DE102007008584B3 - Outer ring for hinge support, has inner lying gliding layer and outer lying carrier layer formed from wound fiber-reinforced composite, where joint exactly opens outer ring and is formed with radial cross-section tapered inwardly - Google Patents

Abstract

The ring (22) has an inner lying gliding layer (26) and an outer lying carrier layer (28) formed from wound fiber-reinforced composite. A joint exactly opens the outer ring and is formed with a radial cross-section tapered inwardly. The gliding and carrier layers are wound on a cylindrical roll shaft. The gliding layer includes plastic fiber as a reinforcing unit that contains polyester filaments and polytetrafluoroethylene particles. The gliding layer has a plastic matrix formed from synthetic resin and epoxy resin. An independent claim is also included for a method for manufacturing an outer ring for a hinge support.

Description

The The invention relates to an outer ring for a joint bearing or such a joint bearing, wherein the outer ring is an inner Slip layer and an outside lying support layer and wherein the sliding layer and the Support layer formed from a wound fiber composite material are. The invention further relates to a process for the preparation such an outer ring, at the successively a sliding layer and a supporting layer Soaked in synthetic resin Fibers wound on a winding mandrel and after curing the winding body thus produced outer rings be formed.

Such a method is for example from the DE 42 20 327 C1 known. In the method disclosed there for the production of spherical bearings, a winding core is used which consists of an alternating arrangement of molding rings for forming the cup-shaped inner profile of the outer ring and separating rings for forming the frontal surfaces. As a sliding layer material resin impregnated PTFE and / or high-strength fibers are proposed, which are wound on the winding core. After curing of the bobbin thus formed and outwardly circumferential removal of material, the outer rings and the separating rings can be removed individually from the shaft. The molding rings remain in this process after removal from the shaft in the outer ring and form the inner ring of the bearing. The disadvantage is that due to the production no bearing clearance can be adjusted and that the outer ring tightly surrounds the mold ring, respectively the inner ring. Such a bearing tends to wear out quickly.

Other methods in which the outer ring and inner ring are manufactured separately and subsequently joined together are well known. Here, one always faces the question of how the outer ring and the inner ring are to be joined together. The DE 84 00 958 U1 For example, proposes to make the outer ring of the radial spherical plain bearing so that it has on one end side axially directed resilient webs, which are deformed upon insertion of the bearing in a housing bore, so that a part of the outer ring with bias to the surface of the previously put inserted, mounted therein ball pivot. Again, there is the disadvantage that the bearing clearance can be set inaccurate in this way. Furthermore, the bearing capacity of the bearing is not restricted due to the circumferentially isolated, elastic webs.

From the WO 89/02542 A1 an outer ring of two nested and / or welded sheet metal pots is known, between which the inner ring is trapped. In this case, the cavity enclosed between the sheet metal cups of the outer ring and the inner ring is subsequently filled with plastic. Similar to the DE 42 20 327 C1 can be adjusted here also no bearing clearance. The manufacturing process is also expensive and the manufacturing accuracy low.

The DE 20 2004 013 251 U1 and the DE 10 2004 041 084 A1 propose an outer ring composed of two rings to solve the problem. The two rings are made according to the DE 20 2004 013 251 U1 frontally connected by means of welding or solder connection cohesively. As material for the outer ring either metal or ceramic is proposed. In the case of DE 10 2004 041 084 A1 the rings of the split outer ring are fixed radially and axially by means of a wound housing. As a material for the housing, inter alia, a fiber composite material is proposed.

A further education from the DE 42 20 327 C1 known method is from the DE 295 12 317 U1 known. Here, the winding core is developed to the effect that the separating rings each have two opposite, axially directed projections. These projections form the mold for insertion in the molded outer rings, which are dimensioned so that the mold ring can be removed under rotation from the cured outer ring and then the actual inner ring can be inserted. Although it is possible in this way to adjust the bearing clearance individually. However, this method has the disadvantage that due to the insertion of the load cross-section of the outer ring is reduced. In addition, the grooves form transverse edges to the running direction, which can cause a lubricant film break and thus insufficient bearing lubrication. Finally, the risk of contamination is increased here.

The DE 20 2005 005 829 U1 treated injection molded bearing housing or bearing body made of plastic, in which the bearing body or the bearing housing are used immediately as a form for the respective counter-rotor. Similar to the case of DE 42 20 327 C1 this results in the disadvantage that in this method no bearing clearance can be adjusted.

The DE 35 24 761 A1 Takes another path by proposing a blasted at one point outer ring on the inner surface with the aid of a tool ring as a casting mold a slide bearing is poured. To remove the tool ring and then insert the inner ring of the outer ring is pulled apart at the parting line and thus bent.

Metallic outer rings for spherical plain bearings, wel che have an axial parting line, are also from the documents GB 1 107 880 A . GB 1 238 302 A and GB 1 346 321 A known. The parting lines of the metallic outer rings are produced due to the fact that the outer rings are bent from prefabricated boards in a bending tools around the inner ring around.

All The aforementioned methods either have the disadvantage that the Do not store with sufficient accuracy and therefore with insufficient Properties can be produced or that the manufacturing process usually several consecutive process steps and processing Different materials require what the manufacturing process Tedious and expensive design and can limit the shelf life of the camp.

The The object of the present invention is to overcome said disadvantages.

The Task is through an outer ring according to claim 1, a spherical plain bearing according to claim 9 and by a method according to claim 12 solved.

The According to the invention, opening the outer ring Parting line is not used differently than in the known prior art demolding a tool or molding ring, but only for assembly, d. H. for later Inserting an inner ring. Compared to the known outer rings with cast sliding layer, is the sliding layer of the outer ring according to the invention with a reinforcing element provided and has a better adhesion to the support layer on what together for an improved stability of the warehouse. In accordance with the invention you look at the elasticity and the production-related material tension of the wound fiber composite material advantage. Because you have found that produced by winding technology bearing rings a big enough, circumferentially acting residual stress, which ensures that the parting line closes again by itself.

at the method according to the invention can the sliding layer and the support layer therefore in a simple manner are wound on a cylindrical winding mandrel. This can done by adding the slip layer either from a single thread or a single fiber, a bundle of filaments or fibers, or a single fiber prefabricated woven or knitted fabric (Pre-Preg) wrapped or around the Winding mandrel is placed. The tubular wound body thus produced with Circular cross section becomes after curing demolded the plastic matrix. One of them, for example, by sawing isolated cylindrical outer ring will open with exactly this one Parting line provided, which due to the residual stress of the wound Ring material closes. The parting line runs preferably in the axial direction and more preferably in one Plane that encloses the cylinder axis of the ring, so that the elastic force is perpendicular to the two frontal cut surfaces and leads to no relative displacement of the open ring ends. In an alternative embodiment extends the parting line in a zigzag pattern or irregular.

Of the Cross-section of the ring is after closing the parting line, if this has a finite cutting width, although no longer ideal circular. This but is not disadvantageous, since it according to the invention at least on the inside is reworked. There is sliding layer material from the ring is removed, so that the sliding layer has a part-spherical inner contour for receiving an inner ring with spherical segment-shaped surface desired dimension receives. In this way, the required bearing clearance is set at the same time. Due to the closed parting line and the exact reworking is ensured that the sliding surface a maximum support cross section over the entire scope receives.

In usually the outer ring also on its outside be reworked. This is the ratio of ring circumference to cutting width of Suspend parting line.

The Sliding layer of the outer ring points as a reinforcing element According to the invention a Plastic thread with polyester filaments and with incorporated PTFE particles on. In a corresponding manner, the inventive method further training.

Becomes the sliding layer directly or indirectly from a plastic thread wound with polyester filaments and with incorporated PTFE particles - indirectly or directly in the above sense, that the overlay either a single plastic thread, a bunch of Plastic threads or one of plastic threads formed knitted fabric or fabric - results in a clear improved reworkability in comparison with known fiber composites.

As a solid lubricant self-lubricating sliding layers of the use of PTFE (polytetrafluoroethylene) or graphite is indeed known. These substances are mixed either in particle form of the plastic matrix or in the case of PTFE in the form of a filament together with other plastic filaments to the plastic thread of the sliding layer twisted. As a synthetic thread, polyester is known to be mostly used polyester. Typically, two polyesters and a PTFE filament are combined to form a thread zwirnt.

however could not yet for All applications satisfactory tribological and mechanical Properties are achieved. PTFE is due to the strong intermolecular bonding of the carbon and fluorine atoms very much slow to react and has a very low surface tension. A chemical reaction of the plastic matrix with the PTFE takes place therefore not or not appreciably held. Especially when using the known plastic threads two polyester and one PTFE filament were found that the PTFE filaments only a very low adhesion to the Reached plastic matrix. This has the consequence that the known Sliding layers are difficult or almost not mechanically reworked could, because the PTFE filaments not infrequently from the fiber composite leached were. The consequence was usually a delamination of the overlay, a deterioration of the tribological properties and the wear resistance the sliding layer.

This Problem is with a sliding layer based on the plastic thread according to the invention with Polyester filaments and incorporated therein, in particular dissolved PTFE particles dissolved. This thread has opposite the known twisted fibers also have the advantage of a greater variability of the content the individual components of the thread or the fiber, in particular its PTFE content. Therefore, can already be in the production of plastic thread modify its properties much more precisely. From the Circumstance that the PTFE particles in contrast to the PTFE filament not related, d. H. by randomly disposed within the polyester filaments and anchored PTFE particles the plastic thread appears roughened and it becomes a better one Adhesive bond between the plastic thread and the plastic matrix reached. After all reinforced the integration of the PTFE particles in the plastic thread the mechanical Maintain the same mainly by form-fitting.

The Slip layer leaves therefore mechanically, d. H. Machining well. The Use of the plastic thread with PTFE particles in the sliding layer is therefore particularly suitable for outer rings according to the invention, in which only later Sliding layer material on the inside of the bobbin removed becomes. In addition to better workability are improved by the Incorporation of PTFE particles also improved wear values, achieved in particular with regard to the depth wear.

Also across from the known sliding layers with PTFE particles as a solid lubricant in the plastic matrix has such a sliding layer according to the invention Advantages. Also acts as a solid lubricant in the plastic matrix namely PTFE strength-reducing, thereby reducing the tribological properties at high load and in aqueous Environment impaired be and while the PTFE particles in the plastic matrix due to different material density mostly assume an inhomogeneous distribution, is the distribution of the particles over the entire sliding surface Seen very homogeneously, as the particles stuck in the fiber / thread are integrated, which extends through the entire thickness of the sliding layer extends. Due to improved homogeneity and improved mechanical Integration will eventually be also achieved improved tribological properties. this applies both for dry running and for use in an aqueous environment.

It has proven to be advantageous when the weight fraction the PTFE particles in the plastic thread between 2 wt .-% and 60 wt .-% and the proportion by weight of the polyester filaments in the plastic thread between 40 wt .-% and 98 wt .-% is. At a higher proportion With PTFE particles, the binding of the particles to the fibers becomes worse and the load capacity of the sliding layer decreases. Especially preferred is the proportion by weight of the PTFE particles in the plastic thread between 2 wt .-% and 40 wt .-%, of the polyester filaments between 60 wt .-% and 98 wt .-% and most preferably the weight fraction of the PTFE particles between 30% by weight and 36% by weight, while the weight percentage of Polyester filaments in the plastic thread between 64 wt .-% and 70 Wt .-% is. In this composition range is the ratio of durability and the tribological properties of the sliding layer for most eligible Sliding partner optimally adjusted.

In this weight ratio the adhesion between the plastic thread and the plastic matrix remains sufficiently high so that good machinability is achieved. On the other hand, the proportion of PTFE particles is sufficiently high to achieve a good sliding property.

As previously noted, the reinforcing element of the fiber composite material the structure of a fabric produced from the plastic thread or Have knitted or the simple winding structure of a single Thread or more parallel or bundled threads, which by winding on a winding core is typically generated.

In this case, the advantages of the plastic thread used according to the invention are particularly effective. Because of its roughness in fact, it is excellently suitable for the production of sliding layers in the winding process, in which the yarn is first passed through a drinking trough with synthetic resin and thereby sufficiently soaked in by the synthetic resin. The winding method has the advantage that it can be used to produce a specific winding structure which is matched to the intended application of the sliding element or the sliding layer. Thus, the fibers can be positioned as stress-resistant as possible, ie the force and stress distribution in the fiber composite.

The sliding layer preferably has a plastic matrix of synthetic resin and particularly preferably of epoxy resin, as for example from DE 23 41 333 A1 is known.

For some applications, PTFE particles are preferably also added to the plastic matrix in addition to the PTFE particles spun in the plastic thread. This measure for improving the sliding properties, for example, from the DE 23 41 333 A1 known. The proportion of PTFE particles in the plastic matrix is at most 40 wt .-%.

alternative For example, the plastic matrix may contain graphite particles. The weight fraction the graphite particle in the plastic matrix is preferably between 1% by weight and 40% by weight.

It can Furthermore, both PTFE particles and graphite particles to the plastic matrix are added, their total weight fraction preferably not more than 40 wt .-% is.

As Also, the sliding layer, so the base layer is made of a wound Fiber composite formed. The fiber-reinforced plastic The support layer is advantageously made of a plastic matrix with a glass fiber as reinforcing element, wherein the plastic matrix is preferably made of a synthetic resin, especially preferably also consists of epoxy resin.

As for the Plastic matrix of the sliding layer is also suitable as epoxy resin Plastic matrix for the Base layer due to excellent adhesion properties, mechanical and dynamic properties.

epoxy resin also has a very good molecular structure moisture resistance and comparatively little tendency to swell. Due to the use the same plastic matrix in the sliding layer and the support layer increase In addition, the binding forces between the sliding layer and the supporting layer. Also the reinforcing element the support layer preferably has the structure of one of the glass fiber produced fabric or knitted fabric wound around a winding core, or in another preferred embodiment, a winding structure on, by winding the glass fiber or a glass fiber bundle on a winding mandrel is generated.

Become the sliding layer and the support layer successively in the winding process deposited on a mandrel, this increases the efficiency of production of the bearing composite material.

Especially Preferably, the parting line is wedge-shaped with a radially inwardly tapering cross-section educated.

in this connection For example, the section with which the parting line is created is selected so that the two frontal cut surfaces after closing the parting line entire area abut each other. The wedge angle of the kerf cut must be thus an angular segment of the circle formed by the outer ring correspond.

The Parting line can by means of form cutter, sawblade and the like. Or by water jet cutting or laser beam cutting be generated. Due to the large internal workpiece clamping was the water jet cutting as procedurally preferred found out. In addition, no tool wear occurs in this method, which is straight in composite materials can lead to short tool life. The joints produced in this way all have a "finite width of cut." A parting line without cutting width and thus without affecting the circular shape of the ring can also be generated in a known manner by fracture separation or the so-called "cracking".

Further The object, features and advantages of the invention will become apparent below based on embodiments explained with the help of the drawings. It demonstrate:

1 a cross section through the plastic thread used in the sliding layer according to the invention;

2a , b is a perspective view of the hinge bearing according to the invention, for the sake of illustration in partial section and in full representation;

3a , b are two diagrams of the coefficient of friction of a radial plain bearing according to the invention under different loads in dry running;

4a , b two diagrams of the coefficient of friction of a radial plain bearing according to the invention under different loads in wet running and

5 a cross section through the joint bearing according to the invention.

The inventively used for the sliding layer of the outer ring as a reinforcing element plastic thread 10 is in enlarged sectional view in 1 shown. This consists of along the thread oriented polyester filaments 12 and contains as a second component PTFE particles 14 , which in a random arrangement in the polyester filaments 12 are spun. In the manufacturing process, there are many possibilities to modify the properties of the thread. For example, the number of polyester filaments 12 per thread 10 be varied depending on the application. However, it should be on sufficient positive engagement with the incorporated PTFE particles 14 be respected.

Likewise, the weight ratio between the polyester filaments 12 and the PTFE particles 14 be varied. However, it has been found to be particularly preferred with regard to adhesion, friction and sliding property when the proportion by weight of the PTFE particles in the plastic thread 14 between 30% by weight and 36% by weight and the proportion by weight of the polyester filaments 12 between 64% by weight and 70% by weight.

The titer of the plastic thread 10 according to 1 has a preferred value between 100 dtex and 600 dtex, in particular between 400 dtex and 550 dtex (1 dtex = 1 g / 1000 m yarn).

These parameters result in a sufficiently strong integration of the PTFE particles 14 in the polyester filaments 12 achieved, which find sufficient support both in favor of wear resistance and for mechanical processing. Therefore, the sliding layer retains its good tribological properties, even if it is reworked, for example by milling grooves or by drilling.

The PTFE particles 14 are further distributed homogeneously over the thread length and thus over the entire woven, knitted or wound structure of the reinforcing element. The string 10 can be due to the partially loose composite, which forms a variety of channels, excellent wet and thus easy to process. The networking of the matrix penetrating into the depths of the channels ensures improved adhesive bonding.

Overall, the plastic thread appears 10 as well as the finished sliding layer roughened or fibrous. This optical roughness is due to the randomly oriented PTFE particles 14 attributed and due to their sliding property not associated with an increased coefficient of friction. Overall, the sliding property of the sliding layer according to the invention in various applications even over a long period of use is consistently good, as in connection with the diagrams according to 3 and 4 becomes recognizable.

2a . 2 B and 5 show the joint bearing according to the invention 20 in different views. It consists of an outer ring 22 that has an inner ring 24 encloses, that is positively and captively surrounds. The outer ring 22 has on its inside a sliding layer 26 and on its outside a base course 28 on.

Both layers 26 . 28 have been successively deposited in a winding process on a mandrel, whereby a typical winding structure is formed. Winding represents a particularly simple and cost-effective production method for rotationally symmetrical sliding elements. The structures of both layers can be individually adapted to the mechanical requirements of the bearing in a simple manner. In addition to simple cross structures of individually deposited threads, the threads can also be grouped into bundles, which allows the corresponding layer to be wound faster. The sliding layer and the supporting layer can also be produced in different methods.

While in the sliding layer 26 and the base layer 28 different reinforcing elements, namely the in 1 shown plastic thread on the one hand or glass fibers in the support layer 28 On the other hand, the plastic matrix in both layers is preferably the same, namely epoxy resin. This is very well suited because of its excellent adhesion and mechanical properties. Alternatively, however, it is also possible, for example, to use unsaturated polyester resins or vinyl ester resins.

For the base course 28 In addition to the proven glass fibers, for example, carbon fibers as reinforcing elements into consideration. Also, the thread can first be pre-processed to a fabric, knitted fabric or other scrim.

The plastic matrix of the sliding layer 26 In many applications solid lubricants such as graphite particles or PTFE particles are added. The base course 28 on the other hand, usually has a plastic matrix without admixture of additional constituents.

The sliding layer 26 has on its side facing inward on a spherical surface profile, which is complementary to the spherical segment that of the inner ring 24 is formed. This Surface profile becomes after curing of the finished bobbin, separating a ring and separating the ring along the parting line 30 produced by drilling or turning. In this case, a very high accuracy is achieved due to the properties of the thread according to the invention described above as a reinforcing element and thereby does not affect the tribological properties of the sliding layer. In particular, the desired bearing clearance can be set very accurately in this way. The sliding layer 26 is due to the profile in the vertex area 27 radially thinner than the support layer 28 , Therefore, the geometry of the hinge bearing already has to be wrapped 20 taken into account and a sufficiently thick overlay 26 be applied.

The inner ring 24 is then in the finished outer ring 22 used, the latter in the region of the parting line 30 is spread. The spreading can be done by pressing in the inner ring 24 or supporting by pulling up the outer ring 22 happen. The outer ring then snaps elastically together due to its internal stress and fixes the inner ring captive. The parting line 30 closes.

The inner ring 24 As usual, has a greater axial length than the outer ring 22 so that when both rings are aligned coaxially, it protrudes symmetrically from both sides. The inner ring 24 also has a central through hole as usual 32 for receiving a shaft to be stored.

The 3a , b show the behavior of the coefficient of friction between a radial plain bearing bush according to the invention and a steel shaft mounted therein, which was determined in a test run in dry running. Here, the shaft with a roughness of R _a = 0.4 to 0.8 was rotated back and forth by an angle of 45 ° and with a peripheral speed of 0.01 m / s. The radially applied specific load in the case of the upper measurement curve was 25 MPa ( 3a ). In the case of the lower trace ( 3b ) a radial specific load of 50 MPa was applied under otherwise identical conditions.

The Results show that after a short break-in period of about 2000 cycles, a minimum coefficient of friction was reached, which in the case of the higher Load over the total test duration of 60000 cycles is approximately constant at 0.05 was. In the case of lower load, the friction coefficient increased after reaching the minimum first slowly from about 0.06, reaching a duration of about 15,000 Cycles but a saturation at about 0.1. The slightly increased Coefficient of friction in the case of lower load is consistent with the wear rate. This was at 25 MPa at a value of 5.1 microns / km (sliding), while he in the case of the higher Load of 50 MPa reached a value of 10.7 μm / km. Through the total increased Wear at greater load of 35 μm compared to 17.5 μm at lower Load is released more solid lubricant, the coefficient of friction lowers. Therefore, especially in the case of higher load also a significant Smoothing the pressurized sliding bearing surface be determined.

The 4a and 4b show the behavior of the coefficient of friction of the mounted in a radial plain bearing bush shaft under wet running conditions, ie in the water. The test conditions were otherwise the same as above. Here, too, it can be seen that the coefficient of friction in the case of the higher load of 50 MPa, lower diagram in 4b , lower than in the case of the low load of 25 MPa, upper diagram 4b , The coefficient of friction reached approximately the same value of 0.1 after a somewhat extended run-in phase compared to dry running at 25 MPa. At 50 MPa, a slightly higher average value of 0.06 compared to dry running was determined. Again, a lower wear rate at 25 MPa of 8.1 microns / km and thus over the entire test period of about 47000 cycles lower wear of 21.25 microns was compared to 27.2 microns / km and 70 microns at 50 MPa detectable. Again, especially in the case of higher load a significant smoothing of the pressurized plain bearing surface could be determined.

In both load cases but was no significant replacement the sliding layer recognizable. The wear values were significantly lower those of the known plastic sliding elements.

The The above results and conclusions can be found on the transferred spherical plain bearings according to the invention, if as sliding partner for the outer ring made of fiber composite material with the PTFE particles containing fiber an inner ring of steel or at least with a steel surface, preferably made of a steel with a surface hardness> 120 HB and especially preferably with a surface hardness> 180 HB is selected. Alternatively, pairings also come from the fiber composite material according to the invention with an inner ring made of ceramic or a metal-ceramic material in question.

10

Synthetic thread

12

polyester filament

14

PTFE particles

20

Spherical Plain bearings

22

outer ring

24

inner ring

26

Overlay

28

base course

30

parting line

32

drilling

Claims (15)

Outer ring for a spherical plain bearing with an inner sliding layer and an outer support layer, wherein the sliding layer and the support layer are formed from a wound fiber composite material, characterized in that the outer ring has exactly this outer ring opening parting line and that the sliding layer contains a plastic thread as a reinforcing element having polyester filaments and incorporated PTFE particles. outer ring according to claim 1, characterized in that the PTFE particles are spun into the polyester filaments. outer ring according to claim 1 or 2, characterized in that in the plastic thread the proportion of PTFE particles between 2 wt .-% and 60 wt .-% and the proportion of polyester filaments between 40% by weight and 98% by weight is. outer ring according to claim 3, characterized in that in the plastic thread the proportion of PTFE particles between 30 wt .-% and 36 wt .-% and the proportion of polyester filaments between 64% by weight and 70% by weight is. outer ring according to one of the preceding claims, characterized in that the sliding layer comprises a plastic matrix of synthetic resin. outer ring according to claim 5, characterized in that the plastic matrix made of epoxy resin. outer ring according to claim 5 or 6, characterized in that the plastic matrix PTFE particles contains. outer ring according to one of the preceding claims, characterized that the parting line is wedge-shaped formed with a radially inwardly tapering cross-section is. Spherical bearing with an outer ring according to one of the preceding claims and with an inner ring. Spherical bearing according to claim 9, characterized that the inner ring has a steel surface with a surface hardness greater than 120 HB. Spherical bearing according to claim 10, characterized that the inner ring has a steel surface with a surface hardness greater than 180 HB. Method for producing an outer ring for a spherical plain bearing, at the successively a sliding layer and a supporting layer impregnated with synthetic resin Fibers wound on a winding mandrel and after curing the winding body thus produced outer rings be formed, characterized in that the sliding layer and Supporting layer are wound on a cylindrical winding mandrel, the outer ring with exactly this opening parting line provided and sliding layer material on the inside of the shape is removed that a part-spherical contour for recording a complementary one Inner ring is obtained. Method according to claim 12, characterized in that that the sliding layer directly or indirectly from a plastic thread wrapped with polyester filaments and with incorporated PTFE particles becomes. Method according to claim 12 or 13, characterized that the parting line with a wedge-shaped, radially inward tapered cross-section is produced. Method according to one of claims 12 to 14, characterized that the parting line is produced by means of water jet cutting.