MX2008010491A - A sealing device for a gas inlet to an oven or the like - Google Patents

Abstract

A pipe (12) for feeding a gas into an oven, a furnaces, or the like (such as a CVI /CVD oven), and in particular into a reaction chamber structure (16) inside the oven, is provided with a gastight tubular sealing device (32) extending radially outside the pipe and defining a path that is practically gastight, along which there extends the as feed pipe. The tubular sealing device is preferably at least partially flexible in the transverse direction and/or the axial direction so as to accommodate positioning defects between a location situated in the reaction chamber and a location where the gas feed pipe penetrates into the oven (which defects may be due, for example, to asymmetrical thermal expansion/contraction).

Description

A SEALING DEVICE FOR A GAS ENTRY TOWARDS AN OVEN OR IF A MILAR The present patent relates in general to furnaces, boilers, treatment chambers and the like, in which a reative gas is introduced as part of a treatment step. A specific example of the invention relates to boilers for chemical vapor infiltration / chemical vapor deposition (CVI / CVD) in which a reactive gas is introduced as part of a method for densifying porous elements, such as porous preforms for pieces of friction. In general, the use of furnaces, boilers, treatment chambers and the like within which a reactive gas is introduced as a treatment step is known (in the following description, the term "furnace" should also be understood more broadly as applicable. to boilers and other treatment chambers of this type). An example is the chemical vapor infiltration method in which a precursor reactive gas is introduced into an oven having porous elements therein (for example, and without limitations, such as porous brake discs). In general, a conventional furnace includes an outer furnace casing that encloses a working space or reaction chamber within which the objects or elements for treatment are placed, a system for causing reactive gas to flow into and out of the oven, and a heating system for heating at least one internal part of the reaction chamber. In a known manner, the reactive gas is forced to infiltrate the porous structure of the porous elements. The reactive gas may include a hydrocarbon gas such as propane. In a known example, a reactive gas is introduced into the interior volume defined by a stack of annular preforms for brake discs that are substantially aligned in the reaction chamber of a furnace. Generally, the gas is forced to move from the inner volume of the stack to the outside of the stack by diffusing between the porous (eg, fibrous) structure of the preforms and / or flowing through void spaces between the adjacent stacked preforms, defined by separators or similar. At least the interior of the reaction chamber is heated by the heating system. Therefore, due to the relatively high temperature of the brake disc preforms, the reactive gas is subjected to pyrolysis and leaves a decomposition product that is deposited on the interior surfaces of the porous structure. As an example, with a hydrocarbon gas, the decomposition product is pyrolitic carbon, thereby obtaining a composite material containing carbon (such as a carbon-carbon material). In general, furnaces of this type are formed by a plurality of components that are assembled together by means of welding, screws or the like, in order to define the various units of the assembled structure. However, various structural defects or anomalies are common in the structure of an oven. For example, the component parts may be misaligned when the furnace is built. In other circumstances, intermittent defects may appear, such as poor alignment between the parts due to differences in thermal expansion when the oven is in use. This happens, for example, when different materials are used in the same assembly. In general, structural defects in such sites lead to free, hollow or similar spaces that occur between the parts, through which external air (which could contain contaminants, for example), can penetrate into the interior of the furnace, and through from which the reactive gas (which among other things is generally flammable), can escape. The site or sites through which gas is introduced into the furnace may present a specific problem, at least as far as reactive gas is concerned., which could escape from the gas flow path instead of being usefully transported into the furnace zone where brake disc preforms or the like are placed. From the foregoing it can be seen that it is desirable to reduce reactive gas leaks from the location where said gas is introduced into the furnace and into the interior of the reaction chamber. Simultaneously, it is useful for the furnace structure to retain its structural adaptability to correct manufacturing errors and imperfections, and the like. In general, according to the present invention, a flexible tubular sealing device is placed around an end of a gas inlet tube at a location where the gas inlet tube enters the body of the oven, and ends at the proximity of a gas inlet opening formed within the reaction chamber. Preferably, at least a portion of the tubular sealing device is transversally flexible (relative to an axis along which the tubular sealing device extends between the wall of the furnace and the gas inlet opening of the reaction chamber) , and / or axially. This flexible part of the tubular sealing device can be comparably rigid. In one example of the invention, the flexible part of the tubular sealing device is made of stainless steel and has a thickness that allows the required degree of flexibility, while the remaining part of the tubular sealing device is made of an Inconel alloy, or Similary. At least the axial end of the tubular sealing device adjacent the inlet of the gas inlet pipe within the furnace housing is welded in place in order to improve the integrity of the gas sealing device. Accordingly, the tubular sealing device described and claimed herein desirably provides a seal around an end of the gas inlet tube where the furnace body penetrates and where it ends in the vicinity of a gas inlet opening formed in the gas chamber. reaction. In addition, the sealing function is maintained despite any poor alignment between the gas inlet pipe and the gas inlet opening (for example, due to construction or installation defects). Finally, the sealing function is also maintained even if the free space between the gas inlet pipe and the gas inlet opening varies in operation because the different parts of the furnace expand in different magnitudes because they have coefficients of different thermal expansion. The present invention can be better understood with reference to the appended figures, in which: Figure 1 is a diagrammatic cross-sectional view of an oven of the present invention, at the location where a reactive gas inlet tube enters the body of the invention. oven and ends in the vicinity of a gas inlet opening formed inside the reaction chamber and disposed within the body of the furnace; Figure 2 is an exploded perspective view of the tubular sealing device of the present invention; and Figure 3 is a fragmentary view of a larger scale of a connection between the first and second axial portions of the tubular sealing device of the present invention. In general, an oven that is used for a CVI / CVD process includes a wall or casing that separates the inside from the outside of the oven, and that defines a volume inside it. Within the furnace volume there is a reaction chamber structure. The reaction chamber inside the CVI / CVD furnace can define by itself another volume within the furnace volume. Items that will be treated or modified, such as porous brake disk preforms, are placed inside the reaction chamber. In general, a reactive gas circulation system is provided to introduce reactant gas into the furnace and to remove it as well. Specifically, the reactive gas is introduced into the reaction chamber inside the furnace. The gas is extracted from the furnace by means of a suitable mechanism known in the art and / or industry, including, but not limited to, by the effect of gas pressure inside the furnace as compared to the pressure outside the furnace. , or by various suction or evacuation mechanisms that are well known in the art. A heating system is adapted to heat at least the interior of the reaction chamber. Heating an oven of this type is generally known in the art. Two known specific examples of heater systems include conductive heating and resistive heating. In order to simplify the following description of the structure, the various conduits, tubes or the like to which reference is made, are described assuming that they have a substantially circular cross-section, although not necessarily always true. Figure 1 is a fragmentary cross-sectional view of the area in which a reactive gas feed tube (1 2) passes through the wall of the furnace (10) for the purpose of supplying a flow of reactive gas within the inside the oven (as represented by the arrow (A) in Figure 1). In a possible example, the diameter of the gas inlet duct (14) formed inside the reaction chamber (1 6) can be defined or adjusted by means of an insert. The insert includes a tube (1 8) mounted in position and secured or retained in some other way in relation to an annular assembly plate (20) having a central opening (20a), generally aligned with the tube (1 8). The assembly plate (20) is, in turn, secured to the surface of the reaction chamber (1 8), for example, by means of bolts (22), as shown in Figure 1. A conventional insulating material may be placed around the periphery of the tube (1 8), and more specifically it may be present in the form of a plurality of annular layers (not shown) that are held together, for example, by means of pins (24). ) or similar. Finally, an outer part of the reaction chamber (1 6) can optionally be covered in a conventional thermal insulating material generally represented as the layer (28). The reactive gas feed tube is terminated in a location that is at least adjacent to a gas inlet conduit (1 4) formed within the reaction chamber (1 6). In some configurations, the reactive gas feed tube (12) may come into contact with the structure, defining the gas inlet conduit (14), or may abut against it in some other way. For reasons explained below, it may be desirable to keep the reactive gas feed tube (12) independent of the gas inlet conduit (14) (ie, so that they are not secured to one another), and even maintain a free space between the reactive gas feed tube (12) and the gas inlet conduit (14). In accordance with the present invention, a tubular sealing device (which has been given the general reference (32)) is provided. The tubular sealing device (32) generally surrounds the transition between the gas supply tube (12) and the gas inlet conduit (14) circumferentially and makes it virtually leak-proof. In order to be able to adapt to the operating conditions within the furnace (particularly as regards temperature), the tubular sealing device (32) is preferably made of metal. At least a part of the tubular sealing device (32) is flexible, and more particularly flexible transversely and / or axially relative to an axis along which the tubular sealing device (32) extends. This flexibility compensates for misalignments or deviations between the gas supply tube (12) and the gas inlet conduit (14), for example, caused by construction defects or asymmetric thermal fatigue, as already discussed. For this reason, for example, the distance between the thermal end of the gas supply pipe (12) and the reaction chamber (1 6) (which contains the gas inlet pipe (14) formed therein) may vary in operation while the internal part of the furnace is heated, due to the different coefficients of thermal expansion. Consequently, even if there is a gap for the size increase or decrease between the gas supply pipe (12) and the gas inlet pipe (14), or even if they move laterally and come out of alignment, the The general assembly remains virtually insulated against leakage, in order to be able to adapt to various misalignments and the like. The tubular sealing device (32) preferably includes at least two axial segments: a first axial part (32a) that is flexible and a second axial part (32b) that is comparably rigid (as compared to the first axial part). The first axial part (32a) preferably has a shape and structure that provide the required flexibility in the transverse and / or axial directions. For example, and as shown in the figures, the first axial part (32a) has a bellows-like shape. In an example of the present invention, the first axial part (32a) is made of stainless steel (such as ASM E 321) or of an Inconel alloy, preferably selected to be capable of withstanding temperatures reaching approximately 500 ° C. It will be understood that it is also necessary to take into account the thickness of the material in order to obtain the required flexibility. The second axial part (32b) may be merely tubular, having a cross-sectional shape corresponding to that of the first axial part (32a) in order to provide continuity. In an example of the present invention, the second axial part (32b) can be made of I nconel. In comparison with the first axial part (32a), the second axial part (32b) is more rigid. As already mentioned, the tubular sealing device (32) generally has the shape of a tubular sheath that is axially and laterally flexible with respect to the transition between the gas supply tube (12) and the gas inlet conduit (14), in order to limit the leakage of reactive gas. The tubular sealing device generally extends axially between a location (34) on the inside of the wall of the furnace (10) and a location (36) at least adjacent to the reaction chamber (16), if It is not that contiguous to this. In the example of construction shown in the figures, the first axial part (32a) is secured to an annular plate (38) by any possible means, providing almost complete sealing in relation to the gas conduit between the first axial part (32a) and the annular plate (38), for example, by welding. The annular plate (38) is mounted securely on the inside face of the furnace wall (10). Any fastening method that provides a good fit between the annular plate (38) and the kiln wall (1 0) can be used, in particular it is possible to use bolts (42) or the like, as shown in the figures. The seal between the annular plate (38) and the wall of the furnace (10) can be further improved in a conventional manner by using sealing rings or the like, placed between them, and / or by welding, as generally shown in the number (39). At the opposite axial end of the tubular sealing device (32), and by way of example, the second axial part (32b) can simply end in an annular ring (44) that can be held in place without being genuinely secured or secured between a surface of the reaction chamber (1 6) (and / or insulating material (28)) and an outer surface of the second axial part (32b). By way of example, the annular ring (44) may have a surface that abuts against an opposite face of the assembly plate (20). In some configurations, it may be advantageous to interpose one or more of the sealing rings (45) between the annular ring (44) and the assembly plate (20). For example, the sealing rings (45) can be made of graphite. In Figure 1, only two of these sealing rings (45) are shown for purposes of illustration. In some configurations, one or more of the additional sealing rings (49) may also have an outer diameter that extends radially outward so that they are placed between the assembly plate (20) and the surface of the chamber. reaction (1 6). In one example of the present invention, the first and second axial portions (32a) and (32b) constituting the tubular sealing device (32) are separate parts that are connected in a gas impermeable manner to the adjacent axial ends of these , by any conventional method that provides an adequate degree of sealing between the first and second axial portions (32a) and (32b). In a specific example, as shown in the figures, the first axial part (32a) (which, as described above, could be formed by a relatively thin metal strip, for example, made of stainless steel) can have a part that forms a flange (50) (in relation to an axis of the first axial part (32a)) at its end adjacent to the second axial part (32b) (see in particular Figures 2 and 3). Correspondingly, the second axial part (32b) has a transversely extending flange or ring (48), which is secured in a conventional manner, for example, by welding (which serves in particular to provide an effective gas-impermeable seal between they). As shown in the figures, and in particular in Figure 3, the part forming a flange (50) and the flange (48) are placed facing each other. A sealing ring (52) (eg, made of graphite) can be interposed between the respective flanges to increase the safety of the gas impermeability between them.

Finally, the flange (48), the flange (50) and the sealing ring (52) between them are held together by a conventional method of fastening, for example by means of nuts and bolts (54), (56). In addition to the tubular sealing device structure described above, it is considered that the materials and / or the construction, for example, of the wall of the furnace (10) of the gas supply pipe (12) of the reaction chamber ( 1 6), thermal insulation (28), etc. , they are well known in the field. In general, all of the components described above should be able to adequately withstand the operating temperatures generally found within the furnace during a CVI / CVD process. In particular, the first flexible axial part (32a) must retain its flexibility through a reasonable working life, taking into consideration the operating temperatures that will be found in its use. Finally, it is necessary to elaborate some of the components of materials that are substantially non-reactive (in particular at the aforementioned high temperatures) to avoid interfering with the chemistry of the densification process implemented in the furnace. Desirably, the tubular sealing device described above, and as claimed herein, can be easily installed in an oven and can be easily removed during maintenance of the oven. Although the present invention is described in the foregoing with reference to certain particular examples for the purpose of illustrating and explaining the invention, it should be understood that the invention is not limited only by reference to the specific details of said examples. More particularly, the person skilled in the art will readily understand that modifications can be made in the preferred embodiments, without going beyond the scope of the invention as defined in the appended claims.

Claims (7)

REVIVAL NAME IS

1 . A device for gas inlet, for passing a gas into an oven from an external part thereof, and towards a gas inlet duct (14) formed inside the reaction chamber (1 6) located inside the oven , said input device includes: a gas tube (1 2) for transporting gas into the furnace, said tube extends between an outer part of the furnace and an inner part thereof, and has an end terminating at least in the proximity of the gas inlet duct formed within the reaction chamber; and a tubular sealing device (32) located radially outward, in relation to the gas tube, the tubular sealing device is secured in gas impermeable form to a first end thereof, at a location on the inner surface of the adjacent oven to a location where the gas pipe penetrates into the furnace, and extends to a location adjacent to the gas inlet conduit, being secured to it in a sealed manner; the gas inlet device characterized in that the tubular sealing device includes a first axial part (32a) which is flexible and a second axial part (32b) that is relatively rigid.

2. A gas inlet device according to claim 1, further characterized in that said first axial structure has a bellows structure.

3. A gas inlet device according to claim 1 or claim 2, further characterized in that said first axial part is made of metal.

4. A gas inlet device according to any of claims 1 to 3, further characterized in that said first axial part is made of stainless steel.

5. A gas inlet device according to any of claims 1 to 4, further characterized in that the second axial part of the tubular sealing part is made of metal.

6. A gas inlet device according to any of claims 1 to 4, further characterized in that the second axial part is made of Inconel.

7. A method for feeding a gas to a reaction gas inlet duct inside a reaction chamber the method consists of: placing a gas transport tube, putting an external part of the oven in communication with an internal part of this , said tube terminating at least in the vicinity of the gas inlet conduit; and substantially isolating the gas transport tube surrounding the gas transport tube with a tubular sealing device which is practically gas-impermeable and which extends from an interior wall of the furnace at the place where the tube penetrates into the furnace until a place adjacent to the gas inlet conduit of the reaction chamber; the method is characterized in that the tubular sealing device is secured in place in such a way that it forms a part that is practically impermeable to the gas through which the tube extends, and because at least a part of the tubular sealing device is transversely flexible, to adapt to the differences in position between the respective ends of the tubular sealing device at the sites where the sealing assembly is secured to the wall of the oven and is adjacent to the gas inlet conduit.