GB2099737A - Manufacture of rolled sections - Google Patents

Abstract

A slab 60 of rectangular section is formed into a pre-blank by rolling it in a passage 61 whose base width is less than or equal to the thickness of the slab used and whose lateral faces are inclined by an angle alpha 1 which is a function of the dimensions of the blank. The rolling upsets the slab ends into mushroom shapes having a thickness of roughly 12% of the slab thickness. The rolling may be carried out using vertical or horizontal rolls. Rolling is completed by carrying out conventional profiling passage rolling to produce the pre-blank 63 and blank 64. <IMAGE>

Description

SPECIFICATION Manufacture of blanks for the production of large rolled sections The present invention relates to a method of manufacturing blanks (semi-finished rolled products) for the production of large rolled sections, in particular large wide-flanged beams having web heights of 1 m.

Conventional rolling processes generally include the following steps: (1) A rectangular or square section (bloom) is produced by rolling a steel ingot in a stand comprising two horizontal rolls (blooming or break-down). This rectangular section may also be produced by continuous casting with or without subsequent rolling in a blooming or breakdown roughing stand in order to obtain the required dimensions. The section must have a width which is slightly less than the width of the first profiling passage which is then used.

(2) This profiling passage is generally provided in a stand comprising two horizontal rolls (blooming or break-down). By carrying out several rolling passes in this profiling passage a blank is obtained whose shape is such that it enables subsequent rolling in the other stands of the rolling mill until the finished product is obtained.

The thickness of the rectangular section must be selected so as to obtain correct filling of all the portions of the cross-section of the blank.

These conventional methods have several drawbacks, viz. the necessity of producing continuously cast strands or sections which are very thick, and the loss of material because the ends of the blanks must in certain cases be scrapped before continuing rolling in the other stands of the rolling mill.

In order to remedy these drawbacks, it has been proposed to use, as the starting product, slabs of rectangular section instead of ingots.

Such methods are based on the following considerations.

As a result of the compression of the width of a slab between two horizontal or vertical rolls, there are formed at the ends of the slab flanges which enable the obtention of a blank by subjecting the slab with widened ends to rolling using either a conventional profiling passage or a universal rolling mill.

The widening of the ends of a slab subject to widthwise compression is a phenomenon which is known to rolling mill operators and which must be taken into account during the rolling of products having a rectangular section. The development of the shape of the free edges of a rectangular section subject to rolling is closely linked to a parameter defined as being the ratio between the projected length of the contact arc and the mean height of the product.

If R is the roll radius, h0 the initial height of the rectangular section, and h1 the final height of the rectangular section, this ratio may be expressed as g = ld/hrn, in which ld=""[R(h0-h1)] and hm = (ho + h1)/2 The widening is defined as being the flow of material taking place in a direction perpendicular to the directions of rolling and reduction.

In the case of a low ratio g, the widening of the free edges which are not subjected to the pressure of direct rolling is preferentially located at the ends of the free edges, providing a shape similar to a diabolo. The mid-height thickness of the section is not affected by the deformation and remains constant.

For a high ratio g, the widening is concentrated at a mid-point of the section height and provides a shape similar to a barrel.

The value of the ratio g which separates the two types of widening is 0.6 to 0.7. In the case of this limit value the widening of the free edges is constant over the entire height of the free edges.

All the method of rolling beams from slabs are based on the type of widening obtained for low values of the ratio g.

However, methods which use a universal rolling mill for the production of the blank may only be applied with difficulty to beams which have a great height and extra-wide flanges.

Moreover, compression of the width of the slab in rolling passages of increasing width does not enable satisfactory control of the shape of the flanges. In addition, the barrel width of two-high roughing mills is often restricted, which prevents a series of rolling passages from being provided between the rolls in the case of beams having a great web height and having extra-wide flanges.

It would be desirable to be able to roll blanks of the required dimensions using only one contoured rolling passage and one smooth rolling passage.

The present invention provides method of rolling blanks for the production of beams, in which a slab of rectangular section is used as the starting product and from this slab there is produced a pre-biank by compression in a rolling passage whose base width is less than or equal to the thickness of the slab used and whose lateral faces are inclined by an angle a1 which is a function of the dimensions of the blank, the thickness of the "mushroom" obtained in this way being greater by approximately 12% than the thickness of the blank flanges.

Preferably, the blank is produced in three stages: (a) Compression of the width of a slab in a rolling passage defined by grooves whose lateral faces having a predetermined slope and the width of whose base is less than or equal to the thickness of the slab. The widening leads to the filling of this passage and the slab has at its ends, in accordance with the width, projections whose shape is similar to a perfectly symmetrical mushroom.

(b) Compression on a compression table of the width of the slab produced in accordance with stage (a). The result of this compression is to deform the mushroom by reduction of the thickness and by widening until flanges are obtained, these flanges fitting as completely as possible the shape of the profiling passage used in step (c) below.

(c) Rolling of the pre-blank produced in stage (b) in a conventional profiling passage until the blank is obtained.

In accordance with the invention, a suitable combination of the angle of inclination of the faces of the contoured rolling passages and the reductions carried out in the contoured rolling passage and in the smooth rolling passage (the compression table) enable a pre-blank shape having the required dimensions to be obtained for each beam.

Preferably, the pre-blank is produced by compression such that the totai reduction carried out produces a widening in such a way that the widths of the head and base of the "mushroom" are substantially identical at the end of the compression with the approximate cancellation of the angle of inclination and the obtention of a flange thickness corresponding to the thickness of the flanges of the blank. The compression may be carried out with a compression table or passage whose width is at least equal to the width of the flanges of the blank increased by the difference between the slab thickness and the blank thickness. The mean width of the flanges of the pre-blank obtained is preferably substantially equal to the thickness of the slab increased by the difference between the flange width and the web thickness of the blank.

Elements may be provided at the base of the first compression passage, these elements being repeated on the following compression table or passage so as to ensure guiding of the slab and eliminated by compression on the smooth table formed by the web of the profiling passage, or, if the table width of the rolls enables this, in a rolling passage having a flat base.

Compression rolling of the pre-blank may be carried out using driven vertical rolls whose arrangement is similar to that of a universal slabbing mill, and in which the vertical rolls may be disposed in a separate stand located as close as possible to a horizontal roll stand having the contoured rolling passage.

Alternatively, use may be made of vertical rolls comprising the said rolling passage as well as a smooth portion and means enabling the rolls to be displaced along their vertical axes.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 diagrammatically shows a rolling passage and an ingot to be rolled; Figure 2 is a perspective view of the leading end of a blank; Figure 3 is a diagrammatic cross-section through a slab being rolled to form a blank with flanges, showing successive stages of reduction; Figure 4A is a side view of the leading portion of a slab after upsetting; Figure 4B is a similar view after a profiling pass; Figure 5 diagrammatically shows part of a rolling passage and a flange of a pre-blank; Figure 6 is a diagrammatic cross-section through a slab being rolled to form a blank with flanges, by a method according to the invention, showing successive stages of reduction; Figure 7 illustrates the transformation of an upset slab to a pre-blank;; Figure 8 shows three different pre-blank flange shapes; Figure 9 shows two different pre-blank flange shapes; Figure 10 shows a slab, an upset slab, and a pre-blank, in profile, with significant dimensions indicated.

Figure 11 is a graph illustrating the deformation of an upset slab; Figure 12 is a graph illustrating the development of the mean width of the flanges of a pre-blank during reduction; Figure 13 is a graph illustrating the decrease of the flange thickness during reduction; Figure 14 is a graph of the reduction per pass of the angle of the facets of the flanges as a function of the initial flange thickness; Figure 1 5 shows a blank and a corresponding pre-blank; Figure 1 6 is a flow chart for calculation of the main parameters of a method according to the invention; Figure 1 7 shows profiles of a compression groove and a compression table, for rolling slabs of great width; Figure 18 shows rolling passages between a pair of horizontal rolls; Figure 1 9 illustrates rolling with vertical rolls;; Figure 20 shows a blank obtained using vertical rolls; Figure 21 shows a blank of reduced web thickness between the vertical rolls; Figure 22A shows the leading end of a preblank; Figure 22B shows the leading end after reduction in a profiling passage; Figure 23 shows a slab being reduced in width in a contoured passage between vertical rolls; and Figure 24 shows further reduction of the slab between smooth portions of the vertical rolls.

Figure 1 shows diagrammatically in dotted lines the rectangular section 10 of an ingot having a thickness H sufficient to ensure the correct filling of the profiling passage 11 in the conventional method of rolling of a blank for beams having wide flanges.

Figure 2 shows one end of a blank obtained after rolling of the rectangular section 10 of thickness H in the profiling passage 11 of Figure 1.

It should be noted that the differences of elongation between the web and the flanges produce a rolling tongue whose length 1 2 causes a considerable loss of material: In addition the large degree of thickness of the rectangular section leads to a defect D necessitating scrapping of the front end before continuing rolling in a universal rolling mill.

Figure 3 illustrates a known method of rolling using a slab 30 as a starting product. It should be noted that the upsetting or compression passages (in which the slab is compressed widthwise) have increasing widths b31 < b32 < b33. The width b33 of the pre-blank 33 should be sufficient to ensure the filling of the profiling passage 35.

Figure 4 shows the ends of the blanks obtained by the use of slabs as starting products. During compression (upsetting), elongation of the ends 41 and 42 subject to rolling is greater than the elongation of the middle 43 (see Figure 4A). As the elongation of the web in the profiling passage is greater than the elongation of the flanges, compensation takes place and the blank consequently has a rolling tongue whose length 14 (Figure 4B) is lower than that obtained in accordance with the conventional method using ingots. The loss of material is therefore considerably reduced.

However, simple upsetting in compression passages of increasing width does not ensure the achievement of a correct shape for the flanges of the pre-blank. Compression of the slab of initial height h0 to the final height hn produces a flange shape which depends essentially on the reductions carried out during compression (Ah).

As the achievement of a final height hn and a final flange width bn depends on the initial height h0 of the slab, there is no freedom with respect to controlling the shape of the flanges during compression.

Figure 5 shows an example of an unsatisfactory result obtained by simple upsetting of a slab in rolling passages. It can be seen that despite the achievement of a sufficient flange width of the pre-blank 51, there is a filling defect 53 which may not be eliminated during rolling in the profiling passage 52.

It is also possible for flanges which are too thick to be obtained in certain compression conditions, which may lead to the formation of folds and an insufficient flange width of the blank.

Bearing the above in mind, it can be seen that the simple compression of the width of a slab does not enable the shape and thickness of the flanges of the pre-blank to be controlled.

The method of the invention, whilst reducing the number of rolling passages required, provides an additional degree of freedom which enables the shape and the thickness of the flanges of the preblank to be controlled so as to ensure the correct filling of the profiling passage.

Figure 6 shows an outline diagram of the method of the invention.

The method as illustrated comprises the following stages: (a) a slab 60 is subjected to compression in a contoured rolling passage 61 until a "mushroom" 62 is achieved at each end of the width of the slab; (b) deformation of the "mushroom" on the compression table of a smooth rolling passage leads to the formation of a pre-blank 63 whose contours fit as completely as possible into the subsequent profiling passage; (c) a blank 64 is produced by rolling the preblank 63 in a conventional profiling passage.

Figure 7 shows the formation of the pre-blank flange from the mushroom obtained during the first passage. It can be seen that rolling on the compression table of the smooth rolling passage leads to the following phenomena: (a) reduction of the thickness of the "mushroom" by a value he = e1 - e2 (b) widening Abo = b2 - b0 and Ab = b2b1 (c) cancellation of the inlination of the facets of the "mushroom": lim a1 =O for r o root; with r = Ah/h (reduction).

The principle of the method of the invention therefore rests on the differences in widening between the head (width bo) and the base (width b) of the "mushroom" when it is subjected to compression on the compression table.

d(bo) b(b1) Ar Ar By selecting a suitable angle of inclination 1 of the facets of the "mushroom" it is possible to obtain pre-blank flanges of the required dimensions.

Figure 8 shows various pre-blank flange shapes 81, 82, and 83 obtained by modifying the value of the angle of inclination of the first passage. The flange shape 81 is obtained from a mushroom having an inclination of 10% and a thickness of 0.198 m. The number of passes carried out in the contoured compression passage and the smooth compression passage were respectively 3 and 17.

In order to obtain the flange shape 82, the inclination and the thickness of the mushroom were respectively 50% and 0.2048 m. The number of passes in the contoured passage and the smooth passage were respectively 11 and 9.

The flange shape 83 was obtained from a mushroom having an inclination of 80% and a thickness of 0.2147 m. The number of passes in the contoured passage and the smooth passage were respectively 1 5 and 5.

Figure 9 shows the possibilities provided by the method of the invention with respect to the control of the thickness of the flanges of the preblank. Both flanges 91 and 92 were obtained from slabs having a height of 1.80 m and a thickness of 0.3 m. The mushroom had an inclination.of 50%.

The flange 91 was subjected to 9 passes in the contoured compression passage and 11 passes in the smooth passage, whereas the flange 92 was subject to 6 passes in the contoured passage and 14 passes in the smooth passage. It is noted that the thickness of the flanges is essentially determined by the thickness of the mushroom produced in the compression pass.

Figure 10 shows the main dimensions which should be taken into account in the method of the invention. The starting slab 101 has a height h0 and a thickness bo After a number of passes through the contoured passage, the upset slab 102 has a height h,, the reduction in height being Sh; the thickness of the mushroom is e1 and its angle of inclination 1. The minimum and maximum widths (head and base) of the mushroom are respectively b0 and b,. After a number of passes through the smooth passage the pre-blank 103 of height h2 has been subject to an additional height decrease Ah2. The flanges of the pre-blank 103 have minimum and maximum widths of b3 and b2 respectively.The thickness of the flange is e2 and its angle of inclination is 2.

In order to roll the pre-blanks to the required dimensions it is necessary to be able to calculate the deformation as a function of the conditions involved.

Figure 11 shows, for different heights h0 of the starting slab, the widening of the base of the mushroom as a function of the reduction carried out. The inclination of the facets of the mushroom was 50%.

For an angle ag, the widening of the base of the mushroom may be expressed by the following relationship: #b1/b0 = a1(#h1/h0)a2 (1) The coefficients a1 and a2 are functions of the initial width h0 of the slab and may be expressed by the following a1 = c1 + d1 h0 (2) a2 = c2 + d2 ho (3) in which c" c2, d1, d are constants.

For a given angle 1 and a given initial width, the relationships (1), (2), and (3) enable the width b1 of the base of the mushroom to be determined for a given absolute reduction Ah,.

The thickness of the mushroom is proportional to the width b1 and may be expressed by the following relationship: e1=Ab1/2 tan a1 (4) in which b, = b1bo (5) From this it is possible to define a mean width bm1 of the mushroom: bm1=(b0+b1)/2 (6) In a similar manner it is possible to define a mean width bm1 of the flanges of the pre-blank: bm2 = (b2 + b3)/2 Figure 12 shows, for an inclination of the facets of the mushroom of 50%, the development of the mean width of the flanges of the pre-blank as a function of the reduction carried out in the smooth compression passage.This development may be expressed by the following relationship: Abm2/bm1 = a3 h2/h1 (7) The coefficient a3 is a linear function of the height h, of the upset slab on output from the contoured compression passage and may be expressed by the following relationship: a3 = c3 + d3 . h1 (8) in which c3 and d3 are constants.

Figure 13 shows the reduction of the thickness of the "mushroom" as a function of the smooth compression passage reduction. The angle of inclination a1 of the mushroom at the outset was 50%. An approximate decrease of the thickness of 12% for an angle a1 = 50% may be supposed: hez/eX =a4~0.12 (9) Figure 14 shows the percentage reduction per pass of the angle of inclination a during the compression in the smooth passage as a function of the initial thickness of the mushroom. The angle was 50%.

The various coefficients used in the relationships (1) to (9) should be determined experimentally for different values of the angle a1.

From this it is possible to determine the main parameters of the method of the invention from the dimensions of the blank which it is desired to obtain.

Figure 1 5 shows the main dimensions of the blank 150 and the pre-blank 151, these being respectively Se and Sp (thickness of the web), be and bp (flange width), ee and ep (flange thickness), and he and hp (height).

From the dimensions of the blank, it is possible to determine the dimensions of the pre-blank using the following relationships: ep = ee (10) h2 = hp = he(20 to 30 mm) (11) bm2 = bp = sp + (beSe) (12) The thickness e1 to be obtained in the first (contoured) passage is given by the relationship (9).

Figure 1 6 shows a calculation chart for the determination of the main parameters of the method of the invention. This calculation is advantageously carried out in a computer.

By using the method of the invention, it was possible to roll beams having a web height of up to 1 m and flange width of up to 0.425 m starting from slabs having dimensions of 2 x 0.3 m2.

The compression of slabs having a great width on an absolutely smooth compression table may, however, lead to undesirable phenomena of obliqueness. In such a case, in order to ensure that the slab is sufficiently stable there is provided at the centre of the compression table a roll profile which ensures that the slab is guided during rolling.

Figure 17 shows these profiles for a compression groove 1 71 and for a compression table 1 72.

The guide elements (173 and 174) may be eliminated by compression of the slab on the compression table constituted by the web of the conventional profiling passage.

The compression table may be replaced by a rolling groove comprising a profile at the base. In this case, the sides of the rolling passage ensure lateral guiding for the engagement of the slab during the final compression passes.

A first variant of the method consists in using, instead of the compression table or passage used following the formation of the mushroom, vertical rolls for the rolling of the blank.

In this case rolling of the blank is carried out as shown in Figures 18, 1 9, 20.

Figure 1 8 shows the formation of the mushroom by compression of a slab of height h0 and thickness eb. The horizontal rolls comprise the passage 1 81 used for the formation of the mushrooms and a second passage 1 82 whose contours correspond to the cavity formed by the web and the internal faces of the flanges of the blank 183 shown in broken line.

The width I of this passage should be at least equal to the height h, of the slab on discharge from the passage 1 81. The depth c'of the grooves of this passage should correspond to the width of a half-flange of the blank measured from its end to the web.

Figure 1 9 shows the subsequent deformation of the slab obtained during the previous stage. The width reduction is carried out by means of driven vertical rolls 191 disposed in the same manner as in a universal slabbing mill or in a separate mill.

The width is reduced by compression until the final width be of the pre-blank is obtained as shown in Figure 20.

During compression by the vertical rolls, the horizontal rolls perform a guide function, and the web is subject to no or only a very slight rolling pressure.

The pre-blank is then rolled to the stage of the final blank by means of the reduction of the thickness of the web to the final value ec, as shown in Figure 21. During this reduction in thickness of the web, the vertical rolls are maintained in a fixed position, their spacing corresponding to the blank width. During each pass, the flanges are thus subjected to lateral compression by the vertical rolls.

The advantage of this variant lies in the fact that the compression passes with the web in a vertical position as carried out during conventional profiling passage rolling may be dispensed with.

This result is increased productivity.

A further advantage with respect to conventional profiling passage rolling is that the blank ends are produced with a better shape.

During profiling passage rolling, the shape of the ends of the pre-blank leads to the formation of "ears" on the portion of the end at whcih there is no web as a result of the selective elongation during compression (upsetting).

Figure 22A shows a pre-blank 220 of thickness eb and Figure 22B the blank 222 of thickness e, which is less than eb, having "ears" 221 which result from an overflow localised in the cordons of the profiling passage caused by the absence of web at this location. This phenomenon may cause difficulties in engagement for compression. In order to limit this, it is necessary to carry out additional compression passes. In addition to the resulting loss of productivity, a greater portion of the ends of the blank must be scrapped before rolling is continued in a universal mill. This phenomenon does not, however, arise if rolling is carried out with driven vertical rolls, as described above.

A second variant of the method of the invention consists in carrying out the first stage of the method as well, i.e. the formation of the mushroom, between vertical rolls. In this case, the first compression passage is disposed on vertical rolls 231, the slab being compressed in the horizontal position as shown in Figure 23.

The following stage, i.e. the deformation of the mushroom leading to the formation of the flanges, is carried out by compressing the slab on the smooth portion of the vertical rolls, as shown in Figure 24, this stage, as well as the following stages, being identical to the corresponding stages of the first variant (Figures 19 to 21) described above.

In order to be able to carry out the smooth pass and table compression by means of vertical rolls, the vertical rolls must be displaceable along their vertical axes. The second variant of the method of the invention (Figures 23, 24) enables the avoidance of the slab width limitations imposed by the maximum travel of the rolls of the horizontal stand, the greatest slab width which may be used being determined by the maximum spacing between the vertical rolls.

The principle of the method of the invention may also be applied to the rolling of other large profiled sections such as, for example, Z or U section inertia sheet piling, flat sheet piling subject to tractive stress on clamps, parallel-flanged channels, etc.

Claims (11)

1. A method of producing a blank having a web and flanges of given dimensions by rolling, the method including subjecting a slab to widthwise compression in a rolling passage defined. by grooves whose lateral faces are inclined at a given angle and whose base has a width which is at most equal to the thickness of the slab, the compression causing upsetting of the lateral ends of the slab into the mushroom shape having a flat head and inclined lateral facets, the thickness of the mushroom shapes being approximately 12% greater than that of the flanges of the blank.

2. A method as claimed in claim 1, further comprising subjecting the upset slab to further widthwise compression causing upsetting to such an extent that the widths of the head and base of the mushroom shape become substantially equal and the inclination of the lateral facets is approximately cancelled, the flanges of the resulting pre-blank having a thickness substantially equal to that of the flanges of the blank.

3. A method as claimed in claim 2, in which the said further widthwise compression is carried out in a rolling passage whose width is at least equal to the sum of the width of the blank flange and the difference between the slab thickness and the blank thickness.

4. A method as claimed in claim 2 or 3, further comprising subjecting the pre-blank to rolling in a profiling passage, the mean width of the flanges of the pre-blank being substantially equal to the sum of the slab thickness and the difference between the flange width and the web thickness of the blank.

5. A method as claimed in any of claims 1 to 4, in which the bases of the grooves defining the rolling passage are provided with a profile which is repeated in a following compression rolling passage in order to ensure guiding of the slab, the corresponding profile formed on the resulting flanges being eliminated in a smooth rolling passage.

6. A method as claimed in any of claims 1 to 5, in which horizontal rolls are used.

7. A method as claimed in claim 6, in which the upset slab coming from the horizontal rolls is subjected to widthwise compression between vertical driven rolls arranged in the manner of a universal slabbing mill.

8. A method as claimed in claim 7, in which the vertical rolls are mounted in a separate roll stand adjacent to the horizontal roll stand.

9. A method as claimed in any of claims 1 to 5, in which vertical rolls are used.

10. A method as claimed in claim 9, including subjecting the slab to widthwise compression in the said rolling passage defined by the said grooves, which are formed in vertical rolls also defining a smooth passage, displacing the rolls in the vertical direction, and subjecting the upset slab to widthwise compression in the said smooth passage.

11. A method as claimed in claim 1, substantially as described with reference to Figures 6 to 17 or Figures 18 to 21 or Figures 23 and 24 of the accompanying drawings.