Plastic Product Material and Process Selection Handbook Part 5 pps

In an injection molding process pressure is applied to force the melt into a mold that defines the product shape in three dimensions Chapter 4.. bridge reinforced plastic bulk molding c

Although there are literally thousands of plastics available, usually no single one will exhibit all desired properties in their proper relation- ships Therefore a compromise among properties, cost, and fabricating process generally determines the material of construction

There is a logical workable elimination approach to the selection of the correct plastic Examples among the specific properties have been reviewed in this chapter that include chemical resistance (Table 2.12), color, crazing/cracldng, clectric/clectronic, flame rcsistancc, impact, odor/taste, radiation, temperature resistance (Figure 2.7), permeability (Table 2.13), transparency (Figure 2.8 and Table 2.14), weathering (Figure 2.9), moisture, etc 1-3, 6, 133, 134, 367, 368,426

Figure 2~ Examples of plastic contraction at low temperatures

2 9 P l a s t i c property 1 2 5

T a b l e 2 + 1 2 C h e m i c a l r e s i s t a n c e o f p l a s t i c s ( c o u r t e s y o f Plastics FALLO)

P L A S T I C ~ ,'m_,,.,.',,,,'

n [ : m !77 i:eoo l.x ~ , ~ - ; IvIATEFllAL ~,] ,0o !," " ' I " 1 " ' ' 1 =~ " 1 ~ " l ~ 1 + r ~- : , l ~ , - ~ i _ j

l i a l s 1-4 H L 1 l ,.i , 7 + : : - : 2-S -5 I-S i ' S 1 S $ I S ' " 1 i-~ 1 0.22-0.2S

Polyethylenes ( U H M W P E -

u l t r a h i g h m o l e c u l a r w e i g h t ) 3 4 3 4 $ 4 1 1 1 [ 1 1 1 1 1 $ 4 <~0,01 ,, ; ~ _~ , ,, , , , , , : : J ; ; : _ ,_ = , ~,

P o l y l m i d e s 1 1 1 1 1 1 2 3 4 '] 5 3 4 2 6 1 1 ] 0 3 - 0 4

[

P o l y p h e n y l e r m O N d e s ( P P O } 4 5 2 3 4 5 1 1 1 1 1 2 1 • 2 3 0 0 6 - 0 , 0 7 ( m o d i f i e d )

I _ : ,: _ , ; ; - :

-=- , .,,: ,

Table 2~ 13 Examples of permeability for plastics

Water

styrene)

copolymer

Ethylene vinyl alcohol I 14-1.21 Fair Very good Very good copolymer

Polyethylene

Linear low density 0.900 0.940 Good Fair Good

Polystyrene

S A N (styrene acrylonitrile) 1.07-I.08 Fair Good Fair to good Polyvinyl chloride

2 9 Plastic property 1 2 9

s , , , r k f=,,!!,,y,,, h~l,I, d.,.,c~sms .

Transparent ABS Good impact properties, good processibility

Acrylic (PMMA) Excellent resistance to outdoor exposure, crystal clarity

Allyl diglycol carbonate Good abrasion/chemical resistance, thermoset

Cellulosics Heat sensitive, limited chemical resistance, good toughness

Excellent toughness, good thermal/flammability characteristics Polyethefimide

Excellent chemical resistance/electrical properties, weatherable, decomposition evolves HCI gas

Styrene acrylonitrile

Styrene butadiene

Styrene maleic anhydride

Styrene methyl methacrylate

Thermoplastic urethane, rigid

Good stress-crack and craze resistance, brittle Good processibility, no stress whitening Higher-heat styrenic, brittle

Good processibility, slightly improved weatherability Excellent chemical/solvent resistance, good toughness

FAB RI s N G PRODUCT

Overview

The profound impact of plastic products to people worldwide and in all industries worldwide includes the intelligent application of processing these plastics These plastics utilize the versatility and vast array of inherent plastic properties as well as the usual high-speed/relative low- energy processing techniques The result has been the development of millions of cost-effective products used worldwide that in turn continue

to have exceptional benefits for people and industries worldwide

In a market economy, which is to say the real world that is ruled by competition, processed plastics will be employed only in applications where they can be cxpcctcd to bring an overall economic advantage compared with other competing products In this connection it is well

to note that the biggest competitor to a given plastic may be another plastic with their respective processing techniques On the basis of an overall benefit assessment taking in the full service of a processed plastic product, it has been shown in millions of cases worldwide that the use

of processed plastics not only makes economic sense but also makes a contribution toward conserving resources

Thcrc arc many factors that arc important in making plastic products the success it has worldwide One of these factors involves the use of the availability of different fabricating processes All processes fit into an overall scheme that requires interaction and proper control of operations based on material requirements Thus fabricating is an important part of thc ovcrall project to produce acceptable plastic products It highlights the flow pattern for the fabricator (manufacturer)

to be successful and profitable Recognize that first to market with a new product captures 80% of market share Factors such as good engineering, process control, etc are very important but only represent

3 9 Fabricating product 131

pieces of the "pie." Philosophical many different ingredients blend together to produce profitable products Fabricating is one of the important main ingredients

With continuing new developments in equipment (and plastics) their quality performance and output rate improves and overhead costs are reduced Result has been the industry worldwide continues to be more productive even though the economy has its ups and downs 13s, 136, 248

In order to understand potential problems and solutions of fabrication,

it is helpful to consider the relationships of machine capabilities, plastics processing variables, and product performance 1 In turn, as an example,

a distinction has to be made here between machine conditions and processing variables For example, machine conditions include the operating temperature and pressure, mold and die temperature, machine output rate, and so on Processing variables are more specific, such as the melt condition in the mold or die, flow rate vs temperature and so

on (Chapter 1)

Fabricating products involves conversion processes that may be described as an art Like all arts they have a basis in science and one of the short routes to processing improvement is a study of the relevant sciences (as reviewed throughout this book that range from the different plastic melt behaviors to fabricating all size and shape products

to meet different performance requirements) The plastic-processing target is to take the plastic in the form of pellets, powders, granules, liquids, etc and converting them into useful products usually through a screw plasticator

Processing of plastic is an art of detail The more you pay attention to details, the fewer problems develop in the process If it has been running, it will continue running well unless a change occurs Correct the problem and do not compensate It may not be an easy task, but understanding what you have equipment-wise can help C o m m o n features of these different processes is as follows:

produces a homogeneous melt (Chapter 1) This is often carried out in a screw plasticator or compounder, where melting takes place

as a result of heat conducted through the barrel wall and heat generated in the plastic by the action of shear via the screw Homogeneity is called for at the end of this stage, not only in terms

of material but also in respect to temperature

These tools include molds and dies for shaping and fabricating

Melt transport & shaping: In a screw plasticator the next step would be to build up an adequate pressure in the plasticator so that

it will produce the desired shape to be fabricated In an injection molding process pressure is applied to force the melt into a mold that defines the product shape in three dimensions (Chapter 4) In

an extruder the die (that initiates the shape) can vary from a simple cylindrical shape to a complex crosshead profile shape (Chapters 5)

screw plasticator melt to stretch the melt to produce orientation and desired shape, as in blow molding, thermoforming, rotational molding, and foaming (Chapters 6, 7, 8, 13)

melt provides coatings and castings as reviewed in Chapters 10, 11,

16

reaction injection molding (Chapter 12) In compression molding the usual material is precompounded or preimpregnated prior to being placed in or around a mold (Chapters 14 and 15)

usually does not require secondary operations However, there are materials or products that may require annealing, sintering, coating, assembly, decoration, etc (Chapter 18)

Processing techniques range from the unsophisticated (high labor costs with low capital costs) to sophisticated (zero or almost zero labor costs with very high capital costs) Production quantity, the material being processed, the available equipment, and the total cost govern decisions

on the appropriate technique Small quantities are usually produced with an unsophisticated approach

Many fabricating processes are employed Which process to use depends upon the nature and requirements of the plastic to be processed, properties required in the finished product, cost of the process, speed, and volume to be produced Some processes can be

3 9 Fabricating product 1 3 3

used with many kinds of plastics; others require specialized processes Recognize that the final actual properties of a processed plastic for an application are directly related to how the plastics are processed If process controls are not properly set up, followed, and continually rechecked to insure meeting part performance requirements, products could be improperly processed This quality control requirement 3 on processing plastics applies to all products

With the beginning of a deeper understanding of process mechanisms and their underlying physical laws and close cooperation between theorists and practical people, has processing technology and machinery design made any real progress This progress will always continue since new plastics and new processing techniques develop There are the basic fabricating processes (Chapter 4-16) however many different modifications continue to be developed (Table 3.1)

bridge reinforced plastic

bulk molding compound

cable extrusion

calendering (different types)

carded package

carousel molding

casting (different types)

C-clamp injection molding

cellular plastic molding

cellular chemical blow molding

centrifugal casting

centrifugal molding ceramic-plastic molding chemical vapor deposition cladding

closed molding coating (different types) coextruded foamed blow molding

coextrusion coextrusion capping coining

coinjection foam molding coinjection molding cold flow molding cold forming cold heading cold molding cold press molding cold stamping cold working, combiform comoforming cold molding compounding

compound molding composite molding Compreg molding compression-injection molding compression molding (different types)

computer-aided extrusion computer-aided molding computer aided processing contact molding contact pressure molding

continuous coating continuous fiber spinning continuous injection molding continuous laminating continuous molding continuous strip molding controlled density molding copolymer molding corrugated pipe extrusion corrugated multilayer pipe extrusion

counter pressure intrusion counter pressure molding crossflow molding cross laminating decompression molding devolatilizing extrusion devolatilizing molding die casting

die-slide molding dip casting dip forming dip blow molding dip molding dip coating doctor blade coating dose molding dosing extrusion dosing molding double-daylight molding double shot molding draw working dry blend molding elastomer molding

extruder {different types)

extrusion blow molding

extrusion compounding

extrusion molding

female forming

fiber forming

fiber placement molding

fiber reinforced molding

fiber spinning (wet, dry, jet, etc.)

foamed molding (many different

types such as injection,

extrusion, calendering, casting,

blow molding, etc.)

foamed reservoir molding

fusible core molding

gas assist molding

gas assist molding without gas channels

gas blow molding gas counter-pressure injection molding

gas counter pressure molding gas injection foam molding gas injection molding gear pump extrusion gear pump injection molding geometric forming geometric molding glass fiber spinning glass mat reinforced molding granular paint injection graphitized fiber spinning grease-free injection molding group transfer polymerization grow molding

hand layup molding heat-cured rubber molding heat sealing

high density molding high frequency molding high pressure foam molding high pressure injection molding high pressure molding horizontal extrusion horizontal injection molding horizontal wheel blow molding horizontal wheel extrusion horizontal wheel forming horizontal wheel molding hot melt molding hot stamping hot working hybrid-electric operating injection molding

hydroclave molding hydromechanical clamp injection molding

impregnation molding impulse sealing infusion molding injection blow molding injection compounding injection-com pression molding injection-die pultrusion injection molding (different types)

injection molding-prepressurized cavity

injection molding stamping injection transfer molding

in-line slot extrusion/

thermoforming n-mold coat molding n-mold decorating intermediate pressure molding ,nterpenetrating blend molding ,ntrinsic molding

inplace molding insert injection molding insert molding intrusion-flow molding inverse lamination investment casting isotactic molding/pressure jet molding

jet spinning lagging molding laminated molding layup molding leatherlike molding Lego molding LIFO injection molding liquid crystal extrusion liquid crystal molding liquid curing extrusion liquid injection molding liquid silicone rubber injection molding

liquid transfer molding lost wax molding low pressure foam molding low-pressure injection molding low-pressure inverted-force injection molding low pressure molding low-profile resin molding machining

male forming manifold molding manual extrusion manual molding manual processing marbleize molding Marco pressure molding Marco vacuum molding Marco vacuum-pressure molding matched die molding

mechanical clamping injection molding

melt lamination melt roll metal injection molding metallizing

metal powder injection molding

3 9 Fabricating product 1 3 5

Table 3~1 continued

metal powder molding plastic-metal molding rotational molding

microencapsulation polyurethane foam molding rotomold ovenless

molding with rotation poromeric molding rotovinyl sheet

melt processable rubber process post-consumer extrusion rubber insert molding

melt processable wood process post-consumer molding salt bath process (different types) metal-plastic molding post forming sandwich molding

molding (compression, injection, powder molding scrapless forming,

molecular density molding powder injection molding screw molding

multi-color injection molding preform molding screw plunger transfer molding

multi-component injection molding premolding Scorim molding

multi-compound molding prepolymer molding scrimp

multi-injection molding prepreg molding (different types) semiautomatic extrusion

multilayer blow molding press lamination semiautomatic molding

multilayer foam extrusion pressure bag molding semiautomatic processing

multilayer foam injection molding pressure fabrication sheet extrusion

multilayer solid-foam extrusion pressure forming sheet molding compound

multilayer solid-foam molding pressure lamination shell molding

multilayer solid e x t r u s i o n processing-artistic shrink wrap

multilayer solid m o l d i n g processing-basics shrink wrap bag processing

multilive feed molding profile extrusion shuttle forming

multi-material molding pullforming shuttle molding

multi-station forming pulp molding sintering

multi-station molding pulse molding skin molding

multiwall molding pultrusion molding skiving

netting pyrolysis carbon fiber spinning sliding insert molding

netting extrusion ram extrusion slip forming

non-porous metal-plastic molding ram injection molding slot extrusion

notched die molding ram molding slush molding

off-center injection molding rapid prototype m o l d i n g smart-card/closed-loop controlled offset extrusion radio frequency molding injection molding

offset molding reaction injection molding SMC continuous fiber molding

one-shot molding reactive polymer processing SMC directionally oriented

open molding recycled compound molding molding

orientaton process {different reinforced foam molding SMC randomly oriented molding types) reinforced plastics (different types) soluble core injection molding

oriented extrusion reinforced reaction injection soluble core molding

oriented molding reinforced reaction molding solvent bonding

oscillating die extrusion reinforced rotational molding solvent casting

overcoat extrusion resin transfer molding solvent molding

overcoat lamination rock-and-roll molding spin casting

overcoat molding roll covering spinneret fiber forming

packaging (different types) rolling spinning

parallel laminating roll milling spline process

pelletizing extrusion room temperature molding spraying (different types)

perforating rotary core molding spray-up molding

photopolymerization rotary molding spread coating

physical blow molding rotary table molding spreader molding

pinhold-free coating rotating die extrusion squeeze molding

pipe blow molding rotating mold turret injection stack blow molding

plastic-concrete process rotational casting stamping

Table 3ol continued

staple fiber spinning

steam chamber-filament spinning

stretch blow molding

strip molding

structural casting

structural foam molding

structural reaction injection

molding

stuffer injection molding

supperplastic forming

syntactic foaming

tape placement wrapped molding

tenter frame forming

thermal expansion molding

thermoforming (different types}

thick compound molding

thin-wall injection molding

thixomolding three-platen injection molding three-station molding toggle clamp injection molding tooling

torpedo molding transfer molding trickle impregnation tube extrusion tubing-heat shrinkable turnkey injection molding twin-sheet forming twin-sheet thermoforming (different types) two-color injection molding two-color molding two-platen clamp injection molding

two-stage injection molding two-station molding ultrasonic fabrication ultrasonic vacuum bag molding ultraviolet molding

vacuum bag molding vacuum casting vacuum coating vacuum forming

vacuum hot forming vacuum press molding vacuum pressure bag molding variable pressure foaming vented extrusion vented injection molding vertical extrusion vertical injection molding vertical wheel extrusion vertical wheel forming vertical wheel injection molding vibration gas injection molding vibration molding

vinyl dispersion vinyl plastisol forming viscous molding void-plastic impregnation vulcanization

waste molding welding wet layup molding wire coating wire coating extrusion wheel blow molding wood-plastic impregnation molding

wood pulp-plastic extrusion

The long list of methods used to process plastics in Table 3.1 includes all types of basic and specialty processes that have been developed over the past century Included are also those that have different names for the same process The different names arc used for diversified reasons that include:

1 used in different industries that have their method of identifying a process based on their market requirements,

2 an old process that may be basically the same or slightly modified requiting a more modern name,

3 promoting new ideas requiring a name to symbolize a ncw

generation, and others

There are overlapping of terms such as molds, dies, and tools and also tcrms such as molding, embedding, casting, potting, etc There are continuous and noncontinuous extrusion processing methods Injection molding includes gas and water injection, insert molding, micro- molding, etc This situation does not cause a problem or should not affect anyone's thinking when examining processes As one may rccognize throughout the world and particularly in the industrialized

3 9 Fabrieatincj product 1 3 7

nations, one might say that there are words or situations that could have more than one meaning The important message here is that it may be important for you to be very specific when describing a process (also materials, designs, and so on)

There are the major families of processing, based on the amount of plastic processed in USA and worldwide They are extrusion (EX) consumes approximately 36wt% of all plastics, injection molding (IM) follows by consuming 32%, blow molding at 10%, calendering at 8%, coating at 5%, compression molding at 3%, and others at 3% Thermoforming, can be considered the fourth major process used; consumes about 30% of the extruded sheet and film that principally goes into packaging

When analyzing processes to produce all types of products, at least 65wt% of all plastics require some type of specialized compounding They principally go through compounding extruders, usually twin- screw extruders (Chapter 5), before going through equipment such as injection molding machines, extruders, and blow molding machines to produce products

It is estimated that in USA there are about 17,000 extruders, 70,000 injection molding machines, and 6,000 blow molding machines producing about one-third of the world's plastic products For the 80,000 IMMs in USA the usual report shows that 30% are under five years old, at least 35% are five to ten years old, and the rest are more than ten years old

In USA machinery sales yearly demand normally is about $1.5 billion (not taking into account the depressed years that occur at least every 10

to 20 years IMM is the largest category that accounts for at least 50% of M1 the machinery sales Blow molding (extrusion and injection types) machines are now at about $505 million, extrusion reaches $440 million, and thermoforming reaches $455 million There are now over 350 USA machinery builders with about five having over 50% of sales 136-139

The plastics industry is comprised of mature practical and theoretical technology Improved understanding and control of materials and fabricating processes (Table 3.2) have significantly increased product performances and reduced their variability resulting in good to excellent return on investments ( R O I s ) 140

Plastic processes permit the fabrication of products whose manufacturing would be very costly or difficult if not impossible in other materials Processors must routinely keep up to date on developments with the more useful plastics and acquire additional information on how to process them The emphasis throughout this book has been that it is not difficult to design and fabricate with plastics

H ~ r ~ s

~ a

I / I

e-I {

3 9 Fabricating product 1 3 9

and to produce many different sizes and shapes of thermoplastic (TP) and thermoset (TS) commodities and engineering plastics, whether unreinforccd or reinforced The bases of material and process selection should be product performance requirements, shape, dimensional tolerances, processing characteristics, production volume, and cost 482 Extruders can be classified as:

1 continuous with single-screws (single and multistage) or multi-

screws (twin-screw, etc.),

2 continuous disk or drum that uses viscous drag melt actions (disk

pack, drum, etc.) or elastic melt actions (screwless, etc.), and

3 discontinuous that use ram actions [thermoset (TS) plastics,

rubbcrs/clastomers, and very low viscosity thermoplastics (TPs)]

and reciprocating actions (injection molding, etc.)

Injection molding (IM) is basically a discontinuous extruder It identifies

a process where a liquid or solid form of plastic is transferred into a mold or other tool in order to fabricate products This IM process has subdivisions that include conventional IM, foam IM, gas-assist IM, water-assist IM, coinjection molding, and continuous IM There arc other molding processes that have their specific names and very diversified methods of operation They include reaction injection molding (RIM), liquid injection molding (LIM), resin transfer molding (RTM), structural foam molding, expandable polystyrene molding, and liquid casting

There are differences in casting, encapsulation, and potting terms however they are often interchangeable; they interrelate very closely to describe processes and performances Both TPs and TSs are used As an example there are reactive TS liquids that are often used to form solid shapes Such plastic systems harden or cure at room temperature or at elevated temperatures because of the irreversible crosslinking of rather complex molecular structures This is different from the hardening of plastics in solution, which harden when the solvent is evaporated The hardening of the reactive plastics produces no by-products, such as gases, water, a n d / o r solvents When reactive plastics are used as impregnates, they are sometimes called solventless systems However, there are plastics and certain additives that release gases and may require degassing during processing

To help in quickly evaluating what machinery is available worldwide that will meet your requirements Plastics Technology publications has set up an online website (www.plasticstcchnology.com) This action follows their annual Processing Handbook and Buyers' Guide that has been published for many decades

Even though modern fabricating machines with all its ingenious microprocessor control technology is in principle suited to perform flcxible tasks, it nevertheless takes a whole series of peripheral auxiliary equipment to guarantee the necessary degree of flexibility (Chapter 18) Examples of this action includes:

1 raw material supply systems;

2 mold/die transport facilities;

3 mold/die preheating banks;

4 mold/die changing devices that includes rapid clamping and

coupling equipment;

5 plasticizer cylinder changing &vices;

6 fabricated product handling equipment, particularly robots with interchangeable arms allowing adaptation to various types of

production; and

7 transport systems for finished products and handling equipment to pass products on to subsequent production stages

Processing and patience

The startup of fabricating lines usually requires changing equipment settings When malting processing changes, allow enough time to achieve a steady state in the complete line before collecting data It may

be important to change one processing parameter at a time As an example with one change such as screw speed, temperature zone setting,

or another parameter, allow time to achieve a steady state prior to collecting data

A major cost advantage for fabricating plastic products in production has been and will continue to be their usual relatively low processing cost The most expensive part of practically all products is the cost of plastics Since the material value in a plastic product is roughly up to one-half (possibly up to 90%) of its overall cost, it becomes important

to select a candidate material with extraordinary care particularly on long production runs Cost to fabricate usually represents about 5% (usual maximum 10%) of total cost

For thosc bclicving plastics arc low cost, it is a misconception; they arc not There arc so-called low cost types (commodity types) when compared to the more expensive engineering types (Chapter 1) Important that one recognizes that it is economically possible to process a more expensive plastic bccausc it provides for a lower processing cost By far the real advantage to using plastics to produce many low-cost products is their low weight with their low processing costs