US2287851A - Automatic speed control for continuous rolling mills - Google Patents

Description

June30, 1942. A. 25mm I 2,287,851

AUTOMATIC SPEED CONTROL FOR CONTINUOUS ROLLING MILLS Filed April 18, 1941 3 Sheets-Sheet l v mvmon ALEXA/V967? 25/72 //v BY P. v

A. ZEITLIN June so, 1942.

AUTOMATIC SPEED CONTROL FOR CONTINUOUS ROLLING MILLS Filed April 18, 1941 3 Sheets-Sheet 2 ATTORNEY A. ZEITLIN June 30,1942.

AUTOMATIC SPEEO CONTROL FOR CONTINUOUS ROLLING MILLS 5 Sheets-Sheet 3 Filed April 18, 1941 FIG. 3.

Patented June 30, 1942 AUTOMATIC SPEED CONTROL FOR CONTINUOUS ROLLING MILLS Alexander Zeitlin, New York, N. Y., assignor, by mesne assignments, to Sperry Products, 'Inc,, a corporation of New York Application April 18, 1941, Serial No. 389,193

7 Claims.

This invention relates to continuous rolling mills which consist of a series of spaced mill stands, usually ten in number, the spaces between the stands being occupied by conveyor systems adapted to carry the metal successively through the mill. The material in a hot strip mill issues from the furnace as a white hot slab of metal which is deposited on the conveyors and fed into the first mill stand and then successively to the remaining stands. Pressure of a high order, amounting to several million pounds, is applied by each of these stands to the material, thinning out and lengthening the same. As the material thins out, the speed of travel increases because the same amount of metal must pass through each mill stand in a given time. This means that as the metal thins out the speed must increase. Since the amount of metal passing through each stand is a function of its thickness and the speed, and since.

the same amount of metal must pass through each stand, it follows that the product of the thickness and the speed must be the same at each mill stand. If this is not the case, then more or less metal will pass through one mill stand than through the others. If more metal passes through the stand than passes through a succeeding stand, for example, then the metal will buckle upwardly, thus forming a cobble, which is extremely dangerous and unless remedied may cause destruction of an entire strip as well as damage to one or more mill stands.

If, on the other hand, less metal passes through a given mill stand than through the preceding mill stand, it will result in a drag upon the metal, causing it to thin out irregularly and thus yield a strip of non-uniform-thickness, which is detrimental and may even cause the entire strip to be ruined.

The present control system in continuous strip mills comprises a control gallery from which vantage point one or more operators can observe the strip as it passes through the mill, and if a cobble or drag is noticed, the operator controls the speeds of certain of the drive motors which rotate the work rolls of the mill stands to speed up or slow down certain rolls in order to level out the sheet. Thiscontrol, however, is necessarily crude and results in merely approximate corrections. Not only is the amount of correc- H tion a matter of guess work, but there is also a variable time lag between the occurrence of the defect in speed and the correction of the same by the operator.

It is the principal object of this invention, 53

therefore, to provide means which will automatically correct the speeds of the driving rolls of the respective mill stands in response to deviations of the amount of metal passing through the mill stands relative to the amounts of metal passing through the other mill stands. For this purpose the driving roll motor speeds are caused to be controlled in response to the product of thickness of material and speed of rotation of said rolls.

Further objects and advantages-of this invention will become apparent in the following detailed description thereof.

In the accompanying drawings:

Fig. l is a side elevation of a rolling mill stand.

Fig. 2 is a front elevation of said stand.

Fig. 3 is a wiring diagram of the motor. control system.

Fig. 4 is a wiring diagram disclosing the method of generating the impulses which control the motor of Fig. 3.

Fig. 5 is a wiring diagram illustrating further the principle of operation of the invention dis-- closed in Figs. 3 and 4.

Fig. 6 is a development of a logarithmic coil of the type employed in Fig. 4.

Referring to Fig. 1, there is shown one end frame member In of a rolling mill stand, which may be one of a series of ten such stands, comprising a continuous rolling mill. A similar frame I0 is spaced back of the frame I0 (see Fig. 2) and between said frames there are mounted the rolls of the mill. The mill may be of the four-high type consisting of two pressure or work rolls H and I 2 and two back-up rolls I3 and M. The back-up rolls are mounted in suitable bearing blocks l5 and I6 slidable in the frame, and within the blocks I5, I 6 there are slidabl mounted other blocks I1, I 8 within which the pressure rolls H and I2 are supported. Pressure between the pressure rolls'is transmitted by way of the back-up rolls by the application of pressure to blocks l5 and I6 by means such as screws 20 which engage said blocks and are actuated from a screw-down motor 2| through clutches 22 and reduction gearing contained in housing 23. The pressure rolls ii and I2 are driven in opposite directions bya motor M through reduction gearing 25.

As the slab of material passes through the first four mill stands, it is thinned out and lengthened, but the length of the strip and the spacing of the first four stands are such that the strip is at no time in two mill stands at the same-time. After passing through mill stand No. 5, however, the sheet has been sufficiently lengthened and the mill stands are sufflciently close together so that before the strip has left mill stand No. 5 it has entered mill stand No. 6. From then on until the strip has passed out of the mill it is at all times in several mill stands at once, and, as set forth in the introduction.

hereto, it will readily be seen that if more metal passes through the pressure rolls of one mill stand than passes through the pressure rolls of the preceding or succeeding mill stands, there will be produced either a drag or a loop or cobble, with the undesirable and sometimes disastrous consequences hereinbefore noted.

The problem which is here solved is a means whereby automatically the speeds of the motors M which drive the respective pressure rolls are controlled in response to the quantity of material passing through the pressure rolls relative to the quantities passing through the pressure rolls of the preceding and succeeding mill stands, so that any variation in the relative amounts of metal will cause certain of said motors to be sped up or slowed down, as the circumstances require, in order that once more the quantity of metal passing through the pressure rolls of the respective mill stand will be the same as the quantity of metal passing through the preceding and succeeding stands. In the case of mill stand No. 5, however, it is only,necessary to control the amount of metal passing through it relative to the succeeding mill stand No. 6 because when the strip of material has entered mill stand 5 it has already left mill stand No. 4 entirely. Similarly, mill stand No. 10 need be controlled only relative to mill stand No. 9 since it is stand of the continuous rolling mill. For the solution of this problem the fact is relied upon that the amount of metal passing through the pressure rolls of any given mill stand is a function of the thickness of the metal and of the speed of the rolls and. hence, the speed of the sheet. If, therefore, the thickness of metal passing through mill stand No. 5 is designated T5 and the speed of the material passing therethrough is designated S5, then the following condition must prevail: T5S5=TeSs:T'iS'i, etc. The invention therefore consists in controlling the motors M of the respective mill stands in accordance with the product of two factors, thickness and speed in relation to these factors in the preceding and succeeding mill stands.

Referring to Fig. 3, it will be seen that the motor M is normally controlled by a Ward-Leonard control system comprising a generator Gw driven by a motor MW, and the speed of the motor M is controlled by controlling the field winding Fw of the generator Gw. For controlling the field Fw there is provided a rheostat 40 from which a hand-controlled contact 4| operates. By means of this rheostat the approximate speed of motor M and therefore of the pressure rolls of a given mill stand may be set. In series with field Fw and the rheostat 40 there may be provided a second rheostat 42 from which operates a contact 43 on an arm 44 which may be carried by the shaft 45 of a motor 46. The armature of said motor is energized from any suitable source of supply, as shown. The field 41 of said motor is adapted to receive impulses generated in response to variations in the relative amounts of material passing through the respective mill stands, and thus the motor 46 is energized to vary the potential taken off rheostat 42 and therefore the voltage impressed on field Fw to change the the final mill speed of motor M in the proper direction either Y to increase or decrease the same as the conditions warrant to bring the amount of material passing through the respective mill stand to a point of equality with the amount passing through the adjacent mill stands. When this is accomplished, no further signal is impressed on field 41 of motor 46 and therefore the motor M will be rotating at the proper speed for this purpose. The impulse which is generated in response to variations in the amount of material passing through a mill stand is amplified by any suitable amp'lifler A before being impressed upon the field coil 41 of motor 46.

The manner in which an impulse or signal is generated when one of the mill stands Nos. 5-10 inclusive is passing more or less quantity of material than adjacent stands will now be described in connection with Figs. 4, 5 and 6. It has been pointed out above that the amount of material is a function of the product of two factors, namely, the thickness of the material passing through the pressure rolls and the speed with which the material passes through the rolls, or, what amounts to the same thing, the speed of the pressure rolls themselves. There is caused to be generated signals responsive to thickness and to speed of the sheet or pressure rolls. For this purpose, a contact arm-5l is caused to operate over a potentiometer coil 52 in accordance with the thickness of the material passing throu h the pressure rolls. For this purpose the arm 5i may be operated from any suitable pressure gauge or thickness indicator (not shown) which may be of the type disclosed in the co-pending application of Alexander Shayne and Alexander Zeitlin, Ser. No. 384,212, filed March 19, 1941, for Strain gauge for rolling mills and the like. potentiometer coil 52 is supplied with power from a suitable power source through a transformer 53. At the same time a voltage is caused to be generated in accordance with the speed of travel of the sheet or the speed of rotation of the pressure rolls. For this purpose, a contact arm 55 .4

may be caused to operate over a potentiometer coil 56 supplied from the same source of power as potentiometer coil 52. The contact arm 55 may be actuated from any suitable speed responsive member (not shown) actuated from the sheet or from the pressure rolls. as. for instance, a speedometer actuated directly from the pressure rolls. If the potentiometer coils, instead of being linear coils with the same number of windings per unit of length. are made logarithmic coils as shown in Fig. 6, then it will be seen that adding the impulse voltages taken off coils 52 and 56 is the same as multiplying the thickness and the speed. By this means the product of the thickness and the speed is obtained and therefore there is obtained a voltage which is a function of the quantity of material passing through the respective mill stand. The total voltage taken off potentiometers 52 and 56 by way of contact arms 5| and 55 is impressed across a potentiometer coil 60 at points GI and 62. Similarly, on mill stand 6 there are provided potentiometer coils 52 and 56' with which cooperate arms 5I and 55' actuated in accordance with the thickness and speeds of the material passing through mill stand N0. 6, and therefore the total voltage taken off these two potentiom= eters represents a function of the amount of material passing through mill stand No. 6. The voltages taken off potentiometers 52' and 56' are impressed across the coil 60 at a point 63 The- -in amounts of material passing through mill stands Nos. and 6 will produce.- Suppose that more material is passing through mill stand No.

5 than is passing through mill stand No. 6. This would normally tend to cause the material to buckle and form a loop or cobble between mill stands Nos. 5 and 6. This condition calls for remedying by either one or both of two means. Either the motor driving the pressure rolls of mill stand No. 5 must be slowed down or the motor driving the pressure rolls of mill stand No. 6 must be speeded up. The effect of more material passing through mill stand No. 5 will be that contact arms 5!. or"'55 or both have-been moved so as to increase the voltage drop'across 6| and 62, over and above'that between 63and 64. Since 62-63 represents of the potential taken all mill stand No. 5 and also of'the potential taken oif mill stand No. 6, if the potentials taken oif these mills are the same, then /2 the potentials are the same'andthe potential drop across 62-63 is constant. Shouldthe potential drop across 6263 increase, as will be the case 'if more material is passing through mill stand No. 5, then an impulse will be generated across the terminals 511, 5b, which will then,be

amplified by amplifier to cause the motor 46 to vary the contact arm 43 and thus change the voltagein coil Fw to-decrease the speed of motor M driving the pressure rolls of mill stand No. 5. At the same tim the increase in potential drop across 62 63 also increases the potential drop across 63-64 and therefore the impulse generated across the terminals 6a, 6b after being amplified by amplifier 50' will vary the motor M on mill stand No. 6 in the opposite direction because the terminals are oppositely connected and thus will speed up motor M driving the pressure rolls of mill stand No. 6. This will be apparent from Fig. 5. Therefore it will be seen that automatically the passage of more material through mill stand No. 5 than mill stand No. 6 causes the motor M of mill stand No. 5 to slow down and the motor M of mill stand No. 6 to speed up.

Mill stand No. 7 is similarly provided with potentiometer coils 52" and 56" over which operate arms SI" and 55" in response to thickness and speed of material passing through mill stand No. 7. The voltages taken oil potentiometer 52" and 56" are impressed across points 62 and 65 of'the potentiometer 60, and it will be seen that half of the potential drop from mill stand No. 7 is shared by half of the potential drop of mill stand No. 6 in opposite direction thereto. Suppose now that in the example taken above, the motor M of mill stand No. 5 were slowed down and the motor M of mill stand No. 6 were speeded up, and at this time a signal came from mill stand No. '7 which indicated that too much material was being supplied to mill stand No. 7, causing a loop. and therefore it would be necessary to speed up motor M of mill stand No. 7 and slow down motor M of mill stand No. 6. It will now be seen that motor M of mill stand No. 6 has received two contradictory impulses, the one due to too much material passing through mill stand No. 5, causing an impulse which would tend to increase the speed of mill stand No. 6, while the one caused by too much material being supplied to mill stand No. 7 would cause the mill stand No. 6 to decrease in speed. These signals,

if equal and opposite, would cancel each other out and the motor M of mill stand No. 6 would take no part in the adjustment. Instead, the motor of mill tand No. 5 would make all of the adjustment in slowing down, while the motor of mill stand'No. 7 would make all of the adjustment in speeding up.

In accordance with the provisions of the patent statutes, I have herein described the principle and operation of my invention, together .with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by'other equivalent means. Also, while it is designed to use the various features and elements in the combination and relations described.

' some ofthese may be altered and-others omitted without interfering with the more general result outlined, and the invention extends to such USE.

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

1. Ida continuous rollingmill comprising a plurality of mill stands, each having pressure rolls and a motor for driving said rolls, means whereby a constant quantity of material may be caused to pass through said rolls per unit of time,

said means comprising means at one mill stand responsive to the quantity of material passing through said rolls per unit of time, means at an adjacent mill stand responsive to the quantity of material passing therethrough per unit of time, means for opposing said plurality of responsive means, and means whereby any differential response controls the speeds of the motors of said mill stands.

2. In a continuous rolling mill comprising a plurality of mill stands, each having pressure rolls and a motor for driving said rolls, means whereby a constant quantity of material may be caused to pass through said rolls per unit of time,

said means comprising means at one mill stand responsive to the product of the thickness and speed of material passing through said rolls,

means at an adjacent mill stand responsive to 7 of material passing the product of the thickness and speed of material passing therethrough, means for opposing said plurality of responsive means, and means whereby any difierential response controls the speeds of the motors of said mill stands.

3. In a continuous rolling mill comprising a plurality of mill stands, each having pressure rolls and a motor for driving said rolls, means whereby a constant quantity of material may be caused to pass through said rolls per unit of time, .said means comprising :means for generating a voltage signal at one mill stand in response-to quantity of material passing through said. rolls, means for generating a voltage signal at the adjacent mill stand in response to quantity through the rolls thereof, means for opposin the signals from the respective stands, and means whereby any difierential voltage signal controls the speeds of the motors of said mill stands.

4. In a continuous rolling mill comprising a plurality of mill stands, each having pressure rolls and a motor for driving said rolls, means whereby a constant quantity of material may be caused to pass through said rollsper unit of time, said means comprising means for generating' a voltage signal at one mill stand in response to quantity of material passing through said rolls, means for generating a voltage signal at the 4- adjacent mill stand in response to quantity of material passing through the rolls thereof, means for opposing the signals from the respective stands, and means whereby any differential voltage signal controls the speeds of the motors of said mill stands to operate the same in directions so as to render said quantities equal.

5. In a continuous rolling mill comprising a plurality of millstands, each having pressure rolls and a motor for driving said rolls, means whereby a constant quantity of material may be caused to pass through said rolls per unit of time, said means comprising means for generating a voltage signal at one mill stand in response to the thickness and speed of material passing through said rolls, means for generating a voltage signal at the adjacent mill stand in response to the thickness and speed of material passing through the rolls thereof, means for opposing the signals from the respective stands, and means whereby any differential voltage signal controls the speeds of the motors of said mill stands.

6. In a continuous rolling mill comprising a plurality of mill stands, each' having pressure rolls and a motor for driving said rolls, means whereby a. constant quantity of material may be caused to pass through said rolls per unit of time, said means comprising means for generating a voltage signal at one mill stand in response to the thickness and speed of material passing through said rolls, means for generating a voltage signal at the adjacent mill stand in response to the thickness and speed of material passing through the rolls thereof, means for opposing the signals from the respective stands, and means whereby any difierential voltage signal controls the speeds of the motors of said mill stands to operate the same in such directions as to render 10 said signals equal.

7. In a continuous rolling mill comprising a plurality of mill stands, each having pressure rolls and a motor for driving said rolls means whereby a constant quantity of material may be caused to pass through said rolls per unit of time, said means comprising means for generating a voltage signal at one mill stand in 'respons'eto ALEXANDER ZEITLIN.

Images