There is disclosed a duct 10 for hot gases, such as a chimney, comprising first and second duct sections 20 each having a generally radially extending mating flange 30, 32. The duct sections 20 are disposed end-to-end such that the mating flanges 30, 32 cooperate with one another to form a joint. The duct also comprises a substantially annular sealing band 44 having a radially extending expansion channel 46 at least partly defined by first and second radially extending channel walls 52, 54. The sealing band 44 is disposed around the joint with the mating flanges 30, 32 disposed within the expansion channel 46. The mating flanges 30, 32 can move within the expansion channel 46 to accommodate dimensional changes of the duct 10 that may occur due to thermal effects.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to British Patent Application No. 1312968.9 filed Jul. 19, 2013. British Patent Application No. 1312968.9 is incorporated herein by reference in its entirety for all purposes.

The invention relates to a duct comprising first and second duct sections disposed end-to-end. The invention is particularly, although not exclusively, concerned with such a duct in the form of a chimney or exhaust to convey the products of combustion to atmosphere, such as a twin-walled or single-walled chimney.

It is known to assemble ducts for hot gasses, such as chimneys, from prefabricated duct sections which are interconnected end-to-end. In one known arrangement each duct section is provided with a flange and a gasket is disposed between the opposing flanges of adjacent duct sections. In order to secure and seal the duct sections together, a sealing band is tightened around the joint between the adjacent duct sections. The sealing band is provided with a V-shaped channel within which the flanges are located. As the band is tightened, the inclined walls that define the V-shaped channel act on the flanges to axially urge them towards one another, thereby compressing the gasket disposed between the flanges and forming a tight seal.

Whilst this arrangement may be satisfactory, during use, hot exhaust gasses passed through the chimney may cause the duct sections to thermally expand, particularly in the radial direction. The radial thermal expansion causes the outer diameter of the flanges to increase and the flanges act on the inclined walls of the V-shaped channel to deform and “open” the channel (i.e. the internal angle is increased) with potential further damage to the flanges and/or gasket. As the chimney cools down, the duct sections contract, but the sealing band remains deformed. This loosens the joint between the two duct sections and compromises the performance of the joint between the duct sections. Repeated thermal expansion and contraction causes further loosening of the joint, further compromising the seal performance and the integrity of the joint.

It is therefore desirable to provide an improved duct which can better accommodate thermal expansion and contraction.

According to an aspect of the invention there is provided a duct for hot gases, comprising: first and second duct sections each having a generally radially extending mating flange, wherein the duct sections are disposed end-to-end such that the mating flanges cooperate with one another to form a joint; and a substantially annular sealing band having a radially extending expansion channel at least partly defined by first and second radially extending channel walls, the sealing band being disposed around the joint with the mating flanges disposed within the expansion channel; wherein the mating flanges can move within the expansion channel to accommodate dimensional changes of the duct that may occur due to thermal effects. The joint may be a sealed joint. The dimensional changes may be thermal expansion and/or contraction of the duct sections. The mating flanges may be able to move within the expansion channel without deforming the expansion channel and/or sealing band and/or flanges and/or gasket (where present). The expansion channel may be configured, such as being dimensioned, to allow the mating flanges to move within the expansion channel.

The duct may be an exhaust duct. The duct sections may be substantially identical. The duct sections may be axially extending. Each duct section may comprise a mating section at opposing ends, the mating section including the radially extending mating flange. The mating section of the first duct section may cooperate with the mating section of the second duct section. The duct sections may be double-walled or single-walled.

The outer diameter of expansion channel may be greater than the outer diameter, or maximum outer diameter, of the mating flanges. The inner diameter of the expansion channel may be less than the outer diameter, or minimum outer diameter, of the mating flanges. The or each mating flange may be annular. The expansion channel may be annular. The expansion channel may be open at its radially inner end. The radial length of the expansion channel may be greater than the radial length of the mating flanges. The abovementioned conditions may be satisfied at ambient conditions and may be satisfied across the working temperature range of the duct which may be between 500° C. and 1300° C., or between 600° C. and 1200° C., or between 700° C. and 1100° C., for example. In some arrangements the temperature may be continuously above 700° C., and may intermittently reach temperatures as high as 1100° C.

The sealing band may comprise first and second side walls that extend away from the first and second channel walls respectively in directions that are oblique to the channel walls. The first and second side walls may extend in the axial direction. The first and second side walls may be radially spaced from side walls of the duct sections. The innermost diameters of the side walls may be greater than the outer diameter of side walls of the duct sections.

The sealing band may be moveable in a transverse plane (i.e. a plane perpendicular to the axis) with respect to the duct sections. This may be referred to as “floating” since the sealing band is not fixed.

The expansion channel may be at least partly further defined by a channel end wall that spaces and connects the channel walls. The channel end wall may define the outer diameter of the expansion channel. The channel walls may be substantially parallel to one another.

The expansion channel may axially urge the mating flanges towards one another. The duct may further comprise a resiliently deformable gasket disposed between the mating flanges. The height of the expansion channel may be less than the combined height of the mating flanges and the non-deformed gasket. The force required to deform the gasket may be less than the force required to deform, or open, the expansion channel.

The sealing band may comprise at least one fastener for securing the sealing band around the joint. The fastener may comprise one or more brackets, bolts, hinges, screws, or other mechanical fasteners.

The sealing band may comprise at least two circumferentially extending parts that are secured together around the joint to form an annulus, and which can be moved apart such that during assembly the sealing band can be located around the joint. The sealing band may comprise at least two completely separable circumferentially extending parts. The sealing band may comprise two circumferentially extending halves which can be moved apart. The two halves may be completely separable.

The expansion channel may have a U-shaped or rectangular cross-section in an axial plane (i.e a plane containing the axis).

The duct may further comprise a substantially annular securing band located around the duct sections so as to secure the duct sections together. The securing band may be located radially outside the sealing band. Insulation material may be disposed inside the securing band and around the joint.

The duct sections and sealing band may be made from a metal, which may be stainless steel, such as austenitic stainless steel. It should be appreciated that other materials may be appropriate.

The duct may be a chimney, such as a twin-walled chimney, which may comprise not only the first and second duct components but also further duct components and/or ancillary components such as tee fittings, elbows and support and attachment components.

The invention also relates to a sealing band for use with a duct in accordance with any statement herein.

According to another aspect of the invention there is provided a kit of parts for forming the duct in accordance with any statement herein, the kit of parts comprising first and second duct sections each having a generally radially extending mating flange; and a substantially annular sealing band having a radially extending expansion channel at least partly defined by first and second radially extending channel walls.

According to a further aspect of the invention there is provided a method of manufacturing a duct in accordance with any statement herein, the method comprising:

disposing first and second duct sections each having a generally radially extending mating flange end-to-end such that the mating flanges cooperate with one another to form a joint; and disposing a substantially annular sealing band having a radially extending expansion channel at least partly defined by first and second radially extending channel walls around the joint with the mating flanges disposed within the expansion channel.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

FIG. 1shows part of a duct for hot gasses, in the form of a chimney10, comprising two axially extending duct sections20disposed end-to-end. As will be described in detail below, in this embodiment the duct sections20are substantially identical and are joined together to form a seal between them. The chimney also comprises an annular securing band12which is disposed around the duct sections20and overlaps them so as to secure the duct sections20together. Although it will be described that the chimney10comprises two duct sections20, it should be appreciated that any suitable number of duct sections20may be joined together to form a chimney10of a desired length.

With reference toFIGS. 2 and 3, the duct section20is substantially cylindrical and extends in the general axial direction. The duct section20is cylindrically symmetric and is also symmetric about a transverse plane (i.e. a plane perpendicular to the axis). The duct section20comprises a cylindrical inner wall22and a generally cylindrical outer wall24having a diameter that is larger than that of the inner wall22. The duct section20also comprises upper and lower annular spacers26,28that connect and space the inner wall and the outer wall22,24. The upper spacer26is disposed towards the upper end of the duct section20and the lower spacer28is disposed towards the lower end of the duct section20. The upper end of the inner wall22is provided with an annular mating flange30that outwardly extends in the radial direction, and the lower end of the inner wall22is provided with a similar annular mating flange32that also outwardly extends in the radial direction. An upper annular groove34is provided in the outer wall24towards the upper end and a lower annular groove36is provided in the outer wall24towards the lower end. The space38between the inner and outer walls22,24can be loose filled or wrapped to provide thermal insulation with an insulating material such as, but not restricted to, mineral wool or ceramic fibre.

As shown inFIGS. 4 and 5, to assemble a chimney, two substantially identical duct sections20are disposed end-to-end with an annular gasket40disposed between the opposing mating flanges30,32. A tubular liner42can be inserted within the inner walls22such that it overlaps the joint between the two duct sections20. The tubular liner42is held in position by resistance welding. In order to seal the joint between the opposing mating flanges30,32a two-part annular sealing band44is located around the joint. As will be described in detail below, the sealing band44has a U-shaped expansion channel46within which the mating flanges30,32and the gasket40are disposed. The sealing band44axially urges the mating flanges30,32together so as to compress the gasket40, thereby forming a seal. An insulating material (not shown) is then placed around the joint, and an annular securing band12is located around the duct sections20to secure them relative to one another. The securing band12has upper and lower radially inwardly projecting flanges14,16that locate within the upper groove34of one duct section20, and the lower groove36of the other duct section20. The securing band12is secured around the duct sections20by two over-centre latches18(FIG. 1).

During use, hot gasses pass through the chimney10and therefore the chimney10may reach temperatures of up to 1100° C., for example. The increase in temperature of the chimney10causes the duct sections20to expand, and as the chimney10cools again the duct sections20contract. This results in the outer diameter of the mating flanges30,32varying between a minimum diameter DIA MIN and a maximum diameter DIA MAX. As will be described in detail below, the sealing band44is configured to accommodate these dimensional changes without being deformed. This results in an improved seal between the duct sections.

FIGS. 6 and 7show the sealing band44in more detail. As shown inFIG. 6, the annular sealing band44is formed from two substantially identical half-bands48that circumferentially extend over 180°. Each end of the half-band48is provided with a bracket50such that the half-bands48can be attached together using fixings, such as nuts and bolts, to form a complete annulus. With the exception of the brackets50, the cross-sectional profile of the sealing band44is substantially constant. As shown inFIG. 7, the sealing band44comprises an annular expansion channel46that extends in the radial direction. The expansion channel46is open at its radially inner end such that it can receive the mating flanges30,32and the gasket40. The expansion channel46is defined by upper and lower radially extending and parallel channel walls52,54, and a channel end wall56that separates and joins the channel walls52,54at their radially outer ends. The sealing band44also comprises upper and lower side walls58,60that axially extend from the radially inner ends of the upper and lower channel walls52,54in opposing directions.

The outer diameter DIA B of the expansion channel46is set such that it is greater than the maximum diameter DIA MAX of the mating flanges30,32and the inner diameter DIA A of the expansion channel46is set such that it is less than the minimum diameter DIA MIN of the mating flanges30,32. As will be described in detail below, this allows the mating flanges30,32to move within the expansion channel46without abutting the end of the channel46.

During assembly, the two half-bands48of the sealing band48are located around the joint and the two mating flanges30,32and the gasket40are located within the expansion channel46. The brackets50are fastened together so as to fix the two half-bands48together. The height of the expansion channel46is less than the combined height of the mating flanges30,32and the gasket40in its resting (non-deformed) state. Therefore, with the mating flanges30,32located in the expansion channel46they are axially forced together to compress the gasket40, thereby forming a seal between the duct sections20. The force required to deform the gasket40is less than the force required to “open” or deform the expansion channel46. This prevents the shape of the expansion channel46from being deformed. The assembled sealing band44“floats” since it is able to move somewhat in a transverse plane. Unlike prior art sealing bands, the floating sealing band44it is not tightened around the joint and the side walls58,60are radially spaced from the side walls of the duct sections20, at least at ambient conditions.

Referring now toFIG. 8, at ambient conditions the radially outer ends of the mating flanges30,32are located within the radially inner end of the expansion channel46. As the temperature of the duct sections20increases, the duct sections20expand in the radial direction and therefore the outer diameter of the mating flanges30,32increases. This radial thermal expansion causes the mating flanges30,32to move within the expansion channel46to accommodate for this thermal expansion. Advantageously, this allows the duct sections20to thermally expand without damaging or deforming the sealing band44or the mating flanges30,32or the gasket40. Specifically, since the expansion channel46is radially extending and is defined by parallel and radially extending channel walls52,54, movement of the mating flanges30,32within the expansion channel46does not open or deform the shape of the expansion channel46. Therefore, when the duct sections20contract, the mating flanges30,32contract radially inwardly and return to their original position. Since the shape of the expansion channel46is not deformed or altered, the channel walls52,54still axially urge the mating flanges30,32towards one another with the same (or at least largely similar) force, thereby maintaining a good seal. This is a significant improvement over prior art arrangements.

Although it has been described that the expansion channel46has a U-shaped profile, it should be appreciated that other cross-sections may be suitable. For example, the expansion channel46may have a rectangular profile. It is important that the expansion channel46is radially extending and is defined by radially extending channel walls. In the above embodiment it has been described that the sealing band44is provided as two completely separable half-bands. This enables it to be assembled around the joint. However, it should be appreciated that in other embodiments the half-bands may be hinged, the band may be a single piece, or may be made from any number of suitable pieces, with or without an overlap, to form a complete annulus.