US1591983A - Process of coating iron or steel articles - Google Patents

Description

No Drawing.

Patented July 13, 1926.

UNITED STATES 1,591,983 PATENT OFFICE.

.IRVIN J. KOEHNLINE, OF BRIDGEPORT, OHIO.

PROCESS OF COATING""I'RON...Q?B STEEL ARTICLES.

' all as will be more fully hereinafter disclosed and particularly pointed out inthe claims.

In order that the precise invention may be the more clearly understood, it is said In coating steel and iron sheets and shapes with tin alone by the methods heretofore proposed of dipping the article in a bath of molten tin, the flux that is necessarily employed usually attacks the metal slightly,- and more or less hydrogen is produced. The action is such that the hydrogen .does not completely escape from the metal before the sheet or shape is plunged below the surface of the molten tin, and it therefore often gives trouble at a later period. Again, upon immersion in the molten tin, the sheet or shape becomes rapidly hotter than it Was before, and any hydrogen or other gas adsorbed by the iron or steel, or present on the surface due to the action of the acid of the flux employed, is rapidly expanded, with the result that said gas forces an exit through the tin coating, before it'is completely set. This escape of the expanded gases causes the formation of microscopic openings or pits in the finished coating which frequently expose the iron or steel at the bottoms thereof. Later, when such tin coated article is immersed in electrolytes, a galvanic couple between the iron and tin is formed'and the corrosion of the iron.becomes rapid.

I have found, however, that a small per centage of aluminum dissolved in the molten tin bath effectually closes such pits by a precipitation of the aluminum onto the ex posed iron when such coated metal is immersed in an electrolyte as will be more fully explained below. .That is, the aluminum being electropositive to iron, under the conditions stated, a couple will be formed and the aluminum present will be deposited onto the iron at the bottom of said pits, as will presently appear.-

Therefore, in carrying out this invention,

Application filed June 20,

1924. Serial No. 721,359.

I coat iron or steel sheets with an alloy of tin and aluminum in a manner similar to that heretofore employed in coating with tin .alone, but avoid the disadvantages stated,

and also accomplish the new results set forth below. a

The proportion of aluminum in the tinaluminum alloy forming the coating is largely restricted by the temperature re-.

quired to maintain a sufficiently fluid melt for hot dipcoatings of this character. Further, as is well known, articlesv coated by a dipping process are usually cooled by an immersion in palm oil, and it is found if more than 10% aluminum is present in the tin-aluminum alloy coating, the tempera ture of the molten bath and of the dipped article will be so high that the palm oil bath will have to be relatively deep ifone is to prevent the palm oil from catching fire at the surface. Therefore, ll prefer to use 1Q% of aluminum or less in the alloy, in order to enable the use of a comparatively shallow cooling bath of oil to receive the tinned iron or steel as it emerges from the molten alloy bath, for there is an advantage in employing shallow baths by means of which the coated sheet or shape is to be sufiiciently.

cooled, when it reaches the air that oxidation will be either nothing or very slight.

A tin-aluminum alloy containing from 1% to 20% aluminum, has a lower density than pure tin, which enables a greater thickness or coating for a given weight per square foot than is the case with plain or pure tin coatings. This greater thickness serves as an additional protection against an unavoidable scratching in handling the articles. As the aluminum is less costly by vwei ht than is tin, my tin-aluminum alloy is 550 industrially less costly than is plain tin coatings of equal weight per unit of area.

Further, tinned iron or steel subjected to corrosion results in the formation of oxidized tin compounds which are physiologically undesirable, particularly when tin vessels are used as food containers, as is the case in making tin cans, because said compounds are more or less poisonous. My alloy containing aluminum being electro positive to both tin and iron it results that under conditions inducing corrosion, it forms compounds of aluminum which are commonly inert physiologically, or nonpoisonous. As all the aluminum must be corroded before the tin is attacked my alloy supplies a coating of vastly greater sanitary qualities than plain tin coatings.

My tin-aluminum coating is found to be harder than P1118 tin and is therefore in less danger of. being scored through the coating to the iron by the necessities of industrial handling in forming cans, etc., than is a pure tin coating. Such scorings in the case of plain or pure tin coatings furthermore expose the iron or steel base to the action of electrolytes, and a tin iron contact thus produced induces rapid corrosion, as

'above stated, While my alloy coating prevents such corrosions. Further, I have found that this'alloy coating gives a longer life to containers and other articles than is the case with plain tin coatings.

same to the coating operation; immersing said articles in a molten bath of tin containing less than 20% of aluminum; and cooling the articles thus coated.

3. The process of coating iron and steel articles which consists insuitably cleaning said articles preparatory to subjecting the same to the coating operation; immersing said articles in a molten bath of tin containing less than 15% of aluminum; and cooling in oil the articles thus coated.

4. The process of coating iron and steel articles which consists in suitably cleaning said articles preparatory to subjecting the same to the coating operation; immersing said articles in a molten bath of tin containing less than 10% of aluminum; and cooling in palm oil the articles thus coated.

5. The herein described new article of manufacture the same consisting of an iron or steel article provided with a coating of tin alloyed with less than 20% of aluminum.

In testimony whereof I affix my signature.

IRVIN J. KOEHNLIN E.