Glass manufacturing – Fiber making apparatus – With designated composition of dies – bushings – or nozzles
Reexamination Certificate
2001-12-17
2004-11-30
Hoffmann, John (Department: 1731)
Glass manufacturing
Fiber making apparatus
With designated composition of dies, bushings, or nozzles
C065S314000, C065S521000
Reexamination Certificate
active
06823698
ABSTRACT:
The present invention relates to high temperature resistant metallurgy for improving the spinner discs utilized in high temperature rotary glass fiberization processes. These processes produce glass fibers through the extrusion of high temperature molten glass through fiberizing orifices in the peripheral sidewalls of the spinner discs. More specifically, the invention relates to the formation of these spinner discs from high temperature resistant aluminide of nickel alloys, i.e. Ni
3
Al and NiAl alloys, rather than the expensive cobalt alloys currently used to make such spinners. The aluminide of nickel alloys of the spinner discs of the present invention exhibit sufficient strength and ductility at room temperature to withstand the harsh thermal shock encountered by these spinner discs during process start-up. At the elevated temperatures utilized in these processes (temperatures in excess of 1800° F.), the aluminide of nickel alloys of the spinner discs of the present invention exhibit creep strengths comparable to the creep strengths of the cobalt alloys presently in use and hot corrosion resistances superior to the hot corrosion resistances of the cobalt alloys presently in use.
High temperature rotary glass fiberization processes fiberize molten glass by using centrifugal force to pass the molten glass through rows of fiberizing holes in an annular peripheral sidewall of a spinner disc. These fiberization processes typically fiberize the molten glass at temperatures in excess of 1800° F. The base plate of a spinner disc has a central bore therein on a rotational axis of the spinner disc for mounting the spinner disc on a drive shaft; an outer annular portion for receiving the hot molten glass to be fiberized; and an inner annular portion intermediate the central bore and the outer annular base plate portion. The spinner disc is normally preheated during the start-up of such high temperature fiberizing operations to reduce the stresses in the spinner disc at the start-up of a fiberizing operation. However, during start-up when the hot molten glass at temperatures in excess of 1800° F. is first introduced onto the outer annular portion of the spinner disc base plate, the temperature differential between the outer annular portion of the base plate and the inner annular portion of the base plate, adjacent the central bore, can be in excess of 800° F. or 900° F. with the temperature of the outer annular portion of the base plate about 1400° F. and the temperature of the inner annular portion of the base plate, adjacent the central bore, about 500° F. This transient temperature differential at start-up sets up transient compressive stresses in the outer annular portion of the base plate and transient tensile stresses in the inner annular portion of the base plate which can cause the base plate of the spinner disc to rupture, come apart or fail and, thus, the spinner disc, which is typically rotating at thousands of revolutions per minute, to fail at the start-up of the fiberizing operation. The potential for such failures presents both operational and safety problems in a commercial production line. Accordingly, an alloy used in the fabrication of such spinner discs should have a yield strength capable of withstanding the high initial transient stresses produced in the spinner disc during start-up.
In addition to having a yield strength that enables the spinner discs made from the alloy to withstand the high initial transient stresses at start-up, the alloy of spinner discs used these high temperature rotary fiberization processes must exhibit creep strengths and corrosion resistances at the elevated temperatures of these processes that provide these spinner discs with a commercially acceptable service life.
Currently, elevated temperature resistant cobalt based alloys are typically used for spinner discs in rotary glass fiberization processes. The cobalt alloys are used for this application due to their superior performance when compared to similar iron based alloys and nickel based alloys without aluminum. When compared to similar iron based alloys and nickel based alloys, without aluminum, at the elevated temperatures utilized in these glass fiberization processes, these cobalt based alloys exhibit superior strength and creep resistance as well as improved elevated temperature corrosion resistance.
The cobalt based alloys used in these spinner discs consist of a strong and corrosion resistant Co—Cr matrix, which is further strengthened, with a dispersion of coarse, strong carbides. Carbides in the microstructures are second phase strengtheners, the bulk of which are produced during the casting-solidification process. Cr
23
—C
6
represent the dominant carbide by volume, however, Mo
x
C
y
carbide also forms. The Mo carbides tend to be more thermally stable, they melt at higher temperatures, yet the process of Mo can be extremely detrimental in certain hot corrosion, sulfidation environments, because it alters corrosion product chemistry and accelerates corrosion. While these carbides are strong and impart improved elevated temperature strength to the cobalt based alloys, they also provide a short circuit path for oxidation, sulfidation, and other forms of elevated temperature corrosion. The carbides have another detrimental feature in that these carbides are the last “portion” of the microstructure to freeze and the first to melt. Hence, for the components contained in the alloy, the phase relied upon for strength melts at the lowest temperature thereby limiting the maximum useful service temperature of the alloy.
Spinner discs fabricated from cobalt-based alloys have a service life ranging from about 35 to about 55 hours. The cobalt based alloys utilized in the fabrication of these spinner discs typically cost in excess of $15.00 per pound and, since they are uniquely formulated to meet the demanding service requirements of glass fiberization, these alloys are worth very little as scrap. To reduce costs manufacturers recycle the alloy and maintain an alloy pool of the specifically formulated cobalt alloy. However, since the alloy acquires impurities during service, the alloy must be refined before it can again be incorporated into the alloy pool. Thus, the manufacturer incurs the expense of maintaining an alloy pool and of refining alloy to be included in the alloy pool from spent spinner discs. With the relatively short service life of these spinner discs and the number of spinner discs utilized on various production lines, the amount of alloy required to maintain an adequate alloy pool for disc fabrication and the expenses incurred in connection with such alloy pools are significant.
For the aforementioned reasons, alloy design and development becomes an engineering trade-off between structure-property-performance-process and alloy costs. Structure-property-performance-process trade-offs must be optimized to attain the best alloy environmental properties (corrosion resistance to the molten glass being fiberized at the elevated temperatures in the fiberizing environment) and the best alloy mechanical properties both at room temperature for startup and at the elevated fiberizing temperatures. The use of relatively low cost alloys with these enhanced environmental properties and mechanical properties will result in optimized disc service life and performance at lower manufacturing costs.
SUMMARY OF THE INVENTION
Attempts to develop new relatively inexpensive alloys to improve spinner disc service life are challenging, as corrosion and oxidation resistance, mechanical properties and alloy costs must be properly balanced. In the aluminide of nickel alloy of the spinner discs of the present invention, the use of intermetallic compounds of aluminides of nickel, i.e. Ni
3
Al and NiAl, offers the ability to strengthen the alloy with phases other than carbides, which, as discussed above, selectively corrode relative to the matrix. In addition, cast aluminides of nickel produce a more homogeneous alloy compared to cobalt alloys and an alumina corrosion resistant film, both of whic
Hoffmann John
Johns Manville International Inc.
Touslee Robert D.
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