METHOD FOR IMPROVING LIGHT GAUGE BUILDING MATERIALS

Abstract

A process is described in which non-structural galvanized steel studs are sequentially chemically treated with a permanganate coating to improve oxidation resistance, followed by treatment with a silicate coating sealant, optionally with zinc surface activation using an acid treatment.

Description

This application is a continuation of U.S. application Ser. No. 12/586,994, filed Sep. 29, 2009, the contents of which are hereby incorporated in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to a process of making building materials adapted for use in building applications (preferably light gauge) in which the building material has been preferably reduced in thickness yet meets ASTM standards or AISI standards (North American Standards for Cold-Formed Steel Framing - General Provisions) for corrosion resistance for building applications at a coating thickness which is essentially equal to or less than that specified for G-40 or equivalent corrosion resistance.

It has been common construction practice for many years to construct non-load bearing walls and partitions in residential and commercial buildings from formed sheet metal. These walls and partitions are, for example, constructed of metal studs and floor and ceiling plates typically of 2″×4″ nominal dimensions, recognizing that other nominal dimensions are within the scope of this application, including but not limited to ⅝″, 2½″, 3⅝″, 4″ and 6″.

Metal has advantages over wood as a material for vertical studs in that metal will not warp over time, will not be subject to termites and other vermin, and will consistently provide a flat surface to which material, such as drywall, forming the outer wall surfaces may be attached. Such metal construction, moreover, provides improved wind resistance for construction in areas at greater risk of hurricanes and tornadoes. Additionally, a metal stud is lighter than a wood stud thereby facilitating construction practices. Notwithstanding the advantages of metal, wood has been the material of choice for the use as vertical non-load bearing studs in substantial part because carpenters prefer its use in the assembly of walls and partitions. One reason for this preference is due to the fact that galvanized (zinc coated) metal used in metal building studs has a tendency to rapidly develop a white film of zinc oxide or hydroxide.

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. 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. However, zinc is a reactive metal and will corrode slowly over time. For this reason, the protection offered by galvanized coatings is proportional to the coating thickness. When base steel is exposed, e.g., by cutting or scratching, the steel is protected by the sacrificial corrosion of the zinc coating adjacent to the steel. This is due to the fact that zinc is more electronegative (more reactive) than steel in the galvanic series.

Historically, galvanizing has proven to be the most economical and effective way to protect steel formed in to metal studs and other building framing components. Galvanizing is a process where steel sheet is immersed into a bath of molten zinc (e.g., 850° F.) to form a metallurgically bonded zinc coating. 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 that is basically zinc. About 0.2% aluminum is 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 coating has good formability and corrosion resistance, and provides excellent sacrificial protection. In some applications, the zinc coating is applied in conjunction with annealing of the metal and these products are often referred to as galvannealed products.

The present method herein described is applicable not only to galvanized steel, but also 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 plus a small addition of silicon (added to at least improve coating adhesion to the steel substrate). Similarly, the present invention may be utilized with aluminized coatings. Additionally, the present method is applicable 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. Conversion to this alloy results in a non-spangle matte finish which makes the sheet suitable for painting after fabrication.

Most light gauge steel is galvanized by unwinding coils of cold rolled steel sheet and feeding the sheet continuously through a molten zinc bath at speeds up to 600 feet per minute. The specified coating thickness is controlled by air “knives” which blow off the excess coating deposited on the steel as it exits the molten zinc bath. The recommended minimum coating requirements for non-load bearing (non-structural) framing members is given with reference to ASTM A 653 (Standard Specification for Steel Sheet) ASTM C 645 (Standard Specification for Non-Structural Steel Framing Members) and A1003 (Standard Specification for Steel Sheet Carbon, Metallic- and Nonmetallic-Coated for Cold-Formed Framing Members). The durability of zinc based coatings is often a function of the amount of wetness (or dampness) of the installation location and the composition of the atmosphere. Water leakage, excessive humidity or condensation will damage any construction material over time, and it will also accelerate the corrosion of galvanized 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. 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 final common corrosion product to form with exposure to the atmosphere is zinc carbonate as zinc hydroxide reacts with carbon dioxide in the air.

In use, galvanized sheet steel is passivated and recoiled for shipment to the fabricator, where the steel sheets are cut and formed in the desired shapes of studs and other light gauge building components. As known in the industry, “white rust” or “white storage stain” is typically manifested as a bulky, white, powdery deposit that forms rapidly on the surface of galvanized coatings under certain conditions. These corrosion products will cause many deleterious 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. The most common condition in which white rust occurs is with galvanized products that are nested together, tightly packed, or when water can penetrate between the items and remain for extended periods of time. It is recognized that while “white rust” is relevant for galvanized steel, galvalume® oxidation products rust black while galvannealed products rust red or orange due at least in part to the iron filings in the coating.

There are a number of steps that can reduce the formation of white rust or other oxidation products. These include keeping the packed work dry, packing the items to permit air circulation between the surfaces, stacking the packed items to allow water to drain, and treating the surface with water repellent or barrier coatings to prevent moisture contact with the galvanized surface. This invention pertains to the last-mentioned solution.

Passivating a galvanized metal prevents the formation of zinc oxide or hydroxide. Typical passivating solutions utilize a dichromate or chromate composition. These compositions are typically applied to the metal via immersion. An untreated surface will show signs of corrosion after 0.5 hours of exposure to a neutral salt spray according to ASTM specification “B 117” and a thin chromate film produced by a dip procedure will show signs of corrosion after 12 to 75 hours of salt spray exposure (see ASTM specification “B 201”).

The prior art advantages of an applied chromation were so important that almost all galvanized metal building products have been chromate coated. The prior art is believed to include four chromations named after their colorations, which are each applied by treating (immersion, spraying, rolling) a zinc-plated surface with the corresponding aqueous chromate coating solution. Moreover yellow and green chromations for aluminum are known which are produced analogously. In any case, these are variously thick layers of substantially amorphous zinc/chromium oxide (or aluminum/chromium oxide) with non-stoichiometric compositions, certain water content, and inserted foreign ions. These are known and classified into method groups in accordance with German Industrial Standard (DIN) 50960, Part 1.

Colorless and Blue Chromations: The blue chromate layer has a thickness of up to 80 nm, is weakly blue in its inherent color and presents a golden, reddish, bluish, greenish or yellow iridescent coloring brought about by refraction of light in accordance with layer thicknesses. Very thin chromate layers lacking almost any inherent color are referred to as colorless chromations. The chromate coating solution may in either case consist of hexavalent as well as trivalent chromates and mixtures of both, moreover conducting salts and mineral acids. There are fluoride-containing and fluoride-free variants. Application of the chromate coating solutions is performed at room temperature. The corrosion protection of unmarred blue chromations amounts to 10-40 hours in the salt spray cabinet according to DIN 50021 SS until the first appearance of corrosion products.

Yellow Chromations: The yellow chromate layer has a thickness of about 0.25-1 μu, a golden yellow coloring, and frequently a strongly red-green iridescent coloring. The chromate coating solution substantially consists of hexavalent chromate, conducting salts and mineral acids dissolved in water. The yellow coloring is caused by the significant proportion (80-220 mg/m²) of hexavalent chromium which is inserted besides the trivalent chromium produced by reduction in the course of the layer formation reaction. Application of the chromate coating solutions is performed at room temperature. The corrosion protection of unmarred yellow chromations amounts to 100-200 hours in the salt spray cabinet according to DIN 50021 SS until the first appearance of corrosion products.

Olive Chromations: The typical olive chromate layer has a thickness of up to 1.5 μu and is opaquely olive green to olive brown. The chromate coating solution substantially consists of hexavalent chromate, conducting salts and mineral acids dissolved in water, in particular phosphates or phosphoric acid, and may also contain formates. Into the layer considerable amounts of chromium(VI) (300-400 mg/m²) are inserted. Application of the chromate coating solutions is performed at room temperature. The corrosion protection of unmarred olive chromations amounts to 200-400 hours in the salt spray cabinet according to DIN 50021 SS until the first appearance of corrosion products.

Black Chromations: The black chromate layer is fundamentally a yellow or olive chromation having colloidal silver inserted as a pigment. The chromate coating solutions have about the same composition as yellow or olive chromations and additionally contain silver ions. With a suitable composition of the chromate coating solution on zinc alloy layers such as Zn/Fe, Zn/Ni or Zn/Co, iron, nickel or cobalt oxide will be incorporated into the chromate layer as a black pigment so that silver is not required in these cases. Into the chromate layers considerable amounts of chromium(VI) are inserted, namely between 80 and 400 mg/m² depending on whether the basis is a yellow or olive chromation. Application of the chromate coating solutions is performed at room temperature. The corrosion protection of unmarred black chromations on zinc amounts to 50-150 hours in the salt spray cabinet according to DIN 50021 SS until the first appearance of corrosion products.

In accordance with the prior art, thick chromate layers affording high corrosion protection >100 hours in the salt spray cabinet according to DIN 50021 SS or ASTM B 117-73 until the appearance of first corrosion products according to DIN 50961 (June 1987) Chapter 10, in particular Chapter 10.2.1.2, in the absence of sealing or any other particular after treatment (DIN 50961, Chapter 9) may only be produced by treatment with dissolved, markedly toxic chromium(VI) compounds. Accordingly the chromate layers having the named requirements to corrosion protection still retain these markedly toxic and carcinogenic chromium(VI) compounds, which are, moreover, not entirely immobilized in the layer.

Reliance on hexavalent or trivalent chromium has many drawbacks. Hexavalent chromium is extremely toxic and as such more costly to work with. Hexavalent chromium will require special disposal procedures. Therefore, there is a need for a chromium-free coating for zinc surfaces (e.g., galvanized steel), particularly for galvanized steel studs which are used in non-structural applications where the thickness of the galvanized steel has been thinned so as to permit the fabrication of additional linear feet of product.

The present method herein described is applicable not only to galvanized steel, but also 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 plus a small addition of silicon (added to at least improve coating adhesion to the steel substrate). Similarly, the present invention may be utilized with aluminized coatings. Additionally, the present method is applicable 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. Conversion to this alloy results in a non-spangle matte finish which makes the sheet suitable for painting after fabrication.

The sequentially applied coatings (preferably without drying between coating application) of the present invention represent an improvement over commercially available corrosion-inhibiting pigments including compounds such as molybdates, phosphates, silicates, cyanamides, and borates that have no inherent oxidizing character that have been used as alternatives to chromate pigments. Coatings that contain these materials can effectively inhibit corrosion as barrier films until the coating is breached, as by a scratch or other flaw. Films or coating that do not contain oxidizing species can actually enhance corrosion on a surface after failure due to the effects of crevice corrosion.

SUMMARY OF THE INVENTION

A process is described for making a corrosion-resistant metal building component is disclosed comprising the steps of:

• • providing a steel sheet (preferably galvanized, but also which has been subjected to a galvalume® and/or aluminizing process and/or galvannealed processing) suitable for use in making metal building components having an initial thickness,
  • rolling the steel sheet by at least approximately 10% (up to approximately 65%) to form a thinner steel sheet,
  • forming said steel sheet into at least one reduced thickness metal building component,
  • applying a first permanganate coating composition wherein permanganate is the major active component by weight containing essentially no hexavalent or trivalent chromium to at least one surface of said building component, said coating composition preferably being an alkali earth metal permanganate wherein said alkali earth metal is selected from the group consisting of potassium, sodium, lithium, cesium and rubidium and applied at a pH of about from 9.0 to 2.0 inclusive, and
  • applying a second silicate sealant composition (preferably an alkali metal silicate sealant, wherein the alkali metal is selected from the group consisting of potassium, sodium, lithium, cesium and rubidium (preferably K)) such that the building component meets the ASTM C 645-08a or equivalent standard (or AISI specification) at a coating weight which approximately equal to or less than that specified by ASTM A 1003-G40.

In another embodiment, a process is disclosed for making a corrosion-resistant building component comprising the steps of:

• • providing a steel sheet suitable for use in making metal building components, said sheet having a surface comprising zinc or a zinc alloy, suitable for use in making metal building components having an initial thickness,
  • applying a first coating composition comprising a permanganate composition (preferably an alkali metal permanganate composition wherein said alkali metal of said permanganate composition is selected from the group consisting of potassium, sodium, lithium, rubidium and cesium) containing essentially no trivalent or hexavalent chromium to said building component, and wherein said and applied at a pH of about 9.0 to 2.0 inclusive;
  • applying a second coating composition comprising a silicate sealant composition to the building component (preferably an alkali metal silicate composition wherein said alkali metal of said permanganate composition is selected from the group consisting of potassium, sodium, lithium, rubidium and cesium);
  • reducing a thickness of said steel sheet by at least approximately 10% (optionally up to approximately 65%);
  • forming said reduced thickness steel sheet into at least one metal building component and wherein said building material meets the ASTM C 645-08a or equivalent standard (e.g., AISI General Provision Standard) at a coating weight which is approximately equal to or less than that specified by ASTM A 1003-G40.

In yet another embodiment, a process is disclosed for making a corrosion-resistant galvanized building component comprising the further step of cleaning the surface of the metal building component, which preferably is galvanized, but also which may have been subjected to a galvalume® and/or aluminizing process and/or galvannealed processing) with a cleaning agent, more preferably acidic, most preferably an acid selected from the group consisting of HCl, H₂SO₄, and H₃PO₄.

As used in this application, the silicate composition is preferably an alkali metal silicate composition, and most preferably a water-soluble silicate salt, which in the potassium form has a chemical formula of K₂SiO₃. The properties of liquid potassium silicates are dependent upon the SiO₂/K₂O weight ratios. The potassium silicates are similar to sodium silicates.

Silicates are converted to solid films or bonds by two methods: (1) evaporation of water (dehydration) or (2) chemical setting mechanism. These can be used separately or in combination. Chemical setting is often used to improve film moisture resistance, to reduce setting time, and to increase ultimate bond strength as needed.

As water evaporates, liquid silicates become progressively tackier and more viscous. As the dehydration continues, the silicate is brought into a final hardened condition. Soluble silicates are formed with higher SiO₂/Na₂O or SiO₂/K₂O ratios. The higher ratio silicates change from an almost water-like condition to a semi-solid state when only a small amount of water is evaporated. Lower ratio silicates, such as sodium silicates, dehydrate more slowly, because their higher alkali content creates a greater affinity for water. Flexibility increases in lower-ratio silicates because of their tendency to hold onto water more tenaciously than higher ratio silicates and thus have some degree of internal plasticization of the film by the residual water. Because the low-ratio silicates tend to retain more water, they are less brittle than the higher ratio silicates.

Silicate films are subject to moisture pick-up and degradation. However, this process can be slowed if water is completely removed from the silicate. Air drying alone usually is not adequate for films or bonds that will be exposed to weather or high moisture conditions. For such applications, heat is usually recommended. Initially, the temperature should be increased gradually to 200-210° F. to slowly remove excess water. Then final curing can be done at least 350-700° F. Heating too quickly may cause steam to form within the film, resulting in blistering or puffing when the steam is released. For some applications, where an insulated coating is desired, this intumescent property can be useful. Infrared and microwave heating have been used successfully for hardening silicate systems.

Silicate coatings and adhesives are inorganic aqueous polymers and they perform most effectively on hydrophilic, non-oily surfaces, where they achieve proper wetting and, hence, maximum adhesion. Generally, a thin continuous silicate film between the surfaces to be bonded provides optimum adhesion.

When coating or bonding metals and other similar rigid materials, the difference in coefficient of thermal expansion between silicate and the bonded surfaces is important. However, where temperatures are relatively constant and there is no mechanical strain, ultrathin silicate films which have been dehydrated by baking can hold permanently. A thin silicate film has greater elasticity and is more serviceable than a thick one for coating or bonding metal. A compatible surfactant in the amount of 0.05-0.1% by weight relative to the silicate will aid surface wetting. Good adhesion to metal often can be obtained after the surface has been thoroughly cleaned with alkali or acid or solvent or is degreased or sandblasted.

In a preferred embodiment, the building component after sequential coating with the two compositions (permanganate followed by silicate), will meet the ASTM C 645-08a standard at a coating weight which is equal to or less than that specified by ASTM A 1003-G 40.

The non-structural building component comprises at least zinc in a coating or alloy, preferably galvanized metal building stud. The initial steel thickness may range from 0.017 inch (17 mils) in thickness to 0.115 inch (115 mils) where the products are metal studs.

The rolling step may be done with a thickness reduction of at least 10%, more preferably 20% and most preferably at least 25% up to approximately a 65% reduction in thickness. Stated another way, galvanized steel sheet may reduced in thickness by at least 10%, more preferably 20%, and most preferably by 25% prior to the application of the conversion coating of the present process. However, reductions in thickness to as thin as 14 mils are within the scope of this invention.

In one embodiment of this invention, the rolling step may be performed after the sequential application of the coatings (permanganate followed by silicate) and the final product will meet the ASTM C 645-08a standard at a coating thickness which is equal to or less than that specified by ASTM A 1003 -G 40. The rolling step may be done with a thickness reduction of at least 10%, more preferably 20% and most preferably at least 25% up to approximately a 65% reduction in thickness.

The present method eliminates the need for hexavalent chromium compositions which, due to their toxicity, are being forced out of the workplace environment. Rather, the invention provides protective coatings which are sequentially applied which have compositions of permanganic acids and silicates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) through (c) are a series of photographic depictions of a galvannealed panel at its original 28 mils thickness after exposure to salt spray for 24, 48 and 75 hours for panels which have been coated with the permanganate composition of this invention at a concentration of 0% (no coating), 20% concentration (80% diluted), 50% concentration (50% diluted) and 80% concentration (20% diluted);

FIGS. 2(a) through (c) are a series similar to FIG. 1 wherein the galvannealed panel has been reduced in thickness from 28 mils to 24 mils (about a 15% reduction in thickness);

FIGS. 3(a) through (c) are a series similar to FIG. 2 wherein the galvannealed panel has been reduced in thickness from 28 mils to 22 mils (about a 20% reduction in thickness);

FIGS. 4(a) through (c) are a series similar to FIG. 3 wherein the galvannealed panel has been reduced in thickness from 28 mils to 21 mils (about a 25% reduction in thickness);

FIGS. 5(a) through (n) are a series of photographic depictions of steel panels at 24 hours of salt spray exposure and wherein FIG. 5(a) is a certified G-40 sample derived from flat steel used as a test comparative known to meet ASTM specification of G-40 for non-structural framing; FIG. 5(b) is a head end of slit coil used for formed Ultra® steel sample (as hereinbelow described) which had been galvannealed with A45 coating pursuant to ASTM A 653/A 653M-08 and reduced in thickness from 0.029″ to 0.0245″; FIG. 5(c) is a second sample of a tail end of slit coil used for formed Ultra® steel sample; FIG. 5(d) is a head end of slit coil used for formed flat steel sample which had been galvannealed with A45 coating (total coating weight of 0.316-45 g/m² and reduced in thickness from 0.029″ to 0.0245″; FIG. 5(e) is a second sample of a tail end of slit coil used for formed flat steel sample similarly reduced in thickness; FIG. 5(f) is an additional tail end of slit coil sample used for formed flat steel sample; FIG. 5(g) is a flat steel sample of cold worked with Ultra® steel process before forming into a stud (head of coil); FIG. 5(h) is a second sample of flat cold worked with Ultra® steel process before forming into a stud (head of coil); FIG. 5(i) is a flat steel sample of cold worked with Ultra® steel process before forming into a stud (tail of coil); FIG. 5(j) is a second sample of flat cold worked with Ultra® steel process before forming into stud (tail of coil); FIG. 5(k) is a sample of formed Ultra® steel stud (head of coil); FIG. 5(l) is a sample of formed Ultra® steel stud (tail of coil); FIG. 5(m) is a sample of formed flat steel stud (head of coil); and FIG. 5(n) is a sample of formed flat steel stud (tail of coil);

FIGS. 6(a) through (n) are a series of photographic depictions of steel panels at 48 hours of salt spray exposure using the series of panels of FIG. 5.

FIGS. 7(a) through (n) are a series of photographic depictions of steel panels at 75 hours of salt spray exposure using the series of panels of FIG. 5;

FIGS. 8(a) through (n) are a series of photographic depictions of steel panels at 96 hours of salt spray exposure using the series of panels of FIG. 5;

FIGS. 9(a) and 9(b) are photographic depictions of galvannealed steel panels which were treated by a sequential application of a 0.8% permanganate solution applied in a bath at 140° F. for approximately 4 seconds followed by 3.0% silicate solution at a bath temperature of 80° F. for approximately 4 seconds followed by a cold reduction in thickness from 0.295″ to 0.244″ in which FIG. 9(a) was bent approximately 60-75° after treatment and each panel was subjected to a 75 hour salt spray test in accordance with ASTM B-117-07a;

FIGS. 10(a) and 10(b) are photographic depictions of galvannealed steel panels, in which the panel in FIG. 10(b) was treated by a sequential combination of a 0.8% permanganate solution applied in a bath at 140° F. for approximately 4 seconds followed by 3.0% silicate solution at a bath temperature of 80° F. for approximately 4 seconds followed by a cold reduction in thickness from 0.028″ to 0.021″, then subject to a 75 hour salt spray test in accordance with ASTM B-117-07a while FIG. 10(a) illustrates a steel panel which was not subject to any pretreatment and subject to a 75 hour salt spray test in accordance with ASTM B-117-07a;

FIGS. 11(a) and 11(b) are photographic depictions of the implications of drying between the sequential application of coatings, in which the galvannealed steel panel in FIG. 11(a) was treated first with a 10% SafeGard™ CC-3400 permanganate solution applied in a bath at 140° F. for approximately 4 seconds followed 24 hours later by the application of a 10% SafeGard™ CC-4000 silicate solution at a bath temperature of 80° F. for approximately 4 seconds followed by a cold reduction in thickness from 0.295″ to 0.244″, then subject to a 36 hour salt spray test in accordance with ASTM B-117-07a and wherein FIG. 11(b) was treated in a manner similar to FIG. 11(a) then subject to a 72 hour salt spray test in accordance with ASTM B-117-07a; and

FIG. 12 is a photographic depiction initially treated using a 0.8% permanganate solution at a bath temperature of 140° F. for about 4 seconds followed by a 2.9% silicate solution at a bath temperature of 80° F. for about 4 seconds followed by a cold reduction in thickness from 0.030″ to 0.016″, a reduction of approximately 47% and illustrating less than 5% red rust after 140 hours of exposure in salt spray.

DETAILED DESCRIPTION OF THE DISCLOSURE

As used in this application, the term “zinc substrate” is intended to cover both zinc parts, and parts that are zinc-plated, particularly metal products which have been galvanized, galvannealed, etc., as discussed previously. The terms “treating” or “coating” are intended to cover dipping, immersion, spraying alone or in combination with a zinc substrate. The term “containing essentially no hexavalent or trivalent chromium cations or chromate anions” should be interpreted to mean that these chemical species are essentially not present in the coating compositions, although some minimal amounts may be present as impurities. “Conversion coating” is a well-known term of the art and refers to the replacement of native oxide on the surface of a metal by the controlled chemical formation of a film or coating. The term “Ultra®” steel is a process of work hardening cold steel with work rolls to alter the surface characteristics. Through this process, the effective thickness of the material is increased to that of the original thickness plus the depth of the ribbing. Patents pertinent to this process are U.S. Pat. Nos. 6,183,879 and 5,689,990 as well as Canadian Patent No. 2,149,914.

The term “G-40” means a hot-dipped galvanized coating which complies with ASTM C 645 Rev. A Standard Specification for non-structural steel framing members and C645, Specification for non-load (axial) bearing steel studs, runners (track) and rigid furring channels for screw application of gypsum board. As known in the industry, the Ultra® steel process creates many radii and peaks and valleys in the steel. Any coating must be strong and flexible so that it does not crack or peel or flake off. As known in the industry, the Ultra® steel process is actually done in a separate process that is located in front of the roll former. Flat steel comes off an uncoiler and goes through the Ultra® process and then is roll formed in a regular roll former. In the series of Figures illustrated in FIG. 5, essentially every possible sample or position in the Ultra® steel process was tested. The terms “approximately” and “about” mean within experimental error pertinent to the steel industry.

Referring now to the drawings, a method described by making light gauge building galvanized metal products, such as metal studs, which a thinned corrosion-resistant galvanized stud (preferably galvanized steel) including the steps of: (a) rolling a roll of galvanized steel by at least 10% (e.g. 20%, or 25%); (b) forming said roll into at least one metallic building component; (c) applying a permanganate composition (preferably an aqueous alkali metal) to at least one surface of the building component (at a concentration ranging from 50% to full strength, 100%) containing essentially no hexavalent or trivalent chromium ions, wherein the preferred alkali metal permanganate composition has an alkali metal selected from the group consisting of potassium, sodium, lithium, rubidium and cesium and is applied at a pH of about from 9.0 to 2.0 inclusive, such that the building component meets the ASTM B 117-73 test and provides a corrosion resistance similar to a like building component made of the initial thickness without the rolling step, (more preferably within 5%) of said building component which had not been reduced in thickness. The method also includes the step of (d) applying an silicate coating (preferably an inorganic alkali metal silicate) to seal said permanganate composition on said at least one side of said building component and wherein said alkali metal is selected from the same group previously identified. The silicate coating may be applied while the permanganate coating is drying.

Manganese Source:

Manganese is one non-toxic, non-regulated metal which has been considered as a chromium or lead replacement. Manganese (like chromium or lead) exhibits more than one oxidation state (Mn⁺², Mn⁺³, and Mn⁺⁴). In addition, the oxidation-reduction potential is comparable to that of Cr(VI) or Pb(IV) in acidic solutions. For example, in acid solution:

Mn⁺³+e⁻→Mn⁺²+1.49 V

Mn⁺⁴+e⁻→Mn⁺³+1.65 V

Cr⁺⁶+3e⁻→Cr⁺³+1.36 V

Pb⁺⁴+2e⁻→Pb⁺²+1.70 V

The Mn(IV) and Mn(III) ions are very good oxidizing species with oxidation-reduction potentials of +1.65 V and +1.49 V (at pH=0), respectively. The hydroxyl and oxygen liberated from water when Mn(IV) or Mn(III) is reduced will oxidize nearby bare metal. This results in a passivated metal surface if sufficient oxygen is released. The potential required to reduce tetravalent or trivalent manganese to divalent manganese is only 0.29 v or 0.13 volts greater than that needed to add three electrons to reduce Cr(VI) to trivalent chromium, Cr(III). Although neither Mn(IV) or Mn(III) match Pb(IV) in terms of redox potential, neither is significantly lower and so comparable passivation of metal is achieved. Mn(II) is formed during corrosion inhibition by the oxidation of base metal in the presence of Mn(IV) or Mn(III) and water. Mn(II) is similar to Cr(III) in that neither is particularly effective as redox-based corrosion inhibitors.

Manganese sources can be nearly any water, alcohol, or hydrocarbon soluble manganese compound in which the manganese is in the divalent, trivalent, tetravalent, or heptavalent oxidation state. Water-soluble precursors are typically used. Inorganic divalent manganese precursor compounds include, but are not limited to, manganese nitrate, manganese sulfate, manganese perchlorate, manganese chloride, manganese fluoride, manganese bromide, manganese iodide, manganese bromate, manganese chlorate, and complex fluorides such as manganese fluosilicate, manganese fluotitanate, manganese fluozirconate, manganese fluoborate, and manganese fluoaluminate. Organometallic divalent manganese precursor compounds include, but are not limited to, manganese formate, manganese acetate, manganese propionate, manganese butyrate, manganese valerate, manganese benzoate, manganese glycolate, manganese lactate, manganese tartronate, manganese malate, manganese tartrate, manganese citrate, manganese benzenesulfonate, manganese thiocyanate, and manganese acetylacetonate.

The manganese source may be a compound with the manganese in the heptavalent oxidation state (permanganates). Heptavalent manganese precursors include, but are not limited to: potassium permanganate, sodium permanganate, lithium permanganate, ammonium permanganate, magnesium permanganate, calcium permanganate, strontium permanganate, barium permanganate, zinc permanganate, ferric permanganate, nickel permanganate, copper permanganate, cobalt permanganate, cerium permanganate, lanthanum permanganate, yttrium permanganate, and aluminum permanganate.

Oxidation Source:

If Mn(III) and/or Mn(IV) compounds are produced via precipitation, an oxidizing species will typically be included in the synthesis solution if divalent manganese compounds are used as precursors for Mn(III) and Mn(IV). Additional amounts of oxidizer may be added to help control and maintain a desired amount of Mn(III)/Mn(IV) in the solution by reoxidizing Mn(III)/Mn(IV) that has become reduced. The trivalent manganese ion is an exceptionally good oxidizing species with an oxidation-reduction potential of +1.49 V at a pH of 0 for the Mn(III)−Mn(II) couple in water, and the tetravalent manganese ion is an even stronger oxidizing species, with a redox potential of +1.65 V under similar conditions. Strong oxidizers are required because of the high potential of their redox reaction. The oxidizers may be gases, liquids, or solids. Solid oxidizers are typically used for this application due to ease of handling and reagent measurement. Other starting materials (manganese source and stabilizer source) will also frequently be solids. Liquid oxidizers may be used, but handling and accurate process metering have proven difficult. Gaseous oxidizers may be the most cost effective and chemically efficient on a large scale, but are also the most problematic due to handling and venting concerns.

Oxidizers suited for the purpose of producing and maintaining the manganese ion in the trivalent or tetravalent charge state include but are not restricted to peroxides and peroxo compounds (including superoxides, persulfates, perborates, pernitrates, perphosphates, percarbonates, persilicates, peraluminates, pertitanates, perzirconates, permolybdates, pertungstates, pervanadates, and organic peroxyacid derivatives), ozone, hypochlorites, chlorates, perchlorates, nitrates, nitrites, vanadates, iodates, hypobromites, chlorites, bromates, permanganates, periodates, and dissolved gases such as oxygen, fluorine, or chlorine. Inorganic and organic derivatives of these compounds may be used. Typical oxidizers for this use are peroxides, persulfates, perbenzoates, periodates, bromates, hypochlorites, gaseous dissolved oxygen, and even the oxygen content of air. In general, any inorganic, organic, or combination species with an oxidation potential of +1.0 V or greater (at a pH of 1) will be capable of oxidizing divalent manganese to the trivalent or tetravalent oxidation state.

Valence Stabilizers:

In some embodiments (although optional), a valence stabilizer is optionally added to establish an electrostatic barrier layer around the cation-stabilizer compound in aqueous solution. The valence stabilizer also provides a timed release of the inhibitor ion, as well as ensuring that the oxidative strength will not be reduced too rapidly. Thus, a valence stabilizer is preferred for the trivalent or tetravalent manganese ion because of its reactivity and to produce controlled trivalent or tetravalent manganese solubilities. Stabilization helps avoid reduction and premature conversion of the ion to the divalent charge-state during compound formation, carrier incorporation, application, and exposure to a corrosive environment. Stabilizers control solubility, mobility, ion exchange, binder compatibility, and the degree of surface wetting. The exact solubility of this compound may be modified by species released into solution by the dissolving metal surface or by the subsequent addition of solubility control agents. A variety of inorganic and organic stabilizers are available that can serve to control solubility. The stabilizer may also act as an ion-exchange host and/or trap for alkali or halide ions in solution.

Any material in the synthesis bath which complexes with trivalent or tetravalent manganese (whether inorganic or organic) and which results in the formation of a Mn(III) or Mn(IV) containing compound that exhibit suitable solubility can serve as a valence stabilizer for trivalent or tetravalent manganese. The assembly of a protective shell around the highly charged Mn(III) or Mn(IV) and its associated oxygen and hydroxyl species can help control the rate at which the manganese is reduced and its oxygen is released. Proper selection of materials for forming the protective shell will allow solubility tailoring of the entire assembly to its intended application environment. Valence stabilizers described above may need some type of additional solubility control to increase the performance of the trivalent or tetravalent manganese-valence stabilizer compound. Additional solubility control agents may be in the form of inorganic or organic compounds. Their use is optional rather than a requirement for effective valence stabilization and solubility control.

Inorganic valence stabilizers are formed around the Mn(III) or Mn(IV) ion by “polymerizing” in synthesis solution. Inorganic stabilizers include molybdates (Mo⁺⁶, Mo⁺⁵, or Mo⁺⁴, for example [Mn⁺⁴Mo₉O₃₂]⁶⁻ and [Mn⁺⁴Mo₁₂O₄₀]⁴⁻), tungstates (W⁺⁶, W⁺⁵, or W⁺⁴, for example [Mn⁺⁴W₁₂O₄₀]⁴⁻ and [Mn⁺³₂W₂₂O₇₄]¹⁰⁻), vanadates (V⁺⁵ and V⁺⁴, for example [Mn⁺⁴V₁₃O₃₈]⁷⁻ and [Mn⁺⁴V₁₁O₃₂]⁵⁻), niobates (Nb⁺⁵ and Nb⁺⁴, for example [Mn⁺⁴Nb₁₂O₃₈]¹²⁻), tantalates (Ta⁺⁵ and Ta⁺⁴, for example [Mn⁺⁴Ta₁₂O₃₈]¹²⁻), tellurates (Te⁺⁶ and Te⁺⁴, for example [Mn⁺⁴Te₃O₁₈]¹⁴⁻), periodates (I^{30 7}, for example [Mn⁺⁴]₃O₁₈]¹¹⁻), iodates (I⁺⁵, for example [Mn⁺⁴I₆O₁₈]²⁻), antimonates (Sb⁺⁵ and Sb⁺³), stannates (Sn⁺⁴), sulfates (S⁺⁶, such as manganese spinels [Mn⁺³(SO₄)₂]¹⁻), and polyphosphates (P⁺⁵, for example [Mn⁺³P₃O₁₀]²⁻ and [Mn⁺³P₂O₇]¹⁻). Many of these inorganics form octahedral and square pyramidal heteropolymetallate structures on precipitation from solution. For example, tellurate ions begin to polymerize near pH 5 in water and will complex with Mn(III) or Mn(IV) ions in basic solution pH's. Therefore, as the pH is raised in the pigment synthesis bath, the tellurate ion polymerizes to polymorphs, which then complex the Mn(II) or Mn(IV) ion.

The most notable valence stabilizer for low and insoluble Mn(III) and Mn(IV) is oxygen (O), as evidenced by the natural stability of such compounds as MnO₂, Mn₃O₄, Mn₂O₃ and MnOOH, all of which contain Mn(III) and/or Mn(IV) ions. In instances where oxygen is used as a valence stabilizer for Mn(III) or Mn(IV), differences in addendum cations (i.e., Ca⁺² in CaMn₂O₄ or Zn⁺² in ZnMn₂O₄) are observed to alter the solubility of the formed compound, and its performance as a corrosion inhibitor in a given binder system.

Additional valence stabilizers silicates (Si⁺⁴, for example [Mn⁺³Si₂O₆]¹⁻), borates (B⁺³, for example Mn⁺³₂B₄O₉), phosphates (P⁺⁵, for example Mn⁺³PO₄), titanates (Ti⁺⁴), zirconates (Zr⁺⁴), and aluminates (Al⁺³). These compounds can also form octahedral or square pyramids, but have a higher tendency to form chain-like structures during calcining or firing. Combinations of these materials, such as phosphosilicates, aluminosilicates, or borosilicates may also function as valence stabilizers for Mn(III) and Mn(IV) compounds.

Surface Activators:

In some embodiments, (although optional), a surface activator is added to the first coating composition in order to assist the formation of coatings at a commercially useful rate. This typically is achieved in the presence of an ion which performs an oxidizing function and enhances the rate of reaction. Compounds providing such ions are often referred to as activators, which typically supply anions such as sulfate, nitrate, sulfamate, fluoride, acetate and formate, usually as salts of sodium or other alkali metals. Such traditional activators can be included in the bath at concentrations for each between about 0.1 gm/l and 5 gm/l.

Suitable for use in combination with or in place of these traditional activators are the class of organic activating agents according to this invention, which can be considered to be accelerating activators that are capable of further enhancing the quality and the rate of coating formation beyond that provided by the traditional activators. These organic activating agents, in addition, operate in the nature of a complexing agent in order to assist in keeping the coating-forming agents in solution. Such organic compounds typically take the form of carboxylic acids or their bath-soluble derivatives, usually salts, which generally have functional groups in addition to those provided by monocarboxylic acids or derivatives such as acetates or formates. Included are compounds having between about 2 and 12 carbon atoms that are polyhydroxy carboxylic acid compounds, for example heptagluconate, or polycarboxylic acid compounds such as oxalic acid, its derivatives, analogues or homologues including the oxalate, malonate, and succinate groups. The compounds may be of the structure: XOOC(CH₂)_nCOOX, wherein n is 0 or 1, and X is hydrogen, alkali metal, ammonium, or an alkali metal-transition element complex. Organic activating agents are most conveniently provided as potassium-titanium complex salts or alkali metal carboxylic acid salts. Bath concentrations range as high as 7.5 gm/l, especially for compounds having polycarboxylic acid groups such as heptagluconate, and may be between about 0.25 and about 4.5 gm/l of the total bath volume for the polycarboxylic or oxalic acid type of compounds.

Buffers:

While optional, certain of the activators, especially those that have multiple carboxylic acid groups, can be present in the bath as a buffer to maintain a desired bath pH range while passivating large surface areas, it is often desirable to include a separate buffering agent as such within the composition. To facilitate handling of the total bath ingredient composition before incorporation into the bath, the buffering agent should be powdered, granulated, or the like and readily dissolved in an aqueous acidic bath. Boric acid is an exemplary buffering agent. Bath concentrations generally do not have to exceed about 5 gm/l, and may be within the range of about 0.25 to about 2.0 gm/l of bath.

As shown in the drawings is a series of rolled panels which have been exposed to various numbers of hours of salt spray exposure. The test panels have been reduced in thickness from a base thickness of about 28 mils to about 24 mils, to about 22 mils, or to about 21 mils, and coated with the alkali metal permanganate composition at a concentration of 0% (no coating); about 20% concentration; about 50% concentration; and about 80% concentration of undiluted composition.

In some embodiments, the process includes a method for the coating of zinc or zinc coated (e.g., galvanized or aluminized or subjected to a galvalume® process or galvannealed processing) articles with a composition containing an alkali metal permanganate composition at a pH of about 9.0 to 2.0. The passified zinc or zinc coated article has a chromium-free permanganate protective conversion coating. As used in this disclosure, a conversion coating is one that reacts quickly with zinc and is more than a barrier coating, but performs as a conductive conversion coating. Without being held to one theory of operation, it is believed that at the molecular level, the conversion coating reacts quickly with zinc forming either a chemical bond, or an associative bond, thereby rendering it more in the nature of a conversion coating, rather than a simply barrier coating.

The alkali metal in the alkali metal permanganate composition is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), cesium (Cs) and rubidium (Rb). The preferred alkali metal is potassium. The concentration of permanganate necessary to produce an acceptable coating is a minimum of 0.001 moles per liter. With potassium permanganate, this is essentially about 0.16 grams per liter. The maximum concentration of the permanganate composition is the saturation point of the salt being used. The solution may have a temperature ranging from about the freezing point of the solution to its boiling point. The preferred temperature range is 60° F. to 180° F. As the temperature of the solution rises, less immersion time is required to form a corrosion resistant coating on the surface of the zinc. The immersion time for preparing a corrosion-resistant coating on a zinc surface is about 2 seconds to 3 minutes at 80° F.-160° F. Preferred immersion times are approximately 4-5 seconds at 140° F.

An alternative to immersion coating is spraying of the permanganate composition. The applicable parameters will have to be adjusted as is known within the skill in the art to make these adjustments to the process parameters.

Once again, without being held to one theory of operation, it is believed that at the molecular level, the conversion coating reacts quickly with zinc substrate forming either a chemical bond, or an associative bond, thereby rendering it more in the nature of a conversion coating, rather than a simply barrier coating, and thereby modifies the surface energy of the zinc substrate. The inclusion of a surfactant impacts the ability to further wet the surface of the zinc substrate. It is believed that the manganese, which is similar in size to chromium, forms various molecular complexes at the surface of the zinc substrate, which upon the sequential application of a silicate coating (preferably without drying interposed therebetween) will further result in a concentration gradient coating in which the permanganate coating and silicate coating form an interfacial bond.

The invention of the application will be better understood by reference to the following examples which serve to illustrate but not to limit the present invention.

EXAMPLE #1

A series of galvannealed panels are conversion coated prepared in accord with the following steps. An alkaline phosphate cleaner (e.g., Sanchem™ 500) is used to clean any residual oils, dirt, or foreign matter from the coating surface, leaving a fresh surface to conversion coat. An acid rise is applied to give the surface a mild acidic character so that it is receptive to the reaction between the zinc and the potassium permanganate moiety (e.g., Safegard™ CC-3400). In a further embodiment, the pH of the acid solution will range from 2 to 9, preferably 3 to 8. The permanganate moiety composition (e.g., Safegard™ CC-3400) is applied to the surface of a series of thinned panels ranging in thickness from 0.028″ (28 mils) to 0.021″ (21 mils) using permanganate concentrations ranging from 0% (no conversion coating) to 80% (20% diluted) conversion coating as compared to an undiluted concentration. The panels were thinned using well-known thinning methodology, e.g., counter-rotating drums. The panels were lastly coated with an inorganic water glass sealant coating (Safegard™ CC-4000) by immersion in a potassium silicate solution (8.3% K₂O and 20.8% SiO₂ with a SiO₂/K₂O ratio of about 2.5, 29.1% solids with viscosity of 40 centipoises) at room temperature, to as high as 195-212° F. for up to one minute. The panel was removed from the silicate solution and rinsed with deionized water. The panel was then placed in a salt-fog at 95° F., according to ASTM Standard B-117. After 75 hours of exposure, the panel showed only minor pitting. The panels (about 6″×12″) were subjected to continuous salt spray for 24 to 75 hours in accordance with ASTM B 117-73, photographic evidence of the results being illustrated in FIGS. 1-4(a) through (c).

FIGS. 1(a) through 1(c) illustrate the control experiment in which the galvanized panel was not thinned prior to the application of the permanganate moiety which was added at a concentration ranging from 0% (no permanganate application) to 20% (80% diluted) permanganate application to 50% (50% diluted) permanganate application to 80% (20% diluted) permanganate application.

FIGS. 2(a) through 2(c) illustrate the impact of an approximate 15% reduction in thickness of the panel from its initial 28 mil thickness and associated impact on corrosion resistance. Only the panels to which the application of at least 50% permanganate moiety has been added meet the ASTM specification.

FIGS. 3(a) through 3(c) illustrate the further impact of an approximate 20% reduction in thickness of the panel from its initial 28 mil thickness and associated impact on corrosion resistance. In a manner similar to that described for FIG. 2, only the panels to which the application of at least 50% permanganate moiety has been applied meet the ASTM specification.

FIGS. 4(a) through 4(c) illustrate the further impact of an approximate 25% reduction in thickness of the panel from its initial 28 mil thickness and associated impact on corrosion resistance. In a manner similar to that described for FIGS. 2 and 3, only the panels to which the application of at least 50% permanganate moiety has been applied meet the ASTM specification.

EXAMPLE #2

As illustrated in FIGS. 5(a) through FIGS. 8(n), a series of photographic depictions of steel panels are provided, ranging in time exposed to a salt spray exposure from 24 hours to 96 hours. The first panel illustrated in (a) is a certified G-40 sample derived from flat steel used as a test comparative known to meet ASTM specification of G-40 for non-structural framing. The second panel illustrated in (b) is a head end of slit coil used for formed Ultra® steel sample which had been galvannealed with A45 coating and reduced in thickness from 0.029″ to 0.0245″. The third panel illustrated in (c) is a second sample of a tail end of slit coil used for formed Ultra® steel sample. The fourth panel illustrated in (d) is a head end of slit coil used for formed flat steel sample which had been galvannealed with A45 coating and reduced in thickness from 0.029″ to 0.0245″. The fifth panel illustrated in (e) is a second sample of a tail end of slit coil used for formed flat steel sample. The sixth panel illustrated in (f) is an additional tail end of slit coil sample used for formed flat steel sample. The seventh panel illustrated in (g) is a flat steel sample of cold worked with Ultra® steel process before forming into a stud (head of coil). The eighth panel illustrated in (h) is a second sample of flat cold worked with Ultra® steel process before forming into a stud (head of coil). The ninth panel illustrated in (i) is a flat steel sample of cold worked with Ultra® steel process before forming into a stud (tail of coil). The tenth panel illustrated in (j) is a second sample of flat cold worked with Ultra® steel process before forming into stud (tail of coil). The eleventh panel illustrated in (k) is a sample of formed Ultra® steel stud (head of coil). The twelfth panel illustrated in (l) is a sample of formed Ultra® steel stud (tail of coil). The thirteenth panel illustrated in (m) is a sample of formed flat steel stud (head of coil) and the fourteenth panel illustrated in (n) is a sample of formed flat steel stud (tail of coil).

The panels shown in FIGS. 7(g) through 7(l) had about 5% red rust at 75 hours of salt spray exposure. These panels continued to corrode as illustrated in FIGS. 8(g) through 8(l) with approximately 25% red rust at 96 hours of salt spray exposure.

The G-40 certified sample is G-40 from a piece of flat steel used to gauge the performance of a test sample to a know sample and a sample that meets the ASTM specification of G-40 or equivalent for non-structural framing. For the panels designated as the second panel through the fourteenth panel above, the panels were cold reduced to a 45A coated galvannealed coil from 0.0296″ to 0.0245″ (Ultra® steel typically least thickness). Cold working stresses and bends and embosses the steel to a large degree. By subjecting the coating to the “Ultra® steel process”, processing which is more rigorous than typical processing such as would occur in regular roll forming, the beneficial results of this invention are achievable in a less rigorous environment. As the above testing indicates, the process will stand up to the cold reduction and will stand up to the Ultra® steel process and then can be roll-formed into a C-stud.

As mentioned previously, and as used in this application, the term “Ultra® steel process” is that which is discussed and described in U.S. Pat. Nos. 6,183,879 and 5,689,990. This process provides a method of producing lightweight thin metal sheet that is flexure resistant, in which the method includes passing flexible sheet material of relatively thin gauge between two rolls each having teeth, each tooth having four flanks, each flank facing in a direction between an axial direction and a circumferential direction, the teeth having rounded corners, the rolls being arranged so that the teeth of one roll extend into gaps between teeth on the other, the rolls being rotated at substantially the same speed about generally parallel axes to form rows of projections on both faces of the sheet passed therethrough without damage to the surface material of the sheet.

When flexible sheet material of relatively thin gauge is passed in the nip between rollers having teeth, the sheet surface can be damaged so that fragments of the sheet come away and accumulate in the spaces between teeth. The fragments then cause further damage to the sheet material which is following behind. The teeth may be rounded in two areas: at the corners of the peak and at the peak. By rounding the corners of the teeth, typically both at the peak and the root thereof, it is possible to cause the sheet material to flow in the clearance between opposed teeth to become more rigid with little or no thinning and without spalling of the sheet material or of the teeth. As a result the rolls suffer less wear and need less cleaning and last longer; the sheet material is rigid and yet lightweight.

The corners of the teeth may be rounded in the range from about 0.05 to 15 mm, and may be in the range of 0.15 to about 4 mm. The extent of radius is related to the size of the tooth which in turn relates to the gauge of the sheet being processed. Where the tooth is relatively small for use with thin gauge sheet, the corner radius is about 0.2 and the peak may be about 1 mil; where the tooth is relatively large for thicker gauge sheet the corner radius is about 1 mil and the peak about 2.5. The ratio of the corner radius to the peak radius thus decreases with increasing size of the tooth. It has been observed that outside these parameters the tooth tends to have corners which can cut into the surface of the sheet material being treated. By virtue of the rounding of the corners and the peaks of the teeth there is no risk that a sheet will occur. Such cracking releases fragments of the sheet material which tend to foul the space between the teeth of the roll which risk breaking the integrity of the surface of the sheet following on behind. In practicing the method of the invention, not only does the sheet surface maintain its integrity but the formed sheet undergoes an enhanced stiffening effect as a result of which the mechanical strength, e.g. rigidity of the sheet is enhanced. The method may even be applied to a thin flexible sheet carrying a coating, e.g. a paint or like film without risk that it will be harmed.

The Ultra® process also provides a set of rolls, rows of teeth being present on the outer surface of the rolls, each tooth having four flanks of involute form, and each flank facing in a direction between an axial direction and a circumferential direction, the corners of the teeth being radiused as defined.

The Ultra® process also provides sheet material having projections on both of its surfaces, a corresponding depression being on the surface opposite each projection, the relative positions of the projections and depressions being such that lines drawn on the surface are non-linear, the sides of the projections lying a line extending between a longitudinal direction and a lateral direction, the overall distance between adjacent projections and depressions being within the range of 2 μm to 5 mm and in the range of four to ten times the gauge, wherein the corners of the projections and depressions are radiused.

The embossing which is described in U.S. Pat. No. 5,689,990 is also applicable to the coatings of this method. As discussed in the '990 patent, sheet material is used having on both of its faces a plurality of rows of projections, each projection having been formed by deforming the sheet material locally to leave a corresponding depression at the opposite face of the material. For example there extends in a first direction, rows of alternating projections and depressions and straight lines which can be drawn on a surface of the material between adjacent ones of these rows. The projections and depressions also form rows which extend in a second direction substantially perpendicular to the first direction and between which further straight lines can be drawn on the surface of the material. Along these straight lines, the overall thickness of the material is substantially equal to the thickness of the plain sheet material from which the material is formed and the material can bend along these lines considerably more easily than it can bend along a centerline of one of the rows. The overall thickness of the sheet material is approximately twelve times the thickness at a point where the thickness has a maximum value, and which thickness is the gauge of the material.

According to one aspect of the '990 disclosure, sheet material is provided wherein the relative positions of the projections and depressions are such that lines drawn on a surface of the material between adjacent rows of projections and depressions are not rectilinear. The overall thickness of the sheet material as viewed in any cross-section in a plane which is generally perpendicular to the sheet material is substantially greater than the gauge of the material. In cross section, sheet material is undulatory and there is no place where the material can be cut along a straight line and the resulting cross section of the material will be rectilinear.

The overall thickness of the sheet material is determined by the heights of the projections at both faces of the material. The height of projections which is sufficient to ensure that lines drawn on a surface of the material between adjacent rows of projections and depressions are not rectilinear depends upon the pitch of the projections and depressions in the rows. It was found that an overall thickness of twice the gauge of the sheet material is generally a suitable thickness and sufficient to avoid rectilinear lines on the surface of the material. The overall thickness may not be more than four times the gauge of the material, or may not exceed more than three times the gauge of the material.

By limiting the overall thickness of the material to a value which is just sufficiently great to avoid the presence of rectilinear lines on either surface of the material, it was found that it was possible to avoid reducing the overall length of the sheet material significantly during formation of the projections. The spacing between the crests of adjacent projections at each face of the material may exceed three times the dimension of each of those crests measured in the same direction as said spacing.

The projections at each face can be assigned to a variety of rows, for example rows extending along the material, rows extending across the material at right angles and rows extending across the material obliquely to the length of the material. In the row with the smallest pitch, the pitch (called herein the minimum pitch) may be within the range 2 mm to 5 mm. The pitch may be within the range four to ten times the gauge of the material. It was found that a pitch may be approximately six times the gauge of the material, in a case where the overall thickness is approximately twice the gauge, avoids the presence of rectilinear lines on either surface of the material and thereby achieves a substantial improvement in bending strength, as compared with the plain sheet material from which the material embodying the invention is formed, without any significant increase in the mass of material per superficial unit of area. In the case where elongated sheet material is used, each projection may be a plurality of flanks facing in respective directions which are neither along the material nor perpendicular to the length of the material.

EXAMPLE #3

As illustrated in FIGS. 9(a) and 9(b), two galvanized test panels were sequentially treated with Safegard™ CC-3400 followed approximately 10 minutes later by Safegard™ CC-4000 with one panel subsequently being bent to 60-75° and then subjected to a 75 hour salt spray test in accordance with ASTM B-117-07a. The experimental tests indicate that the coatings maintained their integrity even after the application of a severe bending stress.

EXAMPLE #4

As illustrated in FIGS. 10(a) and 10(b), two galvannealed steel panels were subject to a 75 hour salt spray test in which the panel in FIG. 10(b) was treated by a sequential combination of a 0.8% permanganate solution at a bath temperature of 140° F. for about 4 seconds followed by a 2.9% silicate solution at a bath temperature of 80° F. for about 4 seconds followed by a cold reduction in thickness from 0.029″ to 0.021″, while FIG. 10(a) illustrates a steel panel which was not subject to any pretreatment and subject to a 75 hour salt spray test in accordance with ASTM B-117-07a. The value of the coating is evident from the large formation of rust on the untreated panel illustrated in FIG. 10a which corroded badly after just 24 hours.

EXAMPLE #5

As illustrated in FIGS. 11(a) and 11(b), the impact of drying time between the sequential application of the coating with permanganate solution and silicate solution is shown. By lowering the time between coats, a synergistic effect is clearly shown. Applying the two coatings with a 24 hour separation between resulted in a panel which did not pass 36 hours of salt spray testing. However, applying the same two coatings with a 10 minute separation between, resulted in a panel which passed 72 hours of salt spray testing. Without being held to any one theory of operation, it is believed that a chemical bond is formed between the metallic permanganate coating and the silicate coating.

EXAMPLE #6 (COMPARATIVE EXAMPLE)

A series of silicates were coated onto zinc plated steel for salt spray corrosion resistance. In this experiment, a six inch by six inch steel panel with a 0.001 inch thick film of electrodeposited zinc was cleaned in a strong alkaline cleaner at 150° F., rinsed in deionized water, placed in a 1% nitric acid solution for 30 seconds (to remove unwanted metal oxides), rinsed in deionized water for a second time, and then placed in a 1% potassium silicate solution for 60 seconds at 140° F., removed, rinsed and then allowed to dry. The panel was allowed to sit for one day, then placed in a neutral salt spray cabinet operated in accordance with ASTM specification B 117. Red rust formed within eight hours.

EXAMPLE #7 (COMPARATIVE EXAMPLE)

The experimental procedure outlined in Example #6 was repeated with a 5% potassium silicate solution. Red rust formed within 12 hours.

EXAMPLE #8 (COMPARATIVE EXAMPLE)

The experimental procedure outlined in Example #6 was repeated with a 10% potassium silicate solution. Red rust formed within 12 hours.

Examples #6 through #8 illustrate the point that the invention requires at least a first coating of permanganate or molybdate, followed by a second coating of silicate. The application of a silicate coating by itself was insufficient to achieve the desirable characteristics of the invention.

EXAMPLE #9

Two galvanized panels that were initially treated using a 0.8% permanganate solution at a bath temperature of 140° F. for about 4 seconds followed by a 2.9% silicate solution at a bath temperature of 80° F. for about 4 seconds followed by a cold reduction in thickness from 0.030″ to 0.016″, a reduction of approximately 47% and illustrating less than 5% red rust after 140 hours of exposure in salt spray.

Therefore what has been shown is that using the technique of thinning said panels by at least 10%, e.g. 20%, or 25%, or ˜50% and coating said thinned panels with a molybdate moiety ranging in concentration of from 50%-100%, a performance similar to an panel which has not been reduced in original thickness is achieved according to ASTM B 117-73. By similar performance, it is understood for purposes of this application, the testing protocol will result in a test result which is about the same, and within 25% performance with a similarly coated panel which had not been thinned. The performance may be within 15%, or within 5%.

Therefore, what has been described in general is a methodology by which a thinned corrosion-resistant stud (preferably comprising a zinc coating, more preferably galvanized steel) is capable of achieving corrosion-resistance similar to a metal stud which has not been thinned, the method including the steps of: (a) thinning a roll of galvanized steel by at least 10% (more preferably 20%, most preferably 25%, and optionally up to ˜50%); (b) forming said roll into at least one metallic stud; (c) applying a permanganate conversion coating composition (at a concentration ranging from 50% to full strength, 100%) containing essentially no trivalent or hexavalent chromium, said permanganate composition may comprise an alkali metal permanganate composition wherein said alkali metal is selected from the group consisting of Li, Na, K, Cs and Rb or a mixture thereof to said stud at a pH of about 9.0 to about 2.0 inclusive; (d) applying an inorganic silicate coating to seal said permanganate composition on said stud; and (e) testing said panel in accordance with ASTM B 117-73 and achieving a performance with said thinned stud within no worse than 25% (e.g. within 15%, or within 5%) of a stud which had not been reduced in thickness. It is recognized that the step of thinning above may be performed either before the sequential application of coatings as illustrated above, or may be performed after the sequential application of coatings.

Also described is a process for making a corrosion-resistant building component comprising the steps of providing a steel sheet suitable for use in making metal building components, said sheet having a surface comprising zinc or a zinc alloy, suitable for use in making metal building components having an initial thickness, forming said rolled steel sheet into at least one metal building component, applying a first coating composition comprising an alkali metal permanganate composition containing essentially no chromium to said building component, and wherein said alkali metal of said alkali metal permanganate composition is selected from the group consisting of potassium, sodium, lithium, rubidium and cesium and applied at a pH of about 9.0 to 2.0 inclusive, and applying a second coating composition comprising an alkali metal silicate sealant composition wherein the alkali metal is selected from the group consisting of potassium, sodium, lithium, rubidium and cesium such that the building component meets the ASTM C 645-08a at a coating weight which is equal to or less than that specified by ASTM A 1003-G 40.

A process is also described by which building components which do not meet ASTM coating weight requirements, (e.g., G-40 or equivalent for non-structural) are coated so that the applicable standards are met.

In the foregoing description, certain terms have been used for brevity, clearness and an aid to understanding the technology; but no unnecessary limitations are to be implied there from beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. This invention has been described in detail with reference to specific embodiments thereof, including the respective best modes for carrying out each embodiment. It shall be understood that these illustrations are by way of example and not by way of limitation.

Claims

1. A process for making a corrosion-resistant metal building component comprising the following steps of:

providing a steel sheet, said sheet having a surface comprising zinc or a zinc alloy selected from the group consisting of galvanized, galvalumed and galvannealed, suitable for use in making metal building components having an initial thickness,

rolling the steel sheet by at least 10% to form a rolled steel sheet in forming a building component,

applying a permanganate coating composition containing essentially no trivalent or hexavalent chromium to said building component, at a pH of about 9.0 to 2.0 inclusive; and

applying an inorganic silicate coating to seal said permanganate composition on said building component, such that the building component meets the ASTM B 117-07a test and provides a corrosion resistance similar to a like building component made of the initial thickness without the rolling step.

2. The process of claim 1 where a permanganate coating is applied to the steel sheet.

3. The process of claim 1 where the initial thickness is 0.017-0.115 inches.

4. The process of claim 1 where the method further comprises a step of adding a valence stabilizer to said permanganate composition.

5. The process of claim 1 where the percent rolling is at least 20%.

6. The process of claim 1 where the percent rolling is at least 25%.

7. The process of claim 1 which further comprises the step of adding a surface activator prior to said step of adding a permanganate composition.

8. The process of claim 1 wherein said inorganic silicate coating is a potassium silicate.

9. A process for making a corrosion-resistant galvanized light gauge metal building stud comprising the following steps of:

providing a steel sheet having a surface comprising zinc or a zinc alloy and having an initial thickness of 0.017-0.115 inches;

applying a permanganate conversion coating composition containing essentially no trivalent or hexavalent chromium to said galvanized steel sheet, said permanganate composition applied at a pH of about 9.0 to 2.0 inclusive;

rolling the steel sheet by at least 10% to form a thinner galvanized steel sheet in forming at least one light gauge metal stud; and

applying an inorganic silicate coating to seal said permanganate composition on said at least one light gauge metal stud, such that the light gauge metal stud meets the ASTM B 117-07a test and provides a corrosion resistance similar to a metal stud made of the initial thickness without the rolling step.

10. The process of claim 9 where the sheet surface is selected from the group consisting of galvanized, galvalumed and galvannealed.

11. The process of claim 9 where the initial thickness is approximately 0.0295 inches. inches.

12. The process of claim 9 where the percent rolling is at least 20%.

13. The process of claim 9 where the percent rolling is at least 25%.

14. The process of claim 9 where said permanganate composition is applied at a concentration diluted to up to about 50% of undiluted permanganate composition.

15. The process of claim 9 wherein said coating is a potassium silicate.

16. A process for making a corrosion-resistant building component comprising the following steps of:

providing a steel sheet suitable for use in making metal building components, said sheet having a surface comprising zinc or a zinc alloy, suitable for use in making metal building components having an initial thickness,

reducing a thickness of said steel sheet by at least 10% to form a reduced thickness steel sheet;

applying a first coating composition comprising an alkali metal permanganate composition containing essentially no chromium to said steel sheet, and wherein said alkali metal of said alkali metal permanganate composition is selected from the group consisting of potassium, sodium, lithium, rubidium and cesium and applied at a pH of about 9.0 to 2.0 inclusive;

applying a second coating composition comprising a silicate sealant composition to the steel sheet;

forming said reduced thickness steel sheet into at least one metal building component and wherein said building material meets the ASTM B 117-07a corrosion-resistance standard at a coating weight which is equal to or less than that specified by ASTM A 1003-G40.

17. The process of claim 16 where the first coating is applied before rolling the steel sheet.

18. The process of claim 16 where building component is a non-structural light gauge galvanized metal building stud.

19. The process of claim 16 where said permanganate composition is applied at a concentration diluted to up to about 50% of undiluted permanganate composition.

20. The process of claim 16 wherein said alkali metal is potassium in both said alkali metal permanganate and said silicate.