CHAPTER-1 INTRODUCTION 3
1.1 Fabrication The polymer material are converted into plastics and used as tubes, sheets, foams, rods, adhesives, etc., The theological properties, softening, tempering, stability, the size and shape are important in describing the method.
These
methods are different kinds of plastics. Broadly speaking the method may be discussed under the following headings, a. Moulding Process b. Foaming Process
1.1.1. Moulding process: In this process the plastics are fabricated under the effect pressure and heat and both thermoplastics and thermosetting plastics may be starting materials. Thermoplastics are produced by this method. In this the material is softened by heating and the hot softened plastic is forced under high pressure into the mold, when it is set by cooling and the mold is.
1.1.2 Foaming process: This involves the blowing of a volatile organic liquid, which is entrapped into a polymer network resulting in the formation of foamed plastics. polystyrene are produced in this process.
1
Foamed
CHAPTER-2
2.1 Components The main components of the pneumatic injection moulding machine are, •
Pneumatic Double acting Cylinder
•
Hooper
•
Barrel
•
Heating Coil and regulator
•
Direction control Valve
•
Flow control valve
•
L-Angle
•
Nozzle
• Die and •
a.
Hose connectors
Pneumatic
Double
Acting
Cylinders: A double acting cylinder is employed in control systems with the full pneumatic cushioning and it is essential when the cylinder itself is required to retard heavy messes. This can only be done at the end positions of the piston stock. In all intermediate position a separate externally mounted cushioning derive most be provided with the damping feature.
The normal escape of air is out off by a cushioning piston before the end of the stock is required. As a result the sit in the cushioning chamber is again 2
compressed since it cannot escape but slowly according to the setting made on reverses. The air freely enters the cylinder and the piston stokes in the other direction at full force and velocity.
b. Hooper: The hopper is used to pour the plastic raw materials in to the barrel.
c. Barrel: The barrel is used to hold the molten and unmated plastic raw materials.
d. Heater and Regulator The heating coil is used to melt the plastic raw materials to the molten Form which is inside the barrel The heating coil regulator is used to regulate the temperature of heating coils according to the type of plastic raw materials used.
e. Direction Control Valve: To control the to and fro motion of cylinder, the fluid energy has to be regulated, controlled and reversed with a predetermined sequence in a pneumatic system. Similarly one may have to control the quantity of pressure and flow rateto generate the desired level of force and speed of actuators. To achieve these functions, valves are used. Valves are fluid power elements used for controlling and regulating the working medium. The main functions of the valves are, • Start and stop the fluid energy • Control the direction of flow of compressed air • Control the flow rate of the fluid • Control the pressure rating of the fluid 3
f. Flow Control Valve: These are used to control the rate of flow of a fluid through the valve. A directional control valve on the receipt of some, external signal, which might be mechanical, electrical or a fluid pilot signal, changes the direction of stops, or starts the flow of fluid in some part of the pneumatic/hydraulic circuit. They can be used to carry out such functions as: 1. Controlling the direction of motion of an actuator 2. Selecting alternative flow paths for a fluid. 3. Stopping and starting the flow of fluid
Purpose: This valve is used to speed up the piston movement and also it acts as a one way restriction valve which means that the air can pass through only one way and it can‟t return back. By using this valve the time consumption is reduced because of the faster movement of the piston.
g. L-angle: Mild steel „L‟ type angle is used to fabricate the frame to mount the all the parts of the injection molding unit.
h. Nozzle: The nozzle is used to inject the molded plastic material into the die.
i. Die: The die is used to produce the required product. By using different Types of die different products can be formed.
4
j. Hose connector: In our pneumatic system there are two types of connectors used; one is the hose connector and the other is the reducer. Hose connectors normally comprise an adapter (connector) hose nipple and cap nut. These types of connectors are made up of brass or Al or hardened steel. Reducers are used to provide inter connection between two pipes or hoses of different sizes. They may be fitted straight, tee, “V” or other configurations. These reducers are made up of gunmetal or other materials like hardened steel etc. Hoses used in this pneumatic system are made up of polyurethane. These hoses can with stand at a maximum pressure level of 10 kg/cm2.
2.2 Technical Data 2.2.1 Double Acting Pneumatic Cylinder Stroke length
:
Cylinder stoker length 160 mm = 0.16 m
Piston rod
:
18 mm = 18 × 10¯³ m
Quantity
:
2
Seals
:
Nitride (Buna-N) Elastomer
End cones
:
Cast iron
Piston
:
EN – 8
Media
:
Air
Temperature
:
0-80 º C
Pressure Range
:
8 × 105 N/m²
5
2.2.2 Solenoid Valve Size
:
0.635 × 10 ¯² m
Part size
:
0.635 × 10 ¯² m
Max pressure range
:
10 × 10 ⁵ N/m²
Quantity
:
2
2.2.3 Flow Control Valve Port size
:
0.635 × 10 - ² m
Pressure
:
0-8 × 10 ⁵ N/m²
Media
:
Air
Quantity
:
1
Max working pressure:
10 × 10 ⁵ N/m²
Temperature
:
0-100 ºc
Fluid media
:
Air
Material
:
Brass
2.2.4 Hoses Max pressure
:
10 ×10 ⁵ N/m²
Outer diameter
:
6 mm = 6 × 10 ¯ ³m
Inner diameter
:
3.5 mm = 3.5 × 10 ¯ ³m
6
2.3General Machine Specifications
a. Drill unit Short capacity
:
0.635 × 10 -² m
Barrel diameter (ID)
:
40 mm = 40 × 10¯ ³m
Clamping
:
Auto clamping
Max Clamping Size
:
100 mm = 0.1m
Type of cylinder
:
Double acting cylinder
Type of valve
:
Flow control valve & solenoid valve
Max air pressure
:
8 × 10⁵ N/m²
Size of machine (L x H)
:
0.4 m x 0.8 m
Weight
:
441.45 N
b. Clamping unit
c. Pneumatic unit
d. General unit
7
2.4 Design Calculation
Pressure applied
:
Max pressure applied the cylinder (p) Diameter of piston rodin(D)
:
Area of cylinder (A)
:
:
12.56 × 10⎯⁴ m² = =
Force exerted in the piston (F)
8 × 105N/m² 4 × 10-2 m
(3.14 D²) / 4
: Pressure applied x Area of cylinder. = 8 N/m2 ×12.56 × 10-4m2 = 10.48 × 102N
8
2.5
DESIGN DRAWINGS
FIG 1
L-BEAM
9
FIG
2
10
BARREL FIG 3
11
SUPPROT FOR BARREL
FIG
12
4
SUPPORT FOR VICE FIG 5
13
ROTATING HANDLE FOR FIXTURE FIG
14
6
PNUEMATIC CYLENDER
FIG
15
7
ASSAMBLY VIEW
FIG 8
16
LAYOUT
DIAGRAM
17
CHAPTER-3 FACTORS INFLUENCING THE DESIGN
The following are the factors influencing the fabrication work, a. Working Stress b. Working strain c. Elasticity d. Hooke‟s Law e. Bulk Modulus f. Poisson Ratio g. Factor of Safety
a. Working Stress: The internal resistance must be equal to the external load if the body is to be in equilibrium. This internal resistance per unit area is called intensity of stress or simple stress. Stress = Internal resistance / Area of cross section.
b. Working Strain: The deformation per unit length is called strain. Strain has no unit since it is only a ratio. Strain = Change in length / Original length
c. Elasticity: The property of a material body to regain its original condition on the removal of the deformation forces is called elasticity.
18
d . Hooke’s law: It states that when a material is loaded with in its elastic limit the stress is proportion to the strain.
Stress / Strain is a constant.
e. Bulk modulus: The ratio of the change in the volume to the original volume of the body is known as the volume strain or the bulk strain.
The ratio of the bulk stress to the bulk strain of a body is called the bulk modulus.
f. Poisson’s ratio: With in the elastic limit the lateral strain bears a constant ratio with the linear strain. The ratio is called the Poisson‟s ratio and is denoted by 1/m Poisson‟s ratio 1/m
=
Lateral strain / Linear
strain. The value of 1/m lies between 0.25 to 0.
g. Factor of Safety: The ratio of ultimate stress to working stress is known as factor of safety. Factor of safety
=
Ultimate stress / Working stress.
19
CHAPTER-4
INTRODUCTION TO POLYMERS The term polymer denotes a molecule made up of the repetition of simple unit monomers. Plastics are produced from the polymers by the combination of latter with compounding of the plastics. The importance of the polymers relates to it existence as a material, when converted into plastics. A polymer is produced from the monomers characterized by reactive centers, as a result of polymerization reaction. This polymerization reaction consists of the use of a catalyst, high temperature & high press. polymer.
Depending on these conditions one gets a
In the modern age, the human beings make use of one or stowed other
material made up of plastics in their daily routine. For one thing, they are complex and giant molecules and are different from low molecular weight compounds like common salt. A polymer like polyethylene does not melt sharply at one particular temperature into a clean liquid. Instead, it becomes increasingly softer sand, ultimately, turns into a very viscous, tacky molten mass. Further heating of this hot, viscous molten polymer does convert it into various gases but they are no longer polyethylene.
4.1 Important Polymers 4.1.1 Polyethylene: This polymer is obtained from ethylene, which is a by product in petroleum industries. The imperial chemical industries produced polyethylene by polymerization of ethylene. There are two types they are, 20
a. Low density polyethylene. b. High density polyethylene.
4.1.2 Polypropylene: The polymer is obtained from polymerization of propylene using co-ordination catalyst with the press up to 5 atmospheres & at temperature range (40-110) yield polypropylene.
4.1.3 PolymethylMethacrylate: Polymethylmethacrylate is produced by radial polymerization of methyl methacrylate which is produced from acetone.
4.1.4 Polyvinyl Chloride: The monomer is prepared from the reaction of acetylene with HC 1, Polymerization is carried out in suspension or emulsion method.
The emulsion
polymerization is carried out at low temperature.
4.1.5 Polyhedral Fluor ethylene: The monomer Tetrafluoro ethylene is prepared from the dechlorination of system dichloride tetra fluroethane. The monomer is subjected to emulsion method of polymerization using peroxide using the indicator.
21
CHAPTER-5 CLASSIFICATION OF POLYMERS 5.1 Thermoplastics and Thermosetting Plastics Plastics are formed by the combination of polymers with compounding ingredients. These are classified as a. Thermoplastics b. Thermosetting plastics. Thermoplastics are materials that can be softened by heat and then formed. Thermosetting plastics are permanently hardened when formed.
During
heating followed by cooling of thermoplastics, the bonds soften but the destruction of materials do not take place on the other hand, in thermosetting plastics, heating affects the chemical structure and the plastics crumble to powder.
Thermoplastics are produced
generally by addition polymerization while thermosetting plastics are produced by condensation polymerization. Thus the processing of these materials has to be done in different manners.
The following materials are thermoplastics: Polyethylene, Polypropylene, Polyvinyl Chloride, Ply Acrylics, Polyamides, Nylon, Polystyrene Celluloses, Polyesters.(Saturated).
22
5.2 Components of plastics The following materials are thermosetting plastics: Phenol-Formaldehyde Resins, Urea Formaldehyde Resins, Mel Amine-Formaldehyde Resins, Polyesters (Unsaturated) Epoxy Resins Silicon.
To produce plastics, it is essential to have polymers blended with some external materials. These external materials are termed “compounding ingredients”. For the purpose of processing of polymers two plastics these are added to give not only the required property to plastics but also sturdiness and economical aspects to virgin polymers. The components of compound of plastics: •
Fillers
•
Plasticizers
•
Colorants
•
Lubricants
•
Sterilizer
•
Anti Oxidants.
5.2.1 Fillers: They are added to the polymers to impart special properties and also to reduce the cost of finished products.
5.2.2 Plasticizers: They are added to the polymers to increase plastic property and induce more flexibility to the plastics.
5.2.3 Colorants: They are added to provide pleasing colors to the plastics. colors are provided by both organic dye stuff and inorganic salts. 23
These decorative
5.2.4Lubricants: These substances are used to get a good finishing. These are added to most of the polymers to improve flow within processing machineries and to reduce friction.
5.2.5 Stabilizers: The polymers may undergo degradation with the formation of conjugated double bonds along the chain, which result in declaration of the polymer. To avoid this suitable materials are added, called stabilizers.
5.2.6 Antioxidants: Polymers are protected against oxidative degradation by incorporating certain compounds called antioxidants.
24
CHAPTER-6
POLYMER PROCESSING
Whether we want to make a toy or fabricate a spacecraft, polymers would often have some crucial role to play. But how does one convert a polymer into a broad spectrum of useful shapes and structures? To answer this question, we need to look at another branch of polymer technology called “polymer processing” which it‟s the theme of this chapter. In a very broad sense, polymer processing may be defined as an engineering specialty used to convert polymeric materials into useful end products.
Most of the
available techniques now employed in processing technology of polymers are basically refined versions of those used in ceramic or metal industries.
In fact, the need to
understand finer aspects of polymer processing surfaced as conventional materials were required to be substituted by those with better finish and elegant. They black ebony or the costly ivory keys in a harmonium or a piano gave way to wooden keys with a covering of celluloid.
25
CHAPTER-7
PROCESSING TECHNIQUES
The very fact that polymeric materials are used in many forms such as rods, tubes, sheets, foams, coatings or adhesives and also as moulded and fabricated articles implies that there must be a variety of ways in which the compound resins can be processed and converted in then finished products. A majority of the articles are either moulded or fabricated, while many others are made by casting liquid pre polymers into a mould and allowing them to cure of cross-link. Fibers are made by a process known as spinning. Today, there are many processes and automatic machines for this purpose, the important ones being calendaring, casting, compression moulding, injection moulding, extrusion moulding, blow moulding, cold forming, thermoforming, foaming, reinforcing, melt spinning, dry spinning and wet spinning.
26
CHAPTER-8 INJECTION MOULDING PROCESS 8.1 injection moulding The injection moulding process is best suited for producing articles made of thermoplastic materials.
Here, the equipment cost is relatively high but the main
attraction is the amenability of the injection moulding process to a high production rate. In injection molding, a definite quantity of molten thermoplastic material is injected under pressure into a relatively cold mold where it solidifies to the shape of the mould.
The injection moulding machine is shown in the process consists of feeding the compounded plastic material as granules, pellets or powder through the hopper at definite time intervals into the hot horizontal cylinder where it gets softened. Pressure is applied through a hydraulically driven piston to push the molten material through a cylinder into a mould fitted at the end of the cylinder. The molten plastic material from the cylinder is then injected through a nozzle material from the cylinder is then injected through a nozzle into the mould cavity.
The mould used, in its simplest form, is a two-part system. One is a movable part and the other stationary. The stationary part is fixed to the end of the cylinder while the movable part can be opened or locked on to the stationary part. The locking device has to be very skillfully designed in order to withstand high operating pressures. Furthermore, a proper flow of the molten material to the interior regions of the mold is achieved by preheating the mould to an appropriate temperature.
Usually, this
temperature is slightly lower than the softening temperature of the plastic material undergoing moulding.
27
After the mould‟s filled with the molten material under pressure, then it is either cooled by cold water circulation or air and then opened so as to eject the molded article. The whole cycle could be repeated several time either manually of in an automated mode.
28
CHAPTER-9
WORKING PRINCIPLE The Pneumatic injection moulding process is best suited for producing articles made of thermoplastic materials. Here, the equipment cost is relatively high but the main attraction is the amenability of the pneumatic injection moulding process to a high production rate.
In pneumatic injection molding, a definite quantity of molten
thermoplastic material is injected under pressure into a relatively cold mold where it solidifies to the shape of the mould.
The pneumatic injection moulding machine is shown in the process consists of feeding the compounded plastic material as granules, pellets or powder through the hopper at definite time intervals into the hot molten plastics.
Pressure is applied through a
pneumatically driven piston to push the molten material through a barrel into a mould fitted at the bellow the nozzle. The molten plastic material from the Hooper is then injected through a nozzle material. The mould used, in its simplest form, is a two-part system. One is a movable part and the other stationary. The stationary part is fixed to the end of the cylinder while the movable part can be opened or locked on to the stationary part.
By using a mechanical locking device, the mould is proper held in position as the molten plastic material is injected under a pressure as high as 15×10-2 N/m2. The locking device has to be very skillfully designed in order to withstand high operating pressures. Furthermore, a proper flow of the molten material to the interior regions of the mold is achieved by preheating the mould to an appropriate temperature. Usually,
29
this temperature is slightly lower than the softening temperature of the plastic material undergoing moulding.
After the mould is filled with the molten material under pressure, then it is cooled by cold water circulation and then opened so as to eject the molded article. The whole cycle could be repeated several times by the same procedure. The double acting pneumatic cylinder is used to inject the molten plastic material into the die.
The flow control valve is used to control the flow of air in to the cylinder. The direction control valve is used to control the direction of piston movement. These all valves are already explained in the above chapter.
30
CHAPTER-10
FABRICATION OF MECHINE
The injection moulding is widely used in the modern age. The human beings make use of one or other material made up of plastics in their routine life. The frame is designed like a chassis frame with the help of L angle. The frame is finished accurately & it has provisions to mount the components. There is also a provision to mount the channels on which the die locking & Die setting system works
The threads are formed on the shafts. The two shafts are mounted on the either side of the channel. On one side square thread is made & thread is made on another side. The shafts are tightened by using of hardware. The two shafts hold two plates by drilling & boring the plate according to the required size. The plates are fixed up and down on the shafts. There is also two shafts to hold two plates rigidly. The upper plate holds the Rack & pinion gear mechanism, Rotating wheel, plunger. The bottom plate holds Hooper, spring, Barrel, nozzle, Heating Coil, Heating Coil Regulator is used to regulate the temperature of Heating coil.
10.1 Rack And Pinion Gear: The rocker & pinion is the main part of the Injection system in injection molding. The plastic cannot be injected without Rack & Pinion. The Rack & Pinion makes the operation of Injecting system.
31
10.1.1
Classification of
Gears: a. Spur gear b. bevel gear c. worm and worm wheel d, helical gear
10.1.2 Construction of Gears: The following are the term used in gears.
a. Pitch Circle: The pitch cycles are the outlines of the imaginary smooth rollers or discs.
b. Pitch Circle Diameter The pitch circle die is the diameter of an imaginary dix which would produce the same motion as that produced by the gear, by poor rolling.
c. Addendum Circle: A circle passing through the tips of the teeth is called addendum circle.
d. Addendum: The part of the tooth out side the pitch circle is called the addendum.
e. Dedendum Circle: A circle passing through the roots of the teeth is called dedendum circle.
32
f. Dedendum: The distance between center to center of two teeth measured along the arc of the pitch circle is called his circular pitch.
g. Module: Module is the length of the pitch circle dia per tooth & is given by.
10.1.3 Working: A gear whose pitch circle dia is infinity is called as rack. The small gear which meshes with rock is called the pinion.
Rock & pinion gear arrangement is used to
convert the linear motion into rotary one & vice versa.
Rotating wheel: The rotating wheel is arranged with the pinion. The Bearings are attached on either side of the pinion to give the support to the wheel rod. By rotating of the wheel. The plunger moves up & down.
Plunger: The plungers are attached with the rack. By making external threads on rack and internal threads on plunger. The plunger is used to compress the molten plastic.
10.2 Types Of Springs: Two types of springs are in common use. a. Helical spring. b. Leaf spring.
33
a. Helical spring: A Helical spring is formed by bending a wire around a mandrel in the form of a helix. The coil in a helical spring is subjected to torsion and hence its known as Torsion spring. Helical spring of two types. •
Closely coiled helical spring.
•
Open coiled helical spring.
Closely Coiled Helical Spring: In a closely coiled helical spring the gap between successive turns is so small that each turn is practically a plan at right angles to the axis of the helix and the wire is subject to torsion. The bending stress is negligible compared to the tensional stress. This spring can take up tensile load only.
Open Coiled Helical Spring: In a open coiled helical spring there is a large gap between the two consecutive turns. As a result of this the spring can take up compression load also.
10.3 Thread: When the job is rotated the tool is automatically moved by the lead screw in the longitudinal direction. The longitudinal feed should be equal to the pitch of the thread to be cut per revolution of the work. The lead screw has a fixed pitch. So, a ratio between the rotation of the head stock spindle and the longitudinal feed is found out. The lead screw is connected by carriage by engaging the half nut lever. So, when the head stock spindle rotates the lead screw rotates at same speed the pitch of the work will be equal to the pitch of the lead screw. So far obtaining different pitches on the work, the speed of the lead screw can be changed by fixing proper change gears between head stock spindle and leadscrew.
34
CHAPTER-11
BILL OF MATERIALS
Sl. No.
Name of The Parts
Material
Quantity
1
Pneumatic cylinder
EN-8
1
2
Direction control Valve
Aluminum
1
3
Flow Control Valve
Aluminum
1
4
Barrel
C.I
1
5
L-stand
Mild steel
1
6
Vice
C.I
1
7
Heating coil
Copper
1
8
Hooper
C.I
1
9
Connector
Polyurethane
5 meter
10
Hose collar
Aluminium
4
11
Reducer
Aluminium
2
12
Nozzle
C.I
1
Table 1.Component
35
CHAPTER-12 COST ESTIMATION 12.1Material Cost:
Sl. No.
Name Of The Parts
Quantity
1
Pneumatic cylinder
1
2000
2
Direction control Valve
1
550
3
Flow Control Valve
1
600
4
Barrel
1
2000
5
L-stand
1
200
6
Vice
1
300
7
Heating coil
1
1500
8
Hopper
1
300
9
Connector
5 meter
100
10
Nozzle
1
50
Table 2. Cost of Components
12.2 Total Cost Total cost
=
Material Cost Charges
=
Rs 7600
Total Cost of Machine = RS 7600
36
Amount In Rs
Total =Rs. 7600
CHAPTER-13 ADVANTAGES AND APPLICATIONS
13.1 Advantages •
This product is an alternative for plastic cups and plates.
•
Cheaper and easily available material is used.
•
The pneumatic arm is more efficient in the technical field.
•
Quick response is achieved
•
Simple in construction.
•
Easy to maintain and repair.
•
Cost of the unit is less when compared other moulding machine.
•
No fire hazard problem due to over loading.
•
Comparatively the operation cost is less.
•
Continuous operation is possible without stopping.
•
It reduces the manual work.
•
It reduces the production time.
•
Occupies less floor space.
•
Less skilled operator is sufficient.
•
Different shape of the components can be made according to the die what are
used. •
Adjustable Temperature setting is done with the help of thermo stator.
37
13.2Applications •
The daily using plastic components can be easily made.
•
It is very useful in small scale moulding industry
•
Textile products can be produced.
•
By changing proper die, we can produce any shape of plastic materials with low
cost.
13.3 Disadvantages
•
Initial cost is high
•
Cylinder stroke length is constant
•
Need a separate compressor
38
CHAPTER-14 CONCLUSION
Due to it‟s low cost, this working model can be successfully inducted in small scale moulding units and can be used to manufacture small plastic component at an acceptable cycle rate within an effective cost component.
Existing market machine cost
45000.00
Component cost
22500.00
Total cost
67500.00
Table 3. Cost evaluation of existing machine
Fabricated machine cost
7600.00
Component cost
7600.00
Total cost
7600.00
Table 4. Cost estimation of fabricated machine
39
As exhibited in the above tables, the newly fabricated machine has brought in a considerable reduction in the cost component when compared to existing cheapest machine available in the market Thus we have successfully fabricated a machine which can remove the initial starting cost hurdle and on basic standards cater to the needs of a small scale industry. After the completion of fabrication the machine is tested with a wide variety of acrylic plastic materials over a variable temperature range and plastic ring as the standard product from the die is manufactured.
This prototype can be subjected to further improvement in product cycle time with the compromise of the cost based component. A few of the changes which can be brought about are:
• Introduction of a pneumatic based clamping system instead of the manual clamping system in order to decrease the cycle time and increase the overall production rate.
• Manual temperature control system can be replaced with a sensor based temperature range control system in order to make the process continuous and improve the cycle time.
40
REFERENCES 1.
Donald V. Rosado, Marlene G. Rosado. 2000 Concise Encyclopedia of Plastics. Springer,
2.
Douglas M. Bryce. 1996. Plastic Injection Molding: Manufacturing Process
Fundamentals. SME,
3.
International Journal of Engineering, Science and Technology, Minimization of sink mark defects in injection molding process –Taguchi approach
4.
McGraw Hill Book Company, Compressed Air Operations Manual, ISBN 0-07-
147526-5.
5.
Oswald, Tim A; Lih-Sheng Turng, Paul J.Gramamn2007. Injection Molding
Handbook 2nd Ed.HanserVerlag.,
6. R.K. Rajput, Heat and Mass Transfer
7. R.S.Khurmi, Machine Design
8. Society for Plastic Engineers, Journal of Injection Molding Technology, ISSN: 1533905X.
9.
Stephen Fenichell, 1996,Plastic: The Making of a Synthetic Century, Harper
Business,ISBN 0887307329.
