Method of manufacturing a measuring tube of a fluid measuring means

Abstract

In a method for producing a measuring tube (10) of a fluid measuring means, a tubular semi-finished product (14) having a through-opening (32) extending in a longitudinal direction (L) of the semi-finished product (14) is provided, a peripheral wall (22) of the semi-finished product (14) having at least one waveguide region (34), which, after the measuring tube (10) is finished, forms a waveguide (24) for the surface acoustic waves of an acoustic measuring means. The semi-finished product (14) is inserted into a shaping tool (43), and at least one core (36) is introduced into the through-opening (32). In a shaping step, at least one axial central section (30) of the semi-finished product (14) is plastically deformed, the through-opening (32) being transformed into a fluid channel (16). The core (36) is finally removed. Fig. 2

Description

Title of the invention: Method for manufacturing a measuring tube of a fluid measuring means

[0001] The invention relates to a method of manufacturing a measuring tube of a fluid measuring means having at least one waveguide zone.

[0002] Fluid measuring means are known which use surface acoustic waves (SAW) to determine the properties of a fluid flowing through a fluid channel. The surface acoustic waves are then excited in an acoustic waveguide by means of an acoustic signal converter and are partly decoupled into the fluid in the form of volume sound waves and then coupled back into the waveguide from the latter. The interference between the surface acoustic waves and the recoupled volume sound waves provides a characteristic signal which is evaluated. The time course and the intensity of the characteristic signal, in particular the time course of the intensity including the time delay, allow, for example, conclusions to be drawn, inter alia, about the sound speed, temperature, homogeneity, flow rate, flow rate, concentration or viscosity.

[0003] The measuring tube used in such fluid measuring means has a continuous fluid channel, the surface acoustic waves to be coupled or decoupled passing in a waveguide in a wall of the measuring tube.

[0004] The objective of the invention is to present a method for manufacturing such a measuring tube in a simple and economical manner, but nevertheless with high precision.

[0005] This objective is achieved by a method of manufacturing a measuring tube of a fluid measuring means, comprising the following steps:

[0006] Method of manufacturing a measuring tube of a fluid measuring means, comprising the following steps:

[0007] - the provision of a tubular semi-finished product having a passage opening extending in a longitudinal direction of the semi-finished product, a peripheral wall of the semi-finished product having at least one waveguide area, which, once the measuring tube is finished, forms a waveguide for the surface acoustic waves of an acoustic measuring means, the waveguide area extending in a longitudinal direction of the semi-finished product and from an outer surface to an inner surface of the semi-finished product,

[0008] - inserting the semi-finished product into a shaping tool by deformation plastic,

[0009] - the introduction of at least one core into the passage opening, a geometry exterior of the core corresponding to an interior geometry of a fluid channel of the measuring tube to be formed from the passage opening,

[0010] - carrying out a shaping step during which a force of pressing is applied to at least one axial middle section of the semi-finished product and at least the middle section is plastically deformed, the passage opening being transformed into a fluid channel, and

[0011] - removal of the core.

[0012] The outer geometry of the core is transmitted to the inner surface of the passage opening during the shaping step, whereby the fluid channel obtains its desired cross-section. In this way, it is possible, with a few simple and quick-to-perform process steps, to manufacture a precise inner geometry of the fluid channel in an easily reproducible manner.

[0013] The excitation, measurement, coupling and decoupling of the surface acoustic waves are most often carried out in a targeted manner at the waveguides formed on the measuring tube. The waveguides are normally an integral part of the measuring tube, but may, however, be geometrically distinct from the rest of the fluid channel wall in the finished measuring tube. The waveguides have, in particular, a planar outer geometry, so that the measuring tube has a flat surface in the surface of the waveguides. The waveguides are most often produced as rectangles, the long sides of which are oriented parallel to the longitudinal direction of the fluid channel.

[0014] In the shaping step, the waveguides are preferably also manufactured from the waveguide regions or are finally completed. The waveguide regions are preferably entirely arranged in the middle section.

[0015] The core is preferably moved rectilinearly and without rotation, which further simplifies the method. The insertion of the core into the middle section is usually carried out without deformation of the inner surface of the passage opening.

[0016] In the shaping step, a radial pressing force which is for example produced by means of a plurality of radially displaceable shaping punches advantageously acts on the semi-finished product. The shaping step can be carried out in a cold forming process or a hot forming process.

[0017] A small number of variants of the semi-finished product has proven sufficient to produce a large quantity of measuring tube variants. For example, it is possible to provide two semi-finished product variants with different outer and / or inner diameters.

[0018] Once the measuring tube is finished, it can be used in a fluid measuring means. For this purpose, one or more signal converters which generate or detect the surface acoustic waves are respectively arranged on one or more waveguides.

[0019] Before the shaping step, the semi-finished product may have an external geometry different from the cylindrical shape, which defines the waveguide regions as well as damping elements and / or reflection elements for surface acoustic waves, this external geometry being at least partially retained during the shaping step. This includes, for example, chamfers and / or modified material thicknesses at the longitudinal ends of the future waveguides. This makes it possible, for example, to machine the measuring tube by chip removal before the shaping step in order to prefabricate the desired components which are to be provided later on the measuring tube.

[0020] In this case, said at least one waveguide zone may already be predefined on the semi-finished product. The semi-finished product must then be appropriately angularly oriented when inserting the semi-finished product into the shaping tool.

[0021] Additionally and / or alternatively, damping elements and / or reflection elements can in particular also be produced during the shaping step by the geometry of the shaping punch and / or the core or by further processing of the outer surface after the shaping step.

[0022] The semi-finished product may have regions with different wall thicknesses in the central section and / or in axially adjacent sections, these different wall thicknesses being retained at least partially during the shaping step. Alternatively or additionally, such regions may also be produced during the shaping step. Changes in the thickness of the peripheral wall of the measuring tube depending on the angular orientation and / or in the axial direction may, for example, be used in a targeted manner to limit surface acoustic waves on the waveguides. Such components can also be easily integrated into the measuring tube in this way.

[0023] In order to obtain a flat waveguide having a constant wall thickness over the dimension of the waveguide, an outer geometry of the middle section in said at least one zone of the waveguide can be transformed from a rounded surface in the peripheral direction into a flat surface in the peripheral direction. Thus, the waveguide can be produced as a flat rectangular surface on the outer surface of the measuring tube, although the semi-finished product is manufactured from a tube with a circular cross-section, which reduces manufacturing costs.

[0024] The long sides of the rectangular surface of the waveguide are preferably oriented in the longitudinal direction. The use of the core, which is inserted into the middle section, also allows the production of such a rectangular surface during the shaping step on the inner surface of the fluid channel.

[0025] By means of the appropriate geometry of the core and the shaping punch, it is generally possible to manufacture a fluid channel with a polygonal cross-section from a semi-finished product with a circular cross-section.

[0026] For example, to compensate for an elastic part of the deformation, i.e. a degree of elastic return of the wall of the measuring tube after the shaping punches have withdrawn, it is possible to press the shaping punches against the measuring tube again with an appropriate force in order to obtain the desired plastic deformation as the end result. For repeated shaping steps, it is also possible to use cores having a different outer geometry or a different cross-sectional size.

[0027] Optionally, after removal of said at least one core, the same core or another core may again be moved through the passage opening in order to improve the precision of the shaping of the internal geometry of the fluid channel.

[0028] It is then, for example, possible to use a core having a slightly larger cross-section than the core that was inserted into the measuring tube during the shaping step. In this case, the inner face of the measuring tube can be smoothed and / or widened in a targeted and precise manner by the passage of the core. It is thus possible to achieve precise calibration of the fluid channel with precisely predefined dimensions.

[0029] As a rule, further machining by chip removal of the fluid channel after the shaping step can be omitted.

[0030] It is however possible, if necessary, to further smooth the inner surface of the fluid channel by passing suitable abrasive liquids through it.

[0031] Two cores which are moved from the axial ends of the semi-finished product into the passage opening before the shaping step and out of it after the shaping step are for example simultaneously used in at least one of the process steps. The two cores should touch each other in the middle section so that if possible, no visible transition is produced in order to create a smooth inner surface in the fluid channel.

[0032] In this way, it is for example possible to create a narrowing of the measuring tube from the axial ends towards the middle section, the fluid channel obtaining in the middle section a smaller cross-section than that of the fluid connections. For this purpose, each core has a smaller cross-section smaller in an area arranged in the middle section than in an axially adjacent area.

[0033] Preferably, a transition zone is respectively produced from an axial end of the semi-finished product to the middle section, in which an inner cross-section and / or an inner geometry of the axial end and the middle section merge continuously. The inner cross-section and / or the inner geometry can be easily defined by the outer geometry, i.e. the shape of the outer peripheral surface of the core. The outer geometry of the core then differs, in a zone arranged in the middle section, from an outer geometry in an axially adjacent zone. The fact that the shape of the transition zone is imposed by the core makes it possible to generate a high quality of these transition zones, which results in a stable flow profile in the fluid channel.

[0034] The inner cross-section may in particular be polygonal in shape in the middle section, and the axially outer cross-section may be circular in shape at the fluid connection.

[0035] In another variant, exactly one core is used, which is introduced into the passage opening and around which the semi-finished product is deformed. The core is then withdrawn to one side out of the passage opening.

[0036] It is then possible to pass this core one or more times through the passage opening in order to calibrate the internal geometry of the fluid channel during a calibration step, i.e. to adapt it more precisely to predefined dimensions.

[0037] During such a calibration step, it is possible to successively pass several cores whose external contours are adapted to each other through the fluid channel in order to obtain a precise geometry of the internal face of the fluid channel.

[0038] It would also be conceivable to carry out one or more steps of the method with two cores introduced in reverse order and one or more other steps of the method with a single core. A calibration step for the fluid channel could for example be carried out with a single core.

[0039] The shape of the cross-section of the fluid connections and the fluid channel can be chosen at the discretion of a person skilled in the art. For example, it is possible to use an equilateral polygon, for example having 3 to 8 sides, for the fluid channel. However, the polygon can also be a rectangle. Shapes having both rounded sides and flat sides are also conceivable.

[0040] In order to optimize the shaping, the geometry of the semi-finished product and the shaping tool can be chosen so that a pressing force is exerted only in sections along the periphery of the measuring tube during the step of shaping. Thus, an outer periphery of the middle section remains approximately identical in sections before and after the shaping step. The corners of a polygon may, for example, be located on the outer periphery of the semi-finished product before shaping. Such sections are preferably located outside the waveguide areas.

[0041] It is possible to keep the axial end sections of the semi-finished product undeformed during the shaping step.

[0042] The invention is described in more detail below using several exemplary embodiments with reference to the appended figures, in which:

[0043] - [Fig.l] shows a measuring tube of a fluid measuring means manufactured in accordance with a method according to the invention in a partially cutaway schematic view;

[0044] - [Fig.2] and [Fig.3] show steps of a method according to the invention for the manufacturing a measuring tube according to a first variant;

[0045] - [Fig.4] and [Fig.5] show other steps of the method according to the invention for the manufacturing a measuring tube in a shaping tool;

[0046] - [Fig.6] shows a measuring tube manufactured by the method according to the invention;

[0047] - [Fig.7], [Fig.8] and [Fig.9] show steps of a method according to the invention for the manufacture of a measuring tube of a fluid measuring means according to a second variant;

[0048] - [Fig.10], [Fig.11] and [Fig.12] show measuring tubes of different geometries manufactured by a method according to the invention;

[0049] - [Fig. 13] shows different internal cross-sectional shapes of a channel of fluid from a measuring tube manufactured according to the method of the invention;

[0050] - [Fig. 14] shows a measuring tube with a transition zone between a section median and an axially adjacent area, manufactured in accordance with the method according to the invention;

[0051] - [Fig. 15] is a view, on an enlarged scale, of a detail surrounded by a circle on the [Fig.14] ;

[0052] - [Fig. 16] shows a partially cutaway schematic view of a measuring tube with different wall thicknesses, manufactured in accordance with the method according to the invention; and

[0053] - [Fig.17] shows a method according to the invention for the manufacture of a tube of measurement in a shaping tool according to a second variant.

[0054] [Fig.l] shows a measuring tube 10 of a flow measuring means not shown in detail, which operates according to the principle of surface acoustic wave (SAW) measurement.

[0055] The measuring tube 10 is manufactured from a tubular semi-finished product 14 (see Figures 2 and 7).

[0056] The measuring tube 10 has a continuous fluid channel 16 which extends between two fluid connections 18 on opposite sides of the measuring tube 10. During measurement, a suitable fluid to be measured flows through the fluid channel 16.

[0057] A connection structure 20, here in the form of two radially projecting flanges, by means of which the measuring tube 10 can be connected to a fluid system, is produced on each of the fluid connections 18.

[0058] One or more waveguides 24 are produced in a peripheral wall 22 of the measuring tube 10. The waveguides 24 are here the areas of the measuring tube 10 on which transmitters and receivers (not shown) for surface acoustic waves are arranged and on which the decoupling and coupling of the surface acoustic waves relevant for the measurement also takes place.

[0059] If there are several waveguides 24, these are distributed along the peripheral direction U, but are for example arranged axially at the same position. The waveguides 24 are made in one piece with the peripheral wall 22 and extend continuously from an outer surface 26 to an inner surface 28 of the measuring tube 10. The waveguides 24 are located in an axial middle section 30 of the measuring tube 10 between the two fluid connections 18. All the waveguides 24 extend along a longitudinal direction L of the measuring tube 10, along which the fluid channel 16 also extends. Each of the waveguides 24 is here flat and rectangular, the long sides of the rectangle extending along the longitudinal direction L.

[0060] In the fluid measuring means, the waveguide 24 is part of an acoustic measuring device, surface acoustic waves being coupled into and decoupled from the waveguide 24.

[0061] In total, at least two signal generators are arranged on the waveguides 24, which can excite surface acoustic waves in the waveguide 24 or receive them from it (not shown).

[0062] The waveguides 24 form a boundary with respect to the fluid flowing through the fluid channel 16, a portion of the surface acoustic waves passing through the waveguide 24 being decoupled into the fluid, passing through it and recoupling at another location in the same or another waveguide 24 and being received by one or more of the signal generators.

[0063] Figures 2 to 6 show the manufacture of the measuring tube 10 from the tubular semi-finished product 14 using a first example.

[0064] First, the tubular semi-finished product 14 (see [Fig.2]), initially of circular cylindrical shape, is optionally machined in a suitable manner, so that, while retaining a circular cylindrical section at the end sections 31 of the semi-finished product 14, the connection structures 20 are produced at the fluid connections 18 (see [Fig. 3]). These connection structures 20 can be produced for example by milling, turning and / or turning.

[0065] The semi-finished product 14 has a passage opening 32 which, once completed, forms the fluid channel 16 of the measuring tube 10.

[0066] In this example, the semi-finished product 14 has a relatively large wall thickness Si, so that material can be removed from the outer surface 26 for the manufacture of the flanges.

[0067] The middle section 30 remains unmachined here, but can optionally be provided from this step with appropriate structures 42 (see for example figures 14 to 16), in which the inclination of the outer surface 26 or the wall thickness of the semi-finished product 14 is for example modified. Such structures 42 form in particular damping elements and / or reflection elements for surface acoustic waves in order to concentrate them at the level of the future waveguides 24.

[0068] The semi-finished product 14 is arranged in a shaping tool 43, if necessary after the preliminary machining operations described (see [Fig.4]).

[0069] One or more waveguide areas 34 which will form the waveguides 24 in the finished measuring tube 10 are predefined on the outer surface 26 of the semi-finished product 14, which will later form the outer surface 26 of the measuring tube 10.

[0070] In a variant, the waveguide zones 34 are physically defined on the semi-finished product 14, for example by machining steps already carried out beforehand, during which the outer surface 26 has been machined, in particular by chip removal, and structures 42 have for example been formed. In this case, the semi-finished product 14 is placed in the shaping tool 43 so as to orient the waveguide zones 34 correctly in the peripheral direction U.

[0071] In another variant, the waveguide areas 34 are obtained by producing the waveguides 24 at these locations of the peripheral wall 22 during the following shaping step. If, as shown in [Fig. 2], the semi-finished product 14 does not yet exhibit any deviation from a circular cylindrical shape, it is not necessary to carry out targeted alignment.

[0072] The shaping tool 43 comprises two opposite cores 36 which can be moved in a straight line in the longitudinal direction L and whose external geometry 38, in a variant, corresponds exactly in diameter and shape to the desired internal geometry of the fluid channel 16.

[0073] The dimensions of the cores 36 are chosen so that they can be inserted into the passage opening 32 in the longitudinal direction L without deformation of the semi-finished product 14. This is illustrated in [Fig.4].

[0074] The two cores 36 are inserted into the passage opening 32 until they are in contact without transition in the middle of the middle section 30.

[0075] The ends of the cores 36 oriented towards the center of the semi-finished product 14 are here constricted in cross-section relative to the axially adjacent sections which are positioned at the fluidic joints 18 (see Figures 4 and 5). In addition, these constricted ends here have a cross-sectional shape different from that of the axially adjacent zones. In a transition zone, the cross-sectional shapes merge continuously and progressively.

[0076] The shaping tool 43 comprises a plurality of shaping punches 40 that can be moved radially relative to the longitudinal direction L. The semi-finished product 14 is housed in the shaping tool 43 in such a way that the shaping punches 40 act only on the middle section 30. This is illustrated in [Fig. 5]. During a shaping step in which a pressing force F is applied to the axial middle section 30 of the semi-finished product 14, the middle section 30 is plastically deformed. The shaping punches 40 are then moved radially, so that the peripheral wall 22 of the middle section 30 is pushed against the cores 36 and thus undergoes plastic deformation. This shaping step can be carried out as a hot forming step or as a cold forming step.

[0077] The passage opening 32 is thus deformed so as to form the fluid channel 16.

[0078] The geometry of the middle section 30 is defined on the outer surface 26 by the contour of the shaping punches 40 and on the inner surface 28 of the passage opening 32 by the outer geometry 38 of the cores 36. The fluid channel 16 thus produced then obtains as inner geometry the outer geometry 38 of the cores 36.

[0079] Depending on an elastic component of the deformation, the shaping tool 43 is for example closed one or more times in order to create the desired internal geometry of the fluid channel 16.

[0080] In another variant, the external geometry 38 of the core 36 is chosen to be slightly smaller than the desired cross-section of the fluid channel 16, in order to take into account an elastic return of the material of the measuring tube 10 after the shaping step.

[0081] In another variant, several shaping steps with several cores 36 having different external geometries are successively carried out, until the fluid channel 16 is completed with the desired dimensions.

[0082] During this shaping step or steps, the waveguide areas 34 are also formed into final waveguides 24. The axial area in which the waveguides 24 extend forms a measuring area 44 in the finished measuring tube 10.

[0083] A narrowing 46 in which the cross-section of the fluid channel 16 is narrowed relative to the cross-section at the fluid connections 18 is also provided here in the axial section of the measuring tube 10 in which the waveguides 24 are arranged ([Fig.6]).

[0084] Between the connection structures 20 and the waveguides 24 there extends axially a transition zone 48 in which the cross-section widens continuously and progressively from the measurement zone 44 to the fluid connections 18 (see for example FIGS. 1 and 5).

[0085] After the shaping step, the cores 36 are removed from the passage opening 32 in the longitudinal direction L, and the shaping tool 43 is opened so that the now finished measuring tube 10 can be removed.

[0086] The axial end sections 31 at the fluid connections 18 and the connection structures 20 remain undeformed here.

[0087] The structures 42 already formed on the semi-finished product 14 before the shaping step, for example damping elements and / or reflection elements for surface acoustic waves, including different wall thicknesses of the peripheral wall 22, are also retained, at least in large part, during the shaping of the semi-finished product 14.

[0088] Before removing the measuring tube 10 from the shaping tool 43, the cores 36 are, if necessary, again pushed into the passage opening 32, which is now formed as the fluid channel 16, and then removed in order to smooth the inner surface 28 of the fluid channel 16. It is also conceivable to use other cores 36 for this step, the shape of which is identical to that of the cores 36 used for shaping, but which allow, for example, the inner surface 28 of the fluid channel 16 to be specified during a calibration step.

[0089] Optionally, another recycling step can be carried out, for example to produce additional elements on the outer surface 26 of the measuring tube 10. The inner surface 28 of the fluid channel 16 is not recycled here.

[0090] However, for example, it would also be conceivable to further smooth the inner surface 28 with abrasive liquids.

[0091] In the illustrated example, the waveguides 34 rounded in the peripheral U direction are transformed into flat and rectangular waveguides 24 (see for example FIGS. 1 and 6).

[0092] In the measuring zone 44, the circular shape of the cross-section of the passage opening 32 is transformed into an approximately square cross-sectional shape of the fluid channel 16, which has four flat surfaces adjacent at right angles as well as rounded corners (see for example [Fig.6]). Here, a waveguide 24 is formed on each side of the square cross-section.

[0093] In the transition zones 48, not only does the diameter of the fluid channel 16 change, but also the shape of its cross-section, which changes from polygonal to circular.

[0094] It would also be possible to use only one core 36 for fluid channels 16 whose internal geometry is not narrowed compared to the fluid connections 18, this core then being inserted into the passage opening 32 over the entire middle section 30 (see [Fig. 17]). The cross-section of the core 36 is at no point larger than the narrowest section of the transformed fluid channel 16, so that the core 36 can be fully inserted into the middle section 30 and removed therefrom after shaping. The figure shows the step in which the core 36 is removed from the fluid channel 16 after deformation.

[0095] In this case too, several cores 36 with slightly different outer geometries are optionally used, as described above, to compensate for an elastic deformation of the measuring tube 10. A core 36 whose outer geometry exactly corresponds to the cross-section of the fluid channel 16 is optionally moved at the end one or more times through the passage opening 32, in order to complete the fluid channel 16 with exactly the desired cross-section.

[0096] [Fig. 13] shows several possibilities for a cross-sectional area 50 of the fluid channel 16 in the measuring area 44, for example in the form of a polygon with 3 to 8 faces, the polygon being able to be regular or irregular, or a hybrid shape with rounded and flat faces. A generally oval or circular cross-sectional shape is of course also conceivable.

[0097] Figures 7 to 9 show, using a second example, the shaping of the semi-finished product 14.

[0098] Unlike the first example which has just been described, the semi-finished product 14 here has a wall thickness s2 less than the wall thickness sb.

[0099] As described above, before insertion into the shaping tool 43, the axial ends 31 forming the fluid connections 18 are machined so as to obtain suitable connection structures 20 (see [Fig.8]).

[0100] The semi-finished product 14 is then placed in the shaping tool 43 and plastically deformed by the shaping punches 40 and the inserted cores 36. [Fig.9] shows the result of the shaping step.

[0101] In this example, the measuring area 44 obtains, as in the first example, a square cross-sectional shape with a fluid channel 16 of square cross-section. However, as described above, other cross-sectional shapes could also be realized.

[0102] Unlike the first example, the shaping tool 43 is designed such that a pressing force is exerted only in sections along the periphery. In this example, these are the future flat side surfaces. No direct force is exerted on the intermediate areas, here the respective corners of the square cross-section. In these areas, the diameter d of the finished measuring tube 10 corresponds approximately to the diameter d of the semi-finished product 14 (indicated in FIGS. 7 and 9), and the initial outer surface 26 and the initial outer periphery of the semi-finished product 14 are at least partially preserved. The previously machined connecting structures 20 are not deformed during the shaping step, or only insignificantly. The same applies to any structures 42 that may be present, exactly as in the first example described above.

[0103] Figures 10 to 12 show other examples of possible embodiments of the finished measuring tube 10.

[0104] In [Fig. 10], the measuring area 44 is transformed into a rectangular cross-section. In the peripheral direction U, the sides of the cross-section are therefore of unequal length. Waveguides 24 are here, for example, produced only on the two longest sides.

[0105] Here, the connecting structures 20 are furthermore not produced in the form of flanges, but in the form of threads. As described above for the flanges, the threads can also be prefabricated before the shaping step and are not deformed during the shaping step.

[0106] [Fig. 11] shows a measuring tube 10 combining a square cross-section of the fluid channel with another type of flange at the fluid connections 18.

[0107] [Fig. 12] finally shows a measuring tube 10 having a circular cross-section of the fluid channel 16 in the measuring zone 44 and flanges at the fluid connections 18.

[0108] Other configurations and combinations of the elements shown are of course possible at the discretion of those skilled in the art. From a few variants of the semi-finished product 14 in terms of diameter d and wall thickness sb s2, it is possible to manufacture a large number of variants of measuring tubes 10 by varying the shaping punches 40 and the cores 36.

[0109] Figures 14 to 16 show the structures 42 already mentioned above in more detail.

[0110] In the transition zone 48, a damping and / or reflection element ending in a point towards the measuring zone 44 is here formed for each of the waveguides 24 on the measuring tube 10, in which the curvature of the fluid connection 18, circular in the peripheral direction U, merges continuously into the flat surface of the waveguide 24.

[0111] Furthermore, in the transition zone 48 and in the structures 42, the cross-section of the measuring tube 10 reduces from the cross-section of the fluid connection 18 to the cross-section of the fluid channel 16.

[0112] Such structures 42 may be prefabricated on the semi-finished product 14 before the shaping step, be produced by the shaping punches 40 and the cores 36 during the shaping step or be made by combining the two methods.

[0113] [Fig. 16] shows that in this example, the wall thickness of the measuring tube 10 also varies from the waveguide 24 in the measuring zone 44 to the fluid connection 18 and increases in this example from a wall thickness ti to a wall thickness t2 and then to a wall thickness t3.

[0114] Furthermore, it is shown by way of example that in different peripheral areas of the measuring area 44, the wall thickness can also vary, for example for different waveguides 24 or inside the waveguides 24 and outside the waveguides 24 (indicated here by t1 and t4).

[0115] These different wall thicknesses are for example produced during the step of shaping the semi-finished product 14.

[0116] All features of the different embodiments and variants may be freely exchanged or combined with each other according to the judgment of the person skilled in the art.

[0117] For reasons of clarity, identical components are not always all designated by reference numbers.

Claims

Claims

1. A method of manufacturing a measuring tube (10) of a fluid measuring means, comprising the following steps: - providing a tubular semi-finished product (14) having a through-opening (32) extending in a longitudinal direction (L) of the semi-finished product (14), a peripheral wall (22) of the semi-finished product (14) having at least one waveguide zone (34), which, once the measuring tube (10) is finished, forms a waveguide (24) for surface acoustic waves of an acoustic measuring means, the waveguide zone (34) extending in a longitudinal direction (L) of the semi-finished product (14) and from an outer surface (26) to an inner surface (28) of the semi-finished product (14), - inserting the semi-finished product (14) into a shaping tool (43), - introducing of at least one core (36) in the passage opening (32),an outer geometry (38) of the core (36) corresponding to an inner geometry of a fluid channel (16) of the measuring tube to be formed from the passage opening (32), - carrying out a shaping step during which a pressing force (F) is applied to at least one axial middle section (30) of the semi-finished product (14) and at least the middle section (30) is plastically deformed, the passage opening (32) being transformed into a fluid channel (16), and - removing the at least one core (36).,

2. Method according to claim 1, wherein the semi-finished product (14) has, before the shaping step, an external geometry different from the cylindrical shape, which defines waveguides (24), damping elements and / or reflection elements for surface acoustic waves, this external geometry being at least partially preserved during the shaping step.

3. Method according to one of the preceding claims, in which the semi-finished product (14) has, in the middle section (30) and / or in axially adjacent sections, zones having different wall thicknesses (tb t2, t3, t4), and these different wall thicknesses (tb t2, t3, t4) are at least partially preserved during the shaping step.

4. Method according to one of the preceding claims, wherein an outer geometry of the middle section (30) in said at least one waveguide zone (34) is deformed from a rounded surface in the peripheral direction (U) to a flat surface in the peripheral direction (U).

5. Method according to one of the preceding claims, wherein after removal of said at least one core (36), the same core (36) or another core (36) is again moved through the passage opening (32).

6. A method according to one of the preceding claims, wherein two cores (36) are used simultaneously, which are moved into and out of the passage opening (32) from axial ends of the semi-finished product (14).

7. A method according to claim 6, wherein each core (36) has a smaller cross-sectional area (50) at an area arranged in the middle section (30) than at an axially adjacent area.

8. Method according to claim 7, wherein, during the shaping step, a transition zone (48) is respectively produced from an axial end of the semi-finished product (14) to the middle section (30), in which an inner cross-section and / or an inner geometry of the axial end and the middle section (30) merge continuously.

9. Method according to one of claims 1 to 5, wherein exactly one core (36) is introduced into the passage opening (32).

10. Method according to one of the preceding claims, wherein during the shaping step, a pressing force (F) is exerted only in sections along the periphery (U) of the measuring tube (19).

11. Method according to one of the preceding claims, in which axial end sections (31) of the semi-finished product (14) remain undeformed during the shaping step.

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