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Stainless steel strip coated with aluminiumRelated Patent Categories: Stock Material Or Miscellaneous Articles, All Metal Or With Adjacent MetalsStainless steel strip coated with aluminium description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070082214, Stainless steel strip coated with aluminium. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATION DATA [0001] This application is a national stage application filed under .sctn.371 of International Application PCT/SE2004/001251, filed Aug. 31, 2004, which claims the benefit of priority to application SE 0302395-9, filed in Sweden on Sep. 5, 2003. FIELD [0002] The present disclosure relates to a method of manufacturing aluminum-coated stainless steel in a continuous roll-to-roll process, which results in an excellent adhesion of a thin covering layer of aluminum. In particular, it relates to aluminum-coated stainless steel strips, which exhibit an excellent adhesion of a thin layer of aluminum on the steel surface and which are suitable for a cost-efficient and productive manufacturing of components for anti-corrosive applications. BACKGROUND [0003] In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art. [0004] It is known that aluminum coatings can be used in anti-corrosive applications. However, for components in smaller dimensions, which are to be produced in a cost-efficient and productive way, there are difficulties in finding a method that can attain the quality and productivity requirements. For productivity reasons, a roll-to-roll coating process is imperative, and for quality reasons, a thin layer with excellent adhesion is needed. [0005] The superior adhesion is required for the functional quality of the final product, but also to enable a cost-efficient and productive manufacturing of components. Thus, a coated strip material with inferior adhesion would cause problems with, e.g., flaking, and this would result in a low yield and also in a disturbance caused by the flakes themselves of the manufacturing process as such, especially if the manufacturing process is in a continuous line. Moreover, more frequent stops would be needed for quality inspections and for cleaning the process line from flakes. All in all, poor adhesion of the coating would result in a non-acceptable high manufacturing cost and low quality. [0006] Known, conventional methods of coating steel with aluminum in a roll-to-roll process are the following: [0007] Cladding the substrate steel material with aluminum foil. The cladding process "metallurgically" bonds metals together, producing a continuous strip. This is a relatively simple and straightforward technology, with a high yield to a low cost. However, the method has some major drawbacks. First of all, there is often a problem with poor adhesion. Further, it is technically difficult to achieve good, uniform thin coatings with cladding techniques. [0008] Dipping can be used to apply low melting point metals to a substrate material by performing the dipping in a melt bath. One obvious drawback with this method is that aluminum has a rather high melting point (658.degree. C.). This results in a high complexity for controlling the process parameters and in a difficulty to achieve an evenly distributed thin covering layer with a good adhesion. [0009] There are also some vapor deposition methods that can be used for depositing aluminum. Most methods are batch-like processes, but there are also some continuous processes. [0010] One example of a roll-to-roll method making use of electron-beam deposition is disclosed in WO 98/08986, which describes a method of manufacturing ferritic stainless FeCrAl-steel strips, by bringing about an aluminum coating of a substrate material in a roll-to-roll process. However, the method described in this patent application is optimized for a product suitable for use in a high temperature corrosive environment, thus requiring a material with a good high-temperature strength and also a good high-temperature corrosion resistance, i.e., oxidation resistance. In this context aluminum plays also a role of being an oxide-forming element, which is beneficial for the high-temperature corrosion resistance. This implies that the substrate material be alloyed with rare earth metals, and also that the aluminum coating is made on both sides of the strip. Moreover, this patent application suggests that a homogenization annealing at a temperature of 950-1150.degree. C. is made in connection to the coating, in order to have the aluminum evenly distributed in the ferrite. This means that the final product in this case is not a coated product with an aluminum layer on the surface. Hence, it is rather a FeCrAl strip product with a uniform distribution of the alloying elements, including also aluminum. Further, this means that there are no special requirements on an oxide free interface and as to good adhesion of the layer. There is, e.g., no other cleaning done before the PVD coating step than ordinary wet cleaning by de-ionized water, to take away residuals of oil. Since the role of aluminum is to diffuse into the ferrite, there is also no requirement on any special evenness of the layer. This method, as disclosed in WO 98/08986, can thus not be used for the present invention. [0011] One other example of an apparatus used in a continuous vapor deposition process is described in U.S. Pat. No. 4,655,168, in which a uniform distribution of thickness is achieved by using special control panels inside the vacuum chamber. The example given is for Zn-coating of a mild steel, but mentioned is that also aluminum can be coated in accordance to said invention. The method is however quite different from the present invention. There is for instance a roll over which the strip is guided that is heated to a temperature above melting temperature for the substance to be coated, and in the case of aluminum this would mean above 658.degree. C. This is a temperature in which structural stability of some stainless steels can be affected negatively. The source of energy for the evaporation to take place is not mentioned and there is also no discussion about any ion etching. There are also no special requirements on an oxide free interface or a good adhesion of the layer. It is described that the layer is uniformly distributed, but no details are given, and no range of tolerances is defined. Also, the system of controlling the distribution of the deposited substance seems to be rather complicated. This method, as described in U.S. Pat. No. 4,655,168, can thus not be used in the present invention. [0012] One further example of aluminum coating using vapor deposition plating is described in U.S. Pat. No. 5,429,843, in which a substance is applied to the surface of a steel material, in a vacuum atmosphere. The steel material is held at a temperature between 100 and 400.degree. C. to form active spots in the surface to enable required properties, e.g., good adhesion. Also ion beam irradiation is used in connection to the coating process, but is done in the same chamber as the coating. The formed layer is to be used as an adhesive layer in a subsequent painting process. In principle two different combinations of coatings are described in this invention, Al+Zn and Al+Ti. However, in both cases it is shown that coating of essentially pure aluminum can not be used for the intended application. For Al+Zn, a co-evaporation of Al and Zn is done, so as to produce an Al/Zn-- coating with a Zn-content of between 3-30% as the optimum. For Al+Ti, a two-layer coating is used to achieve acceptable properties, and with the prerequisite that the layer adjacent to the steel must be the Ti-layer. It is shown that if essentially pure aluminum is coated, problems occur with pitting corrosion starting in pin holes in the coating, and thus also creating a galvanic cell that eventually accelerates corrosion of the steel sheet material. One major difference to the present invention is that the substrate material is a plain steel and not a stainless steel, and also that inhibitors, such as Zn-addition or a Ti-layer, are used to avoid a galvanic corrosion to occur. The method is also significantly different in that the used process is a batch-type coating of steel sheet, and not as in the present invention, a continuous coating in a roll-to-roll process of a stainless strip material. This method, as described in U.S. Pat. No. 5,429,843, can thus not be used in the present invention. [0013] In view of the above, it is an object of the present invention to provide a new roll-to-roll process to accomplish a thin and continuous aluminum coating with excellent adhesion on a stainless steel surface. [0014] Moreover, it is an object of the present invention to make possible a cost-efficient and productive manufacturing of components in anti-corrosive applications of the coated material. [0015] A further objective of the present invention is to obtain a coating with a thickness as uniform as possible. [0016] These and further objects have been achieved in a surprising way by providing a coated steel product including a dense and evenly distributed layer on one side or both sides of a strip substrate, characterized in that said layer consists of essentially pure aluminum and is applied directly on to the strip substrate, a thickness of said layer is maximally 15 .mu.m, a tolerance of said layer is maximally +/-30% of the layer thickness, a Cr content of the strip substrate is at least 10%, and wherein the layer has such a good adhesion so that the coated steel strip can be bent 180.degree. over a radius maximally equal to the thickness of said coated steel strip without showing any tendency to flaking or the like. Further preferred embodiments of the present invention are defined in the dependent claims. SUMMARY OF THE INVENTION [0017] The present disclosure relates to a method of manufacturing aluminum-coated stainless steel, for example in a continuous roll-to-roll process, which results in an excellent adhesion of a thin covering aluminum layer. The aluminum-coated stainless steel strips must have such a good adhesion of the thin layer that they are suitable for a cost-efficient and productive manufacturing of components in anti-corrosive applications. The final product, in the form of aluminum-coated strip material, is suitable for uses as an anti-corrosive component in consumer-related applications that are occasionally used in environments with high humidity or in wet conditions. This component of aluminum-coated stainless steel can then protect another metallic part from corrosion by galvanic currents, thus acting as a sacrificial anode. [0018] In an exemplary embodiment, the aluminum layer is deposited by means of electron beam evaporation (EB) in a roll-to-roll process, to an evenly distributed layer with a thickness of preferably less than 15 .mu.m. The substrate material should be a stainless steel with a Cr content above 10% (by weight) and with a strip thickness of usually less than 3 mm. As a first step, the roll-to-roll process may also include an etch chamber, in order to remove the oxide layer that otherwise normally is present on a stainless steel. [0019] An exemplary embodiment of a coated stainless steel strip product includes a dense and evenly distributed layer on one side or both sides of said a strip substrate, wherein said layer consists of essentially pure aluminum and is applied directly on to the strip substrate, a thickness of said layer is maximally 15 .mu.m, a tolerance of said layer is maximally +/-30% of the layer thickness, a Cr content of the steel strip substrate is at least 10%, and wherein the layer has such a good adhesion so that the coated steel strip can be bent 180.degree. over a radius maximally equal to the thickness of said coated steel strip without showing any tendency to flaking or the like. [0020] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Continue reading about Stainless steel strip coated with aluminium... 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