Motor vehicle brake drums are often formed entirely of cast gray iron. However, while cast gray iron is the preferred material for the braking surface of the brake drum, a full cast brake drum is relatively heavy. In response at least in part to the desire for lighter vehicle components, composite brake drums have been developed which comprise a stamped steel drum back and a rolled steel annular band surrounding a cast iron braking surface.

The structure and method of manufacture of such brake drums are known and are described in more detail in, for example, U. S. Patent Nos. 2,153,364,5,138,757, and 5,345,672, each of which is incorporated herein by reference. In accordance with the conventional practice, these composite brake drums are manufactured by first forming an annular band from sheet steel stock which is then rolled to the desired

configuration, typically having a radially inwardly-turned end flange and a plurality of outwardly directed strengthening ribs. With the annular steel band externally fixtured, molten gray iron is centrifugally cast therein to form a metallurgically bonded composite brake ring. After the ring has cooled, a steel drum back is generally welded to the flange. The radially inwardly directed braking surface of the ring is then finish machined.

While the conventional centrifugal casting method yields quality composite brake drums, it would be advantageous to provide an improved method of manufacturing such composite brake drums which is relatively simpler and less expensive, and an improved mold apparatus for use therewith.

SUMMARY OF THE INVENTION The invention is a method of manufacturing a composite brake drum for a motor vehicle or the like which is comprised of a cast metal, preferably gray iron, drum section and a stamped metal, preferably steel, drum back and annular band surrounding the casting. The steel drum back is positioned in a mold apparatus and molten iron is introduced into a mold cavity defined thereby. The mold and band are maintained in a static condition during the casting process.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings, in which: Fig. 1 is a diametrically sectioned perspective view of a finished brake drum in accordance with a preferred implementation of the invention; Fig. 2 is a sectional view of the mold apparatus of the invention; and Fig. 3 is a sectional view of the composite brake drum positioned within the mold apparatus of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method of manufacturing a composite brake drum for a motor vehicle or the like and a mold apparatus for use therewith. It is to be understood that the specific device illustrated in the attached drawings and described in the following specification is simply an exemplary implementation of the invention defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

Referring now to the drawings, there is illustrated in

Fig. 1 a composite brake drum formed in accordance with the invention and generally designated by the reference numeral 10. The composite brake drum 10 is comprised of an annular shell or band 12, preferably formed of steel, surrounding and metallurgically bonded to a cast gray iron structure or casting 14. The steel band 12 and the gray iron casting 14 together form a composite brake ring 28 having a radially inwardly directed braking surface 30. A drum mounting disc or back 16 is preferably connected to one edge of the band 12 by any known method such as welding. Alternatively, the band 12 and back 16 may be formed integrally, from a single piece of steel. The back 16 has openings 18 and 20 for mounting the brake drum 10 in the conventional manner. The steel band 12 includes a first peripheral edge 12a and a second peripheral edge 12b. The second peripheral edge 12b includes a radially inwardly-turned end flange 22. The steel band 12 further preferably includes a plurality of radially outwardly directed strengthening ribs 26. The ribs are optional and may not be used.

Referring now to Figs. 2 and 3, a mold apparatus for forming a composite brake drum 10 in accordance with the invention is shown. The mold apparatus may be of any type suitable for static casting of the drum 10, such as the type

used in sand casting, permanent mold casting, or lost foam casting, for example. The mold apparatus, denoted generally by reference numeral 40, preferably includes a sand core base 42 having an annular support surface 43 on which the steel band 12 rests. A first annular shoulder 44 extends upwardly from the support surface 43 of the base 42. When the steel band 12 is placed in the mold 40, the first peripheral edge 12a thereof abuts the first shoulder 44 to thereby accurately position the band 12 relative to the mold 40. The base 42 is further provided with a centrally located recess 45 on the upper surface thereof.

The base 42 of the mold 40 also supports a sand core mold member 50 having an annular, vertically extending surface 51 for forming the inner diameter of the resulting gray iron casting 14. The base 42 and mold member 50 may alternatively be formed of a monolithic construction such that they form a single piece. The annular surface 51 extends upwardly from the first shoulder 44 of the base 42 to a second annular shoulder 52. The height of the annular surface 51 is selected to substantially match the axial length of the band 12, so that the radially inwardly-turned flange 22 of the second peripheral edge 12b of the band 12 abuts the second shoulder 52 while the first peripheral edge 12a of the band 12 abuts

the first shoulder 44. The radially inner surface of the band 12 and the surface 51 of the mold member 50 together define a mold cavity 46 (shown in Fig. 2) for forming the cast gray iron casting 14.

The mold member 50 further includes an axially extending, centrally disposed passageway 53 providing communication between the upper surface of the mold member 50 and the recess 45 in the base 42. The passageway 53 is preferably provided with a funnel-shaped opening 54 for receiving the molten iron, as described below. The mold member 50 is also provided with a plurality of generally radially extending gates 55 providing communication between the passageway 53 or recess 45 in the base 42 and the mold cavity 46 defined by the band 12 and the annular surface 51. The gates 55 are preferably formed though circumferentially spaced, radially extending ribs 56. The ribs separate cavities 57 formed in the mold member 50 to reduce the mass of the mold member. Alternatively, the ribs 56 and cavities 57 may not be used and the mold member may be essentially solid, or the mass of the mold member may be reduced using smaller cavities or other known techniques.

Vents (not shown) are also provided to allow for the escape gas during the introduction of the molten metal.

The mold apparatus 40 also optionally includes a

framework 60 which is spaced radially outwardly from the steel band 12 as it is positioned on the base 42. The inner surface of the framework 60 and the respective outer surfaces of the base 42 and the steel band 12 define an insulating space 62 which may advantageously be filled with dry sand or other insulating material. The dry sand or other material in the insulating space 62 serves to insulate the casting 14 to control the cooling rate thereof.

An annular weight 66 may also be preferably employed with the mold apparatus 40 of the invention. The weight 66 is positioned so as to rest on the flange 22 of the band 12, urging the same downward into tight engagement with the first shoulder 44. The annular weight 66 is sized so that the inner diameter thereof is spaced apart from the outer surface of the mold member 50. Alternatively, any annular member may be used in place of the weight 66 to abut the flange 22 for urging the band 12 into tight engagement with the first shoulder 44.

Finally, a source of molten iron is provided (not shown) which communicates with a spout 70 or other suitable structure for delivering molten iron to the opening 54 in the mold member 50.

In the manufacture of a composite brake drum 10 in accordance with the invention, the band 12 is first formed

from sheet steel stock and rolled to a configuration having the inwardly-turned end flange 22 and the strengthening ribs 26. The band 12 is then positioned within the mold apparatus 40. As noted above, the first peripheral edge of the band 12 rests on the support surface 43 of the base 42 and the flange 22 of the second peripheral edge 12b abuts the second shoulder 52. The annular weight 66 is positioned atop the flange 22 of the band 12 to maintain the tight engagement with the second shoulder 52. The space 62 defined by the inner surface of the framework 60 and the respective outer surfaces of the base 42 and the steel band 12 is then filled with dry sand or other suitable material.

Molten iron is delivered to the spout 70, which directs the molten iron into the funnel-shaped opening 54 in the mold member 50. The molten iron flows down the central passageway 53 into the recess 45 formed in the base 42. From the recess 45, the molten iron flows radially outwardly through the gates 55 into the cavity 46 defined by the inner surface of the band 12 and the surface 51 of the mold member 50, filling the same.

Prior to the introduction of the molten iron, the steel band 12 may be heated and/or fluxed to improve the metallurgical bond between the band 12 and the gray iron casting 14.

After the resulting composite brake ring 28 has

sufficiently cooled, it is removed from the mold apparatus 40.

The drum mounting disc 16 is secured to the flange 22 by, for example, welding. Alternatively, the drum mounting disc 16 may be formed integrally with the band 12 in the desired configuration prior to the casting of the gray iron structure 14, in which case the configuration of the mold member 50 and the weight 66 may require some modification from that shown in the drawings. The radially inwardly directed braking surface 30 of the ring 28 is then finished on a cylinder of revolution coaxial with the mounting openings 18 and 20, as is conventional.