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July, 1931

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Mainsforth Colliery has had a somewhat chequered career ; sinking was commenced about half a century ago and coal was reached in June, 1877, just at a time when industry was passing through a period of intense depression after the halcyon days of the Franco-Prussian war. The sinking was abandoned, and it was not until 1900 that operations were started again. Coal was eventually drawn in December, 1905, and the output now reaches 2,900 tons per day.

There are two shafts, the downcast or No. 1 being 14 ft. 6 in. in diameter, the diameter of the No. 2 being 6 in. smaller. Both are sunk to the Harvey seam level, 850 ft. below the surface, from which all the coal is drawn. The shafts are carried down slightly beyond this depth, the No. 1 being 890 ft. deep and the No. 2. 865 ft. deep.

A twin tandem compound engine by Thornewill & Warham serves the No. 1 shaft, the H.P. and L.P. cylinders being 21 in. and 36 in. in diameter respectively, with a 5 ft. stroke. Drop valves are fitted and other accessories include a Fraser & Chalmers overwinder and a Whitmore steam brake. A 14 ft. diameter parallel drum is provided and the winding speed (850 ft. in 22 secs.) is exceptionally high for such a comparatively shallow shaft. The No. 2 shaft is used for men-winding purposes only, the winding equipment having recently been modified by the addition of a set of single-reduction helical gears between the engine and the drum. The engine itself is rather old and the cylinders (15 in. dia. by 30 in. stroke) are too small for direct duty. Ferodo lined post brakes are provided, operated by a Whitmore air engine.

The headgears are of lattice-girder construction and were manufactured by Thornewill & Warham. For the No. 1 shaft flattened-strand ropes of 5¼ in. circumference are in service and pass over 14 ft. diameter pulleys ; they carry a load of 12½ tons each. Locked-coil ropes are provided for the No. 2 shaft and have a circumference of 3¾ in., the pulleys being 10 ft. in diameter. Flat-bottomed rail guides. with dowelled joints, carry the cages in the No. 1 shaft, two being provided for each cage ; three rope guides undertake this duty in the No. 2 shaft, in which in addition two rubbing ropes are suspended between the cages. Bien type kepgear is provided in both cases.

Power Plant.

Practically the whole of the electrical power demand is met by the exhaust steam collected from the fan engine, compressors and winding engines. This is consumed in two mixed-pressure turbo-alternators through the intermediary of a steam accumulator, and normally no live steam is required. Both these sets are of Belliss & Morcom manufacture, with Lancashire Dynamo generators, and generate 3,000 volt current at a speed of 2,400 r.p.m. The first set has a capacity of 1,000 kVA. and is provided with a surface condenser, the pumps being driven at 1,460 r.p.m. through speed-increasing gear supplied by the Power Plant Co. Ltd. The second set is somewhat larger and is rated at 1,250 kVA. In this case a jet condenser is provided, the pump being driven through similar speed-increasing gear by a 90-H.P. Belliss high-speed compound engine.

For the surface motors the 3,000 volt current is stepped down to 440 volts by a 500 kVA. capacity transformer of the British Electric Transformer Company's manufacture, and in addition there are two lighting transformers of 20 kVA. each, one stepping down from 440 to 110 volts for the colliery lights, and the other from 440 to 250 for the local village lighting. A high-tension supply (3,000 volts) is taken down the pit by duplicate shaft cables each of which feeds a British Electric transformer of 350 kVA. capacity, the one supplying the No. 1 Busty and the other the No. 2 Busty and the Harvey seam. Both these units step down to 500 volts and are situated in a substation near the downcast shaft bottom.

Compressed air is supplied at a pressure of 80 lb. per sq. in. by three Belliss & Morcom two-stage units (Fig. 2), two having a capacity of 2,000 cu. ft. per minute each and the third a capacity of 4,000 cu. ft. Cooling water is supplied at the rate of 50 g.p.m. by a Mackley centrifugal pump. The circulating water for both this plant and the turbo-alternators is cooled by a spray pond. A cocoa-matting filter is provided for the intake air, and two receivers, 30 ft. by 9 ft. and 20 ft. by 4 ft., are in service to equalise the discharge. The shaft main is 8 in. in diameter and is fitted with Albion joints.

In line with the compressor units is a 570-H.P. Belliss compound engine which is directly coupled to the colliery ventilating fan through a Wellman Bibby flexible coupling. An alternative drive is provided by a 290-H.P. slipring induction motor through a rope drive (Fig. 5), but the Belliss engine is normally in service in view of the economy secured in maintaining an adequate supply of exhaust steam for the mixed-pressure turbines. The fan is of the well-known Sirocco make and is of the double-inlet type. It is .98 in. in diameter, 6 ft. wide, and is capable of delivering 230,000 cu. ft. of air per minute, at 220 r.p.m., against a water gauge pressure of 4½ in.

Eight Babcock & Wilcox boilers, each having a heating surface of 2,852 sq. ft., provide the colliery steam supply. A pressure of 200 lb. per sq. in. is maintained and the steam is superheated to 550° F., each boiler having a superheating surface of 339 sq. ft. The plant is equipped with chain grate stokers 8 ft. 6 in. long by 6 ft. 6 in. wide, giving a grate area of about 55 sq. ft. The fuel consists of washed slack from a Blackett washery it is brought to a rail-level bunker in wagons and delivered to the boiler feed hoppers by scraper conveyors. Feed water consists of ordinary mine water preheated to about 200° F. by exhaust steam and treated for hardness in a Cochrane preheater and softener situated in the pump house. Three feed pumps are in service, two Weir units undertaking the normal duty, while an older Cameron pump acts as standby.

Screens and Washery.

Screening equipment consists of four units each comprising a tippler jigging screen and picking belt, the undersize (through 1¾ in.) falling on to two rubber bands which convey it to the washery. This, as already mentioned, is of the Blackett type and has six barrels, the coal being elevated to a hopper which feeds a rotary screen. Here it is separated into trebles, double nuts, singles and peas, which are passed to the various barrels. The waste water carries with it a certain quantity of fines, and this is recovered by the apparatus illustrated in Fig. 6. This shows the settling tank from the bottom of which the fines are collected by a travelling scraper chain. This residue is used for firing the boilers.

Method of Working.

The layout of the workings has been influenced by a N.W.-S.E. reversed fault having a throw of 80 ft. This naturally interrupts the continuity of the workings, which are consequently separated into two distinct portions connected, where necessary, by stone drifts. It has already been mentioned that all the coal is wound from the Harvey level, and in order to reach the Busty coal on each side of the fault two dip drifts have been driven, a third drift, an incline, going up to upthrow coal in the Harvey seam. The haulage arrangements are ingenious in view of the measures taken to secure economy of power. Advantage is taken of the favourable load from the Harvey seam to balance the adverse load from the No. 1 Busty seam, and the endless haulage which operates the two is provided with only a 56-H.P. motor. As the drift down to the No. 1 Busty has a gradient of 1 in 6 and is 300 yards in length, and the haulage actually handles half the output of the colliery, the economy, of power which results from this arrangement is very remarkable indeed. The Harvey drift is 500 yards in length and has a gradient of 1 in 835. Coal from the No. 2 Busty is brought to the Harvey level by a 300-H.P. Wild haulage operated from the 500-volt supply. There are various other auxiliary haulages ranging from 40 to 100 H.P., chiefly main-and-tail, and in recent years a number of single-rope haulers have been introduced for pulling tubs out of dip places. These latter units are chiefly of Markham manufacture and have replaced a number of ponies.

The Busty seam has a section of from 4 ft. to 4 ft. 3 in. and is ordinarily worked on the bord and pillar system with square pillars at 44-yard centres. Both the bords and headways places are from 10 to 12 ft. wide and are cut by Hardy headers, the use of which has been so extended within the last few years that now all the narrow work, except in one small district, is accomplished with these machines.

A retreating conveyor system of working is now being developed in this seam and is giving excellent results. The method will be understood by reference to Fig. 10 which shows the layout of a typical district. Three winning roads are driven at 22-yard centres and are flanked on each side by two 44-yard protective pillars. A good sound job is made of the main winning at the outset, the finished width being 16 ft. and the supports consisting of straight girders erected on stone masonry. Bords are driven at right angles at 33-yard centres and are normally carried to a distance of about 360 yards from the winning, conveyor faces being set out when this limit is reached. Two of the 33-yard faces are worked together, that is, the coal from the two faces discharge into the same bord conveyor. Jeffrey conveyor loaders are used on the faces and it will be recalled that these machines are provided with flights, the function of which is to remove the coal after it has been undercut and shot down in the usual way. The conveyor itself is flexible and the flights are pushed into the loose material by ratchet jacks spaced at intervals along the face, some of the coal being thus transported without involving any manhandling whatsoever. A Jeffrey-Diamond sectional conveyor takes the delivery in the bord, this equipment being easily shortened as the daily retreat is made. This conveyor does not run the whole length of the bord, however, 70 yards being the maximum, the remaining distance — from 280 to 300 yards — being equipped with 26-in. Meco belt conveyor which delivers the coal to the main winning. Here the coal is not delivered to the tubs but is taken over by a trunk conveyor which has been developed by the Company specially for this purpose. This is essentially a belt conveyor, the novel feature being that instead of the drive being given from one or more drums at the delivery end, the belt is driven along the whole length from the supporting rollers, which are spaced at 4-ft. centres on the top belt and 8-ft. centres on the return side. To this end the supporting rollers, which are 8 in. in diameter and mounted on ball bearings, are fitted with grooved pulleys around which a 2-in, circumference Langs lay rope is passed. The rope makes two turns around a 2-ft. diameter fleeting wheel which is motor driven through reduction gearing at the delivery end (Fig. 11). A certain amount of tension is put on the belt at the tail end by a screw device, and the rope is given the requisite tension by a loaded bogey running on a short incline about halfway along the run of the conveyor. In addition grooved tension pulleys are placed at 16-ft. centres along the whole length of the conveyor to give the rope an effective grip on the roller pulleys. A clutch is inserted between the reduction gearing and the driving sheave to enable the equipment to be started up without throwing undue shocks on the motor. The belt is 36-in, wide and has a capacity of 100 tons per hour, the speed being 200 ft. per minute. It is built up with five plies of canvas, and was supplied by the Greengate & Irwell Rubber Co. Ltd. Up to the present the equipment has been worked very successfully up to a length of 230 yards, a 40-H.P. motor being sufficient for the drive; but it is hoped to extend the conveyor eventually up to 700 yards or more and in this way eliminate all intermediary haulages between the face and main landing. The equipment was constructed by the Ferryhill Foundry & Engineering Co. Ltd. to the design of the Colliery Company. In the district shown in the sketch plan (Fig. 10) the tubs are brought in sets of 30 and are pulled inbye from 60 to 80 yards beyond the loading point. A 40-H.P. auxiliary hauler is in service for this purpose and in this case it has been possible to arrange for the tubs to be lowered under the jib by gravity, regulation being effected by a tub controller.

Eighteen men are employed on each shift to do all the necessary work, i.e., filling, cutting, drilling, shooting, moving forward the conveyor and resetting the timber. Four faces are manned per shift and as the filling, cutting, shooting, etc., operations are carried out continuously the whole of the four conveyors are never filling at the same time so that a very regular output is obtained. Needless to say, this equalising of the output adds considerably to the value of the system.

The cut is made 4 ft. 6 in. deep by electric chain cutters, one machine being employed on each face. Trouble is experienced with the roof if the faces are kept level and one is kept two or three cuts in advance of the other. The shots are placed at intervals of about ft., Hardy air drills being employed to bore the necessary holes. The output per shift from this system averages 450 tons per man. This is only slightly more than that in the ordinary "broken" districts, but for the retreating system all classes of face work, except shotfiring, are included in this figure, and the coal is delivered into tubs at the landing.

Other Underground Equipment.

Steel arched girders have proved their efficacy for roadway support at Mainsforth and are being used to an ever increasing extent. Three standard sizes are in use — 7 ft. 6 in., 8 ft. and 12 ft., the last being used for the main endless roads and main-and-tail landings. The rolleyways are laid with 28-lb. section rails, the tubs being of 15 cwt. capacity ; these have wooden bodies, the frames being of larch. They are fitted with 10-in, manganese steel wheels of Hadfield's manufacture.

The pumping duty is fairly heavy and is undertaken by a six-stage Mackley pump capable of delivering 800 g.p.m. against a 1,000 ft. head ; it is driven by a 300-H.P. motor by the Lancashire Dynamo Company. In parallel with this unit is a six-stage Mather & Platt pump driven by 300-H.P. motor manufactured by this firm. This latter pump is supplied with 440-volt current from the trans former in the underground substation, but the Mackley receives the high-tension supply (3,000 volts) direct from the shaft cables.

This completes our brief account of the equipment at Mainsforth Colliery, and in conclusion we tender our thanks to Mr. C. Howson, the agent for the group, for enabling us to inspect the plant, and to Mr. L. Watson, the manager, for providing us with many of the data incorporated.

Drawings and Photographs accompanying the article