AT512356A1 - METHOD AND DEVICE AND TOOL FOR MEASURING A HOLE IN A WORKPIECE - Google Patents

Abstract

The invention relates to a method, a device and a measuring insert for measuring a bore in a workpiece. The method comprises the steps of: introducing a fluid into the bore, inserting a measuring insert positioned along the bore into the bore, wherein the largest outer diameter of the measuring insert is slightly smaller than the inner diameter of the bore, so that a gap between the inner circumference of the bore and forming the largest outer circumference of the measuring insert, measuring a backpressure dependent on the width of the gap and / or a flow rate of the fluid, determining the inner diameter of the bore at the current position of the measuring insert by evaluating the measured back pressure and / or the measured flow rate, wherein a is measured graduated hole by a measuring insert is used with a flat face or a stepped shape.

Description

Method and device and tool for measuring a bore in a workpiece 5 Field of the invention

The invention relates to a method and apparatus as well as a measuring insert for measuring a bore in a workpiece. In particular, the invention relates to the measurement of components of a fluid dynamic bearing system 10, for example, a bearing system consisting of a bearing bush and a rotatably mounted in a bearing bore of the bearing bush shaft. The invention serves for the measurement and grouping of bearing bush shaft pairs.

Prior Art 15

Due to manufacturing tolerances in the manufacture of bearing components, especially bearing bushes and fluid dynamic bearing shafts, a grouping, i. H. a pair of bearing bushes and shafts necessary so that the required tolerances, in particular the required width of the radial bearing gap 20 of the fluid dynamic bearings, can be met. In fluid dynamic bearing systems, as used in spindle motors for driving hard disk drives, the width of the radial bearing gap between the outer diameter of the shaft and the inner diameter of the bearing bore, for example, only a few microns. The gap width may vary by no more than 10% to 25 15%, so that the bearing still operates trouble-free under the specified operating conditions.

For measuring bearing bores various methods and methods are known. In the known contact methods, a thin needle 30 is used, at the end of which a carbide stylus is arranged as a scanning element in the rule. Thus, the surface of the bearing bore or the shaft is then scanned and measured. Although this type of measurement is comparatively accurate with measuring accuracies in the micrometer range, it requires, due to the surface roughness of the components to be measured, a complex evaluation of the measurement results. In addition, the touching measurement can damage the surfaces of the components to be measured. Furthermore, the scanning element and the component to be measured must be laboriously positioned relative to each other so that it can be measured with appropriate accuracy.

Other measuring methods for measuring boreholes use optical sensors which work, for example, according to the triangulation principle. These are very time-consuming due to the required evaluation of the measurement results. A major disadvantage of these methods is also that the surfaces to be measured must be reflective, so that a transmitted light beam is thrown back from the measuring surface to the measuring receiver. As with the tactile measuring methods, there is also the problem that the measuring element and the surface to be measured must be positioned and centered exactly to one another.

JP 06137997 A describes a pneumatic method for measuring the inside diameter of a bearing bush of a fluid dynamic bearing, wherein a measuring shaft is inserted into the bearing bush and measured as a measurement standard, the pressure drop of the resulting air bearing. The pressure drop as a measured variable is a measure of the size of the bearing gap between the bearing bore and the measuring shaft. This method is relatively inaccurate.

Other non-contact methods for measuring a bore are described in GB 1544967 and GB 1573682, Here, a cylindrical measuring body is positioned within the bore to be measured. In the measuring body means for introducing compressed air are provided in the gap between the outer diameter of the measuring body and the surface of the bore, so that the measuring body is aligned and centered during the measuring process within the bore. Pressure differences in the gap are detected by means of pressure sensors and from this the radial cylindricity is calculated. The pressure differences can be detected by pneumatic, inductive or capacitive pressure sensors. t "

EP 1 452 829 A1 discloses a measuring method and a device for measuring the inside diameter of a bore at different depths. In the hole a measuring insert is introduced in the form of a ball. The ball has a slightly smaller outer diameter than the inner diameter of the bore and is moved along the bore. At the same time, a fluid, preferably compressed air, is directed from one end of the bore into the remaining gap between the ball and the bore wall. The dynamic pressure which arises as a function of the inner diameter of the bore or the flow rate of the fluid through the gap is measured and evaluated, and the diameter of the bore is determined therefrom. The air pressure measurement method described operates reliably and with sufficient accuracy, but has its limits or can not be applied to bearing bores with a stepped inner diameter in the measurement of the larger inner diameter in the vicinity of the step. Although it is possible to measure from two sides of the stepped bearing bore and use measuring balls each with the corresponding outer diameter, however, can not be measured on the side with the larger bore diameter of the area immediately adjacent to the stage, as the measuring ball hit the step and damage the workpiece would.

Disclosure of the invention

It is the object of the invention to improve a method, a device and a measuring insert for measuring a bore in a workpiece based on a fluid pressure measuring method such that even bores with a stepped inner diameter can be completely measured.

This object is achieved by a method, a device and a measuring insert with the features of the accompanying independent claims.

Preferred embodiments and advantageous features of the invention are indicated in the dependent claims.

The invention describes a method for measuring a stepped bore s in a workpiece, which consists of a section with a smaller inner diameter di and a section with a larger inner diameter d2, at the junction of which a step is formed, the method comprising the steps:

Supplying a fluid into the bore,

Imports of a positionable along the bore measuring insert into the bore 10, which is formed in the measuring range rotationally symmetrical with respect to the direction of movement of the measuring insert, wherein the largest outer diameter of the measuring insert is slightly smaller than the inner diameter of the bore within the positions at which the measurement is performed, so forming a gap between the inner periphery of the bore and the largest outer periphery of the gauge, measuring a backpressure dependent on the width of the gap, and / or a flow rate of the fluid through the gap at a current position of the gauge, and determining the inner diameter of the bore at the current position of the measuring insert by evaluating the measured back pressure and / or the measured flow rate. 20

The invention is based on the fact that the shape of the measuring insert is adjusted accordingly to be able to measure a stepped bore.

In particular, the bore is measured in its section with a larger inner diameter 25 d2 at a distance a, wherein a within the section with a larger inner diameter d2 the distance measure in the direction of movement from the point of a maximum diameter DM of the measuring insert to the step of drilling referred to and with ri = di / 2 and Rm = Dm / 2, the following equation applies:

In particular, it is proposed to use a measuring insert with a flat face or a stepped shape that meets the above criteria. 30 • * «· > ·· * · · * »······ ··· · * * * 5 * * * * j * # ·« «·· * ·· * ·· ♦

Due to the unilaterally flattened or graduated shaping of the measuring insert can be brought up to the stage in the bore and it can also be measured the areas of the hole, which are immediately adjacent to the step. A premature stop of the measuring insert at the edge of the step is avoided and thus damage to the component to be measured or the measuring insert. Due to the stepped shape or the hemispherical shape of the measuring insert, it can only occur that the measuring insert comes to rest flat on the step, whereby no damage to the workpiece or the measuring insert is to be feared.

In a preferred embodiment of the invention, a hemisphere with a flat side is used as the measuring insert. The measuring insert is inserted with the flat side ahead into the bore to be measured. The hemisphere may have on its flat side a molded nose, which continues beyond the step out into the part of the smaller diameter bore to be measured.

In another embodiment of the invention, the measuring insert may be formed as a stepped cylinder or a stepped cylindrical ring. The respective outer diameters of the sections of the measuring insert are adapted to the stepped diameter of the bore to be measured.

The measuring method requires that always sufficient measuring fluid, preferably compressed air, flows through the remaining gap between the measuring insert and the wall of the bore. However, placing the measuring insert on the step would interrupt the flow of fluid, damaging the measuring device or interfering with the measuring process. According to the invention, this can be prevented by ensuring a forced flow of the fluid through appropriate channels or grooves formed on one side of the measuring insert. In particular, however, the measuring process and thus the supply of the fluid can be interrupted upon reaching a threshold value for the measured back pressure or the measured flow rate. 5 «» 6 · * · »* · * · ** ·

According to the invention, therefore, a measuring insert with defined dimensions and with a flat end face or a stepped shape is used in the proposed measuring device in order to be able to measure a stepped bore.

Brief description of the drawings

Figure 1 shows a simplified section through the bearing bush and a part of the measuring insert of the measuring device. io

Figure 2 shows a section through a bearing bush and a part of a measuring insert according to the prior art.

Figure 3 shows a modified shape of the measuring insert. 15

FIG. 4 shows a further modified form of the measuring insert.

FIG. 5 shows an embodiment similar to FIG. 1 with further variables for dimensioning 20

FIG. 6 shows a further modified form of the measuring insert.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 25

1 shows schematically a section through a bearing bush 10 with a bearing bore 12 to be measured together with a measuring insert 24 according to the invention and further components of the measuring arrangement. The bearing bush 10, for example the bearing bush of a fluid-dynamic bearing, has a bearing bore 12 in which a shaft (not shown) can be rotatably mounted. The bearing bore 12 is stepped, d. H. ♦ ♦ • · * • ♦ ·

it has a step 14 which divides the bearing bore 12 into a smaller inner diameter portion (top) and a larger inner diameter portion (lower). To group, d. H. Pairing the bearing bush with a matching shaft, it is necessary, in particular the 5 bearing bore 12 to measure, so that a shaft of this bearing bush 10 can be associated with the bearing bore.

For measuring the bearing bore 12, a fluid pressure measuring method is used, as is basically known from the prior art. The io bearing bushing 10 is placed on a support plate 16, which is opposite to the

Bearing bore is sealed with a seal 18. In the support plate, an air supply 20 for supplying a fluid, preferably compressed air, is provided, through which a permanent air flow 22 can be introduced from below into the bearing bore 12. 15

For measuring the bearing bore 12 of the measuring insert 24, which is formed in this embodiment of the invention, for example, hemispherical, wherein its largest outer diameter is slightly smaller than the smallest expected inner diameter of the bearing bore 12 to be measured within the 2o positions at which the measurement is performed , In the illustrated example, the portion of the bearing bore 12 is measured with a larger inner diameter, to measure the positions Z4 to Z6 of the portion of the bearing bore with a smaller inner diameter, a measuring insert with a correspondingly smaller outer diameter must be used. 25

The measuring insert 24 is attached to a guide rod 26 which is displaceable along the central axis of the bearing bore 12 in the direction of movement 28, so that the measuring insert 24 can be axially positioned within the bearing bore. For measuring the bearing bore 12, the measuring insert 24 with the flattened side is now advanced ahead to a corresponding position of the bearing bore 12, for example position Z3. Between the outer circumference of the * * »* 'η * *« «· .. ·. ··

Measuring insert 24 and the inner circumference of the bearing bore 12 remains a gap 30. Now, an air flow 22 is introduced via the air supply 20 from one end of the bearing bore 12. The air flow 22 strikes the rounded side of the measuring insert 24 and flows around it, the gap 30 acting as a throttle for the air flow 22. As a result, a dynamic pressure P builds up below the rounded side of the measuring insert 24 or an air flow 32 with a certain flow rate arises above the measuring insert 24.

The back pressure P or the flow rate are directly dependent on the width of the gap 30 between the wall of the bearing bore 12 and the outer periphery of the io measuring insert 24. The back pressure P is the greater, the smaller the gap 30 between the measuring insert 24 and the bearing bore 12th is. The smaller the gap 30 between the outer diameter of the measuring insert 24 and the inner diameter of the bearing bore 12, the smaller the flow rate of the air flow 32 is. 15

The measuring device comprises a control and evaluation device 34, which measures the dynamic pressure P below the measuring insert 24 by means of a pressure measuring device 38. Additionally or alternatively, the control and evaluation device by means of a volumetric flow meter 36 to measure the volume flow 20 of the air flow 32, which adjusts after passing through the gap 30. The measured back pressure P or the volumetric flow of the air flow 32 are evaluated and converted into a measured value for the gap width of the gap 30 by means of corresponding conversion factors which were determined by a previously performed calibration. The calibration is carried out by mounting a suitable measuring insert 24 into the measuring device and carrying out a 2-point calibration by means of two metered rings. The rings determine the upper and lower measuring range end value, whereby both the inner diameter and the difference of the inner diameter of the two rings must be within the range specified by the manufacturer of the measuring instrument. A further 30, previously presumptuous ring, serves for verification and lies with his

Inner diameter preferably in the middle of the predetermined by the Meßbereichendwerte range.

The control and evaluation device 34 also controls a pump 40 which is connected to the air supply 20 and generates a corresponding air flow 22. The pressure of the air stream 22 is measured by a pressure measuring device 42.

By means of the hemispherical measuring insert 24 according to the invention, the lower portion of the bearing bore 12 with a larger inner diameter can be measured both at the positions Z1 and Z2 and at the position Z3 without the measuring insert 24 abutting against the step 14 and the workpiece, here the bearing bush 10 , damaged.

In the prior art illustrated in Figure 2, the same measuring device and measurement setup is used as in Figure 1. However, as a gauge insert 124, there is provided a ball which is not adapted to receive a stepped bearing bore 12 at all axial positions measured. It can be seen that although the positions Z1 and Z2 can be measured in Figure 2, but the ball for measuring the position Z3 is not suitable, since the ball surface would then strike already at the level 14 of the bearing bore 12 and the workpiece 10 and the Measuring insert 124 would be damaged.

Figure 3 shows another possible embodiment of a measuring insert 224, which is formed substantially as a hemisphere with a nose-shaped projection 224a on the flat side of the hemisphere. The advantage of this tool 224 lies in the better self-centering in the bearing bore by the flow around the nose-shaped extension 224a with the introduced compressed air.

FIG. 4 shows another measuring insert 324 which is essentially identical to the measuring insert 24 from FIG. On its flat end face, which faces away from the air flow 22, however, this measuring insert 324 has channels 324a, 324b, which also ensure an air flow through the gap 30 when the measuring insert 324 rests on the step 14 of the bearing bore 12. That avoids one

·· ·· »· * · * ·····

Damage to the measuring device or an overpressure in the measuring device. Furthermore, the bearing bore 12 can then possibly also be measured when the measuring insert 324 rests on the step 14. In particular, however, the measuring process and thus the supply of the fluid upon reaching a threshold value for the measured back pressure P or the measured flow rate can be interrupted.

Figure 5 shows the various variables and dimensions in the construction of the measuring insert. The gauge insert 24 is divided into an area located within the larger inner diameter d2 of the bore 12 and an area that may be within the smaller inner diameter di of the bore 12. The outline of the measuring insert 24 must not hit the inner corner of the step 14. First, a definition of the variables follows:

Dm is the maximum diameter of the measuring insert 24 within the larger inner diameter d2 of the bore perpendicular to the direction of travel 28 of the measuring insert and with respect to its axis of symmetry. If this diameter is present at several points of the measuring insert, then the position within the measuring insert 24 must be taken for the position of DM, which has the smallest distance in the direction of movement to the step 14 during the measurement.

Rx is a radius of the measuring insert 24 at any point perpendicular with respect to its axis of symmetry di is the smaller inner diameter of the bore 12 d2 is the larger inner diameter of the bore 12 y \\ r = d ± uncj ^ = da. uncj = Ώμ. is defined: ia is the distance measure in the direction of movement 28 from the point of the maximum diameter Dm of the measuring insert 24 to the step 14 of the bore. b is the maximum pitch in the direction of movement within the portion 5 of the gauge 24 located within the larger inner diameter d2 of the bore 12, from the point of maximum diameter DM of the gauge towards the step 14 in a range Rx > η, which is perpendicular to the direction of movement and symmetrically limited with respect to its axis of symmetry and radially by the distance Rx of the io measuring insert with n < Rx < r2.

When considering a previously used spherical surface as a measuring insert (see Figure 2) applies to a contact of the spherical surface with diameter DM with the contour of the inner corner of the stage 14: 15 Rl = a + n or a = ^ Rΐ ~ 7ι < with R = D / 2 and n = di / 2. 20 d. H. the minimum distance in the direction of travel from the center of the maximum diameter DM of the measuring insert 124 to the step 14 is defined and limited by these values when using a spherical surface according to the prior art. In order to avoid this limitation, the measuring insert 24 in the region of the larger inner diameter d2 of the bore 12 with its outer radius must be designed as follows: 1. In the range n < Rx < RM holds: £ < 2. If areas of the measuring insert 24 are within the smaller inner diameter of the bore 12, the diameter of this part of the measuring insert 24 must be smaller than di and the length of this portion of the measuring insert 24 be sized so that the measuring insert 24 within or 5 above the smaller inner diameter di the bore 12 does not abut before the portion of the measuring insert 24 abuts in the region of the larger inner diameter Ö2 of the bore 12 at the stage

In other words, therefore, the bore 12 must be measured in its section with a larger inner diameter d2 at a distance a, wherein a within the 10 portion of larger inner diameter d2, the distance measure in the direction of movement from the point of a maximum diameter Dm of the measuring insert 24 for step 14 and with η = di / 2 and Rm = Dm / 2 following

Finally, FIG. 6 shows a measuring insert 424, which is designed essentially as a cylindrical disk and also has an extension 424a which extends into the region of the bearing bore 12 with a small inner diameter.

With the measuring insert according to FIG. 6, it is also possible, for example, to measure 20 blind bores in a component 11. Here, however, is the

Air flow 22 is introduced through the tool 424 through a central bore 424b in the channels 424c and 424d in the blind hole. In this case, the region of the measuring insert 424, which dips into the portion of the bore 12 with a smaller inner diameter di, must be designed according to the length of her. 25

The method described with measuring inserts according to the invention also works if in another structure, the supplied air is not supplied from the guide side of the measuring inserts, but the air supply 22 and dynamic pressure measuring device 38 are arranged on the opposite side.

List of Reference Numbers 10 Bearing Bush 11 Component 5 12 Bearing Hole 14 Step 16 Support Plate 18 Seal 20 Air Supply 10 22 Airflow 24 Measuring Insert 26 Guide Rod 28 Direction of Movement 30 Gap 15 32 Air Flow 34 Control and Evaluation Device 36 Volumetric Flow Meter 38 Pressure Measuring Device 40 Pump 20 42 Pressure Measuring Device 124 Measuring Insert (Stand technology) 224 Measuring insert 224a Nose-shaped extension 25 324 Measuring insert 324a, 324b Channel 424 Measuring insert 424a Extension 424b Central bore 30 424 c, d Channel Z1-Z6 Position P Back pressure

Dm Rx s di d2 a b

Maximum diameter of the measuring insert perpendicular to the

Direction of movement with respect to its axis of symmetry

Rx is the radius of the measuring insert at any point perpendicular to its axis of symmetry

Smaller inside diameter of the hole

Larger inside diameter of the bore

Distance measure in the direction of movement from the point of maximum

Diameter Dm of the measuring insert to the level 14

Maximum distance within the measuring insert

Claims: 10

Claims (18)

DR. FERDINAND GIBLER DR DR. WOLFGANG POTH Austrian and European Patent and Trademark Attorneys PATENT CLAIMS 1. Method for measuring a stepped bore (12) in a A workpiece (10, 11) consisting of a smaller inner diameter portion (di) and a larger inner diameter portion (d2), at the junction of which a step (14) is formed, comprising the steps of: supplying a fluid into the Bore (12), imports of a positionable along the bore measuring insert (24, 124, 224, 324, 424) in the bore (12) in the measuring range rotationally symmetrical with respect to the direction of movement (28) of the measuring insert (24, 124, 224, 324 , 424) is formed, wherein the largest outer diameter of the measuring insert is slightly smaller than the inner diameter of the bore within the positions (Z1, Z2, Z3) at which the measurement is performed, so that a gap (3 0) between the inner circumference of the bore and the largest outer circumference of the measuring insert is formed, measuring one of the width of the gap (30) dependent dynamic pressure (P) and / or a flow rate of the fluid through the gap (30) at a current position of the Measuring insert, determining the inner diameter of the bore (12) at the current position of the measuring insert by evaluating the measured back pressure (P) and / or the measured flow rate, characterized in that the bore (12) in its section with a larger inner diameter (d2) in a distance (a) is measured, wherein the measuring insert is positioned in the bore so that the distance (a) within the larger inner diameter portion (d2 > the distance dimension in the direction of movement from the point of maximum diameter Dm of the measuring insert to the step (14) and with = dV2 and Rm = Dm / 2 the following equation applies: q < - γ \ 2. The method according to claim 1, characterized in that as a measuring insert (24, 5 324) a hemisphere with a flat side is used. 3. The method according to claim 2, characterized in that as a measuring insert (224) is used a hemisphere with an integrally formed on the flat side nose (224a). io 4. The method according to claim 1, characterized in that as a measuring insert (424) a stepped cylinder is used. A method according to any one of claims 1 to 4, characterized in that a measuring insert (324; 424) is used which has channels or grooves (324a, 324b; 424c, 424d) formed on the flat side. 6. The method according to any one of claims 1 to 5, characterized in that the supply of the fluid is interrupted upon reaching a threshold value for the measured 20 back pressure (P) or the measured flow rate. Apparatus for measuring a stepped bore (12) in a workpiece (10, 11) consisting of a smaller inner diameter portion (di) and a larger inner diameter portion (d2), at the junction of which 14), comprising: a supply device (20) for supplying a fluid into the bore (12), an introduction device (26) for introducing and positioning a measuring insert (24, 124, 224, 324, 424) in the bore (12) in the measuring range rotationally symmetrical with respect. The direction of movement (28) of the measuring insert (24, 30 124, 224, 324, 424) is formed, wherein the largest outer diameter of the measuring insert is slightly smaller than the inner diameter of the bore within the positions (Z1, Z2 , Z3), at which the measurement is carried out, so that a gap (30) is formed between the inner circumference of the bore and the largest outer circumference of the measuring insert, a measuring device (36; 38) for measuring a ram pressure (P) dependent on the width of the gap and / or a flow rate of the fluid at a current position of the measuring insert, an evaluation device (34) for determining the inside diameter of the bore at the current position of the measuring insert Measuring insert by evaluating the dynamic pressure (P) and / or the flow rate, characterized by a measuring insert (24, 124, 224, 324, 424), which in the measuring section for the larger inner diameter (d2 > is designed so that the measuring insert has a radius Rx at any point perpendicular with respect to its axis of symmetry and, with r ·, -cfi / 2 and r2 = d2 / 2, the maximum radius (Rx) of the measuring insert in the range n < Rx < r2 > where b is in the larger inner diameter measurement range in the range Rx > η denotes the maximum distance within the measuring insert in the direction of movement, measured from the point of the maximum diameter Dm of the measuring insert, which is located towards the step (14) closest to the step (14), and the measuring insert is designed with Rm = Dm / 2 the following equation holds: In the range h < Rx £ RMb < 8. Apparatus according to claim 7, characterized in that the measuring insert (24, 124, 224, 324, 424) is formed with a flat end face or a stepped shape for measuring a stepped bore. 9. Apparatus according to claim 8, characterized in that the measuring insert (24, 324) is designed as a hemisphere with a flat side. 10. The device according to claim 8, characterized in that the measuring insert (224) is designed as a hemisphere with an integrally formed on the flat side nose (224 a). • · ΐ8. * * ♦ · »« tu 11. The device according to claim 8, characterized in that the measuring insert (424) is designed as a stepped cylinder. 12. Device according to one of claims 7 to 11, characterized in that 5 of the measuring insert (324; 424) on a side facing away from the fluid flow or facing side molded channels or grooves (324a, 324b; 424c, 424d). 13. A measuring insert (24, 124, 224, 324, 424) for measuring a stepped bore (12) in a workpiece (10, 11), wherein the stepped bore (12) consists of a portion having a smaller inner diameter (di) and a portion with a larger inner diameter (d2), at the transition of a step (14) is formed, wherein the measuring insert in the measuring range for the larger inner diameter rotationally symmetrical with respect to. 15 Direction of movement (28) of the measuring insert (24,124,224, 324,424) is formed and wherein the Measuring insert has a distance Rx at any point perpendicular with respect to its axis of symmetry and with ri = dt / 2 and r2 = d2 / 2, the distance (Rx) of the measuring insert in the range η < Rm < r2 > where b is in the larger inner diameter measurement range in the range Rx > η denotes the maximum distance within the measuring insert in the direction of movement, measured from the point of maximum diameter DM of the measuring insert located in the direction of the step (14) closest to the step (14), and the measuring insert is designed such that with Rm = Dm / 2, the following applies: 25 In the range n < Rx < RM b < 14. Measuring insert according to claim 13 for measuring a stepped bore by means of a fluid pressure measuring method, characterized by a flat face or a stepped shape. 30 15. Measuring insert according to claim 14, characterized in that it is formed as a hemisphere (24; 324) with a flat side. 16. Measuring insert according to claim 15, characterized in that it is formed as a hemisphere (224) with an integrally formed on the flat side nose (224 a). 17. Measuring insert according to claim 14, characterized in that it is designed as a stepped cylinder (424). 18. Measuring insert according to one of claims 13 to 17, characterized in that it has on a side facing away from the fluid flow or facing side molded channels or grooves (324a, 324b; 424c, 424d). (Dr. F. Gibler or W. Poth)