Surface Treatments Flashcards
(38 cards)
Why are metals normally coated by electroplating
-Provide corrosion protection
-Enhance appearance
-increase electrical resistance
-prepare a metallic surface for subsequent processing
-rebuild surface worn or eroded during service
Examples of why non metallic materials might be coated
-plastic coated to look metallic
-anti reflection on optical glass lenses
- coating in fabrication of semiconductor chips and printed circuit boards
Why should manufactured parts be cleaned
-to prepare surface for subsequent processing
- improve hygiene conditions
-remove contaminants that might chemically react with surface
-enhance appearance and performance of product
Factors to choose cleaning method to be used
- contaminant to be removed
-degree of clean,Iness required
-substrate to be cleaned
-purpose of cleaning
-environment and safety factors
-size and geometry of part
-production and cost requirements
Types of chemical cleaning
Alkaline cleaning
Emulsion cleaning
Solvent cleaning
Acid cleaning
Ultrasonic cleaning
Mechanical cleaning
Removal by means of abrasives or similar mechanical action
Blast finishing
Uses high velocity impact of particulate media to clean and finish a surface (e.g. sand blasting). Media is propelled at target by pressurised air or centrifugal force. Sometimes performed wet in slurry
Shot peeing
High velocity stream of small cast steel pellets is directed at surface with the effect of cold working and inducing compressive stresses into the surface layers. Acts to improve fatigue strength but also accomplishes cleaning
Mass finishing
Finishing of parts in bulk by a mixing action inside a container, usually in the presence of an abrasive media. Mixing causes parts to rub against media achieving desired finish.
What type of parts are usually finished by mass finishing
Small parts which would be uneconomical to finish individually
Tumbling (type of mass finishing)
Uses centrifugal force ina horizontally oriented barrel. Finishing performed by landslide action, where oaths rise in barrel due to rotation then tumble down.
Why is barrel finishing slower than other mass finishing methods
Only the top layer of parts is being finished at any moment.
Disadvantages of barrel finishing
Slow, noisy and large floor space required
Playing
The coating of a thin metallic layer onto the surface of a substrate material,
Electroplating
Metal ions in an electrolyte solution are deposited onto a cathode workpart. Anode generally serves as source of metal.
Electroforming
involves electrolytic deposition of metal onto a pattern until the required thickness is achieved. Pattern is then removed to leave formed part
Patterns used in elecroforming
Solid of expandable
Solid have a taper or other geometry that allow for removable
Expandable air destroyed
How to electro form a non conductive material
Material must be metallized
Electroless plating
Plating driven entirely by chemical reactions. Occurs in an aqueous solution containing ions of metal to be plated. Process uses a reducing agent and workpart surface acts as catalyst for the reaction. Cost is usually greater than electrochemically plating
Advantages of electroless plating
-uniform plate thickness on complex geometries
-process can be used on both metallic and non metallic substrates
-no need for DC power supply
Anodizing
An electrolytic treatment that produces a stable oxide layer onto a metallic surface.
Anodizing use
Decoration and corrosion protection
Anodizing vs electroplating
-in electrochemical, workpart thats coated js cathod. In Anodizin, work is anode and processing tank is cathodic.
-in electroplating, coating grown by adhesion of ions of a second metal. In Anodizing, surface is formed by chemical reaction of substrate metal into an oxide layer
Organic coatings
These are polymers and resins formulated to be applied as a liquids that dry and harden as thin surface films on substrate materials.
