RU2212963C2 - Method for continuous cold rolling of strips in multistand rolling mill - Google Patents

Abstract

FIELD: ferrous metallurgy, namely cold rolling of steel strips in continuous multistand rolling mill. SUBSTANCE: method comprises steps of passing strips through rolling stands; metering and controlling flowrate values of lubricating and cooling fluid in said stands; measuring temperature of lubricating and cooling fluid fed onto rolling rolls; regulating thermal profile of rolling rolls of last stand by sectional (zonal) cooling of them; at rolling process in predetermined time intervals measuring temperature of rolling rolls of last stand and temperature of lubricating and cooling fluid fed onto rolling rolls of last stand; calculating real difference of measured temperature values and comparing said difference with target value; normalizing with use of mathematical relation total consumption of lubricating and cooling fluid in stand group just before last stand between operations for measuring temperature. EFFECT: reduced nonplaneness of rolled strips, lowered consumption of emulsol for preparing lubricating and cooling fluid. 1 tbl, 1 ex

Description

 Method for continuous cold rolling of strips in a multi-stand mill.

 The invention relates to ferrous metallurgy, and more particularly to cold rolling of steel strips in a continuous multi-stand mill.

 The closest in its technical essence and the achieved result to the proposed technical solution is a method of cold rolling strips in a continuous multi-stand mill, including passing strips through rolling stands, measuring and regulating the flow rate of cutting fluid (coolant), measuring the temperature of the coolant supplied to work rolls, as well as regulation of the thermal profile of the work rolls of the last stand by their sectional (zone) cooling in order to ensure the flatness of the rolled strips, and the last stands set (set) the rolling force (and not the amount of compression) [see, for example, A.D. Belyansky, L.A. Kuznetsov, I.V. Franzenyuk Thin sheet rolling. Technology and equipment. - M.: Metallurgy, 1994, p. 158-159, 343 and 364, respectively].

 The disadvantage of this method is the lack of regulation of the total coolant consumption in the stands preceding the last stand, depending on the difference in temperature of the work rolls and the temperature of the coolant supplied to them. The consequence of this is the low efficiency of regulating the flatness of the strips along the sectional cooling channel of the work rolls and, as a result, the low flatness of the finished strips and sheets. In a known manner, the optimum temperature difference between the work rolls of the last stand and the cutting fluid (coolant) supplied to them, called the coolant thermal pressure, is not achieved.

The thermal pressure of the coolant, providing effective regulation of the thermal profile of the rolls, and therefore the flatness of the strips, should be at least 5 ^o C. In the known method, the temperature difference between the work rolls and the temperature of the coolant supplied to them is 0.5 ... 3 ^o C, which not enough to ensure effective regulation of the flatness of the strips along the channel of thermal profiling of the work rolls by their section cooling. This is because the deformation modes in the last stand of the mill and the levels of coolant consumption in the stands preceding the last, used when rolling according to the known method, do not provide sufficient heating of the work rolls and thermal pressure of the coolant.

An unregulated reduction of coolant costs in the stands preceding the last, in order to increase the amount of heat introduced into the last stand with a strip and heat its work rolls, leads to an excess of Δt _d (the temperature difference between the work rolls and coolant supplied to them) over the limit value of 5. . . 30 ^o C. Such a rise in coolant temperature can occur that the heat exchangers of the coolant supply systems in the mill stand will not cope with its cooling. Circulation conditions in the system become unstable and are accompanied by an increase in coolant temperature at the entrance to the stands. The temperature of the work rolls may also excessively increase above 90 ^{° C.} All together, this leads to a violation of the stability of the temperature regime of the mill, which is unacceptable.

 The technical effect when using the invention is to reduce the flatness of the rolled strips and the consumption of emulsol for the preparation of cutting fluid.

где Q₁ - суммарным расход СОЖ в клетях, предшествующих последней клети, устанавливаемый между замерами температуры внутри текущего интервала времени, м³/час;
Q₂ - суммарный расход СОЖ в клетях, предшествующих последней клети, установленный между замерами температуры внутри предыдущего интервала времени, м³/час;
k=0,001...0,5 - коэффициент, безразмерный;
Δt_д - действительная разность температуры рабочих валков последней клети и температуры подаваемой на них СОЖ, ^oС;
Δt_тр - требуемая разность температуры рабочих валков последней клети и температуры подаваемой на них СОЖ, при этом требуемую разность температур Δt_тр устанавливают в пределах 5...30^oС.The specified technical effect is achieved by the fact that the method of continuous cold rolling of strips in a multi-stand mill includes passing strips through rolling stands, measuring and regulating the flow rate of cutting fluid (coolant), measuring the temperature of the coolant supplied to the work rolls, and also regulating the heat profile work rolls of the last stand by their sectional (zone) cooling. During the rolling process, the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them are discretely determined at intervals of time, the actual difference of these temperatures is calculated and this difference is compared with the required one, and the total coolant consumption in the group of stands preceding the last stand is established between temperature measurements by

where Q ₁ - the total coolant consumption in the stands preceding the last stand, established between temperature measurements within the current time interval, m ³ / hour;
Q ₂ - the total coolant flow in the stands preceding the last stand, established between temperature measurements within the previous time interval, m ³ / hour;
k = 0.001 ... 0.5 - coefficient, dimensionless;
Δt _d is the actual difference between the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them, ^o С;
Δt _Tr - the required temperature difference of the work rolls of the last stand and the temperature of the coolant supplied to them, while the required temperature difference Δt _{Tr is} set within 5 ... 30 ^o C.

A decrease in the non-flatness of the rolled strips will occur as a result of the optimal setting of the total coolant consumption in the stands preceding the last during the rolling process. The quality of regulation of flatness through the channel of thermal profiling of the work rolls of the last stand is significantly improved by increasing the heat head supplied to the coolant rolls Δt _d to a level of not less than 5 ^o C, by reducing the supply of coolant in the group of stands preceding the last stand.

The range of changes in the required temperature difference Δt _tr (required thermal pressure) by the proposed method is 5 ... 30 ^o C. Setting the required temperature difference Δt _tr <5 ^o C does not allow to achieve a technical effect, since the thermal pressure of the coolant does not reach the lower the limit of 5 ^o With, necessary for the effective regulation of flatness on the channel of thermal profiling of the rolls. The increase in the required temperature difference above 30 ^o With can lead to a violation of the stability of the temperature regime of the mill, unacceptable overheating of the rolls and coolant supplied to them. Within range 5 ... 30 ^o With the required temperature difference is set depending on the diameter of the work rolls and the capabilities of the heat exchanger of a particular mill. The larger the diameter of the work rolls of the last mill stand in the range of its possible change of 400 mm ≤D≤615 mm and the greater the temperature difference at the discharge from the stand and at the feed to the stand provides a heat exchanger (3 ... 14 ^o C for most mills), the set Δt _{mp more} and vice versa.

 Determination of the temperature of the work rolls by the proposed method can be carried out by measuring using special temperature sensors that are installed in the stand, portable pyrometers, or by calculation using high-precision models of the temperature conditions of the mill.

с величиной относительного отклонения Δt_д от Δt_тр. Его определяют по формуле

, где τ_и - продолжительность интервала времени между измерениями температур, мин; τ_c - время стабилизации теплового напора Δt_д СОЖ после установления нового значения (ступенчатого изменения) суммарного расхода СОЖ в группе клетей, предшествующих последней клети, мин. Время стабилизации τ_c характеризует инерционность процесса изменения Δt_д и зависит от многих конструктивных и переменных технологических параметров. Эта величина может принимать значения 1...30 мин (60...1800 с). Продолжительность интервала времени между измерениями температур выбирают из диапазона 0<τ_и≤0,5 τ_c. Экспериментально установили, что минимальная продолжительность интервала времени, за которое может произойти значимое изменение результата смежных замеров температур (значимое изменение Δt_д) составляет 1,8 с. Следовательно, τ $\genfrac{}{}{0ex}{}{\text{min}}{\text{и}}$ = 1,8 c.The coefficient k establishes the relationship of the magnitude of the relative change in the total coolant flow

with the relative deviation Δt _d from Δt _tr . It is determined by the formula

where τ _and is the duration of the time interval between temperature measurements, min; τ _c is the stabilization time of the heat head Δt _d coolant after establishing a new value (step change) of the total coolant flow rate in the group of stands preceding the last stand, min. The stabilization time τ _c characterizes the inertia of the process of changing Δt _d and depends on many design and variable technological parameters. This value can take values of 1 ... 30 min (60 ... 1800 s). The duration of the time interval between temperature measurements is selected from the range 0 <τ _and ≤0.5 τ _c . It was established experimentally that the minimum duration of the time interval during which a significant change in the result of adjacent temperature measurements (a significant change in Δt _d ) can occur is 1.8 s. Therefore, τ $\genfrac{}{}{0ex}{}{\text{min}}{\text{and}}$ = 1.8 s.

При меньших значениях k не достигается технический эффект. Максимальное значение коэффициента k_max=0,5 устанавливают в случаях, когда τ_и = 0,5 τ_c. Этим ограничивают чрезмерное уменьшение суммарного расхода СОЖ в тех возможных случаях, когда Δt_д≈0, то есть, температура рабочих валков последней клети и температура подаваемой на них СОЖ практически одинаковы, тепловой напор СОЖ в начальный период применения способа практически отсутствует.From here we get the minimum value of the coefficient

At lower values of k, a technical effect is not achieved. The maximum value of the coefficient k _max = 0.5 is set in cases where τ _and = 0.5 τ _c . This limits the excessive decrease in the total coolant consumption in those possible cases when Δt _d ≈ 0, that is, the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them are almost the same, the thermal pressure of the coolant in the initial period of application of the method is practically absent.

Temperature measurement at time intervals makes it possible to take into account the inertia of the stabilization of the actual (actual) thermal pressure of the coolant in the last stand Δt _d after the change in the total coolant flow rate in the mill stands preceding the last one introduced at the previous time interval. As follows from the dependence proposed in the method, in the case of Δt _d <Δt _{tr, the} total coolant consumption established inside the current time interval is less than inside the previous one. On the contrary, if Δt _d > Δt _tr , then the total flow rate is increased. The change in the set total flow rate is stopped when the actual value of Δt _d becomes equal to the required Δt _tr . This achieves such an increase in the heat content of the strip included in the last stand that due to contact heat exchange with the rolls, they are heated to a temperature that provides a sufficient coolant thermal pressure Δt _d ≥5 ^o С, which is necessary for effective regulation of flatness along the heat profiling channel. At the same time, the proposed method prevents the violation of the stability of the temperature regime and reduces the total coolant consumption.

 The analysis of scientific, technical and patent literature shows the lack of coincidence of the distinguishing 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".

 Below is an embodiment of the invention that does not exclude other options within the scope of the claims.

где Q₁ - суммарный расход СОЖ в клетях, предшествующих последней клети, устанавливаемый между замерами температуры внутри текущего интервала времени, м³/час;
Q₂ - суммарный расход СОЖ в клетях, предшествующих последней клети, установленный между замерами температуры внутри предыдущего интервала времени, м³/час;
k=0,001...0,5 - коэффициент, безразмерный;
Δt_д - действительная разность температуры рабочих валков последней клети и температуры подаваемой на них СОЖ, ^oС;
Δt_тр - требуемая разность температуры рабочих валков последней клети и температуры подаваемой на них СОЖ, при этом требуемую разность температур Δt_тр устанавливают в пределах 5...30^oС.Example. During the cold rolling process, the strips are passed through the rolling stands, the flow rates of the cutting fluid (coolant) are measured and regulated in them, the temperature of the coolant supplied to the work rolls is measured, and the thermal profile of the work rolls of the last stand is controlled by their sectional (zone) cooling. Discretely, at time intervals, the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them are determined, the actual difference of these temperatures is calculated and this difference is compared with the required, and the total coolant consumption in the group of stands preceding the last stand is established between temperature measurements according to

where Q ₁ is the total coolant consumption in the stands preceding the last stand, established between temperature measurements within the current time interval, m ³ / h;
Q ₂ - the total coolant flow in the stands preceding the last stand, established between temperature measurements within the previous time interval, m ³ / hour;
k = 0.001 ... 0.5 - coefficient, dimensionless;
Δt _d is the actual difference between the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them, ^o С;
Δt _Tr - the required temperature difference of the work rolls of the last stand and the temperature of the coolant supplied to them, while the required temperature difference Δt _{Tr is} set within 5 ... 30 ^o C.

В таблице приведены примеры осуществления способа с различными технологическими параметрами.Strip rolling from 08 ps steel 2.0 mm thick to a final thickness of 0.5 mm is carried out on a five-stand mill. It was established experimentally for these rolling conditions that the stabilization time of the actual difference between the temperature of the work rolls of the last stand and the temperature of the coolant supplied (coolant thermal pressure) - τ _c - does not exceed 12 minutes. Determination of the temperature of the work rolls using an infrared pyrometer and the temperature of the coolant supplied with a thermometer built into the coolant supply system is carried out at time intervals of 4 minutes. Coefficient

The table shows examples of the method with various technological parameters.

In the 1st example, due to the fact that the set value of Δt _tr was underestimated, a technical effect was not achieved. The rolls of the last stand were not heated sufficiently; the efficiency of their thermal profiling was low. The average flatness error of the strips rolled during this time exceeded 5.0 IU, which led to the transfer of sheet metal to the lower flatness category (PN) according to GOST 19904-90 and partially to marriage (non-ordered products).

In the third example, on the contrary, the set value of Δt _tr did not correspond to the capabilities of the heat exchanger of the coolant supply system of the last stand - it was overestimated. In the rolling process after the 3rd temperature measurement, an excessively low coolant flow rate in stands 1-4 was established. As a result, the temperature of the coolant at the entrance to the last stand began to rise. The rolling thermal regime was violated, which is unacceptable. An excessive increase in the thermal profile of the work rolls in the group of stands preceding the last made it difficult to control flatness in these stands, which ultimately led to an increase in the average flatness error in the finished strip to 4.8 IU.

In the best example 2, there is a correspondence between the initial technological parameters and the set value Δt _tr , which ensures the best conditions for achieving a technical effect. The average error of flatness of the strips did not exceed 2.2 IU, which is guaranteed to provide metal of the highest flatness categories of PO, PV according to GOST 19904-90.

 Thus, the application of the invention allows to reduce the rejection of cold-rolled strips and sheets by flatness by 5-6% and to reduce the total consumption of emulsol used for the preparation of cutting fluid.

Claims (1)

A method of continuous cold rolling of strips in a multi-stand mill, including passing the strips through the rolling stands, measuring and regulating the flow rates of coolant in them, measuring the temperature of the coolant supplied to the work rolls, and also regulating the thermal profile of the work rolls of the last stand in their section zone cooling, characterized in that during the rolling process the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them are discretely determined at intervals of time, the valid battening difference of these temperatures, and this difference is compared with a desired, and the total flow rate of coolant in the group stands preceding the last stand, between measurements of the temperature set depending

where Q ₁ is the total coolant consumption in the stands preceding the last stand, established between temperature measurements within the current time interval, m ³ / h;
Q ₂ - the total coolant flow in the stands preceding the last stand, established between temperature measurements within the previous time interval, m ³ / h;
k = 0.001. . . 0.5 - coefficient, dimensionless;
Δt _d is the actual difference between the temperature of the work rolls of the last stand and the temperature of the coolant supplied to them, ^o С;
Δt _tr - the required temperature difference of the work rolls of the last stand and the temperature of the coolant supplied to them, while the required temperature difference Δt _tr - is set within 5.. . 30 ^o C.

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