‘oint-making and Gland-packing.
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Contributed by an Engineer-in-Charge.
The various joints on steam wagons and tractors are neither complicated nor numerous, but, in spite of this, it is not an uncommon thing to see a vehicle whose joints are " weeping " the engine is partially enveloped in a cloud of steam; condensed water drips about all over the place; and dirt and discomfort reign supreme. The usual remedy, directly a joint starts " blowing," is to tighten the nuts, and this, in many cases, stops the leak ; in others, it may only stop it for a time. Constant tightening of the nuts weakens the bolt or nut until it is unable to stand the strain and gives out; matters have then reached the climax. I have seen men attempt to rivet the edges of the joint with a hammer, and if that did not answer the desired purpose, a caulking tool was used. .• A few years ago, when the pressure in steam-vehicle engines did not exceed foolb. per square inch, almost anything would do for a joint, and many a traction-engine driver has had to use the first thing he could lay hands on II) make a temporary joint, which would enable him to reach a place where he could have a proper repair done, or draw off the road; but, with the pressures of 200lb. and over which are now common, the exercise of care and judgment in the selection of the most suitable material is necessary.
The breaking of joints requires a certain amount of care, otherwise the result will be a fractured flange or cover, due to the careless application of the steel wedges which are generally used to start a cover; special care must be exerCised if they are inserted close to the bolt holes or corners of the steam-chest covers. The wedges employed should be
made of steel, and should be about 2 inches long, inch wide, and I inch thick. They should be drawn clown to a gradual taper, and a sharp edge should be ground smooth on both faces.
In wedging off a cylinder cover, three wedges should be used; they should be placed at equal distances apart and midway between the bolt holes. They should be entered just between the cover and flanges, and all should be driven in a little wav at first. The face of the cover should then be tapped all round with a hammer to assist in loosening the joint, after which the wedges can be driven in a little further, and the operation repeated. If it be found that, when driving the wedges in, the hammer rebounds and the wedge does not move at all, the cover must be tapped until the jointing is loosened a little more. Probably the end of the wedge may be on the spigot of the cover--in this case, it will have to be withdrawn, and a piece of sheet iron placed at the back of it. The wedges must have a perceptible " give " each time they are struck with the hammer if ttey are entering properly, and the cover should show an equal amount of opening all round. In large covers it is the practice to provide special holes midway between the studs; these are drilled and tapped to receive set-screws, which can be screwed up against the cylinder to ease the cover back.
The joints should now be thoroughly scraped, to remove all the old jointing material, both on the cover and cylinder face, and especially round the bolts and studs, to make sure that there is none left. Neglect of this precaution may cause the joint to blow, through the cover not bedding down properly. At the same time, the root of the studs should be carefully examined, as very often the first thread " rises " owing to the fact that the holes were not slightly countersunk before the studs were screwed in ; this leaves " burs " round the studs which might prevent the cover bedding down. A little oil should be put on the studs and nuts, and the studs should be run down to see that they are threaded far enough for the nut to screw down close to the cover in order to hold it securely in place. The cover should be tried on to make sure there is no " bur " or projection likely to keep it away. The ideal joint is the metal-to-metal one, made by scraping ; this is perfectly steam and water tight, although it is too expensive for general use. The alternative types are turned and faced joints which, in themselves, are not steam or water tight owing to the small ridges left by the tools. For this reason some softer material has to be introduced between the faces to effect the desired purpose, the kind of jointing selected being according to circumstances. It should be remembered, however, that the thinner the material the less chance is there of a " blow out occurring.
The joints that are most frequently broken are the hand or mud holes of the boiler, and for these nothing equals the flat rings specially made in all sizes. These rings are smeared over with graphite grease to prevent them sticking, and they can be used over again several times, provided a little of the graphite is used each time. These rings are preferable to plain indiarubber which is apt to deteriorate owing to the heat. The manhole covers, which do not require to be broken so often, can be made with red lead and tar yarn.
A good deal of trouble is experienced by some men in making the manhole joint with red lead. In some cases the cover fits badly, and it becomes necessary to use a thicker jointing in some places than others. Not infrequently the spigot on the cover is too small for the hole cut in the boiler shell, thereby leaving an opening which offers great inducements for the steam to cause a blow-out. If the cover is found to be a bad fit round the stiffening ring outside.the manhole, it should be chipped and filed so that it takes an equal bearing all round; if the spigot on the cover is too small, the only remedy is to have a new cover, although, if the difference does not amount to much, the cover may be kept in such a position that, when screwing up, the opening is equal all round. When jointing the cover up, the red lead should not be applied too thickly, as very often, when screwing the nuts up, the-lead squeezes out, and carries the outside turn or two of yarn with it, so that they are not between the joint at all and are practically useless. Above all, one should not fail to follow the nuts up on the cover as the steam rises; neglect of this precaution has often necessitated the re-making of the joint.
It is the practice with a good many men, on finding that the hand holes and man holes are " weeping " slightly after steam is up, to hammer round the joint ; and this, in many cases, stops them for a time. It is, however, a practice which is not to be recommended, although a joint that is " weeping " only a little will very often take up, but, if there is any doubt about it, it is by far the better plan to make it again before starting than to run any risk of having it blow out on the road, where the facilities for refilling the boiler are absent.
The back cylinder cover is a very important joint, owing to the fact that two of the ends of the guide bars are supported by it in a great many cases, and if it is improperly made and leaks, considerably more trouble will be experienced in remedying the defect than is the case with the front cover. Before breaking this joint it is advisable to have some mark to enable one to put the cover back in the same position as it previously occupied, and this is done by scratching a fine line across the edge of the cover and another. line at right angles to it on the cylinder face. Unless this simple precaution is taken, the ends of the guide bars are apt not to bed fairly and squarely with the cover, and they will probably get broken in screwing up, if of the parallel type, but, in the case of a bored guide, this does not happen. The jointing material used should be as thin as possible; red lead without any yarn is one of the best, as it enables the cover to be screwed up with practically a metal-to-metal joint, and it is then impossible for it to yield and cause a " blow-out," owing to those strains set up • in it which are due to the action of the crosshead. In an emergency, a joint of ordinary brown paper smeared over with boiled linseed oil will be found a suitable, though only a temporary, substitute.
The front cylinder covers and steam-chest covers are broken more often than the back ones, and, for this reason, it is advisable to use some kind of jointing material that can be used again should it be necessary to break the joint. The various kinds of jointing material on the market offer a wide range of choice. For the faced joints usually found on the covers and faces, there is a jointing material made of specially-prepared canvas with very thin brass wire gauze Interwoven between the layers ; this has given good results in practice, and, if smeared over with graphite grease, is capable of being used several times, provided care is used in breaking the joint. The steam chest covers in some engines have a planed face on the inside for the back of the slide-valve to work against and to prevent the valve being lifted off its seat, so that care should be taken when making the joint to see that the jointing material is thick enough to allow free movement of the valve, otherwise a broken valverod, cover, or eccentric strap, will be the result. if, on the other hand, the joint is too thick, the valve will probably be lifted off its seat when using the reversing lever to check the engine. When screwing up the nuts, they should be tightened up equally all round, so that an equal amount of pressure is brought to bear on all sides of the joint. For permanent joints, such as boiler mountings, soft sheet lead is sometimes used, and, if made properly, it answers very well. Should the joints show any signs of leakage and it is impossible to tighten the nuts up, they can be stopped with a small caulking tool and a hammer.
In screwing up the screwed sockets of pipe joints, owing to the fact that the threads run Off at a slight taper, a socket can easily be split, if any great pressure is brought to bear on the pipe tongs : the sockets must nevertheless be screwed up tightly enough to prevent any leakage. If red lead is used, it should be thinned down with boiled linseed oil (not ordinary engine oil as is sometimes done) to about the consistency of thick paint, so that it can be applied to the
threads with a brush. The g-rape. ste previously mentioned can be used instead of red lead, Le..t this latter, wh,st being capable of making a steam or watertight joint Jes not set hard like red lead.
The "running joints " in pipes are mace with special sockets, one end of the socket being faced ur to receive the " back nut " ; this latter also has one side 'aced up, and slightly recessed, to enclose a grommet of tar twine between the nut and the end of the socket ; it should be made sure that these two faces correspond. Leaky sockets can sometimes be stopped by caulking round the ends slightly, although this is only advisable for a temporary job, as the continual vibration is likely to cause it to start leaking again at any moment.
Copper pipes are usually connected by means of " unions," and too great ptessure should not be exerted, in order to bring the recessed faces together, or the threads will become " stripped." In order to prevent this it is necessary to make sure that the pipes come squarely with one another—the nuts will not then have to draw the pipes into line. One should be very careful that the threads are not " ctossed," or a deal of trouble will be experienced with them, even if they are not actually spoiled.
The packing of glands is more important than many men are apt to consider it, and upon the proper packing of a gland depends the success or failure of the job. The packing may be screwed up so tightly that undue friction is set up, causing 'excessive scoring of the rods, or the gland may be continually blowing and wasting a lot of steam. One frequent cause of trouble is due to the omission to draw all the old packing out of the gland. This, becoming hard, cuts and scores the rods in a very short time. Therefore, it is essential, before putting in any fresh packing, to clean all the old packing out of the stuffing box first.
The size of the packing chosen should be such that it is an easy fit between the rod and the stuffing box; it should not be necessary to hammer it out previous to inserting it. On the other hand, it should not be too slack, or it may not fill the box properly when screwed up and so cause leakage. The exact lengths to be used should be measured round the rod, and cut with a sharp knife. To prevent the edges becoming frayed, it should not be cut squarely with the surface of the packing, but slightly on the bevel at both ends. Each ring should he placed in the stuffing box with the cut diametrically opposed to the previous ring. After inserting two or three rings and pushing them down with the packing tool, the gland should be brought up and screwed down to force the rings into their proper positions. The gland should then be run back and a sufficient number of rings put in to fill the stuffing box. The gland can then be finally screwed up, care being taken that it is in the stuffing box far enough to clear the end of the crosshead, in the case of the pistOn rod. Each ring, when being inserted, can be swabbed over with cylinder oil with advantage, and care should be taken to pull the nuts up equally, or the gland will be bearing hard on one part of the rod and be free on the other—the same remarks applying when tightening up the gland.
Of the numerous varieties of jointing material on the market, many are unsuitable and useless, so that drivers will, in all cases, find it best to deal with a firm whose reputation is a good one.