PROCESS OF MAKING BRAKE ROTORS

Abstract: An apparatus and method for casting dimensionally predictable brake rotors is provided. The apparatus includes a first mold portion (12), or cope/ram half, and a second mold portion (16), or drag/swing half, movable relative to each other. The first mold portion (12) and the second mold portion (16) define a mold cavity (14) for casting the brake rotor (24). A fin core (20) is then provided and positioned in the mold cavity (14) for forming a plurality of cooling fins on the brake rotor (24). The fin core (20) is made of a silica sand and carbon sand mixture, wherein the carbon sand is a crushed calcined petroleum coke.

Description: PROCESS OF MAKING BRAKE ROTORS FIELD OF THE INVENTION The present invention relates to an improved disc brake rotor and, more particularly, to a method of casting a disc brake rotor using a fin core being made of a resin-coated silica sand and carbon sand mixture. BACKGROUND OF THE INVENTION Disc rotors are commonly used in vehicle braking systems to provide improved braking performance relative to drum-type brakes. Conventional disc brake assemblies include a disc rotor rotating together with a wheel of the vehicle and a pair of brake pads disposed on opposing sides of the disc rotor. The brake pads typically engage opposing brake pad contact surfaces of the disc rotor to provide factional resistance. Disc brake assemblies further include a mounting member fixed to a stationary portion of the vehicle to support the brake pads. A caliper member is also provided for forcing the brake pads against the brake pad contact surfaces to decelerate the vehicle. Typically, disc rotors are formed by casting using a "green" sand mold and/or a "rigid" mold. Green sand molds used in horizontally casting products generally include a top half, or cope, and a bottom half, or drag. Similarly, green sand molds used in vertically casting products generally include a ram half and a swing half. The halves are typically filled with a clay, sand, and water mixture and are rammed together around a desired pattern to form an internal cavity corresponding to the desired shape. The clay /sand/water mixture is a pliable composition that will readily hold its molded shape. Molten metal may then be poured into the mold cavity to form the outer shape of the desired casting. Rigid molds are generally comprised of a sand mixture, such as silica sand, that can be molded against a pattern and then hardened into a rigid state. These molds are typically hardened using various types of binders, such as clay or organic resins, and subsequently cured using various baking processes, chemical reactions, or reactive gases. Generally, organic resins produce molds that are stronger and harder than those bonded with clay. Cores are commonly placed or inserted into the mold during the casting process to form interior portions in the cast part. These interior portions, such as the space between brake rotor cooling fins, are formed using cores; these interior portions can not be formed using the mold, due to limitations in the casting process. The cores are usually rigid members that have been shaped using the same methods and materials as those described above for rigid molds. During the casting process, the mold and cores are exposed to the extreme temperature of molten metal. The extreme temperature of the molten metal causes the sand mixture, namely the silica sand used in the mold and cores, to thermally expand and/or contract. These dimensional variations in the mold and cores are disadvantageous in that they may produce thermal distortions, such as warpage; cracks; metal penetration; and/or other defects in the mold and cores. It is self-evident that these dimensional variations in the mold and cores lead to dimensional variations in the cast brake rotor. For example, when using silica sand, the width of the cooling fins, which extend between the opposing brake plates of the cast brake rotor commonly, may vary more than 1mm. The width of the cooling fins, and thus the distance between opposing brake plates, is not readily machinable. Therefore, the heat conductivity of the rotor may become uneven resulting in thermal instability of the brake rotor as a result of these dimensional variations. As can be appreciated by one skilled in the art, these dimensional variations further may also effect the rotational balance of the brake rotor and may require additional machining of the outer surfaces to properly balanced the brake rotor. Although these variances are not believed to effect safety, it is now believed that if these variances can be minimized, the brake rotor performance and cooling attributes can be enhanced. Although the above disadvantages and the low thermal stability of silica sand are well known in the art, silica sand continues to be extensively used in the casting of brake rotors because it is relatively inexpensive and readily available. Accordingly, there exists a need in the relevant art to provide a method of casting disc brake rotors that is capable of minimizing dimensional variations between cast parts for improved performance and operational life. Furthermore, there exists a need in the relevant art to provide a method of casting dimensionally predictable disc brake rotors using a cost effective and readily available foundry sand, which overcomes the limitations of a pure silica sand mixture. SUMMARY OF THE INVENTION In accordance with the broad teachings of this invention, a method for casting brake rotors using a fin core having an advantageous composition of silica sand and carbon sand is provided. According to the teachings of the present invention, an apparatus for casting dimensionally predictable brake rotors is provided. The apparatus includes a first mold portion, typically a cope or ram half, and a second mold portion, typically a drag or swing half, movable relative to each other. It should be noted that the cope and drag portions might also be ram and swing portions as used in vertical mold applications. The first mold portion and the second mold portion define a mold cavity for casting the brake rotor. A fin core is then provided and positioned in the mold cavity for forming a plurality of cooling fins on the brake rotor. The fin core is made of a silica sand and carbon sand mixture, wherein the carbon sand is a crushed calcined petroleum coke. Moreover, according to the teachings of the present invention, a method for casting dimensionally predictable brake rotors is also provided. The method including providing a cope portion and a drag portion movable relative to each other. The cope portion and drag portion define a mold cavity corresponding to a first brake surface and a second brake surface of the brake rotor. The method further includes providing a fin core for forming a plurality of cooling fins on the brake rotor. The fin core is made of a silica sand and carbon sand mixture. The fin core is then inserted within the mold cavity. The drag portion and the cope portion are then moved together, thereby enclosing the mold cavity and the fin core. A brake rotor forming material, such as gray iron, is then supplied into the mold cavity, thereby flowing through the fin core. The brake rotor forming material is then solidified and the improved brake rotor is removed. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: FIG. 1 is a front view of a brake rotor forming apparatus; FIG. 2A is a cross-sectional view of FIG. 1, taken along line 2-2, showing the brake rotor forming apparatus having a cope half, drag half, and a fin core according to the present invention; FIG. 2B is a cross-sectional view of FIG. 1, taken along line 2-2, showing the brake rotor forming apparatus having a swing face, a ram face, and a fin core according to the present invention; and FIG. 3 is a perspective view of the fin core according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Referring to the drawings, the forming apparatus of the present invention will be described. As best seen in FIG. 2A, the forming apparatus 10 includes a first mold portion or cope 12 having a mold cavity 14 disposed therein. A second mold portion or drag 16 is provided for mating with first mold portion 12. Second mold portion 16 includes a generally flat surface 18 for enclosing and defining mold cavity 14. First mold portion 12 and second mold portion 16 together form a "green" sand type mold. Forming apparatus 10 further includes a fin core 20 positioned in mold cavity 14, thereby defining a brake rotor cavity 22 for casting a brake rotor 24. As best seen in FIG. 2B, forming apparatus 10 may be a vertical molding apparatus having a plurality of mold cavities 14a, 14b, and 14c. Each of the plurality of mold cavities 14a-c is defined by a swing face 23 and a ram face 25. Swing face 23 is a generally flat surface extending the length of the mold. Ram face 25 is a generally contoured surface extending the length of the mold. It should be appreciated that the plurality of mold cavities 14a-c enables multiple brake rotors to be formed simultaneously. Each mold cavity is generally circular or disc shaped and includes a first side wall 26, a second side wall 28, an outer wall 30, and an inner wall 32. First sidewall 26, outer wall 30, and inner wall 32 of mold cavity 14 are formed in first mold portion 12. Second sidewall 28 of mold cavity 14 is formed in generally flat surface 18 of second mold portion 16. Preferably, outer wall 30 is tapered outwardly and inner wall 32 is tapered inwardly to aid in the insertion of fin core 20, as will be described below. First side wall 26 and second side wall 28 respectively define a first brake pad contact surface 34 for a brake plate 35 and a second brake pad contact surface 36 for a brake plate 37 of brake rotor 24. First 34 and second 36 brake pad contact surfaces are adapted to provide a braking surface for a pair of brake pads (not shown). Mutually facing inner surfaces of plates 35 and 37 are separated by an interior distance A. It should be appreciated that by minimizing the dimensional variation of distance A, improved heat conductivity and corresponding heat dissipation of the finished brake rotor may be realized. As best illustrated in FIG. 3, fin core 20 is generally circular or discshaped and includes an inner or hub portion 38, an intermediate or spoke portion 40, and an outer or flange portion 42. Hub portion 38 is generally ring-shaped and includes an inner tapered surface 44 adapted to closely conform to tapered inner wall 32 of mold cavity 14. Likewise, flange portion 42 is generally ring-shaped and includes an outer tapered surface 46 adapted to closely conform to tapered outer wall 30 of mold cavity 14. Inner tapered surface 44 and outer tapered surface 46 of fin core 20 serve as draft angles to enable fin core 20 to be easily and conveniently inserted into first mold portion 12 before casting. Spoke portion 40 is generally discshaped and interconnects hub portion 38 and flange portion 42. Spoke portion 40 further includes a plurality of generally radially extending slots 48 for forming a plurality of cooling fins 50 in brake rotor 24. In the present embodiment, each of the plurality of generally radially extending slots 48 is arcuately shaped. It is believed that this arcuate shape produces a brake rotor having cooling fins that are more capable of dissipating heat during operation. However, it should be appreciated that any shape of slot, which is conducive to various operating conditions, may be used. As best seen in FIG. 3, fin core 20 is a "rigid" type core made of a silica sand and carbon sand mixture. Preferably, the foundry sand mixture of the present invention is in the range of about ten percent (10%) by weight carbon sand and ninety percent (90%) by weight silica sand to about one hundred percent (100%) by weight carbon sand and zero percent (0%) by weight silica sand, wherein the carbon sand is preferably crush calcined petroleum coke. A mixture of about twenty- five percent (25%) by weight carbon sand and seventy-five percent (75%) by weight silica sand is presently preferred since this concentration still provides good thermal stability of the core while minimizing material costs. However, it should be understood that a foundry sand mixture having 10-100% by weight carbon sand and 90%-0% by weight silica sand, respectively, for the core is within the scope of the present invention. It should further be understood that additional materials, for example, but not limited to, binders, might be added to the mixture used for forming the core. However, the weight of these additional materials is believed to be negligible relative to the carbon sand and silica sand. By way of a non-limiting example, brake rotors that are cast using pure silica sand fin cores typically have a distance "A" between interior cooling surfaces of the brake plates (i.e. cooling fin width) that varies more than 1mm. However, the brake rotors cast using the silica sand and carbon sand mixture of the present invention to form the fin cores have a cooling fin width variance of less than 1mm. Due to this minimal dimensional variation, the brake rotors have improved heat conductivity and resistance to "ripple" since the brake rotors are capable of quickly and evenly dissipating heat produced during braking. Ripple typically occurs when brake rotors are not able to dissipate heat generated during braking, such that the heat causes the rotor to distort or ripple. Preferably, fin core 20 is formed by first adding silica sand to a mullor or mixer for mixing. A resin and catalyst is then combined in the mixer with the silica sand in order to bind the composition together. The mixer folds the mixture for approximately three (3) minutes to thoroughly coat the silica sand with the resin and catalyst. A predetermined amount of carbon sand, preferably 1/3 the amount of silica sand used, is then added and the silica sand and carbon sand mixture is folded for approximately two (2) minutes. This specific amount of carbon sand and silica sand produces a mixture of 25 % by weight carbon sand and 75 % by weight silica sand. However, as stated earlier, the percentage of carbon sand and silica sand may be within the range of about ten percent (10%) by weight carbon sand and ninety percent (90%) by weight silica sand to about one hundred percent (100%) by weight carbon sand and zero percent (0%) by weight silica sand to provide the aforementioned advantages. The silica sand and carbon sand mixture may then be added to an intermediate hopper and injected into a heated core forming mold. The fin core is cured for approximately 45 seconds and ejected from the mold to cure completely. It is anticipated that other binding systems, such as those systems that employ unheated core forming molds and or gas catalyzed resins, may be used in conjunction with the silica sand and carbon sand mixture of the present invention. Once the fin core is completely cured and dried, it may be used in casting a brake rotor. During casting of the brake rotor, first mold portion 12 and second mold portion 16 are opened to enable access to mold cavity 14. Fin core 20 is then inserted into mold cavity 14 such that inner tapered surface 44 and outer tapered surface 46 of fin core 20 closely conform to inner tapered wall 32 and outer tapered wall 30 of mold cavity 14, respectively. Such arrangement thereby defines brake rotor cavity 22. First mold portion 12 and second mold portion 16 are moved together to enclose mold cavity 14 and fin core 20. Molten metal, such as gray iron, is then supplied into brake rotor cavity 22 under gravity through at least one injection port (not shown). The molten metal is then allowed to cool and solidify to provide a dimensionally predictable brake rotor, which is then ejected. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: CLAIMS What is claimed is: 1. A casting apparatus for casting dimensionally predictable brake rotors, said apparatus comprising: a first mold portion; a second mold portion movable relative to said first mold portion, said first mold portion and said second mold portion defining a mold cavity for casting the brake rotor; and a fin core disposed in said mold cavity for forming a plurality of cooling fins on the brake rotor, said fin core being made of a mixture containing at least ten percent (10%) by weight carbon sand. 2. The casting apparatus according to Claim 1 wherein said fin core mixture comprises silica sand and carbon sand. 3. The casting apparatus according to Claim 2 wherein said carbon sand is crushed calcined petroleum coke. 4. The casting apparatus according to Claim 1 wherein said fin core includes: an inner portion for forming an inner diameter of the brake rotor; an intermediate portion extending radially from said inner portion, said intermediate portion having a plurality of generally radially-extending slots disposed therein for forming said plurality of cooling fins on the brake rotor; and an outer portion extending about said intermediate portion for forming an outer diameter of the brake rotor. 5. The casting apparatus according to Claim 4 wherein said fin core further includes: a first tapered surface extending along an inner surface of said inner portion; and a second tapered surface extending along an outer surface of said outer portion, wherein said first and second tapered surfaces aid in the insertion of said fin core into said mold cavity. 6. The casting apparatus according to Claim 1 wherein said fin core silica sand and carbon sand mixture includes about twenty-five percent (25 %) by weight carbon sand and about seventy-five percent (75%) by weight silica sand. 7. The casting apparatus according to Claim 1 wherein each of the plurality of cooling fins of the brake rotor defines a width, a variance of said width of each of said plurality of cooling fins being less than about 1mm. 8. A method for casting dimensionally predictable brake rotors for a vehicle, said method comprising the steps of: providing a first mold portion and a second mold portion movable relative to each other, said first mold portion and second mold portion defining a mold cavity; providing a fin core for forming a plurality of cooling fins on the brake rotor, said fin core being made of a mixture containing at least ten percent (10%) by weight carbon sand; inserting said fin core within said mold cavity; moving said second mold portion and said first mold portion together, thereby enclosing said mold cavity and said fin core; and supplying a brake rotor forming material into said mold cavity and solidifying said brake rotor forming material. 9. The method according to Claim 8 wherein said providing a fin core includes providing a fin core being made of about twenty-five percent (25%) by weight carbon sand and about seventy-five percent (75 %) by weight silica sand. 10. The method according to Claim 9 wherein said carbon sand is crushed calcined petroleum coke. 11. The method according to Claim 8 wherein said providing a fin core includes providing a fin core having: a hub portion for forming an inner diameter of the brake rotor; a spoke portion extending radially from said hub portion, said spoke portion having a plurality of radially extending spokes for forming said plurality of cooling fins on the brake rotor; and a flange portion disposed about said spoke portion for forming an outer diameter of the brake rotor. 12. The method according to Claim 11 wherein said providing a fin core further includes providing a fin core further having: a first tapered surface extending along an inner surface of said hub portion; and a second tapered surface extending along an outer surface of said flange portion, wherein said first and second tapered surfaces aid in the insertion of said fin core into said mold cavity. 13. The method according to Claim 8 wherein each of the plurality of cooling fins on the brake rotor defines a width, said width of one of said plurality of cooling fins varying less than about 1mm from a width of the other of said plurality of cooling fins. 14. The casting apparatus according to Claim 1 wherein said first and second mold portions cooperate to define a green sand mold.

Inventors: MISKINIS GREGORY V, REIERSON SCOTT, MISKINIS, GREGORY, V., REIERSON, SCOTT
Applicants: MISKINIS GREGORY V, REIERSON SCOTT, WAUPACA FOUNDRY INC, MISKINIS, GREGORY, V., REIERSON, SCOTT, WAUPACA FOUNDRY, INC.
Application year: 1999
Main classification: B22C1
IPC codes: B22C1, B22C9, B22D25