Steam Locomotive Construction and Maintenance/Chapter VIII
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Chapter VIII. Erecting Shop
Frames. In the erecting shop all the parts which make up the complete locomotive are assembled and put together. The frame plates, which form the foundation of the engine, are first taken in hand, and are placed in position on opposite sides of a long pit. This pit is made in the floor of the shop between the rails on which the engine will stand later after the wheels have been placed in position. The frames are placed vertically in their natural position, and rest in grooves made in the heads of screw jacks. By means of these jacks the frames can be levelled, and set in the exact positions required. The frame plates are held temporarily at their proper distance apart by long bolts and distance pieces, until the permanent stays are fastened to them. They are then levelled both longitudinally and transversely by means of long straight edges upon which spirit levels are placed. Their vertical adjustment is made by plumb lines. Both frames must be placed exactly opposite to each other in their proper relative positions. This adjustment is made by placing straight edges across the faces of the hornblocks, and using “trammels.” A trammel is a long steel rectangular bar with sliding compass points, the latter being set to a definite distance apart according to the dimensions on the drawings. The trammelling is done diagonally across the frames between points marked on their top edges immediately above the line representing the centres of the axles. This is shown in Fig. 41 in which F F represent the two frames in plan, and A₁ A₂ A₃ the centre lines of the axles. The dotted lines show the
Fig. 41. — Trammelling the Frames.
diagonal directions of the trammels. By trammelling diagonally the “squareness” of the frames is ensured when the distance x₁y₂ is equal to the distance x₂y₁, and y₁z₂ is equal to y₂z₁. At the same time the longitudinal and transverse dimensions must be also checked by trammelling, and x₁y₁ must be equal to x₂y₂ longitudinally, and x₁x₂ equal to y₁y₂ transversely, similar measurements being made for axles A₂ and A₃. The motion plate f (Fig. 42), the cross stay g in front of the firebox, and the drag-box casting h are then temporarily bolted in place to secure the frames together, the bolts used being smaller than the holes in the frames, so that any necessary adjustments can afterwards be made by slightly moving the parts. It is essential that the engine should be built perfectly “square,” otherwise it will not run freely, and endless trouble and extra repairs will result.
A long steel straight edge a (Fig. 42) is fastened across the front of the frames at a suitable height, which may be measured from the drawings. Another straight edge b is fixed across the driving hornblock faces. Thin wires representing the cylinder centre lines are stretched tightly between the two straight edges, their distances apart and from the two frames being measured from the drawings. These wires it will be noticed pass through the bores of the cylinders. In place of the straight edge a, it is very usual to fasten the front ends of the two wires to steel strips fitted across the front end of each cylinder, each strip having a small hole exactly in the centre of the
Fixing the Cylinders. The cylinders are then lowered into place by a crane, and fastened temporarily by ordinary bolts. They rest upon two screw jacks which are packed up on strong planks placed across the pit. In place of the jacks some shops use angle irons fixed temporarily to the frames as supports for the cylinders. It is absolutely necessary that the centre lines of the cylinders, when the latter are fixed permanently, should be exactly parallel to the frames, and the faces of the hornblocks, which determine the alignment of the axles, must be exactly at right angles to the cylinder centre lines.
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Fig. 42. — Erecting Locomotive Frames and Cylinders.
Two longitudinal wires e are also stretched outside each of the frames. These are set with a long square applied to the straight-edge b, to which they must be at right angles, and they must also be parallel to the wires c representing the cylinder centre lines. The straightness and the parallelism of the frames are tested from these lines.
Finally the exact position of the motion plate f is located from the cylinder centre lines cc, since the slide bars are fixed to this plate, and it is necessary for the bore of the cylinder, the piston rod, and the slide bars to have the same centre line.
Permanent Fixing of Frame Attachments. So far the parts have only been bolted up temporarily. 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.
If everything be found in order, all the holes are broached or reamered out to finished sizes, so that where the cylinders or stays are to be united to the frames all the holes in both parts coincide exactly. All bolts and cold rivets connecting these parts to the frames are turned and made a tight driving fit in the holes. The cylinders are bolted to the frames since they may have to be removed for repairs at some future period, and the same applies to the hornblocks, but the motion plate is cold-riveted. The plate g is usually hot-riveted. Various brackets may now be fastened in position, amongst which are angle brackets placed outside the frames at right angles to them. Long angle irons are riveted to the top of the frames. These angle irons and brackets carry the plates which form the platforms along each side of the engine. Occasionally these platforms are placed above the level of the tops of the wheels, but it is more usual for them to be below this level, in which case there are rectangular holes made in them through which pass the upper portions of the wheels. These holes are covered with segmental casings, known as “splashers,” which cover in the protruding portions of the wheels. The platforms, angle irons, and brackets are riveted on by means of portable hydraulic riveting machines similar to those used in the boiler shop.
Erecting the Motion. The cylinders and motion plate being in position the slide bars may now be fixed. For this purpose the wires cc (Fig. 42), representing the cylinder centre lines, are used, and from these the erector can set the bars parallel to the centre lines and equidistant from them above and below. The bars are bolted to faced projections on the back cylinder covers at one end and on the motion plate at the other. Thin brass liners are placed between the bars and these projections, their thickness being adjusted to suit the proper distance apart of the bars. The pistons, with their rings sprung into place and with the piston rods attached, are put in from the front end of the cylinders, and the crossheads are then attached to the piston rods. The crossheads with their slide blocks act as guides in setting the slide bars, between which the slide blocks must work up and down quite freely, but without shake.
The slide valves are placed inside their buckles. These are rectangular frames forged solid with the spindles which pass through the glands in the ends of the steam chest covers. The buckles or frames simply embrace the valves, so that when the spindles are moved by the valve gear, the valves move with them. The valves and buckles are placed in position inside the steam chests, the back ends of the spindles being cottered to the valve rods, which work in circular guides forming part of the motion plate. The accuracy of the work must be such that the centre lines of spindles and guides must either coincide exactly or if, as is frequently the case, there is an offset the centre lines must be perfectly parallel to each other. The spindles must move freely without shake or binding in the guides.
Whilst the above work is being done to the motion, other erectors may be fitting the axleboxes into the hornblocks by filing the side faces until they bear evenly on the horncheeks. The boxes should be a fairly tight fit between the hornblock faces, but not so tight that they cannot move up and down to allow for the vertical movements of the springs. Everything must be perfectly “square,” and the axleboxes on one side exactly in line with those on the other, otherwise the axles would be on the “skew,” and the locomotive would run badly. The hornblock faces on opposite sides of the engine have previously been finished exactly in line and tested across the engine by straightedges, and the machining and boring of the axleboxes is done so accurately by modern methods that the centre of each axlebox is equidistant from each of the hornblock faces.
If the work has not already been done in the wheel shop, the axleboxes, after having been removed from the hornblocks, are fitted to the journals on the axles, to bed down the bearings as described in Chapter VI.
It should be understood that many of the above operations are carried on simultaneously by different gangs of men. For the purposes of quick erection, as many men as possible work together on the same engine under a leading hand or “chargeman,” as he is termed. The chargeman is responsible for the whole work on a single engine, and frequently may have two or three engines in hand at once. He is in turn responsible to the shop foreman, who superintends the whole of the work done in the shop, in which a dozen to twenty engines may be in course of erection.
Boiler, Smokebox, etc. The engine is now ready for the boiler to be placed on the frames. The boiler comes in a finished condition from the boiler shop, with all mountings attached, and is lowered on to the frames by an overhead crane. It is at this stage that the accuracy of the boiler shop work is tested finally, for when the firebox has been lowered down into position between the frames, the expansion angle irons K Fig. 2, must be square so that they rest evenly on the top edges of the frames, whilst at the same time the bottom flange of the smokebox tubeplate or the front end of the boiler barrel, must fit accurately up to the cylinder flange to which it has to be bolted. The accuracy of the work is generally such that no alteration is needed, but it does occasionally happen that in these respects a boiler is slightly out of truth, and a lot of extra chipping and fitting of the expansion angle iron, and heating and setting of the tubeplate flange are then required.
The smokebox is then built up in position. It is made of thin steel sheets riveted together and to the smokebox tubeplate flanges. The front portion is formed of a large angle iron ring, and a plate, in which the smokebox door-hole is formed, is riveted to this ring. The front plate and the sides at the bottom are bolted to flanges on the cylinders. The smokebox must be quite air-tight, for if it draws air through any crevices or through a badly-fitting door, the boiler will not make steam properly, and any incandescent cinders drawn through the tubes will continue to burn in the smokebox and damage the thin plates. The tops of the (inside) cylinders form the floor of the smokebox, and a covering of fire brickwork and cement is placed over them to protect them from corrosion. The blast pipe and steam pipes in the smokebox are then put into position and jointed up to the cylinders. The steam pipe has also to be jointed with a steam tight joint to the T-pipe in the smokebox. The blast pipe is set accurately with a plumb line, since the centre of the top must coincide with the vertical centre line of the chimney, otherwise a one-sided blast would result, which would soon wear a hole in the chimney; also, the boiler would not “steam” properly. The fitting of the smokebox door — of which the hinges must be exactly level and strong enough to prevent the door from sagging — together with the fixing of the blower and blower pipe, complete the work in the smokebox.
Meanwhile other men are engaged in fixing the boiler clothing, cab, and splashers. For the clothing, which is essential to reduce the radiation losses from the boiler, the materials in use were formerly boards of yellow pine wood painted with fire resisting asbestos paint. Now felt sheets, asbestos mattresses, or special blocks of magnesia cut to fit the contour of the boiler are generally used. They are secured to a light framework of angle irons and strips fastened round the boiler, and finally covered with thin steel or planished iron sheets screwed on to this framework. The splashers and cab sides are bolted to the platforms, the front plate of the cab resting upon the top of the firebox shell.
Wheels and Springs. The engine is now wheeled. The finished wheels on their axles have already come in from the wheel shop, and are run on to the rails of the pit over which the engine is being built. They remain at the end of the pit until required, the axleboxes having meanwhile been bedded to the journals as previously described. The engine is lifted by the overhead crane, and the wheels rolled underneath, each pair being placed in position under the corresponding hornblocks. The axleboxes are placed on the journals and the engine lowered very slowly and carefully, a man being stationed by each wheel to guide the axleboxes into the spaces between the horns.
The springs, if of the type placed above the axleboxes, have already been put into position with the side links and pins in place, so that as the engine comes down the central spring pillars bear upon the axleboxes and the weight of the engine is gradually taken by the springs. The hornkeeps are then bolted into position. If the springs are “underhung,” they have to be put into place, after the engine has been lowered on to the wheels, by packing the axleboxes up at a convenient level and then slipping the pins for the links and spring buckles into their respective holes.
Motion Work. To put the connecting rods into place the small end straps and brasses are coupled to the crossheads on each side, and each big end with its brasses is put on to the crank pin journal of the driving axle. As these rods are very heavy, the large end of the rod is made to rest upon a timber baulk placed across the pit, and is then lifted by three men until the butt end slips into the open jaw of the strap, where it is secured by the bolts and cotter.
The eccentric rods and eccentric straps are then coupled up. The eccentric sheaves have already been keyed on at the proper angle to the crank axle in the wheel shop, and nothing remains to be done but to place the straps and rods in position, and couple the latter to the links of the link motion, which are put up at the same time and connected to the valve spindles. The brackets on the frames which carry the reversing shaft are bolted into place temporarily, but are not fixed permanently until the valves have been set, this being the next operation, a description of which is given in the following chapter. For the moment it will be supposed that the valves have been set. The coupling rods are then put on to the pins in the wheels. These rods are formed at the ends with simple circular brass or white metal bushes which are pressed into the holes in the rods by hydraulic pressure. Formerly double brasses secured by cotters, somewhat similar to those used for connecting rods, were used for the coupling rods, but they are now almost obsolete in this country, though still used to a large extent on continental and American engines. 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. Finally the buffer plate with buffers, and the drawgear complete the engine which is then ready for trial.
Time Required for Erecting an Engine. The time taken to erect an engine of ordinary size, say with six wheels all coupled, may be taken to be about 45 hrs. from the time the frame plates are placed in position. Large modern engines with ten or twelve wheels will take a correspondingly longer time. The period mentioned would apply to a well organized works in which a large number of standard engines were being erected together, three of which would be under the care of one chargeman. In smaller works about four weeks may be taken for the erection. A few instances of very rapid erection have been recorded in which special preparations were made for the work. In 1888 the London and North-Western erected a standard mineral engine in 25½ hrs., but this record was beaten in 1891 at the Great Eastern Works at Stratford, when a somewhat similar engine was put together ready for trial in the phenomenal time of 9 hrs. 47 min. by forty-four men and boys. The tender was completed by another gang within the same time. These, however, are quite exceptional cases. It should be understood that in a well-organized works three or four orders, each for a dozen to twenty engines, are in hand at the same time. Thus the first order will be in course of completion in the erecting shop, whilst the boiler, fitting, and machine shops are dealing with the parts for No. 2 order. The forge and foundry and part of the boiler shop have in hand at the same time the forgings, castings, and boiler plates for the third order, and work may also have been begun in the pattern and template shops on order No. 4.
The Tender. Although the tender is constructed and erected in a separate tender shop, it may conveniently be considered here. The frame plates are of the same quality of steel as those of the engine, their thickness, about ⅞ in., being slightly less than that of the engine frames. There are usually four frame plates, which are marked off to templates, drilled, and erected with the necessary cross stays in a similar manner to those of the locomotive.
The wheels, axles, axleboxes, hornblocks and springs are also made in a similar manner, the chief difference being that the wheels, being smaller, do not require wheel lathes with such large faceplates. The wheels are simply pressed on to the axles by hydraulic pressure, and are not secured by keys, as are the coupled wheels of the locomotive.
The tank is a separate structure which is placed upon and fastened to the framing. The plates, about ¼ in. thick for the sides and ⅜ in. for the bottom, are of mild steel of good quality, but not of the specially high grade which is required for boiler plates. The rivet holes are marked off, drilled or punched, and the plates riveted together with angle irons and supporting stays with ½ in. rivets spaced at about 1¾ in. centres.
The tank is bolted to an angle iron, which runs round the top edge of the frame, so that it can be lifted off readily for examination when required.
In erecting the brake gear, both on the engine and on the tender, care must be taken that the brake blocks do not rub against the tyres when the brakes are “off,” otherwise considerable heating and undue wear will occur. The blocks are arranged to be just clear of the wheels at the top side, and about ¼ in. clear at the bottom. The reason for this is that the brake pull rods are below the blocks, whilst the fulcra to which the brake block hangers are attached are above, and therefore the bottom sides of the blocks move through a greater distance when the brakes are applied.