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M.Tech in Health, Safety & Environment
Engineering
Educational Qualification Improvement
Programme
(EQUIP)
SAINT-GOBAIN
Indian School of Petroleum &
Energy
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in association with
University of Petroleum & Energy Studies
S.NO. CHAPTER NAME PAGE NO.
UNIT-I Mechanical components operations 3
UNIT-IIGlass manufacturing Industry
20
UNIT-III Paint manufacturing industry 38
UNIT-IV Automobile manufacturing industry 43
UNIT -V Metal manufacturing industry
Aluminium
Iron
Stainless steel
Copper
53
56
61
68
UNIT-VI Sugar manufacturing industry 79
UNIT-VII Beer manufacturing industry 86
UNIT-VIII Paper manufacturing industry 91
UNIT-IX Petroleum and its products manufacturing 97
UNIT-X Soap manufacturing industry 104
UNIT-XI Fertilizer manufacturing industry 109
UNIT-XII Tyre manufacturing industry 116
UNIT-XIII Phosphoric acid industry 122
UNIT-XIV Sulfuric acid industry 126
UNIT-XV Pesticides manufacturing industry 130
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Basics of manufacturing
Manufacturing is the use of machines, tools and labor to make things
for use or sale. The term may refer to a range of human activity, from
handicraft to high tech, but is most commonly applied to industrial
production, in which raw materials are transformed into finished goods on a
large scale. Such finished goods may be used for manufacturing other, more
complex products, such as aircraft, household appliances or automobiles, or
sold to wholesalers, who in turn sell them to retailers, who then sell them to
end users the "consumers".
Modern manufacturing includes all intermediate processes required for
the production and integration of a product's components. Some industries,
such as semiconductor and steel manufacturers use the term fabrication
instead.
In this subjects we are dealing with mechanical components
manufacturing, glass, Automobile, paint, metals such Al, iron and stainless
steel and copper manufacturing .
Petroleum, Petrochemical products such as fertilizers, soaps, tyre and
chemical & process industry products like sugar, pesticides, paper, acids and
beer are manufactured huge quantities in our country. This material
discusses the basics of manufacturing of these products.
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1. MECHANICAL COMPONENTS MANUFACTURING
1.1 CASTING
Cupola melting This method uses a furnace in stack form as shown
in Figure. In this method is used to produce iron plates or rods from the steel
scraps. Fuel and metal to be melted are in direct contact. The stack is lined
with refractory material and alternate layers of coke and metal are placed in
it. Some minerals, primarily limestone (CaC03), are included with the metals
to be melted. Air is blown through the stack from the bottom through
openings called tuyeres. The bottom layer of coke is ignited initially. Heat
from the burning coke melts the metal, which flows to the bottom of the
cupola from where it can be removed by opening a tap hole. Slag is also
removed from the bottom, from anexit hole just above the one used to
remove molten metal. As the coke
is consumed and the metal charge
melts, the burning gradually
proceeds upward. The upper layers
are preheated by the flow of hot
gases. Additional metal, coke, and
limestone can be added from a
charging door in the upper part of
the stack as the operation proceeds.
Metal charges may consist of steel
scrap, cast iron scrap or pig iron, or,
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more commonly, a combination of them. The molten metal absorbs carbon
from the coke, so cupola melting is generally restricted to cast, malleable,
and ductile iron. The above picture shows the cross section of cupola for
melting cast iron.
SAND CASTINGS
In sand mold casting the mold is made of packed sand. Molten metal is
poured into a cavity in the sand. When the metal cools and solidifies, it has
the shape of the cavity. The sand is removed, normally by a shaking action
that is vigorous enough to cause the mold to break apart. The casting is then
cleaned of sand; flashing and sprues are cut off and any jagged or sharp
edges are ground smooth. The sand mold includes binders to hold thepacked sand together and other additives. Bentonite clay is one of the most
common binders. Organic materials and a certain amount of water are also
used. The sand is either shoveled into the mold flask, dropped or blown from
an overhead chute, or thrown by a sand slinging machine. The sand mixture
is packed around a pattern which duplicates the shape wanted in the cast
part. Various hand and machine approaches are used to compact the sand.
Ramming, squeezing, slinging, and jolting are done before add molten metal.
After the sand has been compacted, the pattern is removed, leaving a cavity
that retains the inverse of the patterns shape. The sand is held together
strongly enough so that it withstands the pressure and any eroding effects of
the melted metal; is porous enough to allow gases to escape; yet it is weak
enough to yield to shrinkage forces when the metal solidifies, and can be
broken up and removed easily from the finished casting. The pattern can be
of almost any material. In low quantity production situations, it may be made
of wood. For repetitive manufacture, steel is more common. Plastics,
aluminum, and other materials are also used. The pattern has the same
shape as the desired cast part, but is slightly larger to provide a shrinkage
allowance for the metal as it cools.
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A typical sand mold is shown in figure and is normally made in two
halves. The pattern is correspondingly split. The top half of the mold is
called the cope; the
bottom half the drag.
Both are held in a box-like
container called flasks.
An entrance channel for
the molten metal into the
mold is provided by a
basin and sprue formed in
the cope half. Runners
and gate are normally in the drag half. If the casting has some hollow or
undercut elements, one or more additional sand pieces, called cores may
be used. If a core is used, it is inserted in the mold cavity. The cope half of
the mold is made similarly to the drag half and, after the pattern is removed,
is inverted and placed over the drag. Pins in the flask insure alignment of the
mold cavity. The two mold halves are held together with a clamp or weight.
Sand mold casting can be used to make simple and complex parts from a
wide variety of metals, though cast iron is the most common. Shapes with
undercuts, contours, re-entrant angles and other complications of shape can
be cast. Castings weighing only one ounce to those of many tons can be cast
with the process.
Typical applications of sand mold casting are: automotive engine
blocks, cylinder heads, connecting rods, crankshafts and transmission cases,
machine tool bases and other mechanical components.
METAL FORMING PROCESS
Many metal forming operations can be performed with the workpiece
metal either hot or cold. The operations performed on workpiece material
that has been heated to make it more malleable for the operation involved.
Metals that are to be hot formed are heated above their recrystallization
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temperature, one that varies with each material but is normally about 0.6
times the melting temperature on the Kelvin (absolute temperature) scale.
For example, steels require a temperature above about 980C. Warm
forming involves heating to a temperature 30 to 60 percent of the melting
point, while cold forming takes place when the metal temperature is below
30% of the melting temperature.)
1.2 HOT ROLLING
It is commonly applied to convert steel ingots to blooms, billets, or
slabs, and to make these shapes into suitable forms. In the process, heated
metal is passed between two rollers whose spacing is less than the thickness
of the metal. The rotation of the rollers moves the metal forward, squeezing
and elongating it. Figure illustrates the process. The process extends and
refines the grain structure of the rolled material. A number of passes may be
required, depending on the thickness desired and the thickness of the
entering material. Reversing rollers are often used to facilitate multiple
passes. Thin sheet or foil is best rolled with small-diameter rollers that are
backed up with larger rollers to provide the necessary rolling force.
As many as twelve rollers in a cluster may be used. Shaped rollers can
produce material with various
cross sections including those
of structural shapes or special
cross sections. Low-alloy or
plain-carbon steel is heated to
about 1200C before rolling
and after being preheated in a
soaking pit. In addition to
ferrous metals, aluminum,
copper and copper alloys,
magnesium, nickel, titanium, and zinc alloys are hot rolled.
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1.3 PRESS OPERATIONS IN INDUSTRY
Press brakes, as illustrated in Figure, are mechanical or hydraulic
presses with long, narrow, stationary beds. The bed lengths range from 2or
3 ft to 30 ft and press tonnages from 10 to several thousand. The ramstroke
is short but adjustable. Dies are long, narrow, and often simple V-dies. Both
sharp and gentle bends can be made, depending on the shape of the dies.
Piercing, notching, forming, shearing, edge curling, beading,
hemming, corrugating, and tube forming can be performed with
suitable dies. In bending, sheet metal, placed between the bed and the ram
is most commonly bent once with each press stroke. The bend occurs when
a shaped punch, attached to the press brake ram, descends against the
workpiece, forcing it into a suitablyshaped die, fastened to the press brake
bed. Multiple bends are made by repositioning the workpiece sheet between
press strokes. Press brakes are used in the bending of long, narrow
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workpieces and for other workpieces made in small quantities where
standard press brake tooling can be employed.
1.4 WELDING
Welded connections and assemblies represent a very large group of
fabricated steel components. The welding process itself is complex, involving
heat and liquid-metal transfer, chemical reactions, and the gradual formation
of the welded joint through liquid-metal deposition and subsequent cooling
into the solid state, with attendant metallurgical transformations.
The material in this section will provide the student with an overview of
the most important aspects of welded design. In order that the resulting
welded fabrication be of adequate strength, stiffness, and utility, the
designer will often collaborate with engineers who are experts in the broad
area of design and fabrication of elements.
ARC WELDING
Arc welding is one of several fusion processes for joining metal. By
the generation of intense heat, the juncture of two metal pieces is melted
and mixeddirectly or, more often, with an intermediate molten filler metal.
Upon cooling and solidification, the resulting welded joint metallurgically
bonds the former separate pieces into a continuous structural assembly (a
weldment) whose strength properties are basically those of the individual
pieces before welding.
In arc welding, the intense heat needed to melt metal is produced by
an electric arc. The arc forms between the workpieces and an electrode that
is either manually or mechanically moved along the joint; conversely, the
work may be moved under a stationary electrode. The electrode generally is
a specially prepared rod or wire that not only conducts electric current and
sustains the arc, but also melts and supplies filler metal to the joint; this
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constitutes a consumable electrode. Carbon or tungsten electrodes may be
used, in which case the electrode serves only to conduct electric current and
to sustain the arc
between tip and
workpiece, and it is
not consumed; with
these electrodes, any
filler metal required is
supplied by rod or
wire introduced into
the region of the arc
and melted there.
Filler metal applied
separately, rather than via a consumable electrode, does not carry electric
current. Most steel welding operations are performed with consumable
electrodes. The figure shows the typical welding arrangement.
WELDING CIRCUIT ARRANGEMENT
An ac or dc power source fitted with necessary controls is connected
by a work cable to the work piece and by a hot cable to an electrode
holder of some type, which, in turn, is electrically connected to the welding
electrode. When the circuit is energized, the flow of electric current through
the electrode heats the electrode by virtue of its electric resistance. When
the electrode tip is touched to the workpiece and then withdrawn to leave a
gap between the electrode and workpiece, the arc jumping the short gap
presents a further path of high electric resistance, resulting in the generation
of an extremely high temperature in the region of the sustained arc.
The temperature reaches about 6,500F, which is more than adequate
to melt most metals. The heat of the arc melts both base and filler metals,
the latter being supplied via a consumable electrode or separately. The
puddle of molten metal produced is called a weld pool, which solidifies as the
electrode and a rc move along the joint being welded. The resulting
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weldment is metallurgically bonded as the liquid metal cools, fuses,
solidifies, and cools. In addition to serving its main function of supplying
heat, the arc is subject to adjustment and/or control to vary the proper
transfer of molten metal to the weld pool, remove surface films in the weld
region, and foster gas-slag reactions or other beneficial metallurgical
changes Filler metal composition is generally different from that of the weld
metal, which is composed of the solidified mix of both filler and base metals.
Shielding and Fluxing High-temperature molten metal in the weld pool
will react with oxygen and nitrogen in ambient air. These gases will remain
dissolved in the liquid metal, but their solubility significantly decreases as
the metal cools and solidifies. The decreased solubility causes the gases to
come out of solution, and if they are trapped in the metal as it solidifies,
cavities, termed porosities, are left behind. This is always undesirable, but it
can be acceptable to a limited degree depending on the specification
governing the welding. Smaller amounts of these gases, particularly
nitrogen, may remain dissolved in the weld metal, resulting in drastic
reduction in the physical properties of otherwise excellent weld metal.
Notch toughness is seriously degraded by nitrogen inclusions.
Accordingly, the molten metal must be shielded from harmful atmospheric
gas contaminants. This is accomplished by gas shielding or slag shielding or
both.
Gas shielding is provided either by an external supply of gas, such as carbon
dioxide, or by gas generated when the electrode flux heats up. Slag shielding
results when the flux ingredients are melted and leave behind a slag to cover
the weld pool, to act as a barrier to contact between the weld pool and
ambient air. At times, both types of shielding are utilized.
In addition to its primary purpose to protect the molten metal, the
shielding gas will significantly affect arc behavior. The shielding gas may be
mixed with small amounts of other gases (as many as three others) to
improve arc stability, puddle (weld pool) fluidity, and other welding operating
characteristics. In the case of shielded-metal arc welding (SMAW), the
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stick electrode is covered with an extruded coating of flux. The arc heat
melts the flux and generates a gaseous shield to keep air away from the
molten metal, and at the same time the flux ingredients react with
deleterious substances, such as surface oxides on the base metal, and
chemically combine with those contaminants, creating a slag which floats to
the surface of the weld pool. That slag crusts over the newly solidified hot
metal, minimizes contact between air and hot metal while the metal cools,
and thereby inhibits the formation of surface oxides on the newly deposited
weld metal, or weld bead.
When the temperature of the weld bead decreases, the slag, which has
a glassy consistency, is chipped off to reveal the bright surface of the newly
deposited metal. Minimal surface surface oxidation will take place at lower
temperatures, inasmuch as oxidation rates are greatly diminished as
ambient conditions are approached.Fluxing action also aids in wetting the
interface between the base metal and the molten metal in the weld pool
edge, thereby enhancing uniformity and appearance of the weld bead.
1.5 GAS CUTTING
Oxyfuel Cutting (OFC) Oxyfuel cutting is used to cut steels and toprepare bevel and vee grooves. In this process, the metal is heated to its
ignition temperature, or kindling point, by a series of preheat flames. After
this temperature is attained, a high-velocity stream of pure oxygen is
introduced, which causes oxidation or burning to occur. The force of the
oxygen steam blows the oxides out of the joint, resulting in a clean cut. The
oxidation process also generates additional thermal energy, which is radially
conducted into the surrounding steel, increasing the temperature of the steel
ahead of the cut. The next portion of the steel is raised to the kindling
temperature, and the cut proceeds. Carbon and low-alloy steels are easily
cut by the oxyfuel process. Alloy steels can be cut, but with greater difficulty
than mild steel. The level of difficulty is a function of the alloy content. When
the alloy content reaches the levels found in stainless steels, oxyfuel cutting
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cannot be used unless the process is modified by injecting flux or iron-rich
powders into the oxygen stream. Aluminum cannot be cut with the oxyfuel
process. Oxyfuel cutting is commonly regarded as the most economical way
to cut steel plates greater than 1 2 in thick. A variety of fuel gases may be
used for oxyfuel cutting, with the choice largely dependent on local
economics; they include natural gas, propane, acetylene, and a variety of
proprietary gases offering unique advantages. Because of its role in the
primary cutting stream, oxygen is always used as a second gas. In addition,
some oxygen is mixed with the fuel gas in proportions designed to ensure
proper combustion.
Plasma Arc Cutting (PAC)
The plasma arc cutting process was developed initially to cut materials
that do not permit the use of the oxyfuel process: stainless steel and
aluminum. It was found, however, that plasma arc cutting offered economic
advantages when applied to thinner sections of mild steel, especially those
less than 1 in thick. Higher travel speed is possible with plasma arc cutting,
and the volume of heated base material is reduced, minimizing metallurgical
changes as well as reducing distortion.
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PAC is a thermal and mechanical process. To utilize PAC, the material
is heated until molten and expelled from the cut with a high-velocity stream
of compressed gas. Unlike oxyfuel cutting, the process does not rely on
oxidation. Because high amounts of energy are introduced through the arc,
PAC is capable of extremely high-speed cutting. The thermal energy
generated during the oxidation process with oxyfuel cutting is not present in
plasma; hence, for thicker sections, PAC is not economically justified. The
use of PAC to cut thick sections usually is restricted to materials that do not
oxidize readily with oxyfuel.
WELDING SAFETY
Welding is safe when sufficient measures are taken to protect the
welder from potential hazards. When these measures are overlooked or
ignored, welders can be subject to electric shock; overexposure to radiation,
fumes, and gases; and fires and explosion. Any of these can be fatal.
Everyone associated with welding operations should be aware of the
potential hazards and help ensure that safe practices are employed.
Infractions must be reported to the appropriate responsible authority.
Oxygen is incorrectly called air in some fabricating shops. Air from the
atmosphere contains only 21 percent oxygen and obviously is different from
the 100 percent pure oxygen used for cutting. The unintentional confusion of
oxygen with air has resulted in fatal accidents. When compressed oxygen is
inadvertently used to power air tools, e.g., an explosion can result. While
most people recognize that fuel gases are dangerous, the case can be made
that oxygen requires even more careful handling
1.6 LATHE AND OTHER OPERATIONS
Lathe operations
It produce, with a cutting action, surfaces of rotation (surfaces having a
round or partly-round cross section), both external and internal, in a work
piece. The work piece is rotated in a lathe, screw machine, or chucking
machine. It is held between centers or in a chuck or collet, or fastened to a
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face place. The cutting tool is fed into the work or along the work, or both, to
produce a part of the desired shape. There are several basic types of lathes
and related machines as described below and many varieties of tools that
can be fed against the workpiece. These machines are used extensively in
the production of parts that contain surfaces of rotation. The basic
operations performed on lathes are the following:
Turning - is the most prevalent lathe operation. In its most common form, a
single-point cutting tool is moved on a precise path with respect to a rotating
workpiece. When the tool moves parallel to the axis of rotation, straight
turning takes place and the surface machined is cylindrical or part of a
cylinder. When the cutting tool moves uniformly closer or farther from the
axis of rotation as it moves longitudinally, a tapered surface is generated
Grooving - The cutting tool, usually ground to the width and bottom shape
required, is fed into the work, cutting a groove of the desired dimensions.
Groves can be cut into any external or internal surface that such a cutting
tool can reach. (Internal grooves are usually called recesses.)
Knurling - is not really a machining (cutting) operation because the knurl is
formed, not cut, in the workpiece. Knurling is a common lathe or screw
machine operation. The hardened hurling tool rolls against the cylindrical
surface of the rotating workpiece with high pressure, causing the surface
material of the workpiece to flow into peaks and valleys according to the
pattern of the hurling tool.
Facing - produces flat surfaces whose plane is at right angles to the axis of
rotation of the part As the part rotates in the lathe, the cutting tool moves
radially toward the axis of rotation, removing material as it advances. It can
also move outward from the center, but the other direction is much more
common. The operation is used to produce flat surfaces on castings and
other parts that usually also require turning or some other lathe operation
Cutting off (parting) - When parts are made in lathes and screw machines
from bar stock, the final operation is to sever the part from the remaining
bar material. This is accomplished by advancing the cutoff tool, a narrow
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grooving tool, radially into the work. When the cutting edge advances to the
axis of rotation of the part, the part is severed and falls to the bed of the
machine. Some machines, which make blanks for further machining or other
operations, are designed to perform only cut off operations and other simple
ones on bar and tubular stock.
Common Lathe operations are shown in figure.
1.7 DRILLING OPERATION
Drilling - The most common tool for drilling, a twist drill, is a rod with helical
flutes and two or more cutting edges at the end. It is rotated about its axis
and fed axially into the work. As it advances, it produces or enlarges a round
hole in the workpiece. The chips are carried away from the hole by the flutesin the drill. When drilling an axial hole with a lathe, the workpiece rotates
rather than the drill.
There are other types of drills that may not have helical flutes. Others may
have only one cutting edge. The drilling process is very common and is used
with a wide variety of machines ranging from the most sophisticated
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computer controlled or multiple spindle machines to hand-held electric or
crank-driven drills.
1.8 GRINDING AND ABRASIVE MACHINING
At the point where the cutting takes place, grinding is very similar to other
machining operations, the difference being that the workpiece is cut by the
sharp edges of small pieces of abrasive material, rather than the edge of a
hardened steel or carbide cutting tool. The irregularly-shaped abrasive
particles may be bonded to a wheel or coated belt, or may be used loose.
The particles commonly consist of aluminum oxide, silicon carbide, cubic
boron nitride, diamond, or other hard materials. The individual abrasive
grains are each smaller than a conventional metalworking cutting tool, andthe grains on a typical wheel make a multitude of minute cuts (Some grains,
depending on their shape, do not cut but instead rub or slightly deform the
surface of the workpiece.) Cutting speeds are high but the depth of cut from
each grain is shallow. A water or water-oil emulsion is often sprayed on the
wheel and workpiece to control the dust that otherwise arises and to
overcome the heating effect of the operation.
Grinding wheels are often porous, especially those designed for use with
softer materials. Asthe wheel cuts, it wears, causing some abrasive particles
to become smooth but causing others to fracture, exposing new sharp
edges. New wheels, and those that have become worn, are dressed with a
diamond tool that removes some of the abrasive material and bonding
agent, exposing sharp edges of new abrasive grains and providing a
straighter, more uniform, cutting surface. Grinding is most commonly a
finish-machining operation to provide a smoother surface or greater
dimensional accuracy, particularly with hardened materials. When used as
the primary metal removal method, the term, abrasive machining is often
used.
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1.9 MILLING
Milling is a means of creating a desired surface with a rotating multi-toothed
cutter. Each tooth of the cutter removes material as the workpiece advances
against it. The axis of rotation of the cutter may be either horizontal or
vertical. The cutter can provide cutting action on its side or at its end (face),
or both. The cutter rotates rather rapidly and its position is normally
stationary; the work moves past the cutter with a suitable depth of cut at a
relatively slow feed rate. Milling is the most common machining operation for
producing flat surfaces, but slots, and contoured or stepped surfaces and
screw threads can also be produced.
The different types of millings are face milling, peripheral milling, slabmilling, form milling, gand milling, straddle milling, fly cutter milling etc.
1.10 SAWING
Sawing is the parting of material through the use of a narrow cutter, a saw,
which contains a series of cutting edges that pass against the work in a
continuous or reciprocating motion. As the cutter is advanced into the work,
material is removed by each tooth, and a slot is formed, eventually
extending through the entire thickness of the workpiece, and severing it into
two pieces.
The chip produced by each tooth is carried in the space between the teeth
until the teeth exit the workpiece. The cutter can be in disk, band, or
reciprocating blade form. Cutting teeth are typically set, i.e., offset slightly
and alternately from both sides of the saw blade to provide a slightly wider
cut (kerf) than the thickness of the blade so that there is room for its
passage. The operation is used to cut billets, extrusions, castings, forgings,
and various other shapes into blanks for further operations. Bars of various
cross sections, rods, angles, and various other structural sections are cut to
length by sawing.
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Circular sawing - uses a saw in the form of a circular disk, with cutting
teeth on the periphery. As the circular saw rotates, it is fed against the
workpiece, machining a narrow slot in the workpiece and eventually severing
it. Circular saws for metal cutting are sometimes called cold sawsbecause
they dont significantly heat the workpiece as friction saws do. They often
have inserted cutter teeth of carbide rather than teeth formed of the blade
material, or have cutter segments fastened to a center disc. Blades are
sometimes large in diameter to permit the sawing of bulky workpieces. Kerfs
are considerably wider than
those on band or hack-saws
because the circular blade must
be thick enough to provide
rigidity. Accurate and smooth
cut surfaces are feasible with
this method. The circular saw
process is used to make blanks
for subsequent operations or to
cut structural members to the
desired length. Figure illustrates
a circular cutoff saw (coldsaw).
Band sawing - is most commonly a cut-off operation. Instead of a circular
disk, the saw is an endless steel band with cutting teeth on one edge. The
blade moves as it cuts in one direction. Cutting is continuous and blade
wear is uniform over the whole length of the blade. Since the blade is
normally thin, little material is lost to chip waste and power requirements are
modest. The work piece or the blade can be fed manually or mechanically.
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2.0 GLASS MANUFACTURING
2.1 INTRODUCTION
Glassmaking involves three basic steps: batching, melting, and
forming. Batching is the preparation of a mixture of sand and stabilizing
oxides, all in fine granular form. Melting involves the heating of the mixture
to change it into a liquid and to further homogenize the various ingredients.
Forming is the creation of useful objects or products from the molten mixture
before it has completely solidified. The process can be carried out on either a
batch or continuous-flow basis, the latter being used in mass production
situations. Normally, forming operations take place immediately after thebasic glassmaking, with the molten glass being cooled to increase its
viscosity for forming.
There are many different kinds of glass. Soda lime glass is used for bottles,
window panes and drinking glasses. Lead-alkali silicate glass has lead oxide
in place of much of the calcined lime and is used for highly worked shapes
including decorative glassware (lead crystal) that is engraved. Borosilicate
glasses, which contain boric oxide, are used when chemical and temperature
change resistance is important, for example, in pharmaceutical containers,
chemical process components and lamp envelopes. Aluminosilicate glasses
are used where high temperature conditions exist. Several other mixtures
may be used when optical properties are important.
2.2 RAW MATERIALS
Silica sand (SiO2) is the most common glass ingredient and has
excellent resistance to attack, low thermal expansion, and resistance to
devitrification (crystallization which impairs the optical and mechanical
properties). However, in its unalloyed state, silica sand is difficult to process
because of its high melting temperature and high viscosity when melted.
Various other oxides are added to silica to improve its processibility and
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modify the properties of the finished glass. When soda-lime glass, the most
common variety, is made, the ingredients consist of about 73 percent sand
(SiO2), about 14 percent soda ash or sodium carbonate (Na2C02) and about
13 percent limestone (CaC03). Sodium oxide, (Na20) is an effective fluxing
agent, i.e., a means for reducing the melting temperature, but too much can
produce glass that is water soluble. Calcium oxide, calcined lime (CaO),
increases the hardness and resistance of the glass to moisture. Alumina
(A1203) improves durability and reduces thermal expansion. Potassium oxide
(K20) from potash, increases durability and helps prevent devitrification,
which has adverse effects. Other glass ingredients include borax or boric
acid for boric oxide (B203), fluorspar (CaF), litharge or lead oxide (PbO),
barium carbonate (BaC03), magnesium oxide (MgO), zinc oxide (ZnO), and
other inorganic materials, some of which are colorants. Glass cullet (factory
scrap or recycled glass), may be added to the mixture. It provides fluxing
action and reduces the energy required for melting. About 30 to 40% cullet
provides the maximum furnace efficiency. In some mixtures, cullet content
can reach 66 percent. A typical commercial mixture has from 7 to about 12
different minerals, 4 to 6 of which are major ingredients.
2.3 COLORING MATERIALS - Glass is colored by adding small quantities
(usually less than 0.5 percent) of certain metal oxides or other metallic
compounds to the glass batch. Copper produces light blue; chromium - green
and yellow; iron - bluish green or yellowish brown; cobalt - intense blue;
nickel grayish brown, yellow, green, blue or violet depending on the glass
matrix; neodymium - reddish violet; manganese - violet; vanadium - green or
brown.
2.4 BATCHING - involves weighing, milling as necessary, and mixing to
produce the glass furnace charge, a blend that can be melted to provide the
composition desired. Quality control, including chemical analyses, must
precede these steps to insure that each raw material is of the proper
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composition with impurities within limits. and of the proper grain size. Grain
or particle size is important and must be controlled so that materials do not
segregate during mixing, storage, and handling and so that they melt
properly. Overly-fine particles of some materials may retard the elimination
of gas bubbles from the melted charge. Milling and screening of raw
materials may be required for some mixtures, though the common practice
is to have suppliers of raw materials provide them with the desired grain size
and size distribution. Water may be added to the batch to the extent of 2 to
4percent to prevent segregation prior to melting. More recently, methods
have been developed to consolidate the batch material in a form that more
easily preserves the uniformity of the batch mixture, provides easier
handling, improved melting, and better uniformity of the glass mixture
during melting.
These consolidation methods usually involve the following steps:
1. reducing and controlling the grain size of the batch materials by various
milling operations and screening, mixture,
2. adding wetting and binding agents to the
3. thoroughly mixing the mixture and additives,
4. consolidation - briquetting, pelletizing or other means of holding the
mixture into a stable but easily handled form, and
5. preheating the consolidation before melting.
Alc. melting - Melting the glass materials, known as the batch, enables the
ingredients to be completely blended to produce glass of the desired
properties and puts the glass in condition for forming. Typical melting
temperatures are approximately 1450 to 1600. Heat is provided by gas, oil
or electricity. Natural gas is the major fuel; propane is used as a standby.
When quantities are small, melting is performed on a batch basis in pot
furnaces or day tanks. High production melting is done in continuous
furnaces that have output levels ranging to several hundred tons per day.
Pots are made of refractory clay and are heated in brick furnaces. Day tanks
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are larger pots for batch production and are typically run on a one-day cycle,
with melting at night and production and refilling the next day. Ten tons is a
typical daily production quantity. Pots are typically round crucibles made of
one piece of refractory material with individual capacities of one to two tons
of glass. Several pots may occupy one furnace. Day tanks are made from
refractory blocks. Continuous furnaces are used for flat glass and for mass-
produced containers and other highproduction items. They are lined with
refractory ceramics and are divided into a large melting section and a small
refining section called a forehearth. The forehearth is used to cool glass from
the melt temperature to a suitable temperature for whatever forming
operation follows. Daily production levels are on the order of 100 to 400 tons
of glass.
The glass charge is fed from one end of the melting area. Temperatures in
the melting area are as high as the glass mixture can tolerate in order to
drive off carbon dioxide, steam, trapped air, and other gases, which could
cause bubbles in the glass. Convection currents in the molten glass, which
result from natural unevenness of heating and cooling from side walls,
provide stirring that helps the glass mixture to become homogeneous. The
molten glass that passes to the refining section does so through an opening
below the surface of the melt, thus preventing any surface foam or scum
from entering the forehearth. The temperature in the forehearth is typically
cooler than that in the melting section by 100 to 200C.
Furnaces may operate continuously for approximately a year before
rebuilding is necessary. With gas and oil furnaces the glass is heated by
exhaust gases that travel above the molten glass. Air for combustion is
preheated by either a preheating chamber in the furnace or by regeneration
where the cold air and cold gas are made to flow through brickwork that
shortly before carried hot exhaust gases from the furnace. The flow is
typically reversed at half-hour intervals. Immersed electrodes are used when
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heat is provided by electrical resistance. This resistance is that of the glass
when current is passed through the molten glass from electrode to electrode.
Electric heating is sometimes used as a booster in gas- or oilfired furnaces.
Electrical heating has quality and environmental advantages and is more
common for batch production of specialty glasses, particularly those with a
volatile component. Electrical induction heating is used for small quantity
work.
2.5 PRIMARY FORMING PROCESSES
Pressing - A gob of molten glass is placed in a mold by an automatic gob-
feeding machine. A plunger descends and presses against the gob of glass
which flows upward around the plunger and outward to fill the mold cavity.
When the glass cools and solidifies, the plunger is withdrawn, the mold is
opened, if necessary (because of undercuts in the part), and the part is
removed. In some cases, excess glass may have to be trimmed from the
part. The process is illustrated by Figure. In production situations, a turntable
is used to carry the molds and may have as many as twenty. As the
turntable indexes to new positions, each mold proceeds step by step through
the full cycle of loading, pressing, cooling, trimming, and ejection or removal.
Pressing is used to make drinking glasses and other household glassware,
lenses, lamp globes, and TV tube parts.
Blowing - is similar to blow molding of plastics. As in blow molding of
plastics, there are two operations, one to make the parison and the other to
make the hollow glass object from the parison. The operation can be manual,
with or without a mold to control the shape of the finished part, or automatic
with a number of process variations.
Hand blowing into the open air, without a mold, but with shaping of the
bubble with the aid of hand tools, has been practiced for centuries. The basic
process with molds is illustrated in Figure. Blowing is used extensively in the
production of glass bottles, containers, and vases and jars.
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Electrically heated
Typical glass pot furnace for melting glass.
Manual blowing - The skilled artisan uses a glassworkers blowpipe
consisting of a metal tube with a wooden handle and mouthpiece at one end
and a nose or gathering head at the other end. Making a container, vase,
drinking glass, etc. with purely manual methods, involves the following
steps:
1. Gathering - The nose end of the blowpipe is immersed in melted glass and
is rotated slowly. The viscous glass sticks to the end of the blowpipe. For
large objects, several repeats of gathering may be required.
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2. The blowpipe is continually rotated to keep the gob of glass centered and
the artisan blows a small amount of air from the mouth through the pipe,
making a bubble in the center of the glass gob and thereby creating a
parison.
3. Marvering - The parison (hollow gob) is rolled against a surface of metal or
stone or wet wood, cooling the surface and imparting a straight or curved
side to the object.
4.The parison is enlarged by further blowing. Further contact of the parison
with the work surface and with hand-held shaping tools in a series of steps,
gradually produces the desired shape.
Some reheating may be required and continual rotation of the blowpipe is
carried out to keep the workpiece circular and centered. Selective cooling or
heating, cutting with shears, and attachment of glass handles or other
elements may be carried out before the object is completed. Figure
illustrates a typical sequence in making a glass pitcher. Figure shows a
collection of glassblowers hand tools. For repetitive blowing of some
particular object, the glassworker may blow the parison into a mold made
from water-soaked wood (beechwood has been traditionally used), graphite,
or cast iron. This reduces or eliminates much of the tool and workpiece
manipulation required, speeds the operation, and reduces the skill required
by the glassworker. Because of the high level of skill required, the use of
manual methods of blowing has declined in favor of machine blowing except
for artistic work. The method is still used for art work, prototypes, and mall
quantity production of bottles, containers, laboratory vessels, and other
specialty glassware.
Lampworking (lamp blowing, and scientific glass blowing) - is the
forming of glass articles from tubing and rods by heating in a gas flame
(lamp). The operation i s essentially manual, but differs from the manual
glass blowing described above in that it starts with a tube or rod rather than
a gob of molten glass. Its primary application is the fabrication of laboratory
apparatus and instruments. Medical, veterinary, food processing, and
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chemical industries require apparatus that use glassware made with this
approach. The tubing or rod is heated by a gas flame and then formed by
any of a variety of manual operations including blowing, bending, flaring,
cutting, sealing, joining, and working with a large number of hand tools. In
higher production situations, the end of a glass rod is heated and placed in a
die that presses the softened material into a small part and severs it from
the rod. Tubing can be similarly heated at the end, which can then be formed
by blowing in a suitable mold. Scientific glass blowing has broadened in
recent years to include working with flat and powdered glass as well as
tubing and rods, and working with a variety of glass types and surface
treatments.
Machine blowing Automatic machine blowing is used in the production of
glass bottles, jars, drinking glasses, and other glass containers that are
manufactured in mass-production quantities. Machine blowing methods have
the following elements:
1. equipment for feeding a gob of melted glass to the machine,
2.a means for converting the gob into a parison, i.e., introducing a hollow in
the gob for later blowing,
3. inflation of the hollow gob (parison) against the inner surfaces of a mold,
4.a means for forming the elements at the open end of the object molded,
5. a means for trimming any excess material from the finished object, and,
6. annealing the finished product.
Material in process may be reheated during the operation sequence. Notable
machine methods are the press-blow, blow-blow, suck-blow and
rotary-mold (paste mold) processes.
SUCKFLOW PROCESS
The original machine developed by M. J. Owens was put into production
around 1904 but has been much further developed since then. The glass is
brought into the parison mold by suction, hence the name, suck-blow
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process. The work is performed on a large rotary table. Motion of molds and
other elements is controlled by cams.
The operating sequence is as follows: The parison mold, with an open
bottom, is lowered into the surface of molten glass. Suction applied to the
top of the mold draws glass into the mold cavity. A pin with a rounded end
puts The neck portion of the bottle is also formed in this mold.
The parison mold is lifted and a knife passes across the bottom of the mold,
severing any excess glass from the parison. At the same time, the rounded
pin at the top is withdrawn, and air pressure in the resulting opening
enlarges the
top of the parison, forming a bubble. The mold opens, freeing the parison
which is held by neck rings at its upper end. The parison is out in the open as
the machine table rotates. The parison elongates from the effects of gravity
and from several puffs of air into the bubble.
The parison enters the blow mold, which closes around it. Air is blown into
the bubble, expanding the parison against the mold walls The neck rings
open and the mold with the bottle inside drops below the pot as the table
continues to rotate. The mold and bottle cool. mold opens and the bottle is
discharged. Figure illustrates the molding action schematically. The machine
is used for largescale production. With smaller bottles, double and triple
molds are used so that each cycle of the machine produces two or three
bottles.
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Suck flow
process
FLAT CLASS PROCESS:
Drawing sheet glass (the
Fourcault process) - The
Fourcault process was the first
successful mechanized production
method for drawing sheet glass
directly from a tank. It was first
carried out on a production basis in
1914. Prior to that, the production
of flat glass was at least partly a
manual operation. The method is
keyed to the debiteuse, a long
clay block with a lengthwise slot.
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The block floats on the molten glass but, when it is pressed slightly down,
into the molten glass, some glass rises out of the slot. This glass is grasped
by an iron bait and is pulled upward past a cooling station and into an
annealing tower. The tower contains rollers that draw the glass upward and
the operation is thereafter continuous. The rate of drawing, among other
factors, determines the thickness of the glass. (Slower drawing yields greater
thickness.) The length of the slot in the debiteuse determines the width of
the ribbon. Width is maintained by pairs of knurled rollers at the edges that
maintain a constant side pull on the ribbon. The drawback of the process is a
tendency toward a small amount of waviness in the sheet, which cannot be
avoided. There may also be fine marks on the glass surface left by the rollers
and some tendency to devitrification caused by the refractory material from
which the debiteuse is made. Figure illustrates the process
Drawing sheet glass (the Colburn or Libby-Owens process) - This
process, seen in Figure, is similar to the Fourcault process but does not use
the debiteuse. Instead, the initial ribbon of glass is picked up from the tank
with a metal bait and immediately controlled by chilled rollers at the
edges. It also is
diverted into a
horizontal
direction by a
polished roller
after traveling
upward only
about 27 in (70
cm). It is
stretched,
flattened, and
supported by
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transporting rollers as it moves into a 200 ft (60 m) annealing l hr. The
drawing speed with the Colburn process is twice that used with Fourcault.
Manufacturing Sequence for Plate glass
1) Raw materials are received and stored2) Materials are weighed and mixed
3) Batch is fed to furnace and melted
4) Molten glass flows from the furnace through forming rolls to form a rough,
continuous ribbon
5) Ribbon is stretched slightly to improve flatness
6) Ribbon travels through annealing l hr
7) Both top and bottom surfaces are ground flat by a series of vertical
spindle, large-disc grinding machines as the ribbon travels past them
8) Both surfaces are polished with similar machines using finer abrasive
9) An acid wash removes grinding residue
10) Sheets are cut from the ribbon
11) Sheets are inspected and sent to storage for later final cutting and
shipment
STEAM BLOWING
Steam blowing - Streams of molten glass flowing from a melting tank
through sievelike platinum bushings are impinged upon by jets of steam. The
jets approach the glass streams at a small included angle, and push them at
a faster rate, causing them to draw into finer fibers. If the steam jets are
strong enough, the fibers will break into shorter lengths. The strength of the
steam jets determines how discontinuous and fine the final fibers will be. The
fibers can be processed in several ways. When used to make thick pads or
wool, they are sprayed with a binder and fall on to a conveyor where they
pile up into wool. The binder is dried and the wool is cut into discrete batts of
fibrous glass. Figure illustrates this process. When made into glass mat, the
fibers are allowed to fall into a thin, web-like mat that is then immersed into
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a bath of binder and then passed through a drying oven. A major use for
such mat is the reinforcement of fiber glass-reinforced plastic products.
PORCELAN
The term porcelain refers to a wide range of ceramic products that
have been baked at high temperatures to achieve vitreous, or glassy,
qualities such as translucence and low porosity. Among the most familiar
porcelain goods are table and decorative china, chemical ware, dental
crowns, and electrical insulators. Usually white or off-white, porcelain comes
in both glazed and unglazed varieties, with bisque, fired at a high
temperature, representing the most popular unglazed variety.
Raw Materials
The primary components of porcelain are clays, feldspar or flint, and
silica, all characterized by small particle size. To create different types of
porcelain, craftspeople combine these raw materials in varying proportions
until they obtain the desired green (unfired) and fired properties. Although
the composition of clay varies depending upon where it is extracted and how
it
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To make porcelain, the raw materials such as clay, felspar, and silica are first
crushed using jaw crushers, hammer mills, and ball mills. After cleaning to
remove improperly sized materials, the mixture is subjected to one of four
forming processes soft plastic forming, stiff plastic forming, pressing, or
casting depending on the type of ware being produced. The ware then
undergoes a preliminary firing step, bisque-firing.It is treated, all clays vitrify (develop glassy qualities), only at extremely high
temperatures unless they are mixed with materials whose vitrification
threshold is lower. Unlike glass, however, clay is refractory, meaning that it
holds its shape when it is heated. In effect, porcelain combines glass's low
porosity with clay's ability to retain its shape when heated, making it both
easy to form and ideal for domestic use. The principal clays used to make
porcelain are china clay and ball clay, which consist mostly of kaolinate, a
hydrous aluminum silicate.
Feldspar, a mineral comprising mostly aluminum silicate, and flint, a type of
hard quartz, function as fluxes in the porcelain body or mixture. Fluxes
reduce the temperature at which liquid glass forms during firing to between
1,000 and 1,300 degrees Celsius. This liquid phase binds the grains of the
body together.
Silica is a compound of oxygen and silicon, the two most abundant elements
in the earth's crust. Its resemblance to glass is visible in quartz (its
crystalline form), opal (its amorphous form), and sand (its impure form).
Silica is the most common filler used to facilitate forming and firing of the
body, as well as to improve the properties of the finished product. Porcelain
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may also contain alumina, a compound of aluminum and oxygen, or low-
alkali containing bodies, such as steatite, better known as soapstone.
The Manufacturing Process
After the raw materials are selected and the desired amounts weighed, they
go through a series of preparation steps. First, they are crushed and purified.
Next, they are mixed together before being subjected to one of four forming
processessoft plastic forming, stiff plastic forming, pressing, or casting; the
choice depends upon the type of ware being produced. After the porcelain
has been formed, it is subjected to a final purification process, bisque-firing,
before being glazed. Glaze is a layer of decorative glass applied to and fired
onto a ceramic body. The final manufacturing phase is firing, a heating step
that takes place in a type of oven called a kiln.
Crushing the raw materials
First, the raw material particles are reduced to the desired size, which
involves using a variety of equipment during several crushing and grinding
steps. Primary crushing is done in jaw crushers which use swinging metal
jaws. Secondary crushing reduces particles to 0.1 inch (.25 centimeter) or
less in diameter by using mullers (steel-tired wheels) or hammer mills,
rapidly moving steel hammers. For fine grinding, craftspeople use ball mills
that consist of large rotating cylinders partially filled with steel or ceramic
grinding media of spherical shape.
Cleaning and mixing
The ingredients are passed through a series of screens to remove any under-
or over-sized materials. Screens, usually operated in a sloped position, are
vibrated mechanically or electromechanically to improve flow. If the body is
to be formed wet, the ingredients are then combined with water to produce
the desired consistency. Magnetic filtration is then used to remove iron from
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the slurries, as these watery mixtures of insoluble material are called.
Because iron occurs so pervasively in most clays and will impart
After bisque firing, the porcelain wares are put through a glazing operation,
which applies the proper coating. The glaze can be applied by painting,
dipping, pouring, or spraying. Finally, the ware undergoes a firing step in an
oven or kiln. After cooling, the porcelain ware is complete.
Forming the body
Next, the body of the porcelain is formed. This can be done using one of four
methods, depending on the type of ware being produced:
Soft plastic forming, where the clay is shaped by manual molding, wheel
throwing, jiggering, or ram pressing. In wheel throwing, a potter places the
desired amount of body on a wheel and shapes it while the wheel turns. In
jiggering, the clay is put on a horizontal plaster mold of the desired shape;
that mold shapes one side of the clay, while a heated die is brought down
from above to shape the other side. In ram pressing, the clay is put between
two plaster molds, which shape it while forcing the water out. The mold is
then separated by applying vacuum to the upper half of the mold and
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pressure to the lower half of the mold. Pressure is then applied to the upper
half to free the formed body.
Stiff plastic forming, which is used to shape less plastic bodies. The body
is forced through a steel die to produce a column of uniform girth. This is
either cut into the desired length or used as a blank for other forming
operations.
Pressing, which is used to compact and shape dry bodies in a rigid die or
flexible mold. There are several types of pressing, based on the direction of
pressure. Uniaxial pressing describes the process of applying pressure from
only one direction, whereas isostatic pressing entails applying pressure
equally from all sides.
slip casting, in which a slurry is poured into a porous mold. The liquid is
filtered out through the mold, leaving a layer of solid porcelain body. Water
continues to drain out of the cast layer, until the layer becomes rigid and can
be removed from the mold. If the excess fluid is not drained from the mold
and the entire material is allowed to solidify, the process is known as solid
casting.
Bisque-firing
After being formed, the porcelain parts are generally bisque-fired, which
entails heating them at a relatively low temperature to vaporize volatile
contaminants and minimize shrinkage during firing.
Glazing
After the raw materials for the glaze have been ground they are mixed with
water. Like the body slurry, the glaze slurry is screened and passed through
magnetic filters to remove contaminants. It is then applied to the ware by
means of painting, pouring, dipping, or spraying. Different types of glazes
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can be produced by varying the proportions of the constituent ingredients,
such as alumina, silica, and calcia. For example, increasing the alumina and
decreasing the silica produces a matte glaze.
Firing
Firing is a further heating step that can be done in one of two types of oven,
or kiln. A periodic kiln consists of a single, refractory-lined, sealed chamber
with burner ports and flues (or electric heating elements). It can fire only one
batch of ware at a time, but it is more flexible since the firing cycle can be
adjusted for each product. A tunnel kiln is a refractory chamber several
hundred feet or more in length. It maintains certain temperature zones
continuously, with the ware being pushed from one zone to another.
Typically, the ware will enter a preheating zone and move through a central
firing zone before leaving the kiln via a cooling zone. This type of kiln is
usually more economical and energy efficient than a periodic kiln.
During the firing process, a variety of reactions take place. First, carbon-
based impurities burn out, chemical water evolves 100 to 200 degrees
Celsius, and carbonates and sulfates begin to decompose 400 to 700
degrees Celsius. Gases are produced that must escape from the ware. On
further heating, some of the minerals break down into other phases, and the
fluxes present (feldspar and flint) react with the decomposing minerals to
form liquid glasses 700 to 1,100 degrees Celsius. These glass phases are
necessary for shrinking and bonding the grains. After the desired density is
achieved 1,200 degrees Celsius, the ware is cooled, which causes the liquid
glass to solidify, thereby forming a strong bond between the remaining
crystalline grains. After cooling, the porcelain is complete.
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3. PAINT MANUFACTURING
Paint is a term used to describe a number of substances that consist of
a pigment suspended in a liquid or paste vehicle such as oil or water. With a
brush, a roller, or a spray gun, paint is applied in a thin coat to various
surfaces such as wood, metal, or stone. Although its primary purpose is toprotect the surface to which it is applied, paint also provides decoration.
Perhaps the greatest paint-related advancement has been its proliferation.
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The first step in making paint involves mixing the pigment with resin,
solvents, and additives to form a paste. If the paint is to be for industrial use,
it usually is then routed into a sand mill, a large cylinder that agitates tiny
particles of sand or silica to grind the pigment particles, making them
smaller and dispersing them throughout the mixture. In contrast, most
commercial-use point is processed in a high-speed dispersion tank, in which
a circular, toothed blade attached to a rotating shaft agitates the mixture
and blends the pigment into the solvent. Today, paints are used for interior
and exterior housepainting, boats, automobiles, planes, appliances,
furniture, and many other places where protection and appeal are desired.
Raw Materials
A paint is composed of pigments, solvents, resins, and various additives. The
pigments give the paint color; solvents make it easier to apply; resins help it
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dry; and additives serve as everything from fillers to anti fungicidal agents.
Hundreds of different pigments, both natural and synthetic, exist. The basic
white pigment is titanium dioxide, selected for its excellent concealing
properties, and black pigment is commonly made from carbon black. Other
pigments used to make paint include iron oxide and cadmium sulfide for
reds, metallic salts for yellows and oranges, and iron blue and chrome
yellows for blues and greens.
Solvents are various low viscosity, volatile liquids. They include petroleum
mineral spirits and aromatic
solvents such as benzol, alcohols,
esters, ketones, and acetone. Thenatural resins most commonly
used are lin-seed, coconut, and
soybean oil, while alkyds, acrylics,
epoxies, and polyurethanes
number among the most popular
synthetic resins. Additives serve
many purposes. Some, like calcium
carbonate and aluminum silicate,
are simply fillers that give the
paint body and substance without
changing its properties. Other additives produce certain desired
characteristics.
Paint canning is a completely automated process. For the standard 8 pint
paint can available to consumers, empty cans are first rolled horizontally
onto labels, then set upright so that the point can be pumped into them. One
machine places lids onto the filled cans while a second machine presses on
the lids to seal the cons. From wire that is fed into it from coils, a bailometer
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cuts and shapes the handles before hooking them into holes precut in the
cans. In paint, such as the thixotropic agents that give paint its smooth
texture, driers, anti-settling agents, anti-skinning agents, defoamers, and a
host of others that enable paint to cover well and last long.
Design
Paint is generally custom-made to fit the needs of industrial customers. For
example, one might be especially interested in a fast-drying paint, while
another might desire a paint that supplies good coverage over a long
lifetime. Paint intended for the consumer can also be custom-made. Paint
manufacturers provide such a wide range of colors that it is impossible tokeep large quantities of each on hand. To meet a request for "aquamarine,"
"canary yellow," or "maroon," the manufacturer will select a base that is
appropriate for the deepness of color required. (Pastel paint bases will have
high amounts of titanium dioxide, the white pigment, while darker tones will
have less.) Then, according to a predetermined formula, the manufacturer
can introduce various pigments from calibrated cylinders to obtain the
proper color.
The Manufacturing Process
Making the paste
Pigment manufacturers send bags of fine grain pigments to paint plants.
There, the pigment is premixed with resin (a wetting agent that assists in
moistening the pigment), one or more solvents, and additives to form a
paste.
Dispersing the pigment
The paste mixture for most industrial and some consumer paints is now
routed into a sand mill, a large cylinder that agitates tiny particles of sand or
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silica to grind the pigment particles, making them smaller and dispersing
them throughout the mixture. The mixture is then filtered to remove the
sand particles.
Instead of being processed in sand mills, up to 90 percent of the water-based
latex paints designed for use by individual homeowners are instead
processed in a high-speed dispersion tank. There, the premixed paste is
subjected to high-speed agitation by a circular, toothed blade attached to a
rotating shaft. This process blends the pigment into the solvent.
Thinning the paste
Whether created by a sand mill or a dispersion tank, the paste must now be
thinned to produce the final product. Transferred to large kettles, it is
agitated with the proper amount of solvent for the type of paint desired.
Canning the paint
The finished paint product is then pumped into the canning room. For the
standard 8 pint (3.78 liter) paint can available to consumers, empty cans are
first rolled horizontally onto labels, then set upright so that the paint can be
pumped into them. A machine places lids onto the filled cans, and a second
machine presses on the lids to seal them. From wire that is fed into it from
coils, a bailometer cuts and shapes the handles before hooking them into
holes precut in the cans. A certain number of cans (usually four) are then
boxed and stacked before being sent to the warehouse.
Byproducts/Waste
A recent regulation concerning the emission of volatile organic compounds
(VOCs) affects the paint industry, especially manufacturers of industrial oil-
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based paints. It is estimated that all coatings, including stains and varnishes,
are responsible for 1.8 percent of the 2.3 million metric tons of VOCs
released per year. The new regulation permits each liter of paint to contain
no more than 250 grams of solvent. Paint manufacturers can replace the
solvents with pigment, fillers, or other solids inherent to the basic paint
formula. This method produces thicker paints that are harder to apply, and it
is not yet known if such paints are long lasting. Other solutions include using
paint powder coatings that use no solvents, applying paint in closed systems
from which VOCs can be retrieved, using water as a solvent, or using acrylics
that dry under ultraviolet light or heat.
A large paint manufacturer will have an in-house wastewater treatmentfacility that treats all liquids generated on-site, even storm water run-off. The
facility is monitored 24 hours a day, and the Environmental Protection
Agency (EPA) does periodic records and systems check of all paint
facilities. The liquid portion of the waste is treated on-site to the standards of
the local publicly owned wastewater treatment facility; it can be used to
make low-quality paint. Latex sludge can be retrieved and used as fillers in
other industrial products. Waste solvents can be recovered and used as fuels
for other industries. A clean paint container can be reused or sent to the
local landfill.
4.0 AUTOMOBILE INDUSTRY
Raw Materials
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Although the bulk of an automobile is virgin steel, petroleum-based products
(plastics and vinyls) have come to represent an increasingly large
percentage of automotive components. The light-weight materials derived
from petroleum have helped to lighten some models by as much as thirty
percent. As the price of fossil fuels continues to rise, the preference for
lighter, more fuel efficient vehicles will become more pronounced.
Design
With the help of computer-aided design equipment, designers develop basic
concept drawings that help them visualize the proposed vehicle's
appearance. Based on this simulation, they then construct clay models that
can be studied by styling experts familiar with what the public is likely to
accept. Aerodynamic engineers also review the models, studying air-flow
parameters and doing feasibility studies on crash tests. Only after all models
have been reviewed and accepted are tool designers permitted to begin
building the tools that will manufacture the component parts of the new
model.
Automobiles:
The production process for automobiles consists of the manufacture of all the
individual parts, including their finishing with heat treatments, plating and
painting, if used, their assembly into various mechanical subassemblies,
followed by the combination of all these subassemblies and parts into a
finished vehicle. Automatic and robotic equipment is interspersed with
human assemblers.
Many of the components assembled on the line are subassemblies that
were, themselves, manually assembled on lines with some interspersed
robotic and automatic assembly stations. Examples of these subassemblies
are the chassis, body, bumpers, fuel pumps, piping and tank, radiator,
suspension system, seats, engine, transmission, drive shaft, rear axle, wheel
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assemblies, instruments and instrument panel assembly, steering system,
brake system assemblies, electrical wiring, battery, generator or alternator,
starter, headlights and interior lighting system, as well as auxiliary
equipments such as air conditioning, radio, stereo, and cruise control.
Some subassemblies are put together completely with dedicated
(special purpose), high production equipment, others with a combination of
robotic and dedicated equipment, with or without manual assembly of some
components.
Robotic operation is common for such operations as welding, painting,
windshield assembly, and placement of heavy components like the engine,
transmission and body assembly. Fully automatic assembly with dedicated
equipment is most common with components such as spark plugs, hydraulic
brake cylinders, shock absorbers and other subassemblies that are used in
multiples in the car.
The Manufacturing Process
Automobile engines - are assemblies of many precision cast,
stamped, forged, and machined parts, some of which are electroplated or
painted. Except for specialty situations where only a very limited number of
a particular engine is built, assembly takes place on an assembly line. Some
portions of the assembly operation may be robotic or mechanized with
special equipment.
The basic engine block is normally an iron casting made in sand molds.
It is then machined extensively by milling, drilling, boring, reaming, grinding,
and honing.The crankshaft is either forged or cast , and is turned and
ground. Connecting rods are usually forged, bored and honed. Pistons are
sand cast or permanent mold cast of aluminum and turned on special
machines. Valves are forged, turned, and ground. Camshafts are forged or
cast, and turned and ground on special machines. Manifolds are cast and
machined by milling and other operations.
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Machine screws to fasten parts together are usually cold headed with
rolled threads. the engine factory or purchased, are included in the
assembly. These include parts that may be stamped from sheet metal, die
cast, or molded from plastics. They also include spark plugs, electrical wiring,
oil and air filters. bearings, seals, insulators, electronic ignition and fuel
metering parts, carburetors, fuel injection parts, coils, drive belts, and
pulleys. After assembly,
the engine is tested for correct operation and power at a test stand. If
satisfactory, it is moved to the final assembly line for installation in an
automobile. Due to the high production volumes that typically accompany
automotive production, many of the parts making operations are highly
automatic and engineered specifically for the component in question. Special
machines and transfer lines are often part of the parts-making operations.
Automobile bodies - Auto body parts are made from sheet steel
although, increasingly, fiberglass reinforced polyester plastic and formed
thermoplastic sheet parts are finding their way into current designs. With the
sheet steel parts, blanking, forming, and deep drawing operations are
performed. These operations are performed on high-production equipment
with compound dies and progressive dies, where applicable, with robotic
unloading of the stamped parts. Body parts are fastened together by
resistance welding and some arc welding, most of it robotic. Weld joints are
made smooth by application of high-lead body solder, sanded smooth. The
welded body assembly is dipped in a cleaning bath and then given a zinc
phosphate treatment to aid in corrosion resistance. Plastic sealers are
applied in locations where moisture can be trapped. The complete metal
body assembly is then painted. The first coat is often applied with the
electrophoretic method, dipping the body into a vat of water based paint.
The selected color is often applied with robotically-manipulated, electrostatic
paint guns, with some manual spray application to selected or difficult-to-
cover areas. A final clear coating is applied similarly, and is buffed and
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polished after it dries. Sound deadening materials are applied in some areas
with rubber-based adhesives.
A polyurethane coating is applied to the bottom surfaces to provide
protection against flying stones gravel and other debris. After painting,
doors, deck lids, hood, trim, windows, doors, bumpers, interior panels, the
dashboard with instruments, seats, lights, radios, speakers, carpeting, and
various hardware items are assembled to the body as part of the final auto
assembly operation. The body is then conveyed to the main assembly line
where it is assembled to the other components that make up the car.
Automobile chassis - the steel frame that supports the car, is used in
many automobiles. However, the more common auto designs now
incorporate a unitized body. With the unitized design, extra members are
added to the body to enable it to support the weight of the vehicle and to
withstand road shocks.
The supporting members then, are in the body assembly rather than part of
a separate chassis. Where a separate chassis is used, it is made from heavy
gauge sheet steel that is blanked, formed, and hole-punched. It is assembled
and arc welded with other similarly-made chassis components into a strong
and rigid assembly. Even with a unitized body, however, there normally is a
sub frame, similar to the earlier chassis but only in the front of the vehicle, to
support the engine, transmission, and front suspension. In many designs
there also is a small rear frame to support the rear axle, differential, and
suspension. These frames are also made of heavy gage steel stampings,
welded together. The net effect of the unitized body construction is a
reduction in vehicle weight.
Automobile windshields - consist of curved pieces of safety glass.
The glass is made with raw materials including potassium, magnesium, and
aluminum oxides, in addition to the more common materials, to provide
hardness and other properties. The molten glass is fed to float glass
equipment to produce a large, flat glass sheet. Each sheet is cut into smaller,
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windshield-size sheets. These are then bent to the desired curvature by
heating them and draping them over. a form of refractory material. Gravity,
and the softness of the heated sheets, causes them to take the shape of the
form. The bent sheet is tempered cleaned and assembled with an internal
layer of plastic and a second layer of glass. These three assembled pieces
are placed in an autoclave, which provides pressure to force the three layers
together and heat to bond the plastic to the glass surfaces. The finished
windshield then undergoes a plastic injection molding operation where it
becomes an insert in an injection mold and a plastic frame is molded around
it. The windshield is then ready for shipment to the automobile assembly
factory.
Components
The automobile assembly plant represents only the final phase in the
process of manufacturing an automobile, for it is here that the components
supplied by more than 4,000 outside suppliers, including company-owned
parts suppliers, are brought together for assembly, usually by truck or
railroad. Those parts that will be used in the chassis are delivered to one
area, while those that will comprise the body are unloaded at another.
Chassis
The typical car or truck is constructed from the ground up (and out). The
frame forms the base on which the body rests and from which all subsequent
assembly components follow. The frame is placed on the assembly line and
clamped to the conveyer to prevent shifting as it moves down the line. From
here the automobile frame moves to component assembly areas where
complete front and rear suspensions, gas tanks, rear axles and drive shafts,
gear boxes, steering box components, wheel drums, and braking systems
are sequentially installed.
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An off-line operation at this stage of production mates the vehicle's engine
with its transmission. Workers
use robotic arms to install
these heavy components
inside the engine
compartment of the frame.
After the engine and
transmission are installed, a
On automobile assembly lines,
much of the work is now done
by robots rather than humans.In the first stages of automobile manufacture, robots weld the floor pan
pieces together and assist workers in placing components such as the
suspension onto the chassis. The worker attaches the radiator, and another
bolts it into place. Because of the nature of these heavy component parts,
articulating robots perform all of the lift and carry operations while
assemblers using pneumatic wrenches bolt component pieces in place.
Careful ergonomic studies of every assembly task have provided assembly
workers with the safest and most efficient tools available.
Body
Generally, the floor pan is the largest body component to which a
multitude of panels and braces will subsequently be either welded or bolted.
As it moves down the assembly line, held in place by clamping fixtures, the
shell of the vehicle is built. First, the left and right quarter panels are
robotically disengaged from pre-staged shipping containers and placed onto
the floor pan, where they are stabilized with positioning fixtures and welded.
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The front and rear door pillars, roof, and body side panels are
assembled in the same fashion. The shell of the automobile assembled in
this section of the process lends itself to the use of robots because
articulating arms can easily introduce various component braces and panels
to the floor pan and perform a high number of weld operations in a time
frame and with a degree of accuracy no human workers could ever
approach. Robots can pick and load 200-pound (90.8 kilograms) roof panels
and place them precisely in the proper weld position with tolerance
variations held to within .001 of an inch. Moreover, robots can also tolerate
the
The bodyis built up on a
separate
assembly line
from the
chassis. Robots
once again
perform most
of the welding
on the various panels, but human workers are necessary to bolt the parts
together. During welding, component pieces are held securely in a jig while
welding operations are performed. Once the body shell is complete, it is
attached to an overhead conveyor for the painting process. The multi-step
painting process entails inspection, cleaning, undercoat (electrostatically
applied) dipping, drying, topcoat spraying, and baking.
As t