JP5863464B2 - Annealing furnace of hot dip galvanizing equipment and operation method in the annealing furnace - Google Patents

Description

  The present invention relates to an annealing furnace of a hot dip galvanizing facility and an operation method in the annealing furnace.

A steel plate, which is one of typical metal materials, is widely used in the fields of automobiles, home appliances, building materials and the like. In recent years, in the automobile industry, in addition to improving durability, the weight of automobiles has been reduced from the viewpoint of improving fuel efficiency and reducing exhaust gas, and the use of high-tensile steel sheets has increased rapidly.
When performing hot dip galvanization, which is one of the surface treatments, on such a high-tensile steel plate, 0.2 to 3 elements (easily oxidizable elements) that the high-tensile steel plate is more easily oxidized than iron such as silicon are used. Since it is contained in an amount of about% by weight, the plating process is performed after an annealing process by a redox method.

  In this oxidation-reduction method, during annealing, a steel plate is first oxidized in an oxidation zone to form an iron oxide layer on the surface of the steel plate, and then the iron oxide layer is reduced to an iron layer in the reduction zone. This iron layer prevents generation of an easily oxidizable element oxide. That is, an oxide of an easily oxidizable element (for example, a silicon oxide film) repels molten zinc and generates a spot-like plating defect, but prevents an oxide of an easily oxidizable element from being generated by the iron layer. And uniform plating.

As described above, when the hot-dip galvanization is performed by annealing using the oxidation-reduction method, if the iron oxide layer is formed nonuniformly and / or insufficiently, the iron layer after reduction is also nonuniformly and / or insufficiently formed. As a result, an oxide of an easily oxidizable element is generated, resulting in poor plating.
Various techniques are known for an annealing process using a redox method as a pretreatment for the hot dip galvanizing process. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-146241) discloses a method of manufacturing hot dip galvanizing that can avoid poor plating of a steel sheet having a high silicon concentration.

  In view of the problem that when the iron oxide layer is thick, the reduction of the iron oxide layer becomes insufficient in the reduction zone, and the iron oxide layer that has not been reduced remains, and stable and good plating cannot be obtained. It was made. In this manufacturing method, a steel sheet is heated in a direct flame heating type direct flame zone, and after surface reduction and annealing in a reducing atmosphere in a vertical reduction zone, it is immersed in a hot dip galvanizing bath and galvanized. The hot-dip galvanized steel sheet manufacturing method is characterized in that, in the vertical reduction zone, the atmospheric gas is caused to flow in a direction opposite to the traveling direction of the steel sheet at least in the entry side region.

  According to this manufacturing method, a flow is formed so that the flow direction of the reducing gas in the reduction zone is opposite to the traveling direction of the steel plate. The flowing gas flow can be suppressed. Further, in the reduction zone, the high dew point gas generated by the reduction of the oxide film flows from the generation position of the high dew point gas to the direct fire heating zone side in the direction opposite to the steel plate traveling direction. Since the high dew point gas does not flow in the traveling direction of the steel plate after the reduction, the reduced steel plate is not oxidized again by the high dew point gas. The gas with a high dew point generated in the reduction zone accumulates in the direction opposite to the direction of travel of the steel sheet, ensuring an atmosphere distribution that gradually reduces the reducibility from the reduction zone inlet to the reduction zone outlet. The maximum reduction power can be secured near the reduction zone exit. As a result, the reduction reaction of the oxide film is stable, and even in a steel sheet to which silicon, which is an easily oxidizable element, is added, a good reduction action is stably exhibited in the reduction zone. As a result, galvanization can be realized stably and satisfactorily.

JP 2007-146241 A

However, the technique disclosed in Patent Document 1 described above pays attention to stably exhibiting a good reducing action in the reduction zone, and does not pay attention to the uniform generation of the iron oxide layer in the first place. . In Patent Document 1, the combustion control of the gas in the oxidation zone, particularly the air ratio control is performed based on the measurement result of the dew point of the atmospheric gas in the reduction zone in the vicinity of the connection between the oxidation zone (direct flame heating zone) and the reduction zone. There is only a description that the thickness of the iron oxide layer formed in the oxidation zone can be controlled. In this case, the iron oxide layer may not be uniformly formed, and there is a question that galvanization can be stably and satisfactorily realized. Moreover, although the technique disclosed in Patent Document 1 may be effective in an annealing furnace having a vertical reduction zone, there is a question about the effect in an annealing furnace having a horizontal reduction zone.

  In order to realize stable and good galvanization, the present applicant has researched and developed a method for uniformly producing an iron oxide layer on the surface of a steel sheet, and in order to produce a uniform iron oxide layer, It was found that two viewpoints of the rapid oxidation (the iron oxide layer is rapidly formed immediately before the reduction to prevent the iron oxide layer from being peeled off by the transport roll) are important together with the stabilization of the atmosphere. However, as described above, Patent Document 1 does not consider such a viewpoint.

  The present invention has been made in view of the above-mentioned problems, and an annealing furnace for a hot dip galvanizing facility capable of pre-treating a steel sheet using an oxidation-reduction method in an annealing furnace and realizing good hot dip galvanizing. And it aims at providing the operating method in the annealing furnace.

In order to solve the above problems, the annealing furnace of the hot dip galvanizing facility of the present invention takes the following technical means.
That is, the annealing furnace of the hot dip galvanizing facility of the present invention is an annealing furnace of a hot dip galvanizing facility that hot dip galvanizes a steel sheet using an oxidation-reduction method. The annealing furnace includes a non-oxidation zone (A zone) that heats a steel plate so as not to oxidize by burning a combustion gas having an air ratio of less than 1 with an open flame burner disposed above and below the steel plate, and the non-oxidation zone An oxidation zone (C zone) that is disposed downstream of (A zone) and burns combustion gas having an air ratio of 1 or more with a direct-burn burner located above and below the steel plate to oxidize and heat the steel plate. The reduction zone (E zone) is disposed downstream of the oxidation zone (C zone) and reduces the oxide film on the surface of the oxidized steel sheet in a reducing gas atmosphere containing hydrogen. Gas flows in the direction opposite to the feeding direction of the steel plate from the exit side of the reduction zone (E zone). In such an annealing furnace for hot dip galvanizing equipment, adjacent to the reduction zone (E zone) among the burners installed in the oxidation zone (C zone) in order to stabilize the oxidizing atmosphere in the oxidation zone (C zone). The air ratio of the reduction zone adjacent burner (D zone burner) that is at least one burner at the top and bottom is higher than the air ratio of all other burners in the oxidation zone (C zone), and the reduction zone (E The air ratio is set to burn the reducing gas flowing in from the belt.

Preferably, in order to stabilize the non-oxidizing atmosphere in the non-oxidation zone (A zone), at least one burner installed in the non-oxidation zone (A zone) is adjacent to the oxidation zone (C zone). The air ratio of the burner adjacent to the oxidation zone (B zone burner) is lower than the air ratio of all other burners in the non-oxidation zone (A zone) and flows from the oxidation zone (C zone). It is preferable that the air ratio is set so as to burn oxygen gas.

Preferably, the air ratio of the burner of the oxidation zone (C zone) is set to 1 or more, the reducing gas flowing from the reduction zone (E zone) is burned, and the oxygen concentration in the burned gas is equal to the oxidation zone. It is preferable that the air ratio of the reduction zone adjacent burner (D zone burner) is set to be the same as the oxygen concentration realized by the air ratio set in the (C zone) burner. .
Preferably, the air ratio of the burner in the non-oxidation zone (A zone) is set to less than 1, and the oxygen concentration in the gas after combustion by burning the oxygen gas flowing from the oxidation zone (C zone) is zero. The air ratio of the oxidation zone adjacent burner (B zone burner) is set to be the same as the oxygen concentration realized by the air ratio set in the oxidation zone (A zone) burner. And good.

Preferably, when the air ratio of the oxidation zone adjacent burner (B zone burner) and the reduction zone adjacent burner (D zone burner) is changed, the strength of the burner jet is maintained or increased. And good.
Moreover, the operating method in the annealing furnace of the hot dip galvanizing equipment of the present invention is the above-mentioned oxidizing zone (C zone) in order to stabilize the oxidizing atmosphere in the oxidizing zone (C zone) in the annealing furnace of the hot dip galvanizing equipment. Among the burners installed in the reduction zone (E zone), the air ratio of at least one burner adjacent to the reduction zone (E zone) is the other of the oxidation zone (C zone). The air ratio is set to be higher than the air ratio of all the burners and to burn the reducing gas flowing in from the reduction zone (E zone).

Preferably, in the operation method described above, among the burners installed in the non-oxidation zone (A zone), adjacent to the oxidation zone (C zone) in order to stabilize the non-oxidation atmosphere in the non-oxidation zone (A zone). The air ratio of the burner adjacent to the oxidation zone (B zone burner) that is at least one burner at the top and bottom is lower than the air ratio of all other burners in the non-oxidation zone (A zone), and the oxidation zone ( The air ratio may be set so as to burn oxygen gas flowing in from (C band).

  By using the annealing furnace of the hot dip galvanizing equipment of the present invention and the operation method in the annealing furnace, the steel sheet can be pretreated using the oxidation-reduction method in the annealing furnace, and good hot dip galvanizing can be realized.

It is a schematic diagram which shows the hot dip galvanization equipment which concerns on embodiment of this invention. (A) is a side view schematically showing the arrangement of side burners in the direct flame zone (non-oxidation zone and oxidation zone) in FIG. 1, (b) is a side view schematically showing the arrangement of another side burner, c) is a cross-sectional view schematically showing the arrangement of the side burners. It is a flowchart which shows the operation method in the annealing furnace of the hot dip galvanization equipment which concerns on embodiment of this invention. It is a figure which shows the air ratio of the side burner at the time of operating using a prior art, and the distribution of the oxygen concentration in an annealing furnace. It is a figure which shows the air ratio of the side burner at the time of operating using a comparative technique (the 1), and distribution of the oxygen concentration in an annealing furnace. It is a figure which shows the air ratio of the side burner at the time of operating using a comparative technique (the 2), and distribution of the oxygen concentration in an annealing furnace. It is a figure which shows distribution of the air ratio of the side burner at the time of operating using the operating method (the 1) which concerns on embodiment of this invention, and the oxygen concentration in an annealing furnace. It is a figure which shows distribution of the air ratio of the side burner at the time of operating using the operating method (the 2) which concerns on embodiment of this invention, and the oxygen concentration in an annealing furnace. It is a figure which shows distribution of the air ratio of the side burner at the time of operating using the operating method (the 3) which concerns on embodiment of this invention, and the oxygen concentration in an annealing furnace. (A) is the perspective view which shows typically another arrangement | positioning of the side burner of the direct fire zone (a non-oxidation zone and an oxidation zone) of FIG. 1, (b) is the side view. (A) is the perspective view which shows typically another arrangement | positioning of the side burner of the direct fire zone (a non-oxidation zone and an oxidation zone) of FIG. 1, (b) is the side view. (A) is the perspective view which shows typically another arrangement | positioning of the side burner of the direct fire zone (a non-oxidation zone and an oxidation zone) of FIG. 1, (b) is the side view.

Hereinafter, an annealing furnace of a hot dip galvanizing facility according to an embodiment of the present invention and an operation method in the annealing furnace will be described in detail with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.
[Hot galvanizing equipment]
In FIG. 1, the schematic diagram of the hot dip galvanization equipment 100 which concerns on this embodiment is shown.

  The steel plate 200 that has been rolled in the upper process continuously passes through the hot dip galvanizing equipment 100 to become a hot dip galvanized steel plate 210. In this embodiment, the steel plate 200 is a high-tensile steel plate (high-tensile steel) containing silicon (Si) in an amount of 0.2 to 3.0% by weight, preferably 1.2 to 3.0% by weight. Moreover, the steel plate 200 containing phosphorus (P) in addition to silicon may be used for increasing the tension.

This hot dip galvanizing equipment 100 is composed of a pre-tropical zone 110, an oxidation-free zone 120, an oxidation zone 130, a reduction zone 140, a cooling zone 150, a snout 160 and a plating pod 170 from the entry side of the steel plate 200. Then, the pre-tropical zone 110, the non-oxidation zone 120, the oxidation zone 130, and the reduction zone 140 constitute an annealing furnace, and in this annealing furnace, pretreatment (heat treatment prior to hot dipping) as described later is performed on the steel plate 200. Apply.

The pretreated steel plate 200 is continuously put into the plating pod 170 and hot dip galvanized. The plating conditions are a weight per unit area of 50 g / m ² , an alloying temperature of 480 ° C., and a plating bath temperature of 440 ° C. In addition, the annealing furnace of this hot dip galvanizing equipment 100 is a horizontal type (horizontal type).
The reduction zone needs to be filled with atmospheric gas, and the gas flows in the direction opposite to the conveying direction of the steel plate 200. The reason why the gas flow direction is determined in this way is to prevent the hydrogen in the reduction zone 140 from reacting with oxygen and burn it in the upstream direct flame zone.

Here, the pre-tropical zone 110, the non-oxidation zone 120, the oxidation zone 130, and the reduction zone 140 constituting the annealing furnace will be described.
The pre-tropical zone 110 is a region where the steel plate 200 is heated to about 400 ° C., and the non-oxidation zone 120 does not oxidize the steel plate by burning the burner at an air ratio of less than 1 (0.9 to 0.98). This is a region to be heated to about 700 ° C. The oxidation zone 130 is an area where the burner is burned at an air ratio of 1 or more to oxidize and heat the steel plate 200. The reduction zone 140 is a region in which a reducing gas such as hydrogen (hydrogen concentration of about 15%) is used as an atmosphere and the iron oxide layer generated on the surface of the steel plate 200 is reduced and heated and annealed at about 800 ° C.

  Further, the non-oxidation zone 120, the oxidation zone 130, and the reduction zone 140 may be configured by a region formed in one annealing furnace, or may be configured by a furnace provided independently. . In the present embodiment, each is constituted by a furnace provided independently, and an intermediate zone (throat) is provided between the non-oxidation zone 120 and the oxidation zone 130 and between the oxidation zone 130 and the reduction zone 140. ) Is provided. In these intermediate zones and in the annealing furnace (pre-tropical 110, non-oxidation zone 120, oxidation zone 130, reduction zone 140, cooling zone 150 and snout 160), a plurality of rolls 180 for conveying the steel plate 200 are arranged. .

The non-oxidation zone 120 and the oxidation zone 130 are direct-fire zones in which the steel plate 200 is directly heated by an open flame burner (side burner). The reduction zone 140 indirectly heats the steel plate 200 by the radiant tube 142 and the steel plate 200. The iron oxide layer on the surface of the iron is reduced.
Specifically, in the direct fire zone, the steel plate 200 is directly heated by a side burner and heated to a predetermined temperature according to a heat pattern set corresponding to the component composition and material standard of the steel plate 200, and at the same time The rolling oil on the surface of the steel plate 200 is removed, and an oxide layer is generated on the surface of the steel plate 200.

Thereafter, in the reduction zone, the steel plate 200 is indirectly heated by the radiant tube 142, and is heat-annealed at a predetermined temperature for a predetermined time in accordance with a heat pattern set corresponding to the component composition and material standard of the steel plate 200. The
The pre-tropical zone 110 and the cooling zone 150 are not described in detail because they have a low direct relationship with the gist of the present invention, but well-known equipment is appropriately employed.
[Side burner in non-oxidation zone and oxidation zone]
FIG. 2A to FIG. 2C show layout diagrams of the side burners in the non-oxidation zone 120 and the oxidation zone 130 which are direct flame zones.

2A shows the arrangement of the side burners in the longitudinal direction of the steel plate 200 in the furnace (the non-oxidation zone 120 or the oxidation zone 130), and FIG. 2C shows the furnace perpendicular to the longitudinal direction of the steel plate 200. A cross section inside (non-oxidation zone 120 or oxidation zone 130) is shown. As shown in FIG. 1, FIG. 2 (a) and FIG. 2 (c), in the furnace of the non-oxidation zone 120 or the oxidation zone 130, the side burner 122 (132) and the side burner 124 (134) are in the longitudinal direction. Are arranged in a pair at the top and bottom. Moreover, as shown in these drawings, the side burners arranged at the same position in the longitudinal direction have different flame injection directions on the upper side and the lower side. The side burner (dots on the circle) that injects a flame from the back side to the near side of the paper surface in FIG. 2 (a) and the side burner (dots on the circle symbol) that injects a flame from the near side to the front side of the paper surface are vertically moved. It is arranged in a pair. By arranging the side burners in this way (while avoiding the mutual influence of the side burners by not facing the side burners), the steel plates 200 conveyed by the roll 180 are moved in the longitudinal direction and the front and back directions. It can be heated uniformly. When the side burners are arranged in this manner, by adjusting the pair of upper and lower side burners (two in the dotted frame shown in FIG. 2A), the vertical direction of the steel plate 200 in the furnace is adjusted. The atmosphere in the cross section can be controlled. For this reason, the oxidation zone adjacent burner (B-band side burner) and the reduction zone adjacent burner (D-band side burner), which will be described later, each have a pair of upper and lower.

  Furthermore, another arrangement of the side burner is shown in FIG. As shown in this figure, the arrangement of the side burners is obtained by shifting the arrangement of the upper or lower side burners in FIG. 2A by about half the arrangement interval of the side burners in the longitudinal direction. That is, also in the arrangement of the side burner shown in FIG. 2B, the cross section in the furnace perpendicular to the longitudinal direction of the steel plate 200 is as shown in FIG. By arranging the side burners in this way, the steel plate 200 conveyed by the roll 180 can be uniformly heated in the longitudinal direction and the front and back directions. When the side burners are arranged in this manner, a cross section perpendicular to the longitudinal direction of the steel plate 200 in the furnace is obtained by adjusting two pair of side burners (two of the dotted line frames shown in FIG. 2B) on the top and bottom. The atmosphere in can be controlled. For this reason, the oxidation zone adjacent burner (B-band side burner) and the reduction zone adjacent burner (D-band side burner), which will be described later, each have two pairs in the vertical direction. Note that, as indicated by the dotted frame shown in FIG. 2B, the direction of the flame may be the same direction or a different direction (considered to be more preferable than the same direction). Further, in some cases, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are two on the upper side, one on the lower side, two on the upper side, one on the lower side, etc. It doesn't matter.

  Thus, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) need to be able to adjust the atmosphere in a cross section perpendicular to the longitudinal direction in the furnace. The oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are two pairs of upper and lower in the arrangement shown in FIG. 2A, and the arrangement shown in FIG. Then, there are two pairs vertically (or three including at least one each above and below). The number of these oxidation zone adjacent burners (B zone side burners) and reduction zone adjacent burners (D zone side burners) depends on the length of the furnace, the number of burners, the arrangement of the burners, etc. (the longitudinal direction in the furnace). It is appropriately set so that the atmosphere in the cross section perpendicular to the surface can be adjusted and the hot dip galvanization can be favorably expressed. Therefore, in the present invention, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are not limited to such numbers and arrangements.

The structure of the side burners 122, 124, 132, and 134 is not described in detail because it has a low direct relationship with the gist of the present invention. For example, the combustion burner disclosed in Japanese Patent Application Laid-Open No. 2009-35783 is disclosed. This structure can be applied as appropriate.
As shown in FIG. 1, the non-oxidation zone 120 is the A-band, the oxidation zone 130 is the C-band, the reduction zone 140 is the E-band, and the intermediate zone between the non-oxidation zone 120 and the oxidation zone 130 is the B-band. An intermediate zone between 130 and the reduction zone 140 is a D zone.

Strictly speaking, since the intermediate zone is between the furnaces, no side burner is arranged, but among the side burners 122, 124,..., 126, 128 installed in the non-oxidation zone 120 (A zone), oxidation is not possible. At least one pair of side burners 126 and 128 adjacent to the band 130 (C band) is defined as an oxidation band adjacent burner (B band side burner).
Further, among the side burners 132, 134,..., 136, 138 installed in the oxidation zone 130 (C zone), at least one pair of side burners 136, 138 adjacent to the reduction zone 140 (E zone) is reduced. A band adjacent burner (side burner of D band) is used.

In the operation method according to the present embodiment, the air ratio in the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) is controlled.
Here, the air ratio will be described. This air ratio is a ratio to the theoretical air ratio of the combustion gas supplied to the side burner (ratio of air to combustion gas when combustion gas and oxygen react and burn without excess or deficiency), and the air ratio is When it is higher than 1, oxygen is in an excess (excess) state, and when the air ratio is lower than 1, oxygen is in a shortage state.

  In the present invention, when changing the air ratio of the side burner, either the amount of air to the side burner, the amount of gas (fuel amount), or the both can be adjusted. It doesn't matter. Note that when an oxidizing atmosphere is desired, it is preferable to increase the amount of air without reducing the amount of gas to reduce the amount of gas, but it is preferable to increase the amount of air without reducing the amount of gas. Therefore, it is preferable to increase the gas amount without decreasing the air amount, instead of making the oxygen insufficient.

By doing so, the air ratio can be manipulated without reducing the combustion energy of the side burner to bring the atmosphere in the furnace into a desired state, and the momentum of the jet of the side burner can be reduced (burner jet and exhaust gas). Mixing with the flow or the flow of the atmosphere is promoted to realize complete combustion), and the temperature of the steel plate 200 can be sufficiently heated.
Furthermore, when adjusting the atmosphere in the furnace, if the air amount is adjusted without adjusting the gas amount, it is only necessary to operate the air supply amount to the side burner, and the equipment (throttle valve) and control ( Flow rate control) is simplified.

  More specifically, for example, in the D zone, since the amount of gas in the furnace is small and the flow velocity in the furnace is low, it is difficult to mix, so it is preferable not to reduce the gas amount of the side burner (thus adjusting the air amount, not the gas amount). . The B band tends to be mixed with a large amount of exhaust gas from the C band and the D band, and even if the air quantity of the side burner is reduced, there is little influence, so it is only necessary to adjust the air quantity. In such a case, it is only necessary to operate the air supply amount to the side burner, and the control of the gas amount becomes unnecessary, so that the equipment cost can be suppressed.

[Outline of operation method]
In order to realize stable and good galvanization, the present applicant has researched and developed a method for uniformly producing an iron oxide layer on the surface of a steel sheet, and in order to produce a uniform iron oxide layer, It was found that two viewpoints of the rapid oxidation (the iron oxide layer is rapidly formed immediately before the reduction to prevent the peeling of the iron oxide layer on the transport roll) are important in addition to the stabilization of the atmosphere.

  In particular, in order to produce an iron oxide layer uniformly, it is necessary to stabilize the atmosphere in the furnace. As described above, in the case of an annealing furnace including the direct flame (non-oxidation zone 120 and oxidation zone 130) and the reduction zone 140, the gas in the furnace flows from the reduction zone 140 side and burns in the direct flame zone. It is exhausted to the outside air along with the exhaust gas in the direct fire zone. When the steel plate 200 is oxidized in an oxidizing atmosphere in the direct fire zone, there is a problem that the atmosphere in the oxidation zone 130 is not stable due to the reducing gas flowing from the reducing zone 140.

  Moreover, since the iron oxide layer may be peeled off by the roll 180 when the steel plate 200 after the iron oxide layer is generated is conveyed in the furnace, the iron oxide layer can be generated as quickly as possible immediately before the reduction zone 140. It is preferable (it is hard to peel off after returning to the iron layer). In order to oxidize rapidly, it is necessary to oxidize after raising the temperature without oxidation. When the temperature of the steel plate 200 is raised in the non-oxidation zone 120, there is a problem that the atmosphere of the non-oxidation zone 120 is not stable due to the influence of exhaust gas flowing from the oxidation zone 130.

Thus, the oxidizing atmosphere in which the steel sheet 200 is oxidized in the oxidation zone 130 is affected by the reducing gas (containing hydrogen) flowing from the reduction zone 140. The non-oxidizing atmosphere in which the temperature of the steel sheet 200 is raised in the non-oxidizing zone 120 is affected by the exhaust gas (containing oxygen) flowing from the oxidizing zone 130. The reducing gas (containing hydrogen) flowing from the reducing zone 140 may be referred to as a reducing gas.
From such a point of view, the present applicant has made intensive research and heated the steel sheet 200 without oxidation, and in order to realize rapid oxidation after reaching a high temperature, the non-oxidizing atmosphere and the oxidizing atmosphere are different from each other. In order to eliminate the influence of the gas flowing in from the region (band), it has been reached that the following method is suitable.

In order to stabilize the atmosphere of the oxidation zone 130, the boundary between the oxidation zone 130 and the reduction zone 140 (intermediate) so that the atmosphere of the oxidation zone 130 does not become unstable due to the reducing gas containing hydrogen flowing in from the reduction zone 140. The reducing gas is completely burned by the flame of the reducing zone adjacent burner (side burners 136 and 138 which are the D zone burners) in the D zone which is the belt.
For this purpose, the flow rate of the burner jet is made higher than the flow rate of the reducing gas flowing in from the reduction zone 140 (as will be described later, the flow rate of the burner jet is not lowered so as not to turn down even if the air ratio is changed). Promotes mixing of jet and reducing gas flow to achieve complete combustion. In this case, the air ratio of the D-band side burner is preferably set to a sufficiently high air ratio so that the reducing gas burns.

  In order to stabilize the atmosphere of the non-oxidation zone 120, a combustion gas containing oxygen flowing from the oxidation zone 130 (oxygen gas), in other words, so that the atmosphere of the non-oxidation zone 120 does not become unstable due to exhaust gas, Exhaust gas is completely burned by the flame of the burner adjacent to the oxidation zone (side burners 126 and 128 which are burners of the B zone) at the boundary between the non-oxidation zone 120 and the oxidation zone 130 (B zone which is an intermediate zone).

  For that purpose, the burner jet and exhaust gas are made larger than the flow velocity of the burner jet (the flow rate of the burner jet is not lowered so as not to turn down even if the air ratio is changed as described later). Promotes mixing with the flow and achieves complete combustion. In this case, the air ratio of the B-band side burner is preferably set to a sufficiently low air ratio so that the exhaust gas burns.

By performing the annealing treatment by the oxidation-reduction method in this way, the atmosphere of the non-oxidation zone 120 and the oxidation zone 130 is stabilized and an iron oxide layer is uniformly formed. Moreover, it becomes possible to produce | generate an iron oxide layer rapidly and can suppress the drop-off | omission with a roll. Thereafter, since the uniform iron oxide layer is reduced to the iron layer in the reduction zone, the plating quality is improved.
[Detailed operation method]
A detailed operation method in the annealing furnace of the hot dip galvanizing facility 100 according to the present embodiment having the configuration shown in FIGS. 1 and 2 will be described with reference to the flowchart of FIG. 3. FIG. 3 is a flowchart showing a procedure of processing executed by an operator who manages the operation of the hot dip galvanizing equipment 100.

  In step (hereinafter, step is described as S) 10, it is determined whether or not the steel plate 200 contains an element that is more easily oxidized than iron such as silicon. At this time, the determination is made based on the component composition and material standard of the steel plate 200 mounted on the hot dip galvanizing equipment 100. If steel plate 200 contains an element that oxidizes more easily than iron, such as silicon (YES in S10), the process proceeds to S12. If not (NO in S10), the process proceeds to S14. Moved to.

In S12, the steel sheet is hot dip galvanized by heat annealing using an oxidation-reduction method. Thereafter, the process proceeds to S16. In S14, since the steel plate 200 does not contain an element that is more easily oxidized than iron such as silicon, hot dip galvanization is performed without changing the operation conditions. After the process of S14, this process ends.
In S16, the air ratio of the C-band side burner is increased (oxygen surplus state) to operate. By operating in this way, an iron oxide layer can be generated on the surface of the steel plate 200 in the oxidation zone 130.

  In S18, it is determined whether or not there is a possibility of uneven plating due to unevenness of the iron oxide layer generated on the surface of the steel plate 200 (unevenness of oxidation). If it is determined that such a possibility exists even if the air ratio is repeatedly adjusted (YES in S18), the process proceeds to S20. If not (NO in S18), the plating process can be performed uniformly, so hot dip galvanization is performed without changing the operating conditions in S22. After the process of S22, this process ends.

  At S20, the air ratio of the reduction zone adjacent burner (D band side burner) is increased, and the reduction band adjacent burner (D band side burner) is not turned down to increase the air ratio. That is, the air ratio is increased without reducing the ability of the reduction zone adjacent burner (the D zone side burner). The turn-down means that neither the amount of gas (fuel amount) nor the amount of air supplied to the side burner is reduced (the same applies hereinafter). Since it does not turn down, the mixing of the sufficient jet flow from the burner adjacent to the reduction zone (side burner of D zone) and the reduction gas flow flowing in from the reduction zone 140 is promoted, and the hydrogen contained in the reduction gas is completely combusted. be able to. Thereafter, the process proceeds to S24.

In S24, it is determined whether or not there is a possibility of uneven plating due to unevenness of the iron oxide layer generated on the surface of the steel plate 200 (uneven oxidation) even under the operating conditions changed in S20. S
If it is determined that there is such a possibility even if the air ratio is repeatedly adjusted under the operating condition changed in 20 (YES in S24), the process proceeds to S26. If not (NO in S24), the plating process can be performed uniformly, so hot dip galvanizing is performed without changing the operating conditions in S28. After the process of S28, this process ends.

  At S26, the air ratio of the oxidation zone adjacent burner (B zone side burner) is lowered, and the oxidation zone adjacent burner (B zone side burner) is not turned down to increase the air ratio. That is, the air ratio is lowered without reducing the ability of the oxidation zone adjacent burner (B zone side burner). Since it does not turn down, mixing of a sufficient jet flow from the burner adjacent to the oxidation zone (side burner of B zone) and the exhaust gas flow flowing in from the oxidation zone 130 is promoted, and oxygen contained in the exhaust gas is completely burned. be able to. Thereafter, the process proceeds to S30.

  In S30, it is determined whether or not there is a possibility of uneven plating due to unevenness of the iron oxide layer generated on the surface of the steel plate 200 (uneven oxidation) even under the operation conditions changed in S26. If it is determined that such a possibility exists even if the air ratio is repeatedly adjusted under the operating conditions changed in S24 (YES in S30), the process proceeds to S32. If not (NO in S30), the plating process can be performed uniformly, so hot dip galvanizing is performed without changing the operating conditions in S34. After the process of S34, this process ends.

  In S32, the air ratios of the A-band side burner, the B-band side burner, the C-band side burner, and the D-band side burner are changed as follows. The air ratio of the C-band side burner is set to 1.0 or more, the air ratio of the D-band side burner is set to the C band, and the oxygen concentration in the gas after combustion by burning the reducing gas containing hydrogen flowing in from the E band The air ratio of the A-band side burner is less than 1.0 and the air ratio of the B-band side burner flows from the C-band so that the oxygen concentration is the same as the oxygen concentration that is set for the side burner. So that the (deficient) oxygen concentration in the gas after burning the exhaust gas containing oxygen is the same as the (deficient) oxygen concentration realized by the air ratio set in the A-band side burner. Change the ratio. Even in this case, the side burner is not turned down.

  In the operation method according to the present embodiment shown in such a flowchart, the air of the side burner is generated so that the unevenness of the iron oxide layer generated on the surface of the steel plate 200 (the unevenness of oxidation) does not occur and the unevenness of plating does not occur. Repeatedly adjusting the ratio. That is, if it is determined that there is a possibility of uneven plating, the air ratio of the reduction zone adjacent burner (D zone side burner) is adjusted (repetitively) (S20). If it is determined that plating unevenness may still occur, the air ratio of the oxidation zone adjacent burner (B zone side burner) is adjusted (repeatedly) (S26). If it is determined that plating unevenness may still occur, the air ratio of the reduction zone adjacent burner (D-band side burner) and the air ratio of the reduction zone adjacent burner (D-band side burner) are (repeated). Adjust (S32).

[Operating state: Oxygen concentration distribution and plating state in the furnace]
Based on the above configuration and flowchart, the operation state when the operation method in the annealing furnace of the hot dip galvanizing facility according to this embodiment is executed will be described with reference to the drawings.
7 to 9 are diagrams showing the air ratio of the side burner and the oxygen concentration distribution in the annealing furnace. FIG. 4 shows the result of using the conventional technique, and FIG. 5 shows the result of using the comparative technique 1. FIG. 6 shows the result using the comparative technique 2, FIG. 7 shows the result using the operating condition changed in S20, FIG. 8 shows the result using the operating condition changed in S26, and FIG. 9 shows the result in S32. The results using the changed operating conditions are shown respectively. That is, FIGS. 7 to 9 correspond to the operation method according to the present embodiment.

In these figures, the bar graph shows the air ratio of the side burner, and the broken line shows the oxygen concentration distribution in the annealing furnace. Since the side burners in the furnace are discretely arranged, the bar graph represents the air ratio of the side burners, but the number of bar graphs and the number of side burners do not correspond exactly.
FIG. 4 shows the distribution of the air ratio of the side burner and the oxygen concentration in the furnace under the operating conditions (no oxidation) of a normal steel plate (mild steel) that does not contain an easily oxidizable element, which is shown as the prior art. Under this operating condition, the air ratio of the side burner is set to 0.95, which is less than 1.0 over the entire area. As can be seen from FIG. 4, oxygen is deficient in the entire area of the furnace because oxygen is insufficient to burn the reducing gas hydrogen and unburned gas.

  FIG. 5 shows the distribution of oxygen concentration in the furnace under the operating conditions where the burner air ratio in the non-oxidizing zone 120 and the oxidizing zone 130 is increased to 1.05. Under these operating conditions, the air ratio of the non-oxidation zone 120 side burner (A zone side burner and B zone side burner) and the oxidation zone 130 side burner (C zone side burner and D zone side burner) is increased. It is set. However, the oxidation zone 130 is affected by the reducing gas flowing from the reduction zone 140, so that the oxygen concentration is in an oxygen-deficient state below 0%, and a stable oxidizing atmosphere is not achieved. Further, the non-oxidation zone 120 is in an oxygen surplus state where the oxygen concentration is 0% or more and is not a stable non-oxidation atmosphere.

  FIG. 6 shows that in order to heat the steel plate 200 in the non-oxidation zone 120 without being oxidized, the air ratio of the side burners of the non-oxidation zone 120 (A-side side burner and B-side side burner) is set to 0.95. In order to rapidly oxidize the steel plate 200 in the band 130, the oxygen concentration in the furnace under the operating conditions in which the air ratio of the side burners in the oxidation band 130 (the C side burner and the D band side burner) was 1.1 was used. Show the distribution. The oxygen-deficient state in the non-oxidation zone 120 (A zone) is realized and a stable non-oxidizing atmosphere is obtained. However, the oxidation zone 130 (C-band) is also in an oxygen-deficient state and is not in a stable oxidizing atmosphere. .

  FIG. 7 shows the distribution of oxygen concentration in the furnace under operating conditions where the air ratio of the reduction zone adjacent burner (side burner in D zone) is increased to 1.3. It can be seen that when the air ratio of the D-band side burner is increased, the oxygen concentration in the oxidation zone 130 is increased and the oxidation atmosphere is stabilized. A uniform iron oxide layer can be generated on the surface of the steel plate 200. However, the oxygen surplus state is present on the downstream side of the non-oxidation zone 120 (the oxidation zone 130 side), which is a slightly undesirable situation for the rapid formation of an iron oxide layer in the oxidation zone 130.

  FIG. 8 shows the distribution of oxygen concentration in the furnace under operating conditions where the air ratio of the oxidation zone adjacent burner (B zone side burner) is lowered to 0.85. When the air ratio of the B-band side burner is lowered, oxygen in the exhaust gas flowing from the oxidation zone 130 can be consumed. It can be seen that the oxygen concentration in the B band is zero. In addition to the oxygen concentration in the oxidation zone 130 becoming higher and the oxidation atmosphere being stabilized, the oxygen surplus state has been eliminated on the downstream side (oxidation zone 130 side) of the non-oxidation zone 120, and the oxidation zone 130 is rapidly oxidized. An iron layer can be generated.

  In FIG. 9, the air ratio of the D-band side burner is realized by the air ratio set in the C-band side burner by burning the reducing gas containing hydrogen flowing from the E band and burning the reducing gas. Further, the air ratio of the side burner in the B zone is set to be equal to the oxygen concentration in the gas after burning the exhaust gas containing oxygen flowing in from the C zone. The distribution of oxygen concentration in the furnace under the operating conditions with the air ratio changed to be the same as the (insufficient) oxygen concentration realized at the air ratio set in the side burner of the belt. By setting the air ratio of the side burner in the D zone as described above, hydrogen in the reducing gas flowing from the reduction zone 140 (E zone) can be consumed, and the oxygen concentration in the oxidation zone 130 (C zone). Can be constant. Similarly, by setting the air ratio of the B side burner as described above, oxygen in the exhaust gas flowing from the oxidation zone 130 (C zone) can be consumed, and the non-oxidation zone 120 (A zone). ) Can be kept constant.

  These are summarized in Table 1.

  As shown in Table 1, the steel sheet 200 annealed by the comparative technique 1 shown in FIG. 5 and the comparative technique 2 shown in FIG. 6 caused plating failure, but the operation shown in the present embodiment shown in FIGS. Since the steel plate 200 annealed by the method can form a uniform iron oxide layer on its surface, no defective plating occurs even when hot dip galvanizing is performed in a later step. The plating state is based on the visual inspection result.

  As described above, according to the annealing furnace of the hot dip galvanizing facility according to the present embodiment and the operation method in the annealing furnace, the atmosphere of the non-oxidation zone and the oxidation zone is stabilized, and the iron oxide layer is generated uniformly. Is possible. Moreover, it becomes possible to produce | generate an iron oxide layer rapidly and can suppress the drop-off | omission with a roll. Thereafter, the uniform iron oxide layer is reduced to the iron layer in the reduction zone, so that the plating quality can be improved.

As a more specific effect of the operation method in the annealing furnace of the hot dip galvanizing equipment according to this embodiment and the annealing furnace,
(1) Spot-like non-plating is improved.
(2) Plating defects due to peeling of the iron oxide layer (oxide film) are improved.
(3) The plating failure due to the lack of the iron oxide layer (oxide film) is improved.

(4) The oxygen concentration in the oxidation zone is stabilized in an excess state without being influenced by the hydrogen concentration of the reducing gas flowing from the reduction zone, and a uniform iron oxide layer (oxide film) can be generated.
(5) The oxygen concentration in the non-oxidation zone is stable in a deficient state without being affected by the residual oxygen concentration in the exhaust gas flowing from the oxidation zone, and the steel plate can be heated without being oxidized. It can oxidize and can suppress peeling by a roller.

(6) Even in the operation of switching between a high-strength steel plate and a normal steel plate, the side burner downstream of the oxidation zone and the side burner downstream of the non-oxidation zone (in other words, the upstream side burner and downstream side of the oxidation zone) The non-oxidizing atmosphere and the oxidizing atmosphere can be easily switched by simply controlling the air ratio of the side burner.
As shown in FIG. 9, in order to make the oxygen concentration of the oxidation zone 130 (C zone) and the oxygen concentration of the non-oxidation zone 120 (A zone) constant, the air ratio of the D zone side burner and the side of the B zone Although the air ratio of the burner was adjusted (S32), in addition to / alternatively, the air ratio of the C-band side burner and the air ratio of the A-band side burner were adjusted to obtain the oxygen concentration in the direct fire zone. You may make it stabilize with the density | concentration of.

[Arrangement of side burner]
As described above, it has been described that defective plating can be improved by adjusting the air ratio of a specific side burner. However, regarding the arrangement of another side burner other than FIGS. 2 (a) and 2 (b), This will be described in detail below.
10, 11, and 12, (a) is a perspective view schematically showing the arrangement of side burners in the direct flame zone (non-oxidation zone and oxidation zone) of FIG. 1, and (b) is a side view thereof. Show.

As shown in FIG. 10, the arrangement of another side burner is employed when the furnace width is wide, and is provided so that the side burners face each other. In FIG. 10B, there are a side burner (a small white circle on a circle) that injects a flame from the back side of the paper surface to the front side, and a side burner (× on the circle symbol) that injects a flame from the front side of the paper surface to the front side. It arrange | positions so that it may mutually oppose. For this reason, in FIG.10 (b), the side burner which injects a flame from the back side of a paper surface to this side (small white circle on a circle mark), and the side burner which injects a flame from the near side of a paper surface to the front side (in a circle mark). X) is shown overlapping. Such an arrangement makes it difficult to take the flame length of the side burner when the furnace width is wide, and even if the side burners face each other, the furnace width is wide and the side burners do not affect each other. Are provided on both sides. Also in this case, the side burners are provided on the upper side and the lower side, and a pair of upper and lower side burners (four in the dotted frame shown in FIG. 10B) are adjusted in the same manner as in FIG. By doing so, the atmosphere in the cross section perpendicular to the longitudinal direction of the steel plate 200 can be controlled in the furnace. That is, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are a pair of upper and lower side burners (four in the dotted frame shown in FIG. 10B). )

  Next, as shown in FIG. 11, another side burner is arranged when the side burner is thinned or used, or when the side burners originally provided on the opposite side are arranged in a staggered manner in the vertical direction. Therefore, it is provided to be face-to-face ignition and staggered up and down. The notation of the side burner in FIG. 11B is the same as that in FIG. In this case, the atmosphere in the cross section perpendicular to the longitudinal direction of the steel plate 200 is controlled in the furnace by adjusting the side burners for two rows (four in the dotted frame shown in FIG. 11B). Can do. That is, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are side burners for two rows (four in the dotted frame shown in FIG. 11B). .

  Next, as shown in FIG. 12, the arrangement of another side burner is provided so as to be a staggered face and a staggered top and bottom. The notation of the side burner in FIG.12 (b) is the same as FIG.10 (b). In this case, the atmosphere in the cross section perpendicular to the longitudinal direction of the steel plate 200 is controlled in the furnace by adjusting the side burners for two rows (four in the dotted line frame shown in FIG. 12B). Can do. There are two rows of side burners (four in the dotted frame shown in FIG. 12B). However, in this case, it is preferable that the interval between adjacent side burners is narrow.

  As described above, the number of these oxidation zone adjacent burners (B zone side burners) and reduction zone adjacent burners (D zone side burners) depends on the furnace length, the number of burners, the burner arrangement, and the like. It is suitably set so that the effect (atmosphere in a cross section perpendicular to the longitudinal direction in the furnace can be adjusted and hot dip galvanization can be exhibited). Therefore, in the present invention, the oxidation zone adjacent burner (B zone side burner) and the reduction zone adjacent burner (D zone side burner) are not limited to such numbers and arrangements.

  By the way, this invention is not limited to embodiment mentioned above, The shape, structure, material, combination, etc. of each member can be suitably changed in the range which does not change the essence of invention. Further, in the embodiment disclosed this time, matters that are not explicitly disclosed, for example, operating conditions, operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. However, matters that can be easily assumed by those skilled in the art are employed.

DESCRIPTION OF SYMBOLS 100 Hot-dip galvanization equipment 110 Pre-tropical 120 Non-oxidation zone 130 Oxidation zone 140 Reduction zone 150 Cooling zone 160 Snout 170 Plating pod 180 Roll 200 Steel plate 210 Hot-dip galvanized steel plate

Claims (7)

An annealing furnace of a hot dip galvanizing facility for hot-dip galvanizing a steel sheet using an oxidation-reduction method. The annealing furnace burns combustion gas having an air ratio of less than 1 with an open flame burner arranged above and below the steel sheet. The combustion gas having an air ratio of 1 or more is burned by a non-oxidation zone that heats the steel plate so as not to oxidize, and a direct-fired burner that is disposed downstream of the non-oxidation zone and disposed above and below the steel plate. An oxidation zone that oxidizes and heats the steel plate, a reduction zone that is disposed downstream of the oxidation zone and that reduces the oxide film on the surface of the oxidized steel plate in a reducing gas atmosphere containing hydrogen, and In the annealing furnace of the hot dip galvanizing equipment where gas flows from the outlet side of the reduction zone in the direction opposite to the feed direction of the steel sheet,
In order to stabilize the oxidation atmosphere in the oxidation zone, among the burners installed in the oxidation zone, the air ratio of the reduction zone adjacent burner that is at least one burner adjacent to the reduction zone is An annealing furnace of a hot dip galvanizing facility, characterized in that it is set to an air ratio that is higher than the air ratio of all burners and burns the reducing gas flowing in from the reduction zone. In order to stabilize the non-oxidizing atmosphere in the non-oxidizing zone, among the burners installed in the non-oxidizing zone, the air ratio of at least one burner adjacent to the oxidizing zone is the non-oxidizing zone. 2. The hot dip galvanizing according to claim 1, wherein the hot dip galvanizing is set to an air ratio that is lower than an air ratio of all the other burners in the band and burns oxygen gas flowing in from the oxidation band. An annealing furnace for equipment. The air ratio of the burner in the oxidation zone is set to 1 or more,
Combustion of the reducing gas flowing from the reduction zone, and the oxygen concentration in the gas after combustion is the same as the oxygen concentration realized by the air ratio set in the burner of the oxidation zone, The annealing furnace for hot dip galvanizing equipment according to claim 2, wherein an air ratio is set. The air ratio of the non-oxidizing zone burner is set to less than 1,
Combustion of the oxygen gas flowing from the oxidation zone, and the oxygen concentration in the burned gas is the same as the oxygen concentration realized by the air ratio set in the non-oxidation zone burner. The annealing furnace of the hot dip galvanizing equipment according to claim 2 or 3, wherein an air ratio is set.   The melting according to any one of claims 1 to 4, wherein when the air ratio of the oxidation zone adjacent burner and the reduction zone adjacent burner is changed, the strength of the burner jet is maintained or increased. An annealing furnace for galvanizing equipment. An annealing furnace of a hot dip galvanizing facility for hot-dip galvanizing a steel sheet using an oxidation-reduction method. The annealing furnace burns combustion gas having an air ratio of less than 1 with an open flame burner arranged above and below the steel sheet. The combustion gas having an air ratio of 1 or more is burned by a non-oxidation zone that heats the steel plate so as not to oxidize, and a direct-fired burner that is disposed downstream of the non-oxidation zone and disposed above and below the steel plate. An oxidation zone that oxidizes and heats the steel plate, a reduction zone that is disposed downstream of the oxidation zone and that reduces the oxide film on the surface of the oxidized steel plate in a reducing gas atmosphere containing hydrogen, and In the operation method of the annealing furnace of the hot dip galvanizing equipment, the gas flows from the outlet side of the reduction zone in the direction opposite to the feeding direction of the steel sheet.
In order to stabilize the oxidation atmosphere in the oxidation zone, among the burners installed in the oxidation zone, the air ratio of the reduction zone adjacent burner that is at least one burner adjacent to the reduction zone is An operating method of an annealing furnace of a hot dip galvanizing facility, characterized in that an air ratio is set to be higher than the air ratio of all burners and to burn reducing gas flowing in from the reduction zone. In order to stabilize the non-oxidizing atmosphere in the non-oxidizing zone, among the burners installed in the non-oxidizing zone, the air ratio of at least one burner adjacent to the oxidizing zone is the non-oxidizing zone. The hot dip galvanizing according to claim 6, wherein the hot dip galvanizing is set to an air ratio lower than the air ratio of all the other burners in the belt and burning the oxygen gas flowing in from the oxidation belt. How to operate the equipment's annealing furnace.