Locally changing the roll gap in the region of the strip edges of a rolled strip

Abstract

Methods and apparatus for locally changing a roll gap in the region of the strip edges (10) of a rolled strip (1) in a rolling stand (2). The roll gap can be changed locally in the region of the strip edges (10) of the strip (1) during the hot rolling. Axial displacement of the working rollers (3, 4) in opposite directions is by a displacement distance s, where s is greater than or less than Δr/tan(α) and Δr indicates the wear of the running surface (8) in the radial direction (R) and α indicates the pitch angle of the conical portion (7) of the respective working roller (3, 4).

Claims

1. A method for locally increasing a size of a roll gap in a region of strip edges of a rolled strip in a rolling stand, wherein the rolling stand comprises: an upper working roller and a cooperating lower working roller, the rollers extending parallel to each other and defining a gap between the rollers, the rollers cooperating for passage of the rolled strip through the gap between the rollers; each working roller having two opposite ends configured for rotational mounting of the working roller; each working roller having, in a respective axial direction thereof, a conical portion followed by a running surface; the upper working roller is oriented in an opposite axial direction to the lower working roller; each working roller having a respective separate displacing device configured and operable for axially displacing the respective working roller; the method comprising: determining a radial wear Δr of the running surface of at least one of the working rollers in a radial direction thereof, and hot rolling a rolled stock in the rolling stand through the gap between the rollers, and causing the radial extent of the running surface of at least one of the working rollers to decrease by Δr during the rolling, while axially displacing the working rollers in opposite axial directions by a displacement distance $s>\frac{\Delta r}{\tan \left(\alpha \right)},$ where α indicates a pitch angle of the conical portion of the respective working roller.

2. A method for locally increasing a size of a roll gap in a region of strip edges of a rolled strip in a rolling stand, wherein the rolling stand comprises: an upper working roller and a cooperating lower working roller, the rollers extending parallel to each other and defining a gap between the rollers, the rollers cooperating for passage of the rolled strip through the gap between the rollers; each working roller having two opposite ends configured for rotational mounting of the working roller; each working roller having, in a respective axial direction thereof a conical portion followed by a running surface; the upper working roller is oriented in an opposite axial direction to the lower working roller; each working roller having a respective separate displacing device for axially displacing the respective working roller; the method comprising: determining a rate of radial wear ({dot over (Δ)}r) of the running surface of at least one of the working rollers in a radial direction thereof, and hot rolling a rolled stock in the rolling stand through the gap between the rollers, and causing the radial extent of the running surface of at least one of the working rollers to decrease at a rate of {dot over (Δ)}r during the rolling, while axially displacing the working rollers in opposite axial directions at a displacement rate of $v\equiv \stackrel{.}{s}>\frac{\stackrel{.}{\Delta r}}{\tan \left(\alpha \right)},$ where α indicates a pitch angle of the conical portion of the respective working roller.

3. A method for locally reducing a size of a roll gap in a region of strip edges of a rolled strip in a rolling stand, wherein the rolling stand comprises: an upper working roller and a cooperating lower working roller, the rollers extending parallel to each other and defining a gap between the rollers, the rollers cooperating for passage of the rolled strip through a gap between the rollers; each working roller having two opposite ends configured for the rotational mounting of the working roller; each working roller having in a respective axial direction thereof a conical portion followed by a running surface; the upper working roller is oriented in an opposite axial direction to the lower working roller; each working roller having a respective separate displacing device configured and operable for axially displacing the respective working roller; the method comprising: determining a radial wear Δr of the running surface of at least one of the working rollers in a radial direction thereof, hot rolling a rolled stock in the rolling stand in the gap between the rollers, the radial extent of the running surface of at least one of the working rollers decreases by Δr during the rolling; and axially displacing the working rollers in opposite axial directions by a displacement distance $s<\frac{\Delta r}{\tan \left(\alpha \right)},$ where α indicates a pitch angle of the conical portion of the respective working roller.

4. A method for locally reducing a size of a roll gap in a region of strip edges of a rolled strip in a rolling stand, wherein the rolling stand comprises: an upper working roller and a cooperating lower working roller, each working roller having two opposite ends configured for the rotational mounting of the working roller each working roller having, in a respective axial direction thereof, a conical portion followed by a running surface; the upper working roller is oriented in an opposite axial direction to the lower working roller; each working roller having a respective separate displacing device configured and operable for axially displacing the working respective roller; the method comprising: determining a rate of radial wear {dot over (Δ)}r of the running surface of at least one of the working rollers in a radial direction thereof, and hot rolling a rolled stock in the rolling stand in the gap between the rollers, and causing the radial extent of the running surface of at least one of the working rollers to decrease at a rate of wear {dot over (Δ)}r during the rolling, while axially displacing the working rollers in opposite axial directions at a displacement rate of $v\equiv \stackrel{.}{s}<\frac{\stackrel{.}{\Delta r}}{\tan \left(\alpha \right)},$ where α indicates a pitch angle of the conical portion of the respective working roller.

5. The method as claimed in claim 1, further comprising: for thin strips with a thickness of between 0.5 and 2 mm, setting a planarity of the strip.

6. The method as claimed in claim 4, further comprising for strips with a thickness of >2 mm, setting a profile of the strip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention are provided by the following description of non-restrictive exemplary embodiments, wherein, in the FIGURES:

(2) FIG. 1 shows a schematic representation of a rolling stand with an upper working roller and a lower working roller for locally changing the roll gap in the region of the strip edges of a rolled strip;

(3) FIG. 2 shows a schematic representation of an apparatus according to the invention for locally changing the roll gap in the region of the strip edges of a rolled strip with the rolling stand as shown in FIG. 1;

(4) FIGS. 3A-3D show a representation of a method not according to the invention for the hot rolling of a rolled strip in a roll gap of a rolling stand; wherein

(5) FIG. 3A shows hot rolling a strip in a roll gap, for a first strip thickness;

(6) FIG. 3B shows the rollers for the strip of FIG. 3A after the rollers are worn;

(7) FIG. 3C shows the rollers for the strip of FIG. 3A worn further;

(8) FIG. 3D shows a detail of FIG. 3C with wearing edges for wearing strip edge portions;

(9) FIGS. 4A-4D show a representation of a method not according to the invention for the hot rolling of a strip in a roll gap of a rolling stand, showing displacement of the working rollers following the wear, wherein

(10) FIG. 4A shows the rollers not axially displaced;

(11) FIG. 4B shows a first axial displacement of the rollers;

(12) FIG. 4C shows a greater second axial displacement of the rollers;

(13) FIG. 4D shows the result of rolling with non-profiled rollers;

(14) FIGS. 5A-5D show a representation of a method according to the invention for locally increasing the size of a roll gap in the region of the strip edges of a rolled strip, wherein

(15) FIG. 5A shows the rollers not displaced axially;

(16) FIG. 5B shows a first axial displacement distance of the rollers;

(17) FIG. 5C shows a second axial displacement of the rollers;

(18) FIG. 5D shows a detail of FIG. 5C and shows control of the roll gap at the strip edges;

(19) FIGS. 6A-6D show a representation of a method according to the invention for locally reducing the size of a roll gap in the region of the strip edges of a rolled strip, wherein

(20) FIG. 6A shows the rollers not displaced axially;

(21) FIG. 6B shows another axial displacement of the rollers;

(22) FIG. 6C shows an effect of wear of the running surface of a roller providing a roller displacement distance;

(23) FIG. 6D shows a detail of FIG. 6C showing reduction of the local roll gap on the regions of the strip edges.

(24) FIG. 7 shows a schematic representation of a portion of a working roller

(25) FIG. 8 shows a schematic representation of the regions of the strip edges of a rolled strip

DESCRIPTION OF EMBODIMENTS

(26) FIG. 1 schematically shows a rolling stand 2 as part of an apparatus for locally changing a roll gap in the region of the strip edges 10 of a rolled strip 1. The specific local changing of the roll gap in the region of the strip edges 10 allows the profile and/or the planarity of the strip 1 to be influenced during hot rolling. The rolled stock is hot-rolled in the roll gap between the upper working roller 3 and the lower working roller 4. Each working roller 3, 4 has two ends 5, which are respectively fitted displaceably in a chock 6 in a roller housing (not represented) of the rolling stand 2.

(27) Furthermore, each working roller 3, 4 comprises a conical portion 7 and a running surface 8 (also see FIG. 7). The upper working roller 3 is fitted in the rolling stand 2 in the opposite axial direction to the lower working roller 4.

(28) The upper working roller 3 and the lower working roller 4 can each be displaced in the axial direction by respective separate displacing devices 9 during operation. The upper working roller 3 is displaced to the right during operation. The lower working roller 4, on the other hand, is displaced to the left (see arrows). Furthermore, the overall roll gap between the upper working roller 3 and the lower working roller 4 can be set by adjusting devices 16.

(29) In order to be able to ascertain the wear of the running surface 8 of the upper working roller 3 during operation, the upper working roller has a device 11 for determining the wear or a wear model. A single device 11 or a single wear model is sufficient if the working rollers 3, 4 are produced from the same material. Of course, it is likewise possible that the upper working roller 3 and the lower working roller 4 respectively have a separate device for determining the wear 11 or a wear model. The measurement of the wear Δr or the rate of wear {dot over (Δ)}r of the running surface 8 of the working rollers 3, 4 in the radial direction may be performed with contact, for example by a roller which contacts the running surface 8, or without contact, for example optically. Since the axial displacement of the working rollers in the rolling stand to compensate for wear is already known from WO 2017/215595 A1, this document is incorporated by reference. However, it is not known from this document how the local roll gap can be specifically changed in the region of the strip edges of the strip.

(30) In FIG. 2, back up rollers 22 are shown at each working roller 3,4. In the FIGURES that follow FIG. 2, the backup rollers are not shown for reasons of overall clarity. Any person skilled in the art in the field of rolling mill technology knows that backup rollers are customary and that they counteract bending of the working rollers.

(31) In FIG. 2, an apparatus for locally changing the roll gap in the region b of the strip edges of a rolled strip in a rolling stand 2 of a five-stand finishing roll train, for example in a combined casting/rolling installation, is schematically represented. The rolled stock (not represented) is fed by a roller table 17 to the finishing roll train with the rolling stands 2a to 2e and are finish-rolled there in the hot state. In the last rolling stand 2e, the wear Δr or the rate of wear {dot over (Δ)}r of the running surfaces 8 of the working rollers 3, 4 is ascertained by measuring technology used by the device 11 (see FIG. 1). Alternatively, it is likewise possible not to ascertain Δr or {dot over (Δ)}r by measuring technology, but by using a so-called wear model.

(32) The apparatus also comprises a measuring instrument 12 for determining the profile or the planarity of the rolled strip. This measuring instrument is arranged downstream of the rolling stand 2 in the direction of mass flow. In the specific case, the actual profile PR.sub.actual is fed to a control device 13. Apart from the actual profile, the desired profile PR.sub.desired is also fed to the control device 13. Taking into account the wear Δr or the rate of wear {dot over (Δ)}r, the measured profile PR.sub.actual and the desired profile PR.sub.desired, the control device 13 calculates the displacement distance s or the displacement rate {dot over (s)} for the upper working roller 3 and the lower working roller 4 (see FIG. 1). The local roll gap in the region of the strip edges of the strip can be specifically changed by axially displacing the working rollers 3, 4 more quickly or more slowly. For very thin strips, this has an effect especially on the planarity of the strip. In contrast, for thicker strips, the local changing of the roll gap in the region of the strip edges has an effect especially on the profile of the rolled strip. After the finish-rolling, the rolled strip is cooled down in a cooling zone 18 and is subsequently conveyed out.

(33) The methods for locally changing a roll gap in the region b of the strip edges 10 of a rolled strip are explained below on the basis of FIGS. 3A-3D, 4A-4D, 5A-D and 6A-6D.

(34) In FIG. 3A, a strip 1 is hot-rolled in the roll gap between the upper working roller 3 and the lower working roller 4. At the beginning, the strip has a thickness Do. Both working rollers 3, 4 respectively have two ends 5, a conical portion 7 and a running surface 8. The upper working roller 3 is fitted in the opposite direction to the lower working roller 4.

(35) After a certain rolling time, the running surfaces 8 of the working rollers 3, 4 are worn in the radial direction by an amount Δr (see FIG. 3B). If the vertical distance between the two working rollers 3, 4 is kept constant, the rolled strip 1 then has a thickness of D.sub.0+2Δr. Continuing the hot rolling has the effect that the running surfaces 8 of the working rollers 3, 4 become worn by the amount 2.Math.Δr (see FIG. 3C), so that the thickness of the strip 1 is then D.sub.0+4Δr.

(36) It is possible to compensate for the change in thickness of the rolled strip 1 by an adjustment of at least one working roller 3 or 4 (see WO 2017/215595 A1).

(37) As can be seen in FIG. 3D, which shows a detail of FIG. 3C, pronounced wearing edges, which lead to a local reduction in the size of the roll gap in the region of the strip edges 10 or to a loading of the strip edges of the rolled strip 1, form in the working rollers 3, 4. As a result, the rolled strip 1 is thinner in the region of the strip edges 10 than in the central region of the strip 1. Since the working rollers 3, 4 are not axially displaced during the hot rolling, the method is not according to the invention.

(38) In FIGS. 4A-4D, the working rollers 3, 4 are axially displaced such that an upper strip edge 10 and a lower strip edge 10 of the strip 1 always rest on an edge between the conical portion 7 and the newly formed (because worn) running surface 8 of the respective working roller 3, 4. The displacement distance of a working roller 3, 4 in the axial direction in this case satisfies the condition

(39) $s=\frac{\Delta r}{\tan \left(\alpha \right)},$
where Δr indicates the wear of a working roller 3, 4 in the radial direction and a indicates the pitch angle of the conical portion. In an equivalent way, the displacement may be set out as governed by the rate of wear {dot over (Δ)}r, a working roller 3, 4 then being displaced in the axial direction at an axial rate of

(40) $v\equiv \stackrel{.}{s}=\frac{\stackrel{.}{\Delta r}}{\tan \left(\alpha \right)}.$
According to FIG. 4B, the wear of the running surface 8 of the working rollers 3, 4 is Δr, which gives a displacement distance of

(41) $s1=\frac{\Delta r}{\tan \left(\alpha \right)}.$
According to FIG. 4C, the wear of the running surface 8 of the working roller 3, 4 is 2.Math.Δr, which gives a displacement distance of

(42) $2.s1=\frac{2\Delta r}{\tan \left(\alpha \right)}.$
The upper working roller 3 is in this case displaced to the right and the lower working roller 4 to the left.

(43) As can be seen from FIG. 4D, this method has the effect that, using a non-profiled working roller 3, 4, the strip 1 has a constant thickness over the width. In other words, the rolled strip 1 is just as thin in the region of the strip edges 10 as in the central region of the strip 1. According to this method which is not according to the invention, the local roll gap in the region of the strip edges is not changed and the strip edges of the strip 10 are neither subjected to loading nor relieved of loading.

(44) In contrast to the prior art, in FIGS. 5A-5D, the working rollers 3, 4 in FIG. 5A are axially displaced as in FIGS. 5B and 5C, such that an upper strip edge 10 at the left side in FIGS. 5B and 5C and a lower strip edge 10 to the right side of the strip 1 always rest on the respective conical portion 7 of the respective working roller 3, 4. The displacement distance of a working roller 3, 4 in the axial direction in this case satisfies the condition

(45) $s>\frac{\Delta r}{\tan \left(\alpha \right)},$
where Δr indicates the wear of a working roller 3, 4 in the radial direction and α indicates the pitch angle of the conical portion. In an equivalent way, if the displacement may be set out as governed by the rate of wear {dot over (Δ)}r, a working roller 3, 4 is then being displaced in the axial direction at an axial rate of

(46) 0$v\equiv \stackrel{.}{s}>\frac{\stackrel{.}{\Delta r}}{\tan \left(\alpha \right)}.$
According to FIG. 5B, the wear of the running surface 8 of the working roller 3, 4 is Δr. This provides a displacement distance of

(47) $s2>\frac{\Delta r}{\tan \left(\alpha \right)}.$
According to FIG. 5C, the wear of the running surface 8 of the working roller 3, 4 is 2.Math.Δr. This provides a displacement distance of

(48) $2.s2>\frac{2\Delta r}{\tan \left(\alpha \right)}.$
The upper working roller 3 is in this case displaced to the right and the lower working roller 4 to the left.

(49) As can be seen in FIG. 5D, which shows a detail of FIG. 5C, by this method the local roll gap in the region of the strip edges 10 of the rolled strip 1 is increased in size or the strip edges are relieved of loading. As a result, the rolled strip 1 is thicker in the region of the strip edges 10 than in the central region of the strip 1.

(50) In FIGS. 6A-6D, the working rollers 3, 4 are axially displaced such that the displacement distance of a working roller 3, 4 in the axial direction satisfies the condition

(51) $s<\frac{\Delta r}{\tan \left(\alpha \right)},$
where Δr indicates the wear of a working roller 3, 4 in the radial direction and α indicates the pitch angle of the conical portion. In an equivalent way, in FIG. 6B the displacement may be set out as governed by the rate of wear {dot over (Δ)}r, a working roller 3, 4 then being displaced in the axial direction at an axial rate of

(52) $v\equiv \stackrel{.}{s}<\frac{\stackrel{.}{\Delta r}}{\tan \left(\alpha \right)}.$
According to FIG. 6B, the wear of the running surface 8 of the working roller 3, 4 is Δr. This provides a displacement distance of

(53) $s3<\frac{\Delta r}{\tan \left(\alpha \right)}.$
According to FIG. 6C, the wear of the running surface 8 of the working roller 3, 4 is 2.Math.Δr. This provides a displacement distance of

(54) $2.s3<\frac{2\Delta r}{\tan \left(\alpha \right)}.$
The upper working roller 3 is in this case displaced to the right and the lower working roller 4 to the left.

(55) As shown in FIG. 6D, which shows a detail of FIG. 6C, this method reduces the local roll gap in the region of the strip edges 10 of the rolled strip 1 in size or the strip edges are subjected to loading. As a result, the rolled strip 1 is thinner in the region of the strip edges 10 than in the central region of the strip 1.

(56) FIG. 7 shows the geometrical definition of the pitch angle α of the conical portion 7 of a working roller.

(57) Finally, FIG. 8 schematically shows the regions b of the strip edges 10 of a strip 1. Typically, the longitudinal extent of the two regions b of the strip edges is up to 10 or 20% of the strip width B, wherein one region b of the strip edges can account for up to 5 or 10% of the strip width B.

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

LIST OF DESIGNATIONS

(59) 1 Strip 2, 2a . . . 2e Rolling stand 3 Upper working roller 4 Lower working roller End of a working roller 6 Chock 7 Conical portion 8 Running surface 9 Displacing device Strip edge 11 Device for determining the wear or the rate of wear 12 Measuring instrument for determining the profile and/or the planarity 13 Control device for axially displacing the upper working roller and the lower working roller 14 Thickness measuring device Device for determining the distance between the upper working roller and the lower working roller 16 Adjusting device 17 Roller table 18 Cooling zone B Width of the strip b Region of the strip edge D Thickness of the strip F Rolling force PR.sub.desired Desired profile PR.sub.actual Actual profile r Radius R Radial direction Δr Wear of the running surface in the radial direction {dot over (Δ)}r Rate of wear of the running surface in the radial direction s Displacement distance S.sub.extent Distance covered by the working roller v Displacement rate X Axial direction α Pitch angle of the conical portion ({dot over ())} First time derivative