US3111046A

US3111046A - Automatic control system for continuous strip mill

Info

Publication number: US3111046A
Application number: US714782A
Authority: US
Inventors: George S Koss; Louis E Ringger
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1958-02-12
Filing date: 1958-02-12
Publication date: 1963-11-19
Anticipated expiration: 1980-11-19
Also published as: GB898613A; LU36874A1; DE126492C; NL103664C; FR1222878A; DE1126492B

Description

Filed Feb. 12. 1958 G. S. KOSS ET Al.

AUTOMATIC CONTROL SYSTEM FOR CONTINUOUS STRIP MILL 4 Sheets-Sheet 1 Mixer 28 u 34 D/scr/mma/or 3, Screw-fizz- Z conlm/ Con/ra/ /5 I Initiation X Ray Gage a ;7 I6 20 I9 fi a7 Amplifier 'f"? -7b/erance Dewar/an 5 Ampllfler Limits Posifian 5 /3 1 /7" 38 Magnetic Amplifier I 33 I b IQ} 35 /7 I 32 Q V INVE/VTORS 37 GEORGE s. K085 and A It orney Nov. 19, 1963 V G. s. KOSS ETAL 3,111,045

AUTOMATIC CONTROL SYSTEM FOR CONTINUOUS STRIP MILL Filed Feb. 12, 1958 4 Sheets-Sheet 2 her. 1

Mixer Mixer 8 r28 6 x28 TD/sor/minotor "Discr/m/notar Am lit/er Am lit/er Screw down Screw down CON/fol Control Control Control r29 4 /n/'t/ot/'on Initiation /4 ii I .4 mp/if/er Rotating ,o/l'f/ Magnet/c mp/I'f Magnet/c m/ VE/V TORS a GEORGE s. K085 and 37 LOU/S E. R/IVGGER Attorney Nov. 19, 1963 Filed Feb. 12, 1958 G. 5. KOSS ET AL AUTOMATIC CONTROL SYSTEM FOR CONTINUOUS STRIP MILL 4 Sheets-Sheet 3 Mixer M lxor 6 2s & F- Disoriminator Discriminator l5 /5 l l mp/ifier Amplifier .Screwdown 5 /z9 Screw-down 5 Control con/m/ Control control Initiation Initiation I3 3 l3 l8 1 g 5 7 a Rotating Rotating Amplifier Amplifier Magnetic Magnet/o Amplifier Amp l/ f/ or IN VE N TORS GEORGE S. K085 and LOU/S E. R/NG'GER Attorney Nov. 19, 1963 AUTOMATIC CONTROL SYSTEM FOR CONTINUOUS STRIP MILL Filed Feb. 12, 1958 G. S. KOSS ETAL 4 Sheets-Sheet 4 Amplifier 42-' M/xer T 5 /28 30 'Discriminator Am fie w Screw down 5 r Control Control I Initiation 30 l+ amp. I 25 I3 Gage -39 /25 I2. -0 o .J

l3 22 Rotating Amplifier B E T 0' a 260 I 7/6 Magnetic f Amp I Amplifier 7 l 26 & Amplifier l/V VE' N T 0R5 1- GEORGE .5. K085 and LOU/5 E. Rl/VGGER A ttarney reheating furnaces (not shown). As the bar 21 enters stand 1, the rolling pressure thereby developed is applied to load cells 2?, under the bearing chocks of the bottom backing roll ill. These cells may be of any suitable type but preferably embody magnetic stress gages such as incorporated in the Pressductor load cells made by ASEA. The load cells apply to an amplifier a voltage signal proportional to the pressure exerted by rolls if and ill. This pressure is proportional to the reduction in the thickness of the strip bar effected in stand It, or, more properly, to the thickness of the entering bar since the thickness of the strip leaving stand 1 does not vary much. Amplifier 23 is of conventional character and may be a vacuumtube amplifier or a transistor amplifier. The output of amplifier 23 is applied to a means for establishing a pressure-reference voltage, such as a motor-operated, selfbalancing, bridge-type potentiometer 2d. The potentiometer normally is connected by a back contact 25a of a relay 25 so as to be operated to a setting corresponding to the thickness of the leading end of strip bar El as it leaves stand 1.

At a predetermined time after the entry of the bar into stand 1 and preferably after the bar has entered stand 2, relay 25 is energized to open its back contacts 25:! and 250 and close its front contact This changes the circuit 7 connection of device 24 so that thereafter the reference voltage previously established thereby will be opposed to the voltage from amplifier 23, developed by load cells 22. Relay .25 may be a motor-current relay, a pressure relay, or a hot-metal detector relay. That is, it may be of a conventional type responsive either to the increased current drawn by the motor driving stand 1, to the increase in the pressure on the rolls of stand it or to the energy radiated by bar 21. Thus, after operation of relay Z5, if any change occurs in the thickness of the bar from that of the leading end thereof, an error signal will be given which is opposed by the previously established reference voltage. The algebraic sum of the opposing voltages is applied to an amplifier 26, of the vacuum-tube or transistor type, the output of which is conducted through circuit 26a. into the automatic control of the screw-down motor 3 of stand 2. This circuit introduces the error signal into device 28 of stand 2 to adjust the screws 12 thereof in a manner to be explained shortly. We also apply the error signal to control the speeds of the motors 13 of stands 1 and 2 by introducing the error signal from amplifier 26 through circuits 26b and 260 to the magnetic amplifiers 17 of stands 1 and 2. This varies the speeds of stands 1 and 2. to maintain the proper tension on the material therebetween in accordance with the adjustment of the screws of stand 2.

The screw-down controller 15 of each stand is under the control of a device 27, such as a potentiometer, which may be adjusted manually or preset by punched-card apparatus, and develops a voltage proportional to the desired screw setting. This voltage is applied to a mixer and discriminator 2d, the output of which is applied to an amplifier 29. The output of amplifier 29 operates a reversing controller 15 for screw motor 14. Devices 2")", 23 and 29 preferably embody General Electric Companys numerical positioning control, modified to suit the requirements of screwdown operation which includes the necessary arrangements for a Selsyn generator 30. The resulting adjustment of the screws by operation of motor M is reflected by generator Till, the output of which is applied through circuit Stun to mixer 22; in opposition to the voltage from the potentiometer 27. Amplifier 26 thus exerts a control over amplifier 29 by virtue of circuit 26a extending to mixer 28. By means of an added manual adjustment in amplifier 2s, e.g., an additional potentiometer the increment of screw adjustment per volt of error signal may be varied. We thus adjust the amount of correction for thickness variation so as to obtain either a uniform or decreasing thickness of the bar as it emerges 1,3, from stand 2. This permits compensation for the tendency of a strip bar to increase in thickness toward the trailing cnd because of the aforementioned temperature effect.

The speed of one of the intermediate stands of the mill, 3 for example, is used as an anchor or reference value, i.e., the speed regulator of its motor is left unchanged, so that the motor speed is affected only to maintain that for which the regulator was originally set manually. Gnce set, the regulator remains unchanged and is not automatically adjusted in response to any of the variable functions attributable to the strip bar being rolled. With the automatic control already described, the rolling of the strip bar proceeds in

stands

1, 2 and 3. As the bar enters stand 4, load cells 31 responsive to the rolling pressure thereby developed, apply a voltage to an amplifier 32. The cells are similar to those shown at 22 and amplifier 32 similar to that shown at 23. The output of ampniler 32 is applied by cricuits 32a and 32b to a selfbalancing, bridgedype potentiometer 33 which operates to establish a reference voltage proportional to the rolling pressure initially developed in stand and, therefore, to the thickness of the leading end of the bar as it leaves stand 4.

After the leading end of the bar has passed through stand 6, a relay 34 operates to change the connections of potentiometer 33 by opening back contact 34:; and closing contact 341;, so that thereafter its voltage is opposed to that of amplifier 32 and the difference or error signal is applied to amplifiers 35', one for each of

stands

4, 5 and 6 over a circuit 35a, Relay 34 is similar to that shown at 25. Each of these amplifiers incorporates an additional potentiometer 351') which will vary the output in accordance with the desired amount of speed change for stands 4, S and 6. The output of each amplifier 35 is applied by a circuit 35c to the speed-regulator of the motor of one stand through amplifier 1'7. By this arrangement, if the portion of the strip bar in stand 4 at any instant is thicker than the leading end of the bar on which the pressure reference was initially established, it will effect an increase in the speed of any one or all of stands 4-, 5 and o depending on the ratio adjustment of potentiometer 35b. If any point along the strip bar is thinner than the leading end, no reduction of tension between stands below that established by the leading end will be elfected. Our regulating system applies only the necessary speed-increasing adjustment to the related control field of magnetic amplifier 17, in the case of excessive strip thickness.

The progressive increase of tension between the last several stands will tend to result in the delivery of strip of uniform thickness out of the last stand. Actually, the thickness correction is efiected in the stand where roll pressure is measured, and the increase in the speeds of subsequent stands is necessary as a consequence, in order to maintain the tension on the strip as it travels through these later stands. We provide means whereby a further increment of mill speed may be introduced to prevent an increase in thickness from growing back in the bar as the rolling continues, due to the temperature effect. For this purpose, an X-ray gage 36 of known construction measures the thickness of the strip emerging from stand 6. The output of the gage drives a positioning device 37, preferably a Selsyn transmitter, which operates an additional potentiometer in device 35 preferably by action of a Selsyn receiver, effective over circuits 37a and 37b, to effect an increase or decrease in the error signal in amplifier 35. Thus, if the thickness of the finished product is excessive, the positioning device 37 will increase the gain of amplifiers 35 causing a further adjustment in the speeds of the motors driving stands 4, 5 and 6 to further increase the tension on the strip therebet-ween.

Thickness gage 36 also applies a voltage to a thickness deviation Selsyn transmitter 38, such as the standard equipment furnished for General Electric Companys X-ray thickness gages, equipped with adjustable tolerance limits. If the thickness of the strip as measured by gage 36 is outside the limits for which device 38 is adjusted, the latter applies a correcting voltage through a front contact 34c of relay 34, to all or some of the screw-down positioning controls 29 through

circuits

38a and 38b connected to the mixer and discriminator 28 of each, so that the thickness of the strip rolled will be brought within the desired range by repositioning of the screws of any or all stands as necessary. This has the result of further adjusting the settings of the rolls of the several stands to compensate for relatively slow change in mill conditions such as temperature of the housings and rolls or wear of the rolls. Normally open contact 340 of relay 34 prevents screw movements due to action of device 38 when there is no strip in the mill.

The first bar of a particular series to be rolled, furnishes a temperature-reference voltage through a temperature gage 39 by closing of the reference-establishing switch 44, such as a flag switch or manually operated switch. Temperature gage 39 preferably embodies a Leeds and Northrup Company Rayotube device which produces an output voltage proportional to measured temperature of the first bar cause a decrease in the roll setbalancing, bridge type potentiometer 40 similar to 24, for comparison with the temperatures of strip bars subsequently to be rolled. After the trailing end of the first bar emerges from stand 1 and before the next bar enters stand 1, a relay 41 operates. This relay, similar to relay 25, closes its contact in response to a reduction in the load current drawn by the motor 18 driving stand 1, to a reduction in the pressure exerted by the rolls or to the termination of radiant energy from the hot bar. Closing of the contact of relay 41, with the closing of contact 25c of relay 25, changes the connections of potentiometer 40 so that the voltages proportional to the temperatures of subsequent strip bars, as developed by gage 39, will be opposed to the reference voltage established on the potentiometer, and the algebraic sum thereof applied to an amplifier 42. The output of amplifier 42 also affects the setting of the mill screws of any or all the stands by modifying the input through mixers and discriminators 2-3. Temperatures lower than the established reference temperature of the first bar cause a decrease in the roll setting, and a temperature higher than the one established by the first bar will result in an increase of the roll setting. The change in the roll setting of stand 1 is performed immediately after the trailing end of the preceding bar leaves stand 1 by operation of relay 25. Similarly, the change in each of the other stands is performed immediately after the trailing end of the preceding bar has left the stand by operation of relays (not shown) similar to relay 25.

Switch 44 is adapted to be manually closed when the operator desires to establish or check temperature reference. When a slab approaches stand 1, relay 41 is energized, but a signal to amplifier 42 is not permitted until the preceding slab has cleared stand 1 or 2 and relay 25 is deenergized, at which time a screw change signal is transmitted depending on the voltage differential of potentiometer 40 and device 39. To complete connections between

devices

39, 49 and 42, relay 41 must be energized with its front contact closed and permissive relay 25 deenergized with its contact closed.

The system described above provides for thickness control by increasing the tension on the strip between the last several stands of the mill. As a modification, we may similarly effect the desired control by decreasing the speeds of the motors driving the first several stands, thereby increasing the tension on the material between these stands. For example, a signal from potentiometer 24 would be applied to

amplifiers

25 and 35" to reduce the speeds of

stands

1, 2 and 3 in a similar manner.

Instead of installing load cells 31 on stand 4, we may install similar cells 31' on stand 5 and utilize the rolling pressure in this stand to control the speed of stands 5 and 6. A switch 43 permits either stand 4 or stand 5 to be selected as the source of the control signal.

Although we have disclosed herein the preferred embodiment of our invention, we intend to cover as well any change or other modification therein which may be made without departing from the spirit and scope of the invention.

We claim:

1. The combination with a multi-stand continuous strip mill, of means responsive to the thickness of the partially reduced strip entering the rolls of the first stand, means controlled by said thickness-responsive means for reducing the spacing between the rolls of the second stand on an increase in the thickness of the strip entering the first stand and increasing the spacing between rolls on a decrease in the thickness of the strip entering the first stand, means controlled by said thickness-responsive means to establish a reference voltage and means actuated by passage of the leading end of the strip through the second stand for connecting said thickness-responsive means in opposition to said reference voltag 2. The combination with a multi-stand continuous strip mill, of means responsive to the temperature of a hot stripbar as it is advanced toward the first stand of the mill, means controlled by said temperature-responsive means for reducing the spacing between the rolls of a plurality of the stands when said temperature is below a predetermined value and for increasing the spacing between the rolls of a plurality of stands when said temperature is above a predetermined value, means also controlled by said temperature-responsive means to establish a reference voltage and means actuated by passage of the trailing end of the bar through the first stand of the mill for connecting said temperature-responsive means in opposition to said reference voltage.

3. The combination with a multi-stand continuous strip mill, of means responsive to the thickness of partially reduced strip entering the rolls of one stand of the mill and means controlled by said thickness-responsive means for increasing the speed of a subsequent one of said stands on an increase in said thickness to control the tension on the strip between two adjacent stands, said thicknessresponsive means including means to establish a reference voltage corresponding to said thickness and means actuated by progress of the strip beyond said one stand for connecting said thickness-responsive means in opposition to said reference voltage.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Automation, March 1956, pages 5257. Rolling Slabs into Strip Steel (C. A. Vossberg), Control Engineering, September 1956, pages 116 and 117.

Claims

1. THE COMBINATION WITH A MULTI-STAND CONTINUOUS STRIP MILL, OF MEANS RESPONSIVE TO THE THICKNESS OF THE PARTIALLY REDUCED STRIP ENTERING THE ROLLS OF THE FIRST STAND, MEANS CONTROLLED BY SAID THICKNESS-RESPONSIVE MEANS FOR REDUCING THE SPACING BETWEEN THE ROLLS OF THE SECOND STAND ON AN INCREASE IN THE THICKNESS OF THE STRIP ENTERING THE FIRST STAND AND INCREASING THE SPACING BETWEEN ROLLS ON A DECREASE IN THE THICKNESS OF THE STRIP ENTERING THE FIRST STAND, MEANS CONTROLLED BY SAID THICKNESS-RESPONSIVE MEANS TO ESTABLISH A REFERENCE VOLTAGE AND MEANS ACTUATED BY PASSAGE OF THE LEADING END OF THE STRIP THROUGH THE SECOND STAND FOR CONNECTING SAID THICKNESS-RESPONSIVE MEANS IN OPPOSITION TO SAID REFERENCE VOLTAGE.