U.S. patent application number 13/367156 was filed with the patent office on 2012-05-31 for apparatuses for controlling the temperature of glass forming materials in forehearths.
This patent application is currently assigned to OCV INTELLECTUAL CAPITAL, LLC.. Invention is credited to Harry Adams, David J. Baker, Byron Bemis, Patrick J. Prescott, Bruno A. Purnode, William L. Streicher.
Application Number | 20120131964 13/367156 |
Document ID | / |
Family ID | 39259351 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120131964 |
Kind Code |
A1 |
Adams; Harry ; et
al. |
May 31, 2012 |
Apparatuses For Controlling The Temperature Of Glass Forming
Materials In Forehearths
Abstract
Forehearths that create a substantially homogeneous temperature
to molten glass forming materials across the end position are
provided. A gas cavity, a weir, a refractory block, or a heating
element in the forehearth may be utilized to reduce a temperature
gradient of molten glass forming materials across the end position.
Reducing the temperature difference of the molten glass forming
material across the end position permits for improved chemical and
physical properties of the glass fibers and the end products formed
from the glass fibers. In addition, a reduction in the temperature
gradient across the end position produces a more homogenous glass
fiber and glass product. Further, a reduction in the shear break
rate occurs when the molten glass forming material has a
temperature that is substantially the same across the end position,
which results in a reduction in the breakage of glass fibers and an
increase in manufacturing efficiency.
Inventors: |
Adams; Harry; (Newark,
OH) ; Purnode; Bruno A.; (Newark, OH) ; Bemis;
Byron; (Newark, OH) ; Prescott; Patrick J.;
(Newark, OH) ; Streicher; William L.; (Granville,
OH) ; Baker; David J.; (Newark, OH) |
Assignee: |
OCV INTELLECTUAL CAPITAL,
LLC.
Toledo
OH
|
Family ID: |
39259351 |
Appl. No.: |
13/367156 |
Filed: |
February 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11638801 |
Dec 14, 2006 |
8113018 |
|
|
13367156 |
|
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Current U.S.
Class: |
65/499 ;
65/495 |
Current CPC
Class: |
C03B 7/06 20130101; C03B
5/182 20130101; C03B 7/02 20130101; C03B 7/07 20130101 |
Class at
Publication: |
65/499 ;
65/495 |
International
Class: |
C03B 37/085 20060101
C03B037/085 |
Claims
1-20. (canceled)
21. A forehearth for conveying a molten glass forming material to a
glass forming apparatus, said forehearth comprising: a flow block
extending a length of said forehearth and defining a flow channel
over which said molten glass forming material flows toward an end
wall, said flow block further defining a plurality of openings
downward through said flow channel operable to deliver said molten
glass forming material to at least one bushing of said glass
forming apparatus, wherein one of the openings closest to said end
wall is an end opening; a roof covering at least a portion of said
flow block and enclosing a gas combustion chamber between said flow
block and said roof, said gas combustion chamber containing
combustion gases to heat said molten glass forming material; and a
glass contact wall positioned in said flow channel downstream from
said end opening and having an upstream face contacting said molten
glass forming material to prevent the passage of molten glass
forming material and an opposed downstream face facing but spaced
from said end wall such that said glass contact wall is located
between said end wall and said end opening; wherein a gas cavity is
formed between the downstream face of said glass contact wall and
said end wall, said gas cavity being devoid of molten glass
material and in flow communication with said combustion chamber for
the flow of said combustion gases thereto, and said gas cavity
being in direct contact with said glass contact wall and said flow
block to transfer heat from said combustion gases in said gas
cavity to said molten glass material proximate said end opening via
said glass contact wall and said flow block.
22. The forehearth of claim 21, wherein said combustion gases
located in said gas cavity radiate heat through said glass contact
wall and said flow block to increase the temperature of said molten
glass forming material at a downstream portion of said end opening
and reduce a temperature gradient of said molten glass forming
material across said end opening.
23. The forehearth of claim 21, wherein said gas cavity has a
dimension of about 1 inch to about 12 inches extending from said
glass contact wall to said end wall.
24. The forehearth of claim 23, wherein said gas cavity has a
depth-extending from a top surface of said glass contact wall to a
top surface of said flow block.
25. The forehearth of claim 21, wherein said gas cavity extends at
least to a downstream end of a bushing block positioned beneath
said end opening of the flow block.
26. The forehearth of claim 21, further comprising gas burners
adapted to inject flames into said gas combustion chamber, and
wherein no additional energy source is adapted to supply energy to
said gas cavity other than said gas burners adapted to inject
flames into said gas combustion chamber.
27. A forehearth for conveying a molten glass forming material to a
glass forming apparatus, said forehearth comprising: a flow block
over which said molten glass forming material flows toward an end
opening, said flow block defining a plurality of openings
therethrough for the passage of said molten glass forming material
from said forehearth to at least one bushing of said glass forming
apparatus, said plurality of openings including a first opening and
said end opening which is located downstream of said first opening
and adjacent an end wall of said forehearth; and a refractory block
supported on said flow block over said end opening, said refractory
block having a thickness and a hole therethrough in register with
said end opening in the flow block for the passage of said molten
glass forming material through said hole and said end opening;
wherein said refractory block extends upstream from said end
opening to alter the flow of said molten glass forming material
over said refractory block so that said molten glass forming
material at said end opening has a depth less than a depth of said
molten glass forming material at said first opening by an amount
equal to the thickness of said refractory block.
28. The forehearth of claim 27, wherein said molten glass forming
material has an upper surface and a bottom surface and said
refractory block forces said molten glass forming material at said
bottom surface towards said upper surface.
29. The forehearth of claim 28, wherein said upstream portion of
said refractory block is submerged in said molten glass forming
material and said upstream portion of said refractory block allows
passage of said upper surface of said molten glass forming material
over said upstream portion of said refractory block.
30. The forehearth of claim 27, wherein the shallower depth of said
molten glass forming material on said refractory block permits heat
from combustion gases to penetrate said molten glass forming
material over said refractory block and increase the temperature of
said molten glass forming material at said end opening and reduce a
temperature gradient of said molten glass forming material between
said first opening and said end opening.
31. A forehearth for conveying a molten glass forming material to a
glass forming apparatus, said forehearth comprising: a gas
combustion chamber including a flow block over which said molten
glass forming material flows to a plurality of openings through
said flow block, said plurality of openings including an end
opening and being operable to deliver said molten glass forming
material to a bushing of said glass forming apparatus; a glass
contact wall positioned downstream from said end opening; an end
wall positioned downstream and adjacent to said glass contact wall;
and a heating element contiguous with said end wall, said flow
block, and at least one of said bushing and a bushing block to
decrease thermal losses in said molten glass forming material
proximate said end opening via heat transfer through said end wall,
said flow block, and said bushing to said molten glass forming
material, wherein said bushing is located in a bushing block below
said flow block.
32. The forehearth of claim 31, wherein said heating element
achieves a temperature of at least 2100.degree. F.
33. The forehearth of claim 32, wherein said heating element is
selected from the group consisting of molybdenum electrodes, nickel
chrome wire, silicon carbide, a platinum wire, a torch, a pipe
having therein hot combustible gases and glow bars.
34. The forehearth of claim 31, wherein said heating element
increases the temperature of said molten glass forming material
positioned adjacent to said glass contact wall and reduces a
temperature gradient of said molten glass forming material across
said end opening.
35. The forehearth of claim 31, wherein said heating element is
distinct from any heating device that heats a bushing located
beneath said flow block.
Description
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
[0001] The present invention relates generally to a forehearth in a
glass fiber forming apparatus, and more particularly, to a
forehearth that provides a substantially homogeneous temperature to
molten glass forming materials across the end position of the
forehearth.
BACKGROUND OF THE INVENTION
[0002] In forming glass fibers, a glass forming material is heated
in a glass melting furnace until the glass forming material is
degraded to a molten state. The molten glass is passed from the
glass melting furnace and into a forehearth linking the glass
melting furnace and a glass forming machine. As the molten glass
flows through the forehearth, it passes downwardly through openings
that are positioned in a spaced relation along the bottom of the
forehearth and into a bushing. Glass streams are then attenuated
through orifices located in the bushing and formed into glass
filaments or fibers by methods known to those of skill in the
art.
[0003] The forehearth is utilized to thermally condition the molten
glass material so that it matches the physical and chemical
requirements of the glass forming machine. The forehearth contains
numerous openings to convey the molten glass material to the
bushings. The initial or first opening is typically called the
"take-off" position and the last opening in the trough of the
forehearth is termed the "end position". It is known in the art
that a temperature gradient is created within the molten glass
material as the molten glass material flows through the forehearth.
For example, the molten glass delivery temperature at the end
position is lower than the molten glass delivery temperature at
other openings. It is also known that the forehearth tends to lose
heat externally from the end wall, thereby causing the molten glass
material at the end position to be substantially cooler and
thermally less uniform compared to the molten glass located at the
other openings.
[0004] The heat loss from the end position is illustrated in FIG.
1. As depicted in FIG. 1, combustion gases flow within a gas
chamber 12 positioned between the roof 14 of the forehearth 10 and
the molten glass forming material 16. Gas burners 15 inject flames
into the gas combustion chamber 12 to elevate and maintain the
temperature of the combustion gases within the gas chamber 12. The
hot gases in the gas chamber 12 are utilized to maintain the
temperature of the molten glass forming material 16 for optimum
delivery. In FIG. 1, the molten glass material 16 flows from left
to right (e.g., downstream) along a flow block 17 between two
sidewalls (not shown) and abuts a glass contact wall 11. The molten
glass forming material 16 exits the forehearth 10 through the end
position 21 formed by an opening in the flow block 17, 17a and the
bushing block 13, 13a. Heat loss occurring through the end wall 18
in the direction of arrows 19 creates a temperature gradient within
the molten glass material 16 at the end position 21.
[0005] The difference in the molten glass delivery temperature
across the end position 21 creates a difference in the viscosity of
the molten glass 16, which may result in variations in the physical
and chemical properties of the glass fibers produced as well as the
end product manufactured with these glass fibers. In addition, the
temperature difference may result in fibers that do not meet
process specifications. Further, the reduced temperature of the
molten glass material 16 at the end position 21 creates a need for
increased power within the bushing to reheat the glass. This
reheating, in turn, negatively alters the bushing's
characteristics. Additionally, the lower temperature of the glass
forming material 16 at the end position 21 causes higher shear
break rates of the resulting glass fibers. Such an increase in the
shear break rate results in a high level of waste and a reduction
in processing efficiency.
[0006] There have been attempts in the art to reduce the
temperature difference within the forehearth and overcome the
above-described problems. Some examples of these attempts are
described below.
[0007] U.S. Pat. No. 4,069,032 to Brax discloses an apparatus that
homogenizes the temperature of the molten glass flowing through a
forehearth. The inventive forehearth includes a roof that has a
roof with longitudinal ridges. These ridges define a central
longitudinal channel in which a current of cooling air passes
therethrough to cool the central, hottest part of the stream of
glass. Side channels promote a local convection of hot gases to
reheat side portions of the molten glass. A plurality of
longitudinally spaced electrodes are suspended from the roof over
the side channels and are inserted into the molten glass to
directly heat the side portions of the channel of molten glass.
[0008] U.S. Pat. No. 4,544,392 to Sheinkop discloses an apparatus
for thermally conditioning a heat softenable material such as
glass. The apparatus includes an auxiliary heated bushing block
that has a non-circular opening to transmit the molten glass from
the opening in the bottom of a forehearth to a fiber forming
bushing. Electrical resistance heater elements protrude through the
ends of the bushing block into the non-circular opening into
contact with the molten glass. By varying the power settings of
each power supply to the heater elements, the molten glass can be
selectively thermally conditioned.
[0009] U.S. Pat. No. 5,327,452 to McMinn discloses a forehearth for
a glass furnace that includes a trough and a roof over the trough.
Two longitudinal ridges in the roof that extend downwardly towards
the surface of the molten glass form three chambers within the
forehearth. The central chamber forms a conduit for the flow of
cooling air over the central part of the molten glass stream. The
side chambers serve as conduits for the flow of combustion gas.
Separate outlets are provided for the cooling and combustion gases.
Controllable dampers are provided on at least the combustion gas
outlets. Balancing the internal pressures between the three
chambers may ensure that there is no significant mixing of the
cooling air and combustion gases. The balancing and adjusting of
the pressure of adjacent heating and cooling chambers allegedly
allows a fine and accurate control of the temperature of the molten
glass.
[0010] Despite these previous attempts to reduce temperature
differences within the forehearth, there remains a need in the art
for an apparatus and method for heating the molten glass material
located at the end position to provide a substantially homogeneous
temperature to the molten glass forming material across the end
position.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
forehearth for conveying a molten glass forming material to a glass
forming apparatus that includes a flow block that extends the
length the forehearth, a roof covering at least a portion of the
flow block, a gas combustion chamber located between the flow block
and the roof, a glass contact wall positioned downstream from the
end opening, an end wall, and a gas cavity positioned between the
glass contact wall and the end wall. The gas cavity may be
positioned a distance from about 1 inch to about 12 inches from the
glass contact wall and extends at least to the end position, and
preferably past the bushing block. Heat from the hot combustion
gases in the gas cavity transfers through the glass contact wall
and into the molten glass located at the end position. This heat
transfer reduces the temperature gradient of the molten glass
forming material across the end position and adjusts the
temperature of the molten glass forming material to a temperature
that is more consistent with the temperature of the molten glass at
the other openings. In addition, by positioning the gas cavity
between the glass contact wall and the end wall and allowing the
hot combustion gases to enter the gas cavity, the end wall is
distanced from the molten glass forming material and a more
homogenous temperature across the end position may be achieved.
[0012] It is another object of the present invention to provide a
forehearth for conveying a molten glass forming material to a glass
forming apparatus that includes a weir supported on the flow block
upstream of the end opening. The weir is rigidly fastened to the
flow block and extends upwardly towards the top surface of the
molten glass material. The shape or form of the weir is not
particularly limited as long as the weir allows the passage of the
molten glass material positioned on or near the flow block over the
weir. In addition, the weir may be formed of any material that can
withstand the temperature of the molten glass forming material. The
weir may be positioned a distance at least 5 inches upstream from
the end position. In operation, the weir forces the molten glass to
flow next to the hot combustion gases in the gas combustion
chamber. As a result, the molten glass material that is forced to
the top surface by the weir remains in close contact with the hot
combustion gases for an extended length of time. Thus, once the
molten glass material passes the weir and approaches the end
position, it has a temperature that is higher and more consistent
with the temperature of the molten glass material at the other
openings in the forehearth.
[0013] It is yet another object of the present invention to provide
a forehearth for conveying a molten glass forming material to a
glass forming apparatus that includes a refractory block supported
on the flow block adjacent to the end opening. The refractory block
has an opening that matches the openings in the flow block and
bushing block so that the molten glass material can exit the
forehearth through the end position. The refractory block may be
formed of any material that is non-corrosive or substantially
non-corrosive in nature. The height of the refractory block may be
any desired height as long as the refractory block remains
submersed in the molten glass forming material. In operation, the
molten glass flows over an upstream portion of the refractory block
where it is more efficiently and quickly heated by the combustion
gases in the gas chamber due to the decreased depth of the molten
glass flow over the refractory block. This depth reduction of the
molten glass forming material permits the heat from the combustion
gases to penetrate the molten glass and more completely heat the
molten glass over the upstream portion of the refractory block,
thereby achieving a temperature that is more consistent with the
temperature of the molten glass forming material located at the
other openings. Additionally, the refractory block decreases the
residence time and the volume of molten glass over the end
position. The shorter residence time reduces the amount of thermal
energy the molten glass may lose before flowing through the end
position, which causes a reduction in the temperature difference of
the molten glass forming material across the end position.
[0014] It is a further object of the present invention to provide
forehearth for conveying a molten glass forming material to a glass
forming apparatus that includes a gas combustion chamber that has a
flow block including an end position, a glass contact wall
positioned downstream from the end position, an end wall positioned
downstream from the end position, and a heater interposed between
the end wall, the flow block, and a bushing located below the flow
block. The heating element is not necessarily restricted in form or
type, and may be any apparatus or device that can provide a
temperature sufficient to raise the temperature of the molten glass
material at the end position to a temperature that is the same as,
or substantially the same as, the temperature of the molten glass
material at the other openings. It is preferred that the heating
element is capable achieving a temperature of at least 2100.degree.
F. The heating element transfers heat through the end wall, flow
block, and bushing block to heat the molten glass material abutting
the glass contact wall and offset the heat loss through the end
wall. Thus, the heating element increases the temperature of the
molten glass material located at the end position to a temperature
that is more consistent with the temperature of the molten glass
material at the other openings. In addition, the increase in
temperature of the molten glass material adjacent to the glass
contact wall reduces the temperature gradient of the molten glass
forming material across the end position.
[0015] It is an advantage of the present invention that uniform or
substantially uniform chemical and physical properties of the glass
fibers may be obtained by reducing the temperature gradient across
the end position.
[0016] It is another advantage of the present invention that a
decrease in shear break rate occurs when there is a uniform or
substantially uniform temperature of the molten glass material
across the end position.
[0017] It is a further advantage of the present invention that the
molten glass flowing through the end position and into the bushing
has a more homogenous viscosity when there is little or no
temperature gradient of the molten glass material across the end
position. As a result, a more homogenous glass fiber and glass
product may be formed.
[0018] It is yet another advantage of the present invention that
there is no need for an additional energy source or a control
system infrastructure when a gas cavity is employed within the
forehearth between the glass contact wall and the end wall.
[0019] It is also an advantage of the present invention that the
heating element permits for the control and custom tailoring of the
particular thermal requirements of a given installation.
[0020] It is a feature of the present invention that the inventive
forehearths provide a substantially homogeneous temperature to
molten glass forming materials across the end position of the
forehearths.
[0021] The foregoing and other objects, features, and advantages of
the invention will appear more fully hereinafter from a
consideration of the detailed description that follows. It is to be
expressly understood, however, that the drawings are for
illustrative purposes and are not to be construed as defining the
limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The advantages of this invention will be apparent upon
consideration of the following detailed disclosure of the
invention, especially when taken in conjunction with the
accompanying drawings wherein:
[0023] FIG. 1 is a schematic partial cross-sectional illustration
of a conventional forehearth depicting the end position and heat
loss through the end wall;
[0024] FIG. 2 is a schematic partial cross-sectional illustration
of one exemplary embodiment of the present invention in which a gas
cavity is positioned between the glass contact wall and the end
wall;
[0025] FIG. 3 is a schematic partial cross-sectional illustration
of another exemplary embodiment of the present invention in which a
weir is inserted into the molten glass flow prior to the end
position;
[0026] FIG. 4 is a schematic partial cross-sectional illustration
of a further exemplary embodiment of the present invention in which
a refractory block is inserted into the molten glass flow prior to
the end position; and
[0027] FIG. 5 is a schematic partial cross-sectional illustration
of yet another exemplary embodiment of the present invention in
which a heating element is utilized to heat the molten glass
material at the end position.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
[0028] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which the invention belongs. Although
any methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are described
herein. All references cited herein, including published or
corresponding U.S. or foreign patent applications, issued U.S. or
foreign patents, and any other references, are each incorporated by
reference in their entireties, including all data, tables, figures,
and text presented in the cited references.
[0029] In the drawings, the thickness of the lines, layers, and
regions may be exaggerated for clarity. It is to be noted that like
numbers found throughout the figures denote like elements. It will
be understood that when an element is referred to as being "on,"
another element, it can be directly on or against the other element
or intervening elements may be present. In addition, it is to be
noted that when an element is referred to as being "adjacent to"
another element, it can be directly adjacent to or next to the
other element or intervening elements may be present.
[0030] The present invention relates to forehearths that provide a
substantially homogeneous temperature to molten glass forming
materials across the end position (end opening) of the forehearth.
As described above, a forehearth contains numerous openings to
convey molten glass material to the bushings. The initial or first
opening is commonly called the "take-off" position and the last
opening in the forehearth is typically termed the "end position".
Uniform or substantially uniform chemical and physical properties
of the glass fibers, and the end products formed from the glass
fibers, may be obtained when there is not a significant temperature
gradient of the molten glass material across the openings. For
example, if there is little or no temperature gradient of the
molten glass forming material across an opening, such as the end
position, the molten glass flowing through the opening and into the
bushing has a more homogenous viscosity. A more homogenous glass
fiber and glass product may be formed when variations in the glass
viscosity are reduced. In addition, a reduction in the shear break
rate occurs when the molten glass forming material has a
temperature that is substantially the same across the opening. As a
result, waste resulting from the breakage of the glass fibers may
be reduced and manufacturing efficiency of the glass fibers may be
increased.
[0031] FIG. 2 illustrates one exemplary embodiment of the present
invention in which a combustion gas chamber 12 within a forehearth
25 is extended past a glass contact wall 11 and into a gas cavity
22. In operation, a molten glass forming material 16 flows
downstream (left to right as depicted in FIG. 2) as depicted by
arrows 28 along flow block 17 through a channel formed between two
vertically positioned sidewalls (not shown) and abuts the glass
contact wall 11. The flow block 17, 17a extends horizontally the
length of the forehearth 25, and may be a wall defining the passage
of the molten glass flow. Hot combustion gases flow through the
combustion gas chamber 12 positioned between a roof 14 and the
molten glass forming material 16. The roof 14 may include a
longitudinally extending series of refractory roof block elements
which at least partially cover the flow block 17, 17a. Gas burners
15, 15a inject flames into the gas combustion chamber 12 to elevate
and maintain the temperature of the combustion gases within the gas
chamber 12. Despite the presence of gas burner 15a, the molten
glass forming material 16 at the end position 21 (end opening)
typically has a reduced or lower temperature compared to the other
openings (not illustrated) within the forehearth 25 as well as a
temperature difference across the end position 21. This is largely
due to the lower temperature of the end wall 18 which does not
conventionally contain a heat source. Thus, heat from the molten
glass forming material 16 flows outwardly (externally) from the end
wall 18 at a greater rate than can be heated, causing the molten
glass material 16 to have a temperature gradient over the end
position 21. As shown in FIGS. 1-5, the end wall 18 is depicted as
being formed of two refractory block elements, 18a and 18b.
[0032] By providing a gas cavity 22 in which the hot combustion
gases can enter and radiate heat, the heat balance across the end
position 21 is improved and the molten glass forming material 16
has a more consistent temperature across the width of the end
position 21. The gas cavity 22 is positioned between the glass
contact wall 11 and the end wall 18. In FIG. 2, the gas cavity is
depicted as being positioned between the glass contact wall and
refractory block element 18b of the end wall 18. The gas cavity 22
extends the gas combustion chamber 12 a distance beyond the glass
contact wall 11. It is to be noted that the gas cavity 22 also
extends at least to the downstream end of the bushing block 13a,
and preferably past, the bushing block 13a. The gas cavity 22 may
extend a distance from about 1 inch to about 12 inches from the
glass contact wall 11, and preferably a distance of approximately 6
inches from the glass contact wall 11. Additionally, the gas cavity
22 preferably has a depth that is equivalent to the distance from
the top surface of the glass contact wall 11 to the bottom surface
of the end wall 18.
[0033] Gas burner 15a in the combustion chamber 12 may be utilized
to provide heat to the gas cavity 22. The hot combustion gases in
gas chamber 12 and in gas cavity 22 release energy to provide heat
in the form of convection and radiation energy to both the
surrounding walls and the molten glass forming material 16. The gas
cavity 22 provides an extended heat source for the end position 21
due to its position adjacent to the downstream end of the flow of
the molten glass forming material 16. In particular, the heat from
the hot combustion gases in the gas cavity 22 transfers through the
glass contact wall 11, the flow block 17a, and the bushing block
13a and into the molten glass 16 located at the end position 21.
This heat transfer reduces the temperature gradient of the molten
glass forming material 16 across the end position 21 and adjusts
the temperature of the molten glass forming material 16 to a
temperature that is more consistent with the temperature of the
molten glass 16 at the other openings. In addition, by forming the
gas cavity 22 between the glass contact wall 11 and the end wall 18
and allowing the hot combustion gases to enter the gas cavity 22,
the end wall 18 is distanced from the molten glass forming material
16 and a more homogenous temperature across the end position 21 may
be achieved. Because the gas cavity 22 passively heats the molten
glass forming material 16, there is no need for an additional
energy source or a control system infrastructure.
[0034] FIG. 3 depicts a second exemplary embodiment of the present
invention in which a weir 23 is inserted into the molten glass flow
16. It is known in the art that the molten glass forming material
16 has a temperature gradient extending from the top surface 24 of
the molten glass forming material 16, which is in contact with the
combustion gas chamber 12, to the bottom surface or bottom portion
26 of the molten glass forming material 16, which is in contact
with the flow block 17. Because the flow block 17 is not subjected
to any external heating, heat from the molten glass 16 flows
outwardly through the flow block 17. This outward flow of heat
reduces the temperature of the molten glass 16 at the bottom
surface 26. In addition, the hot combustion gases in the combustion
gas chamber 12 heat the molten glass forming material 16 at the top
surface 24 more easily than the molten glass forming material 16
flowing at or near the bottom surface 26 due to its proximity to
the heat emanating from the hot combustion gases in the gas chamber
12. Thus, the molten glass forming material 16 exiting the
forehearth through the end position 21 possesses varying
temperatures, which assists in creating a temperature difference
across the end position 21. In addition, because the molten glass
forming material 16 located at the bottom surface 26 has traveled
the longest distance along the flow block 17 and has lost heat
through the flow block 17 along its length, the molten glass
forming material 16 at the end position 21 has a temperature that
is lower than the temperature of the molten glass 16 at the other
openings (not shown).
[0035] In order to heat the molten glass material 16 at the end
position 21, a weir 23 may be positioned transversally and
perpendicularly to the direction of the flow of the molten glass
forming material 16 within the forehearth 30. In the embodiment
illustrated in FIG. 3, the molten glass forming material 16 flows
downstream (left to right as depicted in FIG. 2) in the forehearth
30 as depicted by the arrows 28. Gas burners 15, 15a inject flames
into the gas combustion chamber 12 positioned between the roof 14
and the molten glass forming material 16 to elevate and maintain
the temperature of the combustion gases within the gas chamber 12.
The weir 23 may be formed of any material that can withstand the
temperature of the molten glass forming material 16. Suitable
examples of materials for use in forming the weir 23 include, but
are not limited to, tungsten, tungsten alloys, molybdenum,
molybdenum alloys, platinum, platinum alloys, or a chromic oxide
refractory. Preferably, the material used to form the weir 23 is
non-corrosive or substantially non-corrosive in nature.
[0036] The weir 23 is rigidly fastened to the flow block 17 and
extends upwardly towards the top surface or top portion 24 of the
molten glass forming material 16. The shape or form of the weir 23
is not particularly limited as long as the weir 23 allows the
passage of the molten glass forming material 16 positioned on or
near the flow block 17 over the weir 23. For example, the weir 23
may be formed to have any geometric shape, such as a generally
rectangular, square, or pyramidal shape. Additionally, the weir 23
may be designed to include various geometric notches to direct the
flow of the molten glass forming material 16 from the center of the
weir 23 (such as an inverted "V" shape or having a semicircular or
circular hole in the center). In addition, the weir 23 may have any
desired thickness as long as the weir 23 can withstand the flow of
the molten glass forming material 16 through the forehearth 30.
Desirably, the weir 23 may have a width from about 1.5 inches to
about 3 inches. It is not necessary that the weir 23 be formed of
one integral piece. It is possible that the weir 23 may be formed
of two or more pieces joined together.
[0037] The weir 23 may be positioned a distance at least 5 inches
upstream from the end position 21. In preferred embodiments, the
weir 23 is positioned a distance from about 5 inches to about 10
inches upstream from the end position 21. The weir is preferably
submerged in the molten glass forming material 16 such that the
molten glass 16 flowing over the weir 23 has a depth or thickness
from about 1 inch to about 2 inches. As depicted by the arrows 28
in FIG. 3, when the hot molten glass forming material 16 reaches
the weir 23, the molten glass forming material 16 is forced
upwardly and the molten glass 16 flowing above the weir 23 is
permitted to pass over the weir 23. This upward movement of the
molten glass material 16 forces the "cooler" molten glass material
16 located along the bottom surface 26 of the molten glass material
16 upward to the top surface 24 of the molten glass material 16,
where it is heated by the hot combustion gases in the gas
combustion chamber 12. The presence of the weir 23 forces the
molten glass 16 to flow next to the hot combustion gases in the gas
combustion chamber 12. As a result, the molten glass material 16
that is forced to the top surface 24 by the weir 23 remains in
close contact with the hot combustion gases for an extended length
of time. Thus, once the molten glass forming material 16 passes
over the weir 23 and approaches the end position 21, it has a
temperature that is higher and more consistent with the temperature
of the molten glass material 16 at the other openings (not shown)
in the forehearth 30.
[0038] In a third embodiment depicted in FIG. 4, a refractory block
32 is positioned adjacent to the end position 21 over the flow
block 17 in forehearth 40. As shown in FIG. 4, the refractory block
32 has an opening that matches the openings in the flow block 17,
17a and bushing block 13, 13a so that the molten glass forming
material 16 can exit the forehearth 40 through the end position 21.
The refractory block 32 may be formed of any material that is
non-corrosive or substantially non-corrosive in nature. Examples of
suitable materials include, but are not limited to, tungsten,
tungsten alloys, molybdenum, molybdenum alloys, platinum, platinum
alloys, and a chromic oxide refractory. The height of the
refractory block 32 may be any desired height as long as the
refractory block 32 remains submersed in the molten glass forming
material 16. In some exemplary embodiments, the refractory block 32
may have a height from about 2 to about 3 inches and a length from
about 7 to about 8 inches.
[0039] For descriptive purposes herein, the refractory block 32 is
divided into an upstream portion and a downstream portion located
on either side of an opening in the refractory block 32 positioned
over the end position 21. As the molten glass material 16 flows
through the forehearth 40 in the direction of arrows 28 to the end
position 21, the upstream portion of the refractory block 32 forces
the molten glass forming material 16 positioned on or near the flow
block 17 to flow toward the surface 24. The molten glass 16 flowing
over the upstream portion of the refractory block 32 is more
efficiently and quickly heated by the combustion gases in the gas
chamber 12 due to the decreased depth of the molten glass flow 16.
For instance, the depth (D.sub.1) of the molten glass forming
material 16 is reduced to a depth (D.sub.2) over the upstream
portion of the refractory block 32 a distance equivalent to the
height of the refractory block 32. This depth reduction permits
heat from the combustion gases and heat from the gas burners 15,
15a to penetrate the molten glass 16 and more completely heat the
molten glass 16 located over the upstream portion of the refractory
block 32, thereby achieving a temperature that is more consistent
with the temperature of the molten glass forming material 16
located at the other openings (not shown). Additionally, the
upstream portion of the refractory block 32 decreases the volume of
molten glass 16 over the end position 21 and, consequently, the
residence time. The shorter residence time reduces the amount of
thermal energy the molten glass 16 may lose before flowing through
the end position 21, which, in turn, causes a reduction in the
temperature difference of the molten glass forming material 16
across the end position 21.
[0040] Yet another exemplary embodiment of the present invention in
which a heating element is utilized to heat the molten glass
material at the end position is depicted in FIG. 5. As with the
other exemplary embodiments described herein, combustion gases flow
within a combustion gas chamber 12 positioned between the roof 14
of the forehearth 50 and the molten glass forming material 16. The
hot gases in the gas chamber 12 are utilized to maintain the
temperature of the molten glass forming material 16 for optimum
glass delivery. Despite the presence of the gas burners 15, 15a,
heat loss occurring through the end wall 18 in the direction of
arrows 19 creates a temperature gradient within the molten glass
forming material 16 at the end position 21.
[0041] In order to eliminate or reduce this temperature difference
of the molten glass forming material 16 across the end position 21,
the forehearth 50 contains a heating element or apparatus 34
positioned contiguous to the end wall 18, flow block 17a, and
bushing block 13a, preferably engaged therewith. In FIG. 5, the
heating element 34 is depicted as being contiguous to the
refractory block element 18b of the end wall 18. The heating
element 34 is not necessarily restricted in form or type, and may
be any apparatus or device that can provide a temperature
sufficient to raise the temperature of the molten glass forming
material 16 at the end position 21 to a temperature that is the
same as, or substantially the same as, the temperature of the
molten glass forming material 16 at the other openings (not shown).
Preferably the heating element 34 is capable achieving a
temperature of at least 2100.degree. F. Examples of suitable
heating elements 34 include any heating apparatuses such as
molybdenum electrodes, nickel chrome wire, silicon carbide, a
platinum wire, a torch, a pipe having therein hot combustible
gases, glow bars, and other high temperature thermal sources. One
or more heating elements 34 may be present in the forehearth
50.
[0042] In FIG. 5, the heating element 34 transfers heat through the
refractory block element 18b of the end wall 18, flow block 17a,
and bushing block 13a to heat the molten glass forming material 16
abutting the glass contact wall 11 and offset the heat loss through
the end wall 18, thereby acting generally as a guard heater. Thus
the heating element 34 increases the temperature of the molten
glass forming material 16 located at the end position 21 to a
temperature that is more consistent with the temperature of the
molten glass forming material 16 at the other openings (not shown).
Additionally, the increase in temperature of the molten glass
forming material 16 abutting or adjacent to the glass contact wall
11 reduces the temperature gradient of the molten glass forming
material 16 across the end position 21. The heating element 34
advantageously permits for the control and custom tailoring of the
particular thermal requirements of a given process.
[0043] The invention of this application has been described above
both generically and with regard to specific embodiments. Although
the invention has been set forth in what is believed to be the
preferred embodiments, a wide variety of alternatives known to
those of skill in the art can be selected within the generic
disclosure. The invention is not otherwise limited, except for the
recitation of the claims set forth below.
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