LU83456A1 - PROCESS FOR ROLLING BLANKS FOR THE PRODUCTION OF LARGE PROFILES - Google Patents

Description

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Process for rolling blanks for the production of large profiles

The present invention relates to a process for rolling blanks for the production of large steel sections, in particular large pout-5 connected with large wings with web heights of 1 m.

Conventional rolling processes usually involve the following steps: ^ 10 - A rectangular or square section (bloom) is produced by rolling an ingot on a cage comprising two horizontal cylinders (bloo-ming or break-down). This rectangular section can also be produced by continuous casting with or without subsequent rolling on a roughing blooming or break-down cage in order to obtain the desired dimensions. The section should have a width slightly less than the width of the first profiling groove which is then used.

- This profiling groove is generally placed on a cage 20 comprising two horizontal cylinders (blooming or break down). By carrying out several rolling passes in this profiling groove, a blank is obtained whose shape is such that it allows subsequent rolling on the other stands of the rolling mill until the finished product is obtained. The thickness of the rectangular section must be chosen so as to obtain a correct filling of all the parts of the blank section.

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These conventional methods have several drawbacks: - The need to produce either ingots or very thick continuous casting sections.

5 - The loss of material due to the fact that the ends of the blanks must in some cases be dropped before continuing rolling on the other stands of the rolling mill.

In order to eliminate these drawbacks, it has been proposed to use slabs of rectangular cross section instead of ingots as a starting material. The idea behind these processes is as follows:

By pushing back the width of a slab between two horizontal or vertical cylinders, it forms at the ends of the slab of the wings 15 which make it possible to obtain a blank by subjecting the widened slab at the ends to rolling either in conventional profiling groove or in universal cage.

Λ The widening of the ends of a slab subjected to the discharge is a phenomenon well known to laminators, which must be taken into account when rolling products of rectangular section.

The evolution of the shape of the free edges of a rectangular section subjected to rolling is closely linked to a parameter defined as being the ratio between the projected length of the contact arc and the average height of the product.

If we denote by: R the radius of the cylinders ho the initial height of the rectangular section 30 hl the final height of the rectangular section this ratio can "'write ·, g * · Id hui 35 with ld = VR (ho- hl) and hm = ho + hl 2 - 3 - Widening is defined as the flow of material taking place in the direction perpendicular to the directions of rolling and reduction.

5 For a low g ratio, the widening of the free edges not subjected to the direct rolling pressure, is preferentially located at the ends of the free edges leading to a shape evoking a diabolo. The thickness at mid-height of the section is not affected by the deformation and remains constant.

10 ’For a high g ratio, the enlargement is concentrated halfway up the section, leading to a barrel-like shape.

The value of the ratio g separating the two modes of enlargement is 0.6 15 S 0.7.

For this limit value the widening of the free edges is constant over the entire height of the free edges.

* s 20 All the methods of rolling beams from slabs are based on the widening mode obtained for low values of the ratio g.

However, the methods which use a universal cage for the production of the blank are difficult to apply in the case of beams of great height and having extra wide wings.

Similarly, a discharge of the width of the slab in rolling grooves of increasing width does not allow perfect control of the shape of the wings of the blank. In addition, the table width of the roughing duos is often limited, which prohibits placing a series ht "nerittelitrpn mulrtnt · * ·" dur les oylIndre "dan * lp cnn of the beams-) the * of great height of core and having extra large wings.

35 The object of the invention was to propose a process for rolling blanks to the required dimensions and which only requires the intervention of a rolling groove and a smooth table.

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According to the invention, the roughing is carried out in three stages: a <Returning the width of a slab in a rolling groove 5 whose lateral faces have a determined inclination and whose bottom width is less than or equal to the thickness of the slab.

The widening leads to the filling of this groove and the slab has at the ends, along the width, protuberances whose shape evokes a perfectly symmetrical mushroom.

b. Backflow onto the backing table of the width of the slab produced according to step a.

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This repression has the effect of deforming the fungus by reducing the thickness and by widening until wings are obtained which adapt as perfectly as possible to the shape of the profiling groove.

20 c. Lamination of the pre-blank produced according to step b. in a conventional profiling groove until the blank is obtained.

According to the invention, an adequate combination of the angle of inclination of the faces of the rolling groove and the reductions imposed in the rolling groove and on the press table makes it possible to obtain, for each beam, a form of pre-blank with the required dimensions.

Other characteristics and advantages of the process according to the invention over conventional processes will emerge from the description of the drawings.

’Fig. 1 schematically shows the conventional method of rolling a blank for beams with large wings. The rectangular section whose thickness H is sufficient to guarantee the correct filling of the profiling groove is shown in 35 dotted lines.

Figure 2 shows one end of a blank obtained after laminating the rectangular section of thickness H in the profiling groove 5 of FIG. 1. It is noted that the differences in elongation between core and wings produce a lamination tongue, length 1 constitutes an appreciable loss of material.

In addition, the large thickness of the rectangular section leads to a lining D which requires the end to be dropped before continuing rolling on a universal cage.

Fig. 3 shows the diagram of a rolling process which uses a slab as the starting material. It can be seen that the refouleu-15 ses grooves have increasing widths bl <b2 <b3.

The width of the wings of the pre-blank (b3) must be sufficient to guarantee the filling of the profiling groove (4).

Fig. 20 4 shows the ends of the blanks obtained by the use of slabs as starting material.

During the delivery, the elongation of the ends subjected to rolling is more important than the elongation of the center (core, fig. 4a). 25 The elongation of the profiled groove core being greater than the elongation of the wings, there is compensation and this results in a lamination tongue of the blank whose length 1 (fig. 4b) is less than that obtained following the conventional process using ingots. The loss of material is thus considerably reduced.

30 ”Simple discharge in increasing width grooves. does not however guarantee the obtaining of a correct shape of the wings of the pre-blank.

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Indeed the backflow of the slab of initial width ho to the final width hn produces a form of wings tpii àlbehâ essentially ύ & β reductions imposed! during the backflow (Σλ \ ι).

5 As the production of a final width hn and a final width of the wings bn depends on the initial width ho of the slab, there is no degree of freedom allowing the shape of the wings to be controlled during the delivery.

10 An example of an unfavorable result obtained by simple discharge of a slab in rolling grooves is given in FIG. 5. It is noted that, despite obtaining a sufficient width of the wings from the pre-blank (1), there is a filling defect (3) which cannot be eliminated during rolling in the profiled groove (2).

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It is also possible that under certain delivery conditions, the wings are too thick, which can lead to the formation of folds and insufficient width of the wings of the blank.

It follows from these considerations that the simple delivery of the width of a slab does not make it possible to control the shape and the thickness of the wings of the pre-blank.

The process according to the invention, while reducing the number of rods required, introduces an additional degree of freedom which makes it possible to control the shape and the thickness of the wings of the pre-blank so as to guarantee the correct filling of the profiling groove.

The block diagram of the process according to the invention is shown at 30 in FIG. 6.

The process steps are as follows: a. A slab (1) is subjected to the discharge in a rolling groove 35 until a "mushroom" (2) is obtained.

- 7 -) b. The deformation of the "fungus" on a press table leads to the formation of a pre-blank (3) whose contours fit as perfectly as possible in the profiling groove.

5 Q. Obtaining the blank (4) by rolling the pre-blank (3) in a conventional profiling groove.

In fig. 7 it is explained the formation of the pre-blank from the fungus made in the first groove. It can be seen that rolling on a press table gives rise to the following phenomena: a. Reduction of the thickness of the "fungus" by a value û e = e - e2 b. Enlargements ^ = ^ 2 ”b0 15 and Δ bT = b2 ~ b1 c. cancellation of the inclination of the facets of the lim "mushroom" lim (H1 = 0 for r -? rtQt with r = (reduction) 20 The principle of the method according to the invention therefore rests on the differences in widening between head of width bo and base of width bl of the "fungus" when it is subjected to a backflow on a backing table.

0 <4b) â (4b,) 25 -> -

Or. 0 r

By suitably choosing the angle of inclination 1 of the facets of the "mushroom", it becomes possible to obtain pre-draft wings of required dimensions.

30 ”Fig. 8 shows different shapes of pre-draft wings obtained by modifying the value of the angle of inclination of the first groove. In this figure ni and n2 are the number of passes carried out in a pressure groove resp. on a pressure table.

Fig. 9 shows the possibility offered by the method according to the invention in controlling the thickness of the wings of the pre-blank.

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This thickness is essentially determined by the thickness of the "fungus" produced in the pressure groove.

Fig · 10 shows the main dimensions involved in the process according to the invention.

In order to laminate pre-blanks to the required dimensions, it is necessary to be able to calculate the deformation according to the conditions imposed.

10 Fig. 11 shows the widening of the base of the "fungus" as a function of the reduction imposed.

For an angle <^ 1, the widening of the base of the "mushroom" can be expressed by the following relation: 15 K .a a bi - "^ l * hi) 2 (1) ~ 1 * fan

The coefficients al and a2 are functions of the initial width ho of the slab and can be expressed by the following equations: 20 = C1 + dT h0 (2) a2 = ° 2 - V ho (3>

For an angle ° (l and a given initial width, the relations (1), (2) 25 and (3) make it possible to determine the width bl of the base of the mushroom for a given absolute reduction.

The thickness of the "mushroom" is proportional to the width bl and can be expressed by the following relation: 30 e _ Δ ^ 1

1 - "jrrr W

P «4 1 * with, seen tei ib1 = b1 - bo (5) 35 We can therefore define an average width of the" fungus "bm, = b + b,, r- \ 1 _o 1_ (6) 2 - 9 - f

Fig. 12 shows the evolution of the average width as a function of the reduction imposed on the press table. This evolution can be expressed by the following relation: λ b Δ ^ 2 (7) __ £ "° · η · - b m1 h- | 5 The coefficient is a linear function of the height hl of the slab at the exit of the groove peffeuse and can be expressed by the following relation: a3 = c3 + Vn1 (8) 10

Fig. 13 shows the reduction in the thickness of the "mushroom" as a function of the reduction on the press table.

With a good approximation we can admit a reduction of 15 in the thickness of 12% for an angle 1 = 50%: * e2 = V 0.12 (9) β1

Fig. 14 shows the reduction per pass of the angle ° <1 during the delivery on a press table as a function of the initial thickness of the "mushroom".

The different coefficients involved in the relations (1) - (9) must be determined experimentally for different values of the angle 1

It is therefore possible to determine the main parameters of the process according to the invention from the dimensions of the blank that it is desired to obtain.

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Fig. 15 shows the main dimensions of the blank and the pre-blank.

From the dimensions of the blank, the dimensions of the pre-blank can be determined using the following relationships: e = e (10) P e h_ = h = h - (20 ^ 30 mm) (11) 2 eg hm = b = s + (b -s) (12)

Dm? p p e e - 10 - The thickness e ^ referred to in the first groove is given by the relation (9).

Fig. 16 shows a calculation diagram which leads to the determination 5 of the main parameters of the method according to the invention.

This calculation will advantageously be carried out on a computer.

Using the method according to the invention, it was possible to laminate beams up to a web height of 1000 mm and up to wing widths of 425 mm starting from slabs of dimension 2000 x 300 mm2.

The discharge of very wide slabs onto the discharge table can, however, cause undesirable obliquity phenomena.

In order to guarantee sufficient stability to the slab, a profiling of the cylinder is provided in the middle of the press table which ensures the guiding of the slab during rolling.

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Fig. 17 shows such profiling. The guide backing pads (1) can be eliminated by pushing back the slab on the press table constituted by the core of the conventional profiling groove.

The upsetting table can be replaced by a rolling groove comprising profiling at the bottom of the groove. In this case, the sides of the rolling groove provide lateral guidance when the slab is engaged during the last delivery passes.

A variant of the process consists in using, instead of the table or delivery groove used following the formation of the "fungus", cylinder # Vî * rHr »rtiix hour le Inmlnnj ** df J'éhnurhe.

In this case, the rolling of the blank is carried out as shown in FIG. 18.

Fig. 18.1, shows the formation of the "fungus" by repression of a slab of height h and thickness e, ·

O D

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The horizontal cylinders have the groove (a) used for the formation of "mushrooms" and a second groove (b) whose contours correspond to the chamber formed by the core and the inner faces of the wings of the blank (e) shown. with dots.

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The width 1 of this groove must be at least equal to the height h ·] of the slab at the outlet of the groove (a). The depth θ ′ of the recessed part of this groove must correspond to the width of a wing half of the blank, measured from its end 10 to the core.

Fig.18,2 shows the subsequent deformation of the slab obtained during the previous step. The width reduction is carried out by means of vertical driven cylinders (g) arranged as a universal slab-15 bing cage or in a separate cage. The width is reduced by discharge until the final width bg of the blank is obtained, as shown in fig. 18.3.

During the delivery by the vertical rolls, the horizontal rolls have a guiding function, the core undergoing no or only a low rolling pressure.

The pre-blank is then laminated to the final blank stage by reducing the core thickness to the final value ec, as shown in FIG. 18.4.

During this reduction in thickness of the core, the vertical cylinders are maintained in a fixed position, their spacing corresponding to the blank width b 30

During each pass, the wings are thus subjected to a repression- irtisHf ÎÂtlSt'hT rirtt 1 *** vf'rttrisiuvi The advantage of this variant resides in the fact that it is possible to suppress the repression passes with web in vertical position as carried out during rolling in conventional profiling groove. This results in increased productivity.

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Another advantage compared to rolling in a conventional profiling groove is the obtaining of a better shape of the ends of the blank.

5 In fact, during rolling in a profiled groove, the shape of the ends of the pre-blank leads to the formation of "ears" on the part of the end where there is absence of core due to the elongation selective during refoulement.

10 Fig. 19 shows these "ears" which come from an overflow located in the cords of the profiling groove caused by the absence of a core at this location.

The phenomenon can cause difficulties in engaging the refoulement. In order to limit it, it is necessary to make additional delivery passes.

In addition to the resulting loss of productivity, there is a need to drop more of the ends of the blank before continuing rolling in a universal cage.

When rolling with driven vertical rolls, as described above, this phenomenon does not appear.

The principle of the process according to the invention can also be applied for the rolling of other large profiles such as p. ex. inertial sheet piles in the form of a Z or a U, flat sheet piles stressed in tension on the claws, U irons with parallel wings, etc.

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Claims (4)

1. A method of rolling blanks for the production of beams, characterized in that a slab 5 of rectangular section is used as the starting product and that this slab is subjected to a rolling in three stages: a . A discharge in a rolling groove whose bottom width is less than equal to the thickness of the slab used and 10 whose side faces are inclined at an angle <^ 1 which is a function of the dimensions of the blank, the thickness of the "mushroom" thus obtained being approximately 12% greater than the thickness of the wings of the draft. B. A discharge of the slab obtained according to step a., On a pressure table or a pressure groove whose width is at least equal to the width of the wings of the preform increased by the difference between thickness of the slab and thickness of the blank so that the total reduction imposed produces a widening such that the widths of the top and the base of the "mushroom" become substantially equal at the end of the delivery with the approximate cancellation of the angle ol 1 and obtaining a thickness of wings corresponding to the thickness of the wings of the blank. 25 c. A conventional profiled groove rolling of the blank obtained according to step b., Until the final blank is obtained, the average width of the wings of the blank obtained according to step b. must be substantially equal to the thickness of the slab increased by the difference between the width of the wings and the thickness of the core of the blank. 2. Method according to claim 1, characterized in that the main parameters of the method are determined according to the “calculation calculation shown in FIG. 16. - 2 - 3. Process according to claims 1 and 2, characterized in that provision is made for the presence of backing pads at the bottom of the first cane “lure upsetting, these backing pads being reproduced on the following table or upsetting groove so as to ensure 5 slab guidance. These guide pads are removed by pushing back onto the smooth table formed by the core of the profitable groove, or, if the table width of the cylinders allows, in a rolling groove with a flat bottom. 4. Method according to claims 1,2 and 3, characterized in that steps b and c according to claim 1 are replaced by a delivery of the slab obtained following step a by means of driven vertical cylinders, the arrangement of these cylinders being analogous to that of a universal slabbing cage. The vertical cylinders can be arranged in a separate cage located as close as possible to the horizontal cylinder cage.