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Food Packaging > Lecture 4: Glass > Flashcards

Lecture 4: Glass Flashcards

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1
Q

what is glass?

A

an amorphous and inorganic product of fusion that has been cooled to a rigid condition without crystallizing

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2
Q

what is the major component of common glass?

A

silicon dioxide

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3
Q

what are some major physical properties of glass?

A
  • high melting temp
  • high toughness
  • low or null transparency
  • poor inertness
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4
Q

the glass making process changes inorganic ingredients from ____ to ____

A

crystalline to amorphous state

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5
Q

what temp is needed for the glass making process?

A

1450 - 1500 deg C

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6
Q

what is the basic formula for glass?

A

soda limestone

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7
Q

what consists of soda limestone?

A 
silica
limestone
soda ash
alumina
cullet
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8
Q

what is the chemical name for silica?

A

silicone oxide

SiO2

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9
Q

what is the chemical name for limestone?

A

calcium carbonate

CaO

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10
Q

what is the chemical name for soda ash?

A

sodium carbonate

Na2O

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11
Q

what is the chemical name for alumina?

A

aluminum oxide

Al2O3

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12
Q

what is the chemical name for cullet?

A

recycled glass

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13
Q

what is the highest and lowest composition in soda limestone formula for class?

A

highest: silica sand
lowest: alumina

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14
Q

what is a network former?

A

silicone oxide

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15
Q

what are network modifiers? what is their function?

A

Na2O + CO2

function: enhances melting of silica

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16
Q

what are stabilizers in glass?

what is their function?

A

CaO + CO2

function:

  • increases chemical resistance
  • increases refractive index
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17
Q

what is the function of cullet (recycled glass)?

A

reduces costs and energy

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18
Q

what occurs in the glass furnace?

A
  • decarbonation, dehydration, solid-state reactions, formation of low-melting eutectics, dissolutions
  • ingredients are melted into a molten mass
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19
Q

why is temperature raised in the glass furnace?

why is it cooled?

A

raised: to release gas
cooled: so that glass can be worked

If too hot, it will stick. If too cold, it won’t flow

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20
Q

what are 5 main steps in glass production?

A
  1. batch input
  2. batch melting
  3. sand grain dissolution
  4. fining
  5. refining and conditioning
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21
Q

which part of the glass production is

a) fast and has high energy input?
b) slower and has lower energy input

A

a) batch melting

b) sandgrain dissolution, fining, refining/conditioning

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22
Q

what are 2 routes in melting and sand dissolution?

A
  1. carbonate route

2. silicate route

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23
Q

what is the function of fluxing agents?

A
  • formation of early melt phases
  • decrease of surface tension
  • increase of heat conductivity
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24
Q

some of the mass of normal soda lime silica batches is transferred into what?

A

volatile CO2 (gas release)

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25
Q

during melting, 1kg of normal batch generates how much gas at normal pressure and room temp?

A

100L

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26
Q

what is the effect of adding

a) fine cullet
b) coarse cullet

A

a) early gas release

b) gas release at low viscosity

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27
Q

describe fining of glass melt

A
  • at high temp
  • bubble agglomeration and bubble size growth
  • dissolved gases diffuse from melt into bubbles
  • ascension of growing bubbles to glass melt surface
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28
Q

what is the temperature in which fining of glass melt occurs at?

A

1430-1480 deg C

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29
Q

what is the chemical reaction that occurs in fining of glass melt?

A

Na2SO4 (molten glass) –> Na2O (melt) + fining gases (SO2) + 1/2 O2)

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30
Q

what are two fining gases?

A

SO2 and O2

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31
Q

what is the equation of V ascension?

A

V ascension = (cpg*R^2) / n

p = density of glass melt
n = viscosity of glass melt
R = bubble radius
g = gravity
c = factor
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32
Q

in fining of glass melt, how does temperatures affecting melting?

A

higher temp = melting with lower viscosity

33
Q

describe refining of glass melt

A
  • controlled cooling of the melt

- dissolution of small remaining bubbles in the melt

34
Q

in refining of glass melt, what happens when temperature decreases?

A

decreasing temp = increasing solubility of gases

this reverses the fining reaction

35
Q

what is the individual section machine for?

A

automatically forming bottles

36
Q

describe the process occuring in individual section machine

A
  • molten glass is sheared off in drops called “gobs”
  • bottles/jars are formed in moulds called parison moulds using one of 2 methods:
    1. blow and blow
    2. press and blow
37
Q

what are the 2 functions of the individual section machine

A

shapes

removes heat

38
Q

what are gobs

A

the drops sheared off of molten glass

39
Q

what are parison moulds

A

the moulds used to form bottles and jars

40
Q

describe the blow and blow method

A
  1. gob of glass is dropped into parison mould
  2. mould is sealed and puff of air from top pushes glass into finish neck (settle blow)
  3. puff of air from bottom pushes glass into mould to shape it to a parison (counter-blow)
  4. parison is removed and rotated 180C
  5. parison is transferred to a blow mould (finishing)
  6. air is blown in from the top to expand glass and push it against the mould
  7. mould is opened; red hot bottle is removed and passed to the annealing lehr
41
Q

describe the press and blow method

A
  1. gob of glass is dropped into parison mould
  2. mould is sealed and plunger moves up to form the top of the parison; forces lass downward to form the finish
  3. parison is removed and rotated 180C
  4. parison is transferred to blow (finishing) mould
  5. air is blown from top to expand glass and push it against mould
  6. mould is opened and bottle is removed
42
Q

how is B&B and P&B different in terms of parison forming?

A

B&B: finish first by air, rest of parison by air in gob

P&B: rough parison/ finish by plunger, then completed parison by air

43
Q

how is B&B and P&B different in terms of heat removal?

A

B&B: less

P&B: more

44
Q

how is B&B and P&B different in terms of thickness?

A

B&B: varied

P&B: uniform

45
Q

how is B&B and P&B different in terms of use?

A

B&B: generally narrow necked

P&B: narrow necked and wide mouthed

46
Q

how is B&B and P&B different in terms of speed?

A

B&B: slower

P&B: faster

47
Q

why is glass coated?

A

to improve:

  • quality
  • machinability
  • durability
  • strength
  • appearance
  • functionality
48
Q

coatings can be… (3)

A

nonpermanent
semipermanent
permanent

49
Q

when can coatings be added? (2)

A
  1. before the lehr (hot end) in a 2-step process

2. after the lehr (cold end) in a 1-step process

50
Q

what is an example of a coating? describe it.

A

ionomer resin

  • ethylene and methacrylic acid copolymer
  • acid and solvent resistant
  • transparent with low haze
  • high tensile strength
  • shatterproof
  • lubricates to improve fill speed
  • no labeling adhesive
51
Q

what happens in the annealing lehr?

A
  • glass containers are reheated to soften the glass and remove internal stresses caused by heat
  • containers are heated to 550-700C, then cooled slowly to prevent stresses from re-forming
52
Q

in the annealing lehr, why must containers be cooled slowly?

A

to prevent stresses from re-forming

53
Q

what is the:

a) working point
b) softening point
c) annealing point

A

a) working point = 10^4 poises
b) softening point = 10^7.6 poises
c) annealing point = 10^13 poises

54
Q

glass containers are inspected using what tests?

A

electro-optical, radio frequency and visual tests

55
Q

what happens to defective glass containers?

A

they are recycled as cullet

56
Q

describe the inspection process

A
  1. bottle spacer avoids bottle to bottle contact
  2. squeeze tester (presses between discs)
  3. bore guager finish is measured
  4. check detector (for problem areas)
  5. wall thickness detector (for faults in the walls)
  6. hydraulic pressure tester (internal pressure)
  7. visual check in (final check)
57
Q

when a bottle strikes another object, how can amount of damage be minimized?

A
  1. design features of the bottle

2. surface treatments to reduce impact stress

58
Q

what are 5 main factors of glass that are inspected?

A
  1. internal pressure breakage
  2. verticle load strength
  3. impact strength
  4. resistance to abraision and scratching
  5. thermal shock breakage
59
Q

how is weight/capacity ratio related to thermal shock resistance?

A

lower wt/capacity ratio = higher sudden temperature drop

higher wt/capacity ratio = lower sudden temp drop

60
Q

what are 3 types of defective containers?

give an example of each

A
  1. critical: cracks and overpress
  2. major: rocker bottom and oval finish
  3. minor: heeltap and seeds
61
Q

glass containers used for packaging should have what specifications?

A
  1. description of the container finish

2. dimensions: capacity, ht, diameter, wt, tolerances

62
Q

what are 3 identification marks on glass packaging?

A
  1. plant
  2. company mark
  3. year
63
Q

finishes are designated with what system?

A

a two-number system which describes the bottle and closure

eg. 24/400 bottle will only accept a 24/400 closure

64
Q

what is GPI

A

glass packaging institute

65
Q

if a bottle is labelled 24/400, what does each number refer to?

A

24 (first number): millimeter diameter measured across the inside of the cap’s opening or outside the bottle’s threads

400 (second number): refers to the thread style

66
Q

describe the thread style for:

a) 400
b) 500
c) 600
d) 2000
e) 1600

A

a) continuous thread
b) twist-off
c) crown
d) vacuum
e) roll on

67
Q

what is T-dimension

A

outside diameter of the thread

tolerance range of T will determine the mate between bottle and closure

68
Q

what is E-dimension

A

outside diameter of the neck

69
Q

what is the thread depth

A

difference between E and T dimensions divided by two

70
Q

what is I-dimension

A

the inner diameter of bottle neck

71
Q

what is S-dimension

A

measure from the top of the finish to the top edge of the first thread

the key factor that determines orientation of the closure to bottle and the amount of thread engagement between the bottle and cap

72
Q

what is H-dimension

A

height of the neck finish

73
Q

what are some thermal properties of glass packaging?

A
  • progressively softens until a true liquid state is achieved
  • becomes solid over a temp range when cooling
  • can have repeated melting and moulding without loss of original properties
  • lowest coefficient of thermal expansion among any packaging material
74
Q

the presence of boron and aluminum oxides results in what?

A

it increases the heat resistance of glass

75
Q

among all packaging material, glass has the lowest _____

A

coefficient of thermal expansion

76
Q

the weight and thickness of the final object can increase ____ to ____ with ore efficacy than glass composition

A

resistance to stresses

77
Q

what are optical properties of glass?

A
  • transparency in the visible wavelengths range to microwaves
  • very low UV transmission coefficients
78
Q

what are some disadvantages of glass

A
  • high wt/vol ratio
  • low strength/wt ratio
  • friability
  • susceptible to imperfections

Food Packaging (11 decks)

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