Part 7

The reader, if he has perused this chapter to the present point, is doubtless now asking himself: "How shall I word my order when I want a first-class driving rope?" The safest road to follow is to write to some manufacturer or firm whom you know to be reliable, and ask for so many feet of their transmission rope, giving the name, if you are certain on that point, and, of course, being sure to mention the diameter. In case you do not know the name of his rope, word your order as simply and briefly as possible; for example: "One thousand feet 1-1/2 inches diameter first quality manila transmission rope," and if the concern to which you write is a reputable one, you will receive a four-strand rope, made from Zebu manila hemp, put together with proper twist and lay for the service required.

XVI

A BELTING AND PULLEY CHART[12]

RULE 1. _Pulley Speed._--When the diameter of both pulleys and the speed of one is given, to find the speed of the other: Place the points of spacing dividers upon the two given diameters in inches upon the scale (Fig. 97); then raise the dividers, keeping the space obtained, and place one point on the given speed and the other _above_ it for speed of _S_, or _below_ it for speed of _L_ (_S_ and _L_ meaning smaller and larger pulley, respectively). This point will fall upon the required speed.

[12] Contributed to Power by A. G. Holman, M. E.

Example: If the two pulley diameters are 10 and 25 inches and speed of larger pulley is 120 revolutions per minute, what is speed of small pulley?

Place the points of dividers on 10 and 25 on scale _A_, then lift the dividers and place one point on 120 and the other above it upon the scale; the other point now rests on 300 as the speed of _S_. If the speed of _S_ had been given, one point would have been placed at 300 and the other _below_ it, falling upon 120, the required speed of _L_.

Note.--In applying this rule, if the speed comes beyond the range of scale _A_, the result may be read by carrying the space to the revolution scale on scale _B_, and proceeding in the same way.

Example: Diameter of pulleys 12 and 36 inches and speed of _L_ 500, what is speed of _S_? Place points of dividers on 12 and 36. Now, if dividers are raised and one point placed on 500 and the other above it on scale _A_, it will come beyond the top of the scale. Hence go to scale _B_, placing lower point on revolution scale at 500 and the other point above, which will fall upon 1500, the answer.

RULE 2. _Pulley Diameters._--When the speed of both pulleys and the diameter of one is given, to find diameter of the other: Place points of dividers on the two speeds on scale _A_ or revolution scale _B_. Then place one point of dividers on given diameter and the other above it to find diameter of _L_, or below it for diameter of _S_. The figure thus indicated is the required diameter.

Example: Speeds 180 and 450 and diameter of smaller pulley 20. What must be diameter of _L_?

Place points of dividers on 180 and 450 on scale _A_. Then place one point on 20 (the given diameter). The other point falls at 50, the required diameter of _L_.

If the point falls between two graduations in any problem, the result can be closely judged by the relative position.

The other and more labor-saving use for this chart is its application to belting problems. It is generally conceded that there is no subject of more general interest in practical mechanics and none on which there is a greater difference of opinion than the proper allowance to be made in the selection of belt sizes for given requirements. The general formula for the horse-power transmitted by belting is

_HP_ = _WS_/_C_ in which _HP_ = horse-power,

_W_ = width of belt in inches, _S_ = speed of belt in feet per minute, and _C_ = constant.

The proper values of this constant, or the feet per minute that each inch of width must run to transmit a horse-power, under certain conditions, is the point in question.

On the right-hand side of line _A_ on the chart is a series of lines representing different values for this constant. The lower one, marked 4, represents 400 feet belt speed per minute, the next above is for 500, and so on. Against some of these values are suggestions as to belts often recommended in connection with these constants. For instance, 2 to 6 _S_ suggests the constant 1100 to be used for 2- to 6-inch single leather belt, 1000 for 6-1/2- to 10-inch single, 600 for 2- to 6-inch double, etc.

These suggestions practically agree with the advice of the Geo. V. Cresson Company's catalog and the deductions of Kent's Handbook.

More power may be transmitted than these suggestions will allow, by increasing the tension, but this is accompanied by the disadvantage of requiring extra attention and undue pressure upon bearings.

The use of the chart for horse-power and width of belting is explained by the following rules:

RULE 3. _Horse-power of Belting._--To find the horse-power that can be transmitted when diameter and speed of pulley and width of belt are given: Place one point of dividers on scale _A_ at the width of belt in inches and the other point at the bottom of the line (at 1). Next add this space to the hight representing diameter of pulley by placing lower point of dividers upon the given diameter and allowing the other point to rest upon the scale above. Then holding the upper point stationary, open or close dividers until the other point falls upon the proper constant on the scale at right-hand side of line _A_. Now transfer this space last obtained to the scale _B_ by raising the dividers, carrying them square across to _B_ and placing the point that was on the constant upon the given speed on the revolution scale. Note the location of the other point of dividers upon the horse-power scale, which indicates the horse-power that can be transmitted under the given conditions.

Example: What horse-power can be transmitted by an 8-inch double belt running on a 40-inch pulley at 500 feet per minute? Place one point of dividers on line _A_ at 8 (width of belt) and the other point at bottom of line. Next raise dividers and place lower point on 40 (diameter of pulley) and let the other point fall above upon the scale. Then close dividers until lower point comes to the constant for 6-1/2 to 10 double. Carry this space to scale _B_ with lower point on 500 on revolution scale. Under point now falls upon 84 on horse-power scale, which is the required horse-power.

RULE 4. _Width of Belting._--To find the necessary width of belting when size and speed of pulley and the horse-power are given: Place one point of dividers on scale _B_ upon the horse-power and the other point upon the revolutions. Next transfer this space to scale _A_ by raising the dividers, carrying them square across and placing the point that was on revolutions upon the constant. Then holding the other point stationary, raise the point that was on the constant and open dividers until this point falls upon the given diameter. Now lift the dividers and carry the lower point down to bottom of line (the point 1). The upper point will now indicate the required width of belt.

Note.--If, in finding width of belt, there is doubt about the proper constant to take, a medium value, say 6, may be assumed and a hasty "cut and try" will show in what classification the required belt will come.

Example: What width of belt for 100 horse-power with 40-inch pulley at 500 revolutions?

Place point of dividers on scale _B_ upon 100 on horse-power scale and the other upon 500 on the revolution scale. Then carry the space to scale _A_ with lower point on constant 5. Then resting dividers upon upper point open them until lower point is at 40 (diameter). Finally, raise dividers and place lower point at bottom of line. Upper point is now at 9-1/2, indicating the nearest even width 10 as the answer.

A little practice will make one familiar with these rules, and it will be seen that in the belting rules the four motions perform two multiplications and a division.

XVII

SPLICING ROPE

THE splicing of a transmission rope is an important matter; the points on which the success of the splice, and incidentally the drive, depend being the length of the splice, which in turn depends upon the diameter of the rope and which is given in the table (Fig. 97a); the diameter of the splice, which should be the same as the diameter of the rope; the securing of the ends of the strands of the splice, which must be so fastened that they will not wear or whip out or cause the overlying strands to wear unduly; and the workmanship of the splice, which should be the best it is possible to secure. When splicing an old and a new piece of rope, the new piece should be thoroughly stretched, for, at best, it is an exceedingly difficult task on account of the stretch and difference in diameter of the rope.

========+========+===========+=========+========= | | | | | | | | | | | | Diameter| Square |Approximate|Breaking | Maximum of Rope| of |Weight per |Strength,|Allowable in |Diameter| Foot, | Pounds |Tension, Inches | | Pounds | | Pounds --------+--------+-----------+---------+--------- 1/2 | .25 | .12 | 1750 | 50 5/8 | .2906 | .16 | 2730 | 80 3/4 | .5625 | .20 | 3950 | 112 7/8 | .7656 | .26 | 5400 | 153 1 | 1. | .34 | 7000 | 200 1-1/8 | 1.2656 | .43 | 8900 | 253 1-1/4 | 1.5625 | .63 | 10,900 | 312 1-1/2 | 2.25 | .77 | 15,700 | 450 1-3/4 | 3.0625 | 1.04 | 21,400 | 612 2 | 4. | 1.36 | 28,000 | 800 2-1/4 | 5.0625 | 1.73 | 35,400 | 1012 2-1/2 | 6.25 | 2.13 | 43,700 | 1250 ========+========+===========+=========+========= +====================+========+========== |LENGTH OF SPLICE | | | IN FEET |Smallest| Maximum +------+------+------+Diameter| Number | 3- | 4- | 6- | of | of |Strand|Strand|Strand|Sheaves |Revolutions | | | | in |per Minute | | | | Inches | +------+------+------+--------+----------- | 6 | | | 20 | 1060 | 6 | | | 24 | 970 | 6 | 8 | | 27 | 760 | 6 | 8 | | 32 | 650 | 7 | 10 | 14 | 36 | 570 | 7 | 10 | 16 | 40 | 510 | 7 | 10 | 16 | 45 | 460 | 8 | 12 | 18 | 54 | 380 | 8 | 12 | 18 | 63 | 330 | 9 | 14 | 20 | 72 | 290 | 9 | 14 | 20 | 81 | 255 | 10 | 16 | 22 | 90 | 230 +======+======+======+========+==========

The illustrations and instructions for making standard rope splices are taken, by the courtesy of the American Manufacturing Company, from their "Blue Book of Rope Transmission."

There are many different splices now in use, but the one that experience has proved best is what is known as the English transmission splice. In describing this we take for our example a four-strand rope, 1-3/4 inches in diameter, as spliced on sheaves in the multiple system. The rope is first placed around sheaves, and, with a tackle, stretched and hauled taut; the ends should pass each other from six to seven feet, the passing point being marked with twine on each rope. The rope is then slipped from the sheaves and allowed to rest on shafts, to give sufficient slack for making the splice.

Unlay the strands in pairs as far back as the twines _M_, _M′_, crotch the four pairs of strands thus opened (Fig. 98), cores having been drawn out together on the upper side. Then, having removed marking twine _M_, unlay the two strands 6 and 8, still in pairs, back a distance of two feet, to _A_; the strands 1 and 3, also in pairs, being carefully laid in their place. Next unlay the strands 5 and 7 in pairs, to _A′_, replacing them as before with 2 and 4. The rope is now as shown in Fig. 99. The pair of strands 6 and 8 are now separated, and 8 unlaid four feet back to _B_, a distance of six feet from center, strand 6 being left at _A_. The pair of strands 1 and 3 having been separated, 3 is left at _A_, as companion for 6, strand 1 being carefully laid in place of strand 8 until they meet at point _B_. The two pairs of strands 2-4 and 5-7 are now separated and laid in the same manner, every care being taken, while thus putting the rope together, that original twist and lay of strand is maintained. The protruding cores are now cut off so that the ends, when pushed back in rope, butt together.

The rope now appears as shown in Fig. 100, and after the eight strands have been cut to convenient working lengths (about two feet), the companion strands are ready to be fastened together and "tucked"; this operation is described for strands 2 and 7, the method being identical for the other three pairs. Unlay 2 and 7 for about twelve to fourteen inches, divide each strand in half by removing its cover yarns (see Fig. 101), whip with twine the ends of interior yarns 2′ and 7′; then, leaving cover 2, relay 2′ until near 7 and 7′, here join with simple knot 2′ and 7′, Fig. 102. Divide cover yarns 7, and pass 2′ through them, continuing on through the rope _under_ the two adjacent strands, avoiding the core, thus locking 2′, Fig. 103. _In no event pass 2′ over these or any other strands._ Half-strand 7′ must now be taken care of; at the right of the knot made with 2′ and 7′, 2′ is slightly raised with a marlin spike, and 7′ passed or tucked around it two or three times, these two half-strands forming in this way a whole strand. Half-strand 7′ is tucked until cover 2 is reached, whose yarns are divided and 7′ passed through them and drawn under the two adjacent strands, forming again the lock. The strand ends at both locks are now cut off, leaving about two inches, so that the yarns may draw slightly without unlocking. This completes the joining of one pair of strands, Fig. 104. The three remaining pairs of strands are joined in the same manner.

After the rope has been in service a few days, the projecting ends at locks wear away, and if tucks have been carefully made, and the original twist of yarns preserved, the diameter of the rope will not be increased, nor can the splice be located when the rope is in motion.

XVIII

WIRE ROPE TRANSMISSION[13]

WIRE ropes are extensively and successfully used in the horizontal and inclined transmission of great power of unlimited amount, the advantages over hemp rope belting being: driving at very long distances, comparatively small loss through slipping and the possibility of driving in the open air.

[13] Contributed to Power by C. Boysen, M. E.

Vertical transmission of power, on account of the weight of the rope, is excluded.

Formerly the material used in the manufacture of the wires was best charcoal iron, but now almost exclusively tough crucible-steel wires are used, as steel wire ropes are stronger, do not stretch as much, and last longer than iron ropes.

The wire ropes consist of six strands of from six to twenty wires each, and the strands to form the rope are woven in the opposite direction to the wires in the strand. In the center of each strand and in the center of the rope a cotton core is placed. These cores are of the greatest importance, for by reducing the friction of the wires against each other, they serve to increase the lifetime of the rope, which, according to the strain on the rope and the size of the smallest pulley, is from one to three years.

To prevent rusting, the wire ropes receive a coat of boiled linseed oil, or a hot mixture consisting of three parts of drip oil and one part of resin is applied. This latter mixture at the same time improves the adhesion between the rope and the lining placed in the bottom of the pulleys, thus reducing the loss caused by slipping of the rope. Wire ropes used for the transmission of power should never be galvanized.

The ends of the rope are spliced together, from 10 to 20 feet being necessary for a good splice; great care should be taken that the splice is made by experienced men, and that the rope is made long enough. A rope stretches constantly from the time when placed on the pulleys, the more so when placed on the pulleys tightly. Therefore it has to be made long enough to transmit power without undue tension, and for this reason the distance between the two pulleys has to be long enough and the working strain per square inch of section low enough to allow sufficient deflection in the rope. As a guidance to the amount of deflection necessary, be it said that even in a short drive the deflection of the rope, when not running, should not be less than 2 feet; and for a distance of 400 feet between pulley centers, the deflection of the rope when running should be 5 feet in the driving rope and 10 feet in the driven rope.

Either the top or the bottom rope may be the driving one, the former being preferable; but the ropes should never be crossed.

Power can be transmitted to a distance of 6000 feet and more without great loss; but as two pulleys should on no account be more than 500 feet apart, intermediate stations are placed along the road.

Precautions should be taken against the possibility of the rope swaying. This may be caused either by the influence of the wind, by a bad splice, by the rope wearing too much, by the pulleys not being balanced well or by the pulleys not being in the same plane. It is of importance that the pulleys be exactly in line, and careful attention should be given to the construction and placing of the bearings. Although the bearings are not strained excessively, the steps are usually made long and movable. The connection between the shaft and the pulley is best made by means of tangential keys.

Some engineers, when two ropes are found necessary for the transmission of the power in question, use pulleys containing two grooves each, and make the same kind of pulleys for the intermediate stations of long-distance driving; whereas others advise a separate pulley for each rope, both being connected with each other by a clutch.

The diameter of the smallest pulley has to be large enough in comparison with the diameter of the rope or the thickness of the single wires used to easily overcome the stiffness in the rope. The larger the pulleys, the longer the rope will last.

The rim of the pulley is V-shaped, and the bottom of the groove is dovetailed to receive a lining of wood, rubber or leather, on which the rope rests. The lining increases the friction and reduces the loss caused by slipping of the rope. Leather is the best lining and lasts about three years. Either old belt leather, well saturated with oil, or new leather, boiled in fish oil, can be taken. It is cut in pieces of the same size as the dovetailed part of the groove, and then placed on and pressed together in the latter. The pressing is done by means of a piece of wood. The last remaining small space in the groove is filled with soft rubber. If the lining has to consist of rubber, this is softened and hammered into the groove. For wood lining, thin blocks of the required size are placed into the groove through a hole provided in the bottom of the rim. This slot is closed by a plate and fastened to the bottom of the rim by means of screws after all blocks have been inserted. The lining has to be turned absolutely true, for which reason the filling is done while the pulley is still in the lathe.

Pulleys up to 3 feet in diameter are built with cast-iron arms; whereas larger pulleys have wrought-iron arms made of round iron, cast in the rim and boss. Pulleys under 8 feet 6 inches in diameter are made in one piece, if for other reasons it is not necessary to have them in halves.

Guide pulleys are used for long ropes, especially if there is not sufficient hight above the ground. The guide pulleys are of the same construction as the main pulleys, and for the driving rope they are also made of the same diameter. The diameter of the guide pulleys for the driven rope can be made from 20 to 25 per cent. smaller.

The breaking strength of unannealed wires per square inch of section and according to thickness and quality is: For iron wires from 70,000 to 110,000 pounds, and for steel wires from 110,000 to 130,000 pounds. For thinner wires a higher value is taken than for thick ones.

The diameter of the wires used for making ropes for transmitting power is from 0.02 to 0.1 inch, and on account of the stiffness, no wires above the latter size should be used. A rope consisting of a greater number of thin wires, besides being stronger is more pliable and lasts longer than a rope of the same area consisting of a less number of thicker wires.

INDEX

A

American Mfg. Co., 136

B

Bauer, Chas. A., 54

Beams to carry stringers, finding, 42

Bearings, locating, 3

Belt, building, 94

Belt creep, 106 dressing, 91, 100 comparative test, 102 running off, 101 shifter device upon column, 9 sizes, 132

Belt, leather, selection, 89 marking spliced part, 12 new, putting on, 19, 20 slack, 100 splicing on the pulleys, 81 throwing on, 12 tight, 100 wire-lacing, 12

Belt-clamps, use, 19

Belting and pulley chart, 129

Belting, cleaning, 97 horse-power transmitted, 132, 133 use and abuse, 99 width, 132

Belts, cleaning, 88 keeping clean, 94 leather, care and management, 89 splicing, 72 main line, 5 taking-up, 11

Bird, Prof. Wm. W., 106, 107

Blue Book of Rope Transmission, 136

Board for use in lining countershaft, 35, 36

Boiled linseed oil in wire rope, 144

Bolt and nut for moving pulleys, 62 for hanger, size, 40

Bolt, preventing turning, 11, 21

Boysen, C., M. E., 143

Brands, effect on leather, 90

Breaking strain on shaft, 28 strength of unannealed wires, 146

Bunsen burner, use in moving pulley, 62

Bushing, split, 2

C

Center drive for heavily loaded shaft, 7 stock, 90

Chart, belting and pulley, 129

Cleaning belting, 97

Clutch, rim-friction, arrangement, 5

Clutches, coupling, 31 tightening while shafting is in motion, 7

Collars, split wood, 3

Compass saw, use in locating beams, 45

Contact, extra, securing, 17

Continuous-wrap system of rope drive, 112 -wrap system with direct-acting tightener, 113

Core, cotton, of wire rope, 143 rope, 124

Countershaft, lining, 32, 33, 35, 36, 37

Couplings, flanged bolt, 3

Cresson Co., Geo. V., catalog, 132

D

Deflection of rope, 144

Diameter of splice, 136 rope, 124, 135 of wires for transmission rope, 147

Diameters, pulley, 131

Differential action on ropes, 109, 112, 116

Disks for plumb-bob, 49

Distance of power transmission by wire rope, 144

Dixon, Walter E., M. E. 72,, 89

Dressing, waterproof, for belts, 91

Driving an overhead floor, 6

E

Elbow bolts, 46

Emery cloth for packing, 23, 24

End drive compared with center drive, 7

English transmission splice, 136

Evans, William, 102

F

Farmer, T., Jr., 102

Fastening strands of splice, 136

Fiber, rope, 124

Filled belts, 91

Flanged bolt couplings, 3

G

Gasoline blow torch, use in getting oil out of belt, 88

Gluing a joint, 85

Greene, F. S., 122

Guide pulleys, 146

H

Hanger adjustment, securing, 40, 41 bearing, repairing worn end, 14 positions, marks, 3

Hanger, removing to take off pulley, 63 sliding out of wall box, 1

Hangers, crosswise of shaft, 42

Hangers not allowing vertical adjustment, 3

Heads of hemp, 127