The document extensively outlines the various coating and deposition processes, emphasizing the significance of coatings in enhancing product utility, appearance, and durability. It details different types of coatings, including organic, inorganic, metallic, and conversion coatings, along with their specific applications, advantages, and disadvantages. Additionally, it covers processes such as electroplating, electroforming, and hot-dipping, explaining their mechanisms, benefits, and limitations.

1. Unit 2
Coating and Deposition
Process

2. Definition
Coating is defined as the process in which
a “COAT” ( Layer of material) is applied
over the material to improve product utility.
A coating is a covering that is applied to the
surface of an object, usually referred to as the
substrate

3. Reasons for Coating/Plating
● Corrosive Protection
● Improve appearance
● Wear Resistance
● Increase electrical conductivity
● Give shiny appearance
● To provide an reflective surface (Glass)
● Fabrication of semiconductors

6. Types of Coating
Organic Coating :An organic coating is a type of coating whose primary ingredients are derived
from either vegetable or animal matter or from compounds rich in carbon. These coatings are
primarily used to provide additive type finishes on the materials on which they are applied.
Organic coatings can be monolithic (consisting of only one layer) or two or more layers
Organic coatings act as a protective barrier against corrosion and oxidation. These are
durable coatings applied to a substrate for their decorative or specific technical properties.
Organic coatings depend primarily on their chemical inertness and impermeability. Various
types of organic coatings are available for industrial purposes including primers, adhesive
cements and topcoats (enamel, varnish and paints).
Organic coatings are easy to apply with the help of brushes, sprays, rollers, dips, or by
electrostatic means. Brush application is a slow and lengthy procedure. The coating cures or
dries by evaporation or loss of solvent, polymerization and oxidation.

7. Inorganic Coating: Inorganic coatings can be produced by chemical action, with or without electrical
assistance. The treatments change the immediate surface layer of metal into a film of metallic oxide or
compound which has better corrosion resistance than the natural oxide film and provides an effective
base or key for supplementary protection such as paints. In some instances, these treatments can also
be a preparatory step prior to painting.
Anodizing Anodizing involves the electrolytic oxidation of a surface to produce a tightly adherent
oxide scale which is thicker than the naturally occurring film. Anodizing is an electrochemical process
during which aluminum is the anode. The electric current passing through an electrolyte converts the
metal surface to a durable aluminum oxide. The difference between plating and anodizing is that the
oxide coating is integral with the metal substrate as opposed to being a metallic coating deposition.
The oxidized surface is hard and abrasion resistant, and it provides some degree of corrosion
resistance.
Chromate filming A number of proprietary chromate filming treatments are available for aluminum,
magnesium, cadmium and zinc alloys. The treatments usually involve short time immersion in
strongly acid chromate solutions, but spraying or application by brushing or swabbing can also be used
for touch-up of parts

8. Metallic Coating
Metallic coatings contain a metallic element or alloy. Metallic coatings can be applied by using a sprayer,
electrochemically, chemically or mechanically. These coatings are applied on equipment requiring a shiny or
glossy appearance and protection from sunlight, corrosion and oxidation
● Hot dip galvanizing – A process of coating iron, steel or ferrous materials with a layer of zinc. This
done by passing the metal through molten zinc at a temperature of 860°F (460°C) to form zinc
carbonate (ZnCO3
). Zinc carbonate is a strong material that protects steel and can prevent corrosion
in many circumstances.
● Thermal spraying – A group of coating processes in which finely divided metallic coating materials are
deposited in a molten or semi-molten condition to form a coating. The coating material may be in the
form of powder, ceramic rod, wire or molten materials.
● Electroplating – A process of coating a metal with a thin layer of another metal by electrolysis to
improve the metal's corrosion resistance.
● Sherardizing – The formation of a corrosion-resistant, zinc-iron alloy coating on the surface of steel or
iron. The method involves heating the object in an airtight container that has zinc powder. A thermal
diffusion process occurs and the zinc diffuses into the object’s metal surface, forming the zinc-iron
alloy.

9. Conversion Coating
Conversion coating is a type of coating used on metals in which the
surface that is covered is turned into a coating with electrochemical or
chemical processes.
In addition to corrosion protection, conversion coating also offers
enhanced surface hardness. It also can be used as a decorative primer.
Some of the best examples of this coating type include phosphate and
chromate coatings as well as black oxide. It is normally applied on alloys
like aluminum through chromate conversion or anodizing

10. Precoated Metals Coating
In precoated metals, the metals that are taken for production are coated at initial stages as compared to
conventional production method, in which the metal are coated after the production process. The main
advantages of the pre coated metals are as follows:
Beauty:
Architects, manufacturers and consumers appreciate the beauty and benefits of coil-coated metal, including consistent quality, low cost, design flexibility
and green properties
Durability:
Pre-painted metal products are amazingly durable. With the appropriate surface treatments, pre-painted steel and aluminum can be made virtually
waterproof and weatherproof
Innovation:
Manufacturers of the most advanced green building materials and renewable energy products rely on coil coating technology.
Environment:
The coil coating process itself is considered the most environmentally responsible way to apply paint to steel and aluminum substrate
Cost:
The coil coating process is widely known to be the most efficient, effective and environmentally friendly way to pre-clean, pre-treat, pre-prime and
pre-paint metal

11. Electroplating
1. Definition : Electroplating is process in which an layer of coat is adherent to metal with the help of
electrochemical process
2. The cathode is the workpiece and the anode is the metal
3. The process is controlled by electrical current
4. The workpiece is chemically cleaned before the process
https://youtu.be/t7LSLKvwa5Y

13. Working Principle:
Faraday's Laws of Electrolysis
1) The mass of the substance released is proportional to the quality of the electricity passed through the
cell
2) The mass of the materials liberated is proportional to the electrochemical equivalent.

15. Advantages:
1. Helps to protect metal against corrosion
2. Method can be applied to any metal
3. This method is based upon electrical energy that is available
4. Can be effectively used for precious metals such as gold, silver and platinum
Disadvantages:
1. Pollution emitted through chemical
2. Non-uniform plating due to changing current
3. The set up is costly
Application:
1. Making of Jewellery
2. Chromium Plating in decorative items
3. Improving wear resistance of mechanical components
4. Plating of electrical circuits

16. Electroforming
Electroforming is a metal forming process that forms parts through electrodeposition on a model, known in the industry as
a mandrel.
Conductive (metallic) mandrels are passivated (chemically) to preclude 'plating' and thereby to allow subsequent separation
of the finished electroform.
Non-conductive (glass, silicon, plastic) mandrels require the deposition of a conductive layer prior to electrodeposition.
https://youtu.be/t7LSLKvwa5Y

17. Matrix: An negative image of the
part that needs to be prepared

19. Advantages:
1. High Dimensional accuracy
2. High Surface finish
3. Part of any thickness can be produced
4. Special physical/metallurgical properties can be achieved
5. Wide variety of shapes can be produced
Limitation
1. Rate of production is low
2. Not an economical method of production
3. Process is limited to thin products
4. Limited to certain metal
Application
1. Fine moulds and Dies
2. CDs
3. Jewellery

20. Electroless Plating
Electroless plating, also known as autocatalytic plating, or conversion coating, is a way of plating your part
without using an external power source.
Metal ion +Reducing agent Metal Oxidized product
The process involves placing the part in an aqueous solution and depositing nickel, creating a catalytic reduction
of nickel ions to plate the part without any electrical energy dispersal
https://www.youtube.com/watch?v=MhbjQFhZ1bE

22. Advantages :
1. Uniform deposition
2. High Corrosion resistance
3. Does not require electricity
4. Low cost
5. Can also work on insulators such as plastics and ceramics
Disadvantages:
1. Pollution
2. hydrogen embrittlement ( Leakage of Hydrogen gas and diffusion into surface) due to which
brittleness may increase
Application
1. To make mould and Die
2. To make parts of food processing industry
3. To make turbine blade

23. Hot Dipping Process
Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which
alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a
temperature of around 449 °C (840 °F)

24. A typical hot-dip galvanizing line operates as follows:
● Steel is cleaned using a caustic solution. This removes oil/grease, dirt, and paint.
● The caustic cleaning solution is rinsed off.
● The steel is pickled in an acidic solution to remove mill scale.
● The pickling solution is rinsed off.
● A flux, often zinc ammonium chloride is applied to the steel to inhibit oxidation of the cleaned surface
upon exposure to air. The flux is allowed to dry on the steel and aids in the process of the liquid zinc
wetting and adhering to the steel.
● The steel is dipped into the molten zinc bath and held there until the temperature of the steel
equilibrates with that of the bath.
● The steel is cooled in a quench tank to reduce its temperature and inhibit undesirable reactions of the
newly formed coating with the atmosphere

26. Advantages:
1. Provides Non-toxic corrosive resistance
2. Low cost
3. Surface Harding
Disadvantages:
1. Limited product size
2. Risk of distortion due to high temperature

27. Physical Vapour Deposition
Physical Vapour deposition is the process in which a material is converted to its vapour phase in vaccum
chamber and condensed onto substrate as a very thin film.
It can be applied to wide range of materials. The process is divided into three stepts
● Synthesis of vapour
● Vapour Transport
● Condensation

29. Vacuum Evaporation

30. Chemical Vapour Deposition

32. Ingredients of organic coating and
methods of organic coating

34. Powder Coating