US3882709A - Method for controlling the profile of workpieces on rolling mills - Google Patents

Abstract

There is described a method for controlling the profile of a workpiece on a rolling mill, wherein the workpiece is imparted with a predetermined profile in the roughing stage which is suitable for further control in the following finishing stage. In the finishing stage, the desired profile of the workpiece is attained by adjustment of one or a combination of factors including modifying the rolling loads of the respective roller stands preceding the last stand, cooling of the rolls, and changing the rolling pitch. The final shape control of the workpiece is carried out on the last stand. The adjustment of the rolling load is performed by simulating the desired workpiece profile by means of an even ordered function whose constants represent the load determining factors and by adjusting such constants in accordance with the desired changes in the load conditions.

Description

United States Patent 1191 Kawamoto et a1.

[ 1 May 13, 1975 METHOD FOR CONTROLLING THE PROFILE OF WORKPIECES ON ROLLING MILLS [75] Inventors: Toshiharu Kawamoto; Yoji Itoh;

Kouji Hiyoudo, all of Sakai; Kenya Fukushima, Himeji, all of Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Oct. 15, 1973 [21] Appl. No.: 406,352

[30] Foreign Application Priority Data Oct 16, 1972 Japan 47-10277] [52] US Cl. 72/234; 72/6; 72/16; 72/366 [51] Int. Cl B21b 1/22; B21b 37/00 [58] Field of Search 72/6, 8-12,

3/1971 Fischer et a1, 72/8 11/1971 Sabatini et a1. 72/8 OTHER PUBLICATIONS Primary E.wminerMi1ton S. Mehr [57] ABSTRACT There is described a method for controlling the profile of a workpiece on a rolling mill, wherein the workpiece is imparted with a predetermined profile in the roughing stage which is suitable for further control in the following finishing stage. In the finishing stage. the desired profile of the workpiece is attained by adjustment of one or a combination of factors including modifying the rolling loads of the respective roller stands preceding the last stand, cooling of the rolls, and changing the rolling pitch. The final shape control of the workpiece is carried out on the last stand. The adjustment of the rolling load is performed by simulating the desired workpiece profile by means of an even ordered function whose constants represent the load determining factors and by adjusting such constants in accordance with the desired changes in the load con- 10 Claims, 11 Drawing Figures [56] References Cited UNITED STATES PATENTS 3,049,950 8/1962 Pearson r r I. 72/8 3,248,916 5/1966 Kenyon et a1 72/16 X diti ng,

3,387,470 6/1968 Smith 72/7 3,475,935 11/1969 Kajiwara 72/9 1 4 m2 Fl F5 6 F6 f TENTH] HAY I 3W5 SHEET 1 BY FIG.

FIG.3

FIG.2

mum

FCRmin FCRmax FCR TARGET A JV AVAVA 7 (2) F6 PROFILE CONTROL STOP T A v EX.2 EX.3

SHAPE CONTROL START g mmiomm (I) LONGITUDINAL STRETCH AT EDGES (2) LONGITUDINAL STRETCH AT CENTER FIG.4

PATENTEB HA! I 3 I975 SHEET 2 BF 3 FIG.6

PLATE WIDTH, ROLLING FORCE FIG.7

FIG

[I'll-Ill 3 ITI h- PZQQWEMOQ @ZFOMKEOU Wu PLATE WIDTH M STRETCH FIG.|O

FIG.9

F ROLLING FORCE I [CALCULATING RP, RCI

PIIIENIED HAY I 3 BIS SHEET 3 BF :3

FIG.II

CALCULATING CV CALCULATING Wv| IgXPONENTIALLY SMOOTHING CI,b

I LESTIMATING Cv,Wv OF NEXT COIL] DNHETHER ESTIMATED Cv EXCEEDING LS ZI YES CALCULATING LD [WHETHER LD EXCEEDING LS AL YES CRAMPING LD CALCULATING RP, RC I CALCULATING IRC ICALCULTATING ROUGH Cv BY RLD OR RB] I [WHETHER RLD EXCEEDING LS l YES CRAMPING RLD [RE 'CALCULATING FINISH LD1 CALCULATING? IRC TAKING REFFERENCE LD OF THIS JBAR TAKING THIS B I TAKING FINISH LM OF. THIS BAR I ROUGH LM OF AR Rsg METHOD FOR CONTROLLING THE PROFILE OF WORKPIECES ON ROLLING MILLS FIELD OF THE INVENTION The instant invention relates to a method for controlling the profile of a plate being rolled on a rolling mill to a desired shape.

BACKGROUND OF THE INVENTION As is well known in the art, a rolled plate actually contains, variations in its thickness both in the transverse and the longitudinal directions. The variations in the transverse direction which is across the width of the plate, is expressed in terms of the crown and the wedge which together define the profile of the plate. The Crown is the difference between the thickness along the longitudinal centerline of the plate and the thickness at the longitudinal side edges of the platev The Wedge is the difference in thickness between the front and rear ends of the plate (lzw 12d).

In order to adjust the profile of a plate workpiece, it has been the general practice to measure the thickness of the plate at various positions across its width to enable an operator to make appropriate adjustments such as in the rolling pitch, rolling load distribution, reduction on the driving side as well as on the working side of the mill, and thus to modify the profile based on the actual measured values. However, this method presents inconveniences in that the measurement takes a relatively long time and a modification of the rolling load imposes adverse effects on the plate temperature and precision of the plate thickness. Furthermore, adjustment of the rolling pitch leads to reductions in working efficiency, and adjustment by reduction of the driving side or the working side often entails problems relating to proper passage of the plate through the rolls. Obvi ously, taking into consideration the aforementioned problems, the determination of the optimum values of each of the corresponding factors is prohibitively complicated.

SUMMARY OF THE INVENTION Based on theoretical and experimental studies on the profile control of a plate undergoing hot rolling, the present invention contemplates solving the problem of how to distribute the correction in the crown and wedge values to a number of roll stands in the roughing and finishing stages or mills. The present invention is supported by the findings in these studies and is directed to a method which is capable of providing an optimum profile control.

In hot rolling using a number of roll stands, a limitation is naturally imposed on the profile control capability of each stand. In order to roll a workpiece into a desired profile, a load corresponding to the desired profile should be distributed among the respective roll stands.

In view of the practical problems of actual control mechanisms and adjustments of control settings, the workpiece is preferably rolled in two stages or mills: the roughing mill and the finishing mill. The workpiece is imparted with a rough profile in the roughing stage to a degree suitable for facilitating final shaping into the desired profile in the following finishing stage. In other words, the roughly profiled workpiece is finished into the desired profile with high precision in the finishing stage of the rolling. It is preferable to employ a plurality of roll stands in the finishing stage. The rolling load required to obtain the desired profile is then distributed to all of the roll stands in the finishing stage with the exception of the last one which performs only shape control. Instead of employing a large plurality of roll stands, there may be employed a system using one or several reciprocating multi-roll stands, while distributing the rolling loads to each pass. The load distribution as mentioned above should preferably be applied also to the roll stands in the roughing stage.

The profile control during rolling is performed on the basis of factors such as adjustment of the roll cooling temperature and adjustment of the rolling pitch.

The rolling profile can be simulated in terms of an even ordered function whose constants correspond to the control factors in actual rolling. It is therefore possible to control the rolling profile by adjusting of the constants thereby effectively adjusting the control factors.

It is a primary object of the instant invention to provide a method for controlling the profile of a workpiece on a rolling mill to impart thereto a desired profile.

It is another object of the present invention to provide a method for controlling the profile of a workpiece on a rolling mill without imposing adverse effects on the shape of the workpiece as a result of the profile control.

The above and other objects, features and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings which are employed for the purpose of facilitating the understanding of the present invention and not for the purpose of placing thereon any limitation whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a cross-sectional view of a generally used workpiece;

FIG. 2 is a graphical representation of the relationship between the finishing crown ratio (FCR) and the roughing crown ratio (RCR) as will be obtained in accordance with the workpiece profile control method of the present invention;

FIG. 3 is a block diagram showing a portion of a rolling system employed in the present invention;

FIG. 4 is a graphical representation of profile errors (EX.1 and EX.2) occuring when utilizing a conventional method and profile errors (EX.3) occuring when utilizing present invention;

FIG. 5 is a graphical representation of the relationship between the bending force and crown variations of the roll stand in accordance with the present invention;

FIG. 6 is a graphical representation of the relationship between correction coefficients n 11 plate width (or workpiece width) and rolling force of a roll stand when utilizing the present invention;

FIGS. 7 to 10 are graphical representations of characteristics of a rolling system utilizing the present invention; and

FIG. 11 is a block diagram or a flow chart explaining a workpiece profile control method embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows in a somewhat exaggerated manner the cross-section of a plate which has been rolled by an ordinary method. As shown, the rolled plate P has a varying thickness which is largest in the middle of the plate, as indicated by lit", and is smaller at the side edges as indicated by hw and hd. The plate thus has a crown of he (hw hd)/2 and a wedge of hw lid. The causes of the crown and wedge are well known and it has been the conventional practice to. control them to within predetermined values using a finishing stand. However, such control of the crown often results in wavy edges along the plate as well as overstretching in the middle of the plate which impairs the shape namely the flatness of the plate. In order to avoid such impairment of the shape, it is necessary to bring the profile into an allowable range by rough correction as early as in the roughing stage of the rolling.

This relationship is shown graphically in FIG. 2 where the ordinate represents the rough crown ratio (RCR) and the abscisa represents the finish crown ratio (FCR). The crown ratio (RCR) or (FCR) is expressed RCR or FCR /2 (hd hw)/hc) The straight line 1 is a plot of RCR FCR and the hatched area shows the allowable range of the crown ratio at the end of the finishing stage. A plate having a crown ratio within this range allows finish rolling without causing deterioration in its shape.

In the roughing stage the crown of the plate workpiece is thus corrected to have a value within the allowable range. Fine adjustments are then carried out during the finishing stage so that the plate is imparted with the final desired profile. However, if the last stand in the finishing stage also performs crown control, there still results the adverse effects on the shape of the workpiece as mentioned hereinbefore. Therefore, in

the present invention, the workpiece undergoes no crown control from the last stand of the finishing stage and the crown control is performed by a roll stand or stands preceding the last stand, preferably, by the fifth stand or, if necessary, by the fifth and other preceding stands when the finishing stage includes six stands, the last stand performing only the shape control. The same in connection with the Wedge control. By carrying out the crown and wedge control in this manner, it becomes possible to obtain a product with a desired profile and with excellent flatness.

FIG. 3 diagrammatically shows an arrangement of a mill carrying out the above-mentioned control under various conditions, while FIG. 4 shows the results of experiments conducted using the mill. In FIG. 3,. Fl to F6 are the first to sixth stands of a tandem finish rolling mill. Also shown is a profile measuring device 1, a shape measuring device 2, a profile control device 3, and a shape control device 4. Both profile control and shape control were carried out by way of roll bending and reduction adjustments, and the rolling was carried out in the following three different ways.

EXAMPLE 1 Profile control only using all the tandem finish roll stands Fl to F6.

EXAMPLE 2 profile control by using all the tandem roll stands Fll to F6 and shape control by using stand F6.

EXAMPLE 3 Profile control by using the tandem finish roll stands I F1 to F5 and shape control only by the last roll'stand F6. This last example being according. tothis invention. .5 g As is clear from FIG. 4, the control in Example I atf tains a profile of the target value but showsan ex-f tremely unsatisfactory flatness. The control in Example 2 also results in a profile of the target value but is also I I incapable of correcting the flatness even if the shape r control was utilized to its maximum. The control inExf 1 j ample 3, however issatisfactory both in profile as well I as in flatness and a suitable flatnesscan be obtained using the capabilities of the shape control device. ,ltcan therefore be understood that the method ofthe inven i tion is greatly effective in controlling the profile and r the shape of a plate being rolled; I

According to the present invention, the reduction adjustment is performed in the following: mannenThe gree, as

wherein the coefficient a is determined bythe loaddis; I tribution for the respective roll stands, the kind of} workpiece being rolled and the initial roll curve. The coefficient b is determined by the deviation between i the roll center 0' and the plate center 0, and C is a constant. For example, if the profile is expressed by thei quadratic equation of y a(x b) C of Equation (I), using the definitions mentioned above, the crown C andthe wedge W can be expressed as follows (symbols are as in FIG. 1):

the roll] b) +2c+2a( bywolij, I

From Equations (3) and (4), the contents of the quadratic equation y a(x b) C can be written as Actually by way of example the coefficients a, b are used by, exponentially smoothing the values obtained from the actually measured values C and W,..

On the other hand, in order to control a plate into a desired profile, since the wedge W,. is normally preferred to be zero b should be equal to zero. Thus, the coefficient a should be determined in accordance with a desired crown (1.. There are many factors which influence the coefficient a and they are considered in the present invention as follows.

wherein al represents the influence of the initial roll curve, a2 represents the roll bending amount due to a rolling reaction force a3 represents the resistance to deformation of the workpiece, and a4 is a learning term including heat crown and abrasive wear. For a desired profile the coefficient a can be calculated from the Equation (5) while the factors al, a3 and 04 can be accurately obtained by precalculation and as a result of learning. The roll bending amount a2 for the desired profile may be obtained from the following equation.

Once the roll bending amount a2 is obtained, the rolling reaction force F,- required for producing such a roll bending amount can then be obtained as a function of a2, more particularly, as f (a2). The rolling reaction force F,- is introduced during the finishing process, on a roll stand positioned close to the final roll stand for imparting the desired profile to the workpiece. If the finishing stage includes six roll stands and the aforementioned rolling reaction force F is introduced, for example, by the fifth stand or other preceding stands, the reference load distribution among the first six stands becomes unbalanced, causing irregularities in the total rolling amount. This, however, can be corrected by increasing or reducing the rolling load of the fourth and other preceding roll stands. If sufficient correction cannot be attained with such adjustment, it may be effected through rolling pitch adjustment and roll cooling adjustment.

The load distribution in the roughing stage can be effected in the same manner as in the finishing stage. The crown desired to be produced during the roughing stage, is determined from the relationship shown in FIG. 2. More particularly, the rough crown ratio is first obtained which will produce the allowable range of the finish crown ratio. Then, from the rough crown ratio RCR and the rough finish target thickness hHT, the rough crown C is calculated as follows.

c,., hHT 1 RCR) The load distribution control is then effected in such a manner that the workpiece attains the desired rough crown ratio at the end of the roughing stage. However, the roll bender is also effective for controlling the crown ratio in the roughing stage. Since the bending force and variations in the crown resulting from such bending force, have the relationship as shown in FIG. 5, the difference between the rough crown C in the preceding operation and the presently required rough crown C is obtained as A C,., C m C and the required reference bending force AT can be obtained from FIG. 5. The correction coefficients n, and 17 for the plate width and the rolling reaction force are obtained from FIG. 6, from which the required bending force AT of the roll bender is calculated by the following equation.

AT}? 11 72) ATRS The crown correction effected through load distribution in the roughing stage is mainly performed by the last roughing roll stand with aid of one or two preceding stands which are adapted to compensate for any deficient amounts in the correction. After determining the required rough crown C,., as discussed hereinabove, a correction coefficient n for the plate width W1 is obtained from the graph of FIG. 7 showing the relation between the plate W and the width correction coefficient 1 required roll bending amount RCR, can be calculated from the equation.

Using the required roll bending amount RCR it is possible to obtain the required reference rolling reaction force F from FIG. 9 and the required stretching rate A, from FIG. 8. The stretching rate A of the sixth and last stand R6 in the roughing stage having six roll stands is expressed as A6 2 h, x, x hHT This is sequentially repeated to determine the thickness schedule in the roughing stage.

The rolling reaction force F,- is normalized based upon the kind, width and temperature of the steel plate being rolled and converted into the required rolling reaction force F, upon determination of the screw value in consideration of the spring back of the rolling mill. That is,

This routine learning takes into consideration the learning of the correction coefficient 1 resulting from correction of the curve of FIG. 8 and correction by the operator.

As already discussed with reference to FIG. 2, the allowable range of the finish crown ratio FCR is defined by the determination of the rough crown ratio RCR. As a result, there are obtained a maximum adjustable crown C and a minimum adjustable crown C,.,,,,-,, as follows.

AiM min) rmin AiM V nm.r)

( Next, al is inserted into Equation (3) with b O, to obtain the crown C, as follows.

where W0 represents the body length of the roll. The

value thus obtained is regarded as the initial roll curve but, in practice, an initial roll curve K C, is employed using the correction coefficient K taking into consideration a particular schedule, or the like.

The correction of the wedge can be effected through one or a number of arbitrarily selected roll stands in the roughing stage. Forexample, where the stand R5 is used solely for this purpose, the correction is effected by adjustment of the selsyn difference (levelling WS D5) of the fifth stand R5 and the last stand R6 is used for effecting a correction such as of bending. The regressions measures of the extent to which two variables increase together, or one increases while the other decreases) of the wedge amount W,., the levelling amount R'5 by the fifth stand R5, and the plate width Ware expressed as follows.

W,. 0.00866R5 0.00242W 0.94

Thus, in order to have a wedge of zero value, the levelling amount R'5 of the stand R5 should be R'5 0.28W- 109 K (l/lOOm/i m) wherein K is a learning term.

FIG. 10 shows the relation between the wedge amount W, and the levelling amount R'5 of the fifth stand in accordance with Equation (17) using a fixed plate width (W= W0). If the wedge amount W,. as obtained from Equation (4) deviates from the reference value, levelling is effected in accordance with Equation (18) and the term K is learnt in accordance with a value measured by a profile meter.

If the levelling is effected in an amount R50 and the measured value of the wedge is W a levelling den:

ciency is obtained from FIG. was

The correcting amount is obtained by multiplying the. 5'

deficiency by the gain K That is,

KRNEW KROLI) KG m 6 i The aforementioned various means of profile control are summarized in FIG. 11 by way ofa flow chart. In this figure, the symbol LS represents the limit of standard, LD the load distribution, RP the rolling pitch, RC 7. the roll cooling, IRC the initial roll crown, RLD the roughing load distribution, RE the roll bender and LM the levelling mode.

It will be clear from the foregoing detailed descrip- I tionthat, according to the instant invention, the profile correction is suitably distributed over the roughing and finishing stages and the correction of theprofile is opti-i mally carried out by way of changing the load distribu-- tion and by means of the roll bender, so that the workpiece can be controlled with a desired profile to a high precision.

Since certain changes may be made in theabove described workpiece profilecontrol method without de l T parting from the scope of the inventionasdefmed by i the appended claims, it is'intended that all matter contained in the above description should be interpreted as illustrative and not in a limiting, sense. I We claim:

l. A method of controlling the crown of a workpiece passing through a rolling mill comprising the steps of roughly adjusting the crown by means of a first roughing stage of the rolling mill to produce a profile on the workpiece which is within an allowable predetermined range for a successive second finishing stage of the rolling mill, and finely adjusting the crown by means of said second, finishing stage ofthe rolling mill to pro' -w duce the desired profile on the workpiece by utilizing all but the final stand within said finishing stage.

2. The method of claim 1 further comprising the step; I of controlling the flatness of said workpiece by adjusta ing said last stand.

3. The method of claim 1 wherein said crown is con-, trolled by adjusting the roll temperatures of the stands. 1 if 4. The method of claim 1 wherein the crown control I of said roughing stage is performed by adjusting, the roll.

benders.

ing of at least one roller of astand in said roughing stage. i

8. The method of claim 1 wherein saidcrown is corii trolled by modifying the load distribution among the stands.

9. The method of claim 8 wherein said modifyingoff the load distribution is effected by simulatingfthe de sired crown by an even ordered function and altering;

the constants of said function to control the load distrifunction and altering the constants of the function at bution among the stands. each stands to control the load distribution among the 10. The method of claim 9 further comprising simustands.

lating desired crowns at each stands by an even ordered

Claims (10)

1. A method of controlling the crown of a workpiece passing through a rolling mill comprising the steps of roughly adjusting the crown by means of a first roughing stage of the rolling mill to produce a profile on the workpiece which is within an allowable predetermined range for a successive second finishing stage of the rolling mill, and finely adjusting the crown by means of said second, finishing stage of the rolling mill to produce the desired profile on the workpiece by utilizing all but the final stand within said finishing stage.

2. The method of claim 1 further comprising the step of controlling the flatness of said workpiece by adjusting said last stand.

3. The method of claim 1 wherein said crown is controlled by adjusting the roll temperatures of the stands.

4. The method of claim 1 wherein the crown control of said roughing stage is performed by adjusting the roll benders.

5. The method of claim 1 wherein said crown is controlled by adjusting the rolling pitches at the stands.

6. The method of claim 1 wherein wedge control of the workpiece is performed solely at said roughing stage.

7. The method of claim 6 wherein said wedge control of the workpiece is performed by modifying the leveling of at least one roller of a stand in said roughing stage.

8. The method of claim 1 wherein said crown is controlled by modifying the load distribution among the stands.

9. The method of claim 8 wherein said modifying of the load distribution is effected by simulating the desired crown by an even ordered function and altering the constants of said function to control the load distribution among the stands.

10. The method of claim 9 further comprising simulating desired crowns at each stands by an even ordered function and altering the constants of the function at each stands to control the load distribution among the stands.

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