Flatness measuring and measuring of residual stresses for a metallic flat product

Abstract

A method and apparatus for flatness measuring and measuring of residual stresses in a metallic flat product (1): The method includes bending the flat product (1) in a bending device (3) such that a planar flat product (1) forms an arc (5) with a target bending radius r.sub.0 after bending; measuring the contour and the actual bending radii r(y), in the region of the arc (5) of the bent flat product (1) at a plurality of positions along the width direction of the flat product (1); and determining the flatness of the flat product (1) taking into account the measured contour of the bent flat product (1).

Claims

1. A method for measuring the flatness of a metallic flat product, comprising the following method steps: bending the flat product at a location along the longitudinal direction of the flat product, so that after the bending, the planar flat product forms an arc along the location having a target bending radius r.sub.0; measuring a contour of the flat product in a region along the arc by measuring the actual bending radii r(y), in the region along the arc, of the bent flat product at a plurality of positions (y) in a width direction across the flat product; and determining the flatness of the flat product by taking into account the measured contour of the bent flat product along the length of the arc and across the width of the flat product at the arc.

2. The method as claimed in claim 1, further comprising measuring the contour of the flat product by measuring the actual bending radii r(x,y) of the bent flat product at a plurality of positions (x) along the longitudinal direction of the flat product; and determining the flatness of the flat product at a number of locations (x) along the longitudinal direction of the flat product taking into account the measured contours of the bent flat product.

3. The method as claimed in, claim 1, further comprising storing the determined flatness of the flat product and taking the stored flatness into account during further processing of the flat product.

4. A method for measuring the residual stresses of a metallic flat product comprising the following method steps: bending the flat product, so that after the bending, a residual stress-free flat product forms an arc along the location having a target bending radius r.sub.0; measuring a contour of the flat product at the arc by measuring actual bending radii r(y), in a region along the arc, of the bent flat product in a plurality of positions(y) in a width direction across the flat product; calculating the residual stress .sub.x(y) of the flat product taking into account the measured contour of the bent flat product.

5. The method as claimed in claim 4, further comprising: measuring the contour of the flat product at the arc by measuring the actual bending radii r(x,y), of the bent flat product in a plurality of positions (x) along the longitudinal direction of the flat product; and calculating the residual stress .sub.x(x,y) of the flat product for a number of positions in the longitudinal direction (x) of the flat product taking into account the measured contours of the bent flat product.

6. The method as claimed in claim 5, further comprising storing the residual stresses .sub.xof the flat product and then taking the residual stresses into account during further processing of the flat product.

7. The method as claimed in claim 1, further comprising: measuring an actual bending radius r optically by at least one light beam, emitting the light beam from a light source onto a surface of the flat product along the arc; reflecting the light beam from the surface of the flat product receiving the reflected light beam by a receiver ; and determining the distance between the light source, and the flat product and between the flat product and the receiver by the transit time of the light beam, by the phase difference between the emitted light beam and the received light beam or by means of triangulation.

8. The method as claimed in claim 7, further comprising: projecting a number of light beams onto a surface of the flat product along the arc for defining a light grid; and reflecting the light beams from the surface of the flat product and receiving the reflected light beams by a camera.

9. The method as claimed in claim 7, further comprising arranging a number of light sources and a number of receivers along the width direction (y) of the flat product along the arc and measuring the actual bending radii r(y) essentially simultaneously in the width direction (y) of the bent flat product.

10. A method for regulating the flatness of a metallic flat product, in a rolling mill, comprising the following method steps, rolling the flat product in the rolling mill; measuring the actual flatness P.sub.Act of the rolled flat product claimed in claim 1; determining a regulating error e between a target flatness P.sub.Tar and the actual flatness P.sub.Act, e=P.sub.TarP.sub.Act; determining a correcting variable u as a function of the deviation e by means of a regulator; applying the correcting variable u to an actuator in a rolling stand of the rolling mill, so that the regulating error e is minimized.

11. The method as claimed in claim 1, further comprising at least one of during, shortly before, immediately before, shortly after, and immediately after measuring the contour of the bent flat product, measuring the temperature T(y) of a fiber of the flat product in the width direction (y) and taking the temperature T(y) into account when determining flatness or calculating the residual stress.

12. An apparatus for measuring flatness or for measuring the residual stresses of a metallic flat product, the apparatus comprising: an input-side rolling conveyor located and configured for conveying the flat product; an input-side bending device following the input side rolling conveyor and comprised of at least two entry rollers for contacting opposite surfaces of the flat product, the entry rollers being located for bending the flat product, to form a bending radius r.sub.0in the flat product along a longitudinal length location of the flat product; a distance measuring device for measuring the contour at the actual bending radii r(y), of the bent flat product at a plurality of positions in a width direction (y) of the flat product; and a computation unit for determining the flatness or the residual stresses of the flat product and the computation unit is connected to the distance measuring device for the purpose of exchanging signals.

13. The apparatus as claimed in claim 12, wherein the distance measuring device comprises an optical, distance measuring device.

14. The apparatus as claimed in claim 12, further comprising the distance measuring device is arranged in a vertical direction above the flat product and in a horizontal direction in the region of an apex of the arc of the bent flat product.

15. The apparatus as claimed in claim 12, further comprising: an output-side bending device comprised of at least two exit rollers at opposite surfaces of the flat product and located along the longitudinal length of the flat product spaced from the entry rollers and the exit rollers being configured for bending the bent flat product back toward an unbent condition; and an output-side rolling conveyor located and configured for conveying the bent back flat product from the exit rollers.

16. The apparatus as claimed in claim 15, further comprising at least one of the entry rollers of the input-side bending device is drivable to bend the flat product and/or driving at least one exit roller of the output-side bending device to bend back the bent flat product.

17. The apparatus as claimed in claim 15, wherein at least one of the entry and the exit rollers are drivable so as to form an arc in the flat product along the longitudinal direction of the flat product between the entry and the exit rollers.

18. The method as claimed in claim 4, wherein the calculation of the residual stress of the flat product takes into account the measured contours of the bent flat product according to the formula ${}_x\left(y\right)=E.Math.{\mathrm{.Math.}}_x\left(y\right)=E.Math.\frac{r_0-r\left(y\right)}{r_0}$ wherein E is the modulus of elasticity of the flat product, .sub.x(y) is the elongation in the x direction in position y, r(y) is the measured actual bending radius in position y, and r.sub.0 is the nominal bending radius of the flat product in the apparatus or the mean radius r(y) over the width B.

19. The method according to claim 5, wherein the calculation of the residual stress of the flat product takes into account the measured contours of the bent flat product according to the formula ${}_x\left(x,y\right)=E.Math.{\mathrm{.Math.}}_x\left(x,y\right)=E.Math.\frac{r_0-r\left(x,y\right)}{r_0}$ wherein E is the modulus of elasticity of the flat product, .sub.x(y) is the elongation in the x direction in position y, r(y) is the measured actual bending radius in position y, and r.sub.0 is the nominal bending radius of the flat product in the apparatus or the mean radius r(y) over the width B.

20. The method according to claim 7, wherein the at least one light beam is a laser beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention will emerge from the description which follows of non-restrictive exemplary embodiments, with reference being made to the figures below, in which:

(2) FIG. 1: shows a schematic representation of an inventive apparatus for measuring flatness or for measuring the residual stresses of a flat product.

(3) FIG. 2a: shows a detail of FIG. 1.

(4) FIG. 2b: shows a side view of the strip from FIG. 1.

(5) FIG. 3: shows a schematic representation of an alternative apparatus to the one in FIG. 1.

(6) FIGS. 4 and 5: show respective schematic representations of a first and a second variant of the apparatus shown in FIG. 1.

(7) FIGS. 6a and 6b: show respective representations of the arc from FIG. 1 with different strip tensions.

(8) FIG. 7: shows a representation of the apparatus shown in FIG. 1 with modifiable r.sub.0 and modifiable arc length for thin and thick strip.

(9) FIG. 8: shows a representation of an inventive apparatus having a variable bending radius r.sub.0 over the longitudinal extension.

(10) FIGS. 9a and 9b: show a representation of the influence of tensile stresses in the flat product on a subsequent production process.

DESCRIPTION OF EMBODIMENTS

(11) FIG. 1 shows a schematic representation of an apparatus for measuring flatness or for measuring the residual stresses in a flat product 1 configured as steel strip. After the strip has been rolled in a rolling stand of a finishing rolling line (not shown), the strip 1 is conveyed by an input-side rolling conveyor 2a in a horizontal direction to the input-side bending device 3 with a pair 3a, 3b of entry rollers embodied as driver rollers 7 engaging the strip at its opposite surfaces. The entry rollers 3a, 3b are located relative to the horizontal direction above the path of the strip 1 to bend the strip 1 upward, forming an arc 5 in the strip with a radius of curvature r.sub.0 about the center point M of the arc assuming that the strip is planar or free of residual stresses. The arc 5 is free between the contact lines of the entry rollers 3a, 3b and the contact lines of the exit rollers 4a and 4b, in other words it is not conveyed in this arc region. Arranged above and roughly in the region of the apex of the arc 5 are a plurality of distance measuring devices 6. In the example shown, each light source of a distance measuring device 6 emits a laser beam, which is reflected by the surface of the arc 5 and received back by the receiver in the distance measuring device 6. Thus the distance measuring devices 6 determine the contour of the strip in a number of positions y in the width direction of the strip 1. More specifically, the contour of the strip 1 is determined for example based on the transit time of the laser beam or the phase shift of the reflected light beam in relation to the emitted light beam, allowing the slightest deviations in the contour of the strip to be determined.

(12) As shown in FIG. 2a a number of, in this instance 16, distance measuring devices 6 may be arranged in the width direction y of the strip 1. Alternatively, one distance measuring device 6 may traverse in the width direction y of the flat product.

(13) After the contour has been measured, the strip 1 is bent again by the two exit rollers 4a, 4b above the path set by output side conveyor 2b in the transport direction T and then conveyed on the output-side rolling conveyor 2b in a horizontal transport direction T to a cooling section (not shown). In order for the flatness or residual stress measurement not to be falsified by tension or pressure in the strip, the strip is roughly tension-free and pressure-free in the region of the arc 5. This is achieved for example in that both the entry rollers 3a, 3b and the exit rollers 4a, 4b are embodied as driver rollers 7 and the drive torque of the driver rollers 7 is set so that the strip 5 is essentially tension/pressure-free during measuring.

(14) The contour, in particular the actual bending radii r(y), of the strip is transmitted to a computation unit (not shown), which determines the flatness and/or the residual stresses of the strip and outputs it/them by way of an output unit. The distance measuring devices 6 are connected to the computation unit by way of a bus interface here.

(15) In order not to be restricted to determining the flatness or the residual stresses of the strip 1 only in the width direction y, the strip 1 is moved in the transport direction T, while the distance measuring devices 6 determine the contour of the flat product. From the contour information, which is available for example in the form of a matrix (e.g. the 16 simultaneously analyzed actual bending radii r(y) of the flat product in the width direction can represent one row of the matrix; successive contour sampling steps are performed in adjacent rows of the matrix), it is possible to determine the flatness of the strip. With regard to the formulas for common flatness parameters reference is made to chapter 1.18 Formulas for Strip Flatness in V. B. Ginzburg. High-quality steel rolling: theory and practice, Marcel Dekker Inc., 1993.

(16) To distinguish between up and down, gravity g is shown in FIG. 1.

(17) FIG. 2a shows a detail from FIG. 1.

(18) FIG. 2b shows a side view of the bent up strip 1 with 16 distance measuring devices 6 distributed over the width B of the strip 1. Each distance measuring device 6 emits a laser beam onto the strip 1, which is reflected by the strip 1 and received back by the distance measuring device 6. The analysis of the laser beam allows the actual bending radii r(y) to be determined over the width direction y of the strip 1. The analysis of the contour in the width direction y also allows other shape deviations to be determined, for example a so-called camber of a strip clamped on the entry and exit sides. This is expressed in a gradient of the contour in the y-z plane.

(19) Like the flatness, the residual stresses in the flat product 1 are determined based on the contour of the flat product 1. The residual stress .sub.x(y) of the flat product 1 in the x direction is as follows in a position y in the width direction:

(20) ${}_x\left(y\right)=E.Math.{\mathrm{.Math.}}_x\left(y\right)=E.Math.\frac{r_0-r\left(y\right)}{r_0},$
where E is the modulus of elasticity of the flat product, .sub.x(y) is the elongation in the x direction in position y, r(y) is the measured actual bending radius in position y, and r.sub.0 is the nominal bending radius of the flat product in the apparatus. In a simplified calculation r.sub.0 can be assumed to be the mean radius r(y) over the width B.

(21) FIG. 3 shows an alternative to the apparatus shown in FIG. 1, in which the strip 1 is bent down. In order to avoid measuring being influenced by scale or cooling water, the arc 5 is blown free using compressed air.

(22) FIGS. 4 and 5 show two further inventive alternatives to FIG. 1. In FIG. 4 the entry rollers comprise an upper roller 3a and two lower rollers 3b. The same applies to the exit rollers 4a, 4b. In FIG. 5 the upper and lower entry rollers 3a, 3b respectively and the exit rollers 4a, 4b have the same diameter.

(23) FIGS. 6a and 6b show the apparatus shown in FIG. 1, with an increased strip tension in the strip 1 in FIG. 6a compared with FIG. 1 and a reduced strip tension in FIG. 6b compared with FIG. 1. The actual bending radius in FIGS. 6a, 6b is shown as r; the nominal bending radius from FIG. 1 is r.sub.0. Analysis of the actual bending radius r also allows the tension of the strip 1 to be set specifically. The arc 5 between the entry rollers 3a, 3b and the exit rollers 4a, 4b also serves as a buffer, so that short-term fluctuations between the entry and exit only result in minor tension fluctuations.

(24) In principle the inventive method and the inventive apparatus are suitable for both thin and relatively thick flat products. FIG. 7 shows the changes required in the apparatus going from a thin strip 1 to a relatively thick strip 1. More specifically the lower entry roller 3b is moved to some degree counter to the transport direction T and to some degree in a downward direction, the upper and lower exit rollers 4a, 4b are each movedas shown by dashed arrowsin the transport direction T and the roller 4b is moved to some degree in a downward direction symmetrically to 3b. This increases the radius of curvature r.sub.0 of the arc 5 for the thick strip 1 compared with the radius of curvature r.sub.0 of the arc 5 for the thin strip 1.

(25) FIG. 8 shows a modified apparatus for measuring flatness or for measuring the residual stresses in the flat product 1, wherein the bending radii r is not constant over the longitudinal extension of the flat product 1. More specifically the bending radius after the input-side bending device 3 is r.sub.0,1 and shortly before the output-side bending device 4 r.sub.0,2, where r.sub.0,1>r.sub.0,2. The flat product 1 is coiled after measuring by contour measuring devices 6 (not shown) onto a reel 8. In order to improve the accuracy of the flatness measurement or the residual stress measurement further, the contour of the flat product 1 can be acquired in a number of positions in the longitudinal direction of the flat product 1 in the region of the arc 5. The flatness or residual stress is calculated in each instance from the contours. The at least partially redundant contour information can be used to improve the accuracy of the measurements; for example the results of measuring the flatness or residual stress can be averaged.

(26) FIGS. 9a and 9b show that the knowledge of the residual stresses in a flat product is also important for further production steps. FIG. 9a shows a steel strip 1, which has a region 22 with tensile stresses and away from 22 a region 21 without tensile stresses. The sectional shapes 23-26 of different components 23-26 are also shown, said components being cut out from the flat product 1 using a laser cutting machine. The influence of the tensile stresses on the resulting shapes of the components 23-26 is shown in FIG. 9b. As shown in FIG. 9b, the upper part of the component 24 bends up due to the tensile stresses 22, having an adverse effect on dimensional stability. The same is true of the upper part of the component 23. In any case it can been seen from the representations that the knowledge of the residual stresses is extremely important when manufacturing high-precision components, as otherwise significant component distortion is possible. The sectional shape 26 was determined taking into account the determined residual stress distribution in the sheet-like flat product 1, so that the shape of the component 26 corresponds as far as possible to the desired shape after cutting out.

(27) Although the invention has been illustrated and described in detail using the preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

LIST OF REFERENCE CHARACTERS

(28) 1 Flat product 2a Input-side rolling conveyor 2b Output-side rolling conveyor 3 Input-side bending device 3a Upper entry roller 3b Lower entry roller 4 Output-side bending device 4a Upper exit roller 4b Lower exit roller 5 Arc 6 Distance measuring device 7 Drive roller 8 Reel 9 Rolling stand 21 Region without tensile stresses 22 Region with tensile stresses 23 . . . 26 Sectional shape of components 23 . . . 26 Components B Width of the flat product Gravity M Center point r, r.sub.0 Radius of curvature T Transport direction of the flat product x, y, z x,y,z axis of a Cartesian coordinates system