February 13, 1914 THE COLLIERY GUARDIAN. 349 THE CARRON HAULAGE GEARS. The Carron Company have exceptional facilities for the manufacture of mining plant—haulage gears in particular. Besides being colliery proprietors and iron- masters they have at Carron one of the best equipped engineering works in the country. The haulage gears in use in the company’s mines have been designed and manufactured in their own works, and the success attending their operation and their freedom from breakdown and costly upkeep have led the company to place their experience and manufacturing resources at the disposal of the trade. A typical gear is a portable single-haulage gear of 25-horse power direct driven through a worm and worm wheel. The fleeting wheel is attached to a coned end of the main spindle, so that when desired to shift quarters it may be readily removed. The haulage may then be drawn along the rails to any desired point. The worm is a removable sleeve of phosphor bronze, and the operation of renewing a worm when a spare is kept need not occupy an ordinary mechanic more than an hour or so. All the journals are lubricated separately from the worm itself by ring-type lubricators, and the worm may be inspected at any time by means of the sight hole at the top. Fig. 1 shows an endless rope haulage gear, which has afforded great satisfaction where installed. There are really two haulages, worked by a motor, common to both, through spur gears. At any time, should it be desired, the haulages may be separated, and each worked independently by a slight alteration, and of course a motor to drive each unit. The haulages are worked by means of worm gear, absolutely silent in operation, the thrusts being taken, both for wheel and worm, on Hoffman’s double ball thrusts. A cone brake is applied to the worm spindle, which comes into opera- tion at the instant the clutch is disengaged. The clutches themselves run in oil baths, and are of the Fig. 1. well-known coil clutch type. This gear is made in seven sizes, from 10 to 50 horse-power, giving half this power on each fleeting drum. Fig. 2 represents a belt-driven double endless rope haulage, having strong machine-moulded double helical spur gearing for the first gear. In the 50-horse power size this wheel has 90 teeth, 2 in. pitch and a working face of 7 in. with strong box section arms. It is usually made of specially tough cast iron, but where liable to sudden strain cast steel is recommended. Clutches shown are of the coil type, but band clutches may be substituted. Clutch gear is of the screw type, enabling the gear to pick up its load very gradually. Inter- mediate wheels, including driving wheel, have machine- cut teeth with broad faces, so that the gears run smoothly and with a minimum of noise. A large split wrought iron pulley is keyed to the driving shaft to suit a belt of ample width to prevent slipping. The fleeting wheels are shod with six removable chilled cast iron trods of a “ 0 ” section shape, which have been found the most satisfactory after experimenting with different types. The bedplate is of rolled steel joists 12 in. by 6 in., with ends composed of rolled channels 12 in. by 3J in. and suitable chequered foot plate and connecting gussets, angles, &c., very strong and rigid. Instead of brakes Carron Company’s special silent sliding pawl can be fitted, which works most satis- factorily. The main bearings are siphon lubricated, the remainder being fitted with self-oiling rings. Attention may also be called to a self-contained portable endless rope haulage, with the motor mounted direct on a heavy cast iron bed attached to main steel bed frame. The main spur wheel and pinion have double helical machine-moulded teeth—90 teeth, 2 in. pitch 7 in. width of face with strong box section arms of strong tough cast iron. There is no clutch on this gear, but one can be fitted if desired. The brake is of the differential type, so that on the lever being dropped it engages at once with the wheel and is self-holding, gripping harder as the load increases. It may be gradually applied, and is also self-releasing, similar to a pawl, on the motor being set away, or may be released by hand. The intermediate wheels are machine cut, the driving pinion being of raw hide. The bearings are of the self-oiling type with the exception of the main shaft, which has siphon lubricators. EXPLOSIONS IN MINES, Lecture by Prof. Dixon. Prof. Harold B. Dixon, F.R.S., professor of chemistry at the Manchester University, and a member of the Explosions in Mines Committee, lectured on Monday evening, in the Chemistry Theatre of the University, before a large audience, on mine explosions. Prof. Dixon, of necessity, went over a good deal of ground which is familiar co mining men, but his lecture was pleasantly instructive to most of his hearers. His words were accompanied by experiments vividly illus- trating the dangers of the coalmine. The explosion of firedamp and air, he said, so far as experiments on a small scale had yet been carried, resembled the explosion of coal gas and air. It began comparatively slowly, but increased in velocity and set up vibrations. Now the firing of coal gas and air in small tubes did not produce much violence, and attempts to set up anything approaching the explosion-wave by allowing the flame to travel down long tubes (or by firing a detonator in the mixture) had ended in extinguishing the flame. But since his discovery that the rates of the cyanogen explosions were influenced by the diameter of the tube, they had found at Eskmeals that mixtures of coal gas and air gave violent and rapid explosions in a pipe 1 ft. in diameter. It was possible, then, in spite of failures in small tubes, that in the gallery of a mine firedamp and air might explode with violence. But a study of the great mine explosions of recent years had shown that, although firedamp might have initiated explosions and in some cases contributed to the spreading of the flame, nevertheless the main cause of the violence was the ignition of coaldust thrown up into a cloud in Fig. 2. the air of the mine. The burning of such cloud of dust sent forward a gust of air, raising the dust ahead, and preparing the inflammatory mixture to feed the advancing flame. The flame advanced through the cloud of dust and air with increasing violence, especially when obstructions in the gallery reflected waves back, and caused eddies in the air. Large vibrations were set up in the column of air in the mine, and these caused local compression and more violent combustion. He did not think it possible for a true explosion-wave to be propagated through a dusty mine, but something approaching the explosion-wave in violence and velocity was reached in certain regions traversed by the explosion. It was almost impossible to illustrate a coaldust explosion on a small scale ; it was this difficulty, indeed, that so long delayed the recognition of the danger of coaldust. Even on the large scale special means were required to start an explosion. Just as there were gaseous mixtures that could not be fired by an ordinary flame or a spark, yet can be fired by the impact of an explosion-wave—so there were mixtures of coaldust and inert dust which would propagate an explosion through- out a gallery if ignited by an intense wave of ignited coaldust and air—but could not be ignited by a moderate flame. Conclusions. The conclusions drawn from the experiments were as follow:— 1. The behaviour of coaldust is different according as the mode of ignition differs in character. For example, a flame of burning gas, unaccompanied by any concus- sion or violent disturbance of the air, will fail to cause even pure coaldust to propagate flame for more than a limited distance, when the dust is simply deposited in the path of the flame. In order that an explosion of coaldust should be propagated, it is necessary that the dust should be in suspension in the air as a fairly dense cloud for a considerable distance. When the flame is accompanied by concussion, as is the case with a blown- out or overcharged shot, it is no longer necessary for the coaldust to be previously in suspension in the air ; but it must be so disposed in the region of the shot that the flame following the concussion shall have every chance of igniting a considerable volume of dust-cloud. 2. A mixture of coal and incombustible dusts in equal proportion by weight is non-ignitible even by such a flame as is produced by the firing of a stemmed charge of 24 oz. of blasting powder from a cannon. It will, therefore, not be ignited by the flame of a blown-out shot. A mixture in these proportions (1 : 1) is, however, capable of being ignited by the flame of a coaldust explosion (started by means of a cannon shot) that has already travelled over 200 ft. of our large gallery strewn with pure coaldust: so that after the flame has traversed a gallery strewn with pure coaldust, the explosion can be propagated by a mixture of equal parts by weight of coal and incombustible dust. A mixture containing two parts by weight of incombustible dust to one of coaldust is capable of prolonging the flame of an explosion started by a gunpowder shot in pure coaldust, and propagation of flame may continue for a considerable distance through such mixture before it dies out. Such mixtures might propagate flame indefinitely if the zone of combustion were under higher pressure. Our experi- ments have only dealt as yet with inflammations in the gallery open at one end and without obstructions. 3. A slowly travelling inflammation, such as is pro- duced when a dustcloud is ignited by a large jet of gas (unaccompanied by concussion), is capable of licking up coaldust deposited upon the surface of an incombustible dust and propagating itself for some distance if the incombustible dust is not readily raised in suspension ; but when a lighter incombustible gas, such as flue dust or fuller’s earth, is employed, both coal and incombus- tible dust are raised in suspension together, and the flame soon dies out. 4. A cloud of ignited coaldust may travel a consider- able distance along a clear gallery free from coal or other dust. In many cases also we found that an ignition caused by the cannon and tube succeeded by 250 ft. of pure coaldust travelled 500 ft. along a gallery strewn with 1, 2, or even 3 pounds of incombustible dust to 1 lb. of coaldust per foot run—the mixture of inert dust and coal being largely blown out of the gallery in front of the flame. 5. Incombustible dust is more effective in preventing the ignition of coaldust (by such means as a blown-out shot or a blower of gas) than in checking an explosion that has started in a region containing pure coaldust. The incombustible dust should, therefore, be distributed throughout the mine. If maintained throughout the mine in the proportion of between one and two parts by weight of incombustible dust to one of coaldust, the chances of ignition taking place would be very small. The disposal of the stonedust in zones or in barriers leaving portions of the mine untreated is, therefore, not desirable. 6. In the case of mild inflamma- tions, light incombustible dusts have been found so far to be more effective than heavy dusts. Shaledusts, or even heavier dusts, such as sand, are, however, effective when sufficient violence has been attained to raise them in suspension in the air. We propose to experiment specially on the behaviour and efficiency of various kinds of stone and other inert dusts. 7. The proportion of incombustible dust which it is practicable to employ in any given mine must depend upon the circumstances of that mine. The more that can be used without unduly impeding the work of the mine the better. The roads should be cleared up from time to time, and if coaldust accumulates on the top of the incombustible dust it should be removed or raked in. 8. We consider that it is desirable that dry and dusty mines, where watering is not practicable, should be treated with finely pulverised incombustible dust, and the accumulated dust periodically removed. It may be added that the use of incombustible dust entails little expenditure in plant or machinery; and that should future experiment show that a greater or less quantity of incombustible dust is required than is indicated by the experiments so far made, there will be no difficulty in varying the quantity. Fortunately, an overdose of the remedy will do no harm. The success of incombustible dust can ultimately only be determined by trial. It is, perhaps, impossible to make a dusty coalmine as safe as a mine which contains no coaldust at all. Such safety as is attained must be regarded as relative and not absolute; we are, however, convinced that the dangers of an explosion will be greatly diminished by the use of incombustible dust. Reduction of Oxygen not Feasible. Incidentally Prof. Dixon mentioned Dr. John Harger’s proposal to do away with the possibility of explosions in mines by reducing the quantity of oxygen in the air to 17 or 18 per cent. This, he thought, was not a very feasible plan. For one thing, an overdose would do serious harm—unlike an overdose of stonedust —and again, ignitions were possible even when percen- tage of oxygen was less than 17 per cent. He had known ignition occur when the percentage of oxygen was 15; on one occasion a flame came when the percentage was only 13J. So an explosion might occur in those circumstances, though not so badly, even if the oxygen had been diminished, and he did not think the air would be so pleasant to work in, even if they succeeded in making it safe. The special board for physics and chemistry of the University of Cambridge have appointed Mr. F. E. E. Lamplough, M.A., Trinity, an assessor in chemistry to the examiners for the Mechanical Sciences Tripos.