Stone working – Sawing
Reexamination Certificate
2001-08-22
2004-01-20
Eley, Timothy V. (Department: 3723)
Stone working
Sawing
C051S297000, C451S527000, C451S529000, C451S533000, C451S544000
Reexamination Certificate
active
06679243
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to tools having diamond particles chemically bonded to a matrix support material, and arranged in a predetermined pattern. More particularly, the diamond particles are chemically bonded to the matrix material by a braze compound that wets diamond.
BACKGROUND OF THE INVENTION
Abrasive tools have long been used in numerous applications, including cutting, drilling, sawing, grinding, lapping and polishing materials. Because diamond is the hardest abrasive material currently known, it is widely used as a super-abrasive on saws, drills, and other devices, which utilize the abrasive to cut, form, or polish other hard materials.
Diamond tools are particularly indispensable for applications where other tools lack the hardness and durability to be commercially practical. For example, in the stone industry, where rocks are cut, drilled, and sawed, diamond tools are about the only tools that are sufficiently hard and durable to make the cutting, etc., economical. If diamond tools were not used, many such industries would be economically infeasible. Likewise, in the precision grinding industry, diamond tools, due to their superior wear resistance, are uniquely capable of developing the tight tolerances required, while simultaneously withstanding wear sufficiently to be practical.
Despite their prevailing use, diamond tools generally suffer from several significant limitations, which place unnecessary limits on their useful life. For example, the abrasive diamond or cubic boron nitride particles are not distributed uniformly in the matrix that holds them in place. As a result, the abrasive particles are not positioned to maximize efficiency for cutting, drilling, etc.
The distance between diamond or CBN abrasive particles determines the work load each particle will perform. Improper spacing of the diamond or CBN abrasive particles typically leads to premature failure of the abrasive surface or structure. Thus, if the diamond/CBN abrasive particles are too close to one another, some of the particles are redundant and provide little or no assistance in cutting or grinding. In addition, excess particles add to the expense of production due the high cost of diamond and cubic boron nitride. Moreover, these non-performing diamond or CBN particles can block the passage of debris, thereby reducing the cutting efficiency. Thus, having abrasive particles disposed too close to one another adds to the cost, while decreasing the useful life of the tool.
On the other hand, if abrasive particles are spaced too far apart, the workload (e.g., the impact force exerted by the work piece) for each particle becomes excessive. The sparsely distributed diamond or CBN abrasive particles may be crushed, or even dislodged from the matrix into which they are disposed. The damaged or missing abrasive particles are unable to fully assist in the workload. Thus, the workload is transferred to the surviving abrasive particles. The failure of each abrasive particle causes a chain reaction which soon renders the tool ineffective to cut, drill, grind, etc.
A typical superabrasive tool, such as a diamond saw blade, is manufactured by mixing diamond particles (e.g., 40/50 U.S. mesh saw grit) with a suitable metal support matrix (bond) powder (e.g., cobalt powder of 1.5 micrometer in size). The mixture is then compressed in a mold to form the right shape (e.g., a saw segment). This “green” form of the tool is then consolidated by sintering at a temperature between 700-1200 □C. to form a single body with a plurality of abrasive particles disposed therein. Finally, the consolidated body is attached (e.g., by brazing) to a tool body; such as the round blade of a saw, to form the final product.
Different applications, however, require different combinations of diamond (or cubic boron nitride) and support matrix powder. For example, drilling and sawing applications may require a large sized (20 to 60 U.S. mesh) diamond grit to be mixed with a metal powder. The metal powder is typically selected from cobalt, nickel, iron, copper, bronze, alloys thereof, and /or mixtures thereof. For grinding applications, a small sized (60/400 U.S. mesh) diamond grit (or cubic boron nitride) is mixed with either metal (typically bronze), ceramic/glass (typically a mixture of oxides of sodium, potassium, silicon, and aluminum) or resin (typically phenolic).
Because diamond or cubic boron nitride is much larger than the matrix powder (300 times in the above example for making saw segments), and it is much lighter than the latter (about ⅓ in density for making saw segments), it is very difficult to mix the two to achieve uniformity. Moreover, even when the mixing is thorough, diamond particles can still segregate from metal powder in the subsequent treatments such as pouring the mixture into a mold, or when the mixture is subjected to vibration.
The distribution problem is particularly troublesome for making diamond tools when diamond is mixed in the metal support matrix. In one aspect, the present invention may be particularly effective and useful for diamond saws that employ a metal matrix. For example, such saws are not limited to but may include circular saws, straight blades, gang saws, frame saws, wire saws, thin-walled cutoff saws, dicing wheels, and chain saws. In another aspect, the diamond tool may be a pad conditioner.
Over the decades, there have been numerous attempts to solve the diamond distribution problem. Unfortunately, none of the attempted methods have proven effective and, as of today, the distribution of diamond particles in diamond tools is still mostly random and irregular, except for some special cases such as for drillers or dressers, where large diamond particles are individually set in the surface to provide a single layer.
One method used in an attempt to make the diamond distribution uniform is to wrap diamond particles with a thick coating of matrix powder. The concentration of diamond particles in each diamond tool is tailored for a particular application. The concentration determines the average distance between diamond particles. For example, the concentration of a typical saw segment is 25 (100 means 25% by volume) or 6.25% by volume. Such a concentration makes the average diamond to diamond distance 2.5 times the particle size. Thus, if one coats the diamond to 0.75 times of its diameter and mixes the coated particles together, the distribution of diamond would be controlled by the thickness of coating and may become uniform. Additional metal powder may be added as an interstitial filler between these coated particles to increase the packing efficiency so the consolidation of the matrix powder in subsequent sintering would be easier.
Although the above-described coating metal has certain merit, in practice, uniformity of coating is very difficult to achieve. There are many chemical methods used to coat diamond grit and its aggregates (polycrystalline diamond). For example, Chen and Sung (U.S. Pat. Nos. 5,024,680 or 5,062,865 which are incorporated herein by reference) describe a CVD method for coating diamond grit using a fluidized bed. Sung et al. (U.S. Pat. Nos. 4,943,488 or 5,116,568, which are incorporated herein by reference) describe another CVD method for coating polycrystalline diamond by a fluidized bed process known to one skilled in the art. However, most of these methods can only produce thin coatings (e.g. a few micrometers) that do not affect the diamond distribution.
Moreover, chemical coating methods typically require treatment at high temperatures (e.g. greater than 900 □C.) that may cause damage to diamond. It is well known that synthetic diamond grit tends to form microcracks above this temperature. These micro-cracks are formed by the back-conversion of diamond to graphite at high temperature. The back-conversion is induced by the catalytic action of metal inclusions that diamond incorporates during its synthesis. CVD treatments cannot readily make thick coatings, and those which are formulated are often cost prohibitive. T
Eley Timothy V.
Thorpe North & Western LLP
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