Chapter 27: Surface Processing Operations

What are the two basic mechanisms of corrosion protection provided by hot dipping?

1. Barrier protection, in which the coating simply covers the substrate to protect it 3. Sacrificial protection, in which coating metal corrodes sacrificially to protect the substrate

What are some of the advantages of chemical vapor deposition?

1. Capability to deposit refractory materials at temperatures below their melting or sintering 2. grain size control 3. Process is performed at atmospheric pressure 4. good bonding to substrate surface.

What are the basic types of contaminants that must be cleaned from metallic surfaces in manufacturing?

1. Oil and grease 2. solid particles, such as metal chips abrasive grits, shop dirt, and dust 3. Buffing and polishing compounds 4. Oxide films, rust, and scale

Identify the most common types of coating processes

1. Plating 2. Chemical conversion coatings 3. Vapor deposition processes such as PVD and CVD 4. Organic coating such as painting 5. Porcelain enameling 6. Thermal and mechanical coating processes

Why are metals coated?

1. Provide corrosion protection 2. Enhance appearance 3. Provide a specific color 4. Increase electrical conductivity 5. Increase electrical resistance 6. Prepare surface for subsequent processing 7. Rebuild worn or eroded surfaces

What are some important reasons why manufactured parts must be cleaned?

1. To prepare the surface for subsequent industrial processing 2. To improve hygiene conditions 3. To remove contaminants which might chemically react with the surface 4. To enhance product appearance and performance.

Name some of the important chemical cleaning methods.

1. alkaline cleaning 2. Emulsion cleaning 3. Solvent cleaning 4. Acid Cleaning and pickling 5. Ultrasonic cleaning

identify the four major types of ingredients in organic coatings

1. binder - which are polymers 2. dyes or pigments which provide color 3. solvents 4. additives such as surfactants and plasticizers

What is a conversion coating?

A conversion coating is a thin coating produced by chemical reaction of the metallic surface. The most common conversion coatings are phosphates, chromates, and oxides

How does anodizing differ from other conversion coatings?

Anodizing uses electrochemical processing methods to convert the metallic surface. The best example is aluminum anodizing.

Why is calorizing?

Calorizing is the diffusion of aluminum into carbon steel, alloy steels, and the alloys of nickel and cobalt. The process is also known as aluminizing.

What is the difference between diffusion and ion implantation?

Diffusion is a process in which atoms or molecules move across a boundary between two contacting materials. Ion implantation produces a similar result, but the process involves penetration of high-velocity ions into the surface of a substrate material.

The terms drying and curing have different meanings. What is the distinction?

Drying means evaporation of solvents in organic coating liquid. Curing involves a chemical change in the organic resin which hardens the coating.

How does electroless plating differ from electrochemical plating?

Electroless plating uses only chemical reactions to form the plating; electroplating uses electrolysis

In porcelain enameling, what is frit?

Frit is glassy porcelain prepared as fine particles (powders) by crushing and milling.

What is the difference between physical vapor deposition (PVD) and chemical vapor deposition (CVD)?

In PVD, the coating vapors are synthesized by heating the coating material allowing it to dense as a thin film on the surface of the work part. In CVD a coating is formed on a heated substrae by the chemical reaction or dissociation of vapors and/or gases; the reaction product nucleates and grows on the substrate surafce.

What are some of the applications of PVD?

PVD applications include: decorative coatings on trophies and automotive trim, antireflection coatings on optical lenses, deposition of metal in electronic connections and coatings on cutting tools

What is meant by the term mass finishing?

Parts are mechanically cleaned and deburred in bulk, usually in a barrel by the mixing action of an abrasive media.

What is physical vapor deposition?

Physical vapor deposition (PVD) refers to a family of process in which a material is converted to its vapor phase in vacuum chamber and condenses onto a substrate surface as a very thin film.

Mechanical surface treatments are often performed for reasons other than or in additions to cleaning. What are those reasons.

Reasons for mechanical surface treatments include deburring, improving smoothness, adding luster, and enhancing surface properties.

In addition to surface cleaning, what is the main function performed by shot peening?

Shot peening is primarily used to improve the fatigue strength of metals by cold working the metallic surface

What is the most commonly plated substrate metal?

Steel

Name the commonly used coatings materials deposited by PVD onto cutting tools.

The common coating materials deposited by PVD onto cutting tools are titanium nitride (tiC), and aluminum oxide (AI_2O_3). TiN is probably the most common

Describe the principal methods by which organic coatings are applied to a surface.

The main methods include bushing and rolling, spraying, immersion, and flow coating

What are the two most common titanium compounds that are coated onto cutting tools by chemical vapor deposition?

TiC and TiN

What is meant by the term transfer efficiency in organic coating technology?

Transfer efficiency is the proportion of organic coating liquid that is deposited on the target surface. The rest is waste.