Which of the following is NOT a mechanical finishing process?

Explanation:

Mechanical Finishing Processes:

Mechanical finishing processes are techniques used in manufacturing to improve the surface properties of a material, such as its appearance, texture, and functionality. These processes can include methods that physically alter the surface through mechanical means. Common mechanical finishing processes include burnishing, shot peening, and buffing.

Correct Option Analysis:

Pickling

Definition: Pickling is a chemical finishing process used in metallurgy to remove impurities, such as stains, inorganic contaminants, and rust from metal surfaces. This process typically involves immersing the metal in an acidic solution, which reacts with the surface to clean it. Unlike mechanical finishing processes, pickling relies on chemical reactions rather than physical abrasion or deformation.

Working Principle: The metal is submerged in a bath containing an acid, usually hydrochloric acid or sulfuric acid. The acid reacts with the oxide layers and other contaminants on the metal surface, dissolving them and leaving a clean, reactive surface. After the pickling process, the metal is rinsed and sometimes neutralized to remove any remaining acid residues.

Advantages:

• Effective at removing oxide layers and other contaminants that mechanical processes may not fully eliminate.
• Can prepare metal surfaces for further processing, such as plating or painting.

Disadvantages:

• Involves the use of hazardous chemicals, which require careful handling and disposal.
• May cause surface etching or roughening, depending on the type of acid and duration of exposure.

Applications: Pickling is commonly used in the steel industry to clean hot-rolled steel before further processing, such as cold rolling or coating. It is also used in stainless steel production and other metalworking industries where clean surfaces are crucial.

Important Information:

To understand why pickling is not considered a mechanical finishing process, it is essential to analyze the other options provided:

Burnishing

Definition: Burnishing is a mechanical finishing process that involves rubbing a hard tool against the surface of a metal to improve its smoothness and appearance. This process compresses the surface layers, resulting in a polished finish and increased hardness.

Advantages:

• Produces a high-quality, mirror-like surface finish.
• Enhances surface hardness and wear resistance.

Applications: Burnishing is often used in the manufacturing of precision components, such as shafts and gears, where a smooth surface finish is critical.

Shot Peening

Definition: Shot peening is a mechanical finishing process that involves bombarding the surface of a material with small spherical media, such as steel shots or glass beads. This process induces compressive residual stresses, improving fatigue resistance and surface strength.

Advantages:

• Enhances fatigue resistance and longevity of components.
• Creates a uniform surface texture.

Applications: Shot peening is widely used in the aerospace and automotive industries to improve the durability of critical components, such as springs and gears.

Buffing

Definition: Buffing is a mechanical finishing process that involves polishing the surface of a material using a rotating cloth wheel and abrasive compounds. This process smooths and brightens the surface, enhancing its appearance.

Advantages:

• Produces a high-gloss finish on metal surfaces.
• Removes minor surface imperfections and scratches.

Applications: Buffing is commonly used in the manufacturing of consumer products, such as automotive parts and jewelry, where a polished finish is desirable.

By comparing these processes, it is clear that pickling does not fit the criteria of a mechanical finishing process. While burnishing, shot peening, and buffing all involve physical interaction with the material surface to achieve the desired finish, pickling relies solely on chemical reactions.