Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2002-12-23
2003-12-16
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S295000, C051S293000, C428S403000, C428S404000, C428S141000, C428S144000, C428S148000
Reexamination Certificate
active
06663682
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for coating superabrasive particles with a metal. More specifically it relates to a process for producing diamond abrasive pieces coated with a thin layer of metal chemically bonded to the underlying abrasive which coated pieces are particularly useful for making metal bonded superabrasive grinding and cutting tools or metalized diamond articles.
BACKGROUND OF THE INVENTION
Diamond superabrasives have utmost hardness which allows them to abrade other extremely hard materials. For example, superabrasive tools are often used to form, dress or sharpen other abrasive tools. Therefore grinding and cutting tools that utilize an abrasive portion containing superabrasive are very important in industry.
In a simplified sense, superabrasive tools basically include pieces of superabrasive materials, a tool quality structural metal core and a metal bond holding the superabrasive in a composite structure or as a single superabrasive layer attached to the core. The pieces can be irregular particles sometimes referred to as grit, grains or granules, or they can be articles of precisely predetermined shape such as diamond film and shaped polycrystalline composites. Shaped diamond inserts are also used for machining hard and abrasive materials such as metal matrix composites and aluminum casting alloys. So-called single layer particle tools are defined by an abrasive layer bonded to the core in which the thickness of the layer is the nominal thickness of only a single abrasive piece.
There are numerous ways to make metal bonded superabrasive tools. Many, such as brazing or soldering, involve placing the granules on the core in contact with a bond composition, heating the assembled ingredients until the bond composition liquefies, then cooling to solidify the bond composition. Ideally, the metal bond composition attaches firmly to the metal of the core and adheres the granules to the core. A major shortcoming of this process is that many preferred metal bond compositions are not strongly adhesive to superabrasives. Weak adhesion provides inadequate bond strength which in turn leads to premature loss of the abrasive particles from the tool during operation. This is particularly problematic for single layer particle tools in which it is preferred to have as little bond mass around the granules as possible to expose a maximum cutting surface. If bond thickness is increased to improve adhesion, the abrasive granules are buried more deeply in the bond and present less cutting surface to the work piece. Moreover, during use the thick bond wears away and leaves an inadequate amount of low strength bond to retain the granules which are easily expelled from the tool.
A well known method of enhancing the adhesion of superabrasive to the metal bond calls for utilizing bond compositions which are reactive with the superabrasive so that during tool fabrication the bond composition adheres to the surface of the abrasive particles. However, many powdered metal bond compositions for superabrasive bonding are categorized as non-reactive because they do not chemically bond with the superabrasive. The lack of chemical bonding to the superabrasive leads to premature release of the superabrasive.
A better adhesion improving technique involves incorporating a reactive metal ingredient in the precursor bond composition. This ingredient is characterized by its ability to react directly with the superabrasive to form a strong chemical bond between a metal moiety and the granule. These so-called “active metal” bond compositions thus have both non-reactive and reactive components. Usually the non-reactive components constitute most of the bond composition. The non-reactive components alloy to form a strong and durable bond which is adhesive to the core. The reactive component tenaciously attaches by chemical bond to the superabrasive and is cohesive with the non-reactive alloy. For example, U.S. Pat. No. 4,968,326 to Wiand discloses a method of making a diamond cutting and abrading tool which comprises mixing a carbide forming substance with a braze alloy and temporary binder, applying the mixture to a tool substrate, applying diamond particles onto the mixture coated tool and heating the thus combined materials to initially form a carbide coating on the diamond. Thereafter the carbide coated diamond is brazed to the tool.
Despite improvement over earlier technology, the active metal technique poses the further problem of assuring that the reactive metal ingredient is present at the surface of the superabrasive granules where it is desired to form the chemical bond. In a basic aspect of the technique, the reactive metal ingredient is mixed in particulate form with other components of the metal bond composition. The mixture is then applied either as a paste or dry. Only that portion of the reactive metal ingredient in proximity to the superabrasive bonds directly with the abrasive. Reactive metal ingredient elsewhere in the bond composition is superfluous, or at worst, detrimental to the properties of the overall bond. Therefore, it is important to provide the reactive metal ingredient in as fine a particle size as possible and to blend the reactive metal ingredient into the mixture uniformly to obtain intimate contact between the superabrasive with the ingredient during bond formation.
One proposed approach to solving this problem is to coat the superabrasive granules with the reactive metal ingredient prior to mixing with the other bond components. The reactive metal ingredient would thus be optimally placed at the appropriate time for bond formation. For example, U.S. Pat. No. 5,855,314 to Shiue et al. teaches a coating method in which reactive metal ingredient particles are mechanically bound to the surface of the superabrasive grains. This is accomplished by mixing reactive metal ingredient powder with a liquid binder to form an adhesive paste, mixing the paste with the abrasive grains to wet the grains, and drying the mixture to adhere active component to the grains. Still it is important to reduce as much as possible the particle size of the reactive metal ingredient particles to achieve uniform coverage of the grains. Even if supplied as a fine powder, the reactive metal ingredient is present at the surface in a macromolecular amount and therefore usually in excess of the amount needed to cement the bond to the superabrasive. Because the reactive metal ingredient and superabrasive often are irregularly shaped particles, it is difficult to assure that the coating will either be complete or uniform over the superabrasive surface.
Other methods are known for applying very thin layers of a metal onto an substrate. These include physical vapor deposition (PVD) and chemical vapor deposition (CVD). The former involves infusing electrical or thermal energy to atomize a metal target and allowing the resulting hot metal atoms to condense on the cooler substrate. This procedure does not form a chemical bond between the deposited metal and the substrate. CVD processes introduce a metal compound in a gaseous form into a heated CVD chamber containing the substrate to be coated. The heat causes the gaseous metal compound (e.g., tungsten hexafluoride) to dissociate to metal atoms which coat the substrate while a usually gaseous byproduct of dissociation is removed.
Sometimes rather than merely mechanically coating the substrate with metal, CVD can provide a metal-to-substrate chemical bond. This is a very attractive attribute because it permits the abrasive tool manufacturer to adhere this pre-bonded metal coated superabrasive material to a tool core utilizing a simple flux and brazing or induction furnace process in air. If the metal coating is not chemically bound to the superabrasive beforehand, the tool must be fabricated in a much more complicated and expensive process, such as by brazing in a controlled atmosphere of inert gas or vacuum.
Unfortunately, CVD results in metal-to-substrate bond formation only in some metal/superabrasive systems and only upon applicatio
Andrews Richard M.
Baldoni J. Gary
Geary, Jr. Earl G.
Shaw Douglas H.
Lew Jeffrey C.
Marcheschi Michael
Porter Mary E.
Saint-Gobain Abrasives Technology Company
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