EP0839587B1 - Method for rolling thick plates - Google Patents

Abstract

The method concerns rolling of thick sheet metal from a preliminary material in several successive stages, with different numbers of passes (n) according to a particular desired end product, in one or several roll stands, but preferably in a single hot revers-ing stand. The method is characterised by the fact that from a pass (n-k) onwards to a pass (n-1), where k lies in the range from 1 to n-1, the pass reductions produced at the beginning of the strip are greater than those produced at the end of the strip.

Description

The invention is based on a method for rolling Heavy plates from one material in several sequential work steps directed with one different depending on the desired end product Number "n" of passes in one or more rolling stands, preferably in a warm reversing stand.

When rolling heavy plates from one material in one Heavy plate mill, preferably in one Warm reversing scaffold, development trends exist To maximize productivity and yield (Minimization of side and end cropping losses), Roll as long sheets as possible. Because of this usual process control arise with Hot reversing rollers with relatively small final thicknesses - especially in the last few stitches - very big Rolling force differences between the strip head and strip end, the can be up to 25,000 kN, for example. root cause is that with long tapes because of the taking place Cooling lower rolling stock temperature at the end of the strip, whereby the rolling work or the rolling force increases.

To see the effects of this cooling taking place during Counteracting rolling in successive passes is described in the patent application WO-A-89/11363 proposed, at least after the first deformation step reheating the rolling stock, preferably by means of induction heating and only then carry out the second deformation step. This However, the process is very cost-intensive, since a corresponding one is used for this purpose Furnaces are installed and additional electrical energy is used got to. In addition, this process is very difficult on reversing rolling to apply.

To be essentially constant over the entire length of the hot strip Temperature, without special effort for regulating the temperature, To achieve in the finishing stand is proposed in GB-A-1111576, the opening act roll out wedge-shaped at the last preliminary stitch and then this with his insert thinner ribbon head into the subsequent finishing stand. Based on these Measure shows the finished product has a very uniform structure. A disadvantage of this known method is the large difference in rolling force between the tape head and the tape end, since the colder tape end is now even thicker.

In order to equalize temperatures and rolling forces over the entire strip length, US-A-4555922 describes a method in which at least two early rolling passes in a reversing stand the ends of the rolling stock be rolled out in a wedge shape. The disadvantage here is that this measure in a higher number of passes towards the end of the rolling cycles, with high rolling forces must be applied, are no longer effective.

It is an object of the invention to provide a method with which the described Disadvantages when rolling in several successive passes without causing additional investment and energy costs avoided or significant can be reduced.

The task is solved with the measures of the marking part of claim 1 in a method for rolling heavy plates from a Primary material in several steps, one after the other after the desired end product different number "n" of stitches in one or more rolling stands, preferably in a hot reversing stand, in that from stitch n - k to stitch n (where k is a count number that is in the Range from 1 to n - 1) higher stitch decreases (lower Sheet thicknesses) are rolled than at the end of the strip.

• eine Verringerung der Anforderungen an die Stellsysteme zur Beeinflussung der Blechtoleranzen hinsichtlich Blechdicke, Blechprofil und Planheit des Bleches,
• eine Verbesserung dieser Toleranzwerte selbst, da bisherige Stellgrenzen nicht mehr erreicht werden,
• eine Erweiterung des Produktionsspektrums, da nun Walzkraftspitzen, die bisher dazu führten, daß ein Produkt nicht mehr darstellbar war, vermieden werden.

The measure according to the invention of designing the courses of the sheet thicknesses from one stitch n - k in the subsequent stitches in such a way that higher decreases are made at the strip head than at the strip end means that the rolling forces at the strip head are raised, at the strip end of the subsequent stitch however be lowered. This results in an overall equalization of the rolling force differences per stitch for these passes, which are operated in this way. Furthermore, a total of rolling force peaks are reduced, since the "thinner" strip head of the previous pass is now rolled at the end of a pass. The reduction of the rolling force differences and the reduction of the absolute rolling force peak values have advantages

• a reduction in the requirements for the positioning systems for influencing the sheet tolerances with regard to sheet thickness, sheet profile and flatness of the sheet,
• an improvement of these tolerance values themselves, since previous setting limits are no longer reached,
• an expansion of the production spectrum, since now peak rolling forces, which previously led to the fact that a product could no longer be produced, are avoided.

According to an advantageous embodiment of the invention is the decrease in the number of stitches from the tape head towards the end of the strip - corresponding to the increase in rolled Sheet thickness from strip head to strip end - steady, d. H. linear. In this way, the regulation of the required sheet thickness in a particularly simple manner with the help of the control systems possible.

But it is also possible according to the invention, from the tape head at the end of the tape another, non-linear reduction in Stitch decreases or increases in the rolled sheet thickness perform, for example in the form of another given mathematical function if this is for the Handling of the process control with regard to the required End product is an advantage.

The difference in thickness between the tape head and the tape end is according to the invention with every subsequent stitch set a smaller amount so that according to the Decrease in the average sheet thickness as a result of Rolling progress the thickness difference relative to sheet thickness remains approximately constant and, based on the sheet thickness, is in the range of 1-5%.

The measure according to the invention, the sheet thickness from the strip head Allowing to rise to the end of the tape starts from a stitch n - k, where k is a count from 1 to n - 1. With this The measure can therefore be started from the first stitch (k = n - 1) or later, d. H. with the second, third or fourth stitch etc. The measure ends on the last stitch in which the one from the previous stitch equalized pending difference in thickness and a parallel band, the final product.

The invention is illustrated below in one embodiment explained in more detail in diagrams.

Fig. 1

einen schematischen Stichplan eines Walzvorganges mit elf Stichen nach dem Stand der Technik,

Fig. 2

einen schematischen Stichplan eines Walzvorganges mit 11 Stichen nach dem Verfahren der Erfindung.

Show it:

Fig. 1

a schematic pass schedule of a rolling process with eleven passes according to the prior art,

Fig. 2

a schematic pass schedule of a rolling process with 11 passes according to the method of the invention.

In Figure 1 are in a coordinate system with the Rolling forces (RF) in 1,000 kN as the ordinate and the rolling time (t) in seconds as the abscissa with the entire rolling process shown a total of eleven stitches.

As can be seen in Figure 1, is from the ninth stitch (9) a significant increase in the rolling forces from the strip head starting from the end of the tape by the cooling of the rolling stock taking place in the tenth pass (10) a rolling force difference of 25,000 kN and in the eleventh pass (11) a rolling force difference of 24,000 kN caused. The absolute peak rolling force is in tenth stitch (10) reached at the end of the belt with 76,000 kN.

The result of a rolling process is shown in FIG the method of the invention under otherwise identical conditions as shown in the rolling process of Figure 1.

In this embodiment of Figure 2 was from seventh stitch (7), this corresponds to a k number of 4, the Stitch removal on the tape head raised and corresponding to Reduced end of the band, which leads to the end of the band Sheet thickness was increased. The resulting one The difference in sheet thickness at the end of the strip was 0.6 mm. In the eighth Stitch (8) was the difference in sheet thickness due to a higher Stitch removal at the tape head (for the smaller one overall Sheet thickness) 0.4 mm, for the ninth stitch (9) 0.2 mm and for tenth stitch (10) 0.1 mm. In the last stitch (11) where a parallel strip was rolled as a finished product accordingly also a thickness difference of 0.1 mm (from the tenth stitch) by a higher stitch pickup on Compensate tape head. The course of the increase in thickness from The tape head at the end of the tape was linear for all stitches.

As can be seen from FIG. 2, the temperature-related difference in rolling force between the Tape head and the tape end by raising the Stitch decrease on the tape head significantly reduced. So is this difference for the tenth stitch (10) only 10,000 kN and only 12,000 for the last stitch (11) kN., i.e. compared to the previously used method 50% reduction in rolling force differences achieved.

The maximum rolling force values for the last pass are also significantly lower than with the previously usual methods, as the following comparison shows: Stitch no. k number maximum rolling force in kN previous author The invention 7 4th 48,500 49,000 8th 3rd 55,000 55,500 9 2 71,000 65,000 10 1 76,000 65,000 11 0 63,000 55,000

By the measure of the invention, in the last few stitches roll out the tape with different thickness, namely on the tape head with less thickness, which then to the tape end linear or non-linear according to a certain given mathematical function increases again, not only Differences in rolling force between strip head and strip end reduced, but also the maximum rolling forces per pass degraded. In addition to advantages in the regulation by means of Existing control systems will also be a beneficial influence on the life of the wearing parts of the rolling mill as well as on the rolling energy demand.

The invention is not based on that in the drawing figures described embodiment limited and also not on rolling in reversing stands, but generally with Advantage also on rolling in multiple passes be performed in a row, as well as on the rolling Can be used in rough and finished streets.

Claims (4)

1. Method of reverse rolling coarse metal sheets from a starting material by several successive working steps, with a different number "n" of passes according to the respectively desired end product, in one or more roll stands, preferably in a hot reversing stand, characterised in that from the pass n - k to the pass n (wherein k is a count number which lies in the region of 1 to n - 1), higher pass reductions are rolled at the strip head than at the strip end and the thus-obtained thicker strip ends form the strip head in each succeeding pass, so that in each of these passes following the pass n - k the thinner strip head of the preceding pass is rolled at the strip end.
2. Method according to claim 1, characterised in that the decrease in the pass reductions or the increase in the sheet thickness from strip head to strip end takes place linearly over the entire strip length.
3. Method according to claim 1, characterised in that the decrease in the pass reductions or the increase in the sheet thickness from strip head to strip end takes place non-linearly over the entire strip length and in accordance with another predetermined mathematical function.
4. Method according to one or more claims 1 to 3, characterised in that the sheet thickness difference between the strip head and the strip end decreases with increasing pass number in correspondence with decreasing mean strip thickness, wherein the sheet thickness difference relative to the sheet thickness remains approximately constant and lies in the region of approximately 1 to 5% with respect to the sheet thickness.

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