Aluminum vapor degreasing

Small job shop used TCA in a vapor degreaser to clean aluminum metal parts Firm converted to water-based cleaning system... 

The metal tensile-shear adherends were of 2024-T3 aluminum (Aluminum Co. of America). Their dimensions were 5 by 1 by 1/16 inch. The surface of the aluminum was prepared by first vapor-degreasing in trichloroethylene and then etching for seven minutes at 65 °C. in the following solution ... 

Chlorinated solvents, on the other hand, although nonflammable, are relatively toxic and contribute to pollution. In addition, they may leave chloride residues on the metal surface that can later initiate corrosive attack. They are used largely for vapor degreasing (tri- or perchlorethylene), in which the work is suspended in the vapor of the boiling solvent. Care must be exercised in the vapor degreasing of aluminum, ensuring that adequate chemical inhibitors are added and maintained in the chlorinated solvent in order to avoid catastrophic corrosion (see Section 21.1.4.1) or, in the extreme, to avoid an explosive reaction. 

Several surface preparations of aluminum are widely used in the aircraft industry. " The important steps in all surface preparations are vapor degrease, alkaline clean, rinse with water, chromic acid etch (FPL Etch), rinse with water, anodize with chromic acid or phosphoric acid, rinse with water, and dry at 140-160°F. Details of the procedures for the surface preparation of aluminum and other metals and composites are available from a number of sources. 

Figure 9. Effect of surface treatment on the durability of epoxy/aluminum joints exposed to room temperature water immersion. (1) Anodized, (2) grit-blasted plus vapor degrease, (3) vapor degrease, (4) chromate conversion coating. Reprinted from ref. 3, p. 71, by courtesy of Marcel Dekker Inc.

In a second typ>e of airless vapor degteaser, the air is removed to produce a vacuum. This typ>e of airless machine is the most common — a vacuum-to-vacuum machine, a vacuum vapor degreaser. This is done to expose solvent soDed surfaces which are complex and difficult to thoroughly wet, flush, and dry. Examples are multiport injectors, aluminum/alloy honeycomb stmctures used as pands in constmction of aircraft, metal or glass filtration media, long tubing, and completed assemblies of components. 

The simplest type of surface pretreatment for aluminum or any metal is to solvent-wipe or vapor-degrease the as received metal. This will obviously remove most kinds of loosely adhering dust or dirt or other atmospheric deposits as well as organic greases, lubricants, and... 

KEROSENE. Kerosene has been processed and handled in aluminum alloy equipment. Aluminum alloys have also been us for vapor degreasing equipment. See also Ref (Dp. 135. (3) pp. 218, 219. 

The present test sequence depends on the cleanliness of the striker pin and the aluminum test cups for reliable results. The cups are first put through a trichloroethylene vapor degreasing step following a caustic or chem-mill dip to remove any imbedded material in the aluminum surface, then are deoxidized and rinsed with distilled water. After warm air drying, these cups are stored in a closed container until needed. 

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