- Email: [email protected]
Automatic screwdown system for blooming-slabbing mills with diversified programmes
Automatic Screwdown System for Blooming-slabbing Mills with Diversified Programmes M. FOUASSIN The system works with a combination of one synchrotransformer (selsyn) connected to tapped transformers in order to produce error voltages, zero of which corresponds to a definite selsyn angular position. The tapped transformers are grouped in multiphase simulating transformers connected to a synchro, as shown in Figure 1; the vector diagram is given in Figure 2.
In 1952, a programme controlled screwdown was put into operation on the blooming slabbing of the OugnSe-Marihaye Steel Works in Belgium. The aim of this paper is to describe the digital-analogue system which was designed to solve the electrical problem and To phase discriminator Simulating transformer
o
1
2
3
"
?
':'
:
5
6
7
9
9 I
la
9,
9
10
9
9
I
0
Vector diagram ofa sirrulating transformer
I
2 (a)
Secondary .windings
3
7
IT
ill 5 Cores
I
(2)
Synchro transformer
Prndimary WI
Ings
Synchro· transformer
O I
m
Vernier transformer
'" nov
Synchro stator three phases
][ (b)
Synchro rotor with additio!,)al cross winding
Figure 1
Figure 2
further to describe the many changes found necessary in the programming device to ultimately obtain the operators' agreement that the equipment was operating successfully. Basic Circuit To understand the scheme of the digital-analogue servomechanism a simplified system is described below.
This system gives 10 true zeros per turn of the synchro, when the synchro exciting winding is connected to an alternative voltage and the error voltage is measured between the neutral point and one of the taps numbered 0 to 9. These true zero voltages are separated by angular positions of 36°. Since finer increments are reqUired, these are provided by
446
1959
AUTOMATIC SCREW DOWN SYSTEM FOR BLooMING-SLABBING MILLS WITH DIVERSIFIED PROGRAMMES
adding a cross winding on the synchrorotor and by exciting it through an alternating voltage in or out of phase with the main winding. Ten different voltages are available on the tapped vernier transformer. By the combination of the main field and the cross field, these 10 voltages provide 10 different resultant fields, the directions of which are rotated by increments of 3·6°. When combining one connection on the simulating transformer and one on the vernier transformer, it is possible to
voltage of the vernier transformer to the cross winding of a synchrotransformer. As a matter of fact in 5 years of operation we have encountered no troubles in the relay system. The rest of the equipment consists of three phase-discriminators (one for each channel), an amplitude discriminator to take the correct signal successively from coarse to medium and fine channels, an electronic amplifier and a 300 W amplidyne. The amplified error signal is fed into the pattern field of the
GB Analogic to digItal comparator
M~mory for routine
programmes
S Positioning selsyn PS Power selsyn RA Rotary amplifier G S/D GB T I P
Generator Screw down Gear box Tachometer Motor load transducer
I
I I I I I I _______________ ___ J ~
I
I
I 1
...L..
Strain gauge
Figure 3
obtain any of the 100 error voltages available on one turn of the servosynchro. This system is the basic circuit of the digital-analogue screwdown device which in fact uses 3 channels to cover the required range of 1,650 mm which is the lift of our blooming-slabbing mill. These three channels each have their synchrotransformer and simulating transformer. The synchros, which give a feedback of the roll positions, are geared to the ratio of 1 : IS. The coarse channel has seven 225 mm increments for about half a turn. The medium channel has fifteen IS mm increments per turn and the fine channel has fifteen I mm increments per turn. Relays are used to form a combination of three digits. Every relay connects one of the 15 taps of the simulating transformer of a given channel and at the same time the corresponding tap of the vernier transformer of the next coarse channel. There are 8 relays for the coarse channel, IS relays for the medium channel and IS relays for the fine channel. Only three of them are energized at a time to form one of the 1,650 combinations. Contact loads are insignificant since the coarse contact connects the simulating transformer to the grid of the electronic discriminator and the vernier contact connects a tap of a low
'Rototrol' of a conventional Westinghouse Control System. The d.c. screwdown drive motor is powered from an MG set, the voltage of which is adjusted as a function of the amplifier error signal. The change from 'automatic' to 'manual' control is made by disconnecting the pattern field from previous amplidyne to the system of resistors and relays controlled by the operators' manipulator of the manual control. To the credit of such a system we have to mention that the voltages supplied by the simulating transformer are in the range of 100 V maximum, and even in the case of small error angles, error voltages are still significant in comparison to noise discriminators and amplifiers. We believe it is the main advantage of such a system in comparison with the conventional potentiometer servo system which has the disadvantages of: (a) using very small error signals in the range of a few millimetre displacements and (b) the use of sliding contacts. The accuracy is better than J!-(j mm, but it could not be used to its full capacity for two reasons: (1) the accuracy required by the roller was ± 1 mm for the last passes and ±2 mm for the other passes; and (2) the time allowed for the setting of the next pass did not permit a slow-down to such a speed at which this high accuracy is obtained.
447
1960
M. FOUASSIN
Programming Device
Two programming devices have been tried on this installation. Punched card system
The first one was a system of punched cards. A combination of static matrices uses 24 holes to energize a choice of three relays out of 37. As the card has 80 rows of 12 possible holes, this provides the possibility of a 40 pass programme. This system failed to work because of the diversification of the programmes. Due to the lack of heating capacity of the pit furnaces, and since intermixed hot and cold ingots do not reach the correct temperature in the desired order, it was difficult to follow a determined programme. Thus the operator had to sort out a bundle of cards for the one corresponding to the incoming ingot. This was a serious drawback to the method since it caused an intolerable loss of time to the mill operator. Furthermore, some ingots had to be rolled in other final sizes accor~ing to the analysis of the steel and changes occurred at the last moment so that the previous punched card had to be discarded and replaced. For routine schedule, though the same card could theoretically be used all over again, experience has proved that a hard-paper card does not stand much manipulation without being damaged or having at least its corners broken. Punched steel sheets have also been tried without much success: they also need to be handled carefully. We consider that a punched card programmer is only suitable in big steel plants with repeated routine programmes and when ingots are supplied with sufficient regularity. Uniselector programmer
Considering the punched card system a failure, we turned to uniselectors as a memory device for a pass programme. As one definite position is provided by energizing three relays, one pass is then included in a row of three horizontal contacts of a uniselector and a programme of 25 passes may be stored in 25 rows, that is, in three complete banks of contacts of a 25-step uniselector. The common uniselectors found on the market having generally 25 steps and six banks, two programmes can be stored in one of them. With a commutator the mill operator selects the programme required for the incoming ingot and by pushing the pass advance button sets the roll distance for the first pass. The following passes are obtained by successively pushing the pass advance buttons. This gives an impulse to the uniselector and the brushes scan successively all the taps thus energizing the relays of the digital-analogue servo system. The reliability of such devices is high. Manufacturers guarantee more than 40,000,000 steps as a life-time. A simple calculation shows that at the rate of 30 ingots an hour, an ingot being rolled in 15 passes, and 7,000 hours of operation per year, one uniselector can last about 13 years. Since there are many uniselectors to compose the different mill programmes this duration should be multiplied accordingly. This gave a suitable solution for the routine programmes and the system has been kept in operation on this basis up to the present. Our experience with uniselectors has proved that this device is entirely reliable. As a matter of fact the uniselectors have been in operation under severe conditions. The cabinet placed in the operator's control room was, on account of the heat losses of tubes and rotating amplifiers, brought to a temperature of about 50° Celsius, but as this temperature was detrimental to the equipment, the cabinet was left with the door constantly
open with the result that the whole uniselector unit was covered with a layer of dust. In spite of this no trouble has been encountered up to now with this delicate equipment the contacts of which are self-cleaning. It is preferable to protect the equipment against dust and to provide for maintenance of a reasonable temperature. The uniselector programmer though only used on half of the total tonnage rolled in the mill has shown immediately all the advantages of a pre-set screwdown system, that is, speed and precision of rolling, less fatigue of the operator and, an unexpected result, reduction in the wear of the groove shoulders of the rolls, which paid in a very short time for the whole installation. As a matter of fact the bloom before turned from 90 degrees every two passes is rolled with precision to the exact size of the groove, whereas in a manual setting of the rolls this thickness is inaccurate and causes the bloom to be squeezed in the groove, causing the wear of the shoulders. This installation, as it is planned, is for the long travel of the roll faster in automatic than in manual control, because the speed can be increased over a limit which becomes dangerous by manual control, especially when the operator, having opened the mill for an edge pass of a wide slab, comes back on a slab pass of a thin slab. In manual operation slow down limit switches are set to decrease the motor speed in the under-range from 150 to 30 mm and in the upper range between 1,500 and 1,650 mm, whereas an end limit switch is set at 30 mm and 1,650 mm. These two zones, where the speed of the screw is reduced, disturbed the normal rhythm of succeeding settings and an advantage of the automatic screwdown was to obviate any limit switches and realize high-speed setting on the full range of the roll displacement. For short travel, let us say 40 to 20 mm, the skilled operator can set the mill a fraction of a second faster than the 'automatic', but with less accuracy-sometimes a small inching is necessary to adjust the right setting and therefore there is a little hesitation in pushing the ingot in the groove. On the contrary, by automatic control, the rolls are set to the next pass accurately without any hesitation or delay though with a slightly slower speed. The rhythm of successive settings is quite regular and gives the operator a feeling of safety which decreases his fatigue and increases the number of ingots rolled per hour. Having solved this problem for the routine rolling programme we have decided to improve the system and to extend it to include the odd sizes, that is, for most of the slabs programme. The new system will be an addition to the existing installation which will be altered at the same time by improving the line of amplification to increase the speed response-only 1 electronic amplifier, and 1 rotary amplifier between the digitalanalogue system and the motor generator set will be used. In the electronic gear, transistors will be used to a certain extent, that is, in the phase discriminators, in the amplitude discriminator and in the pre-amplifier. The following signals would then be introduced in the electronic amplifier instead of the rotary amplifier (Rototrol): maximum current, maximum speed, maximum acceleration and deceleration and generator voltage feedback. The new programmer makes use of selectors and transistorized amplifiers as basic devices for the computer. The sequence of operation is briefly as follows: When the operator receives the necessary data on the next incoming ingot and the final size of the slab to be rolled, he registers this information on a push-button keyboard. The type of ingot being memorized in a static matrix by pushing the corresponding key, the operator sets the position of two
448
1961
AUTOMATIC SCREWDOWN SYSTEM FOR BLOOMING-SLABBING MILLS WITH DIVERSIFIED PROGRAMMES
systems of uniselectors, the first for the edge rolling programme (giving the width of the slab) and the second for the slab pass programme (thickness of the slab); then he registers the final width and thickness by pushing successively on a decimal keyboard which in turn positions another group of uniselectors. These uniselectors give corresponding voltages proportional to the dimensions of the incoming ingots and the outgoing products which give an input setting to the two analogue computers which will calculate the number of passes on edge and on slab. The necessary data for the pass number computation is the maximum draft allowed for the rolling of pre-determined ingot size. These data are found in the memory system which is set by the choice of the ingot. The pass number selector is dividing a voltage proportional to the difference between an incoming size and an outgoing size into a series of voltages available along a series of resistors and proportional to each successive rolling passes or draft. An analogue-digital system is transferring this analogue information to the previously described digital-analogue system. It does not make use of complicated circuits since the selector which is selecting the taps on the simulating transformer and on the vernier transformer is provided with an additional bank of contacts connected to a linear tapped transformer, which provides a voltage proportional to the simulated angular displacement. As there are four channels, the voltages are in the ratio of 1: 10, the same as the turn ratio between synchros. This gives by addition a total voltage proportional to the simulated position of the mill (in mm). The operator has two draft buttons, one for slab passes and one for edge passes, which send an impulse on either slab advance pass selectors or on edge advance pass selectors. Each
of them scans the analogue voltage divider to follow the calculated programme. Both serve as memory and the roller switches from the edge pass programme to the slab pass programme according to the necessity of the rolling process. There are features which cannot be described in this short paper but they have to be mentioned. The pass number selector is controlled so it can at every moment change the number of remaining passes. This occurs when the maximum draft allowable is changed, for instance: when the mill motor takes too much or too little current; or when the strain-gauge mounted on the stand indicates that the rolling pressure is too high (temperature of ingot too low). There is also a correction of -150 mm to be made in the edge programme when the slab is rolled into a groove instead of on the bullhead of the mill. This occurs on our mill when the slab is less than 360 mm thick and the signal is sent to the edge programmer. The system described above can be readily applied without much alteration to the problem of programming a plate mill or a roughing mill placed ahead of a semicontinuous wide strip mill. In these two cases the mills are combined with an edger in a reversing rolling process and the speed of the edger has to have a given relationship to the mill speed according to the percentage of draft. The problem of setting automatically the edger motor field is easy since all data for this computation can be taken from the analogue voltages available in the previous system. It has been decided to build this equipment for the bloomingslabbing mill and the plate mill, and it is hoped that some of this new equipment will be in operation before the Moscow Meeting and further information about its operation will then be available.
Summary Because ingot supply and final size of products were changing too frequently, the former automatic screwdown of the Ougn:e Bloomer has been rebuilt. The mill operator registers data relating to ingot and final size of slab both for edge and slab rolling. The system computes the number of passes, taking account of different laws such as the law of pass reduction as a function of slab thickness and width, temperature, and capacity of the mill motor, these data being introduced in a function generator with a view to producing a self-optimizing system.
The device operates, however, as an analogue computer, using uniselectors. The digital positions of the uniselectors set up the different pass positions which are in turn transformed to analogue positions in the screwdown system through simulating transformers, selsyns and servo-amplifiers. Similar equipment will be built for a 132 in. plate mill. It will use the same concept of a computer finding the intermediate passes automatically. In addition, a second computer will set the speed of the edger, according to the draft, in order to match the speed of the plate mill and the edger.
Sommaire Comme la fourniture de lingots et la dimension finale des produits changeaient trop fn:quemment, le systeme automatique initial de serrage des vis du blooming d'Ougn~e a ete reconstruit. Le chef lamineur consigne les donnees relatives au lingot et aux dimensions finales de la brame, tant pour le laminage des flancs que des faces. Le systeme calcule le nombre de passes, en tenant compte de diverses lois, telles que la loi de la 'pression' de laminage en fonction de I'epaisseur et de la largeur de la brame, temperature et puissance du moteur de laminoir, ces donnees etant introduites dans un generateur de fonction, en vue de realiser un systeme auto-optimisant. Le dispositif fonctionne comme un calculateur analogique, utilisant
toutefois des seIecteurs pas a pas. Les fonctions numeriques des selecteurs materialisent les differentes hauteurs des vis, qui sont, a leur tour, transformees en positions analogiques dans le systeme de serrage, a travers des transformateurs de simulation, des selsyns et des servo-amplificateurs. Le meme equipement sera reproduit pour un laminoir a plaques de 3,50 metres. 11 utilisera une conception similaire de calculateur, trouvant automatiquement les passes intermediaires. En outre un second calculateur reglera la vitesse des cylindres de serrage lateral (edger), en fonction des donnees afin de synchroniser les vitesses des cylindres horizontaux et verticaux.
Zusammenfassung Die frtihere automatische Walzenanstellung des Ougn:e-Walzwerkes wurde umgebaut, da AusgangsgroBe und Endquerschnitt der Walzprodukte zu haufig gewechselt werden mtissen. Der Steuermann gibt Daten ftir Ausgangs- und Endquerschnitt der Platine sowohl ftir Hohen- und Breitenwalzung vor. Die Einrichtung berechnet die Stichzahl und berticksichtigt verschiedene Fak-
29-A.R.C.4
toren wie Abnahme des Querschnittes als Funktion der Blockdicke und -breite, Temperatur und Leistung des Hauptantriebs. Diese Daten werden einem Funktionsgenerator zugeftihrt, wodurch sich ein selbstoptimierendes System ergibt. Die Anordnung arbeitet als Analogrechner, wobei jedoch Drehwahler verwendet werden. Die Digitalwerte der Drehwahler verkor-
449
1962
M.
FOUASSIN
pern die verschiedenen Walzenanstellwerte, die ihrerseits mit Polygontransformatoren, Drehfeldsystemen und Servoverstarkern in Analogwerte filr die Walzenanstellvorrichtung verwandelt werden. Die gleiche Anlage solI ein zweites Mal filr eine 132 ZollFlacheisenstral3e errichtet werden. Flir den Rechner zur Ermittlung
der entsprechenden Anstellwerte solI eine ahnliche Konzeption verwendet werden. Zusatzlich soll ein zweiter Rechner entsprechend der Dickenabnahme die Geschwindigkeit der Vertikalwalzen bestirnmen, urn die Geschwindigkeiten von Horizontal- und Vertikalwalzen einander anzupassen.
DISCUSSION M. G. CmuKIN (U.S.S.R.) How long ago was the system realized and what technical and economic results were achieved in its application? M. FOUASSIN, in reply. This system has not yet been put into operation. Technical and economic advantage will be obtained from reduction of roll wear, and increase of productivity of the mill. Furthermore, the work of the operatives will be made easier since they will only have to watch the ingot. Question from the floor Why are three stages of counting used in your system? Were there any failures in the automatic control system, and if so how often? M. FOUASSIN, in reply. Since the maximum displacement of the roll is 1600 mm and the accuracy is 1 mm, three stages of counting are required. Such a system has a sufficiently high accuracy and its cost is not too high. Failures did occur due to the fact that the electronic circuit was made up of ordinary radio components. Question /rom the floor How is the braking and the precision stopping of the electric drives of the screw-down equipment realized?
M. FOUASSIN, in reply. The control is by means of a closed system. The system is non-linear but in the braking zone it becomes practically linear and as a result precision stopping is achieved. A. B. CHELUSTKIN (U.S.S.R.) The system is of great interest due to the .extreme simplicity of the solution of a complicated problem achieved by the use of uniselectors and functional converters. However, it is necessary to point out that simplification was achieved by averaging the functional dependencies between the rate of reduction and the dimensions of the rolled metal. Such averaging is a compromise solution, and in most cases the selected functional dependence will not ensure optimum utilization of the rolling equipment. Apparently for different grades of steel, different functional dependencies have to be used for the same dimensions of the metal. The absence of a number of such functional converters is apparently compensated by the fact that during overloading or underloading of the rolling stand the system is switched over to a functional converter with another coefficient of amplification. It can be assumed that during the process of operation of the system such switching is frequently repeated. However, for some passes the rolIing stand will be either overloaded or underloaded. It will be of great interest to know the final results obtained with this system when it is put into operation.
450
1963
COMPLEMENTARY PAPER TO
Automatic Screwdown System for Blooming-slabbing Mills with Diversified Programmes M. FOUASSIN The new positioning system we will soon be building will make use, like the previous one, of simulating transformers and selsyns. The reduction ratio between steps (or channels) is 1 to 10. The system is made up of four digits: units, tens, hundreds and thousands (reduced to 0 and 1000). The programming system is double, i.e. the first one is intended for roll positioning when slab-roIling an ingot, and the other when edge-roIling it. Each of these two programming systems comprise three groups of four motor selectors . . I. The first group, called the input setting group, comprises four selectors fitted with six arcs having the following functions: (a) Four arcs are connected to the simulating transformers and are giving the setting voltage to the servo controlling the position of the screwdown motor. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. (c) One arc is positioning all the four selectors by repeating the position of another group acting as a computer. 11. The second group is called the computer group and it also comprises four selectors with arcs, i.e., (a) One arc is connected to a positioning system of the input setting by a push button-about eight different ingot sizes. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. 0/10000 mm
~ .
'r-I
0/1 000 mm • C
~ ~_ ~"'.. --
1
4
0/100 mm
~
I
.
J
j J
(c) One arc is connected to the preceding group of selectors to have them repeat the position of each of the computer settings when called for by the operator. (d) One arc is giving a signal which is a function of the width or the thickness of the slab to be used in a function generator, which is described later. (e) One arc gives a signal when the distance between rolls is less than the widest groove, thus modifying the edge programme accordingly. Ill. The third group is called the output setting group and has the following functions: (a) One arc is a part of a positioning system actuated by a pushbutton or keyboard (similar to a comptometer) to introduce the output data. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. (c) One arc is connected to the first group of selectors and to have them repeat the position of the output setting for the last pass. These three groups give the input data to a simple computer system comprising a digital potential divider consisting of a chain of resistors connected to two uniselectors. The first is the' pass number' selector and the second is the' pass sequence' selector. The input and output analogue voltages of the first and third 0/10mm
~
"
} Thickness data to Wlddth intputt dat a f rom an ou pu ,'-------W'dth I system Pass sequ7nce selector
~~-=~~~-==;j:2 ~nnc,:;~
3
.f.
.~~+
1 '1
7
,~
0-1
~.,:
.,
I
I
, :9~= ' '. , 11-3~
';23~
~13
rU
,Pass number selector
~
~~ . .
TJ.
Next pass button
Ingot temperature Motor load I HOUSing strain gauge;
4-----;-
----~~-----------------~-r_-YJ
Figure 1.
Thickness input and output system 451
1964
-
..
M. FOUASSIN
pass button, the first group of selectors, which command the screw position through the system of simulating transformers, is switched to repeat the position of selector group 11 corresponding to pass No. 2. At the same time, the pass sequence selector goes one step forward and connects the comparator to point 3 of the voltage divider. The comparator checks the pass number again and computes the next pass. This sequence is repeated until the pass sequence selector has scanned the whole range of passes. When the last pass is reached, the first group of selectors repeat the position of group III which gives the exact position regardless of any small error given by the computing system, as for instance, small drift of the comparator amplifier. Another interesting feature of this equipment is the automatic correction of the groove depth when rolling on edge in the groove. At the beginning of the rolling process the ingot is always rolled on edge of the bulkhead. It is only when the ingot thickness is less than, say, 360 mm in our mill, that the next pass on edge is made in the widest groove. This means that the roll distance should be corrected accordingly, as for instance in our mill, by twice 75 mm, that is 150 mm, in addition to the draft. This correction is automatically made by a signal from the group 11 selectors from the thickness rolling system, and corresponds to the subtraction of a corresponding analogue voltage in the voltage divider. Furthermore, this correction is not necessarily constant and can be adjusted by the operator to take account of the progressive wear of the finishing groove. This equipment is still on assembly stage; however, the different circuits have been tested and have proved reliable. We hope to have found an acceptable solution to the rolling of very versatile slab programmes. The same equipment will be duplicated for our 132 in. plate mill. It will use a similar conception of the computer, finding automatically the intermediate passes after the input and output data have been introduced by the operator.
groups are fed to the potential divider, whereas the computing group is connected to the same through a comparator. The comparator also receives data from a function generator. This latter introduces in the comparator a voltage proportional to the maximum draft allowed on the mill, taking account of the width, and thickness of the ingot or slab, and is modified eventually according to the quality of the steel and the temperature. This function generator may also receive, during the rolling process, a signal from a motor overload relay or a load cell on the housing in order to reduce the permissible maximum draft. The number of passes is computed by the following operation: (a) By pushing the ingot size button, the selector groups I and II are positioned on the ingoing dimension, and point 1 of the resistors is at a voltage corresponding to that position. (b) By introducing the output data, group III is positioned and the wiper of the pass number selector is at the voltage corresponding to the input condition. Assuming that the wiper is at the start on point 2, the same as the wiper of the pass sequence selector connected to the comparator, it appears at the entry of same, a voltage corresponding to the difference between input and output analogue voltages. This is compared to the voltage given by the function generator. As the allowed draft is much smaller than the difference between output and input, the comparator energizes the motor of the pass number selector until the voltage measured by the comparator is equal or less than the voltage given by the function generator. The number of passes being set, the comparator performs another function. It compares the voltage of point 2 to the analogic voltage given by the selector group 11, which were set at the beginning on the same position as group I, that means pass 1. The comparator energizes the motor selector of 11 and puts it in a position corresponding to the first pass. When the operator calls for pass No. 2 by pushing the next
452
1965
In 1952, a programme controlled screwdown was put into operation on the blooming slabbing of the OugnSe-Marihaye Steel Works in Belgium. The aim of this paper is to describe the digital-analogue system which was designed to solve the electrical problem and To phase discriminator Simulating transformer
o
1
2
3
"
?
':'
:
5
6
7
9
9 I
la
9,
9
10
9
9
I
0
Vector diagram ofa sirrulating transformer
I
2 (a)
Secondary .windings
3
7
IT
ill 5 Cores
I
(2)
Synchro transformer
Prndimary WI
Ings
Synchro· transformer
O I
m
Vernier transformer
'" nov
Synchro stator three phases
][ (b)
Synchro rotor with additio!,)al cross winding
Figure 1
Figure 2
further to describe the many changes found necessary in the programming device to ultimately obtain the operators' agreement that the equipment was operating successfully. Basic Circuit To understand the scheme of the digital-analogue servomechanism a simplified system is described below.
This system gives 10 true zeros per turn of the synchro, when the synchro exciting winding is connected to an alternative voltage and the error voltage is measured between the neutral point and one of the taps numbered 0 to 9. These true zero voltages are separated by angular positions of 36°. Since finer increments are reqUired, these are provided by
446
1959
AUTOMATIC SCREW DOWN SYSTEM FOR BLooMING-SLABBING MILLS WITH DIVERSIFIED PROGRAMMES
adding a cross winding on the synchrorotor and by exciting it through an alternating voltage in or out of phase with the main winding. Ten different voltages are available on the tapped vernier transformer. By the combination of the main field and the cross field, these 10 voltages provide 10 different resultant fields, the directions of which are rotated by increments of 3·6°. When combining one connection on the simulating transformer and one on the vernier transformer, it is possible to
voltage of the vernier transformer to the cross winding of a synchrotransformer. As a matter of fact in 5 years of operation we have encountered no troubles in the relay system. The rest of the equipment consists of three phase-discriminators (one for each channel), an amplitude discriminator to take the correct signal successively from coarse to medium and fine channels, an electronic amplifier and a 300 W amplidyne. The amplified error signal is fed into the pattern field of the
GB Analogic to digItal comparator
M~mory for routine
programmes
S Positioning selsyn PS Power selsyn RA Rotary amplifier G S/D GB T I P
Generator Screw down Gear box Tachometer Motor load transducer
I
I I I I I I _______________ ___ J ~
I
I
I 1
...L..
Strain gauge
Figure 3
obtain any of the 100 error voltages available on one turn of the servosynchro. This system is the basic circuit of the digital-analogue screwdown device which in fact uses 3 channels to cover the required range of 1,650 mm which is the lift of our blooming-slabbing mill. These three channels each have their synchrotransformer and simulating transformer. The synchros, which give a feedback of the roll positions, are geared to the ratio of 1 : IS. The coarse channel has seven 225 mm increments for about half a turn. The medium channel has fifteen IS mm increments per turn and the fine channel has fifteen I mm increments per turn. Relays are used to form a combination of three digits. Every relay connects one of the 15 taps of the simulating transformer of a given channel and at the same time the corresponding tap of the vernier transformer of the next coarse channel. There are 8 relays for the coarse channel, IS relays for the medium channel and IS relays for the fine channel. Only three of them are energized at a time to form one of the 1,650 combinations. Contact loads are insignificant since the coarse contact connects the simulating transformer to the grid of the electronic discriminator and the vernier contact connects a tap of a low
'Rototrol' of a conventional Westinghouse Control System. The d.c. screwdown drive motor is powered from an MG set, the voltage of which is adjusted as a function of the amplifier error signal. The change from 'automatic' to 'manual' control is made by disconnecting the pattern field from previous amplidyne to the system of resistors and relays controlled by the operators' manipulator of the manual control. To the credit of such a system we have to mention that the voltages supplied by the simulating transformer are in the range of 100 V maximum, and even in the case of small error angles, error voltages are still significant in comparison to noise discriminators and amplifiers. We believe it is the main advantage of such a system in comparison with the conventional potentiometer servo system which has the disadvantages of: (a) using very small error signals in the range of a few millimetre displacements and (b) the use of sliding contacts. The accuracy is better than J!-(j mm, but it could not be used to its full capacity for two reasons: (1) the accuracy required by the roller was ± 1 mm for the last passes and ±2 mm for the other passes; and (2) the time allowed for the setting of the next pass did not permit a slow-down to such a speed at which this high accuracy is obtained.
447
1960
M. FOUASSIN
Programming Device
Two programming devices have been tried on this installation. Punched card system
The first one was a system of punched cards. A combination of static matrices uses 24 holes to energize a choice of three relays out of 37. As the card has 80 rows of 12 possible holes, this provides the possibility of a 40 pass programme. This system failed to work because of the diversification of the programmes. Due to the lack of heating capacity of the pit furnaces, and since intermixed hot and cold ingots do not reach the correct temperature in the desired order, it was difficult to follow a determined programme. Thus the operator had to sort out a bundle of cards for the one corresponding to the incoming ingot. This was a serious drawback to the method since it caused an intolerable loss of time to the mill operator. Furthermore, some ingots had to be rolled in other final sizes accor~ing to the analysis of the steel and changes occurred at the last moment so that the previous punched card had to be discarded and replaced. For routine schedule, though the same card could theoretically be used all over again, experience has proved that a hard-paper card does not stand much manipulation without being damaged or having at least its corners broken. Punched steel sheets have also been tried without much success: they also need to be handled carefully. We consider that a punched card programmer is only suitable in big steel plants with repeated routine programmes and when ingots are supplied with sufficient regularity. Uniselector programmer
Considering the punched card system a failure, we turned to uniselectors as a memory device for a pass programme. As one definite position is provided by energizing three relays, one pass is then included in a row of three horizontal contacts of a uniselector and a programme of 25 passes may be stored in 25 rows, that is, in three complete banks of contacts of a 25-step uniselector. The common uniselectors found on the market having generally 25 steps and six banks, two programmes can be stored in one of them. With a commutator the mill operator selects the programme required for the incoming ingot and by pushing the pass advance button sets the roll distance for the first pass. The following passes are obtained by successively pushing the pass advance buttons. This gives an impulse to the uniselector and the brushes scan successively all the taps thus energizing the relays of the digital-analogue servo system. The reliability of such devices is high. Manufacturers guarantee more than 40,000,000 steps as a life-time. A simple calculation shows that at the rate of 30 ingots an hour, an ingot being rolled in 15 passes, and 7,000 hours of operation per year, one uniselector can last about 13 years. Since there are many uniselectors to compose the different mill programmes this duration should be multiplied accordingly. This gave a suitable solution for the routine programmes and the system has been kept in operation on this basis up to the present. Our experience with uniselectors has proved that this device is entirely reliable. As a matter of fact the uniselectors have been in operation under severe conditions. The cabinet placed in the operator's control room was, on account of the heat losses of tubes and rotating amplifiers, brought to a temperature of about 50° Celsius, but as this temperature was detrimental to the equipment, the cabinet was left with the door constantly
open with the result that the whole uniselector unit was covered with a layer of dust. In spite of this no trouble has been encountered up to now with this delicate equipment the contacts of which are self-cleaning. It is preferable to protect the equipment against dust and to provide for maintenance of a reasonable temperature. The uniselector programmer though only used on half of the total tonnage rolled in the mill has shown immediately all the advantages of a pre-set screwdown system, that is, speed and precision of rolling, less fatigue of the operator and, an unexpected result, reduction in the wear of the groove shoulders of the rolls, which paid in a very short time for the whole installation. As a matter of fact the bloom before turned from 90 degrees every two passes is rolled with precision to the exact size of the groove, whereas in a manual setting of the rolls this thickness is inaccurate and causes the bloom to be squeezed in the groove, causing the wear of the shoulders. This installation, as it is planned, is for the long travel of the roll faster in automatic than in manual control, because the speed can be increased over a limit which becomes dangerous by manual control, especially when the operator, having opened the mill for an edge pass of a wide slab, comes back on a slab pass of a thin slab. In manual operation slow down limit switches are set to decrease the motor speed in the under-range from 150 to 30 mm and in the upper range between 1,500 and 1,650 mm, whereas an end limit switch is set at 30 mm and 1,650 mm. These two zones, where the speed of the screw is reduced, disturbed the normal rhythm of succeeding settings and an advantage of the automatic screwdown was to obviate any limit switches and realize high-speed setting on the full range of the roll displacement. For short travel, let us say 40 to 20 mm, the skilled operator can set the mill a fraction of a second faster than the 'automatic', but with less accuracy-sometimes a small inching is necessary to adjust the right setting and therefore there is a little hesitation in pushing the ingot in the groove. On the contrary, by automatic control, the rolls are set to the next pass accurately without any hesitation or delay though with a slightly slower speed. The rhythm of successive settings is quite regular and gives the operator a feeling of safety which decreases his fatigue and increases the number of ingots rolled per hour. Having solved this problem for the routine rolling programme we have decided to improve the system and to extend it to include the odd sizes, that is, for most of the slabs programme. The new system will be an addition to the existing installation which will be altered at the same time by improving the line of amplification to increase the speed response-only 1 electronic amplifier, and 1 rotary amplifier between the digitalanalogue system and the motor generator set will be used. In the electronic gear, transistors will be used to a certain extent, that is, in the phase discriminators, in the amplitude discriminator and in the pre-amplifier. The following signals would then be introduced in the electronic amplifier instead of the rotary amplifier (Rototrol): maximum current, maximum speed, maximum acceleration and deceleration and generator voltage feedback. The new programmer makes use of selectors and transistorized amplifiers as basic devices for the computer. The sequence of operation is briefly as follows: When the operator receives the necessary data on the next incoming ingot and the final size of the slab to be rolled, he registers this information on a push-button keyboard. The type of ingot being memorized in a static matrix by pushing the corresponding key, the operator sets the position of two
448
1961
AUTOMATIC SCREWDOWN SYSTEM FOR BLOOMING-SLABBING MILLS WITH DIVERSIFIED PROGRAMMES
systems of uniselectors, the first for the edge rolling programme (giving the width of the slab) and the second for the slab pass programme (thickness of the slab); then he registers the final width and thickness by pushing successively on a decimal keyboard which in turn positions another group of uniselectors. These uniselectors give corresponding voltages proportional to the dimensions of the incoming ingots and the outgoing products which give an input setting to the two analogue computers which will calculate the number of passes on edge and on slab. The necessary data for the pass number computation is the maximum draft allowed for the rolling of pre-determined ingot size. These data are found in the memory system which is set by the choice of the ingot. The pass number selector is dividing a voltage proportional to the difference between an incoming size and an outgoing size into a series of voltages available along a series of resistors and proportional to each successive rolling passes or draft. An analogue-digital system is transferring this analogue information to the previously described digital-analogue system. It does not make use of complicated circuits since the selector which is selecting the taps on the simulating transformer and on the vernier transformer is provided with an additional bank of contacts connected to a linear tapped transformer, which provides a voltage proportional to the simulated angular displacement. As there are four channels, the voltages are in the ratio of 1: 10, the same as the turn ratio between synchros. This gives by addition a total voltage proportional to the simulated position of the mill (in mm). The operator has two draft buttons, one for slab passes and one for edge passes, which send an impulse on either slab advance pass selectors or on edge advance pass selectors. Each
of them scans the analogue voltage divider to follow the calculated programme. Both serve as memory and the roller switches from the edge pass programme to the slab pass programme according to the necessity of the rolling process. There are features which cannot be described in this short paper but they have to be mentioned. The pass number selector is controlled so it can at every moment change the number of remaining passes. This occurs when the maximum draft allowable is changed, for instance: when the mill motor takes too much or too little current; or when the strain-gauge mounted on the stand indicates that the rolling pressure is too high (temperature of ingot too low). There is also a correction of -150 mm to be made in the edge programme when the slab is rolled into a groove instead of on the bullhead of the mill. This occurs on our mill when the slab is less than 360 mm thick and the signal is sent to the edge programmer. The system described above can be readily applied without much alteration to the problem of programming a plate mill or a roughing mill placed ahead of a semicontinuous wide strip mill. In these two cases the mills are combined with an edger in a reversing rolling process and the speed of the edger has to have a given relationship to the mill speed according to the percentage of draft. The problem of setting automatically the edger motor field is easy since all data for this computation can be taken from the analogue voltages available in the previous system. It has been decided to build this equipment for the bloomingslabbing mill and the plate mill, and it is hoped that some of this new equipment will be in operation before the Moscow Meeting and further information about its operation will then be available.
Summary Because ingot supply and final size of products were changing too frequently, the former automatic screwdown of the Ougn:e Bloomer has been rebuilt. The mill operator registers data relating to ingot and final size of slab both for edge and slab rolling. The system computes the number of passes, taking account of different laws such as the law of pass reduction as a function of slab thickness and width, temperature, and capacity of the mill motor, these data being introduced in a function generator with a view to producing a self-optimizing system.
The device operates, however, as an analogue computer, using uniselectors. The digital positions of the uniselectors set up the different pass positions which are in turn transformed to analogue positions in the screwdown system through simulating transformers, selsyns and servo-amplifiers. Similar equipment will be built for a 132 in. plate mill. It will use the same concept of a computer finding the intermediate passes automatically. In addition, a second computer will set the speed of the edger, according to the draft, in order to match the speed of the plate mill and the edger.
Sommaire Comme la fourniture de lingots et la dimension finale des produits changeaient trop fn:quemment, le systeme automatique initial de serrage des vis du blooming d'Ougn~e a ete reconstruit. Le chef lamineur consigne les donnees relatives au lingot et aux dimensions finales de la brame, tant pour le laminage des flancs que des faces. Le systeme calcule le nombre de passes, en tenant compte de diverses lois, telles que la loi de la 'pression' de laminage en fonction de I'epaisseur et de la largeur de la brame, temperature et puissance du moteur de laminoir, ces donnees etant introduites dans un generateur de fonction, en vue de realiser un systeme auto-optimisant. Le dispositif fonctionne comme un calculateur analogique, utilisant
toutefois des seIecteurs pas a pas. Les fonctions numeriques des selecteurs materialisent les differentes hauteurs des vis, qui sont, a leur tour, transformees en positions analogiques dans le systeme de serrage, a travers des transformateurs de simulation, des selsyns et des servo-amplificateurs. Le meme equipement sera reproduit pour un laminoir a plaques de 3,50 metres. 11 utilisera une conception similaire de calculateur, trouvant automatiquement les passes intermediaires. En outre un second calculateur reglera la vitesse des cylindres de serrage lateral (edger), en fonction des donnees afin de synchroniser les vitesses des cylindres horizontaux et verticaux.
Zusammenfassung Die frtihere automatische Walzenanstellung des Ougn:e-Walzwerkes wurde umgebaut, da AusgangsgroBe und Endquerschnitt der Walzprodukte zu haufig gewechselt werden mtissen. Der Steuermann gibt Daten ftir Ausgangs- und Endquerschnitt der Platine sowohl ftir Hohen- und Breitenwalzung vor. Die Einrichtung berechnet die Stichzahl und berticksichtigt verschiedene Fak-
29-A.R.C.4
toren wie Abnahme des Querschnittes als Funktion der Blockdicke und -breite, Temperatur und Leistung des Hauptantriebs. Diese Daten werden einem Funktionsgenerator zugeftihrt, wodurch sich ein selbstoptimierendes System ergibt. Die Anordnung arbeitet als Analogrechner, wobei jedoch Drehwahler verwendet werden. Die Digitalwerte der Drehwahler verkor-
449
1962
M.
FOUASSIN
pern die verschiedenen Walzenanstellwerte, die ihrerseits mit Polygontransformatoren, Drehfeldsystemen und Servoverstarkern in Analogwerte filr die Walzenanstellvorrichtung verwandelt werden. Die gleiche Anlage solI ein zweites Mal filr eine 132 ZollFlacheisenstral3e errichtet werden. Flir den Rechner zur Ermittlung
der entsprechenden Anstellwerte solI eine ahnliche Konzeption verwendet werden. Zusatzlich soll ein zweiter Rechner entsprechend der Dickenabnahme die Geschwindigkeit der Vertikalwalzen bestirnmen, urn die Geschwindigkeiten von Horizontal- und Vertikalwalzen einander anzupassen.
DISCUSSION M. G. CmuKIN (U.S.S.R.) How long ago was the system realized and what technical and economic results were achieved in its application? M. FOUASSIN, in reply. This system has not yet been put into operation. Technical and economic advantage will be obtained from reduction of roll wear, and increase of productivity of the mill. Furthermore, the work of the operatives will be made easier since they will only have to watch the ingot. Question from the floor Why are three stages of counting used in your system? Were there any failures in the automatic control system, and if so how often? M. FOUASSIN, in reply. Since the maximum displacement of the roll is 1600 mm and the accuracy is 1 mm, three stages of counting are required. Such a system has a sufficiently high accuracy and its cost is not too high. Failures did occur due to the fact that the electronic circuit was made up of ordinary radio components. Question /rom the floor How is the braking and the precision stopping of the electric drives of the screw-down equipment realized?
M. FOUASSIN, in reply. The control is by means of a closed system. The system is non-linear but in the braking zone it becomes practically linear and as a result precision stopping is achieved. A. B. CHELUSTKIN (U.S.S.R.) The system is of great interest due to the .extreme simplicity of the solution of a complicated problem achieved by the use of uniselectors and functional converters. However, it is necessary to point out that simplification was achieved by averaging the functional dependencies between the rate of reduction and the dimensions of the rolled metal. Such averaging is a compromise solution, and in most cases the selected functional dependence will not ensure optimum utilization of the rolling equipment. Apparently for different grades of steel, different functional dependencies have to be used for the same dimensions of the metal. The absence of a number of such functional converters is apparently compensated by the fact that during overloading or underloading of the rolling stand the system is switched over to a functional converter with another coefficient of amplification. It can be assumed that during the process of operation of the system such switching is frequently repeated. However, for some passes the rolIing stand will be either overloaded or underloaded. It will be of great interest to know the final results obtained with this system when it is put into operation.
450
1963
COMPLEMENTARY PAPER TO
Automatic Screwdown System for Blooming-slabbing Mills with Diversified Programmes M. FOUASSIN The new positioning system we will soon be building will make use, like the previous one, of simulating transformers and selsyns. The reduction ratio between steps (or channels) is 1 to 10. The system is made up of four digits: units, tens, hundreds and thousands (reduced to 0 and 1000). The programming system is double, i.e. the first one is intended for roll positioning when slab-roIling an ingot, and the other when edge-roIling it. Each of these two programming systems comprise three groups of four motor selectors . . I. The first group, called the input setting group, comprises four selectors fitted with six arcs having the following functions: (a) Four arcs are connected to the simulating transformers and are giving the setting voltage to the servo controlling the position of the screwdown motor. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. (c) One arc is positioning all the four selectors by repeating the position of another group acting as a computer. 11. The second group is called the computer group and it also comprises four selectors with arcs, i.e., (a) One arc is connected to a positioning system of the input setting by a push button-about eight different ingot sizes. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. 0/10000 mm
~ .
'r-I
0/1 000 mm • C
~ ~_ ~"'.. --
1
4
0/100 mm
~
I
.
J
j J
(c) One arc is connected to the preceding group of selectors to have them repeat the position of each of the computer settings when called for by the operator. (d) One arc is giving a signal which is a function of the width or the thickness of the slab to be used in a function generator, which is described later. (e) One arc gives a signal when the distance between rolls is less than the widest groove, thus modifying the edge programme accordingly. Ill. The third group is called the output setting group and has the following functions: (a) One arc is a part of a positioning system actuated by a pushbutton or keyboard (similar to a comptometer) to introduce the output data. (b) One arc is supplying an analogic voltage proportional to the selector position and digit. (c) One arc is connected to the first group of selectors and to have them repeat the position of the output setting for the last pass. These three groups give the input data to a simple computer system comprising a digital potential divider consisting of a chain of resistors connected to two uniselectors. The first is the' pass number' selector and the second is the' pass sequence' selector. The input and output analogue voltages of the first and third 0/10mm
~
"
} Thickness data to Wlddth intputt dat a f rom an ou pu ,'-------W'dth I system Pass sequ7nce selector
~~-=~~~-==;j:2 ~nnc,:;~
3
.f.
.~~+
1 '1
7
,~
0-1
~.,:
.,
I
I
, :9~= ' '. , 11-3~
';23~
~13
rU
,Pass number selector
~
~~ . .
TJ.
Next pass button
Ingot temperature Motor load I HOUSing strain gauge;
4-----;-
----~~-----------------~-r_-YJ
Figure 1.
Thickness input and output system 451
1964
-
..
M. FOUASSIN
pass button, the first group of selectors, which command the screw position through the system of simulating transformers, is switched to repeat the position of selector group 11 corresponding to pass No. 2. At the same time, the pass sequence selector goes one step forward and connects the comparator to point 3 of the voltage divider. The comparator checks the pass number again and computes the next pass. This sequence is repeated until the pass sequence selector has scanned the whole range of passes. When the last pass is reached, the first group of selectors repeat the position of group III which gives the exact position regardless of any small error given by the computing system, as for instance, small drift of the comparator amplifier. Another interesting feature of this equipment is the automatic correction of the groove depth when rolling on edge in the groove. At the beginning of the rolling process the ingot is always rolled on edge of the bulkhead. It is only when the ingot thickness is less than, say, 360 mm in our mill, that the next pass on edge is made in the widest groove. This means that the roll distance should be corrected accordingly, as for instance in our mill, by twice 75 mm, that is 150 mm, in addition to the draft. This correction is automatically made by a signal from the group 11 selectors from the thickness rolling system, and corresponds to the subtraction of a corresponding analogue voltage in the voltage divider. Furthermore, this correction is not necessarily constant and can be adjusted by the operator to take account of the progressive wear of the finishing groove. This equipment is still on assembly stage; however, the different circuits have been tested and have proved reliable. We hope to have found an acceptable solution to the rolling of very versatile slab programmes. The same equipment will be duplicated for our 132 in. plate mill. It will use a similar conception of the computer, finding automatically the intermediate passes after the input and output data have been introduced by the operator.
groups are fed to the potential divider, whereas the computing group is connected to the same through a comparator. The comparator also receives data from a function generator. This latter introduces in the comparator a voltage proportional to the maximum draft allowed on the mill, taking account of the width, and thickness of the ingot or slab, and is modified eventually according to the quality of the steel and the temperature. This function generator may also receive, during the rolling process, a signal from a motor overload relay or a load cell on the housing in order to reduce the permissible maximum draft. The number of passes is computed by the following operation: (a) By pushing the ingot size button, the selector groups I and II are positioned on the ingoing dimension, and point 1 of the resistors is at a voltage corresponding to that position. (b) By introducing the output data, group III is positioned and the wiper of the pass number selector is at the voltage corresponding to the input condition. Assuming that the wiper is at the start on point 2, the same as the wiper of the pass sequence selector connected to the comparator, it appears at the entry of same, a voltage corresponding to the difference between input and output analogue voltages. This is compared to the voltage given by the function generator. As the allowed draft is much smaller than the difference between output and input, the comparator energizes the motor of the pass number selector until the voltage measured by the comparator is equal or less than the voltage given by the function generator. The number of passes being set, the comparator performs another function. It compares the voltage of point 2 to the analogic voltage given by the selector group 11, which were set at the beginning on the same position as group I, that means pass 1. The comparator energizes the motor selector of 11 and puts it in a position corresponding to the first pass. When the operator calls for pass No. 2 by pushing the next
452
1965