RU2465081C1 - Method of making cold-rolled sheets from aluminium and its alloys - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy and may be used in hot rolling of strips from melt of aluminium and its alloys at foundry rolling units. Proposed method comprises continuous casting of billet of melt and rolling said billet to semi-finished stock. Then, finished strip is fed to process section with application of front and rear tension forces at stands to measure rolling force at final stand. Further, it comprises feeding coolant to semi-finished stock, cold rolling of strip at final stand and coiling strip into bundle. Note here that in rolling strip front end, rear tension created by final stand rolls is kept equal to zero while cold rolling at final stand is performed at strip thickness defined by mathematical expression.

EFFECT: higher quality of finished product with camber not exceeding 0,1 mm per running metre.

14 cl, 1 dwg

Description

The invention relates to the field of metallurgy and can be used in the production of products directly from molten aluminum and its alloys on foundry-rolling units.

A known method for the production of cold-rolled tapes of aluminum and its alloys on rolling mills from slabs (see, for example, Erhard Hermann. Continuous casting. Metallurgical publishing house. Moscow. 1961. Pages 143-145).

The disadvantages of this method:

- discreteness of the process, causing instability of the properties of the tape along its length;

- the presence of restrictions on the weight of the roll.

A known method for the production of tapes of aluminum and its alloys, including continuous casting of a billet from a melt, rolling the billet into a finished tape and winding it into a riot (see, for example, V. A. Chebotarev and V. A. Samsonov. Casting and rolling units for the production of wire rod, sheets and ribbons of non-ferrous metals. "Heavy Engineering", No. 5. 2007. Pages 20-27).

The advantages of this method:

- the continuity of the process, ensuring the stability of the properties of the tape along its length;

- the possibility of obtaining riots of tape with almost unlimited mass, determined only by the technical capabilities of the casting and rolling unit.

The disadvantage of this method is the occurrence of a roll curvature of the tape in the process of winding it on the reel drum, which leads to non-flatness of the tape.

The technical result of the invention is to improve the quality of products by obtaining its ultra-high flatness (with a warp of not higher than 0.1 mm per linear meter) when rolling a cold-rolled strip, provided that it is strictly horizontal when leaving the rolls of the last rolling stand.

The technical result is achieved by using a method for the production of cold-rolled sheet products from aluminum and its alloys, including continuous casting of the billet from the melt, hot rolling of the billet into a tackle and then into the finished tape in several stands with the application of the forces of its front and rear tension and with measuring the temperature of the roll through the stands, as well as measuring the force and moment of rolling in the last stand, supplying coolant to the tackle, releasing the surface of the tape from the remaining cooling liquid, wherein during the rolling of the front end of the tape back tension generated before the last stand of rolls kept equal to zero; cold rolling of the finished tape is carried out at a tape thickness not exceeding (h _k ) _max = D _B · σ _s1 / 10 ⁴ mm, where (h _k ) _max is the maximum allowable thickness of the cold-rolled tape, mm; D _B - winder drum diameter in mm; σ _s1 is the yield strength of the tape caged in the last stand, kgf / mm ² ; the tape after it leaves the last stand is passed under the forward tension T ₁ through the pulling rollers and then under the tension T _{m is} wound in riots; when rolling the tape, the front tension created at the exit from the last stand is maintained equal to T ₁ = 0.67σ _s1 (in · h _k ) kgf, where T ₁ is the front tension in kgf, in - the width of the tape in mm; σ _s1 - yield strength of the tape at the exit of the last stand in kgf / mm ² ; h _to - the thickness of the finished tape in mm; the initial values of the rolling force P ₀ and the rolling moment M ₀ in the last stand are measured at the front end of the tape in the absence of rear tension and with a front tension equal to T ₁ ; at the end of rolling the front end of the tape, the rear tension is increased to a value of T ₀ due to the gradual increase in the speed of rotation of the rolls of the last stand with a constant front tension T ₁ ; in this case, the value of the back tension in the steady rolling process is determined by the formula T ₀ = 0.67σ _s0 (in · h ₀ ) kgf, where σ _s0 and h ₀ are the yield strength of the roll in kgf / mm ² and the thickness of the roll from the penultimate stand; the speed of rotation of the rolls of the last stand is increased until the total rolling moment in this stand becomes equal to the value found by the formulas

F ₀ = in h ₀ ,

where M ₁ is the rolling moment in kgf · mm in steady state;

P ₀ - the initial values of the rolling moment in kgf · mm and the rolling force in kgf, measured when rolling the front end of the tape without rear tension;

D is the diameter of the roll barrel in mm; the main front tension (T ₁ -T _m ) is created by pulling rollers, where T _m is the front tension increment created by the coiler; the pressing force of the pulling rollers to the rolled strip is chosen equal to twice the main front tension (T ₁ -T _m ); when the front and rear tension values equal to T ₁ and T _{0 are} reached, respectively, the ratio of the rotational speeds of the rolls of the last and penultimate stands, as well as the ratio of the rotational frequencies of the rolls of the last stand and pulling rollers, are kept constant in the future with an accuracy of not less than ± (0.16 ... 0.18)% each; while the coolant is fed to the tackle when it enters the last stand, cooling the tackle to 20 ... 40 ° C before it enters the last stand; the vertical position of the reel drum is chosen so that at any given moment in the process of winding the tape into the riot it leaves the rolls of the last stand strictly horizontally.

The proposed technical solution allows to obtain cards with ultra-high flatness due to the following features of this design:

- due to the very precise maintenance of the ratio of the rotation frequencies of the rolls of the last and penultimate stands, as well as the ratio of the rotation frequencies of the rolls of the last stand and pulling rollers, the front and rear specific tension of the roll in the last stand can be raised to (2/3) from the yield strength of the tape, which significantly more than with conventional rolling;

- due to the almost complete elimination of the warping of the tape when it leaves the rolls of the penultimate stand (where preparation of high-quality tackle for the last stand is being prepared), and then at the exit from the rolls of the last stand;

- due to which, as a result, the flatness indices of the hot-rolled strip turn out to be one or two orders of magnitude higher than during ordinary rolling of the strip.

The proposed technical solution is illustrated by a figure, which shows a diagram of a casting and rolling unit:

Figure 1. Side view of the casting and rolling unit.

A casting machine 2 is installed behind capacity 1 for liquid aluminum, followed by rolling stands with drives: the penultimate 3 and the last 4; behind the last stand, pulling rollers 4 with a drive and guillotine shears 6 are installed (drives of rolling stands and pulling rollers are not conventionally shown in the figure).

After scissors 6 placed two winders 7 and 8.

All the machines of the casting and rolling unit are interconnected by a continuously machined roll in the form of a cast billet 9 between the casting machine 2 and the penultimate stand 3, the rolling 10 and between the rolling stands 3 and 4 and the finished tape 11 between the last stand 4 and winders 7 or 8.

Along the line of the casting and rolling unit, meters of rolling temperature were installed: pyrometer 12 - at the exit of the casting machine 2, pyrometer 13 - at the exit of the penultimate stand 3 and pyrometer 14 - at the entrance to the last stand 4; It should be noted that only two pyrometers are involved in the control system of the casting and rolling unit: 13 and 14.

To supply technological coolant to the tackle 10, a collector 15 is mounted above it; there is no similar collector below so as not to disrupt the normal operation of the pyrometers 13 and 14.

The casting and rolling unit operates as follows.

Liquid aluminum from the tank 1 enters the zone of the rotating rolls of the casting machine 2. The temperature of the cast billet 9 emerging from it is measured with a pyrometer 13. Passing through the rolls of the rolling stand 3, the billet changes its thickness to h _о , turning into a tackle 10 for the subsequent rolling stand 4; the temperature of the roll 10 in the interval between stands 3 and 4 is measured with pyrometers 13 and 14.

Having passed stand 4, the rolling 10 turns into a finished tape 11 of thickness h _k , which is wound into a riot on the drum of the winder 7.

After winding a riot full in mass, they include guillotine shears 6, which are volatile (this is indicated by two horizontal counter-directed arrows 16).

Moving at a speed equal to the speed of the tape 11, they cut it; the rear end of the tape formed in this case is wound up in a riot on the drum of the winder 7, and the formed, in turn, front end of the tape 11 is tucked onto the drum of the winder 8 (this is exactly the moment shown in the figure).

An ultra-flat cold-rolled strip 11 emerges from the last rolling stand 4. To avoid the formation of roll curvature on it when winding the reel 7 or 8 onto the drum, the thickness of the finished strip 11 should not exceed (h _k ) _max ; otherwise, tensile stresses (in the upper fibers) and compressions (in the lower ones) that exceed the yield strength of the tape will occur in the outer fibers of the cross section of the tape 11. As a result, plastic deformation of the metal will occur, which will lead to the winding of the rolled tape 11 into a roll.

The above maximum allowable thickness of the finished tape 11 is calculated according to the empirical formula:

where D _B and σ _s1 are the diameter of the reel drum (7 and 8) in mm and the yield strength in kgf / mm ^{2 of the} tape 11, caged in the last stand 4.

Ultimately, the sequence of technological operations in the production of cold-rolled sheet products from aluminum and its alloys is as follows.

In the rolls of the casting machine 2 from the tank 1 serves liquid aluminum. Formed in the machine 2 cast billet 9, having passed rolling stands 3 and 4, turns into a tackle 10 and then into a finished tape 11.

Rolling in the last stand 4 is carried out with the application of longitudinal tension to the roll: rear T _about (to roll 10) and front T ₁ (to the finished tape 11); moreover, when rolling the front end of the tape 11, the rear tension T _o created in front of the rolls of the last stand 4 is maintained equal to zero.

This is necessary in order to be able to measure the initial values of the rolling force P _about and the moment of rolling M _about in the last stand 4, necessary for further technological calculations; while for the front tension support its working value T ₁ ; the value of T ₁ consists of two components: the increment of tension on the winder T _m and tension (T ₁ -T _m ), which is developed by pulling rollers 5; the specified tension is 70 ... 80% of the total front tension T ₁ , i.e. its largest part, and therefore the tension (T ₁ -T _m ) is called the main front tension.

The rear T _about and the front T ₁ tension calculated respectively according to the formulas:

where σ _so and σ _s1 are the yield strength of the roll in kgf / mm ^2, respectively, at the inlet and outlet of the rolls of the last stand 4;

h ₀ and h _to - the thickness of the rolled 10 and tape 11 in mm, respectively;

c - roll width in mm.

And if the set value of the front tension T _{1 is} adjusted according to the current of the electric motors in the drives of the pulling rollers 5 and winders 7 or 8, then the value of the back tension T _{0 is} adjusted as follows.

At the end of rolling the front end of the tape 11, at which the back tension T _{0 was} maintained equal to zero, the rotation speed of the rolls of the last stand 4 is gradually raised until the total rolling moment on the rolls of this stand increases from the initial value M _about to the working value M ₁ ; the latter is calculated by the formula:

F ₀ = in h ₀ ,

where M ₀ and P ₀ are the initial values of the force and moment of rolling in kgf and kgf · mm, respectively, measured during rolling of the front end of the tape 11 in the last stand 4 without rear tension;

σ _so - yield strength of the roll in kgf / mm ² at the exit from the rolls of the penultimate stand 3, calculated in accordance with the readings of the pyrometer 13;

D is the diameter in mm of the roll barrel in the last stand 4.

An increase in the rolling moment from M ₀ , measured in fact, to M ₁ calculated according to the formula (6), indicates that the rear tension has risen from zero to the value T ₀ calculated according to the formula (4); those. back tension is determined indirectly. This method turned out to be more accurate than direct measurement, since the thickness h _{0 of the} roll 10 in front of the last stand 4 can reach 10 mm or more. With such a large thickness, the plastic component during bending of the tape on a tensorolic (not shown conventionally in figure 1), which measures the force of the rear tension, can reach 70 ... 80% of the measured force. Therefore, the measurement error will not be measured as a percentage, but in times.

The surface of the pulling rollers 5 is gummed with hard grades of rubber. Therefore, despite a sufficiently large absolute force N of pressing them against the tape 11 (it reaches 3000 kgf or more), the finished tape 11 is not damaged for two reasons: firstly, due to the elastic flattening of the rubber “shirt”, a sufficiently large area of the mutual the contact of the rollers 5 and the tape 11; secondly, the relatively high coefficient of friction between the rubber and the metal of the tape 11 allows you to limit the relative pressure of the rollers against the tape by their double ratio.

Particular attention is paid to the fact that the tape 11, which comes out of the rolls of the last stand 4, is strictly horizontal (or rather, it should be perpendicular to the vertical axis "0-0" connecting the centers of the rolls of stand 4 (see figure 1)). Otherwise, the roll curvature will be replaced by the longitudinal curvature of the tape 11, which will be formed due to the asymmetry of the deformation zone of the tape in the rolls of the stand 4.

To maintain the indicated symmetry of the deformation zone at any given rolling moment, the horizontalness of the tape 11 exiting the rolls of the stand 4 is supported as follows: for each revolution of the reel 7, it is lowered in plane-parallel mode exactly by an amount equal to the thickness of the wound tape 11.

For this reason, the winders 7 and 8 are installed with the possibility of plane-parallel movement of their drums in the vertical direction, i.e. arrows 17 and 18.

In order to simplify the design of the casting and rolling unit, in the interval between the last stand 4 and the pulling rollers 5, the tape 11 is not subjected to cooling. Instead, the condition was set that the cooling system in the interval between stands 3 and 4 should guarantee cooling of the rolling stock 10 so that it enters the rolls of stand 4 with a temperature of 20 ... 40 ° C. To this end, the collector 15 is configured to control the flow rate of the process coolant.

But the main feature of the proposed casting and rolling unit is that in the spaces between stands 3 and 4, as well as between stand 4 and rollers 5, it operates in the correct stretching machine mode. As you know, the plastic tensile strain of the tape in machines of this type can reach 1.6 ... 1.8%. Therefore, when reaching a predetermined value of the rolling moment M ₁ in stand 4 (and therefore a predetermined rear tension T ₀ ), both ratios of rotation frequencies: rolls of stands 3 and 4, as well as rolls of stand 4 and rollers 5 are kept constant in the future with an accuracy of at least less than ± (0.16 ... 0.18)% for each of both ratios. This requirement stems from the fact that the accuracy of maintaining the ratio of rotational speeds should be at least an order of magnitude less than the maximum possible plastic deformation, i.e. (1.6 ... 1.8)%: 10 = (0.16 ... 0.18)%.

For this purpose, the drives of stands 3 and 4, as well as the pulling rollers 5 are made with a rigid electrical connection between each other according to the speed of the moving processed roll.

Thus, through the use of the proposed method, the quality of the product is improved by obtaining it with ultra-high flatness (with a warp of not higher than 0.1 mm per linear meter), i.e. one to two orders of magnitude higher than with conventional rolling of the tape under conditions of preparation in the penultimate stand of high-quality tackle for the last stand.

Claims (14)

1. A method for the production of cold-rolled sheet products from aluminum and its alloys, including continuous casting of a billet from a melt, rolling the billet into a tackle and then into a finished tape in several stands with the application of the forces of its front and rear tension and measuring the temperature of the roll through the stands, as well as measuring the force and moment of rolling in the last stand, supplying coolant to the tackle, releasing the surface of the tape from the remaining coolant, cold rolling the tape in the last stand and winding Started tape on a drum winder, wherein the rolling of the front end of the tape back tension generated before the last stand of rolls kept equal to zero, characterized in that the cold rolling belt at the last stand is performed at a tape thickness not exceeding
(h _k ) _max = D _B σ _s1 / 10 ⁴ ,
where (h _k ) _max is the maximum permissible thickness of the cold-rolled strip, mm;
D _B - winder drum diameter, mm;
σ _s1 is the yield strength of the tape caged in the last stand, kgf / mm ² . 2. The method according to claim 1, characterized in that when rolling the tape, the front tension created at the exit of the rolls of the last stand is maintained equal to:
T ₁ = 0,67σ _s1 (in · h _k),
where T ₁ - front tension, kgf;
in - the width of the tape, mm;
σ _s1 - yield strength at the exit of the rolls of the last stand, kgf / mm ² ;
h _k is the thickness of the finished tape, mm 3. The method according to claim 1, characterized in that after the tape exits the last stand, the tape is passed through the pulling rollers with a front tension of T ₁ and wound into riots with a tension of T _m = (0.1 ... 0.2) T ₁ . 4. The method according to claim 1, characterized in that the initial values of the rolling force P _about and the moment of rolling M _about in the last stand are measured at the front end of the tape in the absence of rear tension and with a front tension equal to T ₁ . 5. The method according to claim 1, characterized in that the amount of back tension during the steady rolling process is determined by the formula:
T _o = 0.67σ _so (in h _o ),
where σ _so and h _o are the yield strength of the roll (kgf / mm ² ) and the thickness of the roll (mm) at the exit from the rolls of the penultimate stand, respectively. 6. The method according to claim 1, characterized in that at the end of rolling the front end of the tape, the rear tension is increased to a value of T _about due to the gradual increase in the speed of rotation of the rolls of the last stand with a constant front tension T ₁ . 7. The method according to claim 1, characterized in that the rotation speed of the rolls of the last stand is increased until the total rolling moment in this stand becomes equal to the value determined by the formulas:
M ₁ = M _o [1-σ _so · F _p / (2P _o )] + σ _so F _o / (D / 3),
Where

;
F _o = in · h _o ;
M ₁ - rolling moment in a steady process, kgf · mm;
M _o and R _o - the initial values of the rolling moment (kgf · mm) and rolling force (kgf), measured during rolling of the front end of the tape without rear tension, respectively;
D - roll barrel diameter, mm. 8. The method according to claim 1, characterized in that the main front tension (T ₁ -T _m ) create pulling rollers. 9. The method according to claim 1, characterized in that the compressive force of the pulling rollers to the rolled strip is chosen equal to twice the front tension T ₁ . 10. The method according to claim 1, characterized in that when the values of the front and rear tension equal to, respectively, T ₁ and T _about , the ratio of the frequencies of rotation of the rolls of the last and penultimate stands, as well as the ratio of the frequencies of rotation of the rolls of the last stand and pulling rollers are maintained constant in the future with an accuracy of no lower than ± (0.16 ... 0.18)% each. 11. The method according to claim 1, characterized in that the process coolant is supplied to the tackle at the entrance of the tackle to the rolls of the last stand. 12. The method according to claim 1, characterized in that the tackle before entering the rolls of the last stand is cooled to a temperature of 20-40 ° C. 13. The method according to claim 1, characterized in that the finished tape is released from the rolls of the last stand horizontally. 14. The method according to item 13, wherein the horizontal position of the tape at the exit of the rolls is determined by the fact that for each revolution of the drum winder it is lowered by an amount equal to the thickness of the wound tape.

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