JPS62164830A - Temperature controlling method for steel strip in continuous annealing line - Google Patents

Abstract

PURPOSE:To enable efficient and stable continuous annealing of a steel strip by adjusting the line length of a slow cooling zone while maintaining the line speed of the steel strip having a sheet thickness below the critical sheet thickness at a max. speed thereby controlling the end temp. of slow cooling at a specified value. CONSTITUTION:The critical sheet thickness of the steel strip to be annealed is determined from the max. line speed and the power limit of the heating furnace of a continuous annealing line for the steel strip. The line speed is maintained at the above-mentioned max.d speed in the stage of annealing the steel strip having the sheet thickness below the critical sheet thickness. The line length L of the slow cooling zone is adjusted at the same instant by moving a looper roll 1 of the slow cooling zone upward or downward. The end temp. of slow cooling is thereby controlled to the specified value and the continuous annealing of the steel strip is efficiently and stably executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a method for controlling the end temperature of slow cooling to a constant value by adjusting the line length of the slow cooling zone in a continuous annealing line for steel strips. It is something.

(b) Prior Art Regarding the heat pattern in continuous annealing, important control points are the start and end temperatures of heating or cooling, the soaking temperature, and the heating/cooling rate.

A typical heat pattern is shown in FIG. The steel strip is heated (to-t, ), soaked or recrystallized annealed (t+ -t
2) After 1, slow cooling (t2 ”s>, then rapid cooling (1, -
14), the process proceeds to overaging treatment (t<-t5), and the annealing is completed with final cooling (tsta).

Conventionally, in the slow cooling zone of a continuous annealing line, the slow cooling end temperature and slow cooling rate have been controlled by gas jet cooling or by providing gas jet cooling and a heater together. However, since it is originally desirable that the annealing rate after recrystallization annealing be as low as possible, control by gas jet cooling is not very preferable. Furthermore, the heater is also undesirable from the viewpoint of energy and cost.

(/-1 Problems to be Solved by the Invention The problems to be solved by the present invention are that in the slow cooling zone in a continuous annealing line, the cooling rate is not controlled but is left to cool, and the line length of the slow cooling zone is By making the temperature variable, it is possible to obtain a method of controlling the end temperature of slow cooling using the energy of the handle.

2) Means for solving the problem The steel strip temperature control method of the present invention is based on the maximum speed (V0) of the line and the heating furnace capacity limit in a continuous annealing line for the steel strip. (Ho)? f: to decide;
When annealing a steel strip having a thickness below the critical thickness, the temperature at which the slow cooling ends is controlled to a constant value by adjusting the line length of the slow cooling zone while maintaining the line speed at the maximum speed. This solves the above problems.

(, f1 effect) The effect of the slow cooling termination temperature control method of the present invention will be explained.

Generally, the cooling rate of a steel strip is inversely proportional to the plate thickness.

CR=- (1) where CR: cooling rate H: plate thickness a: constant At this time, the amount of temperature drop in the slow cooling zone is expressed by equation (2).

L T=OR-, = π Control... (2) However, T: Temperature drop in the slow cooling zone L: Line length of the slow cooling zone ■ Line speed In equation (2), the line length of the slow cooling zone If is constant, then
If the line speed V is constant, the temperature drop T is inversely proportional to the plate thickness H. Therefore, if the line length is made variable in proportion to the plate thickness H, the temperature drop T will be constant regardless of the plate thickness H.

L=1)-H・・・・・・(3) a・L ”” H7= −・・・・・・(4) ■ However, b=constant By the way, in actual continuous annealing, Fig. 1 As shown in , the line speed V is regulated by the peripheral rotational speed (V0) of the roll in the heating furnace in areas where the plate thickness H is thin, and the line speed V is regulated by the heating furnace capacity (inversely proportional to the plate thickness) in areas where the plate thickness H is thick. regulated by limits. If the rotation speed of the furnace rolls were to be used as a regulation for all plate thicknesses, the heating furnace would always operate at less than its maximum capacity, which would be inefficient. , the line speed difference becomes thicker (
For example, when the plate thickness is 0.4 to 1.6 mm, stable operation becomes difficult (speed difference of 4:1).

Therefore, in actual continuous annealing, as shown in FIG.
In the above case, the heating furnace capacity is restricted (v=dan).

In such a case, at a critical plate thickness H6 or more, the temperature drop ftT remains constant regardless of the plate thickness H even if the line length remains unchanged.

■=1L giant ・・・・・・(5) H-V
Vo-H6 However, below the critical plate thickness H6, unless the line length is variable in proportion to the plate thickness H, the temperature drop T will not be constant regardless of the plate thickness H. Therefore, by substituting equation (3) and v=vo'1 into equation (2), equation (7) is obtained.

Therefore, in the method of the present invention, it is first necessary to determine the critical plate thickness Ho. For a heating furnace in a normal continuous annealing line, the maximum roll rotation peripheral speed (vo) and the heating furnace capacity limit curve are determined from the set processing capacity of the material. Therefore, the critical plate thickness H6 can be determined from these data.

(f) Example In the method of the present invention, for example, as shown in FIG.
By raising and lowering the louver roll 1 in the slow cooling zone, the line length is changed.

Next, specific examples according to the method of the present invention are shown in Table 1 in comparison with the conventional method. In this example, V. =4 m/s
ea, Ho=Q, gm.

(G) Effect According to the method of the present invention, if the steel strip is within the critical thickness,
By adjusting the line length of the slow cooling zone, the slow cooling end temperature can be maintained constant.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between adult line speed and plate thickness. Figure 2 shows a typical continuous annealing heat pattern. FIG. 3 is a schematic explanatory diagram of an embodiment of the present invention. Patent applicant: Sumitomo Metal Industries, Ltd. (5 others)

Claims (1)

[Claims] In a continuous annealing line for steel strip, the maximum speed of the line (
The critical thickness of the steel strip (H_
0), when annealing a steel strip with a thickness below the critical thickness, the line speed is maintained at the maximum speed and the line length of the slow cooling zone is adjusted to determine the slow cooling end temperature. A steel strip temperature control method consisting of controlling the temperature to a constant value.