Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
1997-07-21
2004-04-06
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S103000, C065S158000, C065S162000, C065S382000, C065S401000
Reexamination Certificate
active
06715317
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to a process for the production of a cylindrical component of glass by feeding a glass composition to a heating zone, by softening the glass composition in the heating zone, by continuously deforming the softened glass composition into the component under creation of a deformation zone within which the softened glass composition is plastically deform able, and by determining the cross-sectional geometry of the component.
The invention also pertains to an apparatus for implementing the process with a feed device, a heating device, and a take-off device, where the feed device continuously supplies a glass composition to the heating device, in which the glass composition is softened, and where the component is formed from the softened glass composition by means of the take-off device under creation of a deformation zone.
A process and an apparatus of the general type in question are described in DE-A1 195 36 960. A vertically oriented, tubular starting cylinder of quartz glass is supplied continuously by a feed device to a furnace, in which it is heated and softened zone by zone, starting from the bottom end. By the use of a take-off device, a tube is pulled off from the softened zone, the diameter of this tube being smaller than that of the starting cylinder.
When the quartz glass tube is drawn, a so-called “drawing bulb” is formed between the starting cylinder and the tube. In the area of the drawing bulb, the quartz glass is plastically deformable. The lower end of the drawing bulb has the same cross-sectional dimension as that of the tube, except for a small difference caused essentially by the thermal expansion of the quartz glass.
The outside diameter of the tube is measured below the drawing bulb. This measurement value is used to control the drawing parameters such as the furnace temperature and the drawing speed.
To prevent deviations in the geometry of the tube and to ensure the dimensional accuracy of the drawn-off tube, it is necessary in the known apparatus to maintain, in the area of the drawing bulb, the most homogeneous possible temperature field, which, in the ideal case, is radially symmetric around the longitudinal axis of the tube. When there are problems with the homogeneity of the temperature field, such as those which can be caused by, for example, measurement devices in the furnace area or maladjustments of the longitudinal axis of the tube with respect to the axis of symmetry of the temperature field, deviations from the ideal tube geometry are the unavoidable result. In particular, oval deformations are observed in practice in the case of tubes and rods which are circular in cross section. These deviations from the desired cross-sectional geometry of the component have an interfering effect on the subsequent steps of processing, so that these components must be discarded or must be subjected to expensive reprocessing to make them conform to nominal dimensions. Therefore, an attempt is usually made to ensure the most radially symmetric, homogeneous possible temperature field in the area of the drawing bulb by means of complicated and expensive furnace designs.
SUMMARY OF THE INVENTION
The invention is therefore based on the task of providing a simple and cost-effective process which makes it possible to obtain a component with only slight deviations from the desired cross-sectional geometry and to make available a suitable and flexible apparatus for achieving this end.
With respect to the process according to the invention, the softened glass composition is locally heated or cooled in at least one deformation area, which extends over only a part of the circumference of the deformation zone, as a function of a determined deviation of the cross-sectional geometry from a nominal geometry of the component.
By heating or cooling in the deformation zone, the viscosity of the glass is changed, and thus a controlled effect is exerted on the plastic deformation of the glass composition in the deformation zone. In the process according to the invention, the change in the viscosity and thus also the deformation of the glass composition differ from area to area as we proceed around the circumference of the deformation zone. This is achieved by heating or cooling a deformation area which extends over only a part of the circumference of the deformation zone.
The term “deformation zone” is understood to mean the zone in which the glass composition is plastically deformable and in which, through cooling or heating, the geometry of the component can be influenced. In processes in which the component is drawn from the glass composition, the deformation zone takes on the form of a drawing bulb. In processes in which the component is formed by thickening the glass composition in the deformation zone, the deformation zone can assume some other shape.
In a cross section perpendicular to the axis of the cylindrical component, the deformation area, at least one of which is present, extends over only a part of the circumference of the deformation zone. In the case of a deformation zone with a circular cross section, for example, the deformation area corresponds to an arc of a circle. By exerting local effects on the viscosity in the deformation area, the process according to the invention makes it possible to correct the cross-sectional geometry of the component without the need for tools.
It is also possible for several deformation areas to be distributed around the circumference of the deformation zone, but in any case, as a result of the cooling or heating in the deformation area overall, the viscosity of the glass composition is affected in different ways as we pass around the circumference of the cross section in the deformation zone. It must be remembered that producing a change in viscosity in even a single point in the deformation area will obviously also have an effect on adjacent parts of the deformation zone, although these effects will be obviously be weaker there. It is therefore impossible to precisely define or easily to detect optically a boundary around the deformation area or areas.
The deviation of the cross-sectional geometry from the nominal geometry of the component can be determined while the component is being formed from the softened glass composition. In this case, it is possible for the deviations which have been found to be taken directly into account during the further course of production. But is also possible to achieve the desired cross-sectional geometry by the use of the process according to the invention only after the component has been produced and after the deviations in its cross-sectional geometry have been determined, in which case the glass composition of the component must be softened again. No mechanical reprocessing of the component is required in either procedure.
The deviation of the cross-sectional geometry from the nominal geometry of the component can be determined by direct measurement of the component's geometry outside the deformation zone, but it can also be determined by measuring a suitable dimension in the deformation zone, if this dimension can be correlated with the component's final geometry.
The essential point is that, in the process according to the invention, the requirements on the homogeneity of the temperature profile in the heating zone are relatively low. Unwanted viscosity changes caused by disturbances of the temperature profile in this zone can be easily compensated. Thus, under the assumption that such disturbances will inevitably occur, it is possible to use relatively simple and low-cost heating systems to soften the glass composition without being forced to accept any loss of the component's dimensional accuracy.
The process according to the invention is independent of the concrete form of the cross section of the component. It is suitable, for example, for the production of tubes, rods, or fibers.
A procedure is preferred in which a stream of gas is directed against the glass composition in the deformation area. The glass composition is t
Bräuer Karsten
Fabian Heinz
Friedrich Helmut
Gänsicke Frank
Heraeus Tenevo AG
Milde & Hoffberg LLP
Vincent Sean
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