Glass manufacturing – Apparatus made of special material – Metal-nonmetal composite
Reexamination Certificate
2000-11-03
2003-07-15
Colaianni, Michael (Department: 1731)
Glass manufacturing
Apparatus made of special material
Metal-nonmetal composite
C065S026000, C065S169000, C065S170000, C065S374120, C065S374130, C425S090000, C425S107000, C249S114100, C249S115000, C249S116000
Reexamination Certificate
active
06591636
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to protective coatings for surfaces of glass forming equipment and methods of applying the same thereto, and more particularly to protective coatings for, and methods of applying such coatings to, plungers for forming glass articles, to replace chrome coatings customarily utilized for coating such plungers.
BACKGROUND OF THE INVENTION
Chrome plating has been used on glass forming equipment for more than 40 years. Its primary function has been to provide oxidation and corrosion protection to the forming equipment substrate material. Generally the base material utilized in glass forming equipment may be either 420 stainless steel, H13 tool steel or ductile iron, depending upon the application. Although chromium plating of glass forming equipment has been utilized successfully over many years with different glass compositions, serious problems are encountered when the desired product requires a glass composition containing significant amounts of alkali and/or alkaline components. A problem results which is defined as the build-up of a corrosion product on the surface of the chromium plated forming equipment, which results in unacceptable glass matte surface.
The corrosion product is the result of a reaction involving the alkali and alkaline components of the glass, oxygen, and chromium from the chrome plated forming equipment. The reaction products have been identified as chromate compounds, namely K
3
Na(CrO
4
)
2
, BaK
2
(CrO
4
)
2
and K
3
Ba
2
Cr
3
O
3
. If any one of the three reactants, glass components, the oxygen, or the chrome from the chrome-plated forming equipment were removed from the system, the chromate corrosion problem would cease to exist. In view of the fact that the glass composition is usually dictated by the desired end product, and oxygen is in the atmosphere, it becomes obvious that the most practical solution to the problem is to eliminate the chrome plated forming equipment.
From a pure production standpoint, the need to find a replacement for chrome electroplating of forming equipment, is based upon improved performance of the equipment, however environmental issues also adds impetus to the need for change from the use of chrome plating, since there is a need to reduce the environmental risks associated with chrome electroplating. That is, there is a global trend of hexavalent chrome emission reduction, and the substituted coating materials of the present invention help to reduce such hexavalent chrome emissions.
The chromate corrosion product does not contaminate the glass per se, but accumulates on the chrome-plated glass forming surface and necessitates the replacement thereof in order to produce acceptable ware. In U.S. Pat. No. 5,120,341 to Nozawa et al., the inventors desire to increase the strength of glass containers by decreasing contaminants actually getting into the glass. In order to reduce glass contamination, the patent suggests the use of a gaseous hydrocarbon to coat the mold parts instead of using oil, which creates bubbles and graphite contamination of the glass. In addition, the patent suggests the coating of a plunger with a ceramic or sprayed metal coating which prevents flaking of an oxide layer from the plunger into the glass. Since the ceramic coating can withstand higher temperatures than the metal coating, the patent suggests coating the tip of the plunger with the ceramic coat and the base of the plunger with a self-fluxing metal coating, which cannot withstand the higher temperatures to which the tip of the plunger is exposed.
Further, the sprayed metal coating is less abrasive than the ceramic coating and thus is utilized at the base of the plunger so as to not scratch the glass container about the mouth portion. In another embodiment, the patent suggests the use of a blown air curtain about the plunger which not only cools the plunger but is used mainly in order to prevent foreign substances from attaching to the outside surface of the plunger, which foreign substances would contaminate the newly formed glass. Finally, the patent also suggests the use of an abrasive proof layer between the moving surfaces of the plunger assembly to prevent metal dusts from contaminating the glass, which dust particles would decrease the impact strength of the formed glass container. Unlike the Nozawa et al. Patent, the present invention is not concerned with the contamination of the glass per se, but with the provision of a protective coating to protect substrate material of glass forming equipment, such as a plunger, from oxidation and corrosion.
However, in U.S. Pat. No. 4,830,655 to Franek et al., the inventors were looking for a material to avoid the chemical incompatibilities of known mold materials and glass melts in the forming of glass optical elements with high surface quality. The mold means of the Franek et al. Patent must have a monocrystalline structure and is made from material such as Al
2
O
3
, Cr
2
O
3
(which is being avoided in the present invention), MgAl
2
O
4
and/or ZrO
2
. The shaping device itself is prepared by means of chip forming shaping processes (for example boring, sawing, turning, milling, etc.), from a solid piece of material with subsequent final processing of the mold surfaces (honing, polishing, burnishing, glazing, buffing, etc.). Thus, it can be seen that the Franek et al. Patent does not even contemplate the utilization of a coating applied to a substrate, but actually manufactures the shaping device from a block of material having a monocrystalline structure.
Again, unlike the Franek et al. Patent which forms its shaping device from a solid piece of material by machining the material, the present invention applies a protective coating to additional substrate material for forming glass articles. Thus it has been an object of the invention to not only avoid the utilization of chrome as a plating material, but also to provide an improved corrosion and oxidation resistant coating for glass forming equipment.
SUMMARY OF THE INVENTION
The present invention sets forth corrosion and oxidation resistant coatings and methods of applying the same to glass forming equipment to replace the use of chrome as a plating material on such equipment. Coating materials such as Al
2
O
3
, and Ni/V may be utilized and an undercoat of Ni or nickel alloy may be employed. The method of deposition onto the substrate of the forming equipment may include sputter coating and electron beam physical vapor deposition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The criteria for material selection was based primarily upon the assumed compatibility of a material with the hot glass forming environment, specifically high temperature oxidation and corrosion resistance. Other factors such as material toxicity and availability were also considered. Initially 28 materials were selected to be deposited upon test samples in order to have a broad base from which to select the most optimum coating material.
However, since the problem of the build-up of a corrosion product manifests itself primarily on plunger surfaces utilized to form TV panels, it was important to design a test to model the production pressing process and simulate actual conditions for life and performance predictions specific to such problem. Therefore, specifically designated coated samples were cyclicly immersed in TV panel glass under controlled conditions at elevated temperatures. The controlled test conditions were glass temperature, plunger temperature, dwell (immersion) time, cycle time and test duration.
Since the initial test for the 28 selected materials was designed to simulate production process conditions, the glass temperature was maintained at 1000° C. with the plunger surface temperature controlled at 600° C. Automatic temperature control of the plunger was accomplished by blowing cooling air on the backside of the test plungers. A thermocouple linked to a pneumatically controlled valve regulated the amount of cooling air applied to the plunger. The initial control set was determined with the aid of a contact
Forenz Dominick J.
Fountain Anca D.
Gill Sherry J.
Salisbury Kenneth R.
Sarhangi Ahmad
Bean Gregory V.
Colaianni Michael
Corning Incorporated
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