Method for manufacturing a measuring tube for a fluid measuring device

Abstract

In a method for manufacturing a measuring tube (10) of a fluid measuring device, a tubular semi-finished product (14) having a passage 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) has at least one waveguide area (34) which, once the measuring tube (10) is completed, forms a waveguide (24) for the surface acoustic waves of an acoustic measuring device. The semi-finished product (14) is inserted into a forming tool (43), and at least one core (36) is introduced into the passage opening (32). During a forming step, at least one axial mid-section (30) of the semi-finished product (14) is plastically deformed, the passage 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 for a fluid measuring device

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

[0002] It is known that there are methods for measuring fluids which use surface acoustic waves (SAWs) to determine the properties of a fluid flowing through a fluid channel. The surface acoustic waves are excited in an acoustic waveguide by means of an acoustic signal converter and are partially decoupled in the fluid as body waves, then recoupled in the waveguide from the latter. The interference between the surface acoustic wave and the recoupled body wave provides a characteristic signal which is evaluated. The time evolution and intensity of the characteristic signal, in particular the time evolution of the intensity, including the time delay, allow, for example, inferences to be drawn about, among other things, the speed of sound, temperature, homogeneity, flow velocity, flow rate, concentration, or viscosity.

[0003] The measuring tube used in such fluid measurement means has a continuous fluid channel, the surface acoustic waves to be coupled or decoupled passing through 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 way, but nevertheless with high precision.

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

[0006] Method for manufacturing a measuring tube for a fluid measuring device, comprising the following steps:

[0007] - the supply 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 zone, which, once the measuring tube is completed, forms a waveguide for the surface acoustic waves of an acoustic measuring means, the waveguide zone 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] - the insertion of the semi-finished product into a forming tool by deformation plastic,

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

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

[0011] - the removal of the core.

[0012] The external geometry of the core is transferred to the internal surface of the passage opening during the shaping step, thereby giving the fluid channel its desired cross-section. In this way, it is possible, with a few simple and quick process steps, to easily and reproducibly manufacture a precise internal geometry of the fluid channel.

[0013] The excitation, measurement, coupling, and decoupling of 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 nevertheless be geometrically distinct from the rest of the fluid channel wall in the finished measuring tube. In particular, the waveguides have a planar external geometry, so that the measuring tube presents a flat surface within the surface of the waveguides. The waveguides are most often made in the form of rectangles whose longer sides are oriented parallel to the longitudinal direction of the fluid channel.

[0014] During the shaping stage, the waveguides are preferably also fabricated from the waveguide zones or are definitively finished. The waveguide zones are preferably fully arranged in the middle section.

[0015] The core is preferably moved in a straight line and without rotation, which further simplifies the process. Insertion of the core into the middle section is usually carried out without deformation of the inner surface of the passage opening.

[0016] During the shaping step, a radial pressing force, for example produced by means of a plurality of radially movable shaping punches, advantageously acts on the semi-finished product. The shaping step can be carried out during 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 number of variants of measuring tubes. For example, it is possible to supply two variants of semi-finished products with different outside and / or inside diameters.

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

[0019] Before the forming step, the semi-finished product may have an external geometry different from the cylindrical shape, which defines the waveguide areas as well as damping elements and / or reflecting elements for surface acoustic waves, this external geometry being at least partially retained during the forming step. This includes, for example, chamfers and / or modified material thicknesses at the longitudinal ends of the future waveguides. This allows, for example, machining the measuring tube by chip removal before the forming step in order to prefabricate the desired components that are to be subsequently incorporated into 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 oriented angularly in an appropriate manner when the semi-finished product is inserted into the forming tooling.

[0021] In addition and / or as an alternative, damping elements and / or reflective elements can in particular also be produced during the forming step by the geometry of the forming punch and / or the core or by a subsequent treatment of the outer surface after the forming step.

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

[0023] To obtain a flat waveguide with a constant wall thickness over the waveguide dimension, the external geometry of the midsection in at least one area of ​​the waveguide can be transformed from a peripherally rounded surface to a peripherally flat surface. Thus, the waveguide can be made in the form of a flat rectangular surface on the external surface of the measuring tube, even though the semi-finished product is made from a tube with a circular cross-section, thereby reducing 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 in the middle section, also allows such a rectangular surface to be achieved during the shaping step on the inner surface of the fluid channel.

[0025] Thanks to 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 component of the deformation, i.e., a degree of elastic return of the measuring tube wall after the forming punches have retracted, it is possible to press the forming punches against the measuring tube again with an appropriate force to obtain the desired plastic deformation as the final result. For repeated forming steps, it is also possible to use cores with a different external geometry or a different cross-sectional size.

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

[0028] It is then possible, for example, to use a core with 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 enlarged in a targeted and precise manner by the passage of the core. It is thus possible to obtain precise calibration of the fluid channel with accurately predefined dimensions.

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

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

[0031] Two cores that 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, used simultaneously in at least one of the process steps. The two cores must touch 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 possible, for example, 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 fittings. For this purpose, each core has a smaller cross-section small in an area arranged in the median segment than in an axially adjacent area.

[0033] Preferably, a transition zone is formed from an axial end of the semi-finished product to the mid-section, in which an internal cross-section and / or internal geometry of the axial end and the mid-section merge continuously. The internal cross-section and / or internal geometry can be easily defined by the external geometry, i.e., the shape of the outer peripheral surface of the core. The external geometry of the core then differs, in a zone arranged in the mid-section, from an external 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, resulting in a stable flow profile in the fluid channel.

[0034] The inner cross-section can in particular be polygonal in the middle section, and the axially more outer cross-section can be circular at the fluidic connection.

[0035] In another embodiment, 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, that is to say to adapt it more precisely to predefined dimensions.

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

[0038] It would also be possible to carry out one or more steps of the process with two nuclei introduced in opposite directions and one or more other steps of the process with a single nucleus. A calibration step for the fluid channel could, for example, be carried out with a single nucleus.

[0039] The shape of the cross-section of the fluid fittings and the fluid channel can be chosen according to the judgment of those skilled in the art. For example, an equilateral polygon, with, say, 3 to 8 sides, can be used for the fluid channel. The polygon can, however, also be a rectangle. Shapes with both rounded and flat sides are also possible.

[0040] In order to optimize the shaping process, the geometry of the semi-finished product and the shaping tooling 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, the outer periphery of the mid-section remains approximately identical in segments before and after the shaping step. The corners of a polygon, for example, may be located on the outer periphery of the semi-finished product before shaping. Such segments 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 with the aid of several embodiments with reference to the accompanying figures, in which:

[0043] - Figure 1 shows a measuring tube of a fluid measuring means manufactured in accordance with a method according to the invention in a partially cut schematic view;

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

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

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

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

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

[0049] - Figure 13 shows different shapes of internal cross-section of a channel of fluid from a measuring tube manufactured according to the process of the invention;

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

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

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

[0053] - Figure 17 shows a method according to the invention for manufacturing a tube of measurement in a shaping tooling according to a second variant.

[0054] Fig. 1 shows a measuring tube 10 of a flow measurement 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 fittings 18 on opposite sides of the measuring tube 10. During the 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 made on each of the fluidic fittings 18.

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

[0059] If there are several waveguides 24, these are distributed along the peripheral direction U, but are, for example, arranged axially in the same position. The waveguides 24 are made as a single unit 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 a central axial 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 flat and rectangular, with the longer sides of the rectangle extending along the longitudinal direction L.

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

[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 in the fluid, passing through it and recoupling at another place in the same waveguide 24 or in 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 semi-finished tubular product 14 (see [Fig. 2]), initially of circular cylindrical shape, is optionally machined appropriately so that, while maintaining a circular cylindrical cross-section at the end sections 31 of the Semi-finished product 14, the connection structures 20 are made at the level of the fluid connections 18 (see [Fig.3]). These connection structures 20 can be made, for example, by milling, turning and / or machining.

[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 removal can take place on the outer surface 26 for the manufacture of the flanges.

[0067] The central section 30 remains unmachined here, but can optionally be provided at this stage with suitable 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 modified, for example. Such structures 42 form, in particular, damping elements and / or reflecting 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, where appropriate after the preliminary machining operations described (see [Fig.4]).

[0069] One or more waveguide zones 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 one embodiment, 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 forming tooling 43 so as to orient the waveguide zones 34 correctly in the peripheral direction U.

[0071] In another embodiment, the waveguide zones 34 are obtained by forming the waveguides 24 at these locations on the peripheral wall 22 during the subsequent forming step. If, as shown in [Fig. 2], the semi-finished product 14 does not yet deviate from a circular cylindrical shape, targeted alignment is not necessary.

[0072] The shaping tooling 43 comprises two opposing cores 36 which can be moved in a straight line along the longitudinal direction L and whose external geometry 38, in one 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 medial section 30.

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

[0076] The forming tooling 43 comprises a plurality of forming punches 40 that can be moved radially with respect to the longitudinal direction L. The semi-finished product 14 is housed in the forming tooling 43 such that the forming punches 40 act only on the midsection 30. This is illustrated in [Fig. 5]. During a forming step in which a pressing force F is applied to the axial midsection 30 of the semi-finished product 14, the midsection 30 is plastically deformed. The forming punches 40 are then moved radially, so that the peripheral wall 22 of the midsection 30 is pushed against the cores 36 and thus undergoes plastic deformation. This forming 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 median 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 formed then obtains as its inner geometry the outer geometry 38 of the cores 36.

[0079] Depending on an elastic component of the deformation, the shaping tooling 43 is for example closed once or several 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 slightly smaller than the desired cross-section of the fluid channel 16, in order to take account of 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 zones 34 are also formed into final waveguides 24. The axial zone in which extend the waveguides 24 forms a measurement zone 44 in the finished measurement tube 10.

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

[0084] Between the connecting structures 20 and the waveguides 24 there extends axially a transition zone 48 in which the cross-section widens continuously and progressively from the measuring zone 44 to the fluidic fittings 18 (see for example figures 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 tooling 43 is opened so that the now finished measuring tube 10 can be removed.

[0086] The axial end sections 31 at the level of the fluidic fittings 18 and the connecting structures 20 remain here undeformed.

[0087] The structures 42 already made on the semi-finished product 14 before the shaping stage, for example damping elements and / or reflecting elements for surface acoustic waves, including different 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 tooling 43, the cores 36 are, if necessary, pushed once again into the passage opening 32, which is now formed into a 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 re-machining 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 re-machined here.

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

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

[0092] In the measurement zone 44, the circular shape of the cross-section of the passage opening 32 is transformed into an approximately square cross-section 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 a single core 36 for fluid channels 16 whose internal geometry is not narrowed compared to the fluid fittings 18, this core then being inserted into the passage opening 32 along 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 the core 36 can be fully inserted into the middle section 30 and removed from it 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 also, several cores 36 having slightly different external geometries are used optionally, as described above, to compensate for an elastic deformation of the measuring tube 10. A core 36 whose external geometry corresponds exactly 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] Figure 13 shows several possibilities for a cross-sectional surface 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 either 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 just described, the semi-finished product 14 here has a wall thickness s2 that is less than the wall thickness sb

[0099] As described above, before insertion into the forming tooling 43, the axial ends 31 forming the fluidic fittings 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 forming tooling 43 and plastically deformed by the forming punches 40 and the inserted cores 36. [Fig. 9] shows the result of the forming 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 achieved.

[0102] Unlike the first example, the forming tooling 43 is designed so 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 (shown in Figures 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 forming 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 realizations of the finished measuring tube 10.

[0104] In [Fig. 10], the measurement 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, formed only on the two longer sides.

[0105] Here, the connecting structures 20 are furthermore not made in the form of flanges, but in the form of threads. As described above for flanges, threads can also be prefabricated before the forming step and are not deformed during the forming 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 fluidic fittings 18.

[0107] Fig. 12 finally shows a measuring tube 10 having a circular cross-section of the fluid channel 16 in the measuring area 44 and flanges at the fluidic fittings 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 forming 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 terminating in a point towards the measurement zone 44 is formed here for each of the waveguides 24 on the measuring tube 10, in which the curvature of the fluidic fitting 18, circular in the peripheral direction U, blends 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 is reduced from the cross-section of the fluidic fitting 18 to the cross-section of the fluid channel 16.

[0112] Such structures 42 can 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 processes.

[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 area 44 to the fluidic fitting 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 (denoted here by ti and t4).

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

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

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

Claims

Demands

1. A method for manufacturing a measuring tube (10) of a fluid measuring means, comprising the following steps: - supplying a tubular semi-finished product (14) having a passage 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 area (34), which, once the measuring tube (10) is completed, forms a waveguide (24) for the surface acoustic waves of an acoustic measuring means, the waveguide area (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 forming tool (43), - introducing minus a kernel (36) in the passage opening (32),an external geometry (38) of the core (36) corresponding to an internal geometry of a fluid channel (16) of the measuring tube to be formed from the passage opening (32), - the performance of a shaping step during which a pressing force (F) is applied to at least one axial midsection (30) of the semi-finished product (14) and at least the midsection (30) is plastically deformed, the passage opening (32) being transformed into a fluid channel (16), and - the removal of at least one core (36).

2. A 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 retained during the shaping step.

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

4. A method according to any one of the preceding claims, wherein an external geometry of the mid-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. A method according to any one of the preceding claims, wherein after the 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 any one of the preceding claims, wherein two cores (36) are used simultaneously, which are moved in 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 a zone arranged in the middle section (30) than at an axially adjacent zone.

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

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

10. A method according to any 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. A method according to any one of the preceding claims, wherein axial end sections (31) of the semi-finished product (14) remain undeformed during the shaping step.

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