US2150929A

US2150929A - Method of forming protective coatings on metallic sheets

Info

Publication number: US2150929A
Application number: US144029A
Authority: US
Inventors: Henry L Kohler
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-05-21
Filing date: 1937-05-21
Publication date: 1939-03-21
Anticipated expiration: 1956-03-21

Description

Patented Mar. 21, 1939 METHOD OF FORMING PROTECTIVE COAT- INGS N METALLIC SHEETS Henry L. Kohler, Kansas City, Mo., assignor to Andrew A. Kramer, Kansas City, M0.

N0 Drawing. Application May 21, 1937, Serial No. 144,029

Claims.

, ricated, the bending of a sheet to form a flange.

or a seam, would damage the galvanized coating on the sheet so seriously that it would render the coating partially ineffective, where the bends required to form the flanges, or seams, were made. Consequently the advantage of the heavy galvanized coating on the sheet was largelyiost. This was true because that portion of the sheet at which the galvanized coating was caused to be damaged, or ruptured, by the bending, would hardly be any better than an uncoated sheet, as far as resistance to oxidation, or other corrosion, was concerned, although the remainder of the sheet might be well coated, and would not in any manner corrode under ordinary circumstances. Attempts have been made to overcome this difficulty by a hot dipping process after fab- 0 rication, but this entails many difficulties and requires very expensive equipment and is substantially impossible to successfully perform,

where large sheet metal sections, such as tank sections, have been fabricated, and are to-be 5 protected from oxidation, and other corrosion, by such hot dipping. It is the principal purpose of my invention to provide means for protecting a sheet that has been fabricated, at the bend, or bends, therein, so as to prevent any corrosion thereof at said bend, or bends, even though the original galvanizing coating may have been ruptured in making the bend, and to provide a protective coating at said bend, or bends, that will be even more resistant to corrosion due to certain causes, than the galvanized sheet was before bending or fabrication thereof, and which will resist every kind of corrosion equally as well as the galvanized sheet with a heavy galvanizing coating thereon prior to its fabrication. My improved method may be utilized to give a better protective coating against certain types of corrosion, or corrosion due to certain causes, over the entire area of the fabricated section, if

this should be desired, but is particularly in- I 5 tended for use at and adjacent the bends in the fabricated sheet, whereby any rupture in the galvanizing coating that may have occurred during fabrication, will be closed and the sheet protected at such bends, even more effectively than was the case before bending, even though a rup- 5 ture had occurred in the galvanizing coating during bending. I

In galvanizing iron, or steel, the zinc forms a thin layer of ferrous zinc alloy immediately adjacent the steel or iron of the sheet, which has 10 a much higher melting point than the spelter, or zinc, and immediately sets and thus prevents any further alloying action between the zinc and iron of the steel. The remainder of the spelter forms a coating of almost pure zinc overlying the coatl5 ing of ferrous zinc alloy on the sheet. This outer coating of zinc varies in thickness. considerably, depending on how it is applied to the sheet. Sheets are provided with a heavy coating of galvanizing by repeatedly dipping, or running the 20 sheets through the galvanizing bath. This zinc coating does not have the tensile strength of steel, nor the flexibility of steel, and consecoated at that point. My invention entirely overcomes thisdifflculty and makes the bend, even 35 though a rupture had occurred in the galvanizing coating in the fabrication of the sheet, more resistant to corrosion than was the case prior to fabrication, and particularly resistant to corrosion due to sulphur compounds present in cer- 40 tain oils and similar materials that may be confined in tanks that are manufactured out of galvanized sheets with heavy coatings, such as above referred to.

This is, accomplished by the utilization of mercury in making a protective coating at the bend in the sheet at which a rupture of the galvanizing coating may have occurred. Mercury may be regarded as semi-noble metal, and is particularly resistant to corrosion, because it is not 50 soluble in dilute sulphuric acid, hydrogen sulphide does not affect it as readily as it does zinc, and the amalgams of mercury take on the characteristics of mercury to the extent that these are also highly resistant to corrosion, particularly vanized sheet, particularly at a ruptured placein said coating, by applying mercury thereto, 50

as to amalgamate the mercury with the ruptured zinc particles, some of which may have detached themselves wholly or partially from the remainder of the coating. The mercury may be applied r in the metallic form, but inasmuch as some difliculty is encountered in preventing 10s of mercury because of its extremely mobile character,

it is preferred that an amalgam be made of mercury with zinc, tin, bismuth, lead, or any metal that freely dissolves in mercury, which is applied to the part to be protected. Preferably, an amalgam of the consistency of putty is rubbed on the metal at the place where the same is to be protected, such as at a ruptured place in the coating on the sheet, which permits the excess to be removed with a cloth and thus saved for future use. Also the galvanizing can be amalgamated with mercury by using salts of mercury, the mercury separating out and amalgamating with the zinc It is a purpose of my invention to provide a new and improved method of protecting galvanized sheets in the manner set forth above, and to provide a new and improved protective coating for sheets, and a sheet provided with such a pro- I desire to have it understood, however, that I do tective coating, either over the entire surface thereof or at a bend at which a rupture in the coating may have occurred, or'is likely to occur. It is, of course, necessary to remove the zinc oxide, and other material, that might interfere with the amalgamating action, from the zinc at'the points at which the mercury, or mercury amal- Sam, is to be applied, by using a suitable cleaning solution, which is applied to the galvanized coating and the excess of cleaning fluid'removed before the mercury, or amalgam, is applied.

Other objects and advantages of my inventionwill appear as the description thereof proceeds.

not intend to limit myself -to the particular details described, except as defined in the claims.

In carrying out my improved method to produce the sheets with my new and improved coating thereon, I first fabricate-the sheets to the desired size and shape and then clean each fabricated sheet at the places at which the protective coating is to be provided thereon. The usual method is to clean the fabricated galvanized sheets on the outer sides of all bends therein, and in areas adjacent said bends, so that a zone not only at the place at which the rupture in the zinc coating may exist will be cleaned, but a zone on each side thereof. The cleaning of the galvanized sheet may chloric acid, .or with a solution of tin chloride, antimony chloride, lead chloride, zinc chloride or cyanide of soda. This cleaning solution may be applied with a brush, or swab of some character,

' and the excessmay be removed with a cloth, or

any other suitable means. The mercury is then applied to the cleaned zone at the ruptured place in the coating and adiacentthereto, and in case metallic mercury-is used, great care should be utilized to use'only a small amount of the metal and to spread it by brushing, or otherwise, over a large area of the clean surface of the sheet, so as to prevent any material loss of mercury due be done with dilute hydroto its rolling oi! the sheet because of its great mobility,

The mercury, in being brushed over the sheet, particularly at the ruptured place, or zone, in the zinc coating will amalgamate with the zinc, forming a thin coating of mercury-zinc amalgam over the entire surface that has been cleaned, with which the mercury comes in contact. At the rupture it will combine with the zinc that is broken away from the sheet, forming an amalgam therewith, which will adhere to the sheet closely and make a smooth coating, entirely closing up the break, or rupture, in the galvanizedcoating. The

amalgam thus formed will be somewhat moist at first and can be rubbed off on the fingers to a certain extent, but will gradually harden, and after several days, the sheet at the bend at which the mercury is applied, will have substantially the same appearance as the remainder of the sheet and the amalgam will not rub off, even though the coating may be rubbed persistently for a considerable period of time. The coating thus formed will not be soluble in dilute sulphuric acid, nor in any other dilute acids, being only soluble in hot, concentrated sulphuric acid.

As dilute sulphuric acid is ordinarily formed in oil tanks in which oils are stored that have a large sulphur content, my invention is particularly valuable for use in oil tanks that are made for the storage of such oils, which are commonly known as sour" oils. Also many 0115 give off hydrogen sulphide, and ma moist atmosphere the sulphides of the metals are formed by the action of hydrogen sulphide on the metals. Thus the zinc coating on a sheet in an atmosphere in which hydrogen sulphide and moisture is present, as will be the case in many tanks, particularly oil tanks, will be subjected to the combined action of the hydrogen sulphide and moisture, and transformed into a sulphide of zinc, which is readily soluble in dilute sulphuric aci Where the zinc coating is ruptured, iron will exposed and a sulphide of iron will be formed ina similar manner, by the action of hydrogen sulphide and moist air. On the other hand, sulphides of mercury, lead, tin and bismuth do not dissolvein dilute sulphuric acid. Also zinc and iron sul phides oxidize rapidly in moist air to form sul- 'use of. fabricated galvanized sheets in commercial uses, such as the making of tanks, as, not only will the zinc coating be made more protective by the amalgamation with mercury, but the ruptured portion will be made more resistant to corrosion than was the case prior to bending of the sheet, when the zinc galvanizing coating was undamaged. As a matter of fact, tests made on galvanized sheets provided with my improved protective coating, utilizing the amalgamation of mercury with the zinc to produce the same, show that the portion of' the sheet that is not ruptured and that has not been treated, but which has the full thickness of galvanizing coating thereon, will be attacked by dilute sulphuric acid and other means, causing corrosion, whereas, the amalgam coated portion of the sheet will notin any manner be afiected by such corroding agents as would ordinarily occur in practice.

Instead .of using metallic mercury, my method can be practiced with mercury amalgams. In proceeding with the method when a mercury amalgam is used, the cleaning step is carried out just as previouslydescribed, and after the cleaning of the area that is to be provided with the amalgam coating is completed, the mercury in the-form of an amalgam, is applied. Preferably, the amalgam is made of the consistency of putty, so that it can be rubbed on the metal with substantially no loss of mercury. When this is done, the excess can be removed with a cloth and saved for application to another sheet, or another'portion of the sheet. Amalgams of mercury with zinc, or with tin, or with bismuth, or with lead, or with any metal that freely dissolves in mercury, can be used to make this puttyor paste-like amalgam. The result of the application of such anamalgam to the sheet at the clean place at or adjacent the rupture, or on any portion of a sheet that has been cleaned, where such coating is desired, results in the formingof an amalgam of the mercury and the two metals that are present, in case the amalgam is one of another metal than zinc. Thus a zinc-tin-mercury amalgam, or a zinc-bismuth-mercury amalgam, or a zinc-lead-mercury amalgam, can be formed on a sheet at the place that is being rubbed with the amalgam, depending on the composition of the paste-like, or putty-like, amalgam, that is rubbed on the sheet. If a mercury-zinc amalgam is rubbed on the sheet, the resulting amalgam will, of course, be a zinc-mercury amalgam. It is immaterial whether the amalgam coating is the same composition throughout. Thus, in applying a tin-mercury amalgam to a sheet at the ruptured and adjacent the ruptured places therein, some of the mercury in the tinmercury amalgam, will amalgamate with the zinc, forming a tin-zinc-mercury amalgam, while some of the tin-mercury amalgam will be present without any zinc in it, and this will usually be the top surface part of the coating thus provided, providing the tin-mercury amalgam at the exposed surface of the coating. A similar result would occur with amalgams of mercury and bismuth, or mercury and lead.

Instead of using either the metallic mercury or an amalgam of mercury, the zinc coating can be amalgamated with mercury by utilizing salts of mercury, such as bichloride of mercury, the acetate or the nitrate. In the use of these salts the mercury will separate out as a metal and amalgamate with the zinc. A corresponding amount of zinc will be dissolved, going into combination with the acid radical of the salt, and thus be lost in the process, if any of the salts of mercury, referred 'to above, are used. It is, of course, to be understood that the cleaning step is carried out to remove oxides, grease, or other foreign matter, from the sheet at the place where the amalgamation is to take" place, when the salts referred to, are used, as well as when the amalgam, or the metallic mercury, is used for providing an amalgam coating on the sheet.

It is, of course, to be understood that the entire surface of the sheet can be provided with a coating that is very highly resistant to corrosion, particularly due to the action of hydrogen sulphide in the presence of moisture,'and dilute acids, such as dilute sulphuric acid, by amalgamating mercury with the zinc coating of the sheet over the entire area thereof, either on one or both sides of the sheet, as may be found desirable, this, of course, being done after fabrica- -tion, and it being, of course, understood that either the metallic mercury can be applied, salts of mercury can be utilized, or amalgams of mercury with zinc, lead, tin, or bismuth, can be used to produce this protective coating, the result being that the entire sheet will be coated with a zinc-mercury amalgam that may also contain other metals, which are more resistant to corrosion by the agents referred to than the original zinc coating of the sheet.

What I claim is:

1. The method of increasing the resistance to corrosion of a fabricated galvanized metallic sheet comprising the application of mercury to the sheet after fabrication at ruptures in the zinc coating thereon resulting from such fabrication and spreading the resulting amalgam over said ruptures.

2. The method of increasing the resistance to corrosion of a fabricated galvanized metallic sheet comprising the rubbing of a putty-like amalgam of mercury and another metal on the sheet at ruptures in the zinc coating thereon resulting from such fabrication.

3. The method of increasing the resistance to corrosion of a fabricated galvanized metallic sheet comprising the cleaning of zinc oxide from the same with a solvent at ruptures in the zinc coating of said sheet resulting from such fabrication, the application of mercury to said cleaned sheet at said ruptures and spreading the amalgam thus formed over said ruptures.

4. The method of increasing the resistance. to corrosion of a fabricated galvanized metallic sheet comprising the application of a mercury salt to the sheet at ruptures in the zinc coating thereon resulting from such fabrication after fabrication and spreading the amalgam with zinc thus formed over said ruptures.

5. The method of increasing the resistance to corrosion of a galvanized metallic sheet having ruptures in the zinc coating thereof produced by fabrication operations performed on said sheet after galvanization thereof, comprising the amalgamation of mercury with the zinc coating of said sheet at and adjacent said ruptures after such rupturing fabricating operations have been performed and spreading the resulting amalgam over said ruptures.

6. The method of increasing the resistance to corrosion of a metallic sheet shaped after having been galvanized, comprising cleaning zinc oxide from the same by means of a solvent of zinc oxide at and adjacent ruptures in the zinc coating of said sheet resulting from the shaping thereof, the amalgamation of mercury with the zinc coating at and adjacent said ruptures and spreading the resulting amalgam over the cleaned area at and adjacent said ruptures.

'7. The method of increasing the resistance to corrosion of a metallic sheet shaped after having been galvanized, comprising cleaning zinc oxide from the same by means of a solvent of zinc oxide at and adjacent rupt'ures in the zinc coating of said sheet resulting from the shaping thereof, and rubbing an amalgam of mercury and a metal freely amalgamating therewith on the cleaned area of said sheet at and adjacent said ruptures.

8. In the method of making a corrosion resisting galvanized metallic sheet having a bendtherein producing a rupture in the galvanized coating thereon, the steps comprising cleaning zinc oxide from said sheet at and adjacent said bend and amalgamating mercury with the zinc coating on said sheet over the cleaned area thereof at and adjacent said bend and spreading the resulting amalgam over the ruptured area thereof.

9. In the method of making a corrosion resisting galvanized metallic sheet having a bend therein producing a rupture in the galvanized coating thereon, the steps comprising cleaning zinc oxide from said sheet at and adjacent said bend and applying an amalgam with mercury of a metal freely amalgamating therewith to said sheet over the cleaned area thereof at and adamopao jacent said bend and spreading the resulting amalgam with zinc over the ruptured area thereof.

10. 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 amalgamation of mercury with the zinc coating of said sheet at and adjacent said damaged area after such damaging fabricating operations have been performed and spreading the resulting amalgam over said damaged area.

HENRY L. KOHLER.