JP5488197B2 - Induction heating method for steel strip - Google Patents

Description

  The present invention relates to a steel strip induction heating method used when manufacturing a cold-rolled steel sheet, and more particularly to a method of induction heating an edge portion of a steel strip.

  Generally, cold-rolled steel sheets are manufactured by cold-rolling steel strips paid out from payoff reels on a continuous rolling line. However, cold-rolled steel sheets such as electromagnetic steel sheets (silicon steel sheets), stainless steel sheets, and high carbon steel sheets are cooled. When manufacturing by cold rolling, because the steel strip material has high deformation resistance and poor ductility, cracks called edge cracks occur at the edge of the steel strip during cold rolling, and rolling mills for continuous rolling lines The problem is that the steel strip breaks starting from the ear cracks due to the tension applied between them.

  As one of the techniques for preventing the breakage of the steel strip due to such an ear crack, the edge portion of the steel strip that is cold-rolled in the continuous rolling line is induction-heated to a predetermined temperature on the inlet side of the rolling mill to generate the ear crack. A technique for preventing the above is known (for example, see Patent Documents 1 to 3). However, in ordinary cold rolling, water-insoluble oils (rolling oils) such as mineral oils, natural fats and oils, and synthetic esters are dispersed in water with a surfactant to reduce rolling load and rolling power, and diluted ( The emulsified emulsion serves as a lubricant, and rolling oil is about 1 to 10 mass% as oil droplets having an average particle size of about 5 to 15 μm for the purpose of suppressing temperature rise of steel strips and rolls due to processing heat generation and frictional heat generation during rolling. O / W type (oil-in-water type) emulsion contained at a concentration of 5% is sprayed onto the steel strip as a coolant on the rolling mill entry side and rolling mill exit side.

  Such an emulsion is used at a temperature above the pour point at which the rolling oil, which is an oil agent, does not solidify, but if the use temperature is too high, the emulsified state becomes unstable due to evaporation of moisture or change over time of the surfactant, Since water and oil are easily separated from each other, the steel strip is usually sprayed at a temperature of about 30 ° C to 90 ° C. For this reason, as in the prior art described above, even if the edge of the steel strip is induction-heated to a predetermined temperature on the entry side of the rolling mill, the steel strip is cooled by the emulsion in the immediate vicinity of the roll bite, thereby preventing the occurrence of ear cracks. It becomes difficult to cold-roll the steel strip while maintaining a possible temperature.

  In order to perform cold rolling while maintaining a temperature that can prevent the occurrence of ear cracks, it is necessary to induction heat the edge of the steel strip at the entrance of the rolling mill in consideration of the temperature drop of the steel strip due to emulsion. There is. However, the temperature drop of the steel strip due to the emulsion is not always constant, and as is clear from the following formula described in Non-Patent Document 1, it greatly varies depending on the flow density and concentration of the emulsion.

  Also, when the line speed of the continuous rolling line changes, the cooling zone of the steel strip that comes into contact with the emulsion changes due to the hydrodynamic interaction due to the viscosity of the steel strip conveyed in one direction and the emulsion. The temperature drop of the steel strip also changes greatly when the line speed changes. Further, although the emulsion concentration is controlled within a certain range, fluctuation within a certain range is inevitable. Therefore, depending on the fluctuations in the rolling conditions, even when the edge of the steel strip is induction heated to a high temperature on the entrance side of the rolling mill, the steel strip temperature may be below the ductile / brittle transition temperature in the immediate vicinity of the roll bite.

Japanese Patent Laid-Open No. 03-60813 JP 61-15919 A JP-A-11-290931

"Theory and practice of sheet rolling" The Japan Iron and Steel Institute 1984 P148

  As a method for solving such a problem, a high temperature emulsion is sprayed on the steel strip at the entrance of the rolling mill to keep the steel strip temperature near the roll bite above the ductile / brittle transition temperature, Considering an error in cooling, a method in which the heating temperature by the induction heating device is set higher in advance so that the steel strip temperature immediately before rolling can be ensured to be equal to or higher than the ductile / brittle transition temperature can be considered.

  However, in the former method described above, when the temperature of the emulsion is increased, there remains a problem in the emulsion stability of the emulsion, and it is necessary to select a surfactant that can stably maintain the emulsified state even at a high temperature. In addition to improving lubricity during rolling as described above, emulsions are also used to suppress the temperature rise of rolls and steel strips due to processing heat generation and frictional heat generation. Resulting in problems such as an increase in the thermal crown formed by the thermal expansion of the roll.

On the other hand, in the latter method, when the temperature of the steel strip edge portion becomes too high, shape defects such as ear waves are generated in the steel plate edge portion due to thermal stress caused by the temperature difference between the steel strip edge portion and the steel strip center portion. There arises a problem that drawing breakage or the like occurs during rolling. In addition, the steel strip edge portion is induction-heated more than necessary, and energy is wasted.
The present invention has been made in view of the above-described problems, and its purpose is to reduce the temperature of the emulsion that an ear crack that causes breakage during cold rolling of the steel strip occurs at the edge of the steel strip. An object of the present invention is to provide an induction heating method for a steel strip which can be prevented without increasing the heating amount in advance or setting the heating amount of the induction heating device high.

In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention performs induction heating of an edge portion of a steel strip that is cold-rolled by a rolling mill by an induction heating device disposed on the entry side of the rolling mill. In this method, after measuring the rolling strip entrance side thickness, rolling mill exit side thickness, rolling mill exit speed and rolling mill exit temperature of the steel strip, the temperature immediately before the rolling strip biting of the steel strip is determined. Obtained from each measured value of the rolling mill entry side thickness, the rolling mill exit side thickness, the rolling mill exit side speed, and the rolling mill exit temperature, and the cold rolling conditions of the steel strip, the rolling mill bite The edge of the steel strip is induction-heated by feedback-controlling the output of the induction heating device so that the temperature just before the embedding becomes equal to or higher than the ductile / brittle transition temperature of the steel strip.
The invention according to claim 2 of the present invention is the method of induction heating of a steel strip according to claim 1, wherein the processing calorific value and the frictional calorific value generated during cold rolling of the steel strip are expressed by the following formula (1) and The temperature immediately before biting into the rolling mill of the steel strip is calculated from the formula (2).

  The invention according to claim 3 of the present invention is the method for induction heating of a steel strip according to claim 2, wherein the temperature immediately before the rolling of the steel strip into the rolling mill is calculated from the following equations (3) and (4). Feedback control of the output of the induction heating device.

The invention according to claim 4 of the present invention is the method of induction heating a steel strip according to claim 2 or 3, characterized in that the average rolling load is obtained from the output of a load cell attached to the rolling mill.
The invention according to claim 5 of the present invention is the method of induction heating of a steel strip according to any one of claims 2 to 4, wherein the roll peripheral speed is output from a roll peripheral speed meter attached to the rolling mill. It is characterized by obtaining from.
The invention according to claim 6 of the present invention is the method for induction heating a steel strip according to any one of claims 3 to 5, wherein the roll temperature is obtained from an output of a roll thermometer attached to the rolling mill. It is characterized by that.

  According to the present invention, the edge part of the steel strip induction-heated on the entry side of the continuous rolling line is cooled to the ductile / brittle transition temperature or lower on the entry side of the rolling mill by the emulsion sprayed on the steel strip. Absent. Therefore, the temperature of the emulsion should be increased in advance or the heating amount of the induction heating device should be set higher so that the edge cracks that cause breakage during cold rolling of the steel strip will occur at the edge of the steel strip. Can be prevented.

It is a figure which shows an example of the continuous rolling line used when manufacturing a cold-rolled steel plate. It is a figure which shows the temperature change of the steel strip cold-rolled by the continuous rolling line shown in FIG. It is a figure which shows an example of the induction heating apparatus which induction-heats the edge part of a steel strip. It is a flowchart for demonstrating the effect | action of the control apparatus which feedback-controls the output of an induction heating apparatus.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a continuous rolling line used when manufacturing a cold-rolled steel sheet, and FIG. 2 shows a temperature change of a steel strip cold-rolled in the continuous rolling line. In the figure, reference numeral 1 denotes a payoff reel, and a steel strip 2 paid out from the payoff reel 1 has a welding machine 3, a looper 4 and an induction heating device for welding and joining a tail end of a preceding material and a tip of a following material. After being supplied to the continuous rolling line 6 through 5, it is wound up by a tension reel 7 provided on the outlet side of the continuous rolling line 6.
The induction heating device 5 is for induction heating the edge portion of the steel strip 2 that is cold-rolled in the continuous rolling line 6 with a width of, for example, 100 mm. For example, as shown in FIG. It is comprised so that the edge part of the steel strip 2 may be induction-heated with the child 51,52.

  The continuous rolling line 6 has four tandem rolling mills 8a, 8b, 8c, and 8d arranged in series, and is configured to continuously cold-roll the steel strip 2 with these tandem rolling mills 8a to 8d. Has been. Moreover, the continuous rolling line 6 has a plurality of emulsion spray nozzles 9 for spraying emulsion onto the surface of the steel strip 2, and these emulsion spray nozzles 9 are provided on the inlet side and the outlet side of the tandem rolling mills 8a, 8b, 8c, 8d. Is provided. Further, the continuous rolling line 6 has an air wiper 10 on the exit side of the rolling mills 8a, 8b, 8c, 8d, and the emulsion sprayed from the emulsion spray nozzle 9 onto the surface of the steel strip 2 is transferred from the air wiper 10 to the steel strip 2 It is prevented from staying on the surface of the steel strip 2 by the air jetted onto the surface of the steel strip.

Continuous rolling line 6, also has thickness gauge 11a for measuring the rolling mill entry side thickness _{h 1} and the rolling mill exit side thickness _{h 2} of the steel strip 2, 11b, 11c, 11d, the 11e, these The signals output from the thickness gauges 11a, 11b, 11c, 11d, and 11e are supplied to the control device 18 together with the outputs of the load cells 12a, 12b, 12c, and 12d attached to the rolling mills 8a, 8b, 8c, and 8d. ing.

Further, the continuous rolling line 6 has a laser Doppler plate speed meter 13a for measuring the delivery side of the rolling mill speed _{V O} of the steel strip 2, 13b, 13c, 13d, and 13e, these plates speed meter 13a, 13b, The signals output from 13c, 13d, and 13e are supplied to the controller 18 together with the outputs of the roll peripheral speed meters 14a, 14b, 14c, and 14d that measure the roll peripheral speeds of the rolling mills 8a, 8b, 8c, and 8d. Yes.
Further, the continuous rolling line 6 has a steel strip thermometer 15 for measuring the rolling mill outlet temperature Tout of the steel strip 2 between the rolling mill 8a and the rolling mill 8b, and is output from the steel strip thermometer 15. The signal is supplied to the controller 18 together with the outputs of the roll thermometers 16a, 16b, 16c, and 16d that measure the roll temperatures of the rolling mills 8a, 8b, 8c, and 8d.

  The control device 18 performs feedback control of the output of the induction heating device 5, and is configured to feedback control the output of the induction heating device 5 according to the flowchart shown in FIG. 4, for example. That is, as shown in FIG. 1, when the induction heating device 5 is installed only on the entrance side of the first rolling mill 8a, the steel strip 2 paid out from the payoff reel 1 is supplied to the continuous rolling line 6. Then, the control device 18 takes in the outputs of the thickness gauges 11a and 11b arranged on the entry side and the exit side of the rolling mill 8a, and the processing calorific value Qp generated during the cold rolling of the steel strip 2 is shown in FIG. In step S1 shown, it is calculated from the following equation (1).

In addition, the average rolling load Pm of Formula (1) which is one of the conditions for rolling the steel strip 2 can be obtained from the output of the load cell 12a.
If the processing calorific value Qp has been calculated, the control device 18 takes in the output of the plate speed meter 13b (exit speed V _O ), and the frictional calorific value Qf generated during cold rolling of the steel strip 2 is shown in FIG. In S2, it is calculated from the following equation (2).

In addition, the friction coefficient μ of the formula (2) which is one of the conditions for rolling the steel strip 2 can be obtained by investigating the deformation resistance of the steel strip 2 in advance, and the roll circumference of the formula (2) speed V _R can be determined from the output of the roll peripheral speed meter 14a as one of the rolling conditions.
If the frictional heat generation amount Qf is calculated, the control device 18 takes in the output of the steel strip thermometer 15 and the amount of heat transferred from the steel strip 2 to the roll of the rolling mill 8a when the steel strip 2 is cold-rolled ( Hereinafter, it is referred to as “roll heat removal amount”) Qr is calculated from the following equation (3) in step S3 shown in FIG. 4, and the temperature Tin immediately before the rolling of the steel strip is further calculated in step S4 shown in FIG. Calculate from (4).

In addition, the value calculated | required beforehand by experiment etc. can be used for the equivalent heat transfer coefficient _heq of Formula (3) which is one of the conditions which roll the steel strip 2. FIG. Moreover, although roll temperature Tr which is one of the conditions for rolling the steel strip 2 can be calculated | required from the output of the roll thermometer 16a, it can be calculated | required also from heat conduction calculation separately.
If the temperature Tin immediately before the rolling of the steel strip 2 is calculated, the control device 18 sets the temperature Tin immediately before the rolling of the rolling strip to the ductile / brittle transition temperature of the steel strip 2 shown in FIG. 2 in step S4 shown in FIG. Compare. Here, when the temperature Tin immediately before the rolling mill biting is higher than the ductility / brittle transition temperature, the control device 18 compares the temperature immediately before the biting mill bit Tin with the upper limit set temperature in step S5 shown in FIG. When the temperature Tin immediately before biting into the rolling mill is higher than the upper limit set temperature, a feedback control signal for lowering the output of the induction heating device 5 and setting the temperature Tin immediately before biting into the rolling mill to be equal to or lower than the upper limit set temperature is shown in FIG. Is sent to the induction heating device 5 in step S6 shown in FIG.

  On the other hand, when the temperature Tin immediately before biting into the rolling mill is higher than the ductility / brittle transition temperature, the control device 18 increases the output of the induction heating device 5 so that the temperature Tin immediately before biting into the rolling mill is equal to or higher than the ductility / brittle transition temperature. The feedback control signal is sent to the induction heating device 5 in step S7 shown in FIG. And step S1-S7 mentioned above is repeated until the cold rolling of the steel strip 2 is complete | finished by step S8 shown in FIG.

As in the embodiment of the present invention described above, the rolling mill entry side thickness h ₁ , the rolling mill exit side thickness h ₂ , the rolling mill exit side speed V _O and the rolling mill exit side temperature Tout of the steel strip 2 are measured. After that, the temperature Tin immediately before the rolling of the steel strip 2 was measured for each of the rolling mill entry side thickness h ₁ , the rolling mill exit side thickness h ₂ , the rolling mill exit side speed V _O, and the rolling mill exit side temperature Tout. By continuously controlling the output of the induction heating device 5 so that the temperature Tin immediately before biting into the rolling mill becomes equal to or higher than the ductility / brittleness transition temperature of the steel strip 2, it is obtained from the value and the cold rolling conditions of the steel strip 2. Ductile / brittle transition temperature at the entry side of the rolling mills 8a, 8b, 8c, 8d by the emulsion in which the edge portion of the steel strip 2 heated by induction at the entry side of the rolling line 6 is sprayed onto the steel strip 2 from the emulsion spray nozzle 9 It will not be cooled below. Therefore, the temperature of the emulsion should be increased in advance or the heating amount of the induction heating device should be set higher so that the edge cracks that cause breakage during cold rolling of the steel strip will occur at the edge of the steel strip. Can be prevented.

As shown in FIG. 2, in the continuous rolling line, the ductile / brittle transition temperature is likely to be below the entrance side of the first rolling mill, so the induction heating device 5 is provided on the entrance side of the first rolling mill. Although the steel strip thermometer 15 is provided on the first rolling mill outlet side, the induction heating device and the steel are not limited to the first one but on the second rolling mill entrance side and rolling mill exit side depending on the purpose. A thermometer may be installed.
Moreover, by providing the air wiper 10 on the exit side of the rolling mills 8a, 8b, 8c, and 8d as in the above-described embodiment of the present invention, the emulsion sprayed from the emulsion spray nozzle 9 to the steel strip 2 can be used. It is possible to prevent the steel strip 2 from being excessively cooled.

  When cold rolling a silicon steel plate (3.0% Si) having a ductile / brittle transition temperature of 70 ° C. in the continuous rolling line shown in FIG. 1, a steel strip is formed by an induction heating device 5 arranged on the entry side of the rolling mill 8a. The method of induction heating the two edge portions was performed by the following two methods. That is, the first method is a method of inductively heating the edge portion of the steel strip by the method according to the embodiment of the present invention described above, and the second method is on the rolling mill entrance side of the steel strip by the cooling action of the emulsion. Is calculated in advance by heat transfer simulation, and the amount of induction heating necessary to bring the steel strip temperature to 80 ° C. at a position 25 mm from the edge portion is determined by the induction heating device. This is a method of induction heating the edge of the steel strip as a setup value.

  The 300 steel strips were each rolled by the above two methods, and the fracture occurrence rates during rolling were compared. The fracture occurrence rate in the first control method was 0.3%, whereas the fracture occurrence rate in the second method was 3.0%. Thereby, the fracture occurrence rate could be reduced to 1/10 by applying the first method, and the effectiveness of the present invention could be confirmed.

DESCRIPTION OF SYMBOLS 1 ... Pay-off reel 2 ... Steel strip 3 ... Welding machine 4 ... Looper 5 ... Induction heating device 6 ... Continuous rolling line 7 ... Tension reel 8a, 8b, 8c, 8d ... Tandem rolling mill 9 ... Emulsion spray nozzle 10 ... Air wiper 11a 11b, 11c, 11d, 11e ... Thickness gauges 12a, 12b, 12c, 12d ... Load cells 13a, 13b, 13c, 13d, 13e ... Plate speedometers 14a, 14b, 14c, 14d ... Roll peripheral speedometers 15 ... Steel strips Thermometer 16a, 16b, 16c, 16d ... Roll thermometer 18 ... Control device

Claims (6)

A method of induction heating an edge portion of a steel strip that is cold-rolled by a rolling mill with an induction heating device disposed on the entry side of the rolling mill,
After measuring the rolling strip inlet side thickness, rolling mill outlet thickness, rolling mill outlet speed and rolling mill outlet temperature of the steel strip, the temperature immediately before the rolling mill biting of the steel strip is set to the rolling mill inlet side. Obtained from each measured value of the thickness, the rolling mill delivery side thickness, the rolling mill delivery speed and the rolling mill delivery temperature, and the cold rolling conditions of the steel strip, the temperature immediately before the rolling mill biting is An induction heating method for a steel strip, characterized in that the edge of the steel strip is induction-heated by feedback-controlling the output of the induction heating device so as to be equal to or higher than the ductile / brittle transition temperature of the steel strip. A calorific value and a calorific value generated during cold rolling of the steel strip are calculated from the following formulas (1) and (2) to determine a temperature immediately before the rolling of the steel strip. The induction heating method of the steel strip according to claim 1.

3. The steel strip according to claim 2, wherein the temperature immediately before the rolling of the steel strip is calculated from the following formulas (3) and (4), and the output of the induction heating device is feedback-controlled. Induction heating method.

  The steel strip induction heating method according to claim 2 or 3, wherein the average rolling load is obtained from an output of a load cell attached to the rolling mill.   The induction heating method for a steel strip according to any one of claims 2 to 4, wherein the roll peripheral speed is obtained from an output of a roll peripheral speed meter attached to the rolling mill.   The induction heating method for a steel strip according to any one of claims 3 to 5, wherein the roll temperature is obtained from an output of a roll thermometer attached to the rolling mill.

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