DE102022121689A1 - Conductive self-lubricating sliding element - Google Patents

Abstract

The invention relates to a sliding element with a metallic carrier material and a sliding layer applied thereon based on PTFE or thermoplastic, the sliding layer forming an interface to the carrier material and a sliding surface for contact with a counter-rotor. The sliding element is characterized in that the sliding layer contains conductive particles, each of which extends individually within the sliding layer at least from the interface to the sliding surface.

Description

The invention relates to a self-lubricating sliding element with a metallic carrier material and a sliding layer applied thereon based on PTFE or thermoplastic, in particular for lubricant-free but also for lubricated applications, the sliding layer having an interface with the carrier material and a free sliding surface for contact with a counter-rotor trains.

The typical structure of composite materials for self-lubricating sliding elements consists of a carrier material that is coated and/or impregnated with a plastic or a plastic compound in order to create the sliding properties. The carrier material is metallic and consists of a support material such as a metal strip, e.g. steel, copper, aluminum or their alloys, which is usually coated with a porous metal layer, e.g. made of bronze powder, or itself has a porous structure, such as fabric or expanded metal. Also worth mentioning are material combinations in which the fabric or expanded metal is connected to the support material.

While these metallic components are electrically conductive, conductivity is not present in the usual plastic layers applied thereon as a sliding layer with the tribologically effective additives. PTFE, PPS, POM, PVDF, PFA, PEEK are particularly common as plastic matrix, and various polyamides, polyesters, PES, PAI and others are also used. The way it works can be roughly divided into composite materials in which there is only a thin inlet layer over the metallic carrier material, so that metallic components are exposed after the inlet and create contact with the shaft and thus the conductivity. This is the case with many PTFE based coatings, such as the DE 102013227187 B4 described the case.

Very thin-walled materials with PTFE-based coatings are often used in hinges, which are calibrated without play during assembly by using pins that are oversized compared to the bearing bush bore. These materials can have a structure consisting of carrier material, porous bearing metal and the plastic coating, but materials that are produced by coating and impregnating metal fabrics or expanded metals are also often used, as in the DE 10147292 B4 described. In the latter case, the PTFE-based coating should be so wear-resistant that the carrier material is not exposed over the entire service life, otherwise, due to the equalizing coefficients of friction on the sliding surface and bearing back, a tight fit is no longer guaranteed and the bearing can, for example, migrate out of the housing . In most thermoplastic-based composite materials, such as in the EP 3087142 B1 described, no carrier material is exposed over its service life.

However, there is increasing interest in self-lubricating bearing elements that prevent static charges on the components connected to the bearing elements or, in the case of electrostatic painting, ensure an electrical connection even after components connected via these bearings have been assembled. With such requirements it is necessary that the sliding layer has sufficient conductivity right from the start. The conductivity of the bearings then saves the need to attach additional contacts to the components.

Common additives in PTFE include MoS ₂ , hBN, ZnS, BaSO ₄ , CaF ₂ , Fe ₂ O ₃ , graphite, carbon black, as well as other plastics such as PFA, FEP, ETFE, PEEK, PPS, PAI, polyaramides, aromatic polyesters, hard materials such as glass, Si ₃ N ₄ , SiC, and also carbon fibers. The use of fine lead powder was common, but is becoming increasingly less important due to regulations regarding the toxicity of lead. If thermoplastics form the matrix, PTFE is often added to them, but also portions of the other additives already mentioned.

Of these common additives, graphite, carbon black and carbon fibers are conductive, but their proportion is usually not sufficient to produce conductivity. The use of carbon nanotubes has also been suggested in connection with plain bearings, for example in EP 2804902 B1 , although not to increase conductivity but to improve tribological properties.

Increasing the proportion of common conductive additives such as carbon fibers, graphite, soot, such as in the EP 1875091 B1 described, or the use of fine metal powders until a percolation leading to conductivity is achieved is possible, but leads to a severe impairment of the resilience and wear resistance of the materials as well as an impairment of the processing properties in the usual processes for PTFE dispersion-based, powder-based coil coating or foil base. Nanotubes Although they enable conductivity at lower concentrations, they are comparatively expensive and more difficult to handle.

In the EP 2069651 B1 It was also proposed to remove the top layer of the materials until the substrate material is exposed in order to increase the thermal and therefore also the electrical conductivity. Although this would create conductivity, with conventional PTFE-based materials on porous bronze it has the disadvantage that the initial formation of the transfer layer, which is important for the sliding process, is more difficult, while with thermoplastic-based materials the composition of the surface created by this measure is no longer lubricable enough is. In the case of thin materials with a fabric or expanded metal structure without a carrier material, this would jeopardize the tight fit and thus the general function right from the start due to the same friction on the sliding side and back.

The task is therefore to provide a self-lubricating sliding element that, on the one hand, has the tribological properties required in particular for lubricant-free applications and, at the same time, improved conductivity.

The task is solved by a sliding element with the features of claim 1.

The sliding element according to the invention has a metallic carrier material and a sliding layer applied thereon based on PTFE or thermoplastic, the sliding layer forming an interface to the carrier material and a free sliding surface for contact with a counter-rotor. It is characterized in that the sliding coating contains conductive particles, each of which extends individually within the sliding layer at least from the interface to the sliding surface in order to establish an electrical connection between the carrier material and the sliding surface.

The interface between the sliding layer and the carrier material can be identified in a section (micrograph) through the sliding element using the usual optical aids (light or electron microscope) in a manner familiar to those skilled in the art. The distance between the interface and the sliding surface is called the thickness of the sliding layer.

The conductive particles penetrate the entire sliding layer and establish the electrical contact between the bearing housing via the metallic carrier material and the counter-rotor resting on the sliding surface, right from the start and not only after part of the sliding layer has been removed. This requires that the conductive particles have a size that at least corresponds to the thickness of the sliding layer. Unlike the known conductive fillers, the conductivity of the layer is not primarily dependent on the amount of filler and the associated statistical distribution of the particles. The individual conductive particles create point-by-point electrical contacts along or in the sliding surface, which reliably establish the conductive connection between the connected components and at the same time do not affect the tribological properties and manufacturability of the material as well as the tight fit of the sliding elements.

Sliding elements are understood here to mean, in particular, radial bearing elements or flat sliding elements, such as plain bearing bushes, thrust washers, collar bushings, bearing shells or sliding or guide elements of other geometries.

The conductive particles consist, for example, of metallic or conductive non-metallic materials. For example, coarse graphite or graphite short fibers can be used as non-metallic materials. Metallic materials such as copper or aluminum or alloys thereof are preferred, in particular bearing alloys made of copper-tin, copper-tin-zinc, copper-zinc, copper-aluminum, copper-nickel-silicon, copper-tin-bismuth, aluminum-tin, aluminum -Tin-silicon, aluminum-tin-copper, aluminum-tin-nickel-manganese-copper, if necessary with further alloy additives and/or unavoidable impurities.

For example, so-called bronze and aluminum chips, elongated, twisted particles, produced as turning or milling chips of the corresponding materials, bronze short fibers, as well as spherical and spattered bronze particles can be used as conductive particles, depending on which particle sizes are required or are readily available or more cost-effective are. Aluminum particles are particularly preferred for the sliding layers that are created by coating with powders, as they are less prone to segregation compared to bronze particles, for example, due to their density being more similar to plastic.

The size of the conductive particles should preferably be chosen so that the d50 value of the smallest dimension of the conductive particles is at least 90% of the layer thickness of the sliding layer and the d90 value of the smallest dimension of the particles is not greater than 300%, preferably not greater than 150 %, the layer thickness of the sliding layer.

The “smallest dimension” is understood to be the shortest edge length of the smallest possible cuboid enveloping the particle. For example, in the case of ideally cylindrical fiber sections with a length greater than the diameter, the smallest dimension would correspond to the fiber diameter. Particles can be isolated from a geometrically statistical particle distribution by sieving through longitudinal gaps, for example using a harp sieve with straight longitudinal wires.

The d50 value refers to the value of the statistical size distribution that 50% of the particles fall below or exceed. The d90 value is the value of the statistical size distribution that 90% of the particles fall below or exceed by 10%.

The sliding layer thickness is understood to mean the distance between the highest points of the metallic carrier material, i.e. the interface, and the outer surface of the plastic-based sliding layer, i.e. the sliding surface. To determine the thickness of the sliding layer, the highest elevations of the boundary and sliding surfaces can be used in a section through a sliding element over a visible length of > 1 mm. In practice, the layer thickness can be determined as the difference value of the thickness of the sliding element minus the layer thickness of the metallic carrier material, which can each be measured in a simple manner, for example using a micrometer screw. The layer thickness of the sliding layer is preferably 5 µm to 500 µm and particularly preferably 5 µm to 100 µm.

The fact that the d50 value of the smallest dimension of the conductive particles is at least 90% of the layer thickness of the sliding layer ensures that there are sufficient particles that penetrate the entire sliding layer and enable contact between the mating pin and the carrier material. The fact that the d90 value of the smallest dimension of the conductive particles is not greater than 300%, depending on the porosity of the metallic carrier material at the interface, preferably not greater than 150%, of the layer thickness of the sliding layer ensures that the particles at Coating, for example by rolling, can be pressed into the substrate or plastically deformed in such a way that no disruptive surface roughness occurs.

The use of the conductive particles according to the invention is possible in all embodiments of the generic self-lubricating sliding elements described in the prior art and is particularly advantageous in all applications in which the substrate material is not exposed during the service life. This applies in particular to medium-thick and thick sliding layers, which - as an alternative to the conductive particles used according to the invention - would otherwise be particularly impaired in their tribological stability by larger proportions of finely divided conductive additives. Thick layers are understood to mean layers of 120 µm or more, and thin layers are those between 5 µm and 50 µm. The former are based predominantly on thermal loads, the latter on PTFE. Layers with thicknesses of 50 to 120 µm are referred to as medium-thick layers and can be based on both PTFE and thermoplastic. In principle, the particles according to the invention are also useful for such thin layers if conductivity is required before the substrate is exposed, for example in hinges before painting in the assembled state or if static charges must be avoided regardless of the running-in state. For use in hinges for movable components, for example, sliding elements made of thin-walled materials without a support layer are interesting, in which the metallic carrier material consists exclusively of, for example, steel or bronze expanded metal or steel or bronze mesh and a medium-thick PTFE-based sliding layer of over 50 µm is used comes.

It is advantageous to add particles of 0.1 - 1.2% by volume and particularly preferably 0.2 - 0.9% by volume based on the volume of the sliding layer, i.e. without the metallic carrier material.

This makes it possible to ensure a preferred average density of 1 cm ^-2 to 10 cm ^-2 for the contacts produced by the conductive particles along the sliding surface.

While the thinner layers usually have a PTFE matrix and are made from a dispersion by mixing with the additives and precipitation, thick layers are often based on thermoplastic-based powder mixtures or compound films. Medium thickness layers can have both a PTFE matrix and a thermoplastic base. The conductive particles can be added in all manufacturing processes, but the dispersion-based process is particularly suitable, as density-related segregation can be effectively counteracted by vigorous stirring during precipitation or a late addition during solidification of the coating composition. In the further course of production, segregation is hindered by the incorporation into the highly viscous coagulate.

Furthermore, the volume of the sliding layer preferably consists predominantly of PTFE, i.e. the proportion of PTFE based on the entire sliding layer is more than 50% by volume.

Further additives can be the known additives mentioned at the beginning, such as MoS ₂ , hBN, ZnS, BaSO ₄ , CaF ₂ , Fe ₂ O ₃ , graphite, carbon black, as well as other plastics such as PFA, FEP, ETFE, PEEK, PPS, PAI, Polyaramides, aromatic polyesters, hard materials such as glass, Si ₃ N ₄ , SiC, or carbon fibers.

The metallic carrier material is preferably formed from a single support metal layer or a layer composite with a support metal layer and a bearing metal layer. The sliding element therefore preferably represents a three-layer system or a two-layer system.

The support metal layer or the bearing metal layer is preferably porous, at least near the interface. Regardless of the number of layers, the porous support metal layer or the bearing metal layer serves as an anchor for the sliding layer material, which is, so to speak, impregnated into the porous surface. The support metal layer or the bearing metal layer does not have to be designed to be porous throughout, but can also be designed.

In a preferred variant of the three-layer system, the metallic carrier material consists of steel with sintered bronze.

In a preferred variant of the two-layer system, the metallic carrier material is formed exclusively from a single support metal layer made of steel, a copper alloy or an aluminum alloy.

The metallic carrier material particularly preferably consists exclusively of a metallic fabric or expanded metal made of steel, copper or aluminum or their alloys.

Sintered material as well as fabric or expanded metal are subsumed here under the porous support metal or bearing metal layers.

Conductivity is of particular importance in hinges, for which thin-walled materials are often used, which can be calibrated without play during assembly by using pins that are oversized compared to the bearing bush bore. These materials can have a structure consisting of carrier material, porous bearing metal and the plastic coating, but said carrier material made of metal mesh or expanded metal is often used, which is coated and/or impregnated with the sliding layer material.

According to a particularly preferred embodiment, a PTFE-based sliding layer is applied to such a metallic fabric or expanded metal made of steel, copper or aluminum or their alloys.

The sliding elements according to the invention are used in particular as hinges for lubricant-free joint connections, such as for trunk lids or the like. Since the sliding layer has sufficient conductivity for electrical contacting of the components connected to the sliding elements, unwanted electrostatic charging of the components is avoided from the start and electrical contacting is provided, for example for the purpose of painting.

• 1 eine schematische Schnittdarstellung durch eine erste Ausführungsform eines erfindungsgemäßen 3-Schicht-Gleitelements;
• 2 eine schematische Schnittdarstellung durch eine zweite Ausführungsform eines erfindungsgemäßen 3-Schicht-Gleitelements;
• 3 eine schematische Schnittdarstellung durch eine erste Ausführungsform eines erfindungsgemäßen 2-Schicht-Gleitelements mit Metallgewebe;
• 4 eine schematische Schnittdarstellung durch eine zweite Ausführungsform eines erfindungsgemäßen 2-Schicht-Gleitelements mit Streckmetall.
• 5 ein Diagramm mit den Verlauf des elektrischen Widerstands und der Verschleißfestigkeit in Abhängigkeit von dem Volumenanteil der leitfähigen Partikel; und
• 6 eine graphische Gegenüberstellung der benötigten Volumenanteile verschiedener leitfähiger Füllstoffe.

Embodiments of the invention are explained in more detail below with reference to figures. Show it:

• 1 a schematic sectional view through a first embodiment of a 3-layer sliding element according to the invention;
• 2 a schematic sectional view through a second embodiment of a 3-layer sliding element according to the invention;
• 3 a schematic sectional view through a first embodiment of a 2-layer sliding element according to the invention with metal mesh;
• 4 a schematic sectional view through a second embodiment of a 2-layer sliding element according to the invention with expanded metal.
• 5 a diagram showing the course of the electrical resistance and wear resistance depending on the volume fraction of the conductive particles; and
• 6 a graphic comparison of the required volume fractions of various conductive fillers.

A first embodiment of a sliding element according to the invention in the form of a three-layer system is shown in 1 shown. It consists of a metallic carrier material 10, which in turn is made up of a support metal layer 12, for example a steel support layer, and a bearing metal layer 14 arranged thereon. The bearing metal layer 14 consists, for example, of a sintered bronze, illustrated as a coherent sintered body 15, and forms a porous partial layer of the carrier material 10. On the bearing metal layer, on the side facing away from the support metal layer 12, there is a sliding layer 16, for example based on PTFE, forming an interface 18 applied to the carrier material 10. The free surface of the sliding layer forms the sliding surface 20. The sliding layer is a thin sliding layer with a thickness d of less than 50 μm. As already mentioned, the layer thickness can be determined by first measuring the layer thickness of the metallic carrier material (d _T ) and, after coating, the thickness of the sliding element (d _G ), for example using a micrometer screw, preferably several times at different points, and then from the The difference d=d _G -d _T is formed between the two (mean) values.

The sliding layer 16 contains isolated conductive particles 22, which extend within the sliding layer 16 at least from the interface 18 to the sliding surface 20 and establish an electrical connection between the carrier material 10 and the sliding surface 20.

It should be noted that the grain size of the sintered material and thus also the pore size of the metallic carrier material 10 at the interface 18 is shown oversized for illustration purposes. It is clear here that the d90 value of the smallest dimension of the conductive particles with a large pore size of the metallic carrier material in relation to the layer thickness d can advantageously be up to 300% of the layer thickness d.

A second embodiment of a sliding element according to the invention in the form of a three-layer system is shown in 2 shown. Like the first exemplary embodiment, it consists of a metallic carrier material 10, which is made up of a support metal layer 12 and a sintered bearing metal layer 14 arranged thereon. The bearing metal layer 14 here also forms a porous partial layer of the carrier material 10. On the bearing metal layer, on the side facing away from the support metal layer 12, a sliding layer 16, for example based on PTFE or based on a thermoplastic, is applied to form an interface 18. The free surface of the sliding layer forms the sliding surface 20. The sliding layer is a thick sliding layer with a thickness d of at least 50 μm.

The sliding layer 16 in turn contains isolated conductive particles 22, which extend within the sliding layer 16 at least from the interface 18 to the sliding surface 20 and establish an electrical connection between the carrier material 10 and the sliding surface 20.

This representation makes it clear that for the d90 value of the smallest dimension of the conductive particles for a fine-pored interface or for an interface with low roughness in relation to the layer thickness d, a d90 value of a maximum of 150% of the layer thickness d is sufficient.

A third embodiment of a sliding element according to the invention in the form of a two-layer system is shown in 3 shown. It consists of a metallic carrier material 10, which consists exclusively of a metallic fabric 24, for example made of steel, copper or aluminum. The metallic fabric 24 therefore forms the porous layer of the carrier material 10. On the metallic fabric 24 there is a sliding layer 16, for example based on PTFE or based on a thermoplastic Formation of an interface 18 applied. The free surface of the sliding layer forms the sliding surface 20. The sliding layer is a medium-thick or thick sliding layer with a thickness d of at least 50 μm.

The sliding layer 16 in turn contains isolated conductive particles 22, which extend within the sliding layer 16 at least from the interface 18 to the sliding surface 20 and establish an electrical connection between the carrier material 10 and the sliding surface 20.

A fourth embodiment of a sliding element according to the invention in the form of a two-layer system is shown in 4 shown. It consists of a metallic carrier material 10, which consists exclusively of an expanded metal 26, for example steel, copper or aluminum. The expanded metal 26 therefore forms the porous layer of the carrier material 10. A sliding layer 16, for example based on PTFE or based on a thermoplastic, is applied to the expanded metal 26 to form an interface 18. The free surface of the sliding layer forms the sliding surface 20. The sliding layer is a medium-thick or thick sliding layer with a thickness d of at least 50 μm.

The sliding layer 16 in turn contains isolated conductive particles 22, which extend within the sliding layer 16 at least from the interface 18 to the sliding surface 20 and establish an electrical connection between the carrier material 10 and the sliding surface 20.

Like in the 3 and 4 can be seen, the matrix material (PTFE or thermoplastic) penetrates the sliding layer when applied or rolled onto the open-pored structure of the metallic fabric 24 or the expanded metal 26. Since the mesh size of the metallic fabric 24 as well as the pore size of the expanded metal 26 in the examples of the 3 and 4 can also be larger than the smallest dimension of the conductive particles, these can also be found together with the matrix material within the open-pored structure, not shown here. Table 1 Example no Substrate Plastic base Additives [vol%] Layer thickness [µm] d50 value [µM] Resistance 1 Bronze fabric PTFE PPSO2 (25), hBN (5) 60-80 > 10 ⁷ Ω 1a + Bz chips (0.55) 60-80 100 < 10 ⁴ Ω 2 Expanded steel metal PTFE PPSO2 (40) 60-80 > 10 ⁷ Ω 2a + spattery Bz particles (0.33) 60-80 100 < 10 ⁴ Ω 3 Steel + porous bronze PTFE MoS2 (20) 10-30 > 10 ⁷ Ω 3a + Bz fibers (0.11) 10-30 35 < 10 ⁴ Ω 4 Steel + porous bronze PPS PTFE (15), PPTA (5) 70-100 > 10 ⁷ Ω 4a + spherical Bz particles (0.89) 70-100 100 < 10 ⁴ Ω 5 Steel + porous bronze PEEK PTFE (20) 250-300 > 10 ⁷ Ω 5a + Al chips (1.12) 250-300 300 < 10 ⁴ Ω 6 steel PVDF PTFE (20), PPTA (5) 200-250 > 10 ⁷ Ω 6a + Al chips (0.66) 200-250 300 < 10 ⁴ Ω

Table 1 shows the layer structure of various examples of bearing elements, including the additives contained in the sliding layer, as well as the result of an electrical resistance measurement on these bearing elements. Examples 1 to 6 represent comparative examples without the invention appropriate conductive particles. Examples 1a to 6a are embodiments of the invention with conductive particles.

Examples 1 and 1a contain a CuSn10 bronze fabric with a wire diameter of 0.25 mm as substrate or carrier material. Examples 2 and 2a contain an expanded steel metal based on 0.3 mm thick steel as the carrier material. In Examples 3 to 6 and 3a to 6a, a bare, ground steel with a sintered bronze framework with a pore volume of 35% serves as the carrier material.

These substrates are combined with PTFE-based layers (Examples 1 to 3 and 1a-3a) and with thermoplastic-based layers (Examples 4 to 6 and 4a to 6a).

As stated in Table 1, bronze and aluminum chips, elongated, twisted particles, produced as turning or milling chips of the corresponding materials, bronze short fibers, as well as spherical and spattered bronze particles were used as conductivity additives. In addition to availability and cost considerations, the particle shape is selected based on which particle sizes are required for the respective application or sliding layer thickness. In principle, the particles in the example combinations are therefore interchangeable.

In the examples according to the invention in Table 1, the conductive particles are each selected so that the d50 value of the smallest dimension corresponds to at least 90% of the layer thickness. Due to the manufacturing process, the measurement results for the layer thicknesses vary if they are measured in several places or on several pieces. That's why a range is specified for this.

The electrical resistance over the total thickness of the bearing element is measured with a device consisting of two blocks serving as contacts, which both specifies a contact surface determined by the blocks and also puts a defined load on the material sample, since the material sample completely overlaps the edges of the contact blocks. This creates comparable contact conditions. The contact area is 28.3 cm ² and the sample is loaded with 220 N.

5 shows the course of the electrical resistance and wear resistance starting from the sliding element according to Example No. 1 with increasing volume fraction of added conductive particles, here bronze chips. The quantity corresponding to Example No. 1a is marked on the curve.

The wear resistance was measured on an oscillation test stand on bushings measuring 15 mm x 22 mm x 25 mm (width x inner diameter x outer diameter) at a load of 35 MPa and an average sliding speed of 0.07 m/s. The reduction in thickness of the sliding layer is shown in µm normalized to the friction path length (bearing circumference x revolutions) in km.

From the curve of the resistance measurement it is clearly visible that from approx. 0.05% by volume of bronze chips based on the volume of the sliding layer, the electrical resistance drops quickly to the minimum (or the electrical conductivity increases quickly to the maximum). It is also clearly visible from the wear measurement curve that the wear resistance of the sliding layer drops sharply with a volume fraction of bronze chips above 1.2% by volume. From both observations, the preferred value range A-A' for the volume fraction of the conductive particles to be used based on the volume of the sliding layer is 0.1 to 1.2% by volume. The value range B-B' of 0.2 to 0.9% by volume is particularly preferred.

This quantity corresponds to approximately 1-10 contact points per cm ² on the sliding surface. This range of values ensures sufficient conductivity regardless of the material type. Taking into account the size of the sliding elements or sliding surfaces, for statistical reasons it is advisable to choose a higher density of contact points for very small plain bearings than for very large ones.

If you try to raise the conductivity of the sliding elements to the same level with other additives in the plastic sliding layer, for example > 15% by volume of graphite or > 5% by volume of conductive carbon black are required. The diagram in 6 illustrates this relationship between the volume fractions of different additives required for the same conductivity in comparison to the solution according to the invention. However, this deteriorates the tribological properties of the sliding layers so significantly that the sliding element would be unusable for a large number of applications. This applies in particular to medium-thick and thick sliding layers, which are caused by larger proportions of finely divided conductive additives in their tribological Stability can be particularly affected. An area, as in 5 shown, in which on the one hand the tribological properties and on the other hand the conductivity are simultaneously close to their achievable optimum, cannot be found by simply modifying known compositions.

In summary, it can be stated that only the addition of a few, larger conductive particles according to the invention makes a satisfactory solution possible in terms of conductivity and wear resistance.

The production of the exemplary sliding elements is described below:

Examples 1-3, 1a-3a.

• • Vordispergieren der Zusätze außer PTFE und erfindungsgemäße Partikel in Wasser und Netzmittel mittels geeignetem Mischwerkzeug wie Dissolver o.ä.;
• • Zusatz einer wässrigen PTFE-Dispersion einer Konzentration zw. 20 und 40 Gew.-% und homogenes Vermischen;
• • Koagulation des PTFE durch Zusatz geeigneter Salze, z.B. Aluminiumnitrat oder Säuren, z.B. Zitronensäure;
• • Rühren zur Verfestigung der Masse, ggfs. unter Wasserentnahme und Zugabe eines Lösungsmittels (z.B. Toluol) bis zur Konsistenz, die für das Aufwalzen benötigt wird;
• • Die Zugabe der Leitfähigkeitspartikel erfolgt nach der Fällung während der Verfestigung der Masse. Hierdurch wird eine Entmischung aufgrund höherer Dichte vermieden;
• • Aufwalzen der Masse auf das Trägermaterial;
• • Erwärmen des beschichteten Trägermaterials in einem Ofen auf eine Temperatur über dem PTFE Schmelzpunkt (327°C), z.B. auf 370°C für mindestens 90 s und
• • Verwalzen des heißen beschichteten Trägermaterials auf die benötigte Enddicke.

The materials according to the invention and the PTFE-based reference materials are produced in a known manner

• • Pre-dispersing the additives except PTFE and particles according to the invention in water and wetting agent using a suitable mixing tool such as a dissolver or similar;
• • Add an aqueous PTFE dispersion with a concentration of between 20 and 40% by weight and mix homogeneously;
• • Coagulation of the PTFE by adding suitable salts, such as aluminum nitrate or acids, such as citric acid;
• • Stir to solidify the mass, if necessary removing water and adding a solvent (eg toluene) until the consistency required for rolling;
• • The conductivity particles are added after precipitation during solidification of the mass. This avoids segregation due to higher density;
• • Rolling the mass onto the carrier material;
• • Heating the coated carrier material in an oven to a temperature above the PTFE melting point (327°C), eg to 370°C for at least 90 s and
• • Rolling the hot coated substrate to the required final thickness.

Alternatively, other processes can also be used, for example the production of a mixture of powdered PTFE with the additives in an organic solvent, which is then rolled onto the carrier material.

Examples 4-6, 4a -6a

• • Vermischung aller Bestandteile in Pulverform in einem geeigneten Pulvermischer;
• • Aufstreuen des Pulvergemisches auf das Trägermaterial mit einer Rakelvorrichtung;
• • Erhitzen des bestreuten Trägermaterials auf eine Temperatur oberhalb der Schmelztemperatur des Themoplasten, bei PEEK z.B. auf 390°C;
• • Verwalzen der Schmelze mit dem Trägermaterial;
• • Ggfs. weiteres Erwärmen und Halten bei einer thermoplastspezifischen Prozesstemperatur und
• • Verwalzen des heißen beschichteten Trägermaterials auf die benötigte Enddicke.

The materials according to the invention and the reference materials based on thermoplastics can be produced in a known manner, for example by the following steps:

• • Mix all ingredients in powder form in a suitable powder mixer;
• • Sprinkling the powder mixture onto the carrier material using a doctor device;
• • Heating the sprinkled carrier material to a temperature above the melting temperature of the thermoplastic, for example to 390°C for PEEK;
• • Rolling the melt with the carrier material;
• • If necessary. further heating and holding at a thermoplastic-specific process temperature and
• • Rolling the hot coated substrate to the required final thickness.

Alternatively, other processes can also be used, for example the production of a plastic film by melt extrusion of the component mixture and rolling this film onto the carrier material.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was 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 102013227187 B4 [0003]
• DE 10147292 B4 [0004]
• EP 3087142 B1 [0004]
• EP 2804902 B1 [0007]
• EP 1875091 B1 [0008]
• EP 2069651 B1 [0009]

Claims (14)

Sliding element with a metallic carrier material and a sliding layer applied thereon based on PTFE or thermoplastic, the sliding layer forming an interface to the carrier material and a sliding surface for contact with a counter-rotor, characterized in that the sliding layer contains conductive particles, each of which extend individually within the sliding layer at least from the interface to the sliding surface. sliding element Claim 1 , characterized in that the conductive particles are metallic particles. sliding element Claim 2 , characterized in that the metallic particles consist of copper, aluminum or alloys thereof. Sliding element according to one of the preceding claims, characterized in that the d50 value of the smallest expansion of the particles is at least 90% of the sliding layer thickness and the d90 value of the smallest expansion of the particles is not greater than 300% of the sliding layer thickness. Sliding element according to one of the preceding claims, characterized in that the volume fraction of the conductive particles, based on the volume of the sliding layer, is 0.1 - 1.2%. Sliding element according to one of the preceding claims, characterized in that the volume fraction of the conductive particles, based on the volume of the sliding layer, is 0.2 - 0.9%. Sliding element according to one of the preceding claims, characterized in that the average density of the contacts produced by the conductive particles along the sliding surface is 1 cm ^-2 - 10 cm ^-2 . Sliding element according to one of the preceding claims, characterized in that the volume of the sliding layer consists predominantly of PTFE. Sliding element according to one of the preceding claims, characterized in that the sliding layer has a thickness of over 50 µm. Sliding element according to one of the preceding claims, characterized in that the metallic carrier material is formed from a single support metal layer or a layer composite with a support metal layer and a bearing metal layer. sliding element Claim 10 , characterized in that the support metal layer or the bearing metal layer is porous at least near the interface. Sliding element according to one of the Claims 10 or 11 , characterized in that the metallic carrier material consists of steel with a sintered bronze. Sliding element according to one of the Claims 10 or 11 , characterized in that the metallic carrier material is formed exclusively from a single support metal layer made of steel, a copper alloy or an aluminum alloy. Sliding element according to one of the Claims 10 or 11 , characterized in that the metallic carrier material consists exclusively of a metallic fabric or expanded metal made of steel, copper or aluminum or their alloys.