Lecture 5: Metal Flashcards
describe the chemical rxn of iron to steel
- reduce Si, C, P, S
2. add Mn, Ni, Cr
how does increasing C affect steel?
- increased hardness and tensile strength
- decreased ductility and welding properties
how does increasing Mn affect steel?
- increases strength and hardness
how does increasing P affect steel?
- increases strength and hardness
- decreases ductility
how does increasing Cr affect steel?
- improves corrosion and abrasion resistance
how does increasing Ni and cu affect steel?
- increases toughness, tensile strength, hardness, corrosion resistance
how does increasing Mo affect steel?
increases hardness and tensile strength at high temp
what are 4 common types of steel
- L
- MR
- D
- Ni
what is ETP? what is an advantage of it?
electrolytic tinplate
- the tin-iron alloy layer at interface of tin and steel
- advantage is corrosion resistance
how do you prepare ETP for plating steel?
- electrolytic process in bath of tin sulphate in sulphuric acid
- thermal treatment and rapid quenching
- chemical passivation in solution of sodium dichromate
- application of oily lubricant
what are advantages and disadvantages of chromium coated steel?
adv
- spontaneous passivation
- cheaper
- better heat resistance, coating adhesion and printing
dis
- low abrasion resistance
- less resistant to corrosion in acidic environment
polymer coated steel has resistance against what?
abrasion
corrosion
food interactions
describe the steps of producing aluminum
step 1: Bayer process
- bauxite –> alumina
step 2: hall- heroult process
- alumina to aluminum
- high energy requirement
how does magnesium affect aluminum alloys
- increases mechanical resistance of materials
- reduces corrosion resistance against acids and alkalis
how does manganese affect aluminum alloys
increases corrosion resistance
describe how to make a 3-piece can
- tin steel is cut in large pieces, lacquered and dried
- pieces are cut; body is rolled
- side seams formed
- ends are curled; one end is filled with sealing compound
- body is flanged
- bottom end is attached
- can is tested for leaks
side seams are usually ____
welded
how are side seams usually welded?
electric resistance seam welding
what are reasons to lacquer or line cans?
- to protect inner surface of tin from being damaged by food
- to protect food from being damaged by tin
- to protect outer surface of tin
what are advantages to using coatings
- improve appearance
- increase shelf life
- cost reduction in steel
- increase corrosion resistance
- prevent color/flavour changes
what are requirements of can lacquers?
- non-toxic
- does not affect flavor/color of food
- provide good barrier between food and container
- easy to apply to tin-plate
- does not peel off during sterilization or storage of canned product
- mechanical resistance to can manufacturing
describe preparation for attaching the can end
- can end is curled
- curl is filled with a sealing compound that will act as a gasket to help form a hermetic seal
- can body is flanged to engage the curled end
a 2 piece can could be made of what?
what is the function of each?
- steel: to be thermally processed
2. aluminum alloy: for beverages
a 2-piece can can be made which 4 processes?
when is each of them used?
- shallow draw: sides < diameter
- draw and re-draw: sides > diameter
- draw and iron: walls thinner than bottom
- impact extrusion: aerosol cans
in making a 2-piece can, how does ironing affect wall thickness?
reduces thickness
in aerosol can production, what is an example of a propellant? what is it used for?
nitrous oxide used for UHT cream
other propellants: Ar, N2, CO2
what are properties of metal packaging?
- high strength to wt ratio
- can be heat processed to make shelf-stable products
- have good barrier and protective properties
- tamper proof
what are advantages that aluminum has over steel?
- lighter wt
- lower transport costs
- easier to recover and recycle
- more resistant to corrosion
- easier to open
- not prone to sulfide staining
