RU2021048C1 - Method of preparing rolls for operation - Google Patents

Abstract

FIELD: hot rolling. SUBSTANCE: method involves cooling and heating rolls with increasing roll surface spraying density from 6m/m²h to 10m /m²h, with water temperature being reduced from 70-80 C to 20-30 C in the process of cooling and increased from 20-30 C to 70-80 C in the process of heating. Spraying density and water temperature are gradually varied during the whole cycle of preparing rolls for operation. EFFECT: enhanced reliability in operation. 5 tbl

Description

 The invention relates to the technology of hot rolling on continuous broadband mills and can be used in the preparation of rolls for operation.

 A known method of preparing the rolling rolls for operation, which consists in the fact that after being rolled out of the cage, the rolls are washed and cooling is carried out with jets of variable intensity along the length of the barrel, while the temperature of the cooler is set equal to the average integral temperature of the surface of the roll along the length of the barrel (ed. N 1419773, CL B 21 B 27/10, 1986).

 The disadvantage of this method is that the cooling of the rolls is carried out with constant (in time, albeit with a variable along the length of the barrel) fully irrigation and temperature of the cooler during the entire cycle of preparation of the rolls, which does not provide a minimum level of thermal stresses in the rolls during their preparation.

 The closest in technical essence to the claimed is a method of heat treatment of rolling rolls, including cooling the rolls with liquid, grinding and heating with liquid before subsequent operation, in which before cooling the rolls are treated with a washing solution, and all operations are carried out in one bath (ed. St. N 1660779 , CL B 21 B 27/06, 1986).

 A significant drawback of the known method is the lack of cooling and heating regimes of the rolls regulated by irrigation densities and temperature of the working fluid, which ensure the minimum level of thermal stresses in the rolls during their accelerated cooling after dumping from the stands and heating before filling in the mill stand. The absence of such cooling and heating regimes leads to exceeding the maximum permissible tangential stresses in the surface layers of the rolls during the initial period of their cooling and heating, which leads to cracking in the surface layers of the rolls and their premature failure during operation in the cage.

 The main objective of the invention is to create a method for preparing the rolls for operation, which would provide such a mode of cooling the rolls after dumping them from the stands and heating after grinding before filling in the mill stands, which would ensure the level of thermal stresses in the rolls, not exceeding the maximum permissible values while reducing the flow rate of the cooling (heating) fluid.

The problem is solved in that in the method of preparing the rolling rolls for operation, including rolling the rolls out of the stands, cooling them before grinding and heating them before filling in the mill stands, the preparation of the rolls during their cooling and heating is carried out with an increase in the irrigation density of the surface of the rolls from 6 m ³ / m ² h to 16 m ³ / m ² h, with temperatupu water in the cooling process is decreased from 70-80 ^{° C} to 20-30 ^{° C,} and the heating process is increased from 20-30 ^C to 70-80 ^about With, and the change in the density of irrigation and water temperature is carried out by exponentially throughout the entire roll preparation cycle.

 The basis of the invention, the task of ensuring during the preparation of the rolls the level of potential stresses in the surface layers of the rolls, not exceeding the maximum allowable, while reducing the flow rate of the cooling (heating) liquid, is solved as follows.

The process of cooling rolls of the stands after vyvalki begin to produce a density irrigation surfaces of the rolls 6 m ³ / m ² h and a water temperature of 70-80 ° ^C. Then, gradually over the entire cycle of cooling rolls (cooling rolls total time is determined in each case and it depends on the diameter of shafts, rollers and other material.) increase the density of irrigation to 16 m ³ / m ^2, and the temperature is reduced to 20-30 ° ^C. The heating of the roll start also with irrigation density of 6 m ³ / m ² h and with a temperature of heating water of 20-30 ^o C, gradually continuously increasing density in the irrigation process of heating up to 16 m ³ / m ² h, and the water temperature - 70-80 ° ^C. This method of preparation of rolls for operation can significantly reduce the level of thermal stresses in the surface layers of the rolls during their cooling and heating, as well as reduce the consumption of cooling (heating) fluid. Reducing the level of thermal stresses during the preparation of the rolls provides an increase in the resistance of the rolls.

 In order to determine the optimal irrigation densities and temperatures of the cooling (heating) liquid, computer experiments were conducted on a computer. The experiments were based on the developed mathematical model of thermal processes in the roll. Using a set of computer programs, we determined the temperature distributions in the roll body and the corresponding thermal stresses at different densities of irrigation of the roll surfaces and liquid temperatures during cooling and heating of the rolls.

In the finishing stands of hot rolling mills, two-layer cast iron-chromonickel rolls of the type LPHNd-70 are used, the mechanical properties of which (due to alloying) are close to the properties of cast iron of the type B4 60-2, B4 50-1.5. With thermoelastic failure of the rolls, the most dangerous are the tangential stresses. It is known that the longitudinal tangential stresses of a cylindrical type are an order of magnitude smaller than the ultimate tensile strength. The bending strength of these grades of cast iron is 55-60 kgf / mm ² or 550-600 MPa. Therefore, the permissible tangential stresses in the surface layers of the rolls during their cooling after dumping from the stands and heating before filling in the mill stands should not exceed 55-60 MPa.

в теле валка (МПа) на поверхности и на глубине до 105 мм от поверхности при различных значениях температур охладителя (от 20 до 80^оС). Результаты экспериментов представлены в табл. 1 (плотность орошения составляла 4 м³/м² ч, температура массы прогретого валка - 96^оС. Из табл. 1 видно, что при температуре охладителя 70-80^оС значения термических напряжений в поверхностных слоях валков не превышают предельно допустимый уровень, что свидетельствует о том, что начинать процесс охлаждения валков нужно именно с такой температурой охладителя, постепенно понижая ее до 20-30^оС. Значение минимальной температуры воды в процессе охлаждения (20-30^оС) определяется конечной температурой, до которой необходимо охладить валок перед шлифовкой (как правило, температура цеха), а время охлаждения валка до этой температуры определяется такими параметрами, как диаметр валка, его масса, габариты, исходное температурное состояние и теплофизические характеристики материала валка. Например, для рабочих валков стана 2000 НЛМК с диаметром бочки 800 мм время охлаждения валка (при заявляемых параметрах охлаждения) составит ≈ 1,5 ч. В ходе машинного эксперимента проводили также контроль термических напряжений в поверхностных слоях валка при нескольких промежуточных значениях температуры охладителя (от 70-80^оС до 20-30^оС). При этом по модели определяли соответствующее текущему времени температурное состояние валка. Результаты экспериментов показали, что значения термических напряжений не выходят за пределы допустимых за весь период охлаждения валков с изменением температуры охладителя от 70-80^оС до 20-30^оС.At the first stage of machine experiments, the temperature of cooling water necessary for the optimal level of thermal stresses was determined at the initial stage of cooling the dumped heated rolls. For this, the values of tangential stresses σ

in the roll body (MPa) at the surface and to a depth of 105 mm from the surface at different values of coolant temperature (from 20 to ⁸⁰ ° C). The experimental results are presented in table. 1 (irrigation density was 4 m ³ / m ² h, heated roll mass temperature - 96 ° ^C from Table 1 that at a temperature of 70-80 ^{° C} cooler values of thermal stresses in the surface layers of the rolls does not exceed the maximum allowable level. which indicates that the start rolls cooling process it is necessary from a coolant temperature, gradually lowering it to 20-30 ° ^C. The minimum value of water temperature in the cooling process (20-30 ^{° C)} is determined by the final temperature to which should be cooled roll before thin section (usually the workshop temperature), and the roll cooling time to this temperature is determined by such parameters as the diameter of the roll, its mass, dimensions, initial temperature state and thermal characteristics of the roll material, for example, for work rolls of a 2000 NLMK mill with a barrel diameter of 800 mm roll cooling time (with the claimed cooling parameters) will be ≈ 1.5 hours. During a machine experiment, thermal stresses in the surface layers of the roll were also controlled at several intermediate temperatures Cooler (from 70-80 ^{° C} to 20-30 ° ^C). In this case, the temperature state of the roll corresponding to the current time was determined by the model. The experimental results showed that the values of thermal stresses are within allowable limits over the entire period of cooling rolls with a change in coolant temperature from 70-80 ^C to 20-30 ° ^C.

в теле валка на поверхности и на глубине до 105 мм от поверхности представлены в табл. 2 (температура массы валка составляла ≈ 96^оС).To determine the optimal value of the values of irrigation densities in the initial period of cooling the rolls after dumping them from the stands, corresponding experiments were performed. Irrigation density was varied from 2 m ³ / m ² h to 20 m ³ / m ² h, the temperature was kept constant at 70 ^C. The obtained during machine experiment values tangential stress σ

in the roll body on the surface and at a depth of 105 mm from the surface are presented in table. 2 (the temperature of the mass of the roll was ≈ 96 ^о С).

The results presented in table. 2, indicate that at the initial stage, the cooling of the rolls must be carried out with an irrigation density of not more than 6 m ³ / m ² .

A subsequent experiment was the fact that a computer simulated cooling roll for 1.5 hours while gradually decreases the value of the temperature to 20-30 ^{° C} (this value was fixed), since the value of the final temperature of the roll due to the ambient temperature, at which he goes to resurfacing. During the experiment, the final value of the irrigation densities was changed and the thermal stresses arising at the final stage of cooling were recorded. The experimental results are presented in table. 3.

From the table. 3 that when the final cooling temperature in the range of 20-30 ^{° C} and the water concentration in the last step of cooling to 16 m ³ / m ² h, the values of thermal stresses in the surface layers of the roll do not exceed allowable limits.

The process of heating the rolls in physical essence is the opposite of the process of cooling it. At the initial stage of the heating roll has a temperature the same, which it has at the end of the cooling process, the rollers start the heating process must be water with a temperature of 20-30 ^{° C,} gradually raising it to ^about 70-80 C while changing the irrigation density of 6 m ³ / m ² h to 16 m ³ / m ² h. Carried out computer experiments on a computer confirmed the validity of such parameters for heating the rolls.

 To confirm the impact on the quality of preparation of the rolls of the proposed method, pilot tests were carried out. The preparation of the rolls was carried out according to the claimed method and according to the known method. The results of comparative tests are given in table. 4.

 From the table. 4 shows that when preparing the rolls for operation according to the claimed method, the wear resistance of the rolls increases, which indicates the best technology for preparing the rolls for operation.

 In addition to a visual inspection of the state of the surfaces of the rolls given in table. 4, we measured the residual stresses in the surface layers of the rolls by the magnetoelastic method using the ION-4M instrument (residual stress meter). Stresses were measured at various stages of preparation and operation of the rolls: after rolling out of the stands, after the cooling operation of the rolls, after removing the first, second and third (final) layers by grinding (the thickness of the layers removed was 0.15; 0.2 and 0.1 mm) ; and also after heating the rolls before filling them in the mill stand. The stresses were measured rolls, which were prepared for operation according to the proposed method and rolls prepared according to the known method. The measurement results showed that at all stages of preparation of the rolls for operation, as well as after the rolls were rolled out of the stands, the residual stresses in the rolls, which were prepared according to the proposed method, are 15-20% lower than that of the rolls, which were prepared according to the known method.

 To assess the impact of the method of preparing rolls for use on the quality of the rolled products, corresponding pilot tests were also conducted. In one case, the work rolls of all finishing stands were prepared for filling in the mill according to the claimed method, in the other according to the known. At the same time, campaigns of rolled strips identical in assortment were selected. The results of comparative tests are presented in table. 5.

 From the table. 5 it follows that the preparation of the rolls for operation according to the claimed method helps to increase the yield of sheet 1 grade. This is because when preparing the rolls for operation by the claimed method, more uniform and less wear of the surface of the rolls occurs, the roll profile is more stable during operation, which favorably affects the flatness of the strips, as well as their thickness width.

 An example implementation of the proposed method.

 Preparation of work rolls for operation for the 2000 NLMK mill was carried out as follows.

 Rolls dumped from the stands were placed in specialized chambers equipped with a nozzle collector system, special shut-off and control valves, a tank for preparing water with a supply of sharp steam and a water temperature control sensor, a waste water collection system, as well as flow meters to control irrigation density (flow rate) )

At the initial stage of cooling is performed with water of 70-80 ° ^C. The density of surface irrigation rolls installed - 6 m ³ / m ² h By the developed model, it was determined that the work rolls 2000 NLMK mill having a diameter of 800-820 mm, must be cooled. ≈ 1.5 hours. A water flow controller operating in the remote control mode (fully automatic mode is also possible) gradually (over 1.5 hours) increased the irrigation density of the surface of the rolls from 6 m ³ / m ² to 16 m ³ / m ² hours. At the same time, also within 1.5 hours by reducing the volume of acute th vapor fed into the system, the coolant temperature was reduced to 20-30 ° ^C. Chilled rolls thus transported from the chambers in roll grinding shop for regrinding. Refinished rolls were installed in the same chambers for heating before filling in the mill stand. Heated roll started to carry water having a temperature of 20-30 ^{° C,} gradually raising it in the process of heating to 70-80 ° ^C. The density of the roll surface irrigation water is also gradually increased from 6 m ³ / m ² h to 16 m ³ / m ² h The heated rolls thus prepared were transported to the stands for subsequent filling in the mill.

The application of the proposed method of preparing rolling rolls for use allows you to:
increase the roll resistance by reducing the level of thermal stresses in them;
to improve the quality of sheet metal by stabilizing the profile of the forming roll barrel during operation;
reduce the number of work rolls necessary for the normal operation of the mill, by reducing the specific consumption of rolls per ton of rolled sheet.

Claims (1)

METHOD FOR PREPARING ROLL ROLLS FOR OPERATION, including rolling the rolls out of the stands, cooling them before grinding and heating them before filling in the mill stands, characterized in that the rolls are prepared in the process of cooling and heating with increasing irrigation density of the surface of the rolls from 6 to 16 m ³ / m ² · h, while the temperature of the water during cooling is reduced from 70-80 to 20-30 ^o C, and during heating is increased from 20-30 to 70-80 ^o C, and the change in the density of irrigation and water temperature is carried out gradually throughout the cycle of cooking rolls.

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