FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10 and Rule 13)
1. Title Of The Invention:-
METHOD AND APPARATUS FOR STIRRING AND HOMOGENIZING MOLTEN GLASS
2. Applicant(s):-
(a) Name: STERLITE TECHNOLOGIES LTD.
(b) Nationality: An Indian Company
(c) Address: E1/E2/E3, MIDC, Waluj, Aurangabad - 431136
Maharashtra, INDIA
3. Preamble to the Description:-
Provisional Specification:
The following specification describes nature of the present invention.

FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for stirring and in particular to a method and apparatus for stirring and homogenizing molten glass.
BACKGROUND OF THE INVENTION
[0002] Glass has been an important part of human life since the dawn of civilization as glass may be used for numerous purposes. Glass is generally obtained by mixing glass forming components, silica being the major component and heat-melting the components at a suitable temperature in a glass melting furnace. In order to obtain a good quality end product, stirring and homogenizing of the molten glass by stirrers is well-known in the prior art.
[0003] In accordance with the known art the molten glass is stirred and/or homogenized for several reasons. For instance, the molten glass formed in a furnace or forehearth may contain visible defects in the form of inhomogenities or discontinuities. These defects, known by a variety of names such as stones, cords, seeds, striae, mares, and tails may result from impurities in the glass or incomplete fining or incomplete blending of additives. If not sufficiently removed or dissipated, defects are carried over into the formed glass article, rendering the same unusable for any application.
[0004] Glass may also be stirred to remove thermal irregularities. It is known that when the temperature of the glass is uniform, it has predictable forming characteristics and better quality glass is produced.

[0005] In particular in the manufacture of glass sheets or substrates for use in fabrication of liquid crystal display panels, the chemical and thermal homogeneity of glass plays a vital role for good glass sheet forming operations.
[0006] In accordance with the known art the glass sheet or substrate manufacturing process comprises of melting the glass forming components in a glass melting furnace, fining the molten glass coming out of the glass melting furnace to remove gaseous inclusions, thereafter the glass is stirred for removal of chemical and thermal homogeneity, in form of cord or striae or ream of chemically dissimilar phases, using a stirrer of suitable material and dimensions. It is also known that the non-homogeneous components of the parent glass result from a range of normal occurrences during the melting process including refractory dissolution, melting stratification, glass surface volatilization, and temperature differences. The resulting cords are visible in the parent glass because of color and/or index differences.
[0007] Stirring the molten glass is one approach for improving the homogeneity of glass, wherein the molten glass is passed through vertically-oriented stir chamber, provided with one or more stirrers having a central shaft which is rotated by a suitable rotating means. A plurality of blades extend from the shaft and serve to mix the molten glass as it passes from the top to the bottom of the stir chamber.
[0008] One important aspect about the stirrer is that it has to have a high mixing or stirring efficiency.

[0009] Another important aspect related to the stirrer is the high throughput or the amount of glass stirred per unit time must be high.
[00010] Since the stir chamber along with the stirrer has to operate at very high temperatures of the order of 1500 °C or more, the stir chamber and the stirrer are to be made of material that can withstand such temperatures. Generally, platinum, rhodium or platinum, rhodium based alloys are utilized for fabricating the stir chamber and/or the stirrer, which are obviously exorbitantly expensive. Thus, the size of the stirrer and also the stir chamber has be to be optimized to sustain the stirring efficiency and through put and the cost of making the stirring device be reduced to a minimum.
[00011] If the stirring efficiency of the stirrer along with the through put can be improved, this would lead to increase in productivity as well as reduce the cost of fabricating or having large sized stirrers and stirring chambers.
[00012] Further, the stirring apparatus is known to erode owing to high temperatures and also high viscosity of glass, particularly, the inner portion of the stir chamber and the blades of the stirrer erode, leaving metal particles in the molten glass. This erosion may also occur due to high shear stress between the molten glass and parts of the stirring apparatus. The metal particles may degrade the quality of glass being formed and also result in undesired properties in form of inclusions or defects in the final glass sheets. It is thereby desired to reduce this erosion to a minimum if not completely eliminate them.
[00013] Therefore, there is a need to have an apparatus for stirring the molten glass such that the stirrer not only achieve high throughput and high mixing efficiency but

also the number of defects introduced into the molten glass are reduced, specifically the defects arising from the erosion of the parts of the stir chamber and/or the surfaces of the stirrer as a result of the stirring process.
OBJECTS OF THE PRESENT INVENTION
[00014] Accordingly, an object is to provide a method and apparatus for stirring and homogenizing molten glass.
[00015] Another object is to provide a method and apparatus for stirring and homogenizing molten glass for forming glass sheets or substrates to be used in fabricating display devices.
[00016]Still another object is to provide a method and apparatus for stirring and homogenizing molten glass having a high mixing or stirring efficiency.
[00017] Yet another object is to provide a method and apparatus for stirring and homogenizing molten glass having high throughput or the amount of glass stirred per unit time is high.
[00018] Another object is to provide a method and apparatus for stirring and homogenizing molten glass, wherein the defects introduced into the glass are reduced, specifically, defects arising from the erosion of the parts of the stir chamber and/or the surfaces of the stirrer as a result of the stirring process

[00019] Other objects and advantages of the present invention will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present invention.
BRIEF DESCRIPTION OF FIGURES OF THE INVENTION
[00020] FIG. 1 illustrates a cross-sectional view of a stirring apparatus in accordance with the embodiments of the present invention.
[00021] FIG. 2a illustrates a substantially concave shaped stirrer blade in accordance with one embodiment of the present invention.
[00022] FIG. 2b illustrates a substantially bowl shaped stirrer blade 103bn in accordance with one embodiment of the present invention.
[00023] FIG. 2c illustrates a substantially hemi-spheroid stirrer blade 103bn in accordance with one embodiment of the present invention.
[00024] FIG. 3a illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment, wherein the stirrer blade may have a hole or passage at the apex or vertex of the concave shape or bowl shape.
[00025] FIG. 3b illustrates a cross-sectional view of a stirrer blade in accordance with an alternate embodiment of the present invention wherein the stirrer blade has a pipe or conduit of suitable dimensions instead of a hole or passage.

[00026] FIG. 3c and 3d each illustrates a cross-sectional view of a stirrer blade in accordance with an alternate embodiment of the present invention, wherein the stirrer blade is provided with a patch.
[00027] FIG. 4 illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment of the present invention, wherein the length of the blade is longer in one direction as compared to that in other direction.
[00028] FIG. 4b illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment of the present invention, wherein the length of the blade is substantially equal to the length of the blade in other direction.
DESCRIPTION [NATURE] AND PREFERRED EMBODIMENTS OF THE INVENTION
[00029] The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein
[00030] The present invention achieves the objects by providing a method and apparatus for stirring molten glass such that the stirring apparatus of the present invention achieve high throughput and high mixing efficiency without introducing

defects into the resulting glass, in particular, defects arising from the erosion of the parts of the stir chamber and/or the surfaces of the stirrer as a result of the mixing process.
[00031] FIG. 1 illustrates a cross-sectional view of a stirring apparatus 100 in accordance with the embodiment of the present invention. The stirring apparatus 100 comprises a stir chamber 101 having a substantially cylindrical shape with a port 102a for molten glass to enter the stir chamber 101 and another port 102b for molten glass to move the stirred molten glass out of the stir chamber 101. A stirrer 103 comprising a central shaft 103a with plurality of blades 103bn [where n takes values 1, 2, 3 ...] extending from the shaft 103a which serve to mix the molten glass as it passes from the top to the bottom of the stir chamber 101, is provided enclosed within the stir chamber 101, wherein the stirrer blades 103bn are featured in having a shape which is substantially hemi-spheroid or concave or bowl shaped.
[00032] In accordance with the present invention the provision of the stirrer blades 103bn with substantially hemi-spheroid or concave or bowl shape scoops the molten glass in two directions which aids in better stirring of the molten glass.
[00033] FIG. 2a illustrates a substantially concave shaped stirrer blade 103bn in accordance with one embodiment of the present invention.
[00034] FIG. 2b illustrates a substantially bowl shaped stirrer blade 103bn in accordance with one embodiment of the present invention.

[00035] FIG. 2c illustrates a substantially hemi-spheroid stirrer blade 103bn in accordance with one embodiment of the present invention.
[00036] FIG. 3a illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment, wherein the stirrer blade may have a hole or passage at the apex or vertex of the concave shape or bowl shape, wherein the hole or the passage allows the molten glass flow through it
[0003 7] In accordance with this embodiment the hole or the passage may be such that it directly the flow of the molten glass in a particular direction.
[00038JFIG. 3b illustrates a cross-sectional view of a stirrer blade in accordance with an alternate embodiment of the present invention wherein the stirrer blade has the hole or passage may be a replaced by a pipe or conduit of suitable dimensions, wherein the provision of the pipe or conduit may be utilized to direct the molten glass flow appropriately.
[00039] FIG. 3c illustrates a cross-sectional view of a stirrer blade in accordance with an alternate embodiment of the present invention, wherein the stirrer blade is provided with a patch having a shape of a plate or grid and the patch is positioned such that it covers substantial part of the hole or the passage but is placed at a height h from the hole or passage.
[00040] FIG. 3d illustrates a cross-sectional view of a stirrer blade in accordance with an alternate embodiment of the present invention, wherein the stirrer blade is provided

with a patch having a shape of a plate or grid and the patch is positioned such that it covers substantial part of the hole or the passage but is directly on the hole or passage leaving no space there between.
[00041] FIG. 4a illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment of the present invention, wherein the length of the blade is longer in one direction as compared to that in other direction.
[00042] FIG. 4b illustrates a cross-sectional view of a stirrer blade in accordance with one embodiment of the present invention, wherein the length of the blade is substantially equal to the length of the blade in other direction.
[00043] In accordance with the embodiments of the present invention the blades have a shaped described by the mathematical equation:
z2 = ax2 + py2 + y
wherein a, p and y are constants and x and y are co-ordinates of a point on the surface of blade.
[00044] In accordance with the one embodiment of the present invention the values of the constants a, p and y are chosen suitably so as to have a desired shape of the stirrer blade.
[00045] In accordance with one embodiment of the present the clearance between the stirrer blade and the walls of the stir chamber is kept to a minimum possible value considering the expansion coefficients of the materials of make.

[00046] In accordance with one embodiment of the present invention the stirrer is provided with at least one blade on the stirrer shaft.
[00047] In accordance with one embodiment of the present invention the stirrer is provided with blades such that the ends far away from the shaft are reinforced with reinforcement means so as to withstand the high stress.
[00048] In accordance with one embodiment of the present invention a method of stirring the molten glass using the stirrer with the stirrer blades of the present invention is also disclosed. The method comprises providing a stirring apparatus 100 comprising a stir chamber 101 having a substantially cylindrical shape with a port 102a for molten glass to enter the stir chamber 101 and another port 102b for molten glass to move the stirred molten glass out of the stir chamber 101; providing a stirrer 103 comprising a central shaft 103a with plurality of blades 103bn [where n takes values 1, 2, 3 ...] extending from the shaft 103a which serve to mix the molten glass as it passes from the top to the bottom of the stir chamber 101, enclosed within the stir chamber 101, wherein the stirrer blades 103bn are featured in having a shape which is substantially hemi-spheroid or concave or bowl shaped; stirring the molten glass by rotating the shaft 103a by using the rotating means to achieve molten glass free from chemical and thermal inhomogenities.
[00049] Thus, the provision of substantially concave or hemi-spheroidal or concave shaped stirrer blades on the stirrer in a suitable combination, along with other features

disclosed herein, results in homogenized molten glass suitable for forming glass sheets or substrates to be used in fabricating display devices.
[00050] It is anticipated that the provision of substantially concave or hemi-spheroidal or concave shaped stirrer blades, along with other features disclosed herein, on the stirrer in a suitable combination results in enhanced mixing or stirring efficiency of the molten glass.
[00051] It is further anticipated that the provision of substantially concave or hemi-spheroidal or concave shaped stirrer blades on the stirrer, along with other features disclosed herein, in a suitable combination results in high throughput or the amount of glass stirred per unit time is high.
[00052] It is still further anticipated that the provision of substantially concave or hemi-spheroidal or concave shaped stirrer blades on the stirrer, along with other features disclosed herein, in a suitable combination results in reduced defects in the final glass sheets, specifically, defects arising from the erosion of the parts of the stir chamber and/or the surfaces of the stirrer as a result of the stirring process.
[00053] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood

that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.