Serkan Orhan, 030070165, 5th Week Part2

4)Galvanic Corrosion: [Group: Failure mode]
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Galvanic corrosion, often misnamed “electrolysis,” is one common form of corrosion in marine environments. It occurs when two (or more) dissimilar metals are brought into electrical contact under water. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. Either (or both) metal in the couple may or may not corrode by itself (themselves) in seawater. When contact with a dissimilar metal is made, however, the self-corrosion rates will change: corrosion of the anode will accelerate; corrosion of the cathode will decelerate or even stop.

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Galvanic corrosion is either a chemical or an electrochemical corrosion. The latter is due to a potential difference between two different metals connected through a circuit for current flow to occur from more active metal (more negative potential) to the more noble metal (more positive potential).
Galvanic coupling is a galvanic cell in which the anode is the less corrosion resistant metal than the cathode. Figure 1.5 shows atmospheric galvanic corrosion of a steel bolt-hexagonal nut holding a coated steel plate and electrical control steel box attached to a painted steel electrical post. Both corroded bolt-nut and the steel box are the anodes having very small surface areas, while the coated steel plate and the steel post have very large cathodic surface areas. Corrosion rate can be defined in terms of current density, such as i= I/A where I is the current and A is the surface area. Therefore, the smaller A the larger i. This is an area effect on galvanic coupling. Thus, the driving force for corrosion or current flow is the potential (voltage) E between the anode and cathode. Subsequently, Ohm's law, E = IR = iAR, is applicable. Here, R is the galvanic cell resistance.

(Electrochemistry and corrosion science, Nestor Perez,2004,p. 7)

5)Design For Recycling: [Group: Design Method]

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Design for Recylcing is a list of principles to save and reuse raw materials in order to move towards more sustainable development, the following possibilities can be considered;

• reducing material use through better utilisation and by reducing waste during production

• substituting materials for those becoming rare and expensive

• recycling materials by reusing or reprocessing production waste, products and parts of products.

In what follows, possible types of recycling and recycling processes are explained based on VDI Guideline 2243. Production waste recycling involves reusing production waste in a new production process, for example offcuts (after they have been preprocessed).

Product recycling involves reusing a product or part of it, for example reusing a vehicle’s engine (after it has been reconditioned).

Used material recycling is the reuse of old products and materials in a new production process, for example the reprocessing of materials from scrapped vehicles (after they have been preprocessed). These secondary materials or parts do not necessarily have a lower quality than new materials or parts, in which case they can be reused. When the quality is significantly reduced, they can only be used for other purposes.

Preprocessing and reconditioning make significant contributions to effective recycling.

(Engineering Design - A Sytematic Approach, 3rd Edition, Pahl G., Weitz B., Felhuldsen J, 2007, Pages: 388 - 389)

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Design for Recycling (DfR) is a design approach which aims to reuse as much of a product as possible when it reaches the end of its life. ('End of life' is now widely used to describe the products a consumer has used and then thrown away.) DfR offers an increasingly successful approach to recycling as a sustainable approach to design, manufacturing and disposal. It should be thought of as an integrated design strategy, starting with suitable material selection for a design at its initial stages. Getting the material right helps with its identification and recycling at the end of a product's life. When DfR is built into the beginning of the manufacturing and design process it enhances a product's potential for disassembly, reuse and refurbishment, and supports a product's function and market success. So DfR not only saves resources but makes sound business and economic sense. 

Several international companies have led the field of DfR research and tackled the key problem of ensuring that materials are labelled to identify them and kept them separate for easy reclamation. Once the material has been located it can then be prepared for reuse by cleaning, grading, shredding or blending before being reintroduced into the manufacturing cycle. `Recyclate' is the technical term for a new material made from recycled elements. 

The Japanese car company Toyota offers an interesting case study. In 1998 it claimed to be the industry's first manufacturer to introduce recycling strategies of easy removal at the design stage. Seven years later, Toyota's Eco-VAS programme introduced an environmental evaluation system that included life-cycle assessment (LCA) from the development process through to production, use and disposal. Toyoto claims up to 83 per cent of their vehicles are now recycled. Notable here is the research and investment the company made in the reduction of processing the shredder residue generated by end-of-life vehicles. Another successful innovation is its car-bumper and recycling scheme to recover materials and components, which Toyoto rolled out throughout its Japanese distribution centres. 

Another key strategy for successful DfR is the use of a single type of material (mono-material components) in a product. A good example is the plastic drinks bottle, which previously comprised separate and incompatible plastics for the bottle itself, screw top and sleeve. By introducing a bottle using only one plastic for all three elements, nothing is thrown away after recycling and the material collected is pure-grade PET. This simple idea means that it is no longer necessary to separate the collected material or use chemical separating treatments. The ecobottle is also an example of design aiding DfR, because its conical shape means that bottles can be screwed inside each other and piled up for easy storage before recycling. The low neck of the ecobottles also means that the pile increases by only 1.5 cm for each bottle added. 

New legislation to determine DfR targets within the consumer electronics industry will also shape the future of the design profession. DfR will be given a new impetus to set targets for the safe disposal, recovery, recycling and reuse of electrical and electronic components. 

(Design: the key concepts,Catherine McDermott,2007,pp. 77-78)