Fig. 2600Fig. 2600.
Fig. 2600.
An external side elevation of this hanger is shown inFig. 2600, it being obvious that the hanger is designed for bolting to timbers, or framing overhead.
Fig. 2601Fig. 2601.
Fig. 2601.
Fig. 2601represents a hanger of this class. In this the lower part carrying the bottom bearing is held to the upper by two bolts, as shown, the object being to enable the same to be placed in position on a line of shafting without disturbing the pulleys or the couplings. The lower section with the bottom bearing is removed and again put on after the hanger is set over the shaft.
Fig. 2602Fig. 2602.
Fig. 2602.
Fig. 2602represents an open-sided ball-and-socket hanger in which the plungers can be retired, the bearings removed, and the hanger erected on an existing line of shafting without removing the pulleys or couplings, or disturbing the line of shafting.
Fig. 2603Fig. 2603.
Fig. 2603.
When the face of the framing to which the hangers are to be bolted stands vertical, the hangers are formed as inFig. 2603, in which the ball-and-socket or swivelling feature is maintained as before.
Fig. 2604Fig. 2604.
Fig. 2604.
Fig. 2604represents a wall hanger, which is open in frontsimilar to the hanger shown inFig. 2602, and for the same purpose.
The section of shafting receiving power from the engine or prime mover is usually supported in bearings or pillow blocks. Pillow blocks are also used for vertical shafts, and in cases where the foundation or framing is not liable to lose correct horizontal adjustment.
Fig. 2605Fig. 2605.
Fig. 2605.
Fig. 2605represents a pillow block, in which the ball-and-socket principle shown inFig. 2602is embodied. The bearings have each a ball section fitting into spherical recesses or cups provided in the body of the block, and in the cap, so that the bearings are capable of swivelling as already described with reference to the hangerFig. 2599.
Fig. 2606Fig. 2606.
Fig. 2606.
Fig. 2607Fig. 2607.
Fig. 2607.
A sectional view of a pillow block having this adjustable feature is shown inFig. 2606. To provide increased seating bearing, and also means of side adjustment to pillow blocks, they are sometimes bolted to base plates as inFig. 2607, room being left in the bolt holes to permit of their being moved and adjusted upon the plate. The adjustment may be made by means of wedges, as ata,binFig. 2607. These base plates are usually employed when the pillow block is to be held against a wall.
Fig. 2608Fig. 2608.
Fig. 2608.
An inverted pillow block of similar construction, but designed for the head line (as the length receiving power from the engine or motor is termed) of the shafting, is shown inFig. 2608, but an improved form of the same has plungers so as to effect a vertical adjustment of the bearings.
Fig. 2609Fig. 2609.
Fig. 2609.
When a pillow block requires to be enveloped by a wall it is provided with a wall box as shown inFig. 2609, and within this box is set the pillow block as shown, space being sometimes left to adjust the pillow block laterally within the box by means of a wedge as shown.
Fig. 2610Fig. 2610.
Fig. 2610.
In cases where the shafting requires to stand off from a wall to allow room for the pulleys, brackets or knees, such as shown inFig. 2610, are employed.
Couplings for Line or Driving Shafts.—The couplings for connecting the ends of line shafts should accomplish the followingobjects:—
1. To hold the two shaft ends axially true one with the other.
2. To have an equal grip along the entire length of shaft enveloped by the coupling.
3. To have a fastening or locking device of such a nature thatit will not be liable to work loose from the torsional strains due to the flexure of the shaft, which is caused by the belts springing or straining the axial line of shafting out of the straight line.
4. To be capable of easy application and removal, so as to permit the erection or disconnection of the lengths of shafting with as little disarrangement of the hangers and bearings as possible, and to be light, run true, and be balanced.
To these requirements, however, may be added that, since it is well-nigh impracticable to obtain lengths of lathe-turned shafting of exactly equal diameter, couplings for such shafting require to fill the following further requirements:
5. The piece or pieces gripping the shaft ends must be capable of concentric and parallel closure along the entire area, enveloping the end of each shaft, and must do this at each end independently of the other, and the piece or pieces exerting the closing or compressing pressure must grip the closing piece or pieces, enveloping the shafting over the entire area.
Fig. 2611Fig. 2611.
Fig. 2611.
Fig. 2612Fig. 2612.
Fig. 2612.
Fig. 2613Fig. 2613.
Fig. 2613.
If, for example, a sleeve be split at four equidistant parts of its circumference, and from each end nearly to the middle of its length, as inFig. 2611, any pressure that may be applied to its circumference to cause it to grip the shaft it envelops will cause it to grip the shaft with greater force at one part than at another, according to the diameter of the shaft and the location of the external pressure. Thus, if the pressure be applied equally along the lengtha b, the weaker endbwill close most readily, while atathe support afforded by the unsplit section offers a resistance to closure at the endsaof the split, hence the shaft, even though a working fit to the sleeve bore, will be gripped with least force at the enda. If the shaft were simply a close fit, as, say, just movable by hand on the sleeve bore, the form of the coupling bore would, when compressed upon the shaft, be as shown inFig. 2612, the bend on the necksa,b,c,d, being magnified for clearness of illustration. If the compressing piece covered the compressed sleeve for a lesser distance, the grip would be more uniform, because there would be a greater length of the sleeve to afford the curvesa,b,c,d, as shown inFig. 2613. The grip may be more equalised by boring the sleeve of slightly smaller diameter than the shaft.
Fig. 2614Fig. 2614.
Fig. 2614.
Fig. 2614represents a sleeve carrying out this principle. It is composed of two halves, as shown, bored slightly smaller than the shaft diameter, and is to be compressed on the shaft, which, acting as a wedge, would spring open the sides of the bore until the crown of the bore bedded against the shaft. This, in the case of parallel shaft ends of equal diameter, would hold them with great force axially true, and with equal force and bearing, thus meeting all the requirements. If, however, the end of one shaft were of larger diameter than the end of the other (as has hitherto been supposed to be the case), the end accomplished by boring the sleeve of smaller diameter than the shaft is, that the end of the sleeve is afforded the extra elasticity due to the transverse spring of the sleeve, which permits the edges of each half of the sleeve to bear along a greater length of the shaft end than would otherwise be the case; but the bearing is in this case mainly at and near the edges of the split.
It will be perceived, then, that under this principle of construction, when applied to shaft ends of varying diameters, the metal is left to spring and conform itself to the shape of the parts to be connected, and that there is nothing outside of the condition of relative diameter of shaft to sleeve bore to determine what the direction of the spring or closure of sleeve shall be; but, on the other hand, the principle possesses excellence in that the sleeve being cylindrical and its closure taking place equally at similar points of contact the shafts will be held axially true, one with the other; or in other words, the movements of the metal while sleeve closure is progressing are equally radial to the axis of the sleeve, and there is no element tending to throw the shaft axis out of line one with the other.
If a sleeve have a single split, the manner in which it will grip a shaft smaller than the sleeve’s bore depends upon the manner in which the compression is effected.
Fig. 2615Fig. 2615.
Fig. 2615.
Fig. 2616Fig. 2616.
Fig. 2616.
InFig. 2615, for example, is a ring supposed to be compressed by a pressure applied ataand atb, causing the ring to assumethe form shown by the dotted lines. The centre of the ring bore would therefore be moved fromctod. Now, suppose that the end of one section of shafting were to fit the sleeve bore, then compressing the sleeve upon it would not practically move the centre of the bore; but if the shaft at the other end of the sleeve were smaller than the sleeve bore, the compression of the sleeve to grip the shaft would move the centre of the bore, and, therefore, of the shaft towardsd, hence the axial lines of the shafts would not be held true one with the other. To accomplish this latter object, the compression must be equal all round the sleeve, or it may be applied at the pointseandf,Fig. 2616, although it is better to have the compression area embrace all the circumferential area possible of the sleeve, and to have the movement that effects the compression simultaneous and equal at all points on the circumference of the ring or sleeve, because if these movements are independent, more movement or compression may be given at one point than at another, and this alters the centre of the bore; thus, if more pressure were exerted atethan atf, in figure, the centre of the bore would be thrown towardsf, orvice versâ. If the pressure be concentric, the single split ring or sleeve grips the shaft all round its circumference; hence it is only necessary in this case to maintain the circumference of the sleeve in line to insure that the shaft ends be held axially true one with the other; and if the pressure on the ring be applied equally from end to end its closure will also be parallel and equal, and the shaft will be held with equal force along that part of its length enveloped by the coupling. It is obvious, however, that the piece or sleeve gripping the end of one shaft must be independent of that gripping the other, so as to avoid the evils shown inFig. 2612, while at the same time the casing or guide enveloping the two independent rings or sleeves must guide and hold them axially true, one with the other.
Fig. 2617Fig. 2617.
Fig. 2617.
InFig. 2617is shown an excellent form ofplate coupling, in which most of the requirements are obtained.aandbare the ends of the two lengths of shafting to be connected,canddare the two halves of the coupling driven or forced on the ends of the shafting, and further secured by keys. The end of one half fits into a recess provided on the other half, so as to act as a guide to keep the shafts axially true one with the other, and also to keep the two halves true one with the other, while drilling the holes to receive the boltsewhich bolt the coupling together. The objections to this form are, that it is costly to make, inasmuch as truth cannot be assured unless each half coupling is fitted and keyed to the shaft, and turned on the radial or joint faces afterwards. Furthermore, if the coupling were taken off in order to get a solid pulley on the shaft, the coupling is apt to be out of true when put together again, and, therefore, to spring the shaft out of true. Also, that the bearing, support, or hanger must be open-sided to admit the shaft, and that each coupling, being fitted and turned to its place, would be apt to run out of true if removed and applied to another shaft, whether the same be of equal diameter or not; but if each half coupling be provided with a feather instead of the usual key, the coupling may be readily removed and will remain true when put on again.
Fig. 2618Fig. 2618.
Fig. 2618.
Fig. 2618represents a plate coupling, in which one end of the shaft passes into the bore of the half coupling on the other length of shaft, which serves to keep the shafts in line one with the other.
Fig. 2619Fig. 2619.
Fig. 2619.
Fig. 2619represents a single cone coupling composed of an external sleeve having a conical bore and a split internal sleeve bored to receive the shaft, and turned on its outer diameter to the same cone as the bore of the outer or encasing sleeve. The bolts pass through the inner sleeve, the bolt head meeting the radial face of the inner sleeve while the nut meets the radial face of the outer sleeve, so that screwing up the nut forces the inner sleeve into the outer and closes the bore of the former upon the shaft. This coupling is open to the objection that it cannot grip the ends of the shafts equally unless both shafts be of exactly equal diameter, and the bearing on the smaller shaft will be mainly at the outer end only, as explained inFig. 2611. As a result, the transverse strains on the shaft will cause the couplings to come loose in time.
Fig. 2620Fig. 2620.
Fig. 2620.
Fig. 2620represents a coupling composed of a cylindrical sleeve split longitudinally on one side, as atd; the boltscpass through the split. Diametrally opposite is another split passing partly through as atb. A key is employed at right angles to the two splits as shown. Here, again, the pressure on a shaft that is smaller than the other, of the two shafts coupled, will be mainly at one end, but separation of the shaft ends is provided against by means of two cylindrical pins on the ends of the key fitting into corresponding holes drilled in the shaft, as shown in the side elevation in the figure.
Fig. 2621Fig. 2621.
Fig. 2621.
Fig. 2622Fig. 2622.
Fig. 2622.
InFig. 2621is shown a coupling whose parts are shown inFig. 2622. It consists of a cylindrical ring turned true on the outside and bored conical from each end to the middle of its length, as shown. The split cones are bored to receive the shaft and contain a keyway to receive a spline provided in the shaft ends, and are turned on the external diameter to fit the conical borings in the sleeve. Three square bolts pass through the split cones, which, being square, are prevented from rotating while their nuts are being screwed up.
To put the coupling together one split cone is passed over the end of one shaft and the other over that of the other. The sleeve is then put between the ends of the shaft, the position of the shaft adjusted for length and the split cones pushed up into the sleeve; the bolts are then passed through and screwed up. The forcing of the split cones into the conical borings of the sleeve causes the former (from being split) to close upon the shaft ends and grip them equally tight, notwithstanding any slight difference in the diameters of the shaft, there being left between the ends of the split cones sufficient space to allow them to pass through the conical borings sufficiently to close upon the respective ends of the shafts; the pressure being parallel and equal on each shaft end, because when the cone has gripped the largest shaft the whole movement due to screwing up the nuts is transferred to the cone enveloping the smaller shaft, and by reason of the cones fitting, the closure of the holes in the cones is parallel, giving an even grip along the shaft end and an equal amount of grip to each shaft end.
To remove the coupling the bolts are removed, and the sleeve being moved endways the cones open from their spring and relieve the grip upon the shaft.
It is evident that in their passage through the sleeve casing the cones will move with their axial lines true with the axial line of the casing; and it is equally evident that the taper on the cone accurately fitting the taper in the sleeve bore, the closure of the cone bores must be equal; while at the same time the pressure on the two cones upon the respective shaft ends must be equal, because it is the friction of the cone bores upon the shaft ends which equally resists the motion of both, while the pressure applied to the respective cones is derived from the same bolts, and hence is equal and simultaneous in its action.
To loosen this coupling for removal the bolts must be stacked back and a few blows on the exterior of the outer shell with a billet of wood may loosen the coupling; but if not, a wedge or a cold chisel may be driven in the splits of the cones to loosen them, but such wedge or chisel should not have contact with the sides of the split, either near the bore or near the perimeter, for fear of raising a burr.
Fig. 2623Fig. 2623.
Fig. 2623.
Fig. 2624Fig. 2624.
Fig. 2624.
InFig. 2623is shown a patent internal clamp coupling. It is formed of a cylindrical piece containing a pair of separate clamps, and between these clamps and the outer casing are four screws, two to each clamp; these screws are tapered so as to close the clamp when screwed up and release it when screwed outwards. The holes to receive the shaft ends are bored somewhat smaller than the shafts they are to fit, and the clamps opened to permit the easy insertion of the shaft ends by means of wedgesadriven in the splitbof each clamp, as shown inFig. 2624.
The lower edge of the wedges should be slightly above the bore of the clamp to prevent the formation of a burr or projection of metal when the wedge is driven in. When placed upon the shaft ends and in proper position the wedges are removed and the clamp bore will have contact at and near the edges of the longitudinal split and on the opposite sides of the bore where the keyway is shown, but the pressure of the tape screws will spring the clamps on the side of the longitudinal splits, and increase the bearing area at those points.
The main features of this device are that though the bore be made a driving fit to the shaft, it can, by the employment of the wedges, be put on the shaft with the same ease as if it were an easy fit, while the clamps being separated by a transverse groove may open and close upon the shaft independently of each other, so as to conform separately to any variation in the diameters of the two shaft ends it couples. But it may be noted that since the circumference of each shaft end has a bearing along the line of the coupling bore diametrally opposite to the longitudinal splits, the shafts will not be held quite axially true one with the other unless there be as much difference in the diameters of the separate clamp bores as there is in the diameters of the shaft ends; because to hold two shafts of different diameters axially true one with the other the longitudinal planes of the two circumferences must not at any part of the circumferences form a straight line, as would be the case at that part of the coupling bore at and near the keyway.
It is to be noted, however, that this coupling is formed of one solid piece, and that the strain on the tightening bolts or screws is one of compression only, which tends to hold them firmly and prevent their coming loose.
If the workmanship of a plate coupling, such as inFig. 2617, be accurately and well done, and the proportions of the same are of correct design, so that the strain placed on the same in keying and coupling it up does not distort it, the coupling and the shaft will run true, because the strain due to the key pressure will not be (if properly driven) sufficient to throw the coupling out of true. But the degree of accuracy in workmanship necessary to attain this end is greater than can be given to the work and compete in the market with work less accurately made, because the difference in the quality of the workmanship will not be discernible save to the most expert and experienced mechanic, and not to him even unless the pieces be taken apart for examination. If the bore of the coupling be true and smooth and of proper fit to the shaft thekey pressure, if the key fits on its top and bottom, will not, as stated, be sufficient to throw the coupling out of true. It is true, however, that such pressure is exerted on one half the boreof the couplingonly, being the half bore opposite to the key. On the other diametral side of the coupling the strain due to the key is exerted on the top face of the key.
If, therefore, the key seats in the shaft and in the couplings are in line or parallel, and both therefore in the same plane, the strain due to the key may throw the coupling out of true to the amount that the key pressure may relieve the bore of the coupling (on the half circumference of the shaft of which the key is the centre) from contact or pressure with the shaft. As a result, the coupling may run to that extent out of true, but the shaft would run true nevertheless so long as the nature of the surfaces on the shaft and on the coupling bore was such that the key pressure caused no more compression or closer contact in the case of one half coupling than in the case of the other.
It is obvious that a plate coupling will require at least as much force to remove it from the shaft as it took to put it on, and sometimes, from rusting of the keys, &c., it requires more. If it be removed by blows it becomes damaged, and damage is likely to be also caused to the shaft, while the surfaces having to slide in contact under the pressure of the fit the surfaces abrade and compress, and the fit becomes impaired. But in couplings such as shown inFig. 2621, the gripping pieces are relieved of pressure on the shaft by the removal of the bolts, and the removal of the coupling becomes comparatively easy.
The interchangeability of plate couplings is further destroyed by the fact already stated, that turned shafting is not, as a rule, of accurate gauge diameter, and the least variation in the pressure or fit of the coupling to its shaft is apt to cause a want of truth when the key bears on its top and bottom. The fit of the coupling to its shaft may be, it is true, relied on to do the main part of the driving duty, and the key fitting on the sides only may be a secondary consideration, but in proportion as the fit is relied on to drive, that fit must be tighter, and the difficulty of application and removal is increased.
Another and important disadvantage of the plate coupling in any form is that it necessitates the use of hangers open on one side to admit the shaft, because the couplings must be fitted upon the shaft before the same is erected and should not be removed after being fitted, as would be necessary to slide the end of the shaft through the bearing.
When plate couplings are constructed as inFig. 2617, the removal of a section involves either the driving back of one-half of the coupling so that the other half will clear it, or else the moving endwise of the whole line to effect the same object.
With a plate coupling the half coupling on one end of the shaft must be removed when it is required to put an additional pulley on the shaft, unless, indeed, a split pulley be used, whereas with a clamp coupling, such as shown inFig. 2621, the half coupling at each end may be slacked and moved back, one end of the shaft released, a solid pulley placed on the shaft and the coupling replaced, when it will run as true as before, and the pulley may be adjusted to its required position on the length of shafting.
It is to be remarked, however, that a well-made plate coupling, such as inFig. 2618, makes a good and reliable permanent job that will not come loose under any ordinary or proper conditions.
Fig. 2625Fig. 2625.
Fig. 2625.
Fig. 2626Fig. 2626.
Fig. 2626.
InFig. 2625is shown a patent self-adjusting compression clamp, which is peculiarly adapted to connect shafting that is of proper gauge diameter. It consists of a sleeveamade in two halves, each embracing nearly one-half of the shaft circumference and being bored parallel and slightly smaller than the diameter of the shaft ends. Over this sleeve passes at each end a ringd e, bored conical and fitting a similar cone on the external diameter of the sleeve. On each end of the sleeve is the nutf g, which by forcing the cone ring up the taper of the sleeve causes the two halves of the latter to close upon and grip the shaft. For shafts less than two inches in diameter there are provided in the sleeve two pins to enter holes in the shaft ends in place of keys, but for sizes above that keys are employed. All parts of this coupling being cylindrical it is balanced. The separate parts of this coupling are shown inFig. 2626.
Fig. 2627Fig. 2627.
Fig. 2627.
Fig. 2628Fig. 2628.
Fig. 2628.
Fig. 2629Fig. 2629.
Fig. 2629.
Fig. 2630Fig. 2630.
Fig. 2630.
InFigs. 2627to2630are shown a side elevation and sectional view of another form of shaft coupling.ais the sleeve,b bnuts on the ends of the sleeve, andc ccones fitting taper holes in the sleeve. These cones are split, as shown inFig. 2629, to permit them to close upon the shaft ends. The shaft ends themselves are matched with a half dovetail, as inFig. 2630, which dispenses with the employment of a key.
In coupling shafts of different diameters it is usual to reduce the diameter of the end of the larger to that of the smaller shaft, and to employ a size of coupling suitable for the smaller shaft; but in this case it is necessary that the coupling be placed on the same side of the hanger or bearing as the smaller shaft, otherwise it is obvious that the strength of the larger would, between its bearings, be reduced to that of the smaller shaft.
The couplings for line shafting are usually placed as near to the bearings or hangers as will leave room for the removal of the couplings by sliding them along the shaft.
The couplings on the length of shaft receiving power from the motor are placed outside the bearings, hence on the succeeding lengths there will be one coupling between each pair of bearings, the couplings being in each case as close to each bearing as will allow the coupling to be moved towards the bearing sufficiently topermit the length to be removed without disconnecting the adjacent length from its bearings.
Fig. 2631Fig. 2631.
Fig. 2631.
Fig. 2631represents a very superior form of coupling for line shafts. The ends of the line shaft are reduced to half diameters as shown, and lapped with a horizontal joint at an angle to the axis of the shaft as denoted by the dotted line, which prevents end motion; the ends of the shaft and their abutting surfaces are dovetailed, as shownaandb, and, therefore, perform driving duty. A sleeve envelops the whole joint and is secured by a key. This coupling accomplishes all that can be desired, but requires very accurate workmanship, and on this account is expensive to make.
Fig. 2632Fig. 2632.
Fig. 2632.
Fig. 2632represents a form of coupling suitable for light shafting. It consists of two halvesa a, of cast iron, which are drawn together by the boltc; the centre of the coupling is recessed to enable the coupling to take a better hold on the shaft, which is prevented turning by the pinsd d. This coupling has no projections to catch clothes or belts, and is quickly applied or removed.
Fig. 2633Fig. 2633.
Fig. 2633.
Fig. 2633[38]represents a form of coupling for heavy duty, the transmitting capacity only being limited by the strength of the projectionsa. If the shafts are not axially in line, this form of coupling accommodates the error, since the projectionsamay slide in their recesses, while if the axial lines of the shafts should vary from flexure of the bearings or foundations, as in steamships, clearance between the ends ofaand the bottom of the recesses may be allowed, as shown atb.
[38]From Rankine’s “Machinery and Millwork.”
[38]From Rankine’s “Machinery and Millwork.”
Fig. 2634Fig. 2634.
Fig. 2634.
InFig. 2634is shown a coupling (commonly known as the universal joint coupling) which will transmit motion either in a straight line, or at any angle up to 45°.
It is formed of two double eyes, such asa, connected to a yoke or crosspiecebas shown atc. It is mainly used for connecting shafts or arms carrying tools of some kind, such as rubbers for polishing stone, tools for boring, or other similar purposes in which the tool requires to be rotated at varying angles with the driving shaft.
Pulleys for the transmission of power by belt may be divided into two principal classes, the solid and the split pulley. The former is either cast in one entire piece, or the hub and arms are in one casting, and the rim a wrought-iron band riveted on. The latter is cast in two halves so that they may be the more readily placed upon or removed from the shaft.
On account of the shrinkage strains in large pulley castings rendering them liable to break, it is usual to cast pulleys of more than about 6 feet in halves or parts which are bolted together to form the full pulley. On account of these same shrinkage strains it was formerly considered necessary to cast even small pulleys with curved arms, so that the strains might be accommodated or expended in bending or straightening the curves of the respective arms. It is found, however, that by properly proportioning the amount of metal in the hub, arms, and rim of the pulley, straight arm pulleys may be cast to be as strong as those with curved arms, and being lighter they are preferable, as causing less friction on the shafting journals, and, therefore, being easier to drive.
It is obvious that a pulley for a double belt requires to be stronger than is necessary for a single one, but the difference is not sufficiently great to give any practical advantage by making separate pulleys for single and double belts; hence all pulleys are made strong enough for double belts.
Pulleys are weaker in proportion to their duty as the speed at which they rotate is increased, because the centrifugal force generated by the rotation acts in a direction to burst the pulley asunder, so that if the speed of rotation be continuously increased a point will ultimately be reached at which the centrifugal force generated will be sufficient to cause the wheel to burst asunder. But the speed at which pulleys are usually run is so far within the limits of the pulley’s strength, that the element of centrifugal force is of no practical importance except in the case of very large pulleys, and even then may be disregarded provided that the pulleys be made in a sufficient number of pieces to avoid undue shrinkage strains in the castings, but if solid pulleys are rotated at high velocities the internal strains due to unequal cooling in the mould has been known to cause the wheels to fly asunder when under high speeds.
Fig. 2635represents a solid pulley, the tapered arms meeting the rim in a slightly rounded corner or fillet, and the rim being thickened at and towards its centre. When the width of rim is excessive in proportion to one set of arms a double set is employed as inFig. 2636.
In some forms of pulley the arms and hub are cast in one piece and the rim is formed of a band of wrought iron riveted to the arms. By this means shrinkage strains are eliminated and a strong and light pulley is obtained.
Fig. 2637represents a split pulley in which the two halves are bolted together after being placed on the shaft.
Variable motion may be transmitted by means of an oval driving pulley, as inFig. 2638, it being obvious that the belt velocity will vary according to the position of the major axis of the oval. Arrangements of this kind, however, are rarely met with in practice.
InFig. 2639is shown an expanding pulley largely employed on the drying cylinders of paper machinery, and in other similar situations where frequent small changes of revolution speed is required. Each arm of the wheel carries a segment of the rim, and is moved radially to increase or diminish the rim diameter by sliding in slots provided in the hub of the wheel, a radial screw operated by bevel gears receiving motion from the hand wheel and gear-wheels shown in the engraving. It is obvious that in this case the driving belt must be made long enough to embrace the pulley when expanded to its maximum diameter, the slack of the belt due to reduction of diameter being taken up by a belt tightener.
Fig. 2640Fig. 2640.
Fig. 2640.
Fig. 2641Fig. 2641.
Fig. 2641.
Fig. 2642Fig. 2642.
Fig. 2642.
InFig. 2640is shown a wooden pulley having a continuous web or disk instead of arms. It is built up of segments, the web being secured to the shaft as follows. InFigs. 2641and2642a,bare clamping plates, andca split sleeve fitting easily to the shaft and passing througha,b, while receiving the nuteon the other side. The web of the pulley fits on the shoulderj, and the flangebfits on the shoulderk, so as to keep these parts true or concentric toa. The bore ofais taper to fit the taper ofc; hence the nutein drawingcthrougha, causescto close upon and grip the shaft, while the flangesa,bgrip the pulley and hold it toc.