Fig. 2456Fig. 2456.
Fig. 2456.
The fit of the flange to the boiler, however, should vary according to the kind of bolt used to hold the fitting to the boiler. If stud bolts are used they are supposed to screw into the boiler steam-tight, hence the flange may be fitted so that it has the closest contact with an annular ring extending from the outside of the bolt holes to the central hole of the flange, as shown inFig. 2456, in which the area within the dotted circlecencloses the area to be most closely bedded. This is a highly important consideration in flange joints of every description, for, if a joint is made there, that is all that is necessary, and the fit outside of the bolt holes—that is to say from the bolt holes to the perimeter of the flange—has nothing to do with making the joint, unless the studs or bolts leak, and in that case the leak will find egress beneath the nut, unless grummets are used. A grummet is a washer made of twisted hemp, cotton, or other material, and coated with red-lead putty, and is placed beneath the heads of bolts, or under washers placed beneath nuts to stop leaks. It is not necessary to ease the flange from the bolt holes outward much, but to merely make the flange, or fitting, bed clearly and distinctly the most around the main hole, and outwards to the inside of the bolt holes; for, if there was given too much clearance, the flange would bend from the pressure of the nuts, and would in consequence spring if made of brass, or perhaps break if made of cast iron.
To make the joint, gauze wire, pasteboard, or asbestos board may be used, or if the joint is to have ample time to set, a red-lead joint without the gauze may be used; but in this case it is an advantage to cut up into pieces about3⁄8inch long, and thoroughly shred some hemp, and well mix it in the lead, well beating the same with a hammer.
To preserve red-lead putty from becoming hard and dry, as it will do if exposed to the air, it should be kept covered with water.
In some cases joints of flanges to boilers are made by riveting the flanges to the boiler and caulking or closing the edge of the flanges to the boiler shell; but this possesses the disadvantage that the rivets must be cut off to remove the fitting from the boiler when necessary, and access to the interior of the boiler is necessary in order to attach the fitting again by rivets.
Fig. 2457Fig. 2457.
Fig. 2457.
Fig. 2457(which is taken fromThe American Machinist), represents a joint for boiler fittings, designed to facilitate the breaking and re-making of the joint.crepresents, say, a boiler plate,ba piece having a ball joint seat incground steam tight, andaa flange, say, for a feed pipe; the studsdthread permanently intoc, and the joint is bolted up by the stud nutse. It is obvious that the ball joint betweenbandcpermits the flangeato set at an angle if necessary.
Rust Joints.—These are joints made by means of filling the space between the flanges, or annular spaces, as the case may be, with cast-iron turnings, and compacting them with a caulking tool. Any interstices through which steam or water, &c., might leak become filled by the subsequent rusting of the iron cuttings, the rust occupying considerably more space than the iron from which it was formed.
Fig. 2458Fig. 2458.
Fig. 2458.
Rust joints are employed upon very uneven surfaces, and for pipes for mains to go under ground. In former times this class of joints was much used in engine and boiler work, but of late years it has been to a great extent abandoned. InFig. 2458isshown the method of construction for a rust joint for what are known as spigot and socket joints for pipe work.sis the spigot andpthe socket.r ris a metal ring, bound over with either dry hemp fibre or tarred twine or rope. The remainder of the space between the pipes ata abeing filled with a cement composed of
but when required to set quickly, 1 lb. sal-ammoniac may be used. These ingredients are thoroughly mixed with water immediately before being used, and just covered with water when used intermittently. The cement is put into the spacea a, in quantities sufficient to fill up about3⁄4inch in length of the annular spacea a, and then caulked by being driven in with the tool shown inFig. 2459. Cement is then again put in and the caulking repeated, the process being continued until the whole space is filled.
Fig. 2459Fig. 2459.
Fig. 2459.
In some cases (as in gas mains) the spacea ais filled with melted lead, and when cold caulked with the tool described.
Fig. 2460Fig. 2460.
Fig. 2460.
InFig. 2460is shown the method of making a rust flange joint;a abeing a ring covered with hemp twisted around it, the cast-iron cement being caulked in as before.
The wire rings should be firmly gripped by the bolts to prevent them from moving from the caulking blows, which should be at first delivered lightly.
Fig. 2461Fig. 2461.
Fig. 2461.
In some cases pipes are joined with rust joints, as inFig. 2461in whicha ais a sleeve, there being two rings of wire and hemp inserted as shown.
When flanged joints are made with a scraper, or ground joint, or with rubber, duck, or other similar material to make the joint, the length of the pipe, from face to face of the joint, must be made accurate.
Fig. 2462Fig. 2462.
Fig. 2462.
Fig. 2463Fig. 2463.
Fig. 2463.
Fig. 2462is a face, andFig. 2463(which are fromMechanics), a sectional edge view of an expansion joint, being that used by the New York Steam Supply Company for the steam pipes laid under the streets to convey steam to buildings. The object is to provide a joint which shall permit and accommodate the expansion and contraction of the pipe under varying temperatures.p pare corrugated copper disks secured to the faces of the pipe ends by flanges, as shown, and gripped at their edges by the flanges of the cast-iron casing, and it is obvious that the ends of the pipe may move longitudinally carrying the corrugated disks with it. The cavityais filled with steam, and to support the diskspagainst the pressure segmental blocksbof cast iron are placed behind them, the number of these blocks being as indicated by the dotted radial lines in the figure. It may be added that this joint has been found to answer its purpose to great perfection.
Pipe cutters, for cutting steam or gas pipe by hand, are usually provided with either a rotary wheel which severs by rolling an indentation, or else are provided with cutting tools. The rolling wheel has the advantage that it makes no cuttings, cuts very readily and is not apt to break; on the other hand it is apt to raise around the severed end of the pipe a slight ridge, which with a worn cutter may be sufficiently great as to require to be filed offbefore the threading dies will grip the pipe. Cutting tools are apt to break and require frequent grinding; hence, as a rule, the rolling wheel cutter is generally preferred.
Fig. 2464Fig. 2464.
Fig. 2464.
Fig. 2464represents a cutter of this kind, the pieceacarrying the cutterb, which is operated in the stockcby means of the threaded handleh.
Fig. 2465Fig. 2465.
Fig. 2465.
Fig. 2465represents a pipe cutter in which are a pair of anti-friction rollers and a severing tool bevelled on one edge only so as to leave the end of the pipe face cut square, and the piece cut off bevelled on its face; or by turning the cutter round the reverse will be the case, the piece cut off being flat on its end.
The action of this cutter is, as in the case of the wheel cutter, simply that of a wedge, hence no cuttings are formed.
Fig. 2466Fig. 2466.
Fig. 2466.
Fig. 2466represents a pipe cutter in which a cutting tool is employed, being fed to its cut by the handle which is threaded similar to the handle shown inFig. 2464. The end jaw is operated to suit different diameters of pipe by means of the milled nut shown, which receives a threaded stem on the adjustable jaw.
Fig. 2467Fig. 2467.
Fig. 2467.
Pipe Vice.—The ordinary bench vice is sometimes provided with an attachment to enable it to grip pipe at three points, and, therefore, hold it sufficiently firmly without squeezing it oval, but it is preferable to use a proper pipe vice, such as shown inFig. 2467, which consists of a base frame bolted to the work bench and receiving a serrated die to grip the pipe. The upper die is carried to a frame pivoted on both sides to the base, and is operated to grip or release the pipes by means of the handled screw shown.
Fig. 2468Fig. 2468.
Fig. 2468.
To change the dies one pivot is removed and the upper frame swung open, as inFig. 2468.
Fig. 2469Fig. 2469.
Fig. 2469.
The proper shape for pipe tongs depends upon the number of sizes of pipe the tongs are intended for, but in all cases the point at which the gripping point should be is about as shown inFig. 2469. This enables the edge atato enter the work and grip it. If this point of contact were nearer tocit would be apt to slip upon the pipe, whereas, were it farther towardsb, it would present a less acute angle to the pipe, which would be apt to jam in the tongs.
It is obvious that, if the tongs be moved in the direction ofh, the whole power applied tofacts to cause the edge atato grip the pipe, and that the length fromatoghas an important bearing on the grip ofato the pipe; because the nearerais tognot only the greater the leverage of the legf, but also the lessa, with a given amount of movement offon its pivot, endeavors to enter the pipe; hence the movement ofain a direction to grip the pipe is less in proportion to the movement off, and has a corresponding increase of force. It follows then that the nearer the grip ofais toc, the less, and the nearer the grip tobthe greater, its gripupon the pipe. But, by making the length ofasuch as to grip the pipe in about the position shown in the cut, there is latitude enough in the location at which it will grip the pipe to permit of the tongs being used upon pipe of a somewhat greater or less external diameter, increasing the availability of the tongs. Furthermore, ifagripped the pipe at or too near tob, it would be apt to indent it. The crown of the jawdmay be made to fit to the pipe or to be clear of it; for thin pipe, as solid drawn brass pipe, it should fit so that the pressure will not indent the pipe, but for strong iron pipe it is better to let it clear, which will not only afford a firmer grip, but will also better fit the tongs to take in different diameters of pipe. In some cases, as in adjustable pipe tongs, the jaw surfacedis, for this purpose, considerablyV-shaped, as will be seen presently.
It is obvious that asagrips the pipe automatically, the tongs may be moved through any portion of a rotation that the location may render most desirable. Pipe tongs are designated for size by the diameter of the pipe they are intended for; thus, a pair of inch tongs are suitable for pipe an inch in diameter of bore, the handles or legs of the tongs coming so close together that both can be readily grasped in one hand applied at their extreme ends. If, however, the tongs be applied to pipe of a larger diameter the legs will be wider apart, and one hand will be required to be applied to each leg to force them together. A complete set of pipe tongs, therefore, includes as many pairs as there are diameters of pipe, unless adjustable tongs be used.
Fig. 2470Fig. 2470.
Fig. 2470.
Fig. 2471Fig. 2471.
Fig. 2471.
Fig. 2472Fig. 2472.
Fig. 2472.
Adjustable tongs are made of various forms; thus a simple plan is shown inFig. 2470. The gripping surface of the jaw is shaped as atv, so as to admit varying diameters of pipe, the smaller diameters passing farther up thev, the distance of the endaof jaw, or legf, being regulated to grip the pipe in the proper place by operating the screws, which is tapped into the jawfand pivoted inb, the slotcenablingfto move alongb. The capacity of tongs of this design is about three diameters of pipe, as 1, 11⁄4, and 11⁄2inches. There are various other forms of adjustable pipe tongs, but most of them possess the disadvantage that the adjustable jaw hangs loosely, involving some extra trouble in placing them upon the pipe, because one hand must be employed to guide the loose jaw and adjust its position on the pipe.Fig. 2471represents tongs of this class, the gripping size being varied by moving the jawauponbat the various notches. The end ofbis serrated to afford a firmer grip upon the pipe.Fig. 2472represents another adjustable pipe tongs, which is made in two parts, a straight leveraand hooked leverb, the former passing through a slot in the latter. The back of the straight lever is notched and a serrated fulcrum piececis pivoted in the slotted lever by a pin upon which the leverbreceives its support when the tongs are in operation. The fulcrum piece is provided with a spring which retains the serrated edge in proper position to engage the notches in the levera. By means of the thumb pieced, the piececcan be moved in either direction to increase or diminish the gripping size of the tongs. When the tongs are open the leveracan be moved within the slot and adjusted so that the tongs will fit the pipe. The fulcrum piecec, being pivoted, allows the full length of its serrated edge to come into contact with the corresponding portion of the levera, so that the parts always have a firm bearing and are subjected to an equal wear.
Fig. 2473Fig. 2473.
Fig. 2473.
A common form of pipe tongs of this class is shown inFig. 2473,bbeing pivoted toaby a pin, and changing to various holes inato suit different diameters of pipe.
Erecting Pipe Work.—In erecting pipe work care must be taken to have it align as true as possible, as well as to have the joints tight enough to stand the required pressure without leakage. If the elbows, tees, or other fittings are not threaded true, a pipewhose thread is not true with its axis may be selected or cut purposely to suit the error in the fitting, so as not to leave an unsightly finish to the job.
Fig. 2474Fig. 2474.
Fig. 2474.
Suppose, for example, that inFig. 2474,eis a pipe erected parallel to the wall, but that the holes in its elbows are tapped at an acute instead of at a right angle, then by cutting the thread on the end of pipeduntrue with its axis, its far end will rotate out of true as denoted by the shaded and by the plain lines, and all that will be necessary is to screw up the pipe sufficiently firm to make the joint, but to leave it in the position shown in the plain lines.
If the pipe tightens sufficiently before it has reached that position it may generally be eased by rotating it back and forth in the elbow with the pipe tongs. If this does not suffice, the pipe must of course be threaded sufficiently further along. To cut a pipe out of true to suit an untrue elbow, a very good plan is to cut the end of the pipe at an angle to its axis, which will cause the dies to cant over when starting the thread, but little practice being required to educate the judgment as to how much to do this to suit any given degree of error.
In erecting pipe it is best to begin at one end and screw each successive piece firmly home to its place before attaching another, so that the lengths of the pieces may be accurate and not vitiated by screwing them up and causing them to enter farther into the fittings. If it is probable that the piping may have to be taken down after erection, it should be put up at first screwed together rather tighter than will be necessary, as the thread fits become eased by being moved one within the other. This is especially the case with brass fittings, upon which it is best in cutting the lengths of pipe to have it of full length, as the threads will conform to each other sufficiently to cause the pipe to enter a thread or so farther if the pipe be rotated back and forth a few times in the fitting.
The fit should in all cases be made by tightness of thread fit, and not by the union or elbow face jambing against the end of the thread or the pipe, as joints in which this is the case will usually leak if used under pressure.
The thread of both the pipe and the fitting should be smeared with a thick lead paint. If the pipe is to be used as soon as erected, plain red lead and boiled oil should be used for the paint; but if it may stand a few days it is better to mix white and red lead in about equal quantities, as this, if given time to dry, makes a tighter job. The quantity of this paint should not be more than will thinly cover the threads, otherwise it will squeeze out when the pipes are screwed home, and falling from the end of the pipe within the fitting be apt to be carried by the steam or water to the valves, and getting between them and their seats cause them to leak. The iron cuttings should be carefully cleaned both from the pipe and the fitting for the same reason.
In cases where the piping may require to be used under heavy pressure as soon as erected, it is a good plan to use dry red lead in varnish, thoroughly hammering it to mix it well, and thinning it after it has been so hammered.
In case of emergency a loose pipe may be somewhat improved by wrapping around its thread a piece of lamp wick saturated with this varnish lead, beginning at the end of the pipe and wrapping the thread from end to end.
It is preferable that the stem of the valve stand nearly horizontal, so that any water of condensation may pass freely away with the steam and not collect and lie in the pipe as it does when vertical. If it be quite horizontal the water of condensation will drip through the stuffing box; hence it is better that it stand 10 or 12 degrees from the horizontal.
It is better in all cases to purchase nipples than to make them by hand, because when made in a machine the threads are more true to the axis than those made by hand; especially is this the case in short nipples in which there is not sufficient length to use the guide socket when engaged in threading the nipple with the hand dies.
It is a very good plan in making such short nipples to cut them off the end of a length of pipe that has been threaded by machine, and to screw on the threaded end a coupling. Into this coupling a piece of pipe may be threaded to afford a hold in the vice. If then the nipple is long enough, a guide to suit the size of the nipple may be used in the threading dies, or a guide socket to fit the diameter of the coupling may be used.
A globe valve should be so placed on the pipe that the pressure will, when the valve is closed, fall on the bottom face of the valve, so that the steam may be shut off while the valve stem is being packed.
Cotton lamp wick plaited to fit the packing space, and well oiled, is as good as anything to pack the stem with.
In taking old pipe down a refractory joint may be sometimes loosened by striking it with a hammer while it is under full pipe tongs pressure; or these means failing, the elbow or tee may be heated, which should be done as quickly as possible, so that the fitting may be hotter than the pipe. A very good method of doing this, where it is desired to save the fitting, is to pour red-hot lead over the fitting.
If it is not important to save the fitting, it may be split by a flat chisel, or by cutting a groove along it with a narrow cape chisel; or if the pipe is free the elbow may be rested on an anvil and hammered around its circumference, which will either free it or break it, if of cast iron.
When pipes are to be taken down and re-erected elsewhere they should all be marked to their fittings and places before being taken down, as this will preserve their lengths as near as possible for re-erection. Black japan is an excellent marking for this purpose because it dries quickly.
Re-fitting the Leaky Plugs and Barrels of Cocks.—When a cock leaks, be it large or small, it should be refitted as follows, which will take less time than it would to ream or bore out the cock or to turn the plug, unless the latter be very much worn indeed, while in either case the plug will last much longer if refitted, as hereinafter directed, because less metal will be taken off it in the re-fitting.
After removing the plug from the cock, remove the scale or dirt which will sometimes be found on the larger end, and lightly draw-file, with a smooth file, the plug all over from end to end. If there is a shoulder worn by the cock at the large end of the plug, file the shoulder off even and level. Then carefully clean out the inside of the cock, and apply a very light coat of red marking to the plug, and putting it into the cock press it firmly to its seat, moving it back and forth part of a revolution; then, while it is firmly home to its seat, take hold of the handle end of the plug, and pressing it back and forth at a right angle to its length note if the front or back end moves in the cock; if it moves at the front or large end, it shows that the plug is binding at the small end, while if it moves at the back or small end, it demonstrates that it binds at the front or large end. In either case the amount of movement is a guide as to the quantity of metal to be taken off the plug at the requisite end to make it fit the cock along the whole length of its taper bore.
If the plug shows a good deal of movement when tested as above, it will be economical to take it to a lathe, and, being careful to set the taper as required, take a light cut over it. Supposing, however, there is no lathe at hand, or that it is required to do the job by hand, which is, in a majority of cases, the best method, the end of the cock bearing against the plug must be smooth-filed, first moving the file round the circumference, and then draw-filing; taking care to take most off at that end of the plug, and less and less as the other end of the plug is approached. The plug should then be tried in the cock again, according to the instructions already given, and the filing and testing process continued until the plug fits perfectly in the cock. In trying the plug to the cock, it will not do to revolve the plug continuously in one direction, for that would cut rings in both the cock and the plug, and spoil the job; the proper plan is to move the plug back and forth at the same time that it is being slowly revolved. As soon as the plug fits the cock from end to end, we may test the cock to see if it is oval or out of round. The manner of testing the cock is asfollows:—
First give it a very light coat of red marking, just sufficient, in fact, to well dull the surface, and then insert the plug, press it firmly home, and revolve it as above directed, then remove the plug, and where the plug has been bearing against the surface of the cock the latter will appear bright. If, then, the bore of the cock appears to be much oval, which will be the case if the amount of surface appearing bright is small, and on opposite sides of the diameter of the bore, those bright spots may be removed with a half-round scraper.
Having eased off the high spots as much as deemed sufficient, the cock should be carefully cleaned out (for if any metal scrapings remain they will cut grooves in the plug), and the red marking re-applied, after which the plug may be again applied. If the plug has required much scraping, it will pay to take a half-round smooth file that is well rounding lengthwise of its half-round side, so that it will only bear upon the particular teeth required to cut, and selecting the highest spot on the file, by looking down its length, apply that spot to the part of the bore of the cock that has been scraped, draw-filing it sufficient to nearly efface the scraper marks. The process of scraping and draw-filing should be continued until the cock shows that it bears about evenly all over its bore, when both the plug and the cock will be ready for grinding.
Here, however, it may be as well to remark that in the case of large cocks we may save a little time and insure a good fit by pursuing the following course, and for the given reasons. If a barrel bears all around its water-way only for a distance equal to about1⁄16th of the circumference of the bore, and the plug is true, the cock will be tight, the objection being that it has an insufficiency of wearing surface. It will, however, in such case wear better as the wearing proceeds. Plug and barrel being fitted as directed, we may take a smooth file and ease away very lightly all parts of the barrel save and except to within, say,3⁄8inch around the water or steam-way. The amount taken off must be very small indeed, just sufficient, in fact to ease it from bearing hard against the plug, and the result will be that the grinding will bed the barrel all over to the plug, and insure that the metal around the water or steam-way on the barrel shall be a good fit, and hence that the cock be tight.
The best material to use for the grinding apparatus is the red burnt sand from the core of a brass casting, which should be sifted through fine gauze and riddled on the work from a box made of, say, a piece of 11⁄2pipe 4 inches long, closed at one end and having fine gauze instead of a lid.
A very good material, however, is Bath brick rubbed to a powder on a piece of clean board. Neither emery nor ground glass is a good material, because they cut too freely and coarsely, which is unnecessary if the plug has been well fitted.
Both the barrel and the plug should be wiped clean and free from filings, &c., before the sand is applied; the inside of the barrel should be wetted in and the plug dipped in water, the sand being sifted a light coat evenly over the barrel and the plug. The plug must then be inserted in the barrel without being revolved at all till it is home to its seat, when it should be pressed firmly home, and operated back and forth while being slowly revolved. It should also be occasionally taken a little way out from the barrel and immediately pressed back to its seat and revolved as before, which will spread the sand evenly over the surfaces and prevent it from cutting rings in either the barrel or the plug. This process of grinding may be repeated, with fresh applications of sand, several times, when the sand may be washed clean from the barrel and the plug, both of them wiped comparatively dry and clean, and the plug be re-inserted in the barrel, and revolved, as before, a few revolutions; then take it out, wipe it dry, re-insert and revolve it again, after which an examination of the barrel and plug will disclose how closely they fit together, the parts that bind the hardest being of the deepest colour. If, after the test made subsequent to the first grinding operation, the plug does not show to be a good even fit, it will pay to ease away the high parts with a smooth file, and repeat afterwards the grinding and testing operation.
To finish the grinding, we proceed as follows: Give the plug a light coat of sand and water, press it firmly to its seat and move it back and forth while revolving it, lift it out a little to its seat at about every fourth movement, and when the sand has ground down and worked out, remove the plug, and smear over it evenly with the fingers, the ground sand that has accumulated on the ends of the plug and barrel, then replace it in the barrel and revolve as before until the plug moves smoothly in the barrel, bearing in mind that if at any time the plug, while being revolved in the barrel, makes a jarring or grating sound, it is cutting or abrading from being too dry. Finally, wipe both the barrel and the plug clean and dry, and revolve as before until the surfaces assume a rich brown, smooth and glossy, showing very plainly the exact nature of the fit. Then apply a little tallow, and the job is complete and perfect.
In place of the tallow a soft paste of good beeswax and castor oil is an excellent application, the two being heated in order to thoroughly mix them.
The grinding material must be frequently changed to produce smooth work, because if the grinding cuttings accumulate in it, they will scratch and score the work. Indeed, it is a good plan when convenient, to hold the cock and plug under water while grinding them, and to occasionally lift the plug out, so as to wash out the cuttings.
The surface of a well-ground plug will be in all cases polished, and not have that frosted appearance which exists so long as active grinding is proceeding, and all that is necessary to produce this polish is to well work the plug in its barrel while keeping it quite clean.
Fig. 2475Fig. 2475.
Fig. 2475.
Fitting Brasses to their Journals.—Brass bores always require fitting to their journals after having been bored, because the finished hole is not a true circle, but too narrow across the joint face, as atfinFig. 2475, in which the full lines represent the form of the brass before, and the dotted line its form after being bored and released from the pressure of the devices or chuck that held it while it was being bored. This almost always occurs to a greater or less degree, and it arises from local strains induced from the unequal cooling of the casting in the mould, which strains are released as the metal is removed (in the process of boring) from the surface of the bore. It would appear, however, that if the finishing cut taken by the boring cutter be a very fine one it should leave the hole true and round, but the pressure which is placed upon the bearing to hold it against the force of the cut preventsthe bearing from assuming its natural form until released from that pressure.
If a bearing be bored to very nearly its finished size and first released altogether from the pressure of the holding chuck, or other device, and then re-chucked, it is probable that the finished bore would be practically quite round and true, but such re-chucking is not the usual practice.
Suppose, however, that the bearing shown inFig. 2475, be properly fitted to a journal, still improper conditions arise from wear, because the area of the surfacedbecomes from the weight and from vibration condensed, and finally it stretches, causing the bore atfto close upon the journal and bind it with undue friction.
Fig. 2476Fig. 2476.
Fig. 2476.
If the shape of the bedding part of the brass, or bearing, be such as shown inFig. 2476, the surfacesa bandcwill condense and stretch, closing the diameter of the bore ateand making the sidesg gfit loosely in their places. It is to be observed that a similar condensation of the metal occurs to some extent around the bore of the bearing; but this surface is being continuously worn away by the journal, and it is, therefore, at all times less stretched and condensed than that on the bedding surface.
Fig. 2477Fig. 2477.
Fig. 2477.
There is, therefore, a constant action causing the brass to bind unduly hard at and near its joint facee,Fig. 2476, and thus to cause heating and undue abrasion and wear. To prevent this it is necessary to ease away that part of the brass bore, as is shown inFig. 2477fromjtok, clear of the journal.
But in the case of bearings receiving thrust, as in engine main bearings, the line of pressure is in a horizontal direction; and hence the most effective bore area to resist that pressure has been removed. Furthermore, the bearing area of the brass bore has been reduced, thus increasing the pressure per square inch on the remaining area.
Fig. 2478Fig. 2478.
Fig. 2478.
The methods employed to avoid this evil are as follows:—In the form shown inFig. 2478the joint faces are at an angle instead of being horizontal and parallel to the line of the thrust, or the joint faces may be made to stand at a right angle to the line of journal thrust, so that the crown of the brass will receive the thrust. But the brasses will still close across the joint faces (as already described) as the wear proceeds, and the areas fromjtokinFig. 2477, must still be eased away, requiring frequent attention and giving a reduced bearing area. Furthermore, in proportion as the line of the joint faces of the brasses is at an angle to the line of thrust, the strain on the top or cap brass will fall on the bolts, so that if those joint faces be at a right angle to the line of thrust, the whole strain of that thrust will fall on the bolts that hold the cap and cap brass.
Fig. 2479Fig. 2479.
Fig. 2479.
Another plan is to make the bearing in parts, as inFig. 2479, in which the top and bottom parts of the bearing extend to the joint face on one side, but admit a chock or gib,ain the figure, which may be adjusted by a set-screw as shown. By this means the bearing area may extend all around the bore. In some cases two of such chocks and set-screws, one on each side of the journal, are employed.
Fig. 2480Fig. 2480.
Fig. 2480.
In place of the set-screws, whose ends, from receiving the pressure of the thrust, are apt to imbed themselves into the chock and to thus loosen the adjustment, wedges lifted by bolts passing up through the cap, as shown inFig. 2480, are employed, being preferable to the screws.
Fig. 2481Fig. 2481.
Fig. 2481.
In the Porter Allen engine the wedges pass clear through the bearing, as inFig. 2481, so that they may be pushed up after the manner of a key and their pressure against the side chocks judged independently of the nuts at the top.
In some designs the top and bottom parts of the bearing are free to move in the line of the thrust, and the side chocks or blocks alone are relied on to resist the thrust.
When the brasses are in two halves, they may be fitted so as to have a known degree of bearing pressure upon the journal, and the fit may thus be accurately adjusted, in which case they will weara long time before requiring re-adjustment. On the other hand when the side chocks are used the wear in the line of the thrust may be taken up as it proceeds. In one case the attending engineer cannot alter the fit of the bearing nor the alignment of the shaft, while in the other he can do both. Thus the facilities that enable him to make these adjustments properly also enable him to make them improperly. But this would be of no consequence, providing it could be determined whether the adjustment were improving the conditions without first making it. With an engine at rest it is easy to determine, by means of the connecting rod, whether the chock adjustment is correct, so far as the adjustment of the shaft is concerned, but it is not easy so to determine the pressure of the chock on the journal; nor when each chock has two adjusting screws is it easy to determine when they both bear alike.
When the bearing is in four pieces, and three of them have two screws each, it is still more difficult to operate all so as to have the bearing equal on the journal. The fit to the journal can only be determined by the results: if too easy, the bearing pounds; if too tight, the bearing heats and wears.
But undue wear may take place without heating, and this is one of the greatest objections to this method of adjustment.
Fig. 2482Fig. 2482.
Fig. 2482.
A design of bearing used in American locomotive practice is shown inFig. 2482. Here the joint facesc,bof the brass is bevelled, fitting into a corresponding bevel in the box, which prevents the brass from closing across the joint face; hence, the bearing on the journal may extend all around the brass bore from the oil cavityato the edgesb c. The brass is, in this case, forced to its place in the axle box under hydraulic pressure, and this pressure springs the box open ath, making it wider; but when the box is put to work the brass compresses somewhat, and its surfaces conform more closely to the bedding surface of the box than when first put in, and this causes the box to close slightly ath.
To prevent this closure from carrying the brass with it and close it across the joint face (as in the case of the brass shown inFig. 2476) the following plan is adopted. The brasses, after having been turned in the lathe, are filed along the entire surface (on each side) for a distance of about 11⁄2or 2 inches, so as to clear the bore of the box near the bevelsb,c. When the box is put into the hydraulic press, to have the brass forced in, a centre-punch markjis made, and part of a circlel lis struck; when the brass is home in the box the arc of circlekis made, the distance betweenkandlshowing how much the box has been sprung open by the brass; the amount allowed is about1⁄32of an inch. If, as the brass is pressed in, it is found that this will be exceeded, it is taken out and eased. When the engine is running and the boxes spring to some extent they do not carry the brass with them, because the sides being eased away gives liberty to the box to come and go slightly; the bevels also tend to keep the brass bore open.
Here, then, the brasses may be fitted to align the axle perfectly, and it is not permitted to the engineer to alter that alignment, while at the same time the fit of the brass to the journal being made correct, the engineer cannot alter it. Under these conditions the whole area of the brass is effective in holding the journal, which increases the durability of the brass by keeping the pressure per square inch on the brass bore at a minimum.
If side chocks are used, however, it is better to set them up by wedges than by screw bolts, because from the tightness of the fit of such screws in the tapped holes, it is difficult to determine, with precision, with what degree of pressure the chocks are forced against the journal. Furthermore, the screws may not fit with an equal degree of tightness; hence, when screwed up with an equal degree of pressure, one end of the same chock may be set tighter to the journal than the other end, and any undue pressure of fit at either end tends to throw the shaft out of line as well as inducing undue wear. But when wedges are used to set up the side chocks the nuts operating those wedges may be an easy fit without fear of their becoming loosened (as set-screws in the line of thrust are apt to do).
On the fast engines of the Pennsylvania Railroad solid bronze boxes, without brasses, are used, and when the boxes require truing from having cut or from having worn oval they close them under a steam hammer, closing the bore across and enabling it to be trued out in the lathe without taking much metal out of the crown of the bore. The wedges and adjusting shoes are thickened when this becomes necessary by reason of the box closure or width.
If a brass bore does not bed fully and equally over the entire intended bearing area the part not fitting will at first perform no duty as bearing area, and the whole strain will be thrown upon a less area than is intended by the construction, causing undue abrasion until the brass bore has what is termed worn down to a bearing. The amount of this wearing down to a bearing may be so small as to be scarcely perceptible to ordinary observation, but if the oil that has passed through the journal be smeared upon stiff white paper, as writing paper, it will be found to contain the particles of abraded metal, which will be plainly distinguishable. Under these conditions the journal will have a dull, though perhaps a smooth appearance, and will not have that mirror-like surface which is characteristic of a properly fitted and smooth working bearing, while under a magnifying glass the journal will show a series of fine rings or wearing marks. It is necessary, therefore, that each brass be properly fitted to its journal so that it shall bed fairly and evenly over all the area of its bore that is intended to bear upon the journal.
The most expeditious method of fitting a new bearing box or brass to its journal is to first file the bore until it fits the journal when simply placed thereon by hand, and without going to the trouble to put the brass or the journal in position in the frame which holds them. So soon, however, as the crown of the brass beds to the journal along its whole length, the brass should be placed in its box, or in the frame, and the journal adjusted in its place and rotated so as to leave its bearing marks upon the brass bore, to assist which it may have a faint coat of red marking on its surface. The fitting should be continued both with file and scraper until the whole area of the part intended to bed fits well and issmooth and polished. To produce this result the finishing should be done with a very smooth half-round file, draw-filing so as to leave the marks in a line with the circumference of the bore, and finally with a half round scraper, which will remove the file marks. The degree of contact should be such that, when the bearing is bolted up, brass and brass, as it is termed (which means that the joint faces of the brasses are held firmly together), the journal will rotate as freely as when the top brass is removed, while the contact marks on the top brass have been removed by scraping. By this means the fit will be just sufficient to permit the lubricating oil to pass between the journal and the bearing, and the journal will work freely and easily without any play, knock, or pound. If, when the top brass or bearing is bolted home and the shaft is rotated by hand, that brass on removal shows contact marks on its bore, although it may rotate comparatively easily it will be so tight a fit that the oil cannot pass, and as a result the wear, instead of producing a glossy surface, will produce a dull one, and undue abrasion will ensue even though no rings appear.
When brasses are held in rods that connect two journals together the fitting of the brass bore must be conducted with a view to have the brasses fit their journals all over the intended bearing area of their bores, which can only be accomplished by trying the brass bores to their journals while in the rod, in the manner to be hereafter described with reference to connecting rods and to lining engines.
When a journal is worn in rings, or so rough as to cause destructive abrasion and undue friction, it may be refitted as follows:—First, with a smooth file draw-file the journal in the direction of its length, taking off all the projecting rings. Then sweep a very smooth file that is somewhat worn (which will cut smoother than a sharp file) around the circumference of the journal so that the file marks will be in the plane of revolution. Then wrap a piece of fine and somewhat worn emery paper around the journal, and wrap around it (say twice around) a piece of coarse string, leaving the two ends about two feet long. Take one end of the string in each hand and pull first one end and then the other, causing the emery paper to revolve around the journal and smooth it.
To refit the bearings, first with a smooth half-round file remove the rings or rough surface, and then fit the surface with the file, so that when in its place the journal is rotated the contact marks show a proper bearing. Then draw-file the bore with a smooth half-round file and finish with a half-round scraper, easing away the high spots until the bore shows proper contact and is smooth. A piece of fine emery paper may then be wrapped around a half-round file and the surface smoothed with the emery paper moved across the bore and not in the direction of the circumference of the same. The emery paper should be well worn for the finishing and of a fine grade number, so as to leave a bright polish and not dull marks.
In some practice the bores of brasses are left rough-filed, the file marks being lengthways of the bearing of bore. If the journal requires smoothing it is draw-filed lengthways of the journal. The philosophy of this is, that the file marks will hold the oil and afford unusually free lubrication while the bearing and journal are wearing down to a bearing.
But where the framework holding the bearings and journals are rigid, these bearings and journals may, with care, be fitted to a polished and equal bearing, leaving a smoother surface than that produced by wearing down to a bearing. But if, as in the case of a locomotive, the framework is subject to torsion, rough surfaces left to adjust themselves are possibly better than those accurately fitted, because the whole framework holding the bearings changes its form when the full load is upon it and after put to work, and the fitting done when there was no load upon the parts is no longer quite correct. The lubrication of the bearing, however, should be very free, and the effort appears at present to be to afford more ample oil ways than hitherto even at some sacrifice of bearing area.
Lead-lined Journal Bearings.—If a journal is worn in grooves or undulations it becomes impracticable to properly fit the brass to it without reducing its diameter to remove the rings, and to obviate the cutting and heating which necessarily follow, as well as to obviate the necessity of fitting the brasses at all, Mr. D. A. Hopkins introduced lead-lined bearings; the lead lining being merely auxiliary to the bearing proper, which is made preferably of hard bronze, and to which the thin layer or facing of lead is firmly attached by a soldering process, so that the two metals are virtually one piece. Into this lead facing the journal, under the pressure of the car, moulds or imbeds itself from the start, and afterwards gradually wears its way through it into the hard metal. The perfect fit thus secured under all conditions of the journal, aided with proper lubrication, not only prevents heating, but secures the full wear of the brasses, and makes them at all times perfect counterparts of the journal surfaces.