Borated brake disc rotor

Abstract

A brake rotor, a brake system comprising a brake rotor, and a method for boronizing a brake rotor, wherein the brake rotor comprises a rotor body with a braking surface. The rotor body comprises an iron alloy, and the braking surface comprises a layer of Fe₂B phases within the braking surface. The brake system comprises the brake rotor and a brake pad that can engage with the braking surface. The method comprises boronizing the braking surface and forming an Fe₂B phase on the braking surface, as well as cooling the rotor body to ambient temperature.

Description

INITIATIONVehicle brakes use friction to stop wheels to stop rotating and stop the vehicle. When the brake pedal is depressed or the brake is otherwise applied, hydraulic pressure is applied to one or more brake pads associated with a given wheel. The brake pads are pressed against a rotor connected to each wheel, slowing rotation of the wheel and ultimately stopping it. In this process, kinetic energy is converted into thermal energy, which can lead to relatively high local temperatures at the rotor. The contact between the brake pads and the rotor results in loss of material in both the brake pads and the rotor and the formation of particulates. Depending on the composition, when some rotors wear, tracks or grooves form in the lining or in the rotor.Although the brake pads and disc rotors serve their purpose, there remains room for further developments.SUMMARYIn several aspects, the present disclosure is directed to a brake rotor. The brake rotor includes a rotor body having a braking surface. The rotor body comprises an iron alloy and the braking surface comprises a layer of iron boride phases having the formula Fe 2 B (Fe 2 B phases) in the braking surface.In embodiments of the foregoing, the iron alloy comprises gray cast iron.In each of the above embodiments, the layer further comprises iron boride phases having the formula FeB (FeB phases). Alternatively, the iron boride phases in the layer may be made of Fe 2 B phases.In each of the above embodiments, the braking surface has a hardness in the range of 1500 to 2000 HV (Vickers hardness).In each of the above embodiments, the depth of the layer is in the range of 0.02 millimeter to 2.5 millimeters.In each of the above embodiments, the rotor body is a disc and includes a central hub and a ring gear defined about the central hub, the ring gear including the braking surface. In further embodiments, the ring gear includes cast iron. In further embodiments, the central hub is formed from a second material.In each of the above embodiments, the rotor body is a drum having a central hub and a wall extending from the central hub, an inner surface of the wall including the braking surface.In several additional aspects, the present disclosure is directed to a brake system. The brake system comprises a brake rotor according to one of the above-mentioned embodiments. The brake rotor includes a rotor body having a braking surface. The rotor body comprises an iron alloy and the braking surface comprises a layer of iron boride phases having the formula Fe 2 B (Fe2B phases). The brake system further includes a brake pad engageable with the brake surface.In embodiments of the foregoing, the layer further comprises iron boride having the formula FeB (FeB phases). Alternatively, the iron boride phases in the layer may be made of Fe 2 B phases.In each of the above embodiments, the braking surface has a hardness in the range of 1500 to 2000 HV (Vickers hardness).In each of the above embodiments, the iron alloy comprises gray cast iron.In each of the above embodiments, the rotor body is a disk. Alternatively, the rotor body in each of the above embodiments is a drum.In each of the above embodiments, the brake system further includes a brake operating device, a master cylinder connected to the brake operating device, and a piston connected to the brake pad and the master cylinder, the piston being connected to the master cylinder via one or more hydraulic lines.In several additional aspects, the present disclosure is directed to a method of manufacturing a brake disc rotor. The method includes removing contaminants from a brake rotor. The brake rotor includes a rotor body having a braking surface. The rotor body comprises an iron alloy. The method further comprises borating the braking surface and forming a layer of iron boride phases having the formula Fe 2 B (Fe 2 B phases) on the braking surface, and cooling the rotor body to ambient temperature.In some embodiments of the foregoing, borating comprises contacting the iron alloy with a boron-containing composition, wherein the iron alloy is exposed to a temperature in the range of 700° C. to 1000° C.In further embodiments of the foregoing, the method includes machining the braking surface after boration.In each of the above embodiments, the layer further comprises iron boride phases having the formula FeB (FeB phases). In further embodiments, the method includes removing the FeB phases from the braking surface.In each of the above embodiments, the brake rotor further comprises a central hub and a ring gear defined about the central hub, the ring gear comprising the brake surface. The method further includes assembling the central hub to the ring gear.BRIEF DESCRIPTIONThe drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. FIG. 1 shows a vehicle having a brake system according to an embodiment of the present disclosure in a schematic illustration. FIG. 2 shows a disk rotor according to an embodiment of the present disclosure in an illustration. FIG. 3 shows a disc rotor according to an additional embodiment of the present disclosure in an illustration. FIG. 4 shows a drum rotor according to an embodiment of the present disclosure in an illustration. FIG. 5 shows a braking surface according to an embodiment of the present disclosure in an illustrative cross-sectional view. FIG. 6 shows a flow chart of a method for borating a braking surface of a rotor according to an embodiment of the present disclosure.DETAILED DESCRIPTIONThe following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or use. Moreover, there is no intention to be bound by any explicit or silent theory present in the foregoing introduction, summary, or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals designate like or corresponding parts and features.Although the present technology is described herein primarily in the context of passenger cars, it is not limited to passenger cars. The concepts may be used in a variety of applications, including in connection with utility vehicles, sport utility vehicles, military vehicles, motor cycles, mopeds, locomotives, aircraft, watercraft and other vehicles, as well as other applications in which disk rotors may be installed, including industrial applications such as conveyors, indicators, wind turbines and hose retractors.Reference will now be made in detail to several examples of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used in the drawings and the specification to refer to the same or like parts or steps. The drawings are in simplified form and are not to scale.The present disclosure relates to borated brake rotors, borated brake rotor systems, and methods for borating the brake rotors. FIG. 1 illustrates a vehicle 100 having four wheels 102. A brake system 104 is associated with one or more wheels 102. The brake system 104 generally includes a brake actuation device 110, such as a brake pedal or an electronic brake actuation device. The brake operating device 110 is connected to the master cylinder 112. The master cylinder 112 is connected to the pistons 114 or wheel cylinders (see FIG. 4 ) associated with each wheel 102 via hydraulic lines 116. The pistons 114 or wheel cylinders are connected to the brake pads 118 that, when actuated by the brake actuator 110, can be engaged with the brake rotors 120 connected to each wheel 102. The illustrated brake rotor 120 is a disc rotor; alternatively, however, a drum rotor may be used (see FIG. 4 ).Operation of the brake operating device 110, e.g., depression of the brake pedal or turning on of an electronic brake operating device, generates pressure in the master cylinder 112. The pressure is hydraulically transmitted via hydraulic lines 116 to a piston 114, e.g. a disc brake piston or a wheel brake cylinder (in the case of drum brakes), which is associated with each brake system 104 and each brake disc 120. The pressure causes the pistons 114 to expand and the brake pads 118 to engage and apply a force to the brake rotor 120. The force slows the rotation of the brake rotor 120 and the wheel 102 to which it is connected, and ultimately stops the rotation of the wheel 102.FIG. 2 illustrates a brake rotor 120, particularly a disc brake rotor 120 a. The disc brake rotor 120 aincludes a rotor body 124 that includes one or more braking surfaces 126 that define a ring gear 132 on the rotor body 124 around a central hub 130. The central hub 130 is in the form of a round hat or bell. Although only a first braking surface 126 is illustrated in FIG. 2, a second braking surface 126 is provided on the opposite side of the rotor body 124. The braking surface 126 may have a surface finish of 2 micrometers or less, for example, in the range of 0.3 micrometers to 2 micrometers.The rotor body 124 is formed of cast iron that is an iron alloy that contains 2 to 4 weight percent carbon of the total weight of the cast iron alloy and 1 to 3 weight percent silicon of the total weight of the cast iron alloy. In some embodiments, the cast iron is gray cast iron and the carbon is present in the form of graphite. The cast iron may also contain less than 1.0 weight percent of the total weight of the cast iron alloy manganese, e.g., in the range of 0.5 to 0.9 percent, as well as trace sulfur and phosphorus impurities, which are also less than 0.3 weight percent of the total weight of the alloy. It should be noted that the total weight of the cast iron alloy is 100 percent by weight. Alternatively, the rotor body 124 may also be made of one or more alternative iron alloys such as worm graphite (GJV), spheroidal graphite cast iron (spheroidal graphite iron), and steel.FIG. 3 shows a brake rotor 120, which is also a disc brake rotor 120a, and in which the central hub 130 and the ring gear 132 of the rotor body 124 surrounding it are formed from two separate components rather than from a single component. In some aspects, the central hub 130 is formed from a second material comprising one or more metals, metal alloys, and ceramics. In some embodiments, the central hub is formed of aluminum or an aluminum alloy and the ring gear 132 surrounding the central hub 130 is formed of cast iron or an alternative iron alloy as described above. The central hub 130 is connected to the ring gear 132 by one or more mechanical fasteners or fittings.Further, the ring gear 132 of the rotor body 124 may include a plurality of vent openings 134 extending from the center of the rotor body 124 to the edges 135 of the disc brake rotor 120 a, as illustrated in FIGS. 2 and 3, or through-holes defined between the brake surfaces 126 (not illustrated). Additionally, the rotor body ring gear 132 may include grooves 139 in the braking surfaces 126 (as illustrated in FIG. 3 ) or through-holes defined in the rotor body 124 and extending therethrough from the braking surface 126 to the opposing braking surface.FIG. 4 illustrates an embodiment of a brake rotor 120, particularly a drum brake rotor 120 b. The drum brake rotor 120b includes a rotor body 124 in the general form of a drum having a central hub 130 and a wall 136 extending from the central hub 130. At least a portion of the inner surface 138 of the wall 136 includes the braking surface 126. As with a disc brake rotor 120a, the rotor body 124 is formed from cast iron which is an iron alloy containing 2 to 4 weight percent carbon and 1 to 3 weight percent silicon. In some embodiments, the cast iron is gray cast iron and the carbon is present in the form of graphite. The cast iron may also contain less than 1.0 percent by weight manganese, e.g., in the range of 0.5 to 0.9 percent, as well as trace sulfur and phosphorus impurities, which are also less than 0.3 percent by weight. Alternatively, the rotor body 124 may also be made of one or more alternative iron alloys such as worm graphite (GJV), spheroidal graphite cast iron (spheroidal graphite iron), and steel.The braking surfaces 126 in all of the above-described embodiments and aspects are borated, i.e., surface treated with boron, wherein boron atoms are diffused into the surface 140 and the subsurface (directly below the surface 140) of the rotor body 124 to form an iron boride layer 142 of iron boride phases having the formula Fe 2 B (Fe 2 B phases) 144 (see FIG. 5 ) over the iron alloy 150. In some embodiments, the only iron boride phases in the iron boride layer are Fe 2 B phases. Phases are understood as being a physically homogeneous state of the matter and have a specific chemical composition and a specific type of atomic bonding and arrangement of the elements. The iron boride layer 142 may also include iron boride having the formula FeB (FeB phases) 146, as illustrated in FIG. 5. Further, when graphite phases are present in the iron alloy, such as in gray cast iron, graphite phases may also be present in the iron boride layer 142. Moreover, iron phases or other phases may also be present in the iron boride layer depending on which iron alloy the rotor body 124 is formed from and whether the surface of the iron alloy has been previously treated using one or more of the treatments mentioned below.The Fe 2 B phases 144 develop first and penetrate deeper into the iron boride layer 142 than the FeB phases 146. In other words, FeB phases, if present, are at least 60 volume percent closer to the surface 140 than Fe 2 B phases, which are generally deeper in the iron boride layer 142. The FeB phases 146 are susceptible to exfoliation and the FeB phases 146 may be exfoliation or removed by a machining process as further described herein.As mentioned above, the rotor body 124, including the braking surface 126, may be treated with other surface treatments that include one or more of the following methods: flame hardening, induction hardening, and laser hardening. Additionally or alternatively, the rotor body 124, including the braking surface 126, may be treated by one or more of the following methods: laser build-up welding with an additional iron alloy, austenitic carburizing, nitriding, nitrocarburizing, and ferritic nitrocarburizing. Such treatments may be performed before or after the boration of the braking surface 126. These treatments may affect the composition of the iron boride layer 142.FIG. 6 illustrates a method 600 for forming a borated braking surface 126. If not already provided, the rotor 120 is optionally formed in block 602 by a process that may include melting and casting a molten iron alloy into a mold or additive manufacturing of an iron alloy as a starting material. After forming, the introduced stresses may be relieved by applying heat and / or pressure to the iron alloy.At block 604, the braking surfaces 126 of the rotor body 124, and optionally the entire rotor body 124, are cleaned to remove contaminants such as foreign objects, debris, oil, and oxides that may interfere with the diffusion of boron into the braking surface 126 and the development of iron boride phases in the braking surfaces 126. Purification may be possible through the use of solvent and / or water. Additionally or alternatively, the rotor body 124 may be immersed in an acid bath. In some embodiments, the selected cleaning methods do not alter the surface finish of the braking surfaces 126 of the rotor body 124, which may be 5 micrometers or less, e.g., between 0.3 micrometers and 2 micrometers.In block 606, the braking surface 126, and optionally the entire rotor body 124, are borated. The boration can be performed by at least one of boost diffuse gas boration, powder pack boration, and phase homogenization in electrochemical boration. During the boration, boron or a boron-containing composition is contacted with the iron alloy at a temperature of 700° C. or more, for example, in the range of 750° C. to 1000° C. In one embodiment of boost diffuse gas boration, the iron alloy is exposed to a boron-containing gas at temperatures in the range of 800° C. to 950° C. This method may also be plasma assisted. In one embodiment of powder pack boration, an iron alloy is packed into a powder mixture of boron carbide (B 4 C), an inert filler such as silicon carbide (SiC), and an activator such as potassium tetrafluoroborate (KBF 4) and impregnated in an inert environment, an oven, at a temperature in the range of 950° C. to 1000° C. In one embodiment of phase homogenization in electrochemical boration, the iron alloy is exposed to an electrolyte of molten borax and sodium carbonate at elevated temperatures in the range of 900°C to 1000°C. It should be appreciated that boration may be used to relieve stress in the rotor body 124, and the stress relief step in the forming process may be omitted.In the above-described methods, Fe 2 B phases develop first and then FeB phases develop. The iron alloy is supplied with current for a certain time, generally less than one hour. The Fe 2 B and, if present, the FeB phases develop in the iron boride layer 142 that forms below the surface 140 of the braking surface 126. Preferably, the chosen method is adjusted to limit or prevent development of the FeB phase. Since boration processes proceed at elevated temperatures, the rotor body 124, after boration in block 604, is allowed to cool to ambient temperatures in the range of 18° C. to 30° C., including all values and ranges included therein, in block 608 while maintaining the rotor body 124 in an environment having a temperature in the range of 18° C. to 30° C. The natural cooling may minimize the distortion and deformation of the rotor body 124; however, some deformation may not be prevented.In block 610, the brake surface 126 is machined to the desired tolerances. The machining at this stage may remove all or at least a portion of the FeB phases that may be present in the iron boride layer 142, and also reduce variations that may have been caused by the boration process. In some embodiments, prior to cleaning at block 604 and borating at block 606, the braking surface 126 is remachined to tolerances of ±0.7 mm or less, including any values and ranges included therein, such as ±0.5 mm or ±0.25 mm, and then remachined again to reduce the variations caused by the borating process. For machining the braking surfaces, various methods may be used including one or more of precision milling and precision grinding, e.g., dual disc grinding. Moreover, unless already formed, the rotor body 124 may be drilled or slotted. In block 612, the braking surfaces 126 are completed by polishing the braking surfaces 126.When other treatments are performed that include one or more of flame hardening, induction hardening, laser hardening, laser build-up welding with an additional iron alloy, austenitic carburizing, nitriding, nitrocarburizing, and ferritic nitrocarburizing, the treatments may be performed before or after borating the braking surface 126 in block 604, but before finishing in block 610.In some embodiments, the resulting brake rotor 120 may include an iron boride layer 142 comprising Fe 2 B having a depth in the range of 0.02 millimeters to 2.5 millimeters, including all values and ranges included therein. Additional phases present in the iron boride layer may include iron, graphite, and / or FeB. Further, the borated surface of the Fe 2 B phases may have a greater hardness than the underlying iron alloy. The hardness of the braking surfaces can be in the range of 1500 HV to 2000 Vickers hardness (HV, HV.01), measured according to the test protocol ISO 6507-1:2018 of the International Organization for Standardization, while grey cast iron can have a hardness in the range of 180 HV to 250 HV, for example. Moreover, the borated surface may have a higher wear resistance than the underlying iron alloy. The resulting brake rotor 120 may be incorporated into the vehicle brake system or used in other brake applications as mentioned above.The borated brake disc rotors and brake systems of the present disclosure provide several advantages. These advantages include the formation of hardened and wear resistant braking surfaces. Further, the boration process may replace the steps of stress relief during casting. Another advantage is that the braking surfaces of various rotor shapes, such as drum rotors, one-piece disc rotors, or two-piece rotors, can be treated using the methods described above.The description of the present disclosure is merely exemplary, and modifications that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. Such modifications are not to be construed as a departure from the spirit and scope of the present disclosure.

Claims

A brake rotor comprising: a rotor body comprising a braking surface, wherein the rotor body comprises an iron alloy, and wherein the braking surface comprises a layer of iron boride phases having the formula Fe 2 B (Fe 2 B phases) in the braking surface.The brake rotor of claim 1, wherein the rotor body comprises gray cast iron.The brake rotor of claim 1, wherein the layer further comprises iron boride phases having the formula FeB (FeB phases).The brake rotor of claim 1, wherein the braking surface has a hardness in the range of 1500 to 2000 HV (Vickers hardness).The brake rotor according to claim 1, wherein the iron boride phases in the layer consist of Fe 2 B phases.The brake rotor of claim 1, wherein the depth of the layer is in the range of 0.02 millimeters to 2.5 millimeters.The rotor body of claim 1, wherein the rotor body is a disc and comprises a central hub and a ring gear defined about the central hub, the ring gear comprising the braking surface.The brake rotor of claim 7, wherein the ring gear comprises gray cast iron.The brake rotor of claim 8, wherein the central hub is formed from a second material.A method of manufacturing a brake disc rotor, comprising: removing contaminants from a brake rotor, the brake rotor comprising a rotor body having a braking surface, the rotor body comprising an iron alloy; boronizing the braking surface; and forming a layer of iron boride phases having the formula Fe 2 B (Fe 2 B phases) on the braking surface; and cooling the rotor body to ambient temperature.

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