JPS6160901B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for cooling a strip in a continuous annealing furnace, and is intended to cool the strip so that the temperature distribution in the width direction of the strip is uniform when the strip is cooled with a water-cooled roll. .

When continuously annealing a strip, the strip is heated to the recrystallization temperature, soaked, then rapidly cooled, and then subjected to an overaging treatment.In this case, the strip cooling method after heating and soaking is water quenching, Gas jet systems and water-cooled roll systems are known.

Since the water quenching method has a fast cooling rate, it is easy to manufacture high-strength cold-rolled steel sheets, and when manufacturing soft materials, it has the advantage of requiring a short overaging treatment. During this process, the strip temperature drops too much and reheating is required for over-aging treatment, resulting in high energy costs. On the other hand, according to the gas jet method, although the energy cost is low for soft materials, it has the disadvantage that the overaging time is long and it is difficult to produce high tensile strength plates.

The water-cooled roll method compensates for the shortcomings of these methods. That is, in this method, the strip is cooled by directly contacting the internally cooled metal roll, but in this case, the shape of the strip on the entrance side of the water-cooled roll and the temperature uniformity of the strip in the width direction of the strip are not always constant. This is because with current heating and cooling technologies (such as radiant tube heating, direct flame heating, heater heating, and gas jet cooling), it is difficult to heat and cool completely uniformly in the width direction of the strip. If the rolls are not in uniform contact and the operation is not carried out in this state, the temperature difference between the center and the ends of the strip in the width direction will become large, resulting in uneven material quality and non-uniform strip operation. Problems such as constriction due to cooling and severe meandering due to poor shape will occur.In particular, the roll crown of a water-cooled roll is one type that is made in a cold state.
It is difficult to accommodate all strip sizes and strip shapes on the entry side unless a variable crown roll is created. In addition, since the tracking upward convex crown of the strip is generally applied cold,
There is also a slight drawback that the strip edge is difficult to cool.

The present invention has been proposed in view of the current situation, and in particular changes the strip tension in the water-cooled roll portion according to the temperature in the width direction of the strip passing through the water-cooled roll, thereby adjusting the contact state between the strip and the water-cooled roll. The present invention aims to provide a new strip cooling method that can achieve uniform temperature across the width of the strip at low equipment costs, which cannot be achieved with conventional constant tension operation.

The present invention will be described in detail below. First, FIG. 3 shows a schematic diagram of a general continuous annealing equipment to which a water-cooled roll system is applied. That is, the strip unwound from the payoff reel 10 passes through the cleaning device 11 and the looper 12, enters the continuous annealing furnace, is heated and soaked to the recrystallization temperature in the heating zone 13-soaking zone 14, and then is heated in the gas jet zone 15. It is cooled to a predetermined temperature. The strip is then cooled in a cooling device 16 with a plurality of water-cooled rolls arranged in parallel, and then passes through a reheating zone 17, an overaging zone 18, a final cooling zone 19, and is finally wound onto a tension reel 20. It's becoming like that.

However, in the present invention, when the strip is cooled by the water-cooled roll type cooling device 16, the temperature in the width direction of the strip is uniform on the exit side of the final water-cooled roll, that is, there is no difference in temperature between the central part and the end part in the width direction of the strip. The strip tension will be controlled so that the temperature is always 0°C. In this case, the optimal setting tension value will vary depending on the temperature between the center and end of the input strip of the water-cooled roll in the width direction (the temperature difference in the width direction of the input strip is determined by the strip size, shape, line speed, thermal cycle (varies depending on operating conditions, etc.)

That is, △T ^E (temperature difference in the width direction of the input strip) = Tc ^E - Te ^E △T ^D (temperature difference in the width direction of the output strip) = Tc ^D - Te ^D , where Tc ^E : Center temperature of the strip on the input side (℃) Tc ^E : Inlet strip end temperature (°C) Tc ^D : Outlet strip center temperature (°C) Te ^D : Outlet strip end temperature (°C) In this case, the roll crown of the water-cooled roll is as shown in Figure 1a. Under the condition of amount = 2.0mm, △T ^E = 0℃
The optimal tension at which △T ^D becomes 0 is approximately 1.7Kg/Hz,
When △T ^E = 20℃, it is 1.3Kg/mm ² , similarly △T ^E =
At -15℃, the optimum tension value is 2.0Kg/mm ² , and the optimum tension value differs depending on the temperature difference in the width direction of the input strip (△T ^E ) (the experimental conditions in Figure 1 are strip size: 0.8 ^t) . × ^1200W , line speed
300mpm, and the temperature at the strip edge was measured at a position 50mm from the plate edge).

Therefore, it is necessary to change the strip tension in accordance with the temperature difference in the width direction of the strip on the inlet side within an operable range that does not cause meandering or throttling of the strip. In this case, it goes without saying that the above-mentioned optimum tension value needs to be slightly changed depending on the amount of cold crown of the water-cooled roll. As an example, FIG. 1b shows the relationship between the temperature difference in the exit side strip width direction and the set tension when the roll crown is 0 mm.

FIG. 2 shows an example for realizing this. In the figure, 1 is a water-cooled roll group, 2 is a strip, and bridle rolls 3 are installed on the inlet and outlet sides of the water-cooled roll group 1, respectively. , 3a are installed. Then, the center temperature Tc ^D and the end temperature Te ^D of the strip on the output side are detected by the thermometer 4a arranged on the output side of the strip, and these signals are inputted to the adder 5. In addition, the thermometer 4 placed on the entrance side of the strip measures the center temperature Tc ^E and the end temperature of the strip on the entrance side.
Te ^E is detected and also input to the adder 5.

This adder 5 calculates the temperature difference in the width direction of the input strip (△T ^E - Te ^E from each of the above-mentioned signals, and calculates the temperature difference in the width direction of the output strip (△T ^D ) = Tc ^D
In addition to comparing with -Te ^D , feedback is provided to the exit side bridle roll 3a so that the temperature difference in the width direction of the exit side strip (ΔT ^D ) is 0°C.

In addition, the present invention detects the temperature difference in the width direction of the inlet strip from the inlet strip thermometer 4 in place of or at the same time as the above-mentioned control means, and calculates the temperature difference in the width direction of the outlet strip in the calculator 6 from this value. It is also possible to preset the optimal tension such that ΔT ^D ) is at or close to 0° C., and feed this to the entry side bride roll 3.

In Fig. 2, 6 and 6a are tension meters, and 7 is a tension setting device.The tension setting device 7 sets the tension for each strip size in order to prevent the strip from breaking or constricting due to the tension becoming too high. An upper limit value is set in advance so that the values from the telemetry meters 6, 6a do not exceed this upper limit value.

According to the present invention described above, when the strip is cooled by the water-cooled roll, the strip is cooled uniformly so that there is no temperature difference between the center and the end in the width direction, so meandering of the strip is prevented.
Various excellent effects such as uniformity of the material can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the temperature difference in the width direction of the exit side strip and the tension, in which a is a graph when the water-cooled roll crown amount is 2.0 mm, b is a graph when the water-cooled roll crown amount is 0 mm, and Fig. 2 is a graph when the present invention is carried out. The third figure is a schematic diagram of a general continuous annealing facility that uses a water-cooled roll system. In the figure, 1 is a water-cooled roll group, 2 is a strip, 3,
3a is a bride roll, 4 and 4a are thermometers, 5 is an adder, 6 and 6a are tension meters, and 7 is a tension setting device.

Claims (1)

[Claims] 1. When cooling the strip using a metal water-cooled roll with an internally cooled interior, a tensioning device is installed in front and/or rear of the water-cooled roll to compensate for the temperature difference between the widthwise center and end of the strip on the entry side of the water-cooled roll. A method for cooling a strip in continuous annealing, characterized in that the strip tension is changed by the tension applying device so that the temperature in the width direction of the exit side strip is uniform accordingly.