What is Surface processing?
A process to improve the mechanical or physical propertie sof the material that doesn’t intentionally alter the part geometry.
What is cleaning used for?
Prepare the surface for subsequent industrial processing, such as a
coating application or adhesive bonding
Improve hygiene conditions for workers and customers
Remove contaminants that might chemically react with the surface
Enhance appearance and performance of the product
What are the major chemical cleaning methods?
Alkaline cleaning, Emulsion cleaning, Solvent cleaning, Acid cleaning and Ultrasonic cleaning.
What factors have to be considered when selecting a chemical cleaning process?
The contaminant to be removed
Degree of cleanliness required
Substrate material to be cleaned
Purpose of the cleaning
Environmental and safety consideration
Size and geometry of the part
Product and cost requirements
What is mechanical cleaning and what additional functions can it serve?
Mechanical cleaning removes soils, scales, or films from surfaces using abrasives and also can help with deburring and improving surface finish.
What are the main mechanical cleaning methods?
Blast finishing cleans and finishes surfaces using high-velocity particles (e.g., sandblasting). Shot peening directs steel pellets at a metal surface to create compressive stress. Mass finishing processes parts in bulk by mixing them with abrasive media (e.g., tumbling).
Explain the two surface modification methods
Diffusion: atoms of another element penetrate a material’s surface, with concentration highest at the surface, used in surface hardening (e.g., carburizing, nitriding).
Ion implantation: high-energy ions embed into the surface, altering properties in a much thinner layer than diffusion.
What are some advantage of Ion implantation?
Low temperature processing
Good control and reproducibility of penetration depth of
impurities
Solubility limits can be exceeded without precipitation of
excess atoms
No problems with waste disposal as in electroplating and
many other coating processes
No discontinuity between coating and substrate
What is plating?
Coating of a thin metallic layer onto the surface of a
substrate material
Explain the two methods of plating
Electroplating: electrolytic process in which metal ions in an electrolyte solution are deposited onto a cathode work part.
Hot dipping: Immersion of a metal substrate in a molten bath of a second metal; upon removal, the second metal is coated onto the first with the primary purpose of corrosion protection
What is conversion coating
Family of processes to form a thin film of oxide, phosphate, or chromate on a metallic surface by chemical or electrochemical reaction
What is the main method of conversion coating
Anodising: Surface coating is formed through electrochemical reaction of the substrate metal into an oxide layer
What are the main differences between anodising and electroplating
In electroplating the part is the cathode and coating is form by adhesion of ions to the base metal
Anodising: the part is the anode and the coating is formed through a chemical reaction in of the substrate metal into the oxide layer.
What is vapour deposition
Processes to form a thin coating on a substrate by either condensation
or chemical reaction of a gas onto the surface of the substrate
What are the methods of vapour deposition
Physical vapour deposition (PVD) and Chemical vapour deposition (CVD)
Explain PVD
Step 1: synthesis of the coating vapour
Step 2: vapour transport to the substrate
Step 3: condensation of vapours onto the substrate surface
Has three types: Vacuum evaporation, Sputtering, Ion Plating
Explain CVD
The process is carried out in a reactor where the chemical decomposition of a mixture of gases on the surface of a heated substrate forming a solid film on the substrate
What are the avantages and disadvantages of CVD
Advantages :Lower deposit temperatures, Control of coating grain size, No vacuum, strong bonding between coating and substrate
Disadvantages: specilised equipment needed (chamber and pump), can be expensive, low material utilisation
Explain thermal spraying
A molten or semi molten material is sprayed onto a substrate where they solidify and adhere to the surface.
