Corrosion-resistant bicycle brake disc

Abstract

A bicycle brake disc device (10) having a rotational center axis, the bicycle brake disc device (10) comprising: a core portion (22) containing iron; and a surface portion (23) formed on the outer surface (21a, 21b, 22a, 22b) of the core portion (22), the surface portion (23) containing iron, aluminum, and chromium, and the surface portion (23) having a concentration gradient of chromium in the axial direction parallel to the rotational center axis.

Description

Disc brake systems are widely installed in bicycles. Disc brake systems have at least one brake disc. For a bicycle brake disk, various materials such as aluminum, stainless steel, titanium, and iron have been used.According to the invention, the bicycle brake disk device has a rotational center axis and has an iron-containing core portion and a surface portion formed on the outer surface of the core portion. The surface portion having a concentration gradient of chromium in the axial direction parallel to the rotational center axis includes iron, aluminum, and chromium. An advantage of this configuration is that the bicycle brake disc has better corrosion resistance, wear resistance and structural strength.Preferably, the concentration of chromium decreases from the outer surface of the surface portion toward the core portion. An advantage of such a configuration is that the region of the brake disc which comes into contact with the brake pads is preferably formed in such a way that the greatest possible corrosion resistance, wear resistance and structural strength are achieved.Preferably, the surface portion further comprises a mixed material containing iron and aluminum. An advantage of such a configuration is that the region of the brake disc which comes into contact with the brake pads is preferably formed in such a way that the greatest possible corrosion resistance, wear resistance and structural strength are achieved, wherein the corrosion resistance, wear resistance and structural strength become increasingly smaller with greater distance from the region in contact with the brake pads.Preferably, the surface portion is formed by means of a diffusion process. An advantage of such a configuration is that the mixed iron, aluminum and chromium alloy can be economically obtained in the surface portion of the brake disc, so that the portion of the brake disc which comes into contact with the brake pads is preferably formed to achieve the greatest possible corrosion resistance, wear resistance and structural strength.Preferably, the surface portion is hardened by quenching. An advantage of such a configuration is that the structural strength and wear resistance of the surface portion of the brake disc can be improved.Preferably, the outer surface of the surface portion is formed by means of a grinding process. An advantage of such a configuration is that the desired thickness of the surface section can be achieved in the brake disc, so that it corresponds to the dimensions of the front disc brake system, but the chromium and aluminum content of the surface section is not impaired too much.Preferably, the thickness of the surface portion is more than 10 μm An advantage of such a configuration is that a sufficient concentration of chromium in the outer surface of the surface portion can be achieved during the diffusion process, such that the desired corrosion resistance, wear resistance and structural strength are provided.Preferably, the thickness of the surface portion is more than 50 μm An advantage of such a configuration is that a sufficient concentration of chromium in the outer surface of the surface portion can be achieved during the diffusion process, such that the desired corrosion resistance, wear resistance and structural strength are provided.Preferably, the thickness of the surface portion is more than 70 μm An advantage of such a configuration is that a sufficient concentration of chromium in the outer surface of the surface portion can be achieved during the diffusion process, such that the desired corrosion resistance, wear resistance and structural strength are provided.Preferably, the Vickers hardness (Hv) of the surface portion is greater than or equal to 250. An advantage of such a configuration is that the structural strength and wear resistance of the surface portion are achieved by quench hardening.Preferably, the Vickers hardness (Hv) of the surface portion is less than or equal to 1,000. An advantage of such a configuration is that the structural strength and wear resistance of the surface portion are achieved by quench hardening.Preferably, the bicycle brake disk device further includes an outer member including the core portion and the surface portion, a hub attachment member configured to be mountable to the bicycle hub assembly of the bicycle, and at least one intermediate member connecting the outer member and the hub attachment member. An advantage of such a configuration is that the surface portion with improved corrosion resistance, wear resistance and structural strength is attached to the bicycle brake disc device coupled to the hub assembly of a bicycle as part of the brake system.Preferably, at least the outer member or the at least one intermediate member has at least one through hole having a circumferential surface, and the circumferential surface forms the entire surface portion. An advantage of such a configuration is that the improved corrosion resistance, wear resistance and structural strength extend to all surface regions of the outer member including the circumferential surfaces of the through-holes.Preferably, the at least one intermediate component is integral with the outer component. An advantage of such a configuration is that the number of components for production can be reduced.Preferably, the at least one intermediate component is integral with the hub attachment component. An advantage of such a configuration is that the number of components for production can be reduced.Preferably, the at least one intermediate member is integral with the outer member and the hub attachment member. An advantage of such a configuration is that the number of components for production can be reduced.The at least one intermediate component is preferably separate from the outer component. An advantage of such a configuration is that the surface portion with improved corrosion resistance, wear resistance and structural strength is preferably attached to the outer member which is the part of the bicycle brake disc device that comes into contact with the brake pads.This summary is intended to provide a selection of simplified concepts that are further described below in the detailed description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor to limit the scope of the claimed subject matter. Further, the claimed subject matter is not limited to implementations that eliminate some or all of the disadvantages exhibited in any part of this disclosure.A selected embodiment of the present invention will now be described with reference to the accompanying drawings, wherein: FIG. 1 illustrates a partial side view of an exemplary bicycle brake disc of a front disc brake system according to a disclosed embodiment of the present invention; FIG. 2 illustrates an enlarged partial cross-sectional view of a portion of an exemplary conventional bicycle brake disc; FIG. 3 illustrates an enlarged partial cross-sectional view of a portion of an exemplary bicycle brake disc taken along line A-A' in FIG. 1, in accordance with a disclosed embodiment of the present invention; FIG. 4 is a flow chart illustrating the manufacturing steps for forming a bicycle brake disc of an embodiment of the present invention; FIG. 5A is a graph illustrating the relationship at about 900° C. between the concentration of chromium in the surface portion at a given point, its distance from the outer surface, and the time of the diffusion process for cases where the base iron material is heated to 900° C. in media rich in chromium and aluminum; and FIG. 5B is a graph illustrating the relationship at about 1,000 ° C. between the concentration of chromium in the surface portion at a given point, its distance from the outer surface, and the time of the diffusion process for cases where the base iron material is heated to 1,000 ° C. in media rich in chromium and aluminum.It will be apparent to those skilled in the art from this disclosure that the following description of an embodiment of the invention is intended for purposes of illustration only and is not intended to limit the invention as defined by the appended claims and their equivalents. The present disclosure is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals identify like elements.Referring first to FIG. 1, an exemplary bicycle brake disc 10 of a front disc brake system 1 according to a disclosed embodiment of the present invention is shown. The front disc brake system 10 includes a bicycle disc brake caliper 2 and a brake operating mechanism 3. The bicycle brake disc 10 is fixedly secured to the bicycle hub of a bicycle wheel (not shown). The bicycle disc brake caliper 2 is mounted on the bicycle fork 4, while the brake operating mechanism 3 is fixed to the bicycle handlebar 5. Except for the bicycle brake disc. Referring to FIG. 10, the operation and construction of the front disc brake system 1 are conventional and taught in the prior art. Moreover, while the front disc brake system 1 is illustrated as a hydraulic brake system in this embodiment, it should be understood that the bicycle brake disc 10 may be used with other types of brake systems as well.The bicycle brake disk 10 includes a brake disk base plate 18 that includes an outer member 12 having a core portion and a surface portion (shown in cross section A-A' in FIG. 3 ), at least one or more intermediate member(s) 14 extending radially inward from the outer member 12 and connecting the outer member 12 to the hub attachment member 16, and the hub attachment member 16 coupled to the inner ends of the intermediate members 14 by a plurality of fasteners 6 and configured to be mountable to the bicycle hub assembly of the bicycle (not shown). In this embodiment, the outer member 12, the intermediate members 14, and the hub attachment member 16 are integrally formed as a one-piece member of metal. However, in other embodiments, the outer member 12, the intermediate members 14, and the hub attachment member 16 may be separate pieces that are not integrally formed. For example, in some embodiments, at least one intermediate member 14 may be separate from the outer member 12, and the at least one intermediate member may be integrally formed with the hub attachment member. For example, as shown schematically at 14A, the intermediate members may be formed separately and later secured to the outer member 12 by fasteners such as bolts. In such a configuration, normally all intermediate components 14 are formed integrally with the hub fastening component 16, but separately from the outer component; however, other configurations are also possible, such as, for example, the alternating arrangement of integrally formed intermediate components fastened by fastening means along the circumference of the brake disc. In other embodiments, at least one intermediate member 14 may be integrally formed with the outer member 12 and the at least one intermediate member 14 may be separately formed and secured to the hub attachment member 16 with a fastener, as illustrated at 14B. Usually, in such a configuration, all intermediate components 14 are formed integrally with the outer component 12 and separately from the hub fastening component 16 and fastened thereto; as mentioned above, the integrally formed sides of the intermediate components 14 fastened by fastening means can, for example, also be alternated. As described above in the illustrated embodiment, it will be appreciated that at least one, and usually all, intermediate members 14 are integrally formed with both the outer member 12 and the hub attachment member 16. Furthermore, at least one of the outer component 12 and at least one of the intermediate components 14 can have at least one through-bore 20 a, 20 b. In the illustrated embodiment, a plurality of through-holes 20 a, 20 bare shown, which extend from a first side surface to a second side surface against which the brake pads are pressed, and are distributed with a substantially uniform density over the entire side surfaces of the outer member. The through-holes 20 ensure, on the one hand, that an air flow distributes the heat caused by the brake friction and, on the other hand, make the outer component lighter.FIG. 2 shows a partial cross-sectional view of a conventional exemplary bicycle brake disc that would correspond to a cross-sectional view of the bicycle brake disc taken along dotted line A-A' in FIG. 1. The core portion 222 of the brake disk base plate 221 has an outer circumferential edge 222 aand an inner circumferential edge 222 b. The intermediate members extend radially inward from the inner peripheral edge 222 bof the core portion 222. The brake disc base plate 221 has first and second base surfaces 221 aand 221 bfacing each other in opposite axial directions of the bicycle brake disc 212. The first and second base surfaces 221 aand 221 bare planar surfaces that pass over the core portion 222, the intermediate members, and the hub attachment members. The first and second surfaces 221 aand 221 bdo not necessarily have to be planar in all regions. For example, the first and second bases 221 aand 221 bmay be contoured in the regions of the intermediate members and the hub attachment members.In the related-art embodiment, the bicycle brake disk 212 has been chemically treated by a diffusion process to further include a surface region 230 forming a protection region on the brake disk base plate 221. Typically, the surface region 230 is an alloy zone or layer having a uniform thickness that is chemically formed on all exposed surfaces of the brake disc base plate 221. The thickness of the surface region 230 varies depending on the time period in which the bicycle brake disc 212 undergoes the diffusion process. The mixed material is infiltrated into at least the first and second bases 221 aand 221 b. Using the diffusion process, at least one or both of the peripheral edges 222 aand 222 bof the core portion 222 may also include a diffusion zone. The diffusion zone of the surface region 230 may comprise an aluminum and iron compound in the prior art. In this example, the aluminum diffuses through the iron to the first and second bases 221 aand 221 bto form an alloy. The concentration gradient of the aluminum decreases from the outer surfaces 230 aand 230 btoward the core portion 222, so that the concentration of the aluminum is higher at the outer surfaces 230 aand 230 bwhich directly contact the brake pads of the bicycle disc brake caliper. Thus, the diffusion zone of the surface region 230 overlying the core portion 222 of the brake disc base plate 221 provides both structural strength and corrosion resistance to the bicycle brake disc 212, particularly in areas where the bicycle brake disc 212 contacts the brake pads of the bicycle disc brake caliper.Referring to FIG. 3, there is shown an enlarged, partial cross-sectional view of a portion of the outer member 12 of an exemplary bicycle brake disc 10 taken along dotted line A-A' in FIG. 1, in accordance with a disclosed embodiment of the present invention. The bicycle brake disc having a rotational center axis includes a core portion 22 and a surface portion 23. The core portion 22 of the brake disk base plate 18 contains iron and has an outer circumferential edge 22 aand an inner circumferential edge 22 b. The intermediate members extend radially inward from the inner peripheral edge 22 bof the core portion 22, and the brake disk base plate 18 has first and second base surfaces 21 aand 21 bfacing each other in opposite axial directions of the bicycle brake disk 10. The first and second base surfaces 21 aand 21 bare planar surfaces that extend over the core portion 22, the intermediate members, and the hub attachment members. The first and second surfaces 21 aand 21 bdo not have to be planar in all regions. For example, the first and second bases 21a and 21b may be contoured in the regions of the intermediate and hub attachment members.The bicycle brake disk 10 has been chemically treated in a diffusion process to further include a surface portion 23 forming a protection region on the outer surface of the core portion 22. In some embodiments, the through holes 20 a, 20 bmay also have circumferential surfaces forming the entire surface portion 23 forming a protection region on the outer surface of the core portion 22 by the diffusion process. In the present embodiment, the surface portion 23 is an alloy zone or layer having a uniform thickness chemically formed on all the exposed surfaces of the brake disk base plate 18. However, without limitation to this embodiment, other embodiments may include a surface portion 23 that is chemically formed only in limited areas of the exposed surfaces of the brake disc base plate 18.The surface portion 23 has a concentration gradient and a diffusion zone including a mixed material containing iron, aluminum, and chromium diffused and infiltrated into at least the first and second base surfaces 21 aand 21 b, followed by the concentration gradient of chromium and aluminum in the axial direction parallel to the rotational center axis of the bicycle brake disk device 10. The concentration gradient of chromium decreases from the outer surface of the surface portion 23 toward the core portion, so that the highest concentration of chromium is obtained on the outer surfaces, the first and second outer surfaces 30 aand 30 b, while the lowest concentration of chromium is obtained in the inner parts of the surface portion. Since the highest concentration of chromium is achieved on the first and second outer surfaces 30 aand 30 b, the bicycle brake disc 10 has structural strength and corrosion resistance, particularly in areas where the bicycle brake disc 10 comes into contact with the brake pads of the bicycle disc brake caliper.At least one or both of the peripheral edges 22 aand 22 bof the core portion 22 may also include a diffusion region. In this example, aluminum and chromium diffuse into the first and second bases 21a and 21b to form an alloy. The claimed alloy consisting of iron, aluminum and chromium is excellent over one consisting of only iron and aluminum because the claimed alloy in conjunction with quenching hardness is provided with improved corrosion resistance, wear resistance and structural strength, so that the Vickers hardness (Hv) of the surface portion is greater than or equal to 250 or less than or equal to 1000.Referring to FIG. 4, the manufacturing steps for forming a bicycle brake disc of an embodiment of the present invention are illustrated. The manufacture of the bicycle brake disc comprises four steps: (S 1) pressing, (S 2) diffusion, (S 3) quenching, and (S 4) grinding. In step S 1, the brake disc is formed in a pressing process by pressing the iron base material into the desired shape corresponding to the outer member. Since corrosion resistance can be influenced by the porosity, hardness and surface quality of the core substrate, care must be taken to press an iron base material free from cracks, pores and irregularities.In step S 2, the surface portion is formed by a diffusion process. In the diffusion process, by heating to about 900-1,000 °C, chromium and aluminum diffuse in media (solid, liquid or gaseous) rich in chromium and aluminum into the base iron material, thereby achieving hardness, structural strength, wear resistance, and corrosion resistance. The thickness of the surface portion is controlled by regulating the diffusion time and temperature of the media during the diffusion process. The temperature of the media is maintained within the above range because exceeding the upper temperature limit could interfere with the subsequent quench hardening process.In step S 3, the surface portion of the brake disk is hardened by quenching. In the quenching hardening process, the heated metal is rapidly cooled, preventing the formation of all crystalline structures, resulting in an amorphous metal that is structure-resistant and chip-resistant, thereby achieving a high degree of toughness and ductility. Successful treatment requires that the heated metal be fully cooled and quenched as quickly as possible immediately after the diffusion process. Various quenching media can be used to carry out a successful treatment, such as water, oil, polymers or forced ventilation (recirculated air). The quenching treatment should be controlled so that no internal stresses are formed in the cooled metal. In some embodiments, in the manufacturing method for the brake disc, the quench hardening process may be skipped to reduce manufacturing time and cost. In other embodiments, the brake disc may be subjected to the diffusion process and quench hardening twice to perform the tempering.In step S 4, the outer surface of the surface portion is formed by a grinding process. In the grinding process, a purely optional step, the desired thickness of the surface portion may be obtained by grinding parts of the surface portion starting from the surface and matching the dimensions of the disc brake system while not unduly compromising the chromium and aluminum content of the surface portion. The thickness of the surface portion may in some embodiments be preferably greater than 10 μm, more preferably greater than 50 μm, and most preferably greater than 70 μm In other embodiments, the manufacturing process may be calibrated such that no grinding operation is required to adjust the bicycle brake disc to the dimensions of the disc brake system.As shown in Fig. 5A, the concentration of chromium in the surface portion at a given point depends on its distance from the outer surface. Here, the relationship at about 900° C. between the concentration of chromium in the surface portion at a given point, its distance from the outer surface, and the time of diffusion process is shown for cases where the base iron material is heated to 900° C. in media (solid, liquid, or gaseous) rich in chromium and aluminum. In each diffusion curve, the concentration of chromium in the surface portion decreases as the distance from the outer surface increases. As diffusion times increase, chromium and aluminum have more time available for diffusion through the surface portion, thereby increasing the concentration of chromium throughout the surface portion and allowing chromium and aluminum to penetrate more deeply into the base iron material, which also increases the thickness of the surface portion in the process. However, too long diffusion times may result in too low a concentration of iron in the outer surface of the surface portion, which results in the surface portion losing some of the properties provided by the iron base material, such as excellent heat dissipation. Therefore, in the diffusion process, ideally, balance should be achieved between the end portions of iron, chromium and aluminum in the surface portion.As shown in Fig. 5B, the concentration of chromium in the surface portion at a given point depends on its distance from the outer surface. Here, the relationship at about 1,000 °C between the concentration of chromium in the surface portion at a given point, its distance from the outer surface, and the time of the diffusion process is shown for cases where the base iron material is heated to 1,000 °C in media (solid, liquid, or gaseous) rich in chromium and aluminum. Comparisons between FIGS. 5A and 5B suggest that preferably heating the iron base to 1,000 °C, rather than 900°C, improves the chromium concentration throughout the surface portion. Also, the diffusion curves appear to decrease less steeply than those in cases where the iron base material is heated to 900° C. in media rich in chromium and aluminum. Thus, the data suggest that performing the diffusion process at 1,000 °C, rather than 900°C, results in chromium concentrations that are more consistent near the outer surface. This is particularly advantageous if the outer surface is ground in order to achieve the desired thickness of the surface section, which corresponds to the dimensions of the disc brake system.The above embodiments improve corrosion resistance of a bicycle brake disk made of iron by adding chromium to the outer surface of the bicycle brake disk other than aluminum. As another advantage, according to the embodiment of the present invention, the structural strength and hardness of the outer surface of the bicycle brake disk are improved. As a result, the wear-resistant property is improved.As used herein, the term "comprising" and its derivatives are intended to be open terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps. This concept also applies to words of similar meaning, such as the terms "comprise", "contain" and their derivatives.As used herein, the term "bicycle" and its derivatives are intended to be open terms that specify a vehicle or machine in which a wheel is / is rotated upon pedaling by the action of the feet of the cyclist, and include road bicycles, stationary bicycles, exercise machines, hall bicycles, and the like.The terms of degree such as "about" as used herein are to be understood as an appropriate amount of deviation from the modified term such that the end result is not significantly changed (e.g., manufacturing tolerances).Although specific embodiments of the bicycle brake disc have been described in detail, the specific arrangements disclosed are intended to be illustrative only and not limiting. The features of the above-described various embodiments and modifications thereof may be combined variously without departing from the scope of the disclosure.REFERENCE NUMERALS1 Front disc brake system 2 Caliper 3 Brake operating mechanism 4 Bicycle fork 5 Handlebar 10 Brake disc 12 Outer member 14 Intermediate member 14A Fastener 14B Fastener 16 Hub fastening member 18 Brake disc base plate 20 aThrough hole 20 bThrough hole 21 aFirst base surface 21 bSecond base surface 22 Core portion 22 a Außenumfangs peripheral edge 22 b Innenumfangs peripheral edge 23 Surface portion 30 aFirst outer surface 30 bSecond outer surface 212 Bicycle brake disc 221 Brake disc base plate 221 aFirst base surface 221 bSecond base surface 222 Core portion 222 a Außenumfangs peripheral edge 222 b Peripheral edge 230 Surface region 230 a Außenfläche surface 230 b Surface

Claims

A bicycle brake disk device (10) having a rotational center axis, the bicycle brake disk device (10) comprising: an iron-containing core portion (22); and a surface portion (23) formed on the outer surface (21a, 21b, 22a, 22b) of the core portion (22), wherein the surface portion (23) contains iron, aluminum, and chromium, and the surface portion (23) has a concentration gradient of chromium in an axial direction parallel to the rotational center axis.The bicycle brake disk device (10) according to claim 1, wherein the concentration of chromium decreases from the outer surface (30a, 30b) of the surface portion toward the core portion (22).The bicycle brake disk device (10) according to claim 1, wherein the surface portion (23) further comprises a mixed material containing iron and aluminum.The bicycle brake disk device (10) according to claim 1, wherein the surface portion (23) is formed by a diffusion process.The bicycle brake disk device (10) according to claim 3, wherein the surface portion (23) is hardened by quenching.The bicycle brake disc device (10) according to claim 1, wherein the outer surface (30a, 30b) of the surface portion (23) is formed by a grinding process.The bicycle brake disk device (10) according to claim 1, wherein the thickness of the surface portion (23) is greater than 10 μm.The bicycle brake disk device (10) according to claim 1, wherein the thickness of the surface portion (23) is greater than 50 μm.The bicycle brake disc device (10) according to claim 1, wherein the thickness of the surface portion (23) is greater than 70 μm.The bicycle brake disk device (10) according to claim 1, wherein the Vickers hardness (Hv) of the surface portion (23) is greater than or equal to 250.The bicycle brake disk device (10) according to claim 1, wherein the Vickers hardness (Hv) of the surface portion (23) is less than or equal to 1,000.The bicycle brake disk device (10) according to claim 1, further comprising: an outer member (12) including the core portion (18) and the surface portion (23); a hub attachment member (16) configured to be mountable to the bicycle hub assembly of the bicycle; and at least one intermediate member (14) connecting the outer member (12) and the hub attachment member (16).The bicycle brake disk device (10) according to claim 12, wherein at least one of the outer member (12) and the at least one intermediate member (16) has at least one through hole (20a, 20b) having a circumferential surface, and the circumferential surface forms the entire surface portion (23).The bicycle brake disc device (10) according to claim 12, wherein the at least one intermediate member (14) is integral with the outer member (12).The bicycle brake disc device (10) according to claim 12, wherein the at least one intermediate member (14) is integral with the hub attachment member (16).The bicycle brake disc device (10) according to claim 12, wherein the at least one intermediate member (14) is integral with the outer member (12) and the hub attachment member (16).The bicycle brake disc device (10) according to claim 12, wherein the at least one intermediate member (14) is separate from the outer member (12).

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