Lecture 4: Glass Flashcards
what is glass?
an amorphous and inorganic product of fusion that has been cooled to a rigid condition without crystallizing
what is the major component of common glass?
silicon dioxide
what are some major physical properties of glass?
- high melting temp
- high toughness
- low or null transparency
- poor inertness
the glass making process changes inorganic ingredients from ____ to ____
crystalline to amorphous state
what temp is needed for the glass making process?
1450 - 1500 deg C
what is the basic formula for glass?
soda limestone
what consists of soda limestone?
silica limestone soda ash alumina cullet
what is the chemical name for silica?
silicone oxide
SiO2
what is the chemical name for limestone?
calcium carbonate
CaO
what is the chemical name for soda ash?
sodium carbonate
Na2O
what is the chemical name for alumina?
aluminum oxide
Al2O3
what is the chemical name for cullet?
recycled glass
what is the highest and lowest composition in soda limestone formula for class?
highest: silica sand
lowest: alumina
what is a network former?
silicone oxide
what are network modifiers? what is their function?
Na2O + CO2
function: enhances melting of silica
what are stabilizers in glass?
what is their function?
CaO + CO2
function:
- increases chemical resistance
- increases refractive index
what is the function of cullet (recycled glass)?
reduces costs and energy
what occurs in the glass furnace?
- decarbonation, dehydration, solid-state reactions, formation of low-melting eutectics, dissolutions
- ingredients are melted into a molten mass
why is temperature raised in the glass furnace?
why is it cooled?
raised: to release gas
cooled: so that glass can be worked
If too hot, it will stick. If too cold, it won’t flow
what are 5 main steps in glass production?
- batch input
- batch melting
- sand grain dissolution
- fining
- refining and conditioning
which part of the glass production is
a) fast and has high energy input?
b) slower and has lower energy input
a) batch melting
b) sandgrain dissolution, fining, refining/conditioning
what are 2 routes in melting and sand dissolution?
- carbonate route
2. silicate route
what is the function of fluxing agents?
- formation of early melt phases
- decrease of surface tension
- increase of heat conductivity
some of the mass of normal soda lime silica batches is transferred into what?
volatile CO2 (gas release)
during melting, 1kg of normal batch generates how much gas at normal pressure and room temp?
100L
what is the effect of adding
a) fine cullet
b) coarse cullet
a) early gas release
b) gas release at low viscosity
describe fining of glass melt
- at high temp
- bubble agglomeration and bubble size growth
- dissolved gases diffuse from melt into bubbles
- ascension of growing bubbles to glass melt surface
what is the temperature in which fining of glass melt occurs at?
1430-1480 deg C
what is the chemical reaction that occurs in fining of glass melt?
Na2SO4 (molten glass) –> Na2O (melt) + fining gases (SO2) + 1/2 O2)
what are two fining gases?
SO2 and O2
what is the equation of V ascension?
V ascension = (cpg*R^2) / n
p = density of glass melt n = viscosity of glass melt R = bubble radius g = gravity c = factor
in fining of glass melt, how does temperatures affecting melting?
higher temp = melting with lower viscosity
describe refining of glass melt
- controlled cooling of the melt
- dissolution of small remaining bubbles in the melt
in refining of glass melt, what happens when temperature decreases?
decreasing temp = increasing solubility of gases
this reverses the fining reaction
what is the individual section machine for?
automatically forming bottles
describe the process occuring in individual section machine
- 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
what are the 2 functions of the individual section machine
shapes
removes heat
what are gobs
the drops sheared off of molten glass
what are parison moulds
the moulds used to form bottles and jars
describe the blow and blow method
- gob of glass is dropped into parison mould
- mould is sealed and puff of air from top pushes glass into finish neck (settle blow)
- puff of air from bottom pushes glass into mould to shape it to a parison (counter-blow)
- parison is removed and rotated 180C
- parison is transferred to a blow mould (finishing)
- air is blown in from the top to expand glass and push it against the mould
- mould is opened; red hot bottle is removed and passed to the annealing lehr
describe the press and blow method
- gob of glass is dropped into parison mould
- mould is sealed and plunger moves up to form the top of the parison; forces lass downward to form the finish
- parison is removed and rotated 180C
- parison is transferred to blow (finishing) mould
- air is blown from top to expand glass and push it against mould
- mould is opened and bottle is removed
how is B&B and P&B different in terms of parison forming?
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
how is B&B and P&B different in terms of heat removal?
B&B: less
P&B: more
how is B&B and P&B different in terms of thickness?
B&B: varied
P&B: uniform
how is B&B and P&B different in terms of use?
B&B: generally narrow necked
P&B: narrow necked and wide mouthed
how is B&B and P&B different in terms of speed?
B&B: slower
P&B: faster
why is glass coated?
to improve:
- quality
- machinability
- durability
- strength
- appearance
- functionality
coatings can be… (3)
nonpermanent
semipermanent
permanent
when can coatings be added? (2)
- before the lehr (hot end) in a 2-step process
2. after the lehr (cold end) in a 1-step process
what is an example of a coating? describe it.
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
what happens in the annealing lehr?
- 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
in the annealing lehr, why must containers be cooled slowly?
to prevent stresses from re-forming
what is the:
a) working point
b) softening point
c) annealing point
a) working point = 10^4 poises
b) softening point = 10^7.6 poises
c) annealing point = 10^13 poises
glass containers are inspected using what tests?
electro-optical, radio frequency and visual tests
what happens to defective glass containers?
they are recycled as cullet
describe the inspection process
- bottle spacer avoids bottle to bottle contact
- squeeze tester (presses between discs)
- bore guager finish is measured
- check detector (for problem areas)
- wall thickness detector (for faults in the walls)
- hydraulic pressure tester (internal pressure)
- visual check in (final check)
when a bottle strikes another object, how can amount of damage be minimized?
- design features of the bottle
2. surface treatments to reduce impact stress
what are 5 main factors of glass that are inspected?
- internal pressure breakage
- verticle load strength
- impact strength
- resistance to abraision and scratching
- thermal shock breakage
how is weight/capacity ratio related to thermal shock resistance?
lower wt/capacity ratio = higher sudden temperature drop
higher wt/capacity ratio = lower sudden temp drop
what are 3 types of defective containers?
give an example of each
- critical: cracks and overpress
- major: rocker bottom and oval finish
- minor: heeltap and seeds
glass containers used for packaging should have what specifications?
- description of the container finish
2. dimensions: capacity, ht, diameter, wt, tolerances
what are 3 identification marks on glass packaging?
- plant
- company mark
- year
finishes are designated with what system?
a two-number system which describes the bottle and closure
eg. 24/400 bottle will only accept a 24/400 closure
what is GPI
glass packaging institute
if a bottle is labelled 24/400, what does each number refer to?
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
describe the thread style for:
a) 400
b) 500
c) 600
d) 2000
e) 1600
a) continuous thread
b) twist-off
c) crown
d) vacuum
e) roll on
what is T-dimension
outside diameter of the thread
tolerance range of T will determine the mate between bottle and closure
what is E-dimension
outside diameter of the neck
what is the thread depth
difference between E and T dimensions divided by two
what is I-dimension
the inner diameter of bottle neck
what is S-dimension
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
what is H-dimension
height of the neck finish
what are some thermal properties of glass packaging?
- 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
the presence of boron and aluminum oxides results in what?
it increases the heat resistance of glass
among all packaging material, glass has the lowest _____
coefficient of thermal expansion
the weight and thickness of the final object can increase ____ to ____ with ore efficacy than glass composition
resistance to stresses
what are optical properties of glass?
- transparency in the visible wavelengths range to microwaves
- very low UV transmission coefficients
what are some disadvantages of glass
- high wt/vol ratio
- low strength/wt ratio
- friability
- susceptible to imperfections
