Glass manufacturing – Fiber making apparatus – With specified bushing – tip – or feeder structure
Reexamination Certificate
1994-10-27
2001-03-06
Hoffmann, John (Department: 1731)
Glass manufacturing
Fiber making apparatus
With specified bushing, tip, or feeder structure
C065S495000
Reexamination Certificate
active
06196029
ABSTRACT:
TECHNICAL FIELD
The invention involves a bushing apparatus and method for making fiber from a molten material such as molten glass. More particularly, the present invention involves a bushing apparatus and a method for making fiber that reduces investment while providing a more uniform temperature profile across the orifice plate of the bushing.
BACKGROUND ART
In the manufacture of fiber from molten material, such as molten glasses, it has been common practice to use a bushing made of precious metal alloy. Precious metals are platinum, rhodium, palladium, ruthenium, and iridium. The bushings are electrically heated by their own resistance and are box-like, open on the top and comprise an orifice plate containing many nozzles or tips welded therein, sidewalls, end walls, terminals on the endwalls for connecting electrical cables, a top flange for contacting the underneath side of a forehearth, and usually a perforated plate or screen parallel with, but mounted above, the orifice plate. Usually the bushings are made by cutting the parts from alloy of desired thickness and welding the parts together with similar alloy, but a part or all of the bushing can be made by casting and/or drawing as shown by U.S. Pat. Nos. 4,207,086 and 4,078,413, which disclosures are hereby incorporated by reference.
The depth of the bushing between the top of the bushing and the top of the orifice plate was thought important to allow the glass to homogenize in temperature and viscosity before reaching the nozzles so that there would be uniform flow through all of the nozzles. As the molten glass flows through the openings in the refractory floor of the forehearth, the refractories forming the openings are cooler than the molten glass and remove heat from the molten glass in contact with the refractories. This creates a temperature profile in the column of molten glass entering the bushing. Usually a perforated plate or screen spans the opening close to the top of the bushing and is electrically heated to attempt to remove temperature differences in the glass and to bring the glass to a uniform, desired temperature for fiberization.
Removing the screen, and the sidewalls, from the bushing has been attempted with a much higher fiber break rate just below the bushing being the consistent result. It has been concluded that this higher break rate is caused by increased variation in the temperature and viscosity of the molten glass entering the nozzles due to the absence of the screen or the distance between the screen and the orifice plate, i.e. an insufficient length of the sidewalls in either case. As a result, the sidewalls were increased to try to achieve better glass uniformity. To conserve costly alloy, at least a substantial portion of the bushing sidewalls was made thinner than the orifice plate and the height of the sidewalls and endwalls exceeded at least three quarters of an inch, usually one inches or more, and frequently up to one and one half inch or more as evidenced by U.S. Pat. Nos. 4,272,271; 4,662,922 and 5,244,483, the disclosures of which are hereby incorporated by reference.
Because of the temperatures of the molten material being fiberized and the corrosiveness of the molten material, it is necessary to make the bushing from very expensive alloys like platinum-rhodium alloys typically containing 10-30% rhodium. These alloys are very expensive, usually exceeding seven thousand dollars per pound, and it is not unusual to have many tens of thousands of dollars tied up in each fiberizing position in alloy alone. Thus it has been desirable for decades to reduce the amount of alloy required while at least maintaining, and preferably improving, the variation in the temperature of the molten material entering the nozzles.
SUMMARY OF THE INVENTION
It is an object of the present invention to significantly reduce the amount of metal alloy needed for each fiberizing bushing while maintaining, and preferably improving, the temperature consistency of the molten material entering the nozzles in the orifice plate of the bushing.
Another object of the invention is a process of making fiber from a molten material by flowing the molten material through holes and/or nozzles in an orifice plate of an electrically heated bushing that requires significantly less investment in precious metal alloy than has been required with this type of process heretofore.
These objects are accomplished in the present invention by substantially reducing the height of the sidewalls and the endwalls of the fiberizing bushings and substantially reducing the depth of the bushings while maintaining, and usually improving, the consistency of the temperature and viscosity of the molten material entering the nozzles and/or orifices of the bushing.
The invention comprises a process of making fiber from a molten material by flowing the molten material into an electrically heated, precious metal alloy fiberizing bushing having a flange at the top, of the bushing at least one generally vertical side wall, an orifice plate having holes therein, and a perforated plate mounted in the bushing above the orifice plate, and causing the molten material to flow through the holes whereby fibers are formed below the orifice plate of the bushing in a continuous manner, the improvement comprising the wall or walls of the bushing being of such a length that the height of the bushing from the bottom surface of the flange to the top surface of the orifice plate being greater than about 0.2 inch and less than about 0.65 inch, preferably being no more than about 0.5 inch, and most preferably being about 0.4 inch in height. Normally the bushing would have two sidewalls and two endwalls, but two or all of these can be combined into a single wall, such as where the bushing is circular, oval, etc.
The invention further comprises a fiberizing bushing made of precious metal alloy suitable for being electrically heated and having flange means at the top, of the bushing at least one generally vertical side wall, an orifice plate having holes therein, and a perforated plate mounted in the bushing above the orifice plate, the improvement comprising that the at least one sidewall has a height such that the distance between the top surface of said flange means and the bottom surface of said orifice plate exceeds 0.25 inch but not about 0.75 inch, and preferably not exceeding about 0.62 inch, and most preferably not exceeding 0.5 inch. Although not necessary, it is preferred that the sidewalls are turned up extensions of the orifice plate.
REFERENCES:
patent: 2947028 (1960-08-01), Slayter
patent: 3512948 (1970-05-01), Glaser
patent: 4285711 (1981-08-01), Willis
patent: 4433991 (1984-02-01), Melan
patent: 4488891 (1984-12-01), Grubka
patent: 4536202 (1985-08-01), Perkins
patent: 4740224 (1988-04-01), Fowler
patent: 380596 (1973-05-01), None
Arterburn Russell Donovan
Melia Kurt George
Hoffmann John
Johns Manville International Inc.
Miller John H.
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