Sliding member and manufacturing method therefor

Abstract

To provide a sliding member capable of suppressing a coefficient of friction in an initial stage of sliding, and having excellent wear resistance while maintaining a low coefficient of friction in the middle or later stage of sliding.SOLUTION: A sliding member includes a backing metal layer, a porous metal layer, and a coating layer containing a polytetrafluoroethylene material that coats the porous metal layer. The coating layer comprises a first layer impregnated in the porous metal layer, and a second layer laminated on the first layer. The Martens hardness of the first layer is 15% to 56% higher than the Martens hardness of the second layer. A value of a difference (%) between the Martens hardness of the first layer and the Martens hardness of the second layer is obtained as follows: (Martens hardness of the first layer / Martens hardness of the second layer)×100-100.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an improvement in a sliding member and a method for manufacturing the same.

Background Art

[0002] There is known a sliding member in which a porous metal layer formed on a backing layer is coated with a coating layer made of a polytetrafluoroethylene (sometimes abbreviated as PTFE in this specification) material as a base material. PTFE has a low coefficient of friction and is excellent in chemical resistance and heat resistance, but is inferior in wear resistance. Therefore, it has been common to uniformly fill additives such as solid lubricants and hard particles. For the above, refer to Patent Documents 1 to 3.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the initial stage of sliding of the sliding member, it may be difficult to form an oil film between the sliding member and its counterpart. Therefore, a low coefficient of friction is required for the sliding member itself, in other words, for the coating layer itself that forms the uppermost layer. As sliding progresses, an oil film is formed, so the importance of the low friction property required for the sliding member decreases compared to the initial stage of sliding. However, on the other hand, higher wear resistance is required. The coating layer with PTFE as the base material was uniformly formed as a whole, including the dispersion mode of the additive. It was difficult to flexibly change the sliding performance of such a sliding member according to the progress of sliding as described above. Therefore, an object of the present invention is to provide a sliding member that has a low friction coefficient in the initial stage of sliding and excellent wear resistance while maintaining a low friction coefficient in the middle or late stage of sliding.

Means for Solving the Problems

[0005] As a result of intensive studies to solve such problems, the inventors of the present invention considered that the following effects can be obtained if the surface layer of the coating layer of the sliding member is made softer than its inner layer. That is, in the initial stage of sliding, the relatively soft surface layer can lower the friction coefficient, and after the sliding progresses, the relatively hard inner layer can maintain the original low friction coefficient of PTFE while exhibiting wear resistance. The first aspect of this invention is based on the findings of such inventors. That is, A sliding member comprising a backing layer, a porous metal layer formed on one surface of the backing layer, and a coating layer covering the porous metal layer, wherein The coating layer includes a first layer impregnated in the porous metal layer and a second layer laminated on the first layer, and the martensitic hardness of the first layer is 15% to 56% higher than the martensitic hardness of the second layer. Here, the value of the difference (%) between the martensitic hardness of the first layer and the martensitic hardness of the second layer is obtained as follows: (Martensitic hardness of the first layer / Martensitic hardness of the second layer) × 100 - 100 Sliding member.

[0006] According to the sliding member of the first aspect defined in this way, the coating layer includes a second layer on the surface side and a first layer embedded in the porous metal layer on the inner side thereof, and the inner first layer is made harder than the second layer on the surface side. By setting the difference in hardness to 15% - 56%, the sliding characteristics of the coating layer with PTFE as the base material can be made such that the coefficient of friction is suppressed in the initial stage of sliding, and excellent wear resistance is achieved while maintaining a low coefficient of friction in the middle or late stage of sliding. The martensite hardness here is obtained by implementing a measurement method compliant with the international standard ISO14577. For the martensite hardness of the first layer and the second layer, those measured by pressing a probe perpendicularly against the base material regions (PTFE regions) of the first layer and the second layer that appear in the cross-section of the sliding member can be adopted.

[0007] The second aspect of this invention is defined as follows. That is, In the sliding member of the first aspect, the porous metal layer is buried in the first layer, and the interface between the first layer and the second layer follows the surface of the porous metal layer. Since the porous metal layer is generally formed by sintering metal particles, its surface has an uneven shape along the surfaces of the metal particles and the agglomerates thereof. In the sliding member defined in the second aspect, the interface between the first layer and the second layer follows the surface of the porous metal layer with such an uneven shape. Even if the wear of the relatively soft second layer progresses, the progress is suppressed by the highly wear-resistant first layer at the interface with the first layer. At this time, since there are unevennesses following the surface of the porous metal layer at the interface between the first layer and the second layer, the relatively soft PTFE material constituting the second layer remains in the concave portions. In other words, even if the second layer has almost completely worn away, the relatively soft PTFE material constituting the second layer remains on the surface of the first layer, so a low coefficient of friction can be ensured even in a state where the oil film in the initial sliding stage of the sliding member is insufficient.

[0008] In the above, it is preferable that the PTFE of the first layer and the second layer be the same material. This is for ensuring their reliable bonding. It is preferable to incorporate a solid lubricant into the second layer (third aspect). This is for imparting wear resistance while maintaining low friction. In addition, additives can be incorporated into the first layer including the second layer. The blending amount of this additive is 5% to 40% by volume, and it is desirable that the additive contains a solid lubricant (Fourth aspect). At such a blending ratio, wear resistance can be ensured while maintaining low friction.

[0009] The fifth aspect of this invention defines the manufacturing method of the sliding member defined in the first aspect. That is, a step of forming a porous metal layer on one surface of the backing layer, a step of laminating a first fluororesin material so as to fill the porous metal layer to form a first precursor layer, a first pressing step of pressing the surface of the first precursor layer toward the backing layer to flatten the surface, a step of laminating a second fluororesin material on the pressed first precursor layer to form a second precursor layer, a second pressing step of pressing the surface of the second precursor layer toward the backing layer to flatten the surface, after the second pressing step is completed, a drying step of drying the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer and a sintering step of sintering them, and A manufacturing method of a sliding member, wherein the first precursor layer and the second precursor layer are used as a first layer and a second layer, respectively, to form a coating layer covering the porous metal layer.

[0010] According to the manufacturing method of the fifth aspect defined in this way, the first precursor layer which is a laminate of the first fluororesin material is subjected to two-stage pressing by the first pressing step and the second pressing step, whereas only one-stage pressing by the second pressing step is applied to the second precursor layer. As a result, the first fluororesin material constituting the first precursor layer is more strongly pressed and its density becomes higher than the second fluororesin material constituting the second precursor layer. Therefore, the first layer obtained through the drying step and the firing step has a higher density than the second layer, and thus the former becomes harder than the latter. Before the second pressing step, a step of drying the first precursor layer can preferably be added, preferably between the first pressing step and the step of forming the second precursor layer (Aspect 6).

[0011] In the above, it is preferable that the first fluororesin material constituting the first precursor layer and the second fluororesin material constituting the second precursor layer are the same material, because it more surely connects both layers. In addition to PTFE, the first and second fluororesins may employ one or more of perfluoroalkoxyethylene copolymer resin (PFA), tetrafluoride / hexafluoride propylene copolymer resin, tetrafluoroethylene / ethylene copolymer resin, vinylidene fluoride resin, chlorotrifluoroethylene resin, vinyl fluoride resin, ethylene / chlorotrifluoroethylene resin, etc. In the second pressing step, pressure is applied so that the interface between the first precursor layer and the second precursor layer follows the surface of the porous metal layer (Aspect 7). Thereby, the sliding member defined in Aspect 2 can be obtained.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] FIG. 1 shows a cross-section of the sliding member 1 of the embodiment. This sliding member 1 has a configuration in which a porous metal layer 3 and a coating layer 5 are sequentially laminated on the upper surface of the backing layer 2. In FIG. 1, the shape and size ratio of each element are for clearly showing its existence and do not reflect the actual shape and size ratio. A general-purpose steel plate is adopted for the backing layer 2, and its material, shape, thickness, etc. are appropriately selected according to the conditions under which the sliding member is applied. The material, particle diameter, particle shape, thickness, etc. of the particles constituting the porous metal layer 3 are also appropriately selected according to the conditions under which the sliding member is applied. In this example, a sintered body of spherical bronze-based alloy particles with an average particle diameter of 50 to 200 μm is adopted.

[0014] The coating layer 5 includes a first layer 10 and a second layer 20. The first layer 10 and the second layer 20 are preferably formed of the same PTFE material, but different PTFE materials can also be adopted as long as they can be bonded by sintering. The first layer 10 has a thickness for embedding the porous metal layer 3 therein. The thickness from the porous metal layer 3 to the surface of the first layer 10 (interface 7 between the first layer and the second layer) is not particularly limited, but can be 0 (excluding 0) to 20 μm. By providing such a margin layer 11 in the first layer 10, the unevenness on the surface of the porous metal layer 3 can be reflected on the interface 7.

[0015] The second layer 20 is laminated on the first layer 10, and its surface is maintained flat. The thickness of the second layer 20 (the thickness from the interface 7 to the surface of the second layer 20) can be appropriately selected according to the conditions under which the sliding member is applied. In this example, it is set to 5 to 30 μm. It is preferable to incorporate a solid lubricant as an additive in the second layer 20. Thereby, its wear resistance is improved. The solid lubricant incorporated into the second layer 20 can be 5 to 40% by volume. Improvement in wear resistance can be ensured within this range. In addition to the solid lubricant, additives such as hard particles and fillers can be incorporated into the second layer 20.

[0016] The above additives can also be incorporated into the first layer 10. The additives shall include solid lubricants. In the above, graphite, molybdenum disulfide, fluororesin particles, tungsten disulfide, boron nitride, etc. can be adopted as the solid lubricant. For the hard particles, borides, silicides, oxides, nitrides, carbides, intermetallic compounds, etc. can be adopted. The average particle size of the hard particles can be 0.5 - 20 (μm). The above-mentioned borides are preferably NiB, Ni3B, CrB, CrB, ZrB2, CoB, TiB2, VB2, TaB2, WB, MoB, Fe-B system, etc. The silicides are preferably TiSi2, WSi2, MoSi2, TaSi2, CrSi2, Fe-Si system, Mn-Si system, etc. The oxides are preferably SnO2, SiO2, Al2O3, TiO2, ZrO2, WO, MoO3, Mn-O system, Fe-O system, V-O system, etc. The nitrides are preferably Si2N4, TiN, ZrN, TaN, VN, AlN, C-BN, Cr2N, etc. The carbides are preferably WC, W2C, SiC, B4C, TiC, TaC, VC, ZrC, Mo2C, etc. The intermetallic compounds are preferably Ni-Sn system, Fe-W system, Fe-Mo system, Fe-Mn system, Fe-Cr system, Fe-Al system, Cr-Al system, V-Al system, Ti-Al system, W-Al system, etc.

[0017] Also, as materials for other hard particles, Ni-based self-fluxing alloys (Ni-B-Si system), Co-based self-fluxing alloys (Co-Mo-Si-B system), C, W or Mo may be used. The filler may contain liquid crystal polymer, barium sulfate, etc. The hard particles are particularly preferably metal silicides or metal carbides. For the additives, CaF2, CaCO3, talc, mica, mullite, calcium phosphate, potassium titanate, etc. can be adopted.

[0018] In order to ensure a low friction coefficient and wear resistance, the blending ratio of these additives can be 5 - 40% by volume in the first layer 10 and the second layer 20. The blending ratio of the additives can be made different in the first layer 10 and the second layer 20. In order to ensure a low coefficient of friction and wear resistance, more preferably in the second layer, the compounding amount of the additive including the solid lubricant is preferably 5% to 20% by volume. In the first layer, it is preferably 15% to 35% by volume.

[0019] The coating layer 5 can be formed of two or more layers. In this case, the layer that becomes the uppermost layer is the second layer, and the layer in which the porous metal layer is embedded is the first layer. When the second layer and the first layer are composed of a plurality of layers, the difference between the martensite hardness of the layer in contact with the second layer and that of the first layer is increased by 15% to 56%.

[0020] Next, the manufacturing method of the sliding member 1 in FIG. 2 will be described. A strip-shaped steel material is prepared as the backing layer 2, spherical bronze-based alloy particles with an average particle diameter of 50 to 200 μm are laminated on the upper surface of the backing layer 2 to a thickness of 300 μm, and sintered under the conditions of 900 ° C. and 20 minutes in a reducing atmosphere to form the porous metal layer 3. Next, a first PTFE material that becomes the material of the first layer 10 is prepared. As this first PTFE material, powdery PTFE is used as the base material, and a molding aid is added to a mixture in which an additive is dispersed therein as necessary. As shown in FIG. 2, this material is laminated on a strip-shaped base material A provided with the porous metal layer 3 on the backing layer 2 so that the porous metal layer 3 is hidden (Step 1: S1). This material is rolled with a roller and impregnated into the voids of the porous metal layer 3 to form a first precursor layer (Step 3: S3).

[0021] Next, a second PTFE material that becomes the material of the second layer 20 is prepared. This second PTFE material is the same material as the first PTFE material, and additives and molding aids are added as appropriate. This material is laminated on the first precursor layer in Step 5 (S5) and rolled with a roller to form a second precursor layer (Step 7: S7). At this time, the first precursor layer is further rolled, its density becomes higher than that of the second precursor layer, and the interface 7 between the first precursor layer and the second precursor layer follows the upper surface of the porous metal layer 3 and has an uneven shape as shown in FIG. 1.

[0022] Step 9 (S9) is a drying process, in which the workpiece after the roller treatment in Step 7 is dried under the condition of 100°C to 200°C to volatilize and remove the forming aid. Step 11 (S11) is a sintering process, in which the workpiece after the drying process in Step 9 is heated and sintered under the condition of 380°C to 420°C, and the first PTFE material of the first precursor layer and the second PTFE material of the second precursor layer are respectively cured and bonded to form the first layer 10 and the second layer 20. In Step 13 (S13), further rolling treatment is performed by a roller to adjust the thickness dimension and smooth the surface. Then, the workpiece is cut to form a sliding member.

[0023] FIG. 3 shows a manufacturing method of another embodiment. In FIG. 3, the same elements as those in FIG. 2 are denoted by the same reference numerals and their descriptions are omitted. In the example of FIG. 3, in Step 9A (S9A), the first precursor layer is dried. The drying conditions are the same as those in Step 9. By drying the first precursor layer in Step 9A, the forming aid is removed from the first precursor layer, and the fine space formed thereby is filled by the roller treatment in Step 7. As a result, the density of the second layer is further improved, and thus its hardness is improved.

[0024] Table 1 shows the relationship between the difference in the Martens hardness of the first layer and the second layer and the wear resistance of the sliding members of the examples and comparative examples obtained by the manufacturing method of FIG. 2.

Table 1

[0025] In this example, since the first PTFE material and the second PTFE material are the same material, the martensitic hardness of each layer is adjusted by the addition amount of the molding aid. By adding more molding aid, the martensitic hardness of the PTFE material as the base material becomes smaller. This is because the molding aid is removed during drying, and PTFE formed by adding a large amount of molding aid is likely to have a reduced density. The adjustment of the hardness of the first layer and the second layer can also be adjusted by adjusting, in addition to the addition amount of the molding aid, the material of the molding aid, the drying conditions, the sintering conditions, the degree of polymerization of the PTFE itself, and the like.

[0026] The martensitic hardness can be measured by a measurement method compliant with the international standard ISO14577 for micro-indentation tests. As the test apparatus, a Shimadzu dynamic ultra-micro altimeter DUH-211 manufactured by Shimadzu Corporation was used, and the test was conducted from the cross-sectional direction of the sliding layer with a maximum test force of 5 mN and a holding time of 10 seconds. The measurement locations avoided the filler as much as possible, and the average of 10 measurements was taken as the martensitic hardness. The martensitic hardness MH is obtained as HM = P / A from the test load P and the surface area A into which the indenter (probe) penetrated.

[0027] The test conditions are as follows. Testing machine: Thrust sliding testing machine. Load: 10 MPa. Speed: 1.5 m / second. Lubricating oil: Oil bath. Lubricating oil: VG22. Counter shaft: S45C hardened. Test time: 180 minutes. Although the evaluation is carried out in oil, it is an evaluation in a boundary lubrication environment where almost no oil film is formed because the sliding is performed with as little oil intervening between the counter material and the test piece as possible.

[0028] In Table 1, an example where seizure did not occur during the 180-minute test is marked as "〇", and an example where seizure occurred during the test is marked as "×". The relationship between the test time and the friction coefficient of Example 1, Comparative Example 1, and Comparative Example 2 is shown in FIG. 4. In FIG. 4, the solid line represents the result of Example 1, the dotted line (the rising line on the left side) represents Comparative Example 1, and the broken line (the rising line on the right side) represents Comparative Example 2. × indicates the seizure state. As can be seen from FIG. 4, a low friction coefficient is obtained even in the initial stage of sliding.

[0029] Table 2 shows the sliding characteristics of the sliding members in which various additives are blended in the first PTFE material and the second PTFE material. In Table 2, the blending amount of each composition is in volume %.

Table 2

[0030] In the evaluation results of Table 2, "wear" is evaluated as "double circle" when the difference in thickness before and after the test is less than 20 μm, "single circle" when it is from 20 μm to 30 μm, and "triangle" when it is 30 μm or more. "Final friction coefficient" takes the average value between the test time of 150 minutes to 180 minutes, and is evaluated as "double circle" when the friction coefficient is less than 0.1, "single circle" when it is from 0.1 to 0.3, and "triangle" when it is 0.3 or more. In Table 2, from the results of Example 7 and Example 10 where both "wear" and "final friction coefficient" are "double circle", it can be seen that the addition amount of the additive in the first layer and the second layer is preferably 5 volume % to 40 volume %. In order to ensure a low friction coefficient and wear resistance, more preferably in the second layer, the blending amount of the additive including the solid lubricant is preferably 5 volume % to 20 volume %. In the first layer, it is preferably 15 volume % to 40 volume %.

[0031] In this specification, the average particle diameter means the particle diameter at the integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. The present invention is not limited to the description of the embodiments and examples of the above invention. Various modifications are also included in the present invention within the scope that can be easily conceived by those skilled in the art without departing from the description of the claims.

Explanation of Reference Numerals

[0032] 1 Sliding member 2 Back metal layer 3 Porous metal layer 5 Coating layer 7 Interface 10 First layer 20 Second layer

Claims

1. A sliding member comprising a backing metal layer, a porous metal layer formed on one surface of the backing metal layer, and a coating layer covering the porous metal layer, wherein the coating layer includes a first layer embedded in the porous metal layer and a second layer laminated on the first layer, and the martensitic hardness of the first layer is 15% to 56% higher than the martensitic hardness of the second layer. Here, the value of the difference (%) between the martensitic hardness of the first layer and the martensitic hardness of the second layer is obtained as follows: (Martensitic hardness of the first layer / Martensitic hardness of the second layer) × 100 - 100 Sliding member.

2. The sliding member according to claim 1, wherein the porous metal layer is buried in the first layer, and the interface between the first layer and the second layer follows the surface of the porous metal layer.

3. The sliding member according to claim 1, wherein at least the second layer in the coating layer is blended with a solid lubricant.

4. An additive is blended in the first layer and the second layer of the coating layer, and the blending amount of the additive is 5% to 40% by volume, and the additive contains a solid lubricant. The sliding member according to claim 3.

5. A step of forming a porous metal layer on one surface of a backing metal layer; A step of laminating a first fluororesin material so that the porous metal layer is buried to form a first precursor layer; A first pressing step of pressing the surface of the first precursor layer toward the backing metal layer to flatten the surface; A step of laminating a second fluororesin material on the pressed first precursor layer to form a second precursor layer; A second pressing step of pressing the surface of the second precursor layer toward the backing metal layer to flatten the surface; After the second pressing step is completed, a drying step of drying the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer and a sintering step of sintering them are included, A method for manufacturing a sliding member, wherein the first precursor layer and the second precursor layer are used as a first layer and a second layer, respectively, to form a coating layer covering the porous metal layer.

6. The manufacturing method according to claim 5, including a drying step of drying the first precursor layer before the second pressing step.

7. In the second pressing step, pressing is performed so that the interface between the first precursor layer and the second precursor layer follows the surface of the porous metal layer. The manufacturing method according to claim 6.

8. The method according to claim 5, wherein both the first fluororesin material and the second fluororesin material are polytetrafluoroethylene materials.

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