Methods and apparatus for homogenizing molten glass
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
C03B-005/187
C03B-005/00
출원번호
US-0302661
(2002-11-22)
발명자
/ 주소
Goller,Martin H.
Murphy,James P.
Nolet,Daniel A.
Thomas,Robert R.
출원인 / 주소
Corning Incorporated
인용정보
피인용 횟수 :
8인용 특허 :
14
초록▼
The level of precious-metal inclusions in glass products, e. g., glass substrates for liquid crystal displays, is reduced by stirring molten glass in a stir chamber (11) under conditions such that the magnitude of the shear stress τ on the chamber's wall (19) and on the surfaces of the stirrer
The level of precious-metal inclusions in glass products, e. g., glass substrates for liquid crystal displays, is reduced by stirring molten glass in a stir chamber (11) under conditions such that the magnitude of the shear stress τ on the chamber's wall (19) and on the surfaces of the stirrer (13) is reduced while at the same time, the Q•E product for the system is kept high, where Q is the flow of glass through the stirring system and E is the system's stirring effectiveness.
대표청구항▼
What is claimed is: 1. A method for homogenizing molten glass comprising: (a) providing a cylindrically-shaped, substantially vertically-oriented stir chamber which comprises a wall having an internal diameter Dwall; (b) providing a stirrer within the stir chamber, said stirrer comprising a substan
What is claimed is: 1. A method for homogenizing molten glass comprising: (a) providing a cylindrically-shaped, substantially vertically-oriented stir chamber which comprises a wall having an internal diameter Dwall; (b) providing a stirrer within the stir chamber, said stirrer comprising a substantially vertically-oriented shaft and a plurality of blades which extend outward from the shaft towards the wall of the stir chamber, the maximum diameter of the blades being Dblade; (c) flowing molten glass through the stir chamber, said molten glass having a viscosity μ; and (d) applying a torque T to the shaft of the stirrer to rotate the stirrer within the stir chamber at a speed N as the molten glass flows through the chamber, said rotation of the stirrer within the chamber defining a swept volume V; wherein N, T, V, Dwall, Dblade, and μ are selected to satisfy the relationships: Relationship I: (NTV/μ)0.5≧5.0 kilograms/second, and Relationship II: (2πμNDblade)/(Dwall-Dblade) ≦3.5횞10-3 newtons/meter2, where N is in radians per second, T is in newton-meters, V is in meters3, Dwall is in meters, Dblade is in meters, and μ is in kg/meter-second, and where Relationship I is a measure of stirring effectiveness and glass flow rate, and Relationship II is a measure of sheer stress acting on the stirrer and the stir chamber wall. 2. The method of claim 1 wherein: (NTV/μ)0.5≧10.0 kilograms/second. 3. The method of claim 1 wherein: (2πμNDblade)/(Dwall-Dblade) ≦1.5횞10-3 newtons/meter2. 4. The method of claim 1 wherein T is less than or equal to 75 newton-meters. 5. The method of claim 1 wherein the molten glass flows through the stir chamber at a rate of at least 0.05 kilograms/second. 6. The method of claim 1 wherein the stirrer and the stir chamber wall each comprise platinum or a platinum alloy. 7. The method of claim 6 wherein the glass is liquid crystal display glass and the number of platinum-containing inclusions of a size greater than 10 microns is less than 20 per kilogram of finished glass. 8. The method of claim 1 wherein glass exiting the stir chamber undergoes a change in flow direction and the stirrer comprises at least one member for stirring the glass in the region of the change in flow direction, said at least one member having a longitudinal axis that is substantially parallel to, but not collinear with, the stirrer's shaft. 9. The method of claim 8 wherein the at least one member extends below the bottom of the stirrer's shaft. 10. The method of claim 8 wherein: (i) the stir chamber has a bottom and a side exit port in the region of the bottom, said exit port having a vertical height h, and (ii) said at least one member has a bottom end which is spaced from the bottom of the stir chamber by a distance d, where d satisfies the relationship: description="In-line Formulae" end="lead"2. 0h≦d≦0.7h.description="In-line Formulae" end="tail" 11. The method of claim 10 wherein d≈0.4h. 12. Apparatus for homogenizing flowing molten glass which has a viscosity μ, said apparatus comprising: (a) a cylindrically-shaped, substantially vertically-oriented stir chamber which comprises a wall having an internal diameter D wall; (b) a stirrer within the stir chamber, said stirrer comprising a substantially vertically-oriented shaft and a plurality of blades which extend outward from the shaft towards the wall of the stir chamber, the maximum diameter of the blades being Dblade; and (c) a motor which applies a torque T to the shaft of the stirrer to rotate the stirrer within the stir chamber at a speed N as molten glass flows through the chamber, said rotation of the stirrer within the chamber defining a swept volume V; wherein N, T, V, Dwall,Dblade, and μ satisfy the relationships: Relationship I: (NTV/μ)0.5≧5.0 kilograms/second, and Relationship II: (2πμNDblade)/(Dwall-Dblade)≦3.5 횞10-3 newtons/meter2, where N is in radians per second, T is in newton-meters, V is in meters3, Dwall is in meters, Dblade is in meters, and μ is in kilograms/meter-second, and where Relationship I is a measure of stirring effectiveness and glass flow rate, and Relationship II is a measure of sheer stress acting on the stirrer and the stir chamber wall. 13. The apparatus of claim 12 wherein: (NTV/μ)0.5≧10.0 kilograms/second. 14. The apparatus of claim 12 wherein: (2πμNDblade)/(Dwall-Dblade) ≦1.5횞10-3 newtons/meter2. 15. The apparatus of claim 12 wherein the motor applies a torque to the shaft that is less than or equal to 75 newton-meters. 16. The apparatus of claim 12 wherein the stirrer and the stir chamber wall each comprise platinum or a platinum alloy. 17. The apparatus of claim 12 wherein the stir chamber comprises a side exit port such that glass exiting the stir chamber undergoes a change in flow direction and the stirrer comprises at least one member for stirring the glass in the region of the change in flow direction, said at least one member having a longitudinal axis that is substantially parallel to, but not collinear with, the stirrer's shaft. 18. The apparatus of claim 17 wherein the at least one member extends below the bottom of the stirrer's shaft. 19. The apparatus of claim 17 wherein: (i) the stir chamber has a bottom, (ii) the side exit port is in the region of the bottom and has a vertical height h, and (iii) said at least one member has a bottom end which is spaced from the bottom of the stir chamber by a distance d, where d satisfies the relationship: description="In-line Formulae" end="lead"0. 2h≦d≦0.7h.description="In-line Formulae" end="tail" 20. The apparatus of claim 19 wherein d≈0.4h. 21. Apparatus for homogenizing molten glass comprising: (a) a cylindrically-shaped, substantially vertically-oriented stir chamber which comprises a wall; and (b) a stirrer within the stir chamber, said stirrer comprising a substantially vertically-oriented shaft and a plurality of blades which extend outward from the shaft towards the wall of the stir chamber and create substantial radial flow of the glass passing through the stir chamber; wherein: (i) the stir chamber comprises a side exit port such that glass exiting the stir chamber undergoes a change in flow direction; (ii) the stirrer comprises at least one member for stirring the glass in the region of the change in flow direction, said at least one member having a longitudinal axis that is substantially parallel to, but not collinear with, the stirrer's shaft; and (iii) said at least one member does not create substantial radial flow of the glass passing through the stir chamber. 22. The apparatus of claim 21 wherein the at least one member extends below the bottom of the stirrer's shaft. 23. The apparatus of claim 21 wherein: (i) the stir chamber has a bottom, (ii) the side exit port is in the region of the bottom and has a vertical height h, and (iii) said at least one member has a bottom end which is spaced from the bottom of the stir chamber by a distance d, where d satisfies the relationship: description="In-line Formulae" end="lead"0. 2h≦d≦0.7h.description="In-line Formulae" end="tail" 24. The apparatus of claim 23 wherein d≈0.4h. 25. A method for homogenizing molten glass comprising: (a) providing a cylindrically-shaped, substantially vertically-oriented stir chamber which comprises a wall having an internal diameter Dwall; (b) providing a stirrer within the stir chamber, said stirrer comprising a substantially vertically-oriented shaft and a plurality of blades which extend outward from the shaft towards the wall of the stir chamber, the maximum diameter of the blades being Dblade; (c) flowing molten glass through the stir chamber, said molten glass having a viscosity μ; and (d) applying a torque T to the shaft of the stirrer to rotate the stirrer within the stir chamber at a speed N as the molten glass flows through the chamber, said rotation of the stirrer within the chamber defining a swept volume V; wherein: (i) the glass is a liquid crystal display glass; (ii) the stirrer and the stir chamber wall each comprise platinum or a platinum alloy; (iii) the molten glass flows through the stir chamber at a rate of at least 0.05 kilograms/second; and (iv) Dblade in combination with N. T. V. Dwall and μ are selected based on glass flow rate, stirring effectiveness, and sheer stress acting on the stirrer and the stir chamber wall so that when the molten glass flows through the stir chamber at said rate of at least 0.05 kilograms/second, the finished glass has a level of cord which is sufficiently low to permit the glass to be used as a glass substrate for a liquid crystal display, and the number of platinum-containing inclusions in the finished glass of a size greater than 10 microns is less than 20 per kilogram of finished glass.
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