1. Field of the Invention
This invention relates to high friction surfaces for use in abrasive applications and the preparation of such high friction surfaces. In particular, the present invention relates to abrasive tools prepared by use of a matrix of braze paste and abrasive particles which have been oriented in a preselected pattern.
2. Description of the Prior Art
U.S. Pat. No. 3,918,217, hereinafter referred to as Oliver, discloses an abrasive tool comprising a tool blank having small steel balls secured thereto which have been armed with magnetically oriented carbide particles. The carbide particles are secured together and to the balls by braze metal. An Oliver-type tool is typically prepared, in part, by first securing a single layer of small steel balls to the surface of a tool blank. A magnet is then secured to the tool blank below the balls. Next, magnetizable carbide particles are sprinkled onto the small steel balls. The magnetic flux concentrations produced by the flux path through the small steel balls cause the carbide particles to collect on the outermost portions of the balls to form conical structures. A braze paste consisting of a binder and a braze alloy is then applied to encapsulate all of the elements of the assembly. Finally, the entire assembly is subjected to heating in a brazing furnace which bonds the braze alloy, the magnetizable particles and the balls into a unified structure. When the assembly has cooled, it may be used as an abrasive tool.
Thus, Oliver discloses a technique for preparing an abrasive tool which requires placement of protrusions on the external surface of a tool blank. These protrusions are the necessary surface for the formation of the conical structures of particles. The protrusions may take the form of small steel balls (as described) or shapes formed by machining a profile in the external surface of the tool blank. In either case, the tool blank which is the foundation of the ultimate product must be covered with protrusions. The small steel balls are expensive and require substantial labor to apply. If the protrusions are produced by machining a profile in the external surface of the tool blank, substantial skill and specialized equipment must be used.
Further, to apply carbide particles to protrusions located on a cylindrical structure, the structure must be fixtured and indexed to various rotary positions while the magnetizable carbide particles are applied. Preparing a tool in this manner is very complicated and prone to quality irregularities due to the variety of magnetic and gravitation forces which may be acting on the particles located in different rotary positions about the structure.
Further, the carbide particles form structures which align with the magnetic flux emanating from the magnetized tool blank. In the case of a cylindrical structure, the cones align with magnetic flux emanating radially (or perpendicular to a tangent drawn to the surface) from the circumferential portion of the wheel. The conical structures formed thereby will be symmetrical in all respects, and when used as a cutting tool will offer a negative rake angle to the workpiece. The Oliver technique is capable of producing only these symmetrical conical structures. If more aggressive rake angles are desired, the Oliver technique is not appropriate.
Finally, as with any cutting or abrading tool, heat produced during cutting and abrading is conducted from the point of contact between the tool and the workpiece into the structure of the tool. When using an Oliver-type tool, heat passes from the conical structures through small steel balls and into the tool blank. Since these balls are brazed to the tool blank, they offer little more than point contact and consequently present a substantial impediment to the flow of heat.