JP4430526B2 - Continuous casting method - Google Patents

Description

  The present invention relates to a continuous casting method that can easily and accurately detect clogging of a secondary cooling water pipe in a continuous casting facility and can prevent the occurrence of slab quality defects due to insufficient secondary cooling water amount. is there.

  In continuous casting of steel, molten steel in a ladle is poured into a mold, cooled in the mold (primary cooling) to form a solidified shell, and then cooled while being guided by a guide roll into a water spray zone (secondary cooling) The solidified shell is gradually thickened by cooling, and then gradually pulled out by a pinch roll, cut (bundled) from the solidified portion, and sent to a subsequent process as a slab.

  In the secondary cooling in such a continuous casting facility, the slab is generally cooled by being divided into a plurality of cooling systems (hereinafter sometimes referred to as “loops”). The structure of the secondary cooling zone in the continuous casting facility is shown in FIG. Moreover, the specific structure of the cooling device in each loop is shown in FIG.

  As shown in FIGS. 1 and 2, the cooling water for secondary cooling of the slab is sent from the cooling water main pipe (FIG. 1) to the cooling water pipe (FIG. 2) of each loop, and then the flow meter, the flow rate Air is mixed in a mixing section that is sent to the header via a regulating valve (flow control valve) and further branched into a plurality of parts, and is ejected in a mist form from the nozzle tip.

  The set water amount (the amount of cooling water to be supplied) in each loop is appropriately changed depending on the steel type component and the mold size. In order to control this flow rate, a flow rate adjusting valve is provided for each loop (see FIG. 1, FIG. 1). 2), the amount of cooling water ejected from the nozzle tip is controlled to a set value by adjusting the degree of opening and closing of the valve.

  Incidentally, piping clogging may occur in the cooling system as described above due to adhesion of foreign matters, precipitates, scales and the like. Such “clogging” occurs not only in the cooling water pipe but also particularly in the header, the mixing section, the nozzle tip, the filter in the pipe, and the like. Below, the clogging in these places is generically called “piping clogging”. When such a pipe clogging occurs, the amount of cooling water is insufficient or uneven cooling occurs, leading to poor quality (surface / internal defects) of the rolled product.

  For these reasons, various techniques for detecting the clogged state of secondary cooling water piping have been proposed. As such a technique, for example, in Patent Document 1, a thermocouple for detecting the temperature of the cooling water is provided inside the base end side of the spray nozzle, and the cooling water temperature measured by the thermocouple, and the cooling water supply base tube A method for managing the spray nozzle clogging using the difference between the temperature and the temperature of the nozzle has been proposed.

  Patent Document 2 proposes a technique for detecting nozzle clogging based on the back pressure of the spray nozzle, the amount of cooling water, and the back pressure and the opening degree of the flow control valve. Furthermore, Patent Document 3 proposes a method for determining clogging of a spray nozzle by attaching a pressure gauge to the spray nozzle, measuring the water pressure in the spray nozzle, and comparing the measured value of the water pressure with a threshold value.

  These techniques are useful as techniques that can relatively easily grasp occurrence of spray nozzle clogging. However, in these techniques, it is necessary to provide a thermometer and a pressure gauge for each loop, which not only increases initial cost but also requires maintenance. Further, the pressure difference and the temperature difference may fluctuate greatly depending on the measurement conditions, and it may be necessary to perform filtering (averaging process) for grasping the actual measurement value, which may be inaccurate.

Even if piping clogging can be detected by the various technologies described above, clogging in the nozzle tip, header, and piping cannot be removed during operation due to equipment limitations. The actual situation is that equipment inspection is not possible until the process is completed. As a result, there will be a shortage of cooling water between the time when the operation is temporarily stopped and the equipment is inspected, resulting in a situation in which slab quality (especially surface cracks, internal cracks, center segregation, etc.) cannot be guaranteed. become. If such a situation occurs, the user will be forced to change the appropriation and / or change / addition of the post-process. Until such measures are taken, measures will be taken. It is also an important item in the continuous casting method to promptly cope with slab quality defects that have already occurred (cast slabs where quality defects are expected to occur).
JP 2003-170236 A “Claims”, FIG. 1, etc. Japanese Patent No. 3373007 “Claims”, FIG. 1, etc. Japanese Patent Laid-Open No. 5-309465 “Claims”, FIGS.

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to detect clogging of the secondary cooling water piping in the continuous casting equipment easily and accurately, and to perform casting due to insufficient secondary cooling water amount. It is an object of the present invention to provide a continuous casting method that can prevent the occurrence of poor quality of a piece and can quickly cope with a slab that is expected to have a poor quality if necessary.

  The method of the present invention that has been able to achieve the above-mentioned object is that when continuously cast slabs are continuously cast while being mist-cooled in a continuous casting machine, the opening degree and cooling of the flow rate adjusting valve in each cooling system of the secondary cooling water. Based on the temporal transition of only the amount of water, pipe clogging is detected before the valve opening reaches 100%, and the gist is that the operation is performed with the casting speed being changed based on this result.

  In the above method, it is also useful to assign an identification code to the slab at the time when it is detected that piping clogging has occurred, and to apply the restriction to the initial order and change the subsequent process based on this identification code. By adopting such a configuration, it becomes possible to quickly cope with a slab in which quality defects are expected to occur.

  In the present invention, pipe clogging is detected based on the opening degree of the flow rate adjustment valve and the amount of cooling water in each cooling system, and further, the casting speed is changed based on this result, so that the slab quality is improved. The occurrence of defects can be reduced as much as possible.

  Secondary cooling water is sent to each loop under constant pressure from the cooling water main pipe, but the degree of opening and closing of each flow rate adjustment valve (hereinafter referred to as “flow control valve”) (hereinafter referred to as “valve opening”) The flow rate is adjusted. Therefore, the flow regulating valve used at this time is configured such that the flow rate is adjusted by the valve opening degree under a certain pressure. The valve opening in the present invention is the area ratio of the gap through which the cooling water passes when the valve opening when the flow control valve is fully open is 100%. Can be grasped.

  When using the flow control valve as described above, when operating in a normal state, a certain proportional relationship is established between the flow rate (cooling water amount) and the valve opening. FIG. 3 shows the relationship between the amount of cooling water and the valve opening at this time. When a certain amount of cooling water flows down, the valve opening is also within a certain range. (Indicated by shading), it can be determined that the pipe is not clogged and is in a normal state.

  However, when clogging occurs in the piping, the relationship as described above is lost, and the valve opening degree varies even with the same amount of cooling water. The relationship between the amount of cooling water and the valve opening when clogging occurs is shown by point A in FIG. 3. When the clogging occurs, the valve opening greatly fluctuates and falls outside the appropriate range. That is, when the state shown at point A in FIG. 3 occurs, it can be determined that the pipe is clogged.

  From these results, the relationship between the amount of cooling water and the valve opening during normal operation is grasped (Fig. 3), and the relationship between the amount of cooling water and the valve opening that deviates from this normal state when actual values are measured. When this occurs, it can be grasped that piping clogging has occurred. The reason why the valve opening increases when piping clogging occurs is that the pressure loss in the piping after the flow control valve due to clogging (ie, between the points where clogging has occurred from the flow control valve) It is thought that this is because the

Since the flow regulating valve adjusts the amount of water from the main pipe to the amount of supplied water, it is designed to reduce the amount in accordance with the required amount of water (for example, 1 to 12 m ³ / Hr). In a normal operation state, the valve opening degree is about 10 to 60%. Therefore, when operated in a normal state, the valve opening does not reach 100%, but when piping clogging occurs, the valve opening gradually becomes close to 100%, If the operation is continued in this state, the valve opening becomes 100%, and the cooling water flow rate is insufficient thereafter. When such a cooling water shortage occurs, the surface of the slab is not effectively cooled, resulting in poor quality.

  By adopting such a detection method, it is possible to quickly detect the occurrence of pipe clogging from the relationship between the amount of cooling water and the valve opening, even with existing equipment, without installing a new device such as a pressure gauge or thermometer in each loop. Can be detected.

  In addition, it is difficult to stop the operation immediately when the amount of water is insufficient due to clogging of the pipe. The means for reducing the occurrence of single-quality defects were examined. As a result, it was found that the casting speed should be changed (particularly reduced) until the shortage of water is resolved. By taking such means, it is possible to reduce the required amount of cooling water (set amount of water) according to the casting speed and to reduce the occurrence of slab quality defects due to clogging of piping.

  However, in the loop, when local piping clogging (for example, nozzle clogging) occurs, quality trouble may occur even if the set water amount is apparently satisfied. In order to cope with the occurrence of such quality defects, an identification code is assigned to the corresponding slab, and special management (for example, product UT inspection) and slab care process (for example, scarf care process) in the subsequent process It is useful to carry out additions and changes to the recipient. By taking such measures, it is possible to avoid the occurrence of problems in the user in advance.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  In a certain cooling loop of an actual continuous casting machine, the relationship between the amount of secondary cooling water and the opening of the flow rate adjustment valve (valve opening) in a state where there is no clogging of the pipe was investigated. The result is as shown in FIG. 3, and in the state where there is no clogging of the pipe, the flow rate and the valve opening degree are in a substantially direct relationship, and it can be seen that the valve opening degree changes greatly as the cooling water amount increases. .

  And when the relationship between the amount of cooling water and the valve opening when piping clogging occurred was investigated, the position indicated by point A in FIG. 3 was shown. In other words, it was found that when the pipe clogging occurred, the valve opening was greatly deviated from the appropriate range shown in FIG.

  Based on these results, an appropriate range in the relationship between the cooling water amount and the valve opening degree is grasped (FIG. 3), and the actual measurement value deviates from the appropriate range (points A and B in FIG. 3). The pipe was clogged. At the time when it was determined that clogging occurred, the set water amount was reduced by reducing the casting speed until the casting of the slab charge was completed, and the lack of water amount was avoided. In addition, an identification code is assigned to the slab in the corresponding range, and the slab surface is added to the slab in the subsequent process, the application destination is changed, and ultrasonic inspection is performed at the shipping stage. A system to implement was established.

  As a result, as shown by point A in FIG. 3, the loop (for example, No. 4 shown in FIG. 1) is executed before the valve opening reaches 100% (that is, before water shortage occurs). Loop clogging can be detected.

  FIG. 4 shows the time transition of the valve opening and cooling water amount (loop flow rate) in these series of steps (relationship with casting time), and FIG. 5 shows the time transition of the corresponding casting speed. By changing the casting speed after detecting the occurrence, the set amount of water is reduced (the valve opening is maintained within a predetermined range), and the amount of water is insufficient until one charge is completed (hatching in FIG. 4) In addition, it is possible to quickly cope with slabs that are predicted to have poor quality due to a lack of water.

It is a schematic explanatory drawing which shows the structure of the secondary cooling zone in a continuous casting machine. It is a schematic explanatory drawing which shows the specific structure of the cooling device in each loop. It is a graph which shows the relationship between the amount of secondary cooling water in a cooling system, and a valve opening degree. It is a graph which shows the time transition of a valve opening degree and the amount of cooling water (loop flow rate). It is a graph which shows the time transition of the casting speed corresponding to FIG.

Claims (2)

When continuous casting slabs are continuously cast with mist cooling in a continuous casting machine , the valve opening is determined based on the flow rate adjustment valve opening in each cooling system and the temporal transition of the cooling water amount alone. A continuous casting method characterized by detecting piping clogging before reaching 100%, and operating by changing the casting speed based on the result.   2. The continuous operation according to claim 1, wherein when an occurrence of clogging of the pipe is detected, an identification code is assigned to the slab, and the allocation restriction to the initial order and the change of the subsequent process are performed based on the identification code. Casting method.

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