Hot air circulating heating furnace

Abstract

This invention provides a hot air circulating heating furnace, which can reduce flow losses in the upper reversing channel near the furnace top and the lower reversing channel near the furnace bed, thereby improving circulation efficiency. The hot air circulating heating furnace comprises: a furnace body having a heat source and a furnace bed; and a circulating fan disposed at the center near the furnace top of the furnace body. Inside the furnace body are: an inner wall divided into an inner peripheral region through which a downward flow toward the furnace bed passes and an outer peripheral region through which an upward flow toward the furnace top passes; and a lower reversing channel and an upper reversing channel connecting the inner and outer peripheral regions. The lower reversing channel is near the furnace bed, and the upper reversing channel is near the furnace top. The circulating fan draws in hot air flowing in the upper reversing channel and blows it toward the inner peripheral region, causing the hot air to circulate through the lower reversing channel to the outer peripheral region.

Description

Technical Field

[0001] This invention relates to a hot air circulating heating furnace. Background Technology

[0002] Conventionally, as a heating furnace for heat treatment of an object placed on a rotating platform within a furnace, for example, Patent Document 1 discloses a heating furnace having: a first furnace chamber equipped with a first rotating platform; and a second furnace chamber equipped with a second rotating platform. Furthermore, by separately providing a first fan and a second fan, independent heat treatment at different temperatures can be performed. The first fan homogenizes the thermal environment within the first furnace chamber, and the second fan homogenizes the thermal environment within the second furnace chamber. There are also examples where a first fan and a second fan are provided within a pressurizing device, with the first fan performing heat circulation and the second fan performing heat stirring (see Japanese Patent Application Publication No. 11-083338).

[0003] On the other hand, hot air circulation furnaces are known to heat the object to a predetermined heat treatment temperature by circulating hot air. For example, in the hot air circulation furnace disclosed in Patent Document 2, a stepped receiving chamber for accommodating the object to be heated is provided on the furnace wall. Hot air is delivered to the lower furnace bed by a first fan located above the central part. The hot air then makes a U-turn from the furnace bed and is delivered from the lower receiving chamber to the upper receiving chamber. The returning hot air makes a U-turn at the upper part and is drawn in by the first fan, causing the hot air delivered to the furnace bed to make a U-turn again and circulate. Furthermore, in this hot air circulation furnace, a partition wall is provided to separate the heating zone and the heat spreader zone. In the heating zone, a large amount of high-speed hot air is introduced and circulated for rapid heating. In the heat spreader zone, hot air is circulated to maintain a constant temperature in a state of thermal saturation.

[0004] Furthermore, the hot air circulating heating furnace disclosed in Patent Document 3 includes: a first fan disposed above the central portion for supplying hot air to the heating zone of the aforementioned hot air circulating heating furnace; and a second fan disposed on the wall of the furnace body for supplying hot air to another heat equalization zone. The first fan supplies hot air from the opening of the partition wall separating the heating zone and the heat equalization zone toward the receiving chamber, causing the hot air to rise along the wall of the furnace body and return to the first fan, whereby axial circulation occurs. Conversely, the second fan supplies hot air circumferentially along the outer periphery of the receiving chamber located in the heat equalization zone, causing it to return to the second fan, whereby circumferential circulation occurs.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2-050080

[0006] Patent Document 2: Japanese Patent Application Publication No. 2004-257658

[0007] Patent Document 3: Japanese Patent Application Publication No. 2019-074296 Summary of the Invention

[0008] In the hot air circulation furnace of Patent Document 2, hot air is circulated between the heating zone and the heat spreader zone by a fan located above the central part. Therefore, the fan capacity increases, resulting in a larger furnace structure. Furthermore, the control of the hot air in the heating zone and the heat spreader zone becomes more complex. Therefore, in the hot air circulation furnace of Patent Document 3, a first fan for the heating zone and a second fan for the heat spreader zone are provided. For the heating zone, the first fan generates an axial hot air circulation flow, and for the heat spreader zone, the second fan circulates the hot air circumferentially. This simplifies the furnace structure and zone control. However, as mentioned above, in the heating zone, a large amount of high-speed hot air is required for rapid heating. However, as in Patent Document 1 or Patent Document 3, although two fans are used to circulate the hot air, there is a U-shaped bend in the axial hot air circulation flow, resulting in flow loss and reduced circulation efficiency. Patent Documents 1-3 do not consider the flow loss in the U-shaped bend of the circulating hot air, resulting in poor circulation efficiency.

[0009] This invention addresses the aforementioned technical challenges. Its purpose is to provide a hot air circulating furnace that reduces flow losses in the channels where hot air makes U-shaped turns (hereinafter referred to as reversals) near the furnace top and hearth, thereby improving circulation efficiency.

[0010] To achieve the above objectives, the hot air circulating heater of the present invention comprises: a furnace body having a heat source and a furnace bed; and a circulating fan disposed at the center near the furnace top of the furnace body. The furnace body has: an inner cylindrical wall divided into an inner peripheral region through which a downward flow toward the furnace bed passes and an outer peripheral region through which an upward flow toward the furnace top passes; and a lower reversing channel and an upper reversing channel connecting the inner peripheral region and the outer peripheral region. The lower reversing channel is located near the furnace bed, and the upper reversing channel is located near the furnace top. The circulating fan draws in hot air flowing in the upper reversing channel and blows it toward the inner peripheral region, causing the hot air to circulate through the lower reversing channel toward the outer peripheral region. The hot air circulating heater is further provided with a forced fan that directs the hot air flowing in the upper reversing channel near the furnace top toward the intake portion of the circulating fan.

[0011] In the hot air circulating heating furnace of the present invention, the forced fan is preferably positioned approximately orthogonal to the rotation axis of the circulating fan.

[0012] In the hot air circulating heating furnace of the present invention, the forced fans are preferably arranged in multiple units at predetermined intervals along the circumference of the furnace body.

[0013] In the hot air circulating heating furnace of the present invention, the corners of the lower reversing channel and the upper reversing channel are preferably designed as arc-shaped channels.

[0014] Furthermore, in the hot air circulating heating furnace of the present invention, an annular mounting platform can be arranged on the outer peripheral region so that hot air passes from the lower layer of the mounting frame to the upper layer, and the annular mounting platform has a multi-layer mounting frame that can hold the heated object in a manner that allows it to be moved in and out.

[0015] Invention Effects

[0016] In a hot air circulating furnace, the descending flow of hot air towards the hearth and the ascending flow of hot air towards the furnace top flow through an upper and lower reversing channel, thereby generating an axial hot air circulation flow. However, the inner side of the reversing channel forms a sharp turn, preventing the straight-flowing hot air from making a sharp turn, resulting in flow separation at this corner. This phenomenon is particularly prone to occur in the upper reversing channel on the furnace top side, which is in contact with the intake of the circulating fan, causing hot air to accumulate and deteriorating circulation efficiency. Therefore, a forced draft fan is installed next to the upper reversing channel, in front of the intake, to force the hot air accumulated in the reversing channel, along with the ascending flow, towards the intake of the circulating fan. This eliminates the flow separation phenomenon and allows the hot air accumulated in the upper reversing channel to be rapidly delivered into the circulating fan. As a result, the intake flow rate of the circulating fan increases, enabling a large amount of high-speed hot air to be introduced into and circulated in both the inner and outer peripheral regions. This reduces flow losses and improves circulation efficiency. Attached Figure Description

[0017] Figure 1 This is a partial cross-sectional view of a hot air circulating heating furnace according to an embodiment of the present invention.

[0018] Figure 2 This is a graph showing the change in the exhaust flow rate of the circulating fan in the hot air circulating heater based on the present invention.

[0019] Figure 3 This is a simulation diagram showing the flow separation in the intake section of the circulating fan of an existing hot air circulating heater. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the embodiments described below are merely examples of implementing the present invention and do not limit the scope of the invention.

[0021] Figure 1This is a partial cross-sectional view of a hot air circulating heating furnace according to an embodiment of the present invention.

[0022] A hot air circulating heating furnace 1 includes a furnace body 2, a heat source 3, a furnace bed 4, a circulating fan 5, and a forced-air fan 6. The heat source 3 is configured to inject combustion gases heated by a burner or the like into the furnace. The furnace bed 4 is located at the lower part of the furnace body and has a platform for arranging the materials to be heated. The circulating fan 5 is located near the center of the furnace top where combustion gases are drawn in and blown out as hot air, circulating hot air within the furnace. The forced-air fan 6 is configured to rapidly deliver rising hot air or combustion gases to the intake section of the circulating fan 5. The furnace bed 4 can be a stationary structure where only the materials to be heated are placed, but it is typically configured as a rotating furnace bed with a rotating platform. In this embodiment, the materials to be heated are placed on the platform provided on the furnace bed, heated by hot air circulating within the furnace, and the prescribed heat treatment is completed during one revolution of the rotating platform. A continuous heating furnace capable of sequentially removing the materials to be heated is then used as an example. The detailed structure of each part will be described below.

[0023] The furnace body 2 consists of a cylindrical furnace wall 20, a furnace top 21, and a rotating hearth 4 (hereinafter referred to as the hearth), which are separated from these and capable of rotation. A heat source 3 is provided on the upper outer side of the furnace wall 20. Furthermore, an annular inner cylindrical wall 22 is provided inside the furnace body 2, divided into an annular inner peripheral region 25 through which the downward flow DD toward the hearth 4 flows and an annular outer peripheral region 27 through which the upward flow UD toward the furnace top 21 flows. An annular lower reversing channel 26 is formed in a portion of the hearth 4, and an annular upper reversing channel 28 is formed near the furnace top 21. Therefore, the inner peripheral region 25 and the outer peripheral region 27 are connected by the flow through the upper and lower reversing channels 26 and 28. A cylindrical body 23 is arranged in the center of the furnace body 2 to fill the central space and prevent turbulence in the downward flow DD. In this example, the cylindrical body 23 is arranged to be rotated separately from the hearth 4 and stand upright on the base 40. Furthermore, the inner cylinder wall 22 can divide the total length from the hearth 4 to the furnace top 21, but the method can be appropriately modified as long as the straightness of the hot air is maintained and the circulation flow near the hearth and furnace top is easy to reverse.

[0024] Heat source 3 is preferably a burner, but an electric heater or similar device may also be used depending on the situation. In this example, a burner (not shown) is used, positioned near the furnace top so as to supply combustion gas to the circulating fan 5 located in the center near the furnace top of the furnace body 2. In this example, it is positioned opposite the furnace wall 20 in the central part of the furnace body 2 so as to eject combustion gas into the space of the upper reversing channel 28. That is, the two burners are positioned at a 180° interval on the outside of the furnace body 2. Figure 1 The diagram shows the nozzle 30' opposite to the nozzle 30.

[0025] A circulating fan 5 is located in the center of the furnace body near the furnace top. It draws in combustion gases from the heat source and blows hot air towards the hearth side, creating a downward flow. The downward flow DD of hot air passes through the inner peripheral region 25, reverses in the lower reversing channel 26 to become an upward flow UD of hot air, passes through the outer peripheral region 27, and reaches the upper reversing channel 28. In the upper reversing channel 28, in addition to the upward flow of hot air, combustion gases from the heat source are mixed, causing the temperature of the atmosphere to rise. The heated atmosphere is then drawn back into the circulating fan 5, and thereafter, the hot air circulates between the inner peripheral region 25 and the outer peripheral region 27 inside the furnace body 2 (creating an axial hot air circulation flow).

[0026] The circulating fan 5 uses an axial flow fan. This is because axial flow fans have the characteristic of drawing in and blowing out the surrounding atmosphere without sufficiently agitating it, and although relatively compact, they can deliver a large volume of high-speed air and circulate it. However, as mentioned above, in a hot air circulating furnace with a lower reversing channel 26 and an upper reversing channel 28, the inner side of the reversing channel becomes a sharp turn, so the straight-flowing hot air cannot make a sharp turn, and the flow loss increases in this part. In particular, it is known that the loss is greater in the upper reversing channel near the furnace top. Figure 3 This is a diagram simulating the flow of hot air through the conventional upper reversing channel. Although the simulation diagram is color-coded according to the hot air velocity, it can be seen that while the outer side of the rising flow UD (appearing as a white area) bends sharply towards the center, the inner side cannot bend flexibly, causing flow interruption near the bend angle 29, resulting in flow separation (represented by the darkened area PD). As a result, the outer part of the intake section 50 of the circulating fan 5 cannot be drawn in, easily leading to the accumulation of hot air and combustion gases in the upper reversing channel 28. Furthermore, as described later... Figure 2 In the region where the flow rate becomes negative at a diameter of 1600-1800 mm on the fan blades, it can be seen that the outer part of the blades of the circulating fan 5 cannot be sucked in.

[0027] Therefore, in this embodiment, a forced-flow fan 6 is provided to deliver the hot air accumulated in the upper reversing channel 28 to the intake section 50 (the part with the intake blades) of the circulating fan 5. The forced-flow fan 6 is installed on the furnace wall 20 on the side of the upper reversing channel 28 in a manner that the rotation axis RA1 (in other words, the direction of flow) of the circulating fan 5 is approximately orthogonal to its own rotation axis RA2. The forced-flow fan 6 uses an axial flow fan to draw in atmospheric gas from the rear and blow it to the front, directing the accumulated hot air toward the circulating fan. By providing the forced-flow fan 6, a forced flow toward the circulating fan is generated, eliminating flow separation, and the circulating fan 5 can quickly draw in the hot air accumulated in the upper reversing channel 28. As a result, the intake flow rate of the circulating fan 5 increases, enabling a large volume of high-speed downward flow. In addition, at least one forced-flow fan 6 is provided, but... Figure 1 As shown, two units can be installed at 180° intervals, or multiple units can be installed at specified intervals along the circumference of the furnace body. For example, four forced-action fans can be installed at 90-degree intervals. By installing multiple units, circulation efficiency can be improved. Furthermore, by improving circulation efficiency, rapid heating can be achieved.

[0028] Furthermore, in this embodiment, the corners of the lower reversing channel 26 located near the hearth and the upper reversing channel 28 located near the furnace top are designed as arc-shaped channels. From Figure 2 Simulation results show that hot air stagnation occurs at the corners of the channels, forming a portion SD. To eliminate this stagnation, the corners are rounded to ensure smooth and effective flow. In particular, to prevent the descending flow DD from decreasing in velocity and instead reversing upwards to become an ascending flow, the lower reversing channel 26 has its inner circumferential corners 41 and 42 rounded into an R-shape. Furthermore, regarding the upper reversing channel 28 near the furnace top, to eliminate the stagnation SD and smoothly reverse the ascending flow UD towards the suction section 50, the inner circumferential corners 43 and 44 are also rounded into an R-shape. Thus, by forming the hot air reversing channel into a rounded channel, flow losses in both the descending flow DD and the ascending flow UD are suppressed. Therefore, circulation efficiency can be further improved.

[0029] The hot air circulating heating furnace 1 of this embodiment heats the object to be heated by hot air circulating inside the furnace, mainly performing heat treatment. Therefore, the object to be heated is appropriately arranged inside the furnace body 2. In this example, an annular mounting platform 7 is provided on the rotary table 45 of the furnace bed 4. This mounting platform 7 has multi-layer mounting racks 70 for loading and unloading the object to be heated 8 in a radial direction, and is arranged in the outer peripheral region 27, through which the hot air circulation flows from bottom to top. Furthermore, on the furnace wall 20 of the furnace body 2, each layer of the mounting rack has a loading inlet and a unloading outlet (not shown) for loading and unloading the object to be heated from the outside. Therefore, the object to be heated 8 is arranged on the mounting racks 70, and while the rotary table 45 is rotated by a drive mechanism (not shown), the object to be heated is heated and heat-treated by the hot air passing through the mounting racks 70. For example, control is performed to complete the desired heat treatment during one revolution.

[0030] Furthermore, the mounting platform 7, inner cylinder wall 22, and cylindrical body 23 installed inside the furnace can be made of materials corresponding to the temperature of the circulating hot air or the heat treatment temperature, such as heat-resistant steel or heat-resistant resin. Moreover, the mounting frame 70 is made of a breathable material or structure that facilitates the smooth flow of hot air.

[0031] Furthermore, in the hot air circulation furnace, the outer peripheral area can be divided into a space connected to the heating zone and a space connected to the heat exchange zone, thus creating a hot air circulation furnace equipped with both a heating zone and a heat exchange zone. In the heating zone, a large amount of heat input and high-speed hot air circulation are required for rapid heating. However, according to the hot air circulation furnace of this embodiment, as described above, the flow rate of the circulating gas can be increased by the action of a forced-air fan, thus allowing the heating zone to be set to a smaller size. Furthermore, in the heat exchange zone, after the heated object reaches the target temperature, temperature deviations of each heated object can be suppressed.

[0032] Example

[0033] Regarding the exhaust flow rate of the circulating fan, experiments were conducted to observe the changes in flow rate under conditions of no forced fan (conventional example) and conditions of having a forced fan (example of the present invention).

[0034] Figure 2 In the diagram, the vertical axis represents the exhaust flow rate (m³ / s) of the circulating fan. 3 / min), the horizontal axis represents the diameter (mm) of the circulating fan blades. Characteristic curve a is an example of the present invention, and characteristic curve b is a conventional example.

[0035] like Figure 2 As shown in characteristic curve b, the flow rate at the blade diameter range of 1600–1800 mm exhibits a negative region, indicating a state where no suction is occurring. This diameter range of 1600–1800 mm is related to… Figure 3The areas where flow separation occurs (the black part PD) are roughly the same, indicating that no intake occurs due to flow separation. On the other hand, it can be seen that in characteristic curve a, even on the outer diameter side, including the area with a blade diameter of 1600-1800 mm, the flow rate is uniform, and the intake capacity is improved.

[0036] Thus, by setting up a forced fan, it was demonstrated that the flow separation phenomenon was eliminated, and the hot air in the upper reversing channel was sent to the circulating fan side, resulting in a significant improvement in the exhaust flow rate.

[0037] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments and can be implemented with appropriate modifications as needed. For example, the furnace bed does not have to be a rotary furnace bed; for example, it can also be implemented by placing the object to be heated into a basket and moving it in and out as a whole. Furthermore, the forced fan may not be installed on the outer wall of the furnace body but inside the furnace body.

[0038] Symbol Explanation

[0039] 1-Hot air circulating heater, 2-Furnace body, 3-Heat source, 4-Furnace bed, 5-Circulating fan, 6-Forced fan, 7-Placement platform, 8-Heated object, 20-Furnace wall, 21-Furnace top, 22-Inner cylinder wall, 23-Cylinder, 25-Inner peripheral area, 26-Lower reversing channel, 27-Outer peripheral area, 28-Upper reversing channel, 29-Corner, 30-Spray outlet, 40-Furnace bed base, 41, 43-Inner peripheral corner, 42, 44-Outer peripheral corner, 45-Rotating table, 50-Suction section (suction blades), 70-Placement frame, DD-Downward flow, UD-Upward flow, PD-Separation section, SD-Sedimentation section, RA1, RA2-Rotating shaft.

Claims

1. A hot air circulating heating furnace, comprising: The furnace body, which includes a heat source and a hearth; and A circulating fan is located in the center near the top of the furnace body. The furnace body includes: an inner cylindrical wall divided into an inner peripheral region through which a downward flow toward the hearth passes and an outer peripheral region through which an upward flow toward the furnace top passes; and a lower reversing channel and an upper reversing channel connecting the inner peripheral region and the outer peripheral region, the lower reversing channel being near the hearth and the upper reversing channel being near the furnace top. The hot air circulating heater is characterized by drawing in hot air flowing in the upper reversing channel through the circulating fan and blowing it towards the inner peripheral region, and circulating the hot air through the lower reversing channel to the outer peripheral region. A forced fan is provided to direct the hot air flowing in the upper reversing channel near the furnace top toward the intake of the circulating fan.

2. The hot air circulating heating furnace according to claim 1, characterized in that, The forced fan is positioned approximately orthogonal to the rotation axis of the circulating fan.

3. The hot air circulating heating furnace according to claim 2, characterized in that, Multiple forced fans are arranged at predetermined intervals along the circumference of the furnace body.

4. The hot air circulating heating furnace according to claim 1, characterized in that, The corners of the lower and upper reversing channels are designed as arc-shaped channels.

5. The hot air circulating heating furnace according to claim 1, characterized in that, An annular mounting platform is arranged on the outer peripheral region so that hot air passes from the lower layer of the mounting rack to the upper layer. The annular mounting platform has a multi-layer mounting rack that can hold the heated object in a manner that allows it to be moved in and out.

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