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June, 1946

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The principle of the reversible belt conveyor has much to recommend it, particularly for working thin seams. By using the belt in reverse to take supplies, and even men, inbye, the need for constructing a tubway disappears, and a great deal of dead work in ripping roads of normal height and width is eliminated, for, subject to ventilation requirements being satisfied, the conveyor road need only be high enough to accommodate the conveyor and its bulkiest load.

In design, however, the reversible conveyor presents certain special problems. Accurate alignment and cross-levelling are important with a unidirectional conveyor, but for a reversible conveyor they become vital. To assist in centralising the belt on a unidirectional conveyor it is a common practice to cant the outer ends of the carrying rollers slightly forwards in the direction of belt travel, so that if the belt rides to one side the direction of rotation of the rollers tends to guide it back again; with a reversible conveyor, however, the rollers obviously cannot be set in this manner, but must be placed at right-angles to the run of the belt. This robs the conveyor of its self-centring tendency.

In the reversible conveyor made by Hugh Wood & Co., Ltd., this self-centring tendency has been restored by the use of a special roller set. This set comprises three rollers arranged in troughed formation, with their axes at right angles to the run of the belt and mounted on a rocking framework, which is tilted in the one direction or the other by the movement of the belt. The outer rollers are, of course, inclined upwards in order to trough the belt, and the effect of this tilting action, combined with the upward angularity of the rollers, is to cant the outer ends of the rollers forwards in the direction of belt travel. The conveyor thus becomes self-centring in whichever direction the belt is running.

Other points that must be watched in the design of a reversible conveyor, and are covered in the Huwood design, are the elimination of projections or plate overlaps that might catch the belt fasteners, and the use of at least two driving drums in the drive head so that there is no loss of grip on reverse running.

In Fig. 2 we give a plan of a mechanisation scheme, in course of development at a West Durham colliery, which has been based on the use of Huwood reversible conveyors. The development is in the Ballarat or Top Busty seam, which is 20 in. thick, and lies at a depth of 160 yards and at a gradient of 1 in 50. Immediately above the coal is about 10 ft. 9 in. of strong blue metal, the seam having a seggar floor of 1 ft. 3 in. resting on a 3 ft. 8 in. band of post. The scheme is laid out on a panel system, the method being to drive two main entries from the shaft bottom, three main headings being set off from these entries, and panel gates turned away on either side at 120 yard centres. These panel gates are driven to a normal distance of 250 yards, after which they are holed across to form retreating longwall faces. Six faces are worked simultaneously, each face being cut and filled off once a day, using 12 in. Anderson Boyes machines with a 4 ft. 6 in. jib for cutting, and Huwood 20 in. bottom-belt conveyors for filling off. These conveyors discharge to 20 in. reversible gathering conveyors feeding a 26 in. trunk conveyor.

Tubway canch work ceases at the main entries, the only canch work in the conveyor roads being a 14 in. roof ripping, 6 ft. 6 in. wide, to give a gateway height of 2 ft. 10 in. As the overall height of the conveyor is 15 in., this gives adequate clearance for the transport of coal, men and materials on the conveyor.

A total of 160 hands is employed in the district, including those engaged on extending the main entries and headings, and on ancillary duties, and the output is 576 tons per day, making 3.6 tons per person employed.

A view of the trunk conveyor is given in Fig. l.

Drawings and Photographs accompanying the article