JPS6216255B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling the cooling of a metal plate, and more particularly, to a method for controlling the cooling temperature of a high-temperature metal plate moving in a horizontal direction to a desired temperature. Conventionally, a method for cooling a high temperature metal plate (hereinafter referred to as a strip) that moves horizontally uses air or water as a refrigerant. First, there is air cooling, and an example of this is a gas cooling method that rapidly blows air from above and below the strip.
There is a jet method. This gas jet method has a small cooling capacity and a heat transfer coefficient of 50~
At around 100 Kcal/m ² hr ℃, it is less than 1/200 of the 1 to 6 x 10 ⁴ Kcal/m ² hr ℃ in the case of water immersion cooling described later, and the same cooling capacity as the method using water as the refrigerant can be obtained. This inevitably requires a long cooling process, which poses a problem in terms of equipment. Furthermore, as is well known, in the continuous annealing process for manufacturing cold-rolled steel sheets, control of the cooling end point temperature is particularly important from a metallurgy perspective in order to obtain desired mechanical properties. However, due to the lack of cooling capacity in the gas jet method described above, the strip temperature tends to be higher than the target cooling end point temperature, especially in the low temperature range (100 to 300℃) where the cooling capacity changes greatly as described below. Therefore, accurate temperature control cannot be expected. On the other hand, the method of cooling the strip using water as a refrigerant has a large and effective heat removal capacity as described above, and the (a) water immersion method and (b) water injection method are common. First, there is the water immersion method, which immerses the strip directly in water, so it certainly has a high heat removal capacity, but because the strip is rapidly cooled from high temperature, it may cause shape defects or not reach the desired temperature. It is impossible to control the endpoint. Next, (b) Water injection methods are often used in which water is ejected from a spray nozzle toward the top and bottom surfaces of the strip. An example of this is a cooling system often seen on hot run out tables in the hot coil manufacturing process. This water injection method is
Compared to the water immersion method described above, this method is widely used because the amount of heat removed from the high-temperature metal body can be controlled simply by controlling the amount of water sprayed and the water pressure. However, if the high-temperature metal body to be cooled is thick and retains a large amount of heat, such as a thick plate or hot coil, the temperature will drop slowly and the shape will not deteriorate. When cooling a steel plate that is thin and has a small amount of heat, the cooling water sprayed onto the surface has a large effect on the steel plate, and if it is not evenly distributed, it will cause poor shape. As is well known, the surface of a strip that runs horizontally does not always maintain a horizontal plane; it may be slightly inclined, or there may be localized areas with defective shapes from the beginning, so the injected cooling water is The water drops form on the surface and move while accumulating in the lower parts, resulting in uneven cooling, and the resulting thermal stress induces shape defects. Next, evaluating the water injection method from the viewpoint of end point control (b), as shown in Figure 1, the cooling capacity (heat transfer coefficient) of the cooling water varies greatly depending on the surface temperature of the steel plate to be cooled. The so-called nuclear membrane transition zone (first
(area in figure 1) and nucleate boiling region (area in figure 1, 100
~300°C) is widely known in the literature. That is, when the high-temperature strip is immersed in cooling water, the entire heat transfer surface is instantly covered with a stable vapor film, and thereafter heat transfer occurs via the vapor film. In other words, a state of film boiling occurs (region shown in FIG. 1). The temperature of the heat transfer surface gradually decreases, and eventually the collapse of the vapor film begins locally, creating an unstable transition region where its formation and collapse are repeated, and the temperature decreases somewhat quickly, resulting in a so-called transition boiling state. (area in Figure 1). As the temperature drops further, the collapse of the vapor film spreads to the entire transmission surface, and at the same time many bubbles are generated, resulting in a state of intense nucleate boiling over the entire surface. Due to this disturbance effect, the temperature drops rapidly (region of Figure 1). Cooling capacity is maximum in this region. When the temperature falls below the saturation temperature, there is no boiling and only natural convection occurs. In this region, the cooling rate becomes even slower (region shown in Figure 1). As mentioned above, it is impossible to uniformly control the end point of the entire strip surface to the desired temperature using this water injection method, especially in areas where the cooling capacity changes significantly (between 100 and 300 degrees Celsius). As a result, a temperature difference occurs in the width direction of the strip, and the resulting thermal stress causes shape defects. Also, the temperature
At temperatures below 100°C, the injected cooling water will adhere to the strip surface as water droplets, delaying evaporation and potentially causing rust in subsequent processes, requiring equipment such as an air knife. The object of the present invention is to provide a new method for cooling a high-temperature strip that eliminates the above-mentioned problems. ,
Among the conventional simultaneous upper and lower injection cooling methods, we stopped the injection from the upper part of the strip and developed a single-sided cooling method in which the strip is cooled only by injection from the lower part. If we use this single-sided cooling method, which is limited to the bottom surface injection, and also take into consideration that no water gets on the top surface of the strip, even if the cooling water adheres to the bottom surface of the strip, it will naturally fall, and the temperature will exceed 100℃. With high-temperature strips, evaporation occurs as soon as they are deposited, and they remain attached to the strip for a long time and are not removed. Therefore, even if the temperature of the strip falls within the above-mentioned rapid cooling capacity range (100 to 300 degrees Celsius), it is possible to always accurately control the end point, and to obtain a good finished shape. This is a cooling control method. The reason why the temperature of the high-temperature metal body is limited to 100℃ or higher is because in the low temperature range below 100℃, even though the injection is from the bottom, the evaporation of the sprayed water that adheres to the metal body is delayed and can cause rust. be. Next, an embodiment of the cooling method of the present invention will be described in detail based on the drawings. FIG. 2 is an explanatory diagram of the configuration of a horizontal cooling device for carrying out the cooling control of the present invention, and FIG. 3 is a sectional view taken along the line AA in FIG. 2. Strip 2 in cooling tank 1
moves horizontally in the direction of the arrow. The strip moving device is omitted. Water jets 3 for cooling the strip 2 are jetted from lower nozzles 4 disposed in the center of the strip at regular intervals in the direction of travel of the strip. The water pressure of the water jet 3 is adjusted by opening and closing a main valve 6 and a branch valve 7 provided in the pipe 5. Furthermore, it is preferable to use a wide-angle spray nozzle that can uniformly cool the entire width of the strip with a single nozzle to spread the sprayed water 3 in the width direction of the strip. Since the width of the cooling tank 1 is narrow, a repulsion buffer member 8 is provided so that the cooling jet water 3 from the lower surface of the strip 2 does not collide with both side walls of the cooling tank 1 and splash water onto the upper surface of the strip. This repulsion buffer 8 is unnecessary if the width of the cooling tank 1 is wide enough to prevent splashed water from the side wall from riding on the top surface of the strip. The repulsion buffer should preferably be one in which hair is implanted, but it may also be a blind type with other multi-layer plates facing downwards, and as long as the structure of the buffer does not allow water splashed from the side walls to land on the top surface of the strip, the shape is acceptable. is not limited. A pump 9 supplies cooling water to the pipe 5. Next, the control-related configuration will be explained. Information obtaining devices such as a speedometer 10 for actually measuring the speed of the strip, a strip thickness gauge 11, and a strip thermometer 12 are provided on the inlet side of the cooling tank 1. The present invention does not particularly limit the type and number of these measuring instruments. Reference numeral 13 denotes an information input device for inputting information values measured by the information acquisition device. 14 is a reference level value for setting the final target end point temperature of the strip. Reference numeral 15 denotes an arithmetic unit that performs a comparison operation between the output signal of the information input device and the reference level value 14;
Control signals are sent to the main valve 6 and branch valve 7. A method for controlling the cooling of a strip to a target cooling end point temperature using the cooling control device having the configuration as described above will be specifically explained. Before the strip 2 enters the cooling tank 1, a reference level value 14 is input into the calculator 15 so that the temperature reaches the cooling end point at the exit side of the cooling tank. Next, the speed, size, plate temperature, etc. before cooling are measured using a speed meter 10, a plate thickness gauge 11, a thermometer 12, etc., and the information input device 1
3, it is immediately compared with the cooling end point temperature set value described above in the calculator 15, and a control signal is sent to the pump 9, each main valve 6, and the branch valve 7 by the output controller 16, and each Adjust the flow rate and pressure from the nozzle 4. A plurality of nozzles 4 are provided in the direction of movement of the strip 2, but due to the relationship between the strip temperature before cooling and the cooling end point temperature, only the front seven nozzles spray water, and the rear three nozzles spray water, as shown in Figure 2. Even when closed, intermittent injection is also possible instead of continuous injection. As described above, according to the method of cooling only the bottom surface of the present invention, since the cooling water is not applied to the top surface of the strip unlike the simultaneous upper and lower injection method, there is no water film or puddle on the strip, and the bottom surface of the strip is This is an innovative cooling control method in which the water droplets that adhere to the strip naturally fall and evaporate, and the cooling water sprayed over the entire width of the strip uniformly cools the entire strip width to reach the target cooling end point temperature. There is no particular upper limit to the strip temperature before cooling, but if it exceeds 600℃, the temperature will drop rapidly and there is a risk of shape defects.
Preferably, cooling is performed from a temperature of 600°C or lower. Please note that the above explanation refers to continuous metal strips.
Although the metal body to be cooled is used, the lower surface cooling method of the present invention can also be applied to a cut plate. Below, more specific examples will be given to explain the effects of the present invention. Example Using the cooling device shown in Figure 2, SPCC
A cold-rolled steel plate of SD0.6×1000×coil was made, and the first
The results are shown in the table. As conventional example 1,

【table】

[Table] The test was carried out using a spray device from the bottom as shown in Figure 2 and a temporary top spray device installed at the target position. In addition, in Conventional Examples 2 and 3, cold-rolled steel sheets of the same size were used in separate cooling lines and cooled by immersion in a water bath and by gas jet cooling, respectively. Although the target cooling end point temperature is in the nucleate boiling range, the example according to the present invention can accurately control the end point temperature, has a good shape, has a wide cooling temperature range, and has an end point cooling temperature of 100°C or more. If maintained, cooling with a good surface appearance can be achieved without the need for a dryer to remove water after cooling, and the equipment cost is low, making it a useful thin plate cooling method.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between strip temperature and heat transfer coefficient, FIG. 2 is an explanatory diagram showing an embodiment of the cooling control of the present invention, and FIG.
It is an A sectional view. 1...Cooling tank, 2...Strip, 3...Water jet, 4
... Nozzle, 6... Main valve, 7... Branch valve, 8... Repulsion buffer, 9... Pump, 13... Information input device, 15... Arithmetic unit, 16... Output controller.

Claims (1)

[Claims] 1. When cooling a high-temperature metal plate moving in the horizontal direction, a nozzle is arranged on the lower surface side of the metal plate to inject a refrigerant over the entire width of the lower surface of the metal plate,
The metal plate in the horizontal pass line is characterized by controlling the cooling end point temperature of the high temperature metal plate to an arbitrary temperature of 100°C or higher by adjusting the flow rate, pressure, etc. of the refrigerant injected from the nozzle. Cooling control method.