Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
1999-08-26
2001-09-25
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S576000, C277S577000, C277S622000, C277S627000
Reexamination Certificate
active
06293557
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a sealing apparatus for chemical delivery systems and, more particularly to the process of introducing materials into the interior of tubular members, such as glass starter tubes used in making optical fiber pre-forms.
BACKGROUND OF THE INVENTION
While the following discussion deals with starter tubes and sealing arrangements for optical fiber pre-forms, it is to be understood that principles of the present invention are applicable to other, different applications involving, generally, chemical delivery systems. For example, the sealing arrangement of the invention is usable with the starter tube sealed vacuum system for collapsing the tube into the desired pre-form, as is shown in the aforementioned Mueller et al. application.
Optical fiber of the type used to carry optical signals is fabricated typically by heating and drawing a portion of an optical pre-form comprising a refractive core surrounded by a protective glass cladding. Presently, there are several known processes for fabricating pre-forms. The modified chemical vapor disposition (MCVD) process, which is described in U.S. Pat. No. 4,217,027 issued in the names of J. B. MacChensey et al. on Aug. 12, 1980 and assigned to Bell Laboratories, Inc. has been found to be one of the most useful because the process enables large scale production of pre-forms which yield very low loss optical fiber.
During the fabrication of pre-forms by the MCVD process, reactant-containing gases, such as SiCL
4
are passed through a rotating substrate tube which is made of silica glass. A torch heats the tube from the outside as the precursor gases are passed therethrough, causing deposition of submicron-sized glass particles on the inside surface of the tube. The torch is moved along the longitudinal axis of the tube in a plurality of passes to build up layer upon layer of glass to provide a pre-form tube. Once a sufficient number of layers have been deposited, the pre-form tube is then heated to cause it to be collapsed to yield a pre-form or pre-form rod as it is often called. The delivery system of the reactant gases to the starter tube interior is generally through a fixed metallic hollow tube connected to the source or sources of the gases. It is necessary that the space between the exterior surface of the delivery tube and the interior surface of the glass starter tube be sealed so that the critical gases do not leak out of the starter tube.
In the current method of manufacture, the apparatus which ensures sealed delivery of the deposition chemicals in the gases is a combination of a rotary union element, a structure for holding and sealing the starter tube, and a secondary face seal assembly for routing of purge gases through the structure. This is a complex apparatus that requires frequent maintenance. Existing systems also have the disadvantage of having inherently larger cavities for the accumulation of dead zones of flow, and a tendency to create particle contamination from the rotary union and face seal system. Inasmuch as the chemical delivery system is stationary, the current means of achieving delivery is via the rotary union, featuring a transition of the chemicals from a stationary pipe to a rotary pipe or to the inside of a supply coupling. The chemicals being delivered are at a pressure greater than atmospheric, and the face seal properties are the only restriction to the release of the chemicals to the atmosphere. The rotary union and secondary face seals generate a large quantity of particles from wear, and contribute to the contamination of the coupling. As the seals wear down, excessive leakage occurs both to the atmosphere and into the product (starter tube), resulting in lost product and requiring system maintenance. The complexity of the components involved requires skilled maintenance being performed using requalification through test of the system. Both material and labor costs are, consequently, high.
SUMMARY OF THE INVENTION
The present invention embodies an inventive sealing arrangement for introducing chemicals into the starter tube.
In more detail, the chemicals usually in the form of gases, are delivered into the starter tube by means of a stationary piping system. The rotary union is dispensed with and the delivery tube intruded into the interior of the starter tube. A stationary seal mounting member or hub is attached to the distal, open end of the delivery tube, preferably being threaded thereon, and forms the seal mounting point. A sealing member, sized to fit within the interior of the starter tube and forming a seal with the interior wall thereof is placed on the mounting member and secured thereto by a self-tightening fastener which is threaded onto the hub. The seal between the atmosphere and the interior of the starter tube is maintained by the physical properties of the seal and the deformation of the seal on the mounting member caused by the fastener. In operation, the seal fastener is constantly tightened by the rotation of the starter tube which, in turn, due to the friction between the seal and the inner wall of the starter tube, applies to the seal a torque which is transmitted to the seal fastener, causing it to be continuously tightened. The only wear surface is the contact between the seal and the inside wall of the glass starter tube, which is relatively minor in nature. Any particles generated by this interface wear tend to migrate to the atmosphere instead of into the glass tube inasmuch as the chemical gas pressure within the glass tube is greater than atmospheric. When wear does reach the point that the doping operation is compromised, the seal fastener is unscrewed and the seal discarded, to be replaced by a new seal.
In a second embodiment of the invention, the seal and fastener are combined into a single unit, which can be made completely of the seal material, such as Teflon® for example, and the entire unit discarded when leakage or wear becomes a problem. The mounting hub can be made integral with the end of the delivery tube and threaded to receive the fastener or the combined seal and fastener.
In still another embodiment of the invention, the seal can be made integral with the hub which is threaded to receive the fastener. In this case, the hub is threaded onto the end of the delivery tube, and the end is threaded to receive the fastener.
The numerous features and advantages of the present invention will be clearly presented in the following detailed description, read in conjunction with the accompanying drawings.
REFERENCES:
patent: 3807773 (1974-04-01), Brune
patent: 3900938 (1975-08-01), Blomgren, Sr. et al.
patent: 4217027 (1980-08-01), MacChesney et al.
patent: 4971614 (1990-11-01), D'Annessa et al.
patent: 5445052 (1995-08-01), Nichols, Jr.
patent: 5503438 (1996-04-01), Swauger
Knight Anthony
Lucent Technologies - Inc.
Pickard Albon K.
Thomas Kayden Horstemeyer & Risley LLP
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