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Food Packaging > Glass > Flashcards

Glass Flashcards

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1
Q

What is the major component of glass?

A

silicon (silicon dioxide)

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2
Q

Where can silicon be obtained?

A

quartz, sand, cristobalite, feldspar, kaolinite

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3
Q

What is the structure of glass?

A

amorphous (no crystallizing)

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4
Q

True/False: Glass is an organic product

A

False; inorganic product

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5
Q

Characteristics of silica crystals: (4)

A

very high melt temp.
high toughness
low transparency
poor inertness

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6
Q

The basis of the glass-making process:

A

change inorganic ingredients from crystalline to amorphous state, at temperature above 1450-1500C

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7
Q

What visual differences can be seen in crystalline vs amorphous structures? Why?

A

crystalline: not transparent (crystals reflect light)
amorphous: transparent (light can pass through)

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8
Q

Molecular units in glass have a ____ arrangement, but sufficient ____ to produce mechanical rigidity

A

disordered

cohesion

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9
Q

Basic formula of glass:

A

soda-limestone

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10
Q

What are the various specific ingredients of glass?

A 
silica (SiO2)
limestone (CaCO3 -> CaO)
soda ash (Na2CO3 -> Na2O)
alumina (Al2O3)
Cullet (recycled glass)
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11
Q

What is the largest chemical ingredient of glass?

A

silica sand (SiO2)

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12
Q

What is the role of soda ash in glass?

A

network modifier

fluxes, enhances melting of silica

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13
Q

What is the role of limestone in glass?

A

stabilizer

increase chem resistance, increase refractive index

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14
Q

Why is cullet added to glass?

A

to reduce cost/energy

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15
Q

Boron oxide is added to what types of glass?

A

heat stable glass

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16
Q

Can glass be used to store alkaline material? Why?

A

No; will react slowly with glass and degrade over time

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17
Q

What is used to dissolve glass?

A

HF (only acid that can dissolve silica)

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18
Q

What are metal oxides used for in glass?

A

colorants, bleaching

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19
Q

What are various stabilizers added to glass?

A

Ca carbonate
Mg carbonate
Ba carbonate

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20
Q

What is added to glass as a fining agent?

A

Na sulfate

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21
Q

Sodium and potassium carbonate are added to glass for what reason?

A

fluxes

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22
Q

What is added to achieve amber glass?

A

carbon & sulfur compounds

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23
Q

What is added for blue glass?

A

cobalt oxide

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24
Q

What is added for green glass?

A

ferrous sulfate, chromic oxide

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25
Q

What is added for yellow glass?

A

ferric oxide, antimony oxide

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26
Q

What is added for blue-green glass?

A

cobalt oxide and chromium oxide

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27
Q

What is added for opal glass?

A

calcium oxide

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28
Q

Why does the addition of different metal oxides give various colors?

A

different metal cations have different ionic refractions

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29
Q

basic steps of glass production:

A

raw materials -> mixing -> melting -> forming -> glass

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30
Q

Glass is made in ____ processing

A

batch

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31
Q

the heating step for glass production takes place in a ____, heated to a temp of ____.

A

furnace

1500C (2700F)

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32
Q

What processes happen during the melting of glass? (5)

A 
decarbonation
dehydration
solid-state reactions
formation of low-melting eutectics
dissolutions
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33
Q

The temperature is raised during glass melting in order to ___ ___

A

release gas

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34
Q

In order to work/form the glass, what needs to occur?

A

glass needs to be cooled slightly (otherwise will stick)

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35
Q

After melting, if the temperature is too hot, the glass will _____. If it is too cold, it _____

A

too hot => sticks

too cold => won’t flow

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36
Q

3 process/zones of the glass furnace?

A
  1. melting & sand dissolution
  2. primary fining
  3. secondary fining (refining)
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37
Q

steps in the glass furnace:

A
  1. batch input
  2. batch melting => rough melt
  3. sand grain dissolution => seedy melt
  4. fining => clear melt
  5. refine/condition => conditioned melt
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38
Q

what step in the glass furnace yields the ‘clear melt?’

A

fining

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39
Q

How does the melting process compare to the fining process?

A

melting: fast (1hr), need a lot of energy
fining: longer time (24 hr), lower energy input

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40
Q

the 2 routes for melting and sand dissolution:

A

carbonate route

silicate route

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41
Q

What requires a higher temp? the Carbonate or silicate route for melting?

A

silicate (700-860C)

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42
Q

What is the temperature range for the carbonate route?

A

550-850C

reaction enhanced >820C

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43
Q

what is the purpose of fluxing agents

A
  1. formation of early melt phases
  2. decrease surface tension
  3. increase heat conductivity
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44
Q

About ____% of the mass of normal soda-lime silica bath is transferred into volatile ____

A

14-20%

CO2

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45
Q

1 kg of normal batch will generate ____ L of gas at room temp

A

100

46
Q

True/False: finely crushed cullet will release gas later than coarse cullet

A

False; fine cullet will have early gas release

47
Q

What is glass ‘fining?’

A

eliminate gases through heating -> bubbles (rise to surface)

48
Q

Describe the process of glass fining

A

high temperature, dissolved gases diffuse from melt into bubbles (agglomeration and growth) -> ascend to surface

49
Q

What gases are produced by fining?

A

O2, SO2

50
Q

The greater the glass melt ____, the slower the bubble ascension

A

viscosity

51
Q

lower ___, and lower ___ will increase speed of bubble ascension. Which has the greater impact?

A 
glass melt density
bubble radius (bigger impact; squared)
52
Q

At (higher/lower) temperatures, the melt will have lower viscosity

A

higher

53
Q

What reaches the surface first? bubbles in a melt at 1400C, or bubbles in a melt at 1500C?

A

1500C

54
Q

What reaches the surface first? bubbles of 300um or 600um?

A

300um

55
Q

What is ‘refining’ of glass, what does it achieve?

A

controlled cooling of melt
dissolution of small bubbles remaining
(reverses fining reaction)

56
Q

Bottles are formed automatically in the ___ ___ machine

A

individual section

57
Q

How does a individual section machine function?

A

molten glass ‘gobs’ sheared off

bottles/jars formed in parison moulds (blow & blow method or press & blow method)

58
Q

The main 2 functions of a individual section machine:

A

shape

remove heat

59
Q

2 main processes for shaping:

A

blow and blow

press and blow

60
Q

process of blow & blow (7 steps)

A
  1. gob dropped into parison mould
  2. sealed, settle-blow (air from top push glass into finish/neck)
  3. counter-blow (air from bottom push glass up into mould and shapes it)
  4. parison removed from mould, rotate 180
  5. transfer into blow mould for finishing
  6. blow air from top to expand/press against mould
  7. opened, bottle removed, passed to annealing lehr
61
Q

process of press and blow (6 steps)

A
  1. gob dropped in mould
  2. sealed, plunger moves up; glass forms around it
  3. parison removed from mold, rotate 180
  4. transferred to blow (finishing) mould
  5. air from top expands glass, press against mould
  6. opened, bottle removed, passed to annealing lehr
62
Q

How is the parison formed in blow & blow vs press & blow?

A

blow & blow: form both finish and rest of parison by air

press & blow: form finish/rough parison with plunger; complete with air

63
Q

Does B&B or P&B have greater heat removal?

A

P&B has greater heat removal

64
Q

True/False; P&B glassmaking creates more uniform thickness

A

True

65
Q

True/False: B&B is faster than P&B

A

False; B&B is slower

66
Q

What types of bottles are made in B&B vs. P&B?

A

B&B: narrow neck bottles

P&B: narrow neck or wide mouth

67
Q

The neck of a bottle is known as the ____

A

finish

68
Q

the sloping part of a bottle between the body and finish is called the ____

A

shoulder

69
Q

What is the purpose of coating glass?

A

improve quality, machinability, durability, strength, appearance, functionality

70
Q

True/False: Glass coatings are designed to be permanent

A

False;

can be permanent, semipermanent, or nonpermanent

71
Q

Examples of permanent glass coatings:

A

tin oxide

PE

72
Q

Examples of semipermanent glass coating:

A

PE, silicone

73
Q

nonpermanent glass coatings:

A

PVA, stearate

74
Q

When are glass coatings added?

A

Before the lehr (hot end) - 2 steps

After the lehr (cold end) - 1 step

75
Q

What is the Shat-R-Kote coating? What properties does it give to glass?

A

Ionomer resin (ethylene/methacrylic acid copolymer)

acid/solvent resistant
transparent
high tensile strength (shatterproof)
no label adhesive needed
90% UV block, antioxidant
76
Q

What is ‘annealing?’

A

reheating glass to soften (550-700C), remove internal stresses caused by heat, cool slowly

77
Q

What is the measurmenet unit of viscosity?

A

poises

78
Q

What is the viscosity for the working point, softening point, and annealing point of glass?

A

working point: 10^4
softening point: 10^7.6
annealing point: 10^13

79
Q

How is the softening point of glass determined?

A

glass fibre 1mm stretches under its own weight (1mm/min)

80
Q

What inspection quality control technologies are used for glass?

A

electro-optical, radio frequency, visual tests

detect dangerous and ugly defects -> glass used as cullet

81
Q

What are some machine tests used for glass inspection (7)

A

bottle spacer (avoid contact between bottles)
squeeze tester (presses between discs
bore gauger finish (measure inside/outside diameter)
check detector (candles problem areas)
wall thickness detector (scan wall for faults)
hydraulic pressure tester (gauge internal pressure)
visual check (final check)

82
Q

Some qualities of glass that should be inspected: (5)

A 
internal pressure breakage
vertical load strength
impact strength
resistance to abrasion & scratching
thermal shock breakage
83
Q

True/False: thickness is the most important feature of glass when considering vertical load strength

A

False; shoulder design (bottle shape) is more important factor than glass thickness

84
Q

types of impacts:

A

bottle striking stationary object

stationary bottle hits moving object

85
Q

___ ____ glass is more resistant to internal pressure, but it has poor ________.

A

thick walled glass

thermal shock resistance

86
Q

What shape of glass has better resistance to thermal shock?

A

round/spherical shape

87
Q

(Bigger/smaller) glasses have greater resistance to thermal shock

A

smaller

88
Q

The higher the weight/capacity ratio of bottles, the (higher/lower) the limiting sudden temperature drop

A

lower

89
Q

classifications of glass defects:

A

critical (hazardous or unusable; cracks or overpress)

major (reduced usability; sunken centre, oval finish)

minor (loss of acceptibility; heeltap, seeds)

90
Q

What is a ‘heeltap?’ what are ‘seeds?’

A

heeltap: heavy (thicker) glass on the side
seeds: small bubbles in glass

91
Q

What markings are seen on the bottom of glass bottles?

A
  1. identification of mould (plant, company mark, year)

2. stippling to minimize shock in lehr

92
Q

specifications for glass containers should include:

A
  1. description of container finish

2. dimensions (capacity, ht, diameter, wt, tolerances)

93
Q

Glassware finishes must be compatible with _____

A

the closure type

94
Q

Examples of finishes:

A

sprinkler top, shallow CT, Tall CT, pour-out CT, crown, cork, roll-on, biological, handle

95
Q

Finishes are designated with a ____ system from the ______

A

2 number
GPI (glass packaging institute)

(matches finish with closure)

96
Q

what does the 2 number system for glass finishes describe?

A

1st number: millimeter diameter across inside cap’s opening/bottle threads

2nd number: thread style

97
Q

The various thread styles for closures:

A

400: continuous
500: twist off
600: crown
2000: vacuum
1600: roll on

98
Q

The different ‘dimensions’ of the finish

A 
T: outside diameter of the thread (spiral ridges that allow screw caps)
E: outside diameter of neck
I: inner diameter of neck
S: top of finish to top of first thread
H: height of neck finish
99
Q

What does “T” dimension of finishes determine?

A

mate between bottle and closure

100
Q

What does “S” dimension of finishes determine? (2)

A

orientation of closure to bottle

amount of thread engagement between bottle & cap

101
Q

How do you determine thread depth?

A

difference between “T” and “E”

102
Q

Why do specifications require a minimum “I” dimension for finishes?

A

allow filling tubes to fit

plugs and seal proper fit

103
Q

True/False: melting and remoulding of glass can be repeated indefinitely without loss of properties

A

True

104
Q

The presence of ___ and ____ in glass will hugely increase the heat resistance

A

boron oxides, aluminum oxides

105
Q

Glass has the lowest coefficient of ___ ___ of any packaging material

A

coefficient of thermal expansion (6-8*10^(-6) /C)

106
Q

What has a greater impact on reducing the stress resistance of glass, the composition or the weight/thickness?

A

weight and thickness

107
Q

True/False: Glass can have cracks and flaws, even if it is not visible

A

True; superficial defects lead to stress amplification

108
Q

What are the optical properties of glass? (3)

A

transparent in visible wavelengths
transparent to microwaves
very low UV transmission coefficients (absorb in UV range)

109
Q

Glass can’t be penetrated by: ______ (4)

A

moisture
gases
odors
microbes

110
Q

Can glass react with food?

A

No; inert (does not react or migrate)

111
Q

Advantages of glass as packaging: (10)

A 
good barrier properties
inert
fast filling
can use heat processing
reusable, recyclable
resealable
variety of shapes, colors
adds value (perception)
rigid (stacking)
Printable (or labels)
112
Q

disadvantages of glass as packaging: (6)

A 
high weight/volume ratio
low strength/weight ratio
friability (tend to chip)
susceptible to imperfections
safety (when broken)
energy intensive production

Food Packaging (11 decks)

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