JPS6220260B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for controlling the cooling rate and cooling end point temperature of a steel strip in a continuous annealing line. A jet cooler that jets inert gas is known as a device for cooling a steel strip that has been heated and soaked to a high temperature in a continuous steel strip annealing line to an arbitrary temperature under desired cooling conditions. Conventionally, methods for controlling the outlet temperature of the steel strip to the target temperature include either controlling the number of jet coolers or controlling the jet speed from the nozzle of the jet cooler blow-off box, that is, controlling the air volume by controlling the rotation speed of the blower motor. I was sitting there. The thickness of the material to be threaded in the furnace section of a continuous annealing furnace and the threading speed of the material generally have the relationship shown in FIG. 1st
Region A in the figure is suppressed at the maximum speed on the equipment, and the sheet passing speed v in region B is inversely proportional to the material sheet thickness h. However, the cooling rate R (℃/s) = T ₁ - T ₂ /t =
ΔT/t (T ₁ : Inlet side plate temperature, T ₂ : Outlet side plate temperature, t:
On the other hand, the total length L of the cooling zone is constant due to the equipment, and as shown in Fig. Since it is necessary to operate by changing the partial speed v, the passing time t of the steel strip changes depending on the plate thickness, and t=
The L/v relationship is understood. Therefore, the plate temperature difference ΔT to be cooled is constant because T ₁ and T ₂ are given as target temperatures. The target temperatures T ₁ and T ₂ mentioned here differ depending on the material of the steel strip to be obtained. From the above points, the relationship between the plate thickness h and the cooling rate R is as shown in FIG. That is, in region B, the thinner the plate thickness, the lower the cooling rate R.
It can be seen that the value becomes larger, and the thicker the plate, the smaller it becomes. However, in the conventional temperature control system, when controlling the target temperature _T2 and the cooling rate R, a problem as shown in FIG. 3 occurs, and in the end, it is impossible to control both at the same time. That is, when the injection velocity V _J of the jet cooler is increased, the cooling capacity increases and the outlet temperature reaches T ₃ , resulting in supercooling. (Fig. 3a), conversely, the cooling speed of plate thickness h ₀
If R ₀ is to be set to the cooling rate R ₁ with the plate thickness h ₁ , it is better to reduce the injection speed v _J of the jet cooler, but the cooling capacity will become smaller and the target temperature T ₃ will fall short of the desired temperature. (Fig. 3b) Also, the cooling rate of plate thickness h ₀ is R ₀
→ In the method of changing to R ₁ , if the threading speed v ₀ is reduced to v ₁ , the result shown in Figure 3c will be obtained, and if the cooling capacity of the jet cooler is reduced (the blowing speed or number of jet coolers is reduced). Although the target temperature T ₂ and cooling rate R ₁ can be obtained, a decrease in productivity becomes a problem. This invention aims to solve the above-mentioned problem, and the cooling rate and the cooling end point temperature are determined in advance according to the material of the steel strip to be threaded, and the cooling rate and the cooling end point temperature are determined in advance based on the cooling rate and the cooling end point temperature. It was developed based on the recognition that setting the number of jet coolers and the jetting speed is extremely effective in cooling the steel strip using inert gas jet coolers, and this is explained as follows. It will be understood. FIG. 4 shows the basic idea of this invention. 1 shows a conventional control method. 2 and 3 are the control methods of this invention. This invention makes the cooling rate constant regardless of the plate thickness for the same material by cooling as shown in 2 and 3, and the cooling length (the zone cooled by the jet cooler) Lengths) L ₂ and L ₃ correspond to the number of jet coolers that are proportional to the steel strip threading speed. In other words, since the number of jet coolers is set in proportion to the strip passing speed v, the cooling speed is uniquely determined, and in order to make the strip temperature at the outlet side of the cooling zone reach the target temperature, the number of jet coolers is The injection speed may be set and corrected. In the figure, a indicates the jet cooler length, and b indicates the natural cooling length. However, in the case of Figure 3a in Figure 3 above, the target temperature is supercooled to T ₃ , but by reducing the number of jet coolers, the cooling capacity can be kept constant and the target temperature can be reduced. The case shown in FIG. 3b can be solved by increasing the number of jet coolers. Therefore, the basic idea of this invention is to reduce the injection speed of the jet cooler when the steel strip threading speed is high;
At the same time, it is intended to increase the number of jet coolers, and when the sheet passing speed is slow, the target sheet temperature and cooling rate are simultaneously controlled by increasing the jetting speed and reducing the number of jet coolers. . Control of the injection speed includes, for example, controlling the rotation speed of a blower motor, but is not limited thereto. Next, embodiments of the invention will be described. FIG. 5 is an overall explanatory diagram of the present invention, and FIG. 6 is a detailed diagram of the main part. In the figure, a steel strip 1 is introduced into a cooling furnace 7 via hearth rolls 4 and transferred to the next process via hearth rolls 6. The cooling furnace 7 is provided with a plate thermometer 2 on the inlet side to detect the actual inlet plate temperature, and a plate thermometer 3 on the outlet side to detect the actual outlet plate temperature. The cooling furnace 7 has a built-in jet cooler group 5, and the jet cooler has a blower 13 attached to a blow box 15 that injects cooled inert gas, and the blower 13 has a variable rotation speed motor 14, and A duct 12, a heat exchanger 11, and a gas inlet 10 are provided. Further, a nozzle 16 is carved in the entire area of the blowout box 15 facing the steel strip 1. Generally, in the production of cold-rolled steel sheets with good workability by short-term continuous annealing, the grain size of the steel sheet is optimized and solid solution C is reduced, and the heat cycle for this purpose must be strictly controlled. In this invention, in order to achieve the above-mentioned object, the cooling rate and the target cooling end point temperature are determined in advance from the material of the steel strip to be threaded. Then, by giving a proportional relationship to the threading speed and the number of jet coolers,
Blower air volume (air volume) as cooling speed control
Control is used at the same time. When the temperature difference ΔT' between the actual outlet plate temperature T ₂ ' measured by the thermometer 3 and the target outlet plate temperature T ₂ is calculated, the injection speed (air volume) of the jet cooler 5 is corrected and controlled. When changing from regular operation for cooling thin steel strips to cooling thicker steel strips, the cooling rate can be maintained constant by reducing the number of jet coolers and increasing the amount of gas blown out. It is possible. Thus, the desired cooling rate is always maintained and any target temperature can be managed. Next, Table 1 shows an example in which a thin plate with a thickness of 1.0 mm and made of ordinary steel was controlled at a cooling rate of 35°C/s, compared with the conventional method.

[Table] The mechanical properties at this time were as shown in Table 2 below.

【expressed.
That is, the method of the present invention showed better workability than the conventional method.

[Brief explanation of the drawing]

Figure 1 is a diagram of the threading speed according to plate thickness, Figure 2 is a diagram of cooling rate according to plate thickness, Figure 3 is a diagram of the relationship between cooling time and ΔT, Figure 4 is a diagram of the relationship between cooling length and plate temperature,
FIG. 5 is an explanatory diagram of the method of the present invention, and FIG. 6 is an explanatory diagram of the main part of the method of the present invention. 1... Steel strip, 2, 3... Plate thermometer, 5... Jet cooler group, 13... Blower.

Claims (1)

[Claims] 1. In a continuous annealing line that jets inert gas to cool the high-temperature steel strip after heating and soaking,
The cooling rate and cooling end point temperature are determined in advance based on the material of the steel strip to be threaded, and the number of jet coolers and injection speed are set based on the cooling rate and cooling end point temperature. A method for controlling the cooling rate and cooling end point temperature of a steel strip, characterized in that the injection speed of the jet cooler is modified and controlled according to the temperature difference between the strip temperature and a target temperature.