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Патент USA US3053535

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sept. 11, 1962
K. C. SHIPLEY
3,053,523
INNER COVER FOR BOX ANNEALING FURNACE
Filed June 8, 1959
5 Sheets-Sheet 1
2.9
Sgpt. 11, 1962
K. c. sHlPLEY
3,053,523
INNER COVER FOR Box ANNEALING FURNACE
Filed June 8, 1959
5 Sheets-Sheet 3
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United States Patent
"ice
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3,053,523
Patented'Sept. 11, 1962
2
1
FIGURE 5 is a fragmentary view of a bottom corner
3,653,523
ENNER COVER FÜR EUX ANNEALING FURNACE
Kenneth C. Shipley, Chicago, lll., assignor to Inland Steel
Company, Chicago, lll., a corporation of Delaware
Filed .lune 8, 1959, Ser. No. 818,724
t5 Claims. (Cl. 266---5)
This invention relates to the annealing of steel. It is
especially directed to apparatus for facilitating the box an
nealing of stacked, coiled, flat-rolled steel products.
In the production of cold reducer, flat-rolled steel prod
ucts in relatively thin gauge, steel ingots are initially hot
rolled into slabs 4"»7" thick. These slabs are further
reduced in thickness ‘by additional hot rolling to produce
a hat rolled product having a thickness of about 1/16”-1/s ".
Depending upon consumer requirements, the hot rolled
strip is further reduced in thickness by cold reduction
to produce a steel sheet having a smooth dense surface.
of the inner cover shown in FIGURE 2 illustrating the
flared open end and adjacent reinforcing means.
FIGURE 6 is a plan view of an illustrative diffuser
and separator plate utilized for separating the stacked
coils.
FIGURE 7 is a cross sectional view of the diffuser plate
shown in FIGURE 6 taken along line 7_7.
FIGURE 8 is a fragmentary view of a portion of the
diffuser plate.
In the course of 'a box annealing operation the effect
of the heat treating is influenced not only by the time
of heating and the temperature level maintained, but also
by the atmosphere surrounding the material. In the
annealing of coils of ñat rolled metal products in bell
type furnaces inner covers are employed to enclose the
coiled product and permit the circulation of a controlled
Iatmosphere gas within the confined area. In using inner
covers, bell type furnaces having a removable shell are
Cold reduced, flat rolled products have application as the
base metal in the production of tin plate, `galvanized sheet 20 employed to cover 'the hearth of the furnace. The fur
nace is charged by stacking coils of flat-rolled steel prod
ings, electrical steels, or as `a material of construction in
ucts on the furnace hearth. An inner cover is placed
the fabricating of a variety of sheet metal products.
over the stack of coils and sealed with a ñnely divided
In the cold working of the flatsrol‘led product structural
refractory material such as sand at the bottom. Then the
changes occur `and it is necessary to process anneal the
cold worked material at elevated temperatures to cause 25 furnace shell or portable heating unit is lowered over the
assembly. Provisions are made for supplying a con
recrystallization of the cold worked structure and to soften
stant stream of a gas for control of atmosphere into the
the steel. Although continuous annealing processes are
interior of the inner cover for circulation around the coils.
available, a large proportion of cold rolled strip product
To aid in the distribution of the gas within the inner
is heat treated in a so-called box annealing process where
in coils of the cold rolled sheet steel are stacked in a heat 30 cover, separators are placed between the coils. Control
atmosphere gas is ñrst introduced into -the inner cover to
ing furnace of a suitable design which has facilities for
providing a controlled atmosphere for protecting the steel
coil from oxidation during heating and cooling, and cov
ered by a light inner cover.
The annealing cycle, Which is carried out in the pres
ence of a circulating controlled atmosphere gas such as
purge the interior. This gas also circulates during the
heating, soaking, and cooling phases of the cycle.
In FIGURE l there is illustrated a typical bell type
This furnace consists of a permanent base
or stand 11 which is provided with a peripheral channel
12 and faced with a suitable refractory 13. Refractory
13 is provided with an annular groove 14 in which inner
35 furnace 1o.
nitrogen, or various prepared gases containing nitrogen,
and marketed under trademarks such as DX, NX, I-INX,
cover 15 is placed. Heating cover 16, suitably lined
etc., or other compositions, consists of a heating phase,
a soaking phase, and a cooling phase. During the an 40 with refractory materials 17, is indirectly tired by means
of radiant tubes 18 resting on suitable brackets 19
mounted on the wall of heating cover 16. A suitable
temperature within the range of ll00°-l300° F. and held
gas-air combustion mixture is Supplied to conventional
at this temperature. The heating phase is about 24-48
burner means, not shown, for supplying the heat required
hours and the soaking phase usually takes a total of
about 4-24 hours. Thereafter the charge of cold rolled 45 for the annealing cycle. Base fan 20, located in the base
of the furnace, is employed for circulating the gas for
steel coils is cooled within the heating furnace with a con
controlling the atmosphere within the inner cover in
tinued circulation o-f the atmosphere gases. The cooling
cooperation with the baffled, diffuser element 21 and
phase takes about 60-80 hours. Considerable time is
required to insure the production of sheet steel having 50 diffuser plate l22 resting on the face of the base refractory
13. The gas is introduced into the system by suitable
the desired softness and ductility with -most of the time
inlet and outlet means, not shown. A plurality of flat
being consumed in the heating and cooling cycles.
rolled product coils 25 are stacked on diffuser plate 22
In accordance with this invention there is provided an
with separators 26 being placed between `each coil tO
inner cover for use in box annealing which can be utilized
aid in the distribution of the controlled atmosphere gas
to facilitate the box annealing process and decrease the
nealing phase the cold rolled steel coils are heated to a
heating `and cooling time of the annealing cycle 4without 55 inside the inner cover. Inner cover 15 is placed over
the stack of coils fwith tubular, hollow inner core 27
deleteriously affecting the quality of the annealed dat
positioned within the central openings of the coils with
rolled product.
the open end of inner cover 1S resting within annular
grove 14. Inner cover 1S is sealed to the base 11 by
ployed in heat treating coils »of flat-rolled products in 60 means of a powdered refractory 28 piled about the lower
end of inner cover 15. ‘It will also be noted that the
which is illustrated the use of the inner cover of this in
open end of heating cover 16 rests within peripheral
vention for enclosing the coils and in which a controlled
Referring to the drawings, FIGURE l shows a cross
sectional View of a radiant tube-tired bell type furnace em
atmosphere gas is circulated.
channel 12 which is packed with a suitable pulverized re
illustrative means for reinforcing the outer casing Wall
of the inner cover and facilitating its handling.
’ As hereinbefore mentioned, the box annealing cycle
requires a considerable amount of time. Because it is
FIGURE 2 is a side elevation View of an illustrative 65 fractory 29 to effect the sealing of the heating cover 16
with stand 11. Heating cover 16 is suitably braced and
inner cover employing the features of this invention.
also provided with lifting lug 30 which permits the heat’
FIGURE 3 is a top view of the inner cover shown in
ing cover to be removed by a suitable hoisting device
FIGURE 2 with a portion of the end wall cut away.
and set aside while the furnace is being charged with
FIGURE 4 is a fragmentary view of ran »upper corner
`
‘
of the inner cover shown in FIGURE l illustrating an 70 the coiled products.
3,053,523
necessary for the heated coils to soak at the selected
annealing temperature for a time sufficient to effect the
much as 25% or more, depending upon the size of the
the coil stack such that there is as much lateral clearance
between the outer surface of the coil and the outer
casing as there is between the inner core surface of the
coil and the wall of the inner tubular member. Using
this design the inner cover can be readily positioned
without any interference between the inner tubular core
and the stack coils by using the outer casing as a guide
in placing the inner cover in position.
coils and furnace, by reducing the time required for the
As an illustration of the preferred ratios of the cross
desired modification or improvement in the softness or
ductility of the product, the annealing cycle cannot be
modified by reducing the time required for this phase.
By employing the instant invention, however, it is possible
to cut down on the time of the annealing cycle by as
heating and cooling phases of the annealing cycle. This 10 sectional areas of the outer and inner gas channels, for a
is provided by employing an inner cover such as illus
coil of dat-rolled metal product having an outer diameter
trated in FIGURE 2 which employs an open ended axial
tubular hollow inner core depending within the central
areas of the stacked coils.
The inner core, when
of 73” with a central opening of 24” the dimensions of
the outer cover and inner tubular member are selected
such that the ratio of the annular gas chambers should be
positioned, improves the circulation of the gas within 15 within the range of about 2.4:1 to 125:1. A suitable
inner cover for coils of this size is provided if a lateral
the inner cover and decreases the time required for the
spacing of 4" is provided between the casing and core
stacked coils to be heated throughout to the desired soak
elements of the cover and the coil surfaces adjacent
ing temperature as well as decreases the time required
thereto. It is apparent, however, that depending upon
for the coils to cool to a temperature which would
permit handling after the soaking phase of the appealing
cycle.
In FIGURE 2 is illustrated a specific embodiment
the particular designs employed as well as coil sizes, core
sizes `and other factors, this ratio and illustrative lateral
Inner
spacing can vary and other suitable ratios, as Well as spac
cover 15 comprises an open ended outer tubular casing
35. One end of tubular casing 35 is enclosed by means
ings, can be used in order to effect the objectives of this
of an inner cover for use in the instant invention.
of end wall 36 which is suitably mounted thereon by 25
means of welding or other conventional fastening ex
pedients. To the other end of tubular casing 35 is ñtted
ñared skirt 37 which in use rests within annular groove
invention.
In the illustrative embodiment shown in FIGURE 2,
cover plate was designed for use -in the box annealing of
coiled hot rolled products in which the coils had a maxi
mum diameter of 73” with the central opening having a
diameter of 24". The outer casing was fabricated from
14 provided in base 11 of furnace 10. To facilitate
Ithe handling of inner cover 15 suitable reinforcing is 30 a low carbon, rimmed steel having the following analysis.
provided. In the illustrative inner cover a pair of top
Carbon ___________________________ __
0.07% max.
and bottom rings 38 and 39 fabricated from rectangular
Manganese ________________________ __ 0.32~0.42%.
cross sectional bar stock circumscribe casing 35 adjacent
Phosphomis _______________________ __ 0.015% max.
either end thereof and are welded in place. End wall 36
Sulphur __________________________ __
0.30% max.
35
is braced by means of grid support 40 which consists
One half inch thick steel plate was employed in fabricat
of a plurality of bars 41 radially mounted on the inside
ing the outer casing as Well as the end wall. The outer
of end Wall 36. Axially depending from end wall 36
casing was 14'71/2” long and was circular in cross section
is open ended hollow tubular core 42. One end of inner
having `a 6’9” O.D. The inner tubular hollow core, which
tubular core 42 is enclosed by means of that portion of
40 had an outer diameter of 12”, was fabricated from 1/2”
end wall 36 cooperating therewith. The free end of
thick enameling iron and depended from the end wall to
tubular core 42, however, is open. The tubular core
about 1’7” from the flared open end of the outer casing.
42, which is preferably cylindrical, depends within cas
A pair of diametrically opposed gas inlets were provided
ing 35 preferably `for a distance such that a restricted
on the inner tubular member at the end adjacent the end
gas passage is formed for the extent of the aligned central
wall. These gas inlet ports were semicircular holes hav
openings of the stacked coils. To improve the eifect
ing a 11/2” radius. Suitable reinforcing in the form of
of the inner tubular core 42 gas ports 43 and 44 are
11/2” x 4" steel rings was used adjacent the closed and
provided at the end of tubular member 42 affixed to
open ends of the outer casing. ‘In assembling the various
end Wall 36. These ports permit the ñow of gases Within
components by welding, care was taken to insure that
tubular core 42 and preclude the formation of a “dead
gas-tight seams were provided.
50
air” space at the closed end of tubular member 42 which
In use the inner cover is positioned over the stacked
might have a deleterious effect on the heating efliciency
_coils and heat supplied to the furnace by a suitable heat
of the inner cover of this invention.
ing system. During heating, heat is radiated from the
In use the inner cover of this invention is placed over
furnace heating tubes toward the inner cover. Concur
the stacked coils to provide an outer and an inner cooper
_rently heat accumulates at the top of the furnace and
ating annular gas channel formed, respectively, (l) be 55 lnner cover. A portion of this heat would be conducted
tween the inner wall of the outer casing and the outer
surface of the stacked coils and (2) the outer wall of
tubular core 42 and the inner surface of the central
down the core of the inner cover of this invention and as
the outer casing and inner tubular core become hot, heat
is radiated simultaneously toward both the outer and
lnner layers of the coiled fiat rolled products.
openings of the stacked coils. The ratio of the cross
sectional areas of the respective annular gas channels 60 . With the tubular core disposed within the central open
1ng, the proper tiow of convection currents, which are
is selected such that the free flow area in the center
the principal means for transferring heat from the inner
openings of the coil stack is greatly reduced by means
cover to the coils, is effected. The prepared control at
of the inner tubular core. Accordingly, when a con
mosphere circulates inside the inner cover in a path which
trolled atmosphere gas is circulated within the inner
cover a low pressure high velocity area is created in 65 goes up the outside of the coiled stack yand down the cen
tral opening of the stack with a portion of the hot atmos
the annular gas channel formed in the central opening.
phere being distributed through separator plates placed
This pressure differential will draw the circulating gas
for control of atmosphere through the spacer plates pro
vided between the stacked coils to effect a more rapid
between each coil. By employing the inner cover design
of this invention the pressure and velocity differential of
heating and cooling of the coiled material, depending 70 the circulating gas system is increased. The pressure
dlfferential is important because it causes the circulating
atmosphere to pass through the separator plates heating
or cooling the inner layers of the coils, depending upon
preferred that the inner tubular member have a diameter
the phase of the annealing cycle. Increasing the velocity
with relation to the diameter of the central opening of 75 of the hot gas passing any portion of the coiled surfaces
upon the temperature within the furnace.
To facilitate the placement of the inner cover it is
3,053,523
5
also aids in transferring heat to the coil because with the
increased velocity any insulating surface ñlm is removed
more eñìciently. In cooling the coils the system is very
much the same with the flow of heat being in the opposite
direction.
In FIGURES 6-8 is shown a typical separator plate 50
which consists of an annular ring 51 having a plurality of
solid end wall enclosing one end of said casing, an open
ended inner tubular hollow core having a substantially
circular cross section depending from said end wall and
substantially coaxial with said outer casing, said inner
core being provided with inlet ports adjacent the terminal
end thereof attached to said end wall and with the side
Wall portion of said core below the terminal end being free
from openings, said cover adapted to cover said coils
involute vanes 52 equally spaced on the outer diameter
with said core penetrating said central opening with said
and inner diameter of annular ring 51. To facilitate the
handling of the separator plate a lifting ring 53 of suit 10 outer casing cooperating with the outer surface of said
coil to form a first gas passage for the upward iiow of a
able dimensions is positioned within the opening of an
controlled atmosphere gas, and said inner core cooper
nular ring 51 and welded thereto. The opening in the
ating with the inner surface of the central opening of said
lifting ring has about the same area as the transverse cross
coil to form a second gas passage for the downward flow
sectional area of the core opening of a coiled product
with which it is used.
15 of a controlled atmosphere gas, first and second passages
being interconnected by means of said spacer plates and
In fabricating the inner cover of this invention it is pre
a header space at the top of said inner cover, the ratio
ferred that heat resisting alloys be utilized and that plate
of the cross-sectional area of said ~first passage to the
thicknesses be suñicient to minimize damage to the inner
cross~sectional area of the second passage being sufhciently
cover upon handling. Accordingly, the outer casing
and inner core should be fabricated from materials pref 20 high to provide a low pressure, high Velocity area in
said second passage with respect to said first passage.
erably having a thickness of lle/2%”. 'In order to avoid
3. An inner cover for box annealing a stack of ñat
heat distortion of the inner tubular member an enamel
rolled metal product coils having a central opening, the
ing grade steel can be used because these steels can be
coils in said stack being separated by separator plates
employed at the annealing temperatures without distor
tion. Although it is preferred that the outer casing and 25 placed between said coils, which comprises an open-ended,
outer tubular casing, having a solid outer wall, a solid
inner core have substantially circular cross sections, it is
end wall enclosing one end of said casing, an open-ended
apparent that other tubular configurations can be em
ployed. In addition it is not necessary that the compo
inner tubular hollow core depending from said end wall
nent elements of the heating cover be fabricated from ilat
and substantially coaxial with said outer casing, said inner
plate, and other types of surfaces, such as corrugated, can 30 core being provided with inlet ports adjacent the terminal
end thereof attached to said end wall and with the side
be used.
It is apparent that the instant invention has application
wall portion of said core below the terminal end being
in a variety of annealing processes wherein the steel or
free from openings, said cover adapted to cover said coils
other material to be annealed is in coiled yform and ar
with said core penetrating said central opening with said
ranged in stacks within a suitable bell-type box anneal 35 outer casing cooperating with the outer surface of said
ing furnace. In employing the instant invention to im
coil to form a first gas passage for the upward flow of a
prove the circulation of controlled atmosphere gases
controlled atmosphere gas, and said inner core cooperat
within the inner cover by modifying the velocity and
ing with the inner surface of the central opening of said
pressure differentials within the inner cover, variations
coil to form a second gas passage for the downward flow
in the specifically described inner cover can be made 40 of a controlled atmosphere gas, first and second passages
without `departing from the scope of the invention. It is
being interconnected by means of said spacer plates and
therefore intended that the subject invention, which has
a header space at the top of said inner cover, the ratio
other equivalents and modifications, be defined by the
claims appended hereto.
of the cross-sectional area of said first passage to thev
cross-sectional area of the second passage being sufficiently
I claim:
45 high to provide a 10W pressure, high velocity area in said
l. An inner cover for box annealing a stack of ñat
second passage with respect to said first passage, said
rolled metal product coils having a central opening, the
second passage having at least the same lateral width as
coils in said stack being separated by separator plates
said first passage.
placed between said coils, which comprises an open-ended,
4. An inner cover in accordance with clairn 3 in which
outer tubular casing, having a solid outer wall, a solid 50 said inner core has a substantially circular cross section.
end wall enclosing one end of said casing, an open-ended
5. An inner cover for box annealing a stack of flat
inner tubular hollow core depending from said end wall
rolled metal product coils having a central opening, the
and substantially coaxial with said outer casing, said inner
coils in said stack being separated by separator plates
core being provided with inlet ports adjacent the terminal
placed between said coils, which comprises an open-ended,
end thereof attached to said end wall and with the side 55 outer tubular casing, having a solid outer wall, a solid
wall portion of said core below the terminal end being
end wall enclosing one end of said casing, an open-ended
free from openings, said cover adpated to cover said coils
inner tubular hollow core having a circular cross section
with said core penetrating said central opening with said
depending from said end wall and substantially coaxial
outer casing cooperating with the outer surface of said
with said outer casing, said casing, end Wall, and core
coil to form a first gas passage for the upward iiow of a 60 being fabricated from heat resistant materials of con
controlled atmosphere gas, and said inner core cooperat
struction with said core being fabricated from enameling
ing with the inner- surface of the central opening of said
grade steel, said inner core being provided with inlet ports
coil to form a second gas passage for the downward flow
adjacent the terminal end thereof attached to said end
of a controlled atmosphere gas, first and second passages
wall and with the sidewall portion of said core below the
being interconnected by means of said spacer plates and 65 terminal end being free from openings, said cover adapted
a header space at the top of said inner cover, the ratio
to cover said coils with said core penetrating said central
of the cross-sectional area of said first passage to the
opening with said outer casing cooperating with the outer
cross-sectional area of the second passage being sufficiently
surface of said coil to form a first gas passsage for the
high to provide a low pressure, high velocity area in said
upward ilow of a controlled atmosphere gas, and said
second passage with respect to said first passage.
inner core cooperating with the inner surface of the cen
2. An inner cover for box annealing a stack of flat
rolled metal product coils having a central opening, the
tral opening of said coil to form a second gas passage for
the downward flow of a controlled atmopshere gas, first
and second passages being interconnected by means of said
spacer plates and a header space at the top of said inner
ended, outer tubular casing, having a solid outer wall, a 75 cover, the ratio of the cross-sectional area of said first
coils in said stack being separated by separator plates
placed between said coils, which comprises an open
3,053,523
C)
7
u
passage to the cross-sectional area of the second passage
the upward flow of a controlled atmosphere gas, and said
inner core cooperating with the inner surface of the cen
being sufficiently high to provide a low pressure, high
velocity area in said second passage with respect to said
tral opening of said coil to form a second gas passage for
íirst passage, said second passage having at least the same
the downward tlow of a controlled atmosphere gas, first
lateral width as said first passage.
5 and second passages being interconnected by means of
6. In combination, a bell type box annealing furnace
said spacer plates and a header space at the top of said
having a hearth and removable heating cover, a stack of
inner cover, the ratio of the cross-sectional area of said
first passage to the cross-sectional area of the second pas
a plurality of ñat«rolled metal product coils positioned on
said hearth and having a central opening coextensive with
sage being suñiciently high to provide a low pressure, high
said stack, separator plates disposed between each coil
velocity area in said second passage with respect to said
iirst passage.
8. In combination, a bell type box annealing furnace
having a hearth and removable heating cover, a stack of
a plurality of ñat-rolled metal product coils positioned
15 on said hearth and having a central opening coextensive
layer, and an inner cover resting on said hearth and en
closing said stack which comprises an open-ended, outer
tubular casing, having a solid outer wall, a solid end wall
enclosing one end of said casing, an open-ended inner
tubular hollow core depending from said end wall and
substantially coaxial with said outer casing, said inner
core penetrating said central opening and substantially
with said stack, separator plates disposed between each
coil layer, and an inner cover resting on said hearth and
traversing said stack and being provided with inlet ports
enclosing said stack which comprises an open-ended, outer
adjacent the terminal end thereof attached to said end
tubular casing, having a solid outer wall, a solid end wall
wall and with the sidewall portion of said core below the 20 enclosing one end of said casing, an open-ended inner
terminal end being free from openings, said outer casing
tubular hollow core having a substantially circular cross
cooperating with the outer surface of said coil to form
section depending from said end wall and substantially
a first gas passage for the upward flow of a controlled
coaxial with said outer casing, said inner core penetrating
atmosphere gas, and said inner core cooperating with the
said central opening and substantially traversing said stack
inner surface of the central opening of said coil to form
and being provided with inlet ports adjacent the terminal
a second gas passage for the downward flow of a con*
end thereof attached to said end wall and with the side
trolled atmosphere gas, first and second passages being in
wall portion of said core below the terminal end being
terconnected by means of said spacer plates and a header
ree from openings, said outer casing cooperating with the
space at the top of said inner cover, the ratio of the
outer surface of said coil to form a iirst gas passage for
the upward ñow of a controlled atmosphere gas, and said
cross-sectional area of said ñrst passage to the cross
sectional area of the second passage being sufficiently
inner core cooperating with the inner surface of the cen
high to provide a low pressure, high velocity area in said
tral opening of said coil to form a second gas passage for
the downward flow of a controlled atmosphere gas, first
second passage with respect to said first passage.
and second passages being interconnected by means of
7. ln combination, a bell type box annealing furnace
said spaced plates and a header space at the top of said
having a hearth and removable heating cover, a stack of
a plurality of flat-rolled metal product coils positioned
inner cover, the ratio of the cross-sectional area of said
on said hearth and having a central opening coextensive
first passage to the cross-sectional area of the second pas
with said stack, separator plates disposed between each
sage being sufliciently high to provide a low pressure, high
velocity area in said second passage with respect to said
enclosing said stack which comprises an open-ended, outer 40 first passage, said second passage having at least the same
lateral width as said first passage.
tubular casing, having a solid outer wall, a solid end wall
enclosing one end of said casing, an open-ended inner
References Cited in the file of this patent
tubular hollow core having a substantially circular cross
coil layer, and an inner cover resting on said hearth and
section depending from said end wall and substantially
coaxial with said outer casing, said inner core penetrating 45
said central opening and substantially traversing said stack
and being provided with inlet ports adjacent the terminal
end thereof attached to said end wall and with the side
wall portion of said core below the terminal end being
free from openings, said outer casing cooperating with the 50
outer surface of said coil to form a ñrst gas passage for
UNITED STATES PATENTS
1,794,151
2,214,582
2,325,677
Cope ________________ __ Feb. 24, 1931
Hansen ______________ __ Sept. 10, 1940
Hoak ________________ __ Aug. 3, 1943
OTHER REFERENCES
Steel, July 21, 1947, pages 130, 132, 134, 137 and 140
relied on.
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