Patent Application
20130302600
This invention relates to a process for making a corrosion-resistant coating for zinc or zinc-alloy coated substrates meeting the American Society of Testing and Materials International ASTM B117-11 (hereinafter ASTM B117) standard for continuous salt spray tests of metals and coated metals. The ASTM B117 standard as last amended in August 2011 is incorporated herein by reference.
It is well known that steel rusts when left unprotected in almost any environment. Applying a thin coating of zinc to steel is an effective and economical way to protect steel from corrosion. The most common form of galvanizing metal substrates, either iron, steel or aluminum, is hot-dip galvanizing in which a thick robust layer is deposited on the surface of the metal substrate. The metal substrate is immersed in a bath of molten zinc, at a temperature of about 850° F. (460° C.), to form a metallurgically bonded zinc coating on the metal substrate. The resulting coated metal substrate can be used in much the same way as an uncoated metal substrate. Coils of steel strip, for example, may be hot-dip galvanized in a continuous line, immersing the steel strip in a molten zinc bath at speeds of up to 600 feet per minute. The specified coating thickness is controlled by air “knives” which remove the excess coating deposited on the steel as it exits the molten zinc bath. Galvanized steel is used in applications requiring the strength of steel combined with the corrosion resistance of zinc. The continuous galvanizing process can apply a number of different coatings that vary in thickness, appearance, and alloy composition. The term “galvanized” refers to the standard continuous coating having the primary component being zinc. About 0.2% aluminum may be added to the galvanizing bath to form a thin, inhibiting iron-aluminum layer on the steel surface that ensures formation of the zinc coating. The finished zinc or zinc-alloy coating has good formability and corrosion resistance, and provides excellent sacrificial protection. In some applications, the zinc or zinc-alloy coating is applied in conjunction with annealing of the metal substrate, as explained below. These products are often referred to as being galvannealed.
Other processes to galvanize metal substrates include electrodeposition galvanization, otherwise known as Electrogalvanization, thermal diffusion galvanizing, and galvannealing. Electrogalvanization comprises immersing a steel substrate in a zinc and saline solution with a zinc anode, the steel substrate acting as the conductor. When electricity is passed through circuit a zinc coating is deposited onto the surface of the steel substrate. In thermal diffusion galvanizing, the metal substrate is tumbled with a mixture of zinc powder and accelerator chemicals, generally sand, and heated to slightly below the melting point of zinc. Galvanealled metal substrate results from the combined processes of galvanizing and annealing to produce specialized sheets of steel. To form galvanneal, steel is subjected to the hot-dip galvanizing process to form a zinc-coated steel with a very fine grayish matte finish. The coated steel is then heated, to above the recrystallization temperature, maintained at a suitable temperature for a period of time, and then cooled. The heating and cooling alter the properties of the steel, such as strength and ductility. The zinc coating of galvanneal does not flake off when formed, stamped, and bent. Furthermore, the very fine matte finish acts as a primer, allowing paint to adhere more easily, while affording rust protection. These properties make galvanneal a popular choice in the automotive, signage and electrical equipment industries.
Zinc coatings protect steel by providing a physical barrier as well as cathodic protection to the underlying steel. The main mechanism by which galvanized coatings protect steel is by providing an impervious barrier that does not allow moisture to contact the steel. Without moisture (the necessary electrolyte), there is no corrosion. When base steel is exposed, e.g., by cutting, scratching or abrading, the exposed steel is still protected by the sacrificial corrosion of the zinc coating adjacent to the exposed steel. This is because zinc is more electronegative (more reactive) than steel in the galvanic series, causing the zinc to oxidize before the steel Zinc acting as a sacrificial anode is an advantage absent from paint, enamel, powder coatings and other corrosion preventative methods. However, zinc is a reactive metal and will continually corrode slowly over time, eventually losing its protective qualities. Furthermore, in many applications, after a metal substrate has been galvanized the metal substrate is reduced, usually by cold-rolling, but also by hot-rolling, cutting, or abrading, to desired dimensions, reducing the thickness of the zinc-coating and therefore the effectiveness of the corrosion-resistance provided by the zinc-coating. For this reason, there is a need for a corrosion-resistant coating that provides enhanced corrosion protection for zinc or zinc-alloy coated substrates, even when the coated metal substrate having a zinc or zinc-alloy surface has been reduced.
The process herein described may be applicable not only to galvanized steel, but also to galvannealed carbon steel, which is steel which has been coated with zinc by a hot-dipped process, which converts the coating into a zinc-iron alloy, and subsequently annealed. Conversion to this alloy results in a non-spangle matte finish which makes the sheet suitable for painting after fabrication. Additionally, the present process may be applicable to steel which has been subjected to a Galvalume® process, in which carbon steel sheet is coated with an aluminum-zinc alloy by a continuous hot-dipped process. The nominal coating composition is about 55% aluminum and 45% zinc optionally plus a small addition of silicon (added to at least improve coating adhesion to the steel substrate). This process may be applicable to any form of galvanized metal substrate, including Galvalume® coatings.
The ability of a zinc coating to protect steel depends on zinc's corrosion rate. Freshly exposed galvanized steel reacts with the surrounding atmosphere to form a series of zinc corrosion products (e.g. “white rust” or “red rust”). In air, newly exposed zinc reacts with oxygen to form a very thin zinc oxide layer. When moisture is present, zinc reacts with water resulting in the formation of zinc hydroxide. A common corrosion product to form with exposure to the atmosphere is zinc carbonate as zinc hydroxide reacts with carbon dioxide in the air.
These zinc corrosion products will cause many harmful effects. For example, zinc oxide prevents paint from adhering to the metal as well as accelerates further corrosion of the metal which is unsightly to any galvanized coating's appearance. Pure water contains essentially no dissolved minerals and the zinc will react quickly with pure water to form zinc hydroxide, a bulky white and relatively unstable oxide of zinc. Where freshly galvanized steel is exposed to pure water (e.g., rain, dew or condensation, etc.) particularly in an oxygen-deficient environment, the water will continue to react with the zinc and progressively consume the coating. Therefore, a process for making zinc or zinc-alloy corrosion-resistant metal components with not only exponentially enhanced corrosion-resistance, but also with enhanced adhesion to pre-paints is wanted.
Some commercially available compositions have the capacity to passivate galvanized metal substrates, reducing the formation of zinc corrosion products. These passivators usually utilize a dichromate or chromate composition, typically applied through immersion. Most of these commercially available products provide limited protection to corrosion. An untreated surface will show signs of corrosion after 0.5 hours of exposure to a neutral salt spray according to ASTM specification A1003/A1004, and a thin chromate film produced by a dip procedure will usually show signs of corrosion after 12 to 75 hours of exposure to the salt spray environment. There is a need for a corrosion-resistant coating to provide corrosion resistance exceeding 75 hours of exposure to salt spray environment.
The hot-dip coating process produces many hazardous by-products. For example, when a zinc-phosphate coating is applied to a galvanized metal substrate, via spray coating or dip coating, it must be followed by a rinse step to remove any excess coating composition. The zinc-phosphating rinse water must then be treated to remove any hazardous components. The resultant is a sludge, rich in hazardous components which must be disposed of as hazardous waste according to guidelines set forth by the Environmental Protection Agency (EPA). Sludge also forms in the dipping tanks which must be removed and disposed of according to EPA guidelines. Furthermore, the dipping tanks themselves have a finite lifetime and also must be disposed of according to EPA guidelines. Disposal of hazardous waste is very expensive and time consuming. Therefore, there is presently a need for a coating for a galvanized metal substrate which does not produce hazardous waste by-products which require laborious and expensive disposal.
The presently disclosed corrosion-resistant coating provides enhanced corrosion resistance to the salt spray environment, that may exceed 1,000 hours of protection for metal substrates having a zinc or zinc-alloy surface coating, and over 144 hours for cold-reduced metal substrates having a zinc or zinc-alloy coating. Furthermore, the presently disclosed corrosion-resistant coating provides for a dry-in-place application, negating the requirement for hazardous waste disposal.
Presently disclosed is a process for making a corrosion-resistant metal component comprising the steps of: combining water, at least one zinc phosphate compound and at least one chromium compound to form a first solution; separately combining at least one silicate compound with water to form a second solution; combining the first solution with the second solution such as to form a mixed aqueous solution; combining the mixed aqueous solution with at least one acrylic resin to form a coating mixture; and, applying the coating mixture to a metal substrate having a zinc or zinc-alloy surface to form a coating on the metal substrate, the coating providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy surface of the metal substrate has a weight of 0.04 oz/ft2 (12.2 g/m2).
Also disclosed is a process for making a corrosion-resistant metal component comprising the steps of: combining water, at least one zinc phosphate compound and at least one chromium compound to form a first solution; separately combining at least one silicate compound with water to form a second solution; combining the first solution with the second solution such as to form a coating mixture; and, applying the coating mixture to a metal substrate having a zinc or zinc-alloy surface to form a coating on the metal substrate, the coating providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy surface of the metal substrate has a weight of 0.04 oz/ft2 (12.2 g/m2).
The zinc or zinc-alloy surface may be selected from the group consisting of zinc, zinc alloy, zinc-aluminum alloy, zinc-saline solution, heat-treated zinc-alloy and combination thereof. The coating mixture is capable of reacting with the zinc or zinc-alloy surface of the metal substrate forming a chemical bond with the zinc or zinc-alloy surface. The chromium compound may comprise of a trivalent chromium compound (i.e. chromium (III)). The trivalent chromium compound may be selected from the group consisting of chromium chloride hydrate, chromium (III) potassium sulfate, chromium hydroxide, chromium (III) fluoride, chromium (III) sulfate, chromium (III) sulfide, chromium (III) oxide, chromium (III) 2-ethylhexanoate, chromium (III) nitride, chromium tricarbonyl and mixtures thereof. The chromium compound may also comprise of a hexavalent chromium compound (i.e chromium (VI)). The hexavalent chromium compound may be selected from the group consisting of chromium (VI) halides, hexafluoride, chromyl chloride, sodium chromate, chromium (VI) peroxide, sodium chromate, chromium (VI) oxide, dichromate, potassium chromate, calcium chromate, barium chromate, chromium (VI) oxide peroxide, and mixtures thereof.
Further disclosed is a process for making a corrosion-resistant metal component coating comprising the steps of: combining water, at least one zinc phosphate compound and at least one chromium compound to form a first solution; separately combining at least one silicate compound with water to form a second solution; combining the first solution with the second solution such as to form a mixed aqueous solution; and, combining the mixed aqueous solution with at least one acrylic resin to form a corrosion resistant metal component coating mixture for applying to a metal substrate having a zinc or zinc-alloy surface to form a coating on the metal substrate, the coating providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy surface of the metal substrate has a weight of 0.04 oz/ft2 (12.20 g/m2). In other embodiments, the first solution and the second solution may be combined to form a coating mixture and the coating mixture may be applied to a metal substrate having a zinc or zinc-alloy surface to form a coating on the metal substrate, the coating providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy surface of the metal substrate has a weight of 0.04 oz/ft2 (12.20 g/m2).
The coating mixture may be applied in various manners such as by rolling the coating mixture onto the metal component surface, by spraying the coating mixture onto the metal component surface, or by submersing at least a portion of the metal substrate with a zinc or zinc-alloy surface into a bath of the coating mixture.
a is a photograph of the top view of metal substrate panels, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds, cold-reduced by 16% to 23%, and exposed to the salt spray environment for up to 120 hours.
b is a photograph of the bottom view of metal substrate panels, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (VI), cold-reduced by 16% to 23%, and exposed to the salt spray environment for up to 120 hours.
a is a photograph of the top view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (VI), cold-reduced by 16% to 23%, and exposed to the salt spray environment for up to 120 hours.
b is a photograph of the bottom view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (VI), cold-reduced by 16% to 23%, and exposed to salt spray for up to 120 hours.
a is a photograph of the top view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (III), cold-reduced by 23% to 24%, and exposed to the salt spray environment for up to 120 hours.
b is a photograph of the bottom view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising the presently disclosed corrosion-resistant metal component coating comprising chromium (III) compounds, cold-reduced by 23% to 24%, and exposed to the salt spray environment for up to 120 hours.
a is a photograph of the top view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (VI), cold-reduced by 23% to 24%, and exposed to the salt spray environment for up to 120 hours.
b is a photograph of the bottom view of finished formed studs, having a zinc or zinc-alloy surface, coated with a solution of the presently disclosed corrosion-resistant metal component coating comprising chromium (VI), cold-reduced by 23% to 24%, and exposed to the salt spray environment for up to 120 hours.
Presently disclosed is a process for making a corrosion-resistant coating for zinc or zinc-alloy coated substrates, and for making a corrosion-resistant metal component. Also disclosed is a corrosion-resistant metal component having a corrosion-resistant coating providing chemical resistance.
Referring to
One skilled in the art will understand that a corrosion-resistant coating mixture providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards for a metal substrate having a zinc or zinc-alloy coating weight of 0.04 oz/ft2 (12.20 g/m2) will provide corrosion resistance for varying periods of time depending on the coating weight of the zinc or zinc-alloy surface of the metal substrate and the coating weight of the corrosion-resistant coating applied to the zinc or zinc-alloy surface of the metal substrate. The metric of chemical resistance for at least 150 hours in accordance with ASTM B117 standards for metal substrate having a zinc or zinc-alloy surface with a coating weight of 0.04 oz/ft2 (12.20 g/m2) is a benchmark which provides the effectiveness of the presently disclosed corrosion-resistant coating and is not a limitation to a particular zinc or zinc-alloy coating weight on a metal substrate. For example, the present process includes a corrosion-resistant coating mixture providing chemical resistance to a metal substrate having a zinc or zinc-alloy surface for at least 75 hours in accordance with ASTM B117 standards where the metal substrate having a zinc or zinc-alloy surface with a coating weight of 0.02 oz/ft2 (6.10 g/m2).
The ASTM B117 standard is a widely used standardized salt spray environment cabinet test. Such a salt spray test is used to evaluate the relative corrosive, or chemical, resistance of coated and uncoated materials exposed to a salt spray fog, of 12 ml/hr, at an elevated temperature of 95° F. (35° C.). The ASTM B117 standard specifies that specimens are to be placed within an enclosed salt spray cabinet or chamber and subjected to continuous indirect spray of neutral (pH 6.5-7.2) salt water solution. Such a climate may be constantly maintained throughout the salt spray test period. The water used in the salt spray test is compliant with ASTM D1193 Specification for Reagent Water, Type VI. A salt, usually sodium chloride, is added to the water to achieve a solution comprising 5% salt solution. According to ASTM B117 the default position for the specimens within the salt spray chamber is at an angle of 15-30 degrees from the vertical, positioned such that condensation from one specimen will not drip onto another specimen.
Also disclosed is a process for making a corrosion-resistant metal component coating comprising the steps of combining water, at least one zinc phosphate compound and at least one chromium compound to form a first solution; separately combining at least one silicate compound with water to form a second solution; combining the first solution with the second solution to form a corrosion-resistant metal component coating mixture for applying to a metal substrate having a zinc or zinc-alloy surface to form a coating on the metal substrate, the coating providing chemical resistance for at least 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy coating of the metal substrate has a weight of 0.04 oz/ft2 (12.20 g/m2). In some embodiments, the process for making a corrosion-resistant metal component coating may comprise the steps of combining the first solution and the second solution to form a mixed aqueous solution; and, combining the mixed aqueous solution with at least one acrylic resin to form a corrosion-resistant metal component coating mixture.
Additionally disclosed is a process for making a corrosion-resistant metal component comprising the step of applying a corrosion-resistant coating to a metal substrate having a zinc or zinc-alloy surface to provide a metal component having a corrosion-resistant coating having chemical resistance for more than 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy coating of the metal substrate has a weight of 0.04 oz/ft2 (12.20 g/m2), the corrosion-resistant coating comprising a mixed aqueous solution, the mixed aqueous solution comprising a first solution and a second solution, the first solution comprising water, at least one zinc phosphate compound and at least one chromium compound, the second solution comprising at least one silicate compound and water. In some embodiments, the corrosion-resistant coating may further comprise at least one acrylic resin.
Furthermore, a corrosion-resistant metal component is disclosed, comprising a metal component having a zinc or zinc-alloy coating; and a corrosion-resistant coating providing chemical resistance for more than 150 hours in accordance with ASTM B117 standards where the zinc or zinc-alloy coating of the metal substrate has a weight of 0.04 oz/ft2 (12.20 g/m2), wherein the corrosion-resistant coating comprises a first solution and a second solution, wherein the first solution comprises water, at least one zinc phosphate compound and at least one chromium compound; and wherein the second solution comprises at least one silicate compound and water. In some embodiments, the corrosion-resistant coating may further comprise at least one acrylic resin.
The first solution may comprise between 4 percent and 27 percent by weight of water; between 5 percent and 27 percent by weight of the at least one zinc phosphate compound; and between 5 percent and 27 percent by weight of chromium compound. The corrosion-resistant metal component coating may comprise between 20 percent and 95 percent by weight of the first solution; between 5 percent and 12 percent by weight of the second solution; between 5 percent and 30 percent by weight of acrylic resin; and between 5 percent and 50 percent by weight of water. As used in this disclosure, a range specified as between two end points is inclusive of the end points specified.
The first solution may be combined with the second solution to form a mixed aqueous solution. In some embodiments, the mixed aqueous solution may be combined with a least one acrylic resin. In other embodiments, the mixed aqueous solution may not include the acrylic resin. The at least one acrylic resin may have a pH value of no greater than 3.5. Whereas, the corrosion-resistant metal component coating mixture may have a pH value equal to or below 2.5. In some embodiments the coating mixture may have a pH value between 1.0 and 2.5, inclusive. In some embodiments the acrylic resin may be mixed into the aqueous solution in parts, to avoid curdling or separation of the solution, adding a first part of the acrylic resin into the aqueous solution and completing the mixing of the acrylic resin into the aqueous solution. The aqueous solution with the first part of acrylic resin may be mixed for a period of time, for example 20 minutes, before a second part of acrylic resin is mixed into the aqueous solution. This process may be repeated until all of a desired amount of acrylic resin is mixed into the aqueous solution. Further, after all of the desired amount of acrylic resin has been mixed into the aqueous solution, the solution may be mixed for a further period of time so that the solution may have an even consistency and making it easier to transport.
The corrosion-resistant metal component coating may comprise at least one chromium compound. In some embodiments, the chromium compound may comprise of a trivalent chromium compound. The trivalent chromium compound may be selected from the group consisting of chromium chloride hydrate, chromium (III) potassium sulfate, chromium hydroxide, chromium (III) fluoride, chromium (III) sulfate, chromium (III) sulfide, chromium (III) oxide, chromium (III) 2-ethylhexanoate, chromium (III) nitride, chromium tricarbonyl and mixtures thereof.
In other embodiments, the chromium compound may comprise of a hexavalent chromium compound. The hexavalent chromium compound may be selected from the group consisting of chromium (VI) halides, hexafluoride, chromyl chloride, sodium chromate, chromium (VI) peroxide, sodium chromate, chromium (VI) oxide, dichromate, potassium chromate, calcium chromate, barium chromate, chromium (VI) oxide peroxide, and mixtures thereof.
The corrosion-resistant metal component coating may be applied to a metal component having a zinc or zinc-alloy surface in a number of processes. The coating may be applied through immersion, such that the metal component having a zinc or zinc-alloy surface is immersed into a bath of the presently disclosed corrosion-resistant coating, or the corrosion-resistant coating may be sprayed onto the zinc or zinc-alloy surface of the metal component, with or without the aid of electrolysis. However, of specific benefit, the presently disclosed corrosion-resistant metal component coating may be applied in a dry-in-place process, as shown in
After the corrosion-resistant metal component coating 20 has been applied to the zinc or zinc-alloy surface 11 of the metal strip component 10, a reaction may occur between the zinc or zinc-alloy surface 11 and the corrosion-resistant coating 20. The process for making a corrosion-resistant metal component may further comprise the step of heating the coated metal substrate 10 to further the reaction between the applied coating mixture 20 and the zinc or zinc-alloy surface 11 of the metal substrate 10. Such heating may be provided by a heating apparatus 17, where the metal substrate 10 is passed, via transfer rolls 16, through the heating apparatus 17 to finalize the reaction. The heating apparatus 17 may be an infra-red heating apparatus capable of heating the surface 11 of the metal component 10. In some embodiments the heating apparatus 17 may heat the surface 11 of the metal component 10 to a temperature of between 170° F.-210° F. In other embodiments, the heating apparatus 17 may heat the surface 11 of the metal component 10 to a higher temperature as desired of up to approximately 700° F. The metal strip component 10 may be passed through the coating applicator rolls 12 and the heating apparatus 17 at a speed of approximately 600 ft/min (3.06 m/s). Finally, the coated metal strip component 10 may be re-coiled into coil 9, for later transportation.
The metal strip component 10 having a zinc or zinc-alloy coating, coated with the corrosion-resistant coating 20 will have improved electrical conductivity compared to metal strip 10 having a zinc or zinc-alloy coating, without the corrosion-resistant coating 20. Therefore, the coated galvanize metal substrate may improve weldability over non-coated galvanized metal substrates.
The metal strip component 10 may be subsequently heated to temperatures of at least 700° F. and maintain the corrosion-resistance necessary to satisfy ASTM A-1004/A-1004M-99 and ASTM A-1003/A-1003M-05 testing standards for galvannealed metal substrates 10, or equivalent standards for other forms of galvanized metal substrates 10, including Galvalumed® metal substrates. The ASTM A-1004/A-1004M-99 and ASTM A-1003/A-1003M-05 testing standards are incorporated herein by reference.
The corrosion resistance of uncoated metal substrates, having a zinc or zinc-alloy surface, and metal substrates, having a zinc or zinc-alloy surface, coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) or chromium (III) compounds was determined following the standards and procedures provided by the American Society of Testing and Materials (ASTM) International. Metal substrates having zinc or zinc-alloy surfaces, coated with or without the presently disclosed corrosion-resistant coating, were exposed to a salt fog environment meeting the requirements of ASTM B117. ASTM B117 provides a controlled corrosive environment which has been utilized to produce relative corrosion resistance information for specimens of metals and coated metals exposed in a given test chamber. All corrosion testing practices were performed in compliance with ASTM A-1004/A-1004M-99 and ASTM A-1003/A-1003M-05. While ASTM A-1004/A-1004M-99 and ASTM A-1003/A-1003M-05 are directed to galvennealed panels, one of ordinary skill in the art will understand that the testing under ASTM A-1004/A-1004M-99 and ASTM A-1003/A-1003M-05 is a benchmark, and will appreciate that the presently disclosed corrosion-resistant metal component coating may be applied to all forms of galvanized metal substrate, including, but not limited to, hot-dipped galvanized, galvannealed, electrogalvanized, and galvalume, and meet or exceed the associated ASTM standards. In some embodiments the zinc or zinc-alloy surface is selected from the group consisting of zinc, zinc alloy, zinc-aluminum alloy, zinc-saline solution, heat-treated zinc-alloy solution and combination thereof. According to ASTM A-1003/A-1003M-05, the expected corrosion characteristic for metallic coated sheet steels with nonstructural or non-load-bearing applications is a minimum of 75 hours with less than 10% loss of metallic coating from the surface of the laboratory test samples. The loss of metallic coating from the surface of the laboratory test samples was determined by measuring the percent of red corrosion present after specific times of exposure to the salt spray environment according to ASTM B117.
Galvannealed panels coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds, without the optional acrylic resin, from different production runs were also exposed to the salt fog environment meeting the requirements of ASTM B117 for periods of 312 hours, 504 hours, 744 hours, and 1008 hours. Table 1 provides a summary of the percent of surface area of the panels affected by red corrosion for galvannealed panels coated with the presently disclosed corrosion-resistant coating after being exposed to a salt fog environment. All galvannealed panels coated with the corrosion-resistant coating showed zero percent (0%) of surface area affected by red corrosion for up to 1008 hours of exposure to the salt spray environment. Conversely, the HDG G-60 (NCT) metal substrate panels showed red corrosion over 50% of their surface area after just 120 hours of exposure to the salt spray environment.
In a separate test galvannealed panels were exposed to a salt fog environment meeting the requirements of ASTM B117 for periods of 504 hours, 744 hours, 1008 hours, 1248 hours, and 1512 hours. As illustrated in
Referring to
Table 2 provides a summary of tests performed, showing the percent of red corrosion for zinc-alloy coated panels coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (III) compounds and acrylic resin, having been cold-reduced after coating by 15% to 23% and exposed to a salt fog environment meeting the requirements of ASTM B117, for periods of 48 hours, 75 hours, 96 hours, 120 hours, and 144 hours. All zinc-alloy coated panels, coated with the presently disclosed corrosion-resistant metal component coating, and reduced after coating by 15% to 23%, showed zero percent (0%) surface area of the panels affected by red corrosion after being exposed to salt spray for up to 120 hours. The panels, having a zinc or zinc-alloy surface, coated with the presently disclosed corrosion-resistant metal component coating, and cold-reduced after coating by 15% to 23% exceeded the ASTM A-1003/A-1003M standards by presenting less than three percent (3%) of red corrosion after 144 hours of exposure to the salt spray environment. The zinc-alloy coated panels coated with the presently disclosed corrosion-resistant metal component coating, and cold-reduced by 15% to 23% showed complete resistance to corrosion for up to 120 hours of salt spray, and red rust over less than 3% of the surface area at 144 hours salt spray compared to red corrosion over 75% of the surface area of the standard HDG G-40 (NCT) panels after 144 hours of exposure to the salt spray environment.
Referring to
Zinc-alloy panels coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds and cold-reduced after coating by 16% to 23% from different production runs were exposed to the salt fog environment. Table 3 provides a summary of the percent of surface area affected by red corrosion for zinc-alloy coated panels coated with the presently disclosed corrosion-resistant metal component coating, and cold-reduced after coating by 16% to 23% and exposed to the salt fog environment meeting the requirements of ASTM B117, for periods of 48 hours, 75 hours, 96 hours, and 120 hours. All zinc-alloy panels that were coated with the presently disclosed corrosion-resistant metal component coating, and were cold-reduced after coating by 16% to 23% showed zero percent (0%) of surface area affected by red corrosion. The zinc-alloy panels coated with the presently disclosed corrosion-resistant metal component coating, and cold-reduced by 16% to 23% showed no indication of corrosion for up to 120 hours of the salt spray exposure, compared with the standard HDG G-40 NCT, which presented 50% of red corrosion after 120 hours of the salt spray exposure.
a-b show finished formed studs, having a zinc-alloy surface, coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds and cold-reduced after coating by 16% to 23% were exposed to a salt fog environment meeting the requirements of ASTM B117 for periods of 75 hours, 96 hours, and 120 hours. As illustrated in
Similarly, metal substrates having a zinc or zinc-alloy surface were coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds, cold-reduced by 23% to 24% and subjected to salt spray testing.
The effectiveness of the presently disclosed corrosion-resistant metal component coating comprising chromium (III) or chromium (VI) compounds to protect galvanized metal substrates, such as hot-dip galvanized metal substrates or galvannealed metal substrates, from corrosion is dependent upon the thickness of the zinc or zinc-alloy coating and the thickness of the presently disclosed corrosion-resistant metal component coating. Table 4 provides a summary of the number hours achieved under the salt spray testing environment with less than ten percent (10%) of weight loss for HDG G-30 metal substrates coated with the presently disclosed corrosion-resistant metal component coating. Over 1000 hours of corrosion-free salt spray environment testing were obtained for galvanized metal coated with the presently disclosed corrosion-resistant metal component coating, with a coating weight of at least 0.0106 oz/ft2 (3.23 g/m2). Over 500 hours of corrosion-free salt spray testing was obtained for galvanized metal substrates coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds to a coating weight of at least 0.0053 oz/ft2 (1.61 g/m2). And, over 500 hours of corrosion-free salt spray environment testing were obtained for galvanized metal substrates coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (III) compounds to a coating weight of at least 0.0053 oz/ft2 (1.61 g/m2).
Similarly, the effectiveness of the presently disclosed corrosion-resistant metal component coating comprising chromium (III) or chromium (VI) compounds to protect galvannealed metal substrates from corrosion is dependent upon the coating thickness of the presently disclosed corrosion-resistant metal component coating. Table 5 provides a summary of the number of hours of salt spray testing achieved with less than ten percent (10%) of weight loss after exposing galvannealed A-25 or A-40 metal substrates coated with the presently disclosed corrosion-resistant metal component coating comprising chromium (III) or chromium (VI) compounds to a salt fog environment meeting the requirements of ASTM B117. Over 1000 hours of salt spray testing were obtained for galvannealed metal substrate coated with the presently disclosed corrosion-resistant metal component coating comprising having a coating weight of at least 0.0106 oz/ft2 (3.23 g/m2), while maintaining less than 10% red corrosion on the surface of the metal substrate. Whereas, over 500 hours of salt spray testing were obtained for galvannealed metal substrates coated with presently disclosed corrosion-resistant metal component coating comprising chromium (VI) compounds to a coating weight of at least 0.0053 oz/ft2 (1.61 g/m2), while maintaining less than 10% red corrosion on the surface of the metal substrate. And, over 500 hours of salt spray environment testing were obtained for galvannealed metal substrates coated with presently disclosed corrosion-resistant metal component coating comprising chromium (III) compounds to a coating weight of at least 0.0053 mg/ft2 (1.61 g/m2), while maintaining less than 10% red corrosion on the surface of the metal substrate.
As illustrated in
In one embodiment, the coating mixture may be applied by rolling the coating mixture onto the metal component surface. This direct mode of application may decrease the amount of residual coating mixture. In another embodiment, the coating mixture may be applied by spraying the coating mixture onto the metal component surface, or alternatively, the coating mixture may be applied by submersing at least a portion of the metal substrate with a zinc or zinc-alloy surface into a bath of the presently disclosed corrosion-resistant metal component coating.
As illustrated in
The presently disclosed corrosion-resistant coating may be self-healing. The coating protecting a metal substrate from corrosion may protect the metal substrate even if the metal substrate is cut, scratched or abraded. For example, a metal substrate may become scratched when being cold-rolled using rollers which have surface defects imparting scratches onto the surface of the molten metal. Scratching of the metal substrate may remove the corrosion-resistant coating from that portion, exposing the metal substrate. It is desirable that a corrosion-resistant coating will protect the exposed portion of the metal substrate. One such method of protection is to provide sufficient corrosion-resistant coating material that part of the coating may remain non-reacted with the zinc or zinc-alloy surface. The non-reacted coating may then react with the scratched, exposed, portion of the metal substrate forming a protective coating over it. Thus, the corrosion-resistant coating is self-healing.
While the principle and mode of operation of this invention have been explained and illustrated with regard to particular embodiments, it must be understood, however, that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. Therefore, it is intended that the invention not be limited to the particular embodiments falling within the scope of the appended claims.
This application is a continuation of U.S. application Ser. No. 13/304,822 filed Mar. 30, 2012, the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13304822 | Nov 2011 | US |
| Child | 13947012 | US |
