COOLING WATER TEMPERATURE CONTROL METHOD AND COOLING WATER TEMPERATURE CONTROL DEVICE FOR STEEL SHEET

Abstract

A cooling water temperature control method, includes: calculating thickness of a water film remaining on a steel sheet; calculating a change in the thickness of the water film; calculating a change in temperature of the steel sheet; calculating a steel sheet temperature on an exit side of a draining roll at which a position where the thickness of the water film on the steel sheet becomes zero coincides with an exit side position of a drying equipment, and setting the calculated temperature to a lower limit value; calculating a steel sheet temperature on the exit side of the draining roll at which the steel sheet temperature on the entrance side of coating equipment coincides with a predetermined temperature and setting the calculated temperature to an upper limit value; and controlling the temperature of cooling water within a range of the lower limit value and the upper limit value.

Claims

1-2. (canceled)

3. A cooling water temperature control method for a steel sheet for controlling temperature of cooling water in a line including cooling equipment that cools an annealed steel sheet using the cooling water, a draining roll that removes a water film on the steel sheet cooled by the cooling equipment, drying equipment that is disposed on an exit side of the draining roll and dries the steel sheet, and coating equipment that is disposed on an exit side of the drying equipment and coats the steel sheet, the cooling water temperature control method comprising: (a) calculating thickness of the water film remaining on the steel sheet on the exit side of the draining roll; (b) calculating a change in the thickness of the water film from the exit side of the draining roll to the exit side of the drying equipment considering line speed; (c) calculating a change in temperature of the steel sheet from the exit side of the draining roll to an entrance side of the coating equipment considering the line speed; (d) calculating, using calculation results of (a) to (c), a steel sheet temperature on the exit side of the draining roll at which a position where the thickness of the water film on the steel sheet becomes zero coincides with an exit side position of the drying equipment, and setting the calculated steel sheet temperature to a lower limit value of cooling water temperature; (e) calculating, using the calculation results of (a) to (c), a steel sheet temperature on the exit side of the draining roll at which the steel sheet temperature on the entrance side of the coating equipment coincides with a predetermined temperature and setting the calculated steel sheet temperature to an upper limit value of the cooling water temperature; and (f) controlling the temperature of the cooling water within a range of the lower limit value and the upper limit value set in (d) and (e).

4. A cooling water temperature control device for a steel sheet that controls temperature of cooling water in a line including cooling equipment that cools an annealed steel sheet using the cooling water, a draining roll that removes a water film on the steel sheet cooled by the cooling equipment, drying equipment that is disposed on an exit side of the draining roll and dries the steel sheet, and coating equipment that is disposed on an exit side of the drying equipment and coats the steel sheet, the cooling water temperature control device comprising a processor comprising hardware, the processor being configured to: (a) calculate thickness of the water film remaining on the steel sheet on the exit side of the draining roll; (b) calculate a change in the thickness of the water film from the exit side of the draining roll to the exit side of the drying equipment considering line speed; (c) calculate a change in temperature of the steel sheet from the exit side of the draining roll to an entrance side of the coating equipment considering the line speed; (d) calculate, using calculation results of (a) to (c), a steel sheet temperature on the exit side of the draining roll at which a position where the thickness of the water film on the steel sheet becomes zero coincides with an exit side position of the drying equipment, and set the calculated steel sheet temperature to a lower limit value of cooling water temperature; (e) calculate, using the calculation results of (a) to (c), a steel sheet temperature on the exit side of the draining roll at which the steel sheet temperature on the entrance side of the coating equipment coincides with a predetermined temperature and set the calculated steel sheet temperature to an upper limit value of the cooling water temperature; and (f) control the temperature of the cooling water within a range of the lower limit value and the upper limit value set in (d) and (e).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a flowchart illustrating a flow of cooling water temperature control processing of a steel sheet according to an embodiment of the present invention.

[0017] FIG. 2 is a schematic diagram illustrating a configuration of a cooling water temperature control device for a steel sheet according to an embodiment of the present invention.

[0018] FIG. 3 is a diagram illustrating a result of an experiment performed using the cooling water temperature control device for the steel sheet illustrated in FIG. 2.

[0019] FIG. 4 is a schematic view for explaining a method of cooling and drying an annealed steel sheet on an entrance side of coating equipment.

[0020] FIG. 5 is a schematic diagram for explaining a relation between a steel sheet temperature and a water film thickness.

[0021] FIG. 6 is a diagram illustrating a relation between water vapor concentration and temperature of a water film.

DESCRIPTION OF EMBODIMENTS

[0022] In the following explanation, a cooling water temperature control method and a cooling water temperature control device for a steel sheet according to an embodiment of the present invention is explained.

[0023] FIG. 1 is a flowchart illustrating a flow of cooling water temperature control processing for a steel sheet according to an embodiment of the present invention. As illustrated in FIG. 1, in the cooling water temperature control processing for the steel sheet according to the embodiment of the present invention, first, thickness of a water film remaining on a steel sheet S on an exit side of a draining roll 2 is calculated (step S1). Specifically, thickness h (?m) of a water film remaining on the steel sheet S after draining by the draining roll 2 is proportional to the 0.6 power of line speed and can be calculated by the following Formula (2). Here, ? indicates viscosity (kgf.Math.s/m) of water, p indicates a draining roll linear pressure (kgf/m), v indicates line speed (m/s), E indicates an equivalent Young's modulus (kgf/m.sup.2) of draining roll surface rubber and a steel sheet, and R indicates a draining roll radius (m).

h=3.1??.sup.0.6?p.sup.?0.2?v.sup.0.6?E.sup.?0.4?R.sup.0.6?10.sup.6 (2)

[0024] Subsequently, an evaporation amount of the water film into the atmosphere in a path from the exit side of the draining roll 2 to drying equipment 4 and a steel sheet temperature that changes according to heat of vaporization and heat transfer to the atmosphere at the time when the water film evaporates are calculated (step S2). Specifically, the evaporation amount of the water film into the atmosphere is inversely proportional to the line speed and an evaporation amount m (kg/(m.sup.2.Math.s)) of the water film per unit time can be calculated by the following Formula (3). Here, h.sub.0 indicates a mass transfer rate (m/s), ? indicates the density of water (kg/m.sup.3), ?.sub.0 indicates water vapor concentration of the water film, and ?.sub.? indicates water vapor concentration of the atmosphere.

m=h.sub.0???(?.sub.0??.sub.?) (3)

[0025] On the other hand, the steel sheet temperature that chances according to heat of vaporization and heat transfer to the atmosphere at the time when the water film evaporates is inversely proportional to the line speed and a heat quantity Q (kcal/(m.sup.2.Math.s)) obtained by the steel sheet per unit time can be calculated by the following Formula (4). Here, ? indicates a heat transfer coefficient (kcal/(m.sup.2.Math.s.Math.? C.)), T.sub.0 indicates a steel sheet temperature (? C.), T.sub.? indicates an atmospheric temperature (? C.), m indicates an evaporation amount (kg/(m.sup.2.Math.s)) of the water film, L indicates evaporation latent heat (kcal/m.sup.2), and d indicates a sheet thickness (m) of the steel sheet. When a very short time in a path from the exit side of the draining roll 2 to the drying equipment 4 is represented as ?t, the steel sheet temperature can be calculated by repeatedly performing calculation as follows based on the evaporation amount m and the heat quantity Q of the water film. That is, when the steel sheet temperature at time t=t.sub.n?1 is represented as T.sub.0n?1, the evaporation latent heat (kcal/m.sup.2) at time t=t.sub.n?1 is represented as L.sub.n?1, the heat transfer coefficient (kcal/(m.sup.2.Math.s.Math.? C.)) at time t=t.sub.n?1 is represented as ?.sub.n?1, the atmospheric temperature (? C.) at time t=t.sub.n?1 is represented as T.sub.?n?1, the density of the steel sheet (kg/m.sup.3) is represented as ?.sub.s, the sheet thickness (m) of the steel sheet is represented as d, and the specific heat (kcal/(kg.Math.? C.)) of the steel sheet is represented as c, a steel sheet temperature T.sub.0n at time t=t.sub.n is represented by the following Formula (5). Therefore, by repeatedly calculating the steel sheet temperature T.sub.0n using this formula (5), the steel sheet temperature at each position of the path can be obtained.

Q=?(T.sub.0?T.sub.?)?m.Math.(L/(?.Math.d)) (4)

T.sub.0n=T.sub.0n?1?(L.sub.n?1/?t+2??.sub.n?1/3600?(T.sub.0n?1?T.sub.?n?1))/(?.sub.s?d?c)??t) (5)

[0026] Subsequently, an evaporation amount of the water film by dehumidified air 9 blown against the steel sheet S by the drying equipment 4 and a steel sheet temperature that changes according to heat of vaporization at the time when the water film evaporates and heat transfer to the dehumidified air 9 are calculated (step S3). Specifically, the evaporation amount of the water film into the dehumidified air 9 can be calculated by Formula (3) explained above. On the other hand, the steel sheet temperature that changes according to the heat of vaporization at the time when the water film evaporates and the heat transfer to the dehumidified air is inversely proportional to the line speed. The heat quantity Q (kcal/m.sup.2.Math.s) that the steel sheet obtains per unit time can be calculated by Formula (4) explained above. However, in this case, the temperature (? C.) of the dehumidified air is used as T.sub.? in Formula (4). The steel sheet temperature can be determined in the same manner as described above.

[0027] Subsequently, using processing results in step S1 to step S3, the steel sheet temperature on the exit side of the draining roll 2 is calculated such that a position of complete drying where the thickness of the water film becomes zero coincides with an exit side position of the drying equipment 4. Here, the thickness of the water film at the exit side position of the drying equipment can be calculated by repeatedly performing calculation as follows based on the thickness h of the water film remaining on the steel sheet S after draining and the evaporation amount m of the water film. That is, when the thickness of the water film at the time t=t.sub.n?1 is represented as h.sub.n?1 and the evaporation amount of the water film is represented as m.sub.n?1, the thickness h.sub.n of the water film at the time t=t.sub.n is represented by the following Formula (6). Therefore, by repeatedly calculating the thickness h.sub.n of the water film using this Formula (6), thicknesses of the water film in respective positions of the path can be calculated. On the other hand, the evaporation amount of the water film into the dehumidified air 9 can be calculated by Formula (3) explained above. Therefore, the steel sheet temperature on the draining roll exit side only has to be determined such that the thickness of the water film becomes zero. Since the steel sheet temperature and the cooling water temperature match on the exit side of the draining roll 2, the calculated steel sheet temperature is set to a lower limit value Tmin of the cooling water temperature necessary for completely drying the steel sheet S (step S4). When the cooling water temperature is higher than the lower limit value Tmin, the water film remaining on the steel sheet S on the exit side of the draining roll 2 can be completely dried in the drying equipment 4.

h.sub.n=h.sub.n?1?(?t?m.sub.n?1000) (6)

[0028] Next, in the path from the exit side of the drying equipment 4 to the entrance side of the coating equipment 5, a steel sheet temperature that changes according to heat transfer to the atmosphere is calculated. Specifically, the steel sheet temperature that changes according to the heat transfer to the atmosphere is inversely proportional to the line speed. The heat quantity Q (kcal/m.sup.2.Math.s) that the steel sheet obtains per unit time can be calculated by the following Formula (7). Here, ? indicates a heat transfer coefficient (kcal/m.sup.2.Math.s.Math.? C.), T.sub.0 indicates a steel sheet temperature (? C.), and T.sub.? represents an atmospheric temperature (? C.). When an amount of a rise in the steel sheet temperature in a very short time is represented as ?T, since ?T=Q/(mass of the steel sheet?specific heat of the steel sheet), the steel sheet temperature T.sub.n can be calculated by repeated performing calculation as follows. That is, when the steel sheet temperature at the time t=t.sub.n?1 is represented as T.sub.n?1, the steel sheet temperature T.sub.n at time t=t.sub.n is represented by the following Formula (8). Therefore, by repeatedly calculating the steel sheet temperature T.sub.n using this Formula (8), steel sheet temperatures in respective positions of the path can be obtained.

Q=?(T.sub.0?T.sub.?) (7)

T.sub.n=T.sub.n?1+?T (8)

[0029] From Formula (7) described above, a steel sheet temperature on the exit side of the drying equipment 4 is calculated such that the steel sheet temperature on the entrance side of the coating equipment 5 coincides with a predetermined temperature (for example, 30? C.) and a steel sheet temperature on the exit side of the draining roll 2 is calculated such that the steel sheet temperature coincides with the calculated steel sheet temperature. As explained above, since the steel sheet temperature and the cooling water temperature coincide on the exit side of the draining roll 2, the calculated steel sheet temperature is set to an upper limit value Tmax of the cooling water temperature necessary for completely drying the steel sheet S (step S5). Consequently, a temperature range (the lower limit value Tmin to the upper limit value Tmax) of the cooling water in which the annealed steel sheet S can be cooled to the predetermined temperature or lower and completely dried can be calculated.

[0030] From the above, when cooling the annealed steel sheet S, by measuring the temperature of the cooling water W in a water cooling tank 1 and controlling the temperature to be in the temperature range of the cooling water W calculated by the processing explained above, it is possible to cool the annealed steel sheet to the predetermined temperature or lower and completely dry the annealed steel sheet (step S6). Note that, at this time, since energy efficiency is better when a temperature adjustment margin is smaller, the temperature of the cooling water W is controlled to the lower limit value Tmin, for example, when the measured value of the temperature of the cooling water W is smaller than the lower limit value Tmin.

[0031] Subsequently, a cooling water temperature control device for a steel sheet according to the embodiment of the present invention is explained with reference to FIG. 2. FIG. 2 is a schematic diagram illustrating a configuration of the cooling water temperature control device for the steel sheet according to the embodiment of the present invention. As illustrated in FIG. 2, the cooling water temperature control device for the steel sheet according to the embodiment of the present invention has a configuration in which a heat exchanger 21 is provided in a circulation system of the cooling water W in a conventional cooling/drying system illustrated in FIG. 4. When the temperature of the cooling water higher than the set temperature range, the cooling water W is cooled using a chiller 7 and, when the temperature of the cooling water is lower than the set temperature range, the cooling water W is heated using the heat exchanger 21. In an example illustrated in FIG. 2, the cooling water W is sequentially sent, by a circulation pump 6, to the chiller 7 and the heat exchanger 21 that heats the cooling water W using steam G and is supplied to the water cooling tank 1 again. Consequently, the temperature of the cooling water W in the water cooling tank 1 is controlled within the temperature range of the cooling water W calculated by the processing explained above and the annealed steel sheet can be cooled to the predetermined temperature or lower and completely dried.

EXAMPLES

[0032] FIG. 3 illustrates an experimental result using the cooling water temperature control device for the steel sheet illustrated in FIG. 2. In FIG. 3, the horizontal axis indicates the line speed (mpm). In addition, the vertical axis indicates the steel sheet temperature on the exit side of the draining roll 2 and coincides with the cooling water temperature. Circles in the figure indicate a result in which the water film was successfully completely removed (dried) on the exit side of the drying equipment 4 and crosses indicate a result in which the water film remained (wetted). As illustrated in FIG. 3, it is seen that the cooling water temperature only has to be set to 23? C. or higher in order to dry the water film, for example, at a line speed of 200 mpm. On the other hand, it is seen that in order to set the steel sheet temperature on the entrance side of the coating equipment 5 to 30? C. or lower, since a rise in the steel sheet temperature from the drying equipment 4 to the coating equipment 5 is 2? C., the cooling water temperature only has to be set to 28? C. or lower. From the above, it has been confirmed that, by setting the temperature range of the cooling water within the range of 23 to 28? C., the water film can be completely dried and the steel sheet temperature on the coating equipment entrance side can be set to 30? C. or lower.

[0033] The embodiment to which the invention made by the present inventors is applied is explained above. However, the present invention is not limited by the description and drawings forming a part of the disclosure of the present invention according to the present embodiment. That is, all of other embodiments, examples, operation techniques, and the like made by those skilled in the art and the like based on the present embodiment are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0034] According to the present invention, it is possible to provide a cooling water temperature control method and a cooling water temperature control device for a steel sheet capable of cooling an annealed steel sheet to a predetermined temperature or lower and completely drying the annealed steel sheet even in a cold period or in the case in which a line is started up again after being stopped for a long period.

REFERENCE SIGNS LIST

[0035] 1 WATER COOLING TANK [0036] 2 DRAINING ROLL [0037] 4 DRYING EQUIPMENT [0038] 5 COATING EQUIPMENT [0039] 6 CIRCULATION PUMP [0040] 7 CHILLER [0041] 8 DEHUMIDIFIER [0042] 9 DEHUMIDIFIED AIR [0043] 10 MAKEUP WATER [0044] 21 HEAT EXCHANGER [0045] G STEAM [0046] S STEEL SHEET [0047] W COOLING WATER