Method for manufacturing sliding members and fluid pressure equipment

Abstract

To reduce the width of cracks in the trivalent chromium plating layer. [Solution] A method for manufacturing a sliding member 100, which is provided in a device for sealing a fluid and has a trivalent chromium plating layer 3 formed on the sliding part, comprises a plating layer formation step of forming a 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 of polishing the surface of the trivalent chromium plating layer 3; and a baking step of applying a baking treatment to the trivalent chromium plating layer 3 after the first polishing step.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a surface treatment method for applying a hard and wear-resistant hexavalent chromium plating to a sliding part (piston rod) such as a fluid pressure cylinder or a shock absorber. In the treatment method described in Patent Document 1, after applying hexavalent chromium plating to the sliding part, baking is performed after plating 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, by performing polishing after baking, plastic flow is caused on the surface of the hexavalent chromium plating layer to reduce the width of the cracks that have become larger.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, due to the large environmental load of hexavalent chromium contained in hexavalent chromium plating, replacement with trivalent chromium plating with a small environmental load has been considered. Trivalent chromium plating has the property that its hardness increases significantly by baking compared to hexavalent chromium. Therefore, when the method described in Patent Document 1 is applied to trivalent chromium plating, plastic flow is unlikely to occur during polishing, and the width of the crack grooves cannot be sufficiently reduced. When trivalent chromium plating is applied to the sliding part of a sliding part of a device that seals fluid, if the width of the cracks in the trivalent chromium plating layer is not sufficiently small, there is a risk that the fluid will leak to the outside along the cracks.

[0005] This invention has been made in view of the above-mentioned problems, and aims to reduce the width of cracks in the trivalent chromium plating layer. [Means for solving the problem]

[0006] The present invention relates to a method for manufacturing a sliding member provided in a device for sealing a fluid, wherein a trivalent chromium plating layer is formed on the sliding portion, and is characterized by comprising: a plating layer formation step of forming a trivalent chromium plating layer on a base material or an under-plating layer formed on the surface of a base material; a first polishing step of polishing the surface of the trivalent chromium plating layer; and a baking step of applying a baking treatment to the trivalent chromium plating layer after the first polishing step.

[0007] In this invention, the surface of the trivalent chromium plating layer is polished in a first polishing step before the trivalent chromium plating layer hardens significantly due to the baking process. This generates plastic flow due to polishing, which can reduce the width of cracks before the baking process. Therefore, the expansion of crack width due to the baking process after the first polishing step is suppressed, and the width of cracks after the baking process can be reduced.

[0008] Furthermore, the present invention is characterized by further comprising a second polishing step in which the surface of the trivalent chromium plating layer is polished after the baking step.

[0009] In this invention, the second polishing step can further reduce the width of the crack grooves after the baking process.

[0010] Furthermore, the present invention is characterized in that, in the first polishing step, cracks on the surface of the trivalent chromium plating layer are sealed by polishing.

[0011] In this invention, by sealing cracks before the baking process in the first polishing step, the expansion of the crack groove width due to the baking process can be suppressed, and the crack groove width after the baking process can be further reduced.

[0012] Furthermore, the present invention is characterized in that, in the first polishing step, centerless polishing is performed, in which the surface of the trivalent chromium plating layer is polished using a circular buffing wheel.

[0013] In this invention, the width of cracks before baking can be further reduced by performing centerless polishing, which facilitates plastic flow on the surface of the trivalent chromium plating layer.

[0014] Furthermore, the present invention is characterized in that the polishing is performed in multiple stages during the first polishing step.

[0015] In this invention, polishing is performed in multiple stages, which suppresses the temperature rise of the trivalent chromium plating layer and inhibits crystallization. As a result, the trivalent chromium plating layer is less likely to harden during polishing. Therefore, the width of the crack groove can be effectively reduced by polishing.

[0016] Furthermore, the present invention is characterized in that, in the first polishing step, polishing is performed such that the increase in Vickers hardness of the trivalent chromium plating layer compared to after the plating layer formation step is less than 25%.

[0017] In this invention, by suppressing the crystallization (hardening) of the trivalent chromium plating layer in the first polishing step, the width of the crack groove can be effectively reduced by polishing.

[0018] Furthermore, the present invention is characterized in that in the first polishing step, polishing is performed using the same polishing method as in the second polishing step, but under conditions in which the temperature of the trivalent chromium plating layer does not rise compared to the second polishing step.

[0019] In this invention, the trivalent chromium plating layer is less likely to harden during the first polishing step, so the width of the crack groove can be effectively reduced by polishing.

[0020] The present invention also relates to a method for manufacturing a fluid pressure device provided with the aforementioned sliding member. The fluid pressure device includes a cylinder tube, a piston rod reciprocally provided within the cylinder tube, a seal member provided at an open end of the cylinder tube and in sliding contact with an outer peripheral surface of the piston rod, and a seal member provided between the outer peripheral surface of the piston rod and the inner peripheral surface of the cylinder tube alongside the cylinder head. The sliding member is characterized by being the piston rod.

[0021] The present invention also relates to a method for manufacturing a fluid pressure device provided with the aforementioned sliding member. The fluid pressure device includes an outer tube, an inner tube reciprocally provided within the outer tube, and a sealing member provided on an inner peripheral surface of the outer tube and in sliding contact with an outer peripheral surface of the inner tube. The sliding member is characterized by being the inner tube.

[0022] In these inventions, although the pressure of the internal fluid in the fluid pressure device is high, it is possible to prevent the fluid from leaking to the outside through cracks on the surface of the trivalent chromium plating layer which is the sliding surface.

Advantages of the Invention

[0023] According to the present invention, the groove width of cracks in the trivalent chromium plating layer can be reduced.

Brief Description of the Drawings

[0024] [Figure 1] It is a laser microscope photograph of a cross section after plating layer formation of a sliding member according to an embodiment of the present invention. [Figure 2] It is a schematic diagram of a polishing device that performs polishing in the first polishing step. [Figure 3] It is a schematic diagram showing a trivalent chromium plating layer and cracks in each step of a sliding member according to an embodiment of the present invention. [Figure 4] It is a schematic diagram showing a trivalent chromium plating layer and cracks in each step of a sliding member according to a comparative example of an embodiment of the present invention. [Figure 5]These are laser microscope images of the surface of the trivalent chromium plating layer after baking, where (a) shows a sliding member according to an embodiment of the present invention, and (b) shows a sliding member according to a comparative example of an embodiment of the present invention. [Figure 6] These are laser microscope images of the surface of the trivalent chromium plating layer after the second polishing step, where (a) shows a sliding member according to an embodiment of the present invention, and (b) shows a sliding member according to a comparative example of an embodiment of the present invention. [Figure 7] This is a schematic cross-sectional view of a fluid pressure cylinder provided with a sliding member according to an embodiment of the present invention. [Figure 8] This is a schematic cross-sectional view of a shock absorber provided with a sliding member according to an embodiment of the present invention. [Figure 9] This is a schematic cross-sectional view of a front fork provided with a sliding member according to an embodiment of the present invention. [Modes for carrying out the invention]

[0025] A method for manufacturing a sliding member according to an embodiment of the present invention will be described below with reference to the drawings.

[0026] The sliding member is provided in a fluid pressure device that encloses a fluid, and a trivalent chromium plating layer is formed on the sliding portion.

[0027] A fluid-pressure device that encloses fluid is, for example, a fluid-pressure cylinder 90 used as an actuator, as shown in Figure 7. The fluid-pressure cylinder 90 comprises a cylinder tube 91, a piston rod 92 reciprocally mounted within the cylinder tube 91, a piston 93 provided 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 sealing member 98 provided at the open end of the cylinder tube 91 and slidingly contacting the outer circumferential surface 92a of the piston rod 92. The sealing member 98 is provided on the inner circumferential surface of the cylinder head 94. A sealing member 99 is provided on the outer circumferential surface of the piston 93. The inside 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 in Figure 7, the passages through which fluid is supplied to and discharged from the rod-side chamber 95 and the anti-rod-side chamber 96 are omitted. In the fluid-pressure cylinder 90, the piston rod 92 is the sliding member. In the piston rod 92, a trivalent chromium plating layer is formed on the outer circumferential surface 92a, which is the sliding portion with the seal member 98.

[0028] Furthermore, the fluid pressure device may be, for example, a shock absorber 190 mounted on a vehicle, as shown in Figure 8. The shock absorber 190 comprises a cylinder tube 191, a piston rod 192 reciprocally mounted within the cylinder tube 191, a piston 193 provided at the tip of the piston rod 192, a sealing member 198 provided at the open end of the cylinder tube 191 and slidingly contacting the outer circumferential surface 192a of the piston rod 192, and a rod guide 194 that positions the piston rod 192 so as not to be eccentric with respect to the cylinder tube 191. The inside of the cylinder tube 191 is divided into a compression chamber 195 and an extension chamber 196 by the piston 193. In the shock absorber 190, the piston rod 192 is the sliding member. On the piston rod 192, a trivalent chromium plating layer is formed on the outer circumferential surface 192a, which is the sliding part with the sealing member 198.

[0029] Furthermore, the fluid pressure device may be, for example, a front fork 290 for a motorcycle, as shown in Figure 9. The front fork 290 comprises an outer tube 291, an inner tube 292 that is movable back and forth within the outer tube 291, a damper section 293 provided within the inner tube 292 that generates damping force by the relative movement between the outer tube 291 and the inner tube 292, a bracket 294 connected to the open end of the cylinder 293a of the damper section 293 and the 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 the inner circumferential surface 291a of the outer tube 291 that slides against the outer circumferential surface 292a 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 section 293 includes a cylinder 293a provided at the bottom of the inner tube 292 and filled with hydraulic fluid, a piston 293b slidably positioned within the cylinder 293a and dividing the cylinder 293a into two oil chambers 296a and 296b, and a rod 293c with one end connected to the piston 293b and the other end connected 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 oil chamber 296b communicates with the reservoir chamber 295 through a passage 294a provided in the bracket 294. In the front fork 290, the inner tube 292 is the sliding member. On the inner tube 292, a trivalent chromium plating layer is formed on the outer circumferential surface 292a, which is the sliding part with the sealing member 298.

[0030] In this embodiment, we will describe a case in which a hard trivalent chromium plating layer with a plating thickness of, for example, about 10 to 20 μm is formed on a steel base material, such as a piston rod or inner tube. It should be noted that it is not necessarily required that the trivalent chromium plating layer be formed on the entire surface of the sliding member; it is sufficient if the trivalent chromium plating layer is formed at least on the sliding portion.

[0031] Figure 1 is a laser microscope image of a cross-section of the sliding member 100 after the plating layer formation process described later. As shown in Figure 1, a nickel plating layer 2 is formed on the surface of the steel base material 1 as an undercoat, and a trivalent chromium plating layer 3 is formed on the surface of the nickel plating layer 2.

[0032] The steel base material 1 is, for example, carbon steel such as S15C, S20C, S25C, S30C, S35C, S40C, S45C, or chromium-molybdenum steel such as SCM430, SCM435, SCM440.

[0033] 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. As the undercoat plating layer, other metal plating layers such as a copper plating layer may be used instead of the nickel plating layer 2. Note that the undercoat 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.

[0034] The trivalent chromium plating layer 3 has excellent sliding properties and corrosion resistance, and its formation on the surface of sliding parts improves the quality of those parts. However, during film formation, the trivalent chromium plating is primarily amorphous and tends to be brittle. As shown in Figure 1, wide cracks 4 are prone to forming in the trivalent chromium plating layer 3 after its formation. After the formation of the trivalent chromium plating layer 3, a baking treatment is performed to remove hydrogen absorbed into the layer and prevent hydrogen embrittlement. However, this baking treatment enlarges the groove width W of the cracks 4. Specifically, the baking treatment causes the amorphous structure of the trivalent chromium plating layer 3 to crystallize and shrink, thus enlarging the groove width W of the cracks 4. Since the surface of the trivalent chromium plating layer 3 functions as a sliding surface, a large groove width W of the cracks 4 allows fluid to seep out through the cracks 4. Specifically, if the sliding member 100 is the piston rod of a fluid pressure cylinder, the oil or gas (fluid) sealed in the cylinder tube will seep 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 hydraulic gas) inside the equipment is high, such as in a fluid pressure cylinder, the risk of the fluid seeping out through the cracks 4 is high.

[0035] The present invention was made to reduce the groove width W of the cracks 4 in the trivalent chromium plating layer 3, thereby preventing fluids sealed in the equipment from leaking through the cracks 4 on the surface of the trivalent chromium plating layer 3.

[0036] The following describes in detail the manufacturing method of the sliding member 100 according to this embodiment, specifically the method for forming the trivalent chromium plating layer 3. Figure 3 is a schematic diagram showing the trivalent chromium plating layer 3 and crack 4 at each step. Note that the nickel plating layer 2 is not shown in Figure 3 and Figure 4, which will be described later.

[0037] 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 pretreatment include degreasing to remove organic matter from the surface of the nickel plating layer 2, and acid cleaning to remove oxides from the surface of the nickel plating layer 2. If the nickel plating layer 2 is not formed, a pretreatment is performed to clean the surface of the steel base material 1.

[0038] Next, a plating layer formation process is performed to form a trivalent chromium plating layer 3 on the surface of the nickel plating layer 2. As a method for forming the trivalent chromium plating layer 3, for example, 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, sodium sulfate as a conductive agent, and a trace amount of surfactant is used, with a current density of 30-90 A / dm². 2 Plating is performed with a plating thickness of approximately 10-20 μm under the specified plating conditions. After the plating layer formation process, wide cracks 4 occur in the trivalent chromium plating layer 3, as shown in Figure 3(a).

[0039] 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 plastically flowed by polishing to cover the cracks 4, thereby reducing the groove width W of the cracks 4. In this embodiment, as shown in Figure 3(b), the cracks 4 (specifically, the cracks 4 on the surface of the trivalent chromium plating layer 3) are closed by polishing.

[0040] As shown in Figure 2, in the first polishing step, centerless polishing is performed in which the surface of the trivalent chromium plating layer 3 is polished by the circular buff wheel 20 of the polishing device 10. The polishing device 10 includes the buff wheel 20 as a polishing member for polishing the sliding member 100 as a workpiece, the adjustment wheel 30 as a cylindrical adjustment member for rotating the sliding member 100, the blade 40 provided between the buff wheel 20 and the adjustment wheel 30 on which the sliding member 100 is placed, and the control unit (not shown) for controlling the rotation of the buff wheel 20 and the adjustment wheel 30. In centerless polishing, the sliding member 100 is provided between the buff wheel 20 and the adjustment wheel 30 in contact with both.

[0041] The buffing wheel 20 has an abrasive material on its outer surface and is rotated in direction A (clockwise) in Figure 2, controlled by a control unit via a drive source (not shown). The buffing wheel 20 is positioned along the axial direction of the sliding member 100 and contacts the trivalent chromium plating layer 3 formed on the outer surface of the sliding member 100. As the buffing wheel 20 rotates, the surface of the trivalent chromium plating layer 3 is polished. The adjustment wheel 30 is rotated in direction B (clockwise) in Figure 2, controlled by a control unit via a drive source (not shown). The adjustment wheel 30 is positioned at an angle α in the height direction (upward in Figure 2) with respect to the axial direction of the buffing wheel 20 and the sliding member 100, and contacts the trivalent chromium plating layer 3 of the sliding member 100. Therefore, when the adjustment wheel 30 rotates, the sliding member 100 is subjected to forces in direction C (counterclockwise) and direction D (axial) in Figure 2. Therefore, when the adjustment 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 the entire surface of the trivalent chromium plating layer 3 can be polished. In addition, since it is not necessary to attach a special jig for moving the sliding member 100 in the axial direction, productivity is high.

[0042] The blade 40 is formed with an inclined upper surface 40a. Specifically, the upper surface 40a of the blade 40 is inclined to become lower from the buff wheel 20 side towards the adjustment wheel 30 side. Therefore, when the sliding member 100 is placed on the upper surface 40a of the blade 40, gravity causes the sliding member 100 to be pressed against the adjustment wheel 30. Thus, the sliding member 100 receives force from the adjustment wheel 30 as described above, and is rotated and moved.

[0043] Centerless polishing by the polishing device 10 is performed by positioning the sliding member 100 so that one end 5 is located between the buff wheel 20 and the adjustment wheel 30, and then rotating the buff wheel 20 and the adjustment wheel 30 to pass the sliding member 100 between the buff wheel 20 and the adjustment wheel 30. The "number of polishing cycles" is the number of times the series of operations is performed from the time the sliding member 100 is set until the other end 6 of the sliding member 100 has completely passed between the buff wheel 20 and the adjustment wheel 30.

[0044] In this embodiment, the first polishing step is performed at a temperature at which crystallization of the trivalent chromium plating layer 3 does not progress (in other words, so as not to rise to a temperature at which crystallization of the trivalent chromium plating layer 3 progresses). The "temperature at which crystallization of the trivalent chromium plating layer 3 does not progress" is less than 150°C. Specifically, in the first polishing step, centerless polishing is performed in multiple stages. For example, if polishing is performed only once in the first polishing step, the amount of polishing in one stage will be large in order to achieve the target amount of polishing in a single stage, causing the trivalent chromium plating layer 3 to rise significantly in temperature and reach the temperature at which crystallization progresses. In contrast, by performing polishing in multiple stages, the amount of polishing in each stage is small, and the rise in temperature of the trivalent chromium plating layer 3 in each stage of polishing is suppressed, thus preventing it from reaching the temperature at which crystallization progresses. As a result, the expansion of the groove width W of the crack 4 due to crystallization of the trivalent chromium plating layer 3 is suppressed in the first polishing step. Furthermore, in the first polishing process, crystallization does not progress and the trivalent chromium plating layer 3 does not harden easily. Therefore, polishing makes it easier for the trivalent chromium plating layer 3 to undergo plastic flow, and cracks 4 can be effectively sealed.

[0045] Furthermore, in this embodiment, the first polishing step is performed such 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, it was confirmed that if the Vickers hardness of the trivalent chromium plating layer 3 after the plating layer formation step is adjusted to be 21% or less for a material with a Vickers hardness of 700 HV, then crystallization (hardening) of the trivalent chromium plating layer 3 is suppressed in the first polishing step, and the groove width of the crack 4 can be effectively reduced by polishing. The smaller the increase in Vickers hardness, the more likely the above effect is to be achieved. On the other hand, it was confirmed that the above effect is less likely to be achieved when the increase in Vickers hardness after the first polishing step is 25% or more.

[0046] In the first polishing step of this embodiment, polishing is performed under the following conditions: three polishing cycles, a feed rate (axial movement speed) of the sliding member 100 of 2.0-6.0 m / min, a rotational speed of the buff wheel 20 of 1000-1500 rpm, a Young's modulus of the buff wheel 20 of 35-20 MPa, and an outer diameter of the buff wheel 20 of 250-400 mm. In other words, the adjustment wheel 30 is set to a rotational speed corresponding to the above feed rate. Note that the polishing conditions for the first polishing step are not limited to those described above.

[0047] Then, after the first polishing process, a baking process is performed on the trivalent chromium plating layer 3. The baking process is to remove hydrogen absorbed into the trivalent chromium plating layer 3 and prevent hydrogen embrittlement, and is performed by heating at approximately 200°C for about 2 hours. As mentioned above, the baking process enlarges the groove width W of the crack 4 (see Figure 3(c)).

[0048] After the baking process, 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 plastically flowed by polishing to cover the cracks 4, as shown in Figure 3(d), thereby sealing the cracks 4. Specifically, centerless polishing is performed using the same polishing apparatus 10 as in the first polishing step. This prevents fluid from inside the equipment from seeping out through the cracks 4 and improves the corrosion resistance of the trivalent chromium plating layer 3.

[0049] In this manner, the trivalent chromium plating layer 3 is formed, and the sliding member 100 is manufactured.

[0050] Here, we will explain the difference between the sliding member 100 of this embodiment and the comparative sliding member 200, which does not perform the first polishing step (i.e., the trivalent chromium plating layer 3 is not polished before the baking process). Figure 4 is a schematic diagram showing the trivalent chromium plating layer 3 and cracks 4 of the sliding member 200 at each step. Figure 5 is a laser microscope image of the surface of the trivalent chromium plating layer 3 after the baking process, where (a) shows the sliding member 100 and (b) shows the sliding member 200. Figure 6 is a laser microscope image of the surface of the trivalent chromium plating layer 3 after the second polishing step, where (a) shows the sliding member 100 and (b) shows the sliding member 200.

[0051] In the case of the comparative example sliding member 200, as shown in Figure 4(a), the baking treatment is performed with cracks 4 remaining in the trivalent chromium plating layer 3 during the plating layer formation process. In other words, the cracks 4 are large before the baking treatment. Therefore, as shown in Figure 4(b) and Figure 5(b), 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 process, the cracks 4 cannot be closed, and cracks 4 remain in the trivalent chromium plating layer 3, as shown in Figure 4(c) and Figure 6(b). In the case of trivalent chromium plating, unlike conventional hexavalent chromium plating, the hardness of the plating layer tends to increase with the baking treatment, so even if polishing is performed after the baking treatment, plastic flow of the trivalent chromium plating layer 3 is less likely to occur, making it difficult to close the cracks 4.

[0052] In contrast, in the case of the sliding member 100 of this embodiment, the surface of the trivalent chromium plating layer 3 is polished in a first polishing step before the trivalent chromium plating layer 3 hardens significantly due to the baking treatment. This causes plastic flow due to polishing, which can 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 Figure 3(c) and Figure 5(a). Therefore, polishing is performed in a second polishing step, and the cracks 4 can be reduced to the smallest possible size or closed, as shown in Figure 3(d) and Figure 6(a). Thus, the groove width W of the cracks 4 in the trivalent chromium plating layer 3 can be reduced, and the quality of the sliding member 100 can be improved.

[0053] Furthermore, in this embodiment, the first polishing step is performed using the same polishing method as the second polishing step, but under conditions that prevent the temperature of the trivalent chromium plating layer from rising as in the second polishing step. "Same polishing method" specifically refers to the same method using the same equipment. For example, in the first polishing step, centerless polishing is performed using the polishing device 10 under conditions that result in a higher feed rate for the sliding member 100 and a higher number of polishing passes than in the second polishing step. As a result, the trivalent chromium plating layer 3 is less likely to harden in the first polishing step and is more likely to undergo plastic flow, thereby reducing the groove width W of the crack 4 before the baking treatment.

[0054] According to the above embodiments, the following effects are achieved.

[0055] In the manufacturing method of the sliding member 100, the surface of the trivalent chromium plating layer 3 is polished in a first polishing step before the trivalent chromium plating layer 3 hardens significantly due to the baking treatment. This causes plastic flow due to polishing, which can reduce or close the groove width W of the crack 4 before the baking treatment. Therefore, the expansion of the groove width W of the crack 4 due to the baking treatment after the first polishing step is suppressed, and the groove width W of the crack 4 after the baking treatment can be reduced.

[0056] In a fluid pressure device (fluid pressure cylinder 90, shock absorber 190, front fork 290) equipped with a sliding member 100 manufactured by the aforementioned manufacturing method, although the fluid pressure inside the device is high, it is possible to prevent the fluid from seeping out through cracks 4 on the surface of the trivalent chromium plating layer 3, which is the sliding surface.

[0057] The following describes modifications of the above embodiment. The following modifications are also within the scope of the present invention, and it is possible to combine the configurations described in the following different modifications.

[0058] <Example 1> In the manufacturing method of the sliding member 100 according to the above embodiment, a second polishing step is performed after the baking step to seal the cracks 4. However, if the groove width W of the cracks 4 after the baking step is sufficiently small, the second polishing step is not essential. Even without performing the second polishing step, because the groove width W of the cracks 4 after the baking step is small, the groove width W of the cracks 4 in the trivalent chromium plating layer 3 can be made smaller than that of a sliding member 200 that does not undergo the first polishing step, thereby improving the quality of the sliding member 100.

[0059] <Modification 2> In the manufacturing method of the sliding member 100 of the above embodiment, the cracks 4 are sealed in the first polishing step before the baking step. However, in the first polishing step, sealing the cracks 4 is not essential if the groove width W of the cracks 4 can be reduced. Even without sealing the cracks 4, 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 reduced compared to the sliding member 200 that does not undergo the first polishing step, thereby improving the quality of the sliding member 100.

[0060] <Variation 3> In the manufacturing method of the sliding member 100 according to the above embodiment, centerless polishing is performed in the first and second polishing steps. Centerless polishing, which facilitates plastic flow of the surface of the trivalent chromium plating layer 3, can reduce the groove width W of the crack 4. However, the polishing performed in the first and second polishing steps is not limited to centerless polishing; it may be cylindrical polishing or the like, as long as it can reduce the groove width W of the crack 4 due to the plastic flow of the trivalent chromium plating layer 3.

[0061] <Modification 4> In the manufacturing method of the sliding member 100 of the above embodiment, the first polishing step is performed in multiple stages at a temperature (less than 150°C) that does not cause crystallization of the trivalent chromium plating layer 3 to progress. 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 likely to undergo plastic flow. However, in the first polishing step, if 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 at a temperature that causes crystallization of the trivalent chromium plating layer 3 to progress, but 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.

[0062] <Modification 5> In the manufacturing method of the sliding member 100 of the above embodiment, the first polishing step is performed using the same polishing method as the second polishing step, but under conditions that prevent the temperature of the trivalent chromium plating layer 3 from rising as in the second polishing step. This suppresses crystallization in the first polishing step, making the trivalent chromium plating layer 3 less likely to harden and more likely to undergo plastic flow. However, if 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 the first polishing step is performed under conditions that prevent the temperature of the trivalent chromium plating layer 3 from rising as in the second polishing step. Furthermore, the first and second polishing steps may be performed using different methods.

[0063] The configuration, operation, and effects of each embodiment of the present invention will be described below.

[0064] A method for manufacturing a sliding member 100, which is provided in a device for sealing a fluid and has a trivalent chromium plating layer 3 formed on the sliding part, comprises a plating film formation step of forming a trivalent chromium plating film 3 on a steel base material 1 (base material) or a nickel plating layer 2 (under-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 applying a baking treatment to the trivalent chromium plating film 3 after the first polishing step.

[0065] In this configuration, the surface of the trivalent chromium plating layer 3 is polished in a first polishing step before the trivalent chromium plating layer 3 hardens significantly due to the baking process. This generates plastic flow due to polishing, which can reduce the groove width W of the crack 4 before the baking process. Therefore, the expansion of the groove width W of the crack 4 due to the baking process after the first polishing step is suppressed, and the groove width W of the crack 4 after the baking process can be reduced.

[0066] Furthermore, the manufacturing method for the sliding member 100 further includes a second polishing step in which the surface of the trivalent chromium plating layer 3 is polished after the baking step.

[0067] In this configuration, the second polishing step can further reduce the groove width W of the crack 4 after the baking treatment.

[0068] Furthermore, in the manufacturing method of the sliding member 100, in the first polishing step, cracks 4 on the surface of the trivalent chromium plating layer 3 are filled by polishing.

[0069] In this configuration, the cracks 4 before the baking process are sealed by the first polishing 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.

[0070] Furthermore, in the manufacturing method of the sliding member 100, the first polishing step involves centerless polishing, in which the surface of the trivalent chromium plating layer 3 is polished using a circular buffing wheel 20.

[0071] In this configuration, the groove width W of the crack 4 before baking can be further reduced by performing centerless polishing, which facilitates plastic flow on the surface of the trivalent chromium plating layer 3.

[0072] Furthermore, in the manufacturing method of the sliding member 100, the first polishing step involves polishing in multiple stages.

[0073] In this configuration, polishing is performed in multiple stages, which suppresses the temperature rise of the trivalent chromium plating layer 3 and inhibits crystallization. As a result, the trivalent chromium plating layer 3 is less likely to harden during polishing. Therefore, the groove width W of the crack 4 can be effectively reduced by polishing.

[0074] Furthermore, in the manufacturing method of the sliding member 100, the first polishing step is performed such 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%.

[0075] In this configuration, the crystallization (hardening) of the trivalent chromium plating layer 3 is suppressed in the first polishing process, thereby effectively reducing the groove width of the crack 4 through polishing.

[0076] Furthermore, in the manufacturing method of the sliding member 100, the first polishing step is performed using the same polishing method as the second polishing step, but under conditions that the temperature of the trivalent chromium plating layer 3 does not rise compared to the second polishing step.

[0077] In this configuration, the trivalent chromium plating layer 3 is less likely to harden during the first polishing process, so the groove width W of the crack 4 can be effectively reduced by polishing.

[0078] Furthermore, in the manufacturing method of the fluid pressure device (fluid pressure cylinder 90, shock absorber 190) equipped with the aforementioned sliding member 100, the fluid pressure device comprises cylinder tubes 91, 191, piston rods 92, 192 reciprocally mounted within the cylinder tubes 91, 191, and sealing members 98, 198 provided at the open ends of the cylinder tubes 91, 191 and slidingly contacting the outer circumferential surfaces 92a, 192a of the piston rods 92, 192, the sliding member 100 is the piston rod 92, 192.

[0079] Furthermore, in the manufacturing method of the fluid pressure device (front fork 290) equipped with the aforementioned sliding member 100, the fluid pressure device comprises an outer tube 291, an inner tube 292 provided within the outer tube 291 so as to be able to move back and forth, and a sealing member 298 provided on the inner circumferential surface 291a of the outer tube 291 and slidingly contacting the outer circumferential surface 292a of the inner tube 292, wherein the sliding member 100 is the inner tube 292.

[0080] In these configurations, although the fluid pressure inside the fluid pressure device is high, it is possible to prevent the fluid from seeping out through cracks 4 on the surface of the trivalent chromium plating layer 3, which is the sliding surface.

[0081] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of symbols]

[0082] 100...Sliding member, 1...Steel base material, 2...Nickel plating layer, 3...Trivalent chromium plating layer, 4...Crack, 90...Fluid pressure cylinder (fluid pressure equipment), 91, 191...Cylinder tube, 92, 192...Piston rod, 98, 198...Sealing member, 190...Shock absorber (fluid pressure equipment), 290...Front fork (fluid pressure equipment), 291...Outer tube, 292...Inner tube, 298...Sealing member

Claims

1. A method for manufacturing a sliding member provided in a device for sealing a fluid, wherein a trivalent chromium plating layer is formed on the sliding part, A plating layer formation step in which a trivalent chromium plating layer is formed on a base material or an under-plating layer formed on the surface of a base material, A first polishing step involves polishing the surface of the trivalent chromium plating layer, A method for manufacturing a sliding member, characterized by comprising a baking step of applying a baking treatment to the trivalent chromium plating layer after the first polishing step.

2. A method for manufacturing a sliding member according to claim 1, A method for manufacturing a sliding member, 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, A method for manufacturing a sliding member, characterized in that, in the first polishing step, cracks on the surface of the trivalent chromium plating layer are sealed by polishing.

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

5. A method for manufacturing a sliding member according to claim 1, A method for manufacturing a sliding member, characterized in that the first polishing step is performed in multiple stages.

6. A method for manufacturing a sliding member according to claim 1, A method for manufacturing a sliding member, characterized in that the first polishing step is performed such that the increase in Vickers hardness of the trivalent chromium plating layer compared to after the plating layer formation step is less than 25%.

7. A method for manufacturing a sliding member according to claim 2, A method for manufacturing a sliding member, characterized in that the first polishing step is performed using the same polishing method as the second polishing step, but under conditions that the temperature of the trivalent chromium plating layer does not rise compared to the second polishing step.

8. A method for manufacturing a fluid pressure device comprising a sliding member as described in claim 1, The fluid pressure device comprises a cylinder tube, a piston rod reciprocally mounted within the cylinder tube, and a sealing member provided at the open end of the cylinder tube and sliding against the outer surface of the piston rod. A method for manufacturing a fluid pressure device, characterized in that the sliding member is the piston rod.

9. A method for manufacturing a fluid pressure device comprising a sliding member as described in claim 1, The fluid pressure device comprises an outer tube, an inner tube provided to be movable back and forth within the outer tube, and a sealing member provided on the inner circumferential surface of the outer tube and slidingly contacting the outer circumferential surface of the inner tube. A method for manufacturing a fluid pressure device, characterized in that the sliding member is the inner tube.

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