RU2466806C1 - Method of sheet hot rolling from aluminium and its alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises continuous casting from melt and hot rolling of billet into semis. Then, semis are rolled into finished strip with application of front and rear tension to breakdown, breakdown temperature at stands is measured along with rolling force and moment at last stand. It includes also feeding cooling fluid onto strip, cutting it into sheets and piling the latter. Note here that at the beginning of casting-rolling strip front edge rear tension at last stand is kept approximating to zero. Note also that at steady state of rolling, rear tension magnitude is defined by mathematical expression with due allowance for breakdown yield strength and thickness at outlet of rolls of penultimate stand.

EFFECT: higher quality of strip with corrugation not exceeding 0,1 mm per running metre.

15 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of metallurgy and can be used in the production of directly from the melt of hot rolled strips of aluminum and its alloys on casting and rolling units.

A known method for the production of hot rolled strips of aluminum and its alloys on hot 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 (or riot).

A known method for the production of hot rolled strips of aluminum and its alloys, including continuous casting of the billet from the melt, hot rolling of the billet into the finished strip and its winding into a riot (see, for example, V. A. Chebotarev and V. A. Samsonov. Casting and rolling aggregates 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 product quality by obtaining ultra-high flatness (with a warp of not higher than 0.1 mm per linear meter) when rolling a hot-rolled tape, followed by its division into cards or sheets.

This technical result is achieved by using a method for the production of hot-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 a finished tape on several stands with measurement of the temperature of the roll by stand, with the application to the roll the efforts of its tension and with the supply of coolant to the roll, the release of the surface of the tape from the remaining coolant, as well as the subsequent separation of the continuously moving hot rolled tape on separate cards with stacking them in the pack; wherein the front end of the rolling the preform is carried out with zero tension a peal rear inlet at the last stand and the front finished strip tension at the outlet therefrom is maintained at T ₁ = 0,67σ _s1 (BH _k) kgf, where - the width of the tape in mm; h _to - the thickness of the finished tape in mm; σ _s1 - yield strength in kgf / mm ² at the exit from the rolls of the last stand, which is created by pulling rollers pressed against the tape with a double force T ₁ ; when reaching the steady-state rolling process, the rotation frequency of the rolls of the last stand is gradually increased, thereby raising the rear tension of the peel to the value T ₀ (at a constant front tension T ₁ ), which can be defined as T ₀ = 0.67σ _s0 (b ₀ ) kgf, where h ₀ and σ _s0 are the thickness in mm and the yield strength of the roll in kgf / mm ² at the exit from the rolls of the penultimate stand; at the same time, the rolling moment in the last stand increases, which is defined as

where M ₁ - the moment of rolling in the steady state rolling, kgf · mm; M ₀ and P ₀ are the initial values of the rolling moment in kgf · mm and the rolling force in kgf, measured during rolling of the front end of the tape without rear tension; D is the diameter of the roll barrel in mm.

After reaching the values of front and rear tension equal to T ₁ and T ₀ , 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 further maintained constant with an accuracy of not less than ± (0.16 ... 0.18)%; coolant is fed to the tape between the rolls of the last stand and squeeze rollers in a section of length S, which is regulated by the longitudinal movement of the squeeze rollers until the temperature of the tape at the outlet of them is established in the range of 120 ... 130 ° C, and liquid is used as cooling with a boiling point of 100 ... 110 ° C, as a result of which the removal of its sections from the surface of the tape occurs by natural evaporation, without supplying heat from the outside; Separation of the tape into separate cards is carried out on the go after passing through the pulling rollers.

The proposed method of hot rolling of the tape allows you to get cards with ultra-high flatness due to the following features of this method:

- due to the accurate maintenance of the ratio of the rotation frequencies of the rolls of the last and penultimate stands, as well as the optimal 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 the cutting of a hot-rolled tape, which is in a straight-line state, on separate cards (without winding it in riots), this eliminates the appearance of roll curvature;

- due to this, 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 method is illustrated in figure 1, which shows a diagram of a casting and rolling unit - side view of the casting and rolling unit that implements the method.

Capacity 1 for liquid aluminum is installed in front of the casting machine 2 with a drive, which is not conventionally shown in Fig. 1. Behind the machine 2, a first stand 3 for hot rolling is installed and, further, a second stand 4 for hot rolling with drives, which are not conventionally shown in Fig. 1; hereinafter referred to as the penultimate 3 and last 4 rolling stands, since there can be not two rolling stands, but three and even more.

At the exit from the last stand 4, successively installed: pulling rollers 5 with a drive (not shown conventionally in figure 1), guillotine shears 6, pinch rollers 7 and cassette device 8 for stacking sheets in bundles.

Along the entire line of the casting and rolling unit, up to scissors 6, there is a continuously machined roll: a continuously cast billet 9, a tackle 10 and a finished tape 11.

In the spaces between the casting machine 2 and stand 3, between stands 3 and 4, and also between stand 4 and pulling rollers 5, temperature meters (pyrometers) 12, 13, 14, 15 and 16 are installed, and in the gap between stand 4 and rollers 5, an additional collector 17 is installed.

The molten aluminum from the tank 1 is fed into a casting machine 2, on the rolls of which a continuously cast billet 9 is formed. After the crystallization process is completed, the billet 9 in the form of a solid enters the penultimate stand 3, where a tack 10 is formed from the billet 9, having a thickness h _o . The latter in the hot state enters the last stand 4, from which it comes out in the form of a finished tape 11 having a thickness h _k , under tension T ₁ , which is created by the pulling rollers 5.

The finished tape 11, which has a rectilinear shape in the longitudinal direction, enters the flying guillotine shears 6, in which the tape 11 is divided into separate sheets (cards) on the move 18. They are separated from the continuously rolled tape 11 by pinch rollers 7 and fed into the cassette device 8, where they are placed in a pack.

At the beginning of the casting-rolling process, i.e. at the front end of the roll, the rear tension T ₀ in the last stand 4 is maintained close to zero. This is necessary in order to be able to experimentally fix the initial values of the rolling force P ₀ and torque M ₀ on the rolls of the last stand 4, while the front tension is given the working value T ₁ from the very beginning.

Then, the rotation speed of the rolls of the last stand is increased at a constant speed of rotation of the rolls of the penultimate stand 3 until the back tension increases from zero to a value of T ₀ = 0.67 σ _so (in · h ₀ ), where σ _so and h ₀ are the yield strength the roll and its thickness at the exit of the rolls of the stand 3; in - the width of the roll.

The value of T _{0 is} determined indirectly, by increasing the torque on the roll of the last stand 4; the increase in the speed of rotation of the rolls of this stand is stopped when the moment reaches the value of M ₁ , which is determined on the formula below (7).

The front tension T _{1 is} created by the drive of the pulling rollers 5 due to their pressing against the tape 11 with a force N equal to twice the tension T ₁ .

The proposed method is based on the process of straightening the tackle 10 with a tensile force T ₀ , which is developed in the area between stands 3 and 4. In order to avoid tearing off the tackle, the force T _{0 is} controlled not by its value, but by the value of the plastic deformation of the tackle, which is supported with very high accuracy. For this purpose, the ratio of the rotation frequencies of the rolls of stands 3 and 4 is kept constant with an accuracy of not less than ± (0.16 ... 0.18)% each. A similar pattern occurs in the area between stand 4 and rollers 5.

Coolant is supplied to the rolled strip 11 from the collector 17. The primary removal of this liquid from the surface of the finished tape is carried out by squeezing it by the pulling rollers 5, and the second by natural evaporation of the liquid followed by drying of the tape due to the internal heat contained in the tape 11, t .e. without additional heat supply from the outside.

For this purpose, the temperature of the tape at the exit of the rollers 5 is maintained in the range of 120 ... 130 ° C. At a higher temperature, the rubber decomposes on the surface of the gummed rollers 5. At a lower temperature, the heat supply in the tape 11 will not be sufficient for the natural evaporation and drying of the tape 11 after it leaves the rollers 5.

And since the rolling speed in stand 4 and the thickness h _{to the} finished tape 11 vary from order to order, the duration of the cooling of the tape should also change. For this purpose, change the length of the section "S", limited from the rear side by the rolls of the stand 4, and from the front by the rollers 5; it is along the length of the indicated section that coolant is supplied to the tape 11.

To change the length "S", the pulling rollers 5 are moved along the casting and rolling unit in the longitudinal direction.

In order to more fully evaporate the coolant from the surface of the finished tape, the boiling point of this fluid should be in the range of 100 ... 110 ° C.

In the following numerical example of the proposed method, the tackle 10 before the last stand 4 has a thickness h ₀ = 4 mm, and the finished tape 11 and individual sheets 18 have a thickness h _k = 2 mm; the diameter of the rolls of rolling stands 3 and 4 is equal to D = 300 mm (see figure 1). The tension of the tape 11 at the exit of this stand are equal to T ₀ = 1333 kgf and T ₁ = 950 kgf, respectively; rolling forces in stand 4: at T ₀ = 0, P = 60,000 kgf, and at T ₀ = 1333 kgf, P ₀ = 56,500 kgf, respectively, and the torques on the rolls of stand 4 are M ₀ = 860000 kgf · mm and M ₁ = 970000 kgf · mm; the pressure force of the rollers 5 to the tape 11 is N = 2800 kgf.

Roll temperature t _p :

Under pyrometer No. 12 13 fourteen fifteen 16 t _p , ° C t ₂ = 500 t ₃ = 400 t ₃ = 350 t ₄ = 300 t ₅ = 125

The average length of the irrigation section of the belt 11 is S = 2.5 m. The rolling speed in stand 4 is V ₄ = 0.067 m / s. The width of the tape 11 is equal to = 200 mm

Obtaining the required front tension T _{1 is} ensured by creating the appropriate torque on the drive necks of the pulling rollers and does not cause any problems, and to obtain the required rear tension T _{0 it is} necessary to operate with the moment of rolling M ₁ in the last stand.

For this, as indicated, the force P ₀ and the rolling moment M ₀ , which take place at the front end of the tape when rolling in the last stand without back tension, are first measured. Then find the experimental values:

- average specific pressure in the deformation zone without back tension:

where F _p = (in · l) is the contact area of the roll with the rolled tape;

l is the length of the capture arc;

rolling coefficient

The average specific pressure in the deformation zone with rear tension:

Steady-state rolling moment:

Finally we get the working formula:

Where

.

.

Consider an example of execution.

Initial data:

- the average temperature of the tape in the rolls of the stand 4 t _cp = 325 ° C;

- rolling speed v = 0.067 m / s;

- roll diameter D = 300 mm;

- input tape thickness h ₀ = 4 mm;

- output tape thickness h _k = 2 mm;

- tape material: AMC alloy;

- the yield strength of the tape at the exit from the penultimate stand σ _s0 = 2 kgf / mm ² (t = 400 ° C) and at the exit from the last stand σ _s1 = 3.5 kgf / mm ² (t = 300 ° C);

- base specific pressure σ _0d = 4.8 kgf / mm ² .

Calculation of the initial effort and moment of rolling:

- the total thermomechanical coefficient k _c = k _t · k _ε · k _u = 1.24 · 1.58 · 0.87 = 1.7;

- deformation resistance k _d = σ _0d · k _c = 4.8 · 1.7 = 8.2 kgf / mm ² ;

;- length of the capture arc

;

- stress coefficient n _σ = 2.16;

- initial rolling force:

P ₀ = k _d · n _σ · l · _b = 8.2 · 2.16 · 17 · 200 = 0.06 · 10 ⁶ kgf

- initial rolling moment:

without front tension

(M ₀ ) '= 2P ₀ ψ · l = 2 · 0.06 · 10 ⁶ · 0.5 · 17 = 10 ⁶ kgf · mm

with front tension

M ₀ = (M ₀ ) '- 0.67σ _s1 (h _to c) (D / 2) = 10 ⁶ -0.67 · 3.5 (2 · 200) (300/2) = 0.86 · 10 ⁶ kgf · mm

The values of the initial force P ₀ = 0.06-10 ⁶ kgf and the initial rolling moment M ₀ = 0.86 · 10 ⁶ kgf · mm are conventionally taken as the experimentally measured parameters of the rolling process without back tension.

According to the formula (1), we calculate the rolling moment with the steady rolling process:

We repeat the calculation, changing only the thickness of the tape: h ₀ = 8 mm; h _k = 6 mm; M ₀ = 0.58 · 10 ⁶ kgf · mm. All other data is the same. Then

As you can see, with a threefold increase in the thickness of the finished tape h _{k, the} degree of increase in the rolling moment from (M ₁ / M ₀ -1) 100 = (0.97 / 0.86-1) 100 = 12.5% increased to (0.87 / 0.58-1) 100 = 50%, i.e. 50 / 12.5 = 4 times. Thus, with an intermediate thickness of the finished tape equal to h _k = 3 mm, the degree of increase in the rolling moment will be 22%; this is a fairly good indicator of the sensitivity of the regulation process when lifting the tension of the roll between the penultimate and last stands from zero to a value of T ₀ = 0.67 · 2 (5 · 200) = 1333 kgf, where the thickness at the entrance to the last stand is equal to h ₀ = 5 mm

When switching to the stationary rolling process, in order to avoid breaks in the roll between the penultimate and last stands, as well as between the last stand and the pulling rollers, the ratios of the rotation frequency of the rolls and the pulling rollers are kept constant with an error of not less than ± (0.16 ... 0.18% ) Such a hard range is determined based on the practice of correct stretching machines, when the plastic elongation of the ruling tape by 1.6 ... 1.8% still does not lead to tape breaks, and the accuracy of maintaining this value should be an order of magnitude higher, i.e. ± (0.16 ... 0.18)%.

When calculating the rolling forces, it is assumed that 2/3 of the rear specific tension is subtracted from the specific pressure of the rolling obtained without back tension (a large value cannot be assigned, since this will lead to a tightening of the tape along its width) and the specific pressure is taken into account tension; the influence of the front specific tension of the tape on the specific pressure of the rolling, as experience has shown, can be neglected.

After exiting the rolls of the last stand, the tape passes through squeezing rollers located at a distance S from the rolls. In this section, the tape is abundantly irrigated with coolant - an aqueous emulsion with a concentration of 1.5 ... 2% of the emulsion "B" in it.

The length of the irrigation section S can be changed by moving the squeeze rollers along the belt: from the rolls or to the rolls. In this section, the temperature of the tape should be lowered from 300 ° С to 120 ... 130 ° С, i.e. an average of 175 ° C.

When choosing the heat transfer coefficient for transferring heat from the belt to the coolant, it can be assumed that for a liquid on a steam cushion it is equal to α = 100 kcal / (m ² · h · ha) - see the book AMLitvin. Theoretical foundations of heat engineering. "Energy". Moscow-Leningrad. 1964 p. 236 ... 238.

The heat flux density during heat transfer from the tape to the liquid is determined as q = α (t _liquid. -T _walls ). When t _fluid. = 60 ° С and _wall t = 210 ° С (average), we have q = 100 (210-60) = 15000 kcal / (m ² · hour). At a speed of V = 4 m / min, the belt runs in an hour, the path L = 4 · 60 = 240 meters; the mass of the tape of this length G _hour = 0.003 · 0.2 · 240 · 2.7 = 0.39 tons = 390 kg. With such a mass and the required temperature difference Δt = 175 ° С, the amount of heat to be removed will be Q = G _hour · Δt · C _p = 390 · 175 · 0.11 = 7500 kcal, where C _p = 0.11 is the specific heat of aluminum .

The required area of contact of the tape with the coolant: F _with = Q / q = 7500/15000 = 0.5 m ² . Such a contact area can be provided on a tape length equal to S = F _c / b = 0.5 / 0.2 = 2.5 m; It is at this distance from the rolls that the squeeze rollers should be located; moreover, to quickly adjust the temperature of the tape for each degree of temperature, the rollers must be moved approximately 15 mm, which indicates a good resolution of the proposed method for controlling the temperature of the tape.

, а полная ширина этой площадки равна 2в_сп=22 мм.In order to obtain a front tension force equal to T ₁ = 0.67 · 3.5 · (3 · 200) = 1400 kgf, the force of pressing the rollers to the tape should be N = 2 · 1400 = 2800 kgf. Then for 1 mm of the width of the tape in = 200 mm there is a linear force of 14 kgf / mm. When the diameter of the roller D _p = 500 mm, lined with a jacket made of heat-resistant rubber, the elastic flattening of this shirt will be δ = 0.5 mm. Half the width of the flattening pad is

, and the total width of this site is 2 in _sp = 22 mm.

Then the average contact pressure is P _con = 14/22 = 0.64 kgf / mm ² or 64 kgf / cm ² , which is quite acceptable for hard grades of rubber.

Checking the stock by friction.

Coefficient of friction of rubber on aluminum f = 0.35; the friction force on both pulling rollers T _Tr = 2Nf = 2 · 2800 · 0.35 = 1960 kgf or about 2000 kgf, and only T ₁ = 1400 kgf is needed; those. the required reserve is T _Tr / T ₁ = 2000/1400 = 1.43 or 43%, which is quite enough.

Each sheet 18 cut off from the tape 11 must lie in the cassette 8 with a completely drained surface. To this end, the remaining coolant is evaporated, followed by drying of the surface. For this purpose, the tape in the irrigation section is cooled to 120 ... 130 ° C, which exceeds the boiling point of the coolant, equal to 100 ... 110 ° C. Thus, the evaporation and drying of the surface of the tape in the area from the pulling rollers 5 to the scissors 6 occurs due to the internal heat remaining in the tape after passing through the irrigation section (i.e., without supplying heat from outside).

The calculations found that the method of creating a rear tension T ₀ in front of the rolls of the last stand by accelerating their rotation is reliable. Reliable is the process of regulating the value of T ₀ through regulation of the rolling moment M ₁ .

All this is a good prerequisite for obtaining cards (sheets) with ultra-high flatness by hot rolling.

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

Claims (15)

1. A method of manufacturing stacked hot-rolled sheets of aluminum and its alloys, including continuous casting of a billet from a melt, hot rolling of a billet into a tackle, then into a finished tape in several stands with the application of forces of its front and rear tension, measuring the temperature of the roll according to stands, measuring the force and moment of rolling in the last stand, supplying coolant to the tape, freeing the surface of the tape from the remaining coolant, separation of the continuously moving hot rolled tape n the individual sheets and their stacking, while at the start of the casting-rolling at the leading end of the tape in the last stand of the back tension generated before the rolls of the last stand, is maintained close to zero, and under steady process of rolling back tension value T ₀ determined by the formula
T ₀ = 0.67σ _s0 (in h ₀ ),
where σ _s0 and h ₀ 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. 2. The method according to claim 1, characterized in that when rolling the front end of the tape in the last stand, the front tension created at the exit of the rolls of the last stand is kept equal
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 2, characterized in that the initial values of the rolling force P ₀ and the moment of rolling M ₀ in the last stand are measured at the front end of the tape with a rear tension close to zero and a front tension equal to T ₁ . 4. The method according to claim 3, characterized in that at the end of rolling the front end of the tape in the last stand, 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 . 5. The method according to claim 4, characterized in that the rotation speed of the rolls of the last stand is increased until the total rolling moment in this stand is reached equal to the value determined by the formula
M ₁ = M ₀ [1-σ _S0 · F _P / (2Р ₀ )] + σ _S0 · F ₀ (D / 3),
Where

;
F ₀ = in · h ₀ ;
M ₁ - rolling moment in a steady rolling process, kgf · mm;
M ₀ and P ₀ are the initial values of the rolling moment (kgf · mm) and the rolling force (kgf), measured when rolling the front end of the tape with a rear tension close to zero, respectively;
D - roll barrel diameter, mm. 6. The method according to claim 2, characterized in that the front tension T ₁ create pulling rollers. 7. The method according to claim 6, characterized in that the pressing force of the pulling rollers to the rolled strip is chosen to be equal to twice the front tension T ₁ . 8. The method according to claim 4, characterized in that when the front and rear tensions are equal to T ₁ and T ₀ , respectively, the ratio of the rotational speeds of the rolls of the last and second to last stands and pulling rollers is kept constant with an accuracy of not less than ± (0, 16 ... 0.18)% each. 9. The method according to claim 1, characterized in that the coolant is fed to the tape directly upon exiting the rolls of the last stand in a section of tape of length S. 10. The method according to claim 9, characterized in that the length S of the tape is limited on one side by the rolls of the last stand, and on the other hand, by squeezing rollers. 11. The method according to claim 10, characterized in that the length S of the tape is regulated by the longitudinal movement of the squeeze rollers along the rolled tape. 12. The method according to claim 11, characterized in that the squeeze rollers are moved along the tape until the temperature of the tape at the outlet of them is reached in the range of 120 ... 130 ° C. 13. The method according to claim 9, characterized in that as the coolant using a liquid with a boiling point of 100 ... 110 ° C. 14. The method according to claim 9, characterized in that after passing through the squeezing rollers, the surface of the tape is freed from the remaining coolant by naturally evaporating it and subsequent drying without additional supply of heat from the outside. 15. The method according to claim 1, characterized in that the separation of the continuously moving belt into separate sheets is carried out after the belt has passed through the pulling rollers.

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