US2255780A - Method of applying protective coatings to sheets - Google Patents

Description

Patented Sept 16, 1941 S PATENT OFFICE METHOD OF APPLYING PROTECTIVE COATINGS TO SHEETS Henry L. Kohler, Kansas City, Mo., assignor to Andrew A. Kramer, Kansas City, M0.

N Drawing.

Application October 8, 1938,

Serial No. 234,050

5 Claims. (Cl. 91-681) My invention relates to a method of applying protective coatings to sheets, and more particularly to a method of applying a protective coating to a galvanized steel sheet. This application is a continuation in part of my co-pending application Serial No. 144,029, filed May 21, 1937, patented March 21, 1939, Patent No. 2,150,929.

It is an important purpose of my invention to overcome the difficulty previously existing in using galvanized metallic sheets having a heavy coating of galvanizing, which was that the coating of zinc on the sheet would tend to crack, and peel or flake oil. at the bend when making a sharp bend. As pointed out in the above mentioned patent, the damage thus caused to the galvanizing coating, particularly where a heavy coating of galvanizing is provided on the sheet, will render the coating at least partially ineffective, where sharp bends, such as required to form flanges, or seams, are made, and as a result the advantage of the heavy galvanizing coating on the sheet is largely lost. This is true, as has been pointed out in said above mentioned application, because, at such ruptures in a galvanized sheet, the sheet would be no better than an uncoated sheet in resisting oxidization, or other corrosion, at the point of rupture, although the remainder of the sheet would be well coated.

My invention has for its purpose the provision of a simple, but relatively inexpensive, method of providing means for protecting a sheet that has been fabricated, in a manner so as to prevent any corrosion thereof at a bend, or bends, or other damaged areas thereof, due to fabrication steps, even though the original zinc coating may have been damaged, or ruptured, in bending, or other fabricating operations.

It is a further important purpose of my invention to provide a protective coating, either at a bend or over the entire area of a galvanized metallic sheet, that will be more resistant to corrosion, due to certain causes, than the galvanized sheet was before such treatment, and even before any fabrication steps thereof that might have damaged the coating, were performed thereon, and which protective coating will resist every kind of corrosion equally as well, as does the galvanized sheet at the portions thereof that have had only the heavy galvanizing coating applied thereto prior to its fabrication. As the term is used herein, by fabrication is meant, any bending, cutting or punching operation, or any other operation, on a sheet, that may be performed on the sheet after the same has been rolled and galvanized.

My improved method of providing a protective coating can be utilized to cover the entire area of a galvanized sheet, particularly advantageously for use in a tank that is filled with liquid that may have an undesirable corrosive effect on the usual zinc coating provided on such sheet. In such case the entire inner surface of the tank sections, or sheets, fabricated to a shape and size and punched with suitable holes for securing the sections together, may be treated to make the same more resistant to corrosion, not only at the bends therein, if there are any in the section, but over the entire surface thereof exposed to such corrosion.

It is a particular object of my invention to provide means for curing a defect in the coating at a bend in a galvanized sheet, by treating the sheet in accordance with my method only on the outer side of the bends, which are made in the sheet in forming flanges, or seams, thereon, as the zinc coating is not injured on the inner side of the bend, inasmuch as the injury in the coating is due to the lack of tensile strength of the zinc, which causes the rupturing, or damaging, of the coating on the outer side of the bend.

The heavier the coating of the zinc provided on the sheet,the greater the difiiculty in preventing cracking of the galvanizing or zinc coating, due to making a sharp bend in the sheet, or performing other operations on the sheet, that might rupture or crack the same, this being due to the fact that the tensile strength of the same is very much less than that of either the steel or the ferrous zinc alloy, which lies adjacent the steel of the sheet in a galvanized sheet. My invention not only entirely overcomes the difficulty resulting from the rupturing of the zinc coating at such a bend, or similar place, but makes the sheet more resistant to corrosion, even though the coating has been cracked, or ruptured, at the bend, at the places where the sheet is treated in accordance with my method, than it was prior to fabrication, being particularly resistant to corrosion due to the sulphur compounds present in oils and similar materials.

I accomplish this purpose by amalgamating mercury with a protective coating wherever it is desired to make the same more resistant to corrosion, whether it be only at a rupture in the galvanizing coating of such a sheet or over the entire surface of the sheet. Mercury, and amalgams of mercury, are particularly resistant to corrosion due to acids, such as sulphuric acid, and other acids, and are affected to a much less extent by hydrogen sulphide, than is zinc. Con- 7 use.

siderable diillc'ulty is encountered in applying metallic mercury to a galvanized sheet to produce the amalgam coating, because of its extreme mobility and its high surface tension,

vide such an amalgam that can be readily applied in the desired quantity to produce the protective coating desired, without destroying the crystalline structure of the zinc coating on a galvanized sheet, by merely spreading or rubbing the same on the parts of the sheet that are to be treated. In order to do this, I'provide an amalgam of zinc and mercury that has the consistency of a soft putty, or is of a creamy character. If this is rubbed on the metal at the place where it is to be protected, such as a rupture in the coating on the sheet, a certain amount of the amalgam adheres to the surface of the sheet, both at the zinc coated area and the area where the coating has been ruptured. Due to the putty-like, or creamy, character of the amalgam, the excess can be readily removed with a cloth, or in a similar manner, and saved for futur It is a particular purpose of my invention to provide an amalgam of the above 'mentioned character, that can be applied to a sheet that has been previously galvanized, in such a manner that the amalgam will act on the zinc coatins; so as to amalgamate therewith, so that a zinc-mercury amalgam is produced, which, while at first soft and .capable of being rubbed off with the fingers, will, after twenty-four to forty-eight hours, be just as hard and have a similar appearance to the zinc coating on the sheet before the amalgam was applied. g

It is a further purpose of my invention to provide a method of making a protective coating for metals, which protective coating contains mercury, comprising the step of dissolving in mercury finely divided zinc in such proportions as to form a soft putty-like amalgam paste. This can usually be done at ordinary atmospheric temperatures found in the ordinary work shop, but if any diiliculty is encountered in dissolving the finely divided zinc in the mercury, or it is desired to increase the proportion of zinc to be dissolved in the mercury, the mercury can be heated above the atmospheric temperature for this purpose.

Other objects and advantages of my invention will appear as the description of the same proceeds. I desire to have it uhdersto'od,'-however, that I do not intend to limit myself to the particular details described, except as defined in the claims.

My improved method is carried out on galvanized sheets that have been fabricated to the desired size and shape, by bending, die-shaping, cutting and punching operations, or any of these that may be necessary to produce the article, or sections of an article, of the desired shape from the sheet of metal. After the sheet has been fabricated, it is cleaned at the places at which the protective coating is to be provided thereon,

of injuring the protective coating, or rupturing the same, the galvanized sheets are cleaned only on the outer sides of all bends therein, or any other area at which the coating may have been ruptured, or damaged, and areas adjacent these bends, or other areas where the damage may have occurred. A zone at the place at which the rupture in the zinc coating may exist will thus be cleaned, and also a zone on each side thereof.

A putty-like amalgam of mercury and zinc is made up prior to cleaning the sheets, or is made up in quantity to be used whenever necessary, said amalgam having such proportions of zinc and mercury therein as to produce a soft puttylike material of the consistency of thick paste or cream. The proportions of zinc and mercury that are used to produce this soft putty-like material will vary somewhat, dependent upon the atmospheric temperature existing, as the material must, of course, be of the soft, creamy puttylike character at the temperature at which it is applied to the sheet. Thus in the winter time, when a lowertemperature is encountered, both in the atmosphere and in the material of the sheets themselves, a larger proportion of the mercury to the zinc must be used to produce this soft putty-like coating material. I have found that 15% zinc and 85% mercury by weight will produce an amalgam of the desired consistency in the summer time, while in the winter time,

. when the temperatures are exceedingly low, it is necessary to utilize an amalgam made for this purpose that will have as little as 10% zinc by weight, and .90% mercury by weight, while, if the mercury is heated while the zinc is being incorporated therein, the percentage of zinc can be increased to 20% by weight to 80% by weight of mercury. The relative proportions of the metal, or metals, amalgamating with mercury that have to be utilized depend upon the melting points of the metals that are amalgamated with mercury and the temperature encountered, and the heating makes it possible to incorporate a larger amount of the metal amalgamating with the mercury, than would otherwise be the case. There is no advantage in incorporating too large a percentage of zinc in the amalgam, however, as it must, of course, remain of a creamy character, or a putty-like character, at the temperature at which it is applied to the sheet, and if too large a percentage of zinc is included in the amalgam by adding the zinc to the heated mercury, it will not have the desired consistency at the temperature at which it is to be utilized.

The zinc can be in the form of any small particles, such as shavings, turnings, cuttings, or in the form of a powder or granules.- The finely in the limits above referred to.

divided zinc is stirred into the quantity of mercury that is to be utilized to make the amalgam in the proportions necessary, substantially with- This is ordigam than would otherwise be possible within the limits pointed out above. Care must, of course, be utilized in doing this, that the mercury i not heated to a temperature near the vaporization point thereof.

The soft putty-like amalgam of zinc and mercury, produced as above described, is applied to the cleaned zone, or area, of the galvanized sheet, by a brushing or rubbing operation, the soft putty-like amalgam being brushed or rubbed onto the cleaned area of the sheet with a cloth, or in a similar manner. This rubbing or brushing operation spreads the zinc-mercury amal am over the cleaned area of the sheet and causes a thin layer thereof to adhere to the outer surface of the zinc coating on the sheet. In case there is a rupture of a damaged area in the sheet, from which the zinc has been entirely, or substantially entirely, removed, the zinc-mercury amalgam will adhere to the sheet at this ruptured area also. The amalgam, as soon as it contacts the zinc coating on the sheet, begins to act thereon to amalgamate the zinc on the sheet with some of the mercury in the amalgam. Due to the brushing of the amalgam back and forth over the ruptured area, the composition of the coating at the ruptured area will tend to be substantially the same as on other portions of the sheet to which. the amalgam is applied. Any loose flakes, or particles, of zinc will be dissolved in the amalgam, amalgamating with the mercury in said amalgam.

The action between the zinc-mercury amalgam and the zinc on the sheet will continue until the amalgam has penetrated the entire zinc coating of the sheet, at least down to the ferrous zinc alloy at the surface of the iron or steel of the sheet. After the zinc on the sheet amalgamates with the mercury, the resulting amalgam will gradually become stiffer and harder, as the greater the amount of other metal amalgamated with the mercury the harder and stiffer the amalgam will become. As a result, the penetration of the zinc on the sheet by the zinc-mercury amalgam, will eventually produce a zinc-mercury amalgam throughout the coating on the sheet, which will have lost the soft character that the zinc-mercury amalgam had when applied and will become as hard as the zinc coating originally on the sheet.

Thus, while the amalgam, when first placed on the sheet, will be soft enough that it can be rubbed off on the fingers to a certain extent, after at least twenty-four hours, the coating at the area to which the amalgam has been applied will be hard enough that none of the same will rub off and the sheet can be handled without any damage to the coating thereon, just as readily as was the case with the zinc coating on the sheet originally. The sheet will, after the coating has become hard, have substantially the same appearance as it did before any amalgam was applied thereto, and none of the coating can be rubbed off, even though it may be rubbed persistently for a considerable period of time. The coating will have the characteristic spangled appearance of the zinc coating originally on the sheet. This indicates that the application of the putty-like amalgam to the sheet that has been previously galvanized, while resulting in the dissolving of the zinc on the sheet, in the mercury of the amalgam, does this in such a gradual manner that the liquefaction of the coating material on the sheet takes place at such a slow rate through the thickness of the zinc coating, that the structure of the zinc coating on the sheet is not altered, although the composition changes from substantially pure zinc to a zinc-mercury amalgam, as the amalgamating process proceeds through the coating. The sheet will accordingly have substantially the same appearance two or three days after the amalgam was applied thereto as it had before any application of amalgam thereto.

It is obvious that it may be desirable to not only prevent corrosion at ruptures in coatings on galvanized sheets at bends in such sheets, or similar places, but that the entire area of a sheet, or the entire inner surface of a sheet, or section of a container, for example, that is innermost when it is in place, and which is subjected to the corrosive action of sulphuric acid, or other compounds, which are ordinarily found in oil tanks, or similar receptacles,'may be provided with a corrosion resisting amalgam coating. By utilizing my protective coating, the corrosive action, caused by these sulphur compounds, on the zinc coating of the sheet ordinarily occurring, will be reduced and substantially eliminated, the zinc-mercury amalgam being applied to the inner surface of such an oil tank, or the sections of such an oil tank, made up of sheets that have been bent, out and punched before the application of the amalgam thereto.

The tendency of the sulphur compounds, when acting on the amalgam coating described, is to cause the mercury in the amalgam to form a protective film on the surface that is exposed to the section of the dilute sulphuric acid, or hydrogen sulphide, or other sulphur compounds, this causing some slight loss of some of the zinc, but the mercury arresting this substantially immediately, due to its film forming action.

There is substantially no loss of mercury in carrying out my method, because, if there is any excess of amalgam applied to the sheet, such excess can be removed with a cloth, such as the cloth by means of which the putty-like amalgam has been rubbed on the sheet, and the part thus removed saved for use on another sheet or other portion of the sheet. While it is immaterial whether the amalgam coating is of the same composition throughout, it has been found that if the soft putty-like amalgam, above re ferred to, is utilized, some of the mercury in the amalgam will amalgamate with the zinc immediately, forming a zinc-mercury amalgam, and some of the zinc-mercury amalgam will be present in substantially the form in which it was applied at first, this being on the top surface of the coating. However, if the amalgam above referred to is left in contact with the zinc coating for twenty-four hours or more, and an excessive amount of the amalgam is not used, sufllcient of the mercury will amalgamate with the zinc that all of the zinc will become amalgamated with the mercury, and the resulting coating will be a zincmercury amalgam from the outer surface of the coating to at least the ferrous zinc alloy at the surface of the metal of the sheet. The amalgamation of the mercury with the zinc on the sheet, when completed, causes the coating to have a hard character, because there is so much larger a percentage of zinc in the coating, than there was in the amalgam applied to the sheet, and the coating will have a hard character, similar to that of the zinc, instead of a soft putty-like character, such as the zinc-mercury amalgam that was applied to the sheet, had at the time of application.

When a putty-like amalgam, containing 15% zinc and mercury by weight, is utilized for application to a galvanized sheet that has azinc coating thereon amounting to one ounceper running square foot, or one-half ounce per square foot surface on each side of the sheet, the amalgam resulting will contain approximately 90% zinc and mercury. With heavier coatings of zinc, the percentage of zinc will, of course, be higher. In all cases, the amount of zinc in the amalgam resulting on the sheet will be over 50% and the coating will not lose the characteristics of a zinc coating, except partially, but it'wili be modified in its corrosion resisting characteristics to a considerable extent by the mercury contained therein, making the same less subject to corrosion than the pure zinc coating on the sheet originally.

What I claim is:

1. The method of providing a corrosion resisting coating on a galvanized metallic sheet, comprising making a soft putty-like amalgam of mercury and zinc containing from 80% to 90% mercury by weight, spreading said zinc-mercury amalgam over the zinc coating on said sheet in a thin coat, and leaving the amalgam adhering to said sheet undisturbed thereon until all thereof has amalgamated with the zinc on said sheet.

2. The method of providing a corrosion resisting coating on a galvanized metallic sheet, comprising cleaning zinc oxide, dirt and oil from the area of said sheet to be coated, rubbing a soft, creamy putty-like amalgam of zinc and mercury containing from 80% to 90% mercury by weight on the cleaned area of said sheet, removing excess amalgam from said sheet, and permitting the amalgam adhering to said sheet to penetrate through the entire thickness of the zinc coating on said sheet to form a hard zinc-mercury amalgam therewith.

3. The method of increasing the resistance to corrosion of a galvanized metallic sheet having a damaged area in the zinc coating thereof produced by fabrication operations performed on said sheet after galvanization thereof, comprising the spreading of a soft, creamy, putty-like amalgam of zinc and mercury containing from to mercury by weight over and adjacent the damaged area of said sheet.

4. The method of repairing a rupture in the zinc coating of a galvanized metallic sheet comprising spreading a soft putty-like amalgam of mercury and zinc containing from 80% to 90% mercury by weight over the surface of said sheet at and adjacent said rupture.

5. The method of providing a corrosion resisting coating having substantially the appearance of a galvanizing coating on a galvanized metallic sheet, comprising making a soft, creamy, puttylike amalgam of mercury and zinc containing from 80% to 90% mercury by weight, applying a thin coating of said amalgam to said sheet, removing all the excess of amalgam from said sheet, and leaving said coating undisturbed on said sheet until the same hardens, due to amalgamation of all the zinc on the area of said sheet, having zinc-mercury amalgam applied thereto. with said zinc-mercury amalgam.

HENRY L. KOHLER.