Electric drive for reversing rolling mills

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  • To be Presented at the 33d Annual Convention of the American Institute of Electrical Engineers, Cleveland, O., June 27-30, 1916.

    Copyright 1916. By A. I. E. E. (Subject to final revision for the Transactions.)

    ELECTRIC DRIVE FOR REVERSING ROLLING MILLS

    BY W I L F R E D SYKES AND~DAVID HALL

    ABSTRACT OF PAPER The manner in which the electrically driven reversing rolling

    mill has been adopted especially within the last year, is surprising in view of the strongly entrenched position of the steam driven mill. Electric motors have been used for many years on mills running continuously in one direction, but many motor users have felt that the reversing mill could be better handled with the steam engine. There are naturally many characteristics little understood, due to the limited use in this country today.

    This paper answers some of the questions which are raised and describes the constructions that have been found desirable.

    ELECTRICALLY driven reversing mill has been the * subject of a number of papers* before the Institute in

    which the general scheme of operation has been described in detail. Since these papers were presented this type of mill has been considerably developed and a number of installations made. In addition, a great many new mills are being equipped, and within the next year there will be 15 reversing mills in operation in the United States. The great success that has been attained appears to warrant a review of this subject together with a discussion of some of the characteristics of this equipment.

    Since the first installations were made and mill engineers have been in a position to personally check the operation and economy of equipment, the steam engine for reversing mills has been comparatively neglected. As an indication of the position that the electrically driven mill has attained, the engineers of one of the large steel companies upon making investigation regarding the type of drive to install for new reversing mills, stated that the electric drive would undoubtedly in the very near future entirely supplant the reversing steam engine except

    Electrically Driven Reversing Mills, by Wilfred Sykes. A. I. E. E. TRANSACTIONS, 1911.

    Operation of a Large Electrically Driven Reversing Mill. By Wilfred Sykes, A. I. E. E. TRANSACTIONS, 1912.

    Electrification of a Reversing Rolling Mill of the Algoma Steel Co. By B. T. McCormick, A. I. E. E. TRANSACTIONS, 1912.

    Manuscript of this paper was received April 14, 1916. 739

  • 740 SYKES AND HALL: [June 27

    in perhaps certain peculiar cases. Practically all the new installations of reversing mills contemplated at present will be electrically driven. Although the electrically driven mill has not so far made the advance in this country that it has in Europe, it is characteristic of American practise to quickly adopt any device which has been demonstrated to suit the American conditions. The reversing mill as developed in this country and as shown by the existing successful installations, differs in many respects from European construction. Special attention has been given to the mechanical construction of the reversing motor and every care has been taken to insure that the machine will stand the much rougher handling which it receives in this country.

    As pointed out in one of the papers previously read before the Institute, the reversing plate-mill drive installed at the South Chicago plant of the Illinios Steel Co. was the second drive of this type to be put into operation in the world and it was designed without knowledge of the fact that a similar arrangement was being constructed in Europe. It was a number of years later before a reversing blooming mill was electrified.

    The first successful installation of a reversing blooming mill was that of the Steel Company of Canada at Hamilton, Ont. This installation consists of a double reversing motor capable of developing about 10,000 h.p. maximum, and is supplied with power from a flywheel motor-generator set with two generators. The complete electrical installation is shown in Fig. 1. This mill has been in operation for over three years with very satisfactory results. It is at present working at a rate very considerably in excess of the capacity specified when it was installed. The following are particulars of the mill and driving equipment.

    Size of ingot 15 by 17 in. Weight 4000 lb. Finished material 4 by 4 in. Elongation 16 " Number of passes 19 Capacity, tons per hour 60 Roll diameter 30 in. Pinion diameter 34 in. Speed, full motor field 70 rev. per min. Speed, weakened motor field 100 rev. per min. Driven from motor direct Number of motors 2 Voltage across each a rmature 600 Maximum operating torque 900,000 ft-lb'. Maximum motor horse power 10,000 Number of generators 2 Ra ted power of driving motor of set 1800 h .p . Weight of flywheel 100,000 lb. Speed of flywheel set 500 rev. per min.

  • PLATE XIV. A. !. E. E.

    VOL. XXXV, NO. 6

    Y...

    ISYKESJ F I G . 1 G E N E R A L V I E W OF F L Y W H E E L M O T O R G E N E R A T O R AND

    R E V E R S I N G M O T O R INSTALLED AT THE P L A N T OF THE S T E E L COMPANY OF CANADA.

    LSYKES]

    F I G . 2 R E V E R S I N G M O T O R B U I L T FOR B E T H L E H E M S T E E L COMPANY ASSEMBLED IN S H O P .

  • 1916] BLECTRICALLY DRIVEN REVERSING MILL 741

    The largest installation at present in operation is that of the Bethlehem Steel Co. which drives the 35-in. blooming mill at the Lehigh Plant. Fig. 2 shows the motors as assembled in the shop before shipment. Both of the above mentioned installa-

    FIG. 3SCHEMATIC DIAGRAM OF CONNECTIONS OF LARGE REVERSING MILL DRIVE

    OCB oil circuit breaker with no-voltage and overload trip SR automatic liquid slip regulator A CM alternating-current wound rotor induction motor DCG direct-current separately excited generators DC M direct-current separately excited roll motors CB circuit breakers1 generator field2 main circuit R relay for operating circuit breaker in generator fields FC field controller F flywheel SE shunt exciter for generator and roll motor fields SeE roll motor exciter the field of which is separately excited by the main d-c. circuit S AC Malternating current squirrel cage induction motor V voltmeter A ammeter W wattmeter

    tions have double motors due to the amount of power required. The machines are arranged as shown by diagram, Fig. 3. A somewhat similar drive is installed at the plant of the Central Steel Co., Massillon, O., but a single motor is used for driving the mill, the capacity of the motor being approximately 8000 h.p.

  • 742 SYKES AND HALL: [June 27

    This motor is shown in Fig. 4, which illustrates the machine as installed for driving the mill. Characteristics of these mills are as follows:

    Bethlehem Central Steel Co. Steel Co.

    Size of ingot 19 by 23 in. 18 by 20 in. Weight 10,000 lb. 5,000 lb. Finished material 4 by 4 in. up 4 by 4 in. up Elongation 10-12 av. Up to 20 Number of passes 17-21 19-21 Capacity, tons per hour 100 60 Roll diameter 30 in. 30 in. Pinion diameter 35 in. 34 in. Speed, full motor field 40 50 Speed, weakened motor field... 120 120 Driven from motor direct direct Number of motors 2 1 Voltage across each armature . . . . 600 700 Maximum operating torque 1,550,000 ft-lb. 750,000 ft-lb. Maximum motor horse power. . . 12,000 8,000 Number of generators 2 1 Rated power of driving motor

    of set 2,000 kw. 1,500 kw. Weight of flywheel 100,000 lb. 60,000 lb. Speed of flywheel set 375 rev. per min. 375 rev. per min.

    In the recent installations the reversing motor is arranged to have the characteristics of a compound machine. This is obtained indirectly through a series exciter. The current to be handled in the main circuit may be as high as 10,000 amperes, and it is obvious that it would be extremely difficult to reverse the series field each time the motor is reversed, which would be necessary to keep both fields in the same direction. A series exciter is therefore used, the voltage of wjiich is proportional to the current flowing in the main circuit. The armature circuit of the series machine supplies a separate winding of the field of the motor which may be readily reversed when the direction of rotation current is changed. The switches for reversing this field are operated from the same point on the master switch that reverses the field of the generator. The use of a motor with compound characteristics makes the operation of the mill a good deal easier on the mechanical equipment as the drive has more or less "give" to it. At the same time if there is an extreme load due to excessive draft or cold steel, the motor characteristics tend to compensate by automatically increasing the torque available and decreasing the speed.

    Although the electrically-driven reversing mill has been practically adopted universally for all new installations there is still some misapprehension as to its operating characteristics.

  • PLATE XV. A. I. E. E.

    VOL. XXXV, NO. 6

    1

    1

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    Is..

    [SYKES]

    F I G . 4 R E V E R S I N G M O T O R D R I V I N G BLOOMING M I L L OF C E N T R A L S T E E L COMPANY

    [SYKES] F I G . 12COMPENSATING AND COMMUTATING P O L E W I N D I N G S AS U S E D

    IN R E V E R S I N G M I L L M O T O R S

  • 1916] ELECTRICALLY DRIVEN REVERSING MILL 743

    It is of course natural that engine builders will fight the development of the electric reversing mill drive as much as possible and the following advantages have been claimed by one of the prominent engine builders:

    1 First Cost. The first cost of the reversing engine is only a small fraction of the aggregate cost of an electric dri