Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With purifying or homogenizing molten glass
Patent
1995-10-24
1998-04-28
Griffin, Steven P.
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With purifying or homogenizing molten glass
651341, 651351, 651356, 65346, 65347, 65356, 373 27, C03B 516, C03B 707
Patent
active
057439338
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for defibrating optically dense glass melts, such as a glass melt from basalt by the jet process, having feeding means (or "feeders") for the melt and defibrating aggregates, the feeding means having a feed channel and a subsequent distributing channel with outlet ports to the defibrating aggregates, and the melt being heatable from the surface. The present invention further relates to a corresponding method for applying the inventive apparatus.
2. Description of Prior Art
Apparatus and methods of the type in question have been known for years from practice and are used for producing mineral wool. To prevent the melt flowing to the defibrating aggregates or jets, which are usually in linear arrangement, from cooling off the melt is heated from the surface, this generally being done by hot gas.
With respect to the resulting temperature distribution in the melt stream it is essential that the heat transfer by radiation plays a much smaller part with optically dense or approximately dense glass than with clear glass. With optically dense glass, which includes basalt melts, the thermal transport to the bottom of the feeding means takes place almost solely by thermal conduction. The result is that a considerable temperature difference arises in the melt between the melt surface and the bottom of the feeding means, this difference being in turn dependent on the quality of the bottom insulation in the feeding means, or rather the feed channel. It has thus turned out in practice that the melt flowing through the feed channel has a vertical temperature gradient of up to 20.degree. per cm of melt height. This enormous temperature gradient affects the flow behavior of the melt stream, which is due to the pronounced temperature-dependent march of viscosity. A vertical velocity profile of the melt stream consequently arises, so that the melt located on the top in the feed channel, which is heated from above, flows faster than the melt near the bottom of the feed channel.
Furthermore the mass flowing through the feed channel, which is often referred to as the glass power, itself influences the temperature distribution. At high glass power, i.e. a high glass throughput through the feed channel, the abovementioned temperature gradient is lower, which is due to a shorter sojourn time within the feed channel. However the vertical temperature gradient increases toward the bottom of the feed channel.
The result of the abovementioned influences is that the defibrating aggregrates usually disposed in linear succession are supplied with melt of different temperature. The temperature differences in the melt occurring at the defibrating aggregates are sometimes so high that the operation of the first defibrating aggregate is interrupted by discontinuation of the melt flow due to a temperature decreasing toward the bottom, while the last defibrating aggregate is usually operated at the limit of maximum flow due to overheating. Power differences of up to 100% based on the glass throughput can consequently be detected. This in turn results in different qualities of the wool produced by the successive defibrating aggregrates e.g. by the jet process, which are unacceptable.
There have been attempts in the past to solve the above-described problem of interrupted operation of the first defibrating unit by discontinuation of the glass flow, which is also referred to as falling asleep, in different ways. For example DE-C 29 35 416 proposes an apparatus for uniformly heating a glass stream in a feeder wherein electric heating means leading through the melt stream, among other places, are to ensure a horizontal temperature balance in the feeder. The electric energy is often guided directly through the melt. Due to different temperatures, however, the melt has different conductances, the conductance increasing at a higher melt temperature. Primarily the already hotter melt is consequently heated even further, which is precisely what was to be
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Griffin Steven P.
Isover Saint-Gobain
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