Method for polishing brake piston

Abstract

The present invention provides a method for polishing a brake piston whereby the surface roughness of the lateral surface of a base material of a brake piston that includes a resin material can be brought to a prescribed value easily and quickly using a grinding wheel, and moreover, the life of the grinding wheel can be extended. The method for polishing a brake piston according to the present invention comprises: a first step for performing processing for grinding or polishing an outer circumferential surface 981, which is the lateral surface of a base material 98 of a brake piston 93 that includes a resin material; and a second step for bringing a rotating grinding wheel 31 into contact with the lateral surface 981 of the base material 98 to perform processing for polishing the outer circumferential surface 981 while rotating the base material 98, which has undergone the first step, around a first axis O1 as the center of rotation and advancing the base material 98 in the direction of the first axis O1, wherein the grinding wheel 31 has abrasive grains of different grain sizes arranged along the first axis O1 direction.

Description

How to polish brake pistons

[0001] The present invention relates to a method for polishing a brake piston.

[0002] In recent years, there has been a trend toward replacing metal parts with plastic parts in order to reduce the weight of automobiles. The use of plastic pistons instead of steel pistons for brake pistons used in disc brakes is also being considered. Disc brakes include a disc rotor, a hydraulic cylinder with a seal ring on its sliding surface, and a brake piston mounted in the hydraulic cylinder and equipped with brake pads. When the brakes are applied, the brake piston is moved by hydraulic pressure, pressing the brake pads against the disc rotor.

[0003] In such disc brakes, the sliding resistance between the resin piston and the seal ring has a significant effect on brake characteristics and performance, such as brake feel, and is also affected by the surface roughness of the outer circumferential surface (side surface) of the resin piston.

[0004] For this reason, when manufacturing a resin piston (disc brake), the outer surface of the base material of the resin piston is subjected to a polishing process or the like to set the surface roughness of the outer surface to a predetermined value (see, for example, Patent Document 1, particularly paragraph 0003 of Patent Document 1).

[0005] Japanese Patent Application Publication No. 9-177848

[0006] However, when a resin piston is polished using a polishing device with a grinding wheel, it takes a long time to achieve the target surface roughness of the outer circumferential surface of the base material of the resin piston. In addition, the grinding wheel of the polishing device wears out significantly, resulting in a short lifespan of the grinding wheel, making it unsuitable for mass production.

[0007] An object of the present invention is to provide a method for polishing a brake piston, which can easily and quickly adjust the surface roughness of the side surface of the base material of a brake piston, which includes a resin material, to a predetermined value using a grinding stone, and which can also extend the life of the grinding stone.

[0008] The objects of the present invention are achieved by the following (1) to (9) inventions: (1) A method for polishing a brake piston, comprising: a first step of grinding or polishing a side surface of a base material of a brake piston containing a resin material; and a second step of rotating the base material that has undergone the first step about a first axis and moving it in the first axial direction while bringing a rotating grinding stone into contact with the side surface of the base material to polish the side surface, wherein the grinding stone has abrasive grains of different grain sizes arranged along the first axial direction.

[0009] (2) The method for polishing a brake piston according to (1) above, wherein the grinding wheel has a first layer and a second layer arranged side by side in the first axial direction, the first layer and the second layer are arranged in this order in the direction of travel of the base material, and when the grain size of the abrasive grains in the first layer is A1 and the grain size of the abrasive grains in the second layer is A2, A1 < A2 is satisfied.

[0010] (3) The method for polishing a brake piston according to (1) or (2) above, wherein in the first step, the base material is rotated around the first axis as a rotation center, and a rotating first step grinding stone is brought into contact with the side surface to grind or polish the side surface.

[0011] (4) The method for polishing a brake piston according to (3) above, wherein the grain size of the abrasive grains of the grindstone for the first step in the first step is smaller than the smallest grain size of the abrasive grains of the grindstone for the second step.

[0012] (5) The method for polishing a brake piston according to any one of (1) to (4) above, wherein at least one of the first step and the second step is performed by a centerless polishing method.

[0013] (6) The method for polishing a brake piston according to any one of (1) to (5) above, wherein the second step is performed by a centerless polishing method, and the base material is passed between the grinding wheel and a rotatable adjusting wheel to polish the side surface.

[0014] (7) The method for polishing a brake piston according to any one of (1) to (6) above, wherein the first step and the second step are carried out continuously on a path along which the base material is transported.

[0015] (8) The method for polishing a brake piston according to any one of (1) to (7) above, wherein the resin material contains 20% by mass or more of a phenolic resin.

[0016] (9) The method for polishing a brake piston according to any one of (1) to (8) above, wherein the surface roughness Ra of the side surface of the base material polished in the second step is 0.13 μm or less.

[0017] According to the present invention, the surface roughness of the side surface of the base material of a brake piston, which includes a resin material, can be easily and quickly adjusted to a predetermined value using a grinding stone, and the life of the grinding stone can be extended, which is advantageous for mass production of brake pistons and devices such as disc brakes that have such brake pistons.

[0018] Fig. 1 is a cross-sectional view showing an embodiment of a disc brake. Fig. 2 is a cross-sectional view of the disc brake shown in Fig. 1 in an actuated state. Fig. 3 is a plan view showing an embodiment of a polishing apparatus for a brake piston. Fig. 4 is a perspective view of a first polishing unit of the polishing apparatus shown in Fig. 3. Fig. 5 is a front view of the first polishing unit of the polishing apparatus shown in Fig. 3. Fig. 6 is a perspective view of a second polishing unit of the polishing apparatus shown in Fig. 3. Fig. 7 is a front view of the second polishing unit of the polishing apparatus shown in Fig. 3. Fig. 8 is a view showing a manufacturing process of a brake piston according to an embodiment of a method for manufacturing a brake piston.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description of the brake piston polishing method of the present invention will now be given based on preferred embodiments shown in the accompanying drawings.

[0020] <Disc Brake> First, an embodiment of a disc brake will be described.

[0021] Fig. 1 is a cross-sectional view showing an embodiment of a disc brake. Fig. 2 is a cross-sectional view showing the disc brake shown in Fig. 1 in an actuated state. Figs. 1 and 2 show cross sections of a floating-type disc brake as an example.

[0022] 1, the disc brake 9 according to this embodiment includes a caliper 90 having a hydraulic cylinder 91, a seal ring 92, a brake piston 93, a disc rotor 94, brake pads 951 and 952, and back plates 961 and 962. Such a disc brake 9 is mounted on various vehicles such as automobiles.

[0023] The disc rotor 94 is connected to a rotary shaft (not shown) that rotates the wheels of the vehicle, and is, for example, in the shape of a disk.

[0024] The brake pad 951 is fixed to the brake piston 93 via a back plate 961. On the other hand, the brake pad 952 is fixed to the caliper 90 via a back plate 962.

[0025] The brake piston 93 and the caliper 90 are each provided so as to be movable relative to the frame (chassis) of the vehicle. Therefore, the brake pads 951, 952 also move relative to the frame in response to braking. This allows the disc rotor 94 to be sandwiched between the brake pads 951, 952 from both sides, applying frictional force to the disc rotor 94.

[0026] The caliper 90 has a hydraulic cylinder 91. A brake piston 93 is slidably provided in the hydraulic cylinder 91. A seal ring 92 is provided on the sliding surface of the hydraulic cylinder 91, and provides a liquid-tight seal between the hydraulic cylinder 91 and the brake piston 93.

[0027] When the brakes are applied (the brakes are activated), hydraulic pressure is generated by a master cylinder (not shown), which increases the hydraulic pressure of the brake fluid 97 filled in the hydraulic cylinder 91. Then, as shown in FIG. 2 , the brake piston 93 moves toward the disc rotor 94 (to the left in FIGS. 1 and 2 ), causing the brake pads 951 to press against the disc rotor 94. Meanwhile, as the hydraulic pressure of the brake fluid 97 increases, the portion of the caliper 90 where the brake pads 952 are provided (to the left in FIGS. 1 and 2 ) moves toward the disc rotor 94 (to the right in FIGS. 1 and 2 ), causing the brake pads 952 to press against the disc rotor 94. As a result, the disc rotor 94 is sandwiched between the brake pads 951 and 952, braking the rotation of the rotating shaft to which the disc rotor 94 is connected. Furthermore, when the brake operation is stopped (the brake is released), the brake piston 93 and the caliper 90 move in directions away from the disc rotor 94, thereby stopping (releasing) the braking.

[0028] <Brake Piston> Next, an embodiment of a brake piston will be described.

[0029] As shown in Fig. 1, the brake piston 93 has a cylindrical shape with a bottom. However, the shape of the brake piston 93 is not limited to this and may be, for example, a columnar shape. Furthermore, a groove or the like may be formed along the circumferential direction on an outer peripheral surface 931, which is the side surface of the brake piston 93. The groove is used for assembly in the disc brake 9, etc.

[0030] The brake piston 93 according to this embodiment (the material of the brake piston 93) contains a resin material, and preferably contains a resin material and a filler. This allows the brake piston 93 to be sufficiently lightweight, thereby reducing the weight of the disc brake 9 and the vehicle. This can contribute to reducing the energy consumption rate during vehicle running, for example.

[0031] Furthermore, resin materials have better corrosion resistance than metal materials, so the condition (sliding resistance, etc.) of the brake piston 93 can be maintained for a long period of time, and the performance and operational feel of the disc brake 9 can be maintained for a long period of time.

[0032] The brake piston 93 will be described in further detail below. - Thermosetting Resin - The resin material according to this embodiment is a cured product of a composition containing a curable resin such as a thermosetting resin. By including a cured product of such a thermosetting resin (curable resin), it is possible to reduce the weight of the brake piston 93 while particularly improving the mechanical properties and heat resistance.

[0033] Examples of thermosetting resins include phenolic resins, epoxy resins, unsaturated polyester resins, diallyl phthalate resins, melamine resins, oxetane resins, maleimide resins, urea resins, polyurethane resins, silicone resins, resins having a benzoxazine ring, and cyanate ester resins, and these can be used alone or in combination of two or more.

[0034] Among these, phenolic resin is particularly preferably used as the thermosetting resin, which can further improve the corrosion resistance, wear resistance, mechanical properties, etc. of the brake piston 93. Furthermore, by using the brake piston polishing method according to this embodiment (hereinafter simply referred to as the "polishing method"), the surface roughness of the outer circumferential surface 931 of the brake piston 93 (the outer circumferential surface 981 of the base material 98) can be easily and quickly adjusted to a target value (a predetermined value).

[0035] Examples of phenolic resins include novolac-type phenolic resins such as phenol novolac resin, cresol novolac resin, and bisphenol A-type novolac resin; resole-type phenolic resins such as methylol-type resole resin, dimethylene ether-type resole resin, and oil-molten resole phenolic resins melted with tung oil, linseed oil, walnut oil, or the like; and aryl alkylene-type phenolic resins, and these may be used alone or in combination of two or more.

[0036] Among these, novolac type phenolic resins are particularly preferred as the phenolic resin, as they are useful in terms of availability and workability during kneading.

[0037] Furthermore, although the content of the phenolic resin in the resin material is not particularly limited, the resin material preferably contains 20% by mass or more of the phenolic resin. That is, the content of the phenolic resin in the resin material is preferably 20% by mass or more, more preferably 20 to 35% by mass, and even more preferably 20 to 30% by mass. This further improves the corrosion resistance, wear resistance, mechanical properties, and the like of the brake piston 93. Furthermore, by using the polishing method according to this embodiment, the surface roughness of the outer circumferential surface 931 of the brake piston 93 can be easily and quickly adjusted to a target value.

[0038] Furthermore, a curing agent is added to the composition containing the thermosetting resin as needed. For example, hexamethylenetetramine is used as the curing agent. The amount of the curing agent added is not particularly limited, but is preferably set to 10 to 25 parts by mass, and more preferably set to 10 to 20 parts by mass, per 100 parts by mass of the thermosetting resin.

[0039] The content of the thermosetting resin in the brake piston 93 is not particularly limited, but is preferably 5 to 50 mass %, and more preferably 10 to 40 mass %, which allows the brake piston 93 to have a well-balanced improvement in corrosion resistance, wear resistance, mechanical properties, and the like.

[0040] If necessary, a thermoplastic resin may be added to the composition containing the thermosetting resin.

[0041] Filler The filler mainly improves the mechanical properties of the brake piston 93 .

[0042] Examples of fillers include fibrous fillers, granular fillers, and plate-like fillers. Among these, fibrous fillers are fillers that are fibrous in shape. Examples of fibrous fillers include inorganic fibrous fillers such as glass fiber, carbon fiber, asbestos fiber, metal fiber, glass beads, wollastonite, attapulgite, sepiolite, rock wool, aluminum borate whiskers, potassium titanate fiber, calcium carbonate whiskers, titanium oxide whiskers, and ceramic fibers, and organic fibrous fillers such as aramid fiber, polyimide fiber, and polyparaphenylene benzobisoxazole fiber. These may be used alone or in combination of two or more.

[0043] The term "platy filler" refers to a filler having a plate-like shape, and the term "granular filler" refers to a filler having a shape other than fibrous or plate-like, including irregular shapes. Examples of such plate-like or granular fillers include talc, kaolin clay, calcium carbonate, zinc oxide, calcium silicate hydrate, mica, glass flake, glass powder, magnesium carbonate, silica, titanium oxide, alumina, aluminum hydroxide, magnesium hydroxide, barium sulfate, calcium sulfate, calcium sulfite, zinc borate, barium metaborate, aluminum borate, calcium borate, sodium borate, aluminum nitride, boron nitride, and silicon nitride, and these may be used alone or in combination.

[0044] Among these, it is preferable to use one or more fillers selected from wollastonite, glass fiber, carbon fiber, glass beads, and calcium carbonate. Use of such fillers can particularly improve the mechanical properties of the brake piston 93. Furthermore, by using the polishing method according to this embodiment, the surface roughness of the outer circumferential surface 931 of the brake piston 93 can be easily and quickly adjusted to the target value.

[0045] The filler content in the brake piston 93 is not particularly limited, but is preferably 50 to 90 mass %, and more preferably 60 to 80 mass %. This further improves the mechanical properties of the brake piston 93, and by using the polishing method according to this embodiment, the surface roughness of the outer circumferential surface 931 of the brake piston 93 can be easily and quickly adjusted to a target value. Note that by adjusting the type and content of the filler, the physical properties of the brake piston 93, such as the linear expansion coefficient and dynamic friction coefficient, can be controlled.

[0046] The average particle size of the filler is preferably 0.1 to 20 μm, and more preferably 0.5 to 15 μm, which prevents the filler from significantly affecting the surface properties of the brake piston 93 while still allowing the filler to fully exhibit its function of improving the mechanical properties.

[0047] The average particle size of the filler refers to the particle size at which the cumulative percentage from the small diameter side reaches 50% in the mass-based particle size distribution measured by a laser diffraction particle size distribution analyzer.

[0048] Furthermore, the filler preferably includes a fibrous filler or a plate-like filler having an average major axis of 5 μm or more and 50 mm or less and an average aspect ratio of 1 or more and 1000 or less. This can particularly improve the mechanical properties of the brake piston 93.

[0049] The average major axis and the average aspect ratio can be calculated, for example, from an image of the brake piston 93. Specifically, first, the surface of the brake piston 93 is photographed using a scanning electron microscope. Next, 50 fibrous fillers or plate-like fillers are randomly selected from the obtained image, and their major and minor axes are measured. Here, the major axis of a fibrous filler refers to the fiber length, and the minor axis refers to the fiber diameter. Furthermore, the major axis of a plate-like filler refers to the maximum length on the main surface of the plate-like filler, and the minor axis refers to the thickness of the plate-like filler. The average of the measured major axes is defined as the "average major axis." The average of the measured minor axes is defined as the "average minor axis," and the ratio of the average major axis to the average minor axis is defined as the "average aspect ratio."

[0050] The average major axis of the filler is preferably 0.1 to 100 μm, more preferably 0.2 to 50 μm, and the average aspect ratio of the filler is preferably 1 to 50, more preferably 1 to 40.

[0051] The filler may be surface-treated with a coupling agent such as a silane coupling agent.

[0052] On the other hand, these coupling agents may be added to a composition containing a thermosetting resin, which can, for example, further increase the adhesion between the resin material and the filler, thereby further improving the mechanical properties of the brake piston 93.

[0053] Examples of the silane coupling agent include epoxy group-containing alkoxysilane compounds such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercapto group-containing alkoxysilane compounds such as γ-mercaptopropyltrimethoxysilane and γ-mercaptopropyltriethoxysilane; ureido group-containing alkoxysilane compounds such as γ-ureidopropyltriethoxysilane, γ-ureidopropyltrimethoxysilane, and γ-(2-ureidoethyl)aminopropyltrimethoxysilane; γ-isocyanatopropyltriethoxysilane, γ-isocyanatopropyltrimethoxysilane, and γ-isocyanatopropylmethyldimethoxysilane; Examples thereof include silane, isocyanato group-containing alkoxysilane compounds such as γ-isocyanatopropylmethyldiethoxysilane, γ-isocyanatopropylethyldimethoxysilane, γ-isocyanatopropylethyldiethoxysilane, and γ-isocyanatopropyltrichlorosilane; amino group-containing alkoxysilane compounds such as γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane; and hydroxyl group-containing alkoxysilane compounds such as γ-hydroxypropyltrimethoxysilane and γ-hydroxypropyltriethoxysilane. These may be used alone or in combination of two or more.

[0054] The amount of the silane coupling agent added is not particularly limited, but is preferably 0.01 to 4 parts by mass, and more preferably 0.1 to 1 part by mass, per 100 parts by mass of the filler.

[0055] The composition containing the thermosetting resin may further contain an elastomer, a curing aid, a release agent, a pigment, a flame retardant, a weather resistance agent, an antioxidant, a plasticizer, a lubricant, a sliding agent, a foaming agent, and the like.

[0056] By adjusting the composition, content, and other conditions of the filler, it is possible to adjust the specific gravity of the brake piston 93, for example.

[0057] Furthermore, when the brake piston 93 is at least partially cylindrical or columnar as in this embodiment, its thickness is preferably 5 to 80% of half the outer diameter (radius), and more preferably 10 to 70%, which allows for a good balance between the mechanical properties and the weight of the brake piston 93.

[0058] Furthermore, the surface of the brake piston 93 may be subjected to various surface treatments, such as roughening, polishing, surface modification, etc., as needed. By using such surface treatments, it is possible to adjust the dynamic friction coefficient of the brake piston 93.

[0059] Furthermore, the brake piston 93 may have a coating layer (not shown) provided to cover the outer peripheral surface 931, as necessary. The coating layer may cover the entire outer peripheral surface 931, or may include an uncovered area. The coating layer preferably contains an inorganic material (is made of an inorganic material). The coating layer may be a single layer or may be multilayered. Such a coating layer makes it possible to adjust the dynamic friction coefficient of the brake piston 93.

[0060] <Brake Piston Polishing Device> Next, an embodiment of a brake piston polishing device will be described.

[0061] Fig. 3 is a plan view showing an embodiment of a polishing apparatus for a brake piston. Fig. 4 is a perspective view of a first polishing unit of the polishing apparatus shown in Fig. 3. Fig. 5 is a front view of the first polishing unit of the polishing apparatus shown in Fig. 3. Fig. 6 is a perspective view of a second polishing unit of the polishing apparatus shown in Fig. 3. Fig. 7 is a front view of the second polishing unit of the polishing apparatus shown in Fig. 3. In each drawing, the polishing apparatus for a brake piston is shown schematically.

[0062] 3, a brake piston polishing device 1 according to this embodiment (hereinafter also simply referred to as a "polishing device") has a first polishing section 2 and a second polishing section 3. The brake piston manufacturing device according to this embodiment also has this polishing device 1.

[0063] The first polishing unit 2 is a device that performs a first step (described later) in the brake piston polishing method according to this embodiment, and grinds or polishes an outer peripheral surface 981, which is the side surface of a base material 98 of the brake piston 93, which is the object. In this embodiment, a case will be described where the first polishing unit 2 is a device that performs polishing. In this embodiment, the base material 98 has a cylindrical shape with a bottom.

[0064] The second polishing unit 3 is a device that performs a second step (described later) in the polishing method for a brake piston according to this embodiment, and polishes an outer peripheral surface 981, which is the side surface of the base material 98 that has undergone the first step. The second polishing unit 3 is located downstream of the first polishing unit 2.

[0065] <First Polishing Unit> As shown in Figures 4 and 5, the first polishing unit 2 is composed of a centerless polishing device, and includes a grinding wheel 21 (first-step grinding wheel) that grinds (grinds) the outer peripheral surface 981 of the base material 98, a regulating wheel 22 arranged on the side of the grinding wheel 21, a blade 23 (supporting part) that is arranged between the grinding wheel 21 and the regulating wheel 22 and supports the base material 98, a guide part 24 (entrance side guide part) arranged on the entrance side of the first polishing unit 2 (lower side in Figure 4), a guide part 25 (exit side guide part) arranged on the exit side of the first polishing unit 2 (upper side in Figure 4), a shaft part 26 that rotatably supports the grinding wheel 21, and a shaft part 27 that rotatably supports the regulating wheel 22.

[0066] The first polishing unit 2 is configured to be able to perform both through-feed polishing (through polishing) and in-feed polishing (stop polishing), and either through-feed polishing or in-feed polishing is selected in the first step of the polishing method according to this embodiment. In this embodiment, a case where the first polishing unit 2 performs through-feed polishing will be described as a representative example. Note that the first polishing unit 2 may be configured to perform only one of through-feed polishing and in-feed polishing.

[0067] In the first polishing section 2, the base material 98 advances upward in Fig. 4 along a first axis O1. That is, the direction of advance of the base material 98 is from the bottom to the top in Fig. 4. The bottom side of the first polishing section 2 in Fig. 4 is the inlet side, and the top side in Fig. 4 is the outlet side. The first axis O1 coincides with the central axis (center line) of the base material 98 and is the central axis of rotation of the base material 98.

[0068] In the polishing portion of the first polishing section 2 , the base material 98 is supported by the blade 23 and the regulating wheel 22 , and the outer peripheral surface 981 of the base material 98 is polished by the grindstone 21 .

[0069] Furthermore, the base material 98 is supported by the blade 23 and the guide portion 24 on the inlet side of the first polishing section 2, and the base material 98 is supported by the blade 23 and the guide portion 25 on the outlet side of the first polishing section 2. This will be explained in detail below.

[0070] The grinding wheel 21 of the first polishing unit 2 (the grinding wheel 21 in the first step) has a cylindrical outer shape. The grinding wheel 21 is rotatably mounted relative to the shaft 26 around a second axis O2, which is the central axis of the grinding wheel 21 and the shaft 26, and is rotated in a predetermined direction (clockwise in FIG. 5 in the illustrated configuration) by driving a drive unit (not shown). The second axis O2 coincides with the central axis (center line) of the grinding wheel 21 and the shaft 26, is parallel to the first axis O1 when the base material 98 is placed in the first polishing unit 2, and is parallel to a horizontal plane.

[0071] The grit size (grit) of the abrasive grains of the grindstone 21 is constant throughout the entire grindstone 21. The grit size of the abrasive grains of the grindstone 21 is not particularly limited and may be set appropriately depending on various conditions, but in this embodiment, it is smaller than the smallest grit size of the abrasive grains of the grindstone 31 of the second polishing unit 3 (the grindstone 31 in the second step). Specifically, the grit size of the abrasive grains of the grindstone 21 is preferably #80 to #200, and more preferably #100 to #150. This allows the outer peripheral surface 981 of the base material 98 to be polished quickly and accurately in the first step.

[0072] The type of grinding wheel 21 is not particularly limited and can be appropriately selected depending on various conditions. Examples include a general grinding wheel having general abrasive grains and a diamond grinding wheel having diamond abrasive grains. Among these, a general grinding wheel and a diamond grinding wheel are preferred. The diamond grinding wheel can quickly polish the outer peripheral surface 981 of the base material 98 in the first step. On the other hand, the general grinding wheel can stably polish the outer peripheral surface 981 of the base material 98 in the first step, which leads to a reduction in the cost of the brake piston 93.

[0073] The regulating wheel 22 has a cylindrical outer shape. The regulating wheel 22 is rotatably installed relative to the shaft 27 around a third axis O3, which is the central axis of the regulating wheel 22 and the shaft 27, and rotates in the same direction as the grinding wheel 21 (clockwise in FIG. 5 in the illustrated configuration) by driving a drive unit (not shown). The peripheral speed (circumferential velocity) of the regulating wheel 22 is set to be smaller than the peripheral speed of the grinding wheel 21. In other words, the rotation speed (rotational velocity) of the regulating wheel 22 is set to be smaller than the rotation speed of the grinding wheel 21. The drive unit that rotates the regulating wheel 22 may be omitted.

[0074] In addition, in a plan view, the third axis O3 is parallel to the second axis O2, and the regulating wheel 22 is disposed to the side of the grinding wheel 21 (on the right side in FIGS. 4 and 5) and spaced apart from the grinding wheel 21. The third axis O3 coincides with the central axis (center line) of the regulating wheel 22 and the shaft portion 27.

[0075] On the other hand, the third axis O3, i.e., the regulating wheel 22, is slightly inclined with respect to the horizontal plane so that the outlet side (upper side in FIG. 4) of the first polishing unit 2 is vertically lower than the inlet side (lower side in FIG. 4). As a result, when the first polishing unit 2 operates and the regulating wheel 22 and grinding wheel 21 rotate, a driving force is applied to the base material 98 in the direction of the first axis O1, and the base material 98 moves upward in FIG. 4 along the first axis O1.

[0076] The blade 23 is plate-shaped and is disposed between the grinding wheel 21 and the regulating wheel 22 at a distance from the grinding wheel 21 and the regulating wheel 22 .

[0077] Furthermore, the length of the blade 23 in the direction of the first axis O1 (the direction in which the base material 98 travels) is longer than the lengths of the grinding wheel 21 and the regulating wheel 22, and the lower end of the blade 23 in Figure 4 is located lower in Figure 4 than the lower ends of the grinding wheel 21 and the regulating wheel 22 in Figure 4, and the upper end of the blade 23 in Figure 4 is located higher in Figure 4 than the upper ends of the grinding wheel 21 and the regulating wheel 22 in Figure 4.

[0078] In addition, the vertical upper surface of the blade 23 (the upper surface in Figure 5) is an inclined surface that is inclined with respect to the horizontal plane so that the grinding wheel 21 side of the blade 23 (the left side in Figure 5) is vertically higher than the adjusting wheel 22 side (the right side in Figure 5), and the upper surface of the blade 23 abuts against the outer peripheral surface 981 of the base material 98 and supports the base material 98.

[0079] The guide section 24 has a pair of guide plates 241 and 242 and is disposed on the entrance side (lower side in FIG. 4) of the first polishing section 2 .

[0080] The guide plates 241 and 242 are rod-shaped (longitudinal) and are spaced apart from each other in the horizontal direction in FIGS.

[0081] Also, on the entrance side, the base material 98 supported by the blade 23 is sandwiched between guide plates 241 and 242, and the base material 98 is supported by the blade 23 and the guide plates 241 and 242 and guided between the grinding wheel 21 and the regulating wheel 22.

[0082] The guide section 25 has a pair of guide plates 251 and 252 and is disposed on the outlet side (upper side in FIG. 4) of the first polishing section 2 .

[0083] The guide plates 251 and 252 are rod-shaped (longitudinal) and are spaced apart from each other in the horizontal direction in FIGS.

[0084] On the outlet side, the base material 98 supported by the blade 23 is sandwiched between a guide plate 251 and a guide plate 252 , and the base material 98 is supported by the blade 23 and the guide plates 251 and 252 .

[0085] In this first polishing section 2, the workpiece 98 is supported by the blade 23 and the regulating wheel 22 rotating at a low speed, and the outer peripheral surface 981 of the workpiece 98 comes into contact with the grinding wheel 21 rotating at a high speed, thereby grinding the outer peripheral surface 981 of the workpiece 98 by the grinding wheel 21. At this time, the workpiece 98 tries to rotate together with the grinding wheel 21, but is stopped by the gripping force (frictional force) of the regulating wheel 22, and rotates in the opposite direction to the grinding wheel 21 and regulating wheel 22 (counterclockwise in FIG. 5 in the illustrated configuration) at the same peripheral speed as the regulating wheel 22, with the first axis O1 as the center of rotation. Furthermore, as the workpiece 98 rotates, it passes between the grinding wheel 21 and the regulating wheel 22 and advances along the first axis O1 toward the upper side in FIG. 4 (in the direction of the first axis O1).

[0086] <Second Polishing Section> As shown in Figures 6 and 7, the second polishing section 3 is composed of a centerless polishing device, and includes a grinding wheel 31 (second process grinding wheel) that grinds (grinds) the outer peripheral surface 981 of the base material 98, a regulating wheel 32 arranged on the side of the grinding wheel 31, a blade 33 (support section) that is arranged between the grinding wheel 31 and the regulating wheel 32 and supports the base material 98, a guide section 34 (entrance side guide section) arranged on the entrance side of the second polishing section 3 (lower side in Figure 6), a guide section 35 (exit side guide section) arranged on the exit side of the second polishing section 3 (upper side in Figure 6), a shaft section 36 that rotatably supports the grinding wheel 31, and a shaft section 37 that rotatably supports the regulating wheel 32.

[0087] The second polishing section 3 is configured to perform through-feed polishing, and in the second step of the polishing method according to this embodiment, through-feed polishing is performed.

[0088] In the second polishing section 3, the base material 98 advances along the first axis O1 toward the upper side in Fig. 6. That is, the direction of advance of the base material 98 is from the lower side to the upper side in Fig. 6. The lower side of the second polishing section 3 in Fig. 6 is the inlet side, and the upper side in Fig. 6 is the outlet side.

[0089] In the polishing portion of the second polishing section 3 , the base material 98 is supported by the blade 33 and the regulating wheel 32 , and the outer peripheral surface 981 of the base material 98 is polished by the grindstone 31 .

[0090] Furthermore, the base material 98 is supported by the blade 33 and the guide portion 34 on the inlet side of the second polishing section 3, and the base material 98 is supported by the blade 33 and the guide portion 35 on the outlet side of the second polishing section 3. This will be explained in detail below.

[0091] The grinding wheel 31 of the second polishing unit 3 (the grinding wheel 31 in the second step) has a cylindrical outer shape. The grinding wheel 31 is rotatably mounted relative to the shaft 36 around a second axis O4, which is the central axis of the grinding wheel 31 and the shaft 36, and is rotated in a predetermined direction (clockwise in FIG. 7 in the illustrated configuration) by driving a drive unit (not shown). The second axis O4 coincides with the central axis (center line) of the grinding wheel 31 and the shaft 36, is parallel to the first axis O1 when the base material 98 is placed in the second polishing unit 3, and is parallel to a horizontal plane.

[0092] The grindstone 31 has a first layer 311, a second layer 312, a third layer 313, and a fourth layer 314, each having a different abrasive grain size (grit). Each layer has a cylindrical outer shape.

[0093] The layers are arranged in the following order in the direction of travel of the base material 98: first layer 311, second layer 312, third layer 313, and fourth layer 314. That is, the grinding wheel 31 has abrasive grains of different sizes arranged along the second axis O4 direction (first axis O1 direction). The abrasive grains in each layer have a constant grain size throughout the entire layer. The first and second layers of the present invention are any two of the first to fourth layers 311 to 314 of this embodiment. While the grinding wheel 31 has four layers in this embodiment, the number of layers is not limited to four and may be two, three, five, or more.

[0094] Furthermore, when the grain size of the abrasive grains in the first layer 311 is A1, the grain size of the abrasive grains in the second layer 312 is A2, the grain size of the abrasive grains in the third layer 313 is A3, and the grain size of the abrasive grains in the fourth layer 314 is A4, the relationship A1 < A2 < A3 < A4 is satisfied.

[0095] The grain size of the abrasive grains in each layer of the grinding wheel 31 is not particularly limited as long as it satisfies the above-mentioned relationship and may be set appropriately depending on various conditions. In this embodiment, however, the grain size of the abrasive grains in the first layer 311 is larger than the grain size of the abrasive grains in the grinding wheel 21 of the first polishing section 2. Specifically, the grain size of the abrasive grains in the first layer 311 is preferably #600 to #1500, and more preferably #800 to #1200. The grain size of the abrasive grains in the second layer 312 is preferably #800 to #3000, and more preferably #1000 to #2000. The grain size of the abrasive grains in the third layer 313 is preferably #1000 to #4000, and more preferably #1500 to #4000. The grain size of the abrasive grains in the fourth layer 314 is preferably #2000 to #8000, and more preferably #2500 to #6000. This allows the polishing of the outer peripheral surface 981 of the base material 98 in the second step to be performed quickly and accurately, the surface roughness of the outer peripheral surface 981 of the base material 98 to be easily and quickly adjusted to the target value, and the life of the grinding wheel 31 can be extended.

[0096] Furthermore, the type of each layer of the grinding wheel 31 is not particularly limited and can be appropriately set depending on various conditions. Examples include a general grinding wheel having general abrasive grains and a diamond grinding wheel having diamond abrasive grains. Among these, a general grinding wheel and a diamond grinding wheel are preferred. The diamond grinding wheel can quickly polish the outer peripheral surface 981 of the base material 98 in the second step. On the other hand, the general grinding wheel can stably polish the outer peripheral surface 981 of the base material 98 in the second step, which leads to a reduction in the cost of the brake piston 93.

[0097] The ratio of the grain sizes of the abrasive grains in adjacent layers is not particularly limited and is set appropriately depending on various conditions. That is, A2 / A1 is not particularly limited and is set appropriately depending on various conditions, but is preferably 4 / 3 to 5 / 1, and more preferably 5 / 3 to 5 / 2. A3 / A2 is not particularly limited and is set appropriately depending on various conditions, but is preferably 5 / 4 to 5 / 1, and more preferably 5 / 3 to 5 / 2. A4 / A3 is not particularly limited and is set appropriately depending on various conditions, but is preferably 4 / 3 to 8 / 1, and more preferably 4 / 3 to 4 / 1. This allows the polishing of the outer peripheral surface 981 of the base material 98 in the second step to be performed quickly and accurately, the surface roughness of the outer peripheral surface 981 of the base material 98 to be easily and quickly achieved to the target value, and the life of the grinding wheel 31 to be extended.

[0098] The widths of the layers (lengths in the direction of the second axis O4) are the same as each other. However, the widths of the layers are not limited to this, and for example, all the layers may be different from each other, or some of the layers may be different from each other.

[0099] The regulating wheel 32 has a cylindrical outer shape. The regulating wheel 32 is rotatably installed relative to the shaft 37 around a third axis O5, which is the central axis of the regulating wheel 32 and the shaft 37, and rotates in the same direction as the grinding wheel 31 (clockwise in FIG. 7 in the illustrated configuration) by driving a drive unit (not shown). The peripheral speed (circumferential velocity) of the regulating wheel 32 is set to be smaller than the peripheral speed of the grinding wheel 31. In other words, the rotation speed (rotational velocity) of the regulating wheel 32 is set to be smaller than the rotation speed of the grinding wheel 31. The drive unit that rotates the regulating wheel 32 may be omitted.

[0100] In addition, in a plan view, the third axis O5 is parallel to the second axis O4, and the regulating wheel 32 is disposed to the side of the grinding wheel 31 (on the right side in FIGS. 6 and 7) and spaced apart from the grinding wheel 31. The third axis O5 coincides with the central axis (center line) of the regulating wheel 32 and the shaft portion 37.

[0101] On the other hand, the third axis O5, i.e., the regulating wheel 32, is slightly inclined with respect to the horizontal plane so that the outlet side (upper side in FIG. 6) of the second polishing unit 3 is vertically lower than the inlet side (lower side in FIG. 6). As a result, when the second polishing unit 3 operates and the regulating wheel 32 and grinding wheel 31 rotate, a driving force is applied to the base material 98 in the direction of the first axis O1, and the base material 98 moves upward in FIG. 6 along the first axis O1.

[0102] The blade 33 is plate-shaped and is disposed between the grindstone 31 and the regulating wheel 32 at a distance from the grindstone 31 and the regulating wheel 32 .

[0103] In addition, the length of the blade 33 in the direction of the first axis O1 (the direction in which the base material 98 travels) is longer than the lengths of the grinding wheel 31 and the regulating wheel 32, and the lower end of the blade 33 in Figure 6 is located lower in Figure 6 than the lower ends of the grinding wheel 31 and the regulating wheel 32 in Figure 6, and the upper end of the blade 33 in Figure 6 is located higher in Figure 6 than the upper ends of the grinding wheel 31 and the regulating wheel 32 in Figure 6.

[0104] In addition, the vertical upper surface of the blade 33 (the upper surface in Figure 7) is an inclined surface that is inclined with respect to the horizontal plane so that the grinding wheel 31 side of the blade 33 (the left side in Figure 7) is vertically higher than the adjusting wheel 32 side (the right side in Figure 7), and the upper surface of the blade 33 abuts against the outer peripheral surface 981 of the base material 98 and supports the base material 98.

[0105] The guide section 34 has a pair of guide plates 341 and 342 and is disposed on the entrance side of the second polishing section 3 (the lower side in FIG. 6).

[0106] The guide plates 341 and 342 are rod-shaped (longitudinal) and are spaced apart from each other in the horizontal direction in FIGS.

[0107] Also, on the entrance side, the base material 98 supported by the blade 33 is sandwiched between guide plates 341 and 342, and the base material 98 is supported by the blade 33 and the guide plates 341 and 342 and guided between the grinding wheel 31 and the adjusting wheel 32.

[0108] The guide section 35 has a pair of guide plates 351 and 352 and is disposed on the outlet side of the second polishing section 3 (upper side in FIG. 6).

[0109] The guide plates 351 and 352 are rod-shaped (longitudinal) and are spaced apart from each other in the horizontal direction in FIGS.

[0110] On the outlet side, the base material 98 supported by the blade 33 is sandwiched between a guide plate 351 and a guide plate 352 , and the base material 98 is supported by the blade 33 and the guide plates 351 and 352 .

[0111] In this second polishing section 3, the base material 98 that has undergone the first step is supported by the blade 33 and the regulating wheel 32 that rotates at a low speed, and the outer peripheral surface 981 of the base material 98 comes into contact with the grinding wheel 31 that rotates at a high speed, thereby grinding the outer peripheral surface 981 of the base material 98 by the grinding wheel 31. At this time, the base material 98 attempts to rotate together with the grinding wheel 31, but is stopped by the gripping force (frictional force) of the regulating wheel 32, and rotates in the opposite direction to the grinding wheel 31 and regulating wheel 32 (counterclockwise in FIG. 7 in the illustrated configuration) around the first axis O1 at the same peripheral speed as the regulating wheel 32. Furthermore, as the base material 98 rotates, it passes between the grinding wheel 31 and the regulating wheel 32 and advances along the first axis O1 toward the upper side in FIG. 6 (in the direction of the first axis O1).

[0112] 3, in this embodiment, the second axis O2 and the second axis O4 of the first polishing unit 2 and the second polishing unit 3 of the polishing apparatus 1 are aligned, and the first axis O1 when the base material 98 is placed in the first polishing unit 2 is aligned with the first axis O1 when the base material 98 is placed in the second polishing unit 3. However, this is not limited to this, and it is sufficient that the first and second steps can be performed continuously on the transport path of the base material 98. This allows the outer peripheral surface 981 of the base material 98 to be polished or ground quickly. Note that the first and second steps may not be performed continuously.

[0113] <Brake Piston Polishing Method and Manufacturing Method> Next, embodiments of a brake piston polishing method and a brake piston manufacturing method will be described.

[0114] 8 is a diagram showing the manufacturing steps of a brake piston according to an embodiment of the manufacturing method of the brake piston, and shows the main steps of the manufacturing steps of the brake piston.

[0115] 8, the method for manufacturing a brake piston according to this embodiment includes a step of preparing a base material 98 of the brake piston 93 (base material preparation step), a first step of grinding or polishing an outer peripheral surface 981, which is the side surface of the base material 98, after the base material preparation step, and a second step of polishing the outer peripheral surface 981 of the base material 98 that has been subjected to the first step. The polishing method according to this embodiment also includes the first and second steps.

[0116] <Base Material Preparation Step> In the base material preparation step, a base material 98 of the brake piston 93 is prepared. The base material 98 is obtained, for example, by using a compression molding machine, pouring a preformed and preheated resin-containing composition into a mold, molding, and heating (curing). Furthermore, if necessary, a groove or the like may be formed in the circumferential direction of an outer peripheral surface 981 of the base material 98.

[0117] As described above, the base material 98 contains a resin material, preferably a resin material and a filler, and has a cylindrical shape with a bottom. However, as described above, the shape of the base material 98 is not limited to this and may be, for example, a cylindrical shape.

[0118] <First Step> In the first step, the outer peripheral surface 981, which is the side surface of the base material 98, is ground or polished. In this embodiment, a case where the outer peripheral surface 981 is polished will be described as a representative example. In this embodiment, the outer peripheral surface 981 of the base material 98 is polished by a centerless polishing method using the first polishing unit 2. In this embodiment, a through-feed polishing method (through-polishing method) is adopted. In the first step, an in-feed polishing method (stationary polishing method) may be adopted, or another device may be used. Note that the first polishing unit 2 has already been described in detail, so the following description will omit any overlapping parts.

[0119] 4 and 5, in the first step, the first polishing unit 2 is operated, and the base material 98 is placed on the inlet side of the first polishing unit 2 and supported by the blade 23 and the guide unit 24. The base material 98 is transported to the first polishing unit 2 by a transport device (not shown).

[0120] As a result, the grinding wheel 21 and the regulating wheel 22 rotate in the same direction, and the base material 98 rotates in the opposite direction to the grinding wheel 21 and the regulating wheel 22, around the first axis O1, passing between the grinding wheel 21 and the regulating wheel 22 and proceeding upward in FIG. 4 along the first axis O1. The rotating grinding wheel 21 then contacts the outer peripheral surface 981 of the base material 98, polishing (grinding) the outer peripheral surface 981. This allows the roundness of the base material 98 to be set within a predetermined value. In this way, the outer peripheral surface 981 of the base material 98 can be polished quickly and accurately. The polished base material 98 is supported by the blade 23 and the guide unit 25 at the exit side of the first polishing unit 2.

[0121] The number of times that the base material 98 is polished by the first polishing unit 2 may be one or more times. When polishing is performed multiple times, the polishing conditions such as the peripheral speed of the grinding wheel 21 and the peripheral speed of the regulating wheel 22 may be the same or different.

[0122] In this embodiment, the first and second steps are each performed by centerless polishing. However, this is not a limitation, and either one of the first and second steps may be performed by centerless polishing. That is, it is preferable that at least one of the first and second steps be performed by centerless polishing. When the first step is performed by centerless polishing, polishing of the outer peripheral surface 981 of the base material 98 in the first step can be performed quickly and accurately. Furthermore, when the second step is performed by centerless polishing, polishing of the outer peripheral surface 981 of the base material 98 in the second step can be performed quickly and accurately, making it possible to easily and quickly achieve a predetermined surface roughness for the outer peripheral surface 981 of the base material 98, and also extending the life of the grinding wheel 31.

[0123] <Second Step> The first step and the second step are performed consecutively on the conveyance path of the base material 98. This allows the outer peripheral surface 981 of the base material 98 to be polished quickly. The shape of the conveyance path of the base material 98 is not particularly limited, and may be, for example, linear or curved.

[0124] In the second step, the outer peripheral surface 981 of the base material 98 that has been subjected to the first step is polished. In this embodiment, the second polishing unit 3 is used to polish the outer peripheral surface 981 of the base material 98 by a centerless polishing method. In this embodiment, a through-feed polishing method (through-polishing method) is adopted. Note that other devices may also be used in the second step. Note that the second polishing unit 3 has already been described in detail, and therefore, the same description will be omitted below.

[0125] 6 and 7, in the second step, the second polishing unit 3 is operated, and the base material 98 that has been subjected to the first step is placed at the entrance side of the second polishing unit 3 and is supported by the blade 33 and the guide unit 34. The base material 98 is transported from the first polishing unit 2 to the second polishing unit 3 by a transport device (not shown).

[0126] As a result, the grinding wheel 31 and the regulating wheel 32 rotate in the same direction, and the base material 98 rotates in the opposite direction to the grinding wheel 31 and the regulating wheel 32 around the first axis O1 as the center of rotation, passing between the grinding wheel 31 and the regulating wheel 32 and proceeding upward in Fig. 6 along the first axis O1. The rotating grinding wheel 31 then comes into contact with the outer peripheral surface 981 of the base material 98, and the outer peripheral surface 981 is polished (polished). As a result, the surface roughness of the outer peripheral surface 981 of the base material 98 is set to a target value. As described above, the first to fourth layers 311 to 314 of the grinding wheel 31 are arranged in the order of first layer 311, second layer 312, third layer 313, and fourth layer 314 in the direction of travel of the base material 98, so that the outer peripheral surface 981 of the base material 98 can be polished quickly and accurately, the surface roughness of the outer peripheral surface 981 of the base material 98 can be easily and quickly adjusted to a target value, and the life of the grinding wheel 31 can be extended. The polished base material 98 is supported by the blade 33 and guide portion 35 on the outlet side of the second polishing section 3.

[0127] Furthermore, the number of times that the base material 98 is polished by the second polishing unit 3 may be one or more times. Furthermore, when polishing is performed multiple times, the polishing conditions, such as the peripheral speed of the grinding wheel 31 and the peripheral speed of the regulating wheel 32, may be the same or different. With the above, polishing of the outer peripheral surface 981 of the base material 98 is completed, and the brake piston 93 is obtained.

[0128] The surface roughness Ra of the outer peripheral surface 981 of the base material 98 polished in this second step, i.e., the surface roughness Ra of the outer peripheral surface 931 of the brake piston 93, is preferably 0.13 μm or less, more preferably 0.03 to 0.12 μm, and even more preferably 0.05 to 0.1 μm. This improves the brake characteristics and performance, such as the brake feel, of the disc brake 9. The surface roughness Ra of the outer peripheral surface 981 of the base material 98 is measured in accordance with JIS B 0601:2013.

[0129] As described above, the polishing method for a brake piston according to the embodiment makes it possible to easily and quickly adjust the surface roughness of the outer peripheral surface 981 of the base material 98 of the brake piston 93 to a target value, and also to extend the life of the grinding wheel 21 of the first polishing unit 2 and the grinding wheel 31 of the second polishing unit 3 of the polishing device 1. This is advantageous for mass production of brake pistons 93 and devices such as disc brakes 9 that have the brake pistons 93. It also makes it possible to provide disc brakes 9 that have excellent braking characteristics and performance, such as braking feel.

[0130] As described above, the polishing method for a brake piston according to the embodiment includes a first step of grinding or polishing the outer peripheral surface 981 (side surface) of the base material 98 of the brake piston 93, which contains a resin material, and a second step of rotating the base material 98 that has undergone the first step about the first axis O1 and moving it in the direction of the first axis O1 while bringing the rotating grinding stone 31 into contact with the outer peripheral surface 981 of the base material 98 to polish the outer peripheral surface 981. The grinding stone 31 has abrasive grains of different sizes arranged along the direction of the first axis O1.

[0131] This configuration, which includes the first and second steps, makes it possible to easily and quickly set the surface roughness of the outer circumferential surface 981 of the base material 98 of the brake piston 93 to a predetermined value, and also to extend the life of the grinding wheel 31. This is therefore advantageous for mass production of brake pistons 93 and devices such as disc brakes 9 that have the brake pistons 93.

[0132] Furthermore, in the method for polishing a brake piston according to the embodiment, the grinding wheel 31 has a first layer and a second layer (any two of the first layer 311 to fourth layer 314) arranged side by side in the direction of the first axis O1, and the first layer and second layer are arranged in this order in the direction of travel of the base material 98. Furthermore, when the grain size of the abrasive grains in the first layer is A1 and the grain size of the abrasive grains in the second layer is A2, A1<A2 is satisfied.

[0133] With this configuration, the polishing of the outer surface 981 of the base material 98 can be carried out quickly and accurately in the second step, the surface roughness of the outer surface 981 of the base material 98 can be easily and quickly set to a predetermined value, and the life of the grinding wheel 31 can be extended.

[0134] In addition, in the polishing method for the brake piston according to the above embodiment, in the first step, the base material 98 is rotated around the first axis O1 as the center of rotation, while the rotating grinding wheel 21 (first step grinding wheel) is brought into contact with the outer peripheral surface 981, thereby grinding or polishing the outer peripheral surface 981.

[0135] With this configuration, the grinding or polishing of the outer peripheral surface 981 of the base material 98 can be carried out quickly and accurately in the first step.

[0136] In addition, in the method for polishing a brake piston according to the embodiment, the grain size of the abrasive grains of the grindstone 21 in the first step is smaller than the smallest grain size of the abrasive grains of the grindstone 31 in the second step.

[0137] With this configuration, the grinding or polishing of the outer peripheral surface 981 of the base material 98 can be carried out quickly and accurately in the first step.

[0138] In the method for polishing a brake piston according to the embodiment, at least one of the first step and the second step is performed by a centerless polishing method.

[0139] With this configuration, when the first step is performed by the centerless polishing method, the outer peripheral surface 981 of the base material 98 can be polished quickly and accurately in the first step. Also, when the second step is performed by the centerless polishing method, the outer peripheral surface 981 of the base material 98 can be polished quickly and accurately in the second step, the surface roughness of the outer peripheral surface 981 of the base material 98 can be easily and quickly adjusted to a predetermined value, and the life of the grinding wheel 31 can be extended.

[0140] In the polishing method for the brake piston according to the embodiment, the second step is performed by a centerless polishing method, in which the base material 98 is passed between the grinding wheel 31 and the rotatable regulating wheel 32, and the outer peripheral surface 981 is polished.

[0141] With this configuration, the polishing of the outer surface 981 of the base material 98 can be carried out quickly and accurately in the second step, the surface roughness of the outer surface 981 of the base material 98 can be easily and quickly set to a predetermined value, and the life of the grinding wheel 31 can be extended.

[0142] In the method for polishing a brake piston according to the embodiment, the first and second steps are carried out consecutively on the conveying path of the base material 98 .

[0143] With this configuration, the outer peripheral surface 981 of the base material 98 can be polished or ground quickly.

[0144] In the method for polishing a brake piston according to the embodiment, the resin material of the brake piston 93 (the base material 98 of the brake piston 93) contains 20% by mass or more of phenol resin.

[0145] With this configuration, the corrosion resistance, wear resistance, mechanical properties, etc. of the brake piston 93 can be further improved, and the surface roughness of the outer surface 981 of the base material 98 of the brake piston 93 can be easily and quickly adjusted to a predetermined value.

[0146] In the method for polishing a brake piston according to the embodiment, the surface roughness Ra of the outer peripheral surface 981 of the base material 98 polished in the second step is 0.13 μm or less.

[0147] With this configuration, the brake characteristics and performance of the disc brake 9, such as the brake feeling, can be improved.

[0148] Although the method for polishing a brake piston according to the present invention has been described above based on the illustrated embodiment, the present invention is not limited to this.

[0149] For example, the method for polishing a brake piston of the present invention may be configured by adding any step to the above-described embodiment.

[0150] Furthermore, the method for manufacturing the brake piston may be such that any step is added to the above-described embodiment.

[0151] Furthermore, the brake piston, disc brake, and brake piston polishing device may be configured by adding any element (configuration) to the above-described embodiments.

[0152] According to the present invention, it is possible to provide a method for polishing a brake piston, which can easily and quickly adjust the surface roughness of the side surface of the base material of the brake piston, which includes a resin material, to a predetermined value using a grinding stone, and which can also extend the life of the grinding stone. Therefore, the present invention has industrial applicability.

[0153] REFERENCE SIGNS LIST 1 Grinding device 2 First grinding unit 21 Grindstone 22 Regulating wheel 23 Blade 24 Guide unit 241, 242 Guide plate 25 Guide unit 251, 252 Guide plate 26, 27 Shaft 3 Second grinding unit 31 Grindstone 311 First layer 312 Second layer 313 Third layer 314 Fourth layer 32 Regulating wheel 33 Blade 34 Guide unit 341, 342 Guide plate 35 Guide unit 351, 352 Guide plate 36, 37 Shaft 9 Disc brake 90 Caliper 91 Hydraulic cylinder 92 Seal ring 93 Brake piston 931 Outer periphery 94 Disc rotor 951 Brake pad 952 Brake pad 961 Back plate 962 Back plate 97 Brake fluid 98 Base material 981 Outer circumferential surface O1 First shaft O2 Second shaft O3 Third shaft O4 Second shaft O5 Third shaft

Claims

1. A method for polishing a brake piston, comprising: a first step of grinding or polishing the side surface of a base material of a brake piston containing a resin material; and a second step of rotating the base material that has undergone the first step around a first axis and moving it in the first axial direction while bringing a rotating grinding stone into contact with the side surface of the base material to polish the side surface, wherein the grinding stone has abrasive grains of different sizes arranged along the first axial direction.

2. A method for polishing a brake piston as set forth in claim 1, wherein the grinding wheel has a first layer and a second layer arranged side by side in the first axial direction, the first layer and the second layer are arranged in this order facing the direction of travel of the base material, and when the grain size of the abrasive grains in the first layer is A1 and the grain size of the abrasive grains in the second layer is A2, A1 < A2 is satisfied.

3. A method for polishing a brake piston as described in claim 1 or 2, wherein in the first step, the base material is rotated around the first axis as the center of rotation, and a rotating first step grinding stone is brought into contact with the side surface to grind or polish the side surface.

4. A method for polishing a brake piston as described in claim 3, wherein the grit size of the abrasive grains of the first-step grindstone in the first step is smaller than the smallest grit size of the abrasive grains of the grindstone in the second step.

5. A method for polishing a brake piston according to any one of claims 1 to 4, wherein at least one of the first step and the second step is carried out by a centerless polishing method.

6. A method for polishing a brake piston according to any one of claims 1 to 5, wherein the second step is performed by a centerless polishing method, and in the second step, the base material is passed between the grinding stone and a rotatable adjusting wheel to polish the side surface.

7. A method for polishing a brake piston according to any one of claims 1 to 6, wherein the first step and the second step are carried out consecutively on the conveying path of the base material.

8. A method for polishing a brake piston according to any one of claims 1 to 7, wherein the resin material contains 20 mass % or more of phenolic resin.

9. A method for polishing a brake piston according to any one of claims 1 to 8, wherein the surface roughness Ra of the side surface of the base material polished in the second step is 0.13 μm or less.

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