glass to be print

8/19/2019 Glass to Be Print

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Republic of the Philippines

PANGASINAN STATE UNIVERSITY

Urdaneta Campus, Urdaneta City, Pangasinan

Topic: Manufacturing of Glass

Reporter: Gemar E. Aseniero

Instructor: Engr. Marvin Darius Lagasca

GLASS

Glass is one of three basic types of ceramics. Glass is distinguished by its amorphous

(noncrystalline) structure.

Glass is an inorganic substance in a condition which is continuous with, and analogous to, the

liquid state of that substance, but which, as the result of a reversible change in viscosity during

cooling, has attained so high a degree of viscosity as to be, for all practical purposes, rigid.”

ASTM defines glass as “an inorganic product of fusion that has cooled to a rigid condition

without crystallizing.” Both organic and inorganic materials may form glasses if their

structure is non-crystalline—that is, if they lack long-range order.

Glass, a hard, brittle, and usually transparent material. As a scientific term, the word glass is

often used to refer to any rigid substance that is amorphous (not made up of crystals), with theexception of plastics and certain other substances containing carbon. Glass is an extremely

useful material. It is made into a large variety of familiar products, including windows, jars,

mirrors, light bulbs, lenses, and tableware.

GLASS PROPERTIES

Mechanically Strong

Glass has great inherent strength. Weakened only by surface imperfections, which give

everyday glass its fragile reputation. Special tempering can minimize surface flaws.

Hard

Surface resists scratches and abrasions.

Elastic

Gives under stress---up to a breaking point---but rebounds exactly to its original shape.

Chemical Corrosion-Resistant

Affected by few chemicals. Resists most industrial and food acids.



Thermal Shock-Resistant

Withstands intense heat or cold as well as sudden temperature changes.

Heat-Absorbent

Retains heat, rather than conducts it. Absorbs heat better than metal.

Optical PropertiesReflects, bends, transmits, and absorbs light with great accuracy.

Electrical Insulating

Strongly resists electric current. Stores electricity very efficiently

COMPOSITION

Glass is formed when certain substances are cooled rapidly and do not crystallize—that is, their

atoms do not arrange themselves in the repeating, orderly pattern characteristic of most solids.

Instead, the atoms become fixed in a disorganized pattern characteristic of the atoms of a

liquid. For this reason, scientists often refer to glass as a liquid—a liquid with a very highviscosity (resistance to flowing). The viscosity of glass is so great that it is a rigid material.

The most common substance that can be cooled from the molten state without forming

crystals is silica (silicon dioxide), the chief constituent of sand and sandstone. However, pure

silica is not used for commercial glass products for two reasons: (1) it must be heated to a high

temperature in order to melt, and (2) when molten it has a very high viscosity and is difficult to

form.

Most glass is soda-lime glass. It is made from silica combined with soda ash (sodium carbonate)

and lime. The soda ash lowers the temperature at which the mixture melts and reduces the

mixture's viscosity; the lime makes the glass insoluble. (Silica and soda ash alone yield a type ofglass called water glass, or sodium silicate, which will dissolve in water.)

Small amounts of arsenic oxide, antimony oxide, or other compounds are usually added to glass

as fining agents, substances that help eliminate the gas bubbles formed during the melting

process. Many other ingredients may be added to these basic materials to give the glass specific

colors or other properties. For example, iron oxides can be added to give glass a green color.

HISTORY OF GLASS MAKING

Glassmaking has been practiced for more than 4,000 years. Among the earliest known

examples of glassmaking are ancient Egyptian beads with a glass coating. Around 1500 B.C. amethod of making bottles and jars was developed in which a core made from sand and other

materials was covered with softened glass. After the glass hardened, the core was scraped out.

Blown glass was introduced shortly before the Christian Era, probably in the eastern

Mediterranean region.



Glassmaking reached great excellence in ancient Rome. Some objects were transparent, but

many were opaque. One Roman technique involved dipping a glass object into molten glass of

another color. The coating, when cool, was partially carved away, leaving a cameolike design.

After the fall of Rome, the quality of glassmaking declined, and in many areas glassmaking

ceased. Glassmaking continued in the Near East, where it already had a 2,000-year history.

Islamic glassmakers perfected carving, enameling, and gilding techniques. Knowledge of

glassmaking brought by returning Crusaders led to the revival of glassmaking in Western

Europe during the 11th and 12th centuries.

By the late 15th century, Venice had become the world's glassmaking center. Strong guilds

were established and laws were passed that made spreading information about glassmaking an

offense punishable by death. Nevertheless, the information was spread, and by the early 17th

century, quality glass was being made throughout Europe. Tumblers, goblets, bottles, and other

objects were made in great quantity. The glass used was soda-lime and potash-lime glass with

various impurities that gave it different colors, usually green or brown. Glass of many other

colors, as well as clear glass, was also produced.

About 1675, George Ravenscroft had produced the first vessels of lead glass, which later

became known as crystal. This type of glassware had a much greater clarity and brilliance than

the other types of glass manufactured at that time.

Flat glass was produced up until the 19th century by blowing . In one method, a blob of glass

was gathered on a blowpipe and blown into a large hollow globe. The blowpipe was then

detached from the glass, creating an opening in the globe. An iron rod called a pontil was then

attached to the glass at a point opposite the opening, and the rod was spun to spread the glass

into a disc up to about five feet (1.5 m) in diameter. Small, nearly flat panes could then be cut

from near the outside of the disc.

Another method of flat-glass manufacture consisted of blowing a large cylinder of glass and

then cutting the cylinder open and flattening it out to produce a flat sheet.

A twofold revolution in glassmaking methods took place after 1900. The industry became

almost completely mechanized. Also, scientific knowledge of the physics and chemistry of glass

made it possible to create special glasses for countless new purposes. Many of these

developments were pioneered in the United States. Some of the landmarks were: the first fully

automatic bottle machine (1903); the Colburn continuous method of drawing sheet glass

(1904); quantity production of Pyrex heat-resistant glass (1915); laminated safety glass (1928);

fiberglass (1931); and float glass (1959).

Michael J. Owens (1859-1923) devised the first commercially successful, fully automatic

bottle-making machine in 1903, financed by Edward D. Libbey (1854-1925) and executed with

the aid of engineers William Boch, C. William Schwenzfeier, and Richard LaFrance. As a result of

nine years of refined design work, the "AR" machine was less limited in the design of molds

than the "A" and permitted greater cooling facilities. The general-purpose "AR" had an average

production of 50,400 bottles a day. The last two Owens machines in operation, the AQ, were



operated at Gas City, Indiana, until December 17, 1982. Owens-Illinois is located in Toledo at

the original site of the Libbey Glass Company of 1892.

Floating. Molten glass is allowed to flow onto a bath of molten tin and is then allowed to cool.

The tin has a low melting point and remains liquid at temperatures at which the glass hardens.

The surface of the metal leaves the glass with a very smooth surface. Float glass is used inwindows and other flat glass products. Float process - invented by Sir Alastair Pilkington in

1952 - which manufactures clear, tinted and coated glass for buildings, and clear and tinted

glass for vehicles. The process, originally able to make only 6mm thick glass, now makes it as

thin as 0.4mm and as thick as 25mm.

GLASS MANUFACTURING

Two different types of glass manufacturing are the Float-glass process and Glassblowing

process.

The Float-glass process yields a Sheath of glass material while the glassblowing process

produces glass for containers. In the case of the float-glass process, the molten glass material is

processed on the bed of molten metal. This was majorly used for the windows and other such

needs. The glassblowing process was done by exploiting the inflation nature of the glass

material. The molten glass was blown into the desired shape by introducing air in the molten

glass material. As this blob starts to lose heat, it gets hardened.

THE THREE MAJOR STEPS INVOLVED IN THE GLASS PRODUCTION

1. The Batchhouse involves the handling of the required raw materials. The selection of raw

materials that forms the very initial step in the glass manufacturing is made by considering

various factors that governs the nature of the glass and temperature plays a vital role. The

raw materials are mixed in the required proportion and if needed some of them are also

pre-heated. This is then transferred through the conveyor belt to the furnace. The main raw

material used in the process of glass making is the fused silica. The fused silica requires a

very high glass transition temperature which might not be easy to achieve. And so Soda is

added to this mixture of silica which will help in reducing the glass transition temperature.

This will make the entire mixture water soluble and yield unwanted effects. To avoid this,

lime, Magnesium oxide and aluminum oxide are added. This ultimate mixture produces a

glass material that is of high durability.



Raw Materials

1) Former - This is the main component of glass, which has to be heated to a very

high temperature to become viscous. Silicon dioxide (contained in sand) is the most

common former.

2) Flux - Helps formers melt at lower temperatures. This is usually soda ash orpotash, which was traditionally made from marine plant ashes, or by burning bracken or

trees, respectively.

3) Stabilizer - Keeps the finished glass from dissolving, crumbling, or forming

unwanted crystals. Calcium oxide in the form of limestone, a mineral, is a common

stabilizer.

The mixture of dry materials used to form glass is called the batch. Batch is heated in a

furnace to about 2400˚F. Broken glass, called cullet, is added to the batch to facilitate the

melting process. An imbalance in the batch due to an excess of alkaline flux or too littlestabilizer will cause crizzling, a chemical instability resulting in a fine network of cracks and

deterioration of the glass.

The color of glass may be changed by adding metallic oxides to the batch Examples of

common colorants include:Iron - Colors glass green. Copper - Colors glass light blue.

Manganese dioxide - Can decolorize colored glasses. However, in higher amounts, this

element can create purple and, in even higher amounts, glass that appears black. Cobalt -

Colors glass dark blue. Gold – Colors glass deep red, like rubies

Batch mixing

Glass is made of different ingredients in differing proportions depending on the desired end

product, but most glass (except for some specialist glass) consists of all the "majors" mixed

with small quantities of some of the minors. Thus the minors are weighed first in a special

hopper, and added to the majors with a little water. Water is necessary as in a very dry mix

the fines can blow off the batch as it enters the furnace and clog up the furnace flues. The

two tonne batch is then mixed for between two and three minutes in a rotary mixer, before

being transported to a batch hopper, from which it is slowly fed into a furnace. The mix of

raw materials is dependent on the type of glass desired. Window glass is made from 72%

SiO2, 13% Na2CO3 and 12% CaCO3, while bottle glass has more SiO2 and less CaCO3.

Crystal is made from 45% SiO2 and 44% PbO with 9% K2CO3, and pyrex (used for laboratoryequipment and ovenwear because of its heat resistance) from 80% SiO2 and 12% B2O3. The

remainder in each of these mixtures is made up of the various minors. The actual batching

begins when the raw materials are moved, weighed and mixed, and sent via a conveyor belt

to the charging end of the melting furnace.



2. Hot end handles the manufacture proper- the furnaces, annealing oven and forming

machines, is where the molten glass formed into glass products.

The prepared raw materials are poured into the furnace that is capable of molting the glass at a

very high temperature of 1575°c. It’s the composition and nature of the end glass product

result and the construction of the furnace that decides the transition or the heating

temperature. The furnace is supported by natural gas or the oil. The other process that is a part

of the hot end section is the forming process. In this process, the molten glass material is

shaped into the desired container or sheath form.

Before leaving the annealing lehr, the bottles external surface is coated with polyethylene wax to

protect the surface of the glass and prevent scuffing between bottles.

The air cooling mechanism is used to cool the soft hot glass for taking out the container. This is done

allowed to anneal. Annealing is done with the help of a machine to bring about even hardening of the

glass container. It is done by heating the finished glass container for about 500°.

The process of Internal Treatment is done following the forming process for the containers that are used

for liquids that might chemically react with the glass container. In this process, the sulphur or the

fluorine gas mixture is introduced at very high temperature. This will render a restriction for the glass

container to react with the liquid filled.

3. Cold End- Handles the product inspection and packaging.

The Cold end includes the testing of the glass products that are manufactured. During thisprocess, the completely finished product is tested for any defect and then finally labeled for

shipment. Most common defects that one can find in the glass products are the uneven

surfaces or the small cracks that would have been formed during the production process.

Sometimes, there are chances for the brick lining of the furnace to get mixed with the molten

glass, which might result in the presence of refractory stones in the glass containers. The

bubbles that are formed in the end glass product are known as blisters and it spoils both the

quality and the credibility of the glass material that has been manufactured. Inspecting the

Product before shipping forms the very crucial aspect of glass manufacturing as this process

helps in establishing the quality and standard of the end products. Both manual inspection andmachine based inspection are done by the glass manufacturing companies. Machines are used

in the case of a large scale production. It speeds up the entire process and also increases the

possibility to inspect almost all the glass products that have been manufactured. The inspection

of the products helps to determine the source of defect. And, by detecting the defect’s source,

the future damage for the glass products can be avoided.



STEP-BY-STEP MANUFACTURING OF GLASS CONTAINERS

Raw Materials

Raw materials are selected according to the purity of materials and granulometric size. The

major raw materials used in the glass manufacturing process include Silica Sand, Soda ash, Lime

stone, Feldspar, Sodium Sulphate. Along with the major raw materials colouring materials likeSelenium or Iron Oxide & Chromic Oxide is used.

Batch House

Raw materials are stored in the silos of batch house through a loading hopper interconnected

with vibrators and elevators. Raw materials from the storage silos are proportionately weighed

and dosed on to scales as per the glass formulations. All the weighed raw materials from scale

is discharged to mixer and mixed dry and wet, taken to the furnace storage silo. On route from

mixer to silo recycled glass is added over the batch to complete the batch mixing process.

Furnace

Furnace is a refractory structure for melting the glass raw materials. Batch mixture from silo is

introduced into the furnace by means of batch charger. A burning flame inside the furnace

melts all the raw materials into glass. A temperature of about 1500*C is maintained inside the

furnace for melting. Glass from furnace flows to the IS machines via distributor and fore hearth

for container formation process.

Mould Workshop

Glass bottles have classically been fabricated by employing molds in which the glass bottles are

formed. The metal bottle molds employed in for forming glass bottles are frequently fabricated

from cast iron, having a glass contact surface for defining the shape of the glass.

Forming Machines

The most widely used forming machine arrangement is the individual section machine (or IS

machine). This machine has a bank of 5-20 identical sections, each of which contains one

complete set of mechanisms to make containers. The forming machines hold and move the

parts that form the container. Generally powered by Electric power and compressed air, the

mechanisms are timed to coordinate the movement of all these parts so that containers are

made.There are, two primary methods of making a glass container — the blow and blow

method and the press and blow method are followed. In both cases a stream of molten glass,

at its temperature (1050°C-1200°C), is drawn from the spout bowl through Orifice Ring Punched

through Refractory plungers and cut with a shearing blade to form a weighed Drop of glass,called a gob. Both processes start with the gob falling with gravity to the Scoops and distribute

to the section through Trough and Deflectors, , into the blank moulds to form a pre shape of

the bottle is called Parison and then the Parison passes into the Blow section to Form a

complete shape of the Bottle with Final blow and Finish cooling In the blow and blow process.

In the Press and blow Process drop of glass Pushed from the metallic Plunger and make a pre

shape bottle (parison) and flip into the blow side for the final blow and finish cooling to

complete shape of bottles. The bottle then passes through the main conveyor transfer to the



cross conveyor and transfer unit to the Annealing Lahr for the Annealing Purpose .

Annealing Lehr

Annealing is a process to remove stress and strain from the container glass. As glass cools

immediately it shrinks and solidifies, uneven cooling causes weak glass due to stress to avoid

sudden cooling of containers it is passed through an annealing oven (known in the industry as aLehr) it reduces the container temperature gradually from 650 degree to 100 degree depending

up on the container size or Forming M/C Speed, over a 50 – 180 minute period.

Cold End Coating

At the cold end a layer of typically, polyethylene wax, is applied via a water based emulsion.

This makes the glass slippery, protecting it from scratching and stopping containers from

sticking together when they are moved on a conveyor. The resultant invisible combined coating

gives a virtually unscratchable surface to the glass. Due to reduction of in-service surface

damage the coatings often are described as strengtheners, however a more correct definition

might be strength retaining coatings.

Cold End Inspection Machines

The role of the cold end inspection machine is to inspect the containers for defects , package

the containers for shipment and label the containers. Glass containers are 100% inspected by

automatic machines also by visual inspection, inspect every container for a variety of faults.

Typical faults include checks inspection like finish, neck, shoulder, body, heel area and base, dip

inspection, wall thickness , dimensional inspection, side wall inspection , stress detection,

sealing surface & base inspection, Mould number reader. In addition to rejecting faulty

containers, inspection equipment gathers statistical information and relays it to the forming

machine operators in the hot end. Computer systems collect fault information to the mould

that produced the container. Operators carry out a range of checks manually on samples ofcontainers, usually visual and dimensional checks.

Quality Checking

Sample bottle from each cavity from the running moulds are taken and the following test are

conducted as per quality plan frequency and product specification requirements.

Pressure test Thickness test Line simulation test

Impact test Thermal shock test Weight and capacity test Annealing test Dimensional Test Hotend Coating Test Coldend Coating Test



Finish Coating Test Online Inspection M/C Calibration Sampling for the physical parameter and defects for glass bottles

Palletizing & Shrinking

Glass containers are packed in various ways. Popular are bulk pallets with ranging between1500 and 6000 containers each pallet. This is carried out by automatic machines called

Palletizer, which arrange and stack containers separated by layer pads. Labeled, packed and

shrinked pallets are ready for warehousing and dispatch.

Exporting

Glass container manufacture in the developed world is a mature market business. The

marketing/production challenge is to predict demand in the short 4-12 week term and over the

24-48 month long term. The factory produces around 1-3 million containers a day. Despite its

positioning as a mature market product, glass does enjoy a high level of consumer acceptance

and is perceived as a “premium” quality packaging format.

STEP-BY-STEP MANUFACTURING OF FLAT GLASS

Melting and refining

Fine-grained ingredients, closely controlled for quality, are mixed to make batch, which flows as

a blanket on to molten glass at 1,500oC in the melter.

Float makes glass of near optical quality. Several processes – melting, refining, homogenising –

take place simultaneously in the 2,000 tonnes of molten glass in the furnace. They occur in

separate zones in a complex glass flow driven by high temperatures. It adds up to a continuousmelting process, lasting as long as 50 hours, that delivers glass at 1,100oC, free from inclusions

and bubbles, smoothly and continuously to the float bath. The melting process is key to glass

quality; and compositions can be modified to change the properties of the finished product.

Float bath

Glass from the melter flows gently over a refractory spout on to the mirror-like surface of

molten tin, starting at 1,100oC and leaving the float bath as a solid ribbon at 600

oC.

The principle of float glass is unchanged from the 1950s. But the product has changed

dramatically: from a single equilibrium thickness of 6.8mm to a range from sub-millimetre to

25mm; from a ribbon frequently marred by inclusions, bubbles and striations to almost opticalperfection. Float delivers what is known as fire finish, the lustre of new chinaware.

Coating

Coatings that make profound changes in optical properties can be applied by advanced high

temperature technology to the cooling ribbon of glass.



On-line chemical vapour deposition (CVD) of coatings is the most significant advance in the float

process since it was invented. CVD can be used to lay down a variety of coatings, less than a

micron thick, to reflect visible and infrared wavelengths, for instance. Multiple coatings can be

deposited in the few seconds available as the glass ribbon flows beneath the coaters. Further

development of the CVD process may well replace changes in composition as the principal way

of varying the optical properties of float glass.

Annealing

Despite the tranquillity with which float glass is formed, considerable stresses are developed in

the ribbon as it cools.

Too much stress and the glass will break beneath the cutter. To relieve these stresses, the

ribbon undergoes heat-treatment in a long furnace known as a lehr. Temperatures are closely

controlled both along and across the ribbon. Pilkington has developed technology which

automatically feeds back stress levels in the glass to control the temperatures in the lehr.

Inspection

The float process is renowned for making perfectly flat, flaw-free glass. But to ensure the

highest quality, inspection takes place at every stage.

Occasionally a bubble is not removed during refining, a sand grain refuses to melt, a tremor in

the tin puts ripples into the glass ribbon. Automated on-line inspection does two things. It

reveals process faults upstream that can be corrected. And it enables computers downstream

to steer cutters round flaws. Flaws imply wastage; while customers press constantly for greater

perfection. Inspection technology now allows more than 100 million measurements a second to

be made across the ribbon, locating flaws the unaided eye would be unable to see. The data

drives ‘intelligent’ cutters, further improving product quality to the customer.

Cutting to order

Diamond wheels trim off selvedge - stressed edges - and cut the ribbon to size dictated by

computer.

Float glass is sold by the square metre. Computers translate customers’ requirements into

patterns of cuts designed to minimise wastage. Increasingly, electronic systems integrate the

operation of manufacturing plants with the order book.

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