SELF-LUBRICATING LINERS FREE OF POLYFLUOROALKYL SUBSTANCES (PFAS)

Abstract

A self-lubricating liner is provided that has a matrix material and an ultra-high molecular weight polyethylene (UHMWPE) lubricant embedded in the matrix material. The matrix material and the lubricant are free of polyfluoroalkyl substances (PFAS) such as, but not limited to, polytetrafluoroethylene (PTFE). In some embodiments, the liner further includes a fabric base embedded in the matrix material.

Claims

1. A self-lubricating liner, comprising: a matrix material; and an ultra-high molecular weight polyethylene (UHMWPE) lubricant embedded in the matrix material, wherein the matrix material and the lubricant are free of polyfluoroalkyl substances (PFAS).

2. The self-lubricating liner of claim 1, further comprising a fabric base and/or reinforcing fibers embedded in the matrix material.

3. The self-lubricating liner of claim 1, further comprising a backing supporting the matrix material having the lubricant embedded therein.

4. The self-lubricating liner of claim 1, wherein the lubricant is present in an amount of 20 to 70 wt. %.

5. The self-lubricating liner of claim 1, wherein the lubricant is present in an amount of 28.5 to 37.5 wt. %.

6. The self-lubricating liner of claim 1, wherein the lubricant is selected from a group consisting of a powder, a floc, loose fibers, whiskers, woven fabrics, non-woven fabrics, felts, and any combinations thereof.

7. The self-lubricating liner of claim 1, wherein the matrix material is selected from a group consisting of polyimide, polyamide, nylon, phenolic, acrylate, allyl-based resin, one-part epoxy, two-part epoxy, crosslinked polyethylene (PEX), polyether ether ketone (PEEK), polyoxymethylene, and combinations thereof.

8. The self-lubricating liner of claim 1, wherein the matrix material and the lubricant are free of a component selected from a group consisting of carbon, carbon-based additives, MoS.sup.2, and any combinations thereof.

9. The self-lubricating liner of claim 1, wherein the lubricant has a melting temperature below a cure temperature of the matrix material such that the lubricant densifies the matrix material by filling voids and cracks in the matrix material when exposed to the cure temperature.

10. A self-lubricating liner, comprising: a matrix material; a fabric base embedded in the matrix material; and an ultra-high molecular weight polyethylene (UHMWPE) lubricant embedded in the matrix material, wherein the matrix material, the fabric base, and the lubricant are free of polyfluoroalkyl substances (PFAS).

11. The self-lubricating liner of claim 10, further comprising a backing supporting the matrix material having the lubricant and fabric base embedded therein.

12. The self-lubricating liner of claim 10, wherein the lubricant is present in an amount of 28.5 to 37.5 wt. %.

13. The self-lubricating liner of claim 10, wherein the lubricant is selected from a group consisting of a powder, a floc, loose fibers, whiskers, woven fabrics, non-woven fabrics, felts, and any combinations thereof.

14. The self-lubricating liner of claim 10, wherein the fabric base is a woven fabric having lubricant fibers comprising the lubricant.

15. The self-lubricating liner of claim 14, wherein the fabric base further comprises reinforcing fibers woven with the lubricant fibers.

16. The self-lubricating liner of claim 14, wherein the woven fabric has a weave selected from a group consisting of square, twill, satin, plain, basket, non-woven, felted, randomly oriented, and any combinations thereof.

17. The self-lubricating liner of claim 10, wherein the matrix material is selected from a group consisting of polyimide, polyamide, nylon, phenolic, acrylate, allyl-based resin, one-part epoxy, two-part epoxy, crosslinked polyethylene (PEX), polyether ether ketone (PEEK), polyoxymethylene, and combinations thereof.

18. The self-lubricating liner of claim 10, wherein the matrix material, fabric base, and the lubricant are free of a component selected from a group consisting of carbon, carbon-based additives, MoS.sup.2, and any combinations thereof.

19. The self-lubricating liner of claim 10, wherein the lubricant has a melting temperature below a cure temperature of the matrix material such that the lubricant densifies the matrix material by filling voids and cracks in the matrix material when exposed to the cure temperature.

20. A self-lubricating liner, comprising: a matrix material that comprises phenolic or epoxy; and an ultra-high molecular weight polyethylene (UHMWPE) lubricant embedded in the matrix material, the lubricant being present in an amount of 28.5 to 37.5 wt. %, wherein the matrix material and the lubricant are free of polyfluoroalkyl substances (PFAS).

21. The self-lubricating liner of claim 20, wherein the lubricant has a melting temperature below a cure temperature of the matrix material such that the lubricant densifies the matrix material by filling voids and cracks in the matrix material when exposed to the cure temperature.

22. The self-lubricating liner of claim 20, wherein the matrix material further comprises an additive selected from a group consisting of metal sulfide additives, metal oxide additives, nitride additives, carbon additives, MoS.sub.2, WS.sub.2, ZnS, TiO.sub.2, ZnO, ZrO.sub.2, nitride additives, hexagonal boron nitride (h-BN), silicon nitride (Si.sup.3N.sup.4), carbon fiber, graphite, graphene, carbon nanotubes, fluorinated carbon additives, non-fluorinated carbon additives, and combinations thereof.

23. The self-lubricating liner of claim 20, wherein the lubricant is present in an amount of 33.33 wt. % and has a melting temperature below a cure temperature of the matrix material such that the lubricant densifies the matrix material by filling voids and cracks in the matrix material when exposed to the cure temperature, and wherein the matrix material comprises hexagonal boron nitride (h-BN) and/or silicon nitride (Si.sup.3N.sup.4) in an amount of between 2-8 wt. % with respect to the matrix material.

24. The self-lubricating liner of claim 23, wherein the amount of hexagonal boron nitride (h-BN) and/or silicon nitride (Si.sup.3N.sup.4) is between 2.25-3.5 wt. % with respect to the matrix material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] This application contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0031] FIGS. 1-4 are sectional views of exemplary embodiments of self-lubricating liners according to the present disclosure;

[0032] FIG. 5 is a sectional view of an alternate exemplary embodiment of a self-lubricating liner according to the present disclosure;

[0033] FIG. 6 is an isometric view of an exemplary embodiment of a fabric base in FIG. 5; and

[0034] FIGS. 7-9 illustrate average wear rates per cycle of liners of the present disclosure compared to liners of the prior art.

DETAILED DESCRIPTION

[0035] Referring now to the drawings and in particular to FIGS. 1-4, exemplary embodiments of self-lubricating liners according to the present disclosure are shown and are generally referred to by reference number 10. An alternate exemplary embodiment of a self-lubricating liner according to the present disclosure is shown in FIGS. 5-6 and is generally referred to by reference number 20.

[0036] Liner 10 has a fluorine free lubricant 12 embedded in a matrix material 14. Liner 10 can have reinforcing fibers 16 incorporated in the matrix 14 as shown in FIGS. 2 and 4 or be formed without such fibers as shown in FIGS. 1 and 3. Additionally, liner 10 can be supported on a backing 18 with reinforcing fibers 16 as shown in FIG. 4 or without such fibers as shown in FIG. 3.

[0037] Liner 20 has a fluorine free lubricant 22 and a fabric base 26 embedded in a matrix material 24. Lubricant 22 can be one or more fibers of fabric base 26, can be independent from the fabric base, or combinations thereof. Liner 20 can, in some embodiments, be supported on a backing 28. Of course, it is contemplated by the present disclosure for liner 20 to omit backing 28 and/or to further include reinforcing fibers (not shown) in matrix 24.

[0038] Fabric base 26 can be a woven fabric, a non-woven fabric, a felted fabric, and any combination thereof. In the embodiment of fabric base 26 shown in FIG. 6, the fabric base is a woven fabric. Fabric base 26 can include only fibers 30 that include lubricant 22 or only reinforcing fibers 32 that omit lubricant 22, or combinations thereof. In embodiments where fabric base 26 includes both fibers 30 with lubricant 22 and reinforcing fibers 32, the fibers can be woven together in a pattern. The woven pattern can be any desired pattern such as, but not limited to, weaves selected from the group consisting of square, twill, satin, plain, basket, non-woven, felted, and randomly oriented.

[0039] Fabric base 26 can have any desired thicknesses, such as, but not limited to a thickness from 0.005-0.020 (0.254 mm-0.0508 mm). Reinforcing fibers 32 can be formed of any desired material including, but not limited to, polyester, aromatic polyamide, para-aramid (e.g., Kevlar), meta-aramid (e.g., Nomex), fiberglass, polyethylene, polyether ether ketone (PEEK), and any combinations thereof.

[0040] Advantageously, liners 10, 20 replace the PFAS of the prior art liners with the fluorine free lubricant 12, 22. Simply stated, liners 10, 20 are PFAS free yet provide the desired self-lubricating properties as described herein. In some embodiments, liners 10, 20 have a coefficient of friction of at most 0.35, more preferably at most 0.25, even more preferably at most 0.20 being, and at most 0.10 being most preferred, and any subranges therebetween.

[0041] The fluorine free lubricant 12, 22 is an ultra-high molecular weight polyethylene (UHMWPE), which is a linear (non-branching) semi-crystalline polymer having extremely long polymer chains with a high molecular weight. The molecular weight of the UHMWPE is at least 1 million grams per mole (g/mole), preferably greater than 3 million g/mole, with greater than 4 million g/mole being most preferred and a molecular weight of not more than 9.5 million g/mole, preferably not more than 8.5 million g/mole, with not more than 7.5 million g/mole being most preferred, and any subranges therebetween. Moreover, the UHMWPE of the present application can be two-phase composites of crystalline and amorphous phases.

[0042] In prior art liners that include PTFE as the lubricant, the PTFE melts at approximately 620 F. (327 C.) which is beyond any temperature used in formation of the liner.

[0043] Advantageously and in contrast to these prior art liners that make use of PFAS self-lubricating materials, the UHMWPE of lubricants 12, 22 melt below a cure temperature of matrix material 14, 24. Without wishing to be bound by any particular theory, it is believed that the melting of the UHMWPE of lubricants 12, 22 densifies matrix 14, 24 by filling voids and cracks that are commonplace in self-lubricating liners and adds strength to liners 10, 20. Here, it is believed that the melted UHMWPE is large enough to fill the voids that are present in self-lubricating composites, while being small enough to retain homogeneity, adding wear resistance to the composite and ductility to the matrix material.

[0044] In some embodiments, the self-lubricating liners are used in spherical bearings where the liners are formed around the spherical ball. This formation is known to cause cracks in the liners. Advantageously, liners 10, 20 that are formed with UHMWPE lubricant 12, 22 that melted during processing results in increased the strength, density and performance results compared to liners having lubricants that have not melted during processing.

[0045] Fluorine free lubricants 12, 22 can, in some embodiments, be in the form of powders. The powders can have a particle size between 10 to 100 micrometers (m), preferably between 20 to 80 m, with between 30 to 60 m being most preferred, and any subranges therebetween. Of course, it is contemplated by the present disclosure for fluorine free lubricants 12, 22 to have any desired form including, but not limited to, powders, floc, loose fibers, whiskers, woven fabrics, non-woven fabrics, felts, and any combinations thereof.

[0046] Regardless of the form of lubricants 12, 22, the lubricants are present in a weight percent between 20 to 70% with respect to matrix material 14, 24, preferably between 25 to 60%, with between 30 to 40% being most preferred, and any subranges therebetween.

[0047] Matrix material 14, 24 can be any cured resin of sufficient strength and rigidity. In some embodiments, matrix material 14, 24 can include materials such as, but not limited to, polyimide, polyamide, nylon, phenolic, acrylate, allyl-based resin, one-part epoxy, two-part epoxy, crosslinked polyethylene (PEX), polyether ether ketone (PEEK), polyoxymethylene, and combinations thereof.

[0048] In some embodiments, matrix 14, 24 can include one or more additives such as, but not limited to, metal sulfide additives, metal oxide additives, nitride additives, carbon additives, and combinations thereof. In some embodiments, matrix 14, 24 include a combination of metal sulfide and metal oxide additives.

[0049] Metal sulfide additives can include, but are not limited to, compositions including MoS.sub.2, WS.sub.2, ZnS, and combinations thereof and can be incorporated in an amount of between 0-12 wt. % with respect to matrix material 14, 24, more preferably between 2.5- 7 wt. %, and any subranges therebetween.

[0050] Metal oxide additives can include, but are not limited to, compositions including TiO.sub.2, ZnO, ZrO.sub.2, and combinations thereof and can be incorporated in an amount of between 0-12 wt. % with respect to matrix material 14, 24, more preferably 3-9 wt. %, and any subranges therebetween.

[0051] Nitride additives can include, but are not limited to, compositions including hexagonal boron nitride (h-BN) and silicon nitride (Si.sup.3N.sup.4) and combinations thereof. In some embodiments, the nitride additives can be incorporated in an amount of between 2-8 wt. % with respect to matrix material 14, 24, preferably between 2-5 wt %, with between 2.25-3.5 being most preferred, and any subranges therebetween.

[0052] Carbon and carbon-based additives can include, but not limited to, compositions including carbon fiber, graphite, graphene, carbon nanotubes, fluorinated carbon additives, and combinations thereof. When the carbon additives are graphite and graphene, whether fluorinated or non-fluorinated, the additives are incorporated in an amount of between 0-12 wt. %. When the carbon additives are carbon nanotubes, the additives are incorporated in an amount of between 0-7 wt. %.

[0053] In embodiments where liner 10, 20 is intended for use in contact with metallic materials, matrix material 14, 24 can be free from carbon and carbon-based additives and/or MoS.sup.2, which are believed by the present disclosure to cause negative chemical reactions with the metallic surfaces. As noted above, carbon and carbon-based additives include, but not limited to, carbon fiber, graphite, graphene, carbon nanotubes, fluorinated carbon additives, and combinations thereof.

[0054] It has been determined by the present disclosure that, during the use of self-lubricating liners 10, 20, exposure to load pressures between 5-40 kilopounds per square inch (KSI) or 35-276 megapascal (MPa), cyclic speeds between 10-30 cycles per minute, and angles of oscillation between 50-100. For example, industrial applications of liners 10, 20 are often exposed to load pressures of 10 KSI (69 MPa), while aerospace applications are often exposed to load pressures of 25 KSI (172 MPa) up to 40 KSI (276 MPa).

[0055] Within this mechanical performance range, lubricants 12, 22 within liners 10, 20 are believed to form a transfer film chemically adhered to the substrate the liner is in contact with.

[0056] Testing of exemplary embodiments of self-lubricating liners 20 having fabric base 26 according to the present disclosure are described with reference to FIGS. 7-9.

[0057] In these tests, liner 20 shown in FIGS. 7-9 each has 33.33 wt. % of UHMWPE lubricant 22 in powder form with a particle size between 10 to 100 micrometers and a fabric base 26 made of a meta-aramid reinforcement material, which is commercially available under the tradename NOMEX, with a plain weave and 0.010 thick that are embedded in a matrix material 24 made of a phenolic resin.

[0058] Here, comparison testing of liners 20 and prior art liners was performed on a linear friction testing rig. The test included the use of five prior art fabric-based liners.

[0059] The first type of prior art liner, referred to in FIGS. 7-8, as Liner 1 has a PTFE lubricant in weave with a meta-aramid reinforcement material, which is commercially available under the tradename NOMEX, with a two-by-two twill weave and 0.012 thick and floc lubricant fibers in a matrix of phenolic resin, this is an AS81820 Type A Qualified Liner.

[0060] The second type of prior art liner, referred to in FIG. 7 as Liner 2 has a PTFE lubricant in weave with fiberglass reinforcement in weave in a matrix of phenolic resin.

[0061] The third type of prior art liner, referred to in FIG. 7, as Liner 3 has a PTFE lubricant in weave with a meta-aramid reinforcement material, which is commercially available under the tradename NOMEX, with a natural satin weave and 0.014 thick and floc lubricant fibers in a matrix of phenolic resin, this is an AS81820 Type A Qualified Liner.

[0062] The fourth type of prior art liner, referred to in FIG. 8, as Liner 4 has a PTFE lubricant in weave with a meta-aramid reinforcement material, which is commercially available under the tradename NOMEX, with a plain weave and 0.010 thick and floc lubricant fibers in a matrix of phenolic resin, this is an AS81820 Type A Qualified Liner.

[0063] The fifth type of prior art liner, referred to in FIG. 9 as Liner 5, has a PTFE lubricant in weave with fiberglass reinforcement in a matrix of polyimide resin, which is a liner commonly used in engine systems for commercial and military aerospace.

[0064] The testing rig moves a sample liner with respect to a wear carriage. The testing rig measures a vertical load and a linear load applied on the sample liners. The sample liners oscillate at a sample speed of approximately 34.1 mm/sec with oscillations defined as follows: the linear sample will oscillate from the origin to +0.5 in (12.7 mm), back through the origin to 0.5 in (12.7 mm) for a total oscillation of 2 inches (50.8 mm).

[0065] FIG. 7 compares the average wear rate per cycle of liner 20 at a load pressure of 40 KSI, a speed of 20 cycles per minute (CPM, and a temperature of 70 Fahrenheit (21 Celsius) to Liners 1, 2, and 3.

[0066] In this low temperature, high pressure test, it can be seen that liner 20 provides wear rates within 50% of those of comparative liners 1, 2, and 3 up to about 50,000 cycles.

[0067] FIG. 8 compares the average wear rate per cycle of liner 20 at a load pressure of 40 KSI, a speed of 20 CPM, and a temperature of 330 Fahrenheit (166 Celsius) to Liners 1 and 4.

[0068] In this high temperature, high pressure test, it can be seen that liner 20 provides wear rates lower than those of comparative Liners 1 up to about 100,000 cycles and liner 20 has same wear as Liners 1 and 4 at 100,00 cycles.

[0069] FIG. 9 compares the average wear rate per cycle of liner 20 at a load pressure of 25 KSI, a speed of 20 CPM, and a temperature of 70 Fahrenheit (21 Celsius) to Liner 5.

[0070] In this low temperature, moderate pressure test, it can be seen that liner 20 provides wear rates lower than those of comparative liner 5 up to about 100,000 cycles.

[0071] Advantageously, the testing of FIGS. 7-9 show that liner 20 provides a PFAS free liner with wear properties that meet or exceed those of the prior art, PTFE liners.

[0072] It should also be noted that the terms first, second, third, upper, lower, and the like may be used herein to modify various elements. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated.

[0073] While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated, but that the disclosure will include all embodiments falling within the scope of the appended claims.