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July, 1939

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Of the power required for mechanical coalcutting, a large proportion is expended not in effective work but in churning and grinding the cuttings taken back by the chain. This condition can be alleviated by hand-shovelling, but however efficiently the work is carried out, a considerable proportion of the cuttings is still taken back and packed solid at the back of the cut. These difficulties have led to the introduction of devices designed to retrieve the cuttings from the chains as they are brought out of the cut, the object being to leave the cut clean right to the back with the result that less power is consumed by the coalcutter, shotfiring is more effective and the break at the back of the cut is cleaner.

British Jeffrey-Diamond Limited have recently introduced a gumming device, known as the "Ace" gummer, which operates on a principle different from that employed on any other device for a similar purpose. The gummer is designed primarily for use in conjunction with the B.J.-D. "Ace of Diamonds" coalcutter, and a general view of this machine with the gumming device attached is given in Fig. 1. Fig. 2 shows the gummer about to be placed in position on the coalcutter, and shows its construction. Essentially it consists of a cylindrical cowl which is rotated by a worm drive and encloses three blades which project through slots in the cowl. These blades are independently mounted on a pin located eccentrically inside the cowl in such a manner that each blade is progressively extended as it approaches the cutter chain, and after passing the chain is retracted until it is almost entirely withdrawn within the cowl. These blades intercept the kirvings on the return run of the chain and sweep them through a large opening in the side of the gummer frame. The eccentric mounting of the pin gives a peculiar action to the blades which is particularly suitable for the purpose in view, because each blade as it approaches the chain "reaches out" to it and also approaches it with an accelerating motion designed to sweep the kirvings from the chain. After passing the midpoint the blade "angles" forward, and forms a pocket which holds the kirvings against centrifugal force. One of the blades can be clearly seen in this position in Fig. 2.

The size of the discharge opening in the gummer frame is such that the largest holings can be handled easily, and as the holings are fed into the bottom of the pile the dust nuisance is markedly abated. The device is automatically reversible for cutting to the right or left as desired.

Fig. 2 also serves to illustrate the ease with which the gummer can be placed in position. It is merely slid into place and secured by two swivel bolts, the connection to the worm drive being made through a dog clutch. This dog clutch is spring-loaded to act as an overload safety device in the event of the gummer choking, for example, when passing a close-set pack. After the gummer has been placed in position a guard plate is fixed to the goaf side of the driving head, as seen in Fig. 5, the assembly providing total enclosure for the cutting chain. The addition of the gummer involves no increase in height or width of the "Ace of Diamonds" coalcutter, the increase of length being only 16 in.

Fig. 4 shows how the pile of cuttings is conveniently placed so as to leave ample room for cogging and timbering but at the same time to be out of the line of the conveyor track. In cases where this placing is not convenient a directional chute can be fitted to place the gummings in any desired position between the rear and side of the machine. Fig. 6 is a view looking into a typical holing, and shows that the cut is clear right up to the solid.

Recording wattmeter readings on a B.J.-D. electric "Ace of Diamonds" longwall chain coalcutter, cutting alternatively with and without the "Ace" gummer on the same face and' under identical conditions, are shown in Fig. 3. The power required without the "Ace" gummer was 52 kW as compared with 37.28 kW with the "Ace" gummer in use. This gives a saving of 14.7 kW, or 28.5%. In addition to the saving in power, the machine was able to cut continuously on the full available haulage feed of five notches, as against an average of three notches when the machine was operating without the "Ace" gummer.

Drawings and Photographs accompanying the article