Part 7. Glass

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29 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Part 7. Glass


Glazing


Glass fibres

Glass for Glazing


Raw Materials


Manufacture


Cutting


Toughening and annealing


Properties


Strength


Durability


Insulation


Solar Heat Gain

Three basic types of glass are
manufactured:



Plain

flat

glass

Most

plain

glass

used

in

the

UK

is

now

float

glass
.

In

this

process

liquid

glass

is

cooled

to

give

a

viscosity

sufficiently

high

for

forming

and

it

is

then

drawn

across

the

surface

of

molten

tin
.

This

method

may

be

used

to

produce

very

flat

glass

in

large

quantities
.


Textured,

patterned

and

wired

glass

The

rolled

glass

process

is

used

for

the

manufacture

these

types
.

The

glass

is

drawn

in

a

horizontal

ribbon

on

rollers
.

If

flat

glass

is

required

from

this

process

it

must

be

ground
.


Laminated

glass

This

is

made

with

two

or

more

sheets

of

glass

which

are

bonded

together

with

layers

of

plastic

between

them


Glass for Glazing


Raw Materials


Manufacture


Cutting


Toughening and annealing


Properties


Strength


Durability


Insulation


Solar Heat Gain

Toughened Glass

Cooling jets

Compression

Tension

Compression

The properties of toughened glass


It

is

stronger

in

bending

than

plain

glass

because

bending

stresses

the

outer

layers

in

tension

and

these

are

initially

in

compression
.


For

the

same

level

of

safety

it

is

cheaper

and

lighter

than

laminated

glass
.


If

the

material

is

broken

the

stress

distribution

becomes

unbalanced

and

it

shatters

into

small

and

relatively

harmless

fragments
.


It

cannot

be

cut

so

it

must

be

ordered

to

size
.

This

has

the

advantage,

however,

that

the

stamp

which

is

put

on

every

sheet

will

always

be

there

for

checking
.

(note

that

laminated

glass

can

be

cut)
.


There

are

restriction

on

dimensions

of

holes

near

the

edge

of

a

sheet
.

Glass for Glazing


Raw Materials


Manufacture


Cutting


Toughening and annealing


Properties


Strength


Durability


Insulation


Solar Heat Gain

Transmission and reflection

Solar
transmission
and reflection

Methods of reducing solar heat gain:



Tinted

glass
.

This

absorbs

heat

and

re
-
emits

some

of

it

outwards
.

Care

should

be

taken

that

the

sheet

of

glass

heats

uniformly,

if

the

perimeter

remains

cool

it

may

fail

in

tension
.

There

are

special

glasses

with

low

thermal

expansion

but

they

must

be

very

clearly

labelled

so

that

if

they

are

broken

the

replacement

has

the

same

properties
.


Partially

reflecting

glass
.

This

has

a

thin

film

on

the

inner

surface

which

may

be

added

during

manufacture

or

can

even

be

put

on

in
-
situ

in

older

buildings
.

Note

that

no

glass

gives

one

way

vision

under

all

circumstances,

they

depend

on

the

lighting

on

the

"viewing"

side

being

less

intense

than

the

other

side
.

Solar
glass

Part 7. Glass


Glazing


Glass fibres

Glass fibre reinforcement:


The

original

grades

were
:


E
-
glass


electrical


C
-
glass

chemical

resistant


S
-
glass

high

strength


M
-
glass

low

modulus

E
-
glass is used for most polymer reinforcement
applications.


The glass come in four different
forms



Loose

chopped

strand

(e
.
g
.

for

fibre

reinforced

concrete)


Chopped

strand

mat

(cheap

fabric)


Rovings

(yarn)


Woven

roving

(expensive

fabric)


Fabric Weave Styles

Fabric Weave Styles



2 x 2 Twill






4 Harness Satin

Stitched bi
-
axial

(+/
-
45
°
)

Basic Properties of
Engineering Materials

Comparative Cost

Rival Materials to Glass Fibre