U.S. patent application number 14/008078 was filed with the patent office on 2014-02-27 for radiant tube.
This patent application is currently assigned to KUBOTA CORPORATION. The applicant listed for this patent is Makoto Hineno, Shigeki Nakamura, Hiroaki Okano, Nobuyuki Sakamoto. Invention is credited to Makoto Hineno, Shigeki Nakamura, Hiroaki Okano, Nobuyuki Sakamoto.
Application Number | 20140053826 14/008078 |
Document ID | / |
Family ID | 46931247 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140053826 |
Kind Code |
A1 |
Hineno; Makoto ; et
al. |
February 27, 2014 |
RADIANT TUBE
Abstract
A radiant tube formed of a heat resistant metal includes at
least one bent tube (3A (3C)) which connects straight tubes (2A, 2B
(2C, 2D)) to each other. Combustion gas from a burner 5 is fed
through one of the straight tubes (2A, 2B (2C, 2D)). The radiant
tube is characterized in that at least as the bent tube 3A (3C)
located closest to the burner 5, there is employed a cast body
having an outer diameter ranging from 150 to 210 mm and a wall
thickness ranging from 3 to 8 mm.
Inventors: |
Hineno; Makoto; (Kobe-shi,
JP) ; Sakamoto; Nobuyuki; (Ibaraki-shi, JP) ;
Okano; Hiroaki; (Takatsuki-shi, JP) ; Nakamura;
Shigeki; (Neyagawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hineno; Makoto
Sakamoto; Nobuyuki
Okano; Hiroaki
Nakamura; Shigeki |
Kobe-shi
Ibaraki-shi
Takatsuki-shi
Neyagawa-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
KUBOTA CORPORATION
OSAKA
JP
|
Family ID: |
46931247 |
Appl. No.: |
14/008078 |
Filed: |
March 28, 2012 |
PCT Filed: |
March 28, 2012 |
PCT NO: |
PCT/JP2012/058158 |
371 Date: |
November 11, 2013 |
Current U.S.
Class: |
126/91A |
Current CPC
Class: |
F24H 3/006 20130101;
F23D 14/66 20130101; F23C 3/002 20130101; Y02E 20/34 20130101; Y02E
20/348 20130101; F24H 9/12 20130101 |
Class at
Publication: |
126/91.A |
International
Class: |
F23C 3/00 20060101
F23C003/00; F24H 9/12 20060101 F24H009/12; F24H 3/00 20060101
F24H003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2011 |
JP |
2011-079964 |
Claims
1. A radiant tube formed of a heat resistant metal comprising at
least one bent tube which connects a pair of straight tubes to each
other to facilitate feeding of a combustion gas from a burner
through one of said straight tubes; wherein said bent tube located
closest to said burner comprises a cast body having an outer
diameter ranging from 150 to 210 mm and a wall thickness ranging
from 3 to 8 mm.
2. The radiant tube according to claim 1, wherein the bent tube has
a smaller wall thickness at its portions near the connections to
the straight tubes than the remaining portion thereof.
3. The radiant tube according to claim 1, wherein the radiant tube
comprises a plurality of said bent tubes, all of which comprise the
cast bodies having the wall thickness ranging from 3 to 8 mm.
4. The radiant tube according to claim 1, wherein the straight tube
has a wall thickness of 7 mm or less.
5. The radiant tube according to claim 1, wherein the straight tube
has a smaller wall thickness at its portion near the connection to
the bent tube than the remaining portion thereof.
6. (canceled)
7. The radiant tube according to claim 2, wherein the radiant tube
comprises a plurality of said bent tubes, all of which comprise the
cast bodies having the wall thickness ranging from 3 to 8 mm.
8. The radiant tube according to any one of claims 1-7, wherein the
straight tube comprises a cast body having a greater wall thickness
than that of the bent tube.
Description
TECHNICAL FIELD
[0001] The present invention relates to a radiant tube formed of
cast metal tubes and including at least one bent tube and a pair of
straight tubes connected to the opposed ends of the bent tube, with
combustion gas from a burner being fed through one of the pair of
straight tubes.
BACKGROUND ART
[0002] As prior-art document information relating to a radiant tube
of the above-noted type, Patent Document 1 identified below is
known. This Patent Document 1 discloses a radiant tube including
neck portions provided at two open ends of the bent tube, the neck
portions extending straight for a predetermined length. It is
described that with the above configuration, the compressive stress
on the side of the bent tube and the compressive stress on the side
of the straight tube act uniformly to the welded portions between
the bent tube and the straight tubes, so that there is realized
uniform distribution of the stress due to thermal expansion
occurring at the welded portions, thus providing high resistance
against formation of crack at the welded portions.
PRIOR ART DOCUMENT
Patent Document
[0003] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 10-227420 (paragraph 0007, paragraphs 0015-16, FIG.
1).
SUMMARY OF THE INVENTION
Object to be Achieved by Invention
[0004] However, with the radiant tube disclosed in Patent Document
1, its bent tube is divided into a large-diameter portion disposed
on the outer circumferential side relative to an arcuate center
axis of the bent tube and a small-diameter portion disposed on the
inner circumferential side relative to the center axis and these
large-diameter portion and the small-diameter portion are welded
together in opposition to each other. Therefore, aside from the
problem at the welded portions between the bent tube and the
straight tube, there was possibility that a crack due to thermal
expansion or the like can occur at the two welded portions
extending along the axis of the bent tube.
[0005] In view of the problem provided by the conventional radiant
tube exemplified above, the object of the present invention is to
provide a radiant tube which has high resistance against severe
heat condition imposed by combustion gas fed from a burner, thus
being usable for a longer period of time.
Means for Achieving the Object
[0006] According to the present invention, a radiant tube formed of
a heat resistant metal and including at least one bent tube which
connects a pair of straight tubes to each other, with combustion
gas from a burner being fed through one of the pair of straight
tubes;
[0007] wherein at least as the bent tube located closest to the
burner, there is employed a cast body having an outer diameter
ranging from 150 to 210 mm and a wall thickness ranging from 3 to 8
mm.
[0008] With the radiant tube having the above-described
characterizing feature, as the bent tube located closest to the
burner, thus being subject to the severest heat condition, there is
employed a cast body having a wall thickness ranging from 3 to 8
min. Therefore, in comparison with e.g. a bent tube-obtained by
welding end-to-end tubular bodies formed by pressing of a plate
material, the wall thickness of the tube is more uniform, and no
stress concentration occurs which would otherwise occur at the
welded portions extending along the longitudinal direction of the
bent tube. Therefore, there will hardly occur e.g. a heat-crack due
to sharp temperature rise or sharp temperature drop caused by the
combustion gas of the burner. Consequently, there has been obtained
a radiant tube which has high heat resistance and which can be used
for a longer period of time.
[0009] Moreover, since the thickness of the cast body is reduced to
the range from 3 to 8 mm, there is realized enhanced density of the
metallographic structure due to increase in the cooling rate at the
time of casting. Accordingly, with enhancement in the heat
resistance and heat-shock resistance of the bent tube subject to
the severest heat condition as being located closest to the burner,
there is realized a radiant tube that can be used for an even
longer period of time.
[0010] Further, the reduction of wall thickness at the portion of
the bent tube subject to the severest heat condition facilitates
deformation in response to stress application. As a result, the
heat stress can be absorbed more easily and heat crack due to sharp
temperature rise due to the combustion gas from the burner will
occur less likely.
[0011] Furthermore, the wall thickness reduction of the bent tube
located closest to the burner provides increase in the rate of
temperature rise due to the combustion gas from the burner as well
as decrease in the temperature drop along the direction of wall
thickness. Therefore, the fuel consumption amount too can be
reduced in comparison with the conventional configuration.
[0012] Also, as the wall thickness reduction of the bent tube
located closest to the burner provides weight reduction of the
radiant tube as a whole, the labor required for, its replacement
has been reduced as well.
[0013] According to a further characterizing feature of the present
invention, the bent tube has a smaller wall thickness at its
portion near the connection to the straight tube than the remaining
portion thereof.
[0014] The portion of the bent tube connected to the straight tube
is especially vulnerable to insufficient strength when it is used
due to e.g. the structural weakness on account of being located
near the tube end and embrittlement of its material under the
influence of the heat received at the time of welding. With the
inventive arrangement described above, however, since the wall
thickness of the portion near the connection is reduced relative to
the remaining portion of the bent tube, the density of the
metallographic structure is particularly enhanced due to increase
in the cooling rate at the time of casting. As a result, there is
ensured durability as good as that of the general portion of the
bent tube other than its connection-vicinity portion, for the
severe heat condition imposed by the combustion gas.
[0015] According to a still further characterizing feature of the
present invention, the radiant tube comprises a plurality of said
bent tubes, all of which comprise the cast bodies having the wall
thickness ranging from 3 to 8 mm.
[0016] Conceivably, only the bent tube that is located closest to
the burner may comprise a cast body having the wall thickness
ranging from 3 to 8 mm. With the above inventive arrangement,
however, all of a plurality of bent tubes comprise cast bodies
having the wall thickness ranging from 3 to 8 mm. With this, there
is obtained a radiant tube which has even higher reliability in its
heat resistance and which can be used for an even longer period of
time.
[0017] Moreover, as the arrangement allows even further weight
reduction of the radiant tube as a whole, the labor required for
its replacement operation can be even further reduced.
[0018] According to a still further characterizing feature of the
present invention, the straight tube has a wall thickness of 7 mm
or less.
[0019] With the reduction of wall thickness of the straight tube,
in addition to the wall thickness reduction of the bent tube, as
proposed in the above arrangement, in comparison with an
arrangement of the straight tube alone having a relatively large
wall thickness, there can be ensured higher strength at the
connection portion between the bent tube and the straight tube.
[0020] According to a still further characterizing feature of the
present invention, the straight tube has a smaller wall thickness
at its portion near the connection to the bent tube than the
remaining portion thereof.
[0021] The portion of the straight tube connected to the bent tube
is especially vulnerable to insufficient strength when it is used
due to e.g. the structural weakness on account of being located
near the tube end or embrittlement of its material under the
influence of the heat received at the time of welding. With the
inventive arrangement described above, however, since the wall
thickness of the portion near the connection is reduced relative to
the remaining portion of the straight tube, the density of the
metallographic structure is particularly enhanced due to increase
in the cooling rate at the time of casting. As a result, there is
ensured durability as good as that of the general portion of the
straight tube other than its connection-vicinity portion, for the
severe heat condition imposed by the combustion gas.
[0022] According to a still further characterizing feature of the
present invention, the straight tube comprises a cast bodies having
a greater wall thickness than that of the bent tube.
[0023] With the above-described arrangement, in comparison with an
arrangement using a straight tube having substantially same wall
thickness as the bent tube, it becomes easier to obtain a radiant
tube which has an even higher heat resistance and which can be used
for an even longer period of time.
BRIEF DESCRIPTION OF THE DRAWING
[0024] FIG. 1 is a partially cutaway side view schematically
showing a radiant tube relating to the present invention.
MODE OF EMBODYING THE INVENTION
[0025] Next, one embodiment of the present invention will be
described with reference to the accompanying drawing. It is
understood, however, that the scope of the present invention is not
to be limited by the following description or the illustration, but
that the invention may be embodied in any modified manner as long
as such modification does not deviate from the essential concept
thereof.
[0026] A radiant tube 1 shown in FIG. 1 includes four laterally
oriented straight tubes 2A, 2B, 2C, 2D juxtaposed with an equal
vertical spacing therebetween, with the respective vertically
adjacent straight tubes 2 pairs being connected via total three
bent tubes 3A, 3B, 3C, so that the assembly as a whole forms a
laterally oriented W-shape.
[0027] The radiant tube 1 is supported to a furnace wall 10 of a
heating furnace such as a drying furnace, a sintering furnace, etc.
via the uppermost straight tube 2A and the lowermost straight tube
2D. To the terminal free ends of these straight tubes 2A, 2D, there
are connected burners 5 via heat reservoirs 4 formed of ceramic
honeycomb bodies having high heat recovery efficiency.
[0028] These burners 5 are composed of regenerative type burners in
which the fuel consumption required for burner combustion can be
reduced, in such manner that e.g. when the burner 5 connected to
the uppermost straight tube 2A is operated for combustion, exhaust
gas is discharged through the lowermost straight tube 2D while
exhaust heat is collected by the lower heat reservoir 4, and when
the combustion is switched to the burner 5 connected to the
lowermost straight tube 2D, the combustive air is preheated using
the exhaust heat collected by the lowermost heat reservoir 4.
[0029] By operating the switch valve 6 provided between the
combustive air fun 7 for supplying the combustive air and each
burners 5, it is possible to switch over between a state (indicated
by the solid line) where the combustive air is burned by the burner
5 connected to the uppermost straight tube 2A, and exhaust gas is
discharged through the lowermost straight tube 2D while exhaust
heat is collected by the heat reservoir 4 connected to the
lowermost straight tube 2D and a further state (indicated by the
broken line) where the combustive air is burned by the burner 5
connected to the lowermost straight tube 2D, and its exhaust heat
is collected by the heat reservoir 4 connected to the uppermost
straight tube 2A.
[0030] The exhaust gas past each heat reservoir 4 can be discharged
into the atmosphere via the switch valve 6 and an exhaust gas
treating device (not shown), etc.
[0031] Each and every one of the four straight tubes 2A, 2B, 2C, 2D
and the three bent tubes 3A, 3B, 3C has an outer diameter of 180 mm
and is formed of cast steel (an example of cast body formed of a
heat resistant metal) containing 20-35 wt. % of chrome and 30 to 50
wt. % of nickel.
[0032] The connection between the straight tube 2 and the bent tube
3 is realized by means of welding these from the outer
circumferential faces thereof, with placing the respective end
faces thereof in abutment with each other.
[0033] Among the three bent tubes 3A, 3B, 3C, the first bent tube
3A and the third bent tube 3C located closest to the burners 5 each
comprises a thin-walled cast body having a wall thickness ranging
from 3 to 8 mm.
[0034] The second bent tube 3B located relatively distant from the
burner 5 and the four straight tubes 2A, 2B, 2C, 2D each comprises
a cast body having a wall thickness of 5 mm or 10 mm.
[0035] In the above, the languages "distant" and "closest" refer to
the amounts of distance from the burner 5 in the passageway of
flame or combustion gas generated from the burner 5 and moving
inside the radiant tube 1.
[0036] In this way, as a thin-walled cast body having a wall
thickness ranging from 3 to 8 mm is employed as the bent tube 3
located closest to the burner 5, there can be obtained a radiant
burner 1 having high heat resistance and usable for an extended
period of time.
[0037] A possible reason for the above is as follows. With a bent
tube formed integrally by casting, in comparison with e.g. a bent
tube obtained by welding end faces of the right and left tubular
bodies along the axial direction of the tube, each tubular body
being obtained by pressing of a plate material, the former bent
tube has a more uniform wall thickness and there occurs no local
stress concentration that would otherwise occur at the welded
portions extending along the longitudinal direction of the bent
tube, so that heat crack or the like due to sharp temperature rise
or sharp temperature drop caused by combustion gas from the burner
will occur less likely.
[0038] Further, as the wall thickness of the cast body is reduced
to the range from 3 to 8 mm, there is realized enhanced density of
the metallographic structure due to increase in the cooling rate at
the time of casting, whereby the heat resistance and heat-shock
resistance are enhanced.
[0039] Moreover, the reduction of wall thickness facilitates
deformation in response to stress application. As a result, the
heat stress can be absorbed more easily and heat crack due to sharp
temperature rise due to the combustion gas from the burner too will
occur less likely.
[0040] Furthermore, the wall thickness reduction of the bent tube 3
located closest to the burner 3 provides increase in the rate of
temperature rise due to the combustion gas from the burner as well
as decrease in the temperature drop along the direction of wall
thickness. Therefore, the fuel consumption amount too can be
reduced in comparison with the conventional configuration.
[0041] Also, since the weight reduction of the radiant tube as a
whole, the labor required for its replacement has been reduced as
well.
[0042] The four straight tubes 2A, 2B, 2C, 2D constituting the
radiant tube 1 are manufactured with using the centrifugal casting
technique.
[0043] On the other hand, all of the three bent tubes 3A, 3B, 3C
are manufactured with using the suction casting technique in which
a negative pressure is formed by means of e.g. a vacuum pump inside
the cavity after introduction of molten metal therein. Therefore,
even with the realization of wall thickness reduction, there occurs
no shrinkage cavities or shrinkage looseness which generally tends
to occur at the time of solidification of molten metal, so that
there are obtained bent tubes having favorable surface
conditions.
[0044] Incidentally, for the purpose of further wall thickness
reduction for instance, wall thickness reduction may be implemented
with the straight tubes too with using the suction casting
technique.
[0045] Incidentally, the outer diameter of the four laterally
oriented straight tubes 2A, 2B, 2C, 2D and the three bent tubes 3A,
3B, 3C together constituting the radiant tube 1 is not limited to
180 mm, but can range from 150 to 210 mm. If the wall thickness is
confined within this range, there can be readily obtained the
advantageous effect due to the setting of wall thickness to 3 to 8
mm for the bent tubes 3A, 3B, 3C.
Example 1
[0046] Table 1 below shows results of analysis via simulation of
various properties respecting heat stress imposed on the third bent
tube 3C when the radiant tube 1 shown in FIG. 1 is actually
used.
[0047] In this simulation, in simulating its use as the
regenerative type arrangement, combustion gas was fed alternatively
from the respective burners 5 for a predetermined period and
combustions were effected thereby.
[0048] As shown in Table 1, with varying in many ways the wall
thicknesses of the respective bent tubes 3 and the respective
straight tubes 2, the relationships between these thicknesses and
the various properties about the heat stress imposed on the third
bent tube 3C after combustion gas was fed alternatively from the
respective burners 5 for the predetermined period, were
obtained.
[0049] The numerical values given to the bent tube wall thickness
shown in the table were applied to all of the three bent tubes 3A,
3B, 3C and similarly, the numerical values of the wall thickness of
straight tube were applied to all of the four straight tubes 2A,
2B, 2C, 2D.
[0050] As the material for casting, KHR-48N was employed_KHR-48N is
defined as an austenitric super-heat-resistant alloy having acid
resistance up to 1200.degree. C. and good creep rupture strength
and contains 27 wt. % of chrome, 47 wt. % of nickel and 5 wt. % of
tungsten.
TABLE-US-00001 TABLE 1 bent straight 0.2% proof tube wall tube wall
maximum stress of bent thickness thickness stress tube material No.
(mm) (mm) (MPa) (MPa/1000.degree. C.) evaluation 1 3 5 48.6 135
.largecircle. 2 5 5 44.9 128 .largecircle. 3 7 5 47.2 115
.largecircle. 4 10 5 50.1 87 X 5 5 10 53.3 120 .largecircle. 6 6 10
50.3 128 .largecircle. 7 7 10 51.9 115 .largecircle. 8 8 10 53.5
102 .largecircle. 9 10 10 56.1 87 X 10 13 10 57.4 78 X
[0051] From the determination results of 0.2% proof stress (MPa) of
the bent tube material at 1000.degree. C. shown in Table 1 above,
the following observations can be made.
[0052] By setting the wall thickness of the bent tube 3 to 8 mm or
less, it is possible to ensure values greater than 100 MPa.
Further, the values of 7 mm or less are better than the values of 8
mm or less and the values of 6 mm or less are even better. And, the
smaller the wall thickness, the higher the values tend to be.
[0053] Further, respecting the determination results of the maximum
stress too, there is the tendency of being able to ensure numeric
values of 55 MPa or less by setting the wall thickness of the bent
tube 3 to 8 mm or less.
[0054] Incidentally, it is understood that the respective
tendencies described above can be seen basically throughout in both
of the cases of the wall thickness of the straight tube 2 portion
being 5 mm and 10 mm and the tendencies are not much affected by
the wall thickness of the straight tube 2.
[0055] However, in the case of setting the wall thickness of
straight tube to 5 mm, as far as the determination values of the
0.2% proof stress of the bent tube are concerned, radiant tubes
whose straight tubes have greater wall thickness than those of
their bent tubes tend to show higher numeric values.
Example 2
[0056] In this Example 2, as materials other than KHR-48N, Alloy
230 and KHR-35H were employed. And, like Example 1 above, various
properties about the heat stress imposed on the third bent tube 3C
when the radiant tube 1 shown in FIG. 1 is actually used were
analyzed via simulation.
[0057] In this example too, with varying in many ways the wall
thicknesses of the respective bent tubes 3 and the respective
straight tubes 2, the relationships between these thicknesses and
the various properties about the heat stress imposed on the third
bent tube 3C after combustion gas was fed alternatively from the
respective burners 5 for the predetermined period, were
obtained.
[0058] Table 2 shows the results of Alloy 230 (containing 22 wt. %
chrome, 57 wt. % nickel, 2 wt. % molybdenium and 14 wt. %
tungsten). Table 3 shows the results of KHR-35H (containing 25 wt.
% chrome and 35 wt. % nickel).
TABLE-US-00002 TABLE 2 bent straight 0.2% proof tube wall tube wall
maximum stress of bent thickness thickness stress tube material No.
(mm) (mm) (MPa) (MPa/1000.degree. C.) evaluation 1 5 5 26.3 87
.largecircle. 2 10 10 32.9 65 X
TABLE-US-00003 TABLE 3 bent straight 0.2% proof tube wall tube wall
maximum stress of bent thickness thickness stress tube material No.
(mm) (mm) (MPa) (MPa/1000.degree. C.) evaluation 1 5 5 33.9 100
.largecircle. 2 10 10 42.4 86 X
[0059] From the determination results of 0.2% proof stress (MPa) of
the bent tube materials at 1000.degree. C. shown in Table 2 and
Table 3 above, with the materials other than KHR-48N too, higher
values were obtained with smaller wall thicknesses of the bent tube
3.
[0060] Further, respecting the determination results of the maximum
stress too, there is observed a similar tendency of being able to
obtain smaller values with smaller wall thicknesses of the bent
tube 3.
[0061] Incidentally, the mark "X" employed in the respective tables
above representing evaluation result indicates that there occurred
crack or deformation especially around the bent tube to such a
level to impair the function of the radiant tube as a heating
means.
[0062] (About the Analysis Method)
[0063] In the analyses of the various properties relating to heat
stress imposed on the third bent tube 3c conducted in Example 1 and
Example 2, a software: "Solid Works Simulation"produced by Solid
Works Corp. was used and as its model type, there was employed a
linear isotropic elasticity model with two burner-heat introducing
side ends (the right ends of the straight tubes 2A, 2D in FIG. 1)
being completely restricted to the wall face of the furnace.
[0064] Referring to the size conditions of the radiant tube 1 as
the target of analysis, there were set the width (the length from
the base end of the straight tube 2A, 2D restricted to the wall
face to the curved leading end of the bent tube 3A, 3C): 2276
mm.times.height (the length from the upper face of the uppermost
straight tube 2A to the lower face of the lowermost tube 2D): 1087
mm; and the outer diameter of the tube was set as 187 mm for all of
the straight tubes 2A, 2B, 2C, 2D and the three bent tubes 3A, 3B,
3C.
[0065] The various properties of the respective steel materials
employed in the analyses are shown in Table 4 below.
TABLE-US-00004 TABLE 4 steel type KHR-48N Alloy 230 KHR-35H failure
criterion max von Mises max von Mises max von Mises stress stress
stress elastic modulus 105,000 MPa 72,200 MPa 93,000 MPa Poisson's
ratio 0.3 0.3 0.3 mass density 8200 kg/m.sup.3 8970 kg/m.sup.3 8050
kg/m.sup.3 coefficient of 1.6e-005/.degree. C. 1.61e-005/.degree.
C. 1.8e-005/.degree. C. thermal expansion
[0066] Incidentally, the mutually welded portions of the bent tube
and the straight tube (the area extending for 10 to 30 mm from
respective end faces in abutment at the time of welding) are
portions where shortage of strength tends to occur more easily
during use, due to structural strength shortage on account of being
located near the tube end face and embrittlement of material due to
heat applied thereto during the welding operation. Therefore, for
these welded portions, in order to ensure sufficient resistance
against the severe heat condition from combustion gas, these
portions are formed even thinner, specifically from 1 to 2 mm
thinner than the remaining portions.
[0067] Further, when the radiant tube 1 is put to an actual use, as
a means for receiving the mechanical load, in many cases, adjacent
bent tubes or a portion of a bent tube and a portion of a straight
tube will be supported to each other via an interconnecting piece
provided separately. In such case, in the bent tube and the
straight tube, supported portions thereof to be welded to the
interconnecting piece are formed locally thick (e.g. about 10 mm).
As specific examples of the supported portions, they are the
portions in the base ends of the bent tubes 3A, 3C shown in FIG. 1
which portions are in vertical opposition to each other, the lower
face of the base end portion on the lower side of the bent tube 3B,
the upper face portion of the nearest straight tube 2D, etc.
[0068] It is understood that the values given to the wall
thicknesses of the bent tubes and the straight tubes defined in the
appended claims and recited in the detailed disclosure are to be
applied to the general portions thereof other than these welded
portions and the supported portions.
[0069] The bent tube provided in the present invention is used for
interconnecting a plurality of tubular portions for such purposes
as adjusting the extending direction of the pipe, branching from a
single tube into a plurality of tubes or converging a plurality of
pipes into a single pipe and has a bent curved portion or a bent
portion to such ends. Thus, it is understood that the bent tube as
used in the present invention is not limited to the U-shaped pipe
illustrated in FIG. 1, but is inclusive also of joint pipes having
any desired shapes.
Other Embodiments
[0070] <1> All of the bent tubes 3A, 3B, 3C, including the
second bent tube 3B relatively distant from the burner 5, can be
formed as thin-walled cast bodies having a wall thickness ranging
from 3 to 8 mm.
[0071] <2> When the invention is used not as the regenerative
type burner 5, but as a non-regenerative type in which combustion
gas is fed invariably from the burner 5 connected to the uppermost
straight tube 2, only the first bent tube 3A located closest to
this constantly used burner 5 may be formed as a thin-walled cast
body having a wall thickness ranging from 3 to 8 mm. Alternatively,
however, all of the bent tubes 3A, 3B, 3C can be formed as
thin-walled cast bodies having a wall thickness ranging from 3 to 8
mm.
[0072] <3> The shape of the radiant tube 1 is not limited to
the W-shape described above, but can be a trident shape.
[0073] <4> The numbers of the bent tubes and the straight
tubes together constituting the radiant tube 1 are not limited to
those exemplified above. As long as there is provided at least one
bent tube as a part of its configuration, the radiant tube can be
configured as e.g. U-shaped radiant tube including a pair of
straight tubes and only one bent tube interconnecting the pair of
straight tubes.
INDUSTRIAL APPLICABILITY
[0074] The present invention may be used as a technique relating to
a radiant tube formed of a heat resistant metal and including at
least one bent tube for interconnecting a pair of straight tubes,
and a combustion gas from a burner is fed through one of the pair
of straight tubes.
DESCRIPTION OF REFERENCE NUMERALS
[0075] 2 straight tubes (2A, 2B, 2C, 2D) [0076] 3 bent tubes (3A,
3C) [0077] 5 burners
* * * * *