Patent Description:
<CIT> discloses a shroud cartridge with a composite seal structure according to the preamble of claim <NUM>. <CIT> discloses a labyrinth seal. <CIT> discloses a ring seal attachment system. <CIT> discloses a swirl break. Rotary machines, such as turbomachines, include machine portions where different fluid pressures are present. In order to prevent or limit fluid leakages from a high-pressure area to a low-pressure area in the machine, seals are provided to separate the two areas where different pressures prevail. A typical rotor seal is arranged between a stationary machine component, which is usually integral with the machine casing, and a rotating shaft, which may include a rotating drum, such as a balance drum of a compressor or pump. The rotating shaft extends through the rotor seal assembly, which is stationarily mounted on the stationary machine component and includes sealing members co-acting with the rotating shaft to prevent or reduce fluid leakage.

Typical rotor seals include labyrinth seals, damper or hole-pattern seals, honeycomb seals, pocketed damper seals, abradable seals, and the like.

Some rotor seals include a carrier ring coupled to a seal element. The carrier ring is usually made of metal, is mounted on the stationary part of the machine and operates as a holder for the seal element, which is designed as an insert applied into an annular groove formed in the holder. The seal element is usually made of a suitable polymer, such as a thermoplastic polymer. Seal structures of this kind are sometimes referred to as "composite seals".

The seal element projects radially inwardly from the annular groove in the carrier ring and includes sealing features, such as fins, also referred to as teeth or knives, of a labyrinth seal, which co-act with the rotating part of the machine to provide a sealing action. Opposite the sealing features, the seal element is in surface contact with the inner surface of the annular groove of the carrier ring.

One critical aspect of this kind of seal structure is the reliability of the coupling between the carrier ring and the seal element. Since a pressure difference exits across the two opposing sides of the seal structure, high-pressure fluid from the high pressure side tends to leak through the gap between the carrier ring and the seal element and may reach the bottom of the annular groove. When this happens, the pressure which acts radially inwardly against the seal element may cause the seal element to deform and detach from the carrier ring.

A more effective mechanical coupling between the carrier ring and the seal element in a composite seal structure would be beneficial to achieve better sealing performances and more reliable seal structures.

According to an aspect, a seal structure is disclosed, including a carrier ring having a circumferential outer wall, a first side wall and a second side wall. The first side wall and the second side wall protrude radially inwardly from the circumferential outer wall towards a centerline, i.e. an axis, of the carrier ring. The axis or centerline of the carrier ring coincides with the centerline or axis of the seal structure as a whole. The carrier ring further includes an annular groove formed between the circumferential outer wall, the first side wall and the second side wall. The seal structure further includes a seal element having a first region in surface-to-surface contact with the annular groove and a second, sealing region protruding from the annular groove of the carrier ring toward the centerline of the carrier ring. Moreover, a fastening arrangement formed in the seal structure, is adapted to couple the seal element and the carrier ring to one another. According to embodiments disclosed herein, the fastening arrangement includes a plurality of fastening pins circumferentially arranged around the axis of the carrier ring, extending through at least one of the first side wall and second side wall and each engaging in a corresponding seat formed in the seal element.

The pins provide a safe mechanical coupling between the carrier ring and the seal element.

As understood herein, a carrier ring is usually a monolithic component of annular shape, i.e. component made of a single piece, for instance machined from a single blank.

As understood herein, the seal element is usually an annular, i.e. ring-shaped single piece, i.e. monolithic component, for instance machined from a tubular blank.

In embodiments of the composite seal disclosed herein, the pins provide an efficient coupling between the seal element and the carrier ring, such that radial inward deformations due to pressurized gas leakages are prevented or efficiently reduced.

According to a further aspect, a method for manufacturing a seal structure is disclosed. The method includes a first step of inserting a seal element in an annular groove of a carrier ring. The annular groove is formed between a circumferential outer wall, a first side wall, and a second side wall of the carrier ring, the first side wall and the second side wall protruding radially inwardly from the circumferential outer wall towards a centerline of the carrier ring. After insertion of the seal element in the annular groove of the carrier ring, the seal element is mechanically coupled to the carrier ring, such that the seal element has a first region in surface-to-surface contact with the annular groove and a second, sealing region protruding from the annular groove of the carrier ring toward the centerline of the carrier ring. Thereafter, an inwardly facing surface of the second, sealing region of the seal element is machined to produce sealing features thereon.

Further features and embodiments of the seal structure and of the method of manufacturing are set forth in the appended claims and are further described in the following description of exemplary embodiments.

A new and useful seal structure, specifically for a rotor seal, is disclosed herein. The seal structure includes an annular holder, referred to herein as "carrier ring", which has an annular groove housing an annular insert, referred to herein as a "seal element". The seal element is mechanically coupled to the carrier ring by means of a plurality of pins distributed around the axis of the seal structure and preferably extending parallel to the axis or centerline of the seal structure. As will be explained later on with reference to the detailed description of embodiments, the resulting fastening arrangement prevents or limits radial deformation of the seal element. The particular manner of fastening the seal element to the carrier ring also allows novel and useful methods of manufacturing the seal structure, which can save time and costs, resulting in a seal structure of high precision and efficiency.

While the following description focusses on labyrinth seals, the novel features of the seal structure disclosed herein can be used with advantage also in other types of rotor seals, i.e. seals adapted to co-act with a rotating member of a machine. For instance, the features of the seal structure specifically concerning the mechanical coupling between the seal element and the carrier ring can be used also in abradable seals, honeycomb seals or other seals as recalled in the introductory part of the present specification. In general, features disclosed herein can be used in combined seal structures including a carrier ring and an annular seal element coupled to the carrier ring and projecting therefrom radially inwardly with a sealing region designed for co-action with a shaft or drum.

Turning now to the drawings, <FIG> illustrates a schematic sectional view of a centrifugal compressor <NUM>. The sectional view is taken along a plane containing the rotation axis A-A of the compressor rotor. The section of <FIG> illustrates only a portion of the centrifugal compressor, sufficient for the purposes of the present description.

The centrifugal compressor <NUM> of <FIG> is presented here as an exemplary embodiment of a turbomachine, in which the seal structure of the present disclosure can be advantageously applied. Those skilled in the art of turbomachines will, nevertheless, understand that the seal structure disclosed herein can be applied also to different kinds of turbomachines, and in different positions of the turbomachine. In general, the seal structure can be used whenever sealing around a rotating member, such as a rotor, drum or shaft, between a high pressure area and a low pressure area, is required.

The centrifugal compressor <NUM> includes a shaft <NUM> and one or more impellers <NUM>. In <FIG> three impellers <NUM> are illustrated. While in <FIG> the impellers <NUM> are mounted on the shaft <NUM> for co-rotation therewith in a so-called shrink-fit arrangement, in other embodiments the impellers can be configured as so-called stack-impellers, which are axially stacked and torsionally coupled to one another the aid of a tie-beam and respective Hirth coupling or other coupling features.

In the embodiment of <FIG> a distancing ring <NUM> is arranged between each pair of adjacent impellers <NUM>. A balance drum <NUM> further keyed on shaft <NUM> for rotation therewith. The shaft <NUM>, the impellers <NUM>, the distancing rings <NUM> and the balance drum <NUM> form together a rotor <NUM>, which is mounted for rotation around rotation axis A-A according to arrow f11. The rotor <NUM> is housed in a casing (not shown), wherein the stationary components of the compressor <NUM> are housed. The stationary components include diaphragms <NUM> defining diffusers <NUM> and return channels <NUM> of the compressor.

Each impeller includes an impeller eye <NUM>. By way of illustration, an eye labyrinth seal <NUM> is positioned around each impeller eye <NUM> to reduce gas leakages from the high-pressure side downstream of the impeller to the low-pressure side upstream the impeller. The terms "upstream" and "downstream" are referred to the direction of flow of the process gas through the compressor <NUM>, which is schematically represented by arrows G. Each labyrinth seal <NUM> is mounted in a housing machined in the respective diaphragm of the centrifugal compressor <NUM>.

Shaft labyrinth seals <NUM> are further provided between diaphragms <NUM> and the shaft <NUM>, for instance around the distancing rings <NUM>. The shaft labyrinth seals <NUM> are mounted in respective housings machined in the diaphragms <NUM>.

In the embodiment of <FIG>, a balance drum labyrinth seal <NUM> is also disposed around the balance drum <NUM>.

One, some or all the labyrinth seals <NUM>, <NUM>, <NUM> of the centrifugal compressor <NUM> can be configured according to the present disclosure. Here below, referring to <FIG>, an embodiment of a generic labyrinth seal is described, to illustrate the novel features thereof. Those skilled in sealing technology will be capable of designing labyrinth seals for different uses and different parts within the centrifugal compressor <NUM>, or another turbomachine, embodying the features described below.

<FIG> illustrates an exemplary seal structure <NUM>, which can be used in the eye labyrinth seal <NUM>, in the shaft labyrinth seal <NUM>, in the balance drum labyrinth seal <NUM>, or more generally in any different rotor seal within a turbomachine.

The labyrinth seal <NUM> includes a carrier ring <NUM> and a ring-shaped seal element <NUM>. The axis or centerline of the seal arrangement is labeled A-A and coincides with the rotation axis of the compressor rotor <NUM> when the seal structure is mounted in the turbomachine around the compressor rotor <NUM>.

The carrier ring <NUM> can be made of a metal or a metal alloy. The material used for manufacturing the carrier ring <NUM> can be selected based on the nature of the process gas, which will get in contact with the seal arrangement <NUM>, on the pressures on the two sides of the seal arrangement, on the dimension of the seal, and on other design considerations. For instance, generally in normal, sweet and sour environments with low acidity the following alloys can be employed: aluminum alloys of the series <NUM>, one example of which is AVIONAL® <NUM>; or aluminum alloys of the series <NUM>, one example of which is PERALUMAN®, where AVIONAL and PERALUMAN are a trademarks registered to Constellium Valais SA, Switzerland; or aluminum alloys of the series <NUM>, one example of which is ANTICORODAL®, where ANTICORODAL is a trademark registered to Novelis Switzerland SA, Switzerland, and martensitic stainless steels. In normal environment, carbon steel and low alloy steel can be used. In acid environments austenitic, superaustenitic, duplex and superduplex stainless steels as well Ni-based alloys can be employed. As good design practice, the carrier ring should be made of the same material of the diaphragm.

The seal element <NUM> can be made mainly of a thermoplastic polymer. For instance, the seal element <NUM> can be made of a composite polymeric material having a polymer matrix filled with reinforcing fibers or particles, such as carbon fibers, glass fibers, or the like. Polymers like PEK (polyether ketone), PEEK (polyether ether ketone), PAI (polyamide-imides), PEI (polyethylenimine) and PFA (perfluoroalkoxy alkanes) can be used as options. Reinforcing fibers can be long or shorts (<<NUM>) depending on the required mechanical characteristics or on the available technology.

With continuing reference to <FIG> shows an enlarged cross-section of the carrier ring <NUM> and of the seal element <NUM>.

The carrier ring <NUM> includes a circumferential outer wall <NUM>, a first side wall <NUM> and a second side wall <NUM>. The circumferential outer wall <NUM>, the first side wall <NUM> and the second side wall <NUM> form an annular groove <NUM> therebetween, which houses the seal element <NUM>.

In the embodiment of <FIG>, the circumferential outer wall <NUM> has a broadly cylindrical shape. The inner surface of the circumferential outer wall <NUM> forms the bottom of the annular groove <NUM>. The outer surface of the circumferential outer wall <NUM> forms a fastening feature <NUM> for coupling to an annular seat formed in a stationary member of the turbomachine, for example the compressor diaphragm, in which the seal structure <NUM> is mounted. In the embodiment of <FIG> the fastening feature includes an annular projection extending from the outer peripheral surface of the circumferential outer wall <NUM>. The projection has a cross-sectional shape forming an undercut <NUM> for mechanical coupling to the annular seat in the turbomachine.

Each of the side walls <NUM> and <NUM> includes an inner surface, which can be substantially planar and orthogonal to the centerline or axis A-A of the sealing structure. The inner surfaces of the side walls <NUM> and <NUM> extend radially inwardly from the inner surface of the circumferential outer wall <NUM> and form the flanks of the annular groove <NUM>. Each side wall <NUM> and <NUM> further includes a respective outer surface, which can be substantially parallel to the respective inner surface and can be substantially planar. In some embodiments, on one or both the external surfaces of the side walls <NUM> and <NUM> swirl breakers <NUM> can be provided.

The first side wall <NUM> is manufactured to have a first set of through holes <NUM> extending from the outer surface to the inner surface of the first side wall <NUM>. Similarly, the second side wall <NUM> has a second set through holes <NUM> extending from the outer surface to the inner surface of the second side wall <NUM>.

The seal element <NUM> includes a main body <NUM> with an external cylindrical surface <NUM> in surface contact with the bottom of the annular groove <NUM>. The main body <NUM> further includes side surfaces <NUM> and <NUM> in surface contact with the inner surfaces of the first side wall <NUM> and of the second side wall <NUM>, respectively. Thus, the main body <NUM> includes a first region of the seal element, in surface-to-surface contact with the annular groove <NUM> formed in the carrier ring <NUM>.

Moreover, the main body <NUM> includes a second, region, namely a sealing region, arranged radially inwardly of the first region and labeled <NUM>. The second, sealing region <NUM> has a plurality of sealing features adapted to co-act with a rotating part of a rotor. In the embodiment of <FIG> the seal structure <NUM> features a labyrinth seal and the sealing features include annular teeth, blades or lips <NUM>, which project radially inwardly from the carrier ring <NUM> towards the centerline or axis A-A of the seal structure <NUM>.

A fastening arrangement mechanically couples the carrier ring <NUM> and the seal element <NUM> to one another. In the embodiment of <FIG> the fastening arrangement includes a first set of fastening pins <NUM> and a second set of fastening pins <NUM>. Each fastening pin <NUM> of the first set of fastening pins extends in the through hole <NUM> and has an inwardly oriented end projecting in a seat <NUM> formed in the side surface <NUM> of the seal element <NUM>, which is in surface contact with the side wall <NUM>. Each fastening pin <NUM> of the second set of fastening pins extends in the through hole <NUM>, which extends across the second side wall <NUM> and has an inwardly oriented end housed in a seat <NUM> formed in the side surface <NUM> of the seal element <NUM>, which is in surface contact with the side wall <NUM>.

The seats <NUM> and <NUM> are in the form of blind holes drilled in the seal element <NUM>.

In some embodiments, the holes <NUM> and <NUM> as well as the seats <NUM> and <NUM> are oriented parallel to the axis or centerline A-A of the seal arrangement <NUM>.

In some embodiments, each hole <NUM> and relevant seat <NUM> are collinear with a corresponding hole <NUM> and relevant seat <NUM>, such that pairs of fastening pins <NUM>, <NUM> of the two sets of fastening pins are collinear to one another.

If the seats <NUM>, <NUM> are collinear, each seat can have a length which is less than half the thickness of the seal element <NUM>, i.e. less than half the dimension of the seal element <NUM> in the direction of the centerline, measured between the opposing side surfaces of the seal element <NUM>, where the seats <NUM> and <NUM> are drilled. In <FIG> such thickness is indicated as "T". In this way the collinear seats remain separate from one another in the form of two opposing blind holes.

The holes <NUM> can be equidistant from one another. Similarly, the holes <NUM> can be equidistant from one another. For instance, the holes can be arranged according to a constant angular pitch α (see <FIG>). In some embodiments, the angular pitch α which can be comprised between about <NUM>° and about <NUM>°, preferably between about <NUM>° and about <NUM>°, for instance between about <NUM>° and about <NUM>°. In the embodiment of <FIG> the angular pitch α is <NUM>°.

The fastening pins <NUM>, <NUM> can be locked in the holes <NUM>, <NUM> and in the seats <NUM>, <NUM> in any suitable way, for instance by gluing, soldering, welding or the like. Gluing may be particularly advantageous, as no heat is applied, which may damage the seal element <NUM>.

The fastening pins <NUM>, <NUM> provide a reliable coupling between the carrier ring <NUM> and the seal element <NUM>. The fastening pins <NUM>, <NUM> provide an effective reaction force opposing a radially inwardly acting pressure, which can be generated by pressurized fluid penetrating the gap between the bottom of the annular groove <NUM> and the external cylindrical surface <NUM> of the seal element <NUM>.

The above described seal structure <NUM> can be manufactured in a convenient manner according to the method described below, reference being made to the sequence of <FIG>.

The carrier ring <NUM> can be manufactured by conventional techniques, e.g. by turning, milling or any other chip removal process, starting from a blank, for instance in form of a tube, until the final net shape thereof is achieved, with the exception of through holes <NUM>, <NUM>, see <FIG>. The through holes <NUM>, <NUM> are manufactured in a subsequent step, as described hereafter.

The seal element <NUM> can be manufactured starting from a blank 35B, shown in a cross-sectional view in <FIG>. The blank 35B can have an annular shape, the cross section whereof has a simple square or rectangular shape. The blank 35B can be made by conventional technologies as well as 3D-printing manufacturing technologies.

The blank 35B is then partly machined, e.g. by turning or similar chip-removal procedure, to generate the outer surfaces <NUM>, <NUM>, <NUM> of the seal element <NUM>, i.e. those surfaces which are intended to be in surface contact with the annular groove <NUM> of the carrier ring <NUM>. The inwardly facing surface on which the sealing features <NUM> are provided will be machined in a subsequent step, which will be disclosed below.

The partly machined seal element <NUM> is then introduced in the annular groove <NUM> of the carrier ring <NUM>, as shown in <FIG>.

In the next manufacturing step, through holes <NUM> and <NUM> are drilled through the side walls <NUM> and <NUM>. Drilling is continued to machine the seats <NUM> and <NUM> in the seal element <NUM>.

Once the holes <NUM>, <NUM> and the seats <NUM>, <NUM> have been drilled, the fastening pins <NUM>, <NUM> are introduced and locked, for instance by gluing, see <FIG>.

Once the partly machined seal element <NUM> has been coupled to the carrier ring <NUM>, the second, sealing region <NUM> of the seal element <NUM> can be machined, by turning, for instance, to achieve the final shape, including the teeth <NUM> or other sealing features, see <FIG>.

The process described so far allows very precise machining and reduces the amount of plastic material needed. Deformation of the plastic blank during manufacturing is avoided. Annealing or other heat treatments of the seal element <NUM> to remove thermally induced stresses can be dispensed with.

A modified embodiment (not claimed) of the seal structure <NUM> is illustrated in <FIG>. The same reference numbers designate the same or equivalent parts shown in <FIG> and described above. The main difference between the embodiment of <FIG> and the embodiment of <FIG> concerns the fastening arrangement, which mechanically couples the seal element <NUM> to the carrier ring <NUM>. <FIG> illustrates a single set of fastening pins <NUM>. Each pin <NUM> extends through both side walls <NUM>, <NUM>, as well as through a seat <NUM> which extends across the whole thickness (i.e. the dimension in the axial direction) of the seal element <NUM>, from side surface <NUM> to side surface <NUM>.

To prevent the fastening pins <NUM> from being pushed out from the seal structure <NUM> by the pressure differential between a high-pressure area and a low-pressure area, between which the seal arrangement <NUM> is placed, the fastening pins <NUM> may be provided with an annular ridge <NUM> abutting against the side of the seal structure <NUM> facing the high-pressure area, or with any other feature adapted to retain the fastening pins <NUM> in position against the force resulting from the pressure differential across the seal structure <NUM>.

According to the invention, the holes <NUM>, <NUM> are blind, i.e. restricted to a portion only of the thickness of the relevant side wall, such as not to surface on the side of the carrier ring <NUM> facing the low-pressure area of the machine where the seal structure <NUM> is mounted. In this way the fastening pins <NUM> introduced in the blind holes from the high-pressure side will abut against the bottom of the blind holes and will be retained against the force resulting from the pressure differential across the seal structure <NUM>.

In all embodiments disclosed above the seal element <NUM> is formed by a single integral annular member. While this is particularly advantageous in terms of precision of manufacturing and easy assembling, it is not excluded that the seal element <NUM> be formed by separate annular portions, which are introduced in the annular groove <NUM> of the carrier ring <NUM>. The several annular portions can then be connected to one another by gluing or in any other suitable manner.

<FIG> summarizes the main steps of manufacturing methods according to the present disclosure.

Claim 1:
A composite seal structure (<NUM>) adapted to be mounted in a turbomachine, the composite seal structure comprising:
a carrier ring (<NUM>) having: a circumferential outer wall (<NUM>) with an inner surface and an outer surface, a first side wall (<NUM>), and a second side wall (<NUM>), wherein the first side wall and the second side wall protrude radially inwardly from the circumferential outer wall towards an axis of the carrier ring; wherein an annular groove (<NUM>) is formed between the circumferential outer wall (<NUM>), the first side wall (<NUM>) and the second side wall (<NUM>);
a seal element (<NUM>) having a first region (<NUM>) in surface-to-surface contact with the annular groove (<NUM>) and a second, sealing region (<NUM>) protruding from the annular groove of the carrier ring toward the axis of the carrier ring (<NUM>) and provided with sealing features (<NUM>); and
a fastening arrangement coupling the seal element (<NUM>) and the carrier ring (<NUM>) to one another forming said composite seal structure; wherein the fastening arrangement comprises a plurality of fastening pins (<NUM>, <NUM>) circumferentially arranged around the axis of the carrier ring (<NUM>); wherein each fastening pin of the plurality of fastening pins extends through at least one of the first side wall (<NUM>) and second side wall (<NUM>); and wherein each fastening pin of the plurality of fastening pins (<NUM>, <NUM>) engages in a corresponding seat (<NUM>, <NUM>) formed in the seal element;
characterized in that the plurality of fastening pins comprise: a first set of fastening pins (<NUM>) extending through holes (<NUM>) across the first side wall (<NUM>) and engaging into a first set of the seats (<NUM>) of the seal element (<NUM>); and a second set of fastening pins (<NUM>) extending through holes (<NUM>) across the second side wall (<NUM>) and engaging into a second set of the seats (<NUM>) of the seal element (<NUM>); and wherein the seats (<NUM>, <NUM>) are in the shape of blind holes in the seal element (<NUM>).