RU2225272C2 - Method for cold rolling of strips in multistand mill - Google Patents

Abstract

FIELD: metallurgy, namely processes for cold rolling of strips in continuous multistand mills. SUBSTANCE: method for cold rolling of strips in multistand mill comprises steps of passing strips through four-high rolling stands in which vertical plane of rolling roll axes is shifted relative to vertical plane of backup rolls axes; lowering interstand tensions along rolling direction. Total interstand back tension exceeds forward-stand tension by range normalized with use of mathematical relation taking into account shifting value of rolling rolls relative to backup rolls, rolling effort, radiuses of backup and rolling rolls, order number of stand, quantity of mill stands. Possibility of occurring vibration in mill stands is also normalized. EFFECT: lowered number of rejections caused by surface flaws, enhanced stability of process. 1 dwg, 1 tbl, 1 ex

Description

 The invention relates to metallurgy, and more particularly to processes for cold rolling strip metal in continuous multi-stand mills.

 The closest in technical essence to the proposed one is a method for cold rolling strips in a multi-stand mill, including passing strips through quarto stands, in which the vertical plane of the axes of the work rolls is offset from the vertical plane of the axes of the support rolls, and the reduction of the total inter-stand tension along the course of rolling, which is realized in the well-known multi-stand cold rolling mill (USSR Author's Certificate 1416225, class B 21 V 1/28, publ. 08/15/08).

 In the rolling process according to the known method in all stands, starting from the second, the guaranteed dense pressing of the work roll cushions to the support roll cushions is not achieved. This is because the amount of excess rear tension over the front is not regulated. The displacement of the work rolls relative to the support rolls, the diameters of the work and backup rolls, and also the rolling forces in the stands are not taken into account. In addition, changes in the interstand tension associated with the operation of automatic thickness and tension control systems (CARTiN), which are equipped with all modern cold rolling mills, are not taken into account. As a result, vibration of the stands and slippage of the rolls occur, which degrade the quality of the strips and reduce the stability of the rolling process, which negatively affects the productivity of the mills.

 The technical effect when using the invention is to improve the quality of the rolled strips and the stability of the rolling process.

в клетях, для которых выполняется условие:

где a_i - величина смещения рабочих валков относительно опорных, мм; P_i - усилие прокатки, тc; R_oп, R_p - радиусы опорного и рабочего валков, мм; k_i - эмпирический безразмерный коэффициент, равный 1,05...1,25; i - номер клети; n-число клетей стана; П_i - безразмерный параметр, характеризующий вероятность возникновения вибраций, определяемый по эмпирической зависимости:

где Е - модуль упругости материала полосы, кгс/мм²; U_Сi - скорость деформации, с^-1;

суммарное биение рабочих и опорных валков, мм; h_i - толщина полосы на входе в клеть, мм;

вынужденный (условный) предел текучести полосы на входе в клеть, кгс/мм²; f_i - коэффициент трения при прокатке; F_i - собственная частота вертикальных колебаний клети, Гц (с^-1).The indicated technical effect is achieved by the fact that the method of cold rolling strips in a multi-stand mill includes passing strips through quarto stands, in which the vertical plane of the axes of the work rolls is offset from the vertical plane of the axes of the support rolls, and reducing the total inter-stand tension along the course of rolling. The excess of the full inter-stand rear tension over the front tension is set according to:

in stands for which the condition is satisfied:

where a _i is the displacement of the work rolls relative to the support, mm; P _i - rolling force, tc; R _op , R _p - radii of the backup and working rolls, mm; k _i is an empirical dimensionless coefficient equal to 1.05 ... 1.25; i is the stand number; n is the number of mill stands; P _i is a dimensionless parameter characterizing the probability of occurrence of vibrations, determined by empirical dependence:

where E is the elastic modulus of the strip material, kgf / mm ² ; U _Сi — strain rate, s ^-1 ;

total runout of working and backup rolls, mm; h _i is the thickness of the strip at the entrance to the stand, mm;

forced (conditional) yield strength of the strip at the entrance to the stand, kgf / mm ² ; f _i - coefficient of friction during rolling; F _i - the natural frequency of the vertical vibrations of the stand, Hz (s ^-1 ).

 Improving the quality of the rolled strips and the stability of the rolling process will occur by reducing the tendency for stand vibration to occur due to the guaranteed tight pressing of the work roll cushions to the support roll cushions in those mill stands where vibration is most likely to occur during the rolling process.

The proposed method is illustrated by the rolling scheme in a multi-stand mill with quarto stands, where α ₁ , α _n-1 , and α _n are the angles between the line ОО ₁ connecting the centers of the upper working and back-up rolls and the line ОО connecting the centers of the upper and lower backup rolls in stands 1, n-1 and n, respectively; OO ₁ K is a design triangle in which the leg O ₁ K is equal to the displacement of the vertical plane of the work rolls relative to the vertical plane of the backup rolls a ₁ , a _n-1 and a _n in stands 1, n-1 and n, respectively; R _o , R _p - radii of the backup and work rolls; T _s , T _p - full back and front tension in the stands; P ^Σ is the reaction of the upper back-up roll to the rolling force acting on the upper work roll; P ⁱⁿ , P ^g - vertical (equal to the rolling force in a given stand P) and horizontal components of the reaction P ^Σ, respectively.

 The offset of the work rolls relative to the support rolls along the direction of rolling is used to improve the conditions for gripping the strip by the work rolls, as well as to eliminate distortions of the pair of work rolls in the horizontal plane by unilaterally selecting the gaps along the rolling direction between the pillows of the work rolls and the pillow guides of the support rolls or the stands of the stand. The magnitude of the displacement at different mills is different and, usually, is in the range of 5-12 mm (see Quality management of sheet products. / V.L. Mazur, A.M. Safyan, I.Yu. Prikhodko, A.I. Yatsenko. - K .: Technique, 1997, p. 14-15).

и, принимая во внимание, что Р^в=Р, определяем величину горизонтальной составляющей, действующей на верхний и нижний рабочие валки:

Полную выборку зазоров и плотное прижатие подушек рабочих валков к направляющим подушек опорных валков или к стойкам станины (на схеме не показаны) можно обеспечить, если результирующая заднего Т_з и переднего Т_п натяжения, воспринимаемая каждым рабочим валком, будет больше горизонтальной составляющей межвалкового усилия Р^г.As a result of the displacement, the reaction force of the backup rolls P ^Σ on the rolling force deviates from the vertical. The direction of action of the horizontal component P ^g on the work rolls depends on the direction of displacement of the work rolls relative to the support rolls. If the work rolls are displaced along the rolling direction, then the horizontal component acts in the rolling direction. If the work rolls are displaced against the rolling course (as a rule, only in the first stand; the displacement value a ₁ is taken with a negative sign), then the horizontal component of the reaction of the backup rolls acts on the work rolls in the opposite direction to the rolling direction. The value of the horizontal component P ^g in each stand is determined from the triangle of forces similar to the triangle OKO ₁ :
P ^g = P ⁱⁿ • tgα;
due to the practical smallness of the angle α (up to 2 ^o ), you can take:

and, taking into account that P ⁱⁿ = P, we determine the value of the horizontal component acting on the upper and lower work rolls:

A full selection of gaps and a tight pressing of the work roll pillows to the guide roll pillow guides or to the bed stands (not shown in the diagram) can be ensured if the result of the rear T _c and front T _n tension, perceived by each work roll, is greater than the horizontal component of the roll-through force P ^g .

В отношении (4) в процессе прокатки изменяются величины T_з ⁱ, T_п ⁱ и P_i (натяжения полосы заднее и переднее, а также усилие прокатки в i-й клети). Экспериментально установили, что отношение (4) выполнятся оптимальным образом, если превышение ΔTⁱ заднего натяжения над передним определяется по выражению (1), в котором эмпирический коэффициент k_i учитывает практически возможное отклонение натяжений в двух смежных межклетьевых промежутках (отклонение разности заднего и переднего натяжений в i-й клети) от заданных значений (уставок) вследствие работы системы автоматического регулирования толщины и натяжения (САРТиН). Применение значений коэффициента k_i меньше 1,05 не позволяет достичь технического результата, так как не гарантирует полного выбора зазоров и плотного прижатия подушек рабочих валков к направляющим подушек опорных валков или к стойкам станины. Поэтому сохраняется высокая склонность к возникновению вибраций клетей, что ухудшает качество полос и нарушает стабильность процесса прокатки. Большие значения, чем 1,25, применять не целесообразно, так как может быть нарушено технологически необходимое распределение удельных межклетьевых натяжений. Также могут возникнуть пробуксовки валков вследствие большой разницы между задним и передним натяжением (особенно при незначительных обжатиях) и, как следствие, потеря устойчивости (стабильности) прокатки и возникновение вибраций. Прокатку полос в многоклетьевых станах ведут с удельными (отнесенными к единице площади поперечного сечения полосы) межклетьевыми натяжениями, поддерживаемыми в пределах (0,2-0,4)σ_т, где σ_т, кгс/мм² - предел текучести материала полосы в соответствующем межклетьевом промежутке (см. Технология прокатного производства: Учеб. пособие /В.М. Клименко, А.М. Онищенко, А.А. Минаев, B.C. Горелик. - К.: Выща шк. Головное изд-во, 1989, на стр. 273).Therefore, taking into account the symmetry of the conditions of contact interaction of the upper and lower work rolls with the strip for a guaranteed choice of gaps in the direction opposite to the direction of rolling in all stands, except the first, the following relation should be fulfilled:

In relation to (4), during the rolling process, the values of T _z ⁱ , T _p ⁱ and P _i change (back and front tension of the strip, as well as the rolling force in the i-th stand). It was experimentally established that relation (4) will be fulfilled in an optimal way if the excess ΔT ^{i of the} rear tension over the front is determined by expression (1), in which the empirical coefficient k _i takes into account the practicable tension deviation in two adjacent inter-stand spaces (deviation of the difference between the rear and front tension in the i-th stand) from the set values (settings) due to the operation of the automatic thickness and tension control system (CARTiN). The use of values of the coefficient k _i less than 1.05 does not allow to achieve a technical result, since it does not guarantee a complete selection of gaps and a tight pressing of the pillows of the work rolls to the guide pillows of the backup rolls or to the stands of the bed. Therefore, there remains a high tendency to the occurrence of stand vibrations, which affects the quality of the strips and violates the stability of the rolling process. Larger values than 1.25 are not advisable to apply, since the technologically necessary distribution of specific inter-stand tension can be violated. Slipping of the rolls can also occur due to the large difference between the rear and front tension (especially with minor reductions) and, as a result, the loss of stability (stability) of the rolling and the occurrence of vibrations. Strip rolling in multi-stand mills is carried out with specific (referred to the unit cross-sectional area of the strip) interstand strands maintained within (0.2-0.4) σ _t , where σ _t , kgf / mm ² is the yield strength of the strip material in the corresponding the inter-span gap (see. Technology of rolling production: Textbook. / V.M. Klimenko, A.M. Onishchenko, A.A. Minaev, BC Gorelik. - K .: Higher school. Head Publishing House, 1989, on page . 273).

 Based on the need to maintain specific inter-stand tension in the range of 0.2. ..0,4 from the conditional yield strength, in the proposed method, the action of expression (1) is limited to those cells in which condition (2) is satisfied. If we do not take into account the uneven distribution of the probability of occurrence of vibrations during rolling in the stands of multi-stand mills and establish the excess of rear tension over the front tension regulated by expression (1) in all stands (except the first), then the technologically permissible limits of the change in specific inter-stand tension can be violated.

входящие в выражение (3), определили по известным формулам (Теория прокатки: Учебник для вузов. /Грудев А.П. - М.: Металлургия, 1988, на стр. 81 и 131):

где V_i - скорость прокатки в i-й клети (скорость полосы на выходе из i-й клети), м/с; h_i-1, h_i - толщина полосы на входе и на выходе i-й клети, м; R_p - радиус рабочего валка, м; Н - толщина полосы перед холодной прокаткой в многоклетьевом стане (исходная), м; σ_исх - исходный предел текучести полосы на входе в стан, кгс/мм²; m - коэффициент (кгс/мм²), и k - показатель упрочнения материала полосы (безразмерный). Коэффициент трения f_i в клетях стана рассчитали по методике, приведенной в кн. (Управление качеством тонколистового проката. /В.Л. Мазур, А.М. Сафьян, И.Ю. Приходько, А.И. Яценко. - К.: Техника, 1997, на стр. 28-30). Чем больше значение параметра П_i в практическом возможном диапазоне изменения всех переменных, входящих в выражение (3) и выбираемых для конкретного многоклетьевого стана, тем больше вероятность возникновения вибраций в i-й клети этого стана. Экспериментально установили, что в качестве порогового значения нормированного показателя

для определения клетей, наиболее склонных к вибрациям, можно применить число, обратное их количеству в конкретном многоклетьевом стане, 1/n.The dimensionless parameter P _i characterizes the probability of occurrence of vibrations in the stands of a multi-stand cold rolling mill. The strain rate U _Ci and the forced (conditional) yield strength of the strip

included in expression (3), determined by well-known formulas (Theory of rolling: Textbook for high schools. / Grudev A.P. - M .: Metallurgy, 1988, on pages 81 and 131):

where V _i is the rolling speed in the i-th stand (speed of the strip at the exit of the i-th stand), m / s; h _i-1 , h _i - strip thickness at the input and output of the i-th stand, m; R _p is the radius of the work roll, m; N - strip thickness before cold rolling in a multi-stand mill (initial), m; σ _ref is the initial yield strength of the strip at the inlet of the mill, kgf / mm ² ; m is the coefficient (kgf / mm ² ), and k is the rate of hardening of the strip material (dimensionless). The friction coefficient f _i in the mill stands was calculated according to the technique given in the book. (Quality management of sheet products. / V.L. Mazur, A.M. Safyan, I.Yu. Prikhodko, A.I. Yatsenko. - K .: Technique, 1997, p. 28-30). The larger the value of the parameter П _i in the practical possible range of variation of all variables included in expression (3) and selected for a particular multi-stand mill, the greater the likelihood of vibrations in the i-th stand of this mill. It was experimentally established that as a threshold value of the normalized indicator

to determine the stands most prone to vibrations, you can apply the number inverse to their number in a particular multi-stand mill, 1 / n.

В этой клети заднее натяжение не является межклетьевым и, обычно, на порядок (или в несколько раз на станах бесконечной прокатки, оснащенных натяжными роликами на входе в первую клеть) меньше переднего натяжения, то есть в первой клети имеется технологически обусловленное превышение переднего натяжения над задним (например, на 5-клетьевом стане холодной прокатки 1700 минимальная разность между передним и задним натяжением в практическом интервале их изменений составляет 36 т при максимально возможном натяжении между первой клетью и разматывателем - 4 т; на 5-клетьевом стане 2030 бесконечной прокатки натяжение, создаваемое на входе в первую клеть с помощью натяжных роликов, не превышает 12,5 тс.) Кроме того, экспериментально установлено, что в первой клети, где скорость прокатки наименьшая, вибрации обычно не возникают. Поэтому действие предложенного способа, как правило, распространяется на все клети, кроме первой.In the first stand for a guaranteed choice of gaps in the rolling direction, taking into account the negative sign a ₁ , the following relation should be fulfilled:

In this stand, the back tension is not interstand and, usually, an order of magnitude (or several times less on endless rolling mills equipped with tension rollers at the entrance to the first stand) is less than the front tension, that is, in the first stand there is a technologically determined excess of the front tension over the back (for example, on a 1700 5-stand cold rolling mill, the minimum difference between the front and rear tension in the practical range of their changes is 36 tons at the maximum possible tension between the first stand and the dimensions 4 t; on a 5-stand mill 2030 of endless rolling, the tension created at the entrance to the first stand using tension rollers does not exceed 12.5 tf.) In addition, it was experimentally established that in the first stand, where the rolling speed is the lowest, vibrations usually do not occur. Therefore, the action of the proposed method, as a rule, applies to all stands, except the first.

 Analysis of scientific, technical and patent literature shows the lack of coincidence of the distinctive features of the proposed method with the signs of known technical solutions. Based on this, it is concluded that the claimed technical solution meets the criterion of "inventive step". The following are embodiments of the proposed method, not excluding other options for its implementation within the claims.

в клетях, для которых выполняется условие:

где a_i - величина смещения рабочих валков относительно опорных, а₁=а₂= a₃= а₄=a₅=6 мм; Р_i - усилие прокатки в клетях: P₁=P₂=P₃=1050 тc, P₄=1275 тc, P₅= 1425 тc; R_oп=800 мм; R_p=300 мм - радиусы опорного и рабочего валков, мм; k_i - эмпирический безразмерный коэффициент, равный 1,05...1,25; i - номер клети; n=5 - число клетей стана; П_i - безразмерный параметр, характеризующий вероятность возникновения вибраций, определяемый по эмпирической зависимости:

где E=21000 кгс/мм² - модуль упругости материала полосы; U_Сi - скорость деформации в клетях: U_C1=0,082 c^-1, U_С2=0,172 с^-1, U_C3=0,297 с^-1, U_C4= 0,547 с^-1, U_С5= 0,221 с^-1; h_i - толщина полосы на выходе из клетей: h₁=1,782 мм, h₂= 1,136 мм, h₃=0,773 мм, h₄=0,517 мм (скорость прокатки в клетях: V₁=4200 мм/с, V₂=6600 мм/с, V₃=9700 мм/с, V₄=14500 мм/с, V₅=15000 мм/с);

мм - суммарное биение рабочих и опорных валков (сумма максимально допустимых технологической инструкцией эксцентриситетов пары рабочего и опорного валков);

вынужденный (условный) предел текучести полосы на входе в клети:

кгс/мм²,

кгс/мм²,

кгс/мм²;

кгс/мм²,

кгс/мм², (коэффициенты упрочнения стали 08Ю: m=3,4 кгс/мм², k= 0,6); f_i - коэффициент трения при прокатке в клетях 1...4 (ненасеченные рабочие валки): f₁=f₂=f₃=f₄=0,05, в клети 5 с насеченными рабочими валками f₅=0,07; F_i - собственная частота вертикальных колебаний клетей: F₁= F₂= F₃= F₄=F₅=120 Гц (Исследование вибраций на пятиклетьевом стане 2030. /С. С. Колпаков, В.А. Пименов, Ю.А. Цуканов, В.П. Рубанов. //Сталь, 1993. - 1. - С.47-52 - на стр. 49, 51). В таблице приведены примеры осуществления способа с различными технологическими параметрами. Значения коэффициента k_i для всех клетей стана принимали равным.Example. In the process of cold rolling of strips in a 5-stand mill 2030, strips of steel 08Yu with an initial thickness of 2.5 mm, a width of 1500 mm and a final thickness of 0.5 mm are passed through quarto stands in which the vertical plane of the axes of the work rolls is offset from the vertical plane of the axes of the supporting rolls. Full interstring tension during rolling is reduced. The excess of the full inter-stand rear tension over the front tension is set according to:

in stands for which the condition is satisfied:

where a _i is the displacement of the work rolls relative to the support, and ₁ = a ₂ = a ₃ = a ₄ = a ₅ = 6 mm; P _i - rolling force in stands: P ₁ = P ₂ = P ₃ = 1050 ts, P ₄ = 1275 ts, P ₅ = 1425 ts; R _op = 800 mm; R _p = 300 mm — radii of the backup and working rolls, mm; k _i is an empirical dimensionless coefficient equal to 1.05 ... 1.25; i is the stand number; n = 5 is the number of mill stands; P _i is a dimensionless parameter characterizing the probability of occurrence of vibrations, determined by empirical dependence:

where E = 21000 kgf / mm ² is the elastic modulus of the strip material; U _Сi — strain rate in stands: U _C1 = 0.082 s ^-1 , U _C2 = 0.172 s ^-1 , U _C3 = 0.297 s ^-1 , U _C4 = 0.547 s ^-1 , U _C5 = 0.221 s ^-1 ; h _i is the thickness of the strip at the exit of the stands: h ₁ = 1,782 mm, h ₂ = 1,136 mm, h ₃ = 0,773 mm, h ₄ = 0,517 mm (rolling speed in stands: V ₁ = 4200 mm / s, V ₂ = 6600 mm / s, V ₃ = 9700 mm / s, V ₄ = 14500 mm / s, V ₅ = 15000 mm / s);

mm - the total runout of the working and backup rolls (the sum of the maximum allowable technological instruction for the eccentricities of the pair of working and backup rolls);

forced (conditional) yield strength of the strip at the entrance to the stand:

kgf / mm ² ,

kgf / mm ² ,

kgf / mm ² ;

kgf / mm ² ,

kgf / mm ² , (hardening coefficients of 08Yu steel: m = 3.4 kgf / mm ² , k = 0.6); f _i - coefficient of friction during rolling in stands 1 ... 4 (unsealed work rolls): f ₁ = f ₂ = f ₃ = f ₄ = 0.05, in stand 5 with notched work rolls f ₅ = 0.07; F _i is the natural frequency of the vertical oscillations of the stands: F ₁ = F ₂ = F ₃ = F ₄ = F ₅ = 120 Hz (Study of vibrations on a five-stand mill 2030. / S. S. Kolpakov, V.A. Pimenov, Yu.A. Tsukanov, V.P. Rubanov. // Steel, 1993. - 1. - P. 47-52 - on pages 49, 51). The table shows examples of the method with various technological parameters. The values of the coefficient k _i for all stands of the mill were taken equal.

округлены до сотых долей единицы. Как видно из таблицы, нормированный параметр при заданной настройке стана в третьей клети равен пороговому значению 0,2, а в четвертой клети превышает его. Поэтому для этих клетей установили регламентированное превышение заднего натяжения над передним. В первом и последнем межклетьевых промежутках задавались удельными межклетьевыми натяжениями из диапазона 0,15...0,4 от вынужденного предела текучести полосы.Values of the normalized parameter

rounded to hundredths of a unit. As can be seen from the table, the normalized parameter for a given setting of the mill in the third stand is equal to the threshold value of 0.2, and in the fourth stand exceeds it. Therefore, a regulated excess of the rear tension over the front one was established for these stands. In the first and last inter-stand spaces, specific inter-stand tensiones were set from the range 0.15 ... 0.4 of the forced yield strength of the strip.

In the first example, due to the mismatch of the coefficient k _{i to the} optimum value at the rolling speed of more than 15 m / s, vibrations of the 4th stand were recorded. In order to prevent an emergency, the rolling speed was reduced to 10 m / s, which led to a decrease in mill productivity.

In the fifth example, the value of the coefficient k _i also did not correspond to the optimal one - it was overestimated. As a result, during the rolling process, the specific interstand tension in the first gap turned out to be higher than the technologically permissible limit, the strip surface defects associated with roll slippage in the 2nd stand were recorded, and in the second interstand position, it was close to the boundary value (40% of the forced yield strength stripes). There was a break in the strip, which led to a standstill.

In optimal examples II. . .IV there is a correspondence between the initial technological parameters and the established value of the coefficient k _i . The excess of the rear tension over the front tension in stands 3 and 4, on the one hand, ensured a guaranteed choice of gaps, due to this the absence of vibrations at a rolling speed of more than 15 m / s, and on the other hand, the technologically permissible limits for setting specific cross-braces were not violated tension. The rolling process was carried out stably at high speed (above 15 m / s) without slippage of the rolls, stand vibrations, strip breaks. Thus, the application of the invention allows to improve the quality of the rolled strips by reducing rejects on surface defects by 4-5%, and also to increase the stability of the rolling process, thereby achieving the possibility of increasing the hourly productivity of the mill by an average of 10%.

Claims (1)

A method of cold rolling strips in a multi-stand mill, comprising passing strips through quarto stands, in which the vertical plane of the axes of the work rolls is offset from the vertical plane of the axes of the backup rolls, and reducing the total inter-stand tension along the course of rolling, characterized in that the excess of the full inter-stand rear tension over the front tension set according

in stands for which the condition

where a _i is the displacement of the work rolls relative to the support, mm; P _i - rolling force, tc; R _op, R _p - radii of the backup and working rolls, mm; k _i is an empirical dimensionless coefficient equal to 1.05 ... 1.25; i is the stand number; n is the number of mill stands; P _i - dimensionless parameter characterizing the probability of occurrence of vibrations, determined by empirical dependence

where E is the elastic modulus of the strip material, kgf / mm ² ;

- strain rate, s ^-1 ;

- total runout of working and backup rolls, mm; h _i is the thickness of the strip at the entrance to the stand, mm;

- forced (conditional) yield strength of the strip at the entrance to the stand, kgf / mm ² ; f _i - coefficient of friction during rolling; F _i - the natural frequency of the vertical vibrations of the stand, Hz (s ^-1 ).

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