Method for manufacturing sliding member and fluid pressure equipment

Abstract

This method for manufacturing a sliding member (100), which is provided to equipment in which a fluid is sealed and in which a trivalent chromium plating layer 3 is formed on a sliding part, comprises: a plating layer formation step for forming the trivalent chromium plating layer (3) on a steel base material (1) or a nickel plating layer (2) formed on the surface of the steel base material (1); a first polishing step for polishing the surface of the trivalent chromium plating layer (3); and a baking step for, after the first polishing step, performing a baking treatment on the trivalent chromium plating layer (3).

Description

Manufacturing method of sliding member and fluid pressure device

[0001] The present invention relates to a method for manufacturing a slide member and a fluid pressure device.

[0002] JPH5-311467A discloses a surface treatment method for applying hexavalent chromium plating, which is hard and has excellent wear resistance, to sliding parts (piston rods) of fluid pressure cylinders, shock absorbers, etc. In the treatment method described in JPH5-311467A, after applying hexavalent chromium plating to the sliding parts, baking is performed to prevent hydrogen embrittlement. Microcracks exist on the surface of the hexavalent chromium plating layer, and the width of the microcrack grooves increases after baking. Therefore, polishing is performed after baking to cause plastic flow on the surface of the hexavalent chromium plating layer, thereby reducing the groove width of the enlarged cracks.

[0003] In recent years, due to the large environmental impact of the hexavalent chromium contained in hexavalent chromium plating, replacement with trivalent chromium plating, which has a smaller environmental impact, has been considered. Trivalent chromium plating has the property of significantly increasing its hardness by baking compared to hexavalent chromium. Therefore, when the method described in JPH5-311467A is applied to trivalent chromium plating, plastic flow is unlikely to occur during polishing, and the crack groove width cannot be sufficiently reduced. When trivalent chromium plating is applied to the sliding parts of sliding parts of equipment that contains fluid, if the crack groove width in the trivalent chromium plating layer is not sufficiently small, there is a risk of fluid leaking through the crack to the outside.

[0004] An object of the present invention is to reduce the groove width of cracks in a trivalent chromium plating layer.

[0005] According to one aspect of the present invention, there is provided a method for manufacturing a sliding member that is provided in a device that seals a fluid and has a trivalent chromium plating layer formed on a sliding portion, the method comprising: a plating layer forming step of forming a trivalent chromium plating layer on a base material or on a base plating layer formed on the surface of the base material; a first polishing step of polishing the surface of the trivalent chromium plating layer; and a baking step of baking the trivalent chromium plating layer after the first polishing step.

[0006] FIG. 1 is a laser microscope photograph of a cross section of a slide member according to an embodiment of the present invention after the formation of a plating layer. FIG. 2 is a schematic diagram of a polishing apparatus used in the first polishing step. FIG. 3 is a schematic diagram showing the trivalent chromium plating layer and cracks in each step of a slide member according to an embodiment of the present invention. FIG. 4 is a schematic diagram showing the trivalent chromium plating layer and cracks in each step of a slide member according to a comparative embodiment of the present invention. FIG. 5 is a laser microscope photograph of the surface of the trivalent chromium plating layer after a baking treatment, where (a) shows the slide member according to an embodiment of the present invention and (b) shows the slide member according to a comparative embodiment of the present invention. FIG. 6 is a laser microscope photograph of the surface of the trivalent chromium plating layer after a second polishing step, where (a) shows the slide member according to an embodiment of the present invention and (b) shows the slide member according to a comparative embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a fluid pressure cylinder equipped with a slide member according to an embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of a shock absorber equipped with a slide member according to an embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of a front fork equipped with a slide member according to an embodiment of the present invention.

[0007] Hereinafter, a method for manufacturing a slide member according to an embodiment of the present invention will be described with reference to the drawings.

[0008] The sliding member is provided in a fluid pressure device that seals a fluid, and has a trivalent chromium plating layer formed on a sliding portion.

[0009] An example of a fluid pressure device containing a fluid is a fluid pressure cylinder 90 used as an actuator, as shown in FIG. 7 . The fluid pressure cylinder 90 includes a cylinder tube 91, a piston rod 92 reciprocally disposed within the cylinder tube 91, a piston 93 disposed at the tip of the piston rod 92, a cylinder head 94 connected to and closing the open end of the cylinder tube 91, and a seal member 98 disposed at the open end of the cylinder tube 91 and in sliding contact with an outer circumferential surface 92a of the piston rod 92. The seal member 98 is disposed on the inner circumferential surface of the cylinder head 94. A seal member 99 is disposed on the outer circumferential surface of the piston 93. The interior of the cylinder tube 91 is divided into a rod-side chamber 95 and an anti-rod-side chamber 96 by the piston 93. Note that FIG. 7 omits passages for supplying and discharging fluid to and from the rod-side chamber 95 and the anti-rod-side chamber 96. In the fluid pressure cylinder 90, the piston rod 92 serves as the sliding member. In the piston rod 92, a trivalent chromium plating layer is formed on the outer peripheral surface 92a, which is the sliding portion with the seal member 98.

[0010] The fluid pressure device may be, for example, a shock absorber 190 mounted on a vehicle as shown in FIG. 8 . The shock absorber 190 includes a cylinder tube 191, a piston rod 192 reciprocally disposed within the cylinder tube 191, a piston 193 disposed at the tip of the piston rod 192, a seal member 198 disposed at the open end of the cylinder tube 191 and in sliding contact with an outer circumferential surface 192a of the piston rod 192, and a rod guide 194 that positions the piston rod 192 relative to the cylinder tube 191 so as not to be eccentric. The interior of the cylinder tube 191 is divided into a compression-side chamber 195 and an extension-side chamber 196 by the piston 193. In the shock absorber 190, the piston rod 192 serves as a sliding member. A trivalent chromium plating layer is formed on the outer circumferential surface 192a of the piston rod 192, which is the sliding portion with the seal member 198.

[0011] 9 , the fluid pressure device may be, for example, a front fork 290 for a motorcycle. The front fork 290 includes an outer tube 291, an inner tube 292 provided within the outer tube 291 so as to be able to advance and retract, a damper portion 293 provided within the inner tube 292 and generating a damping force by relative movement between the outer tube 291 and the inner tube 292, a bracket 294 connected to an open end of a cylinder 293 a of the damper portion 293 and an open end of the inner tube 292 to close both open ends, a reservoir chamber 295 provided within the outer tube 291 and partially filled with gas, and an annular sealing member 298 provided on an inner circumferential surface 291 a of the outer tube 291 and in sliding contact with an outer circumferential surface 292 a of the inner tube 292. An annular bearing 299 is provided between the inner circumferential surface of the open end of the outer tube 291 and the outer circumferential surface of the inner tube 292. The damper portion 293 includes a cylinder 293a provided at the bottom of the inner tube 292 and filled with hydraulic oil, a piston 293b slidably disposed within the cylinder 293a and dividing the interior of the cylinder 293a into two oil chambers 296a and 296b, and a rod 293c connected at one end to the piston 293b and at the other end to the outer tube 291. The two oil chambers 296a and 296b communicate with each other through a passage 293d provided in the piston 293b, and the oil chamber 296b communicates with a reservoir chamber 295 through a passage 294a provided in the bracket 294. In the front fork 290, the inner tube 292 serves as a sliding member. A trivalent chromium plating layer is formed on an outer peripheral surface 292a of the inner tube 292, which is the sliding portion with the sealing member 298.

[0012] In this embodiment, a hard trivalent chromium plating layer having a plating thickness of, for example, about 10 to 20 μm is formed on a steel base material that is the base material for a piston rod, an inner tube, etc. Note that it is not necessary to form the trivalent chromium plating layer on the entire surface of the sliding member, as long as the trivalent chromium plating layer is formed at least on the sliding portion.

[0013] Fig. 1 is a laser microscope photograph of a cross section of a slide member 100 after a plating layer forming step described later. As shown in Fig. 1, a nickel plating layer 2 is formed as an undercoat plating layer on the surface of a steel base material 1, and a trivalent chromium plating layer 3 is formed on the surface of the nickel plating layer 2.

[0014] The steel base material 1 is, for example, carbon steel such as S15C, S20C, S25C, S30C, S35C, S40C, or S45C, or chromium-molybdenum steel such as SCM430, SCM435, or SCM440.

[0015] The nickel plating layer 2 is intended to improve the adhesion of the trivalent chromium plating layer 3 to the steel base material 1 and to supplement the corrosion resistance of the trivalent chromium plating layer 3. The nickel plating layer 2 is formed by a known method. Instead of the nickel plating layer 2, other metal plating layers such as a copper plating layer may be used as the base plating layer. Note that the base plating layer is not an essential component, and the trivalent chromium plating layer 3 may be formed directly on the surface of the steel base material 1.

[0016] The trivalent chromium plating layer 3 has excellent sliding properties and corrosion resistance, and its formation on the surface of a sliding part improves the quality of the sliding part. Trivalent chromium plating is primarily amorphous during film formation and tends to be brittle. Therefore, as shown in FIG. 1 , wide cracks 4 are likely to occur in the trivalent chromium plating layer 3 after the plating layer is formed. After the trivalent chromium plating layer 3 is formed, a baking treatment is performed to remove hydrogen occluded in the trivalent chromium plating layer 3 and prevent hydrogen embrittlement. However, the baking treatment increases the groove width W of the crack 4. Specifically, the baking treatment crystallizes and shrinks the amorphous structure of the trivalent chromium plating layer 3, thereby increasing the groove width W of the crack 4. Because the surface of the trivalent chromium plating layer 3 functions as a sliding surface, if the groove width W of the crack 4 is large, fluid will leak through the crack 4 to the outside. Specifically, when the sliding member 100 is a piston rod of a fluid pressure cylinder, oil or gas (fluid) sealed in the cylinder tube will leak out of the cylinder tube through the cracks 4 on the surface of the piston rod. In particular, when the pressure of the fluid (hydraulic oil or working gas) inside the device is high, such as in a fluid pressure cylinder, there is a high risk that the fluid will leak out through the cracks 4.

[0017] The present invention has been made to reduce the groove width W of the crack 4 in the trivalent chromium plating layer 3 and prevent the fluid sealed in the equipment from leaking through the crack 4 on the surface of the trivalent chromium plating layer 3.

[0018] The method for manufacturing the slide member 100 according to this embodiment, specifically, the method for forming the trivalent chromium plating layer 3, will be described in detail below. Fig. 3 is a schematic diagram showing the trivalent chromium plating layer 3 and cracks 4 in each step. Note that the nickel plating layer 2 is not shown in Fig. 3 and Fig. 4, which will be described later.

[0019] First, before forming the trivalent chromium plating layer 3 on the nickel plating layer 2 formed on the surface of the steel base material 1, a pretreatment is performed to clean the surface of the nickel plating layer 2. Examples of the pretreatment include a degreasing treatment to remove organic matter from the surface of the nickel plating layer 2, and an acid pickling treatment to remove oxides from the surface of the nickel plating layer 2. Note that if the nickel plating layer 2 is not formed, a pretreatment to clean the surface of the steel base material 1 is performed.

[0020] Next, a plating layer forming step is performed to form a trivalent chromium plating layer 3 on the surface of the nickel plating layer 2. The trivalent chromium plating layer 3 can be formed, for example, by plating a trivalent chromium plating bath containing chromium chloride or chromium sulfate as a chromium source, formate or malate as a complexing agent, boric acid as a pH buffer, ammonium chloride, potassium nitrate, or sodium sulfate as a conductive agent, and a trace amount of surfactant, at a current density of 30-90 A / dm ２ After the plating layer forming step, wide cracks 4 appear in the trivalent chromium plating layer 3, as shown in FIG.

[0021] Next, a first polishing step is performed to polish the surface of the trivalent chromium plating layer 3. In the first polishing step, the surface of the trivalent chromium plating layer 3 is subjected to plastic flow by polishing so as to cover the cracks 4, thereby reducing the groove width W of the cracks 4. In this embodiment, as shown in (b) of Fig. 3, the cracks 4 (specifically, the cracks 4 on the surface of the trivalent chromium plating layer 3) are closed by polishing.

[0022] 2 , in the first polishing step, centerless polishing is performed to polish the surface of the trivalent chromium plating layer 3 using a circular buff wheel 20 of a polishing device 10. The polishing device 10 includes the buff wheel 20 as a polishing member that polishes the sliding member 100 as a workpiece, an adjusting wheel 30 as a cylindrical adjusting member that rotates the sliding member 100, a blade 40 that is provided between the buff wheel 20 and the adjusting wheel 30 and on which the sliding member 100 is placed, and a control unit (not shown) that controls the rotation of the buff wheel 20 and the adjusting wheel 30. In centerless polishing, the sliding member 100 is provided between the buff wheel 20 and the adjusting wheel 30 in contact with both.

[0023] The buff wheel 20 has an abrasive agent provided on its outer peripheral surface, and a drive source (not shown) is controlled by a control unit to rotate it in direction A (clockwise) in FIG. 2 . The buff wheel 20 is provided along the axial direction of the sliding member 100 and contacts the trivalent chromium plating layer 3 formed on the outer peripheral surface of the sliding member 100. The rotation of the buff wheel 20 polishes the surface of the trivalent chromium plating layer 3. The drive source (not shown) is controlled by a control unit to rotate the adjusting wheel 30 in direction B (clockwise) in FIG. 2 . The adjusting wheel 30 is inclined at an angle α in the height direction (upward in FIG. 2 ) with respect to the axial direction of the buff wheel 20 and the sliding member 100, and contacts the trivalent chromium plating layer 3 of the sliding member 100. Therefore, when the adjusting wheel 30 is rotated, a force in direction C (counterclockwise) in FIG. 2 and a force in direction D (axial) in FIG. 2 act on the sliding member 100. Therefore, when the adjusting wheel 30 is rotated, the sliding member 100 is rotated in the circumferential direction (direction C) and moved in the axial direction (direction D). In centerless polishing, the sliding member 100 is polished by rotating it in the circumferential direction and moving it in the axial direction, so that the entire surface of the trivalent chromium plating layer 3 can be polished. Furthermore, since there is no need to attach a dedicated jig for moving the sliding member 100 in the axial direction, productivity is high.

[0024] The blade 40 is formed with an inclined upper surface 40a. Specifically, the upper surface 40a of the blade 40 is inclined so as to become lower from the buffing wheel 20 side toward the adjusting wheel 30 side. Therefore, when the sliding member 100 is placed on the upper surface 40a of the blade 40, the sliding member 100 is pressed against the adjusting wheel 30 by gravity. Therefore, as described above, the sliding member 100 receives a force from the adjusting wheel 30, and is rotated and moved.

[0025] Centerless polishing using the polishing apparatus 10 is performed by positioning the sliding member 100 so that one end 5 thereof is located between the buff wheel 20 and the adjusting wheel 30, and then rotating the buff wheel 20 and the adjusting wheel 30 to pass the sliding member 100 between the buff wheel 20 and the adjusting wheel 30. Note that the "number of polishing operations" refers to the number of times a series of operations is performed from the time the sliding member 100 is set once until the other end 6 of the sliding member 100 has completely passed between the buff wheel 20 and the adjusting wheel 30.

[0026] In this embodiment, in the first polishing step, polishing is performed at a temperature at which crystallization of the trivalent chromium plating layer 3 does not proceed (in other words, so as not to raise the temperature to a temperature at which crystallization of the trivalent chromium plating layer 3 proceeds). The "temperature at which crystallization of the trivalent chromium plating layer 3 does not proceed" refers to a temperature below 150°C. Specifically, in the first polishing step, centerless polishing is performed multiple times. For example, if polishing is performed only once in the first polishing step, the target polishing amount is achieved in a single polishing, resulting in a large polishing amount per polishing, and the trivalent chromium plating layer 3 is significantly heated and reaches a temperature at which crystallization proceeds. In contrast, by performing polishing multiple times, the polishing amount per polishing is reduced, and the temperature rise of the trivalent chromium plating layer 3 in a single polishing is suppressed, thereby preventing it from reaching a temperature at which crystallization proceeds. As a result, in the first polishing step, the expansion of the groove width W of the crack 4 due to crystallization of the trivalent chromium plating layer 3 is suppressed. Furthermore, in the first polishing step, crystallization does not progress and the trivalent chromium plating layer 3 is less likely to harden, so that the trivalent chromium plating layer 3 is more likely to undergo plastic flow by polishing, and the cracks 4 are more likely to be effectively sealed.

[0027] Furthermore, in this embodiment, in the first polishing step, polishing is performed so that the increase in Vickers hardness of the trivalent chromium plating layer 3 compared to after the plating layer formation step is less than 25%. Specifically, for a material in which the Vickers hardness of the trivalent chromium plating layer 3 after the plating layer formation step is 700 HV, adjusting the increase in Vickers hardness after the first polishing step to 21% or less has been confirmed to suppress crystallization (hardening) of the trivalent chromium plating layer 3 in the first polishing step, and to effectively reduce the groove width of the crack 4 by polishing. The smaller the increase in Vickers hardness, the more likely the above effect is to be achieved. On the other hand, it has been confirmed that the above effect is less likely to be achieved if the increase in Vickers hardness after the first polishing step is 25% or more.

[0028] Specifically, in the first polishing step of this embodiment, polishing is performed under the following conditions: the number of polishing cycles is three, the feed rate (axial movement rate) of the sliding member 100 is 2.0-6.0 m / min, the rotation rate of the buffing wheel 20 is 1000-1500 rpm, the Young's modulus of the buffing wheel 20 is 35-20 MPa, and the outer diameter of the buffing wheel 20 is 250-400 mm. In other words, the adjusting wheel 30 is set to a rotation rate corresponding to the above-mentioned feed rate. Note that the polishing conditions in the first polishing step are not limited to those described above.

[0029] After the first polishing step, a baking step is performed in which the trivalent chromium plating layer 3 is baked. The baking step is intended to remove hydrogen occluded in the trivalent chromium plating layer 3 to prevent hydrogen embrittlement, and involves heating the layer at about 200°C for about two hours, for example. As described above, the baking step increases the groove width W of the crack 4 (see (c) in FIG. 3).

[0030] After the baking treatment, a second polishing step is performed to polish the surface of the trivalent chromium plating layer 3. In the second polishing step, similar to the first polishing step, the surface of the trivalent chromium plating layer 3 is subjected to plastic flow so as to cover the cracks 4 by polishing, thereby sealing the cracks 4, as shown in (d) of Figure 3. Specifically, centerless polishing is performed using the same polishing device 10 as in the first polishing step. This prevents fluid inside the device from leaking out through the cracks 4 and improves the corrosion resistance of the trivalent chromium plating layer 3.

[0031] In this manner, the trivalent chromium plating layer 3 is formed, and the slide member 100 is manufactured.

[0032] Here, the difference between the slide member 100 of this embodiment and the slide member 200 of a comparative example in which the first polishing step is not performed (i.e., the trivalent chromium plating layer 3 is not polished before the baking treatment) will be described. FIG. 4 is a schematic diagram showing the trivalent chromium plating layer 3 and cracks 4 in each step of the slide member 200. FIG. 5 is a laser microscope photograph of the surface of the trivalent chromium plating layer 3 after the baking treatment, where (a) shows the slide member 100 and (b) shows the slide member 200. FIG. 6 is a laser microscope photograph of the surface of the trivalent chromium plating layer 3 after the second polishing step, where (a) shows the slide member 100 and (b) shows the slide member 200.

[0033] In the case of the slide member 200 of the comparative example, the baking treatment is performed in a state in which cracks 4 remain in the trivalent chromium plating layer 3 during the plating layer formation process, as shown in (a) of FIG. 4 . In other words, the cracks 4 before the baking treatment are large. Therefore, as shown in (b) of FIG. 4 and (b) of FIG. 5 , the groove width W of the cracks 4 after the baking treatment is large. In this case, even if polishing is performed in the second polishing step, the cracks 4 cannot be closed, and the cracks 4 remain in the trivalent chromium plating layer 3, as shown in (c) of FIG. 4 and (b) of FIG. 6 . In the case of trivalent chromium plating, unlike conventional hexavalent chromium plating, the hardness of the plating layer is likely to increase by the baking treatment, so plastic flow of the trivalent chromium plating layer 3 is unlikely to occur, and the cracks 4 are unlikely to be closed even if polishing is performed after the baking treatment.

[0034] In contrast, in the case of the slide member 100 of this embodiment, the surface of the trivalent chromium plating layer 3 is polished in the first polishing step before the trivalent chromium plating layer 3 is significantly hardened by the baking treatment. This causes plastic flow due to polishing, making it possible to reduce or close the groove width W of the cracks 4 before the baking treatment. Therefore, the expansion of the groove width W of the cracks 4 due to the baking treatment after the first polishing step is suppressed, and the groove width W of the cracks 4 after the baking treatment can be reduced as shown in FIG. 3(c) and FIG. 5(a). Therefore, polishing is performed in the second polishing step, making it possible to minimize or close the cracks 4 as shown in FIG. 3(d) and FIG. 6(a). Therefore, the groove width W of the cracks 4 in the trivalent chromium plating layer 3 can be reduced, improving the quality of the slide member 100.

[0035] In this embodiment, the first polishing step is performed using the same polishing technique as the second polishing step under conditions that do not increase the temperature of the trivalent chromium plating layer compared to the second polishing step. Specifically, the "same polishing technique" refers to the same technique using the same equipment. For example, the first polishing step is performed using the polishing device 10 under conditions in which the feed rate of the slide member 100 is higher and the number of polishing operations is greater than those in the second polishing step. This makes it difficult for the trivalent chromium plating layer 3 to harden in the first polishing step and facilitates plastic flow, thereby reducing the groove width W of the crack 4 before the baking treatment.

[0036] According to the above embodiment, the following effects are achieved.

[0037] In the manufacturing method of the slide member 100, the surface of the trivalent chromium plating layer 3 is polished in the first polishing step before the trivalent chromium plating layer 3 is significantly hardened by the baking treatment. This causes plastic flow due to the polishing, and the groove width W of the crack 4 before the baking treatment can be reduced or closed. Therefore, it is possible to suppress the expansion of the groove width W of the crack 4 due to the baking treatment after the first polishing step, and to reduce the groove width W of the crack 4 after the baking treatment.

[0038] In a fluid pressure device (fluid pressure cylinder 90, shock absorber 190, front fork 290) including the sliding member 100 manufactured by the above-described manufacturing method, the fluid pressure inside the fluid pressure device is high, but the fluid can be prevented from leaking out through the cracks 4 on the surface of the trivalent chromium plating layer 3, which is the sliding surface.

[0039] Modifications of the above embodiment will be described below. The following modifications are also within the scope of the present invention, and it is also possible to combine the configurations described in the following different modifications.

[0040] <Modification 1> In the manufacturing method of the slide member 100 of the above embodiment, the second polishing step is performed after the baking step to seal the cracks 4. However, in cases such as when the groove width W of the cracks 4 after the baking step is sufficiently small, it is not essential to perform the second polishing step. Even without performing the second polishing step, the groove width W of the cracks 4 after the baking treatment is small, so the groove width W of the cracks 4 in the trivalent chromium plating layer 3 can be made smaller than that of the slide member 200 that is not subjected to the first polishing step, thereby improving the quality of the slide member 100.

[0041] <Modification 2> In the manufacturing method of the slide member 100 of the above embodiment, the cracks 4 are sealed by the first polishing step before the baking step. However, in the first polishing step, it is not essential to seal the cracks 4 as long as the groove width W of the cracks 4 can be reduced. Even if the cracks 4 are not sealed, the groove width W of the cracks 4 after the baking treatment is small. Therefore, the groove width W of the cracks 4 in the trivalent chromium plating layer 3 can be made smaller than that of the slide member 200 that is not subjected to the first polishing step, thereby improving the quality of the slide member 100.

[0042] <Modification 3> In the manufacturing method of the slide member 100 of the above embodiment, centerless polishing is performed in the first polishing step and the second polishing step. By performing centerless polishing, which facilitates plastic flow of the surface of the trivalent chromium plating layer 3, it is possible to reduce the groove width W of the cracks 4. However, the polishing performed in the first polishing step and the second polishing step is not limited to centerless polishing, and may be, for example, cylindrical polishing, as long as it is possible to reduce the groove width W of the cracks 4 by the plastic flow of the trivalent chromium plating layer 3.

[0043] <Modification 4> In the manufacturing method of the slide member 100 of the above embodiment, in the first polishing step, polishing is performed multiple times at a temperature (less than 150°C) at which crystallization of the trivalent chromium plating layer 3 does not proceed. Furthermore, in the first polishing step, polishing is performed so that the increase in Vickers hardness of the trivalent chromium plating layer 3 compared to after the plating layer formation step is less than 25%. This suppresses crystallization, making the trivalent chromium plating layer 3 less likely to harden and more susceptible to plastic flow. However, in the first polishing step, as long as the groove width W of the crack 4 can be reduced by the plastic flow of the trivalent chromium plating layer 3, polishing may be performed so that the increase in Vickers hardness of the trivalent chromium plating layer 3 compared to after the plating layer formation step is 25% or more. For example, polishing may be performed only once.

[0044] <Modification 5> In the manufacturing method for the slide member 100 of the above embodiment, in the first polishing step, polishing is performed using the same polishing technique as in the second polishing step, but under conditions in which the temperature of the trivalent chromium plating layer 3 does not increase as much as in the second polishing step. As a result, in the first polishing step, crystallization is suppressed, making the trivalent chromium plating layer 3 less likely to harden and more susceptible to plastic flow. However, as long as the groove width W of the crack 4 can be reduced by the plastic flow of the trivalent chromium plating layer 3 in the first polishing step, it is not essential that polishing be performed under conditions in which the temperature of the trivalent chromium plating layer 3 does not increase as much as in the second polishing step. Furthermore, the first polishing step and the second polishing step may be performed using different polishing methods.

[0045] The configuration, operation, and effects of each embodiment of the present invention will be described below.

[0046] A method for manufacturing a sliding member 100 that is provided in a device that seals a fluid and has a trivalent chromium plating layer 3 formed on a sliding portion includes a plating film forming step of forming a trivalent chromium plating film 3 on a steel base material 1 (base material) or a nickel plating layer 2 (primary plating film) formed on the surface of the steel base material 1 (base material), a first polishing step of polishing the surface of the trivalent chromium plating film 3, and a baking step of baking the trivalent chromium plating film 3 after the first polishing step.

[0047] In this configuration, the surface of the trivalent chromium plating layer 3 is polished in the first polishing step before the trivalent chromium plating layer 3 is significantly hardened by the baking treatment. This causes plastic flow due to the polishing, making it possible to reduce the groove width W of the crack 4 before the baking treatment. Therefore, it is possible to suppress the expansion of the groove width W of the crack 4 due to the baking treatment after the first polishing step, and to reduce the groove width W of the crack 4 after the baking treatment.

[0048] Moreover, the method for manufacturing the slide member 100 further includes a second polishing step of polishing the surface of the trivalent chromium plating layer 3 after the baking step.

[0049] In this configuration, the groove width W of the crack 4 after the baking treatment can be further reduced by the second polishing step.

[0050] In the manufacturing method of the slide member 100, in the first polishing step, the cracks 4 on the surface of the trivalent chromium plating layer 3 are closed by polishing.

[0051] In this configuration, the first polishing process seals the cracks 4 before the baking process, thereby suppressing the expansion of the groove width W of the cracks 4 due to the baking process, and further reducing the groove width W of the cracks 4 after the baking process.

[0052] In the manufacturing method of the slide member 100, the first polishing step involves centerless polishing, in which the surface of the trivalent chromium plating layer 3 is polished with a circular buff wheel 20.

[0053] In this configuration, centerless polishing is performed, which makes the surface of the trivalent chromium plating layer 3 prone to plastic flow, and the groove width W of the crack 4 before the baking treatment can be further reduced.

[0054] In the method for manufacturing the slide member 100, the first polishing step is performed in multiple steps.

[0055] In this configuration, polishing is performed in multiple steps, which suppresses the temperature rise of the trivalent chromium plating layer 3 and suppresses crystallization, making it difficult for the trivalent chromium plating layer 3 to harden during polishing. Therefore, the groove width W of the crack 4 can be effectively reduced by polishing.

[0056] In the manufacturing method of the slide member 100, in the first polishing step, polishing is performed so that the increase in Vickers hardness of the trivalent chromium plating layer 3 compared to after the plating layer forming step is less than 25%.

[0057] In this configuration, by suppressing crystallization (hardening) of the trivalent chromium plating layer 3 in the first polishing step, the groove width of the crack 4 can be effectively reduced by polishing.

[0058] In the manufacturing method of the slide member 100, the first polishing step is performed using the same polishing technique as the second polishing step under conditions in which the temperature of the trivalent chromium plating layer 3 does not increase as compared to the second polishing step.

[0059] In this configuration, the trivalent chromium plating layer 3 is less likely to harden in the first polishing step, so that the groove width W of the crack 4 can be effectively reduced by polishing.

[0060] Furthermore, in the manufacturing method of a fluid pressure device (fluid pressure cylinder 90, shock absorber 190) equipped with the aforementioned sliding member 100, the fluid pressure device comprises a cylinder tube 91, 191, a piston rod 92, 192 provided so as to be able to reciprocate within the cylinder tube 91, 191, and a sealing member 98, 198 provided at the open end of the cylinder tube 91, 191 and in sliding contact with the outer peripheral surface 92a, 192a of the piston rod 92, 192, and the sliding member 100 is the piston rod 92, 192.

[0061] Furthermore, in the manufacturing method of a fluid pressure device (front fork 290) including the aforementioned sliding member 100, the fluid pressure device includes an outer tube 291, an inner tube 292 that is movably arranged within the outer tube 291, and a sealing member 298 that is arranged on an inner surface 291a of the outer tube 291 and that is in sliding contact with an outer surface 292a of the inner tube 292, and the sliding member 100 is the inner tube 292.

[0062] In these configurations, although the pressure of the fluid inside the fluid pressure device is high, the fluid can be prevented from leaking out through the cracks 4 on the surface of the trivalent chromium plating layer 3, which is the sliding surface.

[0063] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0064] This application claims priority based on Japanese Patent Application No. 2024-153267, filed with the Japan Patent Office on September 5, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A method for manufacturing a sliding member that is provided in a device that seals a fluid and has a trivalent chromium plating layer formed on the sliding portion, the method comprising: a plating layer forming step of forming a trivalent chromium plating layer on a base material or on a base plating layer formed on the surface of the base material; a first polishing step of polishing the surface of the trivalent chromium plating layer; and a baking step of baking the trivalent chromium plating layer after the first polishing step.

2. The method for producing a sliding member according to claim 1, further comprising a second polishing step of polishing the surface of the trivalent chromium plating layer after the baking step.

3. A method for manufacturing a sliding member according to claim 1, wherein in the first polishing step, cracks in the surface of the trivalent chromium plating layer are closed by polishing.

4. A method for manufacturing a sliding member according to claim 1, wherein the first polishing step comprises centerless polishing, in which the surface of the trivalent chromium plating layer is polished with a circular buff wheel.

5. A method for producing a slide member according to claim 1, wherein the first polishing step involves polishing in multiple steps.

6. A method for producing a sliding member according to claim 1, wherein in the first polishing step, polishing is carried out so that the increase in Vickers hardness of the trivalent chromium plating layer compared to after the plating layer forming step is less than 25%.

7. A method for producing a sliding member according to claim 2, wherein in the first polishing step, polishing is carried out by the same polishing technique as in the second polishing step under conditions in which the temperature of the trivalent chromium plating layer does not increase as much as in the second polishing step.

8. A method for manufacturing a fluid pressure device comprising the sliding member according to claim 1, wherein the fluid pressure device comprises a cylinder tube, a piston rod reciprocally disposed within the cylinder tube, and a sealing member disposed at the open end of the cylinder tube and in sliding contact with the outer circumferential surface of the piston rod, and the sliding member is the piston rod.

9. A method for manufacturing a fluid pressure device comprising the sliding member according to claim 1, wherein the fluid pressure device comprises an outer tube, an inner tube that is movably disposed within the outer tube, and a sealing member that is disposed on the inner circumferential surface of the outer tube and that slides against the outer circumferential surface of the inner tube, and the sliding member is the inner tube.

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