Abrading – Rigid tool
Reexamination Certificate
1999-09-27
2001-05-29
Hail, III, Joseph J. (Department: 3723)
Abrading
Rigid tool
C451S541000, C451S548000, C451S556000
Reexamination Certificate
active
06238280
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a cutter containing diamond particles for the abrasive working of hard materials. Furthermore, the invention also relates to a method for forming such cutters.
BACKGROUND INFORMATION AND PRIOR ART
In many applications of construction technology, tools are used, which are tipped with cutters, which contain diamond particles in order to improve their abrasive properties. For preparing boreholes or openings of larger diameter, hollow drill crowns are used, equipped at their front ends with cutting segments. Wall saws and cutting-off wheels for cutting concrete, stone or ceramic are tipped at their periphery with cutting segments. Furthermore, grinding disks are also known for working hard surfaces edged at their flat side with cutters containing diamond particles. The abrasive cutters consist essentially of diamond particles, preferably diamond crystals, embedded in a metallic matrix and have a more or less regular shape. The cutting segments, with which the hollow drill crowns or wall saw blades and cutting-off blades are tipped, have a larger volume and a regular shape.
To produce the abrasive cutters or the larger cutting segments, diamond particles are mixed with a metal powder and optionally further components, such as hard material particles. The mixture of diamond particles, metal powder and optionally further components either is sintered directly and baked together into a cake-like mass, which is broken up once again into small parts in a subsequent step. After the broken parts are screened, the usable screen fractions with the suitable particle sizes are used for coating grinding disks and the like. For producing cutting segments, such as, hollow drill crowns, wall saws or cutting-off wheels, the mixture of diamond particles, metal powder and optionally further components, to begin with, is pressed into the desired shape. The resulting green compact is finally sintered, in order to combine the compressed mixture permanently.
In the case of this known method, it happens, particularly at high concentrations of diamond particles, that the diamond particles within the metal powder, acting as binder, lie directly in contact with one another. The bonding at such diamond-diamond contacts is only weak and can lead to weaknesses within the abrasive cutter. Some improvement in the situation occurs if the diamond particles are coated with a metal layer before they are mixed with the metal powder. However, only relatively thin layers can be deposited at the surface of the diamond particles with the known coating techniques. The deposition usually is accomplished by galvanic means, and layers up to about 5 &mgr;m can be achieved. CVD (chemical vapor deposition) or PVD (physical vapor deposition) techniques are relatively cumbersome and expensive. They are used sometimes in order to bond larger diamond particles better into a polymer matrix. They are generally not suitable for improving the bonding in a metallic matrix. Layer thicknesses, achievable with these coating techniques, generally are also less than those achievable with galvanic methods.
OBJECT OF THE INVENTION
It is an object of the present invention to provide an abrasive cutter and a method for its production, which eliminates the disadvantages of the cutters and of the methods of the state of the art. It is reliably possible to avoid weaknesses resulting from diamond-to-diamond contacts. The method is cost effective and permits coating layers of larger thickness. The invention shall also create the prerequisites for producing cutters with variable properties.
SUMMARY OF THE INVENTION
This objective is accomplished by an abrasive cutter, with the distinguishing features of diamond particles coated with a metallic binder material where the diamond particles have a size in the range of about 50 &mgr;m to about 500 &mgr;m and the coating is applied in a fluidized bed process. The diamond particles are completely enclosed by the coating which has a thickness in the range of about 10 &mgr;m to about 200 &mgr;m. Further a method for the production of the cutter, involves introducing diamond particles into a fluidized bed reactor so they swirl in suspension and spraying a suspension of the metallic binder material onto the diamond particles for coating each particle with a thickness in the range of about 10 &mgr;m to about 200 &mgr;m. The inventive abrasive cutter, comprising at least one diamond particle, preferably at least one diamond monocrystal, and metallic binder material, is distinguished owing to the fact that the diamond particle has a particle size, which is about 50 &mgr;m to about 500 &mgr;m and each diamond particle is surrounded by a coating produced in a fluidized bed process with a wall thickness of about 10 &mgr;m to about 200 &mgr;m. The volume of the coating is at least 30% of the volume of the diamond particle in the fully consolidated state, after individual sintering of the coated diamond particles.
Since each diamond particle is provided with a relatively thick coating, diamond-to-diamond contacts, which could lead to weaknesses in the cutter, are reliably avoided in composite cutters. Coating in the fluidized bed process is relatively simple and can be carried out relatively cost-effectively. The diamond particles are suspended in the fluidized bed and, at the same time, are swirled around. By these means, it is ensured that each diamond particle is provided with the metallic coating to the desired extent. The chemical and/or mechanical bonding of the diamond particles in the metallic matrix is improved, since the coating applied by the fluidized bed process, is denser than the coatings, which can be applied by galvanic methods or by CVD or PVD techniques. By selecting the appropriate fluidized process, the nature of the coating can be varied, for example, in order to change and adjust the properties of the abrasive cutter to the desired extent. The coated diamond particles are sintered individually. As a result, they do not bake together. The breaking of a sinter cake is omitted. The individually sintered, abrasive cutters can be processed further directly. For example, they can be applied directly to the surface of a grinding disk. As a result of the relatively thick metallic coating, the volume of which constitutes at least 30% of the volume of the diamond particles after the sintering process, the coated particles can be soldered directly to the surface. The use of an active solder or the like can be omitted.
The coating of the abrasive cutter permits the diamond particles to be coated with radially different material compositions. In this way, the chemical and physical properties of the coating can be controlled selectively in order to take into account different requirements for the cutter. The regions of different material composition of the coating are formed by different concentrations of alloying components and/or hard materials.
In a variation of the invention, the coating has a layered construction. The layered construction is composed of an innermost hard, chemical bonding layer for the diamond particles and at least one further, outwardly adjoining layer. The innermost layer comprises preferably an alloy of nickel, iron and/or cobalt with 0.5 to 15% by weight of chromium, 1 to 3% by weight of boron, 1 to 5% by weight of silicon or an alloy of copper titanate with a titanium content of 4 to 10% by weight. The at least one adjoining layer comprises 10 to 30% by weight of hard material, preferably tungsten carbide, titanium carbide, silicon carbide, silicon nitride, zirconium oxide, aluminum oxide, titanium boride, tantalum carbide, oxides of rare earth metals or mixtures thereof. The quantitative data in % by weight relate to the percentage of metal in the sintered, coated diamond particles.
In an alternative variation of the abrasive cutter, the regions of different concentrations of alloying components and/or of hard materials do not change suddenly, as in the case of a layered construction, but change essentially constantly from one to the
Dorfmeister Johann
Goedickemeir Martin
Ritt Walter
Tillmann Wolfgang
Brown & Wood LLP
Hail III Joseph J.
Hilti Aktiengesellschaft
McDonald Shantese
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