US3782152A

US3782152A - Apparatus for improving the flatness of rolled strips

Info

Publication number: US3782152A
Application number: US00240400A
Authority: US
Inventors: B Sabatini
Original assignee: Centro Sperimentale Metallurgico SpA; ITALIAN Mfg CO
Current assignee: Centro Sperimentale Metallurgico SpA; ITALIAN Mfg CO
Priority date: 1971-04-22
Filing date: 1972-04-04
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01
Also published as: DE2219323B2; DE2219323A1

Abstract

A device for improving the flatness of metal strips during rolling, comprising a set of cylindrical rollers located side by side, located upstream of the rolling stand, independent from one another and with their respective axes parallel to the axes of the rolling cylinders, in such a manner as to correspond to the strip width. The said cylindrical rollers are so arranged as to take positions always parallel, and mutually staggered in the vertical plane by the action of servo-controls coming from detecting means for the planarity and/or the rolling tension in the strip, said last cited means being located downstream of the rolling stand, through a checking and adjusting equipment.

Description

United States Patent 1191 [111 3,72,111; Sabatini Jan. 1, 119741 [54] APPARATUS FOR IMPROVING THE 3,499,306 3/1970 Pearson 72/17 AT S 0 ROLLED STRIPS 3,534,571 10/1970 Sivilotti et al.. 72/8 2,809,519 10/1957 Kaestner 73/159 Inventor: Bruno Sabatml, Rome, Italy 3,581,536 6/1971 Terwilliger 72/9 [73] Assignee: Centro Sperimentale Metallurgico I S.p.A., an Italian Manufacturing Primary Examiner-Milton Co" Rome [taly Att0rneyl,rvin S. Thompson et al.

22 F1 4 1 Apr 1972 57 ABSTRACT [21 1 Appl' 240400 A device for improving the flatness of metal strips during rolling, comprising a set of cylindrical rollers 10- [30] Foreign Application Priority Data cated side by side, located upstream of the rolling Apr. 22, 1971 Italy 49910 A/71 Stand independent from one amther and with their respective axes parallel to the axes of the rolling cylin- 52 us. c1. 72/9, 72/17 in Such a manner as to correspond to the Strip [511 1m. (:1 B21b 37/12 Width- The Said cylindrical rollers are 80 arranged as [58] Field of Search 72/9. 8. 10, 12, to take Positions always Parallel, and mutually Stag- 72/]7; 73/159 gered in the vertical plane by the action of servocontrols coming from detecting means for the planar- 5 References Cited ity and/or the rolling tension in the strip, said last cited UNITED STATES PATENTS means being located downstream of the rolling stand,

through a checking and adjusting equipment. 3,459,019 8/1969 Stone 72/12 2,21 1,658 8/1940 Hudson 72/234 X 1 Claim, 2 Drawing Figures 1'3 l 0 O i n (1 PATENTH] JAN 1 I974 SHEET 2 0F 2 l APPARATUS FOR IMPROVING THE FLATNESS F ROLLED STRIPS The present invention relates to a device for improving the flatness of rolled strips. More specifically, once a defect of planarity has been detected in a strip during the working thereof, the device according to this invention allows the conditions of rolling to be modified so as to correct said planarity defect without introducing, as a consequence of the correction, any substantial change in the value of the average thickness of the rolled strip.

It is known that the defects of planarity occur during the rolling operation of the strip when the rolling clearance between the cylinders under load is such that the profile of the cross section of the strip issuing from the rolling mill is not geometrically similar to the corresponding profile of the strip entering into the rolling mill, the term rolling clearance under load meaning the gap between the rolling cylinders, in the absence of the material to be rolled, with the modifications induced by the elastic deformations undergone by the cylinders and by the other structures of the rolling mill, under the action of the forces originated during the rolling process.

In turn the clearance between the rolling cylinders, in the absence of the material to be rolled, is determined by the position of the screws for adjustment of the stand and by the effect resulting from the crowning or concavity obtained by the machining of the cylinders, from the thermal expansion of the cylinders and from their wear during the rolling.

It is known that systems at present adopted for adjusting the thickness of the strip, interfere to a greater or lesser extent, with the flatness of the strip itself, as their action determines changes in the shape of the roll gap. The interference is such that for instance the correction of a thickness error implies the introduction of a flatness defect or error. The above interference between the thickness correction and the planarity occurs also reversely as the correction of an error of planarity, with the systems used up to now, implies generally the introduction of a change in the average thickness of the strip. During the rolling operation, errors in both strip flatness and thickness must be corrected and conditions may arise wherein the cited interference between flatness and thickness will decrease the speed of correction and/or will cause oscillations difficult to stop.

The means at present used for rolling strip, so as to reduce flatness and thickness errors are multiple. Even in the variety of their embodiments, these means can be grouped under the following groups:

a. use of a sequence of rolling for the strips, having different widths and different thicknesses, subordinated to the state of wear of the cylinders;

12. intervention from outside on the cylinders, so as to change in a suitable way the shape of the rolling clearance, by means of a modification of the crowning of the cylinders themselves. This intervention can be effected thermally or mechanically. If thermally, it is necessary to cool; in a suitably differentiated way, the roll table and the expansion of the cylinders along the table will be thus adjusted. If mechanically, external forces are applied to the cylinders in order to suitably increase the elastic bending deformation, and to obtain thereon the crowning as required by the particular conditions of rolling and to avoid thus the flatness defects.

The disadvantages deriving from the adoption of the above systems are manifest. In case of mechanical control, the optimum rolling program for the planarity exigencies does not coincide necessarily with the rolling program required by that of the orders to the rolling mill. In the case of the thermal control of the expansion of the cylinders, the process is scarcely satisfactory as it s effect is delayed and furthermore the maximum correction which can be obtained is small due to the small thermal gradients which can be induced between two points on the mass of the cylinder. Likewise, the recourse to the deformation by bending of the cylinders from outside is limited by the strength thereof and by the size of the forces generally required in order to obtain adequate modification of the roll camber. In this case it is furthermore difficult to establish the best conditions at different points along the roll table. In fact a deformation of the cylinder which is capable of improving the planarity in one zone of the strip can produce a result incompatible with the conditions of planarity induced in other zones of the strip.

The main purpose of the present invention is that of providing a device which on the basis of the detection of the possible defects of flatness of the strip at its outlet from the rolling stand, will allow said defects to be corrected without substantially interfering with the average thickness of the rolled strip.

Another purpose of the present invention is that of providing a process allowing the detection of the possible flatness defects during the strip rolling operation and allowing also the correction of said defects by an adjustment which suitably modifies the rolling conditions of the strips without directly interfering with the cylinders of the stands.

The flatness defects in a strip, issuing from a rolling stand, can be detected by devices already known in the present art, based on the determination of the distribution across the strip width of the rolling tension.

The object of the present invention is the provision of a device, located upstream of the stand and capable of modifying, in compliance with the indications of one of the aforesaid detectors located downstream, the rolling conditions within said rolling stand, so as to impart good flatness to the strip issuing from the stand.

The device forming the subject-matter of the present invention, is connected, as aforesaid, to any device detecting the planarity of the strip, located downstream of the rolling stand, and the indicative signals of which are sent to a checking and controlling device (for instance a computer). This equipment, from the compar' ison of said signals with a signal having a standard value, previously programmed, will send a correction signal which intervenes by means of the device of the present invention.

This device consists of a set of cylindrical rollers located side by side, mounted upstream of the rolling stand (called hereinafter the TDC set) independent from one another and normally aligned throughout the width of the strip. Said TDC rollers are individually independent from one another and are capable of taking mutually staggered positions in the vertical plane. During the rolling operation, and provided the strip entering into the stand is subjected to a pull, each roll can be made by the aforesaid measuring and control equipment to perform a suitable vertical displacement, so that the roller itself will support the portion of strip resting on it to a greater or lesser extent, thus inducing in said portion of strip a rolling tension greater or smaller, respectively, with respect to the other portions of the strip.

Thus the rolling conditions will be modified so as to improve the flatness conditions as detected by the detection device.

The present invention will be now described with particular reference to the attached drawings, the purpose of which is illustrative and not limitative. Particularly in the drawings:

FIG. 1 is a diagrammatic perspective view of a rolling device according to this invention.

FIG. 2 is a side view of the device of FIG. 1.

As it will be noted, in said figures in order to avoid useless drawing complications, the parts not absolutely indispensable have been omitted. Particularly, in said figures, the reference numeral 1 denotes the strip being rolled, 2 is an exemplary embodiment by way of non limitative example, of a detection device consisting of a set of rollers (called in the following disclosure TDM set) located downstream of the rolling stand 3; 4 is the set of rollers TDC, 5 is a transducer (one for each TDM roller) measuring the force transmitted to each of the TDM rollers by the portion of strip bearing thereon, 6 is test and control equipment, preferably a computer, which compares the representative signal for the force on each TDM roller with the desired supporting force as previously programmed and which, upon detecting the possible deviations, will suitably modify the mutual position of the TDC rollers so as to compensate for said deviations, 7 is a transducer of the correcting signals sent by the computer to the rollers of the set TDC. The reference numeral 8 and 9 denote devices, for instance electro-hydraulic devices, rendering operative the TDM and TDC rollers.

In order to better understand the operation of the device according to this invention, in the considered case, which however is a non restrictive case, let us consider the strip as subdivided into many longitudinal portions each having a width which is a submultiple of the total width, and equal each to the axial length of each of the rollers of the sets TDC and TDM. Let us suppose, also that the total rolling pull will be distributed downstream of the rolling stand, so that the pull to which is subjected the portion of the strip nearest the person looking at FIG. 2 (this zone has been dashed in FIG. 1) will be greater than the desired pull. At this point the anomaly will be immediately detected as, on the underlying roller of the TDM set, a stress will be exerted,

greater than the average stress exerted on the other rollers of the set. Through the transducer 7 and the electro-hydraulic device 9, the equipment 6 will transmit to the corresponding roller of the TDC set which supports the same portion of the strip, the control for its vertical upwards movement with respect to the other rollers, so as to contribute a greater amount of the support of the strip, with a consequent local increase of the tension at the inlet into the rolling stand. Under these conditions the total tension will devolve to a greater extent on the portion of strip where the correction is required, and to a lesser extent on the remaining portions of the strip, and consequently said strip portion will have a lower yield strength against the deformation by the cylinders and therefore a greater reduction of thickness will be induced therein. (In fact it is known that the resistance of the material to compression by the cylinders decreases with the increase of the stress, to which the material is submitted, the rolling deformation being a function of the pressure of the cylinders and of the tension applied to the strip). Thus the stress to which the portion of the concerned strip is subjected will tend to diminish and thus the planarity error will tend to disappear. As said mechanism operates continuously, the rolling conditions will be the desired ones.

The present invention has been described with particular reference to its specific embodiments it, being however understood that changes or variations might be practically adopted without departing from the scope of the present invention as defined by the appended claims.

Having thus described the present invention, what is claimed is:

1. Apparatus for improving the flatness of metal strips during their rolling, comprising, in combination with a rolling mill stand, a plurality of strip deflector rollers mounted upstream from the rolling mill stand for rotation about axes parallel to the axes of the rolls of the rolling mill stand, the total length covered by said deflector rollers being such as to support the entire width of the rolled strip, means mounting said deflector rollers for movement transversely of their axes and transversely of the plane of the rolled strip independently of each other, and means downstream from said rolling mill stand for detecting nonflatness of said strip across its width and for individually moving said deflecting rollers relative to each other each in a direction and by an amount to correct said nonflatness.