Surface flaw reduction method and heat treatment apparatus

Abstract

To specify a roll that had caused the generation of a deposit when a surface flaw was generated without changing a production process, and to suppress the growth of the deposit of the specified roll.SOLUTION: A surface flaw reduction method includes a measurement step, an identification step of identifying a causal roll, and a removal step. In the identification step, when the depth of the surface flaw measured in the measurement step is deeper than a predetermined threshold value, the forward slip of each conveying roll is changed from a normal reference forward slip in an arbitrary order, and when the pitch of the surface flaw changes, the conveying roll whose forward slip has been changed is identified as a causal roll.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for reducing surface defects and a heat treatment apparatus. [Background technology]

[0002] In the manufacturing process of a strip (such as a plate-shaped metal material), the strip is conveyed by conveying rolls through each process. If a deposit such as a metal oxide adheres to the outer circumferential surface of the conveying roll, a so-called pickup phenomenon occurs. Specifically, the deposit is pressed against the strip by the conveying roll, causing pitch-like defects (hereinafter simply referred to as "surface defects") on the surface of the strip.

[0003] Patent Documents 1 and 2 disclose methods for reducing such surface defects. In the surface defect reduction method of Patent Document 1, the oxygen partial pressure in an annealing furnace is set to an equilibrium oxygen partial pressure or less to change the surface temperature of a transport roll. In addition, the surface defect reduction method of Patent Document 2 involves forming an oxide film on the surface of a transport roll in advance. According to the surface defect reduction methods of Patent Documents 1 and 2, deposits are less likely to accumulate on the outer peripheral surface of the transport roll. This suppresses the pick-up phenomenon, making it less likely that surface defects will occur on the strip. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-151552 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-201985 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, the surface defect reduction method of Patent Document 1 involves changing the furnace temperature setting in the annealing furnace, making it difficult to apply the surface defect reduction method of Patent Document 1 to a specific strip for which it is difficult to change the manufacturing processes, including changing the furnace temperature setting.

[0006] Furthermore, the surface defect reduction methods described in Patent Documents 1 and 2 cannot suppress the growth of deposits that have already formed. Furthermore, once deposits have formed, they may grow larger over time, which may cause the surface defects to gradually become deeper and more harmful.

[0007] The present invention aims to provide a surface defect reduction method and heat treatment device that can identify the roll that caused the deposits when the surface defects occurred and can suppress the growth of the deposits on the specific roll without changing the manufacturing process. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the first configuration of the present invention is a method for reducing surface defects in continuous heat treatment of a strip, comprising: a measurement process for measuring the depth and pitch of surface defects of the strip using a defect sensor installed on the exit side of the continuous heat treatment; an identification process for identifying the causative roll that caused the surface defect among multiple transport rolls that transport the strip; and a removal process for removing adhesions that cause the surface defect from the outer surface of the causative roll identified in the identification process, wherein the identification process is characterized in that when the depth of the surface defect measured in the measurement process is deeper than a predetermined threshold, the forward advance ratio of each transport roll is changed from the normal standard forward advance ratio in an arbitrary order, and when the pitch of the surface defects changes, the transport roll whose forward advance ratio has been changed is identified as the causative roll (first configuration).

[0009] In addition, the surface defect reduction method according to the first configuration may be characterized in that the strip is transported while contacting the outer peripheral surface of each transport roll and receiving frictional force from the transport rolls rotating at a standard forward advance rate, and the removal process involves changing the forward advance rate of the causative roll from the standard forward advance rate to slide the outer peripheral surface of the causative roll against the strip, thereby removing the deposit from the causative roll (second configuration).

[0010] Furthermore, the surface defect reduction method according to the second configuration may be characterized in that the identification process increases the forward slip ratio by 1% or more and 5% or less from the reference forward slip ratio, and the removal process increases the forward slip ratio of the causative roll by 6% or more and 8% or less from the reference forward slip ratio (third configuration).

[0011] In addition, the surface defect reduction method according to any one of the first to third configurations may be characterized in that each transport roll is disposed in a soaking zone of the continuous heat treatment (fourth configuration).

[0012] Furthermore, a surface defect reduction method according to a fourth configuration may be characterized in that the soaking zone includes a plurality of zones separated by a predetermined interval, and each conveying roll is disposed in a distributed manner in each zone, and the identification process includes a cause zone identification process in which the forward rate of the conveying roll is uniformly changed for each zone, and a zone in which the forward rate has changed when the pitch of the surface defects has changed is identified as the cause zone, and a cause roll identification process in which the forward rate of each conveying roll included in the cause zone is changed from a reference forward rate in any order, and a conveying roll in which the forward rate has changed when the pitch of the surface defects has changed is identified as the cause roll (fifth configuration).

[0013] The heat treatment apparatus disclosed in this specification also comprises a heat treatment zone for heat-treating a strip, a plurality of transport rolls arranged in the heat treatment zone and transporting the strip, a defect sensor arranged on the outlet side of the heat treatment zone and capable of detecting surface defects on the strip, and a control unit capable of detecting the pitch of the surface defects based on the detection results of the defect sensor and controlling the forward movement of each transport roll, wherein the control unit is configured to be able to execute a cause roll identification mode in which, when the depth of the surface defect is deeper than a predetermined threshold, the forward movement of each transport roll is changed in an arbitrary order from a normal reference forward movement, and when the pitch of the surface defects changes, the transport roll whose forward movement has been changed is identified as the specific roll that caused the surface defect, and a removal mode in which the forward movement of the cause roll is changed from the reference forward movement, the outer peripheral surface of the cause roll is caused to slide against the strip, and the deposits that cause the surface defects are removed from the outer peripheral surface of the cause roll (sixth configuration). [Effects of the Invention]

[0014] According to the first aspect of the present invention, the depth and pitch of surface defects can be detected by a defect sensor on the exit side of continuous heat treatment. Furthermore, when a surface defect with a depth exceeding a threshold occurs, the causative roll can be identified from the detected pitch. Furthermore, by changing the forward advance of the causative roll, the deposits can be removed and the growth of the deposits can be suppressed.

[0015] Therefore, it is possible to provide a surface defect reduction method and heat treatment device that can identify the roll that caused the deposits when the surface defects occurred without changing the manufacturing process, and that can suppress the growth of the deposits on the specific roll. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a side view of a continuous annealing furnace 1. [Figure 2] FIG. 2 is a diagram showing a schematic image of the strip B before the causal roll identification mode is executed. [Figure 3] FIG. 3 is a diagram schematically showing a captured image of the strip B when the forward advance rate f of the transport rolls a1 to a3 is changed from the state shown in FIG. 2 to a specific forward advance rate fb. [Figure 4] FIG. 4 is a diagram showing a schematic image of the strip B when the forward advance rate f of the transport rolls a4 to a6 is changed from the reference forward advance rate fa to the specific forward advance rate fb in the state shown in FIG. [Figure 5] FIG. 5 is a flowchart showing the overall configuration of the surface defect reduction method according to the present invention. [Figure 6] FIG. 6 is a flowchart showing a detailed configuration of the measurement process. [Figure 7] FIG. 7 is a flowchart showing a detailed configuration of the specifying step. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a continuous annealing furnace 1 (heat treatment apparatus) according to the present invention will be described. Then, a method for suppressing surface defects using the continuous annealing furnace 1 will be described.

[0018] <Continuous annealing furnace 1 according to the present invention> 1 is a side view of a continuous annealing furnace 1. The continuous annealing furnace 1 is an annealing furnace for continuously annealing a strip B after rolling in the manufacturing process of the strip B. The strip B is a metal material (for example, a steel plate) formed into a strip shape.

[0019] The continuous annealing furnace 1 includes a heating zone 2, a soaking zone 3, a cooling zone 4, transport rolls a1 to an (n is a natural number of 2 or more), a flaw sensor 6, and a control unit 7. The heating zone 2 is a zone for heating the strip B. The soaking zone 3 is a zone for soaking the strip B heated in the heating zone 2 so that the interior of the strip B is uniformly heated to a predetermined temperature (specifically, 600 to 900°C). The cooling zone 4 is a zone for cooling the heat-treated strip B discharged from the soaking zone 3.

[0020] The soaking zone 3 is divided into a plurality of zones (in accordance with the drawing, N zones from a first zone Z1 to an Nth zone ZN, where N is a natural number of 2 or more).

[0021] The transport rolls a1 to an are distributed and arranged in the first zone Z1 to the Nth zone of the soaking zone 3. The transport rolls a1 to an are rotatably supported. The rotation speed of each of the transport rolls a1 to an is controlled by the control unit 7, which will be described later.

[0022] The lower surface of the strip B is in contact with the outer peripheral surfaces of the transport rolls a1 to an. The strip B is transported by friction with the outer peripheral surfaces of the transport rolls a1 to an. The strip B is transported from the heating zone 2 side (hereinafter simply referred to as the "entrance side") to the cooling zone 4 side (hereinafter simply referred to as the "exit side"). Hereinafter, the direction in which the strip B is transported will be referred to as the "transport direction." In addition, in FIG. 1 and FIGS. 2 to 5 described below, the transport direction is the direction from the base X of the arrow to the tip X' of the arrow. In other words, the base X side is the entrance side of the soaking zone 3, and the tip X' side is the exit side of the soaking zone 3.

[0023] The flaw sensor 6 is a sensor equipped with an optical camera (for example, a camera-type flaw sensor equipped with a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor).

[0024] The defect sensor 6 captures an image of the surface of the strip B (the surface in contact with the transport rolls a1 to an) at the exit side of the Nth zone ZN of the soaking zone 3 and the entry side of the cooling zone 4. The defect sensor 6 monitors the surface of the strip B based on the captured image. Specifically, the defect sensor 6 detects, from the captured image, the presence or absence of surface defects P on the strip B, as well as the depth and pitch of the surface defects P (more specifically, the presence or absence of pitch, the size of the pitch, and the presence or absence of changes in the pitch, etc.).

[0025] Here, the surface defect P refers to a defect formed on the underside of the strip B. The surface defect P is formed when a deposit (metal oxide, etc.) adhering to the outer peripheral surface of one of the transport rolls a1 to an is pressed against the surface of the strip B. This deposit grows and becomes larger over time. Therefore, if the deposit is left unremoved, the surface defect P will gradually grow larger and become harmful. Note that FIG. 1 illustrates a state in which an deposit O1 is adhering to the outer peripheral surface of the transport roll a5.

[0026] The flaw sensor 6 is electrically connected to the control unit 7. The flaw sensor 6 transmits the detection result to the control unit 7.

[0027] The control unit 7 can individually change the forward advance ratio f of the transport rolls a1 to an to any value.

[0028] Here, the forward ratio f is the ratio between the moving speed of the strip B and the peripheral speed of each of the transport rolls a1 to an. Specifically, the forward rate f is calculated by the following formula (1): where V B is the moving speed of band B. Also, V R is the peripheral speed of the rolls (transport rolls a1 to an) themselves.

[0029]

number

[0030] The normal forward advance rate f when transporting the strip B is defined as a reference forward advance rate fa. Basically, the transport rolls a1 to an transport the strip B at the reference forward advance rate fa.

[0031] The control unit 7 changes the circumferential speeds of the transport rolls a1 to an by individually controlling the rotation speeds of the transport rolls a1 to an. Changing the circumferential speeds of the transport rolls a1 to an changes the forward movement f of each of the transport rolls a1 to an. For example, the control unit 7 can change the forward movement f of the transport rolls a1 to an as follows:

[0032] The control unit 7 can change the forward advance ratio f of the transport rolls a1 to an collectively for each zone (first zone Z1 to Nth zone ZN in FIG. 1). Specifically, for example, the forward advance ratio f of the transport rolls a1 to a3 in the first zone Z1 can be changed collectively from the reference forward advance ratio fa, while the reference forward advance ratios fa of the other transport rolls a4 to an remain unchanged. From this state, for example, the forward advance ratios f of the transport rolls a1 to a3 can be returned collectively to the reference forward advance ratio fa, and the forward advance ratios f of the transport rolls a4 to a6 in the second zone Z2 can be changed from the reference forward advance ratio fa. Note that the order of the zones in which the forward advance ratio f is changed is not limited to this and can be set arbitrarily.

[0033] The control unit 7 is configured to be able to execute a cause roll identification mode and a removal mode. The cause roll identification mode is a mode for identifying the roll (hereinafter simply referred to as the "cause roll") that caused the pitch-like surface defect P among the transport rolls a1 to an. The removal mode is a mode for removing deposits from the outer peripheral surface of the cause roll.

[0034] <About the cause role identification mode> The cause roll identification mode will be described in detail with reference to Figures 2 and 3. Note that the description here will be made taking as an example a case where the cause roll of the surface defect P1 is the transport roll a5.

[0035] Fig. 2 is a diagram showing a schematic image of the strip B before the cause roll identification mode is executed. As shown in Fig. 2, surface defects P1 to P5 have occurred on the strip B. The surface defects P1 to P5 have depths exceeding the above-mentioned threshold and are included in the surface defect P described above.

[0036] The surface defects P1 are formed at equal intervals in the conveyance direction. The positions of the surface defects P1 in the width direction of the strip B are the same. This indicates that the surface defects P1 have a pitch. In other words, the surface defects P1 are formed by deposits O1 adhering to the cause roll.

[0037] On the other hand, the surface defects P2 to P5 are not positioned in the same width direction and are not spaced equally apart in the conveyance direction. Therefore, the surface defects P2 to P5 do not have a pitch pattern and are each caused by a different cause. In other words, it cannot be determined that the surface defects P2 to P5 were caused by the deposit O1 that adhered to the cause roll.

[0038] The flaw sensor 6 detects the above. That is, the flaw sensor 6 detects that the surface flaw P1 has a pitch, and that the surface flaws P2 to P5 do not have a pitch. The flaw sensor 6 also detects that the pitch of the surface flaw P1 is pitch d1. The flaw sensor 6 then transmits these detection results to the control unit 7.

[0039] The control unit 7 executes the cause roll identification mode in response to the detection result of the flaw sensor 6 (i.e., that the surface flaw P1 has been detected to have a pitch characteristic). The control unit 7 then changes the forward advance ratio f of the transport rolls a1 to an for each zone (first zone Z1 to Nth zone ZN) in an arbitrary order (here, from the entrance side to the exit side in the transport direction, from first zone Z1 to Nth zone ZN). At this time, the control unit 7 changes the forward advance ratio f from the reference forward advance ratio fa to a specific forward advance ratio fb. The specific forward advance ratio fb is a value that is 1% or more and 5% or less higher than the reference forward advance ratio fa.

[0040] FIG. 3 is a schematic diagram showing an image of the strip B when the forward forward ratio f of the transport rolls a1 to a3 is changed from the state shown in FIG. 2 to a specific forward forward ratio fb. As shown in FIG. 3, in this case, the pitch of the surface flaw P1 does not change from pitch d1. Therefore, the flaw sensor 6 detects that the pitch of the surface flaw P1 has not changed. The flaw sensor 6 also detects new surface flaws P6 and P7 with depths exceeding the threshold. Furthermore, the flaw sensor 6 detects that the surface flaws P6 and P7 do not have pitch. The flaw sensor 6 transmits these detection results to the control unit 7. Based on these detection results, the control unit 7 determines that the transport rolls a1 to a3 are not the cause rolls.

[0041] Then, the control unit 7 changes the forward advance ratio f of the transport rolls a4 to a6 in the second zone Z2 from the reference forward advance ratio fa to the specific forward advance ratio fb. At this time, the forward advance ratio f of the transport rolls a1 to a3 in the first zone Z1 may or may not be returned to the reference forward advance ratio fa.

[0042] FIG. 4 is a schematic diagram showing captured images of the strip B when the forward forward rate f of the transport rolls a4 to a6 is changed from the reference forward forward rate fa to the specific forward forward rate fb, starting from the state shown in FIG. 4. As shown in FIG. 4, in this case, the pitch of the surface flaw P1 changes from pitch d1 to pitch d2. Therefore, the flaw sensor 6 detects a change in the pitch of the surface flaw P1. The flaw sensor 6 also detects new surface flaws P8 to 11 with depths exceeding the threshold. Furthermore, the flaw sensor 6 detects that the surface flaws P8 to 11 do not have pitch. The flaw sensor 6 transmits these detection results to the control unit 7.

[0043] When the control unit 7 receives this detection result from the flaw sensor 6, it identifies the second zone Z2 as the cause zone. The cause zone is the zone in which the cause roll exists among the first zone Z1 to the Nth zone ZN.

[0044] The control unit 7 then returns all forward advance rates f of the transport rolls a1 to an to the reference forward advance rate fa. The control unit 7 then changes the forward advance rates f of the transport rolls a4 to a6 in the second zone Z2, which is the cause zone, from the reference forward advance rate fa to the specific forward advance rate fb in an arbitrary order (here, the order is transport rolls a4, a5, a6).

[0045] As described above, here, deposit O1 is attached to the outer peripheral surface of transport roll a5. Therefore, when the forward forward ratio f of transport roll a5 is changed to the specific forward forward ratio fb, the pitch of surface defect P1 changes to d2. When the defect sensor 6 detects a change in the pitch of surface defect P1, it transmits this detection result to the control unit 7. Based on this detection result, the control unit 7 identifies transport roll a5 as the cause roll. In this way, the control unit 7 identifies, among transport rolls a1 to an, the roll whose forward forward ratio f was changed at the time the pitch of surface defect P1 changed as the cause roll.

[0046] <About removal mode> When the control unit 7 identifies the cause roll, it executes the removal mode. When the control unit 7 executes the removal mode, it changes the forward advance rate f of the cause roll (transport roll a5 in the above example) to the removal forward advance rate. At this time, it sets the forward advance rates f of the other transport rolls (transport rolls a1 to a4, a6 to an in the above example) to the reference forward advance rate fa. The removal forward advance rate is a value that is 6% or more and 8% or less higher than the reference forward advance rate fa.

[0047] Therefore, at this time, the forward rate f becomes the removal forward rate only for the cause roll (transport roll a5) among the transport rolls a1 to an. Then, the outer peripheral surface of the cause roll (transport roll a5) and the strip B slide against each other. As a result, the deposit O1 is removed by friction with the strip B. This prevents the deposit O1 from growing. Furthermore, once the deposit O1 is completely removed from the cause roll (transport roll a5), no further surface defects P1 will occur.

[0048] <Surface defect reduction method> Next, a method for reducing surface defects according to the present invention will be described. The method for reducing surface defects is a method for reducing surface defects P of a strip B using a continuous annealing furnace 1.

[0049] Fig. 5 is a flowchart showing the overall configuration of a surface defect reduction method according to the present invention. As shown in Fig. 5, the surface defect reduction method includes a measurement step (step St1), a specification step (step St2), and a removal step (step St3).

[0050] In the measurement step (step St1), the flaw sensor 6 measures the presence or absence of surface flaws P on the strip B, the depth of the surface flaws P, the presence or absence of pitch in the surface flaws P, and the size of the pitch of the surface flaws P.

[0051] The identifying step (step St2) is a step of identifying, as the cause roll, one of the transport rolls a1 to an to which the deposit O1 that caused the surface defect P is attached. The identifying step (step St2) corresponds to the cause roll identifying mode described above.

[0052] The removal step (step St3) is a step of removing the deposit from the outer peripheral surface of the cause roll identified in the identification step (step St2). The removal step (step St3) corresponds to the above-mentioned removal mode. The measurement step (step St1) and the identification step (step St2) will be described in detail below.

[0053] <About the measurement process> 6 is a flowchart showing a detailed configuration of the measurement step. In the measurement step (step St1), first, the flaw sensor 6 starts capturing an image of the strip B (step St11). Next, while continuing to capture an image, the flaw sensor 6 detects whether or not there is a surface flaw P deeper than a predetermined threshold in the captured image (step St12). Step St12 is repeated until a surface flaw P deeper than the threshold is detected (No in step St12).

[0054] If a surface flaw P exceeding the threshold value is detected (Yes in step St12), it is determined whether or not the surface flaw P has pitch (step St13). If it is determined that the surface flaw P does not have pitch (No in step St13), the process returns to step St12 and repeats steps St12 and St13 until a surface flaw P having pitch is detected.

[0055] If it is determined in step St13 that the surface flaw P has a pitch (Yes in step St13), the size of the pitch is measured (step St14), and the process proceeds to the identification step (step St2).

[0056] <About specific processes> 7 is a flowchart showing a detailed configuration of the identification step. As shown in FIG. 7, in the identification step (step St2), first, a set value i=1 is set (step St211). The set value i is a value indicating the i-th zone (i-th zone Zi) counting from the inlet side, which is a target zone for changing the forward ratio f.

[0057] Next, the forward forward ratios of the transport rolls in the i-th zone Zi are all changed to the specific forward forward ratio fb (step St212). For example, when i=1, the forward forward ratios f of the transport rolls a1 to a3 in the first zone Z1 are all changed to the specific forward forward ratio fb.

[0058] Then, it is determined whether or not there is a change in the pitch of the surface flaws P (step St213). If there is no change in the pitch of the surface flaws P (No in step St213), 1 is added to i (step St214), and the process returns to step St212. Thereafter, steps St212 to St214 are repeated until a change occurs in the pitch of the surface flaws P.

[0059] If it is determined in step St213 that there is a change in the pitch of the surface defects P (Yes in step St213), the i-th zone Zi is identified as the above-mentioned cause zone (step St215). Next, all forward rates f of the transport rolls a1 to an are returned to the reference forward rate fa (step St216). Note that a series of steps including at least steps St211 to St215 can be considered as a cause zone identification process.

[0060] Next, the forward forward ratio f of the roll located closest to the entry side among the transport rolls a1 to an arranged in the cause zone is changed to the specific forward forward ratio fb (step St217). Next, it is determined whether there has been a change in the pitch of the surface flaws P (step St218). If it is determined that there has been no change in the pitch of the surface flaws P (No in step St218), the forward forward ratio f of the next adjacent roll on the exit side is changed from the reference forward forward ratio fa to the specific forward forward ratio fb (step St219), and the process returns to step St218. Then, steps St218 and St219 are repeated until it is determined in step St218 that there has been a change in the pitch. By repeating steps St218 and St219, the forward forward ratios f of the rolls arranged in the cause zone are changed to the specific forward forward ratio fb one by one in order from the entry side to the exit side.

[0061] If it is determined in step St218 that there is a change in pitch (Yes in step St218), the roll whose forward advance rate f is changed to the specific forward advance rate fb at the timing when the pitch changes is identified as the causal roll (step St220), and the process proceeds to the elimination step (step St3).

[0062] As described above, by monitoring the surface of the strip B with the flaw sensor 6, it is possible to detect the presence or absence, depth, and pitch of surface flaws P. Furthermore, by changing the forward rate f of the transport rolls a1 to an in the order described above based on the detection results of the flaw sensor 6, it is possible to identify the causative roll. Furthermore, by changing the forward rate of a specific roll to a removal forward rate, it is possible to remove deposits from the outer peripheral surface of the specific roll. This makes it possible to suppress the growth of surface flaws P.

[0063] Furthermore, there is no need to change the furnace temperatures of the heating zone 2 and the soaking zone 3. In this way, it became possible to identify the cause roll and remove the deposits without changing the manufacturing process of the strip B.

[0064] From the above, by using the continuous thermal annealing furnace 1 or the surface defect reduction method of the present invention, it is possible to suppress the growth of deposits on the causative roll without changing the manufacturing process. This makes it possible to suppress the pitted surface defects P from becoming harmful, and also to reduce the pitted surface defects P occurring on the strip B.

[0065] <Modification> Furthermore, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, although the transport rolls a1 to an are described as being arranged in the soaking zone 3, they may be arranged in the heating zone 2 or the cooling zone 4 in addition to the soaking zone 3. In this case, the control unit 7 can also execute the above-described cause roll identification mode and cause roll removal mode for the rollers arranged in the heating zone 2 and the cooling zone 4 among the transport rolls a1 to an.

[0066] In this case, the heating zone 2 and the soaking zone 3 can also be considered as one heat treatment section.

[0067] 1, the number of transport rolls a1 to an arranged in each zone (first zone Z1 to Nth zone ZN) is illustrated as three evenly spaced rolls, but is not limited to this. For example, the number may be four or more, two or less, or may not be evenly spaced.

[0068] Furthermore, the flaw sensor 6 is described as detecting the presence or absence of surface flaws P on the strip B, the depth of the surface flaws P, whether or not they have a pitch, the size of the pitch, and whether or not there has been a change in the pitch, but it may also be configured as follows: The flaw sensor 6 transmits an image of the surface of the strip B to the control unit 7. Based on this image, the control unit 7 can detect the depth of the surface flaws P, whether or not they have a pitch, the size of the pitch, and whether or not there has been a change in the pitch, etc.

[0069] The above-described method for reducing surface defects can also be applied to heat treatment processes other than those using continuous thermal annealing equipment.

[0070] Furthermore, the deposits O1 are described as metal oxides or the like, but are not limited to oxides and may be small pieces of metal, dust, or other foreign matter.

[0071] Furthermore, although the control unit 7 has been described as being able to change the forward advance f of the transport rolls a1 to an for each zone collectively, this is not limiting and the following configuration may also be used. For example, a plurality of inspection units may be set by arbitrarily selecting each transport roll (in accordance with FIG. 1, transport rolls a1 to an), and the control unit 7 may change the forward advance f of the transport rolls included in each inspection unit collectively for each inspection unit. Furthermore, the combination of transport rolls included in each inspection unit may have no relation to the first zone Z1 to the Nth zone Zn. One example of this configuration is one in which the first inspection unit includes transport roll a1, transport roll a5, and transport roll a8, the second inspection unit includes transport roll a3 and transport roll a7, and each of the plurality of inspection units includes a plurality of transport rolls. [Explanation of symbols]

[0072] 1 Continuous annealing furnace 2 Heating Zone 3. Equal Tropics 4 Cooling Zone 6. Flaw sensor 7 Control Unit B. Band O1 deposits P1~11 Surface defects Z1~Zn 1st Zone~Nth Zone a1~an transport roll d1 pitch d2 pitch f advanced rate fa standard advanced rate fb specific advanced rate i Setting value

Claims

1. A method for reducing surface defects in continuous heat treatment of a strip, comprising: a measuring step of measuring the depth and pitch of surface defects of the strip using a defect sensor installed on the outlet side of the continuous heat treatment; an identifying step of identifying a causative roll that caused the surface defect among a plurality of conveying rolls that convey the strip; a removing step of removing deposits that cause the surface defects from the outer peripheral surface of the cause roll identified in the identifying step; Equipped with The identification process is a surface defect reduction method characterized in that, when the depth of the surface defect measured by the measurement process is deeper than a predetermined threshold, the forward advance rate of each of the transport rolls is changed in an arbitrary order from a normal reference forward advance rate, and when the pitch of the surface defect changes, the transport roll whose forward advance rate has been changed is identified as the causative roll.

2. the belt-like body is conveyed by receiving a frictional force from the conveying rolls rotating at the reference forward speed while in contact with the outer peripheral surfaces of the conveying rolls, 2. The surface defect reduction method according to claim 1, wherein the removal step involves changing the forward advance of the causative roll from the reference forward advance, causing the outer peripheral surface of the causative roll to slide against the strip, and removing the deposit from the causative roll.

3. The specifying step increases the forward rate by 1% or more and 5% or less from the reference forward rate, 3. The surface defect reduction method according to claim 2, wherein the removal step increases the forward slip of the causative roll by 6% or more and 8% or less from the reference forward slip.

4. 2. The method for reducing surface defects according to claim 1, wherein each of the transport rolls is disposed in a soaking zone of the continuous heat treatment.

5. the soaking zone includes a plurality of zones separated by predetermined intervals, The transport rolls are disposed in a distributed manner in the respective zones, The identifying step includes: a cause zone identifying step of uniformly changing the forward ratio of the conveying roll for each zone, and identifying, among the zones, the zone in which the forward ratio has been changed when the pitch of the surface defects has changed, as the cause zone; a cause roll identifying step of changing the forward advance ratio of each of the transport rolls included in the cause zone from the reference forward advance ratio in an arbitrary order, and identifying the transport roll whose forward advance ratio has been changed as the cause roll when the pitch of the surface defect has changed; 5. The method for reducing surface defects according to claim 4, comprising:

6. a heat treatment zone for heat treating the strip; a plurality of transport rolls disposed in the heat treatment zone and configured to transport the strip; a defect sensor disposed on the outlet side of the heat treatment zone and capable of detecting surface defects of the strip; a control unit that can detect the pitch of the surface defects based on the detection result of the defect sensor and controls the forward advance rate of each of the conveying rolls; Equipped with The control unit a cause roll identification mode in which, when the depth of the surface defect is deeper than a predetermined threshold, the forward advance ratio of each of the transport rolls is changed from a normal reference forward advance ratio in an arbitrary order, and the transport roll whose forward advance ratio has been changed when the pitch of the surface defect changes is identified as the specific roll that caused the surface defect; a removal mode in which the forward advance of the causative roll is changed from the reference forward advance to cause the outer peripheral surface of the causative roll to slide against the strip, thereby removing deposits that cause the surface defects from the outer peripheral surface of the causative roll; A heat treatment apparatus configured to be able to perform the above.

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