January 23, 1914. THE COLLIERY GUARDIAN. 187 are taken out from under a wagon or sent out of the machine shop. It is not the general practice of wagon builders in this country to burnish the journals, but it would pay the owner to go to the slight additional expense of having this done, as the better surface of the journal certainly reduces the liability of the boxes heating. A simple form of tool for this purpose is shown in fig. 7. This tool fixed in the side rest of the journal lathe in usual manner, and the roller is pressed hard against the journal, the rolling action on the journal hardens and produces an extremely smooth surface. One well-known firm of wagon builders reduced the number of hot boxes on their new wagons to a negligible quantity after the adoption of this tool for burnishing the journal. Fie. 9.—Testing Apparatus. It is important also that the wheels on the same axle should be equal in diameter, as if one is larger than the other, the wheel seat collar of the journal of the smaller wheel is forced hard against the brass, and has, of course, a tendency to make the brass heat. Rules for Workmen. Speaking generally, there is a tendency to regard hot boxes as a necessary evil, but this is far from being the case, and every stoppage for hot box should be enquired into with a view to prevention. Every man who attends to hot boxes should try and ascertain the cause. The frame of the vehicle should be tried to see whether it is square, a staff being inserted between the axleguards on the same side to see that they are the same distance apart, and diagonally to see that they are square with the centre line of the axle. If the frame is not square it may account for the hot box. The axleguards should also be tried to see whether they are bent, as the effect of a bent axle guard is to press the brass hard against one of the journal collars, and set up excessive friction and heating. Axleguards which are narrow between the legs and grip the box, preventing easy motion in the guards, are also responsible for a certain number of hot boxes, and at least | in. play must be allowed between the axleguard grooves of the axlebox and the legs of the axleguard. The spring shoes should allow the springs to have | in. play; that is to say, if the springs are 4 in. wide the spring shoe lugs should be at least 4} in. apart. This is especially necessary if the wagon is running on a line which has a large number of curves, and in the case of tank wagons which have a long wheel base. Care should .also be taken to see that the cambre of all the springs is equal, as, if it is not, undue weight may be taken by two of the axleboxes, with consequent heating. The following rules for workmen whose duty it is to attend to hot boxes might with advantage be issued. They should see that 1. Frame of wagon is square. 2. Springs have sufficient play in spring shoes. 3. Axleguards are not bent, and are not tight in box guard grooves. 4. Backs of brasses and bottoms of liners are perfectly level, and brasses not tipping. 5. Springs under any one vehicle are of equal camber. 6. Wheels on same axle are equal in diameter. 7. There is no water in the axleboxes. 8. Axleboxes, when fitted, are correct centres of axleguard grooves relative to the journals. 9. Bearing surfaces of brasses do not show any bright spots, and to report any such cases to head- quarters, as it is probable that the metal has not been properly mixed. 10. Pads are clean and syphon the oil freely. 11. Brasses have not too much bearing surface. If an oil axlebox is running satisfactorily the work- man who examines it every three months should not interfere with the bearing surfaces in any way; he should simply ascertain whether the pads are syphoning properly, and give it a fresh supply of oil if necessary. Design and Workmanship. The designs for the private owners’ axleboxes, brasses, axles, &c., are all issued by the Railway Clearing House, and, provided these are strictly worked to, he should have no trouble. Unfortunately, in the best organised works it is possible for slackness on the part of, perhaps, one individual workman to cause serious trouble. In the case of axleboxes, it sometimes happens that in the foundry the moulder does not exercise sufficient care, and axleboxes are turned out the brass seat of which is not correct with regard to the rest of the box. It may be out of square with respect to the axleguard grooves, and when fitted will concentrate the weight on the front end or back end of the brass, as the case may be. To prevent a box of this description being fitted, the best plan is to have every one tried on an apparatus, designed as shown in fig. 8. The brass is put into its position in the box, and the complete axlebox is put on the dummy journal A, the arms B are then brought round to the position shown (which is the vertical position taken by the legs of the axleguards when the box is in position on the wagon); if they line properly with the axleguard grooves the box is correct. Different sizes of journals can, of course, be fitted to suit different sizes of boxes. Fig. 9 is a photograph of a similar apparatus. Another point which requires attention is the condi- tion of the lathes used for machining and truing up journals; if these are allowed to get into a bad state of repair, or if they are too lightly designed for the work they have to do, a satisfactory job cannot be made, and ' ’ < * » 11 J. r ■ 1 - A'’***' ‘ . S. L V Fig. 10.—Sections of Iron Axles. the journals when machined will not be perfectly true, and will not, of course, run satisfactorily. The Clearing House regulations allow both iron and steel axles to be used, but for oil axleboxes steel axles are much more satisfactory owing to the homogeneous structure of the material. Iron axles, owing to the method of manufacture, are laminated in structure, and these laminations, although invisible to the naked eye, are yet a contributory cause of hot boxes. Fig. 10 shows sections of an iron axle which has been etched, and these figures make it quite clear why iron axles are not as satisfactory as steel axles. As already pointed out, the designs for the brasses are fixed, but some makers, in order to save material lighten the backs; this reduces the strength of the brass, which gets distorted under the load it has to carry, and does not give good results. The brass has also a much shorter life. The composition of brasses varies. Different wagon- makers use different mixtures. A good bearing is one made of bronze and of the following mixture :— Per cent. Copper......................... 83 Tin ............................ 9 Lead............................ 8 Brasses of the following type (composition) are unsuitable for wagons :— Per cent. Copper......................... 57 Zinc......................... 27 Lead........................... 10 Tin ............................ 6 Zinc and lead should not be mixed together, as it has the effect of increasing the friction and wear of the brass considerably. There is also a tendency to segregate, forming hard and soft spots in the bearing, which cause local heating and eventually a hot box. The lead in a copper-tin-lead alloy may be increased up to about 15 per cent., with a reduction in the wear of the brass; as the friction is increased it is not desirable to do this. It is important in all cases to see that good sound castings are used. In the ease of brasses which are lined with white metal, the composition does not signify, provided it has the requisite strength; the essential point is to see that the white metal is suitable for the load. The composition of a suitable white metal for wagon oil axleboxes is as under (see Railway Clearing House drawing 94, dated December 1905):— Per cent. Copper.......................... 7 Tin ........................... 60 Antimony ...................... 13 Lead........................... 20 It is very important that all new axleboxes should be boiled or steamed before being fitted, to clear them of the moulding sand or grit in the oil or grease chambers, as it is, of course, impossible to expect freedom from hot boxes unless this is done. The oils and greases used should be stored in perfectly dustproof casks or tanks, and cleanliness should be insisted on by the person responsible. CONCERNING THE PROBABILITY OF A SPONTANEOUS EXPLOSION * By John Foster. Up to the present time scientific investigation concerning colliery explosions has been confined to the consideration of firedamp and coaldust. An explosion occurs, as in the case of the recent one at the Universal Colliery, and it is readily assumed that either or both of the above, through the medium of flame or shotfiring, did the damage. The experiments conducted in the various parts of the world, especially those at Altofts, have been merely a demonstration of the explosibility of coaldust under the influence of the firing of gunpowder. The experimental explosions produced cannot settle the reason for all colliery explosions, for they do not explain the mysterious explosions which occur from time to time in the underground workings containing neither men or lights. Realising this, we can appreciate the ignorance prevailing, concerning “ the infallible preventive of colliery explosions ” ; and we come to the conclusion that, so far, experimental work upon coaldust has not brought much comfort to miners. A colliery explosion is not the only mystery connected with the mining industry. There is another akin to it— viz., the spontaneous combustion of certain coals, particularly the Midland and Yorkshire coals. Many theories have been propounded to account for the source of the heat necessary for ignition, all totally inadequate to account for the phenomenon of heaps of South Stafford- shire Thick coal firing on the surface unless thoroughly ventilated with perforated pipes. If, then, a slow-moving operation like the spontaneous ignition of coal cannot be explained, 'what are the prospects of a satisfactory elucidation of a high-speed operation like an explosion? Furthermore, since coal spontaneously ignites, there is abundant reason for considering the probability of a spontaneous explosion. If the laws of nature operate of their own accord to set coal on fire, why should they not operate for similar reasons in causing an explosion ? Such a proposition must surely commend itself for scientific investigation, both for the benefit of the miners, and particularly for the colliery officials who bear the brunt of the responsi- bility, and the consequent liability for blame in the event of disaster. * From tne Journal of the Moiimouttsbite Colliery Officials’ Association.