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February, 1934

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The operations which we are able to describe herewith, due to the courtesy of the management of the Lambton group of collieries, are taking place in a district of the Lambton "D" pit,, in the Low Main seam, which lies at a depth of 420 ft. from the surface. At the face in question the seam consists of 2 ft. of coal and is overlain by 3 ft. of banded shale; under the workable seam, which consists of high quality household coal, is a band of exceptionally hard splint underlain by fireclay. This splint, in which the kirf is made, presents a particularly difficult cutting problem. The hard splint is 6 in. in thickness, and if the cut is made in fireclay below, the splint comes down in large slabs, which have to be broken up, and interfere with the working. To make the cut in the coal would involve a serious loss, and it is consequently necessary to take in the band and part of the relatively soft fireclay underneath. With an orthodox type of cutter there is a tendency for the chain either to work up into the coal or to drive downwards into the soft fireclay. To prevent this from occurring and to keep the kirf at such a level that the entire splint band is removed without taking in any of the good coal, a special cutter chain has been designed for the machine, having a greater. number of picks in the top than in the bottom. As indicated below, this type of chain has met the conditions with entire success.

A double-unit face has been opened out, and at the time of our visit was 150 yards in length, but it is intended that future faces shall have a total length of 190 yards. The face is approached by the usual three roads, the mothergate being 8 ft. wide by 6 ft. high and the tail gates each 6 ft. by 6 ft. To enable the gate conveyor to be extended at convenient intervals the mothergate is kept cut about 9 to 12 ft. in advance of the face line, the two cutting machines taking it in turn to undercut the advanced portion. Corrugated steel straps, with wood props set at each end, are used to support the roof, the fillers arranging a temporary cantilever support next to the face by erecting a middler, to enable the cutting machines to pass. After the cut is made the middler prop is moved up to the end of the strap by a member of the cutter team. The straps are 5 ft. in length and are placed 5 ft. apart.

Filling is done on the foreshift, cutting in the afternoon and drilling at night. A crew of ten fillers is employed, five on each side, and a good day's work is represented by 170 tons of coal filled, i.e., 17 tons per filler. Two scrapers are employed in tandem on each side of the face. the whole being operated by a Sullivan scraper haulage situated in the left-hand tail gate. This consists of a sturdy and compact double-drum gear specially designed for this service, and is operated by a 500 volt 25 h.p. motor. The scraper skips were manufactured in the colliery company s engineering shops and are of 10 cwt. capacity. They are constructed with a kind of prow (Fig. 2) at each end, the object of which is to prevent the rectangular corners of the skip proper from catching against the timbering. At the tips of the prows rope rollers of the sectionalised Grainger type are fitted to carry the tail rope. In practice the inbye skips are only able to travel to within about 10 ft. of the fast ends of the face, so that the coal from the nooks has to be cast this distance into the line of travel.

The bridge over the gate conveyor is provided with a hopper, and baffles are fitted to distribute the load. To guard against spillage still further at this point, and also at the discharge end of the gate conveyor, the trough section is modified. Thus instead of being at the standard angle, the two side rollers supporting the belt are set at a slightly steeper angle, this having the effect of heaping the coal in the middle of the belt and leaving the sides, as they flatten out against the normally set rollers, quite clear of coal particles. A similar concentration of the load, which is caused to take place immediately before the delivery end, is also helpful in preventing side spillage. A further feature in connection with the three roller idlers is that they are mounted on one bracket, in a manner which is claimed not only to afford support to the outer ends of the two inclined rollers but also tends to keep the belt central. This is stated to prevent the belt running off and turning over on the driving drum, which may sometimes happen with ordinary troughed belts if the idlers are not continually in adjustment. As a further point, the receiving end of the conveyor is entirely closed in a trough so that small coal cannot penetrate even during periods of heavy overload. Furthermore, the return belt throughout the length of the conveyor is protected by inverted troughs which are so shaped as to prevent the lodgment of any fine coal that may filter through the fasteners or spill from the top belt.

This conveyor was supplied by Hugh Wood & Co. Ltd. and is provided with a 26 in. belt and driven by a 16 h.p. interfrequency motor. It can easily be extended up to the limit set by the power of the motor, which at the present rate of output is equivalent to about 450 yards on the level. The belt has a peak delivery rate of 50 tons per hour, so that it is easily able to deal with the varying feed from the scraper loaders.

Each of the cutters is worked by a crew of two men, the driver, and a mate to look after the timbering; a third man is employed to clean out the kirvings, which are cast back into the goaf. A 75-yard cut is made by each machine in from 6 to 8 hours, including the time required for turning and changing the picks. The cut is 6 in. in height and from 4 ft. 6 in. to 5 ft. in depth.

In the night-shift three men on each side draw the necessary timber, move forward the scraper and bridge, and also extend the gate conveyor twice a week. The three roads are ripped by seven stonemen, and shotholes in the coal, which are placed 2½ yards apart, are drilled by one man on each side of the face. In connection with the shotholes, however, experiments are being conducted with an electric rotary drill.

As the new "Sullivan-Forty" coalcutter is the chief item of interest in the equipment of this face, we take this opportunity of giving some account of its leading characteristics. Of these the relatively high power (40 b.h.p.) and the unique feed mechanism particularly call for emphasis. The high horsepower is of special advantage, as in many cases it enables a satisfactory cut to be made in a useless band or stratum, which would severely tax a lower-powered machine. It is on account of the peculiar feed mechanism, however, that special claims are advanced in the matter of hard holing. With this mechanism the rate of feed is virtually a function of the pull on the haulage rope; that is, the rate of feed is semi-automatically adjusted to the type of the material being cut, no matter whether this varies from hard to soft in quick alternations. When the pull on the haulage rope decreases, indicating softer or freer holing, the feed automatically increases. When the reverse occurs the feed automatically decreases. This results in better clearance of the picks, as they are not continuously crowded into the cut irrespective of the holing, and the stresses to which the machine is subjected are thus minimised. The use of a friction clutch also acts as a valuable safeguard, because in the event of the cut being too heavy the clutch will slip. The clutches are of the multiplate type with very liberal contact area, and intensive operation over a period of two years in America has shown that no undue wear takes place in service.

A view of the feed mechanism is given in Fig. 4. The motor drive is received through pinion a and transmitted through an intermediate shaft carrying pinions b c to a high-speed friction clutch housing d. This housing is keyed solid to a shaft which carries at its farther extremity a pinion e driving through pinions f and g a second friction clutch housing h which gives a low speed. A worm i is mounted freely on the shaft carrying housing d and pinion e, and by means of the friction clutches contained in the housings d and h can receive the drive at either high or low speed. The worm i engages with the worm wheel j which is mounted integral with the spur pinion driving the rope drum.

This feed is infinitely variable between zero and a fixed maximum which can be varied for any particular seam by changing two gears. Only one feed handwheel, k, is employed; by turning it in one direction the fast flitting feed of about 25 ft. per minute is engaged, and by turning it in the opposite direction the variable cutting feed is brought into play. This control wheel can be turned easily by one hand and any desired rate of feed instantly secured even while cutting. Ratchet mechanism is eliminated and alloy-steel helical gears, hardened and ground, are used throughout with the exception of the one bronze worm-wheel. So far as we are aware no feed of this character has ever been applied before to a coalcutter.

The "Sullivan-Forty" electric motors are manufactured by Metropolitan-Vickers Electrical Co. Ltd. to Sullivan design and specification. The power-space ratio is unusually high and every effort has been made to secure maximum reliability. To this end fins are fitted to the casing to allow adequate heat dispersal, and asbestos wound formed coils are employed.

Drawings and Photographs accompanying the article