Glass manufacturing – Processes – Utilizing parting or lubricating layer
Reexamination Certificate
1999-08-03
2001-08-28
Colaianni, Michael P. (Department: 1731)
Glass manufacturing
Processes
Utilizing parting or lubricating layer
C065S024000, C065S025200, C065S062000, C065S169000, C065S170000, C065S181000, C065S375000, C065S102000, C065S111000, C264S334000, C264S430000, C264S484000
Reexamination Certificate
active
06279346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method for reducing and more preferably for eliminating hot sticking between a die, particularly an electrically conducting die, and an inorganic non-metallic material (=an insulator), particularly an insulator of which at least a part is in vitreous state, being in contact with each other at a temperature where the insulator is moldable. The invention is furthermore directed to a process for producing a molded insulator with improved surface quality by using said method and to a device to perform said method.
2. Description of Related Art
Numerous undesirable hot sticking phenomena occurring in complex industrial processes can be attributed to a general problem of hot sticking between a forming die which in general is made from a metal or another electrically conducting material and an inorganic non-metallic material (=insulator), in particular an inorganic insulator like glass, enamel and ceramic, of which at least one of the phases which constitute it is viscous at the temperature in question.
During the hot molding of inorganic insulating materials like glass or enamel or combinations therefrom at a temperature for which said materials have a viscosity of between 1 and 10,000 kPa·s (=10
4
and 10
8
poises) sticking phenomena are encountered between said insulating materials and the forming die or the mold. The forming die may be entirely metal, or ceramic covered with a metallic coating, or metal or ceramic covered with a ceramic coating sufficiently electrically conductive at the molding temperature. The temperature range corresponding to said viscosities is variable according to the composition, from 500 to 1000° C. for certain industrial silica-alkali-lime glasses. These phenomena have appeared in the course of the development of new technologies. For example:
1. Sticking of a molten glass to the metal mold during the manufacture of flasks, bottles, beakers.
2. Sticking of an enamel (mixture of a glass in powder form which is called frit and of a crystallized coloring agent which is called pigment) to the metallic forming die during the forming of glazings of automobiles.
This list is not at all exhaustive.
Some solution have been found for enamels for glazings of automobiles:
Addition of zinc and tin oxides, or of copper sulphates, which act as “anti-stick” components, that is to say they are components which contribute the property of non-sticking—see U.S. Pat. Nos. 4,684,388 (Ford Motor Company) and 4,828,596 (Ciba-Geigy Corporation).
Development of glass frits which recrystallize on stoving—see EP 0 370 683 A1 (Johnson Matthey Public Limited Company) and U.S. Pat. No. 5,153,150 (Ferro Corporation).
This type of solution is only partial however. The success of said compositions depends to a large extent on the forming conditions, and more particularly on the stoving cycle of the enamels.
It is an object of the present invention to limit the sticking problems without acting on the compositions. It is a further object to provide a process for any kind of molding of at least partly vitreous inorganic materials which leads to a better surface quality of the molded article by eliminating or at least reducing said hot sticking problems. Still another object is directed to a device comprising the usual equipment which permits said molding and means by which said sticking phenomena can be reduced or essentially be avoided.
SUMMARY OF THE INVENTION
The present invention overcomes the hot sticking problems by contacting the inorganic non-metallic material to be moulded, hereinafter denoted as an insulator, with a forming die within an electric field at elevated temperatures required for the moulding process.
The inventors have found a method for reducing hot sticking between a die and an inorganic non-metallic material (=insulator) being in contact with each other at a temperature where said insulator is moldable, characterized in that an assembly comprising said die and said insulator is maintained in a polarized state during said contact, whereby the face of said die contacting said material is positively charged and that face of said material contacting said die is negatively charged.
Preferably the insulator consists essentially of inorganic materials, like glass, enamel and ceramic, of which at least one part contacting the die is in vitreous form. As already stated the die may consist of metal, metal alloys or combinations of ceramic/metal, ceramic/semi-conductor or other combinations, with the proviso that the cover layer of said conductor is made from a material which is sufficiently electrically conductive at the operating temperature. This invention therefore preferably applies to inorganic insulator/forming die systems, at temperatures required for the molding of glass.
The inorganic non-metallic material to be molded is an insulator at room temperature but becomes electrically conductive during the thermal treatment at the firing and/or molding temperature. This is the ionic conductivity of the vitreous part of for example an enamel layer which makes possible charge transfers from one side to the other of said layer at said firing/molding temperature.
Said polarization can be achieved and maintained by using any known method for building-up an electrical field, e.g. by applying a voltage or a current to said assembly, by the aid of a plate-like capacitor whose armaments (=plates) are on either side of said assembly or by inducing a current across the insulator/die-interface.
Moreover, if it is decided to create said polarization by applying a voltage, the voltage required to reduce the sticking must be suited to the system, which is influenced by e.g. the nature and thickness of the insulating material, the nature of the forming die or mould, the geometry of the system as well as the moulding conditions, like the pressure and temperature.
By using the inventive method in molding processes an improved surface quality of the molded article is obtained because of the absence of hot sticking defects.
REFERENCES:
patent: 1035390 (1912-08-01), Sievert
patent: 3143413 (1964-08-01), Krapf
patent: 3182103 (1965-05-01), Blaylock, Jr. et al.
patent: 3236620 (1966-02-01), Wiley
patent: 4684388 (1987-08-01), Boaz
patent: 4828596 (1989-05-01), Reinherz
patent: 5153150 (1992-10-01), Ruderer et al.
patent: 5573715 (1996-11-01), Adams et al.
patent: 5578101 (1996-11-01), Blonder et al.
patent: 5894002 (1999-04-01), Boneberger et al.
patent: 0 370 683 (1990-05-01), None
patent: 0 477 785 (1992-04-01), None
patent: 2 641 549 (1990-07-01), None
patent: 58-007367 (1983-01-01), None
The American Heritage Dictionary, Second College Edition; pg 1191, definition of “stave”, 1982.*
Patent Abstracts of Japan, vol. 7, No. 81, Apr. 5, 1983 & JP 58 007367 A, Jan. 17, 1983.
Anquetil Jerome
Papet Philippe
Ribes Michel
Thomas Corinne
Colaianni Michael P.
dmc
Wenderoth , Lind & Ponack, L.L.P.
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