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Colliery Engineering

July, 1956

Underground developments

It was decided to develop the Low Main seam first and from Fig. 9 it will be seen that this has been done on the advancing-longwall conveyor system. Altogether four double unit conveyors, two single unit conveyors in the Low Main seam and development work in the Beaumont seam are producing an output of 1,250 tons per day and this is expected to rise to 1,500 tons per day as development proceeds. Two double-unit conveyors have benks of approximately 100 yards each side, another has benks of 100 yards and 40 yards in length and the other has benks 65 and 45 yards long respectively. One single unit conveyor face is 120 yards in length and the other 50 yards.

Gate and face supports

Gate roads are ripped to 12 ft. by 9 ft., first ripping to this size obviating the need for back ripping. Steel arches, 9 ft. by 5 in. by 4 in., positioned by Weldon struts, are set on stilts 4 ft. apart.

Face operations are cyclic and are carried out on a cut-fill-moveover sequence that is completed in 24 hours. The first longwall faces to commence operation were supported with wooden props set 3 ft. apart under 6 ft. steel corrugated benk bars. Some eight months ago a 100 yard face was equipped with Huwood T.C.R. props in place of the wooden props. In view of the satisfactory results obtained, both from the point of view of roof control and economy in support costs and transport charges, a further two faces have been equipped with these supports and it seems likely that the colliery may standardise on this prop for future faces. One of the features of the T.C.R. prop which influenced the management in their choice was its long extension which makes it adaptable to seams in which the height varies.

The T.C.R. prop is one of the latest developments in the field of coalface support and is a friction type prop which features simplicity of construction and lightness together with a very early-bearing load characteristic. It consists of tubular upper and lower members made from high-quality steel alloys. At the top of the lower or outer member are mounted two clamping rings which form a yoke or friction mechanism connecting the two members. These rings have been designed, using photo-elastic techniques, to produce an evenly distributed pressure around the periphery of the inner member. This is achieved by reducing the cross-sectional area of the ring towards the open side. At the open side of each ring the two ends are drawn together by means of a wedge jaw and counter wedge. The rings or clamp collars as they are termed are constructed from mild steel while the wedge jaw and counter wedge are from carbon-steel forgings as is the bridge piece by means of which the clamp collars are attached to the lowest member. As the counter wedges are driven in they force the wedge jaws inwards and tighten the clamp collars on the inner member.

A mild-steel base plate is fitted to each prop and at the upper end of the lowest member a support collar of the same material is fitted beneath the clamp collars to ensure an ample bearing surface for the lower collar as it moves in or out when tightened or released. This support collar also serves as an abutment for the two dowels at the base of the upper member, thus preventing it from being drawn right out of the lower one and also ensuring, it is claimed, reasonable stability even when the prop is fully extended. A carbon steel-forged, castellated crown plate is fitted to the upper member of the prop.

On the upper edge of the top clamp collar are lugs fitted for the purpose of setting. Two setting devices are used according to the size of the prop being handled. On small props use is made of a clamp and wedge setting device, consisting of an annular hinged ring which is fitted around the prop immediately above the clamp collars. This ring is self-tightening and as a wedge is driven beneath it alongside the lugs on the upper clamp-collar it raises the upper member of the prop against the roof bar with a force proportionate to that applied to the wedge. To hold the prop while the setting device is being applied, one of the clamp-collar counter wedges is tightened temporarily: After setting, both counter wedges are driven firmly home before the setting device is removed. For long props with heavier upper members a rack setting device is used.

With this type of prop it is claimed that the large area of frictional surface between the clamp collars and the upper member result in only relatively light hammer blows being required to set the clamp tight enough to carry its rate load. It is possible to set or release the two clamp collars independently of each other. Thus a load of 40 tons can be sustained with the two clamps set or only half that load if required with one clamp set. When releasing the prop, half the load may be removed at first and the prop subsequently completely released by knocking out the wedge of the second clamp. The wedges are held in place by dowels when loose so that they do not fall out of their wedge jaws and become lost,

Except for six yards of packing at the gate sides, total caving is practised. the breaking-off line being induced by wooden chocks which incorporate Meco quick releases. These chocks, which are set as close to the face conveyor as possible, are 2 ft. square and built of 6 in. square timber. Moving the chocks forward is, of course, facilitated by the provision of the Meco releases which enable quick and safe collapsing; the men responsible for this work travel along the face some distance behind the erectors moving the conveyor forward.

As is usual in this class of work, the chocks are moved forward diagonally to allow the forward chock to get a hold on the roof before the back chock is withdrawn, thus giving protection for the men building the forward chock and securing the roof before the releasing of the back chock. This system allows the chock row to be as close as possible to the solid coal before cutting takes place.

In the Low Main seam, where the floor undulates and is of hard fireclay and the strata immediately above the seam are of a very friable nature, the top band of the seam and the top 4 in. of coal are left in order to form a good roof. In spite of this the roof under the top coal is difficult to support. In the Beaumont seam, which has a strong roof and floor, the whole of the coal is taken.

Coal getting

All the conveyor faces are machine cut with A.B. 15 longwall coal cutters using straight Dreadnought jibs making a 4 ft. 6 in. undercut in coal. Shotholes are drilled 4 ft. apart in the coal, each hole having an average charge of 8 oz. of either Lodespex or Minespex explosive to blow the coal down.

The coal is then hand filled on to bottom-belt Huwood SL5, or 20 in. Meco face conveyors. These deliver on to Meco and Huwood P.F. stage loaders situated in the loading gate which load either on to 26 in. or on to 30 in. Meco gate belts. As is now widely recognised, the use of a stage loader reduces the number of extensions to the gate belt, cuts out the need for the gate belt to have to pass under the lip and, by discharging the coal on to the gate belt at the same speed and direction as that belt, reduces wear on the belting.

The Meco stage loader, it will be remembered, is an all-metal conveyor and uses a double scraper chain as the carrying medium. This chain is of the 3 in. pitch solid-link type, and attached to it by heat treated high-tensile steel rivets, are 1¼ in. square section scraper bars set 18 in. apart. Drive to the scraper chain is obtained from a 15 h.p. squirrel-cage motor through a Fluidrive traction-type fluid coupling a totally enclosed gearbox, and a transmission chain.

The motor, the fluid coupling, and the gearbox are mounted on a common baseplate which forms an integral part of the basic unit of the stage loader. This basic unit has an overall length of 29 ft. 6 in. and comprises a delivery jib with a overhang of 5 ft. 3 in. and a clearance of 2 ft. 5 in., an inclined section, and a 6 ft. reinforced receiving section to which is attached a return sprocket unit incorporating tension-adjusting screws.

All the gate belts at Havannah mine are of Meco manufacture and two sizes are employed-one 26 in, wide and driven by a 30 h.p. motor and the second, 30 in. wide and driven by a 45 h.p. motor-the larger unit being used where it carries the coal from more than one conveyor face. These gate conveyors feed on to a 36 in. Cable Belt conveyor at a central transfer point situated at the Low Main seam level on the intake drift. A view of this transfer point can be seen in Fig. 12.

As the seam is naturally wet, so that excessive amounts of dust are not raised in the air, water sprays are not required at transfer points, which are of the enclosed chute type.

Materials are taken to the face on a set of 2 ft. gauge rails which runs in each loading gate alongside the conveyor structure from the transfer point to the face. Ordinary pit tubs and timber trollies are used in this work and they are hauled by a main-and-tail rope haulage, the driving gear of which is situated near the conveyor head pulley.

The concluding instalment of this article will appear in the August issue of Colliery Engineering and will discuss the present arrangements for conveying in the drift and the surface amenities.

(To be continued)

Drawings and Photographs accompanying the article