JPS6330371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling a metal strip by means of a cooling roll.

Cooling of metal strips using cooling rolls is employed in continuous annealing equipment as a cooling method that provides a high cooling rate and does not damage the surface properties of the strips.

In this cooling method, a cooling medium such as cooling water is passed inside the cooling roll to cool the roll surface, and a metal strip is brought into contact with the roll surface for cooling.

FIG. 1A is a schematic diagram of this cooling method using cooling rolls. Usually, a plurality of cooling rolls 1 are arranged side by side.
A method is adopted in which the metal strips X are successively brought into contact with this. Cooling is controlled by moving the cooling roll 1 in the vertical direction and changing the contact length between the surface of the cooling roll 1 and the metal strip X. As a result, as shown in the developed view of strip
Contact portions α and non-contact portions β are alternately formed.

By the way, in cooling using such cooling rolls, buckling is likely to occur in the metal strip at the non-contact part β between the cooling rolls 1, and in severe cases, this buckling causes a vertical reduction in the line direction called "squeezing". It had the disadvantage of causing wrinkles.

Various proposals have been made in the past as countermeasures to such problems, and the present inventors have also made proposals such as Japanese Patent Application No. 57-138002 and Utility Application No. 57-162460. The former is caused by the fact that the thermal stress generated at the contact start point and the contact end point between the cooling roll and the strip is in opposite directions.In other words, in terms of stress in the strip width direction, Taking advantage of the fact that compression occurs at the contact end point (the cooling roll exit side) and tension occurs at the contact end point (the cooling roll exit side), the contact length and non-contact length are distributed so as to cause mutual interference between them. On the other hand, the latter aims to significantly increase the buckling resistance of the strip near the contact start point in order to deal with the compressive stress at the contact start point, which is the direct cause (or origin) of "squeezing". be.

Although all of these techniques are extremely effective and fully practical, subsequent research by the present inventors has revealed that they have the following drawbacks. In other words, in the former case, when the thickness of the strip to be threaded varies over a wide range in the actual line, the contact length and non-contact length with the cooling roll must be set to an extent that causes sufficient stress interference effect. Sometimes there isn't. In addition, in the latter case, it is necessary to install an uncooled presser roll just before the cooling roll, which makes the equipment complicated and increases construction costs. Since there is no place for the thermal stress generated by the restraint by the rolls to escape, there is a problem in that the shape of the strip is more likely to be distorted.

In view of these points, the present invention was made based on the elucidation of the basic mechanism of thermal stress generation and the occurrence of apertures based on this, and the present invention is to develop a cooling method that can appropriately prevent shape defects such as apertures. This is what we intend to provide.

The thermal stress generated in the cooling roll is large in proportion to the degree of change (i.e., the differential value) in the temperature gradient in the line direction within the strip caused by cooling. This has become clear as a result of theoretical analysis of thermal stress by the present inventors. Figure 2 shows an example of the temperature distribution in the longitudinal direction of the strip (averaged in the strip width direction) in an actual roll cooling line. is the longitudinal position of the strip corresponding to A and the average temperature in the width direction of the strip.

In the figure, parts A, C, and E are parts that are not in contact with the cooling roll 1, and the temperature gradient in the longitudinal direction of the strip in these parts is usually about 10°C/m (for a plate thickness of 0.8 mm and a line speed of 75 mpm). ). Also, parts B and D are parts that are in contact with the cooling roll 1, and if the roll shell of the cooling roll 1 is made of copper,
The temperature gradient in this part in the longitudinal direction of the plate is large, about 170 to 200°C/m. In this way, the temperature distribution (or temperature history) in the longitudinal direction of the strip obtained by roll cooling can be approximately approximated by a polygonal line.
The stress that causes deterioration of the shape of the strip, such as "drawing", is proportional to the difference in slope between the two lines. In other words, if the temperature gradient of the part that is in contact with the cooling roll 1 is α ₁ °C/m and the temperature gradient of the part that is not in contact is α ₂ °C/m, then the thermal stress approximately proportional to |α ₁ − _{α 2} | appear. Therefore, by reducing the difference in slope of the polygonal lines, the compressive stress in the width direction of the strip will be reduced, and as a result, buckling and squeezing can be prevented.

If we sort out such temperature gradients based on various factors in line operation, the amount of temperature drop in the roll cooling equipment required for metallurgy is constant at approximately 300℃ (700℃ → 400℃), so the temperature gradient If the plate thickness is constant, the slower the line speed, the larger it is.

If the line speed is constant, the smaller the plate thickness, the greater the effect.

This is because water is normally used as the cooling medium for the cooling roll, but in this case, even if the flow rate or temperature of the cooling water is changed, the actual cooling capacity of the cooling roll that can be obtained does not change much; This is because the cooling capacity of the cooling roll is assumed to be constant.

To specifically explain the problem of temperature gradient as mentioned above with reference to Fig. 3, Lo-a in Fig. 3 shows that the thickness of the strip plate is
1.0 mm and a line speed of 200 mpm, the strip of the roll cooling section is stretched flat, and Lo-b is the corresponding history of the plate temperature in the line direction. Also, in Figure 3 H-a, the plate thickness is the same as B above.
1.0mm and the line speed is as slow as 100mpm. In this case, if the roll wrapping length is the same as B above, the roll contact time will be longer and the plate temperature will become too low, so the roll wrapping length should be shortened. (Roll 2' position in Figure 3 A)
Along with this, the plate temperature history becomes as shown in H-b. Next, the line speed is 200mpm, the same as in case B above.
However, considering the case where the plate thickness is as thin as 0.5 mm,
In this case, the average temperature of the plate decreases more rapidly than in the case of a plate thickness of 1.0 mm (the cooling rate is greater), so
After all, it is necessary to shorten the roll winding length and shorten the contact time, and the roll winding situation,
Qualitatively speaking, the contact status with the cooling roll and the line direction history of plate temperature are almost the same as those shown in H-a and B above (position of roll 1' in Figure 3 A) when the line speed is slow. It will be the same. From Fig. 3, it is clear that the smaller the line speed and the thinner the plate thickness, the greater the change in the temperature gradient in the strip direction, and the generated thermal stress is also roughly proportional to the change in temperature gradient. do. In order to clarify the difference in temperature gradient, Figure 3
The plate temperature gradient at the first roll portion in Ro-b is indicated by a broken line P in Fig.

Next, regarding the buckling resistance of the strip, in general, the thinner the plate thickness and the larger the plate width, the lower the buckling resistance, and this point can be clearly explained by the theory of elastic buckling.

The above considerations from the viewpoints of both thermal stress and buckling resistance can be summarized as follows.

If other conditions are constant, the thinner the plate, the greater the generated thermal stress and the lower the strip buckling resistance. The strip is therefore extremely easy to squeeze.

If other conditions are constant, the slower the line speed, the greater the thermal stress generated and the easier it is to reduce.

If other conditions are constant, the larger the plate width, the greater the generated thermal stress, and the lower the buckling resistance of the plate. Therefore, it becomes extremely easy to squeeze.

Conventional roll cooling lacks consideration for stable sheet threading that focuses on such thermal stress and buckling resistance. The present invention focuses on such thermal stress and the buckling resistance of the strip, and reduces the cooling capacity of the cooling roll under conditions where the strip is easily drawn, and reduces the amount of change in the temperature gradient of the strip in the line direction, thereby reducing the thermal stress itself. Based on the fundamental idea of controlling the temperature of the strip, we use a high boiling point heat medium that circulates in a closed pipe as the cooling medium that passes through the inside of the cooling roll, and adjust the contact area between the cooling roll and the strip according to the strip passing conditions. With,
The basic idea is to control the temperature gradient in the line direction of the strip during cooling by selecting the operating temperature of the cooling medium (average temperature as it passes through the cooling roll) and adjusting the strip contact ability of the cooling roll. . However, in order to respond to changes in sheet passing conditions and reduce rapid changes in thermal stress through such adjustment, it is necessary to enable rapid changes in the operating temperature of the cooling medium. Therefore, the present invention adjusts the operating temperature of the cooling medium by adjusting the amount of heat exchanged in the heat exchanger and adjusting the amount of cooling medium that bypasses the heat exchanger, and adjusts the operating temperature according to the conditions. This allows for rapid changes.

The present invention will be explained below based on FIG.

In the present invention, a high boiling point heating medium is used as the cooling medium for the cooling roll instead of water, which is commonly used.
Examples of this high boiling point heating medium include triethyl diphenyl (boiling point 340°C). The reason why a high boiling point heat medium is used instead of water as a cooling medium is as follows. In other words, when water is used as a cooling medium, the fact that the heat transfer surface inside the cooling roll locally becomes a boiling heat transfer surface is caused by the equipment (the pressure drop in the piping system increases rapidly) and the quality (the temperature of the roll shell). There is a problem in that the temperature of the strip becomes unstable, causing unevenness in the strip temperature.For this reason, the operating temperature as a heating medium is limited to a range of approximately 80°C to 25°C. Therefore, assuming that the average temperature of the strip is 500°C, the difference between the strip temperature (Ts) and the cooling medium temperature (Tf) is (Ts - Tf)
is max 475℃, min 420℃, and the cooling capacity of the cooling roll is proportional to this temperature difference (Ts - Tf), so the adjustment range of the roll cooling capacity due to water temperature changes is extremely narrow, and the strip cooling capacity can be adjusted by adjusting the strip cooling capacity of the cooling roll. This is extremely insufficient to achieve the purpose of the present invention, which is to control the temperature gradient in the line direction. For this reason, in the present invention, the temperature gradient can be controlled by using a high boiling point heating medium that can widen the adjustment range of the roll cooling capacity as the cooling medium. For example, when alkyl diphenyl (boiling point: approximately 290°C under normal pressure) is used as a high-boiling heating medium, and the operating temperature of this heating medium is approximately in the range of 270°C to 100°C, (Ts−
Tf) is max 400℃, min 230℃. When the line speed is 100mpm and 200mpm, or the plate thickness is
In the case of 0.6mm and 1.2mm, the former is about 2 times the latter.
In the former case, the cooling capacity of the cooling roll needs to be reduced to about half of the latter because twice as much thermal stress is generated, but by using a high boiling point heat medium as described above, it is possible to adjust the cooling capacity in this way. I am able to respond adequately.

As shown in FIG. 4, such a cooling medium is circulated in a closed pipe line 2 via a pump 3, etc., and during this circulation it passes through a cooling roll 1 to be cooled, and is also heat exchanged by a cooler 4. be done. Then, the operating temperature of the cooling medium is selected according to the passing conditions of the strip X, and the roll cooling capacity is adjusted. Specifically, in the case of threading conditions where the shape is likely to be distorted or the stripping is likely to occur, i.e., in the case of thin strips, in the case of wide strips, in the case of threading at slow line speeds, etc. The operating temperature of the cooling medium is increased.
As a result, the cooling capacity of the cooling unit 1 is reduced, and the amount of change in the temperature gradient in the line direction of the strip X is reduced, so that the occurrence of thermal stress due to cooling is suppressed to a low level.

In the present invention, the operating temperature of the cooling medium is adjusted by adjusting the amount of heat exchange in a heat exchanger (cooler) and adjusting the amount of cooling medium that bypasses the heat exchanger, thereby rapidly increasing the temperature of the working fluid. This makes it possible to make significant changes. That is, as mentioned above,
In order to appropriately control thermal stress in response to changes in strip passing conditions, it is not sufficient to simply adjust the operating temperature of the cooling medium; it is necessary to rapidly change the operating temperature. Therefore, the present invention makes it possible to rapidly change the operating temperature by adjusting the operating temperature by using the above two methods in combination.

Here, to explain the adjustment of the operating temperature of the cooling medium as shown in FIG. 4, the closed pipe line 2 for circulating the cooling medium is provided with a cooler bypass pipe line 5 equipped with a flow rate control valve 6. When the opening degree of the flow rate control valve 6 in the cooler bypass pipe 5 is increased while the cooling medium is circulating, the flow rate of the medium bypassing the cooler 4 increases, so the overall The temperature of the cooling medium when it enters the cooling roll 1 becomes high, and the operating temperature of the cooling medium can be freely adjusted by adjusting the opening degree of the flow control valve 6 in this way. In addition, such adjustment of the operating temperature is also performed by adjusting the opening degree of the flow rate control valve 8 of the condenser conduit 7. Water is usually used as the fluid for this cooler, but in the case of water, the water temperature on the cooler inlet side is approximately 25℃, and the water temperature on the outlet side is approximately 40 to 80℃.
This can be used as hot water for strip cleaning at the entrance of the continuous annealing equipment. In the present invention, a temperature control method is adopted that combines two methods: adjustment of the flow rate in the bypass pipe by the above-mentioned flow rate control valve 6 and adjustment of the cooling capacity of the cooler 4, and the operating temperature of such cooling medium is adjusted. The adjustment adjusts the cooling capacity of the chill roll based on the difference between the strip temperature and the cooling medium temperature (Ts - Tf).

In Figure 4, to ensure stable line operation,
The temperature of the cooling medium at the entrance side of the cooling roll is measured, and the medium temperature is controlled by adjusting the bypass flow rate and cooler capacity so that this temperature becomes a preset temperature (target operating temperature) based on the sheet passing conditions. At the same time, the temperature of the strip at the exit side of the cooling roll is measured, and the length of the strip wound around the cooling roll is controlled based on this measured value. Specifically, the process computer 9 controls the operating temperature (target value) of the cooling medium for safe strip threading based on pre-known threading conditions (strip size, line speed, etc.).
Enter the preset value as 10. The temperature detection end 11 measures the temperature of the cooling medium on the inlet side of the cooling roll, and the radiation thermometer 12 measures the strip temperature on the outlet side of the roll cooling section, and these signals are input to the control process computer 9. Here, based on the detected cooling medium temperature and the set operating temperature, a signal for adjusting the opening degree of the flow rate control valve 6 of the cooler bypass flow rate and the cooling fluid flow rate control valve 8 of the cooler is also set. Based on the detected strip temperature, a control signal for raising and lowering the cooling roll is output from the control process computer 9 to each of the control valves 6 and 8 and the roll lifting device 13 to control the length of the strip wound around the cooling roll. The cooling capacity of the rolls and the degree of cooling of the strip are generally controlled.

The line speed is also detected by the line speed detection end 14 (a tachometer generator near the roll cooling section), and based on this detection, dynamic control that follows changes in the line speed can be performed.

Example In a continuous annealing line with a control system as shown in Fig. 4, the plate thickness is 1.2 to 0.4 mm and the plate width is 600 to 1240 mm.
The operation was carried out under threading conditions ranging from 80 to 180 mpm and line speeds of 80 to 180 mpm.

Cooling medium operating temperature max. 275°C, min. 100°C
℃, medium supply flow rate to cooling roll is average per roll.
The machine was operated at a speed of 320/min (5 cooling rolls) and a total media circulation rate of approximately 1600/min. As a result, throttling occurred under conditions that made threading difficult under conventional conditions and caused problems with product shape, etc. It has become possible to stably produce high-quality products even under these conditions.

According to the method of the present invention described above, the amount of cooling of the strip is controlled by adjusting the contact area between the cooling roll and the strip according to the strip running conditions, and the cooling medium that is passed through the inside of the cooling roll is Using a high-boiling heat medium that circulates in a closed pipe, the operating temperature of the cooling medium is selected by adjusting the amount of heat exchange in the heat exchanger and adjusting the amount of cooling medium that bypasses the heat exchanger. By adjusting the strip cooling capacity of the roll, the temperature gradient in the line direction of the strip during cooling can be controlled, so that the operating temperature of the cooling medium and, in turn, the strip cooling of the cooling roll can be adjusted in response to changes in strip threading conditions, etc. Capacity can be quickly and appropriately controlled, and this has the effect that roll cooling of the strip can be performed while appropriately preventing strip shape defects and constriction, regardless of changes in strip passing conditions.

[Brief explanation of the drawing]

FIGS. 1A and 1B are explanatory diagrams showing cooling conditions by cooling rolls. FIGS. 2A and 2B are explanatory diagrams showing the state of cooling by the cooling roll and the temperature change of the strip due to this. FIGS. 3A, 3A, 3B, 3A, 3B, 3A, 3B, 3A and 3B are explanatory diagrams showing the cooling situation by the cooling roll and the temperature change of the strip due to this. FIG. 4 is an explanatory diagram showing the cooling equipment and its control system used for carrying out the method of the present invention. In the figure, 1 is a cooling roll and 2 is a closed pipe line.

Claims (1)

[Claims] 1. A high boiling point heat medium circulating in a closed pipe is used as the cooling medium to be passed inside the cooling roll, and the contact area between the cooling roll and the strip is adjusted according to the strip passing conditions, and the operating temperature of the cooling medium is adjusted. , the temperature gradient in the line direction of the strip during cooling is controlled by selectively adjusting the strip cooling capacity of the cooling roll by adjusting the amount of heat exchange in the heat exchanger and adjusting the amount of cooling medium bypassing the heat exchanger. A method for cooling a metal strip using a cooling roll.