JPS6257697B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field Heat treatment of metal strips, especially cold strips, in particular guiding the winding run of the strips during continuous cooling or heating of the strips in a continuous annealing furnace. Both of these relate to the field of technology for rolls that are responsible for transferring heat between winding contacts.

Problems Cold strip continuous heat treatment furnaces, so-called
Conventionally, the cooling system used in CAL generally uses a gas jet system.

However, this cooling gas circulation fan requires a large capacity of about 5000KW for a monthly production of about 50,000 tons.

On the other hand, the roll cooling method, in which refrigerant is introduced and circulated inside the roll, can be operated with approximately 1/10 the power, so it is becoming the mainstream cooling method for strips, replacing the gas jet method mentioned above. be.

This type of roll generally has a hollow roll body,
By conducting a heat medium for cooling or heating, that is, a refrigerant or a heat medium (hereinafter collectively referred to as a heat medium), into the cavity inside the shell, heat is transferred between the metal strip that is wound around the roll shell and in contact with it. Make giving and receiving take place.

For cooling the metal strip, depending on the temperature, e.g. is used as a refrigerant, while for heating, a heating medium such as Dowsome (trade name) is used.

In any of the above cases, when a liquid is used as a heat medium, when the roll rotation speed increases beyond a certain limit, the heat transfer coefficient that exhibits an almost linear relationship with the metal strip with respect to the rotation speed increases. , suddenly and sharply decreases, and therefore, at roll rotational speeds that include such a rapid change range, the necessary function of the heat conducting roll is lost and it can no longer be used to control the cooling or heating of the metal strip.

OBJECT OF THE INVENTION To provide an advantageous solution to the above-mentioned mismatch in the heat transfer coefficient depending on the rotational speed of the heat transfer roll, that is, to provide an advantageous solution to the heat transfer coefficient inconsistency depending on the rotational speed of the heat transfer roll, that is, to provide an advantageous solution to the heat transfer behavior between the roll and the metal strip during the winding contact. It is the purpose of this invention to eliminate the influence.

Structure of the Invention The above object can be easily achieved by applying a concept based on the following points, as will be described in more detail later.

The roll body is a heat conductive roll for a metal strip that has a hollow roll body, conducts a heat medium for cooling or heating inside the body, and transfers heat between the roll body and the metal strip wound around the outer circumference of the roll body. It is necessary that the following relationship be satisfied between the inner diameter d of the cavity in the shell and the circumferential velocity V of the inner surface of the cavity.

Note d＞V×2.25 d: Inner diameter of the inner cavity (mm) V: Circumferential speed of the inner surface of the inner cavity (m/min) A heat transfer roll that satisfies the above relationship has a metal strip on the inner diameter of the inner cavity. Within the range of rotation speed according to the threading speed according to the outer diameter plus the wall thickness that provides the strength necessary for winding rotation, the heat transfer coefficient between the strip pull and the roll has an approximately linear relationship with respect to the rotation speed. It will be maintained.

Now, Fig. 1 shows the cross section of the heat conductive roll, and in the figure 1
2 is a roll cylinder, 2 is a strip, 3 is a rotary joint, and 4 is a heating medium. As shown in the figure, the heating medium 4 is conducted into the inside of the roll cylinder 1. There is no need to explain the exchange of heat between the roll cylinder 1 and the strip.

However, the threading speed of strip 2, for example, in the case of CAL mentioned at the beginning, is determined by its production capacity, and therefore the number of rotations of the heat transfer roll corresponding to this threading speed is determined by the heat transfer between the strip and the roll. The effect on the rate is a fundamental consideration in controlling the cooling or heating rate of the strip.

Therefore, focusing on the relative flow between the heating medium in the internal cavity of the heat conducting roll and the cavity, we considered the Raynozzle number R _e shown in the following equation, and calculated the effect this has on the heat transfer coefficient between the strip roll and the strip roll. An example of the summarized experimental results is shown in Figure 2.

Re=V・L/ν...(1) V: Circumferential velocity of the inner surface of the cavity in the cylinder (m/min) L: 1/2πd, 〓d: Inside diameter of the cavity (mm) ν: Kinematic viscosity coefficient of the heating medium, In Figure 2, the Raynozzle number at which the almost linear relationship of Re-α breaks down and the heat transfer coefficient α suddenly decreases corresponds to the so-called critical Raynozzle number Re _cr . This data shows that since the inner diameter d is fixed and therefore L=constant condition is followed, an increase in Re up to Re _cr indicates an increase in V, that is, the roll rotation speed, and a rotation exceeding V corresponding to Re _cr In some cases, the heat conductive roll loses its function.

Regarding the results of the investigation into the causes of such a sudden decrease in the heat transfer coefficient α, as shown in FIG. When the rolls are held at the same speed, even when the roll rotation speed is low, the heat medium adheres to the inner wall of the cavity due to its viscosity, so the liquid level is slightly tilted, and in this state, the relative velocity between it and the inner wall of the cavity is , increases according to the rotation speed, and when the increase reaches a certain limit, the heat medium forms a rim-like adhesion around the entire circumference of the inner wall of the cavity, as shown in Figure b, and begins to rotate together with the roll. At that point, the above relative velocity suddenly decreases.

Figure 4 summarizes some of the results of repeated experiments with various internal diameters d of the internal cavity when water is used as a heat medium (temperature range 30 to 70°C) regarding this tendency. In addition, it was found that the larger the inner diameter d, the higher the value of Re _cr . Furthermore, molten salt NaNO ₃ ―KNO ₃ ―NaNO ₂ is used as a heat medium.
Figure 5 shows the results of a similar experiment using (7-53-40wt%). (Temperature range: 200 to 400°C) Also in FIG. 5, it was found that the larger the inner diameter d, the higher the value of Re _cr .

On the other hand, by organizing these experimental data with respect to Re _cr , we found that the limit for the occurrence of a sudden decrease in the heat transfer coefficient α, which depends on the inner diameter d of the internal cavity of the hollow roll and the circumferential velocity V of the inner surface of the cavity, is as shown in Figure 6. We have found that this can be expressed in Both water and molten salt are shown in FIG. 6, and almost the same trends were shown. In the figure, the area above the straight line indicated by d = V x 2.25 belongs to the region where the heat transfer coefficient does not suddenly decrease, and therefore, as already mentioned,
By operating a heat conductive roll having an internal cavity larger than the value of the inner diameter d calculated using the above formula at a rotational speed equal to or lower than the circumferential speed V of the inner surface of the cavity, the metal strip using the heat conductive roll can be cooled or This means that heating control can be performed appropriately.

Effects of the Invention According to the present invention, when the passing speed of the metal strip is determined by the capacity of the continuous heat treatment equipment, the strip can be passed through the strip at an operating speed equal to or lower than the running speed and at a rotational speed of the heat conductive roll determined accordingly. Since a substantially linear relationship between the heat transfer coefficients between the rolls can be ensured, it is convenient for controlling the cooling or heating of the metal strip.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the heat transfer roll, Figure 2 is a graph showing the effect of the Ray nozzle number on the heat transfer coefficient according to the flow conditions of the heat medium in the internal cavity of the hollow roll body, and Figures 3a and b are graphs showing the effect of the Raynozzle number on the heat transfer coefficient. FIG. 4 is a diagram illustrating the flow behavior of the heating medium in the inner cavity depending on the rotation speed, and FIG. FIG. 5 is a graph for the case of a heat medium; molten salt, and FIG. 6 is a graph showing the relationship between the inner diameter of the internal cavity and the inner circumferential velocity, which affects the sudden change in heat transfer coefficient. 1...Hollow roll body, 2...Metal strip,
4...Heating medium.

Claims (1)

[Scope of Claims] 1. For metal strips that have a hollow roll body, conduct a heating medium for cooling or heating inside the body, and transfer heat between the metal strip and the metal strip wound around the outer circumference of the roll body. A heat conductive roll for metal strip, characterized in that the inner diameter d of the internal cavity of the roll body and the circumferential speed V of the inner surface of the cavity satisfy the following relationship. d＞V×2.25 d: Inner diameter of the cavity in the shell (mm) V: Circumferential speed of the inner surface of the cavity in the shell (m/min)