Glass Flashcards
What is the use of tempering glass
- When un-tempered glass breaks, it shatters and produces sharp pieces
- Tempering glass means it breaks into tiny less harmful cube like pieces
What the two types of tempering methods
- Thermal tempered
2. Chemically tempered
Describe the process of thermally tempering glass
- Glass is heated to above annealing temp. (720deg)
- The surface is then quenched by blowing cold air on to it (inside still hot)
- Due to the temperature difference the surface contracts and undergoes compression
Describe the process of chemically tempering glass
- Glass contains dissolved (sodium) ions
- If these ions are exchanged for larger (potassium) ions then the surface becomes compressed
Process:
1. Immerse glass in molten potassium nitrate
Describe difference between thermally and chemically tempering glass
- Chemically is tougher than thermally
- Easier to temper chemically
Why is an aircraft windscreen heated an how is it done
Indium tin oxide is laminated in windscreen which conducts electricity.
Small voltage is set across to heat.
Lamination also helps toughen glass
How do resistive touchscreens work
- 2 ITO coated glass sheets are separated by spaces
- When pressed, these meet and create current
- Can work with gloves on
How do capacitative touchscreens work
- A conductive pointer must be used as the screen works by sensing change in the electrical capacitance between 2 conductive films
How are optical fibres made
Drawn out from pre-forms to form fibres < 150 micrometres
Consists of guiding core, cladding and a protective coating (core has a higher refractive index than the cladding)
Why are optical fibres used in aerospace
- used for “fly-by-wire”
- used in computer communications with entertainment systems
- used because data can be multiplexed in optical fibres
- reduces mass of wiring
What are the benefits to a ‘glass’ cockpit
- by having computers screens this aids safety as the pilot does not suffer from information overload
- simplifies cockpit design
