Glass Flashcards
What is the major component of glass?
silicon (silicon dioxide)
Where can silicon be obtained?
quartz, sand, cristobalite, feldspar, kaolinite
What is the structure of glass?
amorphous (no crystallizing)
True/False: Glass is an organic product
False; inorganic product
Characteristics of silica crystals: (4)
very high melt temp.
high toughness
low transparency
poor inertness
The basis of the glass-making process:
change inorganic ingredients from crystalline to amorphous state, at temperature above 1450-1500C
What visual differences can be seen in crystalline vs amorphous structures? Why?
crystalline: not transparent (crystals reflect light)
amorphous: transparent (light can pass through)
Molecular units in glass have a ____ arrangement, but sufficient ____ to produce mechanical rigidity
disordered
cohesion
Basic formula of glass:
soda-limestone
What are the various specific ingredients of glass?
silica (SiO2) limestone (CaCO3 -> CaO) soda ash (Na2CO3 -> Na2O) alumina (Al2O3) Cullet (recycled glass)
What is the largest chemical ingredient of glass?
silica sand (SiO2)
What is the role of soda ash in glass?
network modifier
fluxes, enhances melting of silica
What is the role of limestone in glass?
stabilizer
increase chem resistance, increase refractive index
Why is cullet added to glass?
to reduce cost/energy
Boron oxide is added to what types of glass?
heat stable glass
Can glass be used to store alkaline material? Why?
No; will react slowly with glass and degrade over time
What is used to dissolve glass?
HF (only acid that can dissolve silica)
What are metal oxides used for in glass?
colorants, bleaching
What are various stabilizers added to glass?
Ca carbonate
Mg carbonate
Ba carbonate
What is added to glass as a fining agent?
Na sulfate
Sodium and potassium carbonate are added to glass for what reason?
fluxes
What is added to achieve amber glass?
carbon & sulfur compounds
What is added for blue glass?
cobalt oxide
What is added for green glass?
ferrous sulfate, chromic oxide
What is added for yellow glass?
ferric oxide, antimony oxide
What is added for blue-green glass?
cobalt oxide and chromium oxide
What is added for opal glass?
calcium oxide
Why does the addition of different metal oxides give various colors?
different metal cations have different ionic refractions
basic steps of glass production:
raw materials -> mixing -> melting -> forming -> glass
Glass is made in ____ processing
batch
the heating step for glass production takes place in a ____, heated to a temp of ____.
furnace
1500C (2700F)
What processes happen during the melting of glass? (5)
decarbonation dehydration solid-state reactions formation of low-melting eutectics dissolutions
The temperature is raised during glass melting in order to ___ ___
release gas
In order to work/form the glass, what needs to occur?
glass needs to be cooled slightly (otherwise will stick)
After melting, if the temperature is too hot, the glass will _____. If it is too cold, it _____
too hot => sticks
too cold => won’t flow
3 process/zones of the glass furnace?
- melting & sand dissolution
- primary fining
- secondary fining (refining)
steps in the glass furnace:
- batch input
- batch melting => rough melt
- sand grain dissolution => seedy melt
- fining => clear melt
- refine/condition => conditioned melt
what step in the glass furnace yields the ‘clear melt?’
fining
How does the melting process compare to the fining process?
melting: fast (1hr), need a lot of energy
fining: longer time (24 hr), lower energy input
the 2 routes for melting and sand dissolution:
carbonate route
silicate route
What requires a higher temp? the Carbonate or silicate route for melting?
silicate (700-860C)
What is the temperature range for the carbonate route?
550-850C
reaction enhanced >820C
what is the purpose of fluxing agents
- formation of early melt phases
- decrease surface tension
- increase heat conductivity
About ____% of the mass of normal soda-lime silica bath is transferred into volatile ____
14-20%
CO2
1 kg of normal batch will generate ____ L of gas at room temp
100
True/False: finely crushed cullet will release gas later than coarse cullet
False; fine cullet will have early gas release
What is glass ‘fining?’
eliminate gases through heating -> bubbles (rise to surface)
Describe the process of glass fining
high temperature, dissolved gases diffuse from melt into bubbles (agglomeration and growth) -> ascend to surface
What gases are produced by fining?
O2, SO2
The greater the glass melt ____, the slower the bubble ascension
viscosity
lower ___, and lower ___ will increase speed of bubble ascension. Which has the greater impact?
glass melt density bubble radius (bigger impact; squared)
At (higher/lower) temperatures, the melt will have lower viscosity
higher
What reaches the surface first? bubbles in a melt at 1400C, or bubbles in a melt at 1500C?
1500C
What reaches the surface first? bubbles of 300um or 600um?
300um
What is ‘refining’ of glass, what does it achieve?
controlled cooling of melt
dissolution of small bubbles remaining
(reverses fining reaction)
Bottles are formed automatically in the ___ ___ machine
individual section
How does a individual section machine function?
molten glass ‘gobs’ sheared off
bottles/jars formed in parison moulds (blow & blow method or press & blow method)
The main 2 functions of a individual section machine:
shape
remove heat
2 main processes for shaping:
blow and blow
press and blow
process of blow & blow (7 steps)
- gob dropped into parison mould
- sealed, settle-blow (air from top push glass into finish/neck)
- counter-blow (air from bottom push glass up into mould and shapes it)
- parison removed from mould, rotate 180
- transfer into blow mould for finishing
- blow air from top to expand/press against mould
- opened, bottle removed, passed to annealing lehr
process of press and blow (6 steps)
- gob dropped in mould
- sealed, plunger moves up; glass forms around it
- parison removed from mold, rotate 180
- transferred to blow (finishing) mould
- air from top expands glass, press against mould
- opened, bottle removed, passed to annealing lehr
How is the parison formed in blow & blow vs press & blow?
blow & blow: form both finish and rest of parison by air
press & blow: form finish/rough parison with plunger; complete with air
Does B&B or P&B have greater heat removal?
P&B has greater heat removal
True/False; P&B glassmaking creates more uniform thickness
True
True/False: B&B is faster than P&B
False; B&B is slower
What types of bottles are made in B&B vs. P&B?
B&B: narrow neck bottles
P&B: narrow neck or wide mouth
The neck of a bottle is known as the ____
finish
the sloping part of a bottle between the body and finish is called the ____
shoulder
What is the purpose of coating glass?
improve quality, machinability, durability, strength, appearance, functionality
True/False: Glass coatings are designed to be permanent
False;
can be permanent, semipermanent, or nonpermanent
Examples of permanent glass coatings:
tin oxide
PE
Examples of semipermanent glass coating:
PE, silicone
nonpermanent glass coatings:
PVA, stearate
When are glass coatings added?
Before the lehr (hot end) - 2 steps
After the lehr (cold end) - 1 step
What is the Shat-R-Kote coating? What properties does it give to glass?
Ionomer resin (ethylene/methacrylic acid copolymer)
acid/solvent resistant transparent high tensile strength (shatterproof) no label adhesive needed 90% UV block, antioxidant
What is ‘annealing?’
reheating glass to soften (550-700C), remove internal stresses caused by heat, cool slowly
What is the measurmenet unit of viscosity?
poises
What is the viscosity for the working point, softening point, and annealing point of glass?
working point: 10^4
softening point: 10^7.6
annealing point: 10^13
How is the softening point of glass determined?
glass fibre 1mm stretches under its own weight (1mm/min)
What inspection quality control technologies are used for glass?
electro-optical, radio frequency, visual tests
detect dangerous and ugly defects -> glass used as cullet
What are some machine tests used for glass inspection (7)
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)
Some qualities of glass that should be inspected: (5)
internal pressure breakage vertical load strength impact strength resistance to abrasion & scratching thermal shock breakage
True/False: thickness is the most important feature of glass when considering vertical load strength
False; shoulder design (bottle shape) is more important factor than glass thickness
types of impacts:
bottle striking stationary object
stationary bottle hits moving object
___ ____ glass is more resistant to internal pressure, but it has poor ________.
thick walled glass
thermal shock resistance
What shape of glass has better resistance to thermal shock?
round/spherical shape
(Bigger/smaller) glasses have greater resistance to thermal shock
smaller
The higher the weight/capacity ratio of bottles, the (higher/lower) the limiting sudden temperature drop
lower
classifications of glass defects:
critical (hazardous or unusable; cracks or overpress)
major (reduced usability; sunken centre, oval finish)
minor (loss of acceptibility; heeltap, seeds)
What is a ‘heeltap?’ what are ‘seeds?’
heeltap: heavy (thicker) glass on the side
seeds: small bubbles in glass
What markings are seen on the bottom of glass bottles?
- identification of mould (plant, company mark, year)
2. stippling to minimize shock in lehr
specifications for glass containers should include:
- description of container finish
2. dimensions (capacity, ht, diameter, wt, tolerances)
Glassware finishes must be compatible with _____
the closure type
Examples of finishes:
sprinkler top, shallow CT, Tall CT, pour-out CT, crown, cork, roll-on, biological, handle
Finishes are designated with a ____ system from the ______
2 number
GPI (glass packaging institute)
(matches finish with closure)
what does the 2 number system for glass finishes describe?
1st number: millimeter diameter across inside cap’s opening/bottle threads
2nd number: thread style
The various thread styles for closures:
400: continuous
500: twist off
600: crown
2000: vacuum
1600: roll on
The different ‘dimensions’ of the finish
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
What does “T” dimension of finishes determine?
mate between bottle and closure
What does “S” dimension of finishes determine? (2)
orientation of closure to bottle
amount of thread engagement between bottle & cap
How do you determine thread depth?
difference between “T” and “E”
Why do specifications require a minimum “I” dimension for finishes?
allow filling tubes to fit
plugs and seal proper fit
True/False: melting and remoulding of glass can be repeated indefinitely without loss of properties
True
The presence of ___ and ____ in glass will hugely increase the heat resistance
boron oxides, aluminum oxides
Glass has the lowest coefficient of ___ ___ of any packaging material
coefficient of thermal expansion (6-8*10^(-6) /C)
What has a greater impact on reducing the stress resistance of glass, the composition or the weight/thickness?
weight and thickness
True/False: Glass can have cracks and flaws, even if it is not visible
True; superficial defects lead to stress amplification
What are the optical properties of glass? (3)
transparent in visible wavelengths
transparent to microwaves
very low UV transmission coefficients (absorb in UV range)
Glass can’t be penetrated by: ______ (4)
moisture
gases
odors
microbes
Can glass react with food?
No; inert (does not react or migrate)
Advantages of glass as packaging: (10)
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)
disadvantages of glass as packaging: (6)
high weight/volume ratio low strength/weight ratio friability (tend to chip) susceptible to imperfections safety (when broken) energy intensive production
