Ernest Leopold Ahrons

“ Naturally when the conditions are such that a large number of similar engines can be constructed together with the help of special tools and “jigs,” the cost per locomotive is very considerably reduced. An isolated engine of a new design is necessarily expensive, but it generally pays a railway company to build such an engine, so that it can be tested thoroughly, and the necessary modifications and alterations made before placing a large order. ”

“ An engine built at a railway company’s works is immediately sent out on a trial run of some 20 to 25 miles without a train. During the trial the working of the motion, springs, brakes, injectors and sandgear is noted carefully. The big end and axlebox bearings must run perfectly cool, and there must be no leakages at any of the joints, to which the fittings and mountings on the boiler are attached. Everything that is not satisfactory is noted for rectification when the engine returns. ”

“ The engine is placed over a special pit in such a way that its coupled wheels drive by friction another set of wheels and axles fixed across the pit. The engine can be run under its own steam at any speed desired, and the draw-bar pull is measured by a special apparatus at the back. Coal, water and oil consumptions at certain speeds over a definite length of time are measured and recorded. This form of test plant, which is extremely valuable for experimental purposes is of American origin, but there is only one in this country, at the Great Western works at Swindon. ”

“ The various pins in the valve gear wear slack in their holes, and the holes in the links through which they pass are found to be enlarged. The metal being case-hardened these holes cannot be re-bored, but they may be made true by lapping them out with a lead mandrel using emery and oil. An alternative and more rapid method now generally employed is to use a special grinding machine with a very small wheel. If the enlarged holes be used as they are, new pins are required, but in many cases the holes are bushed with hardened steel bushes. ”

“ As the tubeplate expands in a vertical direction when the boiler warms up, the tube holes gradually assume an oval shape and leakage then occurs round the tubes. Overheating of the plates, due to occasional shortness of water, causes burning of the plates. Expansion and contraction cause frequent breakages of the stays which unite the roof and sides to the firebox casing, and bulging-in of the plates may then result. The presence of defective side stays is detected by tapping the heads with a light hammer, when an experienced man can tell them by the sound. ”

“ Cylinders. Cylinders are the most important and difficult castings made in the foundry. The difficulty lies in the number of complicated passages which have to be moulded by means of sand cores. If a passage has to be made in a casting, that portion of the mould which represents the passage must, of course, be filled up with a piece of special sand made to the shape and dimensions of the passage, so that when the iron is poured into the mould the metal flows round this “core,” which remains in place until the casting has cooled. ”

“ Axles, especially driving crank axles, are subject to very heavy bending and twisting forces, and are watched very carefully for flaws and cracks. If a minute crack begins to show itself the axle may be allowed to run until the crack develops, when the axle is immediately condemned, the wheels forced off by hydraulic pressure, and a new axle substituted. Other than flaws, the chief running defect is oval wear of the journals which work inside the axleboxes, and a similar oval wear of the crank pins of driving axles. ”

“ The roof stay holes in both the firebox and the top of the shell, when direct roof stay bolts are used, are reamered out with long reamers, and the holes are tapped in position for the stay screw threads. The reamering and tapping of screw threads through the plates are done by means of pneumatic drilling machines. These are driven at high speed by compressed air, and are arranged to take drills, reamers, taps, etc., as required. It may here be mentioned that every modern boiler shop is equipped with a complete air-compressing plant, from which pipes are taken to every part of the shop. ”

“ The work produced in the iron and brass foundries of a locomotive works is similar to that done in most general engineering foundries, except perhaps that locomotive cylinders are somewhat more complicated than those of most stationary engines. The moulding and casting of metals is a separate trade in itself, of which only the briefest mention can be made here. [1]
Iron and Steel Castings. ”

“ An oil treated crank axle should have an ultimate tensile strength of not less than 35 tons per sq. in. with an elongation of not less than 20 per cent, in a length of 2 ins.
There are other methods of making crank axles by building up the second crank web with slabs welded to the bloom in such a way that the twisting of this web through a right angle is avoided. In some foreign works the webs are swaged in dies in their proper positions at right angles.
Miscellaneous Forgings. Connecting and coupling rods are forged solid out of slabs of mild steel ”

“ Before any permanent fixing is done the foreman of the shop has to go over and test the whole of the work, taking measurements longitudinally, transversely, and diagonally to see that frames, cylinders and cross stays are perfectly square and that all dimensions are correct in accordance with the drawings. ”

“ This method of swaging or forming the shape in dies is characteristic of nearly all locomotive forgings, when any quantity has to be made. Naturally it does not pay to make expensive dies when only one or two similar forgings are required. In such cases the forgeman has to work out the shapes with such ordinary swages and tools as are usually to be found in a forge.
The most difficult forging, and the one requiring the greatest care is that for the crank axle. ”

“ A considerable amount of forging is now done by hydraulic press, instead of under a steam hammer. In this case the white hot pieces are welded by squeezing them together under pressure, the process being done in blocks or dies as in the case of hammer forgings. At one large railway works some of the casings in which the buffer heads work are made in this way, more especially for wagons. ”

“ Acetylene welding has been used, chiefly in America, for repairing cylinders, especially in cases where flanges are broken.
Wheels and Axles. With the exception of the boiler these require more attention than any other part of the engine. The wheel “centres” themselves very rarely crack now that they are of cast steel. The former wrought iron driving wheels used sometimes to crack between the spokes at the boss, but these are not made now, though a considerable number are still in service. Broken or flawed tyres are replaced immediately, no attempt being made to repair them by welding. ”

“ In British practice the mountings are not screwed directly into the boiler plates. Steel “pads” or seatings of the same shape as the flanges of the mountings having been previously riveted to the boiler, the flanges are secured to these by studs. The joints are faced and scraped, and either made metal to metal with boiled linseed oil, or a thin sheet of asbestos slightly smeared with red lead is placed between the faces. The nuts are then tightened gradually to make an absolutely steam-tight joint. ”

“ There is also the third or “stamping” department, in which a large number of parts, formerly made by the blacksmith, are now stamped to shape in dies under gravity or “drop” hammers.
All wrought iron and mild steel parts of a locomotive, such as axles, connecting and coupling rods, piston rods, the machinery or “motion,” and a large number of other details are made in one or other of these departments. The springs are made in the spring shop by the spring smiths, and their manufacture is an art requiring special knowledge. Frequently they are purchased outside. ”

“ Boiler Plates and Making the Boiler Barrel. The steel plates are delivered into the boiler shop after they have been sheared to sizes about 1⁄2 in. larger all round than the finished sizes to which they are put together in the boiler. They must be of the very finest quality, since they have to undergo processes, such as flanging, punching, etc., which would inevitably crack or otherwise injure inferior material. ”

“ In boiler barrels up to about 12 ft. long, two plates are generally used instead of three plates as in former practice. For longer barrels three plates are usual, though two are sometimes used. Engines have recently been built for the Great Northern Railway, in which the barrel 11 ft. 51⁄2 ins. long is made of a single plate. Such plates have the advantage of dispensing with a transverse riveted seam, and are consequently stronger, but large plates above certain commercial sizes are more expensive per ton weight.
The plates have to be joined together by riveted joints. ”

“ All lines such as d and e for surfaces which require planing are marked. Vertical centre and other vertical lines are drawn with the blade of a T-square having its broad edge on the table. The bore of the cylinder and all holes are drawn with compasses and centre popped. The dimensions are taken from the drawings, or in the case of standard engines will be measured from gauges specially made for the cylinders of different classes of engines. The whole work must be checked carefully to see that there is sufficient material on all surfaces for planing and boring to finished sizes. ”

“ For instance, the firebox of a locomotive boiler is stayed with a large number of screwed steel and copper stays. In the latest practice these are screwed in machines which are placed in a convenient bay in the boiler shop itself, but it is more often the case that they are made in one of the machine shops, from which they go to the boiler shop. ”

“ To prevent the coupling rods from being thrown off the wheels, washers are placed on the ends of the coupling rod pins, and secured by nuts and taper split-pins.
Only miscellaneous work now requires to be done to complete the engine. The firebars are placed on their bearers in the firebox, and the ashpan is bolted up underneath the firebox. The brake gear has also to be rigged up with all its attendant levers, and the cylinder cocks and levers, sandgear, sandpipes, various steam and water pipes and connections to the tender are then put up. ”

“ In some works the leads are measured, not by marking the valve spindle, but by pressing thin wedges into the space A1 B1 between the edge of the valve and that of the port, so that these edges leave marks on the wedges which can be measured.
If the front lead a1b1 is equal to that a2b2 at the back the valves are properly set “to equal leads,” and no further adjustment is necessary. If, however, the lead a1b1 in fore gear at the front is say 1⁄16 in, whilst a2b2 at the back is say 3⁄16 in., the valve requires adjusting. ”

“ The latest practice is to machine the pistons on a heavy turret lathe, in which a number of tools are fixed in a revolving turret. When one operation has been completed, the turret is turned through an angle to present another tool to the piston for the next operation, and the first tool remains in correct adjustment for use on the next piston in due course. The holes for the piston rod are bored with a large twist drill ”

“ They are tightened in the holes by means of a tube expander, a special tool provided with a number of rollers. This is placed inside the tubes, the metal of which is rolled outwards until they are a tight fit in the holes. In the case of steel tubes a ridge or beading is also rolled on the tube on the boiler side of the firebox tubeplate. Brass or copper tubes are expanded and secured by driving short pieces of steel tube (called ferrules) tightly into the ends which pass through the tubeplate. At the smokebox end the tubes are merely expanded, neither beading nor ferrules being used. ”