Modern Machine-Shop Practice Part 200

[Ill.u.s.tration: Fig. 3046.]

The hammer lever or helve is adjustable for height by means of the screw G and hand-wheel H, which raise or lower the bearings in which the helve journals are carried. This is necessary, because as the helve moves in the arc of a circle the faces of the upper and lower die, or of the hammer and the anvil, as the case may be, can only come fair at one particular point in the path of the hammer; hence in proportion as the blow terminates (by meeting the work surface) farther from the anvil face, the pivot or journal of the helve must be raised, so that the journal will be horizontally level (or as nearly so as possible) with the hammer face at the moment the blow is delivered.

By giving motion to the helve through the medium of cushions, a direct mechanical connection, and the destructive concussion that would accompany the same, is avoided; hence a high speed may be obtained without the frequent breakage that would otherwise ensue.

[Ill.u.s.tration: Fig. 3047.]

Fig. 3047 represents Corr's power hammer, the construction being as follows: The semi-elliptic springs, shown on top and bottom of the beam, serve to balance the stroke, so that the hammer may run from 350 to 450 strokes per minute, with safety to the machinery. The hammer is adapted to almost any form or kind of forging. Large dies may be inserted for various kinds of forming and welding, such as making plough-shares and other articles, which require that the operation be commenced with a light tap, and increased to a heavy blow at the will of the operator.

The whole structure is mounted on a substantial iron bed V, 18 inches deep, 22 inches wide and 5-1/2 feet long. Attached to this bed V are two circular arms L; between them is pivoted near their top, at K, an oscillating frame H, having a longitudinal opening, in which is attached two semi-elliptic springs G G, and two plates I, with trunnions projecting laterally through the oscillating frame at K; the hammer beam F is inserted between the springs G G, and the trunnion plates I, which are bolted firmly to beam F at I; the ends of the trunnions and outsides of the oscillating frame H rest evenly against the inside of the circular arms L; at K a shaft is pa.s.sed through the trunnions and beam F, and made rigid in them with its ends resting in boxing at K. Caps are provided to cover the ends of the boxing and shaft with set-screws projecting against the ends of the shaft, which secures it against end play.

By these mechanical arrangements the beam F and oscillator H are securely attached independently, vibrating on one common centre, allowing no side play of the hammer E, admitting F to the free action of the springs G G; in the lower end of the oscillating frame at N is a lateral opening 10 inches vertically by 6 inches longitudinally and 4 inches laterally, with f.l.a.n.g.es projecting longitudinally one inch into this opening from both sides. This makes the opening two inches smaller on the outside than the internal cavity; the rear and front internal walls are provided with steel plates, 4 by 10 inches, 1/4 thick, resting against the inner ends of four set-screws, not shown, provided to adjust these plates to or from the sliding box at N, to compensate for wear and prevent lost motion. These plates and f.l.a.n.g.es form slides and guides between which a loose box and eccentric is provided with shaft projecting laterally through boxing at N, which project upwards from an adjustable frame immediately under the oscillator H; this permanently locates the eccentric and shaft in the lateral opening in the oscillator H, at N. The adjustable frame mentioned rests on suitable bearings on the inside of the circular arms L, and is fastened down by four bolts pa.s.sing through suitable slots in the adjustable frame, entering the bearings on the arms L. This frame is adjusted back or forth by set-screws S S; this adjustment is for the purpose of giving a greater or less distance between the anvil and hammer at D, as may be desired for large or small work, long or short dies, &c.

The anvil B, weighing about 500 lbs., sits down in the bed at R and rests on circular bearings (between R and B), which radiate to the centre of the top of the anvil at D, and is held rigidly in any position longitudinally desired by set-screws Q Q, with their inner ends resting on shoulders on the sides of the anvil B, which projects down about ten inches; between this lower projection and the internal wall of the bed is sufficient s.p.a.ce to admit of any adjustment desired. This lateral adjustment is accomplished by set-screws R, pa.s.sing through the sides of the bed V, with their inner ends resting against the anvil which holds it rigid at any lateral adjustment. By this arrangement the anvil is accommodated to all and any cla.s.s of work or shape of dies.

The anvil is constructed in two parts. Four inches of the top C may be taken off, leaving a suitable place to insert large dies for various purposes, such as dies for welding plough-shares and dies for forging journals on large shafts. A counter-shaft, provided with suitable pulleys, is attached on the rear end of the bed; this shaft is kept constantly in speed and power by the vertical belt in the direction indicated by the arrow; the other end of the shaft is provided with a f.l.a.n.g.ed pulley, corresponding to a f.l.a.n.g.ed pulley M, on the eccentric shaft; around these pulleys is placed a loose belt, as shown; in contact with this is a press pulley T, adjustably attached by two arms to the projecting end of the treadle P at O. If the foot be placed on the treadle at U and it be pressed down, the break on the opposite side breaks contact with the balance wheel (not shown); the press pulley will at the same time tighten the loose belt on the f.l.a.n.g.ed pulleys. This gives motion to the pulley M, in the direction indicated by the arrow.

Its motion is increased by a heavier pressure until it attains the same speed as the other f.l.a.n.g.ed pulley; this would be the full speed, which may be diminished to any speed desired by lessening the pressure on the loose belt. By this means motion and power is given to the eccentric, which carries back and forth the lower end of the oscillating frame H; this gives vertical motion to the springs G G, and this imparts corresponding motion to the beam F. These springs accomplish a threefold object:

1st. They carry the hammer E up and down.

2nd. They cushion the hammer at the returning points and give off that power which was stored in them while cushioning.

3rd. By the power exerted in the machinery they follow up and impart still greater force to the blow.

It is found by this arrangement of eccentric loose box and oscillator that when the machinery is moved in the direction indicated by the arrow, that the downward stroke is one-sixth quicker than the up stroke; this is a natural result, for the down stroke is performed while the eccentric is revolving above the centre of its shaft and nearest the fulcrum of the operator H. With the present arrangement the downward stroke is performed with 5/12 of the revolution and the up stroke is performed with 7/12; the difference is 2/12, which equals one-sixth. The up stroke is performed while the eccentric is revolving below the centre of its shaft and in that part farthest from the fulcrum of the oscillator H, so if the machinery were reversed the quick stroke would be up and the slow stroke would be down.

[Ill.u.s.tration: Fig. 3048.]

In Fig. 3048 is shown a Kingsley's trip hammer. The main bed or foundation plate A carries the bed plate or frame B, at one end of which are the pillar blocks C, which afford journal bearing to the casting carrying the hammer shaft E, being fastened thereto by the clamp D.

These journals are the centre of motion of the hammer helve E.

At the other end of the bed plate B, are the pillar blocks F, affording journal bearing to the cam and fly-wheel shaft, _a"_ is the tripping cam, which is provided with two toes or cam arms, which meet the tripping piece _b"_, and this gives the hammer two strokes in a revolution of the fly-wheel shaft or cam shaft G. The stroke of the hammer may be altered by means of the set-screws _c"_, which move the pillar blocks F, so that the cam toes _a"_ have contact with the tripping piece _b"_ through more or less of the revolution of _a"_; the pillar blocks F being retained in their adjusted position by means of the set-screws shown below them in the bed piece B.

By the following means provision is made whereby the face of the hammer may be set out of parallel with that of the anvil block or lower die _d'_.

[Ill.u.s.tration: Fig. 3049.]

Fig. 3049 is a sectional view through the pillar blocks C, and casting and clamp D. The pillar blocks C C are carried in a semicircular frame _a'_, hence by uns.c.r.e.w.i.n.g the bolts _b'_ and s.c.r.e.w.i.n.g up the pillar block on the other side, the journals are thrown out of parallel, and the plane of motion of the hammershaft is altered so that the face of the upper die does not meet that of the anvil die fair to an amount which may be varied at will by operating the screws _b'_. The object of this is to enable the forging taper (as in sword blades) with common dies, and thus to save the making of special dies for each degree of taper required.

Similar provision is made in the anvil block which is easier to set, providing the degree of taper is within the limit of its range, of movement, otherwise the hammer also may be set.

Fig. 3050 represents a drop hammer, and Fig. 3051 is a sectional view of the lifting mechanism.

This machine consists of a base or anvil, a hammer which moves up and down between two uprights, and a lifting device, which is secured to the top of the uprights.

A board secured to the hammer pa.s.ses up between two friction rolls, which revolve in opposite directions. When the two rolls are moved towards each other, the friction on the board causes the hammer to rise; and when again separated the hammer will fall. The _back_ roll is keyed to a shaft, on each end of which is a driving-pulley; and thus by the use of two pulleys on the same shaft, equal wear comes on the bearings in which it revolves. The _front_ roll turns freely on its shaft, and is driven by the back roll being geared to it. To secure to the gears both strength and durability, they are made with wide faces, are geared at both ends, and the teeth are of peculiar shape.

The bearings to the shaft, on which the front roll revolves freely, are eccentric to the roll, and a partial revolution of the shaft moves the _front_ towards the _back_ roll, pinching the board. To an arm which is secured to the front shaft is fastened the upright rod, the _upward_ movement of which _opens_ the rolls, and whose downward movement closes the same; the weight of the rod being sufficient to cause the hammer to rise. This arrangement, simple and yet substantial, dispenses with the two eccentric-armed bushings, and the spreading of the upright rod at the top to reach both bushings, which caused so much trouble in the old way. In place of the dog which is usually used to hold up the hammer, (which is limited in adjustment to holes located at fixed distances in one of the uprights, necessitating not only the removal of the dog to another hole, and connecting and disconnecting the same to the treadle, but also the most accurate adjustment of the collar on the upright rod to the dog holding the hammer), we use a pair of clamps, located on the lifter, under the rolls. These clamps, holding the hammer centrally, prevent the side blow against the upright, the inevitable result of the contact of hammer and dog, when the former is only held on one side, as it must be, by the use of the dog. The opening of the clamps by the foot-treadle allows the hammer to fall; and the clamps are so made that the hammer will ascend freely, whether the foot is on the treadle or not, and if the foot is off the treadle, will hold up the hammer at any point where it may be arrested in its upward movement. It will be readily seen that the only adjustment required is that of the collar on the upright rod, to any height of blow desired.

[Ill.u.s.tration: Fig. 3050.]

This machine has two treadles, one connected to the clamps, and the other to a lever which operates the upright rod.

[Ill.u.s.tration: Fig. 3051.]

To obtain repeated blows with one motion of the foot, place the foot upon the treadle connected to the clamps. If variable blows are wanted, place the foot upon the _other_ treadle, and the hammer will follow the motion of the foot. This extra treadle is a late improvement, and is not shown in the cut. The operation required to obtain automatically any number of blows of the same height is described as follows:--

[Ill.u.s.tration: Fig. 3052.]

Pressure upon the treadle opens the clamps and allows the hammer to fall; just before the dies come together, the trip at the bottom which holds up the upright rod is released, and allows the rod to drop; this closes the rolls, causing the hammer to ascend. The hammer continues to rise until it strikes the collar on the upright rod, and, lifting the rod, opens the rolls, removing the pressure upon the board, and allows the trip at the bottom to go under to hold the rod up, and the hammer remains suspended, provided the foot is off the treadle. So long as pressure is kept on the treadle, the blows of the hammer will be continuous; but upon removal of the pressure, the hammer will a.s.sume its original position.

[Ill.u.s.tration: Fig. 3053.]

[Ill.u.s.tration: Fig. 3054.]

[Ill.u.s.tration: Fig. 3055.]

To procure variable blows, the operation is as follows:--

Pressure upon the treadle connected to the lever which operates the upright rod communicates itself to the treadle that opens the clamps, and the hammer falls; a locking device (not shown in cut) keeps this treadle down, and on completion of the variable blows wanted, removal of the foot from the treadle disconnects the locking device, and the hammer goes up to its original position, and is there held by the clamps.

When the work is such that the operator requires an a.s.sistant, variable blows may be obtained by the use of the hand lever by this a.s.sistant.

A gentle pressure upon the treadle will allow the hammer to go down slowly, but it will stop and remain suspended at any point as soon as the pressure is removed. The hammer can also be arrested at any point on its way up, by bringing into action the hand lever, so that the next blow can be given from a state of rest at a less height than the collar is set for. The clamps in holding up the hammer keep the board from touching either roll, and prevent the same from being worn uneven when not in use.

The back roll is made adjustable to different thicknesses of lifting board, as are also the clamps.

[Ill.u.s.tration: Fig. 3056.]

Figures from 3052 to 3056 represent a steam hammer. The head A is set at an angle in the frame. The anvil or die C is oblong, as is also the anvil die D. The object of this arrangement is to enable the workman, after drawing out his work across the short way of the die, to turn it and finish it lengthwise without being inconvenienced by the frame. By this means skew and [T]-shaped dies can be dispensed with, and the full service of the ram utilised. The latter is moved between the guides E E, and held in place by the steel plate F, bolted through the frame B. The valve G is a plain cylinder of cast iron, enlarged at each end to work in the cylindrical seats H H, in which the ports I I are placed. Steam is admitted through the valve J, and circulates round the valve G, between the seats. The exhaust chamber K is below the cylinder, which therefore drains condensed steam into it at each stroke through the lower steam port. The exhaust above the piston pa.s.ses down through the interior of the valve, as shown by the arrow on the drawing. The valve stem L is connected with the valves in the exhaust chamber. No stuffing box is therefore required, there being only atmospheric pressure on each side of it. This combination enables the valve to be so perfectly balanced that it will drop by its own weight while under steam.

[Ill.u.s.tration: Fig. 3057.]

[Ill.u.s.tration: Fig. 3058.]

The automatic motion is obtained by an inclined plane M upon the ram A, which actuates the rocker N, the outer arm of which is connected by a link to the valve stem, and thus gives motion to the valve. The valve is caused to rise in the up-stroke by means of the rocker N and its connections, through the inclined plane. The steam is thus admitted to the top, which drives down the piston, while the valve and its connections follow by gravity, thus reducing considerably the friction and wear upon the valves. In very quick work the fall of the valves may be accelerated by the aid of a spring; or it may be r.e.t.a.r.ded in heavy work by friction springs, so as to obtain a heavier blow by a fuller admission of steam. For general work, however, the arrangement shown is perfectly effective, and as the rocker N is hung upon the adjustment lever P, any required variation can be obtained by the movement of the lever. Single blows can be struck with any degree of force, or a rapid succession of constant or variable strokes may be given.

The anvil O rests upon a separate foundation, in order to reduce the effect of concussion upon the frame. The drawing ill.u.s.trates the arrangement. The bed is long, extending beyond the hammer on each side so as to give plenty of area, and the ends are left open for convenient access in case the anvil should settle and require re-adjustment.

Other forms of hammers having the same general principles of construction are as follows:--

Fig. 3057 represents a double frame hammer, the weight of the hammer being supplemented by steam pressure. The spiral springs shown beneath the cylinder are to prevent the hammer from striking the cylinder and causing breakage from careless handling by the operator. The valve gear is arranged for operation either automatically or by hand.

Fig. 3058 represents a double frame steam drop hammer for stamping work out in formers or dies. The frames are bolted to the anvil base and the ram for the top die is guided by vertical slides on the inner face of the frame. Shoes are provided, whereby the wear of the ram and of the slides may be taken up, and the upper die kept properly matched with the lower one.

[Ill.u.s.tration: Fig. 3059.]

[Ill.u.s.tration: Fig. 3060.]