Chemical milling method for interiors of narrow tubes

Abstract

A method for etching patterns on the interior surface of narrow metal tubes. A thin tube having a narrow internal diameter is dipped into a maskant solution to a depth equal to the distance from the tube end etching is to be stopped. A thixotropic maskant having high edge thickness along the dipped edge is required. The shaft is removed from the maskant and dried. Plural dips to increase maskant thickness may be used, if desired. Both ends of the tube may be dipped to localize the area to be etched away from both ends. The tube is placed in an etching solution which is agitated and replenished as desired. After a suitable period, the tube is removed from the etchant, rinsed, dried and the maskant peeled away. A sharp, even, etched edge results, with a smooth fillet and no leaks of etchant through the maskant. The quality of the etch will be greatly increased where an iron-nickel-chromium alloy such as 718 Inconel is being etched by maintaining the metal ion ratio of the etchant at from about 50 to 60 g/l for the iron ion and from about 35 to 49 g/l for the nickel ion, with the grams per liter of the nickel ion always less than the iron ion.

Dependencies are inferred from the claim text.