كتاب Plastic Injection Molding - Volume I: Manufacturing Process Fundamentals
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 كتاب Plastic Injection Molding - Volume I: Manufacturing Process Fundamentals

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مُساهمةموضوع: كتاب Plastic Injection Molding - Volume I: Manufacturing Process Fundamentals    كتاب Plastic Injection Molding - Volume I: Manufacturing Process Fundamentals  Emptyالأحد 15 سبتمبر 2019, 3:58 pm

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أحضرت لكم كتاب
Plastic Injection Molding
Volume I: Manufacturing Process Fundamentals
Fundamentals of Injection Molding series
By Douglas M. Bryce

كتاب Plastic Injection Molding - Volume I: Manufacturing Process Fundamentals  P_i_m_12
و المحتوى كما يلي :


Table of Contents
Preface xix
How It All Began 1
Evolution of the Screw . 1
Industry Evolution . 2
A Vision of Tomorrow . 3
Processes .3
Energy Efficiency/Desktop Manufacturing
Molds 4
Tooling/Lead Times
Materials .6
Recycling
Business Concepts 7
Education and Training/Alliances/Quality
Summary . 8
Questions 9
The Main Components 11
The Injection Unit 11
Sizing the Injection Unit/Purpose of the Injection Unit/
The Heating Cylinder/The Basic Hopper/The Injection
Screw/Injection Screw Designs/Screw Tip and Check
Ring/Nonreturn Valves and Ball Shutoffs/The Nozzle
Determining Injection Requirements 20
Calculation
The Clamp Unit 21
Sizing the Clamp Unit/How Much Force Is Required?/
Determining Projected Area/What About That D
Dimension?/What Happens If Too Little Clamp Force
Is Used?/What Happens If Too Much Clamp Force Is Used?
Summary . 27
Questions 27viii
Identifying the Parameters . 29
Temperature . 30
Melt Temperature Control 30
Insulation Blankets
Mold Temperature Control . 33
Postmold Shrinkage Control
Hydraulic System Temperature Control 35
Ambient Temperature Control . 35
Insulation Sheets . 36
Pressure 37
Injection Unit 37
Initial Injection Pressure/Holding Pressure (Secondary
Pressure)/Back Pressure
Clamp Unit 39
Hydraulic Clamp System/Mechanical Clamp
(Toggle) System
How Much Pressure Is Needed? 42
Time 44
Gate-to-gate Cycle Time 44
Gate Close Time . 44
Mold Close Time 45
Initial Injection Time 46
Injection Hold Time . 46
Cooling Time . 47
Screw Return Time 47
Mold Open Time 48
Ejection Time 49
Part-removal Time . 49
Mold-inspection Time 49
Distance 50
Mold Close Distance . 50
Injection Distance . 51
Injection-hold Distance 51
Cushion (Pad) 52
Screw-return Distance . 53
Mold-open Distance 53
Ejection Distance 55
Determining Injection-molding Costs . 55
What Information Is Needed? 56
Material Costs/Labor Costs/Machine Costs/
Tooling Costs
Adding It All Up . 64ix
Summary . 65
Questions 65
The Need for Control 67
Part Quality . 67
Part Cost . 68
Parameter Effects 69
What Are the Proper Parameter Values? . 69
The Setup Sheet 70
Installing and Setting up the Mold 72
Sizing and Inspection/Installation Procedure
Optimizing Temperature 78
Injection Cylinder Feed Throat . 78
Injection Cylinder Nozzle Zone . 79
Checking Temperature of Melt
Injection Cylinder Front Zone . 81
Injection Cylinder Center Zone 81
Injection Cylinder Rear Zone . 82
Injection Cylinder Summary . 82
Insulation Jackets/Preheating Material
Mold Temperatures . 84
Cooling Channels/Cascades (Bubblers)/Cooling Pins/
Insulation Sheets/Cooling Related to Cycle Times/Cooling
Related to Standard Runners/Cooling Related to
Hot Runners
Machine and Oil Temperatures 92
Purpose of Heat Exchanger
Ambient Temperatures . 93
Optimizing Pressure . 94
Injection Unit 94
Developing Injection Pressure/How Much Injection
Pressure Is Required?/Initial Injection Pressure and
Time/Holding Pressure and Time/Cushion (Pad)/
Back Pressure/Decompression
Clamp Unit 101
Purpose of Clamp Pressure/How Much Clamp
Pressure Is Required?
Controlling Shrinkage .105
What Is Meant by Shrinkage? .105
Effects of Temperature Adjustments .108
Effects of Pressure Adjustments .109
Postmold Shrinkage 109x
Minimizing Molded-in Stress 111
Defining Stress .111
Influence of Product Design 113
Draft Angles/How Much Draft Is Necessary?/What If
There Is No Draft?/Uniform Walls
The Importance of Drying Materials .118
Hygroscopic Materials 118
Other Materials 119
Summary .119
Questions 120
Focus of the Operator’s Role 121
Consistency . 121
Inspection of Parts 123
Inspection of the Mold 123
Inspection of the Machine .124
Housekeeping 124
Attitude .125
Summary .126
Questions 126
The Importance of Proper Material Selection .127
Plastic Defined .127
Amorphous versus Crystalline 128
Amorphous Materials 128
Crystalline Materials .128
Comparison of Amorphous and Crystalline .128
Polymerization .129
Monomers .129
Polymers 129
What Happens During the Molding Process? 131
Heat 131
Pressure .133
Cooling .133
Cost versus Performance .134
Fillers and Reinforcements .134
Melt Flow Index 135
Why Use the Melt Flow Index? 136
Establishing a Proper Melt Index Value .136xi
Summary .137
Questions 138
Describing the Mold .139
The A and B Plates .139
The Cavity Image .139
The Injection Half of the Mold 141
The Sprue Bushing 141
Runners .142
Flash .142
The Ejector Half of the Mold 142
Ejector Pins 142
Ejector Plates .143
Knockout Rod .143
Mold Design Basics 144
Gate Location 144
Runner Cross Section 146
Venting Concepts .146
Summary .150
Questions 150
Dryer Units 151
Hopper Dryers .151
Floor (Central) Dryers 152
Oven (Drawer or Tray) Dryers 153
How Dry Is “Dry”? 154
Dew-point Measurement/Inexpensive Moisture
Testing (TVI Testing)
Loaders .156
Mechanical Loaders .157
Vacuum Loaders .157
Positive-pressure Loaders .157
Blenders 158
Granulators .159
Mold Temperature Controllers 160
Robots .162
Summary .163
Questions 163xii
Defining Secondary Operations .165
When to Consider Secondary Operations 166
Assembly Operations 167
Ultrasonic Welding .167
Energy Directors/Ease of Welding/Variables That
Influence Weldability
Hot-gas Welding 173
Induction (Electromagnetic) Bonding .174
Spin (Friction) Welding .175
Adhesive Bonding 176
Machining Operations 178
Drilling and Tapping Thermoplastics .178
Drilling and Tapping Thermosets 180
Reaming Thermoplastics and Thermosets 180
Turning and Milling (Thermoplastic and Thermoset) 181
Automated Shape Cutting .181
Water Jet .181
Laser Cutting 182
Surface Finishes and Decorating Procedures .182
Preparation of Surface 182
Flame Treatment/Corona Discharge/Plasma Process/
Acid Etch
Applied Finishes .183
Painting/Plating (Electroplating)/Vacuum Metallizing
(Deposition)/Hot Stamping/Pad Printing (Heat Transfer)/
Screen Printing
In-process Finishes 189
Molded-in Color/Molded-in Symbols/Two-color (Two-shot)
Molding/Textured Surface/In-mold Overlays
Summary .193
Questions 194
Overview 195
Testing .195
Electrical Testing .195
Conditioning Samples/Dielectric Strength/Dielectric
Constant/Volume Resistivity/Surface Resistivity/
Arc Resistancexiii
Physical Testing 197
Shrinkage Rate/Density/Water Absorption/Moisture
Content—Tomasetti Volatile Indicator (TVI)/Melt
Flow Index
Mechanical Testing .203
Tensile Strength/Compressive Strength/Flexural
Strength/Creep/Impact Testing
Thermal Testing 206
Melting Point/Heat Deflection Temperature/Vicat
Softening Temperature/Flammability/Limiting
Oxygen Index
Failure Analysis 211
Overview 211
Stress 211
Differential Scanning Calorimeter .212
Stress/Moisture/T
m
and T
g
Points/Regrind Percentage/
Crystallinity
Calculating Glass Content .214
Furnace Method/TGA Method
Summary .217
Questions 218
Overview 219
What Causes Defects? 219
Defects and Remedies .221
Black Specks or Streaks 221
Blisters .222
Blush .223
Bowing 224
Brittleness 225
Bubbles (Voids) 227
Burn Marks 228
Clear Spots 229
Cloudy Appearance .231
Contamination .232
Cracking .233
Crazing .234
Delamination .234
Discoloration 236
Flash .237
Flow Lines 238xiv
Gloss (Low) 239
Jetting .241
Knit Lines (Weld Lines) 242
Nonfill (Short Shots) 243
Shrinkage (Excessive) 244
Sink Marks 245
Splay (Silver Streaking) .247
Warpage .248
Troubleshooting Tips .249
Rules to Mold By 250
Summary .252
Questions .
Glossary
Additive: A substance added to a plastic compound to alter its characteristics. Examples are plasticizers and flame retardants.
Alloy: A combination of two or more plastics that form a new plastic.
See blend.
Amorphous: A plastic material in which the molecular structure is random and becomes mobile over a wide temperature range. See crystalline.
Anisotropic shrinkage: Shrinkage that occurs more in one direction
than another (usually in the direction of flow; reinforced materials shrink
more across the direction of flow).
Anneal: To heat a molded part up to a temperature just below its melting point and slowly cool to room temperature. This relieves molded
stresses. See conditioning.
Automatic operation: The term used to define the mode in which a
molding machine is operating when there is no need for an operator to
start each cycle.
Barrel: A metallic cylinder in which the injection screw (or plunger)
resides in the molding machine. Also called cylinder.
Blend: A mixture of two or more plastics.
Boss: A projection of the plastic part, normally round, which is used to
strengthen an area of a part, provide a source of fastening, or provide an
alignment mechanism during assembly.
Cartridge heaters: Pencil-shaped electrical heater devices sometimes
placed in molds to raise the temperature level of the mold. Especially
beneficial when molding high-temperature crystalline materials.
Cavity: A depression or female portion of the mold that creates the
external plastic part surface.
Check ring: A ring-shaped component that slides back and forth over
the tip end of the screw. The check ring eliminates the flow of molten
material backward over the screw during the injection process.256 Plastic Injection Molding
Clamp force: The force, in tons or kilonewtons, that the clamp unit of
a molding machine exerts to keep the mold closed during injection.
Clamp unit: The section of the molding machine containing the clamping mechanism. It is used to close the mold and keep it closed against
injection pressure created by the injection process. The clamp unit also
contains the ejection mechanism.
Cold slug well: A depression (normally circular) in the ejection half of
an injection mold, opposite the sprue, designed to receive the first front,
or “cold” portion, of molten plastic during the injection process.
Compression ratio: A factor that determines the amount of shear that
is imparted to plastic material as it travels through the barrel. It is determined by dividing the depth of the screw flight in the feed section by
the depth of the screw flight in the metering section.
Conditioning: Exposing a molded part to a set of conditions (such as
hot oil) that impart favorable characteristics to the product. See anneal.
Cooling channels: Drilled holes or channels machined into various
plates or components of an injection mold to provide a flow path for a cooling medium (such as water) in order to control the temperature of the mold.
Core: (1) An extended or male portion of the mold that creates the internal plastic part surface. (2) A pin or protrusion designed to produce a
hole or depression in the plastic part.
Counterbore: A recessed circular area. Commonly used to fit the head
of an ejector pin (return pin, sucker pin, etc.) in the ejector plate.
Crystalline: A plastic material in which the molecular structure becomes
mobile only after being heated above its melting point. See amorphous.
Cushion: A pad of material left in the barrel at the end of the injection
stroke. It is above the amount needed to fill the mold and acts as a focus
point for holding pressure against the cooling melt.
Cycle: The total amount of time required for the completion of all operations needed to produce a molded part. Sometimes referred to as the gateto-gate time, meaning the time from when an operator first closes the gate
until the time the operator closes the gate again for starting the next cycle.
Cylinder: See barrel.
Decompression: A method of relieving pressure on the melt after preparing it for injection during the upcoming cycle. This minimizes the
drooling that occurs when a shutoff nozzle is not utilized.Glossary 257
Defect: An imperfection in a molded part that results in the product
not meeting original design specifications. These defects can be visual,
physical, and/or hidden.
Draft: An angle (or taper) provided on the mold to facilitate removal
(ejection) of the molded part.
Ejector half: The half of the mold mounted to the moving platen of the
injection machine. Sometimes called the live half or the movable half because it moves. This half of the mold usually contains the ejection system.
Ejector pin: A pin, normally circular, placed in either half of the mold
(usually the ejector half) which pushes the finished molded product, or
runner system, out of a mold. Also referred to as a knockout pin, for
obvious reasons.
Feed throat: The area at the rear end of the injection unit that allows
fresh plastic to fall from the hopper into the heating barrel.
Feed zone: The area of the screw that is at the rear and receives fresh
material from the feed throat.
Filler: Specific material added to the basic plastic resin to provide particular chemical, electrical, physical, or thermal properties.
Flash: A thin film of plastic that tends to form at parting line areas of a
mold. May also be found in vent areas and around ejector pins. Flash is
caused by too great a clearance between mating metal surfaces, which
allows plastic material to enter.
Flight: The helical metal thread structure of the injection screw.
Gate: An opening at the entrance of a cavity (end of the runner system)
that allows material to enter.
Granulator: A machine designed to grind rejected premolded plastic (products or runners). The material generated by this process is called regrind.
Guide pins: A pin (usually circular) that normally travels in a bushing
to provide alignment of two unattached components, such as the two
halves of an injection mold. Also called leader pins.
Heater bands: Bracelet-shaped electrical heaters placed around the
outside circumference of the heating barrel.
Heating cylinder: The section of the injection-molding machine in
which the plastic resin is heated to the proper molding temperature prior
to injection into the mold.258 Plastic Injection Molding
Heating zone: An area of the heating barrel that is controlled by a
temperature controller attached to a set of heater bands. There are four
major zones: rear, center, front, and nozzle.
Hopper: A funnel-shaped container mounted over the feed throat of a
molding machine. It holds fresh material to be gravity-fed into the feed
zone of the heating barrel. Hoppers are normally designed to hold an
average of 2 hours’ worth of material for a given machine size.
Hydraulic clamp: A large hydraulic cylinder that opens and closes the
clamp unit of a molding machine.
Hygroscopic: A term applied to those plastics (such as ABS and nylon)
that absorb moisture from the atmosphere.
Injection capacity: A rating of the maximum amount of plastic material, in ounces or grams, that a machine can inject in a single stroke of
the injection screw or plunger. It is based on the specific gravity of polystyrene as a standard.
Injection molding: The process of pushing a molten plastic material
into a relatively cool mold in order to produce a finished product.
Injection pressure: The pressure that performs the initial filling of
the mold. It is supplied by the injection screw or plunger as it pushes
material out of the heating barrel and into the mold.
Injection unit: The section of the molding machine that contains the
injection components, including the hopper, heating cylinder, screw (or
plunger), nozzle, and heater bands.
Isotropic shrinkage: Shrinkage that occurs equally in all directions.
See anisotropic shrinkage.
Knockout pin: See ejector pin.
L/D ratio: The result of a calculation that divides the entire length of
flighted area on a screw by its nominal diameter.
Land: Describes the area in which the gate, or vent, resides. It can also
be thought of as the length dimension in the L, W, H terminology used
for describing the dimensions of the gate or vent. See also shutoff land.
Leader pins: See guide pins.
Manual operation: The term used to define the mode in which a molding machine is operating when there is a need for an operator to start
and finish each phase of the total cycle.Glossary 259
Mechanical clamp: See toggle clamp.
Melt: Molten plastic prior to injection into a mold. A proper melt has
the consistency of warm honey.
Metering zone: The area of the screw at the front end which contains
properly melted plastic that is ready to be injected.
Mold: The entire tool (cavity, core, ejectors, etc.) needed to produce
molded parts from molten plastic material.
Monomer: A molecular unit of an organic substance, usually in the
form of a liquid or gas. See polymer.
Moving platen: The platen of a molding machine that travels (opens
and closes). It is connected to the clamp unit and is the mounting location for the B, or traveling, half of the mold.
Nonreturn valve: A mechanism mounted in (or at) the nozzle of the injection machine that operates to shut off injection flow at the end of the
injection cycle. It prevents material from the upcoming shot from drooling
out of the nozzle when the mold opens to eject parts from the previous shot.
Nozzle: A device mounted at the end of the heating barrel that focuses
plastic material to flow from the machine into the mold.
Pad: See cushion.
Parting line: A plane at which two halves of a mold meet. Also applies
to any other plane where two moving sections come together and form a
surface of a molded part.
Plastic: A complex organic compound (usually polymerized) that is capable of being shaped or formed.
Platens: The flat surfaces of a molding machine onto which the two
halves of the mold are mounted. One is stationary and the other travels.
There is a third platen (stationary) at the clamp end of the machine
which serves as an anchoring point for the clamp unit.
Plunger: The injecting member of a nonscrew molding machine. Plungers do not rotate (auger) to bring material forward in preparation for
the next cycle, nor do they blend the material as a screw does.
Polymer: A group of long chains of monomers, bonded together in a
chemical reaction to form a solid. This term is often used interchangeably with plastic, but there can be a difference.260 Plastic Injection Molding
Purging: A process of injecting unwanted plastic material from the injection cylinder into the atmosphere for the purpose of changing materials, changing colors, or removing degraded material. Also, the name given
to the mass of material that is purged.
Reciprocating screw: A helical flighted metal shaft that rotates within
the heating cylinder of a molding machine, shearing, blending, and advancing the plastic material. After rotating, the screw is pushed forward
to inject the plastic into the mold. Also referred to simply as the screw.
Regrind: Plastic material formed by granulating premolded material.
Regrind is material that has been exposed to at least one heating cycle.
Residence time: The total amount of time that the plastic material
resides in the heated barrel before being injected.
Runner: Grooves or channels cut into either or both halves of the injection mold to provide a path for the molten plastic material to be carried
from the sprue to the gate(s) of the cavity.
Screw: See reciprocating screw.
Screw speed: The rotating speed of the screw as it augers new material
toward the metering zone. It is expressed in revolutions per minute (rpm).
Secondary operation: Any activity performed after the molding process to produce a finished product suitable for its designed purpose.
Semiautomatic operation: The term used to define the mode in which
a molding machine is operating when there is a need for an operator to
start each cycle.
Shot: A term given to the total amount of plastic material that is injected (or shot) into a mold in a single cycle.
Shot capacity: See injection capacity.
Shutoff land: A raised area of the mold surface surrounding the cavity
image. This area is usually between 0.002 and 0.003 in. (0.005 and 0.008
cm) high and approximately 0.5 in. (1.27 cm) wide, and is used to focus
clamping pressure on the mold. The use of a shutoff land reduces the amount
of force required to keep a mold closed against injection pressure.
Slide: A section of the mold that is made to travel at an angle to the normal
movement of the mold. Used for providing undercuts, recesses, etc.
Sprue: The plastic material that connects the runner system to the
nozzle of the heating cylinder of the molding machine. It is formed by
the internal surface of a bushing that joins the mold to the machine’s nozzle.Glossary 261
Sprue bushing: A hardened bushing that connects the mold to the molding machine nozzle and allows molten plastic to enter the runner system.
Stationary platen A: The platen at the injection end of the molding
machine that does not travel. It contains the A half of the mold and
locates the mold to the nozzle of the injection unit. The moving platen
travels between this platen and stationary platen B.
Stationary platen B: The platen at the clamp end of the molding machine that does not travel. The moving platen travels between this platen
and stationary platen A.
Stress: A resistance to deformation from an applied force. Molded plastic products tend to contain stresses molded in as a result of forces applied during the injection process. These stresses may result in fractures,
cracks, and breakage if they are released during use of the product.
Suck back: See decompression.
Support pillar: A circular rod mold component used to support the ejector half of the mold. It is required because of the tremendous amount of
pressure exerted against the B plate during the molding injection phase.
Thermocouple: A device made of two dissimilar metals which is used
to measure the temperature of a heated area such as a barrel or nozzle.
It sends a signal to a controller which then turns off or on to control the
temperature of that area.
Thermoplastic: A plastic material that, when heated, undergoes a physical change. It can be reheated, thus reformed, repeatedly. See thermoset.
Thermoset: A plastic material that, when heated, undergoes a chemical change and cures. It cannot be reformed, and reheating only degrades
it. See thermoplastic.
Tie bars: Large-diameter rods that connect stationary platen A to stationary platen B. The moving platen contains bushings that are used for
sliding over the tie bars, allowing the moving platen to travel between
the two stationary platens.
Toggle clamp: A mechanical scissors-action system to open and close
the clamp unit of a molding machine. It is operated by a relatively small
hydraulic cylinder.
Transition zone: The area in the center of the screw (between the feed
zone and metering zone). This section has a tapering flight depth condition that compresses the plastic material in preparation for injection.262 Plastic Injection Molding
Undercut: A recess or extension on the molded part, located in such a way
as to prevent or impede ejection of the part by normal machine operation.
Vent: A shallow groove machined into the parting line surface of a mold
in order to allow air and gases to escape from the cavity, or runner, as
the molten plastic is filling the mold. Sometimes also located on ejector
and core pins.
Vented barrel: A heating barrel designed with an automatic venting
port that allows moisture and gases to escape from molten plastic prior
to injection into a mold.xv
List of Tables and Figures
Table I.1 - Evolution of Injection Molding 3
Table II-1 - Determining Clamp and Shot Size Combinations . 12
Figure 2-1 - Injection-molding machine . 12
Figure 2-2 - Injection unit components . 14
Figure 2-3 - Basic hopper design . 15
Figure 2-4 - Typical injection screw design 16
Figure 2-5 - Screw tip and check ring assembly . 17
Figure 2-6 - Ball-type nonreturn valve 18
Figure 2-7 - Typical nozzle assembly 19
Figure 2-8 - Various nozzle assembly styles . 20
Figure 2-9 - L/D ratio of screw . 22
Figure 2-10 - Determining projected area - A 23
Figure 2-11 - Determining projected area - B . 23
Figure 2-12 - Typical mold mounted in press . 26
Figure 2-13 - Small mold mounted in large press . 26
Table III-1 - Suggested Melt Temperatures for Various Plastics 32
Table III-2 - Suggested Mold Temperatures for Various Plastics . 34
Table III-3 - Average Times for Cycle Activities . 45
Table III-4 - Average Machine-hour Rates . 62
Table III-5 - Typical Cycle Times Determined by Wall Thickness 62
Figure 3-1 - Main processing parameters 30
Figure 3-2 - Heating cylinder (barrel) 31
Figure 3-3 - Mold insulation sheets . 36
Figure 3-4 - Developing injection pressure . 38
Figure 3-5 - Applying holding pressure . 39
Figure 3-6 - Applying back pressure . 40
Figure 3-7 - Hydraulic clamp; open (a), closed (b) . 41
Figure 3-8 - Mechanical clamp; open (a), closed (b) 43
Figure 3-9 - Mold closing distances 50
Figure 3-10 - Injection and hold distances . 52
Figure 3-11 - Hold cushion 53
Figure 3-12 - Screw return distance 54
Figure 3-13 - Ejection of finished part . 55
Figure 3-14 - Determining volume of parts and runner system . 57xvi
Table IV-1 - Molding Parameter Adjustments and Effects . 69
Chart 4-1 - Typical setup sheet . 71
Figure 4-1 - Inserting the locating ring in the platen 73
Figure 4-2 - Proper alignment of holding clamps 75
Figure 4-3 - Bridging of the feed throat . 79
Figure 4-4 - Nozzle zone of heating cylinder, or barrel 80
Figure 4-5 - Checking melt temperature 81
Figure 4-6 - Front zone of heating cylinder, or barrel . 82
Figure 4-7 - Center zone of heating cylinder, or barrel . 82
Figure 4-8 - Rear zone of heating cylinder, or barrel 83
Figure 4-9 - Cooling channels in a typical mold . 84
Figure 4-10 - Water cascade (bubbler) . 86
Figure 4-11 - Cooling pin 87
Figure 4-12 - Average cooling times versus thickness . 89
Figure 4-13 - Determining sprue diameters 90
Figure 4-14 - Typical hot runner system . 91
Figure 4-15 - Injection pressure on material . 95
Figure 4-16 - The holding pressure cushion . 99
Figure 4-17 - Developing back pressure 100
Figure 4-18 - Items used for determining projected area .102
Figure 4-19 - Calculating projected area 103
Figure 4-20 - Illustrating shrinkage rate .106
Figure 4-21 - How shrinkage affects dimensions 107
Figure 4-22 - Amorphous versus crystalline shrinkage differences 108
Figure 4-23 - Postmold shrinkage fixture .110
Figure 4-24 - Defining stress 112
Figure 4-25 - Defining draft angle 113
Figure 4-26 - Result of using draft angle 115
Figure 4-27 - Result of not using draft angle 116
Figure 4-28 - Uniform wall thickness .116
Figure 4-29 - Comparing radiused corners to squared .117
Figure 4-30 - Result of abrupt change in wall thickness .117
Figure 4-31 - Proper transition of wall thickness change .118
Figure 4-32 - Wall thickness change without stress .118
Figure 5-1 - Focus of the operator’s role 122
Table VI-1 - Differences in Amorphous and Crystalline Plastics .128
Table VI-2 - Plastics Classifications 129
Table VI-3 - Effect of Flowability on Plastic .137xvii
Figure 6-1 - An ethylene monomer 130
Figure 6-2 - Multiple ethylene monomers prior to polymerization .130
Figure 6-3 - Polymerized ethylene monomers .131
Figure 6-4 - Amorphous molecular chains .132
Figure 6-5 - Crystalline molecular chains .132
Figure 6-6 - Heat sets molecular chains in motion 132
Figure 6-7 - Applying pressure to align molecular chains 133
Figure 6-8 - Performance versus cost .134
Figure 6-9 - Melt flow index machine 136
Figure 7-1 - A and B plates of a two-cavity mold 140
Figure 7-2 - The A half of the mold .141
Figure 7-3 - Typical ejector pin construction .143
Figure 7-4 - Ejector plates 144
Figure 7-5 - Ejector plates actuated by knockout rod 145
Figure 7-6 - Locating gate at thickest section of part .145
Figure 7-7 - Comparison of a round runner cross section with a
trapezoidal cross section .146
Figure 7-8 - Air trapped by incoming flow 147
Figure 7-9 - Venting of parting line .148
Figure 7-10 - Venting of the runner .149
Figure 8-1 - Typical hopper dryer operation 152
Figure 8-2 - Floor dryer unit .153
Figure 8-3 - Typical oven-type dryer .154
Figure 8-4 - TVI test slide .155
Figure 8-5 - Examples of TVI results 156
Figure 8-6 - Vacuum loader .158
Figure 8-7 - Machine-mounted blender .159
Figure 8-8 - Granulator .160
Figure 8-9 - Granulator cutting chamber .160
Figure 8-10 - Mold temperature control unit 161
Figure 8-11 - Connecting control unit to mold 162
Table IX-1 - Ease of Welding (amorphous materials) .169
Table IX-2 - Ease of Welding (crystalline materials) .170
Table IX-3 - Adhesive Bonding Materials Compatibility .177
Figure 9-1 - Ultrasonic welding machine .168
Figure 9-2 - Energy director formula .169
Figure 9-3 - Hot-gas welding process 173xviii
Figure 9-4 - Induction (electromagnetic) welding concept 174
Figure 9-5 - Spin welding 175
Figure 9-6 - Adhesive bond joint examples 176
Figure 9-7 - Drilling point details 179
Figure 9-8 - Design of turning points .181
Figure 9-9 - Spray painting 184
Figure 9-10 - Vacuum metallizing process .185
Figure 9-11 - Typical hot stamp machine .186
Figure 9-12 - Common roll-on decorating method 187
Figure 9-13 - Common peripheral marking method 187
Figure 9-14 - Typical vertical stamping method 188
Figure 9-15 - Typical pad printing machine .189
Figure 9-16 - Screen printing process .190
Figure 9-17 - Two-color molding concept 191
Figure 9-18 - In-mold overlay process .193
Table X-1. Melt Index Value’s Impact on Plastics Properties .204
Figure 10-1 - Dielectric strength .196
Figure 10-2 - Dielectric constant .197
Figure 10-3 - Volume resistivity .197
Figure 10-4 - Surface resistivity 198
Figure 10-5 - Arc resistance .198
Figure 10-6 - Shrinkage rate 199
Figure 10-7 - Density 200
Figure 10-8 - Water absorption 201
Figure 10-9a - TVI moisture content test .202
Figure 10-9b - TVI patterns on test slides .203
Figure 10-10 - Melt flow index .203
Figure 10-11 - Tensile strength testing .204
Figure 10-12 - Compression testing 205
Figure 10-13 - Flexural strength testing .205
Figure 10-14 - Creep testing 206
Figure 10-15 - Notched impact testing 207
Figure 10-16a - Crystalline melting temperature 208
Figure 10-16b - Amorphous glass transition 208
Figure 10-17 - Heat deflection temperature testing .209
Figure 10-18 - Vicat softening temperature testing .209
Figure 10-19 - Flammability testing 210
Figure 10-20 - LOI testing 210
Figure 10-21 - Differential Scanning Calorimeter (DSC) 213
Figure 10-22a - Stress spike on DSC curve .213
Figure 10-22b - Moisture spike on DSC curve .213xix
Figure 10-23 - Determining regrind (crystalline material) 214
Figure 10-24 - Crystallinity curves 215
Figure 10-25 - Samples in furnace .215
Figure 10-26a - TGA chamber .216
Figure 10-26b - TGA curve 217
Figure 11-1 - Distribution of defect causes .220
Figure 11-2 - Black specks or streaks 221
Figure 11-3 - Blistering 223
Figure 11-4 - Blush .224
Figure 11-5 - Bowing 225
Figure 11-6 - Brittleness .226
Figure 11-7 - Bubbles 227
Figure 11-8 - Burn Marks 228
Figure 11-9 - Clear Spots 230
Figure 11-10 - Cloudiness .231
Figure 11-11 - Contamination 232
Figure 11-12 - Cracking 234
Figure 11-13 - Crazing .235
Figure 11-14 - Delamination 235
Figure 11-15 - Discoloration 236
Figure 11-16 - Flash .237
Figure 11-17 - Flow lines .239
Figure 11-18 - Low gloss .240
Figure 11-19 - Jetting 241
Figure 11-20 - Knit lines 242
Figure 11-21 - Short shots .243
Figure 11-22 - Shrinkage 244
Figure 11-23 - Sink marks .245
Figure 11-24 - Splay (silver streaking) 247
Figure 11-25 - Warpage .248


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» كتاب Plastic Injection Molding - Volume III - Mold Design and Construction Fundamentals
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» كتاب Plastic Injection Molding Volume IV
» كتاب Plastic Part Design for Injection Molding - An Introduction
» كتاب The Secrets of Building a Plastic Injection Molding Machine

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