Sliding member and method for manufacturing same

Abstract

The purpose of the present invention is to provide a sliding member in which the coefficient of friction is suppressed in the initial stage of sliding, and excellent wear resistance can be maintained while maintaining a low coefficient of friction in the middle or later stage of sliding. This sliding member is provided with a metal backing layer, a porous metal layer, and a coating layer containing a polytetrafluoroethylene material and coating the porous metal layer, and is characterized in that the coating layer is provided with 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 15-56% higher than the Martens hardness of the second layer, and the Martens hardness of the second layer is 15-56% higher than the Martens hardness of the porous metal layer. Here, the value of the difference (%) between the Martens hardness of the first layer and the Martens hardness of the second layer is obtained in such a manner that (Martens hardness of the first layer / Martens hardness of the second layer) * 100-100.

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 metal backing layer is coated with a coating layer having polytetrafluoroethylene (sometimes simply referred to as PTFE in this specification) as a base material.

[0003] PTFE has a low coefficient of friction and excellent chemical resistance and heat resistance, but poor abrasion resistance. Therefore, additive materials such as solid lubricants and hard particles are usually uniformly filled.

[0004] For the above, refer to Patent Documents 1 to 3.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-156650

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-190870

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2020-200909 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] In the initial stage of sliding of a sliding member, it is sometimes difficult to form an oil film between the sliding member and the object to be slid. Therefore, a low coefficient of friction is required for the sliding member itself, in other words, for the coating layer on its outermost layer itself.

[0012] As sliding progresses, an oil film is formed. Therefore, the importance of the low friction required for the sliding member is reduced compared to the initial stage of sliding. On the other hand, higher abrasion resistance is required.

[0013] The coating layer having PTFE as a base material, including the dispersion state of the additive material, is formed uniformly as a whole. In such a sliding member, it is difficult to flexibly change the sliding performance according to the progress of sliding as described above.

[0014] Therefore, an object of the present invention is to provide a sliding member having a low coefficient of friction in the initial stage of sliding and maintaining a low coefficient of friction while maintaining excellent abrasion resistance in the middle or later stage of sliding.

[0015] Means for Solving the Problems

[0016] The inventors of the present invention have repeatedly conducted in-depth research to solve the above problems, and as a result, they believe that if the surface layer of the coating layer of the sliding member is softer than its inner layer, the following effects can be obtained. That is, in the initial stage of sliding, the relatively soft surface layer can reduce the friction coefficient, and after the sliding proceeds, through the relatively hard inner layer, while maintaining the original low friction coefficient of PTFE, abrasion resistance is exhibited.

[0017] The first aspect of the present invention is completed based on the above insights of the inventors. That is, a sliding member includes a metal backing layer, a porous metal layer formed on one surface of the metal backing layer, and a coating layer containing a polytetrafluoroethylene material that coats the porous metal layer. Among them, the coating layer includes 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. Here, the value of the difference (%) between the Martens hardness of the first layer and the Martens hardness of the second layer is obtained in the following manner: (Martens hardness of the first layer / Martens hardness of the second layer) × 100 - 100.

[0018] According to the sliding member of the first aspect defined in this way, its coating layer includes the second layer on the surface side and the first layer in which the porous metal layer is embedded inside. The inner first layer is harder than the second layer on the surface side.

[0019] Moreover, by making the hardness difference 15% to 56%, it is possible to suppress the friction coefficient of the coating layer based on PTFE in the initial stage of sliding, and to maintain excellent abrasion resistance while maintaining a low friction coefficient in the middle or late stage of sliding.

[0020] Here, the Martens hardness is obtained by implementing a measurement method based on the international standard ISO14577.

[0021] The Martens hardness of each of the first layer and the second layer can be the hardness measured by pressing a detector in the vertical direction with respect to the base material regions (PTFE regions) of the first layer and the second layer that appear in the cross-section of the sliding member.

[0022] The second aspect of the present 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 imitates the surface of the porous metal layer.

[0023] Since the porous metal layer is generally formed by sintering metal particles, its surface becomes an uneven shape along the surfaces of the metal particles and their particle masses.

[0024] In the sliding member defined in the second aspect, the interface between the first layer and the second layer imitates the surface of the porous metal layer having the concavo-convex shape. Even if the wear of the relatively soft second layer is aggravated, this aggravation is suppressed by the first layer having high wear resistance at the interface with the first layer. At this time, since there are concavo-convexities imitating the surface of the porous metal layer at the interface between the first layer and the second layer, a relatively soft PTFE material constituting the second layer remains in the recessed portions thereof. In other words, even if the second layer is almost worn away, the relatively soft PTFE material constituting the second layer remains on the surface of the first layer. Therefore, even in a state where the oil film is insufficient at the initial sliding stage of the sliding member, a low coefficient of friction can be ensured.

[0025] In the above, it is preferable that the PTFE of the first layer and the second layer be the same material. This is to reliably bond the two.

[0026] It is preferable to incorporate a solid lubricant in the second layer (third aspect). This is to impart wear resistance while maintaining low friction.

[0027] In addition, an additive material can be incorporated into the second layer and the first layer. Desirably, the compounding amount of the additive material is 5 vol% to 40 vol%, and the additive material contains a solid lubricant (fourth aspect). At this compounding ratio, wear resistance can be ensured while maintaining low friction.

[0028] The fifth aspect of the present invention defines a method for manufacturing the sliding member defined in the first aspect. That is, a method for manufacturing a sliding member, which includes: a step of forming a porous metal layer on one surface of a metal backing layer; a step of laminating a first fluororesin material 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 metal backing layer to make its surface flat; 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 metal backing layer to make its surface flat; a drying step of drying the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer after the second pressing step, and

[0029] a sintering step of sintering the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer. In the method for manufacturing the sliding member, the first precursor layer and the second precursor layer are used as the first layer and the second layer, respectively, as the coating layers for coating the porous metal layer.

[0030] According to the manufacturing method of the fifth aspect thus defined, the first precursor layer of the laminate as the first fluororesin material is pressurized in two stages by the first pressurization step and the second pressurization step. In contrast, the second precursor layer is pressurized in one stage only by the second pressurization step.

[0031] As a result, the first fluororesin material constituting the first precursor layer is more strongly compacted than the second fluororesin material constituting the second precursor layer, and its density is higher.

[0032] 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 is harder than the latter.

[0033] Before the second pressurization step, preferably between the first pressurization step and the step of forming the second precursor layer, a step of drying the first precursor layer can be added (sixth aspect).

[0034] In the above, preferably, the first fluororesin material constituting the first precursor layer and the second fluororesin material constituting the second precursor layer are the same material, because this will more reliably connect the two layers.

[0035] For the first fluororesin and the second fluororesin, in addition to PTFE, one or more of perfluoroalkoxy ethylene copolymer resin (PFA), tetrafluoro / hexafluoropropylene copolymer resin, tetrafluoroethylene / ethylene copolymer resin, vinylidene fluoride resin, chlorotrifluoroethylene resin, vinyl fluoride resin, ethylene / chlorotrifluoroethylene resin, etc. can also be used.

[0036] In the second pressurization step, pressurization is performed in such a manner that the interface between the first precursor layer and the second precursor layer imitates the surface of the porous metal layer (seventh aspect). Thus, the sliding member defined in the second aspect can be obtained. Brief Description of the Drawings

[0037] Figure 1 is a cross-sectional view of the sliding member of the embodiment of the present invention.

[0038] Figure 2 is a schematic diagram showing the manufacturing method of the embodiment of the present invention.

[0039] Figure 3 is a schematic diagram showing the manufacturing method of other embodiments of the present invention.

[0040] Figure 4 shows the change over time of the coefficient of friction of the examples and comparative examples of the present invention. Detailed Description of the Embodiments

[0041] Figure 1 represents a cross-section of the sliding member 1 of the embodiment. This sliding member 1 has a structure in which a porous metal layer 3 and a coating layer 5 are sequentially laminated on the upper surface of a metal backing layer 2.Figure 1 In this case, the shapes and size ratios of the respective elements are for clearly showing their existence and do not reflect the actual shape and size ratios.

[0042] The metal backing layer 2 uses a general steel plate, and its material, shape, thickness, etc. are appropriately selected according to the conditions applicable to the sliding member.

[0043] The material, particle size, particle shape, thickness, etc. of the particles constituting the porous metal layer 3 can also be appropriately selected according to the conditions applicable to the sliding member. In this example, a sintered body of spherical bronze-based alloy particles with an average particle size of 50 μm to 200 μm is used.

[0044] Preferably, the coating layer 5 includes a first layer 10 and a second layer 20. The first layer 10 and the second layer 20 are formed of the same PTFE material, but different PTFE materials can also be used as long as they can be sintered and bonded.

[0045] The first layer 10 has a thickness that allows the porous metal layer 3 to be embedded therein. The thickness from the porous metal layer 3 to the surface of the first layer 10 (the interface 7 between the first layer and the second layer) is not particularly limited and can be 0 (excluding 0) μm to 20 μm. By providing such a margin layer 11 to the first layer 10, the unevenness on the surface of the porous metal layer 3 can be reflected on the interface 7.

[0046] The second layer 20 is laminated on the first layer 10, and its surface remains flat. The thickness of the second layer 20 (the thickness from the interface 7 to the surface of the second layer 20) can also be appropriately selected according to the conditions applicable to the sliding member, but in this example, it is 5 μm to 30 μm.

[0047] Preferably, a solid lubricant is incorporated as an additive material in the second layer 20. Thereby, its wear resistance is improved. The solid lubricant incorporated into the second layer 20 can be 5 vol% to 40 vol%. The improvement of wear resistance can be ensured within this range.

[0048] In the second layer 20, in addition to the solid lubricant, additive materials such as hard particles and fillers can also be incorporated.

[0049] The above-mentioned additive materials can also be incorporated in the first layer 10. The additive material contains a solid lubricant.

[0050] In the above, the solid lubricant can be graphite, molybdenum disulfide, fluororesin particles, tungsten disulfide, boron nitride, etc.

[0051] The hard particles can be borides, silicides, oxides, nitrides, carbides, intermetallic compounds, etc. The average particle size of the hard particles can be 0.5 to 20 (μm).

[0052] The above borides are preferably NiB, Ni3B, CrB, CrB, ZrB2, CoB, TiB2, VB2, TaB2, WB, MoB, Fe-B series, etc. The silicides are preferably TiSi2, WSi2, MoSi2, TaSi2, CrSi2, Fe-Si series, Mn-Si series, etc. The oxides are preferably SnO2, SiO2, Al2O3, TiO2, ZrO2, WO, MoO3, Mn-O series, Fe-O series, V-O series, 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. As the intermetallic compound, Ni-Sn series, Fe-W series, Fe-Mo series, Fe-Mn series, Fe-Cr series, Fe-Al series, Cr-Al series, V-Al series, Ti-Al series, W-Al series, etc. are preferred.

[0053] In addition, as other hard particles, Ni-based self-fluxing alloys (Ni-B-Si series), Co-based self-fluxing alloys (Co-Mo-Si-B series), C, W or Mo can be used.

[0054] As the filler, liquid crystal polymers, barium sulfate, etc. can be contained.

[0055] The hard particles are particularly preferably silicides or carbides of metals.

[0056] Additive materials can be CaF2, CaCO3, talc, mica, mullite, calcium phosphate, potassium titanate, etc.

[0057] In order to ensure a low coefficient of friction and wear resistance, the mixing ratio of these additive materials can be 5 vol% to 40 vol% in the first layer 10 and the second layer 20.

[0058] The mixing ratio of the additive materials can be different in the first layer 10 and the second layer 20.

[0059] In order to ensure a low coefficient of friction and wear resistance, more preferably in the second layer, the mixing amount of the additive materials including the solid lubricant material is preferably 5 vol% to 20 vol%. In the first layer, it is preferably 15 vol% to 35 vol%.

[0060] The coating layer 5 can be formed by two or more layers.

[0061] In this case, the layer that becomes the uppermost layer is regarded as the second layer, and the layer buried in the porous metal layer is regarded as the first layer. When the second layer and the first layer are composed of multiple layers, the difference in Martens hardness between the layer in contact with the second layer and the Martens hardness of the first layer is increased by 15% to 56%.

[0062] Next, a manufacturing method of the sliding member 1 of Figure 2 will be described. Figure 2 The manufacturing method of the sliding member 1 of Figure 2 will be described.

[0063] Prepare a strip-shaped steel material as the metal backing layer 2, stack spherical bronze-based alloy particles with an average particle size of 50 μm to 200 μm on the upper surface of the metal backing layer 2 with a thickness of 300 μm, and sinter in a reducing atmosphere at 900 °C for 20 minutes to form a porous metal layer 3.

[0064] Next, prepare a first PTFE material that becomes the material of the first layer 10. As this first PTFE material, powdery PTFE is used as the base material, and a molding aid is added to the mixture in which additive materials are dispersed as needed. As shown in Figure 2 Stack this material on the strip-shaped base material A having the porous metal layer 3 on the metal backing layer 2, and hide the porous metal layer 3 (Step 1: S1). Roll-press this material to impregnate it into the voids of the porous metal layer 3 to become a first precursor layer (Step 3: S3).

[0065] Next, prepare a second PTFE material that becomes the material of the second layer 20. This second PTFE material is the same material as the first PTFE material, and additive materials and a molding aid are appropriately added.

[0066] In Step 5 (S5), stack this material on the first precursor layer and roll-press it to form a second precursor layer (Step 7: S7). At this time, the first precursor layer is further pressed, and 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 becomes uneven like the upper surface of the porous metal layer 3 as shown in Figure 1 shown.

[0067] Step 9 (S9) is a drying process, and the workpiece after the roll treatment in Step 7 is dried at 100 °C to 200 °C to volatilize and remove the molding aid.

[0068] Step 11 (S11) is a sintering process, and the workpiece after the drying process in Step 9 is heated and fired at 380 °C to 420 °C to cure and bond the first PTFE material of the first precursor layer and the second PTFE material of the second precursor layer respectively, to become the first layer 10 and the second layer 20.

[0069] In Step 13 (S13), further perform a roll pressing process to adjust the thickness dimension and achieve surface smoothing. Then, cut the workpiece to make the sliding member.

[0070] Figure 3 Another manufacturing method is shown. In Figure 3 it shows, for Figure 2The same elements are labeled with the same symbols and their descriptions are omitted.

[0071] In Figure 3 's example, the first precursor layer is dried in step 9A (S9A). The drying conditions are the same as those in step 9.

[0072] The first precursor layer is dried through step 9A, so that the fine spaces formed by removing the forming aid from the first precursor layer are filled by the roll treatment in step 7. Thereby, the density of the second layer is further increased, and thus its hardness is increased.

[0073] Through Figure 2 The relationship between the difference in Martens hardness and the abrasion resistance of the first and second layers of the sliding members of the examples and comparative examples obtained by the manufacturing method of

[0074] [Table 1]

[0075]

[0076] In each example in Table 1, the first PTFE material and the second PTFE material both use the product name (CD097E manufactured by AGC).

[0077] From the results in Table 1, it can be seen that by making the difference in Martens hardness between the first layer formed of PTFE material and the second layer formed of PTFE material: (Martens hardness of the first layer / Martens hardness of the second layer) × 100 - 100 be 15% to 56%, abrasion resistance can be obtained.

[0078] In this example, since the first PTFE material and the second PTFE material are the same material, the Martens hardness of each layer is adjusted by the addition amount of the forming aid. By adding a large amount of the forming aid, the Martens hardness of the PTFE material as the base material becomes smaller. This is because, since the forming aid is removed during drying, the density of the PTFE formed by adding a large amount of the forming aid is likely to decrease.

[0079] The adjustment of the hardness of the first and second layers can be carried out by adjusting, in addition to the addition amount of the forming aid, the material of the forming aid, the drying conditions, the sintering conditions, the degree of polymerization of the PTFE itself, etc.

[0080] Martens hardness can be measured by a measurement method based on the international standard ISO14577 for micro-indentation test. As a test device, the Shimadzu dynamic ultra-micro-height gauge DUH-211 manufactured by Shimadzu Corporation is used, and the test is carried out from the cross-sectional direction of the sliding layer with a maximum test force of 5mN and a holding time of 10 seconds. The measurement site is kept away from the filler as much as possible, and the average of the 10 measured locations is taken as the Martens hardness. The Martens hardness MH is calculated as HM=P / A based on the test load P and the surface area A of the indenter (probe) intrusion.

[0081] The test conditions are as follows.

[0082] Testing machine: thrust sliding testing machine.

[0083] Load: 10MPa.

[0084] Speed: 1.5m / sec.

[0085] Lubrication: Oil bath.

[0086] Lubricant:VG22.

[0087] Object shaft: S45C quenching.

[0088] Test time: 180 minutes.

[0089] The evaluation was performed in oil, but since the sliding was performed with as little oil as possible sandwiched between the counterpart material and the test piece, the evaluation was performed under a boundary lubrication environment where almost no oil film was formed.

[0090] In Table 1, the case where sintering did not occur during the 180-minute test was recorded as "0", and the case where sintering occurred during the test was recorded as "×".

[0091] The relationship between the test time and the friction coefficient of Example 1, Comparative Example 1 and Comparative Example 2 is shown in FIG. Figure 4 .exist Figure 4 In the figure, the solid line represents the result of Example 1, the dotted line (the rising line on the left) represents the result of Comparative Example 1, and the dashed line (the rising line on the right) represents the result of Comparative Example 2. × represents the sintered state.

[0092] Depend on Figure 4 It can be seen that a low friction coefficient is also obtained in the initial stage of sliding.

[0093] Table 2 shows the sliding properties of sliding members in which various additives were blended into the first PTFE material and the second PTFE material.

[0094] The blending amount of each composition in Table 2 is vol%.

[0095] [Table 2]

[0096]

[0097] In the evaluation results in Table 2, when the difference in thickness before and after the test of "wear" is less than 20 μm, it is evaluated as "double circle", when it is between 20 μm and 30 μm, it is evaluated as "single circle", and when it is more than 30 μm, it is evaluated as "triangle". The "final friction coefficient" takes the average value between 150 minutes and 180 minutes of the test time, and when its friction coefficient is less than 0.1, it is evaluated as "double circle", when it is between 0.1 and 0.3, it is evaluated as "single circle", and when it is more than 0.3, it is evaluated as "triangle".

[0098] 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 material in the first layer and the second layer is preferably 5% by volume to 40% by volume.

[0099] In order to ensure a low friction coefficient and wear resistance, more preferably in the second layer, the compounding amount of the additive material including the solid lubricant material is preferably 5% by volume to 20% by volume. In the first layer, it is preferably 15% by volume to 40% by volume.

[0100] In this specification, the average particle size refers to the particle size at which the integral value is 50% in the particle size distribution obtained by the laser diffraction scattering method.

[0101] The present invention is not limited by any of the descriptions of the above embodiments and examples of the invention. Various deformation modes within the scope that can be easily conceived by those skilled in the art without departing from the description of the claims are also included in the present invention.

[0102] Symbol Explanation

[0103] 1: Sliding member;

[0104] 2: Metal backing layer;

[0105] 3: Porous metal layer;

[0106] 5: Coating layer;

[0107] 7: Interface;

[0108] 10: First layer;

[0109] 20: Second layer.

Claims

1. A sliding member comprising a metal backing layer, a porous metal layer formed on one side of the metal backing layer, and a coating layer containing a polytetrafluoroethylene material covering the porous metal layer, wherein: The coating layer includes a first layer embedded in the porous metal layer and a second layer stacked on the first layer, wherein the Martens hardness of the first layer is 15% to 56% higher than the Martens hardness of the second layer, and the 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.

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 imitates the surface of the porous metal layer.

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

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

5. A method for manufacturing a sliding member, comprising: The step of forming a porous metal layer on one side of the metal 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 metal backing layer to make the surface flat; The step of laminating a second fluororesin material on the pressurized first precursor layer to form a second precursor layer; A second pressing step of pressing the surface of the second precursor layer toward the metal backing layer to make the surface flat; a drying step of drying the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer after the second pressurizing step is completed; and a sintering step of sintering the first fluororesin material of the first precursor layer and the second fluororesin material of the second precursor layer, In the method for manufacturing the sliding member, the first precursor layer and the second precursor layer are used as the first layer and the second layer, respectively, as the coating layer that covers the porous metal layer.

6. The manufacturing method according to claim 5, wherein: include: Prior to the second pressurizing step, a drying step is performed on the first precursor layer.

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

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

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