Mesh belt type continuous sintering furnace and method for producing sintered body

Abstract

The present disclosure pertains to a mesh-belt-type continuous sintering furnace with which it is possible to manufacture a sintered body having exceptional surface properties and in which a mesh belt has a long service life.　The mesh-belt-type continuous sintering furnace according to the present disclosure comprises a furnace body part (2), and a mesh belt (3) that travels inside the furnace body part (2) and transports a material (10) to be heated, wherein: the mesh belt (3) is configured in a reticulate shape from a plurality of stainless steel wires (31); the furnace body part (2) has a preheating part (21) that preheats the material (10) to be heated, a sintering part (22) that sinters the preheated material (10) to be heated, and piping (25) that jets an inert gas; the preheating part (21) has at least one heating device (211) that performs combustion at a mixing ratio in which the proportion of hydrocarbon gas is higher than in a theoretical air-fuel ratio; the sintering part (22) has a heating device (221) by which the atmosphere inside the sintering part (22) can be controlled; and the piping (25) has jetting openings that are opened toward the mesh belt (3) from within a range from beside the mesh belt (3) to below the mesh belt (3), the jetting openings being provided from the furthest-downstream heating device (211) of the preheating part (21) to the upstream side of the sintering part (22).

Description

[Technical field]

[0001] The present disclosure relates to a mesh belt type continuous sintering furnace. This application claims priority to Japanese Application No. 2019-224746 filed on December 12, 2019, and incorporates all of the contents of said Japanese application by reference. [Background technology]

[0002] Patent Document 1 discloses a mesh belt type continuous sintering furnace including a furnace main body and a mesh belt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-009227 A Summary of the Invention

[0004] The mesh belt type continuous sintering furnace according to the present disclosure is A furnace body portion, A mesh belt type continuous sintering furnace comprising: a mesh belt that travels inside the furnace body to transport a heating object; The mesh belt is formed in a mesh shape by a plurality of stainless steel wires, The furnace body includes: A preheating unit that preheats the heating target; A sintering unit that sinters the preheated heating target; A pipe having an injection port for injecting an inert gas toward the mesh belt, the preheating unit has at least one first heating device that preheats the heating object by burning a gas in which hydrocarbons and air are mixed at a mixture ratio in which the proportion of hydrocarbons is higher than the theoretical air-fuel ratio; The sintering section has a second heating device capable of controlling the atmosphere inside the sintering section, The injection port is located between the first heating device closest to the entrance of the sintering section in the direction of travel of the mesh belt within the furnace body and the upstream part of the sintering section, and is positioned in the range from the side to the bottom of the mesh belt in the circumferential direction of the mesh belt. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic diagram showing a mesh belt type continuous sintering furnace according to the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a mesh belt type continuous sintering furnace taken along the line (II)-(II) in FIG. [Figure 3A] FIG. 3A is a top view of a mesh belt provided in the mesh belt type continuous sintering furnace according to the first embodiment. [Figure 3B] FIG. 3B is a cross-sectional view showing the mesh belt taken along the (B)-(B) cutting line in FIG. 3A. [Figure 4] FIG. 4 is a schematic diagram showing a mesh belt type continuous sintering furnace according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Patent Document 1 discloses a mesh belt type continuous sintering furnace that includes a furnace body and a mesh belt. The furnace body has a preheating section, a sintering section, and a cooling section. The preheating section preheats the heating target. The heating target is a molded body made of iron or iron alloy powder. The sintering section sinters the preheated heating target. The cooling section cools the sintered body. The mesh belt travels from the entrance to the exit of the furnace body to transport the heating target. The mesh belt is tensioned and is hung around the entrance pulley and exit pulley of the furnace body.

[0007] Problems to be Solved by the Present Disclosure It is desirable to produce sintered bodies with excellent surface properties.

[0008] Therefore, an object of the present disclosure is to provide a mesh belt type continuous sintering furnace capable of producing a sintered body having excellent surface properties.

[0009] Description of the embodiments of the present disclosure The present inventors have conducted extensive research into the cause of the deterioration of the surface properties of a sintered body and have reached the following findings.

[0010] Usually, the mesh belt is made of a plurality of stainless steel wires in a mesh pattern. In the preheating section, a gas mixture of hydrocarbon and air is burned at a ratio where the proportion of hydrocarbon is higher than the theoretical air-fuel ratio by a heating device such as a gas burner, thereby preheating the heating object. The reason for using a ratio where the proportion of hydrocarbon gas is higher is that decarbonization of the heating object occurs when the mixture is burned at a ratio where the proportion of air is higher.

[0011] When a gas mixture of hydrocarbons and air is burned at a ratio where the proportion of hydrocarbons is high relative to the theoretical air-fuel ratio, the resulting combustion gas contains hydrogen gas, carbon monoxide gas, methane gas, and the like. When the heating target is placed directly on the mesh belt, these combustion gases remain in the space surrounded by the mesh belt and the heating target. When the combustion gas remains in the space and is transported to the sintering section, the methane gas is decomposed in the sintering section. When the methane gas is decomposed, hydrogen gas is generated. The hydrogen gas generation locally increases the concentration of hydrogen gas in the space. This reduces the passive film of the stainless steel wire that constitutes the mesh belt. When the heating target is a compact made of iron or iron alloy powder, when the passive film is reduced in the sintering section, the reduced passive film adheres to the sintered body sintered on the mesh belt. The reduced passive film is a film in which part of the chromium oxide on the surface of the stainless steel wire is altered.

[0012] When the sintered body is removed from the mesh belt at the outlet of the furnace body, the passive film peels off from the stainless steel wire and remains on the surface of the sintered body. This deposit deteriorates the surface quality of the sintered body.

[0013] The present inventors further obtained the following findings in connection with the reduction of the passive film on the stainless steel wire.

[0014] When the passive film is reduced and peeled off, the base metal of the stainless steel wire is exposed. When the mesh belt leaves the outlet of the furnace body and is exposed to the atmosphere, the exposed base metal is oxidized and a new passive film is formed on its surface. The chromium contained in the stainless steel wire is used to form the passive film. That is, when the peeling and formation of the passive film is repeated, the stainless steel wire becomes thinner and the chromium content decreases. This reduces the strength of the stainless steel wire, and as a result, the strength of the mesh belt is reduced. The mesh belt is stretched over the inlet pulley and the outlet pulley under tension and passes through the inside of the furnace body. Therefore, the mesh belt is easily stretched by high-temperature creep. Therefore, the life of the mesh belt is easily shortened.

[0015] Therefore, the inventors have found that by lowering the concentration of the gas capable of reducing the passive film of the stainless steel wire in the space at a specific stage, the reduction of the passive film in the sintered portion can be suppressed, and the reduced passive film can be suppressed from adhering to the sintered body. Furthermore, the inventors have found that if the reduced passive film can be suppressed from adhering to the sintered body, the life of the mesh belt can be extended.

[0016] The present disclosure is based on the above findings. First, embodiments of the present disclosure will be listed and described.

[0017] (1) A mesh belt type continuous sintering furnace according to one embodiment of the present disclosure, A furnace body portion, A mesh belt type continuous sintering furnace comprising: a mesh belt that travels inside the furnace body to transport a heating object; The mesh belt is formed in a mesh shape by a plurality of stainless steel wires, The furnace body includes: A preheating unit that preheats the heating target; A sintering unit that sinters the preheated heating target; A pipe having an injection port for injecting an inert gas toward the mesh belt, the preheating unit has at least one first heating device that preheats the heating object by burning a gas in which hydrocarbons and air are mixed at a mixture ratio in which the proportion of hydrocarbons is higher than the theoretical air-fuel ratio; The sintering section has a second heating device capable of controlling the atmosphere inside the sintering section, The injection port is located between the first heating device closest to the entrance of the sintering section in the direction of travel of the mesh belt within the furnace body and the upstream part of the sintering section, and is positioned in the range from the side to the bottom of the mesh belt in the circumferential direction of the mesh belt.

[0018] The above-mentioned mesh belt type continuous sintering furnace can produce sintered bodies with excellent surface properties for the following reasons.

[0019] Since the preheating section is provided with the first heating device, the combustion gas generated by burning the hydrocarbon gas is introduced into the preheating section. A part of the combustion gas is retained between the mesh belt and the heating object. The nozzle of the pipe for injecting the inert gas opens toward the mesh belt from within the above-mentioned range of the mesh belt configured in a mesh shape. The nozzle is located between the first heating device closest to the entrance of the sintering section and the upstream side of the sintering section. Therefore, before the combustion gas reduces the passivation film of the stainless steel wire, the inert gas is injected between the mesh belt and the compact through the mesh of the mesh belt, and the combustion gas retained therebetween is blown away. Since the sintering section is provided with the second heating device capable of controlling the atmosphere, the reducing combustion gas is not introduced into the furnace. Therefore, the combustion gas does not retain again between the mesh belt and the compact in the sintering section. Therefore, the reduction of the passivation film is suppressed. By suppressing the reduction of the passivation film, the adhesion of the reduced passivation film to the sintered body is suppressed. When the sintered body transported to the outlet of the furnace main body is removed from above the mesh belt, the passive film can be prevented from adhering to the sintered body.

[0020] In addition, the mesh belt of the mesh belt type continuous sintering furnace has a long life for the following reasons.

[0021] As described above, the reduction of the passive film on the stainless steel wire is suppressed, so that the passive film does not peel off and the base metal of the stainless steel wire is not exposed. Therefore, even if the mesh belt is discharged from the outlet of the furnace body and exposed to the atmosphere, the stainless steel wire does not oxidize and a new passive film is not formed on its surface. Therefore, the chromium contained in the stainless steel wire is not used to form the passive film. In other words, the peeling and formation of the passive film is not repeated, so the stainless steel wire does not become thinner and the chromium content does not decrease. Therefore, the strength of the stainless steel wire is not easily reduced, and the strength of the mesh belt is not easily reduced. In addition, the elongation of the mesh belt due to high-temperature creep is suppressed.

[0022] (2) As one embodiment of the above mesh belt type continuous sintering furnace, The piping is preferably provided within the preheating section when viewed from the side of the furnace main body.

[0023] The mesh belt type continuous sintering furnace can more reliably produce sintered bodies with excellent surface properties, because the combustion gas remaining between the mesh belt and the compact is blown away before it reaches the sintering section.

[0024] (3) As one embodiment of the mesh belt type continuous sintering furnace, The inert gas may be nitrogen gas.

[0025] Nitrogen gas is preferred as it is readily available and non-hazardous.

[0026] (4) As one embodiment of the above mesh belt type continuous sintering furnace, A mesh tray is interposed between the mesh belt and the heating target, The mesh tray may be formed in a mesh shape using a plurality of stainless steel wires.

[0027] The mesh belt type continuous sintering furnace can produce sintered bodies with excellent surface properties even when a mesh tray is used. A part of the combustion gas generated in the preheating section is retained both between the stainless steel wire of the mesh belt and the stainless steel wire of the mesh tray, and between the mesh tray and the heating object. Since the mesh belt and the mesh tray are configured in a mesh shape, an inert gas is injected between the above-mentioned two parts through the mesh of the mesh belt and the mesh tray, and the combustion gas retained between the two parts is blown away.

[0028] (5) As one embodiment of the above mesh belt type continuous sintering furnace, When the object to be heated is transported into the inside of the furnace body, the temperature in the preheating section is configured to be 300°C or higher and 800°C or lower, and the temperature in the sintering section is configured to be 1000°C or higher and 1170°C or lower.

[0029] By heating the object to the above temperature, the lubricant and binder are removed from the object in the preheating section. The object is sintered in the sintering section.

[0030] (6) As one embodiment of the mesh belt type continuous sintering furnace, The second heating device may be an electric heater or a radiant tube burner.

[0031] With the above-mentioned configuration, no combustion gas is generated, or even if combustion gas is generated, the combustion gas does not enter the space in the sintered part through which the object to be heated passes, making it possible to control the atmosphere in the sintered part.

[0032] Details of the embodiments of the present disclosure DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same objects.

[0033] First Embodiment [Mesh belt type continuous sintering furnace] A mesh belt type continuous sintering furnace 1 according to the first embodiment will be described with reference to Figs. 1, 2, 3A, and 3B. The mesh belt type continuous sintering furnace 1 includes a furnace main body 2 and a mesh belt 3. The furnace main body 2 includes a preheating section 21, a sintering section 22, and a cooling section. The cooling section is not shown. The mesh belt 3 travels inside the furnace main body 2 from an inlet to an outlet to transport a heating target 10. The mesh belt type continuous sintering furnace 1 according to this embodiment includes the following requirements (a) to (c). (a) The preheating section 21 has at least one first heating device 211 that burns a gas in which hydrocarbons and air are mixed at a mixture ratio in which the proportion of hydrocarbons is higher than the stoichiometric air-fuel ratio. (b) The sintering section 22 has a second heating device 221 capable of controlling the atmosphere inside the sintering section 22 . (c) The furnace main body 2 has a pipe 25 for injecting an inert gas from a nozzle from a specific location between the mesh belt 3 and the object to be heated 10. The details will be explained below.

[0034] [Mesh belt] The mesh belt 3 advances through the interior formed by the two side walls 223 and the top surface of the furnace main body 2 to transport the heating target 10 placed on the mesh belt 3. The mesh belt 3 is formed in a mesh shape with a plurality of stainless steel wires 31. A known mesh belt can be used for the mesh belt 3. The mesh belt 3 is an endless belt, and is stretched over the inlet side pulley 91 and the outlet side pulley of the furnace main body 2 with tension applied. The outlet side pulley is not shown. At least one of the inlet side pulley 91 and the outlet side pulley is used as a driving pulley, and the mesh belt 3 advances due to the drive thereof. In this embodiment, the outlet side pulley is the driving pulley, and the inlet side pulley 91 is the driven pulley. The mesh belt 3 that leaves the outlet of the furnace main body 2 passes under the furnace main body 2 and returns to the inlet of the furnace main body 2.

[0035] [Furnace body] The heating target 10 placed on the mesh belt 3 in the furnace main body 2 is transported by the mesh belt 3 in the order of preheating section 21, sintering section 22, and cooling section. Then, in the furnace main body 2, the heating target 10 is preheated, sintered, and cooled in that order. The sintered heating target 10 is called a sintered body. The cooled sintered body is removed from above the mesh belt 3. The heating target 10 is preferably a powder compact containing Fe powder or an Fe alloy powder not containing C and C powder, or a powder compact containing an Fe alloy powder containing C. The powder compact may be a known one. The heating target 10 enters the furnace main body 2 from the inlet and is transported toward the outlet of the furnace main body 2, so the inlet of the furnace main body 2 is upstream and the outlet is downstream. Similarly, in the preheating section 21 and the sintering section 22, the inlet is upstream and the outlet is downstream.

[0036] (Preheating section) The preheating section 21 preheats the heating target 10. If the heating target 10 contains a lubricant or binder, this preheating removes the lubricant or binder from the heating target 10. Therefore, when the heating target 10 is sintered in the sintering section 22, soot or roughness is unlikely to occur on the surface of the sintered body.

[0037] The preheating section 21 has a first heating device 211 that burns a gas obtained by mixing hydrocarbons and air at a mixture ratio in which the proportion of hydrocarbons is higher than the theoretical air-fuel ratio.

[0038] The first heating device 211 may be, for example, a gas burner. The hydrocarbon fuel may be, for example, butane (CH 10), propane (C3H8), etc. In this embodiment, butane gas is used as the hydrocarbon. The theoretical air-fuel ratio of butane to air is about 32:1. When the hydrocarbon is butane gas as in this embodiment, if it is burned at a mixture ratio where the proportion of butane is higher than the theoretical air-fuel ratio of butane to air, combustion gases such as hydrogen (H2), carbon monoxide (CO), methane (CH4), water vapor (H2O), and carbon dioxide (CO2) are generated. These combustion gases are introduced into the preheating section 21, and the heating target 10 is preheated. A part of these combustion gases is retained in a space 100 (FIGS. 3A and 3B) surrounded by the mesh belt 3 and the heating target 10. The space 100 will be described later.

[0039] The number of first heating devices 211 can be appropriately selected according to the overall length of the preheating section 21, etc. The number of first heating devices 211 may be one or more. In this embodiment, the number of first heating devices 211 is four. The four first heating devices 211 are arranged in parallel with intervals between each other in the traveling direction of the mesh belt 3.

[0040] The temperature of the preheating section 21 can be appropriately selected depending on the type of lubricant and binder contained in the heating target 10. When the heating target 10 is transported into the inside of the furnace main body 2, the temperature in the preheating section 21 can be, for example, 300°C or higher and 800°C or lower, or further 400°C or higher and 700°C or lower.

[0041] (Sintering section) The sintering section 22 sinters the preheated heating target 10. The sintering section 22 has a second heating device 221 capable of controlling the atmosphere in the sintering section 22. The second heating device 221 capable of controlling the atmosphere is different from the preheating section 21 in that it does not generate combustion gas or, even if combustion gas is generated, the combustion gas does not enter the space in the sintering section 22 through which the heating target 10 passes. Examples of the second heating device 221 include an electric heater and a radiant tube burner. The second heating device 221 in this embodiment is an electric heater.

[0042] The sintering section 22 reaches the sintering temperature of the heating target 10 by the second heating device 221. The sintering temperature can be appropriately selected depending on the material of the heating target 10. When the heating target 10 is transported inside the furnace main body 2, the temperature in the sintering section 22 is higher than that in the preheating section 21, for example, 1000°C or higher and 1170°C or lower, and further 1100°C or higher and 1150°C or lower.

[0043] The atmosphere in the sintering section 22 is an inert gas atmosphere. The inert gas atmosphere suppresses oxidation of the heating target 10. Examples of inert gas include nitrogen gas (N2 gas) and argon gas (Ar gas). The inert gas is blown in the opposite direction to the traveling direction of the mesh belt 3 in the furnace main body. Therefore, the inert gas also reaches the preheating section 21. Note that the inert gas that constitutes the atmosphere of the sintering section 22 cannot blow away the combustion gas remaining in the space 100 (FIGS. 3A and 3B).

[0044] (cooling section) The cooling section cools the sintered body. The cooling of the sintered body can be performed, for example, by spraying a cooling gas onto the sintered body. The cooling gas can be an inert gas. As in the sintering section 22, the inert gas can be, for example, N2 gas, Ar gas, etc. The inert gas is preferably the same as the atmospheric gas in the sintering section 22. In this way, the gas concentration in the furnace main body 2 is less likely to change.

[0045] (Plumbing) The piping 25 injects an inert gas. As mentioned above, examples of the inert gas include N2 gas and Ar gas. Among them, N2 gas is preferable because it is easily available and harmless. The injected inert gas is preferably the same type as the atmospheric gas in the sintering section 22. In this case, the gas concentration in the furnace main body section 2 is unlikely to change. The temperature of the inert gas in this embodiment is room temperature (23°C). It is to be noted that heated inert gas may be used as the inert gas. Depending on the durability of the piping 25, the temperature of the heated inert gas is set to a temperature range from room temperature (23°C) to 300°C. By using heated inert gas, the temperature of the heating target 10 is unlikely to decrease.

[0046] 2, the inert gas injection port 251 in the pipe 25 is disposed within a range extending from the side to the lower side of the mesh belt 3 and opens from within that range toward the mesh belt 3. The mesh belt 3 is configured in a mesh shape as described above, and the injection port 251 opens from within the range toward the mesh belt 3, so that the injected inert gas passes through the mesh of the mesh belt 3 and reaches between the mesh belt 3 and the heating target 10. The range extending from the side to the lower side of the mesh belt 3 includes the side of the mesh belt 3, the lower side, and a space between the side and the lower side.

[0047] When the heating target 10 is placed directly on the mesh belt 3 as shown in FIG. 1, the space between the mesh belt 3 and the heating target 10 is a space 100 surrounded by the stainless steel wire 31 of the mesh belt 3 and the heating target 10 as shown in FIG. 3A and FIG. 3B. FIG. 3A shows the heating target 10 placed on the mesh belt 3 in a plan view from the heating target 10 side. For convenience of explanation, FIG. 3A and FIG. 3B show a lattice-shaped mesh belt 3. The mesh belt 3 shown in FIG. 3A and FIG. 3B is shown diagrammatically and does not necessarily correspond to an actual one. For convenience of explanation, FIG. 3A and FIG. 3B show the space 100 by cross-hatching. In addition, the case where the mesh tray 4 is placed directly on the mesh belt 3 and the heating target 10 is placed directly on the mesh tray 4 as shown in FIG. 4 will be described later.

[0048] As shown in FIG. 2, the injection port 251 of this embodiment is disposed on the side of the mesh belt 3 in the circumferential direction of the mesh belt 3, and injects the inert gas from the side of the mesh belt 3 toward the mesh belt 3. The circumferential direction of the mesh belt 3 is the circumferential direction when the traveling direction of the mesh belt 3 in the furnace main body 2 is set as the axis. Although not shown, the injection port 251 may be disposed below the mesh belt 3, and the inert gas may be injected from the lower side of the mesh belt 3 toward the mesh belt 3. Although not shown, the injection port 251 may be disposed in a range from the side to the lower side of the mesh belt 3, and the inert gas may be injected obliquely from that range toward the mesh belt 3. Since the injection port 251 is disposed on the side of the mesh belt 3 as in this embodiment, dust falling from the mesh belt 3 is less likely to enter the injection port 251 than when it is disposed below the mesh belt 3, so that the injection port 251 is not clogged with dust.

[0049] The term "the nozzle 251 is disposed on the side of the mesh belt 3" means that the axis of the nozzle 251 is parallel to the upper surface of the mesh belt 3 and the nozzle 251 faces the side of the mesh belt 3. The upper surface of the mesh belt 3 is the location on which the heating target 10 is placed. "Parallel to the upper surface of the mesh belt 3" includes not only the case where the nozzle 251 is perpendicular to the moving direction of the mesh belt 3 as in this embodiment, but also the case where the nozzle 251 crosses the moving direction of the mesh belt 3 obliquely. When the nozzle 251 crosses the moving direction of the mesh belt 3 obliquely in the furnace main body, it is preferable that the nozzle 251 is disposed so as to jet in the opposite direction to the moving direction of the mesh belt 3 in the furnace main body. In this case, the inert gas jetted from the nozzle 251 has little or no effect on the temperature in the sintering section 22. The term "the side of the mesh belt 3" means a location where the nozzle 251 is perpendicular to both the moving direction and the up-down direction of the mesh belt 3. The term "the nozzle 251 is disposed below the mesh belt 3" means that the axis of the nozzle 251 is perpendicular to the lower surface of the mesh belt 3. The lower surface of the mesh belt 3 refers to the side opposite to the upper portion. The positioning of the injection port 251 between the side and the lower portion of the mesh belt 3 means that the axis of the injection port 251 intersects with the lower surface of the mesh belt 3 without being perpendicular thereto.

[0050] The position of the injection port 251 is between the first heating device 211 closest to the inlet 222 of the sintering section 22 and the upstream part of the sintering section 22 (FIG. 1). The upstream part of the sintering section 22 refers to the part between the inlet 222 of the sintering section 22 and the part where the sintering temperature of the heating object 10 is reached. In this way, before the sintering temperature is reached, the inert gas is injected into the space 100, and the combustion gas remaining in the space 100 is blown away. Therefore, when the sintering temperature is reached, the concentration of the combustion gas in the space 100, particularly the concentration of H2 gas and CO gas, is low. Alternatively, when the sintering temperature is reached, the combustion gas, particularly H2 gas and CO gas, does not exist in the space 100. Since the type of gas injected is an inert gas, even if the injected inert gas remains in the space 100, the concentration of H2 gas and CO gas in the space 100 remains low. When the preheating section 21 has one first heating device 211, the position of the jet orifice 251 is between the first heating device 211 and the upstream part of the sintering section 22. When the preheating section 21 has a plurality of first heating devices 211, the position of the jet orifice 251 is between the first heating device 211 closest to the inlet 222 of the sintering section 22 and the upstream part of the sintering section 22.

[0051] If the concentration of the combustion gas in the space 100, particularly the concentration of H2 gas and CO gas, is high when the heating target 10 reaches the sintering temperature, the passive film of the stainless steel wire 31 constituting the mesh belt 3 is reduced. When the passive film is reduced, the reduced passive film adheres to the sintered body. If the reduced passive film adheres to the sintered body, when the heating target 10 is conveyed to the outlet of the furnace body 2 and removed from the mesh belt 3, the passive film peels off from the stainless steel wire 31 and remains on the surface of the sintered body. As a result, a sintered body with poor surface quality is produced.

[0052] In this embodiment, as described above, the concentration of the combustion gas in the space 100 is low or the combustion gas is not present in the space 100 before the heating target 10 reaches the sintering temperature, so that the reduction of the passive film on the stainless steel wire 31 is suppressed in the sintering section 22. This makes it possible to prevent the reduced passive film from adhering to the sintered body. In other words, even if the heating target 10 is transported to the outlet of the furnace main body 2 and removed from the mesh belt 3, it is possible to prevent the passive film from adhering to the sintered body. This allows the production of a sintered body with excellent surface properties.

[0053] The position of the injection port 251 is preferably closer to the inlet of the preheating section 21 between the first heating device 211 at the most downstream of the preheating section 21 and the point in the sintering section 22 where the sintering temperature of the heating target 10 is reached. The position of the injection port 251 is further preferably between the first heating device 211 at the most downstream of the preheating section 21 and the point in the sintering section 22 where the decomposition temperature of CH4 gas is reached. The decomposition temperature of CH4 gas is about 1000°C. That is, in the sintering section 22, the point where the decomposition temperature is reached is closer to the inlet of the preheating section 21 than the point where the sintering temperature is reached. When the position of the injection port 251 is between the point where the decomposition temperature is reached in the sintering section 22 and the point where the sintering temperature is reached, the position of the injection port 251 is preferably closer to the preheating section 21. When the position of the injection port 251 is between the inlet 222 of the sintering section 22 and the point where the decomposition temperature is reached, the position of the injection port 251 is preferably closer to the preheating section 21. The position of the jet nozzle 251 is particularly preferably within the preheating section 21. That is, the position of the jet nozzle 251 is preferably between the first heating device 211 at the most downstream of the preheating section 21 and the sintering section 22.

[0054] When CH4 gas decomposes, it generates H2 gas. If the position of the injection port 251 is within a range up to the point where the decomposition temperature of CH4 gas is reached, an inert gas is injected into the space 100 before the CH4 gas decomposes, and the combustion gases, particularly CH4 gas, remaining in the space 100 are blown away. By blowing away the CH4 gas before it decomposes, it is possible to prevent the H2 gas concentration in the space 100 from becoming high. Therefore, in the sintered portion 22, the reduction of the passive film of the stainless steel wire 31 is more easily suppressed.

[0055] If the position of the injection port 251 is within the preheating section 21, the inert gas is injected into the space 100 before the combustion gas reaches the sintering section 22, and the combustion gas remaining in the space 100 is blown away. Therefore, in the sintering section 22, the reduction of the passive film of the stainless steel wire 31 is particularly likely to be suppressed.

[0056] As shown in FIG. 1, the position of the injection port 251 in this embodiment is within the preheating section 21 when viewed from the side of the furnace main body 2, and is between the downstream end of the first heating device 211, which is the most downstream of the preheating section 21, and the inlet 222 of the sintering section 22.

[0057] The number of pipes 25 can be appropriately selected and may be one or more. In this embodiment, the number of pipes 25 is two. As shown in FIG. 2, the injection ports 251 of the two pipes 25 are arranged on both sides of the mesh belt 3 in the preheating section 21 in the cross-sectional view of the furnace main body 2, and open toward the mesh belt 3 from both sides. The two pipes 25 extend from the side wall 223 of the furnace main body 2 to the inside of the furnace main body 2, and it is preferable that the injection ports 251 are arranged in a position closer to the mesh belt 3.

[0058] The device may be provided with a pipe 25 arranged on the side of the mesh belt 3 and having an injection port 251 opening from that side toward the mesh belt 3, and a pipe 25 arranged between the side and below the mesh belt 3 and having an injection port 251 opening from there toward the mesh belt 3.

[0059] The amount of inert gas injected depends on the size of the heating target 10 and the mesh size of the mesh belt 3. For example, 3 / h or more 10m 3 / h or less. The amount of inert gas injected is 1m 3 If the inert gas injection rate is 10 m / h or more, the combustion gas remaining in the space 100 is easily blown away. 3 If the injection rate is less than 2 m / h, the injection rate is not excessively high. Therefore, the temperature inside the furnace body 2 is unlikely to drop. 3 / h or more 8m 3 / h or less, especially 3m 3 / h or more 6m 3 / h and below.

[0060] [Application] The mesh belt type continuous sintering furnace 1 according to the embodiment can be suitably used for manufacturing various general structural parts. Examples of the general structural parts include mechanical parts. Examples of the mechanical parts include cam parts of electromagnetic couplings, planetary carriers, sprockets, rotors, gears, rings, flanges, pulleys, bearings, etc.

[0061] [Action and Effect] The mesh belt type continuous sintering furnace 1 according to this embodiment can produce a sintered body having excellent surface properties. The nozzle 251 of the pipe 25 for injecting the inert gas opens from the side of the mesh belt 3 toward the mesh belt 3 between the most downstream first heating device 211 and the sintering section 22. Therefore, the combustion gas remaining in the space 100 is blown away before it reaches the sintering section 22. The second heating device 221 of the sintering section 22 is an electric heater. Therefore, in the sintering section 22, the combustion gas does not remain in the space 100 again. Therefore, in the sintering section 22, the reduction of the passivation film of the stainless steel wire 31 constituting the mesh belt 3 is suppressed, and the reduced passivation film accompanying the reduction of the passivation film is suppressed from adhering to the sintered body. When the sintered body transported to the outlet of the furnace main body section 2 is taken out from above the mesh belt 3, the passivation film can be suppressed from adhering to the sintered body. Since the reduced passivation film is suppressed from adhering to the sintered body in this way, the sintered body can be easily taken out even by a robot hand. That is, the mesh belt type continuous sintering furnace 1 according to this embodiment makes it easy to automate the removal of the sintered body.

[0062] In addition, in the mesh belt type continuous sintering furnace 1 according to the present embodiment, the mesh belt 3 has a long life. As described above, the peeling of the passivation film of the stainless steel wire 31 is suppressed, thereby suppressing exposure of the base metal of the stainless steel wire 31. Therefore, even if the mesh belt 3 exits from the outlet of the furnace main body 2 and is exposed to the atmosphere, the stainless steel wire 31 is not oxidized and a new passivation film is not formed on its surface. Therefore, the chromium contained in the stainless steel wire 31 is not used for forming the passivation film. In other words, since the peeling and formation of the passivation film are not repeated, the stainless steel wire 31 does not become thin and the chromium content does not decrease. Therefore, the strength of the stainless steel wire 31 is not easily reduced, and the strength of the mesh belt 3 is not easily reduced. In addition, the elongation of the mesh belt 3 due to high-temperature creep is suppressed.

[0063] Second Embodiment [Mesh belt type continuous sintering furnace] A mesh belt type continuous sintering furnace 1 according to a second embodiment will be described with reference to Fig. 4. The mesh belt type continuous sintering furnace 1 according to this embodiment differs from the first embodiment in that the heating target 10 is not placed directly on the mesh belt 3, but on a mesh tray 4 placed on the mesh belt 3. The following description will focus on the differences from the first embodiment. Descriptions similar to those of the first embodiment will be omitted.

[0064] [Mesh tray] At least one heating target 10 is placed on the mesh tray 4. When multiple heating targets 10 are placed on the mesh tray 4, the mesh tray 4 places the multiple heating targets 10 together on the mesh belt 3. The mesh tray 4 is formed in a mesh shape from multiple stainless steel wires 41, similar to the mesh belt 3. The mesh tray 4 is placed directly on the mesh belt 3.

[0065] [Furnace body] (Plumbing) As in the first embodiment, the injection port 251 of the pipe 25 is disposed on the side of the mesh belt 3 and opens toward the mesh belt 3 from the side of the mesh belt 3. Therefore, the inert gas is injected between the mesh belt 3 and the heating target 10.

[0066] In this embodiment, the mesh tray 4 is placed directly on the mesh belt 3, and the heating target 10 is placed directly on the mesh tray 4. In this embodiment, the space between the mesh belt 3 and the heating target 10 refers to both the space between the mesh belt 3 and the mesh tray 4 and the space between the mesh tray 4 and the heating target 10. The space between the mesh belt 3 and the mesh tray 4 refers to the space surrounded by the stainless steel wire 31 of the mesh belt 3 and the stainless steel wire 41 of the mesh tray 4. This space is not shown in the figure. The space between the mesh tray 4 and the heating target 10 refers to the space surrounded by the stainless steel wire 41 of the mesh tray 4 and the heating target 10. This space is the same as the space surrounded by the mesh belt 3 and the heating target 10 described with reference to Figures 3A and 3B, and is therefore not shown in the figure.

[0067] As described above, the mesh belt 3 and the mesh tray 4 are configured in a mesh-like shape. Therefore, the inert gas injected from the injection port 251 passes through the meshes of the mesh belt 3 and the mesh tray 4, and reaches both the space surrounded by the stainless steel wires 31 of the mesh belt 3 and the stainless steel wires 41 of the mesh tray 4, and the space surrounded by the stainless steel wires 41 of the mesh tray 4 and the heating target 10.

[0068] [Action and Effect] The mesh belt type continuous sintering furnace 1 according to this embodiment can produce a sintered body having excellent surface properties, similar to the first embodiment, even when a mesh tray 4 is used. Furthermore, the mesh belt type continuous sintering furnace 1 according to this embodiment has a long life for the mesh belt 3. This is because reduction of the passivation film of the stainless steel wire 31 constituting the mesh belt 3 is suppressed, the strength of the stainless steel wire 31 and the mesh belt 3 is unlikely to decrease, and elongation of the mesh belt 3 due to high-temperature creep is suppressed. Furthermore, the mesh belt type continuous sintering furnace 1 according to this embodiment has a long life for the mesh tray 4 for the same reason as the reason for the long life of the mesh belt 3 described in the first embodiment.

[0069] The present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0070] 1 Mesh belt type continuous sintering furnace 2. Furnace body 21 Preheating section 211 First heating device 22 Sintering section 221 Second heating device 222 Entrance of sintering section 223 Side wall 25 Piping 251 Nozzle 3 Mesh belt 31 Stainless steel wire 4 Mesh Tray 41 Stainless steel wire 91 Inlet pulley 10 Heating target 100 space

Claims

1. A furnace body portion, A mesh belt type continuous sintering furnace comprising: a mesh belt that travels inside the furnace body to transport a heating object; The mesh belt is formed in a mesh shape by a plurality of stainless steel wires, The furnace body includes: A preheating unit that preheats the heating object; A sintering section that sinters the preheated heating target; A pipe having an injection port for injecting an inert gas toward a gap between the mesh belt and the heating target placed on the mesh belt, the preheating unit has at least one first heating device that preheats the heating object by burning a gas obtained by mixing hydrocarbons and air at a mixture ratio in which the proportion of hydrocarbons is higher than a theoretical air-fuel ratio, The sintering section has a second heating device capable of controlling the atmosphere inside the sintering section, The injection port is located between the first heating device closest to the inlet of the sintering section in the traveling direction of the mesh belt in the furnace body and the upstream part of the sintering section, and the injection port is located in the range from the side to the lower part of the mesh belt in the circumferential direction of the mesh belt. Mesh belt type continuous sintering furnace.

2. The mesh belt type continuous sintering furnace according to claim 1 , wherein the injection port is provided within the preheating section when viewed from the side of the furnace body.

3. 3. The mesh belt type continuous sintering furnace according to claim 1, wherein the inert gas is nitrogen gas.

4. A mesh tray is interposed between the mesh belt and the heating target, 4. The mesh belt type continuous sintering furnace according to claim 1, wherein the mesh tray is formed in a mesh shape by a plurality of stainless steel wires.

5. 5. The mesh belt type continuous sintering furnace according to claim 1, wherein the temperature in the preheating section is set to be 300° C. or higher and 800° C. or lower when the heating object is transported into the furnace main body, and the temperature in the sintering section is set to be 1000° C. or higher and 1170° C. or lower.

6. The second heating device is an electric heater or a radiant tube burner. The mesh belt type continuous sintering furnace according to any one of claims 1 to 5.

7. A mesh belt type continuous sintering furnace according to claim 1, wherein the amount of the inert gas injected is 1 m 3 / h or more and 10 m 3 / h or less.

8. A process for producing a sintered body using a mesh belt type continuous sintering furnace according to any one of claims 1 to 7, The heating object is a powder compact made of iron or iron alloy powder. A method for manufacturing a sintered body.

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