Unit 2 - Glass Flashcards
What is glass?
A specific type of ceramic
What is a ceramic?
A non-metallic, inorganic solid produced by heat and subsequent cooling
Describe the structure of a ceramic
Rapid cooling stops the atoms from being organised into crystals, making it amorphous and non-crystalline
Give 7 advantages of glass packaging
Transparent, chemically inert, thermally stable, strong in compression, impermeable, total barrier, easily recyclable
Give 4 disadvantages of glass packaging
Thermal shock, weak in tension, heavy, noisy on filling lines
What are the 5 components that make up glass and give their percentages
Silicon dioxide - 70%
Sodium carbonate - 15%
Calcium carbonate - 10%
Aluminium oxide - 5%
Cullet - Variable
Why is cullet added during glass production - what does a 10% addition do?
Reduces energy required for production. 10% lowers energy requirement by 2.5%
What is the purpose of silicon dioxide?
The main ingredient which gives most of the chemical, physical, and mechanical properties
What is the purpose of sodium carbonate?
Fluxing agent which lowers melting point and makes it easier to form
What is the purpose of calcium carbonate?
Modifies the structure to reduce the viscosity (makes it runnier) so it is easier to process
What is the purpose of aluminium oxide?
Changes the structure to improve strength and water resistance
Name the 3 types of glass
Type 1 - borosilicate glass
Type 2 - treated soda glass
Type 3 - untreated soda glass
Describe type 1 glass
- Used for making heat-resistance ovenware (Pyrex)
- Made from mainly silica (70-80%) and boric acid (10%)
- Low alkali content which gives it good chemical durability and thermal shock resistance
- Highly resistant to hydrolysis thus used in laboratory apparatus which needs to be used repeatedly
- Not recyclable in the normal waste streams
Describe type 2 glass
- Inner surface treated with SO2 or NH4SO3 at high temperatures to reduce alkali content
- Etching process results in a frosted appearance, high hydrolytic resistance, and a melting point of 1500°C
- Used for eye drops but must be washed before use
Describe type 3 glass
- Most common type but not for injectables
Give the 5 glass colours and what chemicals are used to make them
Green - chromium oxides
Blue - cobalt oxides
Purple - manganese
Opal - fluorides and phosphates
Red - selenium, cadmium, antimony sulphides
Amber - iron, sulphur, carbon
What thickness of glass is needed for amber and green to become a total UV barrier?
3mm
What are the 8 steps of glassmaking?
- Preparation
- Melt
- Dose
- Form
- Annealing
- Coating
- Inspection
- Packing
Describe the preparation stage of glassmaking
- Raw materials and cullet are ground to even particle size and stored in hoppers
- Ingredients are mixed thoroughly to ensure a homogenous blend
- Weighed out in batches ready for loading into the furnace
Describe the melt stage of glassmaking
- Batches of raw materials are continually fed into the furnace
- Furnace is heated to 1500-1700°C and is broken down into ‘zones’ going from hot to coldest
- Furnace interior is lined with refractory bricks which are able to withstand extreme temperatures for prolonged periods of time
Describe the dose stage of glassmaking
- A plunger forces the glass through an orifice
- Water-cooled mechanical shears cut off precise amounts called gobs (one gob = one container)
- Forehearth feeds multiple shears to increase production
Give the 5 types of forming processes in the glassmaking process
- Blow and blow (narrow neck)
- Press and blow (wide neck)
- Narrow neck press and blow
- Danner
- Vello
Describe the blow and blow glassmaking forming process
- Gob loaded
- Air blown in to shape neck area
- Funnel lifts and glass is pushed into the mould
- Parison is flipped and transferred to blow mould
- Neck ring open
- Air is blown in to form final shape
- Bottle removed from mould
Describe the press and blow glassmaking forming process
- Gob loaded
- Plunger presses gob upwards
- Parison flipped over into blow mould
- Neck ring opens
- Air blown in to form final container shape
- Bottle removed from mould
Give advantages of narrow neck press and blow in glassmaking
- Better glass distribution
- Neck and wall thickness control
- Better visual quality
- No reduction in strength caused by wall thickness variations
Give disadvantages of narrow neck press and blow in glassmaking
- Tooling is more expensive
- Tolerances are higher
- Requires higher temperatures
How many sets of tooling does glassmaking require and name them
2 - parison and finishing mould
Describe the Danner forming process in glassmaking
- Used for tubing up to 70mm in diameter at up to 400m/min
- Glass leaves the furnace as a ribbon and is wrapped around a sleeve then over the tip of a tube
Describe the Vello forming process in glassmaking
- Allows for faster production
- Tubing is drawn off mechanically from a hollow rotating mandrel
- Draw rate affects the diameter and wall thickness
- Tubing is cut to the required length and the end are heated to smooth them
Why must glass be annealed? Describe the process
- Fast cooling can introduce internal stresses which can be relieved through annealing
- Glass is heated to 600°C and cooled slowly to room temperature in a lehr (30m long; takes around 60 minutes)
Why is glass coated?
Used to strengthen the surface and lower coefficient of friction for better handling
Name and describe the types of glass coatings
- Hot-end coatings, such as tin or titanium, can be used as a primer for bonding agent
- Titanium oxide can be used to reduce the effects of UV light on the product, which can cause flavour or colour changes in the product
- Cold-end coatings, such as oleic acid, monostearates, waxes, and silicones reduce friction
What must happen before glass is coated?
Surface must be cleaned first with either detergents or solvents
How are glass coatings applied?
- Coatings are usually spray-applied to give a uniform thickness
- They are then cured to harden the coating
Describe the inspection process of glassmaking
- Inspected at the hot-end for bottle weight and dimensions
- Inspected at the cold-end via electronic inspection for tolerances and defects
- Other tests such as squeeze test for weak points, bore gauge to check neck dimensions, wall thickness checks, crack detection tests, and pressure tests for carbonated drinks
- Rejected containers are recycled as cullet
Describe the packing process of glassmaking
Shipped on pallets with corrugated layer pads and shrink wrap
Name and describe the 6 types of glass decoration methods
- Patterns can be formed into the surface during the moulding process through embossing and debossing
- Surface colouring can be opaque or it can be transparent
- Generally applied by spraying and is used to change the appearance and UV protection
- Frosting makes glass translucent and is achieved through sandblasting or chemical etching
- Surface printing (screen printing) can either be flat or a relief
- Adhesive may be printed on which is then foiled to create a metallic effect
- Ceramic decals are used for >3 colours or when the image is complex and precise definition is needed
- Transfer is applied to a clean surface and fired to fuse it to the surface
- Spot, wraparound, and sleeve labels are a temporary way to decorate glass
- Applied before or after filling
Name the 7 stages of clay / pottery production
- Extract
- Process
- Form
- Drying
- Setting
- Firing
- Glazing
Describe slip casting for pottery
- Slip casting is the most common method - the slip is made by mixing clay with water until it reached the correct consistency (like double cream)
- Slip is poured into a porous mould and the moisture is removed via capillary action, leaving a layer of clay on the mould wall in the correct shape
- Excess slip is poured out and the clay form is removed and trimmed
Why must pottery be dried before entering a kiln?
Vital otherwise water left with expand and turn into steam, which will cause containers to explode in the kiln
Why is pottery glazed?
Makes the surface impermeable and food safe
Describe the economics of glassmaking
- A capital-intensive process requiring a lot of initial investment
- Furnace that runs for up to 15 years
- Bottle-forming equipment
- Annealing lehr
- Storage facilities
- For each tonne of glass, about 1-2 tonnes of raw material is needed
- 374kg of CO2 is produces, but this falls to 320kg if 40% cullet is used
What design considerations should be make during glass production?
- There is often a trade-off between cost of custom tooling and lead time
- Alcohol containers must allow for expansion of the product
- Consumer convenience
- Shape for ease of holding
- Neck finish for easy product access
- No undercuts for product to get trapped
- Convenient closures for opening and resealing
- Filling line convenience
- Low centre of gravity to reduce toppling during filling
- Slight shoulders to reduce contact between packs
- A depression so the label is not damaged
- Storage / display convenience
- Secure stacking - interlock with closure
