Lectures Flashcards
Metal definition
Solid substance with:
- High conductivity (electrical and heat)
- Luster
- Hardness (tensile stress, malleability, and ductility)
High structural strength per unit of mass
Can carry large loads/resist impact damages.
Uses of metals
- Construction
- Tools
- Vehicles
Metals used ages ago
Copper, Tin, Iron, Lead, Gold, Silver, Mercury
3 most common metals used
1) Iron and iron alloys (steel)
2) Aluminum
3) Copper
Properties of nonmetals
- Non-lusterous
- Gas at room temperature
- Brittle
- Poor conductors
Six metaloids
1) Boron
2) Silicon
3) Germanium
4) Arsenic
5) Polonium
6) Tellurium
7) Polonium
Properties of metalloids
- Characteristics in between metals and non metals
- Semiconductors
Classifications of metals
1) Ferrous
2) Non-ferrous
Ferrous metal properties
1) Must contain iron, may contain trace amounts of other elements
2) Magnetic
Types of ferrous metals
1) Iron
2) Wrought iron
3) Cast iron
4) Steel (stainless and galvanized)
Iron
- 8,4
- Most widely used metal (95%)
- Pure iron not commercially used
- Pure iron oxidizes rapidly in presence of O2 and moisture
- Pure iron soft, use alloys to make stronger
Wrought iron
- Less than .03% carbon
- True wrought iron is scarce and expensive
- Forges well, easily bent (hot or cold), can be simply welded
Cast iron
- 2.1 - 4% carbon, 1 - 3% Silicon
- Hard, inflexible, brittle, resistant to deformation and wear
Carbonized steel
- Less than 1.65% Mn, .6% Cu, small amounts Si, S, P
- Low carbon steel (.02 - .3%): Most commonly used – roll steel
- Medium carbon steel (.3 - .45%): Strong and hard, less ductile, now easily welded (cracks after welding), screwdrivers
- High carbon (.45 - .75): Very hard/strong, less ductile, special welding to prevent cracking, used for hammers
- Very-high carbon (More than .75%): Seldom welded, tools and springs
Rolled steel
- Rolling steel into shape
- Cold: Formed when cold more accurately sized and finished surface. Better for welding
- Hot: Blue scale, uniform quality, most economical
Alloy steels
- Alloy steels 1-50% other elements by weight
- Stronger, harder, tougher than carbonized steel
- May require heat treatment
Stainless steel
- Has chromium (min 10.5%, max 26%)
- Film of Chromium oxide that prevents surface corrosion
Galvanized steel
- Zinc to prevent rusting
- Pass steel through molten bath of zinc
- Rust resistant
- Toxic fumes released
Steel identification
1) Principle element in steel
2) Approx % of predominant alloy
3-4) Carbon points
Non-ferrous metals
- Don’t contain iron
- Not magnetic
- More resistant to corrosion
Aluminum
- Most widely used non ferrous metal
- Soft, durable, lightweight
- 1/3 density and stiffness of steel
- 100% recyclable
Copper
- Ductile
- High conductivity
- Pure copper is soft w/ pink exposed surface
Tin
- Silvery, malleable
- Not easily oxidized
Lead
- Soft, heavy, highly malleable, ductile
- Used in batteries
- Toxic
Physical properties of metals: Hardness
- Hardness: Harder = less deformation
- Brinell, Rockwell, Vickers test
- Brinell and Rockwell measure penetration into metal
Physical properties of metals: Ducitlity
- Tensile stress
Physical properties of metals: Malleability
- Deformation under compressive stress
- Ability to form a thin sheet by hammering/rolling
Physical properties of metals: Strength
1) Tensile: Longitudinal stress
2) Compressive: Stress that can stand without being crushed
3) Sheer: Force that causes internal metal to slide against itself
Other physical properties
1) Density
2) Conductivity
3) Radioactivity
Chemical properties of metals
- Strong metallic bonds: High melting and boiling points
- Free electrons carry heat: Good conductors
- Electrons slide easily: Malleable and ducitle
Metal production
- Conversion of ore to final form
- No work when already in final form (Au, Ag, Pt, etc.)
- Extractive metallurgy: Removing valuable metals
Heat treatment
- Alter physical properties
- Annealing (heat the slowly cool), quencing (heat and rapidly cool to harden), tempering (slowly heat up, slowly cool)
Surface treatment
1) Plating: Bonding thin layer of metal to surface
2) Thermal spray: Melted metals sprayed onto surface
3) Case hardening: Hardening surface by infusing with other elements
Chemical heating
- Use oxygen- fuel mixture
- Powdered material fed through gun
- Produces spray
Joining metals
Permanent: Welding, soldering, brazing
Separable: Fastening (screw, nuts and bolts, rivets
Welding
- Melting base material
- Gas welding
- ARC welding (stick, mig, tig)
Oxy-acetylene welding
- More portable than ARC welding
- Can join, heat, or cut metals
- Welding, brazing, cutting, heating, bending
Oxy-acetylene welding safety
1) Secure cylinders
2) Make sure no oil or grease is present
3) Don’t use oxygen as substitute for air
4) Don’t force connections
5) Make sure nobody is in front of cylinders/regulators
6) Wear safety shit
Setting up gas welding
1) Valves loose
2) Open valves slowly (oxygen fully, acetylene 1/2 turn)
3) Adjust pressures
4) Open acetylene and light
5) Add oxygen and adjust to proper flame
Types of flame
- Neutral: Equal amounts of oxygen and acetylene
- Oxidizing: Excess oxygen
- Carburizing: Excess acetylene
Shutting down gas welding
1) Close oxygen then acetylene valves to shut off flame
2) Close oxygen and acetylene main valves
3) Drain out gasses
4) Loosen screws
5) Close torch valves
Methods of gas welding
1) Forehand: Welding rod proceeds flame (less than 1/8 thick)
2) Backhand: Flame proceeds rod (more than 1/8 inch thick)
Gas welding problems
1) Backfire: Popping at tip. Caused by bad gas volume, touching tip, or overheated tip
2) Flashback: Explosion at tip of nozzle w/ hissing sound and smoke. Can be caused by clogged tip, improper gas mix, loose connections, or damaged o-ring.
Stick welding
- DC: Direct current
- Ground clamp: Complete circuit for welding
- Wear hood and safety clothes
- Electrode forms slag
Stick welding safety
- Don’t simultaneously touch electrode and grounding cable
- Don’t weld around combustibles
- Don’t welt in wet areas
- Use correct cable size
Stick welding electrode selection
1) Diameter: Approximately equal to electrode thickness
2) Type: First two letters = tensile strength, third = position, fourth = Current type
Weld and joint types
Weld: Bead (padding), butt, fillet (tee), groove (beveled)
Joint: Butt, lap, tee, edge, corner
Stick welding steps
1) Setup
2) Strike (or tap) ARC
3) Bead
Troubleshooting stick welds
- Burnthrough
- Incomplete fusion
- Slag inclusion
- Undercut
- Cracks
- Porosity
