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why do parts need to be clean
- Prepare surface for subsequent 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
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chemical cleaning and mechanical cleaning.
name chemical cleaning methods
- ▪ Alkaline cleaning - uses alkali to remove oils, grease, etc. most widely used. immersion or spraying followed by water rinse
- ▪ Emulsion cleaning - organic solvents (oils) in an aqueous solution (soaps). must have alkaline cleaning
- ▪ Solvent cleaning - chemicals that dissolve soils - hand wiping, immersion, spraying, vapor degreasing (hot vapors of chlorinated)
- ▪ Acid cleaning - use acid solutions conbimed with water miscible solvents - soaking, spraying, manual brushing. acid pickling is more severe
- ▪ Ultrasonic cleaning - mechanical agitation of cleaning fluid by high frequency vibrations to cause cavitation
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chemical cleaning and mechanical cleaning.
name mechanical cleaning methods
- Blast finishing - high velocity impact of particulate media to clean and finish a surface - sand blasting
- ▪ Shot peening - high velocity stream of small cast steel pellets directed at metallic surface to cold work and induce compressive stresses into surface layers; used to improve fatigue strength of metal, different than blast finishing
- ▪ Mass finishing processes - tumbling, vibratory finishing; mixing action in a container, might be with an abrasive
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if we wanna impregnate the surface with foreign atoms, how!
alter surface chemistry
diffusion - diffusing atoms of a diff material into surface at high temperatures. dont to increase corrosion resistance/oxidation resistacnce
ion implantation - high energy beam of ionized particles, can do in low temp. used to fabricate semiconductor devices
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how to plate. what processes are involved
- 1. electroplating - metal ions in an electrolyte are deposited onto a cathode workpart
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apply faraday's law, C is the amount of plating material deposited onto cathodic workpart per electric charge
- 2. electroforming - electrolytic deposition of metal onto a pattern until required thickness is achieved, pattern is then removed. parts are thicker
- 3. electroless plating - all chemical, no electric current
- 4. hot dipping** - metal substrate is immersed in a molten bath of a second metal. second metal coats the first for corrosion protectio (Zn, Al, Sn, St). galvanizing, aluminizing, tinning
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