Note: Descriptions are shown in the official language in which they were submitted.
Z.3~8
The present invention pertains to a method and
apparatus for the manufacture of glass, especially flat glass,
and more particularly to a glass melting furnace and a method
of operating the same. Glass melting furnaces of one known
form comprise essentially two parts: firstly, a high tempe-
rature melting and refining zone, at the upstream end of which
the raw materials are introduced so as to be melted by heating
means such as burners and, secondly, a somewhat cooler
conditioning zone downstream of the first, in which the glass
is brought to a suitable temperature for withdrawal at the
downstream end of that second zone, as a preliminary to
subsequent operations.
The currents which develop in the molten glass in
; the furnace, as convection currents by reason of temperature
differences from point to point and also due to the withdrawal
of glass at ~he downstream end, produce and overall streaming
of the glass through the furnace. Especially in the
conditioning zone however there develops a downstream current
which occupies approximately the uppermost one-third of the
depth of the glass bath, beneath which a return or upstream
current exists occupying the deeper two-thirds of the bath
depth.
It has been heretofore proposed to introduce into
.
the furnace mëchanical or thermal barriers, fixed or floating,
which extend across the entire width of the furnace so as to
separate the glass bath into two parts and in particular to
~` block flow of the surface layers, and to permit withdrawal
of glass from the cooler, bottom portions of the bath. One
such construction is shown in U.S. patent No. 2,081,595.
It has further been proposed to force the glass to
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flow through openings,disposed through such barriers deep
beneath~the surface of the bath, and it has also been proposed
to effect a stirring of a downs-tream flow which has been
mechanically separated by means of a partition from the
returning upstream flow. The partition is however subjected
to corrosion and its replacement is difficult and costly.
It has also been proposed in U.S. patent No. 1,923,942
to provide a glass melting furnace with forebays extending
therefrom, within which the glass is caused to flow in a
circular or oval pattern around a central cooled portion of
the forebay by the action of glass gathering molds which are
,~ .
carried across an exposed gathering area at the outer limit of
the forebay. One means to cool the central area of the fore-
bay proposed in this patent is a box-like structure of
refractory material which extends downwardly through an open-
ing in the roof over the forebay, with the lower surface of
~h'at structure eith'e'r above or below the level of the glass,
air or otheL heat regulating medium being circulated through
the structure. This structure is concerned however only with
maintaining the finished glass at the proper temperature' at~the,
actual point of its removal from the furnace,
The applicant has found that the quality of the
glass being made can be improved by blocking, by means of a
barrier or boom extending only part-way crosswise of the
furnace, the center portion of the surface downs~ream glass
current and deflecting it downward to be joined with the
underlying upstream return current. The boom permits
however a perfectly free downstream flow of the lateral or
e~ge portions of the bath, in amount sufficient to meet the
needs for withdrawal of glass for use and also to permit
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continued existence of the return current even downstream
of the boom.
The position of the boom must be correctly chosen.
A certain degree of devitrification of the melted glass
particles may take place downstream of the boom, after
contact with the boom structure, and it is necessary that the
temperature of the bath downstream of the boom be sufficiently
high so that these crystalline particles will be completely
remelted there before
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withdrawal fram the furnace.
In addition, the visc~sity of the glass at the location of
the koom is of importan oe . In order that the hydrodynamic action of
the bcom shall be as effective as possible, the viscosity of the glass
in the vicinity thereof should not exceed 102 5 or 316 poises.
Ihe boom provided by the invention is thus particulæ ly
effective when the bemperature of the glass is not belcw 1300C., for
the glass compositions of ordinary ccmmerce.
In acc~rdance with the invention, the boom is disposed in a
mid-portion of a cross-section of the bath, desirably across the axis
or median line of the sufaoe thereof. In order to avoid all in~erference
with the downstream flow along the edges of the ~th at the surfaoe there-
of and with the upstream flow at the bottc~, the boom is made up of
elements of structure which are suspended frcm the loof or crGwn of the
fu~nace. Its length crosswise of the furnace depends on its position
lengthwise of the furnaoe and amounts substantially to the ~7idth of that
portion of the dcwnstream surfaae c;urrent which it is desired to in~errupt.
In a preferred eniodiment of the invention, the boom is given a length
between one-quarter and two thirds the cross-sectional width of the
bath and preferably between one-third and one-half thereof.
The vertical eXtenSiQn and, in a pre~erred emkodime~t, the
tempera~une of the bocm are adjusted-so-as to pro wke a return upstream o~
the desired fraction of the downstream current otherwise existing at the
location of the boom. Desirably the boom extends vertically or the bath
dcwnwards fr~m the surfa oe thereof between about one-fifth and one-half
of the glass bath depth. It may be deeper in the oenter portion than at
~he la~eral ends thereof and may thus have at its lower limit a downwardly
oQnvex
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profile.
Advantageously the boom is made of separate parts
which act both as a discontinuous mechanical obstacle and as
an obstacle by thermal action on the surrounding mass of glass.
The boom of the invention thus possesses two independently var-
iable properties or parameters which can be selected for
optimum effect.
Desirably, the boom is thus made up of refrigerated
tubes or conduits having a loop or hairpin shape, the tubes
lQ being mounted to permit adjustment of their orientation. Addi-
tionally, it is possible to rotate these members so as to
superimpose a mixing effect on the blockage effect.
This supplementary homogenization action mav be
desirable when the furnace is being operated with maximum
throughput. It also may effect a desirable economy of time
in the production of colored glasses upon passage from one
` color to another, and it may aid in surmounting perturbations
or irregularities of flow which sometimes occur when there are
excessive departures from homogeneity in the starting materials.
It will be understood that the foregoing includes
a general description of secondary as well as primary aspects
of the invention. The primary aspects of the invention are
defined below.
:
The apparatus of the present invention is defined
as a glass melting furnace comprising means defining a trough,
; a boom extending part-way crosswise of the trough at a location
intermediate the upstream and downstream ends of the trough,
the boom being disposed above the bottom of the trough, a
~ `
roof above the trough, and means dependent from the roof to
`. 30 support the boom.
u The method of the present invention is defined as
,
~ a method of conditioning molten glass which comprises flowing
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the molten qlass lengthwise of a trou~h, between upstream
. and downstream ends thereo~, obstructing at a location
between those ends a barrier, flow-impeding means extending
. partway crosswise of the trough from the surface of the glass
: part-way of the bottom of the trough, and circulating a cooling
fluid through the flow-impeding means.
Brief Description of the Drawings
The invention will now be further described in
terms of a number of presently preferred embodiments and by
reference to the accompanying drawings in which:
FIG. 1 is a plan diagrammatic view of a melting
furnace in accordance with the invention as seen beneath
the roof thereof;
.~ FIG. 2 is a longitudinal vertical axial sectional
~` view through the furnace of F~G. 1, taken on the line 2-2 of
: FIG. l;
FIG. 3 is a transverse sectional view of the furnace
of FIGS. 1 and 2, taken on the line 3-3 of FIG. 2 but showing
roof thereof;
FIG. 4 is a view similar to that of FIG. 3 but illustra-
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ting a modified form of furnace in accordance with the
invention:
FIG. 5 is a diagrammatic representation of a boom
according to the invention made up of plural elements;
FIG. 6 is a plan diagrammatic view of the boom of
FIG. 5 with, however, the boom elements shown in inclined
position and showing also the pattern of glass flow in the
vicinity of the boom;
FIG. 7 is a sectional view similar to FIG. 3 but
showing still another form of furnace in accordance with the
invention;
FIG. 8 is a perspective view of a boom made up of
rotatable elements.
FIG. 9 is a diagram illustrating the support of the
elements of the boom of FIG. 8 from the roof of the furnace;
and
FIG. 10 is a diagram showing the support and
rotating means for one of those elements.
Description of Preferred Embodiments
;, 20 The furnace of FIGS. 1 to 3 includes side walls 50
and 51, ena walls 52 and 53, a bottom 54, and a roof 55.
Heating means such as burners 56 are distributed lengthwise
of the trough thus formed and maintain a suitable distr~bution
` or gradient of temperatures lengthwise of the furnace, i.e.
~` from left to right in FIG. 1, with the upstream zone 1 being
,~ hotter and constituting a melting and refining zone, whereas
a cooler zone 2, downstream of zone 1, may be regarded as a
`',!; conditioning or tempering zone. The raw materials are
charged in at the upstream, left end as indicated at 3, and
;~ 30 withdrawal of the prepared glass is effected at the downstream
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right end 4, over a sill 57.
A boom 5 according to the invention is disposed in
the bath on the central portion of the downstream current,
with the burners 56 being partly upstream and partly down-
stream of the position of the boom. As indicated in FIG. 1,
the boom extends across the median line or longitudinal axis
of the furnace, indicated as the section line 2-2 in FIG. 1.
The boom operates on approximately two-fifths of the width
of the bath so that lateral downstream or edge currents 6 are
permitted to flow unobstructedly toward the outlet end.
FIG. 2 shows the vertical position of the boom 5,
extending downwardly approximately to the upper limit of the
` return glass current 7.
FIG. 3 is a transverse sectional view of the furnace
~ of FIGS. 1 and 2. The boom may comprise a plurality of
; ~ elements, diagrammatically and collectively indicated at 8,
; supported by tubes 9 which are cooled by water jackets 10
in order to prevent corrosion thereof at the high temperatures
obtaining in the furnace.
FIG. 4 illustrates another embodiment of the furnace
of the invention in which the boom takes the shape of a
serpentine coil, disposed similarly however to the boom of
FIGS. 1 to 3 in the central downstream flow portion of the
bath cross-section. The operation of this boom is to increase
the viscosity of the glass in the vicinity thereof so that
that portion of the downstream current of glass which ~;
encounters it strikes a chilled zone and is entrained by the
deeper portions of the bath so as to be carried upstream
again.
FIGS. 5 and 6 illustrate a plural-element,
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discontinuous boom in accordance with the invention made up
of metallic tubes 13 which are cooled by water circulated
through them via suspensory portions 12 of the kubes. The
tubes may thus be formed into rectangular or other 1QP
shapes as indicated. These tubes are effective as a boom ox
barrier primarily by thermal action. They cool a portion of
the bath in the region which they occupy and thereby produce
a substantially continuous barrier or retarding screen over
that region
Each loop can be individually controlled in
orientation by rotation about a vertical axis.
By such rotation the boom acquires, as indicated in
FIG. 6, a thickness in the direction of flow lengthwise of
the furnace which is greater than the thlckness of the loops
themselves. The resulting action may be similar to that of
a series of inclined shutters.
The arrows 14 in FIG. 6 show that the side flow
- (at the surface of the bath) continues downstream for feed
~ of the plunger or other glass withdrawal mechanism of the
;
furnace (not shown) whereas the central portion of the
downstream surface current, encountering the boom formed ~y
the loops 13, is turned backward to join the upstream current
at the bottom of the bath. The arrows 15, while shown in a
horizontal plane, are intended diagrammatically to indicate
that the central surface portion of the current is turned
downwardly and then back upstream.
The tubes 13 of FIG. 5 may be mounted for adjust-
~` ment in height so as to permit achievin~ optimum form of
~r~ the boom. Those nearest the side walls of the furnace may
,~ 30 be less deeply immersed in the glass bath than those in the
;`~ middle so as to provide a more effective action in the
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middle portion than at the edges.
FIG. 7 illustrates still another embodi~ent of the
furnace of the invention including an essentially thermal boom
made up of bubbling elements 16 from the roof. Such elements
are known in and of themselves. They comprise tubes, usually
disposed with an open end near the bottom of the furnace,
through which bubbles can be blown into the mass of glass so
as to effect a mixing or stirring thereof.
According to the present invention instead, each
tube for the supply of gas bubbles extends down into the
bath only to the dividing line, approximately between the
upstxeam and downstream currents, the emission of bubbles
being effected over the desired fraction of the width of the
furnace by the provision of a suitable member of bubbling
tubes.
The rate of production of bubbles must be a sub-
; stantial one in order to achieve by partial blockage of the
downstream flow a return thereof as part of the deeper
upstream flow.
Control of the flow pattern of the glass in
~,~ accordance with the invention is particularly advantageous
.
for the manufacture of glass in furnaces operating at or near
capacity. In such a case, the hydrodynamic flow pattern
which is developed in the bath by reason of the geometry of
the furnace, the rate of glass withdrawal and the various
th~rmally induced currents of convection may result in a
flow pattern which departs materially from the optimum for
the desired quality of glass. Corrective action may then be
taken, especially with respect to the central downstream
portions of the downstream cuxrent flow by imposing on them
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a modified flow pattern by interposition of a boom in
accordance with the invention. In this way, a more uniform
flow pattern can be obtained with a resulting more homogene-
ous quality for the glass.
FIG. 8 is a figure similar to FIG. 6 but showing in
perspective another boom according to the invention made up of
individually adjustable and rotatable loop-shaped cooled tubes
17. The source of coolant, which may include a water-tight
rotating joint for each tube, is not shown. The tubes may
have each approximately the shape of a twisted figure eight,
the upper and lower lobes of which are crosswise to each
other. Means, such as for example those shown in FIG. 10,
may be pro~ided to rotate the tubes so that they will function
as stirring or agitating as well as cooling and blocking
elements.
Each of the tubes 17, when rotated, carries with
;~. .
it a quantity of glass whose viscosity is increased by the
cooling effect exerted by the tube.
The downstream glass current engages the tubes 17
and they therefore play a double role of blocking and mixing,
varying directly with their speed of rotation.
' The number of tubes employed depends upon the
~ lateral width desired for the boom. Speed may vary from 0
,~ to a maximum at which bubbles become impxisoned in the glass
~` or at which cavitation takes place.
The speed of the rotation of the tubes may, for
example~ be ten revolutions per minute, corresponding to a
, ,.
: linear speed at the radially outermost portions of the tubes
amounting to about 300 meters per hour.
~` 30 The tubes 17 may be of such size and may be so
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cooled as to extract on the average from the glass a quanti~y
of heat between 50 and 100 therms per hour, and preferably
of the order of 75 therms per hour. This requires at least
25 liters per minute of water flow and preferably some 50
liters per minute for a tube, the diameter of whose loop is
of the oxder of from 0.25 to 0.30 meters.
- - The direction of ro~ation of the stirring elements
or tubes may be chosen to achieve the following effects:
l. To gather the glass toward the axis or median
line of the furnace. In this case, the stirring elements on
each side of that median line will rotate in the same direction,
those on one side rotating in the direction opposite to those
- on the other side and the direction of motion being toward
the median line on the upstream side of the stirring elements.
2. Instead, the stirring elements can be employed
to disperse the glass away from the median line of the furnace.
The sense of rotation of the stirring elements will then be
` opposite to that described in the immediately preceding
; paragraph.
3. A stirring action may be imposed by pairs of
the stirring elements each one turning in a direction opposite
to that of its neighbors.
It is also possible in accordance with the invention
to employ alternate fixed and rotative boom elements or to
have rotating elements in the center and stationary ones at ``
the lateral extremities of the boomO
FIG. 8 illustrates a series of stirring and cooling
elements disposed in large and rotating in the same direction
but dephased successively 90 with respect to each other. The
space between adjacent elements is such that the xegion o~
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effective action of each one overlaps at least slightly with
the correspon~ing zone of action of the adjacent stirring
element. The crossed or twisted figure eight shape
illustrated is favorable to achieving this result.
FIG. 9 shows half of the roof 18 of a melting
furnace and the position of the stirring elements 17 by
reference thereto. Successive or adjacent stirring elements
are displaced angularly by 90 and their zones of operation
overlap, as in the construction of FIG. 8 just described.
The upper limit of the stirring, cooling and
blocking tubes 17 is no higher than the surface of the glass
bath 4. The lower limit is preferably no lower than the
neutral interface surface or zone which separates the down-
stream surface current and the bottom upstream current. It
is in general desired not to perturb the upstream current.
FIG. 10 shows a device for control adjustment and
optionally for rotation of the stirring tubes. The tube 17
is supported in a sleeve 18 held in two bearings 19. These
bearings are fixed to a frame 20 connected by fastening
,
means 21 and 22, which may be conventional, to a beam 23 which
,` is parallel to the longitudinal slot 24 in the furnace roo~
The sleeve 18 carries a conical gear 25 which is driven by
a pinion 26, which in turn receives it motion from a motor
27 via a shaft 28. To permit control of the phase angle of
the separate tubes 17, the pinion 26 can be disengaged from
the pinion 25 by rotation of the sha~t 28 about a vertical
axis 29 by means not shown. The assembly comprising the
tube 17, its sleeve and support 20 may be raised or lowered
by means of a tackle (not shown). Refractory plugs 30 ana
31 close the opening 24. The loop-shaped portion of the
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stirring element 17 grazes at its upper limit the surface of
the glass bath 32. Selection of the number of elements in
the boom, the speed (when rotated) ana the disposition of the
elements and the degree of their immersion depends upon the
dimensions of the furnace and the composition of the glass
being made.
It will thus be seen that the invention provides
a glass melting furnace comprising means defining a trough,
illustrated in FIGS. 1 and 2 at the side, end and ~ottom walls
of the furnace thereshown, and a boom as generally indicated :.
at 5 in those figures, extending part-way crosswise of the
trough astride the median line thereof, at a location inter-
mediate the upstream and downstream ends 3 and 4 of the ~
trough, the boom being disposed above the bottom of the trough
as particularly illustrated in FIG. 2~ The invention like
wise provides a method of conditioning molten glass which
comprises flowing the glass lengthwise of a trough between .
upstream and downstream ends thereof, and obstructing the
~ownstream flow of glass at a location between those.ends ' ,~
and part-way only across the width of the trou~h and part-way
only from the surface of the glass to the bottom of the
trough. The obstructing action may be combined,with a cooling
action and with a stirring actionr the cooling desirably bein~
carried out at a rate substantially between fifty a~d .one
hundred therms per hour and per square meter of obstructed
width of glass flow.
While the invention has been hereinabove described
in terms of a number of presently preferred embodiments of
the apparatus thereof, and in terms of a number of presently '
.
; 30 preferred modes of practice of the method thereo-f, the
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invention itself is not limited thereto but rather comprehends
all modifications of and departures fxom those preferred
embodiments and modes properly falling within the scope of
~ the appended claims.
-~ As used herein, the term "therm" means one thousand
kilogram calories.
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