JPS59166629A - Cooling method of steel strip - Google Patents

Abstract

PURPOSE:To uniformly cool a steel strip in the width direction thereof in good cooling efficiency, by keeping the temp. of atmospheric gas directly before being rolled into the gap between a cooling roll and the steel strip, higher than the average value of the temp. of the steel strip prior to cooling and the surface temp. of the cooling temp. CONSTITUTION:A steel strip 1 is run while being wound around internally cooled roll groups 2a, 2b, 2c, 2d, 2e. In this case, the entire atmospheric temp. of a cooling chamber 3 is kept higher than the average value of the temp. of the steel strip 1 prior to cooling and the surface temp. of each cooling roll. In addition, high temp. gases are injected from flat nozzles 4a, 4b, 4c, 4d, 4e arranged to the wedge shaped spaces between the steel strip 1 and the rolls 2a, 2b, 2c, 2d, 2e. By this constitution, the temp. of the atmospheric gas directly before being rolled into the gaps of the steel strip 1 and each roll is made higher than the average value of the temp. of the steel strip 1 and the surface temp. of each roll and the close contact of the steel strip to each roll is made well.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling a steel strip using internally cooled rolls by improving the degree of adhesion of the steel strip to the rolls and obtaining uniform cooling in a direction of 11 m.

Methods for cooling high-temperature steel strips in continuous annealing furnaces, etc. include a gas jet method that sprays gas, a mist cooling method that sprays a gas-liquid mixture mist, a water spray method, a method that immerses the steel strip in water, and a roll that is internally cooled. There is a roll cooling method in which a steel strip is wrapped around the material to cool it. Among these methods, the gas jet method has the disadvantage that the energy consumption of the blower is large. In addition, in methods where water and steel strip come into direct contact, there are problems such as the formation of an oxide film on the surface of the steel strip due to the presence of oxygen in the water, which causes discoloration. In this case, post-treatment equipment is required, which increases equipment costs. There are major drawbacks. In contrast to these methods, the roll cooling method is being adopted for continuous annealing φ, etc. because it has the characteristics of low energy consumption and equipment cost, and good surface quality of the copper strip.

However, in the roll cooling method, cooling tends to be uneven in the width direction, and therefore, there is a problem that flatness is likely to deteriorate due to uneven cooling, especially in thin objects. The inventors conducted various studies on this problem and found that the lifting of the copper strip due to thermal expansion of the gas in the gap between the roll and the steel strip was one of the causes of uneven cooling, and the present invention was developed. reached. The contents will be explained below.

If we look at the contact surface between the steel strip and the cooling roll microscopically, the contact surface pressure generated by the tension of the steel strip is extremely small, so the contact is only at a small portion of the fine irregularities on the surface, as shown in Figure 1. do not have. Here, the true contact area S1 and the apparent contact area S. The ratio between .

31 P Where, P: Contact pressure (kg/Ryu2) H: Hardness of the softer material kg/llll2) When the steel strip is wrapped around a roll (the wrapping angle is arbitrary), the contact pressure P is as follows: It is determined by the formula.

σ t P= −(kg/mm2) (21 where σ
; Tensile stress (kg/Ryu2) t: Plate thickness (IIIl) R: Roll radius (fin) To give a standard calculation example, for example, σ-1kg/Ryu2,
If t = 0.4 degrees, R = 400 fins, P = 0.0
01kg / III 2, that is, approximately 0.1 atmosphere,
Assuming high temperature and assuming H = 20 kg / 2, =
0.00005 (0,005%). That is, possible.
is extremely small, and it can be seen that even if the conditions change and so changes, most of the apparent contact area remains non-contact. In this non-contact area, atmospheric gas is present when the copper strip is wound on a roll. Therefore, the temperature Tq of this gas is equal to the temperature of the atmospheric gas immediately before it is sandwiched between the roll and the steel strip, and immediately after it is sandwiched between the steel strip and the roll (for a very short time). ) is also approximately equal to the temperature of the atmospheric gas. After being sandwiched between the steel strip and the rolls, the steel strip is heated by the steel strip and cooled by the rolls, and in a short period of time reaches a value T that is approximately - the average value of the steel strip temperature - and the roll surface temperature TR. If we look at it in more detail, the temperature in the gap close to the steel strip is close to Ts, and the temperature close to the roll is close to Doox, but this temperature distribution is not suitable for the phenomenon explained below. Since it does not have much effect, below we will consider the average value of the gas temperature in the gap as 7.) In this way, the temperature changes from 1'6 to T1 after being sandwiched between the steel strip and the rolls, so the gas temperature changes from 1'6 to T1. The pressure &/or volume W of “changes.” Considering the gas as a perfect gas, the change at this time follows the following equation.

However, the unit of Tq is ("c").

Here, the phenomenon in the case of the conventional roll cooling method will be examined using calculation examples. In the conventional roll cooling method, the ambient temperature To in the cooling chamber is considerably lower than the steel strip temperature π. Here, we will consider the case of the primary cooling zone of a continuous annealing furnace for cold-rolled steel sheets.
=150°C. Also, Ts=700'c,
TR=100°C, and the atmospheric pressure is 1 atm. The tension σ, the plate thickness t, and the roll radius R are the same as in the calculation example described above. Therefore, the surface pressure P generated by tension is 0
．． It is 1 atm. According to the above theory, T1 and therefore l will increase from 150°C to 400°C, and from equation (3), the value of &■ is -i-7-a-=
It becomes 1.6 times. Therefore, if the volume of the gas does not change, the pressure will increase by 1.6 times to /J1.6 atm. However, the force trying to press the steel strip against the roll is 1.1 atm, which is the sum of the outside atmospheric pressure of 1 atm and the surface pressure due to the tension of 0.1 atm, which is 1.1 atm.
．． Less than 6 atmospheres and unbalanced.

Therefore, in reality, the volume of the gas increases by about 1.45 times, so that PcTV◇ becomes 1.6 times and h becomes 1.1 atm.

At this time, the volume of the gas increases by 1.45 times, so the steel strip separates from the roll and floats.

From the above calculations, it is considered that in the conventional method, the copper strip often lifts due to thermal expansion of the gas. Furthermore, it is thought that the degree of floating differs in the width direction because the expanded gas gradually escapes from the surrounding gaps.

As analyzed above, in the conventional technology, there was a problem that the adhesion between the steel strip and the cooling roll was insufficient, resulting in lower cooling efficiency and uneven cooling in the width direction of the copper strip. .

An object of the present invention is to solve the problems of the prior art and to provide a method for cooling a steel strip with good cooling efficiency and uniformity in the width direction.

According to the present invention, in a method of cooling a steel strip by continuously bringing the steel strip into contact with the surface of a cooling roll, the temperature of the atmospheric gas immediately before being drawn into the gap between the cooling roll and the steel strip is cooled. There is provided a method for cooling a steel strip, characterized in that the temperature of the steel strip is set to be higher than the average value of the previous steel strip temperature and the surface temperature of the cooling roll.

The method of the present invention can be achieved by increasing the temperature of the entire atmospheric gas in the cooling chamber housing the cooling roll so that the temperature of the copper strip before cooling is higher than the average value of the surface temperature of the cooling roll.
Alternatively, gas is blown into the wedge-shaped space between the steel strip and the roll just before the steel strip is wound around the cooling roll, and the temperature of the gas is made higher than the average value of the temperature of the copper strip before cooling and the surface temperature of the cooling roll. It can also be achieved by doing.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

FIG. 2 is a schematic diagram of a roll chiller, the entire vessel of which is placed within a cooling chamber, for carrying out the method of the invention.

Steel strip 1 has internally cooled roll groups 2a, 2b, 2c,
It runs wrapped around 2d and 2e. The entire cooling device is placed in a cooling chamber 3, and the atmospheric gas is adjusted.

According to the present invention, the temperature of the entire atmosphere in the cooling chamber 3 may be maintained higher than the average temperature of the temperature of the steel strip 1 before cooling and the surface temperature of the cooling roll 2a, or as shown in FIG. Flat nozzles 4a, 4 arranged in wedge-shaped spaces between the cooling rolls 2a, 2b, 2c, 2d, and 2e.
High temperature gas may be injected in steps b, 4c, 4d, and 4e.

According to the method of the invention, the ambient temperature T in the cooling chamber. 400
The phenomenon when the temperature is 700°C or 700°C will be theoretically analyzed in the same manner as described above.

When To is 400'c, there is no change in gas temperature, so the gas in the gap is at 1 atm, and the external pressure is 1.1
Of the atmospheric pressure, the gas in the gap receives 1 atm, and the roll receives 0.1 atm in the direct contact area. More T. If the temperature is higher than 400℃, for example, Ts7
00″C, then by the same calculation as above, Pa Ve
If the value of is in the gap: o: even i = 0.7 times.

Therefore, if we consider that ■ does not change, & becomes 0.7 times that is, 0.7 atm, and the gas in the gap receives 0.7 atm out of the 1.1 atm pressure from outside, and the remaining 0.4 atm directly. The roll will be in charge of the contact area. In other words, the copper strip is pressed against the roll with a pressure four times greater than the surface pressure due to tension.

(Actually, in such a case, the steel strip is sucked by the roll υ), so the volume of the gap, that is, the volume of gas ■, decreases somewhat, and ■ becomes a value slightly larger than 0.7 atm. Become. ) It is difficult to check whether the above phenomena occur as calculated, but as explained below, the atmospheric gas temperature or the injection gas temperature T.

The effect of the present invention was confirmed by experiments of the present invention to increase the , and the above estimation was confirmed to be correct, at least qualitatively.

Example A gas spraying nozzle was installed on the inlet side of the cooling roll installed in the primary cooling zone of a continuous annealing furnace for cold-rolled steel sheets, and gas at various temperatures was sprayed between the roll and the copper strip. Plate thickness Q,
A cooling experiment was conducted on a steel strip with a diameter of 4 mm, a plate width of 1200 mm, an entrance temperature of 650 °C, and a tensile stress of 1 kg/mm2. In this experiment, the roll surface temperature was about 120°C. As a result of the experiment, the blown gas temperature T. The lower the value, the more uneven the cooling in the width direction became, and there was a tendency for the cooling near the edges to become insufficient, and at the same time, the flatness deteriorated more significantly. On the other hand, when - is 600'c or more, non-uniform cooling in the width direction and deterioration in flatness were hardly observed.

Figure 3 shows the injection gas temperature T. shows the relationship between the cooling rate of the steel strip and the cooling rate of the steel strip. The cooling rate is the value at the center of the width. From Figure 3, To
Although this seems contrary to the conventional wisdom that a high cooling rate actually increases the cooling rate, it can be seen that the phenomenon predicted from the above theory is occurring. Note that when - is small, a phenomenon occurs in which the edge is difficult to cool, so if the cooling rate of the copper strip is considered as an average over the entire width, this tendency becomes even stronger.

The results of the above experiments are interpreted as follows.

The close contact between the steel strip and the roll is due to the thermal crown (convexity) of the cooling roll due to the heat from the steel strip and the shape of the plate on the entry side (medium elongation, ear wave, etc. However, the steel strip used in the experiment was almost flat). The degree differs in the width direction.

That is, areas where the surface pressure is weak, and in extreme cases, floating areas, etc. occur. When the percentage is low, the thermal expansion of the gas in the gap will promote such floating, and as mentioned above, it is assumed that the escape of gas from the gap will also differ in the width direction. As the number of parts increases, the degree of floating also varies in the width direction. Therefore, the cooling rate differs in the width direction, and the degree of shrinkage due to the temperature drop differs in the width direction, resulting in deterioration of flatness.

On the other hand, when 1″0 is high, the steel strip is attracted to the roll, so the steel strip and roll are in close contact over the entire width.At this time, due to the influence of thermal crown, plate shape, etc. It is thought that the contact pressure of
If the steel strip and roll in the state shown in the figure are closer than usual and the volume of the gap is small, it is considered to be quite small. In addition to this, in the roll cooling method, the heat conduction through the gas in the gap occupies a larger proportion than the heat conduction through the direct contact part, which has an extremely small area, so even if the pressure changes and T It is estimated that the way heat is transferred does not change much. For this reason, it is thought that when the ox is high, cooling will be uniform in the width direction. The slope of the graph in Figure 3 is T. The fact that it is small when it is large and large when it is small by 1 is consistent with the above reasoning.

As described above, the present invention has made it possible to uniformly cool the steel strip. The gap between the roll and the steel strip is about the same size as the surface roughness, so the amount of gas in the gap is smaller than that of fluorine. Therefore, a nozzle is used to inject high-temperature gas between the roll and the steel strip. When spraying, the amount can be quite small.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the state of contact between the cooling roll surface and the steel strip. FIG. 2 is a schematic diagram of an apparatus for carrying out one embodiment of the method of the invention. FIG. 3 is a graph showing the relationship between the temperature of the injection gas and the cooling rate of the steel strip. (Main reference numbers) 1: Steel strip, 2a-2e: Cooling roll, 3. Cooling room, 48
~4e: Gas injection nozzle, Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Masahiko Arai Figure 1 Figure 3 Figure 8 Bi0 200 400 600 80
0C72 sharpness is power or 0 degree [°C]

Claims (3)

[Claims] (1) In the method of cooling a steel strip by continuously bringing a copper strip into contact with the surface of a cooling roll, the temperature of the atmospheric gas just before it is drawn into the gap between the cooling roll and the steel strip is adjusted to the temperature before cooling. A method for cooling a copper strip, characterized by making the temperature of the steel strip higher than the average value of the surface temperature of the cooling roll. (2) In a method of cooling a steel strip by continuously bringing the steel strip into contact with the surface of the cooling roll in a cooling chamber that accommodates a cooling roll, the temperature of the atmospheric gas in the cooling chamber is lower than that of the steel strip before cooling. A method for cooling a steel strip, characterized in that the temperature is set to be higher than the average value of the surface temperature of the cooling roll. (3) In a method of cooling a copper strip by continuously bringing the copper strip into contact with the surface of a cooling roll, a wedge-shaped space between the copper strip and the roll is placed at a position immediately before the steel strip wraps around the cooling roll. A method for cooling a steel strip, which comprises blowing a gas and making the temperature of the gas higher than the average value of the temperature of the steel strip before cooling and the surface temperature of a cooling roll.