US2425484A

US2425484A - Electrically driven rotary shear

Info

Publication number: US2425484A
Application number: US684856A
Authority: US
Inventors: Edmund S Murrah
Original assignee: Morgan Construction Co
Current assignee: Siemens Industry Inc
Priority date: 1946-07-19
Filing date: 1946-07-19
Publication date: 1947-08-12
Anticipated expiration: 1964-08-12

Description

1947. E. s. MURRAH 2.425,484

ELEGTRIGALLY DRIVEN ROTARY SHEAR Filed July 1.9, 19% I5 $heets--$heet 1 INVENTOR. Emz mm .8. MURRAH A TT'OWA/EY Aug. 12, 1947. E. s. MURRAH BLECTRICALLY DRIVEN ROTARY SHEAR Filed July 19; 1946 i4 dl 3 Shams-Sheet 2 (I? {LB (27 vv Tf 4 INVENTOR. EDMUND S. MURRAH 4" r ATTOR Y Aug. 12, 1947. E. s. MURRAH 2,425,434

ELECTRICALLY DRIVEN noun swam Filed July 19, 1946 3 Shuts-Sheet 3 k bb INVENTOR. S. MURRAH BAR SPEED BAR SPEED c 6 5 h L L Q m c w Y DB w w w N E 0 0 0 m n n n. w U U m m m m O V O 0 kbw E f E E 5 2 fm fim R R m m m A 5 E H E H H 5 H 5 5 6 E E. L L c m Y C C 5 yet i i ca e we an 2,i25,elil i E LE OTRMJAILLY DER/EN .ltQl'llAltlY SHEAR Edmund S. Mini-rah, Worcester, Mass, assignor to Morgan ilonsti'uction Company, Vlorcester, Mass, a corporation oi Massachusetts Application .July 19; 19%, Serial No. 68%,856

- (6i. add-43$) llll (Claims. i

This invention. relates to electrically driven rotary shears, and more particularly to sc -called flying shears adapted to sever longitudinally moving material into predetermined lengths.

For many years there has been a demand for an electrically driven rotary shear capable of cutting metal billets into accurate lengths as they issue at comparatively high speed from the final stand of the rolling mill, but the inherent diflicuL ties in this situation have heretofore prevented a satisfactory solution. The principal diihculty arises from the necessity for matching the speed of the shear knives with the speed of the billet at the time of the cut, while allowing sufficient range for adjustment in the length of the severed pieces. Unless these speeds are properly synchronized, the cut will not be made in a proper manner and the shear may be seriously damaged. Obviously, if a shear having say a nine foot shear circumference or knife circle operate at a uniform speed in synchronisrn with the billet and makes a cut at every revolution, the severed lengths will be nine feet long. Also if such a shear is arranged for rnis-cuts so that it cuts every two revolutions or every three revolutions, the severed lengths will be eighteen or twenty-seven feet long respectively. In other words, it is relatively simple to cut lengths which are equal to or multiples of the shear circumference. Ordinarily however the billet must be out into lengths which; are not so directly related to the size of the shear, and it therefore becomes necessary to provideacyclic variation in the speed of the shear, which presents a dlfilfiult problem because of the inertia of the moving parts. It has been proposed to effect this cyclic speed variation by various mechanical means, for example by rocking a differential gearing in the shear drive, but such constructions add to the inertia problems and are very bulky and expensive. It has also been proposed to vary the speed of the electric motor which drives the shear, in a cyclic manner, but no suitable and operative construction of this type has been disclosed heretofore. l 'urtheidiificulties arise from the fact that the speed of the billet is usually subject to considerable variation, and it therefore becomes necessary to maintain a proper cutting speed for the shear knives and a uniform length for the severed pieces despite such variation in billet speed.

It is accordingly one object of the invention to provide an electrically driven rotary shear which will cut rapidly moving stock into accurate lengths.

It is a :l'urther object or" the invention to provide an electrically driven rotary shear capable of cutting metal billets as they emerge at relatively high speeds from a rolling mill.

It is a further object of the invention to pro vide an electrically driven rotary shear which may be readily adjusted to vary the length or" the severed pieces while maintaining proper synchronisrn of the speed of the shear with the speed of the stock; as each cut is made.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention and in which like reference numerals indicate like parts,

Fig. l is a somewhat diagrammatic plan view of a rotary shear and a portion of an associated billet mill;

Fig. 2 is a section taken on the line 2-2 of Fig. 1;

Fig. 3 is an electrical wiring diagram showing one means for driving the shear and controlling the speed thereof;

Fig. 4 is a fragmentary view showing a m0dification in the diagram of Fig. 3;

Fig. 5 is a graph showing certain relationships of the shear speed to the shear revolutions, ob-

"tainable with the arrangement shown in Fig. 3;

Fig, 6 is a graph similar to Fig. 5, showing still further relationships;

Fig. 'l is a graph showing certain relationships of the shear speed to the shear revolutions, ob tainable with the arrangement shown in Fig. 4', and

Fig. 8 is a graph similar to Fig. 7, showing still further relationships.

Referring first to Figs. 1 and 2, there is provided a rotary shear id arranged to cut a hot metal billet B into predetermined lengths as it emerges from the finishing stand l l of a continuous billet mill and While a portion or the billet is still between the mill rolls l2. These rolls are driven by an electric motor it which is connected to the rolls by the usual mill pinions (not shown) located within a pinion hOllSll'lg l5, and the usual universal spindles it. The motor i l also drives a small pilot generator ll. A suitable roller table it? supports the billet between the mill stand 1 i and the shear iii. A flag lid is located in the path of the billet to control a normally open switch 2 l.

The rotary shear id may be of any suitable type, and for purposes of illustration I have shown a shear constructed in accordance with the disclosure of the patent to Morgan et al. No. 2,157,000, granted May 2, 1939. This shear cornprises a pair of opposed horizontal crank shafts 23 rotatably supported in a frame 24 and connected to one another by gears 25. These gears are arranged to be driven by four electric motors 21 which are connected to the gears by pinions 28. Each crank-shaft 23 carries a knife head having a knife 3| thereon, and each knife head has a rearwardly extending tail rod 32 with a roller 34 on its end, the roller being guided in a slot 35 in a stationary plate 36. At each revolution of the crank shafts, the knives 3|, will meet to sever the billet as it travels longitudinally between them. For purposes of control, as will be explained hereinafter, a limit switch mechanism 3! is connected to the upper crank shaft 23 to be driven thereby.

Referring now to Fig. 3, it will be seen that ill) the fields 39 of the shear motors 21 are connected across a suitable source 48 of constant voltage direct current, under the control of a main switch 4|. These motors are provided with the usual mechanical brakes which may be held in the released position by one or more solenoids 42. The armatures of the motors 21 are connected in a circuit with a direct current generator 43, this circuit including a normally open switch 44 under control of the coil 45 of a magnetic contactor. This coil also controls a normally open switch 46 which is connected in series with the solenoid 42 across the source 40. The generator 43 is driven by a motor 41 which is energized from a source 48 of alternating current. The field 50 of the generator 43 is energized by a direct current generator 5| forming a regulating exciter, which is driven by a motor 52, this motor being energized from a source 53 of alternating current. The exciter 5| is preferably of the well-known amplidyne type having, in addition to the usual anti-hunt field and load control fields (not shown), a control field 55 and a reference field 56. This provides a Ward Leonard or adjustable voltage control for the shear motors 21 so arranged that the speed of these motors will be a function of the voltage supplied by the generator 43, this voltage in turn being under the control of the regulating exciter 5|. The reference field 56 is more powerful than the control field 55, and these two fields oppose one another.

In order to control the voltage which is sup plied by the exciter 5i to the generator field 50, certain control apparatus is provided and will now be described. Thus the pilot generator H (which is driven by the mill motor l4 of Fig. 1) has two opposed

fields

58 and 59. The field 58 is connected in circuit with one winding of a transformer 60, the other winding of the transformer being connected across the terminals of the generator 43. There are also shown four

resistances

62, 63, 64 and 65, and a rectifier 66. A magnetic contactor is provided having a coil 68 controlling two normally open switches 69 and 10, and a normally closed switch H. A further magnetic contactor is provided having a coil 13 controlling six normally open switches l5, 16, ll, l8, l9 and 80. A further magnetic contactor is provided having a coil 82 controlling a normally closed switch 83 and two normally open switches 84 and 85. A still further magnetic contactor is provided having a coil 81 controlling a normally closed switch 88 and two normally

open switches

89 and 90. The limit switch mechanism 3'! includes three

switches

92, 93, and 94 which are controlled by three

rotatable cams

95, 96 and 9l respectively arranged to rotate once for each cycle or cut oi the shear l0. Thus ii the shear makes a cut at each revolution, as in the particular case illustrated, the cams will rotate at the same speed as the shear. If the shear is arranged to make niis-cuts and to cut say every two revolutions or every three revolutions, the cams should rotate at one-half or one third the speed of the shear, respectively.

The electrical connections for the various switches and other devices will now be described. The resistance 63 is connected in series across the terminals of the generator 43. The rectifier 66, the switch 15, the exciter control field 55, and the armature of the pilot generator I! are connected in a series circuit which in turn is connected across a portion of the resistance 63, The resistance 62 is connected across the switch 15. The switch 16 and the reference field 56 of the exciter 5| are connected in series across the source 40. The resistance 64, the'switch 89, and the field 59 of the pilot generator are connected in series across the source 40. This resistance 64 is provided with a slider I to form an adjustable rheostat, and the switch 69 is connected across a portion 01 the resistance by means of this slider. The resistance 65, the switch 88, and the field 59 of the pilot generator are connected in series across the source 49. The flag switch 2| and the coil 68 are connected in series across the source 40. The switch 10 and the coil 13 are connected in series across the source 45. The switch H, the switch 83, and the coil 13 are connected in series across the source 40. The switch 93 is connected in parallel with the switch 83. The switch 18 is connected in series with the coil 45 across the source 40. The switch 92 is connected in series with the coil 82 across the source 40. The switches H, 19, and 84, and the coil 82 are connected in series across the source 40. The

switches

80 and 85, and the coil 81 are connected in series across the source 40. The switches 9|] and 94 are connected in a series circuit which in turn is connected across the switch 85.

It will now be apparent that in the operation of this embodiment of the invention, the switch 4| will be closed, and the generator 43 and the exciter 5| will be driven at substantially constant speeds by their respective motors 4! and 52. The pilot generator l1 will be driven at a speed Which bears a definite ratio to the speed of the mill rolls l2 and of the billets B issuing therefrom. As the front end of a billet approaches the flag 2!]. the switch 44 will be in its open position, and the shear motors 21 will be stationary. The shear l0 will be stationary, with the crank shafts 23 approximately degrees from the cutting position, and the earns 95, 96 and 9'! positioned as shown in Fig. 3. As the front end of the bar engages the fiag 20, it will close the switch 2| and energize the coil 68 closing the switches 69 and 10, and opening the switch H. the coil 13 will be energized, thus closing the

switches

15, 1 6, ll, l8, l9 and 80. As the switches '15 and 16 close, the exciter fields 55 and 56 will be energized, so that the excitcr 5| will energize the field 50 of the generator 43. The closed switch 11 will provide a holding circuit for the coil 13. As the switch 18 closes, the coil 45 will be energized. thus closing the switches 42 and 44 and starting the shear motors 21, which will accelerate and bring the speed of the shear knives 3| into syn- ChlOnlSIl'l with the speed of the billet before the As the switch 10 closes,

knives have reached the cutting position. In the meantime, the front portion of the billet B will have reached a position between the knives, and as the knives come together they will cut a short crop from the front end of the billet.

The shear speed is held equal to the billet speed, during each cut, by the action of the regulating exciter 5| in conjunction with the pilot generator H. The excitation of the pilot generator field 59 is constant, and determined by the value of the resistance 65. The excitation of the reference field 5B is also constant, whereas that of the control field 55 varies with the speed of the pilot generator H and with the voltage output of the shear generator 43. Since the two fields 55 and 56 oppose one another, the latter being the greater, the voltage or output of the regulating exciter 5| is a function of the difference between the excitations ofthese fields. The voltage produced by the pilot generator I! and the voltage produced by the shear generator 43 act in opposition to one another incontrolling the excitation of the control field 55, and the regulating exciter 5! will vary the excitation of the shear generator 43 to 'maintain a balanced condition such that the shear speed is equal to the billet speed. Thus, if the billet speed should increase ever so little, the pilot generator l1 would provide a greater voltage, in opposition to the shear generator voltage, thus decreasing the excitation of the control field 55, and causing the regulating exciter to increase the excitation of the field 59, which will increase the voltage produced by the shear generator 43 and increase the speed of the shear motors 21. As the shear reaches billet speed, the voltage produced by the generator 43 will have increased just enough to establish a balanced condition. The function of the rectifier 66 is to block the flow of electricity in one direction, and. thereby prevent the control field 55 from being reversed, as might otherwise occur under certain conditions, The purpose of the resistance 62 is to permit a limited flow of current through the control field 55 even with the switch open. The transformer 80 operates only during periods of shear motor acceleration or deceleration, when the voltage applied to the transformer by the shear generator 43 is changing. At such times a current will be induced by the transformer to excite the pilot generator field 58 in such a direction as to oppose the rate of shear motor acceleration or deceleration, as the case may be and thereby prevent the control from over shooting. At other times, the field 58 Will remain unexcited.

At the completion of the cut, and preferably immediately after the shear knives have cleared the billet, the cam 95 will close the limit switch 92 momentarily, thereby energizing the coil 82,

thus opening the switch 83 and closing the switches 84 and 85. At the same time, cam 91 will close the limit switch 94. Closing the switch 85 will energize the coil 87, thus opening the switch 88 and closing the

switches

89 and 90, the latter completing a holding circuit for the coil 81. As the switch 88 opens and the switch 89 closes, the energization of the pilot generator held 59 will be placed under the control of the rheostat 64 rather than the resistance 65, and the shear motors 21 will decelerate or accelerate as the case may be) to an idling speed which may be either less than or greater than the cutting speed, depending upon the particula lengths which are to be cut from the billet. Thus if the severed lengths required are longer than the circumference of the shear circle, i. e., the orbit of the centers of the shear cranks, the idling speed must be less than the cutting speed. If the required lengths are less than the shear circle circumference, the idling speed must be greater than the cutting speed. The idling speed, and consequently the lengths of the severed pieces, may be controlled by adjusting the slider I00.

After the shear has operated at its idling speed for a time, and as the knives again approach. the billet, the cam 91 will open the limit switch 94 and de-energize the coil 8?, thereby closing the switch 88, and opening the

switches

89 and 90. This will again place the excitation of the pilot generator field 59 under the control of the resistance 65, and as a result the shear motors will promptly accelerate or decelerate (as the case may be) to synchronous cutting speed. This speed will be attained before the knives engage the billet, and the cut will accordingly be made in a proper manner.

Fig. 5 shows therelationship of the shear speed to the shear revolutions when cutting lengths which require a slowing down of the shear between cuts. As indicated, the shear will travel at bar speed during each cut, and as soon as the knives have cleared \the' bar the shear will slow down to an idling speed which is determined by the setting of the rheostat64. At a predetermined point in the revolution of the shear, it

'will start to accelerate to bar speed in time for Fig. 6 shows the relationship of the shear speed to the shear revolutions when cutting lengths which require a speeding up of the shear between cuts. In this case the shearrwill travel at bar speed during each cut, and as soon as the knives have cleared the bar the shear will accelerate to an idling speed which is determined by the When the shear.

setting of the, rheostat 64. reaches a predetermined position it will start to decelerate to bar speed in time for the next cut. The full lines, the dotted lines, and the dot-anddash lines indicate various idling speeds which may be employed to produce various lengths of severed pieces.

As the tail end of the bar leaves the flag 29, the switch 2| will open, de-energizing the coil 68, opening the switches 69 and I0, and closing the switch H. Opening the switch 69 will increase the eifective resistance of the rheostat 84 and thereby reduce the idling speedof the shear. The coil 13 will remain energized through the switches 11' and 93, despite the opening Of the switch 10. As the cam 95 closes the switch 92, and the cam 91 closes the switch 94, the coil 82 will be energized, opening the switch 83, and closing the switches 84 and 85. Closing the switch 85 will energize the coil 81, which will open the switch 88, and close the

switches

89 and 90. Closing the switch 89 will place the shear under the control of the resistance 64, which has already been increased an effective amount by the opening of the switch 68, and the shear will imme diately decelerate to a very low idling speed. The cam will open the switch 92 shortly after it was closed, but the coil 82 will remain energized through the closed switches l I, 19 and 84. As the shear cranks reach the position shown in the drawings, the cam 96 will open the switch 93 and thereby de-energize the coil 13, opening the i and B5.

accuses 7 switches l5, 16, "ll, "l8, "l9 and ill]. switch 19 will deenergire the coil 82, theie...- ,r clos ing the switches 83 and opening the switches B4 Opening the switch 80 will de-cnergize the coil 81, thereby closing the switch 88 and opening the

switches

89 and 90. Opening the switch (B will (lo-energize the coil 45 and open the switches 42 and 44, thus disconnecting the shear motors 21 from the generator 43 and deenergizing the brake solenoid 42. The mechanical brakes will thereupon bring the shear to an immediate stop.

With the Ward Leonard system and amplidyne control, as described, very rapid changes in shear motor speed are obtainable, and as a result the shear may be used for cutting billets at high speeds and it may be readily adjusted to cover a wide range of severed lengths. During deceleration of the shear motors, which occurs once for each cut, the speed reduction is effected by means of regenerative braking. In other words, when the voltage produced by the generator 43 is re duced, the shear will drive the motors 21, which will serve as generators, and they in turn will drive the generator 43, which will serve as a motor to drive the motor 41, the latter operating under these conditions as a generator to return electrical energy to the source 43. Such regenerative braking very effective in producing extremely rapid deceleration, and it results in a considerable saving in power consumption.

It will be noted that in the embodiment illustrated in Fig. 3 the switch 94, which initiates the speed change required to return the shear to bar speed in preparation for each cut, is controlled mechanically by the cam 91. Thus the required speed change always begins at a definite point in the rotation in the shear.

In Fig. 4 there is shown a slight modification in which the cam 91 is omitted, and the switch 94 is controlled by an electronic time delay relay H having a rheostat III which permits adjustment of the time delay. Operation of this relay is initiated by closure of a normally open switch l|2 controlled by the coil 81, the arrangement otherwise being the same as in Fig. 3.

In the operation of the modification shown in Fig. 4, the coil B! will be energized by the action of the cam 95 (as previously described in connection with the embodiment of Fig. 3) immediately after the knives have cleared the bar, thus closing the

switches

89, 90 and H2, and opening the switch 88. This Will cause the shear motors to decelcrate (or accelerate, as the case may be) toward the idling speed determined by the setting of the rheostat 64. Closing the switch H2 will place the relay H0 in operation, and after a predetermined delay (dependent upon the setting of the rheostat l l I) this relay will time out and open the switch 94, de energizing the coil 81. As in the Fig. 3 arrangement, this Will cause the shear motors to accelerate (or deceleratc as the case may be) to the cutting speed. Thus the opening of the switch 54, which initiates the speed change required to return the shear to bar speed in preparation for each cut, will take place at a predetermined time after the knives have cleared the bar and the cam 55 has closed the switch 92. By adjusting this time, tl'iroueh the medium of the rheostat ill, the length of the severed pieces may be controlled.

'7 illustrates diaerammatlcally the changes in sheer speed which take place when the Fig. 4 arrangement i used to cut lengths requiring a slowing down of the shear between cuts. As

ljlrlening; the

indicated by the full lines, the dotted lines, and the dot-and-dash lines, the shear will revolve at bar speed during eachcut, decelerate as soon as the knives clear the bar, and accelerate to bar speed at varying times dependent upon the adjustment 0f the time delay relay H0. If the lengths to be out are only slightly longer than the circumference of the shear circle, the acceleration may begin before the shear has reached its idling speed.

Fig. 8 similarly shows the speed changes which take place when the lengths to-be out are such as to require a speeding up of the shear between cuts. The lines indicate that the shear will accelerate promptly as the knives clear the bar, and decelerate to the bar speed before the next cut is made, the deceleration starting at varying times dependent upon the adjustment of the time delay relay III). In the case of lengths which are only slightly shorter than the shear circle circumference, the deceleration will start before the shear has reached its idling speed.

It will now be apparent that the invention provides an electrically driven rotary shear which is capable of cutting very rapidly moving stock into accurate lengths. In particular the invention makes it possible to cut metal billets as they emerge from a rolling mill and while a portion of the billet is still passing through the rolling mill. The arrangement is such that the cuts will be made accurately and in a proper manner despite variations in the delivery speed of the mill.

Having thus described my invention what I claim a new and desire to secure by Letters Patent is:

1. Shearing apparatus comprising a rotary flying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, means to accelerate the motor and to decelerate the motor once for each cutting cycle of the shear, and means effective during such deceleration to cause the motor to operate as an electric generator.

2. Shearing apparatus comprising a rotary flying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, means establishing a cutting speed for the motor corresponding to the speed of the material, means establishing an idling speed for the motor different from the cutting speed, means to change the motor speed from cutting speed to idling speed and vice versa once for each cutting cycle of the shear, one of the speed changes being a deceleration, and means effective during such deceleration to cause the motor to operate as an electric generator.

3. Shearing apparatus comprising a rotary flying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, mean establishing a cutting speed for the motor corresponding to the speed of the ma terial, means establishing an idling speed for the motor cliiierent from the cutting speed, means operating in timed relation with the shear and effective shortly after completion of each. cut to change the motor speed from cutting sp ed to idling speed, means effective before the next cut to change the motor speed to cutting speed, one of the speed changes being a deceleration, and means effective during such deceleration to cause the motor to operate an electric generator.

4. Shearing apparatus comprising a rotary flying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, a main electric generator connected in circuit with the motor and having a field, means to excite the generator field, and means to change the excitation of the generator field and thereby change the speed of the motor twice during each cutting cycle of the shear, one of the changes in excitation causing the generator voltage to be reduced so that the motor will operate as an electric generator and decelerate at a rapid rate.

5. Shearing apparatus comprising a rotary fiying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, a main electric generator connected in circuit with the motor and having a field, a regulating exciter connected incircuit with the genmeans to excite thecontrol field, and means to increase and decrease the excitation of the control field once during each cutting cycle of the shear and in timed relation to the rotation thereof, thereby producing a cyclic variation in the speed of the shear.

6. Shearing apparatus comprising a rotary fiying shear for cutting longitudinally traveling material, means for feeding material to the shear, an electric motor connected to the shear to drive the same, a main electric generator connected in circuit with the motor and having a field, a regulating exciter connected in circuit with the generator field, the exciter having a reference field and a control field, means providing a constant 35 excitation for the reference field, means to excite the control field, and means to increase and decrease the excitation of the control field once during each cutting cycle of the shear and in timed relation to the rotation thereof, thereby 40 producing a cyclic variation in the speed of the shear.

'7. Shearing apparatus comprisingamtary'fiyulating exciter connected in circuit with the generator field, the exciter having a control field.

a pilot generator having a field, means subjecting 1 the control field to a voltage which is a,,function of the voltage produced by the main generator and of the voltage produced by the pilot generator, means to drive the pilot generator at a speed bearing a definite ratio to the speed of the material, means to excite the pilot generator field, and means to increase and decrease the excitation of the pilot generator field once during each cuttingcycle of the shear and in timed relation to the rotation thereof, thereby producing acyclic variation in the speed of the shear.

9. Shearing apparatus comprising a rotary fiying shear for cutting longitudinally traveling metal bars, a rolling mill arranged to deliverbars to the shear and to control the speed of the bars, an electric -motor connected to the ferator field, the exciter having a control field, 2o shear to drive the same, a main electric gen-- erator connected in circuit with the motor and having a field, a regulating exciter connectedtincircuit with the generator field, the exciter having a control field, a pilot'generator having a; field, means subjecting the control field to a voltage which is a function of the voltage produced by the main generator and of, the voltage pro- 10. Shearing apparatus comprising a rotary fiying shear for cutting longitudinally traveling metal bars, a rolling mill arranged to deliver bars to the shear and to control the speed of the bars, an electric motor connected to the shear to drive the same, a main electric generator con- "nected in circuit with the motor and having a:

ing shear for cutting longitudinally traveling "ma terial, means for feeding material to the shear, an electric motor connected to the shear to drive the same, a main electric generator connected in circuit with the motor and having a field, a regulating exciter connected in circuit with the generator field, the exciter having a control field, a pilot generator connected in circuit with the control field, the pilot generator having a field, means to drive the pilot generator at a speed bearing a definite ratio to the speed of the material, means to excite the pilot generator field, and means to increase and decrease the excitation of the pilot generator field once during each cutting cycle of the shear and in timed relation to the rotation thereof, thereby producing a cyclic ffield, a regulating exciter connected in circuit with the generator field, the exciter having a control field, a pilot generator having arfield, means subjecting the control field to a voltage which is a function of the voltage produced by the main generator and of the voltage produced by the pilot generator, means to drive the pilot generator at a speed bearing a definite ratio to the speed of the rolling mill, means providing two excitation circuits for the pilot generator field, the first of the excitation circuits being such as to establish a cutting speed for the shear in synchronism with the speed of the bars and the second excitation circuit being such as to establish an idling speed for the shear different from the cutting speed, and means operable in timed relation with the rotation of the shear to render the first excitation circuit effective during each 'cut and to render the second excitation circuit efiective for a portion of the cycle between successive cuts.

EDMUND S. MURRAH.