Plastic and nonmetallic article shaping or treating: processes – Carbonizing to form article – Agglomeration or accretion
Patent
1993-10-25
1995-07-25
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Carbonizing to form article
Agglomeration or accretion
B29C 7104
Patent
active
054359465
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of dielectric insulating materials used under friction and in particular ceramic materials. Although such materials in particular comprise organic materials such as monolithic or composite insulants and polymers, the present invention will be described solely in connection with ceramics, but it must be understood that this only constitutes an example and must not be interpreted as having a limitative character with respect to the applications of the invention.
At present, there are numerous mechanical friction devices using mobile ceramic elements which are in mechanical contact with one another. This is in particular the case with heat motors, where ceramic parts slide with respect to one another. This is also the case with certain clutches, special bearings or running gears produced from ceramic parts. It also occurs to an ever increasing extent in the field of valves and fittings, where the ceramic material is ever more frequently used for producing valves.
The valves of taps or faucets are formed from two generally disk-shaped parts, which have off-centered openings with respect to the tap rotation axis and which can slide on one another. According to the relative position of one of the disks with respect to the other, the openings coincide to a greater or lesser extent making it possible to control the passage of a fluid. The surfaces of the contacting ceramic parts undergo a finishing treatment ensuring that they have a roughness and planeity appropriate for sealing the said tap. The use of ceramic parts in this field and in those referred to hereinbefore offers numerous advantages, including a perfect seal, an absence of wear even under a period of prolonged operation, unalterability and very high resistance to even the most aggressive or corrosive chemical agents.
In spite of this, it is unfortunately found that the adhesion forces between the ceramic parts in contact and under pressure spontaneously evolve as a function of numerous parameters and in particular the operating time. In particular, a prolonged stoppage under pressure of the use of said parts often leads to a considerable increase in the friction coefficient and sometimes even to seizing or total locking and this is virtually impossible to obviate. This defect of ceramic friction structures, for which hitherto there has been no remedy, casts doubts on the future of these products in such applications.
The present invention is directed at a process for the preparation of ceramic materials for friction parts free from self-adhesion phenomena under stress or during aging and which makes it possible to completely and definitively obviate the disadvantages referred to hereinbefore.
This process for the preparation of ceramic materials for parts subject to friction, in which the chemical component constituting the ceramic material is subject to the successive operations of pressing, sintering, polishing the surface obtained, cleaning the solid gangue resulting from the polishing and roasting in the presence of oxygen is characterized in that the preceding operations are completed by a treatment serving to increase the dielectric susceptibility and make it homogeneous in the mass in the vicinity of the friction surfaces which are to come into contact with one another and increase the mobility of the charges.
The essential means of the present invention consisting of treating the ceramics to obtain an increase in their dielectric susceptibility making it homogeneous in the mass has resulted from recent theoretical research which has revealed that the auto/self-adhesion, seizing and locking phenomena previously observed had an electrostatic origin.
The electrostatic theory of adhesion is based on the calculation of the pressure due to the presence of electrical charges localized at the interface of the insulating materials having different dielectric susceptibilities. It has experimentally been shown that a polarization energy accumulates in any insulating material around faults or defects (in the sens
REFERENCES:
patent: 4894255 (1990-01-01), Page et al.
patent: 5296171 (1994-03-01), Christin et al.
Journal of the American Ceramic Society, vol. 67, No. 21, Feb. 1984, C. J. McHargue et al.: "Lattice Modification in Ion-Implanted Ceramics", pp. 117-123.
Bach Pierre
Blaise Guy
Faure Claude
Le Gressus Claude
Treheux Daniel
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