Abstract:
A nozzle for substantially laminar dispersion of gases at an angle to a central axis has a conically shaped portion and a stem portion. A chamfered bore allows a smooth entry of gas or vapor under pressure into a longitudinal bore within the stem portion which extends into the conical portion. A plurality of angularly oriented bores extend from the sloping face of the conical portion into the longitudinal bore forming sharp ridges at their intersection with the longitudinal bore, with the centerlines of the angular bores, all intersecting within the longitudinal bore. The conical portion is truncated and an axial bore extends from the truncated portion into the longitudinal bore. The diameters of the angular bores, the axial bore, and the longitudinal bore are chosen to insure the formation of sharp ridges to the exclusion of flat surfaces or lands.

Description:
RELATED APPLICATIONS 
     This invention is related to those shown in U.S. patent application Ser. No. 09/383,716 of P. M. Mueller and Ser. No. 09/383,780 of P. M. Mueller, both filed on Aug. 26, 1999, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a nozzle and sealing apparatus for chemical delivery systems using a gas delivery tube and, more particularly, to the process of introducing materials into the interior of tubular members through the nozzle. 
     BACKGROUND OF THE INVENTION 
     The following discussion deals with starter tubes and the gas delivery system for optical fiber pre-forms, but it is to be understood that principles of the present invention are applicable to other, different applications involving, generally, chemical delivery systems wherein the chemicals are in gaseous or vapor form. 
     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 deposition (MCVD) process, which is described in U.S. Pat. No. 4,217,027 issued in the names of J. B. MacChesney et al. on Aug. 12, 1980 and assigned to Bell Telephone 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 into a rotating substrate or starter tube which is made of silica glass. A torch heats the tube from the outside as the precursor gases are introduced therein, causing deposition of submicron-sized glass particles or soot 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 soot 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 rotating or fixed metallic hollow tube connected to the source or sources of the gases. 
     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 supply 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. 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. 
     In Mueller patent application Ser. No. 09/383,716, there is shown a sealing system that eliminates many drawbacks characteristic of prior art delivery systems, as enumerated in that application, such as, for example, the rotary union, by internally sealing the starter tube by means of a self tightening seal and mounting arrangement therefor. The basis of the arrangement of that application makes use of a constant rotational capability of the seal mounting hub for the self tightening feature. 
     In all such systems, it is generally the case that the chemical delivery tube is plugged at its distal end which protrudes into the starter tube, and ports are formed in the tube behind the plug, for example, two ports one hundred and eighty degrees apart, for allowing the gas to enter the starter tube interior toward the interior walls thereof, thus creating a radial nozzle. Such an arrangement, which is in widespread use, has the inherent disadvantage of having small port orifices through which all chemicals must be delivered to the starter tube. The ports act as orifice points with the inherent possibility of creating gas expansion problems, such as condensation and pressure drop related issues. The arrangement is non-self purging and does not allow for a complete unobstructed flow of products out of the delivery tube. Further, the plugging of the end of the delivery tube creates a dead zone or eddy volume between the plug and the orifices, where chemicals may become trapped or may pool. Potential contamination in the area (or volume) may build up in the absence of any means of self purging. As a consequence, frequent maintenance of the nozzle end of the delivery tube is necessary. In addition, gas flow exiting the nozzle is non-laminar, and, hence, does not guarantee a uniformity of coating of the interior wall of the starter tube, which is highly desirable. 
     SUMMARY OF THE INVENTION 
     The present invention is a dispersion nozzle for affixing to the delivery or distal end of the gas delivery tube, replacing the plug and orifice arrangement common in the prior art. 
     The nozzle of the invention is roughly conical in shape and has a cylindrical portion or stem extending from the rear or base of the conical portion. The stem is sized to be a press fit into the distal end of the delivery tube, and the nozzle, i.e, cone and stem, has a central bore extending from the rear toward the front (cone tip) of the nozzle. The tip end of the cone is truncated and has an axial bore therein communicating with the central bore, the axial bore having a smaller diameter than the central bore. Also communicating with the central bore are four circumferentially equally spaced, angularly oriented, bores which extend from the sloping face of the cone toward the central bore, such that they intersect. The rear end of the stem, that is, the end of the stem remote from the base of the cone, has an interior chamfer leading into the center bore which provides for a smooth flow of the gas into the bore and out of the angular bores and the axial bore. As a consequence, gases flowing into the central bore are dispersed into the starter tube both axially and radially. The gases within the nozzle flow uniformly without eddying, and, inasmuch as all passages in the nozzle are self purging, no dead zones are formed. The passageways, or bores, formed in the nozzle are sized such that no large pressure drop occurs during the chemical delivery, thereby minimizing any temperature change and likely condensation of the chemicals in the process area. With such an arrangement, flow out of the nozzle is substantially laminar and uniform. 
     As a consequence of the unique structure and performance of the nozzle of the invention, dead zones and eddies are substantially eliminated and contamination within the nozzle is minimized with a consequent minimization of the necessity for periodic maintenance. 
     These and other features and advantages of the present invention will be more readily apparent from the following detailed description, read in conjunction with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of an MCVD system utilizing the nozzle of the present invention; 
     FIG. 2 is a perspective, partially cross-sectional view of the delivery end of the delivery tube as used in the prior art for the system of FIG. 1; 
     FIG. 3 is a perspective, partially cross-sectional view of the delivery end of the delivery tube using the nozzle of the present invention; 
     FIG. 4 is a perspective view of the front face of the nozzle of the invention; 
     FIG. 5 is a perspective view of the rear of the nozzle of the invention; and 
     FIGS. 6 a  through  6   e  are various views of the nozzle of the invention. 
    
    
     DETAILED DESCRIPTION 
     As was discussed in the foregoing, gaseous pressure reactants together, usually with oxygen, are introduced into the rotating glass starter tube in a constantly moving stream from the distal or delivery end of a delivery tube. Homogeneously produced glass particles, commonly called “soot” collect on the tube walls and are fused thereto by a constantly moving hot zone. In FIG. 1 there is shown, diagrammatically, a typical arrangement for accomplishing the foregoing. 
     The apparatus  10  of FIG. 1 comprises a lathe  11  which has, axially disposed between the tailstock  12  and a headstock  13 , a starter tube  14  into which the gases are delivered from the distal end  15  of a delivery tube  16 . Tube  14  is held and rotated by an arbor  17  which is driven by suitable means, not shown, within headstock  13 , and which, preferably, extends through headstock  13 , as shown. Delivery tube  16  also extends, within the arbor shaft, through the headstock  13 . In accordance with the teachings of the aforementioned Mueller applications, delivery tube  16  is sealed within tube  14  by a sealing member  18  of the type disclosed in the Mueller applications. As pointed out in those applications, such a sealing arrangement makes it possible to use a non-rotating delivery tube  16 , thereby eliminating the need for a rotary union which, in the prior art, makes the transition from a stationary gas supply to a rotating delivery tube. Insofar as rotation of the starter tube  14  is concerned, it may be either clockwise or counter-clockwise. For purposes of the present discussion, and following the protocol of the Mueller applications, rotation will be considered as being counter-clockwise as viewed from the tailstock  12  toward the headstock  13 . 
     Delivery tube  16  is held in a stationary position within arbor  17  by suitable means  19 , which may take any of a number of forms and is connected at its proximal end to a suitable coupler  21  to which is connected a supply conduit  22  connected at its other end to a stationary pressurized gas supply  23 . A heat or flame source  24  is movably mounted on the lathe  11  for back-and-forth traversal of the length of tube  14 , as indicated by the arrows. 
     The sealing member  18  is self-tightening, as pointed out in the Mueller applications, i.e., as tube  14  rotates, it tends to tighten the seal mount, which is accomplished, for example, by a left-hand thread mounting arrangement. 
     In FIG. 2 there is shown in perspective, partially cross-section, a typical delivery nozzle arrangement  26  at the distal end  15  of delivery tube  16 , that is in common use today. The nozzle  26  comprises a plug  27  which preferably is a press fit within the distal end  15  of tube  16 . A plurality of radially disposed ports or orifices  28  are formed in delivery tube  16  in a region adjacent the rear of plug  27 , but free from any blockage thereby. In those installations when tube  16  rotates, a pair of ports  28 , one hundred and eighty degrees (180°) apart suffice to deliver the gases. Where the tube  16  is stationary, as shown in FIGS. 1 and 2, it is preferable that there be several such ports  28  spaced about the circumference of tube  16 . Seal member  18  is preferable mounted on delivery tube  16  by suitable mounting nuts  29  and  31 , as shown and described in one or more of the aforementioned Mueller applications. It is to be understood that other mounting arrangements for sealing member  18  might readily be used in place of nuts  29  and  31 . 
     In operation, gas under pressure is delivered in the direction of the arrow through delivery tube  16  which, at the distal end  15 , is blocked by plug  27  so that the gas is emitted through orifices or ports  28  in the direction of the interior wall of tube  14 . The ports  28 , being necessarily small, can create gas expansion problems such as condensation and pressure drop related problems. The ports, during prolonged usage, tend to clog up, thereby interfering with a free flow of gas. The space between rear of plug  27  and the ports  28  is a dead zone or eddy volume where chemicals and contamination particles may become trapped or pool, and which also disrupts the laminar flow of the gas, thereby causing possible non-uniformity of the coating on the interior wall of the tube  14 . 
     FIG. 3, which is substantially the same view as that of FIG. 2 depicts, in place of the plug and orifice nozzle  26  of FIG. 2, the nozzle  32  of the present invention, which is, preferably, a press fit in the distal end  15  of tube  16 . It is to be understood that, although the arrangement of FIG. 3 is for gas delivery into a starter tube  14 , the nozzle  32  is readily adaptable for use in other type systems. Nozzle  32  may also be used with a rotating delivery tube  16 . 
     FIGS. 4 and 5 are perspective views of the front and rear respectively of nozzle  32 . The nozzle  32  of FIGS. 4 and 5 which preferably is made of stainless steel, comprises a truncated cone portion  33  and a stem portion  34  which extends rearwardly from the base  36  of cone portion  33 . Stem portion  34  is preferably sized to be a press fit in distal end  15  of delivery tube  16 , and has a longitudinal central bore  37  extending into the interior of cone portion  33 . As pointed out hereinbefore, central bore  37  has a chamfer  38  at the rear end of stem portion  34  which lessens disruption of the gas flow as it enters bore  37 . Instead of a chamfer, the sloping surface  38  may be formed in other ways to have a rounded entrance lip  40 , which makes for an even smoother entrance into bore  37  for the gas stream. The gas makes a relatively smooth, disturbance free, transition from the interior of delivery tube  16  into central bore  37 . Extending into the interior of cone portion  33  from the sloping face thereof are a plurality of angularly oriented bores  39 , which, as shown, are substantially equally spaced from each other. Four such bores  39  are shown. It is possible that a different number of bores might be used, however, it has been found that four angular equally spaced bores are sufficient to achieve the desired performance from nozzle  32 . The tip or nose of cone portion  33 , which is truncated, has an axial bore  41  extending therefrom into the interior of nozzle  32 . Axial bore  41  is preferably smaller than the angular bores  39  and central bore  37 , with which it is coaxial, so that, in operation, a majority of the gas, which is under pressure, flows out of angular bores  39 , as will be discussed more fully hereinafter. 
     As best seen in FIG. 5, the diameter of the angular bores  39 , all of which are preferably of the same diameter, is so chosen that they intersect with central bore  37  to create sharp angular ridges  42  rather than flat surfaces or lands, which would be the case if they were of a smaller diameter. The ridges  42  function to divert the gas stream flowing in central bore  37  with a minimum of disturbance, into the angular bores  39  in substantially equal portions. Thus, the gas flow remains laminar and eddying is minimized. Because the four angular bores  39  create a much greater discharge area than axial bore  41 , the major portion of the gas exits through these ports. Although axial bore  41  is of smaller diameter, its diameter is so chosen that it intersects with angular bores  39 , thereby eliminating any flat areas which might block some gas and thereby create eddies. As can be seen in FIG. 5, axial bore  41  and angular bores  39  form, therebetween, sharp ridges  43  which produce a smooth transition of the gas into axial bore  41  and angular bores  39 . With the bores  39 , whose centerlines may, but not necessarily, intersect within bore  37 , configured in this way, and with bore  41  intersecting them, no flat surfaces or lands are formed in the interior of nozzle  32  and the gas flow, as a consequence, remains laminar despite being diverted from axial flow into bores  39 . 
     FIG. 6 a,  which is a side elevation view of nozzle  32  depicts the intersection of the centerlines of bores  39  within bore  37 . In addition to this orientation of the centerlines which are at an angular Ø relating to the central axis of nozzle  32 , the diameter of bores  39  is large enough so that the bores in effect, intersect each other, thereby forming the sharp ridges  42  which, as pointed out hereinbefore, insure the smooth transition of the gas flow from axial to angular. As an example, it has been found that an angle Ø of forty-five degrees (45°) and a bore  39  diameter to central bore  37  diameter ratio approximately 0.7 assures the desired configuration, i.e., the formation of sharp ridges  42  and  43 . The diameter of bore  41  to bore diameter  37  ratio is approximately 0.5 in this example. It is possible that the angle Ø may be chosen to be within a range of angles, and other diameter ratios might be used so long as the desired ridges are formed. However, the relationships given here have been found to yield excellent results. 
     From the foregoing it can be appreciated that the nozzle of the invention is a marked improvement over prior art nozzles, especially in that it is self purging, devoid of dead zones, does not cause eddying in the gas flow, and produces substantially laminar, uniform flow to the interior wall of the starter tube. 
     In conclusion, it should be noted that it will be obvious to those skilled in the art that many variations and modifications may be made to the preferred embodiment or embodiments without substantial departure from the principles of the present invention. All such variations and modifications are intended to be included herein as being within the scope of the present invention as set forth in the claims. Further, in the claims hereafter, the corresponding structure, materials, acts, and equivalents of all means or step plus function elements are intended to include any structure, materials, or acts for performing the functions with other specifically claimed elements.