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Air Carbon Arc Cutting

In the air carbon-arc cutting (AAC), the arc is normally obtained between a copper- coated graphite or carbon electrode and the workpiece with the molten metal being forced out by means of compressed air at apressure of 550 to 690 kPa. It may be possible to use a very low pressure of order of 280 kPa in some manuan torches for field application but is not generally recommended. The air consumption is in the range of 85 to 1400 L/min depending on the thickness of the metal being cut. The copper coating is used to reduce the oxidation of the electrodes and to help cool the electrode. 

(Rao P. N., Manufacturing Tehcnology Vol. I, 2009, p. 394-395)

 Hot Dipping 

Zinc is the metal most widely applied by this method, and for heavy steel sections is the only one. Tin and lead are commonly applied by hot-dipping but not for structural steelwork. Aluminum is also applied by this method, particularly to sheet steel, which is marketed as a pre-coated product, often as Zn-Al-coated steel. Although aluminium can be applied to havier sections of steel by hot-dipping, it is a more difficult and expensive process then for zinc and is rarely, if ever, used. However, if an economic form of this process could be developed it might well prove to be a suitable method of coating with alıminium, which, in many situations, provides a higher degree of corrosion resistance than does zinc.

Zinc is particılarly suited to hot-dipping because of its low melting point (420 ⁰C) and the nature of the alloy layer formed during the process. For many years hot-dipped galvanising has been specified by BS 729:1971 (1986). A new International and European Standard BS EN ISO 1461:1999 has now been published. Aluminium is by no means as easy to apply by dipping techniques. It has a higher melting point than zinc (660⁰C) and this means that the bath usually has to be operated at a temperature over 700⁰C. At this temperature the reaction between aluminium and steel is rapid, resulting in high dross formation. Futhermore, at this temperature, because of the reaction with steel, it is necessary to use ceramic-lined tanks, which are more expensive than the standart steel type used for Zinc. Aliminium oxides readily to produce an oxide (Al₂O₃) and this makes fluxing more difficult than with zinc. Oxide particles may also become entrapped in the coating.


(Bayliss D. A., Deacon D. H., Steelwork Corrosion Control, 2002 p.169)

Buffing

The purpose of buffing is to improve the surface appearance of the metal and to produce a smooth, tihht surface. Buffing is used as a fina finishing opperation and is particularly adaptable to finishing a localized area of a part. Items such as body prostheses, pacemakers, and heart valves reauire a highly buffed, tight surface to prevent entrapment of particles. Close fitting parts for euipment, such as the modern guidance systems and electronics appilications, require highly polished surfaces obtained by buffing. In addition, sheet sizes too large to be proccesed by other abrasive finishing methods, such as mass finishing or wet blasting, can be economically processed by buffing.

(Donachie M.J., Titanium: A Technical Guide, 2000, p.90)

Superfinishing

Superfinishing is an abrading process, efficient in surface refining of cylindrical, flat, spherical and cone shaped parts. It is not primarily a dimension changing process but mainly used for production fnished surface of fine quality on metals. Only a slight amount of stock is removed (avarage 0.002 to 0.02 mm on a disc). The smoother finishes do not have scratch exhibit any directional effect. The honing process involves two motions whereas superfinishing requires three to five even more. As a result of this motions the abrasive particle path is random and never repeat itself.

The operation is mainly concerned with external work. Superfinishing is generally used for:

(i)                 Correcting inequalities of geometry

(ii)               Removing surface fragmention.

(iii)             Reducing surface stresses and burns and thus restoring surface integrity

(Rajput R. K., A Textbook of Manufacturing Technology: Manufacturing Processes, p. 552)