Patent Publication Number: US-8118079-B2

Title: Casting noise-damped, vented brake rotors with embedded inserts

Description:
This application claims priority based on provisional application 60/956,422, titled “Casting Noise-Damped, Vented Brake Rotors with Embedded Inserts,” filed Aug. 17, 2007 and which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This specification pertains to the casting of brake rotors with cooling vents and embedded inserts. More specifically, this specification pertains to an arrangement of cores that enable sand casting of pairs of such brake members. 
     BACKGROUND OF THE INVENTION 
     There is interest in the manufacture of brake rotors that are vented for cooling and contain sound damping inserts. Such rotors are often used for braking of vehicle wheels. 
     In many embodiments such brake rotors have a round hub for attachment to a vehicle wheel and a radially outwardly extending rotor portion attached to the central hub. In vehicle operation the hub and rotor rotate about a central axis coincident with the rotational axis of the wheel to which they are attached. The rotor is shaped like an annular disk with an annular body, extending radially from the hub, that has two flat, parallel, annular faces (sometimes called “cheeks”) and a circumferential end surface. One cheek of the rotor is on the hub side of the brake rotor structure and the other cheek is the rotor surface on the opposite side of the rotor body. In a braking operation, pads of friction material are pressed tightly against the then rotating cheeks of the rotor to stop rotation of the rotor and attached wheel. Such braking friction produces heat in the rotor and mechanical vibrations. Sometimes the vibrations result in high frequency noise (typically brake squeal). 
     In some rotor designs the rotor body is solid, but in many rotors the body portion contains several generally radially extending, transverse vanes defining intervening air ducts for air cooling of frictional heat produced in the rotor body during braking. The vanes are formed generally centrally of the rotor body to leave one or two outboard durable body thicknesses for braking pressure applied against the cheek surfaces. In order to suppress brake squeal it is desired to provide an annular, typically flat insert piece in one or both rotor body portions outboard of the vanes. It is also desired to cast rotor material around the noise damping insert body so as to form suitable noise damping (typically by coulomb friction damping) surface regions between contiguous faces of the enclosing cast rotor metal and the insert material. 
     By way of example and as an illustration, annular insert plates may be steel stampings, with or without a coating of particulate material, for frictional contact with the engaging inner face surfaces of the cast rotor material. And the rotor and hub may be formed of a suitable cast iron composition. 
     It has been a challenge to devise a practical and economical method of manufacturing such noise damped, vented brake rotors with vanes for cooling and inserts for vibration damping. This specification provides an assembly of cores, typically three specially designed and complementary resin-bonded sand cores, that enables sand casting of pairs of such rotors. An assembly of cores is also provided that enables sand casting of more than two rotors at the same time. 
     SUMMARY OF THE INVENTION 
     In accordance with an embodiment of this invention, a sand mold casting process is provided for casting of a pair (or multiple pairs) of vented brake rotors with inserts embedded in the vane-containing rotor bodies of the castings. For purposes of description of a brake rotor and the disclosed casting process, it is assumed that when a brake rotor is attached to a vehicle corner, the hub portion of the brake rotor lies outwardly (outboard) on the rotational axis of the wheel and the annular rotor body lies inboard of the hub along the rotational axis of the wheel. Each brake rotor has internal vanes between outboard and inboard rotor body portions. The outboard and inboard body portions have outer faces that will be engaged by brake pads in vehicle operation and inner faces that merge with the air passage defining vanes. An insert for coulomb friction damping may be enclosed within either or both of the rotor body portions. In the following illustration, a particle coated, steel insert is enclosed within the inboard rotor body. 
     In this illustrative embodiment, a multiple-part (typically two-part) sand mold is prepared with complementary facing (e.g., cope and drag) mold bodies each having casting cavity surfaces that define the outboard (hub-side) surfaces of two facing, side-by-side brake rotors. The mold bodies also define the outboard face of the hub and the outboard rotor cheek faces of the two rotors. A three-part sand core assembly is constructed to lay between the facing mold cavity surfaces and to define the inboard side of each rotor. The sand mold may be arranged in a horizontal or vertical attitude for metal casting. 
     Two of the sand cores may be identical. They may be shaped to be assembled face-to-face, and termed “rib-cores” in this specification for convenient reference. Each assembled rib core is shaped to define the following inboard surfaces on one of the pair of cast rotors: the inboard face of the rotor hub, the inner face of the outboard rotor body, the vanes for venting the rotor body (hence the “rib core”), the inner face of the inboard rotor body, and tab supports for a cast-in-place damping insert. The third sand core is of annular shape and further shaped to lie between radially outer portions of the facing rib-cores. This core is aptly described as a “splitter core” and it defines outer cheek faces of the inboard rotor bodies. The cores are further shaped to support a sound damping insert between each rib core and an interposed splitter core. 
     In the assembly of the cores for casting, a sound damping insert is placed on each side of the splitter core and inside the facing and sandwiching rib cores. The assembled three core bodies and inserts may be clamped together and positioned between the facing mold bodies. The mold pieces may be provided and arranged with molten metal flow passages for horizontal or vertical attitude of the parts to be cast. The assembly permits simultaneous casting of one or more pairs of similar or identical insert-containing, noise damped, vented brake rotors. 
     Other objects and advantages of this invention will be apparent from a description of illustrative preferred embodiments which follows with reference to the following drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of a sand cast brake rotor with a hub and rotor body with vanes for flow of cooling air. The rotor body portion of the casting encloses an insert for columbic frictional damping of vibrations in the rotor during vehicle braking. 
         FIG. 2  is a cross-sectional view of a two-part sand mold with an assembly of three sand cores for casting a pair of brake rotors, each with a vibration damping insert, and vanes for cooling. 
         FIG. 3  is an oblique view of the top side of a rib core for a sand core assembly for casting a pair of rotors like the rotor illustrated in  FIG. 1 . 
         FIG. 4  is an oblique view of the bottom side of the rib core illustrated in  FIG. 3 . 
         FIG. 5  is an oblique view of a splitter core for the core assembly illustrated in  FIG. 2 . 
         FIG. 6  is an enlarged view of a portion (circled and identified with a “ 6 ”) of the bottom side of the rib core of  FIG. 4 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In this illustrative embodiment of the invention a representative brake rotor is shown. A method is disclosed for simultaneously casting one or more pairs of such rotors in a sand mold using a set of three resin bonded sand cores for each pair of rotors. 
     Referring to  FIG. 1 , brake rotor  10  is a braking member adapted to be mounted to a vehicle wheel, not shown. Brake rotor  10  is mounted to a wheel of, for example, an automotive vehicle on the inboard side of the wheel (with respect to the assembled vehicle) for stopping the rotation of the wheel in operation of the vehicle. A brake caliper device presses friction pads against the sides of the rotor to stop its rotation. Four such brake rotors  10  may be used on a vehicle, one with each of the four wheels. Brake rotor  10  is round and shaped for rotation about a central axis through center  16 . The rotational axis of brake rotor  10  is coincident with the rotational axis of the wheel to which it is attached. 
     Brake rotor  10  comprises a hub  12  and a rotor  14 . Hub  12  comprises a radial hub surface  18  providing an attachment interface to a vehicle wheel, and an axial hub surface  20  that is connected at one side to rotor  14 . Typically, the brake rotor is carried on wheel bearing studs and the wheel is also carried on the bearing studs. Hub  12  is typically bolted to the wheel although bolt holes are not illustrated in  FIG. 1 . In an assembled vehicle wheel, radial surface  18  of hub  12  is the outermost portion (the outboard side) of brake rotor  10 . 
     Rotor  14  comprises an outboard annular rotor body  22  and an inboard annular rotor body  24  that sandwich several radial vanes  26 . Radial vanes  26  may have a curved (or partially spiral) configuration. When brake rotor  10  is rotating with the vehicle wheel to which it is attached, air is pumped by centrifugal force from the radial interior of rotor bodies  22 ,  24  through air flow spaces  28  between and bounded by radial vanes  26 , outboard rotor body  22 , and inboard rotor body  24 . Brake rotor  10  also comprises one or more inserts for sound damping. In vane-containing brake rotor  10 , such an insert may be located in one of the rotor bodies  22 ,  24 , or both. In this embodiment of the disclosure, an annular sound damping insert  30  is enclosed within inboard rotor body  24 . Annular sound damping insert  30  has parallel, radially extending side faces for columbic frictional engagement with the surrounding cast metal of inboard rotor body  24 . Sound damping insert  30  also comprises a plurality of radial tabs  32  distributed uniformly around its outer circumferential surface for use in the casting of rotor metal as will be described. In  FIG. 2 , annular sound damping inserts  30  are illustrated as extending across the full radial dimension of inboard rotor body  24  but a smaller insert may extend only part way across a rotor body. 
       FIG. 2  is a cross-sectional view of a sand mold and coring combination  40  for casting a pair of like (or identical) brake rotors  10  at the same time. Sand mold and coring combination  40  is illustrated in a horizontal casting mode but may, with minor adaptation for flow of cast molten metal, be employed in a vertical casting mode. In this illustrative embodiment, sound damping insert  30  is formed of stamped steel (with a thin coating of refractory particles) and the balance of brake rotor  10  is formed as a wear resistant cast iron. In other embodiments, the insert  30  may be formed of, for example but not limited to, aluminum, stainless steel, cast iron, any of a variety of other alloys, or metal matrix composite. In other embodiments, the coating over the sound damping insert  30  may include, for example but not limited to, particles, flakes, or fibers including silica, alumina, graphite with clay, silicon carbide, silicon nitride, cordierite (magnesium-iron-aluminum silicate), mullite (aluminum silicate), zirconia (zirconium oxide), phyllosilicates, or other high-temperature-resistant particles. In various embodiments, the coating over the insert  30  may have a thickness of ranging from about 1 μm to about 500 μm. 
     Sand mold and coring arrangement  40  comprises cope  42  and drag  44 . The cavity defining surfaces of cope  42  and drag  44  may be substantially identical when two identical brake rotors  10  are being cast with one brake rotor being formed, as illustrated, in each of the cope  42  and drag  44 . 
     Supported within and between cope  42  and drag  44  molds is a combination of two identical and facing rib cores (upper rib core  48  in  FIG. 2  and lower rib core  50 ). Sandwiched between rib cores  48 ,  50  is a single annular splitter core  52 . Each of the cores  48 ,  50 ,  52  may be a hardened sand core which could be coated with refractory or non-refractory type coating for better surface finish. Each of the cores  48 ,  50 ,  52  may be molded separately of resin bonded sand using suitable methods known in the art. In one embodiment, an annular sound damping insert  30  is then positioned between each of the rib cores  48 ,  50  and the annular splitter core  52 . As described below, the rib cores  48 ,  50  are designed to receive the insert  30  and the plurality of radial tabs  32 . 
     Each of the cores  48 ,  50 ,  52  is round and when the cores are assembled as illustrated in  FIG. 2  their circumferential edges are substantially aligned. The three-core combination (rib cores  48 ,  50  and splitter core  52 ) and the inserts  30  may be assembled and held together with clips  54  or other suitable securing fasteners for easy assembly on drag  44  and enclosure by placement of cope  42  as illustrated in  FIG. 2 . In casting, molten metal may be introduced through a runner system in cope  42  and drag  44  molds and at suitable in-gate openings (not shown, for simplicity of illustration) at the parting faces of the cope  42  and drag  44  and into openings (not shown) in the outer edges of rib cores  48 ,  50  and/or splitter core  52 . 
     Reference may also be made to  FIG. 3  for a view of the top surface of rib core  48  and to  FIG. 4  and  FIG. 6  for a view of the bottom surface of rib core  48  as that core is placed in sand mold and coring arrangement  40  illustrated in  FIG. 2 . An oblique view of annular splitter core  52  is provided in  FIG. 5 . 
     As stated, rib cores  48 ,  50  have the same shape because they are being used to cast like brake rotors  10 . Accordingly, a description of rib cores will be made with reference to rib core  48  as illustrated in  FIGS. 2 ,  3 ,  4 , and  6 . Rib cores  48 ,  50 , and splitter core  52  are suitably molded of resin bonded sand in shapes to facilitate the casting of a pair of brake rotors  10 . 
       FIG. 3  illustrates the upper side  60  of rib core  48  as it is positioned in the sand mold and core assembly  40  of  FIG. 2 . When looking at an oblique view of the upper side  60  of rib core  48 , as seen in  FIG. 3 , structural features of the rib core  48  for defining inboard surfaces of brake rotor  10  are illustrated from a different perspective than in the sectional view of  FIG. 2 . 
     Rib core  48  is round and its upper side  60  has a hub-shaping portion  62  for defining the inboard surfaces of radial hub surface  18  and axial hub surface  20  in the casting of brake rotor  10 . Hub shaping portion  62  has a central portion  70  for defining the axial opening in brake rotor  10 . Surface  63  of rib core  48  defines the inboard surface of outboard annular rotor body  22  and has holes  64  for forming radial vanes  26  in brake rotor  10 . The peripheral edge  66  of rib core  48  lies against an inner surface of a cope  42  or drag  44  mold member. An inner circular edge  68  of rib core  48  cooperates with the respective mold member to define the round outer edge surface of outboard annular rotor body  22 . 
       FIG. 4  illustrates the bottom side  71  of a rib core  48 . The bottom side  71  of rib core  48  comprises a round central flat surface  72  for lying against a like surface of a like rib core (for example rib core  50  in  FIG. 2 ). The bottom side of rib core  48  comprises a round tapered surface  74  for engaging an edge of splitter core  52 , a surface  76  for engaging an inner circular edge of annular sound damping insert  30 , a surface  78  for defining an inner surface of inboard annular rotor body  24 , and holes  64  for vanes  26 . The bottom side  71  of rib core  48  has a round surface  80  for receiving an annular sound damping insert ( 30  in  FIGS. 1 and 2 ). In the embodiment of  FIG. 4 , surface  80  has twelve radial extensions  82  for receiving radially extending locating tabs ( 32  in  FIGS. 1 and 2 ). Surface  84  of rib core is configured to lie against a like surface of a like rib core (for example rib core  50  in  FIG. 2 ). 
     In-gates for the admission of molten metal (not shown) may be formed in surface  84  between radial extensions  82 . When the sand mold and core arrangement  40  are in a horizontal position as illustrated in  FIG. 2 , such in-gates may for example be formed between every other radial extension. When the sand mold and core arrangement  40  are in a vertical position such in-gates may be formed in the lower region of the mold and core arrangement. 
       FIG. 6  illustrates an enlarged portion of  FIG. 4  showing a portion of an annular sound damping insert  30  lying on rib core surface  80  with a tab  32  of the damping insert  30  lying on a slightly enlarged core surface  82 . A suitable number of tabs  32  are used to support damping insert  30  on rib core  48  (and splitter core  52 ) during casting of brake rotors  10 . Tabs  32  may extend beyond the intended outer peripheral surfaces of inboard annular body  24  and the tabs  32  may be removed by machining from the cast brake rotor as a finishing operation. 
     An oblique view of a surface  90  of splitter core  52  is presented as  FIG. 5 . In this embodiment of the disclosure, both surfaces of splitter core  52  are alike. As seen on  FIG. 2 , annular splitter core  52  is shaped to fit between a pair of rib cores ( 48  and  50  in  FIG. 2 ). The outer circumferential surface  92  is shaped to align with the outer surfaces  66  of the sandwiching rib cores and to fit against interior surfaces of cope  42  and drag  44  mold members. Surface  94  of splitter core  52  lies against complementary surface  84  of an adjacent rib core  42 . Radial indentations  96  are formed in surface  94  for receiving radial insert tabs  32  in an assembled sand mold and coring combination  40 . Splitter core surface  98  is shaped to define inner surfaces of inboard annular body  24 . Surface  100  supports an inner edge of annular sound damping insert  30  and surface  102  is shaped to engage a complementary surface on a facing rib core (core  48  in  FIG. 2 ). 
     Thus, a pair of like rib cores  48 ,  50  and a complementary splitter core  52  are shaped to hold two annular sound damping inserts, like inserts  30  in  FIG. 2 . The cores  48 ,  50 ,  52  and inserts  30  are shaped and conveniently assembled as described above with respect to drawing  FIGS. 2-6 . The assembly is placed in complementary sand mold bodies for the casting of a pair of brake rotors having cooling vents and cast-in-place sound damping inserts. 
     In the above embodiment the core assembly was designed to hold a pair of sound damping inserts for casting into the inboard annular rotor bodies of two like brake rotors. But the core assembly may also be adapted for incorporating the insert in the outboard annular rotor body or in both inboard and outboard rotor bodies of the sand mold-cast, vented brake rotor shapes. 
     In another embodiment (not shown), more than two rib cores with inserts can be assembled having a splitter core to produce more than two sound damped rotors. For example, the cope  42  and drag  44  molds may be constructed and arranged to support two sets of facing rib cores  48 ,  50 . A splitter core  52  is sandwiched between each set of facing rib cores  48 ,  50 . In this manner, four sound damped rotors may be produced simultaneously. In other embodiments, the cope  42  and drag  44  molds may support any suitable number of sets of facing rib cores in a similar repeating arrangement. 
     Practices of the invention have been shown by examples that are presented as illustrations and not limitations of the invention.