Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
10905Z8
This appllcatlon is a divislon of Canadian Patent
Applicatlon No. 212,480 filed October 29, 1974 entitled TWIN-P*~T
CONTINUOUS CASIING METHOD AND APPARATUS.
DESCRIPTION
The present lnventlon relates to continuous casting methods
and apparatus wherein thetemperature of the flexible castlng belt in
twin-belt casting machlnes ls controllably elevated prlor to contact
with the molten materlal being cast.
FIELD OF THE INVENTION
In twin-belt casting machines the material being cast,
which ls lllustratlvely shown herein as molten metal, ls fed lnto a
castlng region between opposed portlons of a pair of revolving flexible
metal belts. The movlng belts confine the molten metal between them and
carry the molten metal Along as lt solldifies between them. Spaced rollers
having na~row rldges support and drlve the belts and also guide the belts
as they move along through the casting region. The vast quantltles of
heat liberated by the molten metal as lt solid~?~les are withdrawn through
the portlons of the two belts which are ad~acent to the metal being cast.
; This large amount of heat ls withdrawn by cooling the reverse surfaces of
the belts by means of rapldly moving substantlally continuous films of
liquld coolant travelllng along against these reverse surfaces.
Each of the two flexible casting belts ls revolved around
a belt carriage in a path defined by maln rolls located in the carriage
and arcund which the belt passes. In some twin-belt caating machines ?
there are two main rolls at opposlte ends of the carrlage defining an
oval path for the belt to travel. In other twin-belt casting machines
there are three or more main rolls in each carrlage defining the belt path.
In sc~e twin-belt caating machlne installations the
upper and lower casting belts converge directly opposlte
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each other around opposed nip rolls to form the entrance to
the casting region, and the molten metal is fed into the
machine through a pouring spout extending into the entrance.
IThis is often called an "injection feeding" technique. In
lother twin-belt casting machine installations the lower cast- I
! ing belt is arranged to support a poo} of molten metal adjacenit
to the entrance between the upper and lower belts. 'rhis
~latter arrangement is called an "open pool" or "closed pooln
lcasting technique, depending upon whether the surface of the
molten pool is open to the atmosphere or is closed over by a
protective barrier to exclude the atmosphere. Variations of ,1
these molten metal feeding techniques are sometimes employed, ¦
such as a partially open pool. However, as used herein, all '
1lof the various techniques for feeding molten metal into a I i
,,twin-belt casting machine are intended to be included within
the descriptive phrase: "open pool, closed pool or injection
feeding" .
The present invention can be employed to advantage
''in any of these various twin-belt casting machines whether
llusing two, three, or more main rolls in each carriage, and thel
¦invention can also be employed to advantage regardless of ¦ -
'rhether the molten metal is being fed into the machine by an
jopen pool, closed pool, or injection feeding.
I For further information about twin-belt casting
,jmachines, the reader may refer to one or more of the following
¦United States patents in the name of Clarence W. Hazelett or R
William Hazelett and Richard Hazelett: 2,640,235; 2,904,860; 1
3,036,348; 3,041,686; 3,123,874; 3,142,873; 3,167,830;
',,3,228,072; and 3,310,849.
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Prior Art
In the prior art, efforts were made to minimize the heating
effects of the molten metal on the casting belts of twin-belt machines.
The high velocity liquid coolant was applied to the reverse surfaces of
the belts a relatively long time before the molten metal came in contact
with their front faces. Also, the high velocity liquid coolant was
applied to the reverse surfaces of the belts a relatively great distance
ahead of the point where the lten metal came in contact with their
front faces.
In addition, relatively thick insulative coatings were often
applied to the front faces of the flexible metal casting belts. It
was these insulative coatings which were at the interface between the
molten metal and the casting belts and served to reduce the rate of
heat transfer from the molten metal into the belts.
Nevertheless, in the prior art, as the molten metal began
to be carried along downstream with the belts near the entry to the
casting region, momentary or permanent belt distortion could occur due
to buckling resulting from thermal expansion. Efforts were made in
the prior art to minimize any such distortion by applying high tension
forces to the belts, and one or more of the main rolls were sometimes
contoured slightly as by reverse crowning to counteract such distortion,
as described and claimed in United States Patent No. 3,123,874.
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ilO905Z8 i
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~he Invention
The invention provides continuous casting methods,
!l and apparatus in which the temperature of the flexible cast-
lling belts in twin-belt casting machines is controllably
s elevated prior to contact with the material being cast, which
,~is illustratively shown as molten metal. The casting belts
,may be elevated in temperature by various methods and
,lapparatus, as explained in connection with the various illus-
~trati~2 embodiments of the invention which are described.
o !l In some embodiments of the invention, one or
more banks of high intensity infra-red heaters may be direct-¦
~ed at close range against the front faces of the casting belts
to elevate their temperature before the belts c e into con- j
lltact with the molten metal. The banks of infra-red heaters j
15 ll may be arranged to heat the casting belts before they reach ¦
I! the nip rolls at the entrance to the casting region or during,
travel of the belts around the nip rolls or bo~h before and
during travel around the nip rolls. i
ll In other embodiments of the invention, hot fluid,
I!such as steam, may be circulated within hollow nip rolls to
¦lelevate the temperature of the casting belts before the belts¦
¦come into contact with the molten metal or to control the
jchange in temperature of the casting belts.
Il In further embodimentQ of the invention, the
¦!high velocity liquid coolant may be directed onto the reverse¦
¦surfaces of the casting belts, so that this cooling effect
¦occurs only momentarily before or simultaneously with the
l'contact of the molten metal against the casting belts.
'Special fingernail-like extensions are shown attached to li~uid
,Icoolant nozzles nested within deep grooves in the nip rolls.
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1090528
These fingernail extenders mask off the coolant I
streams from the reverse surface of the casting belt and !
spread out the coolant streams to form a sharply defined !
coolant layer. This sharply defined coolant layer enables
the cooling action to be precisely started by application to
,the reverse surface of the casting belt very near to the
point where the molten metal approaches the front surface
,~of the casting belt. The cooling effect of the liquid
I,coolant in conjunction with the nip roll may be controlled
10 ,'by insulating the deep grooves in the nip roll or by insulat-
,ing the narrow ridges between these grooves.
Hot fluid, such as steam, may be directed into
; ,
Ithe deep grooves of the nip roll beneath the casting belts
¦Ito aid in elevating and controlliny their temperature.
,I Mechanical and thermal sensors may be employed to
sense any di3tortion in the casting belts near the entry to -
~the casting region and to monitor the belt temperature, and
l'the elevation of the temperature of the ca3ting belts ahead
¦~of the casting region is controlled to optimize the casting
¦lconditions as determined by these sensors.
¦I Various zones of heating may be provided, 80 that
'the temperature of the main central area of the casting
~belts is controllably elevated lndependently of the edge
ilportions of the belts and vice versa.
25 ¦1 A number of advantages and benefits, as indicated
: llhereinafter, are provided by employing the invention in twin-
i,belt casting machines: ¦ ;
, 1. Casting belt distortion and transverse buck-
,ling along the casting region near and downstream from the
'lentry of the molten metal due to differential transverse I `-
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llthermal expansion is markedly reduced and often is complételyl
!iovercome. I
2. Thermal shock to the belt and to the insulat-!
ive coating on the belt due to contac~ of the molten metal atl
'the entry to the casting region are markedly reduced because j
the temperature of the insulative coating and belt are
gradually elevated before contact with the molten metal
occurs. The operating lives of the belt and its coating are¦
l!thereby increa~ed.
1~ 3.Reduction in differential temperatures and resulj-
ant reduction in belt stresses enhances belt life and operati~g
,Iconditions in the machine.
¦1 4. The belt coating may be dried or cured to
lachieve more consistent thenmal resitance or other desired
'characteristic such as absolute minimizing of moisture conten
before contact with the molten metal.
5. ~he provision of mechanical probes to sense
1I the belt shape and thermal probes to sense the temperature
~¦profile enables overall precise control of the twin-belt cast
¦¦ ing operation to be obtained.
¦! 6. By virtue of the minimization or elimination-
¦of differential or non-uniform thermal expan3ion and d*~tortic n
Ilor buckling effects, lighter or simpler or thinner or more
¦¦durable belt coatings with less insulating value (lower
25- 11 thermal resi-~tance) can be utilized. These result in saving~
¦¦in belt fabrication time and material costs and also extend
¦Ithe operating lives of belts and coatings to provide oper- -
,l,ational savings.
,! ,. Because coatings of less insulative value can ¦
!~ be employed, the effective rate of cooling of the material
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10905z~ 1 1
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~Ibeing cast is accelerated, and consequently faster casting j
,Irates can be used in such cases, i.e. the tonnage output of
the casting machine per hour can be increased. !
1 8. The control of belt flatness and thermal factors'
s ,at the entry to the casting region and downstream from the
'entry enable improved metallurgical behavior to be achieved.
9. By minimizing or eliminating belt distortion, ¦
the thin cast shell which initially forms from the molten '
l~metal adjacent to the belt is stabilized. Localized variable
heat transfer rates are avoided because the casting belt does
not distort but rather it remains stable in position against
the thin cast metal shell being formed. Thus, more uniform
,!metallurgical properties can be attained, a more consistent
¦Icast shape is provided, and more consistent surfaoe appearance ,
I!is obtained over the top and bottom surfaces of the cast
Iproduct. ' ¦
¦~ 10. More difficult or more critical alloys can be
jlcast with greater commercial suitability in twin-belt
¦I'machines.
~1 11. Thinner sections of metal alloys of acceptable
Iquality and sound structure are enabled to be cast in twin-
¦Ibelt machines employing the invention. ,
Il 12. By minimizing or eliminating belt distortion ,~
¦land by controlling the temperature conditions a more uniform ,,
' 25 !¦feed rate of lten metal into the casting machine can be
I,lattained for all types of metal feeding, beca,use the volume of
¦the casting region remains more constant and the shrinkage of
'the metal being cast is more nearly constant.
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The various additional features, advantages and ¦
~objects of the present invention will become more fully ¦
understood from a consideration of the following detailed ¦
description in conjunction with the accompanying drawings.
ij BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of the outboard
jlside of a continuous casting machine of the twin-belt type
embodying the present invention;
!! FIG. 2 is an elevational view of the input
~lend of the machine of FIG. l;
¦~ FIG. 3 is an enlarged partial sectional view
showing the entrance to the casting region in detail;
FIGS.4 and 5 are sectional views taken along the
¦ planes 4-4 and 5-5 in FIG. 3 and shown further enlarged; .
1I FIG. 6 is a sectional and elevational view taken
¦along the plane 6-6 in FIG. 7 showing the end of one of the .
wrap_around coolant nozzles with a fingernail extender for-
controlling and positioning the application of coolant;
FIG. 7 is a side elevational view of thiS nozzle and
fingernail extender; .
¦ FIG. 8 is a perspective view of a flexible casting ,i
¦belt in the prior art; .
FIG. 8A is a diagrammatic plot of the belt tempera-
ture profile along the longitudinal section 8A-8A i~ FIG. 8; .
li . FIG. 8B is a diagrammatic plot of the belt tempera-
iture profile along the transverse section 8B-8B in PIG. 8;
¦l FIG. 9 is a perspective vie~ of a flexible casting
ilbelt being utilized with the present invention;
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FIG. 9A is a diagrammatic plot of the belt tempera
ture profile along the longitudinal section 9A-9A in FIG. 9;
. FIG. 10 is a sectional view of another type of
~ twin-belt casting machine embodying the pre~ent invention:
l, FIG. 11 is an enlarged elevational sectional view
showing mechanical and thermal sensors associated with the
lower casting belt of a twin-belt casting machine embodying
the invention, such as the machines shown in FIG. 1 or FIG.
ilo;
lo l! FIG. 12 is a sectional view showing apparatus
,~for feeding hot fluid, such as steam into a hollow nip roll ~ ¦
of a t~in-belt casting machine, such as the machines shown . ¦ ¦
.in FIG. 1 or FIG. 10, for elevating and controlling the
llcasting belt temperature;
, FIG. 13 is a partial sectional view illustrating
.the action of the curved coolant tubes nested between the
ridges of the nip roll of a prior art twin-belt casting
~¦machine; . ~ :
',j FIG. 14 is a partial sectional view taken along
¦Ithe curved line 14-14 in FIG. 3. FIG,.14 is intended to be ¦
¦Icompared with FIG. 13, because FIG. 14 illuQtrate~ the ad-
vantageous action of the fingernail extenders in cooperation
¦with the curved coolant tube~ nested between the ridge~
of the nip roll for controlling the application of the
coolant to the belt;
jl FIG. 15A i~ a diagrammatic plot of the longitudinal
temperature profile of the casting belt in a m~achine embodyin5
the inven~ion. FIG. 15A shows a curve similar to the curve
shown in FIG. 9~;
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FIGS. 15B and 15C show other diagrammatic
,plots of longitudinal temperature profiles of casting belts,
being taken along planes corresponding in position to 9A-9A ,
~in FIG. 9 in machines embodying the invention; i
1I FIG. 16A is a diagrammatic plot of the transversq
temperature profile taken along the plane 16A-16A in FIG. 9
through the casting belt of a machine embodying the invention;¦
FIGS. 16B and 16C show other diagrammatic
llplots of transverse temperature profiles taken along
,,planes corresponding in position to 16A-16A in FIG. 9 in
machines embodying the invention in which the edge portions ¦
'of the belt are elevated in temperature.
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DETAILED DESCRIPTION ¦ .
l In the continuous casting machine 10 shown in ¦
IFIGS. 1 and 2, the lten metal is introduced from a tundish
¦12 located at the input end of the machine. The molten meta~
¦¦Passes into and is solidified in a casting region C defined
. between the spaced parallel surfaces of a pair of wide endles
flexible casting belts 14 and 16. In operation, these belts
~'are revolved around an upper and a lower belt carriage U and
L, respectively. The two sides or edges of the casting
l region C are defined by a pair of laterally separated flexible
¦ endless side dam~ 18, which travel between the upper and lower
Icasting belts in the casting region and which revolve around
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the lower carriage L to complete their circuit of travel.
An arcuate guide 20 carrying multiple small pulley wheels 22
serves to guide each of the side dams as it ved into the
entrance to the casting region. Only one of the side dams
i~18 and only one of the arcuate guides 20 can be seen in
FIG. 1. In FIG. 2, the tundish 12, side dams 18 and
arcuate guides 20 have been omitted for clarity of
lillustration. I
i The carriages U and L of the upper and lower
~belt are supported from the back 24 of the machine 10 mounted ¦
llon a base 26. The upper belt carriage U includes a pair ¦
¦lof main rolls 28 and 30 located at the upstream and downstrea~
!lends of this carriage. Similarly, the lower belt carriage L !
llincludes a pair of main rolls 32 and 34 at its upstream
iland downstream ends.
¦~ In the machine 10, ~he downstream rollR 30
and 34 serve to tension and to steer the respective belts
l on their carriages. The type of twin-belt machine shown in
¦ FIGS. 1 and 2 is sometimes called a "two roll" or ~two
I pulley" machine because there are two main rolls on each of t~ e
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lO90S28
carriages. The upstream rolls 28 and 32 define the entrance or nip
portion of the casting region and are used to drive the belts on the
respective carriages. These rolls 28 and 32 are belt support means
and for convenience they will be referred to as the "nip" rolls. The
power mechanism 36 for driving the nip rolls is shown in Figure 2 with
universal coupled drive shafts 38 and 40 extending from the power
mechanism to the nip rolls. A pair of lift cylinders 42 acting through
a lever system 45 serve to raise the whole upper carriage when it is
desired to open up the casting region C or to change the thickness of
the product to be cast.
As the upper casting belt 14 is revolved, it moves in an oval
counterclockwise path as seen in Figure 1. This belt travels from
the top of the downstream roll 30 to the left over to the top of the
nip roll 28 and then curves 180 in passing down around the upper nip
roll into the entrance to the casting region and moves toward the
right along the casting region C to the bottom of the downstream roll
30 and then curves 180 in passing up around this downstream roll.
Similarly, as the lower casting belt 16 is revolved, it moves in an
oval clockwise direction as seen in Figure 1. It curves 180 in passing
up around the lower nip roll 32 into the entrance to the casting region
and again curves 180 in passing down around the downstream roll 34
where it begins its return trip to the nip roll.
The outer surface of each casting belt which faces the
casting region (see also Figure 3) is called the "front" face F. The
surface facing inwardly toward the main rolls is
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10305Z8
called the "reverse" or "back" face R of the belt. The belts
lare made of relatively thin sheet steel, and the front face
often has a finely roughened texture produced by sand blasting.
'A coating of thermal insulation material is often adhered to !
Ithis roughened surface. f
!! The reverse surfaces of each belt are cooled by i
¦Ihigh velocity layers of liquid coolant, usually water, force-~
¦jfully propelled along these surfaces. An intense coolant
llflow is employed usually amounting to thousands of gallons
per minute to remove the large amount of heat being released ¦
as the molten metal is solidifying.
f In order to initiate these high velocity layers 43 f
~¦(FIG. 3) of coolant, the nip rolls 28 and 32 are formed with ¦
¦¦m~ltiple clo-~ely adjacent deep grooves 44 tas seen most clearJ
ly in PIGS. 3, 4 and 5) defining relatively narrow fins 4~ be~-
llween neighboring grooves. A plurality of curved wrap-around
¦¦coolant tube~ 48 and 52 having an oval cross sec'tion are
l nested in the respective grooves of the nip rollsi 28 and 32.
¦ As seen in FIG. 1, large diameter header pipes 50 and 54 are
¦ rigidly secured to the respective coolant tubes 48 and 52 and !-
feed coolant into these curved tubes. These cur~ed tubes
¦48 and 52 have been formed essentially to the same radius as
¦the associated nippulley and are cantilevered from the large
~rigid header pipes 50 and 54, respectively.
Near the entrance to the casting region, as shown
in FIGS. 3 j 4 and 5, the ends of the tubes 48 and 52 are
formed into nozzles 56 positioned close to the reverse face
R of each belt. These nozzles are aL~ed at small angles
ill
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approaching tangency toward the reverse belt face R. The
cross-sectional area of the nozzle bore is substantially ¦
'less than the oval passages within the tubes 48 and 52, so
that each stream 57 of coolant issues from its nozzle 56 at i
,high velocity. The fingernail-like extensions 61, which are ¦
'attached to the nozzles 56, are novel and their purposes
,and functions will be described further below. These finger-
,!nail extensions 61 are shown more clearly in FIGS. 6 and 7.
i As shown in FIG. 3, the molten metal 55 from the ¦
"eundish 12, passes through an insulated spout 58 which is
;aimed directly into the entrance E to the casting region.
~The end of this spout is shown projecting into the casting
¦,~entrance slightly beyond a line 60 joining the axes of the
Irolls 28 and 32. In other words, the end of this spout 58
Illis positioned just beyond the point of tangency of the belts ¦ ¦
14 and 16 and their respective nip rolls 28 and 32. m e
entry E of the casting region begins at the exit face of the
nozzle 58. The molten metal 55 initially comes into contact
¦,with the front faces of the casting belts at the entry E.
¦~ For further information about twin-belt casting
¦machines, the reader may refer to the United States patents
listed in the introductory portion of the specification.
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Det-ailed Description and Analysis of Prior ~rt
¦ In a prior art twin-belt ca,sting machine, belt
iidistortion could occur under certain operating conditions
hear the hot entrance to the casting region, as illustrated
,'in FIG. 8. This distortion or transverse buckling, as in- !
¦~dicated at 62, could occur momentarily or more or less conti-
Inuously, depending upon operating conditions, and was caused
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by restraint of the transverse thermal expandion of the
casting belt near the hot entrance by cold framing on three
sides 71, 72 and 73 of this buckling region. The transverse
'buckling 62 (FIG. 8) was principally caused by the transverse'
cold framing occurring in the region 71 ahead of the initial ,
l'line 64 of contact of the molten metal with the casting belt.,
I' The prior art practice of applying insulative
coating on the front belt face and of maintaining substantial'
i longitudinal tension 63 across the full width of the belt did
¦Iminimize distortion over a majority of the casting region.
i~Nevertheless, these prior art practices often did not elimi-
jnate transverse buckling at 62 in a region just downstream
i,from the entrance E, as will be explained.
I In the prior art as shown in FIG. 8, the lower ¦
l~casting belt is indicated by 16' and the lower nip roll by 32il.
¦jThe entrance region E extends transversely across the belt
¦,~approximately along the position of the line 64 of initial
¦Imetal contact. The cold regions of the belt are shown by
l!dotted shading. The full width of the belt as it wrap~ around
l¦the nip roll 32' was cold. It was chilled by the nip roll
¦¦itself, which approached ambient temperature. Also, the
belt was chilled by the coolant stream~ 57 which struck the
reverse surface R many inches ahead of the line'of tangency
1 60 (FIG. 3), for the fingernails 61 wer~ absent in the prior ; '~
- 25 ~ art.
¦1 As shown in FIG. 13, in the prior art, twin-
,!belt caqting machines, the streams of coolant 57 from the noz
.,
zles 56 were applied'directly to the reverse surface R of ~he
cas~ing kelt 16'. To assure that the coolant was adequately
'spread out on the belt and was closely hugging against the
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belt, the nozzles 56, in the prior art, were positioned a
substantial distance ahead of the line 64 at the entrance E
to the casting region C where the molten metal first came
into contact with the casting belt. The shaded areas 106
. .
in FIG. 13 show the pattern of the coolant spreading out
'against the reverse belt surfaces, and this occurs a substan-
tial distance and a substantial time before the contact line
64 of molten metal occurs m e coolant spread out in the
l,channels between the respective narrow ridges 46 of the roll
l32'. As a result of the substantial length of travel of the
i,coolant pattern 106 along the casting belt, the region of the
belt 71 ~FIG. 8B) ahead of the casting region was markedly
chilled by the coolant. m us, the full width of the belt
as it approached the entrance E formed a first cold frame 71
~FIG. 8).
i The initial cold condition of the belt is shown
,¦in FIG. 8A by the low level of the longitudinal temperature
¦jprofile curve 81. After the belt passed the entrance line
l,164 at E, the molten metal 55 came in contact with its front
¦~face F. The temperature of the belt rapidly rose up after
contact with the molten metal, as indicated by the upwardly
¦sloping profile 82. Soon the mean temperature of the main -
¦central portion of the belt reached the elevated level, as
¦indicated by the elevated profile at 83.
! The shaded edge portions 72 and 73 indicate two
,more cold frames. These edge portions 72 and 73 project
outwardly beyond the side dams, and they remained substantial-
ly at ambient temperature along both edges of the casting
region.
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The temperature profile extending transversely
' across the belt along the section 8B-8B is shown in FIG. 8B. i
The low level portions 92 and 93 of this profile indicate i
' the ambient temperature of the two edge portions 72 and 73. i
1i The elevated central portion 94 shows the elevated mean
temperature of the hot main central portion of the belt in
the casting region.
~ Accordingly, the main central portion of the
¦Ibelt after passing the line 64 of initial metal contact
I rapidly rose (as at 82j in temperature and correspondingiy
attemped to expand. The cold frame portions 71, 72 and 73
restrained this expansion. The edge framing 72 and 73
~lrestrained the longitudinal expansion somewhat, but this
jledge framing was mostly overcome by the high longitudinal
¦Itension 63 used in the prior art. The lead-in, or pre-
lentrance, transverse, cold framing 71 imposed a severe res-
traint on the expanding belt, causing ~rior art distortion
~! or transverse buckling 62 to occur just downstream from the
I initial metal contact line 64 at the entrance E. The amount
I of buckling 62 depended upon the operating conditions, but
generally it increased with the melting temperature of the
metal 55 being cast. ~
Also, the sudden rise in temperature 82 (FIG. 8A)
I subjected the belt and its coating to thermal shock and
¦ differential expansion stresses.
Elevation of Casting Belt Temperature Before
Initial Contact with MolteN Metal
Il _ .
In order to overcome this problem of distortion
~!or transverse buckling closely downstream from the entrance E¦
,dueto transverse restraint of this region's thermal expan~ion
10905Z8
in accordance with the invention, the temperature of each
' casting belt is elevated ahead of the line 64 and the appli- I
!i i
cation of the coolant streams 57 to the re~erse surface may
~,be sharply defined and precisely controlled so as to be
,lapplied to the belt at a line closely related to the line 64 ¦
i of initial metal contact with the belt. This control of
the coolant will be explained in greater detail further belowJ
l' In order to elevate the temperature of the casting
¦¦belts, as shown in FIGS. 1 and 2, a first bank 66 of multiple
llradiant heaters 68 held by supports 67 is mounted to heat the~
l~upper stretch of the upper belt during its return trip toward
¦Ithe top of the nip roll 28. This first heater bank is mount-¦
ed on the upper carriage structure U and is positioned to
commence heating the upper belt 14 an appreciable distance
- 15 llahead of the nip roll 28 for significant pre-heating (and
transver-~e expansion) to occur before the belt 14 encounters
¦nip roll 28. In this embodiment, the intensive radiant pre-
l¦heating of the upper belt begins at a point approximately
!!equidistant between the downstream pulley 30 and the nip pul-
~lèy 28.
jl Heaters 68 may be electrically energized or they
may be fossil fuel fired, for example gas fired, of the so-
called flameless radiant type. It is preferable to use elec-
¦trical energy if it can be obtained economically because ther
¦is no chance thereby of contaminating the coating on the fronti
iface of the belt. Flameless gas fired radiant heaters can
'!be used satisfactorily if the fuel flow rate i9 carefully ad-
~usted so that there are no tongues of flame issuing from the
l¦burner housing 68.
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10905Z~
i, The radiant heaters 68 are capable of providing in- i
~Itensive radiant energy and are positioned closely adjacent
¦and parallel to and uniformly spaced from the front belt
Isurface, and they include polished reflectors 69 extending
llacross the width o~ the belt for reflectively directing as
¦much of the available radiant energy toward the belt ac~ I .
possible. It has been found to be of advantage to mount all
heaters at a small spacing from the front face F of the belt.
~¦For example, a small spacing of approximately one inch from
lO I~the front belt face F has been found to work to advantage with'
jlthe reflectors 69 aimed at an angle of incidence perpendicular,
¦Ito the belt face F.
A second bank 76 of similar heaters 68 is similarly ¦
!¦mounted by means of an arcuate support 77 along a curved path ¦
¦¦nested about the nip pulley 68. This second radiant heater
~bank 76 further heats the belt 14 as it is travelling down
around the nip roll 28.
Similarly, for heating the lower stretch of the
,lower belt during its return trip toward the bottom of the nip~
~oll 32, there is a third bank 86 of similar radiant heaters
¦68 ~ mounted by a support 87. ThiCt lower ban~ 86 is
~ositioned to begin heating the lower be}t 16 an appreciable
. distance ahead of the nip roll 32 for significant pre-heating
¦I(and transverse expansion~ to occur before the belt l 6
~'encounters the nip roll 32. In this embodiment, the intensivle
¦radiant pre-heating of the lower belt begins at a point approxi-
¦1 tely equidistant between the downstream roll 34 and the nip
¦loll 32. A fourth bank 96 of similar heaters is mounted by
l_ ans of an aFcuate support 97 in curved relationship nested
' ' ' .
il I .
,l -20-
i~ ~0905Z8 .
about the nip roll 32. This fourth bank 96 further heats I
, the lower belt 16 as it is travelling up around the nip roll !
32. 1-
These heaters are connected so that the four
banks 66, 76, 86 and 96 can be independently controlled.
The first and third banks 66 and 86 are used to pre-heat
the stretches of each belt before the belt begins to wrap
around the nip roll 28 or 32. The second and fourth banks ¦
l~76 and 96 serve to further heat each belt while it is in
, contact with its nip roll.
If more than sufficient pre-heating i~ being
obtained for casting a particular product, then the number
~ of heaters 68 for each belt may be reduced. Also, one of
Iithe banks 66 or 67, 86 or 96 for each belt may be energized ¦
llwithout energizing the other bank. However, for most cases,¦
it is believed that it is preferable to utilize a relatively ¦
large number of heaters ~paced over a relatively large seg- ¦
llment of belt travel, as shown, so that the elevation ln belt '
¦¦temperature is accomplished relatively gradually to min~ize ¦
,Ithermal gradients and to minimize differential expansion.
In addition, by vi~tue of the fact that the radiant heat is
being applied to the front face F of each belt, it can be
used to cure or dry any coating material applied to the belt.
!l Zone ~ontrol of 8e1t Pre-~-eating
~¦ In the machine shown in FIGS. 1 and 2, the heaters~
68 are all controllable with respect to three zone~. The
first zone 1 (FIG. 2) spans transversely across the main
'central portion of each belt for a width equal to the width ',
iof the casting region C. The second and third zone-~ (2) an~
i !
i
--2 i--
il lO905Z8
, . ,
(3) span transversely across the respective edge portions - I
,o~ each belt outside of the casting region. The second ~
and third zones of each heater are ganged together so that the
two edge portions of each belt can be correspondingly and
S equally pre-heated independently of the amount of pre-
heating being applied across the main central portion 1 of
each belt.
. . .
l~ Controlling ~he Coola~t Streams from the Curved
~! Nip Roll Tubes to Aid Belt Pre-Heating ' I
!~ In order to enhance the effect of the pre-heatingl !
of each belt, the fingernail shields 61 ~FIG~. 6 and 7) may
be employed. These shields 61 are attached by welding or
brazing at 98 and 99 to the nozzle 56 of each of the ¦ ;
~l,curved coolant tubes 48 and 52. These fingernail extensions j
11 61 are generally rectangular in shape and they are sharply
tapered to a precise edge 100 extending sufficiently far down, ;
~,stream from the nozzles to form the coolant streams into
lilayers before applying the coolant to the belt. In this
¦¦machine, the fingernail extensions project more than two
!¦inches beyond the end of the nozzle 56. These fingernail
~¦shields 61 have a width just slightly less than the width
of the groove 44, as shown in FIGS. 4 and 5. They provide
¦¦controlled and delayed application of the coolant to the
~'reverse face R until the desired point, for example just
llimmediately before the belt tangent line 60 (FIG. 3~. In
~this illustrative embodiment, the coolant streams 57 do not ~ ~ `
contact the pre-heated belt until approximately one-half
inch or less before the molten metal contacts the belt.
The action of these nozzle tube extensions 61 may ¦ -~
0905Z8
be more fully understood from a review of FIG. 14. The
,~ ,
coolant streams 57 strike the extenders and spread out ~ i
laterally across them, as shown by the curved patterns 108.
A uniform layer of coolant is thereby formed before the
travelling liquid reaches the edge 100 of these extenders.
The fast moving layer of coolant leaves the edge 100 and
travels a short distance before coming in contact with the
reverse surface of the belt. The pattern which this coolant
forms in engaging the belt is shown by the shaded area 110
,' in FIG. 14. It is noted that the line 109 where the coolant
initially contacts the belt is accurately defined as compared
with the curves 106 (FIG. 13). Accordingly, the well defined
l line 109 enables the coolant application to be accùrately
! controlled and to be positioned close to the line of tangency
60, where-the belt is separating from the ridges 46 on the
, roll and also to be positioned close to the line 64 where th !
i' molten metal contacts the front face of the belt.
.,lj ,
As seen enlarged in FIG. 7, the inner surface
', 112 of the extenders 61 is smooth and is tapered by grinding
l,~ to form a sharp edge 100- The outer surface 114 of the
extenders is curved in a gentle arc commensurate with the ar i
~¦ of the belt so that the tip 100 can be positioned closely adl
¦I jacent to the surface of the casting belt, as shown in FIG.3.¦
ll It is important that effective cooling action be
, present on the rear ~urface of the belt at or near the
, position 64 (FIGS. 8 and 14) where the molten metal initially
i! comes into contact with the front face of the belt.
~l When the extensions 61 are used, the nozzles 56
i' at the ends of the curved tubes 48 and 52 are enabled to be
' positioned significantly farther downstream near the molten
1 metal line 64 as compared with the bare nozzles 56 of the
Il prior art, because of the increased control over the coolant
"
, ~ .
,, -23
, ~09OSZ8
~
stream patterns.
. Consequently, the fingernail extenders 61 serve
the functions of spreading out the coolant to form a layer
', while at the same time preventing the coolant from prematurely
l'engaging the belt. By virtue of the fact that the coolant ¦
is formed into a stabilized layer, its application to the belt
' 16 can be delayed until line 109 which is located only a
.ismall distance before the line 64 at which the molten metal
i contacts the belt. ¦
!
l' A Number of Beneicial.Ef~ects..of.~re~
' Heating the ~asting Belts - ¦
,. The advantageous results of pre-heating the beltj
plus controlled and delayed applicatlon of liquid coolant to
¦Ithe belts is shown in FIGS. 9 and 9A. The longitudinal
'ibelt temperature profile has a steady rise along the curve ¦
101, so that substantially full operating temperature and ful,
Ipre-expansion occurs in the pre-entrance region. As shown
by the arrows 104, the full transverse pre-exapnsion has
lloccurred before the casting belt reaches the tangency line at¦
~,the entrance.
' A very narrow cool transverse section 102 may bel
~produced over the narrow band 110 (FIG. 14) where the coolant¦
jcontacts the belt before the molten metal contacts the belt.
j¦However, this cool transverse section 102 is so narrow that
I'it does not have any significant restraining effect on the
,Ibelt. The pre-heated, pre-expanded belt being stabilized by
',~lying curved around the nip roll 32 completely dominates the j
narrow cool band 102. Very quickly the belt temperature
rises back up at 103 to its full operating temperature. The
', .
"
~. ~
-2~-
` ~ lO905Z8
'beneficial effect is to eliminate or minimize to an insigni-
'ficant level the tendency of the belt to distort-or buckle.
Thermal shock to the belt and its coating are minimized and
stresses due to differential thermal expansion are minimized.,
Other beneficial effects and advantages are discussed
elsewhere.
Pre-Heating of Casting Belts in Twin-Belt
Machines Having More than Two-Main RoIls
in Each Carriage
,l The twin-belt casting machine 10A shown in FIG. ld
includes more than two main rolls in each belt carriage U and'
L. For clarity of illustration, only the input or upstream
"end of the machine is shown. There are nip rolls 28 and 32 -
,having deep grooves 44 with narrow ridges 46. Belt-tensioning
l~rolls 200 and 202 serve to apply tension to the casting belts
14 and 16. Other main rolls ~not shown~ are located at the ¦
downstream end of the machine.
The molten metal feeds from a tundish 12A through
~a spout 58 leading into the machine in an injection feeding
" .
20 li arrangement. For further information about twin-belt cast-
ing machines with injection feeding and having more than two
main rolls in each carriage, the reader may refer particularl~
to Patents Nos. 3,167,830 and 3,310,849 among those listed in ¦
Ilthe introduction. The first of these patent~ ghows a ~three-
2~ Ijroll" machine and the second shows a "four-roll~ machine.
~1 A bank 66A of infra-red heaters 68A mounted on
¦3a support frame 67A serves to heat the stretch of belt 14
~between the main rolls 200 and 28. Additional heaters, such
,as shown at 68A', may begin heating the belt while it is stil~
,,travelling around the roll 200 preceding the nip roll 28.
These heaters 68A and 68A' are shown as being fossil fuel
fired, in this example they are gas fired, and they are mount
,.. I'
;, ~, . I
19~528 '
~ed to be spaced only a small distance from the front face of
;the belt 14. These heaters are of the flameless gas burning
,type producing intensive infra-red radiation. If desired,
, ,electrically energized heaters 68A may be used in lieu of
,fuel-fired ones. ~
, The heater support,67A is pivoted at 204 to a
,''mounting frame 206 which is connected to the upper carriage
,' U. A position adjustment mechanism 208 extends between the ,
~!fixed mounting 206 and the pivoted heater support 67A. Thus,l
'lthe position of the heaters 68A and 68A' can be set in accord
,~~ance with the position of belt 14 as determined by the adjust
!,, able belt-tension roll 200. - ¦
Il Another bank 86A of similar heaters 68A mounted ~
,on a support frame 87A serves to heat the stretch of the belt¦
lS jll6,between rolls 202 and 32. The support-87A is pivoted at ,
i,205 to a mounting 207 for the tundish 12A. An adjustment ~
!~'mechanism 209 extending between the fixed mounting 207 and . i
- j'.the pivoted heater support 87A serves to adjust the position !
I,of the heaters 68A, in accordance with the location of the ¦
~Ibelt as determined by tensioning roll 202. The heaters 68A ~
¦,,on the frame 87A extend generally vertically and are trans- ¦
versely inclined to provide uniform o~erlapping pre-heating .¦
jeffect on the belt 16. This mounting arrangement of the I
Illower heaters-is accommodating to the limited available space ¦
~Ibetween the tundish mounting 207 and the lower carriage L.
¦Insulating pads 210 and 211 are shown attached to the tundish !
mounting 207 to avoid over-heating of this mounting by the
'bank 86A of intensive infra-red heaters directed at the front ¦
!'j'face of the belt 16.
0 j, The curved coolant tubes 48 and 52 extending
!from header conduits 50 and 54 and nested within the roll
'jgrooves 44 may be equipped with fingernail extenders 61
, -26-
- . !
` 1090528
. ~
i . 1-
i similar to those described above.
Whereas the belts 14 and 16 in the machine 10
travel approximately 180 around the nip rolls 28 and 32,
the belts in the machine lOA (FIG. 10) travel approximately
1i 90 around their nip rolls. In spite of this difference
between the machines and the differences in arrangement and
'mounting of the heaters 68 and 68A, the advantages and effects,
~of the belt pre-heating in the machine lOA are similar to
those described above for the machine 10.
,,~ . I
,, Additional Methods and Apparatus for l
l Pre-Heating the Castinq-Belts
As shown in FIG. 12, the casting belts can be pre-
i heated by heating the nip rolls 28 and 32 in either the
,'machine 10 or lOA. This pre-heating of the nip rolls can be ¦- i
!~ carried out in conjunction with the use of the radiant heaters
68 or 68A, if desired. Alternatively, the heating of the
lnip rolls can be carried out without the use of the radiant
heaters. ~t is preferred that the radiant heaters be
Ilutilized because they ~erve to heat the fron~ face of the bel~
l¦which is the same surface as co~e~ in contact with the molten
¦metal.
1, As shown in FIG. 12, hot heating fluid, such as
¦Isteam, is supplied through an insulated pipe 160 connected to --
lia passage 161 within a stationary gland memhier 162. This
~,passage 161 communicates through an opening 164 with an axiall
,llpassage 165 in a rotating gland member 167. The passage 165 !
is connected to a distributor pipe 166 extending axially
~through the hollow nip roll, such as roll 3~ shown. The far
~!end of the distributor pipe 166 is supported by an annular
,shoulder 168, and there are a plurality of orifices 170 at
,,
~'.
,~
I
-27-
~.(19(~528
spaced points along the length of the distributor pipe 166. mese
orifices 170 eject sprays 171 of the hot fluid directed against the
inner surface of the hollow roll 32.
me spent fluid returns, as indicated by the arrows 172,
through the annular space 173 within the hub portion 174 of the roll
32. me revolving gland member 167 is screwed at 175 into the hub
174 and has a plurality of radial passages 177 communicating with a
channel 178 in a second stationary gland member 180 connected to a
drain pipe 182. me hub 174 is supported by a bearing 184 in the carriage
frame 186. Bearings 181 support the stationary gland 180 on the rotating
gand 167, and a pair of sliding seals 183 are located on either side of
the channel 178. A bearing 187 supports the stationary gland 162 on the
projecting end 163 of the rotating gland 167 with a sliding seal 188
between these glands.
Another method for pre-heating the casting belts is to inject
hot fluid, for example such as dry steam, which may be superheated, if
desired, directly into the nip roll grcoves 44 beneath the reverse
surfaces-R of the casting belts. me manner in which this hot fluid
is injected into the grooves 44 is to position conduits (not shown) near
the header pipes 50 and 54 in the machine 10 or lOA. Nozzles for the
hot fluid (not shown) are connected to such conduits similar to the way
in which the coolant tubes 48 and 52 are connected to the headers 50
and 54. mese hot fluid nozzles are aimed into the spaces around the
coolant tubes within the respective grooves 44, and the coolant tubes
48 and 52 are insulated from this hot fluid.
Insulating the Nip Rolls
While the fingernail extenders 61 mask off the coolant from
the belt, it is to be noted from Figure 14 that the coolant layers 108
may strike the side surfaces of the ridges 46 on the nip rolls, producing
a cooling action on the roll itself. Since the nip rolls have substantial
arcs of
- 28 -
. 10905Z8
, !
contact with the belts, this cooling effect is conducted into
the belts.
In order to insulate the grooves 44 from the .
coolant, a thermal insulation coating 190 (FIGS. 4 and 5~ can
be applied, as by painting or spraying, to cover the side
walls and bottom of each groove 44.
Alternatively, the rim portions of the ridges 46
can be fabricated as rings (not shown) separate from the main' ¦
body of the nip roll. These rings are then mounted onto the
nip rolls with a layer of insulation material thermally ,
isolating the rim portion of each ridge 46 from the remainder
of the nip roll.
Belt Pre-Heating Control Methods and Apparatus
'i In order to provide precise control over the 1,
,~pre-heating of the belt, and in order to sense whether any
transverse buckling 62 (FIG. 8) is occurring, mechanical
'sensors M and thermal sensors T (FIGS. 1, 9, 10 and 11) may
~be installed.
~ The mechanical sensors M include push rod~ 116
,,~FIG. 11) mounted in bore holes 118, drilled into coolant
¦applicator and scoop members 120. These coolant applicator ¦
~! and scoop members 120 are generally similar to tho~e shown in
United States Patent No. 3,041,686, mentioned in the intro-
~,duction. The end 118' of each bore hole 118 near the belt
25 i8 of reduced diameter for providing a close but loose slidinc
fit with the probe rod 116. The reduced bore 118' serves to
support and guide the end 117 of the probe engaging the
reverse surface R of the casting belt 16. At the other end ¦
i of the bore hole 118, spaced away from the casting belt, there
, , I '-
,., ~
~, . I
1'
-29-
1090528
is a collar bushing 122 secured to the probe rod 116. This
collar bushing has a sleeve portion 124 extending into the
bore 118. These sleeve portions 124 provide a close sliding
' fit for guiding the other end of the probe rod 116. The
~ colIar 122 acts as a stop to limit the amount of the tip end
117 which can project from the memb~ers 120.
Spring means 126 urge the pro~es 116 toward the'
belt. This spring means 126 is formed ~y a block of resilient
l,material, such as rubber, seated in a socket 128 in a mounting
j~bracket 130, attached to a coolant header conduit 132. An
electro-mechanical transducer unit 134 is attached by screws ,
136 to the mounting bracket 130. This transducer 134 has a j
movable element 138 engaging the end of the probe rod 116. ¦
IThus, movement of the probe rod 116 produces a corresponding ¦
,movement of the element 138.
i Within each transducer unit 134 is means for
converting the amount of displacement of the movable element ¦
138 into a corresponding electrical signal. This means for
I~converting mechanical movement into an electrical signal may
l~utilize an electromagnetic or a piezo electric or a reluctanc
lprinciple similar to the manner in which the motion of a
¦phonograph needle is converted into a corresponding electric j
signal. The particular mechanical-to-electrical transducing
l¦means utilized in the units 134 is not being claimed and so
~! it is not described in further detail. :
¦l~ Any buckling of the belt displaces the push rod
116 causing a corresponding movement of the element 138.
~'This tion of the element 138 causes the transducer 134 to
',generate an electrical signal as a function of the movement, ',
liand this electrical signal is fed from the unit 134 through
- an electrical cak,le connection V.
,,1, . .
.,', . ,
-30-
lO905Z8 l
There is a fast mov~ng film of coolant 43
(FIG. 3~ travelling along the reverse surfaceg of each of thel
,belts 14 and 16 in FIG. 11. This coolant film is omitted ~,
,from FIG. 11 for clarity of illustration. There are gutters,
,140 provided for removal of the excess coolant as shown in
FIG. 11, and their operation is described in detail in U.S. I
,,Patent No. 3,041,686, mentioned above. I
! The thermal probes T, as shown in FIG. 11,
include a probe member 142 having a thermistor therein adapte~
,to engage the reverse surface of the casting belt. The r
probe member 142 is movably mounted in the bore of a housing
144, and a spring member 146 seated in this bore urges the ¦
probe li2 against the reverse surface of the casting belt.
!,The thermistor in the temperature probe'l42 provides anelec- ¦
,trical signal as a function of the temperature of the reverse¦
'surface of the belt. This eleçtrical signal is fed from the
!!
"respective thermal probes through electrical cables W.
, A firqt thermal probe is positioned closely ad- ¦
,jjacent to the nip rolls, as seen in FIGS. 1 and 10. This
llfirst thermal probe Tl is shown in detail in F~G. 11. The
first mechanical probe M has its probe rod 116A mounted at an
~iangle in a support 19~. By virtue of being mounted at this
, ~,angle, the tip 117A of'the probe 116~ engages the reverse
- ¦Isurface of the casting belt relatively close to the line 64 t~G.14)
I,at which the molten metal first contacts the casting belt.
As illustrated in FIGS. 1, 9 and 10, there are
'three thermal probes T, indicated by dots in FIG. 9, and four
~mechanical probes M, arranged in a row. There are a
plurality of these rows of probes positioned across the width !
, , . l
,,i . I ..
'' -31- , I
1 - 109052~1 1
!!
of the casting belt. For example, FIG. 9 shows six rows of
¦Ithese mechanical and thermal probes T and M. The housings
144 of the thermal sensors are shown mounted on support
l!members 194 in the belt carriage which are secured to the con
¦lduits 132 connected to a frame member 186. The support 196
¦¦for the first mechanical sensor is shown connected to a frame
member 194 by a diagonal brace 197. A curved shield plate ~
198 is positioned near the ridges 46 of the main roll. This !
plate 198 shields the first thermal sensor Tl and the nearby
fir~t mechanical sensor Ml from any drops of coolant which
¦may be carried by the ridges 46. The finned belt-guiding
rollers, which are sometimes called belt back-up rollers, are~ ¦
shown at 192. ¦ !1
, - . .~
I As diagrammatically illustrated in FIGS. 1 and
¦10, in order to provide automatic control of the pre-heating ¦
__ I of the casting belts, the various electrical cables V and W I ;
from the mechanical probes M and thermal probes T are connect
ed to a control circuit 150. These control circuits -~erve to ¦
~ontrol the energization of the banks of infra-red heater~ 66
76, 86 and 96 and 66A and 86A. In addition, these control 1 I
_ = circuits 150 may al o control the relative energization of ~ '-
the center zone 1 and the two end zones 2 and 3 (FIG. 2) of
these heaters.
l It is to be understood that the heaters 68A of ¦
the machine lOA in FIG. 10 can be arranged for zone control
¦similar to that described for the heaters 68 in the machine 10.
FIG. 11 ~hows the molten metal 55 and the ¦
l solidifying skins 212 of solidified metal gradually forming ¦
¦ adjacent to the facing surfaces of the respective belts 14 and
16. It is to be understood that this representation of the
l¦solidifying shells 212 is for purpose-~ of illustration and
¦lis not drawn to scale. The solidification rate in the cast- ¦
I r I
' ! ~
5Z8
in zone C depends upon many factors, including the composition of
the molten metal 55, speed of the machine, thickness of the casting
being made, and so forth.
Various Controlled Belt Pre-Heating Methods
and Arrangements
Various controlled belt pre-heating metho~sand arrangements
can be employed as will be explained in connection with Figures 15A,
B and C and Figures 16A, B and C.
Figure 15A corresponds with Figure 9A and shows the method
of pre-heating the casting belt in which there is a narrow region 102
of slight cooling produced by the narrow area of coolant 110 (Figure 14)
which contacts the casting belt slightly before the molten metal.
If desired, the relative positions of the nozzles 56 and
fingernail extenders 61 and the end of the spout 58, Figures 3 and 10,
; where the molten metal first contacts the belt, can be arranged so
that the position 109 (Figure 14) where the controlled coolant first
contacts the reverse side of the belt almost coincides with the line
64 where the molten metal first contacts the front face of the belt.
When this adjustment is achieved, the result is to provide a pre-heating
pattern as shown in Figure 15B, in which the pre-heating tem~erature
curve lOlB directly meets with the temperature curve 103 downstream from
the entrance to the casting region. In other words, Figure 15B shows
an actual continuity of the pre-heating temperature profile with respect
to the temperature profile in the casting region.
If desired, the pre-heating of the casting belt can be carried
out to a higher temperature lOlC, as shown in Figure 15C, in other words,
a temperature overshoot 105 is provided. The result of this temperature
overshoot is that the pre-expansion 104 (Figure 9) is greater and thereby
tends to stretch the casting belt transversely to assure that the belt
is held flat at the entrance to the casting region.
- 33 -
' 1CrJ0 5 ~ '
FIG. 16A shows.a transverse temperature profile
curve 92, 93, 94 taken along the plane 16A-16A in FIG. 9.
;The edge portions of the belt as shown at 92 and 93 are much
cooler than the mean temperature 94 of the main central area
s 'of the belt near the casting region. If desired, as shown
in FIG. 16B, the edge portions of the belt in the zones 2 and !
',3 (FIG. 2) and corresponding zones in FIG. 10 can be pre- ' I
'heated to provide a transverse belt temperature profile, as ~ .
,'shown in FIG. 16B, in which the temperature profile 928 and
.l93B of the belt edge portions is more nearly equal to the
temperature profile 94 of the center portion of the belt.
There is some loss of heat from the edge portions of the belt ,
.such that when the edge portions are pre-heated to the same
''temperature as the center portions, some cooling of the edges
!will occur as'the belt moves along through the casting region.
.This edge cooling explains the profile shown in. FIG. 16B in
which the level of temperature in the edge portions 92B and
93B is somewhat lower than the central temperature profile 94.
1l If desired, as shown in FIG. 16C, a temperature ¦
~lovershoot can be provided in the heating of the edge portions ¦ .
,,as shown by the temperature profile 92C.and 93C. m is tem- ' .
Iperature overshoot compensates for the subsequent cooling of
,the belt edge portions as the belts travel along the casting ..
Iregion. -
! As a further step for heating up and maintaining . .'the temperature of the edge portions of the belts 14 and 16,
'~the coolant application nozzles 2i4 (FIG. 11~ from the coolant~
conduits 132 may be selectively temporarily blocked off by
lug means, such as screw plugs inserted into the bores of t
'these nozzles. m e nozzles 214 are selectively blocked off
.
i ' , i,
-34-
lO905Z8 1-
....... ...........................................................
with respect to the edge portions of the casting belt lying
outside of the casting region, i.e. in the regions corres-
ponding with zones 2 and 3 in FIG. 2. Thus, the cooling
applied to edge portions of the belts associated with the
temperature profiles 92, 93 or 92B, 93B or 92C, 93C in FIGS.
16A, B or C is minimized. In the region ~zone 1) corres-
ponding with the main central portion of each belt passing
adjacent to the casting region, the nozzles 214 remain open
, to apply and propel the coolant along the reverse surface of ¦
1`0 ~~ the casting belt.
If the distance between the side dams 18 is
increased for enlarging the width of the casting rgion C
to cast wider product, then corresponding ones of the nozzlesl
. 214 are unplugged to apply the coolant across the full width i
of the wider casting region, and vice v sa. Also, if such
a change in casting width is made, the zone control for the
~heaters 68 or 68A may be correspondingly adjusted.
The Methods and Apparatus of the Invention Can
,1 Be Applied to Twin-Belt Machin-es of All Types
1 Although FIGS. 1, 3 and 10 illustrate twin-belt
~casting machines in which the molten metal is supplied to the
llcasting reg~on by injection feeding, it is to be understood
llby those skllled in the art that the methods and apparatus of~
I! the invention can be applied to twin-belt casting machines
,~regardless of whether the feeding of the molten metal is by
¦open pool, closed pool or injection feeding. In the cases
of an open pool or closed pool feeding, the nip roll for the !,
lower casting belt may be located farther upstream than the
nip roll for the upper belt. These relative possible posi-
30- ''tions of the nip rolls are shown in patents 2,904,860;
,., I .
-35-
~ 10905Z8 ~ , I
13,036,348; 3,123,874; 3,142,873; 3,228,072; and FIGS. 14A,
14B, 14C, 14D and 14E of patent 3,167,830. The me~hods and
apparatus of the invention are arranged accordingly.
Mean Belt Temperatures are Il}us- i
5trated and Described
The varii~us belt temperature profile curves and
associated description illustrate and describe the mean tem-
peratures of the belt as taken in a section through the thick
I ness of the belt at any given location. It is to be under- I 10 llstood that there is a temperature gradient throug~ the thick-i
ness of the belts as seen in FIGS. 3 and 11. The front face
F of the two belts adjacent to the molten metal 55 or the
solidifying metal 212 in the casting region C are quite hot. ¦
~ The rear faces R adjacent to the liquid coolant are much coolt
! er. Thus, it is to be understood that the specification, dra*-
ings and claims are speaking about mean belt temperatures.
For example, in FIG. 15C, the temperature over- ¦
shoot 105 indicate~ that the mean belt temperature along the
'~profile curve lOlC is elevated above the mean belt temperatur
along the profile curve 103.
The temperature sensors T are sensing the
temperature of the rear surface R. Because the temperature
of the metal being cast is known, the mean belt temperatures
llcan be estimated by using these sensors.
il - In the case of the reglons of the belt approach-
iiing the nip rolls, sensors T' (FIGS. 1 and 10~ can be in-
llstalled to engage the belt before it reaches the nip roll.
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,
.. Addition~l Methods for Insulating
the-Nip Rolls
The insulating of the nip rolls is discussed
in the specification further above. Additional methods for
''5 'insulating the nip rolls will now be discussed.
As will be understood from FIGS. 3, 4, 5, 12, 13
ana 14, the ridges 46 on the nip rolls 28 and 32 are re- '
latively narrow and the intervening grooves 44 are much wider~
.than these ridges. A method for effectively thermally in- !
10. ,sulating the nip rolls from the reverse surfaces of the belt
is the machining of a narrow secondary groove, such as
.illustrated in FIGS. 4 and 5 at 216 into the perimeter of eac~
ridge 46. Only one ridge is shown in FIGS. 4 and 5 with'
such a narrow secondary groove, and it is to be understood
'that these grooves 216 can be machined into the perimeter of
each ridge. ¦ i
ese secondary grooves 216 significantly reduce ¦
.the area of the perimeter of ridges 46 in contact with the
reverse surfaces of the casting belts, and thus these narrow
'secondary grooves effectively provide thermal insulation
.,directly at the interface between nip roll and belt......... ''
t If desired, the perimeter of the ridges 46 con-
.taining these narrow seconaary groove~ can bte hardened as
'by induction heat treating, to increa~e the wear resistance
I,of these ridges. This hardening of the metal offsets the
,!reduction in area of the perimeter of the ridges with respect
~to wear resistance.
.. .. . .
il In addit~on, a thermally insulative material,'for ¦
~jexample such as epoxy re~in, can be inserted into these narro~
secondary grooves 216.
.I These narrow secondary grooves 216 can be arranged
,
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1~90 5Z8
. I
to reduce the effective area of the periphery of the metal
ridges 46 to one-half or less of the area thereof previously !
in contact with the reverse surfaces of the belt. Thus, the
conduction heat transfer at this interface between nip roll
and belt by this secondary grooving method can be cut down
to one-half and less of that which would occur with the con-
figuration of ridges previously used.
~' A durable thermally insulative material, for
example such as epoxy resin or polyurethane, can be held in ',
,'the narrow secondary grooves 216 and project slightly beyond
,the perimeter of the ridges 46 under operating conditions to
prevent metal-to-metal contact between the belt and ridges
46. Where a thin layer of durable insulative material is
,applied to the perimeter of each ridge 46, to prevent metal-
to-metal contact between the belt and ridges 46, such a layer~
is Xeyed into the secondary grooves 216.
, Further AsPects of Controlling Belt Temperature
, In connection with FIG. 12 it is discussed
,'that the casting belts can be pre-heated by heating the nip
lirolls 28 and 32. Another way in which the heating of the
,'nip rolls can be utilized and controlled to advantage is to
lreduce the flow of heat from the pre-heated belts into the
,¦nip rolls. The heaters 68 or 68A (FIG. 1 or 10) elevate the
'Itemperatures of the belts, with the front faces becoming
I'elevated to a higher temperature than the rear surfaces.
IlThe heated nip rolls then serve to maintain the elevated
',temperature of the rear surfaces. In effect the heated nip
rolls are serving to stabilize the tem~eratures of the
,,previously heated belts. 'I
In connection with FIG. 15C overshooting of the J
,,elevation of mean belt temperatures is discussed. One
. . .
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, 1(~905Z8
desirable objective in this overshooting method is to pre-
heat the belts so that the temperatures of the metal surfaces
~of the belts adjacent to the coatings on their front faces
F becomes essentially the same ahead of the casting region
as it is in the casting region. Thus, temperature conditions
at the interface between the metal of the belt and the coat- '
ing on the belt are stabilized, and thereby thermal shock at
this interface is avoided, whereby belt o-fferating life is
extended.
It has already been discussed that the relative
positions of the nozzles 56 and the end of the spout 58 can
~be arranged so that the position where the coolant first
contacts the reverse side of the belt almost coincides with I ¦
the position where the molten metal first contacts the front
face of the belt. In some cases these components may be ¦
arranged so that the molten metal intentionally does contact f
the front face of the belt before the coolant contacts the
reverse æurface; however, there are critical limits to this
delayed coolant application. These limits on the amount of
'delayed coolant application vary with the thickness of the
~! :
metal in the belt and with the speed of movement of the belt,
a3 shown in the following table which pertains to casting
aluminum based metal. In this table "X thickness" means
'Itimes the thickness of the metal in the belt.
ll Belt Speed in Maximum Delay Distance
Feet per Minute for Coolant Application
~, 20 6 X thickness
3 X thickness
, Thus, for example, with a belt metal thickness
,of 0.050 of an inch at a casting speed of 20 feet per minute
,. !
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1~90528
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- the maximum delay distance for coolant application is 0.3
inch.
One reason why it is an advantage to delay
coolant application is that there are transient conditions
occurring where the molten metal and coolant are initially
contacting opposite sides of the belt. The insulative coat-
ing on the belt tends to delay the moment when the heat from
;,the molten metal reaches the belt metal, i.e., it is a
relatively slow response heating effect as compared to the
action of the coolant which is applied directly to the belt
metal to produce a relatively quick response cooling effect.
The delaying of the application of the coolant serves to i5
compensate for the delay when the heat reaches the belt
metal. Thus, both heating and cooling effects are cauæed
,. , ;
15 ;to commence at effectively the same moment on the belt metal
iin the casting region to enhance operation.
, The above table applies to casting aluminum
'Ibased metalæ. When casting metals having higher melting
temperatures, such as copper or steel then the permissible
lmaximum delay is correspondingly reduced. When casting
jmetals having lower melting temperatures, then the permissible
Imaximum delay is correspondingly increased.
In summary, depending upon the operating 1
Iconditions, the coolant may be initially applied to the ¦ -
ireverse surface of the casting belt within a range from a i --
small distance before, to a small distance after, the position!
I; , ~ , .
jlwhere the molten metal initially comes into contact with the
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- front face of the respective casting belt.
In connection with FIG. 11 it is discussed that
the coolant application nozzles 214 may be selectively
¦blocked off with respect to the edge portions of the casting
belt lying outside of the casting region. This is done to
minimize cooling of the edge portions of the belts to preservq
the pre-heated belt temperatures established ahead of the
entrance to the casting region. The objective is to maintain
lthe temperatures of the edge portions of the belt at least
~,as great as the temperatures in the belt across the full
width in the casting region.
A further method of preserving the pre-heat in
the edge portions of the belts is to apply hot liquid of
'controlled temperature to these edge portions while cold
j~liquid coolant is being applied to the main central portions
,of the belts in the casting region. The way in which this is j
,~accomplished is to insert an insulated pipe line (not shown)
into the coolant conduit 132 ~FIG. 11). This insulated pipe ¦
l'is connected to insulated localized chambers (not shown)
,,directly feeding the groups of nozzles 214 associated with
the two edge portions of the belt. Thi~ insulated pipe line
¦¦and localized chambers are arranged so that they do not
¦obstruct the flow of coolant to the remaining nozzles 214.
'IThe hot liquid used may be hot water.
¦¦ Since the coolant 11quid and hot liquid are
travelling longitudinally along the reverse surface of the I -
! belt at high velocity in a relatively thin layer, there is
,jvery little tendency for these different temperature liquids
,to mix at their common boundary.
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11)90528
With respect to FIGS. 1 and 10, it is to be
understood that the control circuits 150 can be used to
control the temperature of the hot fluid fed into the line ,
160 (FIG. 12) for controlling the temperatures of the
respective nip rolls 28 and 32 (FIGS. 1 and 10). Moreover,
the control circuits 150can also be used to control the
temperature of the hot liquid to be applied to the edge
portions of the belts as described in the preceding paragraph.
Extending Belt Operating Life
,, ;
Another aspect of extending belt operating life
will be discussed in connection with FIGS. 9, 9A and 14.
To provide background information for understanding this
~aspect, it is noted that in the prior art the casting belts, I
which are made of sheet steel, with insulative coating on the,
front face, tend gradually to become s~tretched longitudinally
during operation. This stretching occurs in the main central
'casting region of the belt relative to its edge portions.
IThus, over a period of time the belt may become very slightly!
~baggy or slack in the main central region relative to the edge
'portions. This stretching is caused by the thermal cycling
~of the main central region plus the flexing thereof occurring j
I~in passing around the main rolls. This slight bagging only
¦occurs when the operating conditions are so severe that the j
~thermal cycling and flexing cycling carry the belt metal into
¦its plastic deformation state as distinguished from the
llelastic deformation state. Whenever such slight bagging
,,becomes undue in amount for the casting operations being
carried out, then the belt is removed and replaced.
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As shown in FIGS. 9, 9A and 14, the initial
application of the coolant to each belt can be arranged
relative to the initial contact of the molten metal such
that there is.a narrow cool section 102 extending transversely
across the belt between the pre-heated expanded region 104 .
and the casting region. The control of pre-heating and
'.control of initial coolant application can be used to widen
or narrow this section 102 as may be desired. The thermal
.~expansion occurring adjacent to this narrow cool section 102 ,
';tends to stretch the metal of the belt in this narrow cool
section laterally. Moreover, this lateral stretching . ~ ¦
tendency occurs continuously during operation and progres-
sively for each incremental por~ion of the main central
.region of the belt, i.e., it is occurring cyclically and
,sequentially for each part of the main central region during
.each revolution of the belt. The result is that this lateral
I.stretching tendency compensates somewhat for the tendency of
,the belt to become baggy and thereby extends the belt oper-
lating life. ¦
1l . It is noted that the tendency of the belt to become
!i
'.,baggy increases with higher belt operating temperatures in the
casting regiondue to the combined effects of higher molten ¦ :
¦¦metal temperatures and the belt coating practices being
llemployed. Advantageously, the pre-heating 104 is controlled
land can be increased correspondingly to the higher belt
operating temperatures. Thus the lateral stretching ~ : .
.ltendency applied to this narrow cool section 102 can be
.,increased in the case of higher belt operating temperatures
,'to match and thereby to compensate for the increased
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~()9(~528
longitudinal stretching.
This lateral stretching can be considered as corrective
transverse stretching carrying the belt metal into the plastic deformation
state transversely to compensate for the belt metal being carried into
the plastic deformation state longitudinally. The corrective lateral
stretching is correlated to the longitudinal stretching and can be con-
trolled by the pre-heating teinperature applied to the belt and by varying
the size of the c~ol section 102. As a result the tendency toward bag-
giness, if occurring, can be compensated to the extent desired to extend
the belt operating life.
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