Stone working – Sawing
Reexamination Certificate
1999-09-20
2001-09-11
Eley, Timothy V. (Department: 3723)
Stone working
Sawing
C051S297000, C451S527000, C451S529000, C451S533000, C451S544000
Reexamination Certificate
active
06286498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved metal bond diamond tools. More particularly, the present invention relates to improved diamond tools wherein the diamond particles are distributed in a predetermined pattern in a metal matrix in order to decrease cost and/or increase the useful life of the tool.
2. State of the Art
Diamonds and cubic boron nitride(CBN) have been widely used as superabrasives on saws, drills, and other tools which utilize the superabrasive to cut, form or polish other hard materials. In 1996, the total value of superabrasive tools consumed was over 5 billion dollars (U.S.). It has been estimated that more than half of the superabrasive tools were consumed in sawing applications such as cutting stones, concretes, asphalts, etc.
Diamond tools are particularly indispensable for applications where other tools lack the strength and durability to be practical substitutes. For example, in the stone industry where rocks are cut, or sawed, diamond saws are the type which are sufficiently hard and durable to do the cutting. If superabrasives were not used, many such industries would be economically infeasible. Likewise, in the precision grinding industry, superabrasive 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 the tremendous improvements which diamond and cubic boron nitride have provided for cutting, drilling and grinding tools, there are still several disadvantages which, if overcome, would greatly improve performance of the tools, and/or reduce their cost. 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 separated too far, the work load (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 work load. Thus, the work load 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 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). The “green” form is then consolidated by sintering at a temperature between 700-1200° C. to form a single body with a plurality of superabrasive 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 matrix powder. For example, for drilling and sawing applications, a large sized (20 to 60 U.S. mesh) diamond grit is 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, or polyemide).
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 matrix. Thus, finding a method for increasing the performance of the diamond or CBN superabrasive material, and/or decreasing the amount of the abrasive which is needed, is highly desirable. Such has been accomplished by the invention set forth herein. The invention is particularly effective and useful for diamond saws, the largest value category of all superabrasive tools, although it is applicable to all abrasive tools.
Over the decades, there have been numerous attempts to solve the diamond or CBN distribution problems. Unfortunately, none of the attempted methods have proven effective and, as of today, the distribution of diamond or CBN particles in superabrasive tools is still random and irregular, except for some special cases such as for drillers or dressers, where large diamond particles are individually set by hand 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 and mixes the coated particles together, the distribution of diamond would be controlled by the thickness of coating and may become relatively 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 is yet another limitation associated with the current methods of coating diamond grits. Many times a metal bond diamond tool requires different sizes of diamond grits and/or different diamond concentrations to be disposed at different parts of the same diamond tool. For example, saw segments tend to wear faster on the edge or front than the middle. Therefore, higher concentrations are preferred in these locations to prevent uneven wear and thus premature failure of the saw segment. These higher concentration (known as “sandwich” segments) are difficult to fabricate by mixing coated diamond with metal powder to achieve a controlled distribution of the diamond particles in the segment. Thus, despite the known advantages of having varied diamond grit sizes and concentration levels, such configurations are seldom used because of the lack of a practical method of making thereof.
In summary, current arts are incapable of efficiently controlling the uniformity of diamond or CBN dist
Eley Timothy V.
Thorpe North & Western LLP
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