The Iron Age 1916-03-02: Vol 97 Iss 9

11eV ransmitted? insmit it? Under tension should the elt be placed on the pul- To within a com- paratively recent time was the only one de to answer in laying belt drive. Some f-thumb, such as “A belt 1 in. wide, was then applied to necessary. Such a 6, ere anything but could and probably the work required oi power, bearings BELT DRIVE will at all times LISHED 1855 New York, March 2, 1916 VOL. 97: No. 9 Transmitting Power by Leather Belting’ A Series of Tables, Embodying Latest Investigations, Show- ing Tensions and Horsepowers at Which Belts Will Give Best Service and Cost the Least for Maintenance and Repairs laying out of a belt drive, assuming the sizes to have been determined, involves the answer to each of three separate questions drive is to be designed to give the most satis- results. These are: What horsepower is to What size of belt should be used of these ques- attempt was 1100 ft. per will transmit 1 how wide a belt gave results & ry. While the was at the ex- belt itself. ST SATISFACTORY most satisfactory ve is that one the necessary of power, and at time cost the or repairs and ance, and cause possible loss ine shutdowns for the purpose of making fact that airs in working hours. any belt can be made of power up to _ the th of the belt by increasing the tension under Any increase in al tension beyond a certain figure, which is placed on the pulleys. ich 1916, by Robert Thurston reserved All rights of i) ROBERT THURSTON KENT varies with the conditions, will result in a decrea life of the belt, more frequent breakdowns, greater pressure on the bearings, with a consequent creased expenditure of power, all contributing higher cost for belt maintenance. Therefore, wh the first cost of a properly designed drive may be somewhat higher than that of one laid out ac cording to some rule-of thumb, the extra expendi ture will be justified by the greater service that will be obtained from the more expensive belt and the actually lower total cost, taken over a term of years, which includes not only the first cost, but also the charges for re pairs and maintenance and the loss caused by belt breakdowns in work ing hours FACTORS TO BE CONSIDERED IN BELT DRIVES The earlier rule for belting practice consid ered but two factors speed of belt and horse- power to be transmitted As a matter of fact the theory of transmitting power by belting show that there are other fac tors to be cons dered and the work of such inve gators as Taylor, Barth and Nagle has indicated ie ee er that there are still other practical considerations rious Formu for Horse ; : : . tted by Belting that cannot be neglected if the drive is to be satisfactory. To have a belt drive that is to trans mit a predetermined horsepower and show the low- est total cost, the following considerations must be taken into account when the drive is laid out: The conditions of use of the belt, whether it drives a machine and is readily aceessible, or whether it drives a countershaft or some other inaccessible pulley; the velocity at which the belt will travel; the arc of the pulley with which the belt is in con- ‘7 eee MPS = 528 THE IRON tact; the tension per square inch of cross-section AGE March 2. ) De Ar nta under which it is first placed on the pulleys; the tension per square inch of cross-section to which 50 0.82 | 191.5 | 136.75 108.1 || 0.55 | 145.75 | 91 10 1.72 189.0 133.5 118.5 1.20 144.25 89 0 2.82 187.5 132.0 124.4 1.87 | 143.25 8S . ‘ ba . aia ala 7 a ci A ; _ 100 83 187.0 131.25 126.5 2.53 | 143.0 R7 oy gaat ae Ee a eee 200 4.64 186.5 | 130.70 127.7 | 3.05 | 143.0 | 87.7 SQUARE NCH OF CROSS SECTIK A ARE 100 5.42 186.5 130.75 127.8 3 54 143.0 87.7 600 6.18 186.75 | 131.0 | 127.4 || 4.00] 143.5 | 883 1800 6.91 | 187.0 | 131.25 126.6 || 4.43 | 143.5 | 88.50 000 7.59 | 187.25 | 131.75 125.3 || 4.82 | 144.0 | 89.0 Ne 500 9 1 188.5 133.25 120.2 5.60 145.5 90.5 = O00 10.27 1900.5 135.25 113.0 6.02 147.0 92 5 : 50) 11.02 19 137.75 103.9 6.03 | 149.25 95. 2a = : = I 11.2¢ 195 ¢ 4() 02 0 5.53 151.5 QR 2 22. : 504 10.94 198 144 80.3 | 4.46 | 154.25 | 100 =< = = = vin 147 65.8 | 2.75 | 156.75 | 104.1 - 0) R 3 0 19 8 0 33 159.75 | 106 SN) 1) De ntac I LS 7 1? 12n J { 7 180.25 | 124.0 149 ) 9.4 9 0.7 138.5 101 0.51 | 146.75 92.5 53 | 179.0 | 121.75 | 155.3 8 103 .2 50 1.68 0 137.5 | 111 1.12) 145.5 90.5 LOO 4.78 | 178.5 | 120.0 Lot é St.0 103.9 750 2.65 | 189 134.25 | 116.7 1.76 | 144.5 89.5 120 77 178.0 120.5 158.6 3.78 137 81.0. 104.0 1000 61 189.5 133.0 119.1 9.38 | 144.25 R9 25 140 72 | 178.0 120.5 158.4 4.38 | 138.0. $1.25 103.3 00 1.3 188.5 132.75 | 120.2 2.87 144.0 89.25 1600 Of | 278.20 | E210 | 156.6 || 4.06 | 138.25) 8 102.0 100 5 188.5 | 132.75 120.5 || 3.34 144.0 89.25 LSO0 8 53 178.5 121 156 9.47 138 s 100 1600 . gi 188 133.25 120.2 3.77 144.5 RO 5 2000 9.36 | 179.25 | 122.0 | 154.5 || 5.95 | 139.0 s 18.1 1800 6.53 | 188.5 | 133.25 | 119.8 || 4.18 | 144.75 | 89.75 2500 11.20 181.0 124.5 147.8 6.55 tl 29 S vv 2000 7.17 189.0 133.5 118.2 4.55 | 145.0 90.25 3000 12.62 183.5 27.5 ISS 7.40 14 ) 55.0 a 4 2500 8 60 190 25 135.0 113.5 || 5.29 146.25 91.75 500 13.51 186.75 131.0 127.4 7.39 146.25 | ) ) WN) 9.71 191.75 137.0 106.8 5.69 148.0 93.5 4000 13.80 190.0 135.0 103.8 6.77 149 19.25 , 5500 10.41 193.75 | 139.25 98.2 5.70 149.75 95.75 1500 13.40 193.75 | 139.2 98.2 >. 4 152 9S 40) 1000 10.65 196.25 142.0 87.9 5.23 | 152.0 99.0 5000 | 12.20 | 197.75 | 143.75} 80.5 || 3.37, 156.0 | 103.0 2 4500 || 10.35 | 199.0 | 145.0 76.0 || 4.22 | 154.5 | 101.0 9000 10.15 201.75 148.2 og 0.40 159.5 106.25 - 5000 9.43 01.7 148.0 62.2 2 60 157.0 104.95 5500 7 R&S 4 51 95 417.1 0.32 159 75 106 25 170 Degrees Arc ( 250 | 1.0 185.25 | 129.5 132.6 0.67 | 142.0 86.25 SS 100 2.18 | 182.0 125.75 | 143.9 1.45 | 140.0 84.0 } 750 3.40 180.75 | 123.5 149.7 2. 2¢ 139.0 82.5 Og 1000 4 61 180.0 123.0 152.9 } 04 139.0 82 95 0.3 1200 5.57 179.5 122.5 153.3 }. 65 138.75 82 95 100 ¢ 1400 6.49 179.5 122.5 153.0 4.2 139.0 82 50 99 1600 7.38 180.0 123.0 152.3 4.78 139.0 83.00 1800 & 24 180.25 123 .25 151.1 5.20 139.50 83.5 17.0 2000 9.05 180.75 123.75 149.4 ».75 140.0 84 95 4 2500 10.83 182.5 126.0 143.0 6.66 142.0 Nf 87.9 3000 || 12.21 | 184.75 | 129.0 | 134.3 || 7.16] 144.25] 8 8.7 3500 13.08 187.75 | 132.25 123.3 7.15 | 146.75 2.25 { 4000 13.37 191.0 136.0 110.3 6.56 149.75 ».49 4 4500 12.97 194.5 140.25 95.1 >. 29 152.75 9 R 8 5000 11.81 198.5 144.5 78.0 2 156.2 i | 5500 9 83 202.25 148.75 rf 0.39 159 106.2? 1) Degrees Ar ( 4 96 186.25 131.0 126.9 0. 64 143.0 N 84 sy 2 09 183.75 27.75 138 1.39 41.0 50 27 182.25 25.75 143.8 17 140.0 s 8 1000 4.43 | 181.75 | 125.0 146 92 | 140.0 § { 1200 5 26 181.25 124.5 147.3 51 139 i 1400 6.25 181.25 124.5 147.2 4.07 140 .{ 83.7 6. { 1600 7.11 | 181.25 | 125.0 | 146.6 | 4.60! 140.95 84.25 94.9 L800 7.94 181.75 125.25 145.5 5.09 140.5 84.75 3.4 2000 8.72 182.25 126.75 143.8 ». 54 141.0 85.25 1.4 2500 | 10.44 | 184.0 127.75 | 137.8 || 6.42 142.7 7.5 847 3000 11.77 186.0 130.5 129.5 6.90 144.7 ( 75.5 500 12.61 189.0 133.5 119.0 6.90 147.25 5 4000 12.89 192.0 137.0 106.4 6§ 150.25 ( 4500 12.52 195.25 141.0 41.8 5.11 153 .2 5000 11.40 199.0 145.0 7 4 15 156.5 5500 9.49 02.75 149.95 X } ig Rel Between Velocity of Belt and Horsep »D Arc of ( Tr itted, per Square Inch of Belt Cross-Section ve ; db Means ’' Barth’s Formula oo || see lames | te are ih} ae a7 the belt may be allowed to fall in service before it 750 3.12 a 0 | 128.0 co : 07 as is taken down and retightened. A variation in an) 1000 4.24 R395 127.0 0.0 RO ] 0 5 ; i Sa os 1200 5.13 | 183.0 | 126.5 141.2 7 | 140 one of these factors will affect the horse-power tha 4 5.99 183.0 126 41.2 0 141 . i: : : aa ie ss se. nf 1600 6.82 | 183.0 | 1270 1406 || 4.41 ai 1 the belt will transmit, and will also affect the life 000 7-62 | 183.5 a 2 | =e aa ae the belt and the total cost of it. 206 8.37 | 183.75 | 12 138.0 0 87 Ree ; : ae eae 2500 10.02 | 185.5 | 129.5 32 16 143.5 | [The tables which accompany this article aré 300 3 187.5 132.0 124.4 f 145.5 2.9 . oa ° . “ae ak 500 = “ 190.0 | 135.0 4 , 148 0 based on the latest investigations of belting pra 500 || 12:08 | 196:0 | 1420 | 88 on! 153 tice—those of Carl G. Barth—and show the horse 5 2.03 96 142.0 8 t ) . m fo 4 5000 || 10.96 | 199.75 | 145.75 | 72 02 15 1¢ power that will be transmitted under any given s* 5500 9.12 03.25 149.75 44 { ( 159.75 0 2 o4e . nae . “ lar of conditions, and also the initial tensions unde! aia . which the belts should be put up, and the minimum ( egZTees rc ot 1 ° . ° Pe in tensions to which they may be allowed to fall in 50 || 0.87 | 190.0 | 134.75 114.6 | 0.58 | 144.75] 90.0 | 7 service before retightening. The formulas upon 500 |) 1.90 | 187.0 | 131.5 5 tartare to 8 which they are based will be explained after exam- 750 | 98 185.75 , 130.0 31.0 7 2 86.7 85.8 ; . y ss 1000 4.04 | 185.0 | 129.0 133.4 67 | 142.0 | 8 88 _( ples in the use of the tables have been given. ; » { A. 28.5 34.6 21 1 f 88 re : - has roe 571 | ioe6.| iss 87 Ah gd 7 2 The are of contact of the belt on the pulley ha : ee = eee a ; > : ' : 4 - ho 1600 |} 6.51 | 185.0 | 120.0 134.2 | 4.21 | 142.25 | 8 86.9 a direct bearing on the horsepower that can 1800 7.27 185.0 129.25 133 4 64 142.5 2 85 z - 1 fi “st The 2000 7.99 | 185.5 | 129.5 | 131.9 || 5.08] 143.0 | 87.7 83.8 transmitted and should be determined first. 5 9 57 7.0 31.5 126.4 5.89 | 144.5 so 4 ol . ] oO 5000 | 10.81 | = 0 133 > | 188 || 6.34) 146 25 175 , arc on the smaller pulley is the one that should e oon il cael mee teas) oe perl aee | oe 'S considered, as the horsepower transmitted is limited 4000 || 11.85 | 194.0 | 139.25! 97.7 |] 5.82] 151.0 7.5 18.( . 7 : na a a Bho 4500 |{ 11.50 | 197.0. | 143.0 | 84.4 | 4.69 | 153.75 | 100 4.4 by it. If the smaller pulley is the driver, it limit 5000 |} 10.48 | 200.25 | 146.5 69.2 | 2.89 | 156.75 | 104.( 19.1 ; 3 can the 5500 || 8.73 | 203.75 | 150.25 | 52:4 | 0.35 | 139.75 | 10% : the amount of power that can be delivered to + belt, while if it is the driven it limits the amount ee | Sena ae 1916 138 03 195 19 50 OSS 875 ‘ 6 ] 179 1 l l ot ee ee oe C TABLE , OO m0) uv 50 > 00 0) + OO 50 00 50 00 50 00 yi) th 16.50 in TABLE THE IRON SECTIONAL ‘ CONTACT OF AGE OF ON “~~ s,LER PULLEY, DEGREES 529 168 Es ~ THE IRON TABLE IV.—VELOCITY OF ’ : t S38 4 if on 4 : ; t i } 4 4 4 44 47¢ ‘7 { ? ? . ; 86.4 = ) 4 ) 110 ‘ ) 19% ‘ 14 : I 18 4 19 } 8 l 84 f yey { re WO 524 } } 14 4 { 4 +4 455.1 74 } i at z . ’ : : £05 +4 +/ 64 s san ~ } $507 4 4 + {711 7 { i t 5025. ¢ 44 S64 power that the belt can deliver to it. The curves Fig. 3 show the influence of arc of contact upon horsepower transmitted. Table III indicates the are of contact of the belt on the smaller pulley for usual range of pulley sizes and line distances. Equally or more important than arc of contact is the velocity of the belt. With a given effective pull in the belt, up to the point that centrifugal ten- sion begins to exert an influence, the horsepower transmitted varies directly with the velocity. At a certain point the centrifugal tension begins to the center AGE March 2 BELTS, FEET PER MINUTE Q » 8 48 2 ‘ { { 731 3g ; 7 0 ) 4} t 2 ‘ +4 : 147 $ 147 47 } 1 497.4 ) 47.1 } 96.9 64 48 } "5 45 v4 t i] 139 { : at 10) 4 . “4 SY 44 $87 18 t 141 l Uy) { i 4 it ; 327.3 10.4 m 77.0 92.7 408 ; 458.2 476.5 523 .€ 44 i ' 12.¢ f 654.5 80.7 1.1 720 748.8 i 0 4 $16 \ S ) SS4.9 7 TT 5: f l } 81 10 { $ 1005 M 1089 1068 12.7 1157 ) 1781 1225 { 9 43. 1203 t 56. € UY 0 1361.4 ) { 1380 439.9 1497.4 { 07.9 | 1570.8 | 1633 } l 7 1769 t lio Ls 1M t s ISS4.9 iY 2042.1 t 2010 094.4 178 s l 213¢ 225 2314.4 4 235 9450.5 : 87 187.1 258 i 4 US .4 13 618.0 9722.8 t 827.4 2945 .2 3065 .2 8.0 )5 $1 72.5 | «3403.5 S 15 x 9 8 74 ) } $ 927 0 4084 : i } $054 $254.2 4424 t t 1395S $581.5 14.9 19 : + 5236 44 $4 : t t 654.8 0 4974 547 appreciably decrease the effective pull, and a still further increase of belt velocity will actually de- crease the horsepower transmitted. The rule-o! thumb formulas neglected the effect of centrifugal tension, and indicated that an indefinite increase 1n velocity increased indefinitely the horsepower trans- mitted. As a matter of fact, within practical work- ing tensions, the effect of centrifugal tension be- comes so great that at velocities in the neighbor- hood of 6800 ft. per minute the belt will fail t transmit any power whatever. The curves of Fig. 2 show the relation between horsepower transmitt« d : 1 2, 1916 THE IRON AGE 931 fABLE IV. (CONT.).—VELOCITY OF BELTS, FEET PER MINUTE IAMETER OF PULLEY, INCHE 98 9 0 4 4 42 44 : 7 s 4.2 19 { ‘ { s 3.2 0 t.2 t 7 4185.9 $39.8 4 4 ' 66.5 79 7 118 445.1 497 t 49.8 7€é i ‘ 12.5 439 $55 7 934 s 659.7 | 72 ‘ ¢ ¥ I 531.4 49 t +0 769 “4 t x 4 a { x 754 7 8 a7 " | ; ; 7 f 7 S4 { 989 . f { 709 ‘ ( 4 t ; a9 t ' Ss M 8 l t 7 s M } f 24.7 ‘ 6) 910) 1068 | 138 43 } ' 1157 1361.4 129.4 ‘ 10¢ ) s 124¢ 14 ’ 1138.8 l t 135 4 $ 157 i M ‘ s 1214.7 l t $24 s f 7 S4 ) i ; 129 i tl4 : ‘ ; 4 1365 ¢ 14 f t t ‘ 442.5 iv 7 6.0 18.4 S i4 ‘ { : 8 } t 5 932 ; 1.0 6 ' 4] { t $20.4 S : 55 1 t : ‘ ! ' t : t i { is i ‘ 4.4 0 { ‘ } 885.0 { s2.4 14 : 0 ) } i { s { ; $16.4 i 10 t ; 14 + , 4 14 ‘ } 3796.0 4 , i ; $ 4175 i $ 1 } ) | 4555 ‘7 1 d t ) 14 51 4 l 0 t 40 belt velocity, while those in Fig. 1 show the epower transmitted according to Barth’s for as, on which the tables are based, Nagle’s for- 1 and some of the more common rules-of-thumb. IV gives the belt velocity obtained by a ing number of revolutions per minute of the | range of pulley sizes. USE OF THE BELTING TABLES ing determined the arc of contact of the belt smaller pulley, and the velocity, the horse- r that will be transmitted can be read directly the proper section of Table I. In the third enth columns of the table will be found the per square inch of cross-section under which ne and countershaft belts respectively should on the pulleys, while the fourth and eighth show the tensions below which they should allowed to fall in service. The use of the presupposes that the belts will be subjected lar inspection and measurement of tension to ire that the belts in service do not fall below ninimums. tables are calculated for belts of 1 sq. in. ss-section, but the figures can be adapted to f any size by means of the constants in Table ch show the relative cross-sectional area of different widths and thicknesses. As the wer transmitted under a given set of condi- iries with the cross-sectional area, a simple cation of the figures given in Table I by per constant as given in Table II will give red result. The same statement applies to sion values. Multiplying the values given in | for the initial and minimum tensions will total tension under which the belt under ration should be put up, and also the total below which it should not be allowed to fall ce. following examples will make clear the use tables: he three steps of a lathe cone pulley have ers respectively of 14, 16 and 18 in. and a - - —-- - wr ~ “ ralirecch ry ee | I ‘ Ar Ey Mi ( ' uniform face of 5 in. The countershaft cone has the same diameters, and rotates at 110 r.p.m. The distance between the center lines of the machine spindle and the countershaft is 8 ft. What size of belt will be necessary to deliver 3 hp. at the machine cone, with the belt on the largest step of the machine cone, and what horsepower will be de livered by it when it is on the smallest step of the machine cone? The difference in diameter of the largest and smallest cone steps is 4 in. Referring to Table III, we find that for a center line distance of 8 ft., a 4-in difference in diameter will give an are of contact of the belt on the smaller pulley of 178 deg., which for all practical purposes we can regard as 180 deg. Table IV shows that a 14-in. pulley at 110 r.p.m. will give a belt velocity of 403.2 ft. per minute. Turning now to Table I, we find in the section headed “180 deg. arc of contact” that a belt of 1 sq. in. cross-sectional area will transmit 1.05 hp. at 250 ft. per minute, and 2.27 hp. at 500 ft. per minute. The power transmitted at speeds inter- mediate to those given in the tables increases very nearly in proportion to the increase in the speed. The difference in speed between 250 ft. and 403 ft. per minute is 153 ft. per minute, and between 250 ft. and 500 ft. per minute is 250 ft. per minute. The difference in horsepower transmitted at 250 ft. and 500 ft. per minute is 1.22 hp. Therefore at 403 ft. per minute the horsepower transmitted would be 153 1.05 + 1.22 > 1.05 + (1.22 X 0.612) 1.79 hp As it is desired to transmit 2 hp., the cross- sectional area of the belt will be 3-— 1.79 = 1.676 sq. in. The width of belt that should be used on a cone pulley of 5-in. face should not exceed 41% in., and we therefore look in Table II opposite 4% for the figure most nearly corresponding to 1.676. This we find to be 1.719, under *% in. Therefore, a belt 414 x % in. will be ample to transmit the required horsepower. It should be put on the pulleys under a total initial tension (see column 3, Table 1) of 1.719 X§ 183.75 — (183.75 180.25 x >) = 1.719 x 181.61 = 312 1b. approx. F By the same sort of calculation we find from column 4 of the table that the belt should be taken down and retightened when its total tension is 215 lb. To find the horsepower that the belt will trans- mit when it is on the smallest step of the machine cone, we ascertain from Table IV its velocity, which in this case will be that of an 18-in. pulley at 110 r.p.m., or 518.3 ft. per minute, which we can con- sider as 500 ft. The are of contact will be the same as before, and can again be taken as 180 deg. From Table I we see that the horsepower transmitted by a belt of 1 sq. in. cross-sectional area is 2.27, and multiplying this figure by the area of the belt in question, 1.719, we obtain as the horsepower trans- mitted 3.9. II. A 25-hp. motor is located in the roof trusses of a machine shop, driving the shafting for a group of machines. The motor has a speed of 1100 r.p.m., the motor pulley being 9-in. diameter and 9-in. face. The motor frequently is required to carry an overload of 10 per cent, or a total load of 27.5 hp. The center line distance between the motor and line shaft is 18 ft. The line shaft pulley is 30 in. diam- eter. The present belt is 8 in. wide and 7/16 in. thick. Is it heavy enough for the load, and if not, what size of belt should be used? At what tension should the belt be put up, and at what tension should it be retightened? As the belt is in an inaccessible position, the fig- ures in the countershaft section of Table I will apply. From Table III the are of contact is 172 deg. and the answer to our questions will therefore be found in the section of Table I headed “170 deg. are of contact.” From Table IV the velocity is ascertained to be 2591.3 ft. per minute. Inasmuch as we actually have a larger are of contact than 170 deg., we can assume the velocity to be slightly lower and read the horsepower directly from the table (column 6) as 6.66 opposite the velocity 2500 ft. per minute for a belt of 1 sq. in. of cross-sectional area. The total power to be transmitted is 27.5, and therefore a belt of 27.5 — 6.66 = 4.129 sq. in. cross-sectional area will be necessary. THE IRON AGE March 2, | } In Table II, under 7/16 in. thickness we fin, value 3.5 opposite 8 in. width, and therefore belt at present in use is too small, and if used require retightening at shorter intervals than «ye desirable, due to the necessity of running it uni oy higher initial tensions than are consistent with d practice. If we desire to use the same widi belt, which is quite as wide as should be used . pulley of 9 in. face, we must increase its thick: Table II shows that an 8 x %-in. belt will hav: area of 4 sq. in., and an 8 x 9/16-in. belt will have an area of 4.5 sq. in., and as the former will trans- mit without trouble 6.60 « 4 = 26.64 hp., it can be safely used without increasing the tensions given in the table to any degree. It might perhaps be ad- visable to retighten the belt at a slightly higher figure than that given in the table as the minimum tension. Assuming the 8 x \%-in. belt to be used. the tension at which it should be put on the pulleys (column 7, Table I) will be 4 142 = 568 Ib., and the tension at which it should be retightened (col- umn 8, Table 1) 4 * 85.5 = 342 Ib., or to be on the safe side, 350 lb. total tension. OBJECT OF THE TABLES AND FORMULAS The argument may be advanced that the values given in the tables call for heavier belts and lower tensions than are the usual practice. The answer to this is that that is precisely what they are intended to do. The object of the formulas and practice of Barth, which are based on the nine years of experi- ment by Taylor, is not to find the smallest belt which will transmit a given horsepower. It is rather to find the belt which under the specified con- ditions of service will not only transmit the desired power but will give the best service and in the long run cost the least for repairs and maintenance, and insure the longest life of belt. In doing this, the total cost of belting will be far less than if the short-sighted policy of light belts and high tensions is adopted. Furthermore, the adoption of the Barth practice will insure an almost absolute freedom from belt breakdowns, and the loss, due to stoppage of production, caused by a single belt breakdown may far exceed the difference in cost between the light belt and the heavier one that would have avoided the trouble. It is poor economy to attempt to save money by skimping the belting. THEORY OF BELTING PRACTICE As the theory on which the tables are based is elaborately explained by Mr. Barth in his paper entitled “The Transmission of Power by Leather Belting,” presented before the American Society of Mechanical Engineers in January, 1909, no at- tempt will be made here to discuss it except to present the formulas involved, together with the briefest possible explanation of them. The starting point of Mr. Barth’s theory is the discarding of the commonly held but erroneous 4s- sumption that the sum of the tensions in the two sides of a running belt is constant. In place of this he has proved the theorem that the sum of the square roots of the tensions in the two strands 0! the belt remains constant. From this assumption, he has by a process of mathematical reasoning de- rived the formulas given below, the correctness ol which has been amply substantiated in practice. Another common assumption proved erroneous |S that the coefficient of friction between the belt and pulley is constant at all velocities of the belt. An expression showing the relation of the coefficient 0! friction to the velocity of the belt has been derived, according to which the coefficient increases as the velocity arises. The periods at which belts run- 9 1 NM Sy 1916 at different speeds will require retightening e nearly constant if they are all made to do work at such initial tensions as under full will result in the same sum of the tension in eht side and one-half the tension in the slack t the two extremes of the initial tensions, efore and just after retightening. This con- will be expressed by the equation ti+%t=—A = a constant iniform period of use before retightening is hly desirable condition of shop operation. the formulas below the following notation is minimum initial tension, lb., to which belt can be allowed to fall in service. maximum initial tension, lb., to which belt is retightened. tension in tight strand of running belt. tension in slack strand of running belt. effective pull in the running belt, lb. = t, — t,,. The above values are all per sq. in. of cross-section. coefficient of friction between the belt and the pulley. of contact of belt on pulley, in radians 0.017453 are in deg. velocity of belt, ft. per min. basis of the Naperian system of logarithms 2.71828. 1 aconstant. For machine belts and other belts readily accessible A = 240; for countershaft belts or inaccessible belts A = 160. The effective pull of a belt is determined by the formula x are (e 04-1) (2A — 0.00001036V°") =-=——— [1] De oad 1. 1 The horsepower is calculated from the effective | by means of the formula Hp. (p X V) 33000 [2] if it is desired to know the tensions in the tight slack sides of the running belt, these can be rrived at by the following formulas: i+p 2(A p) - [4] (he formula of greatest value to the belt user that for the minimum and maximum allowable il tensions in the belt. This determines the on under which the belt should be put on the s in order to give the greatest satisfaction, the tension below which it should not be allowed Bi ll in service if it is to transmit the desired power. This formula is 4A—p+v (44 — p)* — 9p" ; — [5] 12 e use of this formula as it stands, using as of A 240 or 160 for machine and counter- belts respectively, will give the minimum | tension, or tension in the belt at rest, below the belt should not be allowed to fall, and the at which it should be retightened. By making 20 Ib. for machine belts and A = 240 lb. for tershaft belts, this formula will give the maxi- nitial tension, tm, to which the belt should tightened, and the tension at which it should tarted in service when it is first put on the ising formula (1) to determine values of p, be found more convenient if for the expres- , the expression 109-0°758¢¢ js substituted, c the are of contact in degrees. use of the formulas is simple, and requires er mathematical ability than that of facility THE IRON AGE in handling a table of logarithms. The process, however, is tedious and the determination of the horsepower and tensions involves a great number of separate computations, and would be impractical were there many belts in question. In his paper, before mentioned, Mr. Barth prepared a series of graphical charts which contained the solution of the equations. He has also developed a slide rule in which are embodied all the variables enumerated above, and which offers a means of solving rapidly the greater number of belt problems within the usual shop range. The charts, however, are difficult to understand and are not readily followed by the average person. Furthermore, it is exceedingly dif- ficult to read them closely enough to be sure of exact results. The slide rule is far superior to the charts, but, again, many persons find difficulty in handling the ordinary slide rule, to say nothing of the more complicated belt-slide rule with its multi- plicity of slides. For these reasons it has been considered wise to calculate the accompanying tables, which contain all the information embodied in the slide rules, and present it in a form that may be readily used by a person of even less than aver- age ability. VERTICAL AIR COMPRESSOR Two-Stage Unit Combining Both Power and Air Cylinders in One Casting The Lyons Atlas Company, Indianapolis, Ind., has placed on the market a portable self-contained two-stage vertical air compressor driven by an in- ternal combustion engine. It is built in capacities ranging from 35 to 150 cu. ft. per minute with a maximum pressure of 200 lb. Although the com- pressor illustrated is of the stationary type, a truck mounting may be used. The compressor is charac- terized by a small number of moving parts; the ab- sence of stuffing boxes, piston rods and governor belts; the provision of large cooling surface per unit of cylinder volume and the locating of all the work- ing parts either in plain sight or within easy reach from the outside of the compressor. By removing the holding-down bolts between the base and the frame and disconnecting the pipe on one side of the engine, the frame may be swung back on the hinges to give access to the crankcase for inspec- tion and adjustment. The compressor consists of a two-stage direct driven air compressor combined with a four-cycle single-acting vertical internal combustion engine, so as to make the power and the air cylinders one con- tinuous casting requiring only a single differential piston, one connecting rod and one crank. The en- gine, which runs in a clockwise direction when viewed from the governor side, as in one of the ac- companying illustrations, can be started by hand or by air which has been previously compressed and stored in a receiver or pressure tank. The speed regulation is provided by an inertia weight pivoted to the bellerank carrying the exhaust roller. As the speed rises above the normal rate, the weight hangs back, thus placing a spring under tension. This stressing of the spring is relied upon to keep the suction valve closed and the exhaust valve open during the suction stroke until such time as the speed decreases when the spring relaxes and the regular cycle of operations is resumed. The inertia required to enable a hit and miss governing device to maintain a constant speed regardless of the fact that there are two air compressing strokes for each 534 THE working stroke of the engine, is provided by two heavy flywheels and crank disks which practically fill the crankcase and reduce clearance. The fuel used by the engine is gasoline but the engine may be arranged to take al, illuminating or producer gas. A sight feed nder lubricator is relied upon to serve both ends he stepped piston, a peripheral groove gathering the surplus oil fed by the lubricator and delivering it through drilled holes to the upper and lower bear- ings of the connecting rod. natul ao Cy! i of t Grease cups are pro vided for the crankshaft bearings and are relied upon to provide an air seal. The final pressure, which is either 100 or 200 Ib., is reached through two compression. When the air piston is at the top of the stroke, the crankcase stages ol is full of air at atmospheric pressure ad mitted through the port A, which registers with a port in the nearest crank disk. As the piston travels downward, this air is compressed in after which it through the passage B and the valve C into the annular chamber D and raises the absolute pressure there to approximately 20 Ib. As the piston starts on the upward stroke, the valve C closes, and when the pressure in the annular space D equals that of the receiver, the discharge valve E opens and permits the air to pass into the re- ceiver during the remainder of the upward stroke. This pressure is relied upon to assist the piston on the upward stroke, and it is emphasized that the location of the port in crank disk is such that the port A will not open until atmospheric pressure is reached. The circulating water used is taken through the ypening F’ at the bottom of the air cylinder jacket and passes upward and entirely around the air the crankcase flows cylinder, thus absorbing the heat of compres- sion. In this way, it is pointed out that when the water passes from the air cylinder jacket to that of the power cylinder its temperature has been increased sufficiently to maintain a high IRON kerosene or AGE March 2. | Cylinder Z Center Line « Gasoline Engine Driven Two -Stage Air Compressor thermal efficiency throughout the combined cycle. An unloading device can be furnished at an extra cost to open the air admission valve between the and the annular chamber D when the pressure reaches a predetermined point. In this way, it is emphasized, the load is removed from the engine, which is permitted to run light until the pressure is reduced below the maximum for which the unloading device has been set. crankcase Crane Controller Operated by a Rope The Cutler-Hammer Mfg. Company, Milwaukee, Wis., has recently added a reversible drum type to its crane and hoist controller line. It is designed for intermittent speed regulating duty, such as is met with in crane and hoist intended for overhead mounting indoors. The control is by a rope passing over the sheave at the right of the controller. service and is A New Type of Crane and Hoist Controller Operated fron the Floor by a Rope March 2, 1916 » types are ordinarily made: one to provide a 50- reduction in the speed with only half the full- rent, is designed for general crane and hoist Wherever the average load has to be handled by e at a steady slow speed, as is the case in foun- he builder recommends the use of the second ch will reduce the speed 90 per cent under light- ditions. Keyless Lock Labor Decision Reversed Indiana Supreme Court has reversed the lower decision in the case of the Keyless Lock Com- Indianapolis. The trial court had decided against embers and officers of three lodges of the Iron ’ Union, enjoining the union from picketing and herwise hampering the company’s plant to e it, and awarding judgment for $6,000 damages. versal is because of the erroneous admittance of ce by the court over objections by the defendants. gher court says that it was error to admit in evi- a resolution introduced by one of the defendants international body reflecting against courts and nmental officers and not adopted by the associa- - that it was error to admit evidence outside the is- prejudicing a party; that it was error to admit nents of a telephone conversation with a strike- er, who was hired and, after leaving the shop, Air Compressor Arranged with the Receiver Tank at the honed he would not return, as it was not res gestae, that it was error to admit the statement that the had been interfered with, as it was a conclusion ne of the ultimate facts in issue. e Supreme Court says it approves the doctrine of ht of any number of persons to do that which is for one person to do, and that members of labor may peaceably combine to better their condition, iinst the idea that there may be an unlawful com- n to do that which is lawful for an individual to he court holds that there was some evidence of e by the defendants and that, as there was no to modify the judgment, the judgment would ad there not been error in the conduct of the le original decision in this case was set forth in ‘ON AGE of July 17,1913. The Keyless Lock Com- aS operating an open shop and the Iron Molders’ engineered a strike to force its unionization. The nad at first endeavored to get the company to non-union employees to join the organization atening them with dismissal if they refused. It _— that the question of wages was in any olved, THE IRON AGE 0 Oo ul Fuel-Oil-Engine-Driven Air Compressor An air compressor said to be capable of operating on the lowest grades of fuel distillates has been piaced on the market by the Chicago Pneumatic Tool Com pany, Fisher Building, Chicago, Ill. It is of the stand ard horizontal type of construction and is built stationary and portable styles, the latter having eithe a tank mounting, as illustrated, or being furnished with skids. Both single and duplex machines are bui and the special feature aside from the ability to bur cheap grades of fuel valves. The compressors are of the straight line type with the air cylinder bolted to the main frame and connected in tandem to the power end. The power cylinders are of the valveless, two-cycle, low-compression type, igni tion being secured by a hot plate system at the end of the compression stroke the same as in a Diesel engine A small oil pump injects the fuel against the hot plate on the piston as it approaches the end of the com pression stroke, and it is emphasized that the com bustion is so complete that when the exhaust port is opened the fuel loss is negligible. This can also be reduced by using water with the oil, the exact amount admitted to the combustion chamber being controlled by a flyball governor. The single compressors have six standard lengths of stroke ranging from 8 to 21 in is the use of the builder’s flat d Underneath and the Fuel Oil Engine Which Drives It Mounted End and the smaller sizes can be tank mounted as shown, or set on skids, while the larger ones are designed for stationary use only. Among the uses to which these compressors may be put are the pumping of oil and water by various systems in industrial plants, and for use wherever compressed air produced at a low figure can be utilized In tests made of these compressors, it has been found possible to compress air to 100-lb. pressure at a cost of 56c. per 9-hr. day for each 100 cu. ft. of free air delivered every minute to the receiver, this figure being based on the use of fuel at 3c. per gallon. The fuel used by these comprssors is any mineral oil of 26 deg 3eaume scale or lighter, containing not over 1 per cent sulphur. Bills are pending at the present time in New York, New Jersey and Virginia looking to the establishment of a law based on the American Society of Mechanica! Engineers’ boiler code, and according to Thomas E Durban, Erie, chairman of the administrative council of the American Uniform Boiler-Law Society, bills may shortly be introduced into Maryland and Rhode Island legislatures. The Composition of Some German Shel's Influence of Various Elements on the Physi- cal Properties—Phosphorus and Sulphur Mechanical and Chemical Testing Limits German shells in large quantities were thrown on the northeast coast of England on Dec. 16, 1914, by German war vessels which made a raid at that time. Many members of the Cleveland Institution of Engi- neers secured fragments of these shells for determining their composition. Dr. J. E. Stead assembled these analyses and presented the results with his comments and conclusions in a paper before that society on Jan. 10, 1916, an abstract of which is as follows: The pieces analyzed in most cases were small frag- ments, and it was consequently impossible to judge of the dimensions of the shells of which they formed a part. Judging from information received from Hartlepool and other places, it is certain that there were shells of many sizes—from 11.2-in. armor-piercing Table of Analyses of High-Explosive German Shells - n ¢ 2 € #€ BE ¢ Where Found 3 86 3 g€6 80 6, 2 Ss #5 85 85 @o sa 8 5 6h Sa 3a Sa Sh Ma & ZO a a a fy O & West Hartlepool ] 0.60 0.73 ... 0.062 0.085 SS ad West Hartlepool 2 O.70 O.80 0.85 0.027 0.043 ... Bd West Hartlepool... 3 06.670 0.515 0.336 0.037 0.048 0.083 62 West Hartlepool. . t O.870 1.094 0.252 0.037 0.028 0.080 65 West Hartlepool. . » 0.465 0.794 0.824 0.088 0.028 0.090 55 West Hartlepool.. 6 0.600 0.655 0.597 0.046 0.051 West Hartlepool.. 7 0.820 1.266 0.186 0.048 0.052 West Hartlepool.. & 0.765 0.655 0.364 0.030 0.045 West Hartlepool.. 9 0.630 0.550 0.400 0.042 0.077 West Hartlepool, S-it, @nell.<.... 10 O.86 1.03 0.186 0.053 0.045 West Hartlepool 11 1.12 1.00 0.23 0.054 0.038 Whitby and Scar- I i is ts 12 0.850 1.330 . 0.080 0.105 Whitby and Scar- Ns a ae : 13 0.60 my 0.334 0.071 0.069* 59 Whitby and Scar- bro’. \ 14 0.74 1.170 0.261 0.044 0.064 §2 Dunkirk 15 0.675 0.380 0.078 0.083 0.043 Ypres . 16 06.700 1.108 0.221 0.041 0.079 Flanders 17 0.98 1.05 ... 0.055 0.086 Flanders 18 9.92 0.98 ... 0.059 0.065 Flanders 19 0.74 0.98 : 0.054 0.050 Germany 20 =06.393 1.400 0.210 0.035 0.041 France ; 21 0.930 0.970 0.164 0.032 0.048 *Nitrogen 0.0112 per cent shells down to 4-in. high-explosive shells. Many of the larger shells had not burst and it was possible to measure them. Shrapnel! shells do not appear to have been used. The shells used may be divided into two classes, armor-piercing shells and high-explosive shells. The armor-piercing shell fragments were easily detected by the presence of nickel and chromium—elements uni- versally added to steel used in that connection. It may be noted that the Germans affixed to the armor-piercing shells the soft-nose pieces which are invariably used with shells of this description. The analyses of frag- ments of these shells were made by F. Saniter, and were as follows: Iron (by difference), 91.862 per cent; carbon, 0.840 to 0.50 per cent; manganese, 0.581 per cent; silicon, 0.401 to 0.42 per cent; sulphur, 0.033 to 0.028 per cent.; phosphorus, 0.032 per cent; nickel, 3.100 per cent; chromium, 3.351 per cent. The several analyses and their sources are given in the table. PHYSICAL APPEARANCE OF THE FRAGMENTS Most of the fragments examined were small, and the fractures generally indicated material of very high tenacity. There were a few large pieces and these had a much coarser crystalline structure than the smaller ones. It is well known that the appearance of the fractured surfaces of metals broken by sudden shock is a very useful guide in forming a correct judg- ment of the physical character of the material. If the surfaces are more or less coarsely granular and the 536 fracture has traveled in straight planes, the materia! is usually relatively weak. Such fractures somewhat resemble the fractures of lump sugar. If they are more finely granular the surfaces are not usually flat and frequently have tongues or pointed strips of meta! attached to the fracture, suggesting a tearing acti: and tough material. Some of the inner and outer surfaces of the shel! fragments were fissured by a multitude of fine cracks, generally parallel to the vertical axis of the shel! The flat surfaces of one of the base plugs where it came into contact with the explosive charge were sim- ilarly broken up into fissures, but these did not extend to the outside of the plug. The force must have been of such violence as to tend to tear the metal to pieces and produce disintegration. One writer, in describing the German shell frag- ments, said: “One can have little conception of the terrible nature of these until they are handled. They bristle all over with horrible points and edges—some as keen as a razor.” One peculiarity is the manner in which the fragments broke, leaving what may be described as “sheer fractured surfaces,” with sharp knife-like terminations. The tracks of the fractures were often at angles of 35 to 45 deg. to tangents of the shells, and the broken surfaces of many of them had a somewhat fibrous appearance, characteristic of great toughness. Tests made on the fragments of both the coarsely granular and fibrous varieties confirmed the conclusion that the former were brittle and the latter extremely tough. THE PRESENCE OF NITROGEN i The fragment corresponding to analysis No. 13 in the table was particularly interesting. It had “sheer fractures” on both its sides, was of fine crystalline structure, and evidently ideal in its character, yet this contained about 0.07 per cent sulphur, and the same amount of phosphorus. Moreover, it contained 0.011 per cent nitrogen, an indication that it was made by the Bessemer process, for no open-hearth steel, so far as is known, contains nearly so much of that ele- ment. As acid-Bessemer converters are rare if not non-existent in Germany, it is justifiable to conclude that the steel is basic-Bessemer. It had a fine micro- structure with practically no free ferrite, due to the exceedingly high manganese content. In _ metallo- graphical terms the steel was sorbitic, consisting of unsegregated pearlite. On reheating to about 800 deg. C., and cooling in about half an hour to 400 deg. C., and then to 15 deg. C., its original structure and hardness were reproduced. The Brinell hardness num- ber was 255, equal to about a tenacity of 56 to 57 tons per square inch. What the elongation was could not be determined, but it certainly would not exceed 12 per cent. Little comment is necessary on the armor-piercing shells. A broken piece from the point was exceedingly hard, as indicated by the Brinell machine. The shell had evidently exploded on coming into contact with something not hard enough to damage the point itself. VARIATIONS IN COMPOSITION On examining the analyses of the high-explosive shells one cannot help being struck with the very wide range in the composition. Comparing the maximum and minimum amount of each element, we have: Car- bon, 0.393 to 1.12 per cent; manganese, 0.380 to 1.4! per cent; silicon, 0.078 to 0.597 per cent; sulphur, 0.027 to 0.083 per cent; phosphorus, 0.028 to 0.105 per cent. Out of the twenty-one analyses, ten show more than 1 per cent manganese, seven show more than 0.” per cent silicon, twelve more than 0.2 per cent silicon, three show more than 0.07 per cent sulphur, eight more March 2, 1916 .06 per cent phosphorus. carbon is 0.75 per cent. hat is the reason for these great variations? One , of course, say with certainty, but there are only <planations one can offer: That the German authorities have been careless ir selection of the steel; that the occasional pre- e bursting of a shell in a gun and the consequent iction of the gun and the gunners did not matter, ey had so many guns and men to spare—a sug- gestion actually made in this country, but which is isly absurd. 2. That the German experts have | that, provided the steel is suitable for the pur- required, a great latitude in the composition and ysical properties is permissible. The first hypothesis may be dismissed without much nsideration; the shells sent into our towns, varying greatly in composition, obviously did not burst in the 9 An examination of the larger fragments of German shells did not lead to the discovery of anything the nature of rokes or surface flaws, and the very high percentage of silicon and manganese in most of m suggests that soundness was considered as of rimary importance. The fact that nitrogen was found a relatively large quantity in one of the best speci- mens leads to the conclusion that nitrogen is not harmful and that probably basic-Bessemer steel has been found quite suitable, provided a sufficient quantity f silicon and manganese is present to insure sound- The average percent- THE STRESSES ON A SHELL 4 \ny intelligent person with no engineering or special knowledge of the subject would tell us at once that the stresses put on a shell in the gun are com- pressive, not tensional. That if the shell were made ‘f lead instead of steel the sudden compressive force applied to the base would cause the shell walls to bulge outward and to become reduced in length, and that very soft steel would probably behave in the same manner. Therefore, the Germans were careful to avoid this and made steel strong enough to resist deforma- tion by compression in the guns. We may conclude, therefore, that what was feared vas bulging more than breakage by shock. It cannot denied by anyone who knows that steel containing © per cent carbon and above 1.2 per cent manganese brittle to shock, and that if such material were made a rail and were tested in the usual way, it would y to pieces under a falling-weight test, yet steel shells that description did not burst in the German guns, t burst on us. Every rail-maker knows that a shell ontaining 0.10 per cent sulphur and phosphorus, 0.45 r cent carbon, and 0.8 per cent manganese would be liable to break under shock than such steel if ur and phosphorus were entirely absent. ry} MECHANICAL VERSUS CHEMICAL TESTING (he analyses of the German shells naturally make question our own practice and specifications, which ‘d to the rejection of material such as would be epted in Germany. Our authorities may have proofs do not know of justifying their specifications, but to that because a shell has burst in a gun, therefore steel is at fault, is not justifiable; neither is it tiable to form any dogmatic conclusion without mple proof. One method of testing shells gives con- e proof that steel of a certain origin, which is present admitted by our authorities, is quite ble for high-explosive shells. Further trials are ted which it is proposed to ask some of the “emen responsible for our specifications to attend itness. One thing which must be admitted is that teel is proved by suitable mechanical testing to tistactory, on no account should it be rejected on ‘al analyses, for one remembers that mechanical ng is the base on which rests all chemical specifi- | CONCLUSIONS conclusion, judging from the analyses of the n shells, it would appear: the Germans are not particular in having shell steel rm quality THE IRON oj oS -~1 AGE That the steel used is generally of relatively high tenacity, and much more liable to break up by shock than what we produce and prescribe. That most probably some of the German shells are made by the basic-Bessemer process, judging from the relatively large amount of nitrogen present in one of the toughest and best fragments, which also contained 0.07 per cent sulphur and phosphorus. That the analyses of the armor-piercing shells correspond with analyses of similar material made in other countries That if the high-explosive shells with between 0.07 and 0.1 per cent phosphorus did not burst in the gun, it seems probable that great freedom from that element has been found to be unnecessary. In view of these considerations, is there not reason for our authorities to doubt the expert advice given them—on which, of course, they must depend—to re- strict so drastically the allowable quantity of both sul- phur and phosphorus, thereby restricting the output of shell steel? As the question can so readily be settled by making suitable mechanical tests on the finished shells such as I myself have made with convincing re- sult on material at present barred, is it not in the national interest that such tests should be made with- out delay by the authorities at headquarters? If the results of my mechanical tests are confirmed then the obvious thing to do is to alter the specifications forthwith. If the mechanical tests are found to be conclusive, then it would be a national crime to reject material on any chemical specification before submit- ting the steel in question in the form of a finished shell to the more convincing mechanical test. LATER SHELLS SHOW LOWER MANGANESE Commenting editorially on Dr. Stead’s paper, the London Jron and Coal Trades Review said: “It would have been most interesting if Dr. Stead had been able to throw more light on the analyses of German shell steels. Analyses, for instance, of German shells from the beginning of the war up to the present time should give a good deal of information as to the manganese position in Germany. Presumably all the naval s