CAR Material Selection & Properties 2 — Questions and Answers
Question 1: Which property makes copper tubing in refrigerators particularly valuable during recycling?
- High corrosion resistance and conductivity (Correct answer)
- Low melting point for easy processing
- Magnetic properties for easy separation
- High density for compact storage
Correct answer: High corrosion resistance and conductivity
Copper's excellent electrical conductivity and corrosion resistance make it highly sought after in secondary metals markets.
Question 2: What is the primary concern when recycling appliances containing polyurethane foam insulation?
- The foam is too heavy to transport
- Foam may contain ozone-depleting blowing agents that must be recovered (Correct answer)
- Polyurethane cannot be recycled at all
- The foam dissolves in water during processing
Correct answer: Foam may contain ozone-depleting blowing agents that must be recovered
Older polyurethane foam was blown with CFCs or HCFCs, requiring controlled recovery to prevent atmospheric release.
Question 3: Which appliance component is most likely to contain mercury and requires special handling?
- Compressor oil
- Thermostat switches and relays (Correct answer)
- Plastic door gaskets
- Stainless steel drum
Correct answer: Thermostat switches and relays
Mercury tilt switches and relay contacts were commonly used in older appliance thermostats and must be removed before shredding.
Question 4: Galvanized steel in appliances is coated with which material to prevent corrosion?
- Chromium
- Nickel
- Zinc (Correct answer)
- Tin
Correct answer: Zinc
Galvanization applies a zinc coating to steel, providing sacrificial cathodic protection against rust.
Question 5: What distinguishes Type 304 stainless steel commonly found in dishwashers from carbon steel?
- It contains 18% chromium and 8% nickel alloy additions (Correct answer)
- It is coated with a plastic film for corrosion resistance
- It has a higher carbon content than regular steel
- It is non-metallic and cannot be magnetized
Correct answer: It contains 18% chromium and 8% nickel alloy additions
Type 304 (18-8) stainless steel's chromium and nickel content creates a passive oxide layer that resists corrosion.
Question 6: Which plastic resin code is commonly found on polypropylene washing machine tubs?
- #1 (PET)
- #2 (HDPE)
- #5 (PP) (Correct answer)
- #7 (Other)
Correct answer: #5 (PP)
Polypropylene (PP, resin code #5) is used for washer tubs due to its chemical resistance, durability, and heat tolerance.
Question 7: During appliance shredding, eddy current separators are used to recover which material?
- Ferrous metals like iron and steel
- Non-ferrous metals like aluminum (Correct answer)
- Glass and ceramics
- Plastic polymers
Correct answer: Non-ferrous metals like aluminum
Eddy current separators induce opposing magnetic fields in non-ferrous conductors like aluminum, physically ejecting them from the conveyor stream.
CAR Material Selection & Properties 2
Which property makes copper tubing in refrigerators particularly valuable during recycling?