Cutting tool for machining abrasive materials, notably wood-based materials

Abstract

Cutting tool for machining by removal of matter from abrasive materials such as a material based on wood particles; tool characterized in that it is composed of a mounting endowed with at least one machining element, and of which at least the machining edge is composed of a high-homogeneity oxide ceramic platelet composed of Al.sub.2O.sub.3 and ZrO.sub.2, with this platelet being obtained from: a homogeneous Al.sub.2O.sub.3XZrO mixture of Al.sub.2O.sub.3 nano-particles of average size smaller than 1 m, and ZrO.sub.2 nano-particles of tetragonal structure and average size smaller than that of the Al.sub.2O.sub.3 particles, with the ZrO.sub.2 content X being between 5 and 20% in mass of ZrO.sub.2 in relation to the total mass, with the mixture being formed into a plate via the gel-casting process followed by sintering or controlled cold isostatic compression, and with the plate (or platelets resulting from the division of the plate) being mechanically honed to produce the cutting edge.

Claims

1. Cutting tool for machining by removal of matter from abrasive materials, including material based on wood particles; tool characterized in that it is composed of a mounting endowed with at least one machining element, and of which at least the machining edge is composed of a high-homogeneity oxide ceramic platelet composed of Al.sub.2O.sub.3 and ZrO.sub.2, with this platelet being obtained from: a homogenous Al.sub.2O.sub.3XZrO mixture of Al.sub.2O.sub.3 nano-particles of average size less than 1 m, and ZrO.sub.2 nano-particles of tetragonal structure and average size smaller than that of the Al.sub.2O.sub.3 particles, with the ZrO.sub.2 content X being between 5 and 20% of mass of ZrO.sub.2 in relation to the total mass; with the mixture being formed into a plate via the gel-casting process, followed by sintering or controlled cold isostatic compression, and with the plate (or platelets resulting from the division of the plate) being mechanically honed to produce the cutting edge.

2. Machining tool in accordance with claim 1, characterized in that the average ZrO.sub.2 particle is smaller than 0.5 m.

Description

DRAWINGS

(1) The invention herein will be described hereafter in a more-detailed manner by means of an example of manufacture of a machining tool via removal of material, based on the tables of the physical characteristics of different oxide ceramics; thus:

(2) FIG. 1 is a table presenting the physical characteristics of 7 samples of Al.sub.2O.sub.3- and 3YZ.sub.rO.sub.2-based oxide ceramic;

(3) FIG. 2 is a table of these same physical characteristics of a cutting platelet made of a combination of Al.sub.2O.sub.3 and ZrO.sub.2 in accordance with the invention.

DESCRIPTION OF METHODS OF IMPLEMENTATION OF THE INVENTION

(4) The invention addresses a cutting tool for the machining of abrasive materials. This tool is composed of a mounting for installing the tool in the machine. The mounting accommodates one or more cutting platelets, which are what comes into contact with the material to be machined. The cutting platelets are made of a oxide ceramic of alumina Al.sub.2O.sub.3 and zircon ZrO.sub.2, according to a mass ratio of 5 to 20% of zircon in the total mass.

(5) The alumina Al.sub.2O.sub.3 and zircon ZrO.sub.2 are in the state of nano-particles (sub-micron particle size). The Al.sub.2O.sub.3 particles are of less than one micron in size, while the ZrO.sub.2, particles are smaller than the alumina Al.sub.2O.sub.3 particles and, preferably, smaller than 0.5 m. The ZrO.sub.2 particles are regularly distributed throughout the mass of alumina Al.sub.2O.sub.3 particles. The ZrO.sub.2 particles initially have the crystalline structure of a tetragonal network. The homogenous mixture of particles is used for producing oxide ceramic plates via the gel-casting process, which conserves this homogenous distribution. The molding of the plate via the gel-casting process is followed by a baking (sintering).

(6) Trials undertaken with platelets (gel-casting plus sintering) have shown that the cutting edge resulting from molding alone did not have particular strength, and suffered chipping or cracking of the cutting edge.

(7) According to the invention, the ceramic plate obtained via the gel-casting process and sintered is then cut into platelets of the desired dimensions, according to the cutting tool. The cutting plate(s) are secured to a metal mounting, which is itself then secured to the tool's mounting.

(8) The tool is sharpened in a subsequent phase, to produce the cutting edge of the platelets. Under the effect of the machining of the platelet and of its cutting edge, the ZrO.sub.2 particles increase in volume, changing from the structure of a tetragonal network to that of a mono-clinical network, as has been shown by microscopic examinations before and after the machining in the mounted state. This is because while, before the machining of the cutting edge, the ceramic only presented a very small transformation (around 1 to 2%) of the incorporated zircon, which changed from the tetragonal state to the mono-clinical state; after machining, the cutting edge had undergone a major transformation in structure.

(9) The mechanical honing of the cutting edge gives rise to strong mechanical stresses in the structure. These stresses can be assimilated to a pressure thatwhen combined with the high temperature rise produced by the mechanical honingcauses the change of phase of the ZrO.sub.2 nano-particles from the tetragonal structure to the mono-clinical structure.

(10) Furthermore, this increase in volume is then further amplified by the work with the tool, namely the machining of the abrasive material, as was shown by microscopic examinations.

(11) The change of structure gives rise to an increase in the volume of the ZrO.sub.2 particles, which thereby exert internal stresses on the Al.sub.2O.sub.3 particles, and block them. These micro-compression stresses in the micro-structure considerably improve the micro-mechanical strength of the joins of grains. The same result is obtained with platelets manufactured in accordance with the controlled CIP (cold isostatic compression) process, because the tetragonal structure of ZrO.sub.2 grains is no longer transformed into a mono-clinical structure except by the gel-casting process followed by sintering. Therefore, the invention results from the specific composition of Al.sub.2O.sub.3XZrO.sub.2 oxide ceramics (with 5<X<20% m.) manufactured via a process restricting the population of defects, such as the gel-casting process or the CIP process with preparation of the powder before sintering. The result is a notable improvement in the resistance of grains to detachment and, therefore, to wear by abrasion during the machining of abrasive materials by an identified grain micro-compression mechanism.

DOCUMENTARY REFERENCES

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