Glass

Glass has been manufactured in New Zealand for over

one hundred years, and is a common part of our daily

lives. It is used commonly in windows, bottles, jars

and domestic glassware, as well as as a material for

artwork, such as stained glass. It is manufactured

from cheap and abundant raw materials, and is readily

recycled.

MANUFACTURING OF GLASS

• Glass is produced in a two step process, and then shaped to make it suitable for a

variety of applications.

• Step 1 - Batch mixing

• The mixture of ingredients to make up the glass (silica, Na2CO3, CaCO3 and

recycled glass, together with small quantities of various other minor ingredients)

are mixed in a rotary mixer to ensure an even mix of ingredients and fed into the

furnace.

• Step 2 - Batch melting

• The mixture is heated to 1500-1550oC, where the ingredients melt, various

chemical reactions take place and CO2 and SO3 are evolved.

• Shaping plate glass

• The molten glass is cooled to 1000oC in a drawing canal, and then drawn up a

tower (the drawing tower) where it is pressed into the desired width and thickness,

and cools to 280oC. Individual plates of glass are snapped off at the top of the

tower and further cooled before being put into storage ready for sale.

• Molding glass containers

• Here molten glass is channeled off in forehearths (heated channels) where it is

slowly cooled to tempertaures of 1100 - 1150oC to increase its viscosity. Precisely

weighed slugs of glass are cut off, molded with compressed air, cooled slowly in

annealing lehrs (special ovens) and coated with a special spray to prevent

scratching.

Introduction: Many high-rise buildings now made of

glass. The glass used is typically of the type not glossy

, to avoid excessive glare to people who were outside

the building. In addition, the glass that absorbs

infrared waves are used to prevent heat from

penetrating into the building . This can lead to high

costs of air conditioners . In addition, the use of

double-glazed windows for heat insulation outside

from entering , and cool air in the building of out of

buildings in hot climates or otherwise in cold climates .

*

*Architectural glass:

Rolled glass Toughened glass

Laminated glass Float Glass

ROLLED GLASS• Definition --> a flat glass of considerable thickness that

is made by passing a roller over molten glass betweenthickness strips placed on the edges of the castingtable.

• Rolled glass is used for some flat glass, and means thatthe sheet of glass rolls along the assembly line as it ismanufactured.

• The glass used for this purpose is typically whiter incolour than the clear glasses used for otherapplications.

• This glass can be laminated depending on the depthof the pattern to produce a safety glass.

Example Of Rolled Glass

Float Glass

• made by floating molten glass on a bed of molten tin through float process

• As the continuous ribbon of glass floats along the tin bath, it is cooled gradually until it has hardened enough to go off into a conveyor system (the tin remains molten at this stage) for cutting and packing.

• The float process or Pilkington process is generally acknowledged as the best way of producing glass.

• This method gives the glass uniform thickness and very flat surfaces with no distortion and high clarity

• Tinted float glasses can be made by adding colouring agents during the melt process.

Toughened Glass

(Toughened glass is created with uneven heating that causes the cooling glass to

form layers instead of a solid sheet, making it much more resistant to impact than

"annealed" glass.)

The technique used to create toughened glass involves heating glass objects to

beyond the annealing point (600°C). Once the glass is heated, the outside is

cooled by air jets. This method solidifies only the outside, leaving the interior

molten and fluid. as the inner layers try to follow, they throw the outer layers into

compression, tending to close the microscopic cracks. That's what creates the

various layers within the glass. Because of its layering, the surface of this glass is

more resistant to impact.

•Advantages:1. Superior strength compared to annealed glass. (four to five times stronger than standard

glass.)

2. When failure occurs, glass panels shatter into small pieces that rather than sharp shards as is the case with annealed glass.

3. Good chemical resistance but attacked by hydrofluoric acid

4. If toughened glass breaks, it shatters into relatively harmless small granules.

•Disadvantages1. Cutting or edge working only able to done before toughing

2. Because of the balanced stresses in the glass, damage to any portion will eventually result in the glass shattering into thumbnail-sized pieces. The glass is most susceptible to breakage due to damage to the edge of the glass, where the tensile stress is the greatest.

3. Because the glass has more unity in its tensile strength, it would be more likely to explode completely if enough force was applied.

4. This glass is also more costly to produce, because of the extra step needed to cool the exterior.

LAMINATED GLASS

WHAT IS LAMINATED GLASS

2 sheets of glass bonded with thin film of plastic such as Polyvinyl Butyrate under pressure at a temperature about 100 Celsius.

The interlayer keeps the layers of glass bonded even when broken

This produces the characteristic ”spider web” cracking pattern when the impact not enough to pierce the glass.

AD VANTAGE OF LAMINATED GLASS

Provides a high degree of resistance to injury from flying glass in case of impact

-if laminated glass breaks instead of shatter and cause injury it will tend to adhere to the plastic interlayer.

The only glass that provide durability, high performance & multifunctional benefits while preserving the aesthetic appearance of glass.

Cutting is possible where 2-ly glass is easily cut by scoring & breaking each side in turn.

Sound reduction

-absorbing the sound passed through it because of air space between glass.

UV control

-95 % sun rays block by the film in laminated glass. Visible comes in, while UV light is blocked.

Impact resistance

-in the cases of storms such as hurricanes, tornadoes and large thunderstorms, laminated glass windows provide the strongest layer of protection possible.

DISADVANTAGE OF LAMINATED GLASS

The strength is less than toughened glass

Inadequate airspace

-the noise reduction property come from the airspace between two panes of the laminate, not from vinyl layer itself. If the windows are installed without the benefit of the airspaces, then the noise reduction properties is

greatly reduces.

Installed with poor construction

-no window is going to be energy efficient and soundproof if the frame is ill-fitting or poorly constructed.

APPLICATIONS OF LAMINATED GLASS

Glazed doors and side panels

Low-level glazing (located below 800mm from the floor)

Household furniture

Kitchen cabinet glazed doors and shelving

Bathroom shelving

Shop windows

Shopping Centre's

Public bar, shelving, partitions and mirrors.

Car windshields

Fire Performance

Can be considered as fire resistance of the glass

Direct contact with aggressive substances in the air / water losing their fire-resistant properties quicker flame propagation

Ordinary glass has poor fire performance tendency of shattered when heated

Period of 60 minutes stability and integrity to BS 476 part 8 (1972) can be achieved by use of wired glass or heat treated borosilicate glass, that can be laminated with float glass if high impact resistance is also required

Safety & GlassGlass is described as safe if, in a standard impact test,

any of the four condition is met:

a) There is no breakage

b) No shear or opening through which a 76 mm diamater

Sphere can be passed freely

c) Disintegration occurs but 10 largest crack - free

particles 3 min. after impact together weight no

more than the mass equivalent to 6500mm of the

original test piece.

d) Breakage results in several pieces but none of these

present sharp edges that are pointed or dagger-like.

Durability of Glass

• Glass doesn’t affected by atmosphere and

most acids except Hydroflouric Acid.

• Alkalis that occur in cement / chemical

paint strippers, attack glass and destroy the

smooth surface and light transmission

properties

The factors affecting glass strength and therefore durability are:

• Size

• Mechanical loading rate

• State of stress

• Temperature changes

• Surface and edge finishes

STRENGTH OF GLASS

• Strength of any glass unit is determined largely by

the effect of any surface imperfections it may contain.

• The highest strength obtained immediately after

manufacture, though strengths are still variable.

• Strength reduces with ageing as surface imperfections

increase whether by chemical attack or simply mechanical

abrasion.

• Glass that has weathered for some years being much

weaker than new glass.

• For this reason, old glass is more difficult to cut and

more likely to fracture due to movement / fixing stresses.

CONCLUSION

• Glass is widely used:

A. Safe in most of the condition,

B. Very durable,

C. Fire resistance,

D. Strong.

Thank you