DE2045302B2 - PROCESS FOR LEVELING HOT STRIP FOR HEAVY PLATE - Google Patents

Description

35

The invention relates to a method for leveling hot strip for heavy plates, in which the Strip that has not yet been subdivided in at least one roller straightener exceeds the yield point Experiences bending strain.

Numerous attempts have already been made and proposals for methods for straightening Hot strip has been made in order to obtain heavy plate blanks, the conventionally rolled heavy plate are comparable. However, previous attempts and suggestions have not been successful. Of the The reason for the previous failures is that when cutting heavy plates from hot strip strong deformations result because the cutting, as in the case of flame cutting, with the supply of large Amount of heat takes place, so that the use of such heavy plates is limited and not in can be used in all cases where conventionally rolled heavy plates are used come.

From an economic point of view, however, there is no question about the production of heavy plate from hot strip much more advantageous than conventional sheet metal rolling. Because of this, they are in the past Great efforts have been made to find a method for straightening hot strip without that it has so far been possible to solve the problems at hand.

Methods for bending straightening are known; however, they do not deal with deviations in flatness, only as a result of the previous bending and straightening when cutting hot strip into heavy plate appear. For example, from US Pat. No. 34 59 027 eir method for bending straightening is known in which the zi straightening band of plastic deformation with a degree of deformation up to 1.5%, i.e. below one Work hardening, is subjected. Furthermore, US Pat. No. 3,360,973 describes a planetary rolling mill known for the cold straightening of strip, in which the strip is straightened with a decreasing bending radius. A A similar process is described in US Pat. No. 3,312,049, which, however, mainly relates to mil dealing with the difficulties in inserting the beginning of the tape into the gap between the first two rollers) and in view of this, proposes that one of the two opposing sets of rollers be adjustable to train.

From the German Auslegeschrift 16 02591, which does not belong to the state of the art, there is also one Known roller straightening machine, the straightening roller sets are arranged in such a way that each other opposite rollers move into one another almost to their entire diameter. This device serves to straighten cold strip and works according to a process in which with the help of an additional A tension is impressed on the cold strip to be straightened during the stretching.

Finally, in "INDUSTRIE-ANZEIGER", Volume 89, No. 99 of December 12, 1967, pp. 23 to 26, various straightening machines for heavy plate described, in which = the heavy plate to be straightened plastically is deformed and accordingly experiences bending strains beyond the yield point. The one for it The required minimum radius of curvature of the sheet depends on the sheet thickness and the yield point elongation away.

Proceeding from the aforementioned prior art, the invention is based on the object of creating a straightening method which, after cutting or subdividing the straightened hot strip, produces heavy plates with a high degree of flatness. Accordingly, the invention aims at eliminating flatness errors which, due to the internal stresses resulting from straightening, do not occur until the hot strip is cut. The solution to this problem is that, according to the invention, in a method of the type mentioned at the beginning, the bending strain in the outer fiber 772 /? = 0.6 to 3.0%, where Γ is the thickness and R is the radius of curvature of the neutral fiber when bent.

In the method according to the invention, the hot strip is exposed to unusually high leveling forces, which lead to the fact that when the tape is divided into individual panels, there are significantly fewer warps ergesen than that with conventional straightening with much lower straightening forces or lower Elongation is the case. The output is correspondingly high in the method according to the invention Blecii within the given tolerances.

The method according to the invention can be carried out with a device that consists of a pay-off reel, a cold straightening machine with a straightening force that is sufficient to reduce the residual tension in the hot strip and another cold straightening machine with a lower straightening force to reduce residual stresses in the outer fiber of the tape and a pair of scissors.

Originally the term hot strip within the meaning of the invention Surface-treated, for example, dry and wet descaled hot sand can also be used.

The invention is explained below with reference to the exemplary embodiments of the illustrated in the drawing further explained in the drawing shows

FIG. 1 shows a schematic representation of a cross section through three straightening rolls, F i g. 2 the sector of a straightening roll,

3 shows a diagram to illustrate the Method for measuring deflections on sheet metal,

Fig. 4 is a diagram showing the relationship between sheet thickness and bending elongation results,

F i g. 5 shows a diagram with measured values of the deflection L in the longitudinal and rolling direction of sheet metal that has been cold-straightened in the usual way and of sheet metal blanks made of hot strip which are cut by flame cutting,

6 to 11 diagrams with measured values of the deflection L of cold-straightened conventional sheet metal, cold-straightened hot strip according to the invention and its blanks after flame cutting,

Figures 12 and 13 are diagrams for illustrative purposes the relationship between the mechanical properties and the bending elongation of elements,

Fig. 14 is a diagram showing the relationships between that plotted on the ordinate Deformation factor, d. h, the ratio to the elastic elongation, and that on the abscissa plotted number of repeated bends,

F i g. 15 is a diagram showing the change in the distribution of the Residual stress results from various processes,

15a shows the change in distribution in the case of the exclusive Cold straightening with a maximum bending elongation of 0.6 to 3.0%,

15b shows the changes in light cold straightening with a bending elongation of up to 2.0%,

15c shows the changes during cold straightening with high straightening pressure and a maximum bending elongation from 0.6% to 3.0% with subsequent slight cold straightening with a bending elongation of up to 2.0% and

16 shows an apparatus for carrying out the method according to the invention.

First of all, in the context of the invention, the bending elongation serves as a benchmark for the cold straightening of a Hot strip, where the elongation is calculated from the permanent deformation under the following assumption:

1. The central plane of the hot strip is assumed to be a neutral fiber that is neither stretched nor is compressed;

2. The shape of the cold-straightened strip is assumed to be a series of arcs.

According to FIG. 1, the hot strip 3 is placed between a plurality of upper rolls 1 and lower rolls 2 curved and cold-straightened.

The neutral fiber is marked with 4, the sheet metal thickness with T, the intermediate roughness between the roller surfaces with I and the pitch circle with ^.

Under the above assumption, the curvature AOB of the neutral fiber between the straightening rollers can be viewed as an arc of a circle and results from FIG. 2 has the following relationship, where R is the radius of curvature of the neutral fiber:

AD: DB =

do =

Hence the radius of curvature results in:

DO = R (I - COSa)

AD = R sin i.

and if * is eliminated:
AD ² + DO ²

D.

2DO

R can therefore be determined from equations (1) and (2).

On the other hand, the bending strain results from:

^f R 2R

(3)

(M) From the above equation (3), ε can be determined by substituting the equation (2) for R depending on the tape thickness T.

The following is an example of measuring a warpage of the sheet 7 with reference to FIG. 3 of the drawing. If the band 7 is bent in the direction of its rear side 7 ', as shown in solid lines, this warping is to be regarded as a positive warping (+), while a bending in the direction of the opposite side 7 "is to be regarded as a negative warping (-) consider is.

As can be seen from Fig. 3 results, the sheet 7 is suspended from its central part 5 or stands upright, and a strand is tensioned in the rolling direction at points A to £, which are distributed across the width. The resulting largest distance between the tensioned strand and the sheet 7 represents the warping of the plate. L denotes the length of the plate in the rolling direction.

If sheet metal blanks are produced from the sheet metal 7 by flame cutting, the warpage in these is shown in FIG. 3 resulting way measured. The width b is 150 mm, the length L 3 m and the warpage or deflection a is given in mm.

The reason for specifying the width as 150 mm results from the fact that sheet metal blanks of this thickness are usually produced. In addition, the warping of sheet metal blanks can be different Thickness easily determined from the warping of a sheet metal blank of the aforementioned thickness will.

Under the above-mentioned conditions of the warp measurement, the sheet metal blank can, as far as its Warp a is less than 20 mm and the length is 3 rr than normal rolled, i.e. H. not cut; Sheet metal are considered. Thus, a warpage or deflection a of 20 mm represents a length of sheet metal of 3 m is a practical limit.

In a test, hot strip with a thickness of 4.5 to 16 mm was unwound from a bundle first slightly smoothed and then according to the invention cold-straightened as well as cut to length and closed lent stacked.

The operation is shown in FIG. Danacl the federal government is fed from the rolling mill by means of a coil conveyor 1 to a coil crane 2, which au a trolley 3 drops that they to a

Discharge reel 4 brings. When unwinding, the federal government is aligned and the tape is initially over a Block shears 11 and trimming shears 12 fed to a straightening machine 5, in which the strip after Method according to the invention is directed. This can be done in such a way that the tape initially bent repeatedly giving it a certain stretch and then the stretch below the usual Increasing the roller spacing is reduced. Half of the straightening can be done with a higher Bending elongation of the outer fiber and in the second half with a low bending elongation of the outer fiber take place.

The advantage of the aforementioned method is that the number of bending rollers compared to conventional process is around half less. In the present case, there are two straightening stands, namely a straightening stand 5 for a high bending elongation and a second straightening stand 6 for a low one Flexural strain for use. Between the straightening machines 5 and '6 there is a pair of metal shears, so that the roller straightener 6 only sheet metal blanks are fed. The reason for this is that im In view of the fact that the roller straightening machine 5 gives the tape a strong bending elongation and the The beginning of the strip is difficult to grasp, the roller spacing when inserting the beginning of the strip into the roller straightener must be reduced and only then a high bending elongation is achieved; in the case of However, straightening can be done continuously with reeled strip, since only the beginning of the strip has a Requires changing the roller spacing and consequently a high throughput is possible. The beginning of the band must be pushed into the straightening machine 5 or into its gap; this is done with the help of of the pay-off reel 4. If the impact force is low, the belt is often damaged by grinding marks, in addition, the beginning of the strip often falls out of the nip.

If 5 blanks are fed to the roller straightener, the dimensional accuracy of the blank goes lost and the blanks must then be cut to size again, which results in a results in a noticeable impairment of performance.

The roller straightening machine 6, on the other hand, only works with a relatively low bending strain, so that the The aforementioned difficulties do not occur here even when sheet metal blanks are straightened. Rather, the cutting accuracy and dimensional accuracy are significantly improved.

After leaving the roll straightening machine 6, the sheet metal cuttings are fed to a measuring device 8 fed and stacked and deposited on a conveyor 10

Cold straightening in the two roller straightening machines 5, 6 takes place under the following conditions:

Intensive tests have shown that the warpage or curvature of a sheet metal blank is less than 20 mm and there is no impairment of the mechanical properties if the Bending elongation of the outer fiber is 0.6 to 3.0%. This can be seen from the diagram in FIG The relationship between sheet metal thickness and elongation of the outer fiber is shown in conventional processes for heavy plate up to 0.5%, while the bending elongation according to the invention is 0.6 to 3.0%.

In particular with a big expansion below 0.6%, the deflection of the sheet metal blank is greater than 20 mm, while with a bending elongation of over 3.0%, difficulties arise on the roller straightening machine, in particular result at the inlet angle and also impaired the mechanical properties of the sheet will. The second light cold straightening takes place with a bending elongation that slowly increases by less than 2.0%, preferably 0.6 to 0.4%, reduced to the limit of elasticity.

ίο In detail, a hot strip of the quality SS 41 with a thickness of 6.0 mm was dressed and straightened in the conventional manner and then cut to a length of 3040 mm. In Fig. 5, the curve of the deflections at points A to E (Fig. 3) of a cut sheet are shown in dashed lines and the curve of the deflections of a sheet cut to size by means of flame cutting is shown in dotted lines Flame cutting by more than 100 mm between plus and minus. Such sheet metal blanks can therefore no longer be used universally.

The solid curve in FIG. 6 relates to the deflections or curvatures of a sheet metal blank from the same collar as the sheets in FIG. 5, doi'i, this sheet was subjected to a slight straightening with about 20% normal bending elongations. The dashed curve in Fig. 5 relates to a steel sheet of the same collar that has been straightened with a bending elongation of the outer fibers of 0.54%, while the dash-dotted curve relates to a cut of the aforementioned sheet. The individual values were taken along the cutting lines A to E (Fig. 3) measured. The above-mentioned deflection of the outer fiber is 0.54% less than the flexural elongation according to the invention of 0.6%, so that the deflections are more than 20 mm and these sheets are outside the scope of the invention.

The dashed curve in FIG. 7 refers to the Deflections of a sheet metal from the collar mentioned in connection with FIG Straightening has experienced a bending elongation of 0.88% and cuts with absolute deflections below 20 mm revealed. That is, the hot strip was given a flexural elongation according to the invention during straightening

In the diagram of FIG. 8 deflections are plotted, which arise with a bending elongation of 1.07% revealed. It turns out that the bending of the blanks after the flame cutting is even less were than in the attempt at FIG. 7th

The dashed curve of the diagram in FIG. 9 refers to a three meter long and 1.25 mm thick sheet metal blank of a steel strip (X-46) with a thickness of 16 mm, with a bending elongation of

0.54% was directed. The dash-dotted curve shows the deflections after the flame cutting of the directed band section again. Due to the bending elongation, which is below 0.6%, the deflections exceed of the blank 30 mm and show that the flexural elongation of this experiment was not sufficient.

The deflections when straightening what is mentioned in connection with FIG. 9 result from FIG Tape with a flexural elongation of 0.62%, i.e. i.e., in the Order of magnitude of the lower limit value for the bending elongation according to the invention, based on the dash-dotted curve shows that the deflections after the flame cutting are about 20 mm lie.

The diagram of Fig. 11 gives the deflections again, as found when straightening the tape with a bending elongation of 0.77%. It turns out that the Deflections after the flame cutting were in any case less than 20 mm.

The mechanical properties of the above-mentioned metal sheets result from the diagrams in FIGS. 12 and 13. FIG. 12 shows the influence of different bending strains in connection with FIGS. 5 to 8 mentioned sheets on the yield point, elongation and tensile strength. The individual diagrams show that, with the exception of the unchanged or slightly reduced yield point, the values after straightening are better than those of the original sheets. The solid curves L relate to the mechanical properties in the rolling direction, while the dashed curves C relate to the mechanical properties transverse to the rolling direction or across the width. In a similar way, FIG. 13 shows an improvement in the mechanical properties of the metal sheets in the experiments relating to FIGS. 9 to 11.

In the case of cutting between the two straightening machines, the sheet metal cross-section and the Distortions from cutting corrected again by subsequent cold straightening.

It is difficult to determine the dimensions of a heavy plate in the case of cutting while straightening adhere to, but they can by a subsequent light cold leveling to eliminate hot rolling resulting residual stresses in the outer fiber can be corrected.

14a shows three different types of processes in two-stage straightening. Curve A relates to straightening with a standard gradient, curve C to preferred straightening, and curve B to straightening in which strong cold straightening takes place with a gradient, which is less than the standard gradient and the slight cold straightening with a gradient which is greater than the standard gradient. Ki is the ratio of the respective actual bending strain to the elastic limit.

The curves in diagrams 14b, 14c and 14d show the distribution of the residual stress in hot-rolled sheet, which have been cold-straightened according to the three types of processes mentioned above.

The three curves clearly show that when straightening according to curve A in FIG. 14a, the average residual stress is relatively large in comparison with the residual stresses of the straightening process according to curve C in FIG. 14a and that the residual stress of the outer fibers of the steel sheet is not significantly reduced.

When straightening according to curve B in FIG. 14a, the reduction in the residual stress is the worst; in particular, in this case the residual stress in the outer fiber has only been reduced to a very small extent.

While in the particularly preferred straightening according to curve C in Fig. 14a the average « Residual stress and the residual stress both in the outer fiber and in the area of the neutral fiber arr are the least. The cold straightening according to curve C was carried out in two stages, one with strong: Deflection and once with a slight deflection. The first d. H. strong judging occurs ir in such a way that at the beginning an intensive sagging with a bending elongation of 0.6 to 3.0% and einetr

ίο gradient takes place which is greater than that which results from curve A in FIG. 14a (connection of the high flexural elongation with the elastic limit corresponding to Ki = 1). The final or second judge takes place with only low flexural elongation and cinerr

is gradient which is less than that which is found for curve A in FIG. 14a results.

Referring to Figure 15, it can be seen that the preferred combination of strong straightening and easy straightening Alignment with regard to an effective cold funnel is advantageous with regard to the distribution of the residual stresses is. As FIG. 15a shows, only the Residual stresses in the area of the neutral fiber are reduced, while the residual stresses in the Outer fiber cannot be decreased enough. On the other hand, according to FIG. 15b, the light cold funnel only the residual stresses in the outer fiber are reduced.

The combination according to the invention of an initially strong cold straightening with a subsequent slight cold straightening results in an optimal distribution and effective reduction of the residual stresses according to FIG. 15c. In addition, the number of bending rollers required is reduced compared to straightening according to curve A in FIG. 14a to about half and the tension equalization in the sheet metal is not disturbed by subsequent processing, for example flame cutting, so that hot-rolled sheets with technological properties result with regard to the absolute deflections of the sheet metal blanks and the mechanical properties without any problems Withstand comparison with conventional heavy plate.

With regard to the initial gradual decrease in deflection during severe cold straightening and the final gradual decrease in deflection during light cold straightening within the framework of the values according to the invention, it comes down to the gradual decrease in deflection in between

so between the strong cold straightening and the lighter one Cold straightening is not essential.

From the above it can be seen that even then there is no impairment of the mechanical properties results when the strong cold straightening is inadmissible from the standpoint of conventional straightening methods

The invention makes it possible to produce sheet metal blanks from hot strip which, in terms of their properties conventional heavy plates are comparable, but can be produced much more economically.

In addition 9 sheets of drawings

709526/186

Claims (4)

Patent claims: 1. A method for straightening hot strip for heavy plates, in which the not yet subdivided strip undergoes bending strains exceeding the yield point in at least one roller straightening machine, characterized in that the bending strain in the outer fiber TI2R = 0.6 to 3.0%, wherein Γ is the sheet metal thickness and R is the radius of curvature of the neutral fiber when bending 2. The method according to claim 1, characterized in that that the flexural elongation of 0.6 to 3.0% initially rapidly and then gradually up to Elastic limit is reduced. 3. The method according to claim 2, characterized in that the bending strain initially with a is then reduced with a smaller gradient than it is with a continuous one Would result in a decrease in the bending elongation up to the elastic limit. 4. The method according to claim 2, characterized in that that the tape first removes the residual stresses in the area of the neutral fiber cold-straightened and then cold-straightened again to remove the residual stresses in the outer fiber will.