Abstract:
An assembly method and an arrangement of components in a fluid energy machine, in particular a turbocompressor, with a longitudinal axis. The arrangement includes: an inner bundle to be arranged in an outer casing of the fluid energy machine, a low-pressure unit of the fluid energy machine, at least one cover of the fluid energy machine for the axial end-side closure of the outer casing on at least one end side, wherein these components are arranged axially adjacent to one another in the sequence cover, low-pressure unit, inner bundle and the cover is releasably attached to the low-pressure unit and the inner bundle is releasably attached to the low-pressure unit such that there results a transportable unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2015/058412 filed Apr. 17, 2015, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102014207461.4 filed Apr. 17, 2014. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to an arrangement of components of a fluid energy machine, in particular of a turbocompressor, with a longitudinal axis, comprising an inner bundle for arrangement in an outer housing, a low-pressure insert, and at least one cover for the axial face-side closure of the outer housing at at least one face side. 
       BACKGROUND OF INVENTION 
       [0003]    Such fluid energy machines or arrangements of the type mentioned in the introduction are already known from, for example, EP 2 024 646 B1 or EP 1 952 030 B1. The latter document also describes an assembly method for a turbocompressor described therein. A fluid energy machine, in the case of which an axial face-side cover is provided for closing off a shell part of an outer housing, is already known from WO 2012/041757 A1. 
         [0004]    U.S. Pat. No. 3,927,763 and DE 10 2012 203 144 A1 have already disclosed pot-type compressors with a face-side closure cover of the outer housing. 
         [0005]    A field of use of the invention is that of turbo-type fluid energy machines, in particular turbocompressors, which have a so-called pot housing, wherein said pot housing has a shell part which is open axially at the face side on both sides and which is closed off in pressure-tight fashion axially at the face side by way of covers. As presented in EP 1 952 030 B1, so-called inner bundles are inserted axially into said pressure-type outer housing pots, wherein, in general, a rotor equipped with impellers extends axially in the coaxial center of the inner bundle. 
         [0006]    A field of use of the invention furthermore lies in the field of centrifugal operating machines, that is to say radial turbocompressors or radial turboexpanders. All embodiments here which relate to radial turbocompressors also apply, mutatis mutandis, with a corresponding reversal of the flow direction, to radial turboexpanders. 
         [0007]    Geometric statements such as radial, axial, tangential or circumferential direction always relate—unless stated otherwise—to the central axis of the longitudinal extent of the inner bundle, of the outer housing or of the axis of rotation of the rotor, wherein said axes are substantially coincident aside from slight planned or tolerance-induced deviations which are not of relevance for the present invention. Planned deviations may arise for example from rotational-speed-dependent changes of the oil film of oil bearings. 
         [0008]    The assembly of a radial turbomachine in an axial direction is always associated with particularly great outlay, because the so-called inner bundle, connected to further components, for example the rotor, must be assembled to form a transportable unit and must be inserted axially without damage into the pot housing, which is generally of cylindrical form. Here, damage can be caused to adjacent components, for example to the corresponding cover seals or to the shaft seals, or damage can be caused in the event of an offset of the rotor relative to the static components—that is to say the stator—of said transportable unit. 
         [0009]    Assembly utilizing gravitational force by way of a vertical insertion of said transportable unit into the outer housing is often ruled out at least at the operating site, because this necessitates a crane in the machine hall, which has a corresponding lifting height and load capacity. Furthermore, said assembly must subsequently be rotated into the operating position again, which likewise harbors the risk of damage and necessitates a reorientation of the housing. 
         [0010]    EP 1 952 030 B1 addresses this in that, on the outer housing, a running surface is provided, and the assembled arrangement composed of a rotor, an inner bundle and further components is inserted axially into the outer housing by way of an additional apparatus, wherein the additional apparatus is substantially in the form of a horizontal C-shaped hook, such that one limb of the C is supported on the top of the outer housing and the other limb is affixed in flexurally rigid fashion to the inner bundle or is partially formed by the inner bundle. Such an apparatus has only a limited load capacity and is therefore suitable only for machines up to a particular structural size. Owing to the high torques, the apparatus can be easily deformed. 
       SUMMARY OF INVENTION 
       [0011]    Taking the highlighted problems and disadvantages of the prior art as a starting point, it is an object of the invention to provide an arrangement of the type mentioned in the introduction, which arrangement permits, in particular, efficient assembly and at the same time does not increase the installation outlay. 
         [0012]    It is a further aim of the invention to improve the standardization for different structural sizes of a fluid energy machine or of a radial turbocompressor. 
         [0013]    The invention solves the above disadvantages and problems of the prior art by way of an arrangement and by way of a method as per the independent claims. The respectively back-referenced subclaims comprise advantageous refinements of the invention. 
         [0014]    In the context of the invention, a fluid energy machine is to be understood to mean a turbomachine which converts technical work into flow work or vice versa. The invention in particular relates to a radial turbocompressor. The invention is basically also applicable, mutatis mutandis, with a corresponding flow reversal, to radial turboexpanders. In particular, the so-called inner bundle of the arrangement is intended for being arranged in an outer housing or an outer housing shell of a fully assembled machine. 
         [0015]    In the nomenclature of the invention, the attribute “face”, for example in the case of “face side” or “at the face side”, is defined in relation to the longitudinal axis, and refers to an areal extent with a surface normal in the direction of the longitudinal axis. 
         [0016]    Here, the inner bundle comprises in particular the static flow-guiding components, which can also be referred to as flow stators or simply as stators. In the fully assembled arrangement of the fluid energy machine, a rotor extends along the central longitudinal axis of the inner bundle, which rotor has impeller blades or at least one impeller. In the case of a radial turbomachine, the inner bundle generally comprises the return stages by means of which, in the case of a compressor, the flow is, downstream of each impeller, returned radially inward from a radially outward direction. Furthermore, the so-called return stages have the task of imparting a different swirl to, or changing the swirl of, or substantially eliminating the swirl from the preceding impeller or the impeller blade stage from, the process fluid which absorbs or outputs the flow work. 
         [0017]    The component referred to by the independent claim as “low-pressure insert” is, in the case of the radial turbocompressor, the flow guide of the inlet into the machine, and is also commonly referred to as induction insert. In general, and advantageously, a radial turbocompressor with an arrangement according to the invention has a process fluid supplied to it radially during operation, and is, by way of the low-pressure insert, distributed on the circumference about the axis of rotation or longitudinal axis of the machine and diverted into the axial direction and supplied to the inlet of the first impeller. 
         [0018]    In the context of the invention, an outer housing for an arrangement according to the invention is in the form of a substantially cylindrical shell which, axially at the face side, advantageously on both sides, is designed to be closable, or is closed, by way of a cover. Said two covers advantageously have an identical axial fitting direction. This means that the cover, affixed according to the invention to the transportable unit, is led axially through the shell-like, advantageously internally cylindrical, structure of the outer housing in the direction of the final position of the cover. 
         [0019]    During the axial movement, the inner bundle of the transportable unit advantageously reaches a final position which is advantageously defined by an axial abutment in the outer housing for the inner bundle. 
         [0020]    In said position of the transportable unit, the cover may already be arranged in its axial final position, wherein said cover closes off the outer housing axially at the face side on one side. 
         [0021]    Alternatively, and advantageously, the cover is, in said axial position, moved axially away from the inner bundle in the direction of a final axial position. 
         [0022]    In both cases, it is advantageous, in the case of a radial turbocompressor, for a radial projection to be provided on the outer housing shell, which projection projects radially inward and on which projection the cover is supported so as to be prevented from being offset axially out of the outer housing shell. Said support absorbs the internal pressure acting on the cover in the case of the compressor. 
         [0023]    In the case of the cover being separated from the inner bundle during the course of the assembly process, it is expedient for the cover to be pulled axially into the final position by way of a pulling apparatus provided on the outer housing. This may be realized for example by way of molded pieces or lugs provided on the outer housing and by way of screws that interact therewith, wherein for example the screws, which extend through a recess in the lugs, pull the cover axially in the direction of a final position when said screws are screwed in each case into a counterpart thread provided in the cover. This arrangement can permanently fix the cover in the final position on the outer housing during operation, such that the cover is securely positioned even in the presence of a negative pressure in the outer housing. 
         [0024]    The shoulder in the outer housing for the cover is advantageously provided over the entire circumference and has at least one seal or interacts with a seal or with a seal carrier, such that, in the presence of an internal positive pressure, the cover of the transportable unit is forced axially outward and bears sealingly against said seal of the outer housing. 
         [0025]    In the context of the invention, a transportable unit is to be understood to mean that the unit can be moved from a pre-assembly site to a final assembly site by way of conventional transportation aids without being damaged. The transportation aids include, for example, vehicles with corresponding support apparatuses and also cranes which, by way of corresponding load attachment means on the transportable unit, can lift said unit and also move it in a horizontal direction. Here, the transportable unit is provided for being fastened at defined suspension points by way of the attachment means and otherwise requires no additional stabilization, but rather inherently exhibits adequate stiffness such that no damaging offsetting of the individual components relative to one another occurs. 
         [0026]    The arrangement according to the invention permits a particularly efficient process of assembly of a corresponding fluid energy machine, because the mounting of a cover in the shell-like outer housing for the axial face-side closure on one side of the outer housing and the axial insertion of the inner bundle and of the low-pressure insert can be performed in a single assembly step. The arrangement composed of the cover, the low-pressure insert and the inner bundle is advantageously also assigned the rotor, which extends along the longitudinal axis of the inner bundle or the axis of rotation of the rotor coaxially through said components, in such a way that said components surround the rotor in ring-shaped fashion at certain axial positions provided for that purpose. The rotor is advantageously fixed radially and axially in the arrangement. Here, the rotor advantageously does not have the task of imparting a centering or fixing action. 
         [0027]    In a conventional embodiment, it is necessary for a cover to be arranged on or affixed to the outer housing shell in a separate mounting step before the rotor and/or the inner bundle are inserted into the outer housing. 
         [0028]    Said configuration of the arrangement according to the invention is particularly advantageous if the outer housing is closed off axially at the face side on both sides by way of in each case one cover, wherein the first cover has the same axial assembly direction as the second cover and must accordingly be led in an axial direction through the outer housing shell before it reaches its final position. 
         [0029]    The arrangement according to the invention therefore promotes the standardization of a fluid energy machine with an arrangement according to the invention, because, during the course of the standardization of the outer housing, it is advantageously the case that only the one or more covers is/are designed individually for a particular structural size, or advantageously, the one or more covers is/are also of identical design for a range of structural sizes and is/are merely carrier(s) for individualized other assemblies. Said individualized other assemblies include in particular a shaft seal affixed to the cover, which shaft seal is also supported on the cover, and a bearing unit which is affixed to and supported on the cover, which bearing unit serves for the radial and/or axial mounting of the rotor. Such a modular construction with individualization of the cover assemblies permits a uniform design of the outer housing shell across a range of structural sizes of the fluid energy machine. 
         [0030]    Another embodiment of the invention provides that the inner bundle is detachably fastened to the low-pressure insert and the cover is detachably fastened to the low-pressure insert such that said three components are secured relative to one another so as to be prevented from being offset axially, radially and in a circumferential direction. Here, it is advantageously possible for a shaping of the cover extending in the circumferential direction to be coordinated with a second shaping, extending in the circumferential direction, of the low-pressure insert, such that radial centering of said two components with respect to one another is realized when they are in abutting contact. For a defined position in the circumferential direction with respect to one another, it is possible for in each case at least one centering pin to be provided between the individual components, which centering pin is inserted in form-fitting fashion into corresponding recesses of the two adjacent components. The intermediate bases and the low-pressure insert are braced against one another, in particular in the direction of the longitudinal axis, that is to say advantageously horizontally, by way of screws or similar fastening elements. 
         [0031]    The cover, which is moved axially through the outer housing in the direction of the final position, may be detachably fastened to the low-pressure insert or positioned there in centered fashion by being placed on loosely. In order that the cover is correctly positioned in the circumferential direction, it is expedient for the circumferential position on the inner bundle or on the low-pressure insert to be secured, for example by way of a centering pin. 
         [0032]    An axial fixing of the cover, as a constituent part of the transportable unit, to the transportable unit is advantageously designed such that said fastening is removable from the outside—that is to say from outside the outer housing—in the fully assembled state. This may particularly expediently be realized by way of a first mounting sleeve which axially supports the cover on the rotor, wherein the rotor extends through an opening of the cover. 
         [0033]    Here, it is advantageous for the cover to also be a carrier of a shaft seal in order to seal off the gap between rotor and cover during operation. 
         [0034]    For this purpose, too, it is the case in a preferred embodiment of the invention that the low-pressure insert is formed in one piece in a circumferential direction, comprising a cover-side first flow contour, guide vanes and a bundle-side second flow contour, wherein the cover is affixed to the first flow contour, and the inner bundle to a second flow contour by way of fastening options already discussed above. Here, it may advantageously be provided that the guide vanes are the only direct connection between the cover-side first flow contour and the bundle-side second flow contour. The low-pressure insert may in this case be formed for example as a welded construction, in the case of which the guide vanes are welded to the flow contour. Another possibility is provided by milling machining proceeding from a unipartite solid or by way of spark erosion. Another possibility for the manufacture of the low-pressure insert consists in the use of additive manufacturing methods, for example by way of laser sintering. 
         [0035]    In order that, in the region of a parting joint of the low-pressure insert, no complicated seal arrangements are required in the region of the vicinity of the outer housing, it is advantageous if the low-pressure insert is of undivided form in the circumferential direction, or has no parting joint extending in a radial direction. In terms of assembly, this embodiment is possible according to the invention because, in general, the low-pressure insert can be pushed axially onto the rotor, which is generally combined with the inner bundle in form-fitting fashion, and affixed to the inner bundle. In the same way, the cover is advantageously pushed onto the rotor or affixed to the low-pressure insert. In order that no axial division of the rotor is required, it is expedient if the inner bundle or the assembly of return stages in the case of a radial machine is of divided form in a circumferential direction at a parting joint. Here, it is furthermore expedient for the inner bundle to be composed of axial inner bundle subsections which are individually of divided form in each case at a parting joint. Here, it is expedient for the individual inner bundle sections to each have a lower part and an upper part, and for the lower parts of the inner bundle subsections to be able to be joined together axially to form an inner bundle lower part, and the upper part of the inner bundle subsections can be combined, by being detachably fastened to one another axially, to form an inner bundle upper part, in that both the inner bundle lower part and the inner bundle upper part individually form a transportable unit as an intermediate step of the assembly process. 
         [0036]    The arrangement according to the invention advantageously has, in an axial extension on that side of the inner bundle which is averted from the cover or from the low-pressure insert, a high-pressure collector which is advantageously of undivided form in a circumferential direction. Said undivided form of the high-pressure collector also has advantages with regard to the elimination of the need for a seal for a parting joint. 
         [0037]    In order for the rotor to be added, without being damaged, to the arrangement according to the invention as a transportable unit, it is expedient for the first mounting sleeve to be provided which supports the rotor radially on the cover during transportation of the transportable unit comprising the rotor. Said first mounting sleeve is expediently designed so as to be removable axially from the outer side of the cover. Accordingly, it is advantageously the case that, firstly, the cover is affixed, detachably fastened or loosely placed on to the low-pressure insert in centered fashion, and subsequently, the first mounting sleeve is affixed, as a centered support for the rotor, to the cover. In this way, the rotor is guided concentrically with respect to the longitudinal axis in the inner bundle. For the purposes of support of the rotor with a centering action, it is expedient for a second mounting sleeve to be provided between the rotor and the high-pressure collector and to support the rotor on the high-pressure collector. The second mounting sleeve is also advantageously designed such that it can be removed from the outside from the arrangement after completed insertion into the outer housing. Here, at least one mounting sleeve may be of divided form in the circumferential direction and assembled by way of fastening elements such that the rotor is radially clamped. It is advantageous for at least one mounting sleeve, or both mounting sleeves, to bare not only radially against the rotor but also axially against a rotor shoulder, such that an axial offset is prevented owing to the form fit for the mounting sleeves with respect to the inner bundle, the cover and the low-pressure insert. 
         [0038]    This axial securing of at least one mounting sleeve, advantageously of both mounting sleeves, permits the axial securing, already discussed above, of the cover, which is advantageously arranged axially loosely on the low-pressure insert and by means of which the first mounting sleeve can be secured axially. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    Below, the invention will be discussed in more detail on the basis of a specific exemplary embodiment with reference to drawings, in which: 
           [0040]      FIGS. 1-5  show, in each case in an illustration of a longitudinal section, an arrangement A comprising components of a fluid energy machine FEM. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0041]    All directional statements such as axial, radial, tangential or circumferential direction always relate—unless stated otherwise—to the longitudinal axis X of the rotor. The longitudinal axis X of the rotor R corresponds to the axis of rotation of the rotor R during operation. The central longitudinal axes of the impellers, of the inner bundle IB, of an outer housing OC, of a cover COV, of a low-pressure insert LPU and of a collector COL run in substantially coincident fashion, aside from planned or unplanned deviations which are not relevant in the context of the invention. 
         [0042]      FIGS. 1-5  show, in each case in an illustration of a longitudinal section, an arrangement A comprising components of a fluid energy machine FEM, specifically of a turbocompressor TCO, with a longitudinal axis X. Here,  FIGS. 1-5  show different stages of the assembly of the components in the context of an assembly process in successive steps, wherein  FIG. 1  illustrates the smallest number of components and  FIG. 5  illustrates the greatest number of components. 
         [0043]    In  FIG. 1 , lower parts of axial inner bundle subsections RS 1 , RS 2 , RS 3  have been assembled axially on one another axially along the longitudinal axis X to form an inner bundle lower part IBL of an inner bundle IB. The lower parts of axial inner bundle subsections RS 1 , RS 2 , RS 3  have been fastened to one another by way of screws. A rotor R extending along the axis X with four impellers IMP 1 , IMP 2 , IMP 3 , IMP 4  arranged in succession has been lowered into the inner bundle lower part IBL. Here, measures are implemented to ensure that the rotor R does not lie directly, for example via shaft seals, on the inner bundle lower part IBL and cause damage. 
         [0044]      FIG. 2  shows the assembly sequence that follows the illustration of  FIG. 1 , in which an inner bundle upper part IBU assembled axially from axial constituent parts has been mounted radially onto the inner bundle lower part IBL, so as to yield a complete inner bundle IB through which the rotor R extends along its longitudinal axis X. The longitudinal axis X extends substantially along a parting joint plane of the inner bundle IB. In this way, the rotor R has been connected in form-fitting fashion to the inner bundle IB, because the individual impellers IMP 1 , . . . , IMP 4  of the rotor R are fixedly affixed to a shaft SH of the rotor R, for example by way of a shrink fit. In order that the shaft SH can be of axially undivided form, the inner bundle IB, or the constituent parts of the inner bundle IB, are designed such that they can be broken down into lower parts and upper parts—that is to say divided in the circumferential direction at the parting joint. 
         [0045]      FIG. 3  shows a further stage of the assembly of the arrangement A. A low-pressure insert LPU has now been mounted onto the inner bundle IB in an axial direction and has been connected axially to the inner bundle IB by way of fastening elements FEL 
         [0046]    Like the individual axial subsections RS 1 , RS 2 , RS 3  of the inner bundle IB, the low-pressure insert LPU is also equipped with a central axial opening, such that the rotor R or the shaft SH of the rotor R can extend through said opening. By contrast to the components of the inner bundle IB, the low-pressure insert LPU is of undivided form in a circumferential direction. The low-pressure insert LPU has a first flow contour IGV 1  averted from the inner bundle IB and has a second flow contour IGV 2  which is situated relatively close to the inner bundle IB, wherein the first flow contour IGV 1  is fixedly connected to the second flow contour IGV 2  by way of guide vanes VA. The axial fastening by way of the first fastening elements FE 1  of the low-pressure insert LPU to the inner bundle IB is configured such that the second flow contour IGV 2  is fixedly screwed to the inner bundle IB. The first flow contour IGV 1  is in this case fastened to the second flow contour IGV 2  only by way of the guide vanes VA. The guide vanes VA are in this case advantageously formed in one piece with the two flow contours IGV 1 , IGV 2 . Said unipartite form may advantageously be realized by way of welding, or else may be the result of a manufacturing process proceeding from a solid. In the case of manufacturing from a solid, use may be made of a cutting machining process or machining by way of spark erosion. An alternative manufacturing method for the low-pressure insert LPU is provided by the relatively new method of “additive manufacturing” (for example laser sintering or selective laser melting). In the radial direction, the low-pressure insert LPU is positioned on the inner bundle IB by way of a first centering section CS 1 . Furthermore, an assembly aid is provided by way of dowel pins PB 1 , such that incorrect or wrongly positioned installation of the inner bundle IB relative to the low-pressure insert LPU in the circumferential direction is also prevented. 
         [0047]    On the side illustrated axially on the right in  FIG. 3 , opposite the side of the low-pressure insert LPU, there is also affixed to the inner bundle IB a collector COL which is centered and fastened axially on the inner bundle IB. Here, a third abutment shoulder ensures correct radial orientation of the collector COL on the inner bundle IB. 
         [0048]    Furthermore, the collector COL is secured relative to the inner bundle IB by way of fastening elements FE 3 . 
         [0049]    In order that damaging contact does not occur between the rotor R and the stator parts cover COV, inner bundle IB and collector COL, a first mounting sleeve AS 1  (see  FIGS. 4, 5 ) is affixed to the cover COV, and a second mounting sleeve AS 2  is affixed to the collector COL, which mounting sleeves secure the rotor R on said two components so as to prevent it from being offset and serve as a support for supporting the weight force and other forces. 
         [0050]      FIG. 4  shows the situation of the insertion of the arrangement A into an outer housing OC in which an insertion aid ASS also supports the insertion of the arrangement A counter to the weight force and orients the arrangement A centrally. Before the insertion as in  FIG. 4  is performed, the cover COV is mounted onto the component combination illustrated in  FIG. 3 , which component combination is arranged axially on the low-pressure insert LPU. By way of dowel elements PB 2 , the cover COV is also secured on the low-pressure insert LPU so as to be prevented from rotating in a circumferential direction, and a second centering shoulder CS 2  ensures a correct radial orientation of the cover COV on the low-pressure insert LPU. Axially, the cover is fixed to the rotor by way of the first mounting sleeve AS 1 , which rotor is held axially in position in the second mounting sleeve AS 2 . The unit TU thus formed is then mounted onto the insertion aid ASS. 
         [0051]    The two mounting sleeves AS 1 , AS 2  can be dismounted from the cover COV from the outer side and also mounted again and can be dismounted from the collector COL from the outside and also mounted again. The second mounting sleeve AS 2  is of divided form in the circumferential direction, such that the rotor R or the shaft SH of the rotor R can be fixedly clamped in the radial direction by the mounting sleeve AS 2  in a manner which is not illustrated. An axial offset of the shaft SH with respect to the mounting sleeves AS 1 , AS 2  is furthermore prevented by axial abutment of in each case one radial shoulder of the shaft SH against the respective mounting sleeve AS 1 , AS 2 . On the cover COV and on the collector COL there are provided, in each case, suspension points CON, by means of which the arrangement A including the rotor R can be suspended and moved as a transportable unit TU. Following an axial insertion of the arrangement A into the outer housing OC, the mounting sleeves AS 1 , AS 2  are removed from the arrangement A. Following the insertion into the outer housing OC, the cover COV comes to bear against a shoulder of the outer housing OC from the inside. Here, after a final position of the inner bundle is reached, the cover COV is advanced axially from the inner bundle and is pulled into its axial final position. Here, a separate seal carrier (not illustrated) can ensure that the cover COV bears sealingly against the outer housing OC. Alternatively, a seal may also be provided in the outer housing OC or in the cover COV at a suitable location—in particular so as to make abutting contact in the axial direction. 
         [0052]    In  FIG. 5 , it is illustrated that a first attachment point HP 1  is provided on the cover COV and a second attachment point HP 2  is provided on the high-pressure collector COL, and the elements cover COV, low-pressure insert LPU, inner bundle IB, high-pressure collector COL are detachably fastened to one another such that the elements can be transported in suspended fashion, without being offset relative to one another, at the attachment points HP 1 , HP 2  without further support. For this purpose, said transportable unit TU is suspended by the attachment points HP 1 , HP 2  on a traverse LF which permits suspension without lateral forces. 
         [0053]    The transportable unit TU or the arrangement A has at least one roller W 1 , advantageously a roller pair, by means of which the arrangement A is displaceable on the insertion aid ASS and in the interior of the outer housing OC with low friction such that the arrangement A can be moved into the final mounting position in the outer housing OC. A second roller W 2  is provided on a mounting bracket ASS 2  which is affixed axially to the collector COL and which permits additional orientation in the radial direction of the arrangement A on the insertion aid ASS and in the outer housing OC before the final position is reached.