JPS6070128A - Method for controlling temperature of strip with continuous annealing furnace - Google Patents

Abstract

PURPOSE:To prevent temp. deviation of strips with a furnace consisting of a direct fire heating zone having excellent responsiveness and a radiant tube RT heating zone which does not have the excellent responsiveness by increasing preliminarily the temp. of the RT heating zone to a prescribed temp. CONSTITUTION:Plural strips with which heating load is different and which are required to increase the heating load in heating zones are passed through a continuous annealing furnace consisting of a direct fire heating zone 2 having excellent increasing and decreasing characteristics (responsiveness) of furnace temp. The temp. of the zone 3 is increased to the heating temp. which the strips require before the strips arrive at the annealing furnace. On the other hand, the temp. of the zone 2 is decreased by as much as the temp. is increased in the zone 3 so that the temp. of the strips now under annealing is maintained at the prescribed temp. The temp. of the zone 2 is then increased to the heating temp. that the strips require at the point of the time when the strips arrive at the annealing furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of a strip in a continuous annealing furnace.

During continuous annealing of the strip, in order to subject the strip to bright annealing that does not cause oxidation, a reducing gas is passed through the heating zone of the continuous annealing furnace and other necessary furnace zones, and as a heat source, It is known to use radiant tubes or electric heaters. Since the heating zone of such a continuous annealing furnace has a relatively small heat transfer coefficient to the strip (30-40 kA 7m" h°C), it is necessary to annealing with a longer heating zone in order to increase productivity. Also, because the heating zone has a large heat capacity, it is not possible to quickly raise or lower the furnace temperature, and therefore it takes time for the furnace temperature to reach the set value. Following the strip being processed, when the strip variety is changed and strips with significantly different dimensions or heat cycles are successively processed,
The strip temperature in the heating zone deviates from the appropriate value for a considerable amount of the strip after the product type change and the strip before the change.

Conventionally, in order to prevent plate temperature deviation, a joint material made of multiple coils was connected between the strips before and after changing the product type, and while the joint material passed through the heating zone, the furnace temperature of the heating zone was adjusted to the appropriate temperature. A method is adopted in which the value increases or decreases. However, this method wastes the joint material and is uneconomical. In addition, various methods have been proposed for connecting the joint material, controlling the strip temperature, and preventing the board temperature from deviating (in particular, Kaisho 5
1-86009, JP-A-52-28409, JP-A-52-28412 and JP-A-52-29410)
However, it was not necessarily sufficient in terms of controlling the production speed without reducing the production speed and without causing deviation in plate temperature.

In view of the above-mentioned current situation, the present invention provides a method for controlling the plate temperature of a strip in a continuous annealing furnace, which allows highly efficient annealing without causing deviation in plate temperature when changing the type of strip. In this continuous annealing furnace, the heating zone is composed of an open flame heating zone and a radiant tube heating zone, and multiple types of strips with different heating loads are continuously applied to the continuous annealing furnace, which requires an increase in the heating load in the heating zone. During continuous annealing throughout the process, before the strips with different heating loads reach the annealing furnace, the furnace temperature of the radiant tube heating zone is increased to the heating temperature required by the strips with different heating loads. , On the other hand, the furnace temperature of the direct fire heating zone is lowered by the furnace temperature increase of the radiant tube heating zone to maintain the plate temperature of the strip currently being annealed in the heating zone at a predetermined temperature; When the strips with different heating loads reach the annealing furnace, the furnace temperature of the direct-fired heating zone is increased to the temperature required by the IJ tube with the different heating loads, thus B) It is characterized in that the plate temperature in the heating zone of the U-tube is controlled to a predetermined temperature.

The method of this invention will be explained in detail below.

FIG. 1 shows an example of the configuration of a continuous annealing furnace used in the plate temperature control method of the present invention. In Figure 1, ■
is the heating zone, 2 is the direct heating zone, 3 is the RT heating zone (radiant tube heating zone), 4 is the RT soaking zone (radiant tube soaking zone), 5 is the cooling zone, 6 is the shelf zone, and 7 is the adjustment cooling zone. The radiant tube zone is divided into an RT heating zone 3 and an RT soaking zone 4, and the RT heating zone 3 and the direct flame heating zone 2 constitute the heating zone of the annealing furnace. Heating methods in the direct flame heating zone 2 include a non-oxidizing furnace method, a bright flame radiation tube method, and the like. Although Fig. 1 shows an example of the configuration of a vertical annealing furnace,
A similar heating zone configuration is used in the horizontal annealing furnace.

As shown in FIGS. 1 and 2, the strip L led to the continuous annealing furnace is preheated to a temperature ST in a preheating zone 1, then heated to ST in a direct heating zone 2, and then to RT. It is heated in the heating zone 3 to a temperature of ST2. The strip L is then soaked in an RT soaking zone 4 to a temperature of ST3, cooled in a cooling zone 5 to a temperature of ST, and then in a shelf zone 6 to a temperature of ST.
The shelf treatment is performed at a temperature of , and the ST
, and is cooled down to a temperature of .

In the above-mentioned continuous annealing furnace, strip plate temperature control when continuously annealing strips with different heating loads in the heating zone, that is, strips with different dimensions or heat cycles, is performed as follows. It will be done. That is, the heating zone is composed of the direct-fire heating zone 2, which is excellent in raising and lowering the furnace temperature (hereinafter referred to as responsiveness), and the RT heating zone 3, which is poor in the responsiveness of the furnace temperature. When it is necessary to reduce the heating load, as shown in Fig. 3, the plate temperature ST in the open heating zone is lowered to, for example, ST,', and the plate temperature ST2 in the RT heating zone is reduced to ST2'. Just do it.

On the other hand, when it is necessary to increase the heating load, there is a limit to the increase in plate temperature in the open heating zone because oxidation occurs in the strituzo, and as shown in Figure 3, there is a limit to the increase in plate temperature in the open heating zone. Board temperature S
Raise T1 to, for example, ST,' to increase the plate temperature S in the RT heating zone.
T2 cannot be set to ST2''.

Therefore, it is necessary to increase the plate temperature in the RT heating zone, which has poor responsiveness.

Therefore, in the present invention, the heating load is increased as follows.

(1) First, from the dimensions of the strip with different heating loads to be annealed, the heat cycle and the target line speed,
Target plate temperature STI in the direct flame heating zone of the next strip
and the target plate temperature ST2# in the RT heating zone, and further calculate the RT heating zone furnace temperature* T2 necessary to raise the strip to this plate temperature ST2'' and the time required to raise the temperature to the furnace temperature T-. Calculate the required time τ.

(2) Next, as shown in FIG. 4, the temperature is increased so that the furnace temperature T2 of the RT heating zone rises to the furnace temperature T2* by the time the next strip reaches the annealing furnace. Taking into account the required time τ, the furnace temperature T2 of the RT heating zone is set to the furnace temperature T2.
Set to . The RT heating zone furnace temperature T2 gradually increases with the passage of time τ and reaches the temperature T2* required for the next strip during time τ.

(3) On the other hand, in order to prevent the plate temperature ST2 of the strip currently being annealed in the RT heating zone from changing due to the increase in the RT heating zone furnace temperature T2, in response to the increase in the RT heating zone furnace temperature T2,
The furnace temperature of the direct flame heating zone is gradually lowered, and the plate temperature ST of the strip currently being annealed in the direct flame heating zone is gradually lowered.

(4) Next, when the next strip reaches the annealing furnace, as shown in Fig. 5, the plate temperature of the next strip in the direct-fired heating zone is changed from ST to the temperature specified in (1) above. If the plate temperature is increased to ST, ”, the plate temperature is increased to ST, ” in the open flame heating zone, and 5T2I in the RT heating zone.
This means that the heating load has been increased.

According to the above (1) to (4), strip temperature control in the direct fire heating zone and RT heating zone requires a strip that requires an increase in the furnace temperature and heating load of the RT heating zone in advance. Since the temperature is raised to the specified temperature, the next strip can be appropriately annealed, and the annealing of the strip before the product type change is not affected.

Therefore, when changing the type of strip to one that requires an increase in heating load, the strip can be annealed at the maximum line speed without causing temperature deviation between the strip before and after the type change.

FIG. 6 is a configuration example of a control system provided in a direct-fire heating zone and an RT heating zone of an annealing furnace for carrying out the present invention. In FIG. 6, 8 is a control device, and the control device 8 includes a direct flame heating zone outlet plate thermometer 9 provided at the outlet of the direct flame heating zone 2, and a direct flame heating zone outlet plate thermometer 9 provided in each heating zone of the RT heating zone 3. Furnace temperature measurement thermocouple 10. , 102...10n
A signal from the RT heating zone outlet plate thermometer 11 provided at the outlet of the RT heating zone 3 is inputted, and on the other hand, a signal from the control device 8 is input to the direct flame heating zone via a direct flame heating zone plate temperature controller 12'. Furnace temperature controller 1 for each RT heating zone to combustion device 12
3. '.

13□'..., 13n' to the combustion device 13. of each heating zone of the RT heating zone. , 13□..., 13n. The control device 8 constantly manages the dimensions, heat cycle, material, and line speed of the strip that is continuously passed, and performs the above-mentioned strip temperature control.

Since the present invention is configured as described above, when changing the type of strip to one that requires an increase in the heating load in the heating zone, the annealing process can be efficiently performed without causing deviation in plate temperature between the strip before and after the change. can do.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a continuous annealing furnace used in the sheet temperature control method of the present invention, FIG. 2 is a heat cycle diagram showing an example of the strip plate temperature in the annealing furnace of FIG. 1, and FIG.
A heat cycle diagram showing a method of reducing the heating load, FIG. 4 is an explanatory diagram showing the plate temperature control method of the present invention, and FIG.
FIG. 4 is a heat cycle diagram for the method, and FIG. 6 is a block diagram of a control system for implementing the method of the present invention. In the drawings, 2...Direct heating zone, 3...RT heating zone, 4...R
T isotropic zone. Applicant: Nippon Kokan Co., Ltd. Agent: Natsuo Shioya (and 2 others) Figure 1 4 Figure 2 Figure 3

Claims (1)

[Scope of Claims] A continuous annealing furnace in which the heating zone is composed of a direct flame heating zone and a radiant tube heating zone, and a plurality of types of strips with different heating loads, which require an increase in the heating load in the heating zone. During continuous annealing, the furnace temperature of the radiant tube heating zone is raised to the heating temperature required by the strips with different heating loads before the strips with different heating loads reach the annealing furnace. rise, while
The furnace temperature of the direct fire heating zone is lowered by the increase in furnace temperature of the radiant tube heating zone to maintain the plate temperature in the heating zone of the strip currently being annealed at a predetermined temperature, and then the heating load is reduced. When the different strips 1- reach the annealing furnace, the furnace temperature of the direct-fired heating zone is set to
A strip plate in a continuous annealing furnace characterized in that the temperature of the strip in the heating zone of the strip with different heating loads is increased to a required temperature, and thus the plate temperature in the heating zone of the strip with different heating loads is controlled to a predetermined temperature. Temperature control method.