JP3369241B2 - Extraction billet temperature control method for rotary hearth heating furnace - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the temperature of an extracted billet in a rotary hearth heating furnace of a seamless steel pipe production line. 2. Description of the Related Art In the production of a seamless steel pipe by an inclined rolling method, generally, first, a billet is charged into a heating furnace, heated to a temperature at which the pipe can be produced, and then piercer, which is an inclined roll punch, is used. After manufacturing the hollow shell, elongation rolling in the elongation mill,
Finally, the diameter is reduced to the product size by a constant diameter rolling mill. In a billet heating process of a seamless steel pipe production line, a rotary hearth heating furnace is generally widely used. In the process of manufacturing the seamless steel pipe, if the billet has a heat bias in the circumferential direction at the time of piercing and rolling by a piercer, a difference in deformation resistance due to a temperature difference in the circumferential direction causes a difference in deformation resistance between the high temperature part and the low temperature part, resulting in a circumferential deviation. Meat is generated, and the wall thickness of the hollow shell after perforation becomes uneven and remains as uneven thickness of the final product.
Since the billet circumferential heat deflection during piercing and rolling by the piercer is determined at the time of heating furnace extraction, in order to keep the circumferential wall thickness unevenness within the target range, the billet circumferential heat deflection at the time of heating furnace extraction is suppressed within the target range. It is necessary to. [0003] In a rotary hearth heating furnace, the hearth from which the billet has been extracted in the final extraction zone rotates to the charging inlet, and the billet is charged and mounted on the hearth. However, the hearth temperature at the time of charging the billet varies greatly depending on the operating conditions. That is, the hearth temperature at the time of billet charging is inevitably low when extracting low-temperature materials, and the hearth temperature at the time of billet charging is high when heating high-temperature materials. Furthermore, between the billet extraction port and the charging port is a low temperature zone because there is no burner, and if the billet extraction is stopped for a long time in the low temperature zone,
The hearth is considerably lower in temperature than the hearth in other locations. As a result, the billet temperature distribution during heating is greatly affected by the hearth temperature at the time of billet charging. However, in the past, the hearth temperature at the time of charging the billet was constant or the hearth temperature on the billet extraction side, and in particular, when operating irregularly, the billet was constantly changed due to the influence of the hearth temperature. There has been a problem in that the accuracy of temperature calculation is reduced, and the accuracy of extraction temperature prediction is reduced, resulting in deterioration of control accuracy. As a method of controlling the billet temperature at the time of extraction of the rotary hearth heating furnace for this purpose, a cross section temperature distribution of a round billet extracted from the heating furnace is predicted and calculated, and the maximum temperature deviation obtained from the calculation result is Temperature deviation of round billet-If the thickness deviation occurrence warning standard or more obtained in advance based on the thickness deviation rate correlation, change the heating condition, and, with the deviation deviation occurrence reference value larger than the reference value or more In such a case, a method has been proposed in which extraction or perforation of round billets from a heating furnace is interrupted (Japanese Patent Publication No. 60-12129). [0005] The above-mentioned Japanese Patent Publication No. Sho 60-12
The method disclosed in Japanese Patent No. 129 calculates the hearth and billet temperatures every moment from the furnace temperature of each zone in the furnace, the steel type and diameter of the billet, and the billet interval in the furnace, and predicts the maximum billet temperature deviation at the time of extraction. It does not solve the problem of the decrease in billet temperature calculation accuracy due to the hearth temperature at the time of charging the billet. SUMMARY OF THE INVENTION It is an object of the present invention to prevent a decrease in billet temperature calculation accuracy due to a hearth temperature at the time of billet loading in the rotary hearth heating furnace, improve the heating control accuracy, and improve the peripheral temperature during piercing and rolling. It is an object of the present invention to provide a method for controlling the temperature of an extracted billet of a rotary hearth heating furnace capable of reducing wall thickness deviation in the direction. [0007] The present inventors have conducted various tests and studies to solve the above problems. As a result, the hearth is divided into a plurality of points in the circumferential direction, the thickness direction and / or the radial direction, and the hearth temperature at each point is continuously calculated. The billet temperature is calculated as the hearth temperature at the time of charging the billet, and the set furnace temperature of each zone is calculated based on the result, whereby the billet temperature due to the hearth temperature at the time of billet charging is calculated. The inventors of the present invention have found that a decrease in the calculation accuracy can be significantly suppressed, and have reached the present invention. That is, the present invention provides a rotating hearth,
Circuit divided into a plurality of zones having a heater and a thermocouple.
By controlling the temperature of each zone of the BOF
Ri, in the extraction billet temperature control method of a rotary hearth type heating furnace to control the billet temperature, the heating furnace results furnace in each zone
Based on the temperature and the furnace hearth position information
The hearth temperature in the billet heating furnace charging position and the charged billet temperature are determined by continuously calculating the hearth temperature in the billet , and the determined hearth temperature and billet temperature in the heating furnace charging position are determined.
A method of controlling the temperature of an extracted billet of a rotary hearth heating furnace, wherein a set furnace temperature of each zone of the rotary hearth heating furnace is arithmetically controlled based on the temperature of the furnace. [0009] [act] In this invention, the actual furnace of the pressurized hot furnace zones
Based on the temperature and the furnace hearth position information
The hearth temperature in the billet heating furnace charging position and the charged billet temperature are determined by continuously calculating the hearth temperature in the billet , and the determined hearth temperature and billet temperature in the heating furnace charging position are determined.
Based on the temperature, the set furnace temperature of each zone of the rotary hearth heating furnace is arithmetically controlled. Specifically, the hearth of the rotary hearth heating furnace is divided into a plurality of points in the circumferential direction, thickness direction and / or radial direction of the heating furnace, and the hearth temperature at each point is changed from the start of the operation to the rotary hearth type heating furnace. The calculation is continuously performed based on the actual furnace temperature of each zone of the heating furnace and the in-furnace position information of each point of the hearth. Based on the result, the billet temperature was calculated as the hearth temperature at the nearest position when charging the billet as the hearth temperature at the time of charging the billet.From the result, the furnace temperature set for each zone of the rotary hearth heating furnace was calculated. Since calculation and control are performed, it is possible to eliminate a decrease in billet temperature calculation accuracy due to the hearth temperature at the time of billet charging. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention, FIG. 2 is an explanatory diagram of a piercing and rolling state in a piercer, FIG. 3 is a correlation diagram showing a correlation between circumferential heat deviation of a billet and a wall thickness deviation after a piercer, FIG. 4 shows the difference in heating control between the case where the method of the present invention is used when the hearth temperature at the time of billet charging is considerably lower than usual and the case of the conventional method where the hearth temperature at the time of billet charging is constant. (A) is a graph showing a relationship between each zone of the heating furnace and the furnace temperature, and (B) is a graph showing a relationship between each zone of the heating furnace and the heat deflection in the billet circumferential direction. As shown in FIG. 1, a billet 4 is charged onto a hearth 3 in a rotary hearth heating furnace 2 by a charging machine 1. In the rotary hearth heating furnace 2, a plurality of billets 4 are usually heated simultaneously on the hearth 3, and are heated while moving through the heating furnace as the hearth 3 rotates. The billets 4 heated to a predetermined temperature in the heating furnace are extracted one by one from the heating furnace by the extractor 5. Thereafter, as shown in FIG. 2, the billet 4 is pierced and rolled by a piercer using a roll 6 and a plug 7 and a guide shoe (not shown).
It becomes. The heating furnace 2 has a thermocouple (not shown) attached to each zone. The heating furnace 2 is also provided with a pulse generator (not shown) for tracking the positions of the hearth and the billet in the furnace. The arithmetic and control unit 9 inputs the actual temperature of each zone of the rotary hearth heating furnace 2 from the thermocouples of each zone and the tracking information of the hearth 3 and billet 4 from the pulse generator every moment. At the same time, information necessary for temperature calculation such as steel type, dimensions, furnace billet interval, etc. for each billet is input from a host computer (not shown). The arithmetic and control unit 9 divides the hearth 3 of the rotary hearth heating furnace 2 into meshes in the circumferential direction, the thickness direction, and / or the radial direction of the heating furnace. The hearth 3 initial temperature is determined on the assumption that it is room temperature before the start of operation. Thereafter, the arithmetic and control unit 9 calculates the hearth temperature of each mesh based on the actual furnace temperature input from the thermocouple of each zone from the start of operation and the position information of each point of the hearth 3 input from the pulse generator, Operate continuously. The calculation of the hearth temperature by the arithmetic and control unit 9 is as follows.
For example, in the case of a two-dimensional case in the traveling direction and the thickness direction, it is obtained by solving the following equations (1) to (3). ## EQU1 ## Where C: specific heat of the hearth ρ: density of the hearth T: temperature of the hearth t: time X, Y: coordinate axes of the hearth (progression direction, thickness direction) λ: thermal conductivity Fc of the hearth : View factor Fb for the upper wall of the hearth with respect to the furnace wall Fb: View factor Φc for the billet on the upper surface of the hearth Φc: Overall heat absorption rate between the upper surface of the hearth and the furnace wall φb: Overall heat absorption rate between the upper surface of the hearth and the billet Φa: Furnace Overall heat absorption rate between the lower floor and the atmosphere Tb: Billet surface temperature Tc: Actual furnace wall temperature in the billet existing zone Ta: Atmospheric temperature Tu: Upper hearth surface temperature Tl: Lower hearth surface temperature n: Normal direction of the hearth surface However, when calculating the hearth temperature, a thermocouple may be embedded at each point of the hearth, and the calculated temperature at each point of the hearth may be corrected based on the actually measured value. Is obtained. Based on the result, billet temperature calculation is performed using the temperature of the nearest hearth at the time of charging the billet as the hearth temperature at the time of charging. The arithmetic and control unit 9 calculates the set furnace temperature of each zone of the rotary hearth heating furnace using the billet temperature calculation result as follows. Various methods have conventionally been proposed for calculating the set furnace temperature. For example, the method can be obtained by the following method. That is, the calculation of the set furnace temperature satisfies the target extraction temperature condition (Equation (4)) and the target extraction circumferential temperature deviation condition (Equation (5)) to lower the furnace butt temperature and reduce heat loss due to exhaust gas. Evaluation function (expression (6))
Is determined by a linear programming method. The billet target extraction temperature deviation in the circumferential direction has the following physical meaning. In other words, FIG. 3 is a diagram showing the correlation between the billet in the circumferential direction and the vertical axis representing the wall thickness deviation after piercer rolling on the horizontal axis. From FIG. 3, it can be seen that in order to keep the thickness deviation after the piercing within a certain target range, it is necessary to make the circumferential heat deviation of the billet within a certain target. ## EQU2 ## Tmm: Predicted extracted billet average temperature at current furnace temperature Tsm: Predicted extracted billet circumferentially deviated heat at current furnace temperature Tmo: Target extracted billet average temperature Tso: Target extracted billet circumferential deflected Ti: i zone Current furnace temperature Xi: i-zone setting furnace temperature αi: influence coefficient on billet average temperature at the time of extraction of i-zone furnace temperature change βi: influence coefficient on billet circumferential heat deflection at the time of extraction of i-zone furnace temperature change Wi: per zone FIG. 4 shows that in a rotary hearth heating furnace composed of four zones, the temperature control by the method of the present invention is performed when the hearth temperature at the time of billet charging is considerably lower than usual. This is a comparison of the billet temperature control results obtained when the temperature control is performed by the conventional method (when the hearth temperature at the time of charging the billet is constant). As shown in FIGS. 4A and 4B, in the case of the conventional method indicated by the broken line, when the billet temperature fluctuates greatly, a billet temperature calculation error occurs and the control accuracy deteriorates. In the case of the method of the present invention shown by the solid line, accurate control can be performed even when the hearth temperature fluctuates when charging the billet. As described above, according to the method of the present invention, in the rotary hearth heating furnace, the billet temperature calculation accuracy during heating is improved by continuously calculating the hearth temperature. As a result, the accuracy of heating control can be improved, and uneven wall thickness in the circumferential direction during pipe production can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an embodiment of the method of the present invention. FIG. 2 is an explanatory view of a piercing and rolling state in a piercer. FIG. 3 is a correlation diagram showing a correlation between circumferential heat deviation of a billet and a wall thickness deviation after piercing. FIG. 4 shows the difference in heating control between the case where the method of the present invention is used when the hearth temperature is considerably lower than usual and the case of the conventional method where the hearth temperature at the time of billet charging is constant. ) Is a graph showing the relationship between heating furnace zones and furnace temperature, (B)
The figure is a graph showing the relationship between each zone of the heating furnace and the heat deflection in the billet circumferential direction. [Description of Signs] 1 Billet loading machine 2 Rotary hearth heating furnace 3 Hearth 4 Billet 5 Billet extractor 6 Rolling roll 7 Plug 8 Hollow shell 9 Computing controller

Claims (1)

(57) [Claims 1] A rotating hearth, a burner and a thermocouple
Each of the rotary hearth heating furnaces divided into multiple zones having
Control billet temperature by controlling zone temperature
In the method of controlling the temperature of the extracted billet of the rotary hearth heating furnace to be controlled, the actual furnace temperature and furnace hearth
Based on the placement information, the hearth temperature in each of the zones is continuously calculated to calculate the hearth temperature at the billet heating furnace charging position .
And determining the charged billet temperature , and based on the determined hearth temperature and billet temperature of the heating furnace charging position, arithmetically controls the set furnace temperature of each zone of the rotary hearth heating furnace. Method for controlling the temperature of the extracted billet of a rotating hearth heating furnace.