CORROSION RESISTANT BRAKE COMPONENT

BACKGROUND OF THE INVENTION

This invention relates in general to brake drums or disc brake rotors and, in particular to, an improved brake drum or disc brake rotor having improved corrosion resistant characteristics.

It is known to apply an inorganic protective coating to the entire surface of a brake component, such as a disc brake rotor, or selected surfaces thereof, to inhibit the corrosion of the component.

One inorganic coating which is used commercially for brake components is available under the tradename SermaGard. SermaGard is manufactured by Sermatech International Inc. of Limerick, Pennsylvania. SermaGard is comprised of aluminum particles in a ceramic binder and contains soluble chromates.

Typically, SermaGard is applied to a rotor by first cleaning the rotor by sand blasting or by immersion in an alkaline bath. The SermaGard coating is then applied to the rotor by dipping or spraying. Next, any excess SermaGard coating is removed from the rotor. The rotor is then placed in an oven where it is heated to a temperatures of 650°F (340°C) for a period of at least 30 minutes to thermally cure the coating so that it fully develops water resistance and weathering capabilities. In particular, the curing of the coating results in a chemical reaction of the chromate compound which causes it to change from a hexvalent chrome to a trivalent chrome. This enables the rotor to meet the specific corrosion resistance specifications, such as, for example, certain salt spray requirements. One such salt spray requirement requires the coated brake component to withstand exposure to a 5% salt fog solution for a selected time period.

Another inorganic protective coating which is used commercially for brake components is available under the tradename Dacroment. Dacroment is manufactured by Metal Coatings International of Chardon, Ohio. Dacroment, like SermaGard, is cured at temperatures in the range of 610°F to 650°F (320°C to 340°C) for a period of 50 to 60 minutes in order to cause a chemical reaction of the chromate compound so that the rotor meets certain salt spray requirements

Because each of the above inorganic coatings contain soluble chromates, they need to be heated in order to cause a chemical reaction of the chromate compound so that the coating sufficiently bonds mechanically to the surfaces of the brake component to meet satisfactory corrosion resistance specifications, such as, for example, certain salt spray requirements. Such heating results in increased manufacturing costs and raises environmental concerns.

An inorganic protective coating which is used commercially for steel bridges, ships, and offshore applications is available under the tradename IC 531 HighRatio ^m zinc silicate. IC 531 is manufactured by Inorganic Coatings, Inc. of Malvern, Pennsylvania, and dries in 15-45 minutes at a temperature of 75°F (24°C) .

SUMMARY OF THE INVENTION

This invention relates to an improved brake drum or disc brake rotor having an inorganic corrosion resisting coating, comprising a zinc dust based coating having a silicate binder, applied to selected surfaces thereof. It has been found that the use of a silicate binder in the organic coating provides the associated brake component with improved corrosion resistant characteristics. In particular, when applied to the braking surface, corrosion resisting effectiveness of this coating lasts substantially longer than the prior art. Even after it appears the

coating has "worn off" , more residual coating remains on the brake surfaces to inhibit corrosion for longer periods of time compared to the prior art. It is believed that these improved characteristics are directly attributable to the use of a silicate, as opposed to a chromate, binder. In addition, while heat can optionally be used to expedite drying of the inorganic coating, the use of the inorganic coating of the present invention does not require heat to create a chemical reaction which is necessary to cure the prior art inorganic coatings.

Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view an improved disc brake rotor constructed in accordance with the present invention. FIG. 2 is a perspective view an improved brake drum constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is illustrated in FIG. 1 an improved disc brake rotor, indicated generally at 10, constructed in accordance with the present invention. The rotor 10 shown in this embodiment is an "unvented" type of rotor and comprises a main body including a centrally located mounting surface 12, and an outer friction disc 14. The mounting surface 12 and friction disc 14 are integrally cast as one-piece during a casting process, and can be formed from either steel, iron or aluminum.

The mounting surface 12 includes a centrally located pilot hole 16, and a plurality of lug bolt receiving holes 18 equally spaced circumferentially about the opening 16. A lug bolt 20 extends through each of the holes 18 for mounting and securing a wheel (not shown) thereto.

The friction disc 14 shown in this embodiment defines a pair of brake friction surfaces 14A and 14B, which are spaced apart in a generally parallel relationship relative to one another. As is known, the brake friction surfaces 14A and 14B are adapted to be engaged by a pair of friction linings of a disc brake assembly (not shown) . The construction of the rotor 10 thus far described is conventional in the art.

In accordance with the present invention, an inorganic corrosion resistant coating is applied to selected surfaces of the rotor 10 to inhibit corrosion thereof. Such a suitable inorganic coating is IC 531. IC 531 is a water-based inorganic coating and comprises an admixture of zinc dust to a silicate binder. The zinc dust contains 96% zinc dust, 3% zinc oxide, 0.030% lead, and 0.08% cadmium. The silicate binder contains 30% potassium silicate.

Preferably, the entire disc brake rotor 10 is coated with IC 531 by dipping or spraying methods. However, only selected portions of the rotor 10 can be coated with IC 531. For example, in the embodiment of the rotor 10 shown in FIG. 1, all the surfaces of the rotor 10 can be coated with IC 531 except for the friction surfaces 14A and 14B thereof.

FIG. 2 illustrates an improved brake drum, indicated generally at 40, constructed in accordance with the present invention. As shown therein, the brake drum 40 includes a generally cylindrical body 42 and a mounting surface 44. The mounting surface 44 includes a centrally located pilot hole 46, and a plurality of lug bolt receiving holes 48 (only two holes 48 shown) equally spaced circumferentially about the opening 46. A lug bolt (not shown) extends through each of the holes 48 for mounting and securing a wheel (not shown) thereto.

The cylindrical body 42 defines an inner cylindrical braking surface 42A and an outer cylindrical surface 42B.

As is known, the inner cylindrical surface 42A is adapted to be engaged by a pair of friction linings of a drum brake assembly (not shown) . The construction of the brake drum 40 thus far described is conventional in the art.

In accordance with the present invention, selected surfaces of the brake drum 40 are coated with IC 531 to produce a corrosion resistant brake drum. Preferably, the entire brake drum 40 is coated with IC 531. However, only selected surfaces of the brake drum 40 can be coated with the IC 531. For example, all the surfaces of the brake drum 40 can be coated with IC 531 except for the braking surface 42A thereof.

One advantage of the present invention is that when the coating is applied to the braking surfaces of the associated rotor 10 or drum 40, the corrosion resisting effectiveness of this coating lasts substantially longer than the prior art. Thus, the associated brakes can be applied for more cycles before the coating appears to be worn off from the associated braking surfaces of the rotor or drum. Also, even after it appears that the coating is worn off, more residual coating remains on the rotor or drum to inhibit corrosion thereof for longer periods compared to the prior art. This is especially advantageous in new vehicles where the vehicle is braked several times and remains outside on a lot for a length of time before being sold to a customer.

Another advantage of the present invention is that the coating does not have to be thermally cured like the prior art. This allows the coated rotor 10 or drum 40 of the present invention to be dried at room temperature, room temperature being approximately 75°F (24°C) . As a result of this, the energy and environmental costs associated with rotor or drum of the present invention are less than the energy and environmental costs associated with the prior art.

While the invention has been described as being able to dry the coating on the rotor or drum at room temperature, the coating can be dried at elevated temperatures if it is desired to expedite the drying time of the coating on the rotor or drum. However, both the surface and ambient temperatures should be at least 40°F (4°C) , and the surface temperature should be at least 5°F (-15°C) above dew point.

Also, while the rotor 10 of the present invention has been described and illustrated as an unvented type of rotor, the invention can be used with other types of rotors. For example, the invention can be used to coat an entire "vented" type of rotor (not shown) or selected portions thereof, such as for example, only the mounting surface of the rotor, or only the ribs or fins of the rotor, or both the mounting surface and the ribs can be coated. In addition, the invention can be used to coat an entire integral hub and rotor (not shown) or selected portions thereof, such as for example, only the hub, or only the mounting surface, or both the hub and mounting surface can be coated.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiment. However, it must be understood that the invention may be practiced otherwise than as specifically explained and illustrated without departing from the spirit or scope of the attached claims.