JP3526779B2 - Method for preventing deformation of muffle for continuous sintering furnace - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing deformation of a muffle used in a continuous sintering furnace for sintering powder metallurgy products and the like. The muffle referred to in this specification is
It refers to an overall cylindrical heat-resistant metal object that separates the atmosphere around the sintered body from the heat insulating material (such as a refractory lining) and the heater of the furnace. 2. Description of the Related Art In a continuous powder metallurgy sintering furnace, hydrogen, nitrogen or a modified gas derived from a hydrocarbon-based gas is used as an atmosphere in the furnace, and the furnace is usually operated at a high temperature of 900 ° C. or higher. I do. In the sintering furnace, heat-resistant cast steel or heat-resistant steel plate welding is used to keep the atmosphere clean by avoiding the reaction between the atmosphere gas and the components in the refractory lining material, or to save energy in the equipment. Structured muffles are widely used. FIG. 2 is a diagram showing a sectional configuration of a continuous powder metallurgy sintering furnace. The sintering furnace 60 includes a dewaxing unit 61 which is an RBO (Rapid burn Off) device for performing preheating and dewaxing from an upstream side to a downstream side in a sintering body feeding direction (arrow in the figure). The sintering section 63 and the cooling section 65 are provided continuously. The compact is placed on the mesh belt 67, inserted into the dewaxing unit 61 from the insertion opening, conveyed through the sintering unit 63 and the cooling unit 65, and carried out of the furnace from the end of the cooling unit. The muffle 71 is the sintered part 6
3 is incorporated in the main sintering furnace 62. FIG. 3 is a sectional view showing an example of a heat-resistant cast steel muffle. The following values are for the mesh belt width 6
This is an example of a 10 mm furnace. The muffle 71 is made of cast steel using a Ni-based alloy and has a thickness of about 13 mm. The cross section of the muffle is semicircular, the height at the center is about 350 mm, and the width at the bottom is about 700 mm. On the outer surface except the bottom of the muffle 71, a corrugated projection 73 extending in the circumferential direction is provided. The corrugated projections 73 are provided for the purpose of reducing the deformation of the muffle at a high temperature during operation of the sintering furnace. A mesh belt 67 is laid on the bottom surface 77 of the muffle 71 so as to move endlessly in the longitudinal direction. The mesh belt 67 is made of stainless steel wire or heat-resistant alloy steel wire and has a width of 6 mm.
It is 10 mm and the thickness is about 15 mm. A corrugated projection 75 having a height of about 40 mm is also formed on the outer surface of the bottom portion 77, and this corrugated projection 75 is also intended to increase the high-temperature durability of the muffle. Below the muffle 71, a hearth plate 79 made of SiC is laid on one side, and further below that there is a hearth 62a (refractory, shown in FIG. 2). FIG. 4 is a cross-sectional view showing an example of a plate welding structure muffle. The muffle 71 'is made by welding a Ni alloy steel plate. Ribs 73 and 75 are usually welded to the outer surface of the muffle for the same effect as the corrugated projection of the heat-resistant cast steel muffle. The atmosphere gas is supplied into the muffle 71 from a gas inlet 81 on the downstream side of the furnace 62 of the high-temperature sintering section 63. The running surface of the mesh belt 67 is accurately leveled along the entire length of the equipment so that the supplied atmospheric gas flows at an appropriate ratio to both the inlet at the upstream end 71a and the outlet at the downstream end 71b of the muffle 71. Must be kept. The muffle 71 is connected to a casing 87 of the cooling unit 65 by a flange 85 on the downstream side (unloading side). The casing 87 of the cooling unit 65 is fixed to a gantry 89. On the upstream side (insertion side), the muffle 71 is connected to the dewaxing furnace 69 by a flange 83. When the temperature of the sintering section 63 is increased, the muffle 71
Expands in the longitudinal direction. Since the downstream end 71b of the muffle 71 is fixed, the upstream end 71a extends in the upstream direction. In order to absorb the extension of the muffle 71, the dewaxing furnace 69 is movable in the longitudinal direction. That is, a rotatable wheel 91 is provided on the bottom surface of the dewaxing furnace 69, and is mounted on a rail 96 provided horizontally on a gantry 93. Therefore, the dewaxing furnace 69 moves in the longitudinal direction on the rail 96 in accordance with the extension of the muffle 71, and absorbs the extension of the muffle 71. FIG. 5 shows the deformation of the muffle which appears in a fixed position substantially at the entrance of the sintering furnace 62 after a long use time (for example, 3 to 4 years). FIG. 3 is a cross-sectional view schematically showing Floor 7 of muffle 71 as shown
The part 2 is deformed as if it were lifted up, and the width dimension is narrowed accordingly. In such a case, the running of the mesh belt is hindered, so conventionally, the muffle was replaced every three or four years. The present inventors have considered the cause of the deformation of the muffle as follows. In the sintering furnace described above,
The elongation of the muffle in the longitudinal direction is absorbed. However, the dewaxing furnace 6 structurally mounted on the gantry 93
9 does not change from the level at the time of installation even during operation. On the other hand, the insulating material of the main sintering furnace 62 and the portion of the corrugated protrusion 75 on the bottom of the muffle 71 expand upward and become slightly higher than the level adjusted at the time of installation, so that the bottom of the dewaxing furnace 69 and the muffle 71 Height shift occurs on the bottom. The present inventors have thought that this displacement may cause the bottom surface of the muffle 71 to be raised and narrowed in the width direction. In other words, it has been considered that a bending force acts in a direction in which the bottom surface of the muffle 71 is on the compression side to cause bending deformation. An analysis of the cause of the bending force and the magnitude of the force is as follows. The height of the corrugated protrusion 75 provided for the purpose of increasing the hot strength of the floor portion of the muffle 71 is 4
Although it is about 0 mm, attention was paid to how much the height of this floor changes due to thermal expansion at the operating temperature. The muffle material has an average coefficient of thermal expansion ≒ 1.8 × 10 ^-5 . The amount of thermal expansion of the corrugated protrusion is 40 mm in height, the average thermal expansion coefficient and the difference between the operating temperature and the room temperature = (1150-20) ° C.
Is 0.81 mm. The thermal expansion of the refractory from the bottom of the furnace shell to the bottom of the muffle is actually 1.
When the two are added, the bottom surface of the muffle (the running surface of the mesh belt) becomes 2 mm or more higher than the time of assembly at the operating temperature. On the other hand, since the dewaxing furnace 69 is installed on the gantry 93, its level does not change from the assembled state even under high-temperature operation. Therefore, when the furnace temperature reaches the operating temperature, the downstream end of the flange-connected dewaxing furnace 69 is raised by about 2 mm due to the thermal expansion of the muffle 71 and the refractory, and the dewaxing furnace 69 moves in the traveling direction. A slightly uphill condition is formed. If the strength of the muffle is infinite, raise the entire dewaxing furnace to 2 mm from the gantry.
Should be levitated. However, the muffle strength is a finite value and this does not occur. When the state is actually observed during operation, the downstream side (muffle 71 side) wheel 91a of the two pairs of wheels 91 is lifted and floats from the furnace gantry. Therefore, the present inventor decided to solve this problem structurally mechanically. FIG. 6 is a diagram schematically showing a load acting on the muffle in order to analyze the bottom elevation of the muffle. As shown in FIG. 5, the muffle can be regarded as a beam in which the dewaxing furnace is deposited at the tip of the overhang with the point where the bottom surface bulge occurs as a fulcrum. The secondary moment of area and the section modulus at the fulcrum position (A) are roughly as follows. Moment of inertia ^{of: I = 1.27 × 10 9 mm} 4 section modulus: 0.2% proof stress of Z = 2.66 × 10 ⁶ mm ³ The muffle material under operating temperature ≒
Since it is 4 kg / mm ² , Young's modulus E ≒ 2000 kg / mm ²
Can be considered Front wheel position of dewaxing furnace (C)
Is 2 mm, the bending amount (= δ mm) of the load application point (B), which is the center of gravity of the dewaxing furnace, is calculated in a simple proportion as follows: δ = 2 × 1600/2100 ≒ 1.5 mm. At the load application point (B), the load (= W kg) that causes this amount of deflection is W = 6 · E · I · δ / l ₁ · EXP3 (2 + 3l ₂ / l ₁ ) [l ₁ = 1600mm, l ₂ = 2800 mm] = 6x2000x1.27x10 ⁹ x1.5 / 1600 ³ x (2 + 3x2800 / 1600) = 770 kg. By the way, the total weight of the dewaxing furnace is about 1800
Since the weight is kg, the dewaxing furnace 69 acts as a load on the muffle 71, and it is considered that a bending stress always acts as shown in FIG. This is proved by the fact that the wheel 91a on the downstream side of the dewaxing furnace floats on the gantry. Therefore, the bending moment (= M kg-mm) acting on the fulcrum (A), which is the muffle ridge, is M = W · L ₁ = 770 × 1600 ≒ 1.23 × 10 ⁶ kg-mm. Therefore, the maximum bending stress: σ kg / mm ² becomes σ = M / Z = 1.23 × 10 ⁶ /2.66×10 ⁶ = 0.46 kg / mm ² . Here, the 100,000-hour fatigue rupture strength, which is used as a measure of allowable stress in the structural design published by the muffle maker, is 0.11 kg / mm ^2. Is far beyond. Since the operating temperature of the sintering furnace is at a temperature level higher than or equal to the annealing temperature for the muffle material, the muffle is annealed with a small amount of bending to minimize the internal stress. That is, the deformation in the bent state is fixed by annealing. In this way, it is estimated that the deformation is repeatedly accumulated every time the temperature rises, and that the amount of deformation increases with the elapse of time, causing the bottom to be raised and the width to be narrowed. In addition, because the processed product is in the process of raising its temperature to the sintering temperature, deformation occurs in a fixed position, and the temperature often fluctuates up and down with the fluctuation of the processing amount (heat load) even during operation. Therefore, it is presumed that the generation of bending stress and the annealing are repeated in a short time cycle even during the operation operation, not limited to merely raising the temperature for operation preparation. Compared with the heat insulating material, the thermal expansion coefficient of the heat-resistant metal is about 5 times larger, so that the higher the wavy projection on the bottom surface of the muffle intended to increase the hot strength, the more ironically the wear due to the deformation of the muffle is increased. The result is to promote. The present invention has been made in view of such problems, and has as its object to provide a method for preventing bending of a muffle in a continuous sintering furnace for sintering powder metallurgy products and the like. I do. Means for Solving the Problems and Embodiments of the Invention In order to solve the above-mentioned problems, a method for preventing muffle deformation for a continuous sintering furnace according to the present invention comprises the steps of: A method for preventing deformation of a muffle mounted on a furnace, wherein the muffle is placed on a heat insulating material of the main sintering furnace, and a dewaxing furnace or a cooling device is provided at an end in a longitudinal direction (a feeding direction of a sintered body). Connected to the dewaxing furnace or cooling device,
A structure (floating structure) that can move in the same direction in accordance with the thermal expansion in the longitudinal direction of the muffle, and further, the muffle connection part of the dewaxing furnace or the cooling device is placed on the muffle in accordance with the movement in the longitudinal direction. by vertically by a dimension corresponding to the vertical direction thermal expansion of the heat insulating material and muffle the sintering furnace for, by the high temperature during operation of the sintering furnace
Even when the muffle is thermally expanded, the dewax
The height of the bottom of the cooling furnace or cooling device is the bottom of the above muffle.
It is characterized by being made equal to. [0020] Dewaxing furnace connected to muffle or cold
By moving the cooling device in the vertical direction by a height corresponding to the vertical thermal expansion of the muffle and the heat insulating material supporting the muffle, the height of the bottom surface of the dewaxing furnace or the cooling device becomes heat.
It was made equal to the bottom surface of the muffle after expansion . Thus, the vertical thermal expansion of the furnace body caused by the temperature rise is absorbed by the rise of the dewaxing furnace or the cooling device corresponding to the elongation of the muffle generated in the transport axis direction. As a result, the bending of the muffle can be eliminated and the durability can be improved, which is economically advantageous. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view schematically showing a muffle type continuous sintering furnace according to an embodiment of the present invention. FIG. 1 (A) is a view showing the entire configuration, and FIG. 1 (B) is a gradient for adjusting the level of the dewaxing furnace in accordance with the amount of thermal expansion in the height direction of the sintering furnace refractory and the muffle. It is a figure which expands and shows the rail attached with. The muffle type continuous sintering furnace 10 is provided with a dewaxing section 11, a sintering section 13, and a cooling section 15 in this order from the upstream. Each part is hollow, and a mesh belt 17 is laid at the bottom. The formed body is placed on the mesh belt 17 and inserted from the upstream, conveyed in each part, and carried out from the end of the cooling unit. The muffle 21 is the sintered part 13
Is built in. The rail 46 is provided with a gradient for adjusting the level of the dewaxing furnace in accordance with the sum of the thermal expansion amount of the refractory of the present sintering furnace and the muffle 21 in the height direction. The dewaxing unit 11 is provided with an RBO (Rapid burn).
Off) Also called a device. Here, the inserted molded body is preheated, and the wax contained in the molded body is removed. On the bottom surface of the dewaxing furnace 19, wheels 41 are provided at two places in the longitudinal direction. The wheel 41 is rotatably mounted on a rail 46 laid on the gantry 43 so as to extend in parallel with the longitudinal direction, and freely moves bidirectionally along the longitudinal direction. The gantry 43 is provided with an air cylinder 47 connected to the dewaxing furnace 19, and pulls the dewaxing furnace 19 upstream. The rail 46 is inclined so as to become higher toward the upstream by 2 mm when the muffle 71 is maximally extended (95 mm in length). As described above, when the muffle 21 expands due to high temperature, the dewaxing furnace 19
Moves upstream along the slope by the amount of thermal expansion of the muffle 21 and further rises by the amount of thermal expansion at the bottom of the muffle. A detailed demonstration operation example will be described later. The high-temperature sintering section 13 is mainly composed of a main sintering furnace 12 formed of a heat insulating material such as a brick, and is located downstream of the dewaxing section 11 and fixed on a gantry 45. . A muffle 21 is incorporated in the furnace 12. The upstream end 21a of the muffle 21 is connected to the downstream end of the dewaxing furnace 19 by a flange 33. At the bottom of the furnace 12 of the high-temperature sintering section 13, spaces 49 are provided at intervals. In this space 49, a heater 51 is arranged. The heater 51 is further arranged in a space above the muffle 21 in the furnace 12. Further, a hearth plate made of SiC for receiving the bottom surface of the muffle 21 (see FIGS. 3 and 4) is laid over the entire length in the sintering furnace. A muffle 21 is provided downstream of the sintering furnace 12.
Is provided. From the gas inlet 31, a modified gas or the like usually made of hydrogen, nitrogen, or a hydrocarbon-based gas is introduced into the muffle 21. In this high-temperature gas atmosphere, the compact conveyed into the muffle 21 is sintered by the heater 51 described above. The cooling section 15 is located downstream of the sintering section 13 and is composed of a water jacket 37 placed on a pedestal 39. The water jacket 37 is divided and manufactured in the longitudinal direction, and each part is fixed by a flange. The sintered compact is cooled here. The upstream end of the water jacket 37 is the downstream end 21 of the muffle 21.
b is connected by a flange 35. The mesh belt 17 is connected to the dewaxing unit 1.
Insertion table 55 installed on the upstream side of
5 is laid so as to rotate endlessly along the bottom surfaces inside the dewaxing unit 11, the sintering unit 13, and the cooling unit 15 between the take-out tables 57 installed downstream of the unit 5.
The mesh belt 17 is driven by a drive roll 59 and driven at a speed of about 120 mm / min. Next, the operation of each part when the muffle 21 expands due to the high temperature during operation of the sintering furnace will be described.
As described above, when the sintered part is kept at a high temperature, the muffle 2
1 expands in the transport axis direction. At this time, since the downstream end 21b of the muffle 21 is connected and fixed to the water jacket 37, the upstream end 21a extends in the upstream direction along the longitudinal direction. Since a rotatable wheel 41 is provided on the bottom surface of the dewaxing furnace 19, the rail 4
6 on the upstream side by the amount of expansion of the muffle. The heat insulating material of the muffle 21 and the main sintering furnace 12 which supports the muffle 21 expands upward, but the dewaxing furnace 1
9 is mounted on the gantry 43 which is not affected by heat, so that the level does not change even during operation. For this reason, a height difference occurs between the level of the dewaxing furnace 19 and the level of the main sintering furnace. However, as the bottom level of the muffle rises due to this thermal expansion, the muffle 21
The dewaxing furnace 19 connected to the ascending rail moves upward on the inclined rail 46 having a slightly upward slope in the traveling direction. As described above, by moving the dewaxing furnace 19 upward by a height corresponding to the vertical thermal expansion amount of the muffle 21 and the heat insulating material supporting the muffle 21,
The level gap between the muffle 21 and the dewaxing furnace 19 has been eliminated. As a result, the vertical thermal expansion of the furnace body caused by the high temperature is absorbed by the rise of the dewaxing furnace corresponding to the elongation of the muffle generated in the longitudinal direction. Therefore, the bottom surface of the muffle from the insertion port to the carry-out port is kept horizontal, and generation of bending stress on the muffle is avoided. The results of a demonstration operation using a continuous muffle type sintering furnace having a dewaxing furnace having a length of 2100 mm and a sintering section having a length of about 3700 mm are shown. Dewaxing furnace is 500 ~
The temperature of the sintering section is controlled at 1150 ° C. at 900 ° C.
In this sintering furnace, the change in height of the bottom of the muffle during high-temperature operation is 2.2 to 2.5 mm. The rails on which the wheels of the dewaxing furnace were mounted were placed on the furnace gantry in such a manner that the rails were inclined in the upstream direction so that the height was increased by 2 mm when the muffle was fully extended, as shown in the above example. Using the above-mentioned sintering furnace, the temperature was suspended once a week and the temperature was raised repeatedly, and the system was operated for 3.5 years. As a result, it was found that the bending of the muffle could be suppressed to a much smaller extent than before this measure. confirmed. As is apparent from the above description, according to the present invention, the muffle of the muffle type continuous sintering furnace can be prevented from being deformed, and the maintenance cost of the furnace can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view schematically showing a muffle type continuous sintering furnace according to an embodiment of the present invention. FIG. 1A is a diagram showing the entire configuration, and FIG. 1B is an enlarged diagram showing rails of a dewaxing furnace. FIG. 2 is a diagram showing a cross-sectional configuration of a continuous powder metallurgy sintering furnace. FIG. 3 is a sectional view showing an example of a heat-resistant cast steel muffle. FIG. 4 is a sectional view showing an example of a heat-resistant steel plate welded structure muffle. FIG. 5 is a cross-sectional view schematically illustrating deformation of a muffle used for a long period (for example, 3 to 4 years). FIG. 6 is a view schematically showing a load acting on the muffle in order to analyze a bottom elevation of the muffle. [Description of Signs] 10 Muffle type continuous sintering furnace 11 Dewaxing part (preheating part) 12 Main sintering furnace 13 High temperature sintering part 15 Cooling part 17 Mesh belt 19 Dewaxing furnace 21 Muffle 31 Gas inlet 33, 35
Flange 37 Water jacket 39, 43,
45 Mount 41 Wheel 46 Rail 47 Air cylinder 49 Space 51 Heater 55 Insertion table 57 Removal table 59 Drive roll 71 Muffle 72 Floors 73 and 75 Corrugated projections and ribs 77 Bottom part 79 Hearth plate

Claims (1)

(57) [Claims 1] A method for preventing deformation of a muffle provided in a main sintering furnace of a continuous sintering furnace; placing the muffle on a heat insulating material of the main sintering furnace. It is mounted and connected to a dewaxing furnace or a cooling device at an end in the longitudinal direction (sending direction of the sintered body). In accordance with the movement in the longitudinal direction, the muffle connection part of the dewaxing furnace or the cooling device is connected to the heat insulating material of the main sintering furnace on which the muffle is placed and the vertical thermal expansion of the muffle. Operation of the sintering furnace by raising and lowering by the dimension corresponding to
When the above muffle is thermally expanded due to high temperature,
Even if the height of the bottom of the dewaxing furnace or cooling device is above
A method for preventing deformation of a muffle for a continuous sintering furnace, wherein the muffle is made equal to a bottom surface of the muffle.