US2506364A - Heat-treating aluminum foil - Google Patents

Description

Patented May '2, 11950 UNITED STAT HEAT-TREATING ALUMINUM FOIL Alexander G. Jarvieand Cyril H. Hannon, Pittsfield, Mass, assignors to General Electric Company, a corporation of New York N Drawing. Application March 3, 1948, Serial No. 12,897

1 Claim.

This invention relates to the heat treatment of aluminum foil, either in roll or stacked form,

in an atmosphere and, more particularly, in an atmospher designed to prevent sticking of adjacent layers of aluminum foil during and after heat treatment.

One of the steps in the manufacture of aluminum foil is an annealing operation which is used to impart ductility to the foil and to remove lubricants from the surface of the foil. The lubricant, which may comprise a hydrocarbon oil, a metallic soap solution or the like, is applied to the foil to control friction and heat generated during the rolling process. The ordinary processes of annealing have not been successful in removing all of the lubricant Without resulting in the oxidation of the lubricant and the aluminum surfaces. The net result is that the layers of the foil stick together, thus resulting in severe losses during subsequent unwinding and rewinding. This result is particularly objectionable in the subsequent use of the annealed foil in the manufacture of capacitor rolls Where the winding of such rolls is carried on in high speed Windin'g machines. In such case any tendency of the foil to stick seriously interferes with the winding operation and causes excessive breaking and uneven winding of the foil.

We have discovered that the sticking of aluminum foil during the annealing process may be prevented by heating it in an atmosphere of controlled composition, characterized by specified limits on the percentage of the gas constituents. We have discovered that the atmosphere used may be reducing, neutral, or oxidizing in chemical nature, to the limited extent of certan prescribed percentages of the gas constituents.

According to our invention th controlled atmosphere comprises not less than 70% by volume of nitrogen, not more than by volume of carbon dioxide, not more than 1% by volume of oxygen, less than 2.1 by volume of water vapor, the remainder comprising reducing gases.

It is, therefore, the primary object of this invention to provide an atmosphere in which the annealing of aluminum foil is carried out in an atmosphere comprising primarily nitrogen in a major proportion and reducing gases, oxidizing gases, or both in definitely limited quantities.

As an example of our invention, an atmosphere having the following composition has been found to be satisfactory for annealing aluminum foil in stacked or coil form whereby the foil is prevented from sticking during and after the annealing operation:

Not less than by volume of nitrogen Less than 1% by volume of oxygen Less than 2.1% by volume of water vapor Not over 10% by volume of carbon dioxide The remainder comprising reducing gases, such as hydrogen, carbon monoxide and methane.

While th method of preparing the above atmosphere is not critical to the present invention, such an atmosphere can be obtained by incompletely burning a hydrocarbon mixture such as city gas in a reaction chamber. By varying the proportions of air and gas burned in a manner well understood by those skilled in the art, the composition of the resulting gases coming from the reaction chamber may be controlled so as to produce any desired composition within the range set forth above. Where the ratio of air to gas is such that nearly perfect combustion is obtained the resulting gas becomes strongly oxidizing in nature. Thus, if nearly all the hydrogen, carbon monoxide and methane are consumed, the resulting atmosphere will be high in nitrogen and will also contain more than 10% carbon dioxode. On the other hand, if such gaseous mixture is partially burned by using a smaller amount of air, the nitrogen and carbon dioxide content will be lower. For the purposes of our invention, it is essential that the nitrogen content should not drop below 70% by volume of the total atmosphere. It is also necessary that the oxygen content of the atmosphere be maintained within predetermined limits or sticking of the foil will result. As previously stated, the oxygen content should be less than 1%, preferably in amounts of about 0.6%. This sticking of the foil also accounts for the 10% limitation on the content of the carbon dioxide as well as the limitation on the amount of water vapor that may be present.

In racticing the method of our invention, with the view in mind of preventing the adjacent layers of the aluminum foil from sticking during and after the annealing step, the aluminum foil is placed in an enclosed space and enveloped in a controlled atmosphere as outlined above. This atmosphere is maintained in the enclosed spaced during the entire period of the annealing operation. After the annealing operation is completed the aluminum foil is allowed to cool and may then be removed from the heating chamber. No further treatment of the aluminum foil is necessary to facilitate its being unwound and rewound into capacitor rolls without the interlayer sticking that has been so prevalent in the processes employed prior to our present invention.

It is to be understood that the above description is merely illustrative and that the invention is not to be limited in any respect except as defined in the following claim.

What we claim as new and desire to secure by Letters Patent of the United States, is:

The method of preventing interlayer sticking during the heat treatmentof aluminum foil in coil form which comprises heating the coil :at annealing temperatures in a closed chamber in an atmosphere consisting of the incomplete combustion products of a mixture of gaseous hydrocarbons, said atmosphere consisting by volume of not less than 70% nitrogen, not more than 10% carbon dioxide, not more than 1% oxygen, less than 2.1% water vapor and the remainder a mixture of the reducing gases, carbon monoxide, hydrogen and methane.

ALEXANDER G. JARVIE.

CYRIL H. HANNON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES "PATENTS Name Date Schon Feb. 13, 1940 OTHER REFERENCES Controlledntmospheres for the Heat Treatment ofMetalspages 93, 94, and 282. Edited by Jenkins. Published in 1946 by Chapman and Hall, Ltd, London, England.

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