PTFE polymer-based sliding material having fillers which improve the tribological properties

Abstract

The invention relates to a PTFE polymer-based sliding material having fillers which improve the tribological properties, wherein the fillers comprise at least one phosphate, in particular calcium phosphate, calcium pyrophosphate, magnesium phosphate, magnesium pyrophosphate, lithium phosphate, hydroxyapatite or combinations thereof, and at least one metal sulfide, wherein the fraction of the metal sulfide is >2% by volume. The invention also relates to uses of said sliding material.

Claims

1. Polytetrafluoroethylene (PTFE) polymer-based sliding material having fillers for improving tribological properties, characterised in that the fillers comprise a primary filler having calcium phosphate and at least one metal sulphide; the at least one metal sulphide is at least >2% by volume; contents of the fillers by volume are determined by weight and density; the at least one metal sulphide comprises Tin(IV) sulphide (SnS.sub.2), Bismuth (III) sulfide (Bi.sub.2S.sub.3), Tungsten disulfide (WS.sub.2), Zinc sulfide (ZnS), Copper (II) sulfide (CuS) or a combination thereof; the PTFE polymer-based sliding material having a PTFE polymer-base that comprises at least 70% by volume of PTFE; and the PTFE polymer-based sliding material comprises secondary fillers having solid lubricants with Barium sulfate (BaSO.sub.4).

2. The PTFE polymer-based sliding material according to claim 1, characterised in that the PTFE polymer-base comprises at least 80% by volume of PTFE; the contents of the fillers comprise up to 30% by volume of the PTFE polymer-base; and the PTFE polymer base includes up to 10% by volume of other polymers or combinations thereof, including polyvinylidene (PVDF), polyfluoroalkyl (PFA), fluorinated ethelene propylene (FEP), ethylene chlorotrifluoroethylene (ECTFE), or ethylene tetrafluoroethylene (ETTE).

3. The PTFE polymer-based sliding material according to claim 1, characterised in that an amount of the calcium phosphate in the PTFE polymer-based sliding material is in a range of 1-30% by volume.

4. The PTFE polymer-based sliding material according to claim 1, characterised in that an amount of the metal sulphide as fillers is more than 3% by volume, or is at most between 10-30% by volume of the PTFE polymer-based sliding material.

5. The PTFE polymer-based sliding material according to claim 1, characterised in that a ratio of the volume of the calcium phosphate to the at least one metal sulphide is in a range of 6:1 to 1:2.

6. The PTFE polymer-based sliding material according to claim 1, characterised in that the secondary fillers include lithophones, or fluorides, or both lithophones and fluorides, and the fluorides include calcium fluoride, or pigments, or both calcium fluoride and pigments.

7. The PTFE polymer-based sliding material according to claim 1, characterised in that the PTFE polymer-based sliding material comprises further tertiary fillers that include carbon fibres, glass fibres, polymer fibres including aramid fibres, and/or the solid lubricants include graphite, soot, boron nitride (BN) and/or plastic particles; the plastic particles include perfluoropolyether (PFPE), aramid (PPTA), polypropylene sulfur dioxide (PPSO.sub.2), phosphorus triiodide phosphorus (III) iodine (PI) and polyamide-imide (PAI) particles, polyacrylate particles (PAR), bisphenol A (PBA) particles, polybenzimidazole (PBI) particles; and/or metal oxides, including ferric oxide (Fe.sub.2O.sub.3), aluminium oxide (Al.sub.2O.sub.3) Silicon dioxide (SiO.sub.2) Chromium dioxide (CrO.sub.2) titanium dioxide (TiO.sub.2), copper oxide (CuO), magnesium oxide (MgO), zinc oxide (ZnO), and/or hard material particles; and the hard material particles include ceramic particles comprising silicon carbon (SiC), silicon nitride (Si.sub.3N.sub.4), boron carbide (BC), cubic boron nitride (BN); and/or fluorides, including sodium fluoride (NaF), aluminium fluoride (AlF.sub.3) and/or layered silicates, including kaolin, mica, wollastonite, talc, silica; and/or metallic fine powders, and the metallic fine powders include bronze and bismuth, and/or pigments or mixed phase oxide pigments, including cobalt aluminate (CoAl), chrome antimony titanium (CrSbTi), cobalt titanate (CoTi), iron alumina (FeAl), manganese ferrite (MnFe) or cobalt chromite (CoCr).

8. The PTFE polymer-based sliding material according to claim 1, characterised in that the PTFE polymer-base is in a range of 50-95% by volume of the PTFE polymer-based sliding material.

9. A plain bearing composite material having a metallic support layer, including steel or bronze; having a porous backing layer, including bronze; and having the PTFE polymer-based sliding material according to claim 1 filling pores of the porous backing layer.

10. A plain bearing element manufactured from the plain bearing composite material according to claim 9.

11. The plain bearing element according to claim 10, characterised in that the plain bearing element is a sliding rail, or a sliding shoe, or a sliding pad, or a plain bearing shell, or a plain bearing bushing, or a plain bearing collar bushing.

12. The PTFE polymer-based sliding material according to claim 2, characterised in that an amount of the calcium phosphate in the PTFE polymer-based sliding material is in a range of 1-30% by volume.

13. The PTFE polymer-based sliding material according to claim 2, characterised in that an amount of the metal sulphide as fillers is more than 3% by volume, or is at most 30% by volume of the PTFE polymer-based sliding material.

14. The PTFE polymer-based sliding material according to claim 2, characterised in that a ratio of the volume of the calcium phosphate to the at least one metal sulphide is in a range of 6:1 to 1:2.

15. The PTFE polymer-based sliding material according to claim 2, characterised in that the secondary fillers include lithophones, or fluorides, or both lithophones and fluorides, and the fluorides includes calcium fluoride, or pigments, or both calcium fluoride and pigments.

16. The PTFE polymer-based sliding material according to claim 2, characterised in that the PTFE polymer-based sliding material contains further tertiary fillers that include carbon fibres, glass fibres, polymer fibres including aramid fibres, and/or the solid lubricants include graphite, soot, boron nitride (BN) and/or plastic particles; the plastic particles include perfluoropolyether (PFPE), aramid (PPTA), polypropylene sulfur dioxide (PPSO.sub.2), phosphorus triiodide phosphorus (III) iodine (PI) and polyamide-imide (PAI) particles, polyacrylate particles (PAR), bisphenol A (PBA) particles, polybenzimidazole (PBI) particles; and/or metal oxides, including ferric oxide (Fe.sub.2O.sub.3), aluminium oxide (Al.sub.2O.sub.3) Silicon dioxide (SiO.sub.2) Chromium dioxide (CrO.sub.2) titanium dioxide (TiO.sub.2), copper oxide (CuO), magnesium oxide (MgO), zinc oxide (ZnO), and/or hard material particles; and the hard material particles include ceramic particles comprising silicon carbon (SiC), silicon nitride (Si.sub.3N.sub.4), boron carbide (BC), cubic boron nitride (BN); and/or fluorides, including sodium fluoride (NaF), aluminium fluoride (AlF.sub.3) and/or layered silicates, including kaolin, mica, wollastonite, talc, silica; and/or metallic fine powders, and the metallic fine powders include bronze and bismuth, and/or pigments or mixed phase oxide pigments, including cobalt aluminate (CoAl), chrome antimony titanium (CrSbTi), cobalt titanate (CoTi), iron alumina (FeAl), manganese ferrite (MnFe) or cobalt chromite (CoCr).

17. The PTFE polymer-based sliding material according to claim 1, characterised in that the PTFE polymer-base is in a range of 50-95% by volume of the PTFE polymer-based sliding material.

18. A plain bearing composite material having a metallic support layer, including steel or bronze; having a porous backing layer, including bronze; and having the PTFE polymer-based sliding material according to claim 2 filling pores of the porous backing layer.

Description

(1) In the drawings:

(2) FIG. 1 shows a schematic sectional view of a metal/plastic sliding bearing composite material according to the invention;

(3) FIG. 2 shows measurement results of wear values of sliding bearing members made of the above sliding materials;

(4) FIG. 3 shows measurement results of friction coefficients of sliding bearing members made of the above sliding materials.

(5) FIG. 1 shows a schematic sectional view of a sliding bearing composite material 2 according to the invention with a metallic support layer 4, typically of steel, and with a porous carrier layer 6. The porous carrier layer 6 is formed by a sintered layer of bronze-based metallic particles 7. The particles of the carrier layer 6 form coherent macroscopic cavities (which are not shown to scale), in which a polymer-based sliding material 8 according to the invention is impregnated. The sliding material 8 fills the pores of the support layer 6 substantially completely. The matrix-forming polymer component of the sliding layer material 8 is based on PTFE in the sense defined above. The polymer component is advantageously made of PTFE. The sliding layer material 8 further comprises fillers incorporated in the matrix-forming polymer component, namely one or more phosphates and one or more metal sulfides. Other fillers in addition to phosphates and metal sulfides may prove to be advantageous and are also not shown. In particular, the above-mentioned secondary and/or tertiary fillers are suitable.

(6) FIG. 2 shows the result of wear measurements and FIG. 3 of friction coefficient measurements on sliding bearing elements, which were measured with sliding bearing composite materials using sliding materials of the above examples 1 to 9. The sliding bearing composites comprise a metallic support layer of steel, a porous support layer of the type described above, and a polymer-based sliding material filling the pores of the support layer. The examined sliding bearing elements differ only with regard to the composition of the sliding material.

(7) The wear resistance and friction coefficients were determined in a rotation test with a sliding speed of 2 m/s under a load of 0.75 MPa. The test parameters are given in the table below.

(8) TABLE-US-00002 Test Test parameters parameters Lubrication Dry run condition Counter body 100Cr6 Load 0.75 MPA Sliding speed 2 m/s Test time 15 h

(9) For this purpose, a bush was produced as a sliding bearing element having an inner diameter of 20 mm and an outer diameter of 23 mm and 15 mm width, comprising the sliding material according to the above examples 1 to 9.

(10) Example 2, which contains only calcium phosphate as a filler, serves as reference example, to the measured values of which the other examples are related. Examples 1 and 3 to 5 are not comparative examples according to the invention. Examples 6 to 9 show sliding materials according to the invention.

(11) The sliding materials to which calcium phosphate and a metal sulfide have been added as fillers and which thus correspond to the invention show a significantly and surprisingly lower wear than the comparative examples and the reference example.

(12) The wear resistance can be further improved by targeted combinations of calcium phosphate with metal sulfides as further solid lubricants (primary fillers), such as Bi.sub.2S.sub.3 (Example 6), SnS.sub.2 (Example 7) or WS.sub.2 (Example 8). Furthermore, a mixture of phosphate and primary fillers (here Bi.sub.2S.sub.3) and secondary fillers, here BaSO.sub.4 as a solid lubricant, were investigated, which further improves the wear values (s. Example 9). Especially the examples 8 and 9 show a more than 50% lower wear than the references with consistently good friction coefficients.