DE102012002913A1 - Method for manufacturing ball and socket joint for piston assembly of hydrostatic piston machine, involves manufacturing ball part and filling undercut of ball part with filling element, such that undercut is filled in some regions - Google Patents

Abstract

The method involves manufacturing a ball part (10) and filling an undercut (12) of the ball part with a filling element (30) such that the undercut is filled in some regions. The assembly of the ball part and the filling element is inserted into a mold (40), which is reproduced by a socket part (20). The mold is filled with a liquid plastic under pressure, where the plastic material is hardened. The ball and socket joint consisting of the ball- and socket part is de-molded and the filling element is removed from the ball and socket joint. Independent claims are also included for the following: (1) a piston assembly for a hydrostatic piston machine with a piston and a sliding piece; and (2) a filler element formed as a ring with inner side formed as negative form of sphere.

Description

The invention relates to a method for producing a ball joint according to the preamble of claim 1, further a piston assembly with a ball joint, which can be produced by this method and a filling part, which is used in the execution of this method.

From the DE 10 2004 060 945 A1 a ball joint is known, which is used for the piston assembly of a hydrostatic piston engine, in particular a swash plate motor or a Schrägachsenmotors or the corresponding pump. The two parts of the ball joint, namely the ball part with the ball and the adapted socket part simultaneously form the piston or the shoe of the piston assembly. In this case, the ball part can optionally be designed as a piston or as a sliding block. The same applies to the pan part. In DE 10 2004 060 945 A1, the sliding shoe consists of a thermoplastic, namely reinforced PEEK. Such plastics show a comparatively large shrinkage during solidification. The corresponding ball joint therefore jams or has too much play. The shoe is not formed accurately enough, so that the local leakage oil flow is large. Furthermore, the metal part loses hardness due to the high temperatures during thermoplastic injection molding.

From the DE 26 01 345 C2 is known a ball steering, in which both the ball part and the socket part made of a thermoplastic material. This ball joint is produced in the assembly injection molding process, ie it is first the ball part separately produced by injection molding. This ball part is inserted into the mold of the cup part, which is then filled with liquid plastic. The ball of the ball part thus forms part of the mold for the pan part. Accordingly, exactly the pan is adapted to the ball. The result is a ready to install ball joint. The ball part can be treated with a teflon spray before encapsulation so that the ball and socket parts do not adhere to one another and thus a sufficiently large clearance between the ball and socket parts is established so that the ball joint does not stick.

One might now think to make the piston of the piston assembly made of plastic. However, in a hydrostatic piston machine, this must be designed very precisely so that the cylinder space of the hydrostatic piston engine is pressure-tight. The required accuracy can not be achieved with a thermoplastic. In contrast, thermosets are known, which show virtually no change in shape during curing or whose shape change is so reproducible that it can be taken into account in the design of the mold. Examples include bulk molding compound (BMC) or phenol molding compound (PF) called. However, these plastics have a very low viscosity when filled into the mold. It is therefore very easy to form so-called webs on the injection molded component. These arise when liquid plastic penetrates into the joints of the various tool parts. This problem is exacerbated by the fact that the ball and socket parts have undercuts which require separate slides in the mold, which further increases the number of parting lines. The said webs hinder the mobility of the ball joint and can not subsequently be easily removed so that the required pressure tightness of the piston assembly and the hydrostatic piston machine is guaranteed.

The object of the invention is to provide a Montagespritzgussverfahren for the ball joint of a piston assembly of a hydrostatic piston machine, which is particularly suitable for the use of low-viscosity thermosets. Namely, the said webs should be avoided. In addition, the corresponding mold should be constructed so simple that several ball joints can be made in a single process run. Such a mold is also referred to as a multi-cavity mold.

• – Herstellen des Kugelteils;
• – Auffüllen der Hinterschneidung des Kugelteils mit einem gesonderten ersten Füllteil, so dass die Hinterschneidung der Kugel bereichsweise ausgefüllt ist;
• – Einlegen des Verbundes aus Kugelteil und erstem Füllteil in eine erste Gussform, welche das Pfannenteil abbildet;
• – Füllen der ersten Gussform mit einem flüssigem ersten Kunststoff, der unter Druck steht;
• – Aushärten des ersten Kunststoffes;
• – Entformen des Kugelgelenks bestehend aus Kugel- und Pfannenteil;
• – Entfernen des ersten Formteils vom Kugelgelenk.

This object is achieved by a method according to the independent claim, which comprises the following steps:

• - making the ball part;
• - filling the undercut of the ball part with a separate first filling part, so that the undercut of the ball is partially filled;
• - Inserting the composite of the ball part and the first filling part in a first mold, which images the pan part;
• - filling the first mold with a liquid first plastic that is under pressure;
• - curing the first plastic;
• - Mold removal of the ball joint consisting of ball and socket part;
• - Removal of the first molded part from the ball joint.

The innovation according to the invention consists in the first filling part, which partially fills the undercut of the ball. The first filling part partially forms the socket part, with the remainder being imaged by the first mold. Since the composite ball joint and first molded part has no undercuts, can be dispensed with corresponding slider in the first mold. The first mold is accordingly simple and can be easily provided with multiple shaping cavities for the simultaneous production of multiple ball joints.

The separate first filling part can be designed in terms of its material properties and dimensions so that it rests so close to the associated casting mold that no low-viscosity thermoset can get into the corresponding joints. The formation of webbed is thus avoided.

In the dependent claims advantageous refinements and improvements of the invention are given.

The first plastic can be filled into the first mold from the opposite side of the ball, preferably pressure-controlled. In the area of the sprue, a lower accuracy and uniformity of the socket part is to be expected. This would be particularly disturbing in the field of engagement between ball and pans. The break point was therefore located at most far from this intervention. The filling of the first plastic is preferably carried out pressure-controlled, so that the loads of the internals of the mold are small. This is to avoid that the first filling part deformed excessively, so that no webs arise. Further, the pan part may have thin channels for conducting hydraulic fluid. The corresponding thin needles on the first mold could be bent by excessive inflow velocities, which are avoided by the pressure control. In addition, this arrangement allows the break point that multiple forming cavities can be arranged in the first mold. Furthermore, voids in the socket part can be avoided.

The ball part can be made of metal uplifting span. Preferably, the piston of the piston assembly is made of metal, since this must be made very accurate.

• – Einlegen eines gesonderten zweiten Füllteils, welches die Hinterschneidung des Kugelteils vollständig ausfüllt, in eine zweite Gussform, welche das Kugelteil abbildet;
• – Füllen der zweiten Gussform mit einem flüssigen zweiten Kunststoff, der unter Druck steht;
• – Aushärten des zweiten Kunststoffes;
• – Entformen des Kugelteils.

In contrast, however, it is preferred if the ball part is made of plastic, because such a ball part is cheaper than one made of metal. For its preparation, the following method is proposed:

• Inserting a separate second filling part, which completely fills the undercut of the ball part, into a second casting mold, which images the ball part;
• - filling the second mold with a liquid second plastic which is under pressure;
• - curing the second plastic;
• - Removal of the ball part.

Again, a filler is used, which is slightly different than the first filling part, since it must fill the entire undercut on the ball part. The advantages of the second molded part are the same as those of the first molded part, so that reference can be made to the above statements.

The second plastic can be filled in the second mold from the opposite side of the second filling part, preferably pressure-controlled. Here are the same advantages that were already mentioned for the sprue on the first mold.

The first and / or the second filling part may be integrally formed in the form of a ring with a slot extending in the radial direction, wherein it consists of flexible material. Although in principle multi-piece filling parts come into consideration, one-piece filling parts are preferred because of the lower production costs. The filling part must surround the ball part so that it can image the ball in the area of the undercut. For this ring can be removed from the ball part, it is provided with a radial slot. At the same time, the material of the filling part is so flexible that it can be bent sufficiently far elastically to allow disassembly. Thus, the filling part is not damaged during disassembly, so that it can be reused several times to save costs.

The first and / or the second filler part can consist of a thermoplastic, fluorine-based plastic, preferably perfluoroalkoxy copolymer (PFA). When selecting the material for the filler is to be considered that this can be produced inexpensively. Therefore, a thermoplastic was selected to make the filling member in the spatter casting process. Furthermore, the filling part must not adhere to the ball joint or its casting mold, so that it can be dismantled without problems. Furthermore, the filling part must be able to withstand the temperatures necessary for the curing of the thermoset of the ball joint without causing any dimensional changes. Finally, the filling part must have the above-mentioned flexibility. In the case of the thermosets Bulk Molding Compound or phenolic molding compound, which is particularly preferred because of its low shrinkage during curing, mold temperatures of about 170 ° C. occur during curing. All these requirements are particularly suited to fluorine-based plastics. Perfluoroalkoxy copolymer (PFA) has proven particularly suitable.

The first and / or the second filling part can be adapted at room temperature substantially free of play to the associated casting mold, wherein it a larger coefficient of thermal expansion than the associated mold, wherein the mold is preheated prior to filling with plastic. The annular, slotted filling part expands due to the heating, so that it bears against the associated casting mold under pretensioning. As a result, the slot is completely closed. Furthermore, the joints to the mold are completely sealed, so that no thin thermosetting plastic can penetrate. It should be noted that the filling part is elastic, so that it deforms under the action of the biasing forces until the genanten column are completely closed. This effect is significantly responsible for the fact that the ball joint has no webbed membranes after injection molding.

The finished ball joint can be exposed for a predetermined time to a room temperature which is elevated in relation to the room temperature in order to set the desired clearance in the ball joint by post-crosslinking of the thermoset. For this purpose, the ball joint can be fed to a tempering furnace.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

1 a rough schematic cross section of the first mold with the first filling part;

2 a rough schematic cross section of the second mold with the second filling part;

3 a perspective view of a filling part; and

4 a perspective sectional view of the filling part according to 3 ,

1 shows the first mold 40 with the first filling part 30 for producing the finished ball joint or the finished piston assembly 10 ; 20 , It should be noted that the first and second molds were named according to the order of mention in the claims and not according to the timing of the method according to the invention. It should also be noted that the invention will be described below by way of example, in which the sliding block the ball part 10 and the piston the pan part 20 is. Nevertheless, the conditions can be reversed.

The first mold 40 includes a major part 44 in which, for example, eight identical cavities 41 evenly distributed along a circle are arranged, in 1 only one of these shaping cavities is shown as an example. The thin liquid Duroplastmasse, namely Bulk Molding Compound or Phenolformmasse is fed centrally in said circle and in a star-shaped sprue 42 to the individual forming cavities 41 distributed. At the transition between the sprue 42 and the piston or pan part 20 is a break point 43 provided with a small cross-sectional area. Said cross-sectional area is designed so that the piston 20 easy from the sprue 42 can be canceled, at the same time the shaping cavity 41 can be filled in as short a time as possible. At the sprue 42 is still a pressure sensor 49 provided for determining the liquid pressure of the low-viscosity thermosetting plastic, so that these pressure-controlled in the first mold 40 can be filled. The pressure sensor 49 can be covered with a thin sealing membrane to avoid incorrect measurements. The filling pressure is selected so that the shaping cavity 41 completely, evenly and quickly fills, the flow forces are on the internals located there in any case so low that they are not damaged, for example, bent. Due to the low viscosity of the Duroplastmasse the filling pressure can be chosen small from the outset. The sprue 42 is located on the of the ball part 10 opposite side of the first mold 40 , so that the ball joint engagement by the inflow at the sprue 42 is disturbed as little as possible.

The shaping cavity 41 in the main part 44 The first mold is circular-cylindrical, so that the piston 20 is also circular cylindrical. It should be noted that it is crucial for the function of the hydrostatic piston engine that this cylinder shape is made very accurate. It is therefore on a single part, namely the main part 44 the first mold 40 intended.

The inner shape 21 the piston 20 is from a first closure 46 pictured, the shaping cavity 41 in the main part 44 at the same time from the in 1 Closes liquid-tight on the right side. In the 1 illustrated inner shape 21 of the piston 20 is largely to be understood in the sense of any embodiment. The crucial design detail is the size of the free cross section 22 in the area of the transition to the ball part 10 or to the shoe. When operating the hydrostatic piston engine, hydraulic oil is supplied from the inside 21 of the piston 20 over the hydraulic channel 13 in the shoe 10 to the sliding surface 15 promoted, so that is on the sliding surface 15 forms a hydrostatic lubricating film. The sliding surface 15 is for this purpose (deviating from the illustration) formed with a specially designed surface shape. The fluid transfer connection must be independent of the angular position between the piston 20 and shoe 10 consist. Therefore, at the ball 11 of the sliding shoe 10 a cut 14 provided, which of said free cross-section 22 on the piston 20 opposite. The reduction 14 and the free cross section 22 overlap in any position of the ball joint 11 ; 20 at least partially.

The annular first filling part 30 is on the prefabricated shoe 10 assembled. This composite is then placed in the second closure 47 the first mold 40 used. The second closure 47 with the ball part 10 and the first filling part 30 is then against the main body 44 the first mold 40 pressed until the local shaping cavity 41 is sealed liquid-tight. It should be noted that the first filling part 30 , as in 3 and 4 shown as a slotted ring made of an elastic material, making it easy on the ball part 10 can be mounted. It only forms a small area of the sphere 11 of the ball part 10 from, namely the area that the movement path of the ball joint 10 ; 20 Are defined. The first filling part 30 is at room temperature substantially free of play to a circular cylindrical recess 45 in the main part 44 the first mold 40 customized. The first mold 40 However, it is preheated to about 170 ° C during the injection molding process, with the first filler 30 of perfluoroalkoxy copolymer (PFA) expands more than the main part 44 the first mold 40 from steel. Consequently, the first filling part 30 under bias in the cylindrical Aufnehmung 45 absorbed, while it is at the same time against the ball part 10 suppressed. Thus, all joints between the main part 44 , the first filling part 30 and the ball part 10 tightly closed. The same applies to the radial slot in the first filling part 30 to.

Attention is still on the sealing in the area of the reduction 14 on the ball part 10 , There is in the first lock 46 a sealing ring 48 provided, which can be obtained as Abdichtnormalie example of Fa. Hasco. This is the shaping cavity 41 also completed liquid-tight at this point.

After the first mold 40 is closed, the thin liquid Duroplastmasse is pressure-controlled in the shaping cavity 41 filled. Due to the temperature of the first mold of about 170 ° C, the thermoset material, which is stable at room temperature, hardens quickly. The preferred thermosets Bulk Molding Compound or Phenolformmasse show a slight shrinkage, so that the finished ball joint 10 ; 20 not stuck. To stick the pan part 20 on the ball part 10 can prevent the ball part 10 before insertion into the first mold 40 be sprayed with a release agent such as Teflon. Beyond the layer thickness of the release agent beyond the play of the ball joint 10 ; 20 be adjusted, which should be just so small that a low-friction mobility is given.

After opening the first mold 40 can be the composite ball joint 10 ; 20 and first filling part 30 in 1 to the right from the main body 44 be ejected, with the sprue 42 at the break point 43 is separated. This is possible only because the said composite because of the first filling part 30 has no undercuts that could hinder the ejection movement. After the said composite from the first mold 40 has been removed, the first filling part 30 from the ball joint 10 ; 20 removed and used again for injection molding.

2 shows a rough schematic cross section of the second mold 60 with the second filling part 31 for the production of the ball part 10 , The second mold 60 again comprises a main part 64 with several shaping cavities 61 , which are arranged uniformly along a circle, wherein the thin liquid Duroplastmasse from the circle center ago via a star-shaped sprue 62 is supplied. In the area of the sprue 62 is again a pressure sensor 71 provided for determining the liquid pressure of the thermoset compound so that it can be filled under pressure control. The shaping cavity 61 will be on the sprue side 62 with a lock 65 sealed liquid-tight. The sprue 62 is on the ball 11 of the ball part 10 opposite side of the second mold 60 , so that the formation of the ball 11 through the inflow at the gate 62 not disturbed. The break point 63 at the transition to the ball part 10 is again designed with a small cross-sectional area, thus the ball part 10 easy from the sprue 62 can be separated.

In the main part 64 is a substantially circular cylindrical first slider 66 linearly guided, so that this in 2 to the right from the main body 64 can exit if the shutter 65 is open. At the first slider is one half of the ball 11 of the ball part 10 imaged without undercutting. The remainder of the ball 11 is on a separate second filling part 31 displayed. This will be on the first slide out 66 put on and from this in the main part 64 moved to the desired position. This is the second filling part 31 with a circular cylindrical holding recess 34 fitted to the first slider 66 is adjusted. The outer peripheral surface 35 of the second filling part 31 is circular cylindrical, so that the adapted counter-shape on the main body 64 is easy to produce.

Next is a second slider 67 provided within the first slider 66 linearly guided. The second slider 67 becomes as well as the first slider 66 hydraulically set in motion. It is mainly present for the thin needle 68 for mapping the hydraulic channel (no. 13 ; 1 ) is not damaged during injection molding. In particular, the second slider 67 last in the second mold 60 retracted, so that when placing the second filling part 31 on the first slide 66 not damaged. Next he is from the second mold 60 pulled out before the other moving parts of the first mold 60 be moved so that the demolding forces acting on the ball part 10 act, are low and this is not damaged. The needle 68 is preferably made of chrome steel or coated non-sticky so that it can be easily withdrawn.

The needle 68 on the second slider 67 is on both sides of the ball part with sealing standards 69 ; 70 sealed, so that there are no webbed. The sealing ring 69 prevents the penetration of low-viscosity thermoset between the first and the second slide 66 ; 67 , The second sealing ring 70 prevents the penetration of low-viscosity thermoset between the needle 68 and the closure 65 , The second sealing ring 70 also serves to support the bending forces when filling the low-viscosity thermosetting plastic mass on the needle 68 act. The second sealing ring 70 therefore extends over a correspondingly long length. The already mentioned pressure control during filling of the thermoset also takes place, so that just these bending forces are limited, so that the filigree needle 68 not damaged, especially bent.

After the thermoset in the preheated to about 170 ° C second mold 60 is cured, the composite of ball part 10 and second filling part 31 from the first slider 66 in 2 to the right from the main body 64 the second mold 60 ejected. This is only possible because the said composite because of the second filling part 31 has no undercuts that could hinder the ejection process. Subsequently, the second filling part 31 from the ball part 10 decreased. The annular second filling part 31 For this purpose, as well as the first filling part is provided with a radial slot and made of a flexible material. It is therefore during disassembly of the ball part 10 not damaged and can be reused several times for injection molding.

3 shows a perspective view of a filling part 30 ; 31 , 4 shows the same filling part 30 ; 31 in a perspective sectional view. The following explanations apply to both the first and the second filling part 30 ; 31 ,

The annular filling part 30 ; 31 extends with a constant cross-sectional shape over the circumference of the ring. On the inside of the ring it is partially with the negative mold 32 provided a ball. With regard to the cross-sectional shape of the filling part 30 ; 31 Incidentally, the comments on 1 and 2 directed.

The filling part 30 ; 31 is up to a radial slot 33 designed rotationally symmetrical. The slot 33 is just executed, wherein the slot plane contains the axis of symmetry. The filling part 30 ; 31 consists of a fluorine-based plastic, preferably perfluoroalkoxy copolymer (PFA). This material is thermoplastic and can be processed inexpensively by injection molding. The production of the filling part 30 ; 31 preferably takes place parallel to the production of the piston assembly or the ball joint, so that the filling parts 30 ; 31 only in small quantities must be stored. It should be noted that the required number of filling parts is substantially smaller than the number of ball joints, since the filling parts are used several times.

The named material of the filling part 30 ; 31 is so elastic that the filling part 30 ; 31 can be bent without damage to mount it on the ball part or to dismantle it. At the same time the cured thermoset does not adhere to the filling part 30 ; 31 , Next, the filling part 30 ; 31 easily withstand the temperatures of about 170 ° C in the first and second molds without being damaged.

It should also be pointed out that the duroplastic for the ball and the cup part can be provided with fillers such as carbon fiber, glass fibers or mineral to increase the strength and stability. Further, Teflon admixtures may be provided to improve the sliding and wear properties.

LIST OF REFERENCE NUMBERS

10

spherical part

11

Bullet

12

undercut

13

hydraulic channel

14

reduction

15

sliding surface

20

socket part

21

piston cavity

22

free cross section

30

first filling part

31

second filling part

32

Area with the negative shape of a sphere

33

slot

34

holding recess

35

Outer circumferential surface

40

first mold

41

shaping cavity

42

sprue

43

breaking point

44

Bulk

45

cylindrical recess

46

first closure

47

second closure

48

seal

49

pressure sensor

60

second mold

61

shaping cavity

62

sprue

63

breaking point

64

Bulk

65

shutter

66

first slide

67

second slider

68

needle

69

first sealing ring

70

second sealing ring

71

pressure sensor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004060945 A1 [0002]
• DE 2601345 C2 [0003]

Claims (16)

Method for producing a ball joint ( 10 ; 20 ) for the piston assembly of a hydrostatic piston engine, wherein the ball joint is a ball part ( 10 ) and a pan part ( 20 ), wherein the ball part ( 10 ) a ball ( 11 ), which has an undercut ( 12 ), wherein the pan part ( 20 ) to the ball ( 11 ), whereby it is in the undercut ( 12 ), the method comprising the steps of: - producing the ball part ( 10 ); - filling the undercut ( 12 ) of the ball part ( 10 ) with a separate first filling part ( 30 ), so that the undercut ( 12 ) the ball ( 11 ) is filled in areas; - inserting the composite of ball part ( 10 ) and first filling part ( 30 ) in a first mold ( 40 ), which the pan part ( 20 ) maps; Filling the first mold ( 40 ) with a liquid first plastic which is under pressure; - curing the first plastic; Demoulding the ball joint consisting of ball and socket part ( 10 . 20 ); - removing the first filling part ( 30 ) from the ball joint. A method according to claim 1, characterized in that the first plastic in the first mold of the ball part ( 10 ) opposite side, preferably pressure-controlled, is filled. Method according to one of the preceding claims, characterized in that the ball part ( 10 ) Span is lifting made of metal. Method according to one of the preceding claims, characterized in that the ball part ( 10 ) is produced by a process comprising the following steps: - inserting a separate second filling part ( 31 ), which the undercut ( 12 ) of the ball part ( 10 ) completely into a second mold ( 60 ), which the ball part ( 10 ) maps; - filling the second mold ( 60 ) with a liquid second plastic; which is under pressure; - curing the second plastic; - demolding the ball part ( 10 ). A method according to claim 4, characterized in that the second plastic in the second mold ( 60 ) of the second filling part ( 31 ) opposite side, preferably pressure-controlled, is filled. Method according to one of the preceding claims, characterized in that the first and / or the second filling part ( 30 ; 31 ) is integrally formed in the form of a ring with a slot extending in the radial direction, wherein it consists of flexible material. Method according to one of the preceding claims, characterized in that the first and / or the second filling part ( 30 ; 31 ) is reused several times. Method according to one of the preceding claims, characterized in that the first and / or the second filling part ( 30 ; 31 ) consists of a thermoplastic, fluorine-based plastic, preferably perfluoroalkoxy copolymer. Method according to one of the preceding claims, characterized in that the first and / or the second filling part ( 30 ; 31 ) is produced by injection molding. Method according to one of the preceding claims, characterized in that the first and / or the second plastic is a thermoset, preferably a bulk molding compound or a phenolic molding composition. Method according to one of the preceding claims, characterized in that the first and / or the second filling part ( 30 ; 31 ) at room temperature substantially free of play to the associated casting mold ( 40 ; 60 ), wherein it has a larger thermal expansion coefficient than the associated casting mold ( 40 ; 60 ), the casting mold ( 40 ; 60 ) is preheated with plastic prior to filling. Method according to one of the preceding claims, characterized in that the first and / or the second casting mold ( 40 ; 60 ) several shaping cavities ( 41 ; 61 ), preferably via a star-shaped sprue ( 42 ; 62 ) are interconnected. Method according to one of the preceding claims, characterized in that the finished ball joint ( 10 ; 20 ) is exposed for a predetermined time to an elevated temperature relative to room temperature. Piston assembly of a hydrostatic piston engine, comprising a piston and a sliding shoe, wherein optionally the piston or the sliding shoe as a ball part ( 10 ) with a ball ( 11 ), an undercut ( 12 ), wherein the other part than to the ball ( 11 ) adapted pan part ( 20 ), wherein it is in the undercut ( 12 ), characterized in that both the piston and the sliding shoe consist of a duoplast, preferably a bulk molding compound or phenolic molding compound, wherein the piston assembly according to a method according to claims 1, 2 or 4 to 12 can be produced. Filling part for use in a method according to one of claims 1 to 13, characterized in that the filling part ( 30 ; 31 ) is integrally formed in the form of a ring with a slot extending in the radial direction, wherein it is on the inside of the ring in sections with the negative mold ( 32 ) is provided with a ball, wherein it consists of an elastic material. Filling part according to claim 15, characterized in that the filling part ( 30 ; 31 ) consists of a thermoplastic, fluorine-based plastic, preferably perfluoroalkoxy copolymer.

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