Modern Machine-Shop Practice Part 164

The joint is made by using, in place of the gauze wire, one or two thicknesses of the pasteboard, duck, or canvas, cut out to the size of the f.l.a.n.g.e, and with the necessary holes to receive the standing bolts and leave the bore of the pipe clear. If the f.l.a.n.g.e of the joint is of copper, bra.s.s, or wrought iron, or, if of cast iron, is of sufficient strength to permit it, one disk may be made the full size of the f.l.a.n.g.e, and a second may be made to have an external diameter sufficiently large to fit snugly inside of the bolt holes, which will form sufficient thicknesses if the f.l.a.n.g.e is a fair fit to its seat; if it is not, however, three, or even four, thicknesses may be used, in which case at least one of them should fit inside the diameter of the f.l.a.n.g.e across the bolt holes, as described. The disks being prepared, we spread on the first one a thin coating of red-lead putty, and then lay another canvas disk on, again adding the putty until the whole is completed. We then spread a thin layer of the putty around the hole of the seat and that of the f.l.a.n.g.e, place the disk in position and screw the joint up, tightening down the nuts until they bring the f.l.a.n.g.e to an equal seating all around and not sooner on one side than on another, for in that case the red-lead putty will be squeezed unevenly, and too much on the side screwed up to excess. The nuts should be screwed up very tight; the joint wiped, the protruding canvas cut off, and the joint is complete.

For very rude and rough joints, whether used under pressure or not, we may make, for either water or steam, a joint as follows: Taking four or five strands of hemp, we saturate them with a coating of white lead ground in oil, applying just sufficient to make the fibres of the hemp cling well together. We then plait the strands and coat the whole rope thus formed with red-lead putty, and place the strand around the hole of the joint, taking care that the ends lap evenly, so that the joint shall be of even thickness. It is better, however, to bend a piece of lead or iron wire to suit the size and shape of the hole in the joint, and then wind the hemp and red lead around the wire. And in cases where the f.l.a.n.g.es of the joint are sufficiently strong to have no danger of their breaking from the pressure due to s.c.r.e.w.i.n.g up the nuts, the piece of lead wire, if given a neat b.u.t.t joint or neatly lapped, may be employed without any red-lead putty or hemp; this does not, however, make a good permanent joint. In cases where a joint requires to be made thick to accommodate the length of the pipe, pasteboard may be used in the place of canvas, giving to it a thinly-spread coating of red-lead putty on each side, and, if possible, leaving the pasteboard a trifle too thick and springing open the f.l.a.n.g.es of the joint to get the pasteboard into position without sc.r.a.ping off the red-lead putty.

Where it is required that a joint stand great heat or fire, asbestos board, about 1/16 inch thick, makes a good and permanent joint. It is coated with red lead mixed thinly with boiled oil, containing as much as it will soak up, leaving a thin layer of the lead upon the surface of the asbestos. The holes for the bolts to pa.s.s through in the duck, canvas, pasteboard, or asbestos joint should be cut large enough to well clear the bolts.

For cold water, where it is not subject to great variations of temperature, common sheet lead makes a very good joint; but under excessive changes of temperature the expansion of the pipes will soon cause the sheet lead to squeeze out and the joint to leak.

Joints are frequently made with copper wire rings, made of a diameter to pa.s.s around the hole of the joint and lie within the diameter of the bolt holes, and brazed together at the ends; but if the joint be rectangular instead of circular the wire must either lie in a recess, or else a shoulder must be left for the wire to abut against, which will prevent its blowing or becoming forced out by the pressure.

In some practice softened sheet copper about 1/32 inch thick is used to make joints on surfaces that have been planed. Joints of this kind are used for locomotive steam chests.

Rubber joints are used to make steam, water, and air-tight joints, and are usually made from what is known as combination rubber--that is, sheet rubber having a linen or other web running through it; with one such web it is called single, and with two webs two-ply, and so on.

There is in many cases, however, an objection to this form of joint, in that it compresses; and hence in the case of the steam chest, for example, it affects the distance of the slide-spindle hole in the chest from the seat, and throws it somewhat out of line with the eccentric. In long eccentric rods the variation is of course minute; but still it exists, and must exist, since it is impossible to tell exactly how much the rubber will compress in making the joint. Furthermore, if it is required to break such a joint, the rubber will very often cling so tenaciously to the seat in one place and to the chest in the other, that it will tear asunder in breaking the joint. To obviate this as much as possible, however, we may chalk the rubber on one face and slightly oil it on the other, so that the oil will aid the rubber in clinging to one face, while the chalk will a.s.sist it in separating from the other face of the joint.

Rubber joints slowly compress after being under pressure a day or so, and also if subjected to heat; hence they should have their bolts screwed up after becoming heated, or after having stood some time. It is advisable also that the rubber be as thin as the truth of the surfaces will admit. If it is necessary to use more than one thickness of rubber, the thickness may be made up of rings, whose diameter will just pa.s.s within the bolt holes.

The holes in a rubber gasket should be made larger than the bolt holes, so that there shall be no danger of the bolt, when being inserted, catching the gasket.

If the f.l.a.n.g.es should not come fair, and it is determined not to set them fair, the rubber should be as thick as the widest part of the opening between them, and shaved off to suit the thin side of the joint, and in this case the bolts must be tightened very uniformly and gradually around the joint to secure a tight one. If there is room to shave the gasket to the amount of taper, and use in addition a ring around the bolt holes, it will make a safer job.

When the gasket requires to be split to pa.s.s it around or over a rod, it should be cut through to the canvas on one side, and a short distance off cut through to the canvas on the other side; the rubber may then be stripped carefully back from the canvas and the latter cut through and pa.s.sed over the rod, when the rubber may be put back and sewed to the canvas again.

Sheet rubber with a gauze wire insertion instead of canvas makes an excellent joint.

[Ill.u.s.tration: Fig. 2452.]

In Fig. 2452 is shown a method of making a steam-tight joint largely employed in England, upon the steam chest joint where the cylinders of crank shaft (inside cylinder) engines are bolted together. A is the f.l.a.n.g.e of one cylinder, which is bolted to the other by the bolt B. C is a strip of copper let into a dovetail groove cut one half in one cylinder, and the other half in the other. After the bolts B are all firmly screwed home, hammer blows are delivered upon the top of the copper strip as denoted by the arrow E, expanding the copper so that it completely and closely fills the dovetail groove, and makes a steam-tight groove.

In riveting the copper it is necessary to hammer it evenly all along lightly, and only sufficiently to make it closely fill the groove, otherwise it will spring the joint open, and cause it to leak, notwithstanding the bolts B, which will give under the extreme strain.

Temporary joints are sometimes made by bending a piece of lead wire into a ring or frame, of such a size as to well clear the inside of the bolt holes. The ends are neatly joined, and the lead wire compressing and accommodating itself to the inequalities of the surfaces forms a joint.

[Ill.u.s.tration: Fig. 2453.]

[Ill.u.s.tration: Fig. 2454.]

JOINTS FOR BOILER FITTINGS.--Let it be a.s.sumed that the casting shown in Figs. 2453 and 2454 requires to be fitted to a boiler, both being new.

In this case, the holes for the studs or bolts should first be drilled in the f.l.a.n.g.e of the casting, which will reduce its weight and render it easier to handle. The casting should then be held against the boiler in its proper position and location; and, with a fork scriber whose width of points is equal to the widest s.p.a.ce between the face of the casting f.l.a.n.g.e and the boiler, pa.s.s the fork scriber around the fitting or casting with one point against the boiler sh.e.l.l and the other pressed against the edge of the casting, the result being to mark around the f.l.a.n.g.e of the latter a line exactly following the surface or contour of the boiler, and at a distance from the boiler the nearest that will suffice to properly bed the casting to the boiler surface, or, in other words, the line that will exactly mark the amount of metal requiring to be cut off the f.l.a.n.g.e face to make it bed all over; and that face may, therefore, be cut down to the line. In chipping and filing it, however, the straight-edge may be used to advantage as follows:--

[Ill.u.s.tration: Fig. 2455.]

Suppose the casting f.l.a.n.g.e to be gripped in the vice facing the operator, as in Fig. 2455, and that L L represents the scribed line: then the cape chisel cuts may be carried clear across the f.l.a.n.g.e, coming exactly down to the line on each side of the f.l.a.n.g.e, while a straight-edge S may be used as shown to show when the cut is carried across level. Then, when the intermediate s.p.a.ces are cut out with the flat chisel the surface will be of correct shape, and the surface may be rough filed. The casting should be cut clear down to the lines, and if the job has been properly set, marked and faced, no further trying will be necessary previous to marking the bolt or stud holes in the boiler.

It is well, however, if the operator is inexperienced in this kind of work, to again set the casting in its proper position to correct the fit. But, with proper care, all the holes in the boiler may be marked without any second fitting of the f.l.a.n.g.e, since the operation properly performed is bound to give correct results. In doing a job of this kind it must be borne in mind that it is very easy to consume more time in trying and altering the job than is required under proper conditions to do the entire job; hence, in setting the casting, preparatory to marking it with the fork scriber, nothing is near enough that does not carry with it a conviction of perfect reliability; and if any doubt exists it is better to go through the process again. If the casting f.l.a.n.g.e varies much in shape from its seat, and rocks or is unsteady, wooden wedges may be placed beneath it, or a few pellets of stiffly mixed red lead may be placed on the boiler where there is most room between it and the casting, the boiler surface being coated or painted with red marking, so that the pellets shall adhere to it and not to the f.l.a.n.g.e face. If the casting is too heavy to be steadied by hand, one hole may be drilled in the boiler and a temporary bolt inserted to hold the casting while setting it in position, and marking with the fork scriber.

When the f.l.a.n.g.e is approaching a fit, it must be placed in position on the boiler and the stud holes marked on the boiler with an ordinary scriber, its point being pressed against the boiler while it is pressed against the side of the hole in the casting f.l.a.n.g.e and traversed around it, so as to scribe on the boiler surface circles corresponding to the holes in the f.l.a.n.g.e. From the centres of these circles others of the proper size of the tapping holes may be struck and the tapping holes may then be drilled, and the studs put in. The remainder of the fitting operation consists in applying red marking on the boiler surface, bolting the casting to its place and filing the high spots. The marking is made to show plainly upon the f.l.a.n.g.e by light hammer blows with a piece of wood interposed between the hammer and the f.l.a.n.g.e face to prevent piercing the latter. These blows, however, should be lightly delivered, or they will cause the marking to be deceptive.

[Ill.u.s.tration: Fig. 2456.]

The fit of the f.l.a.n.g.e 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 f.l.a.n.g.e 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 f.l.a.n.g.e, as shown in Fig. 2456, in which the area within the dotted circle C encloses the area to be most closely bedded. This is a highly important consideration in f.l.a.n.g.e 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 f.l.a.n.g.e--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 f.l.a.n.g.e from the bolt holes outward much, but to merely make the f.l.a.n.g.e, 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 f.l.a.n.g.e would bend from the pressure of the nuts, and would in consequence spring if made of bra.s.s, 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 about 3/8 inch 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 f.l.a.n.g.es to boilers are made by riveting the f.l.a.n.g.es to the boiler and caulking or closing the edge of the f.l.a.n.g.es to the boiler sh.e.l.l; 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.

[Ill.u.s.tration: Fig. 2457.]

Fig. 2457 (which is taken from _The American Machinist_), represents a joint for boiler fittings, designed to facilitate the breaking and re-making of the joint. C represents, say, a boiler plate, B a piece having a ball joint seat in C ground steam tight, and A a f.l.a.n.g.e, say, for a feed pipe; the studs D thread permanently into C, and the joint is bolted up by the stud nuts E. It is obvious that the ball joint between B and C permits the f.l.a.n.g.e A to set at an angle if necessary.

RUST JOINTS.--These are joints made by means of filling the s.p.a.ce between the f.l.a.n.g.es, or annular s.p.a.ces, 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 s.p.a.ce than the iron from which it was formed.

[Ill.u.s.tration: Fig. 2458.]

Rust joints are employed upon very uneven surfaces, and for pipes for mains to go under ground. In former times this cla.s.s of joints was much used in engine and boiler work, but of late years it has been to a great extent abandoned. In Fig. 2458 is shown the method of construction for a rust joint for what are known as spigot and socket joints for pipe work. S is the spigot and P the socket. R R is a metal ring, bound over with either dry hemp fibre or tarred twine or rope. The remainder of the s.p.a.ce between the pipes at A A being filled with a cement composed of

Sifted cast-iron borings 100 lbs.

Sal-ammoniac 1/2 lb.

Sulphur 1/2 lb.

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 s.p.a.ce A A, in quant.i.ties sufficient to fill up about 3/4 inch in length of the annular s.p.a.ce A A, and then caulked by being driven in with the tool shown in Fig. 2459. Cement is then again put in and the caulking repeated, the process being continued until the whole s.p.a.ce is filled.

[Ill.u.s.tration: Fig. 2459.]

In some cases (as in gas mains) the s.p.a.ce A A is filled with melted lead, and when cold caulked with the tool described.

[Ill.u.s.tration: Fig. 2460.]

In Fig. 2460 is shown the method of making a rust f.l.a.n.g.e joint; A A being 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.

[Ill.u.s.tration: Fig. 2461.]

In some cases pipes are joined with rust joints, as in Fig. 2461 in which A A is a sleeve, there being two rings of wire and hemp inserted as shown.

When f.l.a.n.g.ed joints are made with a sc.r.a.per, 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.

[Ill.u.s.tration: Fig. 2462.]

Fig. 2462 is a face, and Fig. 2463 (which are from _Mechanics_), 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 P are corrugated copper disks secured to the faces of the pipe ends by f.l.a.n.g.es, as shown, and gripped at their edges by the f.l.a.n.g.es 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 cavity A is filled with steam, and to support the disks P against the pressure segmental blocks B of 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.

[Ill.u.s.tration: Fig. 2463.]

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 off before 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.

[Ill.u.s.tration: Fig. 2464.]

Fig. 2464 represents a cutter of this kind, the piece A carrying the cutter B, which is operated in the stock C by means of the threaded handle H.