JP5697771B2 - heating furnace - Google Patents

Description

  The present invention relates to a heating furnace for performing a heat treatment in an atmosphere of an inert gas or the like.

Conventionally, as a heating furnace for performing heat treatment such as ceramic binder removal, a hot air circulation type heating furnace for heating an object to be processed by circulating hot air in an inert gas atmosphere or an air atmosphere has been used. ing. This hot air circulation type heating furnace has a furnace body having an airtight heating chamber inside, and heat treatment is performed while introducing an inert gas or air into the heating chamber.
When heat treatment is performed in the hot-air circulation type heating furnace, a gas containing volatile components generated from the heat-treated object is ignited and explodes rapidly to expand, thereby causing abnormal pressure in the heating chamber. There is a concern that the heating furnace body may be damaged.
For this reason, in the conventional heating furnace, when the pressure in the heating chamber abnormally increases, an explosion-proof valve is provided to release the increased pressure from the heating chamber, and an abnormal increase in pressure occurs in the heating chamber. However, it has been performed to avoid or reduce damage to the heating furnace body (see, for example, Patent Document 1).

JP 60-129591 A

Since the abnormal rise in pressure generated in the heating chamber is caused by the rapid expansion of the gas, the pressure rise rate also becomes rapid. For this reason, in order to avoid damage to the heating furnace body, it is necessary to quickly release the pressure in the heating chamber.
In this regard, the explosion-proof valve used in the above-described conventional heating furnace cannot ensure a sufficient opening area even if the valve is opened due to its structure. There was a risk that the pressure could not be released.

Therefore, for example, as shown in FIG. 7, the pressure release device X is provided in the hot air circulation type heating furnace 8. The pressure release device X includes a wide-diameter relief pipe 82 having one end connected to the heating chamber 80, a lid 83 that releasably closes an opening 86 at the other end of the relief pipe 82, and a peripheral edge of the opening 86. A plurality of guide shafts 84 erected at predetermined intervals in the circumferential direction to guide the movement of the lid 83 in the opening direction, and the lids are wound around the shafts along the guide shafts 84 to close the openings 86. And a compression spring 85 for pressing 83. In the pressure release device X, when the pressure in the heating chamber 80 is abnormally increased, the lid 83 is lifted against the pressing force of the compression spring 85 by the pressure, and the opening 86 is opened. The pressure inside is released. According to this pressure release device X, since the relief pipe 82 and its opening 86 have a wide diameter, a wider opening area can be secured compared to the explosion-proof valve, and the pressure in the heating chamber 80 can be quickly released. I can expect.
However, in the pressure release device X, since the lid 83 is pressed by the compression spring 85, even if the pressure rises abnormally in the heating chamber 80, the opening 86 at the other end of the relief pipe 82 opens only slowly. For this reason, it takes time to secure a sufficient opening area. Further, if the lid 83 is tilted without being lifted up uniformly when the lid 83 is opened, the lid 83 may be caught on the guide shaft 84 and the opening 86 may not be smoothly opened.

For this reason, as shown in FIG. 8, instead of the lid 83, a structure in which the relief pipe 82 is closed by a rupture disk 93 that is ruptured by an increase in pressure in the heating chamber 80 has been used. According to the pressure release device X shown in FIG. 8, the rupture disk 93 can be ruptured by abnormal pressure increase in the heating chamber 80, and the inside of the heating chamber 80 can be communicated with the outside. Thereby, an opening can be opened more smoothly and promptly.
However, in the pressure release device X using the rupture disk, a wide-diameter rupture disk is required to secure an opening area that can quickly release the pressure in the heating chamber 80. Since the rupture disk is intended for bursting, the heat insulating property is low, and if it has a wide diameter, there is a concern about energy loss in the heating chamber 80 or deterioration of temperature distribution, so it must be reduced in diameter. In such a rupture disk with a reduced diameter, even if the opening is smoothly and quickly opened, a sufficient opening area cannot be secured, and as a result, the pressure in the heating chamber 80 may not be released quickly. It was.

  The present invention has been made in view of such circumstances, and provides a heating furnace capable of quickly releasing the abnormally increased pressure even when the pressure in the heating chamber abnormally increases. Objective.

In order to achieve the above object, a heating furnace according to the present invention includes a furnace body having a heating chamber therein, and a furnace port formed on a front side wall of the furnace body for taking in and out an object to be processed. A furnace port door that seals the furnace port so that it can be opened and closed, a lock device that locks the furnace port door with respect to the furnace body when the furnace port is closed by the furnace port door, and a back surface of the furnace body A pressure release port that opens to the side wall on the side and releases the pressure in the heating chamber to the outside of the heating chamber; a pressure release door that has heat insulation that seals the pressure release port so as to be openable; and the pressure release port is sealed Locking means for unlocking the pressure release door when the pressure in the heating chamber rises above a predetermined pressure while locking the pressure release door in a state, and the pressure release door includes the lock Under the pressure release door when unlocking by means The pressure release door is provided on the side wall of the furnace body so as to be rotatable about the central axis located on the part side toward the outside of the heating chamber, and the lock means seals the pressure release port. The pressure release door is a toggle clamp that presses and locks the upper end side toward the side wall, and the pressure release door is viewed from the central axis direction with the pressure release port closed. It is characterized by being provided so that the upper end part of this may be located just above a lower end part .

According to the heating furnace configured as described above, the pressure release door is locked with the pressure release port sealed, and the pressure release door is unlocked when the pressure in the heating chamber rises above a predetermined pressure. Since the lock means is provided, when the pressure in the heating chamber rises abnormally, the lock by the lock means is released by the pressure received by the pressure release door, and the pressure release door can be opened. For this reason, the pressure release port can be quickly opened.
Furthermore, since the pressure release door has a heat insulating property, even if a large opening area of the pressure release port is ensured, the thermal efficiency of the heating chamber and the temperature distribution are not deteriorated.
As described above, according to the heating furnace of the present invention, since the pressure release port can be quickly opened while sufficiently securing the opening area of the pressure release port, even if the pressure in the heating chamber rises abnormally, Pressure can be released quickly and sufficiently.

In the heating furnace, the pressure release port is provided on a side wall of the furnace body, and the pressure release door is positioned on a lower end side of the pressure release door when the lock is released by the lock means. because outwardly of the heating chamber to the central axis is provided on the pivotally said side wall, pressure relief door, provided on the side wall of the furnace body, located at the lower end portion side of the pressure relief door Since it can be rotated around the central axis toward the outside of the heating chamber, when the lock is released due to an increase in pressure in the heating chamber, the pressure release door also has its own weight in addition to the pressure received by the pressure release door. It rotates by acting. As a result, the pressure release door can be rotated more quickly, and the pressure release port can be opened more quickly.
Further, since the locking means is a toggle clamp that locks the pressure release door with the pressure release port sealed against the side wall, the pressure release door is securely closed with the pressure release port sealed. Since the pressure received by the pressure release door can be directly applied to the toggle clamp, the locked state by the toggle clamp can be released according to the pressure in the heating chamber. Further, since the toggle clamp itself is simple and inexpensive, the lock means can be made inexpensive and highly reliable.
Furthermore, a flange portion facing the periphery of the pressure release port in the side wall when the pressure release port is closed may be formed on the entire periphery of the periphery of the pressure release door.

The pressure release door may be formed in a horizontally long rectangular shape.
In this case, the rotation distance of the upper end portion of the pressure release door until the pressure release door is rotated and fully opened can be shortened as compared with the case where the pressure release door is vertically long, so that the pressure release door is fully opened. The time required until is reduced. Thereby, a pressure release port can be opened more rapidly.

  According to the heating furnace of the present invention, even when the pressure in the heating chamber increases abnormally, the abnormally increased pressure can be quickly released.

It is sectional drawing of the heating furnace which concerns on one Embodiment of this invention. It is a side view of a heating furnace. It is sectional drawing of pressure release door vicinity. It is a perspective view of a toggle clamp. It is a perspective view of the toggle clamp which shows the state which canceled the lock | rock of the pressure release door. It is a side view of a toggle clamp. (A) is sectional drawing of the heating furnace which concerns on a prior art example, (b) is sectional drawing of guide shaft vicinity. It is sectional drawing of the heating furnace which concerns on another prior art example.

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a heating furnace according to an embodiment of the present invention.
In FIG. 1, a heating furnace 1 constitutes a so-called hot air circulation type inert gas oven that heats an object to be processed by circulating hot air in an inert gas atmosphere, and a heating chamber that accommodates the object to be processed. 10, a box-shaped furnace body 11, a heater 13 for heating the atmospheric gas in the heating chamber 10, and a stirring fan 15 for circulating the atmospheric gas in the heating chamber 10 are provided.

The furnace body 11 is constituted by an upper wall 11a, a bottom wall 11b, and a side wall 11c, in which a heat insulating material 5 such as glass wool is filled in a box formed of a heat-resistant steel plate or the like. Furthermore, the furnace body 11 has a heating chamber 10 having airtightness formed by being surrounded by a heat-resistant steel plate or the like.
A side wall 11c (left side in FIG. 1) on the front side of the furnace body 11 is formed with a furnace port 12 for taking in and out an object to be processed in the heating chamber 10, and the furnace port 12 can be opened and closed. A furnace door 2 for sealing is provided.
Like the walls 11a to 11c of the furnace body 11, the furnace port door 2 is configured by a box body formed of a heat-resistant steel plate or the like filled with a heat insulating material 5 such as glass wool. The furnace body 11 is rotatably attached.
The furnace port door 2 can be locked to the furnace body 11 by a plurality of locking devices 21 when the furnace port 12 is closed. A packing 22 is attached to the periphery of the furnace port door 2 to seal the space between the periphery of the furnace port 12. The packing 22 is pressed between the peripheral edge of the furnace port door 2 and the peripheral edge of the furnace port 12 when the furnace port door 2 is closed and locked, thereby sealing the heating chamber. 10 is tightly sealed.

  Further, the furnace body 11 is provided with an air supply port (not shown) for supplying atmospheric gas into the heating chamber 10 and an exhaust port (not shown) for exhausting the inside of the heating chamber 10. The atmosphere in the heating chamber 10 can be made an inert gas atmosphere by exhausting the air in the heating chamber 10 and supplying an inert gas such as nitrogen gas or argon gas.

  Further, a pressure release port 14 for releasing the pressure of the heating chamber 10 to the outside (atmosphere) of the heating chamber 10 is formed on the side wall 11c (the right side surface in FIG. 1) on the back side of the furnace body 11, and the pressure is increased. A pressure release door 3 is attached to seal the release port 14 in an openable manner.

FIG. 2 is a side view of the heating furnace 1 for illustrating the mode of the pressure release door, and FIG. 3 is a cross-sectional view of the vicinity of the pressure release door.
Referring to FIGS. 2, 3, and 1, the pressure release port 14 is formed in a horizontally long rectangular shape having a lateral width longer than the longitudinal width, and is open to the side wall 11 c. It communicates with the outside of the furnace.
The pressure release door 3 is constituted by a box formed of a heat-resistant steel plate or the like filled with a heat insulating material 5 such as glass wool, similar to the walls 11 a to 11 c and the furnace door 2, and corresponds to the pressure release port 14. And it is formed in the horizontally long rectangular shape whose horizontal dimension is longer than the vertical dimension. Therefore, the pressure release door 3 has the same heat insulating properties as the walls 11 a to 11 c and the furnace door 2.

Further, a flange portion 3 a is formed on the entire periphery of the peripheral edge portion of the pressure release door 3. The flange portion 3 a has a rectangular shape whose edge is slightly larger than the pressure release port 14, and in the state where the portion of the box body filled with the heat insulating material 5 is inserted into the pressure release port 14, It is formed so as to face the peripheral edge (each edge 141 to 144) of the pressure release port 14.
And the pressure release door 3 closes the said pressure release port 14 by covering the pressure release port 14 in the state which pressed the flange part 3a with respect to each edge 141-144 of the pressure release port 14 up, down, left, and right.

The pressure release door 3 is attached to the side wall 11 c via three hinges 31. One end of each hinge 31 is attached to the lower end portion 33 of the pressure release door 3, and the other end is attached to the lower edge 142 of the pressure release port 14. Therefore, the rotation shaft 311 of each hinge 31 is located on the lower end 33 side of the pressure release door 3.
As described above, the pressure release door 3 can be rotated toward the outside of the heating chamber 10 around the rotation shaft 311 of each hinge 31 located on the lower end 33 side of the pressure release door 3. 3, the pressure release port 14 can be opened by rotating from the state in which the pressure release port 14 is closed by covering the pressure release port 14 toward the outside of the heating chamber 10.

A heat-resistant sealing material 30 having a substantially rectangular cross section interposed between the pressure release door 3 and the furnace body 11 is attached to the flange portion 3a of the pressure release door 3 over the entire circumference. When the pressure release port 14 is closed by the pressure release door 3, the heat-resistant sealing material 30 is sealed in pressure contact with the peripheral edge of the pressure release port 14 on the side wall 11 c side, that is, the upper, lower, left and right edges 141 to 144. Then, the heating chamber 10 is sealed. Further, as shown in FIG. 3, a seal ring 39 is attached to the flange portion 3 a so as to be disposed on the inner side of the heat-resistant sealing material 30 and to be interposed and sealed with the furnace body 11.
The pressure release door 3 is pressed toward the furnace body 11 (each edge 141 to 144 of the pressure release port 14) by a toggle clamp 41, which will be described later. The seal ring 39 and the heat-resistant sealing material 30 are The clamp 41 is pressed against each edge 141 to 144.
The pressure release door 3 can be sealed between the side wall 11c by the seal ring 39 pressed against each edge 141 to 144 and the heat-resistant sealing material 30, and when the pressure release port 14 is closed, The heating chamber 10 can be tightly sealed.

  Lock means 4 is attached to the upper edge 141 of the pressure release port 14 in the side wall 11c. As shown in FIG. 2, the lock means 4 includes three toggle clamps 41 that press the upper end portion 32 of the pressure release door 3 in a state where the pressure release port 14 is closed toward the side wall 11c. Each toggle clamp 41 is arranged at predetermined intervals in the left-right width direction with respect to the upper edge 141 of the pressure release port 14.

4 is a perspective view of the toggle clamp, FIG. 5 is a perspective view of the toggle clamp showing a state in which the lock of the pressure release door is released, and FIG. 6 is a side view of the toggle clamp.
Each toggle clamp 41 includes a base bracket 411, a handle lever 413, a clamp lever 415, and a link 418.

  The base bracket 411 is fixed to the bracket 40 protruding from the upper edge 141 of the pressure release port 14 in the side wall 11c. The handle lever 413 has a base end (right end in FIG. 6) supported by the lower portion of the base bracket 411 via a first pin 412 so as to be rotatable. The clamp lever 415 is supported at the upper part of the base bracket 411 via the second pin 414 so that the base end (upper end in FIG. 6) is rotatable. Further, a bolt 410 extending in a direction orthogonal to the longitudinal direction (left and right direction in FIG. 6) is attached to the tip (lower end in FIG. 6) of the clamp lever 415. The bolt 410 is fastened from both sides by a pair of nuts 419 while penetrating the tip of the clamp lever 415. One end (right end in FIG. 6) of the link 418 is rotatably supported via a third pin 416 near the base end of the clamp lever 415. The other end (left end in FIG. 6) of the link 418 is rotatably supported via a fourth pin 417 at a substantially intermediate position in the axial direction of the handle lever 413.

Here, the locked state and the unlocked state by each toggle clamp 41 will be described.
First, when each toggle clamp 41 is changed from the unlocked state to the locked state, the handle lever 413 is in a substantially horizontal state from the unlocked position (position shown in FIG. 5) in which the handle lever 413 is inclined obliquely upward. It is rotated to the lock position (position shown in FIGS. 4 and 6). Then, the clamp lever 415 rotates downward toward the pressure release door 3 via the link 418, and the flange portion 3a located at the upper end portion 32 of the pressure release door 3 is directed toward the side wall 11c by the head portion 410a of the bolt 410. Press to be locked. At this time, the center position of the third pin 416 on one end side of the link 418 moves upward from the lower side of the line segment m connecting the first pin 412 and the fourth pin 417 of the handle lever 413 to the upper side. To do. As a result, each toggle clamp 41 is secured in a stable locked state.

  On the other hand, when each toggle clamp 41 is changed from the locked state to the unlocked state, the handle lever 413 is rotated from the locked position to the unlocked position. Then, immediately after the rotation of the handle lever 413 to the unlock position, the third pin 416 on one end side of the link 418 moves downward beyond the line segment m with a slight delay, and can be unlocked. It becomes unstable. From this state, as the handle lever 413 is rotated to the unlocked position, the clamp lever 415 is rotated to a substantially horizontal position via the link 418, and the head 410 a of the bolt 410 is moved to the flange of the pressure release door 3. Separated from the part 3a. Thereby, the press by the head 410a of the volt | bolt 410 is cancelled | released, and the pressure release door 3 will be in a lock release state.

Moreover, the release of the locked state by each toggle clamp 41 is performed even when the pressure of the heating chamber 10 abnormally increases.
That is, when the gas containing the volatile component generated from the object to be heat-treated is ignited and explodes, it rapidly expands, and when the pressure in the heating chamber 10 rises to near the limit pressure, the heating furnace 1 main body is damaged. Is concerned. For this reason, even when the pressure in the heating chamber 10 rises to the vicinity of the limit pressure that may damage the main body of the heating furnace 1, it is necessary to release the locked state by the toggle clamps 41.

In short, in this embodiment, the pressure in the heating chamber 10 (relative pressure with respect to atmospheric pressure) is used at, for example, 1 kPa or less, but the pressure in the heating chamber 10 is generated by generating gas from the object to be processed as described above. When the abnormal rise occurs, the walls 11a to 11c, the furnace door 2, and the pressure release door 3 receive the pressure.
Among these, the pressure release door 3 tries to rotate toward the outside of the heating chamber 10 by the received pressure, and the pressure release door 3 presses the bolt 410 of the toggle clamp 41 toward the outside of the heating chamber 10. .
Here, when the pressure in the heating chamber 10 rises to near the limit pressure (for example, 50 kPa), the pressing force against the toggle clamp 41 by the pressure release door 3 becomes higher than the pressing force due to the locked state of the toggle clamp 41, and the pressure The release door 3 rotates the clamp lever 415. As a result, the third pin 416 of the link 418 is displaced to the lower side of the line segment m, and the toggle clamp 41 is brought into an unstable state that can be unlocked.
In this state, when the head portion 410a of the bolt 410 of each toggle clamp 41 is further pushed back by the flange portion 3a of the pressure release door 3, the clamp lever 415 becomes the main body, and the handle lever 413 is locked via the link 418. Rotates to the release position. As a result, the pressure release door 3 rotates to open the pressure release port 14.

  And as the three toggle clamps 41 applied in this embodiment, each toggle pressure by the pressure release door 3 when the pressing force as the lock means 4 in the locked state is increased to the limit pressure in the heating chamber 10. A pressure smaller than the pressing force against the clamp 41 (locking means 4) is selected. Specifically, B-II downward pressing type toggle clamp (product number: 40A) manufactured by Kakuda Kogyo Co., Ltd. is selected.

In such a heating furnace 1, the pressure release door 3 is locked in a state where the pressure release port 14 is sealed, while the pressure release door 3 is locked when the pressure in the heating chamber 10 rises above a limit pressure as a predetermined pressure. Is provided, and when the pressure in the heating chamber 10 rises abnormally, the lock by the lock means 4 is released by the pressure received by the pressure release door 3 and the pressure release door 3 is opened. The pressure release port 14 can be quickly opened.
Furthermore, since the pressure release door 3 has heat insulation properties, even if the opening area of the pressure release port 14 is ensured to be large, the thermal efficiency and temperature distribution of the heating chamber 10 are not deteriorated.
As described above, according to the heating furnace 1 of the present embodiment, the pressure release port 14 can be quickly opened while sufficiently securing the opening area of the pressure release port 14, so that the pressure in the heating chamber 10 is abnormally high. Even if it rises, the pressure can be released quickly and sufficiently.
As a result, even if an abnormal increase in pressure in the heating chamber 10 occurs, damage to the main body of the heating furnace 1 can be avoided.

  In the present embodiment, the predetermined pressure, which is the pressure in the heating chamber 10 at which the locking means 4 unlocks the pressure release door 3, is set as the above limit pressure. Thus, the pressure can be set lower than the above limit pressure.

  In the present embodiment, the pressure release door 3 is provided on the side wall 11 c of the furnace body 11, and rotates toward the outside of the heating chamber 10 around the central axis located on the lower end 33 side of the pressure release door 3. Therefore, when the lock is released due to an increase in pressure in the heating chamber 10, the pressure release door 3 rotates by its own weight acting in addition to the pressure received by the pressure release door 3. As a result, the pressure release door 3 can be rotated more quickly, and the pressure release port 14 can be opened more quickly.

  Moreover, since the pressure release door 3 of the present embodiment is formed in a horizontally long rectangular shape, the rotation distance of the upper end portion 32 of the pressure release door 3 until the pressure release door 3 is rotated and fully opened is set. , It can be shortened compared to the case of being vertically long. As a result, the time required for the pressure release door 3 to be fully opened is shortened, and the pressure release port 14 can be opened more quickly.

  In the heating furnace 10, the locking means 4 is a toggle clamp 41 that locks the pressure release door 3 with the pressure release port 14 sealed against the side wall 11c, so that the pressure release port 14 is sealed. Thus, the pressure release door 3 can be securely locked. Furthermore, since the pressure received by the pressure release door 3 can be directly applied to the toggle clamp as a pressing force, the locked state by the toggle clamp 41 can be released according to the pressure in the heating chamber 10. . In addition, since the toggle clamp 41 has a simple configuration and is inexpensive, the locking means 4 can be made inexpensive and highly reliable.

  In addition, this invention is not limited to the said embodiment, The other various modifications are included. For example, although the case where the heating furnace 1 is configured as a hot air circulation type inert gas oven has been described in the above embodiment, the present invention is not limited thereto. For example, the present invention can be applied to a hot air circulation oven in which a wet gas containing water vapor or an atmospheric gas containing other chemical components is circulated to heat-treat the workpiece.

  Moreover, in the said embodiment, although the toggle clamp 41 was used as the locking means 4, it is not limited to this. For example, a replaceable part such as a support pin is broken by a turning force toward the outside of the heating chamber 10 generated in the pressure release door 3 when the pressure in the heating chamber 10 exceeds a limit pressure receiving value, thereby Locking means for releasing the locked state may be used.

  Moreover, in the said embodiment, although the limit pressure in the heating chamber 10 was 50 kPa, this limit pressure is set according to the rigidity of the furnace body 11. For this reason, when the limit pressure is set to be low because the rigidity of the furnace body 11 is low, a lock unit that reliably releases the lock state of the pressure release door is selected according to the pressure.

  Moreover, in the said embodiment, although the locking means 4 which consists of the toggle clamp 41 was attached to the upper end part 32 side of the pressure release door 3, and the hinge 31 was attached to the lower end part 33 side, it replaces with a hinge and the lower end of the pressure release door 3 You may attach a locking means to the part 33, or you may attach a locking means to the circumference | surroundings of the pressure release door 3. In this case, when the lock by the locking means is released, the pressure release door can be quickly opened by dropping and opening the pressure release door.

  Furthermore, in the above embodiment, the horizontally long rectangular pressure release door 3 is used. However, the horizontally long oval pressure release door or the trapezoid whose length in the height direction is shorter than the length of the upper side and the lower side. It may be a pressure release door having a shape or a parallelogram shape.

DESCRIPTION OF SYMBOLS 1 Heating furnace 10 Heating chamber 11 Furnace body 11c Side wall 14 Pressure release port 3 Pressure release door 4 Locking means 41 Toggle clamp

Claims (2)

A furnace body having a heating chamber therein;
Formed on the front side wall of the furnace body, and a furnace port for taking in and out the workpiece into the heating chamber;
A furnace port door that seals the furnace port so that it can be opened and closed;
A locking device for locking the furnace port door to the furnace body when the furnace port is closed by the furnace port door;
A pressure release port that opens to the side wall on the back side of the furnace body and releases the pressure in the heating chamber to the outside of the heating chamber;
A pressure release door having heat insulation, which seals the pressure release port so as to be openable;
Lock means for unlocking the pressure release door when the pressure in the heating chamber rises above a predetermined pressure while locking the pressure release door in a state where the pressure release port is sealed;
Equipped with a,
The pressure release door is provided on the side wall of the furnace body so as to be rotatable around the central axis located on the lower end side of the pressure release door toward the outside of the heating chamber when the lock is released by the locking means. And
The locking means is a toggle clamp that presses and locks the upper end side of the pressure release door in a state of sealing the pressure release port toward the side wall,
Further, the pressure release door is provided such that the upper end of the pressure release door is located immediately above the lower end when viewed from the central axis direction with the pressure release port closed. <Br / > Heating furnace.   The flange part facing the peripheral edge of the pressure release port in the side wall when the pressure release port is closed is formed on the peripheral part of the pressure release door over the entire circumference. Heating furnace.

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