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December, 1936

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It is generally held that the haematite deposits of Lancashire and Cumberland have replaced the limestone in which they occur by metasomatic action. For a replacement deposit the ore is remarkably localised, being invariably associated with fault fissures, and even found in veins, but generally the ramifications are quite irregular and are essentially mined as masses. Like many mineral deposits the original source from which this iron was derived is a matter of geological speculation, but it is sufficient for us that it is there, and of this we are in no doubt as its ruddy stains were with us even to the second change of clothing and a. second bath, in spite of the fact that the management kindly placed the staff wardrobe at our disposal in consideration of the fact that our old clothes were regarded as not being quite old enough. But it is excellent stuff for all that, and is eminently suited to the acid Bessemer process, as the analysis in Table 1 will show.

The general disposition of the ore bodies is shown in the accompanying sketches. The beds of limestone assume a total thickness of some 200/240 ft., and the haematite, which is generally restricted to the middle 80 ft., is associated with a main north and south fault of 80 ft. throw. A secondary system of east and west faulting and branch faulting generally serves to enlarge the deposits at intersecting points.

The general scheme of operation Is to sink the shafts to the bottom of the deposit and to drive roadways to traverse the entire length. From these development roads, rises are driven (Fig. 2) to the upper limits. Many of these rises are used later as hoppers to store broken ore, which can be drawn from doors at the bottom as required. Intermediate levels are turned off from the rises at intervals of 25 ft. and from these the ore is worked on a variation of the pillar and stall system that is, the intermediate roadways and their connected offshoots are driven 10 ft. high by 10 ft. wide to form pillars from 30 ft. to 40 ft. square. In this way a middling of unworked ore, 15 ft. in thickness, is left between each set of adjacent levels.

In robbing the pillars a start is made at the boundary of the deposit and at the roof, that is, on the top level. The pillars are split into either two or four with further roads 8 ft. to 10 ft. wide and then robbed by taking off slices 3 ft. to 4 ft. wide to the full height of 10 ft. As the pillars are removed, the roof is allowed to cave, the object of this method of working being to cause the roof to cave continuously and systematically and, indeed, the entire operations are directed to securing the successful achievement of this end.

In the lower levels the middling is thinned down to a few feet in thickness at the same time as the pillars are being sliced. Finally, the pillars are robbed to the point when they can be shot out completely (see Fig. 1) by explosives and the whole of the middling allowed to collapse. The ore brought down by this operation is subsequently recovered by a system of spiling, a typical working place being illustrated in Fig. 3.

At Beckermet, the first sinking was begun about 34 years ago and the ore is now exploited by two shafts. The No. 1 shaft is 1,380 ft. deep and is of the three-compartmented rectangular type measuring 18 ft. by 7 ft. 9 in. Two compartments are devoted to winding ore, and one to the rising main, pump rods, cables, etc. A timber lining is inserted consisting of 12 in. by 4 in. pitch-pine carried by bearer sets at regular intervals. The cages are of the single-decked variety and carry two bogies per deck. Each bogie holds 18 cwt. of ore and has a tare of 7 cwt. the bodies are of steel and were supplied by Robert Hudson Limited of Leeds, and are mounted on locally made wheels and axles in which, however, Skefko taper roller bearings are incorporated. The No. 2 shaft, 1,240 ft. deep, is situated about half a mile distant and is only used for winding men and materials; it is fully equipped for winding ore, however, whenever necessary.

The winding engine for the No. 1 shaft is of Robey make and has twin cylinders, 22 in. diameter by 40 in. stroke, which are coupled to a bi-cylindro-conical drum rising from 8 ft. to 11 ft. in diameter.

Steam is provided by a battery comprising four Babcock & Wilcox boilers and two Lancashire units by Yates & Thom, all operating at a pressure of 150 lb. per sq. in. Two of the B. & W. units are fitted with this firm's mechanical stokers, while both the Lancashires are fitted with Turbine furnaces and Sugden superheaters. The feed water is handled by two Weir pumps each having a capacity of 5,250 g.p.h., heating being effected in a B. & W. feedwater heater using exhaust steam from the winding engine and feed pumps. Soft water for the feed is obtained from a neighbouring stream from which it is raised to a concrete reservoir by a three-throw ram pump driven by a pelton wheel, utilising drainage water from the mine.

Until recently the mine was dewatered by a ram pump driven by a Hathorn Davey triple-expansion steam engine, this equipment being capable of raising 50,000 g.p.h. with a 7 ft. 6 in. stroke. It has now been reduced to standby service, however, the pumping duty being undertaken by duplicate Mather & Platt 8-stage Plurovane units (Fig. 5) direct-coupled to 475 h.p. 3,000 V 3 ph. 50 cycle motors of Metro-Vick manufacture. Each pump is capable of delivering 800 g.p.m. against the total head of 1,440 ft. and, of course, normally only one is in service at a time. The new rising main consists of 15 ft. lengths of 10 in. dia. steel tubes 3/8 in. thick, coated with bitumen inside and out and connected by bolted joints. Two telescopic joints are fitted and serve the double purpose of allowing for temperature effects and enabling the connections to the existing mains to be more conveniently made. Auxiliary pumping is effected by a 500 V d.c. three-throw ram pump and a number of Worthington compressed-air units.

Electrical energy is derived from a 3,300 V overhead line fed by the Grid, but apart from a 10 kVA 100 V lighting transformer, this supply is used for the Plurovane pumps only. The other electrical services of the mine are provided for by two 200 kW 500 V d.c. sets driven by Robey compound engines. Control of the H.T. supply is effected by a three-panel G.E.C. truck-type board on the incoming side and a two-panel English Electric metalclad draw-out type board on the outgoing side. Two British Insulated three-core cables of the p.i., l.c., d.w.a., non-bleeding type take the current down the shaft.

Compressed air is provided by two Alley & Maclellan 290 r.p.m. compound steam-engine driven two-stage compressors having a capacity of 2,500 cu. ft. of free air per min., the final pressure being 80 lb. per sq. in.

The main ventilation is natural ; as No. 1 pit is 140 ft. deeper than No. 2 pit and also the No. 2 shaft surface level is 150 ft. higher than the No. 1 shaft, the thermal conditions favour a constant draught. This effect, moreover, is intensified by the fact that the No. 1 shaft, the downcast, is wet and the air current is assisted by the dynamic and cooling action of the water, whereas the No. 2 shaft, being dry, offers no counter resistance. Auxiliary ventilators underground consist of a 15 in. dia. 5,000 cu, ft., per min. Sirocco fan, belt driven by a Mayor & Coulson 500 V d.c. motor; a 20 in. Rateau compressed-airdriven turbo-blower; and a number of smaller fans and venturi jet injectors.

Underground equipment

For development work bar-type machines are for the most part used. For robbing the pillars, the jackhammer has proved to he an excellent machine, and for the rises stoping machines are used. The drifters are provided with 1¼ in. round hollow steels, while the jackhammers and stoping machines utilise a 7/8 in. hexagonal section. Holman, Ingersoll-Rand, Climax, Hardy and Gardner-Denver are the makes represented, all being of the wet-drilling type.

The holes are charged with Blasting Gelignite and Eversoft Gelamex, according to circumstances; ordinary fuse firing is normally used but delay-action fuse is adopted when firing rounds in the development headings.

In connection with the face operations, a mist projector for settling the dust calls for special mention. It is illustrated in Fig. 4, and consists of a standard Gardner-Denver air-line oiler fitted with suitable water and air connections for coupling to the pressure pipes which are laid into every working, and also an open branch pipe to enable the resulting jet spray to be directed into the working place after blasting. The charge consists of a pint of oil which mixes with the water to reduce the surface tension and so induce a fine spray capable of easily "wetting" all dust particles. The jet is blown for about ten minutes after blasting, after which the men are enabled to renew their work, even in large places.

All the haulage work is done mechanically throughout the mine except on a few short, level runs when trailers are still used. The main haulages are of the endless-rope type, the bogies being attached in sets of three by a screw clip. Auxiliary work is undertaken by "Turbinair" and "Pikrose" tuggers which are particularly useful for pulling full tubs up dip workings. Wherever possible, of course, self-acting inclines are adopted and a number of gravity-balance drop-shaft winders are also in operation.

Particular care is taken with the track, which is laid with flat-bottomed rails weighing 27 lb. to the yard. They are dogged to 6 in. by 3 in. larch sleepers, the track gauge being 2 ft. 6 in. The roadways are for the most part driven in solid ground and thus need no support, but when necessary steel arches are used as shown in Fig. 6. Two sections of arch are used, 5 in. by 4 in. and 4 in. by 3 in., according to the strength required, and are strutted with angle-iron distance pieces and backed by timber or corrugated sheets.

Ore handling

Hand decking is employed at the surface, the bogies being subsequently raised by a 12 h.p. creeper to a height from which they gravitate to the tipplers. These are two in number and are of the automatic revolving type supplied by Head Wrightson & Co. Ltd. The ore falls on to a shaker feeder which discharges it to a plate-type picking belt, 4 ft. wide and 90 ft. long, and thence to a cross belt 4 ft. wide and 26 ft. long. From here it is loaded into hopper wagons and taken to the blast furnaces at Workington.

Drawings and Photographs accompanying the article