JPH08278001A - Radiant tube mounting structure - Google Patents

Abstract

(57) [Summary] [Purpose] The radiant tube used in the heating furnace is free from thermal expansion in the axial and height directions, and has excellent stability.
Provide a mounting structure that can extend the service life. [Structure] The exhaust gas side of a W-type or U-type radiant tube is fixed to a bank 14, and the lower portion of the burner side straight pipe 3 of this radiant tube is supported by a pedestal 35 via a torsion bar 36 attached to the bank,
The burner-side end portion is a radiant tube mounting structure in which a bellows 32 for allowing inflatable in-furnace gas sealing is mounted between the bank and the burner-side end portion while penetrating outside the furnace with a gap from the bank 14. [Effect] It is possible to prevent damage to the tube attachment part, achieve stable support and a long service life, and achieve stable operation and reduction in maintenance costs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a W-type or U-type radiant tube mounting structure used in a heating furnace such as a continuous annealing furnace or a continuous galvanizing furnace.

[0002]

2. Description of the Related Art The structure of a typical conventional W type radiant tube is shown in FIG. In order to prevent oxygen from entering the furnace, the radiant tube 1 is welded to the bank 14 at the end 2 on the burner 17 side and the end 10 on the recuperator 18 side, and the bank 14 is further connected to the furnace wall 15
Welded to and fixed to each.

In the furnace, the support receiving portion 13 at the tip of the third bend 8 is supported by a supporting jig 16 from the furnace wall on the side opposite to the burner, and the first bend 4 or the second bend 4 is used. A saddle 11 is provided between a lower portion of the straight pipe 5 and an upper portion of the third bend 8 or the third straight pipe 7, and a saddle 1 is provided between the second bend 6 or the third straight pipe 7 and the fourth straight pipe 9.
2 are provided.

By the way, the radiant tube is heated by high temperature and is restrained by the above-mentioned supporting and mounting structure against thermal expansion, and thermal stress and deformation occur. As a result, the strength of the tube material deteriorates due to long-term use, and the radiant tube cracks. It becomes unusable due to deformation such that it touches the board or plate, so it must be replaced each time.

Regarding this thermal stress and deformation, FIG. 9 and FIG.
Will be described in more detail. There are two conditions of heat load on the radiant tube, namely, when the furnace is heated and when it is in normal operation.

FIG. 9 shows a state in which the furnace is heated from room temperature to a normal operating state. Due to the combustion of the burner 17, the temperature of the first straight pipe 3 rapidly rises, and the temperature difference between the portion after the first bend 4 and the portion thereof greatly opens. This temperature difference is due to the difference between the first straight pipe 3 and the fourth straight pipe.
The straight pipe 9 may reach several hundreds of degrees Celsius in an instant.

In this case, the first straight pipe 3 suddenly moves in the axial direction 19
Begins thermal expansion. For example, the first of the radiant tubes
The typical temperature of each straight pipe from the straight pipe to the fourth straight pipe is 600 ° C,
400 ℃, 300 ℃, 200 ℃, length 2000mm,
Assuming that the linear expansion coefficient of the tube is 17 × 10 ⁻⁶ and the linear expansion coefficient of the tube is 17 × 10 ⁻⁶ mm, the burner side end portion 2 when the recuperator side end portion 10 is fixed tends to move to the outside of the furnace by about 11 mm. .

With respect to this thermal expansion, when the burner side end 2 is fixed to the bank 14, thermal expansion is restricted between the bank and the first bend 4 and thereafter, so that the first straight pipe 3
A large compressive force 21 is generated at, and a bending moment 22 is generated at the bend portion. As a result, a large stress is generated in the first straight pipe.

A large bending moment 23 is generated in the first bend 4 due to the deformation restraint of the saddle 11.
As a result, stress concentration occurs on the side surface of the bend portion, and the upper portion of the saddle receives a large force.

Normally, the temperature of the furnace is raised and lowered repeatedly for repairing the furnace. However, the above-mentioned large stress is caused by the deterioration of the material due to aging, the thinning of oxidation, the accumulation of thermal fatigue, and the temperature deviation due to the generation of scale. At the time of occurrence, cracks 24 on the first straight pipe burner side
Or a crack 25 occurs on the side surface of the first bend.

FIG. 10 shows a state during normal operation. The temperature in the furnace reaches around 900 ° C., and the temperature of the radiant tube 1 becomes several tens of degrees higher than that. At this time, the temperature of the bank 14 is usually 100 ° C. to 200 ° C., whereas the radiant tube 1 in the furnace is a high temperature exceeding 950 ° C., and therefore the jig 16 for supporting the furnace wall at the tip of the third bend 8 is used. As a starting point, thermal expansion in the height direction 20 reaching the third bend 8, the saddle 11, and the first bend 4 causes the first straight pipe 3
The tip of the is forced to deform upwards considerably.

For example, in the case of a radiant tube in which the axial distance between the first straight pipe and the fourth straight pipe is 900 mm, the bank temperature is 150 ° C. and the radiant tube temperature in the furnace is 95.
0 ° C., assuming a thermal expansion coefficient of the radiant tube and 17 × 10 ^-6, the vertical extension of the bank portions about 2.3m
m, the vertical extension of the tip is about 14.5 mm,
There is a difference of 10 mm or more.

Due to the above results and the restraint of deformation by the saddle 11, an extremely large bending moment 26 is applied to the first straight pipe.
And a large bending moment 27 is also generated in the first bend 3. As a result, stress concentration occurs on the side surface of the bend portion, and the upper portion of the saddle receives a large force.

At this time, the difference in thermal expansion between the straight pipes in the axial direction 19 is small and does not pose a problem as much as when the temperature is raised. The radiant tube is exposed to high temperatures for a long time, undergoes creep deformation due to the above-mentioned stress and the effect of its own weight, and is subject to temperature deviation due to aging deterioration of the material, oxidative thinning, and generation of scale. 1st straight pipe crack 2 similar to 24 of 10
8, or the buckling 29 under the first bend and the extreme decrease in the sectional rigidity of the tube due to the buckling 29 lead to the buckling 30 of the second straight pipe, and the end of the service life of the radiant tube is reached.

As described above, the radiant tube, particularly the first straight tube and the first bend, is restrained by the supporting portion from the furnace wall, the saddle between the tubes, and the rigidity of the tube itself, and when the temperature rises, the axial force and bending It is greatly affected by the moment and bending moment during normal operation. Therefore, relaxing the binding force extends the life of the radiant tube.

As a means for relaxing this constraint, a structure in which the burner side end is slidably attached to the furnace wall through a bellows is disclosed in Japanese Patent Laid-Open No. 05-272708 and Japanese Utility Model Laid-Open No. 01-38415. ing.

Japanese Patent Laying-Open No. 05-272708 shows a structure in which a bellows for absorbing the axial extension of the burner side straight pipe is attached to the end portion on the burner side. See also Kaihei 0
In Japanese Patent Publication No. 1-38415, one end of a tube is not fixed to a bank, a gap is provided so that thermal expansion in the axial direction and height direction of the tube is free, and oxygen is prevented from entering the furnace. , A bellows is provided between the tube and the bank to seal the inside of the furnace, and a part of the burner and the tube weight is supported by a spring attached to the bellows installed between the burner and the recuperator.

[0018]

[Patent Document 1] Japanese Unexamined Patent Publication No.
The structure of Japanese Patent No. 5-272708 cannot absorb the elongation in the vertical direction that occurs in the tube. In the structure of Japanese Utility Model Laid-Open No. 01-38415, the tube is basically only supported by the supporting device between the recuperator side end, the third bend tip and the furnace wall, and the first via the spring and the burner. Straight tube support is unstable.

Therefore, the bellows is largely displaced due to the tilting of the tube, and the upward displacement of the tube causes the first bend to be loaded with the weight of the burner and the first straight pipe, and creep deformation progresses.

The present invention has been proposed in order to solve the above-mentioned problems, and frees the thermal expansion in the axial direction and the height direction of the tube to reduce cracks and deformation generated in the tube, and This structure provides a radiant tube mounting structure that has excellent stability and long life due to the structure that receives the weight of the burner and the tube itself.

[0021]

According to the present invention, the exhaust gas side of a W-type or U-type radiant tube is fixed to a bank, and the lower portion of the burner side straight pipe of the radiant tube is inserted into a bank via a torsion bar. It is supported by a pedestal, and the burner side end is penetrated outside the furnace with a gap from the bank, and an expandable bellows for in-furnace gas sealing is attached between the bank and the burner side end. It is a radiant tube mounting structure.

[0022]

The operation of the present invention will be described below.

FIG. 1 is a drawing showing a structural example of the present invention.
Recuperator 1 of radiant tube 1 as shown
8 side end 10 is welded to bank 14 while burner 1
The end on the 7th side is penetrated to the outside of the furnace by leaving a gap 31 from the bank 14, and a bellows 32 for the purpose of a stretchable seal is attached between the bank and the tube.

The supporting structure in the furnace is the same as the conventional one.
That is, the support receiving portion 13 at the tip of the third bend 8 is supported by the support jig 16 from the furnace wall on the side opposite to the burner, and further, the lower portion of the first bend 4 or the second straight pipe 5, A saddle 11 is provided between the third bend 8 and the upper portion of the third straight pipe 7, and a saddle 12 is provided between the second bend 6 or the third straight gap 7 and the fourth straight pipe 9. The lower part of the burner-side straight pipe is supported by a spring 34 and a pedestal 35 on the spring, which are attached to a spring fixing jig 33 attached to the bank 14.

FIG. 2 is a detailed view of a mounting structure using a torsion bar. The torsion bar 36 is fixed to a fixing jig 33 attached to the bank 14, and the lever 34 protruding from the torsion bar is connected to the first straight pipe 3 via a jig 38 rotatable by a pin 37. A pedestal 35 that supports the above from below is attached.

The position A in the figure is the position of the pedestal when the radiant tube is not attached, and no torque is applied to the torsion bar. Position C is the position of the initial pedestal with the radiant tube attached,
Initial rotation is given to the torsion bar via a lever, and torque is generated. In this position, the first
The straight pipe 3 is pushed up vertically by the pedestal 35.

When the temperature of the radiant tube is raised, thermal expansion 40 occurs in the axial direction of the first straight pipe 3, and the tube slides on the pedestal. At this point, the vertical displacement of the first straight pipe 3 is not remarkable, and the tube needs to overcome the friction with the pedestal. Normally, when the burner side is fixed, the force received by the bank reaches about 2 to 3 ton, so there is no problem with the frictional force being sufficiently high. As described above, a structure that can be freely deformed in the horizontal direction and the vertical direction and that is always subjected to the weight of the burner or a part of the tube can be realized.

During normal operation, thermal expansion causes upward displacement 39 in the first straight pipe, the torsion bar rotates in the direction in which the torque is released, the lever 34 rotates, and the pedestal 3 moves.
5 rises following the displacement of the first straight pipe. Position B shows the maximum upward displacement after operation. Even at this position, torque should be applied more than position A when there is no load so that the burner and part of the tube may be under their own weight. It is necessary to design the torsion bar.

Next, the actual design procedure will be described with reference to FIG. Here, assume that the length of the torsion bar lever is R, the lever angle in the unloaded state is θ _A , the lever angle at the maximum upward displacement is θ _B , and the lever angle before mounting the temperature is θ _C. To do.

Regarding the above θ _A , θ _B , and θ _C , the upward displacement δ _BC due to thermal expansion from the initial stage of mounting must satisfy the maximum displacement, and the pedestal must be pushed up even during the maximum displacement. That is, the following expressions (1) and (2) need to be established.

[0031]

[Equation 1] θ _A ≧ θ _B ≧ θ _C ………… (1)

[0032]

(2) δ _BC = R · (sin θ _B −sin θ _C ) ... (2)

As an example, δ _BC may be determined by the following equation (3).

[0034]

(3) δ _BC = H ・ α ・ (T _T −T _R ) ... (3)

Here, H is the distance between the axes of the first straight pipe and the fourth straight pipe, α is the coefficient of linear expansion of the tube material, T _T is the average temperature of the tube, and T _R is the tube temperature before temperature rise. .

Next, the first pedestal by the maximum upward displacement
Assume a straight pipe pushing force F _B. F _B is push-up force of the pedestal even during maximum displacement needs to support a portion of the burner to its own weight and self-weight of the tube. As an example, it may be determined by the following formula (4).

[0037]

[Formula 4] F _B = W _V + W _T ………… (4)

Here, W _V is the dead weight of the burner, and W _T is the dead weight of the first straight pipe.

Under the above assumption, the torque acting on the torsion bar at the time of the maximum upward displacement is given by the equation (5), and therefore the diameter of the torsion bar can be determined by the equation (6).

[0040]

[Formula 5] T _B = F _B · R · cos θ _B ………… (5)

[0041]

[Equation 6] D = [32 · T _B · L / {(θ _A −θ _B ) · π · G}] ^1/4 (6)

Here, L is the length of the torsion bar, and G is the transverse elastic coefficient of the material of the torsion bar.

At the time point C when the radiant tube is attached to the bank, the torque determined by the equation (7) acts on the torsion bar determined by the equation (6).

[0044]

[Equation 7] T _C = (θ _A −θ _C ) · π · D ⁴ · G / (32 · L) …… (7)

Therefore, the first straight pipe receives the force determined by the equation (8) from the pedestal.

[0046]

[Equation 8] F _C = T _C / R · con θ _C ………… (8)

The optimum torsion bar can be designed by using the above equations (1) to (8), but as a constraint condition, the shear stress and the pushing force acting on the torsion bar at the time of initial torque load before temperature rise are within the limits. Shall be

The former shear stress is expressed by the equation (9), and it is necessary to satisfy the equation (10) with respect to the allowable shear stress. The difference between θ _A and θ _B is made small so that the shear stress τ _B acting on the torsion bar at the time of maximum displacement becomes considerably smaller than τ _C.

[0049]

[Formula 9] τ _C = 16 · T _C / (π · D ³ ) ………… (9)

[0050]

[Equation 10] τ _C ≤ τ _S ……… (10)

Further, the pushing-up load F when the initial torque is applied
_C inevitably becomes higher than F _B, but it is necessary to make it as small as possible. As an example, it may be considered within the constraints of Expression (11).

[0052]

[Equation 11] F _C <2 × F _B ………… (11)

The specifications of the torsion bar are determined so as to satisfy the above constraint conditions. The force applied to the radiant tube body by this torsion bar is the magnitude obtained by subtracting the burner weight and a part of the radiant tube's own weight.

The bellows 32 on the burner side only has a purpose of sealing, and the deformation is about 2 in the longitudinal direction.
It is only necessary to be able to vary by 0 mm and about 15 mm in the height direction, and it is possible to easily use a general bellows that also serves as a seal.
Moreover, maintainability is very good.

[0055]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIG. 1 and an enlarged detailed view of essential parts thereof.

The radiant tube is used in a continuous annealing furnace, and the lengths of the first straight pipe and the fourth straight pipe are 2500 mm,
The second straight pipe and the third straight pipe are 1650 mm. The distance between the axes of the straight pipes is 300 mm. The outer and inner diameters are 194 mm and 177 mm, respectively, and the material is JIS G5
122 / SCH22.

The support structure using the torsion bar is shown in FIG.
As shown in (a) and (b), two torsion bars 36
The structure using a and 36b was used. The length L of the torsion bar is 200 mm, the length R of the lever is 200 mm, the lever position θ _A at no load is 34 °, the lever position θ _B at maximum heat load is 30 °, and the pushing force by the pedestal at that time. 150 kg (75 kg per torsion bar),
Lateral elastic modulus of torsion bar material is 8000kg / mm
^{If the value is 2} , the diameter of the torsion bar is 15 mm.

Assuming that the maximum vertical displacement at the time of maximum heat load is 12 mm, the initial lever position θ _C is 2
It becomes 6 °, and the pushing force by the pedestal at that time is 290 k
g (145 kg per torsion bar).
The shear stress generated in the torsion bar is 41
kg / mm ^2, no problem at maximum heat load 21 kg / mm ^2, and the in strength.

A radiant tube having this structure is shown in FIG.
Produced with the conventional radiant tube shown in
A combustion test was performed. Figures 5 and 6 show the results of trial calculation of the axial force and bending moment generated in the tube from the temperature of the radiant tube obtained in the combustion test, and the actual measurement of the vertical displacement of the first straight pipe under the maximum heat load. Values are shown in FIG.

From these figures, in the case of the mounting structure according to the present invention, both the axial force and the bending moment are greatly reduced, and the first straight pipe is moved in parallel as a whole.
It can be seen that the bending deformation is small.

Six years have passed since the radiant tube according to the present invention was put into an actual furnace, but it has been operating without any abnormality. The conventional structure has an average of 3 to 4 years, and it has been possible to extend the service life.

[0062]

As described above, according to the present invention, the lower portion of the straight pipe on the burner side of the radiant tube is supported by the pedestal via the torsion bar, and the end portion on the burner side is penetrated from the bank to the outside of the furnace to form a bank. By using a mounting structure with a bellows for sealing that can expand and contract between
It reduces cracks and deformations that occur in the tube due to thermal distortion and thermal expansion, prevents damage to the tube attachment parts, and stabilizes the radiant tube support and prolongs its service life, thus maintaining stable operation. Also, it has excellent effects such as reduction of maintenance cost.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a mounting structure according to an embodiment of the present invention.

FIG. 2 is a view for explaining the operation of the mounting structure of the present invention.

FIG. 3 is a diagram illustrating a designing method of the present invention.

FIG. 4 is a detailed view of essential parts of the embodiment shown in FIG. 1, (a)
Is a side sectional view, and (b) is a front view.

FIG. 5 is a drawing showing a result of trial calculation of an axial force generated in a tube.

FIG. 6 is a drawing showing a result of trial calculation of a bending moment generated in a tube.

FIG. 7 is a diagram showing a displacement measurement result of a first straight pipe in a combustion test.

FIG. 8 is a side sectional view showing a structure of a conventional general W-shaped radiant tube.

FIG. 9 is a view for explaining deformation and damage form of a conventional radiant tube during temperature rise.

FIG. 10 is a view for explaining deformation and damage of a conventional radiant tube during normal operation.

[Explanation of symbols]

 1 Radiant tube 2 Burner side end of radiant tube 3 1st straight pipe 4 1st bend 5 2nd straight pipe 6 2nd bend 7 3rd straight pipe 8 3rd bend 9 4th straight pipe 10 Radiator tube recuperator side end Part 11 Saddle between radiant tubes 12 Saddle between radiant tubes 13 Third bend tip support receiving part 14 Bank 15 Heating furnace furnace wall 16 Furnace wall supporting jig 17 Burner 18 Recuperator 19 Axial direction (horizontal direction) 20 Height direction (vertical direction) ) 21 1st straight pipe axial direction force 22 1st straight pipe bending moment (at temperature rise) 23 1st bend bending moment (at temperature rise) 24 1st bend crack (example) 25 1st bend lower part buckling (temperature rise) 26) 1st straight pipe bending moment (during normal operation) 27 1st bend bending moment (during normal operation) 28 1st straight pipe crack ( Normal operation) 29 First bend lower buckling (during normal operation) 30 Second straight pipe buckling 31 Burner side clearance 32 Core bellows for gas seal 33 Bank side torsion bar mounting jig 34 Torsion bar lever 35 Pedestal 36 Torsion bar 37 pins 38 Pedestal side lever mounting jig 39 First straight pipe vertical displacement 40 First straight pipe horizontal displacement 41 Refractory attached to bank

Claims (1)

[Claims] 1. An exhaust gas side of a W-type or U-type radiant tube is fixed to a bank, and a lower portion of a straight pipe on a burner side of the radiant tube is supported by a pedestal via a torsion bar attached to the bank, and the burner side is supported. The radiant tube mounting structure is characterized in that an end portion is penetrated to the outside of the furnace with a gap from the bank, and a bellows for expanding and contracting a gas inside the furnace is mounted between the bank and the end portion on the burner side.