Tweet

---

March, 1938

---

The operation of "gumming" or "scuffling" out the kerf in the track of a coalcutter is at best a brutal and ineffective business, and is one in which, moreover, the human machine is employed at the worst disadvantage. In consequence it was with more than ordinary interest that we availed ourselves of an opportunity to see a new mechanical gummer put through its paces at Ashington Colliery, a courtesy we owe to the Ashington Coal Co. Ltd. This machine excites technical interest on account of its mechanical simplicity and ingenuity and, what is much more important, practical interest on the score of its performance. Indeed, it is difficult not to be enthusiastic about this machine, and we may as well admit that we are.

We can perhaps best give justification to this statement by summarising some of the points which impressed us when we saw this machine at work. (1) It definitely leaves the cut cleaner than can ever be accomplished by hand gumming, no matter what pains are taken and whatever the number of gummers that can be economically employed; in the cut we inspected the amount of gum left in the bottom of the cut never exceeded ¾ in. in thickness and it was evenly distributed, enabling the back of the cut to be everywhere visible. (2) The amount of dust was definitely reduced; exactly how much of course can only be established by an elaborate series of comparative measurements, but the improvement is unmistakable. (3) No kirvings were re-entering the cut to be pulverised to powder by the cutter chain and jib, and to this fact may be attributed the reduction in the dust. (4) The mechanical gummer formed an effective chain guard but in no way hampered the action of the cutting machine; at the time of our visit two-thirds of the yard face had been cut before half the shift was over. (5) The officials and machine men were obviously pleased with the device; the north-country miner is not given to gush, but his sober praises, in spite of the inevitable teething difficulties with which he had been troubled in the preliminary trials, could not have afforded us clearer evidence that here was a good thing. As we have mentioned teething troubles, due chiefly to the wrong quality of gears that were supplied, it is only fair to say that the cutter and gummer attachment is now regularly traversing its face with complete freedom from breakdowns.

A further point, and it is of significance that it was put forward by one of H.M. Inspectors after seeing the machine, is that increased safety is likely to result due to the ventilation current being able to sweep the cut clear of gas in seams where accumulations are likely to occur.

The new gummer is a product of Austin Hoy & Co. Ltd., and represents the perfection of a study of the gumming problem extending over a period of two years. Before describing the apparatus in detail it will perhaps be as well to state the underlying principle on which the design of the machine is based. With a chain coalcutting machine the picks actually drag out from 85 to 90 per cent. of the kirvings quite clear of the cut, and if anything like this proportion can be prevented from returning, hand gumming can be eliminated. In practice, however, the bulk of kirvings are packed back into the cut by the return side of the chain, and have to be laboriously removed by hand. And whatever care is exercised in this operation it is safe to say that more than 10 per cent. of the kirvings are left behind even in the best of conditions.

In the new mechanical gummer the kirvings are effectively prevented from returning into the cut. As they are dragged out by the chain they are discharged on to a horizontal disc, which rotates with the drive sprocket of the cutter chain, whence they are centrifuged to a rotary elevator of a novel type and delivered to a miniature belt conveyor leading either to the goaf or to the main face conveyor. Alternatively the kirvings can simply be deposited on the floor behind the machine. Not only is the cut left nearly clean but the whole operation is relatively dustless; this latter fact is rather astonishing, but it must be remembered that the kirvings, as they are pulled fresh from the cut, are in granular form rather than dust, and it is in the subsequent grinding that the bulk of the fine dust is formed. Also as the Hoy device is substantially enclosed, the dust has not the same opportunity of being distributed into the atmosphere.

The essentials of the machine are shown diagrammatically in Fig. 2. It will be seen to comprise three elements — a solid disc keyed to the drive shaft, a compartmented wheel into which the kirvings are thrown centrifugally by the disc and from which they drop at the rear, and a swivelled conveyor to deliver the kirvings either to the main face conveyor or into the goaf. The compartmented elevator wheel absorbs less than 1 h.p. and is driven, together with the small belt conveyor, by light gearing from the main motor. This conveyor is swivelled so that it can be threaded through the props to deliver most of the kirvings past one line of props. All this equipment, which can be fitted into dimensions of 24 in. high and 30 in. wide, is automatically reversed when the coalcutter is reversed for a return cut, and even for two way cutting the correct direction of motion is given without the use of extra gears or the need for extra controls. Indeed there are no controls, which is one stage better than foolproof or interlocking controls. An overload safety clutch, with ball or roller detents to give sensitive and uniform action, and emitting a loud warning noise when slipping, is inserted in the elevator and conveyor drives to prevent damage in case of jamming. This occurs in practice, only when large wooden chocks (used for jib control) are picked up. The effectiveness of the device was demonstrated to us during our inspection of the gummer by deliberately inserting a chock ; after a momentary stop for removal, gumming was immediately resumed.

The whole mechanism is impressively simple; there are no cams, rollers, ratchets, or indeed any delicate parts. By far the roughest work — expelling the holings from the turmoil around the shaft sprocket — is done by the centrifugal disc, and as this is a solid piece of high-carbon steel of 40-50 tons tensile strength there can be no question as to its mechanical soundness. Being keyed to the sprocket shaft no additional gears are required to rotate it, nor is the risk of picks fouling in any way increased. The cutter chain is effectively enclosed by guards which cannot be removed without making the device inoperative, and hence the difficult question of cutter and chain protection is solved. The ¾ in. of kirvings left in the cut is not enough to cause regrinding by the chain as the outside picks alone touch it; and no complications are caused so far as pick changing is concerned. The gearhead will cut as close to the bottom as any machine having a bottom plate, but it cannot be operated without such a plate, or skid. Jibbing in and cutting out are done as at present, the elevator and conveyor sections being detached for these operations. The effective length of the coalcutter is increased only slightly and the overall height and width fall within 24 in. and 30 in. respectively. It should be understood that the gummer determines the height and width irrespective of the size of the coalcutter. The added weight is under 400 lb., including the elevator and conveyors, which are removable. The heaviest detachable unit weighs 300 lb. All the driving gears are totally enclosed and run in oil. We understand that the disc and elevator wheels absorb between one and two horsepower and the conveyors about one horsepower. Against this it is estimated that there will be a substantial balance in the saving of power due to the elimination of grinding and repacking the gum in the cut.

The capacity of the gearhead is about 16 cu. ft. per min., i.e., 6 cwt. of coal kirvings or about 12 cwt. of stone kirvings. As a convenient approximation it may be assumed that a jib makes 7 lb. of coal kirvings (14 lb. stone) per inch depth of kerf, per foot of undercut, per foot of feed. Thus when operating with a 5-ft. jib cutting a 5½-in. kerf, half in coal and half in stone, the weight of material cut is 700 lb. per min. when a 30-in, feed is employed. Obviously it would be impossible for a trained athlete, working in the open air with plenty of space, merely to push such an amount of material a short distance for any appreciable period of time. But working in the confines of a coal seam and at the point of maximum coalcutting dust immediately behind a machine with inadequate light and with little supervision, the result is that the human gummer shovels only as much gum as will allow a machine to proceed without choking itself and stopping. In fact it cannot reasonably be expected that anyone would do more than this in such circumstances.

It can, we think, be legitimately claimed for this equipment that it is something more than a labour-saving device; it achieves what cannot be accomplished effectively by extra gummers — a clean cut at the back. Very often the floor or roof squeezes in so rapidly that cleaning is impossible once the cutter has passed; hence the gearhead not only does mechanically what cannot be done by hand but it also offers the possibility of separating the kirvings from the round coal. If, of course, the cut is made in the seam itself the gearhead enables the kirvings to be delivered in an uncontaminated state direct to the face conveyor.

The economic advantages are rather difficult to assess. A clean cut naturally offers optimum conditions for the explosive or other agent used to bring down the coal. The clean floor behind the machine means much in the convenience with which the conveyor can be moved forward and set up, and no time is lost in removing the usual heap of gum. There is also the saving in power, not perhaps so important in itself as in reduced wear and tear. Since the gum is loaded out separately it is conceivable that a better price will be obtained for the remaining coal and that the cleaning will be simplified or effected at less cost. The improved working conditions due to the reduced dust are another asset to which it is impossible to attach an £. s. d. value. Reference has already been made to the unmistakable improvement observed in the dust conditions; this improvement is understandable enough when it is remembered that the whole gumming attachment is fully enclosed. The only point at which we could see the dust being discharged into the atmosphere in any appreciable quantity was at the outfall of the auxiliary conveyor. Against this one source of dust with the mechanical gummer there are three distinct sources with hand gumming; in the first place there is the dust produced by the regrinding of the kirvings in the cut; in the second there is the quantity produced by shovelling away enough of the gum to allow the cutter to run satisfactorily; and thirdly, there are the serious clouds which are raised when the finely ground gum is shovelled into the goaf or on to the face conveyor. This reduction in dust is a very tangible asset from both the safety standpoint and the better conditions afforded to the miner in which to work. Nothing is more expensive than human labour, and it is a wise economy to direct the utmost attention to its elimination, and when this is impossible to ensuring that the conditions are such that the human machine has decently humane conditions in which to function with proper efficiency.

Drawings and Photographs accompanying the article