Annealing furnace

Abstract

The present invention provides an annealing furnace that can remove lubricating oil adhering to a workpiece by burn-off during the annealing process. [Solution] An annealing furnace for annealing a workpiece W to be processed with lubricating oil attached, comprising a furnace body 10 having an inlet 11 for inserting the workpiece W and an outlet 12 for removing the workpiece W, wherein a heating zone 13 is provided inside the furnace body 10 for heating the workpiece W with a plurality of direct-fired burners 41-49, the heating zone 13 having a plurality of zones 31-33 along the transport direction of the workpiece W from the inlet 11 to the outlet 12, the air ratio of the burners 41-49 is adjusted to be different for each of the plurality of zones 31-33, the zone closest to the inlet 11 among the plurality of zones 31-33 is designated as the first zone 31, and the first zone 31 is characterized in that the air ratio of the burners 41-43 is higher in the first zone 31 than in the other zones 32,33.

Description

Technical Field

[0001] The present invention relates to an annealing furnace for annealing an object to be treated to which a lubricant is attached.

Background Art

[0002] An object to be treated using metal as a material may be annealed (annealed) for the purpose of improving, adjusting, and improving mechanical properties such as removing internal stress, adjusting hardness, and improving workability. Annealing is carried out by heating the object to be treated to a high temperature in a furnace, holding it at that temperature for a certain period of time, and then slowly cooling it. In the process of heating the object to be treated to a high temperature, in many cases, a layer of oxide called oxide scale is formed on the surface of the object to be treated. While this oxide scale protects the surface of the object to be treated, it affects the mechanical properties, so it is desirable to remove it during the annealing of the object to be treated. Patent Document 1 discloses a method for manufacturing a steel sheet including a step of pickling an object to be treated to remove oxide scale separately from the annealing step. Patent Document 2 discloses a method for manufacturing a high-strength steel sheet having a pickling step of removing the oxide scale on the surface of a hot-rolled steel sheet obtained in a hot-rolling step by pickling separately from the annealing step. Patent Document 3 discloses a processing process for an NPR steel bar coil including a grit blasting step of treating the oxide scale, surface defects, and lubricating powder of a bright die on the surface of an NPR hot-rolled steel bar separately from the annealing step. Patent Document 4 discloses a method for manufacturing an oil-tempered wire that anneals in a nitrogen atmosphere in the furnace to suppress the oxide scale coating. Patent Document 5 discloses a method for manufacturing a hot-rolled steel sheet in which the oxide scale on the surface of the steel sheet is reductively removed by passing a reducing atmosphere through the sheet.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] Workpieces made of metal are processed into sheets, pipes, wires, etc., and then annealed. Lubricating oil is used during such processing. After processing, the workpieces are usually transported with lubricating oil still attached to their surface. However, if annealing is performed with the lubricating oil still attached to the surface, soot and other substances will be generated from the lubricating oil and adhere to the workpiece. This soot and other substances generated from the lubricating oil cannot be removed by pickling or other methods after annealing, and will degrade the quality of the workpiece. Therefore, it is desirable to degrease the workpiece and remove the lubricating oil before annealing. Patent documents 1 to 3 include a process to remove oxide scale by pickling or blasting, separate from the annealing process. While this removes lubricating oil along with the oxide scale, the degreasing process must be performed separately from the annealing process, leading to increased complexity of the work. Patent documents 4 and 5 describe suppressing oxide scale by using a nitrogen atmosphere inside the furnace, or reducing and removing oxide scale by using a reducing atmosphere, but they do not consider degreasing at all.

[0005] The present invention aims to solve the problems of the conventional technology and to provide an annealing furnace that can remove lubricating oil adhering to a workpiece by burn-off during annealing. [Means for solving the problem]

[0006] To solve the above problems, the present invention is shown below. [1] The annealing furnace of the present invention is an annealing furnace for annealing a workpiece to be treated with lubricating oil attached, The furnace body comprises an inlet for inserting the object to be processed and an outlet for removing the object to be processed, The furnace body is provided with a heating zone inside which the workpiece is heated by a plurality of direct-fire burners. The heating zone has a plurality of zones along the direction of transport of the workpiece from the inlet to the outlet, The air ratio of the burner is adjusted to be different for each of the multiple zones. The gist of this invention is that the zone closest to the inlet among the multiple zones is designated as the first zone, and the air ratio of the burner in the first zone is higher than that of the other zones. [2] The annealing furnace of the present invention may have an air ratio of 1.0 or more for the burner in the first zone. [3] In the annealing furnace of the present invention, the first zone may be heated by the burner until the temperature of the workpiece reaches the evaporation temperature of the lubricating oil. [4] In the annealing furnace of the present invention, any one of the plurality of zones excluding the first zone may be designated as a second zone, and the burner in the second zone may have a lower air ratio than the burner in the other zones. The annealing furnace in [5][4] may have an air ratio of less than 1.0 for the burner in the second zone. In the annealing furnace of [6][4], the zone closest to the outlet among the multiple zones can be designated as the second zone. [7] The annealing furnace of the present invention is provided with at least three of the above-mentioned zones, including the first zone. The air-fuel ratio of the burners can be set such that the burner in the first zone closest to the inlet has the highest air-fuel ratio, and the burner in the zone closest to the outlet among the multiple zones has the lowest air-fuel ratio. [8] In the annealing furnace of the present invention, each of the multiple burners may be connected to an air supply system having a regulator for adjusting the amount of air supplied to the burner. The annealing furnace [9][8] may further include a controller connected to the regulator for controlling the air ratio of the burner for each zone.

[10] In the annealing furnace of the present invention, the furnace body may have a flow direction adjuster that directs the gas flow in the furnace from the outlet towards the inlet. In the annealing furnace of

[11]

[10] , the flow direction adjuster may be provided for each zone. In the annealing furnace of

[12]

[10] , the furnace body has a measuring instrument for measuring the oxygen concentration in the first zone, A controller may be further provided, which is connected to the measuring instrument and controls the air ratio of the burner for each zone based on the oxygen concentration obtained from the measuring instrument. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an annealing furnace that can remove lubricating oil adhering to a workpiece by burn-off. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram illustrating an example of an annealing furnace according to an embodiment. [Figure 2] A graph showing the temperature change of the object being treated in the heating zone. [Figure 3] A graph showing the air ratio in each zone within the heated area. [Modes for carrying out the invention]

[0009] The matters presented herein are illustrative and for the purpose of exemplarily explaining embodiments of the present invention, and are described for the purpose of providing an explanation that is considered to be most effective and easy to understand for the principles and conceptual features of the present invention. In this regard, it is not intended to show the structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, and it is to clarify to those skilled in the art how some forms of the present invention are actually implemented by the description in conjunction with the drawings.

[0010] The annealing furnace of the present invention is an annealing furnace for annealing a workpiece W to which lubricating oil is attached. It includes a furnace body 10 having an inlet 11 for inserting the workpiece W and an outlet 12 for taking out the workpiece W. Inside the furnace of the furnace body 10, a heating zone 13 for heating the workpiece W by a plurality of direct-fired burners 41-49 is provided. The heating zone 13 has a plurality of zones 31-33 along the conveying direction of the workpiece W from the inlet 11 to the outlet 12. For each of the zones, the burners 41-49 are adjusted so that the air ratio is the same within the same zone, and the air ratio is adjusted to be different between adjacent zones. Among the plurality of zones 31-33, the zone closest to the inlet is taken as the first zone 31, and the burners 41-43 in the first zone 31 are characterized by having a higher air ratio than the burners 44-49 in the other zones 32, 33 (see FIG. 1).

[0011] The annealing furnace of the present invention is for annealing a workpiece W. Annealing is a heat treatment aimed at removing internal stresses and improving the properties of the metal material used for the workpiece W, and is performed by heating the workpiece W to a high temperature and then gradually cooling it. The workpiece W to be subjected to the annealing furnace is not particularly limited with respect to the material, shape, etc., as long as a metal material is used. The material of the workpiece W can be, for example, metals such as iron, aluminum, and copper, or alloys such as iron alloys like steel and stainless steel, aluminum alloys like duralumin, nickel alloys like Inconel and Hastelloy, or copper alloys like brass and cupronickel. Of these, iron and iron alloys are used in a wide range of applications and fields, and are therefore useful as materials for the workpiece W. The shape of the workpiece W can be, for example, linear, tubular, columnar, plate-shaped, or material. Of these, linear workpieces W can be annealed after being wound into an annular or coil shape.

[0012] The workpiece W is often annealed after undergoing various processes such as molding, and lubricating oil is applied to the surface of the workpiece W after such processing. The annealing furnace of the present invention is capable of removing lubricating oil by burning it off during annealing of a workpiece W with lubricating oil adhering to its surface, in other words, by burn-off, thereby enabling degreasing of the workpiece during the annealing process. Therefore, the annealing furnace of the present invention primarily targets objects to be processed that have lubricating oil adhering to them. Furthermore, while the annealing furnace of the present invention primarily processes objects to be treated with lubricating oil, it does not necessarily only process objects to be treated with lubricating oil; it can also process objects to be treated without lubricating oil.

[0013] The type, composition, application, and form of the lubricant are not particularly limited, as long as it is one that is commonly used in the processing of the workpiece W. Examples of lubricants include liquid lubricants used by immersing the workpiece in liquid form or by coating the surface of the workpiece, and solid lubricants used by adhering them to the surface of the workpiece in powder form. Lubricating oils typically contain organic compounds. The type and composition of these organic compounds are not particularly restricted, but examples include compounds containing carboxyl groups, hydroxyl groups, or enol groups.

[0014] Examples of organic compounds contained in lubricating oils include stearic acid compounds and ester compounds. Stearic acid compounds are compounds consisting of stearic acid, which has a carboxylic acid skeleton (-COOH) in its molecule. Ester compounds are compounds that have an ester bond (R-COO-R') in their molecule. Specific examples of organic compounds include metal soaps, which consist of fatty acids such as stearic acid, lauric acid, ricinoleic acid, and octic acid, and metals such as lithium, magnesium, calcium, barium, and zinc; more specifically, calcium stearate and sodium stearate.

[0015] The annealing furnace of the present invention comprises a furnace body 10 for annealing a workpiece W (see Figure 1). The workpiece W is placed inside the furnace body 10 and annealed. The furnace body 10 has an inlet 11 for inserting the material to be processed W into the furnace and an outlet 12 for removing the material to be processed W from the furnace. The material to be processed W is transported through the furnace body 10 from the inlet 11 to the outlet 12. In other words, the direction of transport of the material to be processed W within the furnace body 10 is from the inlet 11 to the outlet 12.

[0016] The furnace body 10, which anneals the workpiece W, is equipped with a heating zone 13 for heating the workpiece W. Furthermore, a cooling zone 14 for slowly cooling the workpiece W can be provided inside the furnace body 10. Within the furnace body 10, the heating zone 13 is located on the inlet 11 side in the direction of transport of the workpiece W, and the cooling zone 14 is located on the outlet 12 side in the direction of transport of the workpiece W. Furthermore, within the furnace body 10, the heating zone 13 and the cooling zone 14 can be partitioned from each other. The partitioned heating zone 13 and cooling zone 14 can each have an inlet and an outlet for inserting and removing the material to be processed W.

[0017] In the furnace body 10, the outlet of the heating zone 13 can be connected to the inlet of the cooling zone 14. In this case, the workpiece W can be heated in the heating zone 13 and then cooled slowly in the cooling zone 14, immediately following the heating treatment. Furthermore, if the heating zone 13 and the cooling zone 14 are connected, the inlet of the heating zone 13 can be the inlet 11 of the furnace body 10, and the outlet of the cooling zone 14 can be the outlet 12 of the furnace body 10. In other words, when the heating zone 13 and the cooling zone 14 of the furnace body 10 are connected, the processing and transport method of the annealing furnace of the present invention can be a continuous method that continuously performs heating and slow cooling of the workpiece W.

[0018] A conveying device 15 for transporting the material to be processed W can be provided inside the furnace body 10. The type and structure of the conveying device 15 are not particularly limited, as long as it is capable of transporting the material to be processed W inside the furnace. Specific examples of the conveying device 15 include conveyors such as belt conveyors and roller conveyors, and walking beams. The furnace body 10 may be equipped with a front table 16 in front of the inlet 11 for holding the workpiece W to be inserted into the furnace. The furnace body 10 may also be equipped with a rear table 17 behind the outlet 12 for holding the workpiece W removed from the furnace.

[0019] The furnace body 10 may be equipped with a flow direction adjuster that directs the gas flow within the furnace from the outlet 12 to the inlet 11 of the furnace body 10. In other words, unburned gases such as carbon monoxide (CO) and hydrogen (H2) tend to be generated inside the furnace body 10, at the outlet 12 side where the temperature is lower. The flow direction regulator directs the gas flow inside the furnace from the outlet 12 to the inlet 11 of the furnace body 10, thereby sending the unburned gases generated at the outlet 12 side to the higher-temperature inlet 11 side for combustion.

[0020] As a flow direction regulator, the furnace body 10 may be equipped with an exhaust hood 18 at the inlet 11. The exhaust hood 18 is installed to cover the inlet 11 and to be able to open and close. The exhaust hood 18 has an exhaust mechanism such as an exhaust fan or exhaust blower, and by exhausting the gas inside the furnace to the outside through the inlet 11 of the furnace body 10, the direction of the gas flow inside the furnace can be made to move from the outlet 12 of the furnace body 10 towards the inlet 11. The flow direction regulator is not particularly limited to the exhaust hood 18 described above, as long as it can direct the gas flow direction within the furnace from the outlet 12 to the inlet 11 of the furnace body 10. For example, the flow direction regulator can also be composed of an exhaust duct connected to the inlet 11 side of the furnace body 10 and an exhaust mechanism such as an exhaust fan or exhaust blower installed inside the exhaust duct.

[0021] The furnace body 10 may have an oxygen concentration meter 19 on the side of the furnace inlet 11 for measuring the oxygen concentration inside the furnace. When the furnace body 10 has an oxygen concentration meter 19, it is possible to monitor whether the oxygen concentration on the side of the furnace inlet 11 is sufficient for burning gas, etc. In addition, by placing the oxygen concentration meter 19 closer to the furnace inlet 11, it is possible to monitor whether the oxygen concentration in the first zone 31, described later, is sufficient for burning (burning off) the evaporated lubricating oil. In particular, when using the exhaust hood 18 (flow direction adjuster) to send unburned gas towards the furnace inlet 11, it is desirable to prevent the unburned gas from being exhausted outside the furnace. To prevent the unburned gas from being exhausted outside the furnace, it is desirable to burn the unburned gas sufficiently on the furnace inlet 11 side, i.e., in the heating zone 13, and monitoring the oxygen concentration is useful for such sufficient combustion. The furnace body 10 may include measuring instruments for measuring the temperature of the workpiece W (hereinafter referred to as "actual temperature (Ts)") and measuring instruments for measuring the temperature inside the furnace (hereinafter referred to as "processing temperature (Tf)").

[0022] In the annealing furnace of the present invention, the inside of the furnace body 10 is filled with atmospheric gas, thereby creating an atmosphere suitable for annealing inside the furnace. The type of atmospheric gas is not particularly limited as long as it can create an atmosphere suitable for annealing inside the furnace; for example, an exothermic denaturing gas can be used. Incidentally, exothermic modified gases are gases produced by incomplete combustion of hydrocarbon gases such as propane when reacted with air (oxygen).

[0023] The annealing furnace of the present invention can supply an exothermic modification gas as an atmospheric gas into the furnace body 10 using a burner as the gas supply system. In other words, the annealing furnace of the present invention is equipped with direct-fired burners 41-49 in the heating zone 13, and these burners 41-49 are used as a gas supply system to generate an exothermic modified gas by reacting hydrocarbon gas with air (oxygen) and burning it, which can then be supplied into the furnace as an atmospheric gas. Furthermore, when generating an exothermic denatured gas using burners 41-49 as the gas supply system, the exothermic denatured gas generates heat on its own, so the burners 41-49, which are also part of the gas supply system, can be used as a heat source to adjust the processing temperature (Tf). The exothermic modified gas is produced by incomplete combustion of hydrocarbon gas in a burner at an air ratio of 1.0 or less. Therefore, the exothermic modified gas, which is the atmospheric gas, is essentially produced in the burners 47-49 of the second zone 32 and the burners 44-46 of the third zone 33, as described later. In addition, the burners 41-43 of the first zone 31, as described later, produce normal exhaust gas (e.g., carbon dioxide) resulting from the combustion of hydrocarbon gas. However, by using the exhaust hood 18 (flow direction adjuster) described above to direct the gas flow from the outlet 12 to the inlet 11 of the furnace body 10, the flow of such exhaust gas into the second zone 32 and the third zone 33 can be suppressed.

[0024] In the annealing furnace of the present invention, a plurality of burners 41-49 are arranged in a heating zone 13 within the furnace body 10 for heating the workpiece W to be annealed. These burners 41-49 are of the direct-fire type, which inject combustion gases generated by burning fuel into the furnace. Although not specifically shown in the diagram, a fuel supply system is connected to burners 41-49, and hydrocarbon gases such as propane are supplied as fuel. Furthermore, an air supply system 50 is connected to burners 41-49, and air is supplied to them (see Figure 1). Burners 41-49 heat the workpiece W by burning hydrocarbon gas and air, which are fuels, and creating a high-temperature atmosphere in the heating zone 13.

[0025] The installation positions of the burners 41-49 within the furnace body 10 are not particularly limited, and the burners 41-49 can be installed on the bottom, top, and both sides of the furnace. In addition, the burners 41-49 are not limited to being installed on only one of the bottom, top, and sides of the furnace, but can also be installed on two or more of the bottom, top, and both sides, for example, on the bottom and top, or on both sides. The arrangement of the multiple burners 41-49 is not particularly limited, as long as they are arranged along the conveying direction of the workpiece W within the furnace body 10. For example, the multiple burners 41-49 can be arranged in a straight line along the conveying direction, in a staggered pattern along the conveying direction, or in a spiral pattern extending in the conveying direction. The spacing between the multiple burners 41-49 is not particularly limited and can be either even or uneven.

[0026] In the annealing furnace shown in Figure 1, for the sake of explanation, the burners 41-49 inside the furnace body 10 are positioned at the bottom of the furnace, and the multiple burners 41-49 are arranged in a straight line along the conveying direction. Furthermore, for the sake of explanation, the multiple burners 41-49 will be referred to as the first burner 41, second burner 42, third burner 43, etc., starting from the inlet 11 side of the furnace body 10. For example, nine burners 41-49 are depicted in Figure 1, with the one closest to the inlet 11 side of the furnace body 10 (left side in the figure) being designated as the first burner 41, and in order from the inlet 11 side to the outlet 12 side, they will be designated as the second burner 42, third burner 43, fourth burner 44, fifth burner 45, sixth burner 46, seventh burner 47, eighth burner 48, and ninth burner 49.

[0027] The air supply system 50 connected to the burners 41-49 is equipped with valves 51-59 as regulators for adjusting the amount of air supplied to the burners 41-49 (hereinafter also referred to as "actual air volume"). The type of valves 51-59 is not particularly limited as long as it allows for adjustment of the actual air volume, and examples include electric valves and solenoid valves. Among these, electric valves are preferable as regulators for adjusting the actual air volume because the amount of opening can be controlled by an electrical signal. Valves 51-59 adjust the amount of air supplied to burners 41-49, and by burning hydrocarbon gas in burners 41-49, an atmospheric gas (exothermic modified gas) can be generated. The generated atmospheric gas fills the furnace body 10, making the atmosphere inside the furnace suitable for annealing.

[0028] The air supply system 50 is branched into multiple branches and connected to multiple burners 41-49. Valves 51-59 are attached to each of the air supply systems 50 connected to the multiple burners 41-49, allowing the actual amount of air to be adjusted individually for each burner 41-49. Here, for the sake of explanation, the valves 51-59 connected to the first burner 41 will be referred to as the first valve 51, the valve connected to the second burner 42 as the second valve 52, and so on. For example, in Figure 1, the first to ninth burners 41-49 are depicted in order from the inlet 11 side of the furnace body 10, and the valves 51-59 connected to the first to ninth burners 41-49 will be referred to in order from the inlet 11 side to the outlet 12 side as the first valve 51, second valve 52, third valve 53, fourth valve 54, fifth valve 55, sixth valve 56, seventh valve 57, eighth valve 58, and ninth valve 59.

[0029] In addition to the first to ninth valves 51-59 described above, the air supply system 50 may also have a main valve 60 that allows or restricts the intake of air into the air supply system 50. The main valve 60 can be used as a regulator to adjust the total amount of air supplied to the multiple burners 41-49. Furthermore, the air supply system 50 may have sub-valves 61-63 that can adjust the actual air volume for multiple units (three units in Figure 1) of the first to ninth burners 41-49 at once. In Figure 1, three sub-valves 61-63 are provided. For the sake of explanation, they will be referred to as the first sub-valve 61, the second sub-valve 62, and the third sub-valve 63, in order from the inlet 11 side to the outlet 12 side of the furnace body 10.

[0030] The first to ninth valves 51-59, the first to third sub-valves 61-63, and the main valve 60 described above can be electrically connected to the controller 20. The controller 20 is for controlling the air-fuel ratio (λ) of the burners 41-49 during combustion, and primarily controls the air-fuel ratio (λ) of the burners 41-49 by changing the opening of the first to ninth valves 51-59 and the first to third sub-valves 61-63, thereby adjusting the actual amount of air supplied to the burners 41-49. Furthermore, the controller 20 can be electrically connected to the oxygen concentration meter 19. In this case, the controller 20 can control the air ratio (λ) of the burners 41-49 based on the O2 concentration inside the furnace body 10 (particularly the heating zone 13 and the first zone 31) measured by the oxygen concentration meter 19.

[0031] Specifically, the controller 16 incorporates a computer that includes an arithmetic processing unit such as a CPU (Central Processing Unit) or MPU (Micro Processing Unit), and a storage area such as an HDD, SSD, or ROM. The means of adjusting the actual amount of air supplied to the burners 41-49 by changing the opening degree of the valves 51-59 is stored as a program in the memory area of ​​the controller 20. Furthermore, the air ratio (λ) and O2 concentration suitable for heat treatment using the annealing furnace of the present invention are stored as preset values ​​in the memory area of ​​the controller 20. The controller 20 can control the air ratio (λ) by having the computer execute a program stored in the memory area based on the set values ​​stored in the memory area.

[0032] The air-fuel ratio (λ) of burners 41-49 during combustion can be changed by adjusting the actual amount of air supplied to burners 41-49 using valves 51-59 and / or sub-valves 61-63. The air-fuel ratio (λ) is a coefficient that represents the difference between the theoretical amount of air and the actual amount of air, where the theoretical amount of air is the minimum amount of air required for the complete combustion of the combustible components in the fuel. The air-fuel ratio (λ) can be calculated using the formula λ = A / A0, where A0 is the theoretical amount of air and A is the actual amount of air. The ideal value for the air-fuel ratio (λ) is λ = 1.0. However, the actual value of the air-fuel ratio varies depending on the atmosphere and conditions. Therefore, the air-fuel ratio (λ) is usually adjusted to fall within a range defined by an upper and lower limit.

[0033] The heating zone 13 has multiple zones 31-33 along the transport direction of the workpiece W from the inlet 11 to the outlet 12 of the furnace body 10. The air ratio (λ) of the burners 41-49 is adjusted to be different for each of the multiple zones 31-33. More specifically, each of the multiple zones 31-33 is equipped with one or more burners 41-49. Within each of the multiple zones 31-33, the burners 41-49 in the same zone are adjusted to have the same range of air ratio (λ). Furthermore, adjacent zones 31-33 in the conveying direction are adjusted so that the range of air ratio (λ) of the burners 41-49 in each zone is different.

[0034] In other words, multiple zones 31-33 can be provided by adjusting the range of air ratio (λ) of multiple burners 41-49 arranged along the conveying direction in the heating zone 13 so that it varies for each burner, one or more burners. Multiple zones 31-33 can be divided into zones according to the range of the adjusted air ratio (λ) of the burners 41-49. In other words, the air ratio (λ) of the burners 41-49 can be set in multiple zones 31-33 within a range determined by upper and lower limits for each zone. The number of zones 31-33 provided in the heating zone 13 is not particularly limited to an upper limit as long as the lower limit is two or more, but from the viewpoint of making the adjustment and control of the burner air ratio suitable and easy, the upper limit is preferably five or less, more preferably four or less, and particularly preferably three or less. The size (length in the conveying direction) of zones 31-33 is not particularly limited. The size of zones 31-33 can be varied depending on the number of burners 41-49 that are adjusted to the same air ratio (λ) range along the conveying direction. For example, if the number of burners 41-49 in each zone 31-33 is the same, each zone 31-33 can be made of uniform size, and if the number of burners 41-49 in each zone 31-33 is different, each zone 31-33 can be made of uneven size.

[0035] The air ratio (λ) of burners 41-49 is set within a range defined by upper and lower limits for each of the multiple zones 31-33, and is adjusted within the range of the air ratio (λ) set for that zone 31-33. If multiple burners 41-49 are located within a single zone 31-33, the air ratio (λ) of each burner 41-49 can be adjusted to be the same for all burners 41-49, provided that it is within the range of the air ratio (λ) set for that zone 31-33, or the air ratio (λ) of each burner 41-49 can be adjusted to be different. When adjusting the air ratio (λ) of multiple burners 41-49 within a single zone 31-33 to be different, the actual amount of air is adjusted arbitrarily for each burner 41-49.

[0036] Here, "different burner air ratios" in multiple zones 31-33 means that the range of burner air ratios set for each zone is different, and specifically, it means that either the upper limit or lower limit of the air ratio range, or both the upper and lower limits, are different values. "Having the same burner air ratio across multiple zones 31-33" means that the range of the burner air ratio set for each zone is the same, specifically that both the upper and lower limits of the air ratio range are the same.

[0037] Furthermore, "high burner air ratio" in multiple zones 31-33 means that, when comparing the upper limits of the air ratio ranges set for each zone, one upper limit is higher than the other upper limit. This "high burner air ratio" includes not only cases where, when comparing the lower limits of the air ratio ranges set for each zone, one lower limit is higher than the other lower limit, but also cases where the lower limits are the same value. In multiple zones 31-33, "low burner air ratio" means that when comparing the lower limits of the air ratio ranges set for each zone, one lower limit is lower than the other lower limit. This "low burner air ratio" includes not only cases where, when comparing the upper limits of the air ratio ranges set for each zone, one upper limit is lower than the other upper limit, but also cases where the upper limits are the same value.

[0038] Inside the furnace body 10, the heating zone 13 is heated to a temperature suitable for annealing (hereinafter also referred to as the "processing temperature (Tf)"). The workpiece W being transported in the heating zone 13 is heated up until its temperature (hereinafter also referred to as the "actual temperature (Ts)") reaches the processing temperature (Tf), and then held at the processing temperature (Tf) for a certain period of time (see Figure 2). Of the multiple zones 31-33 provided in the heating zone 13, zone 31, which is closest to the inlet 11 of the furnace body 10, is used to raise the actual temperature (Ts) by heating the workpiece W. Furthermore, in zone 32, which is closest to the outlet 12 of the furnace body 10, the processing temperature (Tf) of the workpiece W is primarily maintained.

[0039] In the following explanation, we will use as an example a configuration in which three zones 31-33 are provided in the heating zone 13, as shown in Figure 1. The zone closest to the inlet 11 of the furnace body 10 will be designated as the first zone 31, the zone closest to the outlet 12 of the furnace body 10 will be designated as the second zone 32, and the zone between the first zone 31 and the second zone 32 will be designated as the third zone 33.

[0040] Of the multiple zones 31-33, the first zone 31, which is the zone closest to the inlet 11 of the furnace body 10, is adjusted so that the burner air ratio (λ1) is higher than that of the other zones 31-33 (see Figure 3). In Zone 31, where the burner's air-fuel ratio (λ1) is adjusted to be high, the increased oxygen concentration allows for a higher flame temperature in burners 41-43. In the first zone 31, where the flame temperature of burners 41-43 is high, the actual temperature (Ts) of the workpiece W can be raised in a short time.

[0041] The first zone 31 can be used as a degreasing chamber for degreasing the lubricating oil adhering to the surface of the workpiece W. In other words, in the first zone 31, the flame temperature of the burners 41-43 is high, and the actual temperature (Ts) of the workpiece W within the first zone 31 reaches the evaporation temperature of the lubricating oil (see Figure 2), causing the lubricating oil to evaporate from the surface of the workpiece W, thus enabling degreasing.

[0042] Furthermore, the first zone 31 can also be used as a combustion chamber for burning the lubricating oil evaporated from the surface of the workpiece W. In other words, the lubricating oil evaporated from the surface of the workpiece W can be burned in the heating zone 13, which is set to the processing temperature (Tf). In particular, the first zone 31 has a high oxygen concentration, which allows the evaporated lubricating oil to be burned effectively. In more detail, in Zone 1 31, the air ratio (λ1) of burners 41-43 is high, and the oxygen concentration is high, so the carbon in the lubricating oil reacts with oxygen as shown in the following equations (1) and (2) and combustion occurs. C+1 / 2O2→CO formula (1) C+O2→CO2 formula (2)

[0043] Alternatively, even in the heated zone 13, in the second zone 32 and third zone 33, where the air ratio (λ) is lower than in the first zone 31, the lubricating oil may not burn completely, resulting in unburned components such as soot. With respect to this unburned material, if a flow direction regulator such as the exhaust hood 18 described above is provided, the direction of gas flow in the furnace is set to move from the outlet 12 to the inlet 11 of the furnace body 10, so that the unburned material can be sent to the first zone 31. The unburned material sent to Zone 31 burns when the carbon content in the unburned material reacts with oxygen as shown in equation (3) below. C+CO2→2CO Equation (3) In other words, the evaporated lubricating oil is burned in the atmosphere of the heating zone 13 at the processing temperature (Tf), and CO and CO2 are produced after combustion. Furthermore, any unburned portion of the evaporated lubricating oil is sent to Zone 31, which has a high oxygen concentration, and burned there. CO2 is generated from the unburned portion after combustion. The CO and CO2 generated after combustion as described above are also included as components in the atmospheric gas (exothermic modified gas) that fills the furnace body 10, thus suppressing contamination of the furnace atmosphere by evaporated lubricating oil.

[0044] Here, a flow direction regulator, such as the exhaust hood 18 described above, which directs the gas flow direction inside the furnace from the outlet 12 to the inlet 11 of the furnace body 10, is not limited to providing only one exhaust hood 18, but can be provided in multiple locations. For example, flow direction regulators consisting of exhaust ducts, exhaust fans, exhaust blowers, etc., can also be installed in the second zone 32 and the third zone 33. If flow direction adjusters are also installed in the second zone 32 and the third zone 33, the annealing furnace can exhaust gas from the flow direction adjusters for each of the first to third zones 31 to 33, thereby directing the gas flow in each of the zones 31 to 33 from the outlet 12 to the inlet 11 of the furnace body 10. Furthermore, if flow direction regulators are provided for each zone, unburned components such as lubricating oil and hydrocarbon gases generated in the first zone 31 can be burned by the burners 41-43 in the first zone 31, where the oxygen concentration is high. Any unburned material generated in Zone 2 31 and Zone 33 can be burned off by the pilot burners (igniters, etc., that ignite the burners) provided in each zone. In particular, the burners in Zone 2 31 and Zone 33 incompletely combust hydrocarbon gases at an air ratio of 1.0 or less, which tends to generate unburned material, but this unburned material can be burned off in each zone. Alternatively, if unburned material generated in Zone 2 31 or Zone 33 cannot be completely burned in each zone, the unburned material will ultimately be sent to Zone 1 31 for burning.

[0045] The air-fuel ratio (λ1) of the burner in the first zone 31 is not particularly limited, as long as it is higher than that of the other zones 32 and 33. Specifically, the air ratio (λ1) of the first zone 31 is preferably 1.0 or higher (λ1 ≥ 1.0) from the viewpoint of using it as a degreasing chamber. More preferably, the air ratio (λ1) of the first zone 31 is 1.1 or higher and 1.6 or lower, and even more preferably 1.2 or higher and 1.5 or lower, from the viewpoint of using it as a combustion chamber. In the annealing furnace shown in Figure 1, the first zone 31 is equipped with three burners: a first burner 41, a second burner 42, and a third burner 43. The first burner 41, the second burner 42, and the third burner 43 can all have the same air ratio (λ1), or they can all have different air ratios (λ1), or two of the first burner 41, second burner 42, and third burner 43 can be set to the same air ratio (λ1) and the other one to a different air ratio (λ1).

[0046] Figure 3 is a graph showing the air ratio for each zone. For example, the three burners in Zone 1 31 shown in Figure 3—the first burner 41, the second burner 42, and the third burner 43—all have the same air ratio (λ1). To make the air ratios (λ1) of all three burners, i.e., the first burner 41, the second burner 42, and the third burner 43, the same, the controller 20 is used to adjust the opening degrees of all the valves of the first valve 51, the second valve 52, and the third valve 53 to the same opening degree. Alternatively, by using the controller 20 to adjust the opening degrees of all the valves of the first valve 51, the second valve 52, and the third valve 53 to the same opening degree and then adjusting the opening degree of the first sub-valve 61, it is possible to simultaneously control the air ratios (λ1) of all three burners, i.e., the first burner 41, the second burner 42, and the third burner 43. In addition, to make only one or two or more of the first burner 41, the second burner 42, and the third burner 43 have different air ratios (λ1), the controller 20 is used to appropriately adjust only one or two or more of the opening degrees of the first valve 51, the second valve 52, and the third valve 53.

[0047] From the perspective of using the first zone 31 as a degreasing chamber, it is desirable to heat the workpiece W until it reaches the evaporation temperature of the lubricating oil, that is, to raise the actual temperature (Ts) of the workpiece W to be equal to or higher than the evaporation temperature of the lubricating oil. The lower limit value of the actual temperature (Ts) of the workpiece W in the first zone 31 is not particularly limited as long as it is equal to or higher than the evaporation temperature of the lubricating oil. However, when the lubricating oil contains the above-mentioned organic compound, from the perspective that its evaporation temperature is approximately 300°C, it can be set to 300°C or higher. The lower limit value of the actual temperature (Ts) is preferably 350°C or higher, more preferably 400°C or higher. The upper limit value of the actual temperature (Ts) of the workpiece W in the first zone 31 is not particularly limited as long as it is equal to or higher than the evaporation temperature of the lubricating oil. However, when the actual temperature (Ts) is excessively raised, there is a possibility of creating an atmosphere where soot and the like are likely to occur due to the lubricating oil. Therefore, it is preferable that Ts < Tf, where Tf is the processing temperature in the heating zone 13. Specifically, from the perspective that the processing temperature (Tf) during heating in annealing is generally 600°C or higher, the upper limit value of the actual temperature (Ts) can be set to 600°C or lower. The upper limit value of the actual temperature (Ts) is preferably 580°C or lower, more preferably 550°C or lower, and even more preferably 500°C or lower.

[0048] The temperature of the heating zone 13, including the first zone 31, that is, the processing temperature (Tf) of the workpiece W in the heating zone 13, can be determined according to the material of the workpiece W, etc., and is not particularly limited. From the perspective of using the first zone 31 as a combustion chamber, it is preferable that the lower limit of the processing temperature (Tf) be equal to or greater than the combustion temperature of the lubricating oil. In particular, when an iron-based material is used for the workpiece W, the processing temperature (Tf) during heating in annealing is generally 600°C or higher. Since this is above the combustion temperature of the lubricating oil, the lower limit of the processing temperature (Tf) in the heating zone 13 can be 600°C or higher. Preferably, the lower limit of the processing temperature (Tf) is 620°C or higher, and more preferably 650°C or higher. The upper limit of the processing temperature (Tf) can usually be 1200°C or less. Preferably, the upper limit of the processing temperature (Tf) is 1000°C or less, and more preferably 900°C or less. Note that the temperature of Zone 1 31 may differ slightly from the processing temperature (Tf) based on the burner flame temperature, but in practice it will not differ significantly from the processing temperature (Tf) and will be approximately the same as the processing temperature (Tf).

[0049] Of the multiple zones 31-33, the second zone 32 is adjusted so that the burner air ratio (λ2) is lower than that of the other zones 31 and 33 (see Figure 3). In Zone 2 32, where the burner air ratio (λ2) is adjusted to be lower, the lower oxygen concentration allows for a lower flame temperature for burners 47-49. In the second zone 32, where the flame temperature of burners 47-49 is low, the actual temperature (Ts) of the workpiece W can be maintained at the processing temperature (Tf).

[0050] The second zone 32 can be used as a low-oxidation chamber to suppress oxidation of the material W being treated. In other words, in the heat treatment related to annealing, it is necessary to raise the workpiece W to a certain temperature (treatment temperature (Tf)) and then hold it at that temperature (treatment temperature (Tf)) for a certain period of time. In the second zone 32, because the flame temperature of the burners 47-49 is low, the workpiece W is held at the treatment temperature (Tf) within the second zone 32 without its actual temperature (Ts) rising. Furthermore, when the workpiece W is held at the processing temperature (Tf), if oxygen is present in the atmosphere, the workpiece W will be oxidized. Since the oxygen concentration is low in the second zone 32, by using the second zone 32 as a low-oxidation chamber, oxidation of the workpiece W when it is held at the processing temperature (Tf) can be suppressed.

[0051] The air-fuel ratio (λ2) of the burner in the second zone 32 is not particularly limited, as long as it is lower than that of the other zones 31 and 33. Specifically, the air ratio (λ2) of the second zone 32 is preferably less than 1.0 (λ2 < 1.0) from the viewpoint of using it as a low-oxidation chamber. More preferably, the air ratio (λ2) of the second zone 32 is 0.75 or more and 0.99 or less, and even more preferably 0.85 or more and 0.95 or less, from the viewpoint of providing an atmosphere suitable for heat treatment related to annealing.

[0052] In the annealing furnace shown in Figure 1, the second zone 32 is equipped with three burners: the seventh burner 47, the eighth burner 48, and the ninth burner 49. The seventh burner 47, the eighth burner 48, and the ninth burner 49 can all have the same air ratio (λ2), or they can all have different air ratios (λ2), or two of the seventh burner 47, the eighth burner 48, and the ninth burner 49 can be set to the same air ratio (λ2) and the other one to a different air ratio (λ2).

[0053] For example, the three burners in Zone 2 32 shown in Figure 3—burner 47 (number 7), burner 48 (number 8), and burner 49 (number 9)—all have the same air ratio (λ2). To set the same air ratio (λ2) for all three burners, the 7th burner 47, the 8th burner 48, and the 9th burner 49, the controller 20 is used to adjust the opening of each valve, the 7th valve 57, the 8th valve 58, and the 9th valve 59, to the same degree. Alternatively, by using the controller 20, the air ratio (λ2) of all three burners, the seventh burner 47, the eighth burner 48, and the ninth burner 49, can be controlled simultaneously by adjusting the opening of the third sub-valve 63 after adjusting the opening of all three valves, the seventh valve 57, the eighth valve 58, and the ninth burner 49. Furthermore, in order to set one or more of the seventh burner 47, the eighth burner 48, and the ninth burner 49 to different air ratios (λ2), the controller 20 is used to appropriately adjust the opening degree of one or more of the seventh valve 57, the eighth valve 58, and the ninth valve 59.

[0054] The actual temperature (Ts) of the workpiece W in zone 2 32 is the same as the processing temperature (Tf) of the workpiece W in heating zone 13. Furthermore, the temperature of the second zone 32 is approximately the same as the processing temperature (Tf) of the heating zone 13. In addition, due to differences in the flame temperature of the burner, the temperature of the second zone 32 and the temperature of the first zone 31 may differ slightly, but in substance, both are approximately the same as the processing temperature (Tf) of the heating zone 13, and no significant temperature difference occurs that would affect the heat treatment.

[0055] In the annealing furnace shown in Figure 1, the zone closest to the outlet 12 of the furnace body 10 is designated as the second zone 32. However, in the annealing furnace of the present invention, the zone closest to the outlet 12 of the furnace body 10 is not necessarily designated as the second zone 32. In other words, the second zone 32 is a zone in which the air-fuel ratio (λ2) of the burner is lower than that of the other zones, and the location of the second zone 32 in the heating zone 13 is not particularly limited. For example, another zone with a higher burner air ratio (λ) than the second zone 32 can be provided between the second zone 32 and the cooling zone 14. In this case, the other zone provided between the second zone 32 and the cooling zone 14 will be the zone closest to the outlet 12 of the furnace body 10.

[0056] Of the multiple zones 31-33, the area between Zone 1 31 and Zone 2 32 is Zone 3 33. Zone 33 is adjusted so that the burner air ratio is lower than that of Zone 131 and higher than that of Zone 232 (see Figure 3). The third zone 33 can be used as an intermediate chamber to suppress mutual interference between the first zone 31 and the second zone 32.

[0057] In other words, because the air ratio of the burner in the first zone 31 and the second zone 32 is completely different, when they are placed adjacent to each other, the oxygen in the first zone 31 will affect the heat treatment related to annealing, especially in the second zone 32. Therefore, in the third zone 33, the air ratio of the burner is adjusted to be lower than that of the first zone 31 and higher than that of the second zone 32, thereby suppressing mutual interference between the first zone 31 and the second zone 32.

[0058] The air-to-burn ratio of the burner in zone 33 is not particularly limited, as long as it is lower than that of zone 131 and higher than that of zone 232. Specifically, the air ratio of the third zone 33 is preferably around 1.0 from the viewpoint of using it as an intermediate chamber. More preferably, the air ratio of the third zone 33 is 0.95 or more and 1.2 or less, and even more preferably 0.99 or more and 1.1 or less.

[0059] In the annealing furnace shown in Figure 1, the third zone 33 is equipped with three burners: a fourth burner 44, a fifth burner 45, and a sixth burner 46. The fourth burner 44, the fifth burner 45, and the sixth burner 46 can all have the same air ratio, or they can all have different air ratios, or two of the fourth burner 44, the fifth burner 45, and the sixth burner 46 can be selected to have the same air ratio and the other one to have a different air ratio.

[0060] For example, the three burners in Zone 33, Zone 33, namely the 4th burner 44, the 5th burner 45, and the 6th burner 46, are all set to different air ratios. Specifically, the fourth burner 44, which is closest to the first zone 31 among the three, has a higher air ratio than the other two; the sixth burner 46, which is closest to the second zone 32 among the three, has a lower air ratio than the other two; and the fifth burner 45 has a lower air ratio than the fourth burner 44 and a higher air ratio than the sixth burner 46. As described above, in order to have different air ratios for all three burners, the fourth burner 44, the fifth burner 45, and the sixth burner 46, the controller 20 is used to adjust each of the valves, the fourth valve 54, the fifth valve 55, and the sixth valve 56, to different opening degrees.

[0061] In the third zone 33, the actual temperature (Ts) of the workpiece W is raised from the evaporation temperature of the lubricating oil to the processing temperature (Tf) of the workpiece W in the heating zone 13. The temperature of the third zone 33 may differ slightly from the processing temperature (Tf) of the heating zone 13 due to the difference in burner flame temperatures, but it is essentially the same as the processing temperature (Tf) of the heating zone 13. In other words, the temperature of the third zone 33 does not differ significantly from the temperatures of the first zone 31 and the second zone 32 to the extent that it affects the heat treatment.

[0062] Furthermore, intermediate chambers such as the third zone 33 described above are not limited to one; multiple intermediate chambers can be provided. These intermediate chambers are intended to suppress mutual interference between zones, or between the heating zone 13 and the cooling zone 14. For example, as described above, if another zone is provided between the second zone 32 and the cooling zone 14, this other zone can be used as an intermediate chamber to suppress mutual interference between the heating zone 13 and the cooling zone 14.

[0063] In the annealing heat treatment using the above-described annealing furnace, the workpiece W is inserted into the furnace from the inlet 11 of the furnace body 10 without undergoing normal pickling treatment or the like, with lubricating oil still adhering to its surface (see Figure 1). The workpiece W inserted into the furnace body 10 is transported through the furnace body 10 from the inlet 11 to the outlet 12, during which time it is heated at the processing temperature (Tf) in the heating zone 13 and slowly cooled in the cooling zone 14, thereby undergoing annealing heat treatment.

[0064] The heating zone 13 for heat-treating the workpiece W has multiple zones 31-33, arranged in order from the entrance 11 side along the direction of transport of the workpiece W, namely the first zone 31, the third zone 33, and the second zone 32. In the multiple zones 31-33, the range of air ratios (λ) set for burners 41-49 differs for each zone, with the air ratio (λ1) in the first zone 31 being higher than the air ratios (λ) in the second zone 32 and the third zone 33 (see Figure 3). As a result, in the first zone 31, the flame temperature of the burners 41-43 is higher than in the other zones 32 and 33, causing the actual temperature (Ts) of the workpiece W to rise to the evaporation temperature of the lubricating oil within the first zone 31 (see Figure 2). As a result, the lubricating oil adhering to the surface of the workpiece W evaporates in the first zone 31, and the workpiece W is degreased. Furthermore, since the oxygen concentration is higher in the first zone 31 compared to the other zones 32 and 33, the evaporated lubricating oil is burned in an atmosphere at the processing temperature (Tf) in the first zone 31.

[0065] The degreased workpiece W is heated from its actual temperature (Ts) to the processing temperature (Tf) in the third zone 33, and then maintained at the processing temperature (Tf) in the second zone 32. In the second zone 32, the range of setting the air ratio (λ) of burners 47-49 is lower than in the first zone 31 and the third zone 33 (see Figure 3). Therefore, in the second zone 32, the oxygen concentration is low, which can suppress the oxidation of the material being treated W. Furthermore, in the third zone 33, the setting range for the air ratio (λ) of burners 44-46 is lower than in the first zone 31 and higher than in the second zone 32. The third zone 33 is designed so that the first zone 31 and the second zone 32 do not interfere with each other and affect the atmosphere (oxygen concentration) of each other. [Industrial applicability]

[0066] The present invention allows for the evaporation of lubricating oil during the annealing heat treatment, thereby degreasing the workpiece, and is useful for annealing workpieces to which lubricating oil has adhered. [Explanation of Symbols]

[0067] 10; Furnace body, 11; Inlet, 12; Outlet, 13; Heating zone, 14; Cooling zone, 15; Conveyor, 16; Front table, 17; Rear table, 18; Exhaust hood 19; Oxygen concentration meter, 20; Controller, 31; Zone 1, 32; Zone 2, 33; Zone 3 41; 1st burner, 42; 2nd burner, 43; 3rd burner, 44; 4th burner, 45; 5th burner, 46; 6th burner, 47; 7th burner, 48; 8th burner, 49; 9th burner, 50; Air supply system, 51; 1st valve, 52; 2nd valve, 53; 3rd valve, 54; 4th valve, 55; 5th valve, 56; 6th valve, 57; 7th valve, 58; 8th valve, 59; 9th valve, 60; Main valve, 61; First sub-valve, 62; Second sub-valve, 63; Third sub-valve, W; Workpiece.

Claims

1. An annealing furnace for annealing a workpiece to be treated with lubricating oil adhering to it, The furnace body comprises an inlet for inserting the object to be processed and an outlet for removing the object to be processed, The furnace body is provided with a heating zone inside which the workpiece is heated by a plurality of direct-fire burners. The heating zone has a plurality of zones along the direction of transport of the workpiece from the inlet to the outlet, The air ratio of the burner is adjusted to be different for each of the multiple zones. An annealing furnace characterized in that, among a plurality of the aforementioned zones, the zone closest to the inlet is designated as the first zone, and the air ratio of the burner in the first zone is higher than that of the other aforementioned zones.

2. The annealing furnace according to claim 1, wherein the air ratio of the burner in the first zone is 1.0 or greater.

3. The annealing furnace according to claim 1 or 2, wherein the first zone is heated by the burner until the temperature of the workpiece reaches the evaporation temperature of the lubricating oil.

4. The annealing furnace according to claim 1, wherein any one of the multiple zones excluding the first zone is designated as a second zone, and the burner in the second zone has a lower air ratio than the burner in the other zones.

5. The annealing furnace according to claim 4, wherein the air ratio of the burner in the second zone is less than 1.

0.

6. The annealing furnace according to claim 4, wherein the zone closest to the outlet among the plurality of zones is the second zone.

7. The multiple zones include at least three, including the first zone. The annealing furnace according to claim 1, wherein the air ratio of the burners is highest for the burner in the first zone closest to the inlet, and lowest for the burner in the zone closest to the outlet among the plurality of zones.

8. The annealing furnace according to claim 1, wherein each of the multiple burners is connected to an air supply system having a regulator for adjusting the amount of air supplied to the burner.

9. The annealing furnace according to claim 8, further comprising a controller connected to the regulator for controlling the air ratio of the burner for each zone.

10. The annealing furnace according to claim 1, wherein the furnace body has a flow direction adjuster that directs the gas flow within the furnace from the outlet towards the inlet.

11. The annealing furnace according to claim 10, wherein the flow direction adjuster is provided for each zone.

12. The furnace body has a measuring instrument for measuring the oxygen concentration in the first zone, The annealing furnace according to claim 10, further comprising a controller connected to the measuring instrument and controlling the air ratio of the burner in the first zone based on the oxygen concentration obtained from the measuring instrument.

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