Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
2000-09-29
2002-09-24
Hoffmann, John M (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S475000, C065S495000
Reexamination Certificate
active
06453702
ABSTRACT:
The present invention involves an improved bushing apparatus for making fibers, particularly glass fibers and an improved method of making and using glass fiberizing bushings.
In the manufacture of continuous fibers from a molten material like molten glass, the molten material is often generated by a tank furnace and distributed to a plurality of fiberizing bushings via one or more channels and one or more bushing legs connected to the channel(s). Each bushing leg comes off the channel at about 90 degrees and contains a plurality of bushings that are spaced apart.
Precious metal bushings made from alloys of platinum and rhodium and used for making continuous glass fibers are well known, having been in use for more than 50 years. Many types of bushings exist for converting molten glass into continuous glass fiber and products. Typical types of bushings are shown in U.S. Pat. Nos. 3,512,948, 4,155,732, 4,272,271 and 4,285,712, the disclosures of which are hereby incorporated by reference. All the bushings shown in these patents teach the use of a perforated plate or screen, welded to the endwalls and sidewalls at some distance above a tip plate containing hundreds or thousands of nozzles or tips where molten glass first emerges from the bushing and is converted to continuous glass fibers by cooling and drawing, attenuating, in a known manner. Some of these patents teach various means of reinforcing the tip or orifice plate through which the molten material flows to form fibers. The bushings are electrically heated by their own resistance and are box-like, open on the top and comprise an orifice plate containing many orifices or tips welded therein, side walls, end walls, terminals on the end walls 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 as is known.
These bushings work well as long as the tip plate remains fairly flat. At the high temperature at which these bushings operate, usually above 2000 degrees F., the platinum-rhodium alloy tip plate creeps (stretches permanently under load) and sags with time until the amount of sag becomes so great that it is no longer possible to cool the tips and the molten glass forming the fibers below the tips sufficiently uniformly, at which time the break rate of fibers becomes very high and uneconomical. Very soon after the first fiber breaks out on a bushing making E glass, the most common glass used to make continuous fiber products, all of the fibers break out in a chain reaction due to one or more beads of molten glass falling from the broken out tip into the array of fibers from the other tips.
It is common practice to support tip plates from below the bushing with linear supports between rows of tips at one or more locations. These linear supports usually run down the length of the tip plate and must be a refractory and electrically insulating material or separated from the bushing with such a material.
In spite of the supports, the portions of the tip plate between the supports still sags and causes the temperature profile of the tip plate to be non-uniform because it causes tips to be different distances away from the cooling means commonly used such as finned cooling tubes or cooling fins. When this happens, portions tip plate, and tips therein, that have sagged the least run considerably hotter than the tips in the portions of the tip plate that have sagged the most because of the distance between the tips and the cooling means.
Since the heat transfer at these very hot temperatures is very dependent on the distance between the hot surface and a cold surface, distance variations are very critical to keeping the molten glass within an acceptable temperature range and viscosity to maintain fiberization, particularly in larger bushings containing 1600 or more tips or orifices. When tips, due to sag, get very close or touch a cooling tube or fin, the cooling rate causes the molten glass to cool excessively resulting in a viscosity so high that the fiber either breaks in the attenuation zone below the tip or in a much smaller diameter fiber which is broken more often due to defects in the molten glass that cause a higher break rate as the fiber diameter becomes smaller. Also, even if the cooling in the vertically lowest tips is not so great that too frequent breaks occur, nevertheless the fiber diameters generated from those tips are out of specification to the low side making the fiber diameter distribution from the entire bushing undesirable or unacceptable to the customers.
The cooling means can be adjusted some to compensate for sagging tip plates and tip ends being at a different level in different portions of the bushing, but this requires great skill in very uncomfortably hot conditions. Because of this and the proximity to surfaces that will produce severe burns, adjustments are not made as often as they should be. Also, frequently the bushing tips are damaged during such adjustments causing excessive fiber breaks from those tips and/or necessitating that those tips be crimped shut, reducing the productivity of the bushing. When this becomes uneconomical, the bushing must be shut down, removed and a new bushing installed. Often, for some time before the bushing is changed out, the bushing runs at a significantly lower productivity than a new bushing that has not yet sagged significantly.
It is very expensive to replace a bushing. As a result of development, large bushings of 3000 or more tips, such as 4000 or more tips, are now used for making the majority of the tonnage of continuous glass fiber produced today. Such bushings cost several thousands of dollars to fabricate even though the precious metal from removed bushings is recycled. A typical large producer will have more than 200 of such bushings in production. In addition to the fabrication cost of a new bushing, the labor, lost production and other damage to the forehearth and adjacent bushings adds substantial additional costs to the total cost of removing an inoperative bushing and installing a new bushing. These costs typically amount to more than $5,000 per bushing change.
It would be very advantageous to find a way to prevent, or substantially retard the rate of, tip plate sagging, thus extending the production time and average productivity or fiberizing efficiency of each bushing. The fiberizing efficiency is the percentage of time that the bushing is producing good fiber product compared to the total time the bushing is operating e.g. an operating efficiency of 94 percent means that the bushing is producing good fiber product 94 percent of the total time that the bushing is at operating temperature.
SUMMARY OF THE INVENTION
It is an object of the present invention to significantly reduce the rate of sag of tip or orifice plates on precious metal bushings improving the temperature consistency of the molten material exiting the tips or orifices in the tip or orifice plate of the bushing at over 1800, preferably 1900 degrees F. during the life of the bushing and to increase the average fiberizing efficiency over the life of the bushing and to increase the life of the tip or orifice plates 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 has a tip or orifice plate that resists sagging better than prior art bushings and that results in a better average efficiency during the normal bushing life than has been experienced with prior art processes.
Another object of the invention is a bushing used for, and a method of, making continuous glass fiber products that result in glass fibers having a lower variation of fiber diameters in the array of fibers coming from the bushin
Arterburn Russell Donovan
Hanna Terry Joe
Higginbotham James Melvin
Hoffmann John M
Johns Manville International Inc.
Touslee Robert D.
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