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A. ^^;;; , '$ * && . & { →|× - -·:::::::*№tas, ' .. •§¶√≠√≠√∞)*( ),,, · , , , , ºſ º Laecae--*******) -•¿•**- - L-:-***ºſſº*· ..! • №. !!” ş(*) º. (~~~~ (*)(>) ::: ~~~~~, șº - -` ».-^~ * * * *.*. • * * ***** *** *-3. - . ***¿¿.*.*..*..*; 3: ... . *** # *. º: * " * -, - *: , N„caeſº }}';þRSITYOR ¿ſyg º ARY THE DESIGN QE SPECIAL, BLOOM S.HEARS A THESIS FOR THE DEGREE OF MECHANICAL ENGINEER, UNIVERSITY of MICHIGAN. 1916. Guy D. Newton. l. The invention of a mill for rolling steel car-wheels and gear-blanks made it necessary to build a suitable shear for cutting the stock for the mill. The pieces must be cut so as not to leave a fin, and with as little distortion as possible. The ordinary type of bloom shear, with one stationary, and one moving blade which crushes its way thru the metal will cut, the blooms very rapidly and cheaply, but the pieces cut are so badly distorted that they cannot be handled in a wheel-mill. To overcome this difficulty several styles of shears were designed, but only one built, so far as the writer knows. In the following pages three of these designs Will be discussed: a rotary shear with motor drive, a spiral shear with a hydraulic drive, and a hydraulic plunger shear. We will first take up the rotary shear, as one working upon this principal was built, and is now in use. - We shall confine ourselves to the principals involved, such as the power required, choice of motor and fly-wheel, etc., and not attempt to work out all of the details. R O T A R Y S H E A R. The operation of this machine Will be readily understood from a study of the diagram, Plate, 3., and of the assembled drawing of the shear, Plate, 4., The bloom is revolved between the two rotating knives, each of which makes a spiral shaped cut as shown. The right hand knife cutting the cross- hatched portion of the bloom and the left hand knife cutting the blank portion. For this shear the blooms must of course be cylindrical, and must be carried on a table which will allow them to rotate freely. It is not necessary however, to provide means for rotating the blooms as the drag of the knives has been found sufficient for this. The table for carry- ing the bloom consists simply of a 12" steel pipe supported by rollers to allow free rotation. The bloom lies on the pipe ana is prevented from rolling off by a horizontal bar of steel on either side. This arrangement is shown dotted in connection with the spiral shear, Plate, 3. A hydraulic cylinder acting against the end of the bloom forces it into the shear and the pieces as they are cut off, are allowed to fall into a pit, beneath the machine from which they are removed by any convenient, means. The first question to be considered in attacking a problem of this kind should be that of the power required. The amount of published data on the subject, is not, extensive. we were unable to find any data of actual shearing tests of steel at high temperatures. - - The Iron Age, of Feb. 15th., 1916. publishes an abstract of a paper by A. Schwarze, describing an electric bloom shear in which it, is stated that "the knife forces itself into the hot metal at a considerably lower pressure than e.coo. pounds per square inch." On page 299, in Machinery's Handbook, in a numerical example, 6,000 pounds per Sq. in-, is assumed as the shearing strength of hot steel slabs. # Mr. Wm. C. Coryell writes that steel direct from the furnace has a shearing strength of about 3, COO pounds per sq. in. If it has been out, of the furnace about one minute 8,000 pounds, and if it has been out of the furnace about, four min- utes 16,000 pounds per Sq. inch. none of the above figures were based on actual tests so far as the writer knows. * Mr. Coryell was formerly steam engineer at the Youngstown branch of the Carnegie Steel Co. In order to obtain some definite information on the subject a small experimental rotary shear was built, and a series of tests made. This shear is shown by the blue print, Plate, 1-, and by the two photographs on Page, 5. The fly-wheel is six feet in diameter, and its moment of inertia is 217.875. The blades are geared down as shown to one twentieth of the speed of the fly-wheel, and were designed to cut bars of any size up to 3" in diameter. The cutting is done in exactly the same manner as by the large shear, each blade cutting a spiral strip 3/8" wide as the bar revolves due to the pull of the blades which move in a tangential direction. In order that the blades should not be burned off they were made rather blunt, as shown by the sketch, Fig. 3. As it was necessary to place the blades exactly opposite each other in order to get A-247, 2 the desired shape of cut, it will be seen that the action is not strictly a shear. The blades really crºush their way thru the metal. • The first, blades were steel. castings, but, as these soon gave out the edges were turned Gºff and "bits", forged from tool steel were bolted on as shown by the photograph, Fig. 5. , page, 7- In order to center the piece to be Gut, the plate shown by Fig. 6. , Page, 7. , was bored to fit over the ends of the blade shafts. The hole in the center of the plate is for inserting the stock. The shear was driven by a belt from a pulley on the line shaft, to a clutch pulley on the fly-wheel shaft of the shear, as shown by blue print, Plate, l. The speed of the fly-wheel was rec- orded by means of a chronograph. A projecting key on the fly-wheel shaft, raised the end of the lever a, Figs. l and 2. Page, 5., making a contact at b, thus operating the pen of the chronograph at each revolution of the fly-wheel. By throwing off the power and rec- ording the number of revolutions made by the wheel in slowing down, we were able to compute the friction of the machine when running light, and also the power used in shearing. It was thought that we would be able to scale the time of each revolution during the cut- ting, and as we could determine the position of the blades at any time, compute the energy expended in making each portion of the cut. The drum of the chro- nograph revolved very slowly however, thus bringing the revolution 5 So close together on the chronograph sheet that we were unable to get any consistant, fig- ures in that Wray. Another thing that contributed to oz//* failure was the fact, that the stock did not always rotate in the same Way, so we were not able to tell just what area was sheared during each revolution of the fly-wheel. Fig. 7. , Page 7. , is a photograph of cut #40 which shows that the stock made only 1/2 of a revolution and then stopped and the blades crushed their way thru. In this case the piece was not cut. completely off. A small wedge shaped piece about 1/20 of a square inch at e, and d, being uncut. The steel was heated in a gas furnace which was located some distance from the shear, so that at least so seconds were reqûired to draw the stock from the furnace and place it in the shear. The question of determining the tem- perature of the steel at the time of shearing gave some trouble at first. Our first idea was to wire a thermo-couple to a piece of steel of the same size as the one to be cut, and withdraw them from the furnace at the same time and read the temper- ature of the one at the time the other was being cut. It was found however, that the couple cooled Off much more rapidly than the steel. - We next, tried inserting the couple in a small iron pipe, and this pipe in a larger ©flé, etc . , thus making a mass of iron as nearly as poss- ible equal to that of the piece to be sheared. This arrangement gave better results but still was not satisfactory. So We finally thought of the plan of artiling a hole in the steel and inserting the thermo-couple, as shown in the photograph, Fig. 4. Page, 7. It is believed that this arrangement, gave fairly accurate results. Our only trouble with this was due to the fact, that the thermo-couple wires break very easily at a temperature around 2000 deg- rees Fah. Cold they will stand a great deal of bending. In making a test, we proceed as follows, - The two pieces of steel of the same diameter are heated at once, the thermo-couple being inserted in ** 10. one of them. When the steel is hot the shear is started and we are ready to make the cut. The piece of paper which is usually kept between the two contact points at b, Fig. 1 . , Page 5. , is removed for exactly one minute, thus recording the speed of the fly-wheel on the chronograph sheet. Then the steel to be sheared is brought, as quickly as possible and just before it is inserted between the blades of the shear the paper is again removed from between the contact points, and the clutch thrown out, the bar inserted, and the fly-wheel allowed to come to rest. We now have a record of the speed of the fly-wheel and the number of revolutions it makes in coming to rest after making the cut- Plate 2., is a sample chronograph sheet with this data. This will allow us to compute the power tised in shearing the steel if we know the amount of energy used up in friction in the machine. Frequent friction tests were made as the friction gradually decreased as the bearings became worn. Several of the earlier shearing tests were thrown out due to the uncertainty thfººthe friction load. It was also found that, the friction could be considerably reduced by frequent, oiling. In order to know the temperature of ll. the steel at the time of shearing, the pyrometer is read at the instant the steel is removed from the furnace. And the time at, which the steel leaves the furnace and the time at which it enters the shear are noted. As soon as the shearing has been done, the piece of steel with the pyrometer attached is removed from the furnace and the temperature is read every 5 or 10 seconds as it, Gools off. After several. trials we are able to plot, a curve of ten- peratures, on time as abscissa, by which we can tell very nearly the temperature of the piece of steel which is being sheared. It is only necessary to know the temperature at which it leaves the furnace and the time that has elapsed until it, enters the shear. Curves 1,2,3,4, and 5 are the temperature curves for the various sizes of steel used. The triction of the shear was deter- mined each day in the following manner:-The shear and chronograph were both started, and the piece of paper removed from between the contact points for exactly one minute in order to record the speed of the fly-wheel. After waiting a few seconds to cause a break in the chronograph record, the paper was again removed and at the same time the clutch was thrown out and the fly-wheel allowed to come to rest. From the number of notches in the chronograph record we were able to compute the friction of the shear, thus.- The kinetic energy of the fly-wheel = 1/2 I w: I = the moment of inertia, – 217.875 (Computed) - w = angular velocity = 37N radians per second- & * N = number of revolutions per minute. Example :- N = ll.5 R. P. M. W = 3.1416 x 115 x 2 = 1.2.04 2 a 60 : º ºr WT = 1.2. Q4 = 145.03 Then the kinetic energy = £1.7-2.É a lag.cº. : 15606 foot, pounds. Then the kinetic energy of the fly-wheel, divided by the number of revolutions the wheel makes in coming to rest, when running light, will be the friction of the shear in foot, pounds per revolution. The average of several tests was usually taken as the true fric- tion load for each days run. The power required to shear the bar was determined as follows:- On the chronograph record count the revolutions made in one minute, and also the number of revolutions made while coming to rest after the cut has been made. Then the shearing power is equal to the kinetic energy of the fly-wheel at the initial 13. * speed, minus ( the friction per revolution multi- plied by the number of revolutions made while coming to rest). Example :- Run. 27. (see tabulated results, Page, 14) At 118 R. P.M. the kinetic energy = 16640. ft. lbs. The friction at that time was 39, ft. lbs. per rev. The fly-wheel made 264 revolutions in coming to rest, after making the cut. Then the shearing power = 16640-(39x264)=6340 ft. lbs. : The area of the bar cut - 3 - 1.4 sq. inches. Therefore the shearing power per sq. in. = 3342 =301.9ft. lbs. 3. i4 The force required to shear one sq.in. (shearing strength) would then be 2010 -- 1/12 = 24.00 pounds. The tabulated results of the tests will be found on Page 1.4. - On curve sheet #7 the shearing powers per sq. in. are plotted on temperatures as abscissa. Curve l , shows the results of tests #9, #1C, #ll and #12. The steel sheared in this case was a one inch bar of mild steel having a tensil strength when cold of about 50,000. lbs. per sq.inch. Curve 3 - , shows the results of tests #13, #14 and #15. In this case the pieces sheared were from a 1 1/4” bar of high carbon steel having ºf Z/7/vº A/7//i. º º º 3. Z. --- º ººzºº Wºº-ººººººº… Zºº / Sº Zºº º P Fº ºf ºzº º, º ZººZºº, Zºº º º: º º º Zºº” ºººººº. ºf Zºº. *** * º º, ºf º,..., Sºeº, º ſº, º ºsº -3. - 7 * * * * ºeº 5/23. Gºº. Zºº Zºº ºv. 2. A-22 ºzº A. ºlº / e º ſº. º goooº... / 2 & 2" L º | 24 º º 2 Zºº 2 × 2 / 722. Zºº ºA. 5. º º _2 º º º Zºº º Z. º º Zºº” Zºº - 3 × 23 º 232 oz. … º º A 223 yeº Zºº º, Zºº /* * * ZºZº. Zºº e Zºº 22/2 2… - |… º º Zºo. ºf Zºº & Zºº. A Zºº. º º e ). Zºº & 22.522 ºf 7. - … e. a zºº Le sº º ſº. Zºº /º/2 2 & 7 ||32 & 7º 2 - 3 & 2 & 7º - . Zºº /2 23.2% º 3 5. Zºº 2/*2 || 23 Zºº 2. – - … . . . . . . º - Zºo & 25 || 2 & * Zºº º º … 23. A 22 2. 2 º' W. Zºº 2,5-º 2 º' W. 2.2 - 22 . A. … . 24 ºº ºZ. - A. V º º º 3 º A. º º º º A. º A. A. 5. º 2. º º º º 22 º º º V A. º | | º a tensil strength when cold of about 85,000 lbs. per sq. inch- Curve 2. , shows the results of tests #16 to #42 inclusive. These bars were cold rolled steel shafting, 1 7/16", 2", and 2 1/2" in diameter. The 2 1/2" pieces, (#40, #41 and #42) were not completely cut off, but the error is slight. Two cuts were made on 3" shafting but, the results are not included in the table because the cuts were very incomplete. Our range of temperatures is not, as great as we had hoped. We were unable to get any successful cut at a temperature above 1950 degrees Fah. A3 the melting point of steel is about, 2500 degrees Fah., we have indicated by dotted lines what seems to be the probable path of the curves. They should all fall to zero at the melting point. On curve sheet, ſº the shearing strength per sq. iri, is plotted on temperature as abscissa. As stated on Page 13. , the shearing strength is computed on the assumption that if it reqāires 2000. ft. lbs. of energy to shear one sq. in. of steel, that is a force of 2000lbs. acting thru one ff. , it will require a force of 12x 2000. = 24,000 lbs. acting thru a distance of one inch to shear the same area. ſº, º √∞ √° √ ) ()= º, ºs vºº ººyºººº… :º) :Z = Z – Z ſº ºs º aeº =|7 x ≤ x ſº^ º^ º^ = ºº/ º -º / = Z* ,x ſº^º/ º * ºº ,A/. = ~~~~ ~~~~ ~~~~ - ºººº ZZZZZZZZZ, Zºººā Zº (Zºº) - ~~~~ |: ae,№ º,, ,ſºlº, ºººº! ººººº Zv , , , (Z = z) = ∞ a√∞ √∞ √∞', ,º^ ºººv ^ºº^ (º: / o -> ~~~~) = º, , , , ) → ∞ √° √∞/∞ ().ſº z ºz ºº ^ = y zºzº (º Zººzº ººººººº :Zºzz! = 、 | ~ ~º ~º ~º ~~~~);ººººººº/ = _, | || || ººººººº ſºººººº :) ººs » º ^º) ºººººººº !! !! !! !! ººº ! ºººº°′ſººſ/, // | /º), ººººººº ºººººººº !ººº/, ±) ſººſ ºſºſ,ºººſºlº, , , , ,ººz | Zºº / p / ¿º Lºzºyl ſºº|(°, ′′′ .ºººº||× ºººz º.º.ººººººººººz ºſz, ſºº /|ſº, º az a ſººſ ºſ º ſººſ ſºlº,ſº, 2/ ∞ √° ſ√≠√∞ √°.|× ſg)ºººº|×. |×· · · ·:·º·:·º·:·º·:·º·:· ºstvº), ſººv) veze, ſººs ~ | ~ ~ ~ |ºs_,_, |・, , , , , , e,|-Aſ I (ºº ſºººº , | ºg ae ae º, yeye, ſºº-º--:| , ، ، ، ، ، ، ، ،| ---- :::::: ~~~~ ~~~~ ~ | ~~~~~~ ~ | ~~~~ ~ | ~~~~ ~~~~ ~~~~ ~ | ~~~~~(_)~~~~ ~~~~|~~~~~ ~ || … , sºy || ~ ~ ºvº -, , , , ,º , , , , ,§ 2, Zºº, zºº,ºººººº,,,%,,,,, ºººººº zº Zººzº º Zººrºº (7) | cºlº, z ≠√∞ √° √ √∞/∞:7 Z Z, CZ, Z Z 2,7, 7 , ! 17. We are now able to determine what power is required to shear a 12" bloom if we know the temperature of the bloom. Going back to our temperature curves again we have computed the amount of heat radiated from each square inch of surface of the metal in one half minute, at various temperatures. The method and tabulated results are given on blue print Page, 16. These results are not strictly correct, as we have assumed that the radiation remains Constant, during a half minute. It really decreases as the temperature of the steel drops. However the error is not great. On curve sheet #6. , we have plotted the mean radiation per sq. inch, as given in the table Page 16. , except that we have multiplied the figures by two, plotting the radiation per minute instead of per half minute. ... " The dotted curve on curve sheet, ſº shows the radiation per sq. in. of surface, per minute, computed by Stefan's law. R = crº Where R = radiation, and 1 = absolute temperatures. These two curves do not lie a great distance apart, but they curve in opposite directions. Now that we know approximately what heat is radiated per sq. in. of surface we can know 18. about what the temperature of our lz" bloom will be when we wish to shear it... Referring again to Plate 3. , it will be seen that the cutting takes place during about two fifths of a revolution of the knife. If we allow four seconds for the cutting, our knife must make a complete revolution in 10 seconds, and we will have six seconds in which to advance the **: bloom for the next cut. A 20 ft. bloom will usually --- have to be cut into about 25 pieces. At six cuts per minute this will take about four minutes, § {} º to be safe we will say the steel will be out of the furnace five minutes before it is completely out up. It will be at a temperature of at least, 2200 degrees Fah. when it, leaves the furnace. We will now compute the drop in temperature of a 12" bloom in five minutes, using a section one inch long as a unit. Weight of sec. 1" long, - 31.7 pounds. Area of sec. l" * = 37.7 sq.inches. Specific heat, of steel, O. 113 The total heat, per inch length, in the bloom at 2200 degrees Fah. of 2660 deg. absºlute temperatute will be, 2660 x .118 x 31.7 =9950 B.T. U. Radiation per sq.in. per min. from curve #6= 3.9 B.T.U. Total radiation = 3.9 x 37.7 = 147.2 B.T. U- Total heat, in the bloom after one minute will 19. be, 9950 - 147.2 = 98.02.8 B.T. U. 9832.8 Q. 113 x 3 l = 7 bloom after one minute. Continuing in this way we = 2160 = the temperature of the find that the temperature of the bloom after five minutes is 2010 degrees Fah. Referring to curve sheet #8, curve #2. , we find the shearing strength per sq. in. at 2010 deg. Fah, is 16100 pounds. Having determined the shearing strength of the steel we are now in position to discuss the design of a 12" shear. The total area of a 12" bloom is ll:3.1 sq. inches, and each knife cuts an area of 56.55 sq. inches. As may be seen by the diagram on Plate 3. , the cutting is accomplished during a stroke of 43 inches, and the resistance to the knife is about the same as would be offered by a flat plate 43" wide of the same area, if the knife starts at one edge and cuts across the plate. The average force on each knife Would be *# 101.22 = 21175 pounds. The maximum force is of course greater as the blade does not take a full "bite" until the bloom has made one half of a revolution. And also as the cut progresses the distance of the working portion of the blade from the center of the knife increases, thus increasing the resisting moment. To be safe then, we should design our shear for a maximum of 40,000 lbs. resis- 20. tance on each knife during the cutting strokes because a delay of two or three minutes during the cutting would increase the shearing strength of the steel considerably. Referring to the diagram, Plate 3. , we have assumed point c, as the center of resistance to the blade and drawn the line ch, to represent, the tangential force of 40,000 lbs. Line oc, will then be the direction of resistance of the bloom, And ca, the direction of the thrust against the knife shafts. Completing the triangle of forces we find shak the radial thrust against the knife shaft to be 49500 lbs. 9ſ course this might be changed con- siderably if it were shown that the center of res- istance is not at the point c, but at some point farther out. There is also a frictional regist- ance due to the thrust of approximately 50,000% against the bearings carrying the knives. With the knives mounted on 9" shafts, and driven by a 36" gear, this force figured at the pitch circle of the driving gear would be, if the coefficient of friction is o.o.B, * 52.22: 25 it. = 625 lbs., 18 for each knife. It is believed however that we 21 - can safely assume that 40,000 lbs. tangential force will-be our maximum load. In addition to the force required to do the cutting, there is also a certain amount of energy expended in setting the bloom in motion. Therefore, during the first quarter of the stroke we should add a force sufficient to accelerate a bloom 20 ft. long by 12" in diameter, from rest tºp a velocity of 1/2 revolution per sec. in one sec. 2 This will require an energy, E = 1/2 I 09. A = ***** 2: 22–2–432 z_2 *-B = 2 2 1.44 x 32.2 x 2 40 = 3.1416 radians per second. £8.2 × 2:13.6 ± 2-liig 2 1 = * x 9.5 g Then E = = 291 ft. lbs. This force acts thru a distance of about 1 - 33 feet, and one half of the load is carried by each knife. The tangential force on each knife due to this 10ad would be, *-*-*4 = 102.1bs. sº As this takes place at the beginning of the stroke before the knife gets a full "bite", it can be neglected. - This shear is to be driven by an electric motor and to reduce the speed from that of the motor to 6 RPM. , the speed of the knives, will require 3 pairs of gears. (see Plate 4-) The first, reduction will be from the motor to the fly-wheel shaft. For the second reduction a pinion on the fly-wheel shaft will drive the gear (2), on the auxiliary shaft. And for the third reduction a pinion (3), on the auxiliary shaft will drive the two gears (4), one of which is keyed to the axle of each knife. The knife runs 6 RPM., and if we make the auxiliary shaft, run 14 RPM, , a 7 to 1. red- uction from the fly-wheel shaft will give us a speed of 98 RPM., for the fly-wheel. FLY-WHEEL. In a machine where the load fluct- uates from friction load to a maximum several times a minute as in a shear, a suitable fly-wheel is absolutely essential in order to equalize the load upon the motor as much as possible. The best condi- tion so far as the motor is concerned, would be for the load on the motor to be constant and equal to the average of all the loads. As this can hardly be attained, the usual method is to let the fly- wheel do all the work of cutting, leaving for the motor only the friction load and the work of speeding up the fly-wheel between cuts. The work of cutting a 12" bloon at 2010 des.faa..which is the lowest temperature at which we ordinarily expect to work, is equal to the area of the bloom times the shearing power per sq. in. , as given by curve 2. on gurve sheet #7. Or the work = 113.1 x 1390 = 157000 ft.lbs. This must equal the kinetic energy which the fly- wheel looses during the cutting, or must equal the difference between the kinetic energy of the fly- wheel at 98 RPM. and 30 RPM. if we allow about 20% reduction in speed. 2. o = 1/2 I wº. 1/2 14, Then 157, QC W. K. - I : TET, where K = the radius of gyrations w = e−4+2 = 10.26, and w”- 105. 30 - . . . 4. – 22–4 =# ===== 4 * 6C 2 If K = 5ft, . K = 25. 2 8, 37, and 4, : 7Q. 2 5 Arid I = W #.a = ºf x Q, 78 E = 1/2 I wº- 1/2 w x 0.78wº o.39W wº Therefore, 157,000 =(0.39 x 105w)-(0.39×70w)= 13.66w. 157, QQQ w = *:::::= = 11500 lbs. ww.of fly-wheel. As we have assumed a rather large fluctuation, inspeed we will be justified in making our fly-wheel lift. in diameter outside, with a rim weight of 12,000 lbs. This will give us a per- ipheral velocity of 98 x 11 x 3.1416 = 3386 ft - per minute, which is well within the limits of safety • MOTOR. In addition to the work of shearing the bloon the motor must also carry the friction load. As this cannot be exactly determined it is customary to allow 25% of the motor rating for the friction load. If the work of cutting is 157,000 ft. lbs • , and six cuts are made per minute, the cutting will require 6 x 1570.00 =942,000 ft. lbs. 942OOO - - --- 2: 2 - - 33000 3. 6 HP And the motor rating should be 4/3 x 23.6 = 38. HP. of energy per minute, or But, as the motor is running at friction load over half of the time we should probably use a 60 HP, motor. And the speed characteristic should be such that the motor will slow down as the load increases, add will increase in speed as the load decreases. If we choose a compound wound motor having a speed variation from light to full load of 15%, and a speed variation from 25% friction load to full load of about 10%, the load condition would be somewhat as shown by the curve, Plate 5., in which the ordinates represent, the torque and the abscissa the time of shearing, in seconds. The Motor is running at friction at £riºtism speed with the torque represented by the ordinate of A, until the peak load is reached. This is represented by the area ABCD, and should equal the torque required to shear the bloom. The speed now rapidly falls off and the torque curve of the motor follows the line AE. At E, the shearing has been finished and the fly-wheel begins to speed up again. We designed our fly-wheel to do all of the work of gutting with a reduction of about 20% in speed, but the torque represented by area AED., is delivered by the motor, and only the portion ABCE, by the fly-wheel. So the speed will probably not be reduced more than 12%. The tárque represented by the area DEF is that required to speed up the fly-wheel again. Area DEF must of course equal area ABC.E. GEARS. In designing the gears we have used the formula, W = spfy, in which one tooth is made to take the whole load, which is considered as distributed over the entire length of the tooth. The tooth is figured as a beam loaded at one end. W = load transmitted in pounds. p = pitch in inches. f = face in inches. s = the safe working stress, y = a factor depending on the shape of tooth- We will start with the last reduction, gear (4), and pinion (3) as we have decided that these gears should be designed for a load of 40,000 lbs. at the pitch line. We will assume 36, 18 tº inches and 15.5 inches as the pitch diameters of the gear and pinion respectively. Making the pitch 4.06 inches we will have 28 teeth on the gears and 12 teeth on the pinion. If we assume f as ll" and apply our formula , its we will get a fiber strain of 8,930 lbs. for the gear, and 17,200 lbs. for the pinion. These fiber strains are rather large but still safe for steel gears at a peripheral speed of less than 100 ft. per minute. As gears (4) make 6 revolutions per minute, pinion (3) must make ** = 14 RPM. And as pinion (3) drives both gears (4), it must transmit, a force at the pitch line of 2 x 40,000 of 80,000 lbs. For the gears (2) which drives the auxiliary, we will assume a diameter of 84 inches, a face of 8 inches, and a pitch of 3.1416 inches, which will give us 84 teeth. The force transmitted Will be *; x 15.5 = 14,760 lbs. And the perip- heral speed will be 7 x 3.1416 x 14 = 308 ft-per min. Applying the formula we get a fiber strain of 5090 lbs. for gear (2), and for pinion (l) which drives gear (2) a fiber strain of 6785 lbs. 27. As these Strairis are higher than would be safe for cast iron, at a peripheral speed of 308 ft. per minute, we will make this pair of gears of steel also. And as gear (2) makes 14 RPM, , pinion (1) Willmake ++++ = 98 RPM., which is the speed for which we designed our fly-wheel. SHAFTII.G. The greatest strain upon the shafts carrying the knives is the combined bending and tortional strees due to the force exerted upon the gear (4) by the pinion ts). This is 40,000lbs. at the pitch line of gear (4). If 1 = the distance from the center of the gear to the center of the bearing, and r = the radius of the gear, then M, 5 = Pl, - 40,000 x 14 = 560,000 inch lbs. And 7 T = Pr, 40,000 x 13 = 720,000 inch lbs. And the combined strain is equivalent to that, which would be produced by a single twisting moment. Te , where Te = Mr Vºrº. (See Unwin, Page 215) On page 218. Unwin gives a table of shaft diameters figured for a stress of 9,000 lbs. per sq-in, for various values of T, and k, where k = #. 560.000 In this case k = ± = 0.77 From the table 720,000 we find that a shaft about 9.25 inches in diameter will be required. We will use a 9 inch shaft. The auxiliary shaft must sustain a combined tortional and bending stress due to the two forces of 40,000 lbs. each, at the pitch line of pinion (3). - 1.5 inches. - In this case + = r = 7.75 " P = 80,000 lbs. º And P’ = 47,000 lbs. (See stress diagram on Plate, 6.) Then T = Prº = 80,000 x 7.75 = 620,000 in-lbs. And M = P'1 = 47,000 x 15 = 705,000 " " M 705, QQQ *- T 620,000 1-13 From the table we find that the auxiliary shaft, will also have to be 9" in diameter. The fly-wheel shaft must carry the combined stresses of the bending moment M due to the weight of the fly-wheel, and the tortional stress T due to the load transmitted, which is the same as that transmitted by pinion (1) • H = 16,000 x 16 = 256,000. T = 14,760 x 6 = 88,560. - 256,000 And k 68,560 This calls for a 7 inch shaft. 2.89 ------- MOTOR PINION & GEAR. Taking the motor speed at 500 RPM. at friction load, it will require a 5 to i reduction to the fly-wheel shaft. A lot pinion on the motor will call for 50" gear on the ris-me- shaft. The peripheral speed will be * #444 #–822– 1309 feet per minute. With a pitch of 2.094 inches, we will have is teeth on the pinion ana's teeth on the gear. While it is not expected that these gears will take the shock of shearing the bloom, it is thought best to design them heavy enough for the task. The load transmitted will be ###2+* = 3540 lbs. 25 Assuming a face of 5", and applying our formula we get a fiber strain for the gear of 29.30 lbs, and for the pinion of 4510 lbs. While these fiber strains are rather high for a peripheral speed of 1309 ft-per minute, they are still safe for steel gears. BEARINGS, The bearings are all made large, so we need figure only one of them. We will take the worst case, that of the knife shaft bearing on the gear end, where there is a load equal to the resul- tant of three forces: the thrust of the knife due to the resistance of the bloom, the reaction due to the turning force of 40,000 lbs. upon the gear, and the reaction due to the tertional resistance of the bloom to the knife. The thrust of the bloom against the knife is carried equally upon each bearing and is equal to gºod = 30,000 lbs. The reaction due to the tortional resistance upon the knife is also divided equally between the bearings, and is equal to *222 = 20,000 lbs. And by taking moments about the center of the cutside bearing we have the reaction due to the turning force upon the gear equal to *** * * = 56,000 lbs. By constructing a stress diagram as shown, Plate, 6., we find the pressure on the bearings to be 70,000 lbs. The bearing is 18" long by 9" in diameter, and has a projected area of 162 sq. inches. The pressure pervsq.inch , then is, #º = 4:32 lbs. As the pressure is intermittant and the speed of rotation is slow, this is a safe pressure and babbitted bearings should give good service- The qaestion of the most suitable blade to use can only be settled by experience. It must not be so thin as to become red hot, while making a cut as it would wear away too rapidly- 31. The wear in any case will be great and also there will be considerable tendency to warp, as the knives must be water coolea continually during the operat- ion of the shear. so the design should be such that the worn blades may be easily removed and new ones put in place. The construction shown on Plate, 3., is only a suggestion, and may not be found the best in practice. It is probable that a so called "high speedt steel, that can be heated up to around 600 degrees . . , before its structure changes, will be found the most suitable material for the blades. 32 * H Y D R A J L I C S P T R A L. S. H. E. A. R. While electric power is largely used in steel mills, there are some machines which are perhaps better operated by hydraulic power. Among these are heavy shears and punches. The spiral shear shown in Plate, 7 is the result of an effort to design a hydraulic shear to work on the same principal as the rotary shear. As will be seen the cutting action is the same, the blades are mounted on levers which are tied together by a link. The ends of this link are connected to the cylinders as shown. As the plunger of the large cylinder moves out, the left hand knife moves up and the right hand knife moves down, the bloon is caught between the blades and the erreet is the same as in the rotary shear. When the stroke has been completed the blades are brought back to - their original position by the small cylinder. - The general arrangement of this shear may not be the best that could be devised, as the same result might have been obtained in a number of ways. The cylinders could be connected at any angle. The machine wauld have been shortened considerably by placing the cylinders in a vertical position, one at either side of the knives as could have been easily done. or the small cylinder could have been omitted if we had made the large cylinder aouble acting, but this would call for insiae pack- ing which is always a source of trouble. - In the arrangement as We hatre it. the Small cylinder need only be large enough to overcome the friction of the machine. But as the pressure will be on this cylinder all of the time, the water being forced back into the supply main during the cutting stroke, the large cylinder must be large enough to do the work of shearing the bloom and in addition to overcome the reletional resistance and the force exerted by the small cylinder . - The "bite" is the same, and the length of stroke is the same as that of the rotary shear, so the energy required to make the cut will be the same. We might figure then, as in the rotary shear, a force of 21175 lbs • acting thru a distance of 3.6 feet, for each knife, as the energy required to shear the bloom. But in this case we have no fly- wheel to carry us over the peak load so we must assign our cylinders for the maximum load, which we should expect to be as high as 30,000 lbs. at times. We need not, however design the other parts of the machine for a load greater than the cylinders can exert. If we construct a force polygon (see plate 6). making the assumption that the tangential force at the blades will be 30,000 lbs., we find that we have a thrust of 36,000 lbs. against the blade sharts. We shall not go into the design of the details of $his shear except to figure the diameters of the cylinders. In the worst case the tangential force of 30,000 lbs. will act at a distance of 48" from the center of rotation, while the force exerted by the cylinders is applied at a distance or se inches from the center. The force exerted by the cylinder 36 80,000 lbs. If we figure the customary 25% for for the shearing alone alone must be friction, we will have 26,670 lbs. as the force that the small cylinder must exert during the return stroke. And with a water pressure of 500 lbs • per sq. inch, which is about what is commonly maintained in steel mills, the plunger must have an area of # = 53,3 sq. inches, or approximately an - 8 inch plunger's The large cylinder must exert a pressure of 80,000 lbs. to shear the bloom, plus 26,670 lbs. to overcome the friction, plus 26,670 lbs. 35. to overcome the resistance of the small cylinder, or a total of about 134,000 lbs. The large plunger 134,228 5QC A diameter of 18 l/2 inches will give us an area of then, must have an area of = 268 sq. inches. 268 - 8 sq. inches. The stroke of the knife is 43 inches, and if allow one inch at each end for clearance, the stroke of the cylinder will be # * = 34 inches, or 2.833 feet, . As the pressure is on the small cyl- inder all of the time it will balance an equal area of the large cylinder during the cutting stroke, and the work done during the cutting stroke is the same as would be done by a plunger having an area equal to the difference between the areas of the two plungers. On the return stroke however, the small plunger does work against the friction of the machine • so the total work done in cutting one piece is equal to the area of the large plunger in sq - inches, times the pressure per sq. inch, times the length of the stroke in feet. This will be 268.8 x boo x 2.833 = 380,750 foot lbs. And if 6 cuts are made per minute, the power consumed will be *####–4 = 69.2 horse power. 36. This is more than twice the power consumed by the motor driven shear due to the con- dition that the full stroke must always be made, and the pressure is constant, throughout the stroke and is sufficient to overcome the maximum resistance. r 37, H Y D R A J L I C P L U N G E R S H E A. R. The drawing on Plate, 9 illustrates What might naturally be the first method considered in designing a shear for this purpose. No attempt has been made to develop the design further than is necessary to bring out, the difficulties encoun- tered, and enable us to make a comparison of this machine with the two machines previously discussed. The usual method of figuring the energy required to shear a bloom is to multiply the area of the bloom in sq. inches, by the shearing strength, and by the stroke in feet. Quoting from Machinery's Handbook, Page 290. ,- "A hot slab shear cuts slabs 4" by 15" at a shearing stress of 6000 lbs. per sa. INch. This gives a pressure between the knives of 4 x 15 x 6000 = 360,000 lbs. The total energy required is *#2 *-* = 120,000 ft-lbs." It, Wiil. be seen that if the slab is turned on edge, we will have the same pressure between the knives and a stroke of 1.5", so the energy required to shear the slab on edge will be ******* = 450,000 ft.lbs. And to shear a plate l" thick by 60" wide, which will have the same area, the energy required will 38. be ******* * 30,000 ft. lbs. This latter figure is evidently correct, or nearly so, but for a long stroke as in shearing a 4" by 15" slab on edge the result, obtained by this formula Beems doubtful. . For if the pressure between the knives is equal to the area of the slab times the shearing strength, it Will not be constant throughout the stroke, but will decrease as the area to be sheared decreases, being a maximum at the beginning of the 3troke and zero at the end of the stroke. Also in shearing a hot slab on edge it is doubtful if the pressure required is ever equal to the area times the shearing strength as the metal at the edges will give way before the remote portions at the center of the slab are effected at all. While it, is very probable that our results will be higher than they should be, we will figure the power required to shear the 12" bloom in this shear, by the usual method. The area of the bloom is 113.1 sq. inches. The shearing strength we have found to be 16, 100 lbs per sq.inch. The pressure between the knives will then be 16, 100 x liº. 1 = 1, 220,910 lbs. And the energy expended in shearing the bloom, if the stroke of each piston is 7" to allow one inch clearance between each 39. blade and the bloom when the blades are withdrawn, will be ******** = 2,124,500 Ft-Lbs. i.º - And the horsepower expended if & cuts are made per º 2, 124,500 x 6 — a - Tº * = 336 HP. Arld in thi 33000 336 HP. Arld in this minute, Will be - case we have not added the usual 25% for friction. 40. CONCLUSIONS. Each stroke of a hydraulic cylinder consumes a fixed amount of energy. This energy is the product of the stroke in feet, by the area of the piston in sq. inches, and the water pressure in pounds per sq- inch. So in the case of our shear this is constant regardless of the size or temper- ature of the bloom to be cut. The hydraulic plunger shear as we have designed it will consume 2,124,500 ft. lbs. of energy in making one complete stroke, and this whether it shears a bloom or whether it meets no *ēs; stance whatever. This figure is doubtless much too high as a much smaller cylinder would probably do the work. This is a subject, that should be inves- tigated further. We found, opage 35. , that the spiral shear would consume 360,750 ft.lbs. of energy at each stroke, and this when once established is constant for each stroke of the machine. With the motor driven shēafº we have a very different condition. The fly-wheel is to furnish the energy required to make the Gutt, and it will give up just the energy required to overcome the resistance met. On page 23. , we find that, 157,000 ft - lbs. of energy are required to make a cut, not including the energy consumed by friction, which is taken care of by the motor. This is the Worst, case, that is, it is for a 12 inch bloom and the last cut made when the shearing strength has been found to be l6, lºo lbs. per sq.inch. The first, cut, when the bloom has been out of the fur- nace not, more than one minute would require very much less energy. Also if a smaller bloom is out the energy consumed will be less • It will be seen that, the advantage lies largely with the motor driven shear. 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