Unit 2 - Glass

Question 1

What is glass?

Answer 1

A specific type of ceramic

Question 2

What is a ceramic?

Answer 2

A non-metallic, inorganic solid produced by heat and subsequent cooling

Question 3

Describe the structure of a ceramic

Answer 3

Rapid cooling stops the atoms from being organised into crystals, making it amorphous and non-crystalline

Question 4

Give 7 advantages of glass packaging

Answer 4

Transparent, chemically inert, thermally stable, strong in compression, impermeable, total barrier, easily recyclable

Question 5

Give 4 disadvantages of glass packaging

Answer 5

Thermal shock, weak in tension, heavy, noisy on filling lines

Question 6

What are the 5 components that make up glass and give their percentages

Answer 6

Silicon dioxide - 70%
Sodium carbonate - 15%
Calcium carbonate - 10%
Aluminium oxide - 5%
Cullet - Variable

Question 7

Why is cullet added during glass production - what does a 10% addition do?

Answer 7

Reduces energy required for production. 10% lowers energy requirement by 2.5%

Question 8

What is the purpose of silicon dioxide?

Answer 8

The main ingredient which gives most of the chemical, physical, and mechanical properties

Question 9

What is the purpose of sodium carbonate?

Answer 9

Fluxing agent which lowers melting point and makes it easier to form

Question 10

What is the purpose of calcium carbonate?

Answer 10

Modifies the structure to reduce the viscosity (makes it runnier) so it is easier to process

Question 11

What is the purpose of aluminium oxide?

Answer 11

Changes the structure to improve strength and water resistance

Question 12

Name the 3 types of glass

Answer 12

Type 1 - borosilicate glass
Type 2 - treated soda glass
Type 3 - untreated soda glass

Question 13

Describe type 1 glass

Answer 13

1. Used for making heat-resistance ovenware (Pyrex)
2. Made from mainly silica (70-80%) and boric acid (10%)
3. Low alkali content which gives it good chemical durability and thermal shock resistance
4. Highly resistant to hydrolysis thus used in laboratory apparatus which needs to be used repeatedly
5. Not recyclable in the normal waste streams

Question 14

Describe type 2 glass

Answer 14

1. Inner surface treated with SO2 or NH4SO3 at high temperatures to reduce alkali content
2. Etching process results in a frosted appearance, high hydrolytic resistance, and a melting point of 1500°C
3. Used for eye drops but must be washed before use

Question 15

Describe type 3 glass

Answer 15

1. Most common type but not for injectables

Question 16

Give the 5 glass colours and what chemicals are used to make them

Answer 16

Green - chromium oxides
Blue - cobalt oxides
Purple - manganese
Opal - fluorides and phosphates
Red - selenium, cadmium, antimony sulphides
Amber - iron, sulphur, carbon

Question 17

What thickness of glass is needed for amber and green to become a total UV barrier?

Answer 17

3mm

Question 18

What are the 8 steps of glassmaking?

Answer 18

1. Preparation
2. Melt
3. Dose
4. Form
5. Annealing
6. Coating
7. Inspection
8. Packing

Question 19

Describe the preparation stage of glassmaking

Answer 19

• 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

Question 20

Describe the melt stage of glassmaking

Answer 20

• 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

Question 21

Describe the dose stage of glassmaking

Answer 21

• 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

Question 22

Give the 5 types of forming processes in the glassmaking process

Answer 22

1. Blow and blow (narrow neck)
2. Press and blow (wide neck)
3. Narrow neck press and blow
4. Danner
5. Vello

Question 23

Describe the blow and blow glassmaking forming process

Answer 23

1. Gob loaded
2. Air blown in to shape neck area
3. Funnel lifts and glass is pushed into the mould
4. Parison is flipped and transferred to blow mould
5. Neck ring open
6. Air is blown in to form final shape
7. Bottle removed from mould

Question 24

Describe the press and blow glassmaking forming process

Answer 24

1. Gob loaded
2. Plunger presses gob upwards
3. Parison flipped over into blow mould
4. Neck ring opens
5. Air blown in to form final container shape
6. Bottle removed from mould

Question 25

Give advantages of narrow neck press and blow in glassmaking

Answer 25

1. Better glass distribution 2. Neck and wall thickness control 3. Better visual quality 4. No reduction in strength caused by wall thickness variations

Question 26

Give disadvantages of narrow neck press and blow in glassmaking

Answer 26

1. Tooling is more expensive 2. Tolerances are higher 3. Requires higher temperatures

Question 27

How many sets of tooling does glassmaking require and name them

Answer 27

2 - parison and finishing mould

Question 28

Describe the Danner forming process in glassmaking

Answer 28

- 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

Question 29

Describe the Vello forming process in glassmaking

Answer 29

- 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

Question 30

Why must glass be annealed? Describe the process

Answer 30

- 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)

Question 31

Why is glass coated?

Answer 31

Used to strengthen the surface and lower coefficient of friction for better handling

Question 32

Name and describe the types of glass coatings

Answer 32

- 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

Question 33

What must happen before glass is coated?

Answer 33

Surface must be cleaned first with either detergents or solvents

Question 34

How are glass coatings applied?

Answer 34

- Coatings are usually spray-applied to give a uniform thickness - They are then cured to harden the coating

Question 35

Describe the inspection process of glassmaking

Answer 35

- 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

Question 36

Describe the packing process of glassmaking

Answer 36

Shipped on pallets with corrugated layer pads and shrink wrap

Question 37

Name and describe the 6 types of glass decoration methods

Answer 37

- 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

Question 38

Name the 7 stages of clay / pottery production

Answer 38

1. Extract 2. Process 3. Form 4. Drying 5. Setting 6. Firing 7. Glazing

Question 39

Describe slip casting for pottery

Answer 39

1. 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) 2. 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 3. Excess slip is poured out and the clay form is removed and trimmed

Question 40

Why must pottery be dried before entering a kiln?

Answer 40

Vital otherwise water left with expand and turn into steam, which will cause containers to explode in the kiln

Question 41

Why is pottery glazed?

Answer 41

Makes the surface impermeable and food safe

Question 42

Describe the economics of glassmaking

Answer 42

- 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

Question 43

What design considerations should be make during glass production?

Answer 43

- 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