Apparatus for drying and / or consolidating at least partially porous optical fiber preform

Abstract

An apparatus (10) for drying and / or consolidating an at least partially porous optical fiber preform, comprising a cover (30), a cover cap (32), and a sealing assembly (70) comprising a first sealing element (80) housed within an interior space (34) of the cover (30) and a second sealing element (90) on top of the cover cap (32), the first sealing element (80) and the second sealing element (90) include respective first and second annular seals (82, 92) and first and second expandable members (83, 93) configured to allow passage of the support bar (18) and configured to expand, contract and bend, each of the first and second annular seals (82, 92) is located radially inward of the respective first and second expandable members (83, 93) and is operatively connected to the respective first and second expandable members (83, 93), the respective annular seals (82, 92) being dimensioned to be adapted to directly contact the support bar (18).

Description

Technical Field

[0001] The present disclosure relates to a device for processing an optical fiber preform, in particular to a preform for producing a transmission optical fiber. Background Art

[0002] A common procedure for obtaining a glass preform to be drawn down into an optical fiber suitable for telecommunications applications comprises a first process for producing a solid glass core rod and a second process for adding an outer cladding to the core rod, for example by depositing soot around the core rod or by enclosing the core rod in a glass tube (rod-in-tube technique).

[0003] The core rods may be manufactured by external deposition processes such as external vapor deposition (OVD) and vapor axial deposition (VAD), or by internal deposition processes such as modified chemical vapor deposition or furnace chemical vapor deposition (MCVD / FCVD), or plasma chemical vapor deposition (PCVD). When manufactured by OVD or VAD, a soot precursor body is formed, which is dried to remove water and consolidated to form a core glass body. To reduce the diameter of the glass body, it is often stretched after consolidation and then the glass body is cut into a plurality of core rods.

[0004] A flame hydrolysis deposition process, such as by OVD, is often used to form the cladding region on the core rod because it allows a relatively fast and economical process for producing soot optical preforms from the core rod. The partially porous soot preforms are subsequently treated with a desiccant and then consolidated into a dense glass preform in a furnace at a temperature above the glass transition temperature.

[0005] In a process commonly used for dehydration and consolidation, a porous or partially porous soot preform is inserted into a furnace including a cylindrical muffle. After vitrification, the preform is then pulled above the furnace as a transparent silica glass preform.

[0006] Drying is performed by heating the preform in the presence of one or more drying gases, such as a mixture of helium and chlorine, to a typical temperature of about 1100° C. Consolidation is performed by heating the dried preform, typically to a temperature between 1400° C. and 1600° C.

[0007] Given that drying and consolidation occur at different temperatures, furnace muffles are often configured with different zones for the drying phase and the consolidation phase. In some furnaces, during consolidation, the preform descends through a central hot zone that is set at a temperature that causes consolidation of the soot preform. In furnace tubes configured to accommodate preforms moving across zones at different temperatures for dehydration and consolidation, it is typically desirable that the length of the chamber be at least twice the length of the preform.

[0008] By using larger preforms, such as preforms of increased length (eg, in excess of 2 m), cost savings may be achieved.

[0009] WO 2018 / 177514 A1 relates to an apparatus and method for drying and consolidating preforms, comprising a chamber for accommodating at least a length portion of the preform, wherein the chamber can be connected to a first elongated chamber of a furnace tube so as to form a vertical extension of the first elongated chamber. The drying process can start with a preform that is not fully inserted into the furnace tube, and the total length of the furnace tube can be kept relatively short relative to the length of the preform.

[0010] Unpublished patent application IT102022000010907A relates to an apparatus for drying and / or consolidating an optical fiber preform, comprising:

[0011] a muffle configured to accommodate the preform, the muffle having a muffle opening at its top side, the muffle opening being configured to allow the preform to pass through;

[0012] an extension tube configured to receive at least a length portion of the preform, the extension tube being removably attached to the muffle tube to close the muffle opening to form a single chamber,

[0013] a cover arranged on the top side of the extension pipe to define an internal space and including a discharge port, and

[0014] - A sealing assembly operatively connected to the cover and comprising an annular seal and an expandable member configured to allow passage of a support rod and configured to expand and contract in a vertical direction, wherein the annular seal is located radially inward of the expandable member and operatively connected thereto and has an inner diameter configured to directly contact the support rod.

[0015] US2006 / 0112733 A1 addresses the problem of how to suppress gas leakage in the joint between the furnace muffle and the cover. The apparatus for preparing a glass preform described in the document includes a furnace muffle in which a main body of a soot glass deposit is arranged; a cover for sealing an inlet-outlet of the furnace muffle, and a heater for heating the main body of the soot glass deposit. Summary of the invention

[0016] Dehydration and consolidation of the optical fiber preform in the furnace is typically carried out under the flow of an inert gas or a gas mixture containing an inert gas. Helium is a preferred inert gas because it can be easily dissolved in the preform as a single gas (e.g., during consolidation) and as a diluent carrier gas (such as during dehydration with chlorine-containing compounds or during fluorine doping of the preform).

[0017] Applicants have observed that the quality of the consolidated preform depends, among other factors, on the gas flow rate of helium during preform processing. In particular, defects in drawn optical fiber due to the presence of air have been associated with insufficient helium flow in the furnace. In many cases, bubbles / holes affect discontinuous short lengths of optical fiber, and these defects are generally referred to as "airlines".

[0018] Air lines and defects associated therewith can be detected from diameter measurements of the optical fiber during the drawing process, and in particular from diameter oscillations. A parameter indicative of the quality of an optical fiber is the so-called draw cumulative defect ratio (DCDR), which is defined as the ratio of the sum of the lengths (e.g. in meters) of defective drawn fiber portions shorter than 18 m to the total drawn fiber length. A good quality of an optical fiber is typically associated with a DCDR value of less than 2%, preferably less than 1%.

[0019] In a process commonly used for dehydration and consolidation, the soot preform is inserted into a furnace comprising a quartz muffle tube, which is generally cylindrical in shape. The preform is suspended by a handle, which is connected to the preform or is integral with the preform and is used for inserting the preform into the furnace or extracting it from the furnace, and is typically used for rotating the preform about its longitudinal axis. To this end, the upper end of the preform handle is connected to a motion system for translational and rotational movement.

[0020] The hood or any cover closing the top of the furnace tube requires a central aperture for the preform supported by the handle to be inserted / extracted into / from the furnace tube. The applicant has noticed that if on the one hand the central aperture should be designed to minimize or avoid gas leakage from the furnace, on the other hand any design should allow safe up and down movement and rotation of the supporting handle within the central aperture.

[0021] Furthermore, the applicant has observed that the support handle, which is typically made of quartz, is often not accurately machined. This can result in gas flowing out of the top center orifice during vertical movement and rotation of the preformed handle.

[0022] The applicant has considered that, although the gas quantities involved are expected to be small, the helium consumption may actually be significant, considering that the process time for preform dehydration and consolidation may last for example 16 to 20 hours, with a helium consumption of about 25-35 l / min.

[0023] The quartz support handle carries a relatively heavy preform (e.g., 5-100 kg) while performing vertical and rotational motion. Under these conditions, the handle is susceptible to stress accumulation, which can cause off-axis bending, resulting in ovality or more generally lack of consistency in the consolidated preform.

[0024] The Applicant has considered a furnace comprising a muffle closed at the top by a hood and has designed a sealing assembly positioned inside the hood which is intended to reduce the leakage of process gases from the chamber of the furnace to the outside.

[0025] Disclosed herein is an apparatus for drying and / or consolidating an at least partially porous optical fiber preform, the apparatus comprising:

[0026] a furnace comprising a muffle extending along a vertical axis and forming a muffle chamber configured to accommodate the preforms, the muffle having at its top side an upper muffle opening configured to allow the preforms to pass therethrough;

[0027] a hollow connecting member having an inner diameter configured to allow the passage of the preform and extending along a vertical axis, the connecting member being removably connected to the muffle tube at the muffle opening;

[0028] - a cover positioned on top of the connecting member, the cover being removably connected to the connecting member or being integral with the connecting member, the cover having an inner space vertically aligned with the connecting member, wherein the cover comprises a cover cap closing the cover at the cover top, wherein the cover cap comprises a through hole axially aligned with the muffle opening, the cover cap through hole being configured for passage of a cylindrical support rod supporting a handle, the cylindrical support rod supporting the handle being used to suspend the preform; and

[0029] a sealing assembly comprising a first sealing element housed within the interior space of the cover and a second sealing element on top of the cover, the first sealing element and the second sealing element both being substantially centered about a vertical axis,

[0030] Wherein, the first sealing element and the second sealing element include corresponding first and second annular seals and first and second expandable members, the first and second expandable members having a generally tubular shape, being configured to allow a support rod to pass through and being configured to expand, contract and bend, wherein each of the first and second annular seals is located radially inside the corresponding first and second expandable members and is operably connected to the corresponding first and second expandable members, and the size of the annular seals is designed to directly contact the support rod.

[0031] The first and second sealing elements of the present description allow for the use of reduced helium flow rates during processing of preforms by preventing direct or indirect infiltration of air into the processing chamber and maintaining the quality of the consolidated preform.

[0032] The first and second expandable members may expand and contract primarily in the vertical direction, but may also expand and contract, albeit to a lesser extent, in the radial direction. The first and second expandable members may also flex in the event that the support rod is not aligned with the vertical axis.

[0033] Providing a sealing assembly including an axially expandable member (similar to the expandable member of the present disclosure) allows absorbing mechanical stresses caused by potential deviations not only in the axial direction but also in the radial direction, which may be caused by vertical movement and rotation of the support handle and / or small changes in internal pressure in the processing chamber due to gas flowing in the processing chamber. Given its flexibility, the expandable member can help improve the centering of the support handle and manage micro-variations in pressure.

[0034] In one or more embodiments, the expandable member is made of a polymer material. For example, the expandable member is made of a thermoplastic polymer. For example, the expandable member is made of a thermoplastic fluoropolymer such as PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene) or PFA (perfluoroalkoxyalkane).

[0035] In one embodiment, the connecting member comprises a tubular body extending along a vertical axis of the device.

[0036] In one embodiment, the connecting member has a length taken along the vertical axis (Z) of from 5 cm to 20 cm.

[0037] In one embodiment, the tubular body has a finned outer surface.

[0038] In one embodiment, each of the first expandable member and the second expandable member comprises:

[0039] - a corrugated portion configured to expand, contract and bend;

[0040] - an axially non-expandable portion which adjoins the corrugated portion along the vertical axis; and

[0041] - A base adjacent to the corrugated portion and opposite the non-expandable portion, the expandable member base extending radially outwardly from the corrugated portion.

[0042] In one embodiment, the first and second annular seals are joined to the non-axially expandable portions of the associated first and second expandable members.

[0043] In one embodiment, the non-axially expandable portion that joins the first annular seal and the second annular seal is located on top of the corrugated portion.

[0044] In one embodiment, each of the first and second annular seals has an inner diameter configured to directly contact the support rod. In one embodiment, the inner diameter of each of the first and second seals is sized to tightly connect with the support rod.

[0045] The first and second expandable members have an inner diameter that varies over the length, decreasing to a minimum value that is larger than the inner diameter of the associated annular seal so as to allow passage of the support rod.

[0046] In one embodiment, the cover comprises a cover side wall and a lower flange located opposite to the cover cap. The cover lower flange extends radially inward from the cover side wall and has an inner diameter substantially equal to the inner diameter of the connecting member.

[0047] In one embodiment, the apparatus of the present disclosure further comprises a lower cover plate configured to be positioned on the lower flange of the cover. The lower cover plate has a through hole aligned with the through hole of the cover cap and an outer diameter greater than the inner diameter of the connecting member.

[0048] The lower cover plate defines an interior space of the hood together with the hood side walls and the hood cover.

[0049] In one embodiment, the cover is removably connected to the connecting member. In this case, the connecting member includes an upper flange at the top of its tubular body and extending radially outward from the tubular body, and the cover lower flange is positioned on this upper flange of the connecting member and connected to it, for example by a connecting element, such as a screw.

[0050] In one embodiment, the cover is integral with the connecting member, and the cover lower flange is integral with the tubular body of the connecting member. In this case, the cover lower flange is a common flange for both the connecting member and the cover.

[0051] In one embodiment, the sealing assembly further comprises:

[0052] - a plurality of springs extending parallel to the vertical axis of the device and arranged to radially surround the first sealing element; and

[0053] - an annular supporting flange arranged on the lower cover plate, a plurality of springs being constrained at one end to the supporting flange and extending from the supporting flange towards the cover.

[0054] In one embodiment, each of the plurality of springs is mounted on a corresponding vertical support element that is fixed to the support flange. Each of the plurality of springs may be longer than the corresponding vertical support element and may have a length that is dimensioned to extend from the annular flange to the cover.

[0055] In one embodiment, the first sealing element is mounted on the annular support flange via an expandable member base.

[0056] In one embodiment, the apparatus of the present disclosure further includes an upper cover plate disposed on the cover and having a central through hole aligned with the through hole of the cover.

[0057] In one embodiment, the second sealing element extends from the upper cover plate in axial alignment with the first sealing element.

[0058] In the present description and claims, "axial direction" or "axially" means a direction substantially parallel to an axis taken along the main extension of the furnace, in particular the muffle, and the vertical movement of the preform.

[0059] “Radially” or “radial direction” means a direction substantially perpendicular to the axial direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will now be described in more detail below with reference to the accompanying drawings, in which some but not all embodiments of the present invention are shown. Generally, the same reference numerals will be used for possible variant embodiments of similar elements. The accompanying drawings of the illustrated embodiments are schematic representations.

[0061] For the purposes of this description and the appended claims, unless otherwise indicated, all numbers expressing quantities, amounts, percentages, and the like are to be understood in all instances as being modified by the term “about.” Furthermore, all ranges include the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0062] For the purpose of this description and the appended claims, the words "a" and "an" should be read to include one or at least one and the singular also includes the plural, unless it is obvious that there is another meaning. This is done merely for convenience and to give a general sense of the disclosure.

[0063] Figure 1 is a partial front view of an apparatus for drying and consolidating an optical fiber preform according to an embodiment consistent with the present disclosure, the apparatus being at a stage of a process in which the preform is partially inserted into a muffle of a furnace.

[0064] Figure 2 is a partial perspective view of a shrouded muffle of a furnace according to an embodiment consistent with the present disclosure, with the muffle partially shown.

[0065] Figure 3 yes Figure 2 A partially exploded perspective view of a shrouded muffle tube.

[0066] Figure 4is a partial perspective view of a top portion of a shrouded muffle according to an embodiment consistent with the present disclosure. Some components are shown in cross-section.

[0067] Figure 5 is a partial perspective view of a top portion of a shrouded muffle according to yet another embodiment consistent with the present disclosure. Some components are shown in cross-section.

[0068] Figure 6 is an exploded perspective view of a first sealing element according to an embodiment consistent with the present disclosure.

[0069] Figure 7 Yes Figure 6 An exploded perspective view of a sealing assembly of a first sealing element and a second sealing element.

[0070] Figure 8 is an exploded perspective view of a cover and a connecting member according to an embodiment, wherein the cover and the connecting member are separate elements.

[0071] The present disclosure may be implemented according to one or more of the present embodiments optionally combined together. DETAILED DESCRIPTION

[0072] Figure 1 There is illustrated an apparatus 10 for processing an optical fiber preform 16 in an embodiment consistent with the present disclosure. The apparatus 10 comprises a furnace 20, which may be of conventional type, comprising a muffle 11 of substantially cylindrical shape. The furnace 20, and in particular the muffle 11, extends along a vertical axis indicated by Z. The double arrow L indicates the axial or vertical direction in which the preform 16 moves upward or downward into or out of the muffle 11.

[0073] When referring to the apparatus 10, the terms "upper" and "lower" or "top" and "bottom" or "below" and "above" are defined relative to the axial or vertical direction L. These terms are used to indicate the relative position of elements to each other in the apparatus or during processing of preforms.

[0074] With reference to elements of a device, the terms “inner” and “outer” or “radially inner” and “radially outer” or “inward” and “outward” or “radially inward” and “radially outward” are intended to refer to relative radial positions thereof.

[0075] The muffle tube 11 has an inner side wall forming a hollow muffle chamber of a substantially cylindrical shape. The muffle tube and thus the muffle chamber have a generally elongated shape configured to accommodate the optical fiber preform 16. The muffle tube 11 has an inner side wall forming a hollow muffle chamber of a substantially cylindrical shape. Figure 4 and Figure 51 ), has an upper opening 15, hereinafter indicated as muffle opening, which is configured to allow the passage (insertion / extraction) of a preform 16 in the muffle tube 11. The upper opening 15 is centered on the Z axis.

[0076] The up and down movement of the preform 16 into the muffle is along the Z axis.

[0077] The muffle 11 is made of glass, in particular quartz. Conventionally, the muffle is made of high purity quartz to avoid contamination in the preform during heating, and is used for processing silica-based preforms for producing transmission optical fibers.

[0078] exist Figure 1 In the embodiment shown in FIG. 1 , the furnace 20 is designed for drying and consolidating a porous preform. In the present application, "porous preform" means a completely porous preform (e.g., for forming a glass core rod) and a partially porous preform including a porous soot layer, the partially porous preform being used to form an intermediate cladding and / or an outer cladding on a glass core rod.

[0079] The furnace 20 includes at least one heater, such as a first heater 12, which surrounds the muffle tube 11 in the upper length of the muffle tube. The first heater 12 defines a first heating zone, which extends within the upper length of the muffle tube 11 and thus the furnace chamber. In operation, the first heating zone is set at a first temperature suitable for dehydration and / or doping of the porous layer of the preform. For example, the first temperature is from 850° C. to 1350° C.

[0080] A second heater 13 positioned below the first heater 12 with respect to the axial direction L surrounds the muffle 11. The second heater 13 defines a second heating zone extending within the lower length of the muffle 11. In operation, the second heating zone is set at a second temperature suitable for consolidating the porous preform into a solid glass preform. The second temperature is higher than the first temperature and is typically from 1450° C. to 1600° C.

[0081] In one embodiment, the furnace includes a single heater including a first heating zone and a second heating zone.

[0082] Typically, the total length of the muffle 11 and therefore the furnace chamber (taken on the Z axis) is greater than the length of the preform 16, so that the preform 16 can move up and down inside the furnace chamber in the direction L. In one embodiment, the length of the furnace chamber is at least 1.5 times the length of the preform to be processed. For example, the preform has a length of from 2.0 meters to 3.5 meters.

[0083] Typically, the first heater 12 and the second heater 13 are annular to surround the muffle 11. For example, each of the heaters 12, 13 includes one or more annular heating elements.

[0084] The size of the muffle 11 may be designed based on the size of the preform to be processed in the apparatus 10 so as to allow the preform 16 to move up and down without the inner sidewall of the muffle 11 touching the preform.

[0085] Typically, the preform 16 is provided with a preform handle 17 of known type and made of quartz, which preform handle 17 may be attached to the preform or be integral with the preform.

[0086] The preform handle 17 is suspended and supported by a support rod 18. The support rod 18 terminates in a retaining portion 18a, which is located at the bottom end of the support rod 18 and is configured to retain the preform handle 17. Figure 1 In the non-limiting example of , the retaining portion 18a is a C-shaped hook integral with the support rod 18. The hanging of the preform 16 can be performed in different known ways, such as by providing a portion of enlarged width in the preform handle (not shown).

[0087] Typically, the porous preform 16 is gradually inserted into the muffle 11 of the furnace during dehydration and consolidation. The processing of the preform 16 begins with the full insertion of the preform 16 into the muffle 11.

[0088] In a known manner, the support rod 18 is operatively connected to a kinematic system 22 mounted on a support structure 23, such as a tower, which is only Figure 1 2 and 3. The tower 23 can be erected on a support plane 24, for example with an open floor area for communicating with a muffle located below the support plane. The movement system 22, which can be of known type, is designed for the vertical movement of the preform 16, i.e. for the insertion and extraction of the preform in the muffle 11, and for the rotational movement of the preform about the Z axis.

[0089] A hollow connecting member 40, which will be described in more detail below, is removably fixed to the muffle 11. The cover 30 is arranged on and connected to the connecting member 40. Figure 1 During the machining period shown, the cover 30 is in its open condition. Both the cover 30 and the connecting member 40 are positioned in axial alignment relative to the muffle 11 .

[0090] In a non-limiting manner, the cover 30 has a width in the radial direction that is greater than the width of the connecting member 40, in particular, greater than the width of the tubular body 42, which will be described in more detail below. The cover 30 includes a cylindrical cover sidewall 31 and a disc-shaped cover cover 32, which is configured to close the cover at its top ( Figures 2 to 5 ). The cover 32 is positioned above and axially aligned with the cover sidewall 31. A sealing assembly 70, described in more detail below, is operatively associated with the cover 32. When the preform is fully inserted into the muffle 11, the cover 32 is arranged on the cover sidewall 31 so as to close the muffle 11 from the top.

[0091] The furnace 20 includes one or more gas inlets. Figure 1 The gas inlet means 26 are only schematically indicated in the figure, and are connected to the chamber of the muffle tube 11 for supplying one or more gases, which pass through the preform 16 and / or around the preform 16. Figure 1 In the non-limiting example illustrated in , the gas enters the furnace chamber from the bottom of the muffle 11 and flows upwards. Typically, the gas outflow opening is located at the opposite side of the furnace relative to the gas inlet member 26.

[0092] In one embodiment, the preform 16 moves through a first heating zone of a first heater 12 of relatively limited length (ie, shorter than the length of the preform), and then moves to a second heating zone of a second heater 13 .

[0093] The dehydration process starts with drying the portion of the preform positioned in the first heating zone, so that the portion of the preform 16 inserted into the muffle 11 is located above the second heating zone. In this way, consolidation of the lowermost part of the preform does not occur before it is dried. The preform 16 is maintained in this position for a period of time, such as from 60 minutes to 90 minutes. Subsequently, the preform is gradually lowered through the first heating zone at a given rate so that the entire preform is dehydrated when the entire preform length has passed through the first heating zone. The rate of descent may be, for example, from 2 mm / min to 10 mm / min.

[0094] As the preform is driven downwardly through the first heating zone, successive longitudinal portions of the preform are exposed to the first heating zone and subsequently to the second heating zone.

[0095] Typically, during dewatering and consolidation, the preform is rotated about its longitudinal axis to improve the axisymmetry.A rotation transmission mechanism (not shown) coupled to the support rod 18 transmits the rotation to the preform 16 in a manner known per se.

[0096] The muffle 11 may extend below the second heating zone for a length configured to accommodate the entire preform as a cooling zone.Typically, cooling is performed after consolidation while flowing an inert gas, such as helium, through the muffle.

[0097] In one embodiment, the porous glass soot preform is a silica-based porous glass preform, which is used to make low-attenuation silica-based optical fibers used in telecommunication systems. The porous soot layer can be formed by known methods, such as flame hydrolysis of silica-based soot or combustion of a silica-based reactant as octamethylcyclotetrasiloxane (OMCTS, also known as D4).

[0098] The apparatus 10 is suitable for drying and consolidating a porous optical fiber preform. In one embodiment, the preform has a porous outer cladding formed around a glass core rod before undergoing dehydration and / or consolidation. After consolidation, the solid glass preform can be drawn into an optical fiber in a manner known per se.

[0099] It will be appreciated that the arrangement of the heating zones relative to the preform may be different from that described above and Figure 1 For example, in an alternative to the illustrated embodiment, the furnace 20 may have a single heating zone for dehydration and / or consolidation. The present disclosure encompasses furnaces designed for dehydration or consolidation of porous preforms.

[0100] After cooling, the muffle 11 is opened by lifting the cover 32 from the cover side wall 31 to allow the preform 16 to be removed from the muffle 11 .

[0101] refer to Figure 1 The outline of the process described can be applied to Figures 2 to 8 Any of the embodiments shown in, and more generally disclosed herein, particularly apply to assemblies contemplating cover 30 and connection member 40 being attached to one another as separate components (e.g., from Figure 4 ) or built as a single piece (such as from Figure 5 In the latter case, the cover 30 comprises a connecting member 40 which is connected to the muffle 11 .

[0102] Figure 2 is a partial perspective view of a shrouded muffle tube of an apparatus according to an embodiment consistent with the present disclosure, and Figure 3 yes Figure 2 A partially exploded perspective view of the same muffle tube with a cover.

[0103] The hollow connecting member 40 is removably connected to the muffle tube 11 at the muffle opening 15. The hollow connecting member 40 has a generally cylindrical shape with an inner space 48 (eg, Figure 8). The connecting member 40 comprises a tubular body 42 extending on a vertical axis z. The inner diameter of the tubular body 42 is configured to allow the passage of the preform when in an operating condition.

[0104] The tubular body 42 has an outer surface 43 ( Figure 4 , Figure 5 and Figure 8 Indicated in ). In an embodiment, the outer surface 43 is finned, with a plurality of heat dissipation fins 44 extending outwardly therefrom. The heat dissipation fins 44 may be arranged parallel to each other.

[0105] The connecting member 40 comprises a lower flange 41 positioned at the bottom of a tubular body 42 and integral therewith. The lower flange 41 is fixed to the muffle 11 by means of fastening elements (not shown).

[0106] The connection member 40 may be made of metal such as aluminum or anodized aluminum.

[0107] The cover 30 is removably mounted on or integral with the connecting member 40, and has an interior space 34 aligned with the interior space 48 of the connecting member 40 (in Figure 3 and Figure 5 (instructions).

[0108] As described above, the cover 30 includes the cover side wall 31 and the cover cover 32. The cover cover 32 includes a central through hole 57 ( Figure 3 ), the central through hole 57 is axially aligned with the upper opening 15 of the muffle furnace and is configured for the support rod 18 to pass through so as to suspend the preform 16 via the preform handle 17.

[0109] The diameter of the through hole 57 of the cover 32 is sized to leave radial clearance around the support rod 18 for axial movement through the cover 30 with limited radial excursion.

[0110] The cover sidewall 31 and the cover cover 32 define a cover interior space 34 .

[0111] The through hole 57 communicates with the internal space 34 of the cover.

[0112] In the embodiment shown in the drawings, the cover side wall 31 has an upper flange 33 extending radially outward therefrom at its top. The upper flange 33 is integral with the side wall 31. The cover 32 is disposed on the upper flange 33 of the cover side wall 31. In the embodiment shown in the drawings, the cover 32 is arranged on the upper flange 33 without being fastened.

[0113] The cover 32 may be held in place by its weight exerting a downward force.

[0114] In another embodiment (not shown), the cover 32 may be fastened to the side wall 31 or the upper flange 33 by means of fastening elements.

[0115] The cover 30 is made of metal such as aluminum or anodized aluminum.

[0116] In the embodiment illustrated in the drawings, the cover 32 is made of two half-discs 32a and 32b connected to each other. For example, the two parts 32a, 32b are fixed to each other by fixing brackets.

[0117] This arrangement may facilitate maintenance of the components, although it should not be considered limiting.

[0118] The hood side wall 31 includes an outlet hole 38 for the outflow of the process gas flowing in the muffle tube 11 ( Figures 2 to 5 ). These gases can pass through a pressure control line (not shown).

[0119] In addition to the outlet opening 38, the hood 30 may be provided with a gas discharge port 37. The gas discharge port 37 is a useful safety port in case of unwanted gas discharge. To this end, the gas discharge port 37 is connected to an external exhaust duct (not shown in the figure).

[0120] When the hood 30 is connected to the muffle 11 via the connecting member 40 (either integral with the hood or as a separate element connected to the hood) and closed by the hood cover 32, a sealed chamber is formed which communicates with the outside through the through hole 57 of the hood cover 32.

[0121] refer to Figure 1 , Figures 3 to 5 and Figure 7 , the cover 30 includes a lower cover plate 35, which, in operation, is arranged in the interior space 34 of the cover 30. The lower cover plate 35 is disc-shaped and is sized to cover the hollow interior space 48 of the connecting member 40. The lower cover plate 35 has a central through hole 55, which is configured for the passage of the support rod 18 for suspending the preform 16.

[0122] The through hole 57 of the cover 32 and the through hole 55 of the lower cover plate 35 both have circular cross-sections, the centers of which are substantially located on the same axis (ie, the Z axis), ie, the through holes 55 and 57 are axially aligned with each other.

[0123] In an embodiment, the lower cover plate 35 is made of an inorganic material, such as a metal (eg, anodized aluminum), a mineral, or a ceramic material.

[0124] Figure 4An embodiment of a hooded muffle of the device 10 is illustrated, wherein the hood 30 and the connecting member 40 are two separate elements connected to each other along the Z axis. As described above, the lower flange 41 of the tubular body 42 is connected to the muffle 11. The connecting member 40 also includes an upper flange 46 positioned opposite the lower flange 41. The upper flange 46 is integral with the tubular body 42.

[0125] The lower flange 41 and the upper flange 46 extend outwardly from the tubular body 42 , and in particular, extend outwardly from the sidewall of the connecting member 40 .

[0126] exist Figure 4 In the embodiment shown in FIG, the cover 30 includes a cover lower flange 39 which is integral with the cover side wall 31 and opposite to the cover cover 32. The cover lower flange 39 extends inwardly from the side wall 31 to leave a central opening facing the hollow space 48 of the connecting member 40. The cover lower flange 39 has an upper support surface 52. The cover 30 and the connecting member 40 are connected to each other by the connection between the cover lower flange 39 and the upper flange 46 of the connecting member 40.

[0127] The cover 30 is arranged on top of the connecting member 40 by positioning the cover lower flange 39 on the connecting member upper flange 46 and fastening them to each other by means of bolts 47. To this end, the cover lower flange 39 and the upper flange 46 are provided with a corresponding plurality of through holes axially aligned with each other for inserting the bolts 47.

[0128] The lower cover plate 35 is arranged on the hood lower flange 39 .

[0129] Figure 5 A further embodiment of a shrouded muffle tube of the apparatus 10 is shown. Figure 4 , the cover 30 is integral with the connecting member 40. The cover 30 includes a cover lower flange 51 having an upper support surface 52. The support surface 52 extends parallel to the cover cap 32. The lower flange 51 is integral with the cover sidewall 31 and the tubular body 42 of the connecting member 40. The lower flange 51 extends radially inwardly relative to the cover sidewall 31 to leave a central opening facing the hollow space 48 of the connecting member 40.

[0130] exist Figure 5 In the embodiment of FIG. 5 , the lower cover plate 35 is arranged on the support surface 52 of the lower flange 51 .

[0131] In an embodiment, an O-ring gasket 53 may be interposed between the upper support surface 52 of each hood lower flange 39, 51 and the lower cover plate 35. The O-ring gasket 53 may be made of a material based on a carbon allotrope such as graphite. When the lower cover plate 35 is lowered together with the preform 16 and the cover cap 32 to close the muffle 11, the O-ring gasket may dampen the contact between the support surface 52 of the hood 30 and the lower cover plate 35.

[0132] The inward extension of the lower hood flange 39 or 51 is configured to allow the passage of preforms.

[0133] The sealing assembly 70 is arranged at the cover 30 . The sealing assembly 70 is substantially centered on the vertical axis Z so as to be aligned with the central through hole 57 of the cover 32 .

[0134] The sealing assembly 70 includes a first sealing element 80, Figure 6 In operation, the first sealing element 80 is positioned within the interior space 34 of the cover 30. The lower cover plate 35 provides a base for positioning and securing the first sealing element 80 within the interior space 34 of the cover 30.

[0135] The first sealing element 80 is substantially axially aligned with the housing through-hole 57 and the central through-hole 55 of the lower cover plate 35 .

[0136] The first sealing element 80 includes an annular seal 82. The seal 82 is in direct contact with the support rod 18 supporting the handle 19. In particular, the inner diameter of the seal 82 is configured to directly contact the outer diameter of the support rod 18. In one embodiment, the inner diameter of the seal 82 is sized to have a tight connection with the support rod 18.

[0137] In one embodiment, the annular seal 82 includes a sealing lip 82a (at Figure 6 The seal 82 may further include, for example, a garter spring (not shown) coupled to the sealing lip 82a for more closely contacting the support rod 18 when the support rod 18 moves axially and rotates about its axis.

[0138] In an embodiment, the annular seal 82 is made of a thermosetting elastomeric polymer, such as a fluoropolymer (fluoroelastomer), which is generally suitable for continuous use at relatively high temperatures up to 200-300°C.

[0139] The first sealing element 80 further includes an expandable member 83 configured to expand or contract in an axial direction, particularly in a direction L. The expandable member 83 has a tubular shape, and its inner diameter is configured to allow the support rod 18 to pass therethrough.

[0140] In one embodiment, the expandable member 83 is made of a thermoplastic polymer. For example, the expandable member is made of a thermoplastic fluoropolymer such as PFTE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene) or PFA (perfluoroalkoxyalkane). In the embodiment shown in the accompanying drawings, the expandable member 83 includes a pleated portion 83a configured to expand and contract in a vertical direction L and a non-axially expandable portion 83b adjacent to the pleated portion 83a in an axial direction. In one embodiment, the non-axially expandable portion 83b is integral with the pleated portion 83a.

[0141] The length of the corrugated portion 83a varies in the axial direction L from a minimum value to a maximum value.

[0142] The inner diameter of the pleated portion 83a can vary over its length as long as its minimum inner diameter is greater than the inner diameter of the annular seal 82, thereby allowing the support rod 18 to pass through. Due to the pleated shape of the pleated portion 83a and the associated constraint in the axial direction, when in operation, the expandable member 83 has an overall inner and outer diameter that can vary along its length.

[0143] In an embodiment, the minimum inner diameter of the expandable member 83 is greater than the inner diameter of the annular seal 82 , such that under typical conditions during preform processing, the support rod 18 is in contact only with the seal 82 .

[0144] The non-axially expandable portion 83b has an annular shape, and its inner diameter and outer diameter are coaxial with each other. In the expandable member 83, the size of the minimum inner diameter is designed to leave a radial gap around the support rod 18 for axial movement with limited radial offset. In one embodiment, the minimum inner diameter of the expandable member 83 corresponds to the inner diameter of the non-expandable portion 83b.

[0145] The first sealing element 80 includes a hollow base 84 positioned at the bottom of the expandable member 83. The expandable member base 84 is adjacent to the pleated portion 83a and is opposite to the non-expandable portion 83b relative to the pleated portion. The hollow base 84 extends radially outward from the pleated portion 83a and has an inner diameter substantially equal to the inner diameter of the non-axially expandable portion 83b. In an embodiment, the expandable member base 84 can be integral with the pleated portion 83a, such as Figure 6 As shown in the figure.

[0146] The base 84 includes a plurality of holes 85 for securing the first sealing element 80 to the lower cover plate 35 of the hood 30 , as described in more detail later.

[0147] The annular seal 82 is operatively connected to the non-axially expandable portion 83b. In the embodiment shown in the drawings, the annular seal 82 is accommodated in the non-expandable portion 83b of the expandable member 83 and is held in place, for example, by compression. The non-axially expandable portion 83b has a radial cavity configured to accommodate the annular seal 82, which is located in the radial cavity so as to extend until the most radially inward position ( ) of the first sealing element 80 relative to the central axis Z. Figure 4 and Figure 5 ). In this way, the radially inwardmost position of the first sealing element 80 corresponds to the inner diameter of the annular seal 82.

[0148] In embodiments where the annular seal 82 includes a sealing lip 82a, the inner diameter of the sealing lip represents the radially inward-most location of the first sealing element.

[0149] The expandable member 83 is disposed so that the non-expandable portion 83b accommodating the annular seal 82 is located above the folded portion 83a.

[0150] The diameter of the through hole 57 of the cover 32 may be larger than the outer diameter of the non-expandable portion 83 b of the expandable member 83 .

[0151] Since the annular seal 82 is operatively connected to the support rod 18 and the first sealing element 80 is connected to the cover 30 by fastening the expandable member 83 to the lower cover plate 35 by the hollow base 84, the first sealing element 80 is suitable for compensating any potential offset between the "fixed" elements 82 and 84 by the pleated portion 83a.

[0152] Mainly, the axial movement of the expandable member 83 occurs in the expandable pleated portion 83a.

[0153] Being operatively connected to the support rod 18, the first sealing element 80 provides a sealing engagement with the support handle 18, which effectively reduces the escape of process gas from the interior of the sealed chamber (primarily from the central hole 55 of the lower cover plate) without impairing the movement of the support handle 18 through the chamber.

[0154] The sealing assembly 70 is designed to at least partially seal the through hole 55 of the cover plate 35 by means of the first sealing element 80. At the same time, the sealing assembly 70 is designed to allow the support rod 18 of the preform handle 17 to move vertically and rotate through the through hole 57 of the cover 32.

[0155] The sealing assembly 70 includes a support flange 73. The support flange 73 is a substantially cylindrical ring. The support flange 73 is positioned on the lower cover plate 35 to surround the central hole 55 thereof. The support flange 73 has an inner diameter and an outer diameter, and the inner diameter is greater than the diameter of the through hole 55 of the cover plate 35.

[0156] The annular support flange 73 may be made of metal such as (anodized) aluminum or steel.

[0157] The sealing assembly 70 comprises a plurality of springs 71 (six springs in the non-limiting illustrated example) extending in the Z axis, radially surrounding the first sealing element 80, and in particular the expandable member 83. The springs 71 are mounted on respective vertical support elements 72, such as vertically arranged rivets.

[0158] The spring 71 is fixed at one end to an annular flange 73 by means of a vertical support element 72. In the embodiment shown in the drawings, each vertical support element 72 comprises a male pin 72a, and the annular flange 73 comprises a plurality of through holes 74 configured to receive a corresponding male pin 72a ( Figure 7 ).

[0159] The spring 71 may be a coil spring or a helical spring, the length of which at rest (uncompressed) is greater than the length of the vertical support element 72, so that the upper length portion of the spring can extend or contract in the vertical direction l. The length of the spring 71 is selected so that the spring remains partially compressed between the annular flange 73 and the cover 32.

[0160] In the embodiment of the accompanying drawings, the hollow base 84 of the first sealing element 80 is arranged on the annular flange 73, specifically, on the upper surface of the annular flange. The plurality of through holes 85 of the hollow base 84 are arranged to correspond to the plurality of through holes 74 of the annular flange 73. The lower cover plate 35 is provided with a plurality of through holes 56 corresponding to the plurality of through holes 74 of the annular flange 73. In this way, the through holes 85, 74 and 56 are axially aligned with each other. The convex pin 72a of the vertical support element 72 is then inserted into the plurality of through holes 74, and the first sealing element 80, the spring 71 and the annular flange 73 are fastened to the lower cover plate 35.

[0161] It should be appreciated that other configurations for securing the first sealing element 80 and / or the spring 71 to the lower cover plate 35 are contemplated.

[0162] The first sealing element 80, and in particular the expandable member 83, is vertically constrained at one end by the close contact of the annular seal 82 with the connecting rod 18, but the expandable member 83 can freely move axially at any other place over the allowed length. The annular seal 82, which is operatively surrounded by the non-axially expandable portion 83b, tightly engages the support rod 18 so as to close the central hole 55 of the cover cover plate 35.

[0163] The first sealing element 80 as described above significantly improves the sealing capability of the device.

[0164] The applicant has observed that the upward movement caused by the pressure of the gas flowing upward from the muffle can be counteracted by the downward force exerted by the weight of the cover. The applicant has realized that a lower cover plate having a weight greater than the pressure exerted by the gas flowing in the muffle will further hinder the gas from flowing out of the connecting member.

[0165] During processing of the preform, the cover 32 of the cover 30 pushes the spring 71 slightly in the axial direction downwards towards the lower cover plate 35. During processing, gas outflow can escape through the outlet holes 38. However, in the event that the pressure of the gas outflowing from the muffle 11 increases undesirably, the weight of the cover 32 forces this gas to flow out of the gas discharge port 37, if on the one hand this pressure would push the lower cover plate 35 upwards.

[0166] The partially compressed state of the seal assembly 70 between the lower cover plate 35 and the cover 32 may be preset and selected by considering the expected processing parameters.

[0167] refer to Figures 2 to 5 The cover 30 includes an upper cover plate 36 disposed on the outer side of the cover 30 and on the cover cap 32. The upper cover plate 36 has a through hole 58 (axially aligned with the through hole 57 of the cover cap 32) Figure 3 ), the through hole 58 is configured to allow the support rod 18 to pass therethrough.

[0168] The upper cover plate 36 in the drawings is disc-shaped, although other shapes are possible as long as a central through hole 58 is provided.

[0169] The provision of the upper cover plate 36 increases the weight applied downwardly by the cover. In an embodiment, the weight of the upper cover plate 36 and the cover 32 may be selected so that their sum is greater than the pressure in the muffle during processing of the preform 16.

[0170] The upper cover plate 36 is made of metal such as steel or anodized aluminum.

[0171] In an embodiment, the total weight of the cover 32 and the cover plate 36 is from 5 kg to 12 kg, preferably from 6 kg to 10 kg.

[0172] The sealing assembly 70 of the device 10 includes a second sealing element 90 positioned on top of the cover 32 outside the cover 30. The second sealing element 90 corresponds to the first sealing element 80 and has the same Figure 6 The first sealing element 80 shown in FIG. 8 is essentially the same component.

[0173] The second sealing element 90 is positioned in alignment with the through-hole 58 and is configured to allow passage of the support rod 18 , as described in detail below.

[0174] The second sealing element 90 is substantially axially aligned with the cover through hole 57 and the central through hole 55 of the lower cover plate 35. The second sealing element 90 includes an annular seal 92, which is sized to surround the support rod 18 ( Figure 4 and Figure 5 ). In particular, the inner diameter of the seal 92 is configured to directly contact the outer diameter of the support rod 18. In one embodiment, the inner diameter of the seal 92 is sized to contact the outer surface of the connecting rod 18 when the connecting rod 18 moves axially and rotates about its axis. In an embodiment, the annular seal 92 is tightly connected to the support rod 18.

[0175] In one embodiment, the annular seal 92 includes a sealing lip (not shown) for engaging with the support rod 18. The seal 92 may also include, for example, a garter spring (not shown) coupled to the sealing lip for more closely contacting the support rod 18 when the support rod 18 moves axially and rotates about its axis.

[0176] In an embodiment, the annular seal 92 is made of a thermosetting elastomeric polymer, such as a fluoropolymer (fluoroelastomer), which is generally suitable for continuous use at relatively high temperatures up to 200-300°C.

[0177] The second sealing element 90 includes an expandable member 93 configured to expand, contract, and bend, particularly in or away from the direction L. The expandable member 93 has a tubular shape, the inner diameter of which is configured to allow the support rod 18 to pass therethrough.

[0178] In one embodiment, the expandable member 93 is made of a thermoplastic polymer. For example, the expandable member is made of a thermoplastic fluoropolymer such as PFTE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene) or PFA (perfluoroalkoxyalkane). The expandable member 93 includes a pleated portion 93a and a non-axially expandable portion 93b, the pleated portion 93a being configured to expand and contract in the vertical direction L, and the non-axially expandable portion 93b being adjacent to the pleated portion 93a in the axial direction ( Figure 7 ; elements 32 and 36 are omitted in the figure). In one embodiment, the non-axially expandable portion 93b is integral with the corrugated portion 93a.

[0179] The provision of the second sealing element 90 helps to maintain the alignment of all components within the housing 30 relative to the muffle 11. In addition, the second sealing element further improves the sealing of the housing aperture 57, thereby preventing the process gas from flowing out to the environment.

[0180] The second sealing element 90 includes a hollow base 94 adjacent to the expandable member 93 and extending radially outward from the expandable member 93. Specifically, the base 94 is adjacent to the pleated portion 93a and opposite to the non-expandable portion 93b, and the base 94 extends radially outward from the pleated portion 93a.

[0181] The base 94 of the second sealing element 90 is fastened to the cover 32. The hollow base 94 includes a plurality of holes 95 for fastening the sealing assembly 90 to the cover 32. To this end, each of the upper cover plate 36 and the cover 32 has a plurality of through holes corresponding to the through holes of the hollow base 94 for inserting fastening elements 54, such as screws or bolts, such as Figures 2 to 5 as shown in .

[0182] exist Figure 4 In the embodiment shown in FIG. 8 , the hollow base 94 is fixed to the upper cover plate 36 , which in turn is fixed to the cover 32 .

[0183] exist Figure 2 , Figure 3 and Figure 5 In yet another embodiment shown in , a hollow base 94 is arranged between the cover 32 and the upper cover plate 36. The upper cover plate 36 is fixed to the cover 32 by means of a fastening element 54. The fastening element 54 passes through a plurality of holes 95 of the hollow base 94 to fasten the second sealing element 90 between the cover 32 and the upper cover plate 36. This configuration can improve the stability of the sealing assembly 90 when the support rod 18 is lowered into the furnace 20. Providing the cover plate 36 above the base 94 helps prevent any lifting of the base 94 made of a soft material. In this embodiment, at least a portion of the pleated portion 93a of the second sealing element 90 passes through the central hole 58 of the upper cover plate 36 so that the annular seal 92 is placed above it.

[0184] At the beginning of the preform dehydration or consolidation process, the optical fiber preform 16 is suspended and supported by the preform handle 17 connected to the support rod 18. Above the preform handle 17 - and therefore above the optical fiber preform 16 - the cover 32 and optionally the cover upper cover plate 36 and the second sealing element 90 have been fixed to each other and connected to the support rod 18. The first sealing element 80 is in turn connected to the lower cover plate 35, on which the annular support flange 73, the spring 71 and the vertical support element (for example, a rivet) 72 are mounted.

[0185] At the same time, the hood 30 is connected to the furnace 20 by means of the connecting member 40 in an “uncovered” condition, ie the hood does not comprise a lower cover plate 35 and is not closed by the hood cover 32 .

[0186] according to Figure 4 or Figure 5In the embodiment of the present invention, when the optical fiber preform 16 is lowered toward and into the furnace 20 by the motion system 22, the cover lower cover plate 35 contacts the cover lower flange 39 or 51, optionally by inserting an O-ring gasket 53 between the cover 30 and the connecting member 40. Therefore, the sealing assembly 70, in particular the first sealing element 80 fixed to the lower cover plate 35 by the annular support flange 73 and the spring 71 and the vertical support element (such as a rivet) 72, is inserted into the cover inner space 34 and is enclosed therein by the cover cover 32. The above-mentioned weight of the cover cover 32 and the optional upper cover plate 36 ensures proper sealing of the cover inner space 34.

[0187] Example

[0188] The new device, denoted Device B, was able to ensure satisfactory performance, with a DCDR < 1% for 1-55 He slpm, whereas Device A, which did not include the sealing assembly of the present disclosure, completely failed at the same helium flow rate.

[0189] A number of glass optical fiber preforms are made by using an apparatus, namely apparatus B, as described above and in accordance with reference Figure 4 Embodiment described.

[0190] Apparatus A comprises a muffle tube, on top of which is covered a cylindrical body, which is similar to the connecting member of the present disclosure. This cylindrical body and the upper portion of the muffle tube are surrounded by a chamber similar to the hood of the present disclosure. The chamber has an upper orifice, which is closed by a quartz cover and an aluminum cover connected to the handle support rod when the support handle lowers the preform in the muffle tube. The quality of the fiber drawn from the optical fiber preform is checked by determining the DCDR value. The DCDR value is defined herein as the ratio between the sum of all fiber length portions less than 18 meters of the drawn optical fiber that were found to be defective in the diameter measurement during drawing and the total drawn fiber length.

[0191] Table 1

[0192] He flow rate (slpm) DCDR Device A DCDR Device B 5 100％ <1％

[0193] Referring to Table 1, at a relatively low He flow rate value of 5 slpm (standard liters per minute), device A exhibits unsatisfactory performance with very high DCDR values, and in practice, all fiber length sections shorter than 18 m are defective, and there are no fiber length sections longer than 18 m without defects. The He flow rate required to achieve satisfactory performance is at least 15 slpm, and in some cases 20-30 slpm.

[0194] In contrast, at the same helium flow rate, at a He flow rate of 5 slpm, device B showed satisfactory performance with a DCDR value of less than 1%.

Claims

1. An apparatus (10) for drying and / or consolidating an at least partially porous optical fiber preform, comprising: a furnace (20) comprising a muffle (11) extending along a vertical axis (z) and forming a muffle chamber configured to accommodate a preform (16), the muffle (11) having an upper muffle opening (15) at its top side configured to allow the preform (16) to pass through; a hollow connecting member (40) having an inner diameter, configured to allow the passage of the preform and extending along the vertical axis (z), the connecting member (40) being removably connected to the muffle tube (11) at the upper muffle opening (15); - a cover (30) positioned on top of the connecting member (40), the cover (30) being removably connected to the connecting member (40) or being integral with the connecting member (40), the cover having an inner space (34) vertically aligned with the connecting member (40), wherein the cover comprises a cover cap (32) closing the cover at its top, wherein the cover cap (32) comprises a through hole (57) axially aligned with the muffle opening (15), the through hole (57) of the cover cap being configured for passage of a cylindrical support rod (18) supporting a handle (19), the support rod being used to suspend the preform (16); and a sealing assembly (70) comprising a first sealing element (80) housed within the interior space (34) of the housing (30) and a second sealing element (90) on top of the cover (32), the first and second sealing elements being substantially centered about the vertical axis (z), Wherein, the first sealing element (80) and the second sealing element (90) include corresponding first and second annular seals (82, 92) and first and second expandable members (83, 93), wherein the first and second expandable members have a generally tubular shape, are configured to allow the support rod (18) to pass therethrough and are configured to expand, contract and bend, wherein each of the first and second annular seals (82, 92) is located radially inside the corresponding first and second expandable members (83, 93) and is operatively connected to the corresponding first and second expandable members (83, 93), and the corresponding annular seals (82, 92) are sized to directly contact the support rod (18).

2. The device according to claim 1, wherein: The connecting member (40) comprises a tubular body (42) extending along the vertical axis (Z).

3. The device according to claim 2, wherein: The tubular body (42) has a finned outer surface (43).

4. The device according to any one of the preceding claims, wherein: Said connecting member (40) has a length taken along said vertical axis (Z) of from 5 cm to 20 cm.

5. Apparatus according to any one of the preceding claims, wherein: Each of the first and second expandable members (83, 93) comprises: - a corrugated portion (83a, 93a) configured to expand, contract and bend, - an axially non-expandable portion (83b, 93b) which adjoins the corrugated portion (83a, 93a) along the vertical axis (z), and - a base (84, 94) adjacent to the corrugated portion (83a, 93a) and opposite to the non-axially expandable portion (83b, 93b), the base (84, 94) extending radially outward from the corrugated portion (83a, 93a), The first and second annular seals (82, 92) are respectively joined to the non-axially expandable portions (83b, 93b).

6. The device according to claim 5, wherein: The non-axially expandable portion (83b, 93b) engaging the annular seal (82, 92) is located on top of the corrugated portion (83a, 93a).

7. Apparatus according to any one of the preceding claims, wherein: Each of the first and second annular seals (82, 92) has an inner diameter configured to directly contact the support rod (18).

8. The device (10) according to any one of the preceding claims, wherein: The hood (30) includes a hood side wall (31) and a lower flange (39; 51), the lower flange (39; 51) being positioned opposite to the hood cover (32), the lower flange (39; 51) of the hood extending radially inward from the hood side wall (31) and having an inner diameter substantially equal to the inner diameter of the connecting member (40).

9. The device (10) according to claim 8 further includes a lower covering plate (35), which is configured to be positioned on the lower flange (39; 51) and has a through hole (55) aligned with the through hole (57) of the cover (32), wherein the outer diameter of the lower covering plate (35) is greater than the inner diameter of the connecting member (40).

10. Apparatus according to claim 8 or 9 when dependent on claim 2, wherein: The cover (30) is removably connected to the connecting member (40), the connecting member (40) including an upper flange (46) positioned at the top of its tubular body (42) and extending radially outward from the tubular body, and wherein the lower flange (39) of the cover is positioned on and connected to the upper flange (46) of the tubular body of the connecting member (40).

11. Apparatus according to claim 8 or 9 when dependent on claim 2, wherein: The cover (30) is integrated with the connecting member (40), and the lower flange (51) of the cover is integrated with the tubular body (42) of the connecting member (40), and the lower flange (51) of the cover is a common flange of the connecting member (40) and the cover (30).

12. Apparatus according to any one of the preceding claims, wherein: The sealing assembly (70) further comprises: a plurality of springs (71) extending parallel to the vertical axis (Z) and arranged to radially surround the first sealing element (80), and An annular support flange (73) is arranged on the lower cover plate (35), and the plurality of springs (71) are constrained to the support flange (73) at one end and extend from the support flange (73) toward the cover (32).

13. The device according to claim 12, wherein: Each of the plurality of springs (71) is mounted on a corresponding vertical support element (72), the corresponding vertical support element (72) is fixed to the support flange (73), each of the plurality of springs (71) is longer than the corresponding vertical support element (72), and wherein the length dimension of each of the plurality of springs (71) is designed to extend from the annular flange (73) to the cover (32) under a preset partial compression condition.

14. The device according to any of the preceding claims, further comprising an upper cover plate (36) arranged on the cover (32), the upper cover plate (36) having a central through hole (58) aligned with the through hole (57) of the cover (32).

15. The device according to claim 14, wherein: The second sealing element (90) extends from the upper cover plate (36) and is axially aligned with the first sealing element (80).

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