JP2008001934A - Hot-dip galvanization equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-dip galvanization equipment capable of changing the environment in oxidation region, that is, from an oxidation environment to a non-oxidation region and from a non-oxidation environment to an oxidation region, in a short period of time and capable of changing the kind of steel. <P>SOLUTION: Following four types of hot-dip galvanization equipment are provided: equipment (1) in which a steel sheet containing elements more easily oxidizable than iron is irradiated with a flame in an oxidation zone to form an iron oxide film on its surface after being raised in temperature, and the steel sheet is hot-dip-galvanized after the iron oxide film is reduced in a reduction zone, and the oxidation zone and the reduction zone are formed in a furnace 1 or a furnace 2; equipment (2) in which a plurality of burners 3 for irradiating the steel sheet with a flame in the oxidation zone are arranged in the equipment (1); equipment (3) in which, when representing the distance between the tips of the burners 3 and the steel sheet 2 by h, and the distance between the burners by L, the formula of L<10h is satisfied; and equipment (4) in which, when representing the width of the burner by W, the formula of L<2W is satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to a technical field related to hot dip galvanizing equipment, and in particular, a steel plate containing an element (for example, Si, Mn) that is more easily oxidized than iron is improved in plating properties by an oxidation-reduction method. It belongs to the technical field regarding the hot dip galvanizing equipment used when hot dip galvanizing later.

  Steel sheets that contain elements that are easier to oxidize than Fe (hereinafter also referred to as easily oxidizable elements), if the content of easily oxidizable elements is high, oxidizable elements concentrate on the surface of the steel sheet during the annealing process (reduction furnace) before plating. Since wettability with molten zinc deteriorates, there is a problem that non-plating occurs.

As a measure to prevent the occurrence of non-plating for steel plates containing such easily oxidizable elements (hereinafter also referred to as easily oxidizable element-containing steel plates), a thick oxide film of 400 to 10,000 mm was formed on the steel plate surface in a non-oxidizing furnace. Thereafter, an oxidation-reduction method in which annealing is performed in a reduction furnace has been proposed (see, for example, JP-A-55-122865). That is, a non-oxidizing furnace is used under oxidizing conditions (oxidizing atmosphere), and after forming a thick oxide film on the surface of the steel sheet in this furnace, the iron oxide film is reduced in a reducing furnace, and then hot-dip galvanized. A hot dip galvanizing method (hereinafter also referred to as a hot dip galvanizing method for easily oxidizable element-containing steel sheets) has been proposed.
JP 55-122865 A

  In the case of a normal general steel sheet, after annealing in a non-oxidation furnace, annealing is performed in a reduction furnace, and then hot dip galvanizing is performed to produce a hot dip galvanized steel sheet. Following hot-dip galvanized steel sheet manufacturing, when hot-dip galvanizing of easily oxidizable element-containing steel sheets, it is necessary to change the non-oxidizing furnace from a non-oxidizing atmosphere to an oxidizing atmosphere. .

  After manufacturing a hot-dip galvanized steel sheet for an easily oxidizable element-containing steel sheet, and subsequently manufacturing a hot-dip galvanized steel sheet for a normal general steel sheet, it is necessary to change the non-oxidizing furnace from an oxidizing atmosphere to a non-oxidizing atmosphere. It takes time to exchange gas.

  For this reason, it is difficult to change the steel type of the target steel sheet for hot dip galvanization, and there is a problem that the steel type cannot be changed easily. In addition, this steel type change is a change from a normal general steel plate to an easily oxidizable element-containing steel plate, or a change from an easily oxidizable element-containing steel plate to a normal general steel plate.

  The present invention has been made in view of such circumstances, and its purpose is to change the atmosphere in the oxidation region (change from an oxidizing atmosphere to a non-oxidizing atmosphere, or change from a non-oxidizing atmosphere to an oxidizing atmosphere). An object of the present invention is to provide a hot-dip galvanizing facility that can be changed in a short time and can easily change the steel type.

  As a result of intensive studies to achieve the above object, the present inventors have completed the present invention. According to the present invention, the above object can be achieved.

  The present invention thus completed and capable of achieving the above object relates to a hot dip galvanizing equipment, which is the hot dip galvanizing equipment according to claims 1 to 4 (the hot dip galvanizing according to the first to fourth inventions). Equipment), which has the following configuration.

  That is, in the hot dip galvanizing facility according to claim 1, after heating the steel sheet containing an element that is more easily oxidized than iron in a non-oxidation zone, a flame is irradiated in the oxidation zone to form an iron oxide film on the steel plate surface. , A hot dip galvanizing facility for performing hot dip galvanization after reducing the iron oxide film in a reduction zone, wherein the non-oxidation zone, oxidation zone, and reduction zone are formed in one or two furnaces This is a hot dip galvanizing facility [first invention].

  The hot dip galvanizing equipment according to claim 2 is the hot dip galvanizing equipment according to claim 1, wherein a plurality of rows of burners for irradiating a flame in the oxidation zone are arranged [second invention].

  The hot dip galvanizing facility according to claim 3 is L <10h, where h is the distance between the burner tip and the steel plate in the oxidation zone, and L is the distance between the burners. [3rd invention]. The hot dip galvanizing equipment according to claim 4 is the hot dip galvanizing equipment according to claim 2 or 3, wherein the width of the burner is W and the distance between the burners is L, L <2W. Fourth invention].

  According to the hot dip galvanizing equipment according to the present invention, the change of atmosphere in the oxidation region (oxidation zone) (change from the oxidation atmosphere to the non-oxidation atmosphere, change from the non-oxidation atmosphere to the oxidation atmosphere) should be performed in a short time. Can be changed easily.

  The hot dip galvanizing equipment according to the present invention, as described above, irradiates a flame in the oxidation zone after raising the temperature of the steel plate containing an element that is more easily oxidized than iron (easily oxidizable element-containing steel plate). A hot dip galvanizing facility for forming an iron oxide film on a steel plate surface and reducing the iron oxide film in a reduction zone, followed by hot dip galvanization, wherein the non-oxidation zone, oxidation zone, reduction zone is 1 or 2 The hot dip galvanizing facility is characterized by being formed in a furnace.

  According to this hot dip galvanizing equipment, after heating an easily oxidizable element-containing steel sheet in a non-oxidation zone, a flame is irradiated in the oxidation zone to produce an iron oxide film on the steel plate surface, and the iron oxide film is reduced in a reduction zone Then, hot dip galvanization can be performed. That is, the easily oxidizable element-containing steel sheet can be hot dip galvanized after the plating property is improved by the oxidation-reduction method.

  At this time, when there is a single flame irradiation means, the flame portion becomes an oxidizing atmosphere and becomes an oxidation zone, and when there are a plurality of flame irradiation means, the region between the flame portion and the flame becomes an oxidation atmosphere and becomes an oxidation zone. .

  The volume of the oxidation zone is much smaller than the volume of a non-oxidizing furnace (used in an oxidizing atmosphere) in the conventional hot dip galvanizing method for easily oxidizable element-containing steel sheets. That is, it is not good to oxidize the steel sheet gradually in the oxidation zone, and it is preferable to rapidly oxidize and generate an oxide film rapidly (Japanese Patent Application No. 2004-369311), so the length of the oxidation zone (the length in the running direction of the steel plate) ) May be short, but rather short, and it is preferable that the temperature of the oxidation zone is reduced because the oxidation zone can be rapidly oxidized after being heated without oxidation, and the oxidation zone can be shortened. Is much smaller than the volume of a non-oxidizing furnace (used in an oxidizing atmosphere) in the conventional hot dip galvanizing method for easily oxidizable element-containing steel sheets. In addition, in the hot dip galvanizing equipment according to the present invention, the non-oxidation zone, the oxidation zone, and the reduction zone are formed in the furnace of 1 or 2, so that the conventional hot dip oxidization element-containing steel plate galvanizing method is used. The number of intermediate zones between the furnaces is smaller than in the case of the furnace, and the volume in the furnace is correspondingly smaller.

  After performing hot dip galvanizing on the above-mentioned easily oxidizable element-containing steel plate, when performing hot dip galvanizing on a normal general steel plate, the irradiation of the flame in the oxidation zone is stopped. If it does so, the atmosphere of an oxidation zone will change very rapidly compared with the case where the non-oxidation furnace in the hot dip galvanizing method of the conventional easily oxidizable element containing steel plate is changed from an oxidizing atmosphere to a non-oxidizing atmosphere. That is, since the volume of the region of the oxidation zone is small as described above, when the flame irradiation in the oxidation zone is stopped, the oxidation zone is very fast and the oxidation zone is not an oxidation atmosphere, and a non-oxidation atmosphere (non-oxidation atmosphere or reduction atmosphere). A non-oxidizing atmosphere mixed with gas). At this time, a non-oxidizing atmosphere is maintained in the non-oxidizing zone.

  Therefore, after the hot dip galvanizing to the steel sheet containing the easily oxidizable element is finished, the hot dip galvanizing to the ordinary general steel sheet is started much faster than the conventional hot dip galvanizing method of the steel sheet containing the easily oxidizable element. be able to.

  After hot dip galvanization of this ordinary general steel plate, when hot dip galvanizing is performed on a steel plate containing an easily oxidizable element, irradiation of a flame in the oxidation zone is started. If it does so, the atmosphere of an oxidation zone changes very rapidly compared with the case where the non-oxidation furnace in the hot dip galvanizing method of the conventional easily oxidizable element containing steel plate is changed from a non-oxidizing atmosphere to an oxidizing atmosphere. That is, since the volume of this oxidation zone is small as described above, when the flame irradiation is started, the oxidation zone atmosphere becomes an oxidation atmosphere very quickly. At this time, a non-oxidizing atmosphere is maintained in the non-oxidizing zone.

  Therefore, after the completion of hot dip galvanizing on ordinary steel sheets, hot dip galvanizing on steel sheets containing easily oxidizable elements is started much faster than the conventional hot dip galvanizing method for steel sheets containing easily oxidizable elements. be able to.

  As can be seen from the above, according to the hot dip galvanizing facility according to the present invention, the atmosphere in the oxidation region (oxidation zone) can be changed in a much shorter time than the conventional hot dip galvanizing method for easily oxidizable element-containing steel sheets. (A change from an oxidizing atmosphere to a non-oxidizing atmosphere, a change from a non-oxidizing atmosphere to an oxidizing atmosphere) can be performed, and therefore, the steel type can be easily changed. That is, the steel type of the steel plate to be hot dip galvanized can be easily changed.

  The annealing line of the conventional hot dip galvanizing equipment has a non-oxidizing furnace and a reducing furnace in this order, and the conventional hot dip galvanizing method for easily oxidizable element-containing steel sheets is an oxidation process of the non-oxidizing furnace as described above. Although it is used in the atmosphere, in such a conventional hot dip galvanizing equipment, as mentioned above, it takes time to change the furnace atmosphere, so it is difficult to change the steel type of the target steel sheet for hot dip galvanization, The steel grade cannot be changed easily. As a countermeasure, it is conceivable to add an oxidation furnace so that an annealing line of a hot dip galvanizing facility has a non-oxidation furnace, an oxidation furnace, and a reduction furnace in this order. In this way, it is considered that the atmosphere gas can be changed in a shorter time than in the case of the conventional hot dip galvanizing equipment, and the steel type can be changed easily. However, when the steel sheet to be hot dip galvanized is a steel sheet containing an easily oxidizable element, an oxidizing gas flows through the intermediate zone between the non-oxidizing furnace and the oxidizing furnace, and the steel sheet gradually oxidizes and There is a concern that rapid oxidation is difficult to perform, and that wettability with molten zinc is lowered, and it is difficult to perform good hot dip galvanizing. Moreover, there is an intermediate zone between the furnaces, and the volume in the furnace increases accordingly.

  If the non-oxidation zone, the oxidation zone, and the reduction zone are formed in separate furnaces, there is a concern as described above.

  Therefore, in the hot dip galvanizing facility according to the present invention, as described above, the non-oxidation zone, the oxidation zone, and the reduction zone are formed in one or two furnaces. Here, the fact that the non-oxidation zone, the oxidation zone, and the reduction zone are formed in one furnace means that the non-oxidation zone, the oxidation zone, and the reduction zone are all formed in one furnace. Say. The formation of a non-oxidation zone, an oxidation zone, and a reduction zone in a furnace of 2 means that a non-oxidation zone, an oxidation zone, or a reduction zone, a non-oxidation zone, or a non-oxidation zone and an oxidation zone of one furnace. It means that it is formed inside and the remaining zone (oxidation zone and reduction zone or reduction zone) is formed inside the other one furnace. This non-oxidation zone or non-oxidation zone and oxidation zone are formed inside one furnace, and the remaining zone is formed inside one other furnace. The oxidation zone and the reduction zone are formed inside the other furnace, the non-oxidation zone and the oxidation zone are formed inside the one furnace, and the reduction zone is the same as that of the other furnace. It is formed inside.

  When the non-oxidation zone, oxidation zone, and reduction zone are formed in one or two furnaces as described above, when the above-mentioned non-oxidation zone, oxidation zone, and reduction zone are formed in separate furnaces Compared with, the volume in the furnace becomes smaller by the amount of the intermediate zone. Among these, when the non-oxidation zone, the oxidation zone, and the reduction zone are formed in one furnace, there is no intermediate zone, so the presence of the intermediate zone between the non-oxidation furnace and the oxidation furnace described above There is also an advantage that there is no concern that rapid oxidation will be difficult.

  When the non-oxidation zone, oxidation zone, and reduction zone are formed in two furnaces, the non-oxidation zone and oxidation zone are formed inside one furnace, and the reduction zone is formed inside the other furnace. Even in the case where the steel plate is used, there is an advantage that there is no concern that rapid oxidation of the steel sheet may be difficult due to the presence of the intermediate zone between the non-oxidation furnace and the oxidation furnace. In this respect, it is preferable to the case where the non-oxidation zone is formed inside one furnace and the oxidation zone and the reduction zone are formed inside one furnace. Considering the volume of the furnace, it is most preferable that the non-oxidation zone, the oxidation zone, and the reduction zone are formed in one furnace.

  As described above, the hot dip galvanizing equipment according to the present invention is formed in a furnace having one or two non-oxidation zones, oxidation zones, and reduction zones. Thus, in order to form a non-oxidation zone, an oxidation zone, and a reduction zone in one or two furnaces, a flame may be irradiated in the oxidation zone. More specifically, this can be realized, for example, by arranging a plurality of burners for irradiating a flame in an oxidation zone [second invention]. That is, when the non-oxidation zone is burned at an air ratio of less than 1, and a reducing gas is introduced into the reduction zone and the burner is ignited and a flame is irradiated toward the steel sheet, the burned area at an air ratio of less than 1 is A non-oxidizing atmosphere is formed, a non-oxidizing zone is formed, a region between the flame part and the flame is an oxidizing atmosphere, an oxidizing zone is formed, and a region where reducing gas is introduced becomes a reducing atmosphere and a reducing zone is formed. It is formed. The burner arrangement may be a single row. In this case, the flame part becomes an oxidizing atmosphere and becomes an oxidation zone.

  When a burner for irradiating a flame in the oxidation zone is arranged, when performing hot dip galvanization on the easily oxidizable element-containing steel sheet, the burner is ignited and the flame is irradiated in the oxidation zone. When hot dip galvanizing is performed on a general steel sheet, the burner is stopped (fire extinguishing) and the flame irradiation in the oxidation zone is stopped.

  When multiple rows of slit burners are installed as the above burner, if the flames are arranged so that they overlap each other, the oxidation rate of the steel sheet is effectively increased locally due to the influence of the flame, so that rapid oxidation can be performed and oxide film growth The speed is increased, and the wettability with the hot dip zinc is improved, so that the hot dip galvanization can be performed.

  A local oxidizing atmosphere can be secured even with one burner, but the oxidation rate is low when the width of the burner flame is narrow. Therefore, it is conceivable to use a burner that irradiates a wide flame such as a flat burner, but in this case, it is difficult to lengthen the flame to reliably irradiate the steel plate, and it is difficult to oxidize the steel plate. .

  If a plurality of burners are arranged in such a manner that the flames overlap each other, an oxidation zone is formed between the burners. In particular, rapid oxidation can be performed and the oxide film growth rate is increased. In such an arrangement, the interval between the burners is small and the volume of the oxidation region is small, so that the atmosphere replacement (change) is faster, and therefore the steel type can be switched (changed) in a shorter time.

  When multiple rows of burners are installed in the oxidation zone, the air ratio of the burners is, for example, 1.0 or more. In this case, each burner jet is jetted onto the steel plate and then flows to the burner side while being recirculated toward the burner nozzle, so there is residual oxygen in the vicinity of the steel plate between the burners, and an oxidizing atmosphere is ensured.

  There is a reduction zone after the oxidation zone, and the atmosphere gas in this reduction zone flows into the oxidation zone. Therefore, due to the arrangement of the burner, the atmosphere in the vicinity of the steel sheet is partially reduced.

  If the burner spacing (distance between the burners) is too large, the burner jets do not sufficiently collide with each other after the respective burner jets collide with the steel sheet. There is a concern that reducing gas may flow between the burners from the exhaust gas flow path and the steel sheet surface may be reduced.

  When the distance between the burner tip and the steel plate in the oxidation zone is h and the distance between the burners is L, if L <10h, the above-mentioned possibility is surely resolved. [Third Invention] In other words, when L <10h, the burner jet is sufficiently fast about 5 times on one side in the sheet passing direction, and the burner jets collide with each other and flow uniformly to the burner side. It is possible to prevent the reducing gas from the furnace from being caught between the burners, and as a result, the possibility of reduction of the steel sheet surface can be surely eliminated.

  Further, when the width of the burner is W and the distance between the burners is L, when L <2W, the above-described possibility can be reliably eliminated [fourth invention]. . That is, when the burner width W is wide, even if the burner interval L is relatively long, it is easy to ensure the atmosphere between the burner jets as in the above case, and when L <2W is satisfied, the burner side flows. It is possible to prevent the reducing gas from the reduction furnace from being caught between the burners, and as a result, the possibility of reduction of the steel sheet surface can be reliably eliminated.

  According to the hot dip galvanizing equipment according to the present invention, as described above, the atmosphere gas can be changed in an extremely short time, and therefore, the steel type of the steel sheet to be hot dip galvanized can be easily changed. Become. In addition, there are the following advantages and effects.

  That is, compared with the case where the above-mentioned non-oxidation zone, oxidation zone, and reduction zone are formed in separate furnaces, the number of intermediate zones is small (there may be no intermediate zone), so the furnace is compact. Become. There are usually rolls in the intermediate band, but the number of rolls can be reduced together with the intermediate band (it can also be made free of rolls), making it difficult for the iron oxide layer to peel off and ensuring good surface properties. Become. Since there are no partition plates or intermediate chambers, pressure loss is small and furnace pressure fluctuations are small. Because there is no intermediate zone, there is no drop in the furnace gas temperature. When the gas in the reduction zone flows into the oxidation zone and the gas in the oxidation zone flows into the non-oxidation zone, the number of intermediate zones is small (there may be no intermediate zone), so the gas flows after being cooled in the intermediate zone Therefore, the furnace temperature is less likely to fluctuate and the furnace temperature tends to be constant.

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

[Comparative Example 1]
A hot dip galvanizing facility according to Comparative Example 1 is shown in FIG. This hot dip galvanizing equipment is applied to a conventional hot dip galvanizing method for easily oxidizable element-containing steel sheets. As shown in FIG. 2, this hot dip galvanizing equipment has a preheating furnace 12, a non-oxidizing furnace 13, and a reducing furnace 15 as an annealing furnace, followed by a cooling zone 16, a snout 17, a galvanizing bath. 18. A throat (intermediate zone) 19 is installed between the furnaces. A roll 11 is disposed in the throat portion and in each furnace.

  Using the above hot dip galvanizing equipment, hot dip galvanizing was carried out on steel plates containing easily oxidizable elements. Details will be described below. As the easily oxidizable element-containing steel plate, a high-tensile steel plate having a steel component composed of C: 0.1% by mass, Si: 1.8% by mass, Mn: 1.5% by mass, the balance being Fe and inevitable impurities was used. While running the steel plate 2, the steel plate 2 is heated to about 200 ° C. in the preheating furnace 12, then heated to 700 ° C. in the non-oxidizing furnace 13 (used in an oxidizing atmosphere) at an air ratio of 1.0 or more, and reduced in the reducing furnace 15 ( Heat annealing to about 800 ° C at a hydrogen concentration of about 15%. Thereafter, the annealed steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling.

  After hot dip galvanizing on such an easily oxidizable element-containing steel plate, the non-oxidizing furnace 13 was switched to a non-oxidizing atmosphere, and thereafter, normal galvanizing was performed on a general steel plate. Details will be described below. As an ordinary general steel plate, a steel plate made of C: 0.1% by mass, the balance being Fe and inevitable impurities was used. While this steel plate 2 is running, it is heated to about 200 ° C. in the preheating furnace 12, heated to 700 ° C. in the non-oxidizing furnace 13 (non-oxidizing atmosphere) at an air ratio of 0.9 to 0.98, and the reducing atmosphere (hydrogen concentration) in the reducing furnace 15. Heat annealing to about 800 ° C at about 15%). Thereafter, the annealed steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling. At this time, it took several tens of minutes to switch the non-oxidizing furnace 13 to the non-oxidizing atmosphere. In other words, after changing the air ratio of the burner, it became possible to perform non-oxidative heating after replacing the atmosphere, and this took several tens of minutes.

  After hot dip galvanizing on such a normal general steel sheet, the non-oxidizing furnace 13 was switched to an oxidizing atmosphere. That is, the air ratio of the burner of the non-oxidizing furnace 13 was switched from 0.9 to 0.98 and changed to an oxidizing atmosphere. Thereafter, hot dip galvanization was performed on the easily oxidizable element-containing steel sheet. Details will be described below. As the easily oxidizable element-containing steel sheet, the same high-tensile steel sheet as in the case of hot dip galvanizing to the easily oxidizable element-containing steel sheet was used. While the steel plate 2 is running, it is heated to about 200 ° C. in the preheating furnace 12, heated to 700 ° C. at an air ratio of 1.0 or more in a non-oxidizing furnace 13 (used in an oxidizing atmosphere), and reduced in a reducing furnace 15 (hydrogen concentration about 15). %) And heat annealing to about 800 ° C. Thereafter, the steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling. At this time, it took several tens of minutes to switch the non-oxidizing furnace 13 to the oxidizing atmosphere. That is, after changing the air ratio of the burner, it became possible to oxidize after replacing the atmosphere, which took several tens of minutes.

[Example 1]
FIG. 1 shows a hot dip galvanizing facility according to Example 1 of the present invention. This hot dip galvanizing equipment has a preheating furnace 12 similar to that in Comparative Example 1, and has a furnace 1 having a non-oxidation zone, an oxidation zone, and a reduction zone following this preheating oven, as shown in FIG. Then, following the furnace 1, the cooling zone 16, the snout 17, and the galvanizing bath 18 similar to those in the comparative example 1 are provided. A throat (intermediate zone) is installed between the preheating furnace 12 and the furnace 1. A roll 11 is disposed in the throat portion and the furnace 1.

  As shown in FIG. 1, two rows of burners 3 are arranged in the oxidation zone, and the flame 4 is irradiated toward the steel plate 2 using the burners 3, thereby oxidizing the atmosphere between the burners (between the burners 3) 6. Can be. An oxidation-free burner 10 is disposed in the oxidation-free zone, and an oxidation-free atmosphere 5 is formed here. A radiant tube 8 is provided in the reduction zone, and a reducing atmosphere 7 is formed by introducing a reducing gas therein. Such a non-oxidation zone, an oxidation zone, and a reduction zone are formed inside one furnace 1.

  An example of the state of the flame in the oxidation zone is shown in FIG. 3 (side sectional view). When the distance between burners (distance between the burners) L is small, it can be seen that the jets 4 of the burner flame overlap each other. It can also be seen that the distance h between the burner tip and the steel plate is also related to whether or not the jets of the burner flame overlap. In FIG. 3, reference numeral 20 denotes an overlapping portion of the jets 4 of the burner flame.

  An example of the state of the flame in the oxidation zone is shown in FIG. 4 (front sectional view). Since the jet 4 of the burner passes through the burner side flow path 21, when the distance L between the burners is wider than the width W of the burner, the atmospheric gas from the reduction zone flows from the burner side flow path to the steel plate surface. Recognize.

  Using the above hot dip galvanizing equipment, hot dip galvanizing was carried out on steel plates containing easily oxidizable elements. Details will be described below. The distance L between burners in the oxidation zone of the hot dip galvanizing equipment, the distance h between the tip of the burner 3 and the steel plate 2, and the width W of the burner 3 were set to satisfy L <10h and L <2W. More specifically, L = 9h and L = 1.8W. The air ratio of the burner in the oxidation zone was set to 1.0 or more. As the easily oxidizable element-containing steel plate, a high-tensile steel plate having the same composition as in Comparative Example 1 was used. While the steel plate 2 is running, it is heated to about 200 ° C. in the preheating furnace 12, and then heated to 650 ° C. in the non-oxidation zone (in the non-oxidation atmosphere 5) in the furnace 1, and the oxidation zone (in the oxidation atmosphere 6). To 700 ° C., and annealed to about 800 ° C. in a reduction zone (in a reducing atmosphere 7 with a hydrogen concentration of about 15%). Thereafter, the annealed steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling.

  After hot dip galvanizing on such an easily oxidizable element-containing steel sheet, the burner 3 in the oxidation zone is stopped (extinguishing) and the irradiation of the flame 4 is stopped, and this oxidation zone is removed in a non-oxidizing atmosphere (non-oxidizing atmosphere or reducing gas). Then, hot dip galvanization was performed on a normal general steel sheet. Details will be described below. As a normal general steel plate, the same general steel plate as in Comparative Example 1 was used. While this steel plate 2 is running, it is heated to about 200 ° C. in the preheating furnace 12, and then heated to 700 ° C. in the non-oxidation zone (in the non-oxidation atmosphere 5) in the furnace 1, and the reduction zone (hydrogen concentration about 15%). In a reducing atmosphere 7), heat annealing is performed to about 800 ° C. Thereafter, the annealed steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling. At this time, the time required for making the oxidation zone non-oxidizing atmosphere was extremely short (instant). That is, when the burner was extinguished, the atmosphere immediately became non-oxidizing.

  After hot-dip galvanizing of such a normal general steel plate, the burner 3 in the oxidation zone is ignited and irradiation of the flame 4 is started, and this oxidation zone is set to the oxidizing atmosphere 6. Hot dip galvanized. Details will be described below. The air ratio of the burner in the oxidation zone was set to 1.0 or more. As the easily oxidizable element-containing steel plate, a high-tensile steel plate having the same composition as in Comparative Example 1 was used. While the steel plate 2 is running, it is heated to about 200 ° C. in the preheating furnace 12, and then heated to 650 ° C. in the non-oxidation zone (in the non-oxidation atmosphere 5) in the furnace 1, and the oxidation zone (in the oxidation atmosphere 6). To 700 ° C., and annealed to about 800 ° C. in a reduction zone (in a reducing atmosphere 7 with a hydrogen concentration of about 15%). Thereafter, the annealed steel plate 2 is cooled in the cooling zone 16 and immersed in the galvanizing bath 18 at about 420 ° C. The immersed steel plate 2 is pulled up from the galvanizing bath 18 while traveling. At this time, the time required to set the oxidation zone to the oxidizing atmosphere 6 was extremely short (instant). That is, at the same time when the burner was ignited, oxidation could be started instantaneously.

  As can be seen from the above, in the case of the hot dip galvanizing equipment according to Example 1 of the present invention, compared with the case of the hot dip galvanizing equipment according to Comparative Example 1, in the oxidation region (oxidation zone) in a very short time. The atmosphere can be changed (change from oxidizing atmosphere to non-oxidizing atmosphere, change from non-oxidizing atmosphere to oxidizing atmosphere), and therefore the steel type can be changed easily.

  In Example 1, the burners 3 are arranged in two rows, and the flame 4 of the burners 3 is irradiated toward the steel plate 2 to create an oxidizing atmosphere 6 between the burners, thereby forming an oxidation zone. Instead, it is possible to use means for irradiating the steel sheet with a jet (flame) adjusted in oxygen concentration or water vapor concentration. In this case, an oxidizing atmosphere may be formed between the jets (flame) in an oxidizing atmosphere. it can.

  According to the hot dip galvanizing equipment according to the present invention, the atmosphere in the oxidation region (oxidation zone) can be changed (from the oxidizing atmosphere to the non-oxidized state) in a much shorter time than in the case of the hot dip galvanizing method of the conventional oxidizable element-containing steel sheet. Change to atmosphere, change from non-oxidizing atmosphere to oxidizing atmosphere), and therefore the steel grade of the steel plate subject to hot dip galvanization can be easily changed. In the case of frequent changes, it can be used particularly preferably.

It is a schematic diagram which shows the hot dip galvanizing equipment which concerns on Example 1 of this invention. 2 is a schematic diagram showing a hot dip galvanizing facility according to Comparative Example 1. FIG. It is a sectional side view of the oxidation zone in the hot dip galvanization equipment concerning Example 1 of the present invention, and is a figure showing the state of the flame in this oxidation zone. It is a front sectional view of the oxidation zone in the hot dip galvanization equipment concerning Example 1 of the present invention, and is a figure showing the state of the flame in this oxidation zone.

Explanation of symbols

  1-Furnace, 2-Steel plate, 3-Burner, 4-Flame, 5-Non-oxidizing atmosphere, 6-Oxidizing atmosphere, 7-Reducing atmosphere, 8-Radiant tube, 10-Non-oxidizing Burner, 11--roll, 12--preheating furnace, 13--non-oxidation furnace, 15--reduction furnace, 16--cooling zone, 17--snout, 18--galvanizing bath, 19--throat (intermediate) Belt), 20—flame overlap, 21—burner side flow path.

Claims (4)

  After heating the steel sheet containing an element that is easier to oxidize than iron in the non-oxidation zone, irradiate a flame in the oxidation zone to generate an iron oxide film on the steel plate surface, and after reducing the iron oxide film in the reduction zone, A hot dip galvanizing equipment for hot dip galvanizing, wherein the non-oxidation zone, the oxidation zone, and the reduction zone are formed in one or two furnaces.   The hot dip galvanizing equipment according to claim 1, wherein a plurality of rows of burners for irradiating a flame in the oxidation zone are arranged.   The hot dip galvanizing equipment according to claim 2, wherein L <10h, where h is the distance between the burner tip and the steel plate in the oxidation zone and L is the distance between the burners. The hot dip galvanizing facility according to claim 2 or 3, wherein L <2W, where W is a width of the burner and L is a distance between the burners.

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