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Food Packaging > Lecture 5: Metal > Flashcards

Lecture 5: Metal Flashcards

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1
Q

describe the chemical rxn of iron to steel

A
  1. reduce Si, C, P, S

2. add Mn, Ni, Cr

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2
Q

how does increasing C affect steel?

A
  • increased hardness and tensile strength

- decreased ductility and welding properties

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3
Q

how does increasing Mn affect steel?

A
  • increases strength and hardness
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4
Q

how does increasing P affect steel?

A
  • increases strength and hardness

- decreases ductility

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5
Q

how does increasing Cr affect steel?

A
  • improves corrosion and abrasion resistance
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6
Q

how does increasing Ni and cu affect steel?

A
  • increases toughness, tensile strength, hardness, corrosion resistance
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7
Q

how does increasing Mo affect steel?

A

increases hardness and tensile strength at high temp

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8
Q

what are 4 common types of steel

A
  1. L
  2. MR
  3. D
  4. Ni
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9
Q

what is ETP? what is an advantage of it?

A

electrolytic tinplate

  • the tin-iron alloy layer at interface of tin and steel
  • advantage is corrosion resistance
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10
Q

how do you prepare ETP for plating steel?

A
  1. electrolytic process in bath of tin sulphate in sulphuric acid
  2. thermal treatment and rapid quenching
  3. chemical passivation in solution of sodium dichromate
  4. application of oily lubricant
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11
Q

what are advantages and disadvantages of chromium coated steel?

A

adv

  • spontaneous passivation
  • cheaper
  • better heat resistance, coating adhesion and printing

dis

  • low abrasion resistance
  • less resistant to corrosion in acidic environment
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12
Q

polymer coated steel has resistance against what?

A

abrasion
corrosion
food interactions

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13
Q

describe the steps of producing aluminum

A

step 1: Bayer process
- bauxite –> alumina

step 2: hall- heroult process

  • alumina to aluminum
  • high energy requirement
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14
Q

how does magnesium affect aluminum alloys

A
  • increases mechanical resistance of materials

- reduces corrosion resistance against acids and alkalis

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15
Q

how does manganese affect aluminum alloys

A

increases corrosion resistance

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16
Q

describe how to make a 3-piece can

A
  1. tin steel is cut in large pieces, lacquered and dried
  2. pieces are cut; body is rolled
  3. side seams formed
  4. ends are curled; one end is filled with sealing compound
  5. body is flanged
  6. bottom end is attached
  7. can is tested for leaks
17
Q

side seams are usually ____

A

welded

18
Q

how are side seams usually welded?

A

electric resistance seam welding

19
Q

what are reasons to lacquer or line cans?

A
  1. to protect inner surface of tin from being damaged by food
  2. to protect food from being damaged by tin
  3. to protect outer surface of tin
20
Q

what are advantages to using coatings

A
  • improve appearance
  • increase shelf life
  • cost reduction in steel
  • increase corrosion resistance
  • prevent color/flavour changes
21
Q

what are requirements of can lacquers?

A
  • 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
22
Q

describe preparation for attaching the can end

A
  • 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
23
Q

a 2 piece can could be made of what?

what is the function of each?

A
  1. steel: to be thermally processed

2. aluminum alloy: for beverages

24
Q

a 2-piece can can be made which 4 processes?

when is each of them used?

A
  1. shallow draw: sides < diameter
  2. draw and re-draw: sides > diameter
  3. draw and iron: walls thinner than bottom
  4. impact extrusion: aerosol cans
25
Q

in making a 2-piece can, how does ironing affect wall thickness?

A

reduces thickness

26
Q

in aerosol can production, what is an example of a propellant? what is it used for?

A

nitrous oxide used for UHT cream

other propellants: Ar, N2, CO2

27
Q

what are properties of metal packaging?

A
  • high strength to wt ratio
  • can be heat processed to make shelf-stable products
  • have good barrier and protective properties
  • tamper proof
28
Q

what are advantages that aluminum has over steel?

A
  • lighter wt
  • lower transport costs
  • easier to recover and recycle
  • more resistant to corrosion
  • easier to open
  • not prone to sulfide staining

Food Packaging (11 decks)

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