Metal Flashcards
Main metals used for food packaging:
Aluminum
Iron
Mineral sources of iron (ores):
hematite
magnetite (highest %)
limonite
siderite
Ore source for aluminum:
Bauxite
True/False: there is greater amounts of iron than aluminum in the Earth’s crust
False
Al is 8.1%, Fe is 5%
Iron is usually transformed into ____ for food packaging
steel
the raw materials for steel production: (3)
C (Coal)
CaCO3 (limestone)
Fe2O3 (iron ore)
What is slag? how is it made
CaSiO3
made from CaO (from limestone) + SiO2
in making iron into steel, you need to reduce __, ___, ___, ___, and add ___, ___, ___
reduce Si, C, P, S
Add Mn, Ni, Cr
An increase in % of Carbon in steel will have what effect on the properties?
increase in hardness, tensile strength
decrease in ductility and welding properties
What can be added to steel to increase corrosion and abrasion resistance?
Cr
What steel component will increases hardness/tensile strength, especially at high temperatures?
Mo
What is the effect of increasing Mn in steel?
increase strength and hardness
What is the effect of increasing P in steel?
increase strength and hardness
decrease ductility
What is ductility?
ability to be stretched into a wire
What is the effect of increasing Ni and Cu in steel?
increase toughness, tensile strength, hardness, corrosion resistance
What are common types of steel for food packaging? (4)
Type L (high purity, low P/residual metals) Type MR (higher P/residual metals) Type D (Low C, high S, stabilized) Type Ni (Added Ni)
What steel is used for highly corrosive products?
Type L
What steel are drawn and ironed cans made from?
Type D
What is Ni steel used for?
Can ends, aerosol domes
What is Type MR steel used for?
mildly/non corrosive products (low acid)
What is used to describe metal hardness?
temper
the different temper grades:
T1 (46-52) - soft, for deep draws T2 (50-56) - moderate draws, closures T3 (54-63) - shallow draws, gen. purpose T4 (58-64) - bodies/can ends T5 (62-68) - bodies/can ends
What temper grades can be used for can bodies and ends?
T4 or T5
What are types of plating steel?
Electrolytic tinplate (ETP)
Chromium coated steel
Polymer coated steel
What is ETP?
electrolytic tinplate (plated steel) tin-iron alloy later at interface of tin/steel -> gives corrosion resistance
Steps for preparing ETP: (4 steps)
electrolytic process: bathe tin sulfate in sulfuric acid
thermal treatment (260-270C) & rapid quenching
chemical passivation in Na dichromate solution
apply oily lubricant
advantages (5) vs disadvantages (2) of chromium coated steel?
good: spontaneous passivation (thinner), cheaper, better heat resistance, coating adhesion, printing
bad: low abrasion resistance, decrease resistance to corrosion
What is polymer coated steel coated with? What does this achieve?
Polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), fluorinated perfluoroethylenepropylene (FEP)
resist abrasion, corrosion, food interactions
For a highly acidic food, what would be a good steel coating?
polymer coating (PTFE, PFA, or FEP)
2 processes needed to convert aluminum ore into aluminum:
- Bayer process
2. Hall heroult process
Requirements of the Hall Heroult process:
cryolite (Na3AIF6)
huge amount of energy needed
The bayer process converts ___ into _____
Bauxite
alumina
Aluminum can be combined with many metals such as _______, to form various ____.
Mn, Si, Fe, Mg, Cu, Cr
alloys
Magnesium in aluminum alloys will increase _____ but decrease _____
increase mechanical resistance
decrease corrosion resistance
What can be added to aluminum alloys to increase corrosion resistance?
Mn
List in order of increasing mass thermal capacity: Aluminum, carbon steel, stainless steel
stainless steel < carbon steel < aluminum
True/False: steel has a greater thermal expansion than aluminum
False; aluminum has greater thermal expansion
which is a better conductor, steel or aluminum?
aluminum (>carbon steel > stainless)
true/false: aluminum has a higher melt point than steel
false
which is more dense, steel or aluminum?
steel
Which has a higher tensile strength, steel or aluminum?
steel
2 types of cans:
2 piece
3 piece
Parts of a can:
Top: canner’s end
Canner’s end seam
body (side seam, side wall beading)
bottom: manufacturer’s end
manufacturer’s end seam
True/False: expansion panels are found in all metal cans
False: only in thermally processed cans
What types of can body seams are there?
welded seam
soldered seam
The can bottom is sealed by _____ while the top is sealed by ______
the maker
the canner (after filling)
A ____ seam joins the ends to the can body
double
3 piece can production steps (7 steps)
- tin steel cut in large pieces, laquer & dry
- cut pieces for ends & body -> rolled
- form side seams
- ends curled, one end filled with sealing compound
- body flanged (may be beaded)
- bottom attached
- test for leaks
What is the purpose of beading cans?
strength in heat processing
What are can flanges?
ridges at can body rim, for clinching with can ends
How are side seams on cans formed, for thermally vs nonthermally processed?
welded electrically, laquered
clinched in non-thermally processed products
Describe the process of electric welding for cans
electric resistance seam welding:
can pressed (force) between two copper electrodes (applies heat)
then coat with laquer and test integrity
Reasons to lacquer cans? (5)
improve can appearance increase shelf life cost reduction in steel corrosion resistance prevent color/flavor change in food
requirements for can lacquers: (7)
nontoxic
don’t affect flavor/color of food
good barrier between food/container
easy to apply
doesn’t peel off during processing or storage
mechanical resistance to manufacturing operations
economical
Examples of coating types for cans:
acrylics alkyds epoxys butadiene phenolics vinyls oleoresins
What is a can coating that has recently raised consumer concerns? Why?
Bisphenol A (BPA) synthetic estrogen activity? (endocrine disruptor); possible leaching into food
What type of coating is fruit enamel, and what is it used for?
oleoresinous
dark berries/cherries that need protection against metallic salts
What type of coating is used for corn, peas, and other sulfur-bearing products? What type is it?
C-enamel
Oleoresinous with suspended zinc oxide
What is citrus enamel used for and what type of coating is it?
citrus products and concentrates
modified oleoresinous, polybutadienes
What is beverage can enamel used for, and what type of coating is it?
veg juice, red fruit juice, corrosive fruits, non-carbonated beverages
2-coated with resinous base and vinyl top coat
What is done in preparation of attaching the can end to the body?
- curl can end
- fill with sealing compound (act as gasket to help seal)
- flange can body
A completed double seam on a can will be ____ layers thick at its thickest point
5
The steps of double seaming (2)
First operation:
chuck presses cover down on can
seaming roll will push end curl around flange
Second operation:
seaming roll + chuck will push seam flat
What materials can be used for 2-piece cans?
steel (type D) for thermally processed product
aluminum alloy for beverages
Different processes to make 2 piece cans: (4)
shallow draw (sides < diameter)
draw & redraw (sides > diameter)
draw & iron (walls thinner than bottom)
impact extrusion (aerosol)
True/False: beverage cans are made of aluminum
True (aluminum alloys)
What process would you use to make a 2-piece can with thin walls and a thick bottom?
draw and iron
describe the shallow draw process. What products usually use these can types?
feed sheet of metal in
machine presses into mold
unload -> can
shallow cans: tuna, sardines,
Describe the draw and redraw process
similar to shallow draw, but then RESHAPE (redraw):
metal moved from base to wall so that diameter is reduced
final product is taller thinner can
Describe the draw and iron process
similar to shallow draw (create shallow cup)
then push through a ring -> makes deeper cup
continue pushing through smaller and smaller rings (x3) to ‘iron’ walls (stretch and make longer, thinner)
base shaped by bottom die
trim top -> follow remainder of can processes
example of can using the draw and iron process:
soda cans
The wall ____ is reduced while the wall ____ is increased in the ironing process
thickness
length
The main inner contents of an aerosol can:
propellant liquid phase (product)
main parts of an aerosol can:
valve
dip tube (to access product)
can body
What can be done to prevent the product from being affected by the propellant?
placed in plastic bag
Examples of aerosol propellants:
NO, Ar, N2, CO2
What is the process of impact extrusion?
metal slug (chunk of metal) placed in die
pressed at high velocity with a punch
forces metal up and out, forming walls
(height determined by stripper plate)
What is the ‘gauge’ of aluminum foil referring to?
thickness
Properties of aluminum foil: (5)
complete barrier (thicker -> better barrier) foldable printable/embossable reflective matte/shiny
good properties of metal packaging: (5)
high strength to weight ratio can be heat processed long storage excellent barrier/protective prevents tampering
quality control measures of metal plates and foil (2)
thickness
hardness
Quality control measures of metal cans: (8)
porosity of coating side seam double seam examination pressure testing vacuum testing dye testing axial load testing pull tab testing
advantages of aluminum over steel: (5)
lighter (lower transport cost) easier recovery/recycling more corrosion resistant easier opening (pull tab) not prone to sulfide staining
advantages of aluminum beer bottles over glass: (4)
lighter
less fragile
keep beer cooler
light barrier
