads.

The front mast and boom are welded and both contain four main members braced all round the mast supports the boom by multiple ropes. The diameter of the tub is some 44 ft. and the pressure on it about 5 lb. per sq. in.

The turn-table is composed of two parts: the upper supporting the main machinery and the lower incorporates the girders which carry the walking machinery bearings, swing shaft bearings and supports for the swing roller circle. The feet, each weighing some 28½ tons, are 48 ft. long by 8 ft. 6 in. wide by 4 ft. 11 in. high; the pressure on them is about 10 lb. per sq. in., and the machine steps, backwards, about 7 ft. 6 in. at a time. The crew normally consists of three men, a driver, greaser and banksman, but at present also includes an electrician.

Apart from its size, the main feature of interest is, of course, the machinery. The drag line is all electric, using Ward-Leonard control, and powered from its own special power station built on the site. This latter contains five 750 kVA sets, any four of which are required to run simultaneously to operate the machine and one being a standby. These generators are driven by 900 h.p. General Motors diesel engines and power is supplied at 4,160 V through a trailing cable 4 in. diameter to a synchronous motor housed centrally at the back of the engine room. Situated laterally either side of this main synchronous motor, and on the same shaft, are two pairs of 250 V generators ; one pair for the two hoist drum motors and the other pair for the two drag drum motors. The h.p. of each of these four motors is 425, and the ropes are 2 in. and 2½ in. diameter for hoist and drag respectively.

In addition to the above and not on the same shaft there are three slewing motors having a separate Ward-Leonard set. The h.p. of each of these is 125.

The drag motors operate the walking gear through a dog clutch. Apart from this, the Ward-Leonard control eliminates the necessity for any other clutches.

In addition to the foregoing is a separate 35 h.p. motor for raising the boom, the ropes for this operation being 1¾ in. diameter. When the boom is in its working position it is held on safety stay ropes of 2½ in., 2 in. and 1 1/8 in. in diameter.

The control room is very neat and compact, the driver having a reasonably good view and not being "cluttered-up" with controls.

Drawings and Photographs accompanying the article