[44]Scalesarecorded the reduction of the load on the testing device forverticalbelts by the tension of the loose part of the belt (t.). Scalesb, by that of the tight side of the belt (T).
[44]Scalesarecorded the reduction of the load on the testing device forverticalbelts by the tension of the loose part of the belt (t.). Scalesb, by that of the tight side of the belt (T).
The total power expended per revolution is about 2,000 ft. lbs., therefore .03 is lost.
Under light loads, the internal resistance, which is nearly constant in amount, may be a large percentage of the power transmitted, while under heavy loads the percentage of slip may become the principal loss.
It would be difficult to work out, or even to use, a general expression for the efficiency of belt transmission, but, from the foregoing, it would seem safe to assume that 97 per cent. can be obtained under good working conditions.
When a belt is too tight, there is a constant waste in journal friction, and when too loose, there may be a much greater loss in efficiency from slip. The allowance recommended of 2 per cent. for slip is rather more than experiment would indicate for any possible crawl or creep due to the elasticity of the belt, but in connection with this, there is probably always more or less actual slip, and we are inclined to think that in most cases this allowance may be divided into equal parts representing creep and slip proper. Under good working conditions, a belt is probably stretched about 1 per cent. on the tight side, which naturally gives 1 per cent. of creep, and to this we have added another per cent. for actual slip in fixing the limit proposed.
The indications and conclusions to be drawn from these experiments are:
1. That the coefficient of friction may vary under practical working conditions from 25 per cent. to 100 per cent.
2. That its value depends upon the nature and condition of the leather, the velocity of sliding, temperature, and pressure.
3. That an excessive amount of slip has a tendency to become greater and greater, until the belt finally leaves the pulley.
4. That a belt will seldom remain upon a pulley when the slip exceeds 20 per cent.
5. That excessive slipping dries out the leather and leads toward the condition of minimum adhesion.
6. That rawhide has much greater adhesion than tanned leather, giving a coefficient of 100 per cent. at the moderate slip of 5 ft. per minute.
7. That a velocity of sliding equal to .01 of the belt speed is not excessive.
8. That the coefficients in general use are rather below the average results obtained.
9. That when suddenly forced to slip, the coefficient of friction becomes momentarily very high, but that it gradually decreases as the slip continues.
10. That the sum of the tensions is not constant, but increases with the load to the maximum extent of about 33 per cent. with vertical belts.
11. That, with horizontal belts, the sum of the tensions may increase indefinitely as far as the breaking strength of the belt.
12. That the economy of belt transmission depends principally upon journal friction and slip.
13. That it is important on this account to make the belt speed as high as possible within the limits of 5,000 or 6,000 ft. per minute.
14. That quarter-twist belts should be avoided.
15. That it is preferable in all cases, from considerations of economy in wear on belt and power consumed, to use an intermediate guide pulley, so placed that the belt may be run in either direction.
16. That the introduction of guide and carrying pulleys adds to the internal resistances an amount proportional to the friction of their journals.
17. That there is still need of more light on the subject.
Forging.—The operation of forging consists in beating or compressing metal into shape, and may be divided into five classes, viz., hand-forging, drop-forging, machine-forging, forging under trip or steam hammers, and hydraulic forging. In purely hand forging much work is shaped entirely by hand tools, but in large shops much work is roughed out under trip or steam hammers, and finished by hand, while some work is finished under these hammers. In drop forging the work is pressed into shape by dead blows, which compress it into shape in dies or moulds. In machine forging the work is either formed by successive quick blows rather than by a few heavy ones, or in some machines it is compressed by rolling. In hydraulic forging the metal is treated as a plastic material, and is forced into shape by means of great and continuous pressure.
In all forging the nature or quality of the iron is of primary importance; hence the following (which is taken fromThe English Mechanic), upon testing iron, may not be out of place.
“The English Admiralty and Lloyds’ surveyor’s tests for iron and steel are asfollows:—
“Two strips are to be taken from each thickness of plate used for the internal parts of a boiler. One-half of these strips are to be bent cold over a bar, the diameter of which is equal to twice the thickness of the plate. The other half of the strips are to be heated to a cherry-red and cooled in water, and, when cold, bent over a bar with a diameter equal to three times the thickness of the plate—the angle to which they bend without fracture to be noted by the surveyor. Lloyds’ Circular on steel tests states that strips cut from the plate or beam are to be heated to a low cherry-red, and cooled in water at 82° Fahr. The pieces thus treated must stand bending double to a curve equal to not more than three times the thickness of the plate tested. This is severe treatment, and a plate containing a high enough percentage of carbon to cause any tempering is very unlikely to successfully stand the ordeal. Lloyds’ test is a copy of the Admiralty test, and in the Admiralty Circular it is stated that the strips are to be one and a half inches wide, cut in a planing machine with the sharp edges taken off. One and a half inches will generally be found a convenient width for the samples, and the length may be from six to ten inches, according to the thickness of the plate. If possible, the strips, and indeed all specimens for any kind of experimenting, should be planed from the plates, instead of being sheared or punched off. When, however, it is necessary to shear or punch, the piece should be cut large and dressed down to the desired size, so as to remove the injured edges. Strips with rounded edges will bend further without breaking than similar strips with sharp edges, the round edges preventing the appearance of the small initial cracks which generally exhibit themselves when bars with sharp edges are bent cold through any considerable angle. In a homogeneous material like steel these initial cracks are apt to extend and cause sudden fracture, hence the advantage of slightly rounding the corners of bending specimens.
Fig. 2824Fig. 2824.
Fig. 2824.
“In heating the sample for tempering it is better to use a plate or bar furnace than a smith’s fire, and care should be taken to prevent unequal heating or burning. Any number of pieces may be placed together in a suitable furnace, and when at a proper heat plunged into a vessel containing water at the required temperature. When quite cold the specimens may be bent at the steam-hammer, or otherwise, and the results noted. The operation of bending may be performed in many different ways; perhaps the best plan, in the absence of any special apparatus for the purpose, is to employ the ordinary smithy steam-hammer. About half the length of the specimen is placed upon the anvil and the hammer-head pressed firmly down upon it, as inFig. 2824. The exposed half may then be bent down by repeated blows from a fore-hammer, and if this is done with an ordinary amount of care it is quite possible to avoid producing a sharp corner.
Fig. 2825Fig. 2825.
Fig. 2825.
“An improvement upon this is to place a cress on the anvil, as shown atFig. 2825. The sample is laid upon the cress, and a round bar of a diameter to produce the required curve is pressed down upon it by the hammer-head.
Fig. 2826Fig. 2826.
Fig. 2826.
“The further bending of the pieces thus treated is accomplished by placing them endwise upon the anvil-block, as shown inFig. 2826. If the hammer is heavy enough to do it, the samples should be closed down by simple pressure, without any striking.
Fig. 2827Fig. 2827.
Fig. 2827.
“Fig. 2827is a sketch of a simple contrivance, by means of which a common punching machine may be converted temporarily into an efficient test-bending apparatus. The punch and bolster are removed, and the stepped cast-iron blockafixed in place of the bolster. When a sample is placed endwise upon one of the lower steps of the blockathe descending stroke of the machine will bend the specimen sufficiently to allow of its being advanced to the next higher step, while the machine is at the top of its stroke. The next descent will effect still further bending, and so on till the desired curvature is attained. It would seem an easy matter, and well worth attention, to design some form of machine specially for making bending experiments; but with the exception of a small hydraulic machine, the use of which has, I believe, been abandoned on account of its slowness, nothing of the kind has come under the writer’s notice.
“The shape of a sample after it has been bent to pass Lloyds’ or the Admiralty test is that of a simple bend, the sides being brought parallel. While being bent the external surface becomes greatly elongated, especially at and about the point of the convex side,where the extension is as much even as fifty per cent. This extreme elongation corresponds to the breaking elongation of a tensile sample, and can only take place with a very ductile material. While the stretching is going on at the external surface, the interior surface of the bend is being compressed, and the two strains extend into pieces till they meet in a neutral line, which will be nearer to the concave than to the convex curve with a soft specimen. When a sample breaks, the difference between the portions of the fracture which have been subject to tensile and compressive strains can easily be seen.
Fig. 2828Fig. 2828.
Fig. 2828.
“Fig. 2828shows a piece of plate folded close together; and this can generally be done with mild steel plates, when the thickness does not exceed half an inch.
“Common iron plates will not, of course, stand anything like the foregoing treatment. Lloyds’ test for iron mast-plates1⁄2inch thick, requires the plates to bend cold through an angle of 30° with the grain, and 8° across the grain; the plates to be bent over a slab, the corner of which should be rounded with a radius of1⁄2inch.
Fig. 2829Fig. 2829.
Fig. 2829.
“When the sample of metal to be tested is of considerable thickness, as in the case of bars, it is often turned down in a lathe to the shape shown inFig. 2829, so as to reduce its strength within the capacity of the machine. The part to be tested has usually a length between the shoulders of 8, 10, or 12 inches, and must be made exactly parallel with a cross-sectional area apportioned to the power of the machine and the strength of the material to be tested. When it is desired to investigate the elastic properties of materials, it is desirable to have the specimens of as great a length as the testing apparatus will accommodate.
Fig. 2830Fig. 2830.
Fig. 2830.
Fig. 2831Fig. 2831.
Fig. 2831.
“Many of the early experiments on the tensile strength of wrought iron were made with very short specimens, such as inFig. 2830, which is a sketch of that used formerly in the royal arsenal at Woolwich. This had no parallel length for extension at all, its smallest diameter occurring at one only point. Mr. Kirkaldy, to whom is due in a great measure the honour of having raised ‘testing’ to an exact science, discovered that this form of specimen gave incorrect results. He found that experiments with such specimens, more especially when the metals were ductile, gave higher breaking strains than were obtained with specimens of equal cross-sectional area having the smallest diameter parallel for some inches of length. This was due to the form of the specimen resisting to some extent the ‘flow’ or alteration of shape which occurs in soft ductile materials previous to fracture. He accordingly commenced to use a specimen of the form shown inFig. 2831, with a parallel portion for extension of several inches in length, and specimens like that inFig. 2830became a thing of the past.
“The specimens shown in the figures admit of being secured in the testing machine in many different ways. But whatever description of holder be employed, two absolute requirements must be kept in view. The holders must be stronger than the sample, and they must transmit the stress in a direction parallel to the axis of the sample without any bending or twisting tendency.
Fig. 2832Fig. 2832.
Fig. 2832.
“Fig. 2832gives two views of a very effective method of holding round specimens, used by Mr. Kirkaldy in his earlier experiments carried out for Messrs. Napier & Sons, of Glasgow. The enlarged ends of the samples are clasped in split sockets provided with eye-holes for attaching them to the shackles of the testing machine, the halves of the sockets being held together during the experiment by small bolts passing through the projecting lugs.
Fig. 2833Fig. 2833.
Fig. 2833.
“Fig. 2833explains the plan adopted for testing the strength of bolts and nuts in the same series of experiments.
Fig. 2834Fig. 2834.
Fig. 2834.
“A good holder for lathe-turned samples is shown inFig. 2834. Close fitting socket-piecesb bembrace each end of the specimen, and also the turned collar at the extremity of the shacklea. The halves of the socket are held together by a collarc, the interior of which and exterior of the socket rings are turned to an equal taper, so that the socket-pieces are held quite firmly when the collarcis simply slipped over them by hand. When the experiment is over, a few taps with the hammer will remove the collarc.
Fig. 2835Fig. 2835.
Fig. 2835.
“Samples of plates for tensile testing are usually shaped likeFig. 2835. The parallel portionbis generally 8, 10, or 12 inches long, as in the case of the turned specimens. Two minor points in the preparation of specimens may be here alluded to. In the first place the holesa amust be made large enough to obviate any danger of the pins which are placed in these holes to secure the specimen being sheared in two before the specimen breaks. In the second place, enough material must be left around these pin or bolt holes to prevent the probability of the metal tearing away between the hole and the edge of the plate. The pin holes must be placed exactly in a line with the axis of the specimen, and the partbmust be quite parallel in width, so that the strength (and the elongation during the testing) may be, as nearly as possible, equal throughout the length ofb. The shoulders, asc, should be easy curves, so that sharp corners may be avoided. When a number of such specimens are required at the same time, the strips of plate may be clamped together and planed or slotted to the desired width as one piece, but the tool marks should be afterwards removed by careful draw-filing.
Fig. 2836Fig. 2836.
Fig. 2836.
“When the plates are thin, small side pieces are riveted on the sides of the ends to be clamped, as shown inFig. 2836. These stiffen those ends and afford a larger bearing for the securing pins. The connection with the shackles is made by means of steel pins passing through the end holes, and when specimens like2835are properly prepared, the direction of the stress on them must be in a line with their axis.Fig. 2837shows another form of plate specimen in which the holes are dispensed with, the ends being held in themachine by friction clips, as shown. These specimens are more easily prepared, and from the absence of holes may be made of a very narrow strip of plate.
Fig. 2837Fig. 2837.
Fig. 2837.
“InFig. 2837the jaws or forked arms of the shackle are closed to form a rectangular ring, as shown in section in the figure. Two of the interior faces are tapered inwards to the same angle as the back of the wedges or clipsa a′, which are perfectly smooth and free to slide upon the inclined or tapered surfaces of the shackles. The faces of the wedges, however, which come in contact with and grip the specimen to be tested, asb, are fluted or grooved, so that the friction of the edges against the specimen is much greater than against the inside surfaces of the shackles. The result of the arrangement is, that when the shackles are pulled, the wedgesa a′are tightened against the specimen with a degree of force proportionate to the load on the specimen, which is prevented from slipping through the clips by the ‘bite’ of their fluted faces. The grooves on the faces of the clips need not be deep—a depth of a little more than1⁄16, with about the same distance apart, answering well for ordinary loads. With deep grooves and a wider pitch apart, the danger of the specimen breaking in the clips is increased. The inclination of the backs of the wedgesa a′to the faces may be at an angle of 5 or 6 degrees. When the taper is too small, the removal of the halves of the specimen after breaking is sometimes difficult, while on the other hand, when too great, the specimen is apt to slip between the wedges while being tested. The wedges exert a very considerable outward pressure, and the jaws of the shackles must be made strong enough to resist any strain likely, under extreme conditions, to fall on them, otherwise they will speedily become unfit for use. In securing a specimen care must be taken that its axis is in the direct line of strain, and the opposite clips should be driven in equally so that the stress may act fairly upon it. Parallel planed strips of metal, without any enlargement at the ends, may be tested in these friction clips, though, of course, there is a chance of the specimen breaking within them. Turned specimens may also be held by such clips; as also may rough, unturned round and square bars, an advantage when it is desired to immediately ascertain approximately the strength of metal samples.”
Open fires for hand forging purposes are mainly of two classes, those having a side and those with a bottom or vertical blast.
Fig. 2838Fig. 2838.
Fig. 2838.
Fig. 2838represents a side draft forge.fis the fireplace, usually from 3 to 5 feet long,tis the tuyère through which the blast enters the fire,bbeing the blast pipe. To preventtfrom being burned away it is hollow as ats, and two pipespandp′connect to the water-tankw, thus maintaining a circulation of water throughs;vis simply a valve or damper to shut off the supply of air from the tuyère;dis the opening to the chimneyc.
The side blast, though not so much used as in former years, is still preferred by many skilful mechanics, on the ground that it will give a cleaner fire with less trouble. The method of accomplishing this is to dig out a hole in the fire bed and fill it in with coked coal, which will form a drain through which the slag or clinker may sink, instead of remaining in the active fire and obstructing the blast.
In cases where the fire requires to be built farther out from the chimney wall than the location of the tuyère permits, it may be built out asfollows:—
Fig. 2839Fig. 2839.
Fig. 2839.
Fig. 2840Fig. 2840.
Fig. 2840.
A barb,Fig. 2839, is placed in the tuyère hole and supported at the other end atp. The coal is well wetted and packed around and above the bar, which is then pulled out endwise, leaving a blast hole through the coal, as is shown in the end viewFig. 2840.
Fig. 2841Fig. 2841.
Fig. 2841.
Fig. 2841represents a patent tuyère of vertical or bottom draft, in which the blast passes through pipeaand circulates aroundb, finding egress atcinto the fire.cis hollow and receives water from the tankfby the piped. The steam generated in the nozzlecis conveyed to the tanks by the pipee.
Fig. 2842Fig. 2842.
Fig. 2842.
Fig. 2843Fig. 2843.
Fig. 2843.
Figs. 2842and2843represent a blacksmith’s forge, for work up to and about 4 inches in diameter. It consists of a wind-boxa, supported on brickwork which forms an ash-pitgbeneath it. To this box is bolted the wind-pipeb, and at its bottom is the slidee. In an orifice at the top ofais a triangular and oval breakerd, connected to a rod operated by the handlec. Thisrod is protected from the filling which is placed between the brickwork and the shellfof the forge by being encased in an iron pipei. The blast passes up around the triangular oval pieced. The operation is as follows: whendis rotated, it breaks up the fire and the dirt falls down into the wind-box, cleaning the fire while the heat is on. At any time after a heat the slideemay be pulled out, letting the slag and dirt fall into the ash-pit beneath. It is a great advantage to be able to clean the fire while a heat is on without disturbing the heat.
Fig. 2844Fig. 2844.
Fig. 2844.
Blacksmiths’ anvils are either of wrought iron steel faced, or of cast iron steel faced, the faces being hardened. It is sometimes fastened to the block by spikes driven in around the edges. A better plan, however, is to make the block the same size as the anvil, and secure the latter by two bands of iron and straps, as shown inFig. 2844, because in this way the block will not come in the way of arms or projecting pieces that hang below the anvil. The square hole is for receiving the stems of swages, fullers, &c., and for placing work over to punch holes through it, and the round is used for punching small holes.
The proper shape for blacksmiths’ tongs depends upon whether they are to be used upon work of a uniform size and shape, or upon general work. In the first case, the tongs may be formed to exactly suit the special work. In the second case, they must be formed to suit as wide a range of work as convenient.
Suppose, for example, the tongs are for use on a special size and shape of metal only; then they should be formed so that the jaws will grip the work evenly all along, and therefore be straight along the gripping surface. It will be readily perceived, however, that if such tongs were put upon a piece of work of greater thickness, they would grip it at the inner end only, and it would be impossible to hold the work steady. The end of the work would act as a pivot, and the part on the anvil would move about. It is better, therefore, for general work to curve the jaws, putting the work sufficiently within the jaws to meet them at the back of the jaw, when the end will also grip the work. By putting the work more or less within the tongs, according to its thickness, contact at the end of the work and at the point of the tongs may be secured in one pair of tongs over a wider range of thickness of work than would otherwise be the case. This applies to tongs for round or other work equally as well as to flat or square work.
To maintain the jaw pressure of the tongs upon the work, a ring is employed, the tong ends being curved to prevent the ring from slipping off.
After a piece of work has left the fire it should, if there are scales adhering upon it, have them cleaned off before being forged, for which purpose the hammer head or an old file is used, otherwise the forging will not be smooth, and the scale will be hammered into the surface. This will render the forging very hard to operate upon by steel cutting tools, and cause them to dull rapidly. For the same reason it is proper to heat a finished forging to a low red heat and pass a file over its surface, which will leave the forging soft as well as free from scale. A forging should not be finally finished by being swaged or forged after it has become black hot, because it produces a surface tension that throws the work out of true as the metal is cut away in finishing it.
Work to be drawn out is treated according to the amount of elongation and reduction of diameter required. Thus, suppose a piece of square work to require to be drawn out, then it is hammered on its respective sides, being turned upon the anvil so that each successive side shall receive the hammer blows. It is essential, however, that the piece be forged square, or in other words, that during the forging the sides be kept at a right angle one to the other, or else the work will hammer hollow, as it istermed; that is to say, the iron will split at the centre of the bar, which occurs from its being forged diamond-shaped instead of square. If a piece required to be forged diamond-shaped, it must be forged square until reduced to such dimensions as will leave sufficient to draw out while altering its form from the square to the diamond-shape.
In very small work, which is more apt to hammer hollow than large work, the end of the piece is left of enlarged size, as shown in the figure, the strength of the enlarged end serving to prevent the hammering hollow, which usually begins at the end of the piece; the end is in this case forged last. In the case of round work the same rule holds good, inasmuch as that a round bar may be forged smaller to some extent, either by hammer blows or by swaging, but if the forging by hammer blows be excessive, hammering hollow is liable to ensue.
The blacksmith’s set of chisels consists of a hot chisel for cutting off hot iron, a cold chisel for cutting cold metal, a hardy, which sets in the square hole in the anvil,C-chisels, which are curved somewhat like the carpenter’s gouge, and a cornering orV-chisel, in which the cutting edges are at a right angle one to the other.
The hot chisel has its edge well curved in its length, and is kept cool by lifting it from the work after each hammer blow, and by occasionally dipping it in water. Lifting it also prevents it from wedging in the work. The cold chisel is tempered to a blue, and answers virtually to the machinist’s chisel. The hardy is used for small work, which is laid upon it and struck with the hammer. TheC-chisel is used, not only in curved corners, but also to cut off deep cuts, answering, like the cape or cross-cut chisel of the machinist, to relieve the corners of the hot chisel. The cornering chisel is used for square corners, situated so that the hot chisel cannot be used. The blacksmith’s punch is made well taper, so that it shall not wedge in the hole it produces.
For large holes a small punch is first used, and the hole enlarged in diameter by driving in punches of larger diameter. If this swells the work at the sides, it is forged down while the punch is in the hole.
The first blow given to the punch is a light one, so as to leave an indentation that will mark the location, and enable its easy correction if necessary. The blows delivered after the correct location is indented are quick and heavy; but a piece of soft coal is inserted and the punch placed on top of it, the gases formed by the combustion of the coal serving to prevent the punch from binding in the hole. Between the blows the blacksmith lifts the punch and moves the handle part of a lateral rotation, which prevents it from becoming fast in the hole. The punch should not be suffered to get red hot, but must be removed and cooled, a fresh piece of green soft coal being inserted in the hole just previous to the punch. If the punch is allowed to become as heated as the work, the end will “upset” or swell and become firmly locked. Should the punch lock in the hole a few blows will usually loosen it, but in extreme cases it is sometimes necessary to employ another punch from the opposite side of the work. Unless in very thin work, the hole is punched half way from each side, because by that means a short stout punch may be used.
It is obvious that when the hole requires to be bell-mouthed or of any other form, the punch must be made to correspond.
The tools employed by the blacksmith, other than tongs, hammers, chisels, and punches, are composed mainly of “fullers” and “swages” of various kinds. The fuller is essentially a spreading tool, while the swage may be termed essentially a shaping one.
Fig. 2845Fig. 2845.
Fig. 2845.
InFig. 2845, for example, letarepresent an end view of an anvil,bthe bottom, andcthe top fuller, and the effects of blows uponcwill be mainly to stretch the piece in the direction of its length without swelling it out sideways.
Fig. 2846Fig. 2846.
Fig. 2846.
Fig. 2847Fig. 2847.
Fig. 2847.
Fig. 2848Fig. 2848.
Fig. 2848.
Fig. 2849Fig. 2849.
Fig. 2849.
If the work requires to be swelled sideways we turn the fuller the other way around, as inFig. 2846, in which it is supposed that one side of the work is to be kept flat, hence no bottom fuller is employed. The action of a fuller may be increased in the required direction by leaning in the direction in which we desire to drive the iron; thus, suppose we require to spread the end of a rectangular bar from the full lines to the dotted ones inFig. 2847and the first fuller across the piece as ata,Fig. 2848, and then spread out the end by fullering, as inFig. 2849, inclining the fuller in the direction in which we desire to forge the iron.
Fig. 2850Fig. 2850.
Fig. 2850.
It is the roundness of the face of the fuller that serves to control the direction in which it will drive the iron, since the curve acts somewhat on the principle of a wedge. Suppose, for example, that the faces were flat, as inFig. 2850, and the iron would spread in both directions, the same as though the hammer were used direct, and if the work were intended to be kept parallel it would frequently require to be turned on edge to forge down the bulge that would form on the edge.
Fig. 2851Fig. 2851.
Fig. 2851.
Fullers are, however, also used as finishing tools for curves or corners, an example being given inFig. 2851, which represents a fuller applied to finish the round corner of a collar.
Fig. 2852Fig. 2852.
Fig. 2852.
Fig. 2853Fig. 2853.
Fig. 2853.
Fig. 2854Fig. 2854.
Fig. 2854.
For finishing plane surfaces the flatter shown inFig. 2852is employed,wrepresenting the work. For inside surfaces the flatter requires to be offset, as inFig. 2853, in whichlrepresents a link whose faceamay be flattened by the flatterf. There is a tendency in this case for the flatter to tip or cant; and to avoid this and regulate the flatter upon the work, a side foot is sometimes added, as atainFig. 2854.
Swages are shaped according to the kind of work they are to be used for.
Fig. 2855Fig. 2855.
Fig. 2855.
Fig. 2856Fig. 2856.
Fig. 2856.
Fig. 2855, for example, represents a top and bottom swage for rounding up iron. For general work the recesses or seats of such swages would be made considerably oval, as inFig. 2856, the work being revolved slightly after each blow. This capacitates one swage for different sizes of iron. When, however, a swage is to be used for one particular size only, its cavity may be made more nearly a true half circle and may envelop one half the diameter of the work, so that when the top and bottom swages meet, the work will be known to be of the required diameter without measuring it. If the seat were made a true half circle it would lock upon the work, preventing the smith from revolving it and making it difficult to remove the swage.
Fig. 2857Fig. 2857.
Fig. 2857.
If the conditions are such that a swage must be used to perform forging rather than finishing, its seat should beV-shaped and not curved. Suppose, for example, that a piece of iron, say, 6 inches in diameter, required a short section to be forged down to a diameter of 3 inches, then the swages should be formed as inFig. 2857, because otherwise the effects of the blow will act to a certain extent to force the iron out sideways, for reasons which will be explained presently.
Fig. 2858Fig. 2858.
Fig. 2858.
Fig. 2859Fig. 2859.
Fig. 2859.
Fig. 2860Fig. 2860.
Fig. 2860.
In some cases, for small work, the upper swage is guided by the lower one: thus, inFig. 2858is a swage for a cross piece, and the outside of its base is squared and fits easily within the upper part of the lower one shown inFig. 2859. For verysmall work, on which the hand hammer is sufficiently heavy to perform the swaging, a spring swage may be use: thus, inFig. 2860is a swage for pieces of3⁄8,5⁄16, and1⁄4inch in diameter, and having a square stem fitting into the square hole in the anvil.Fig. 2861represents a spring swage for a pin having a collar, and it may be observed that the recess to form the collar must be tapered narrowest at the bottom, so that the top swage will readily release itself by the force of the spring, and so that the work may easily be revolved in the lower one. A similar tool is shown inFig. 2862, designed for punching sheet metal cold, the diedbeing changeable for different sizes of punchesp.
Fig. 2861Fig. 2861.
Fig. 2861.
Fig. 2862Fig. 2862.
Fig. 2862.
Fig. 2863Fig. 2863.
Fig. 2863.
For large hand-made forgings the swage block, such as inFig. 2863, is employed,srepresenting a stand for the block, whose dimensions are larger than the block, so that the latter may be rested on its face in the stand when the holes are to be used.
Fig. 2864Fig. 2864.
Fig. 2864.
Fig. 2864represents a swage block mounted on bearers, so that it may be revolved to bring the necessary cavity uppermost.