US 2671736 A
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Description (OCR text may contain errors)
Patented Mar. 9, 1954 METHOD OF PROTECTING NORMALLY COR- .RODIBLE METALS FROM oonnosron Anton J. Zoeller, West New York, N. J.
No Drawing. Application October 11, 1950,, Serial No. 189,684
(Cl. ML-49) 6 Claims.
1 This invention relates to a method for protecting a normally corrodible metal from corrosion. In particular, this .invention is concerned with inhibiting the corrosion of ferrous metals, e. g., soft iron, various steels, cast iron, etc. al-
though it is, of course, applicable to other metals including their alloys as set forth hereinafter.
An example of a difficult problem in industry is the corrosion of the metallic parts of water meters and other instruments which are made of various construction metals. This corrosion is accelerated due to galvanic effects resulting from the presence of dissimilar metals exposed to water which contains salts dissolved therein and, therefore, acts as an electrolyte. Normally one of the parts of a water meter such as a bottom is made of cast iron in order that if freezing of the Water passing through the meter occurs, this portion will rupture instead of permitting damage of the more expensive parts of the meter.
Replacement of these meter bottoms necessitated by their rapid corrosion offers a serious maintenance problem. Many attempts have been made prior to this invention to overcome this form or other forms of corrosion but these attempts have been only partially successful. The present invention provides a simple, economical and practical means for successfully inhibiting this andother forms of metal corrosion.
A particular object of this invention is, therefore, to provide a method for inhibiting the corrosion of ferrous metals such as soft iron, various steels, and cast iron; .copper; brass; bronze; zinc; aluminum; magnesium alloys; and various hearing metals such as copper-nickel, cadmiumnickel, silver-nickel, etc.
A further object of the present invention is to provide a method of inhibiting :the corrosion of such metals when exposed to conditions favoring galvanic effects.
Another object of this invention is to provide a method of imparting corrosion resistance to a normally corrodible metal which is relatively permanent in nature and not effected by temperatures as high as 500 F.
A further object of this invention is to treat normally corrodible metals by a process which will impart corrosion resistance to the metal and will at the same time permit the firm and uniform adherence of .a protective or decorative coating material such .as oil paints, red lead paints, rubber base paints or coating compositions, various synthetic resins, aluminum paints, etc.
Other objects and purposes of this invention will become apparent from the description appearing hereinafter.
In its broadest aspect the present invention impregnates the surface of a corrodible metal with a normally solid petrolatum, for example,
the product known by the trade-mark Vaseline. This impregnation with its resulting improved corrosion resistance is achieved by preheating the metal to a temperature within .a critical range, immersing the heated metal for a short period of time in a liquid bath of normally solid petrolatum and then withdrawing the metal from the liquid bath. The invention further contemplates the added feature of the application of a film of a protective or decorative coating material to a surface of the treated metal. Any paint, resin or other plastic material which is normally applied to the surface of a metal for protecting it from corrosion or for decoratin the same may be applied to the metal treated by the process of this invention and it will adhere firmly and uniformly.
The petrolatum which is employed in the practice of this invention is preferably selected with reference to the following considerations: (1) it should be solid at room temperature; (2) it should have a melting point not substantially above 125 F., preferably between F. and F.; (3) it should have a relatively high flash point, preferably not substantially below 250 F.; (4) the :petrolatum should be refined and free of injurious impurities if the metal treated for in hibiting corrosion is to be used for transferring drinking water or other liquids which must not be contaminated. In practicing the invention, it has been determined that the melted petrolatum of the liquid bath should be maintained at a temperature slightly above its melting point, preferably about 10 F. above the same.
For the purpose of illustrating the invention cast iron has been selected as the corrodible metal. It is, however, .to be understood that any other ferrousmetal or metal of the type previously recited may be treated similarly for retarding corrosion.
The cast iron to ,be treated should initially :be cleaned by any convenient method such as sand blasting. After the cleaning operation in accordance with this invention, the metal is preheated to a temperature between 600 'F. and 1000 F., preferably between 800 F. and 900 F. The temperature range set forth, namely 600'F. to 1000 F. has been determined to be a critical temperature range for the process of this invention. The use of preheating temperatures below 600 F. or above 1000 F. results in a treated metal article which does not have a sufiicient corrosion resistance to make the process commercially feasible. However, if the metal article is preheated within this temperature range, the treated product has outstanding corrosion resistance properties which are permanent in nature and will withstand for example heating to a temperature up to about 500 F.
In particular, preheating within a temperature range of between 800 F. and 900 F. produces the most satisfactory results in that the maximum corrosion resistance results.
After preheating the cast iron to the desired temperature within the aforesaid critical range, the next step of the process is to totally immerse the heated metal in a liquid bath of a normally solid petrolatum which is at a temperature just above its melting point. The time of immersion should be for only a short period of time normally between approximately 4 and 7 seconds and preferably between 5 and 6 seconds. After the elapsed time of immersion the article should be promptly withdrawn and drained.
In order that the petrolatum will not heat up excessively during the immersion step and reach the flash point, it is desirable that the vessel containing this liquid bath be heat conductive in order to permit dissipation of the heat. Furthermore, a relatively large weight of petrolatum in relation to the weight of the metal treated should be used. For example, a ratio of 20:1 by weight when used will safely permit the petrolatum to absorb the excess heat of the metal without approaching its flash point temperature.
When corrodible metals are treated by the process described above there occurs as evidenced by microscopic examination an actual if only slight surface penetration. The appearance of the treated metal is somewhat dull as compared with the luster of the untreated clean metal. There is a slight feel of greasiness barely perceptible to the touch but there is no visible coating which may be scraped off or burned off at a temperature below approximately 500 F. The above changes in the appearance and character of the processed metal and further studies have indicated that a definite chemical change results during the treatment of the metal in accordance with this process. The exact chemical change occurring to the petrolatum and possibly even to the crystalline structure of the metal is not understood but as stated its presence is apparent.
The improved result in the corrosion resistance of the metals treated by the process of this invention is attributed to a retardation in the rate of corrosion. For example, cast iron when treated according to the process of the present invention has been examined under controlled conditions for determining its corrosion resistance as compared with an untreated cast iron. At the beginning of the test, evidence of corrosion of about the same rate is apparent in both the treated and untreated cast iron. However, as the test proceeded, corrosion occurred in the untreated cast iron at a much greater and accelerated rate. Thus, it has been found that over an extended period of time an untreated metal subject to the same conditions of corrosion as a treated metal of the same kind loses approximately 3% by weight because of its corrosion whereas the latter treated metal loses only approximately 0.67% by weight. These tests indicate strongly that the corrosion resistance to a metal afforded by the process of this invention is not merely due to a protective coating of petrolatum. The fact that initially both the treated and untreated articles have approximately the same rate of corrosion and that later the treated metals rate of corrosion is retarded as compared with the untreated metal indicates the presence of more than a protective coating and in theory is attributed to an unknown chemical change.
A unique feature of the present invention is that the corrosion resistance process results in a treated metal which will permit the application of any coating material normally used for protecting a metal from corrosion or for decorating the same. It is unexpected that a normally solid petrolatum may be applied to a metallic surface in accordance with any practice and still permit coating materials to adhere firmly and uniformly to the surface of the treated article. Further, it is unexpected that an enamel paint may be baked on a surface of the treated metal at temperatures as high as 400 F. without interfering with or destroying the anti-corrosion properties resulting from the process of this invention.
The foregoing description of the invention has been set forth for the purpose of illustration only and is not, therefore, to be considered limiting. The nature and scope of this invention is set forth in the claims wherein:
1. A method of protecting a ferrous metal from corrosion which comprises preheating the metal to a temperature between 600 F. and 1000 F., immersing the heated metal in a molten liquid bath consisting of a petrolatum normally solid at room temperature, having a melting point between F. and F., and having a flash point substantially below 250 F., for a period of between 4 and 7 seconds, then withdrawing the metal from said bath and then applying a paint to the pretreated metal without removal of the petrolatum before applying said paint.
2. The method of claim 1 wherein the ferrous metal is cast iron.
3. A method of protecting a cast metal from corrosion which comprises preheating the metal to a temperature between 600 F. and 1000 F., immersing the heated metal in a molten liquid bath 1 consisting of a petrolatum normally solid at room temperature, having a melting point between 95 F. and 125 F., and having a flash point substantially below 250 F., for a period of between 4 and 7 seconds, then withdrawing the metal from said bath and then applying a paint to the pretreated metal without removal of the petrolatum before applying said paint.
' 4. The method of claim 1 wherein the paint that is applied is an enamel which is baked on the pre-treated metal without removal of the petrolatum before applying said paint.
5. The method of claim 4 wherein the ferrous metal is cast iron.
6. The method of claim 3 wherein the paint applied is an enamel which is baked on the pre treated metal without removal of the petrolatum before applying said paint.
ANTON J. ZOELLER.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,098,368 Caifall June 2, 1914 2,135,022 Anderson Nov. 1, 1938 2,135,023 Anderson Nov. 1, 1938' FOREIGN PATENTS Number Country Date 284,191 Great Britain Apr. 23, 1929 OTHER REFERENCES Johnson, Materials of Construction, 5th Ed. (1919), page 642.