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Stress Corrosion Corrosion Fatigue Fretting Corrosion Heat Treatment |
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Processes and materials used in corrosion control
Metal Finishing. Aircraft parts are almost always given some type of surface finish by the manufacturer. The main purpose is to provide corrosion resistance increase wear resistance or to provide a suitable base for paint. In most instances the original finishes cannot be restored in the due to nonavailability of equipment or other limitations. However, an understanding of the various types of metal finishes is necessary if they are to be properly maintained in the field and if the partial restoration techniques used in corrosion control are to be effective. Surface Preparation. Original surface treatments for steel parts usually include a cleaning treatment to remove all traces of dirt, oil, grease, oxides, and moisture. This is necessary to provide an effective bond between the metal surface and the finish. The cleaning process may be either mechanical or chemical. In mechanical cleaning the following methods are employed : wire brush, steel wool, emery cloth, sandingblasting, or vavor blasting. Chemical cleaning is preferred over mechanical since none of the base metal is removed by cleaning. These are various chemical processes now in use, and the used will depend on the material being cleaned and the type of foreign matter being removed. Steel parts are pickled to remove scale, rust, or other foreign matter, particularly before plating. The pickling solution is kept in stoneware tank and is usually heated by means of a sream coil. Parts not to be electroplated after pickling are immersed in lime bath to neutralize the acid from the pickling solution. Electrocleaning in another type of chemical cleaning used to remove greas, oil,organic matter. In this cleaning process, the metal is suspended in a hot alkaline solution containing special wetting agents, inhibitors, and materials to provide the necessary electrical conducticity. An electric current is the passed through the solution in a manner similar to the used in electrolpating. Aluminum and magnesium parts are also cleaned by using some of the foregoing methods. Blast cleaning is not applicable to thin aluminum sheets particularly alclad. Steel grits are not used on aluminum or corrosion resistant metal. Polishing, buffing, and coloring of metal surfaces play a very important part in finishing of metal surfaces. Polishing and buffing operations are sometimes used when preparing a metal surface for electroplating, and three operations are used when the metal surface requires a high-luster finish. Electroplating. Electroplating is the processes of transferring metal from one object to another by chemical and electrical means. Several reasons for applying plated coatings are : (1) To protect the base metal (metal being plated) against corrosion. Tin, zinc, nickel, and cadmium are some of metals used to form a protective coating on another metal by electrolytic action. (2) To protect the base metal against wear, caused by abrasion or fretting corrosion. Chromium plating is extensively used for wear resistance on gages, dies, oleo piston, and cylinder barrels. Nickel plating can also be used thi purpose. (3) To produce and retain a desired appearance (color and luster), as well as improve resistance to tarnish. Gold, nicke, or chromium plating can be used this application. (4) To protect a base metal against some special chemical reaction : for example, copper plating is sometimes used prevent certain parts of component manufactured of steel from absorbing carbon during case hardening. (5) To increase the dimensions of a part. This process, known as "building up" may be applied to parts accidentally made undersize, or to worn part. Nickel or chromium plating is commonly used for this purpose. (6) To serve as base for further plating operations, reduce buffing coats, and ensure bright deoposits of nickel or nickel and chromium. Copper is commonly used this purpose. |
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| Corrosion of ferrous metals. | ||
| One of the most familiar types of corrosion is ferrous oxide,.. | ||
| Corrosion of aluminum and aluminum alloys. | ||
| Corrosion attack on aluminum surfaces is usually quite obvious, | ||
| Corrosion of magnesium alloys. | ||
| Magnesium is the most chemically active of the metals used,. | ||
| Treatment of titanium and titanium alloys. | ||
| Attack on titanium surfaces is generally difficult to detect | ||
| Protection of dissimilar metal contacts. | ||
| Certain metals are subject to corrosion when placed in contact with other metals | ||
| Processes and materials used in corrosion control. | ||
| Aircraft parts are almost always given some type surface finish | ||
| Chemical treatment. | ||
| Parco Lubrizing in a chemical treatment for iron and steel parts | ||
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