Surface Technology - 230317 Flashcards
Advantages of nickel coating
decoration, wear resistance
Mechanical properties nickel coating with low PH (1-4)
LOW: hardness, stress, tensile strength. HIGH: elongation
Mechanical properties nickel coating with high PH (5-6)
HIGH: hardness, stress, tensile strength. LOW: elongation
How do you get the best quality in the edges?
chemistry: better edges, better appearance, Electro: low quality in the edges
In what stage of the process should you do the coating of a piece?
coating before, as early as possible, thermal treatment after the coating
Advantages of galvanizing (zinc coating)
- abundant mineral (cheap)
- galvanized steel is fully recycable (no losing of physical or chemical properties)
- zinc corroted layer (whiterust) is also protective, decades of protection
stages of galvanizing
Surface preparation (degreasing, mild acid). Galvanizing, (dipped into molten zinc), chemical reactions between zinc and iron in steel.
What are the critical parameters in the process?
steel temperature, zinc temperature
What is better for welding?
Zinc iron in the middle, iron is always good for welding.
Aluminum welding
It was not possible to assure that the welding points will work. Welding point of aluminum lower than steel, aluminum high thermal conductivity, difficult to control that the high energy will be concentrated in one point. Now, short time, high energy and this solves the welding problem.
Aluminum painting or steel painting
Primer is always needed.
Most difficult part for corrosion of a car
When it rains, some water goes inside the door since the glass is not sealed completely (it can open).
Typical zinc thicknesses
100 microns of zinc, streetlights, motorway signals. 10 microns of zinc, automotive industry for appearance.
Corrosion intensity as a function of the environment
Indoor, country, Urban, Marine, Industrial (it grows)
Main cause of corrosion
Salt + water. In winter countries: salt to avoid slipping. In warm countries: The seawater.
Two different types of corrosion
Dry corrosion: oxygen. Wet corrosion: acid, base, water + salt.
Possible uses of PVD
Physical Vapor Deposition: Improves conductivity and has a lot of uses in Electronics. Gold coating.
When is a good idea to choose an organic coating?
When the material is not weldable, you paint it and it will get protected.
What is the Daniell-Element electrochemical cell?
Anode: Zinc and zinc sulfate, eventually dissapears. Gives electrons.
Cathode: Copper and copper sulfate, receives electrons.
Converts chemical energy into electrical energy.
Steel high UTS vs. Low UTS (Zufestigkeit)
High: brittle, expensive. Low: ductile and absorbs energy, allowing damage and not transmitting it to the passengers.
Typical thicknesses for sheet metals
Car: 1mm sheets
Buildings: 10mm thickness
Typical processes for Zinc coating
Electrocoating: precise, good elongation.
Dripping: huge parts, buildings and machines.
