Handling & Storing Aluminum
Aluminum is one of the easiest materials to keep in good condition. It has a high resistance to corrosive conditions normally encountered during shipment and storage, and a little care will maintain its original appearance for a long time. The principal things to guard against are Conditions that might cause surface abrasions or water stains.
Suppliers make every effort to pack aluminum so that "traffic marks" or "rub marks" do not occur during shipment and so that it remains dry. All incoming shipments should be inspected promptly, however, since both transportation lines and suppliers have a time limit in which damage claims will be honored.
Traffic marks may appear as scratches, surface abrasions or a condition resembling cinders embedded in the metal. They result from mechanical abrasion and subsequent oxidation of the abraded areas. Their principal disadvantage lies in this unsightliness and their effect on finishing operations. To avoid traffic marks suppliers pack the metal so that it is not subjected to undue flexing or twisting and so that the units within a package do not rub against one another. Products subject to damage by flexing or bending usually are packed on skids or in lumber boxes. Paper or chipboard is used where necessary for cushioning thin or soft metal. Steel strapping is used to reinforce skids and boxes and to bind wrapped bundles.
Water stains are nonmetallic in appearance and, while usually whitish, may appear iridescent, depending upon the alloy or degree of oxidation. They are caused by the entrapment of moisture between the adjacent surfaces of closely packed material. The purer aluminum alloys are more resistant to water stain, while the condition seems most pronounced on those alloys having high magnesium content, water stain is a superficial condition and the mechanical properties of the metal having such stains are not affected. If a shipment of aluminum arrives in a wet condition, it should be thoroughly dried before storing. This may be done by evaporation in air or by means of dry air currents. When the moisture is removed in this manner within a short period after the metal becomes wet, staining is usually prevented. If staining has occurred, and the moist condition causing it is removed, the stain will not continue to develop. Once safely dry, the metal should not be stored near such obvious water sources as steam end water pipes, and it should be kept at a reasonable distance from open doors and windows.
Condensation is perhaps the most troublesome cause of water stains. It may be prevented by avoiding conditions where the temperature of the metal drops below the dew point of the surrounding air; or, conversely, conditions where the moisture of the air increases enough to carry the dew point above the metal temperature. It is almost impossible to insure that a sudden fall in temperature or increase in humidity does not occur in the places of storage.
Aluminum packed in original boxes should never be left in the open, because the greater variations in temperature and humidity outdoors increase the possibility of condensation. Even if the package is wrapped with "waterproof" paper, the impossibility of obtaining a perfect seal makes outdoor storage highly undesirable. So called waterproof packages are designed solely for the protection of the metal during shipment and are not meant to withstand any extended exposure to the weather.
If possible cold metal should be placed in a dry storage place until its temperature has increased substantially before it is brought into a heated room with a higher humidity. This may be accomplished by placing a new shipment in temporary storage where its temperature is raised slowly to that of the permanent storage room.
Where water stains have occurred, the degree of staining may be judged fairly accurately by the relative roughness of the stained area. If the surface is reasonably smooth, the stain is merely superficial, and its appearance can be improved by mechanical or chemical treatments. Scratch brushing or the use of steel wool and oil-is effective in removing water stain. If a chemical dip without undue etching is preferred, an aqueous solution containing ten percent by volume of sulfuric acid and three per cent by weight of chromic acid at about 180"F may be employed.
In storing aluminum it is desirable to avoid contact between it and other metals since this sometimes results in scratches or other marks. The use of wood faced shelving racks and bins is recommended. It is also good practice to keep aluminum away from caustics, nitrates, phosphates, and most acids.
In the continuous use of large quantities of metal, the oldest stock should be used first. Occasional checking of the stock on hand will help to prevent any serious corrosion.
1330 N. Kraemer Blvd. - P.O. Box 6380 - Anaheim, CA 92816
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