Plastic Product Material and Process Selection Handbook Part 17 potx

5 4 4 Plastic Product Material and Process Selection Handbook time when the melt extrudes through the orifice and the slits overlap, a crossing point is formed where the emerging threads

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5 4 4 Plastic Product Material and Process Selection Handbook

time when the melt extrudes through the orifice and the slits overlap, a crossing point is formed where the emerging threads appear to be welded but it is a uniform melt flow through the matching/aligned slits For flat netting, the sliding action is in opposite direction

Mechanical movement action in a die is used to extrude these different profiles such as tubing or strapping with varying wall thicknesses or perforated wall It is usually accomplished by converting rotary motion

to a linear motion that is used to move or oscillate the mandrel For certain profiles, such as the perforated tubing, the orifice exit would include a perforated section usually on the mandrel

Very popular are the wet-cut underwater pelletizer The die face is submerged in a water housing and the pellets are water quenched followed with a drying cycle T h r o u g h p u t rates are at least up to 50,000 l b / h (22,700 k g / h ) Smaller units are economical to operate as low as 500 l b / h (227 k g / h )

The water-spray pelletizer, with a rotating knife, uses a water-jet-spray cooling action as pellets are thrown into a water slurry Throughput is about 100 to 1300 l b / h (45 to 590 k g / h )

The hot-cut pelletizer has melt going through a multi-hole die plate

A multi-blade cutter slices the plastic in a dry atmosphere and hurls the pellets away from the die at a high speed Usually the cutter is mounted above the die so that each blade passes separately across the die face and only one blade at a time contacts the die Pellets are then air a n d / o r water quenched, followed with drying if water is involved Throughput is up to at least 15,000 l b / h (6810 k g / h ) The water-ring unit has melt extruded through a die plate and cut into pellets by a concentric rotating knife assembly Pellets are thrown into a rotating ring of water inside a large hood After cooling in the water, they are spirally conveyed to a water-separated and then to a drying operation

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17 9 Mold and die tooling 5 4 5

With the rotating-die unit, a rotating hollow die and stationary knife is used The die, which looks like a hollow slice from a cylinder, has holes on its periphery; melt is fed into the die under minimal pressure and centrifugal force generated by the die rotation causes the melt to extrude through the holes Pellets cut as each strand passes a stationary knife arc flung through a cooling water spray into a drying receiver

Coextrusion Die

Coextrusion can be performed with flat, tubular, and different shaped dies The simplest application is to nest mandrels and support them with spiders or supply the plastic through circular manifolds a n d / o r multiple ports Up to 8-layer spiral mandrel blown film dies have been built that rcquire eight separate spiral flow passages with the attendant problem of structural rigidity, interlayer temperature control, gauge control, and cleaning Many techniques arc available for cocxtrusion, some of them patented and available under license (Chapter 5)

For flat dics there arc basically the fccdblock (single manifold) or the adapter (multimanifold) dies with a third system that combines the two basic systems This third system provides processing alternatives as the complcxitics of cocxtrusion increases The feedblock method combines several monolaycr manifolds in a common body creating a multimanifold fccdblock die Each manifold processes a distinct layer of product until thc flows from all manifolds arc merged into a singlc multilaycr flow and extruded from a set of common lips With the single manifold die the plastics meet (combine surface to surface) and spread to a given web width 143

There arc dies with at least 115 layers of coextrudcd plastics that have been produced (Chapter 5) Mechanical movement action converting rotary motion to a linear motion is used to move or oscillate the mandrel in a die Result is to extrude different profiles such as tubing or strapping with varying wall thicknesses or perforated wall This Dow patented process generates hundreds of layers, each one thinner than the wavelength of light 2~ The tubing die generates a large number of layers by rotation of annular die boundaries

It can bc accomplished by a novel cocxtruded blown film (or flat film) die Product produccs iridescent effects simply by taking advantage of some basic optical principles Alternating layers of two plastics, such as

PE and PP, with at least 115 (and many more) produce an extruded film 0.5rail (0.013 mm) thick Individual plastic components arc forced through a fecdport system into a die in alternating layers extending radially across the annular gap [Figure 17.14) Simultaneously rotation

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546 Plastic Product Material and Process Selection Handbook

of the dies inner mandrel and outer ring, deform the layers into long thin spirals around the annulus

Figure 17.14 Examples of layer plastics based on four modes of die rotation

The increased intcrfacial surface area related to rotational speed multiplies the number of layers Overall the number of layers and layer thickness is determined by the dimensions of the annulus, the number of feed ports for each phase, the extrusion rate, and the rotational speed of the die mandrel and ring relative to the feed ports The resulting four basic layer patterns are generated by four modes of the die rotation Case 1 has the inner die mandrel rotating while the outer ring is stationary where layers are thicker near the outer ring Case 2 has the inner die mandrel stationary while the outer ring rotates with layers thinner near the outer ring In Case

3 both inner and outer die members rotate at the same speed and direction; the result is that layers of curved open-end loops and thicker layers are in the center Case 4 has inner and outer die members counter- rotating at equal speed generating the maximum number of symmetrical layers with the thickest in the center All these examples have layers that are concentric The deformation is usually so large that the spiral characteristic

is indistinguishable when examining the extrudate in the cross section

Computer

The use of computers has become part of the lifeline in producing dies and other tools and products via its displays a n d / o r developing physical prototypes Creating physical models can be time-consuming and provide limited evaluation, however they can be less expensive By employing kinematic (branch of dynamics that deals with aspects of motion apart from considerations of mass and force) and dynamic analyses on a design within the computer, time is saved and often the result of the analysis is more useful than experimental results from physical prototypes Physical prototyping often requires a great deal of manual work, not only to create the parts of the model, but also to assemble them and apply the instrumentation needed as well

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CAD (computer-aided design) prototyping uses ldnematic and dynamic analytical methods to perform many of the same tests on a model The inherent advantage of CAD prototyping is that it allows the engineer to fine-tune the design before a physical prototype is created When the prototype is eventually fabricated, the designer is likely to have better information with which to actually create and test the prototype model Engineers perform kinematic and dynamic analyses on a CAD prototype because a well-designed simulation leads to information that can be used

to modify design parameters and characteristics that might not have otherwise been considered 1 Kinematic and dynamic analysis methods apply the laws of physics to a computerized model in order to analyze the motions within the system and evaluate the overall interaction and performance of the system as a whole It allows the engineer to overload forces on the model as well as change location of the forces Because the model can be reconstructed in an instant, the engineer can take advantage of the destructive testing data Physical prototypes would have

to be fabricated and reconstructed every time the test was repeated There are situations in which physical prototypes must be constructed, but those situations can often be made more efficient and informative by the application of CAD prototyping analyses

CAD prototyping employs computer-aided testing (CAT) so that progressive design changes can be incorporated quickly and efficiently into the prototype model Tests can be performed on the system or its parts in a way that might not be possible in a laboratory setting It can also apply forces to the design that would be impossible to apply in the laboratory 332-334

Tooling and prototyping

~ Z Z Z 2 2 - 2 ; ~;222;2 2 Z Z Z ; 2 .DD?L 22 22.Z 2.222 Z 2 2 2 2 2 2 2 ~ 2 2 2 - 2 L ~ _ T Z ;[ Z Rapid tooling (mold and die) and product rapid prototyping provides reducing development cyclcs Rapid tooling (RT) and rapid prototyping (RP) is any method or technology that enables one to produce a tool or product quickly The term rapid tooling refers to RT- driven tooling A prototype is a 3-D model suitable for usc in the preliminary testing and evaluation of a mold, die or product It provides a means to evaluate the tool's or product's processing performances before going into production The ideal situation is for the prototype to bc the actual tool made in production However, tcchniqucs such as machining stock material to using RT or RP methods, can make prototypes for preliminary or final evaluation prior

to manufacturing the tool or product 336

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The technology of RT and RP provides a quick way timewise between design creativity ideas and the fabricated product More precision tooling and prototype materials continue to become available with system speeds keep increasing The plastics and other industries arc actively engaged in using these rapid systems As an example the USA international space agencies arc experimenting with RP to quickly replace parts in space vehicles 337

Various methods are used Two prime groups exist that arc identified as indirect (or transfer) and direct The indirect methods involve the use

of a master pattern from which the tool is produced Reduction in time

to produce tools, repeatability, meeting tight dimensions, and other factors influence the use of direct methods Ultimately, companies want

to produce the molds directly, although most of the direct tooling methods are not without limitations Many different companies worldwide are actively pursuing RT approaches and eliminating or decreasing limitations

Indirect tooling methods are many Examples include cast aluminum, investment metal cast, cast plastics, cast kirksite, sprayed steel, spin- castings, plaster casting, clcctroforming, room temperature vulcanizing (RTV) silicone elastomer (Chapter 2 Silicone Elastomer), elastomer/ rubber, reaction injection, stereolithography, 338-344 (Table 17.4), direct metal laser sintcring, and laminate construction

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Material & structure generation

Photopolymer system; point-by-point irradiation

with a HeCd resp an argon ion laser

with an argon ion laser

Self-adhesive film; cutting of the films

layer by layer with a thermal electrode

Thermoplastic filaments (PA, etc.)as well as

wax; melting the plastic in a mini extruder

Photopolymer system; irradiation of the entire

surface with a UV lamp

with a HeCd laser

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AUXILIARY EClUIPMENT

Introduction

Within the plastics industry an important part is the machinery auxiliary sector also called secondary sector To provide the millions of plastic products used worldwide many different fabricating lines are used These lines have primary and auxiliary equipment Primary equipment refers to the machine that fabricates a product such as an injection molding machine, extruder, blow molder, thermoformcr, etc (Chapters

4 to 17) Auxiliary equipment (AE) supports the primary equipment This type equipment is required in order to produce products that fit into the overall manufacturing cycle There arc many different types supporting non-automated to automated upstream and downstream production in-line or off-line systems maximizing the overall processing efficiency of productivity and reducing operating cost Examples of this equipment have been reviewed throughout this book This chapter provides an overview to this very large market (Figures 18.1 and

18.2).345-351

A few of the many AE are accumulator, assembly, blender, bonding, chemical etching chiller, cooling, computer, flash remover, conveyer, cutter, decorating, dicer, die heater, dryer, dust recovery, engraving, fabricating, fastening, feeding, finishing, gauging, granulator, 47~ grinder, heater, instrumentation, joining, knitting, labeling, leak detector, loading, machining, material handling, measuring, metering, mixer, mold extractor, mold heat/chiller, monitoring, part handling, pclletizcr, plating, polishing, primary machine component, printing, process control for individual or complete line, pulverizing, purging, quick mold or die changer, recycling system, robotic handler, 177 router, saw, scrap reclaimed, screen changer, screw/barrel backup, scaling, separator, sensor/monitor control, shredder, software, solvent recovery,

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18 Auxiliary equipment 551

Figure 18ol Examples of plant layout with extrusion and injection molding primary and

auxiliary equipment

Figure 18,2 Example of an extrusion laminator with auxiliary equipment

solvent treater, statistical process controller, statistical quality controller, storage, take-off equipment, testing equipment, trimmer, vacuum debulking, vacuum storage, water-jet cutting, welding, and others

AE can sometimes cost more than the primary equipment It is important to properly determine requirements and ensure that the AE

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interface into the line (size, capacity, speed, etc.) otherwise many costly problems can develop They have become more energy-efficient, reliable, and cost-effective The application of microprocessor- and computer-compatible controls that can communicate with the line (train) results in pinpoint control of the line A set of rules have been developed and used by equipment manufacturers that help govern the communication protocol and transfer of data between primary and auxiliary equipment

Ideally, fabricating thermoplastic (TP) or thermoset (TS) plastic products will be finished as processed For example almost any type of texture, surface finish, or insert can be fabricated into the product, as can almost any geometric shape, hole, or projection There are situations, however, where it is not possible, practical, or economical to have every feature in the finished product Typical examples where machining might be required are certain undercuts, complicated side coring, or places where parting line or weld line irregularity is unaccept- able Another common machining/finishing operation with plastics is the removal of the remnant of the flash, sprue a n d / o r gate if it is in an appearance area or critical tolerance region of the part

These secondary operations can occur in-line or off-line They include any one or a combination of operations such as machining, annealing (to relieve or remove residual stresses and strains), post-curing (to improve performance), plating, joining and assembling (adhesive, ultrasonic welding, vibration welding, heat welding, etc.), cutting, finishing, polishing, labeling, and decorating/printing The type of operation to

be used depends on the type plastic used As an example with decorating

or bonding, certain plastics can be easily handled while others require special surface treatments to produce acceptable products

Heat sealing is usually applied to the joining of pliable plastics sheet (less than 50 mils thick) and is limited to use on thermoplastic materials The heat may be provided by thermal, electrical, or sonic energy A wide variety of heat sealing systems are available

Plastic sections, which are too thick to be heat-sealed, may usually be welded There are three major methods in commercial use; heat, solvent, and ultrasonic In general, these methods are limited to use with thermoplastic materials These welding techniques have done much to lower the total cost of using plastics in the construction and other industries

In addition to the various welding techniques, adhesives may join plastic parts Both thermoplastic and thermosetting resins may be bonded and parts made of different resins are often treated in this

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18 9 Auxiliary equipment 5 5 3

manner There is a wide range of suitable adhesive materials including various monomers, solvents, and epoxies that are in general commercial use The exact material chosen will be a function of the plastic materials

to be joined and the environmental and end use conditions to which the finished part will be subjected

The increasing use of plastics as construction materials has led to a renewed interest in decorative finishes for plastic products There are a wide variety of secondary operations that can be used for adding decoration to molded parts Progress is also being made in providing decorative surfaces in the mold itself The first use of this is in wood- like panels for wall decoration and furniture parts such as cabinet doors Plastics may be printed upon, painted by a variety of processes, wood- grained by essentially a printing process, electroplated, metallized, and hot stamped with gold or silver leaf Plastic film and sheeting are generally printed or embossed in order to get decorative surfaces Printing is also used in the mass production of such plastic articles as labels, signs, and advertising displays

There has been increasing interest in the process of electro-plating plastics Plating can produce chromelike, brass, silver, gold, or copper surfaces in both smooth and textured forms There are several systems available commercially for plating plastic materials In the case of certain plastics such as electroplated ABS, it can be surface-treated chemically

to promote bonding of the metals in subsequent steps

This action eliminates the need for a costly mechanical roughening process that most other materials require The depositing of a metal surface on plastic parts can increase environmental resistance of the part, also its mechanical properties and appearance As an example a plated ABS part (total thickness of plate 0.015 in.) exhibited a 16% increase in tensile strength, a 100% increase in tensile modulus, a 200% increase in flexural modulus, a 30% increase in Izod impact strength, and a 12% increase in deflection temperature Tests on outdoor aged samples showed complete retention of physical properties after six months

It is possible for plated plastics to corrode if the metal coating is not properly applied or if it is damaged in such a way as to allow electrolytic interaction in the plating layers However, the plastic substrate will not corrode itself, nor will it contribute to further corrosion of the plating layers In general, plated plastics will fare better than metals when exposed to corrosive environments

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Material/product handling

_ _ _ _ Z _ _ ~ _ _ ~ Z Z ~ Z ~ 7 ~ ~ _ Z _ Z ~ _ ~ J _ _ Z

Design of the raw material and fabricated product handling system has

a major impact on the plant's manufacturing costs and housekeeping It

is based on the different materials used, annual volume of each material, number of different colors, production run lengths, etc A properly designed pneumatic system generates plastic velocities of at least

5000 f t / m i n ( 1500 m / m i n )

Material handling can start with delivery of bulk plastic to the plant that can be by trucks or rail cars Trucks typically carry 1,250 ft 3 (36 m 3) of material Most often the truck has a positive displacement-pumping unit or the user supplies a pressure system to the silos Rail cars can store up to 5,200 ft a (148 m 3) in 4 or 5 compartments with user providing unloading systems to the silos Unloading costs are largely determined by the throughput required

Plastics may be supplied in different quantifies There are drums [from

15 lb (6.8 kg)], bags [50 lb (23 kg)], gaylords [cardboard box usually lined with plastic sheet holding 1,000 lb (454 kg)], or bulk fabric sack bags [also called super sacks, super bags, or jumbo bags holding 2,000 lb (908 kg)] that bulk because of low volume usage, costs, moisture situation, etc To move materials from these containers systems rquires: vacuum tube conveyors, dumper and pressure unloader, or fork truck hoist, etc Plastic storage box containers are also used rather than bags or drums Box sizes and weights vary and conform to a standard size pallet

on which they arc shipped and moved in the plant

Bulk density of material influences solids conveying and processing plastic It is the weight of a unit volume of the material including the air voids The actual material density is defined as the weight of unit volume of the plastic, excluding the air voids

If the bulk density is more than 50% of the actual density, the bulk material likely will be reasonably easy to convey in a material handling system and through a plasticator (Chapter 3) With bulk density less than 50% of the actual density, then solids conveying problems are likely

to occur in a material handling system and through a plasticator When the bulk density becomes less than 30% of the actual density, a conventional plasticator usually cannot handle the bulk material Such materials may require special feeding devices, such as crammer feeders

or special extruder design, for example a large-diameter feed section tapering down to a smaller diameter metering section

Different methods arc used to move plastic that range from manual methods to full automation for raw material to fabricated parts Use

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18 9 Auxiliary equipment 5 5 5

includes automatic bulk systems, in-line granulators, parts removal robots, conveyors, stackers or orienters, etc The equipment chosen must match the productivity requirement of the line

When conveying plastics a properly designed system is to take the shortest distance The shortest distance between two points is a straight line The maximum conveying distance is usually 800 equivalent ft (244 m) A gradual upward slope is never better than a vertical lift When the plastic passes through a 45 ~ or 60 ~ elbow, it ricochets back and forth creating turbulence that destroys its momentum

With vacuum/pressure the conveying action provides double the conveying rates of vacuum alone Plastic lines are not recommended for conveying lines since static electricity will be generated and will interfere with the movement of plastics A rather simple and useful test

to determine if material is going to be difficult to convey can be used Take a handful of the plastic and squeeze it firmly Upon opening your hand, if the lines in your palm are filled with fines, it will be difficult

Fines are very small particles, usually under 200 mesh, accompanying larger forms of powders When plastics are extruded and pelletized, varying amounts of oversized pellets and strands are produced, along with fines When the plastics are dewatered/dried or pneumatically conveyed, more fines, fluff, and streamers may be generated They can develop when granulating plastics Usually they are detrimental during processing so they are removed or action is taken to eliminate the problem during pelletizing, grinding scrap, etc

In addition to conveying plastic, there is a wide variety of tasks for warehousing such as storing raw materials, additives, auxiliary equipment, spare parts, molds, dies, tools, processed plastic parts, etc They require handling and storage procedures that are logged economically Various systems are used successfully such as the unit warehouse that makes use of pallets, cages, and similar equipment It employs a certain organizational scheme for integrating order picldng and transportation The system is perfected by integration of the inward and outward flow (input-output matrix) of goods, the factory administration, process control, quality control, etc

Various properties and characteristics of materials used in the plastics industry that can be conveyed pneumatically affect the sizing and design

of the conveying system As an example the specific gravity is an aid in determining how much airflow is needed to lift a particle in an air stream Particle size is also a consideration in pneumatic conveying systems The material has to be tested to determine the amount of fines and dust that may be contained in the material This will help determine the type of

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airflow in a system, whether it is a vacuum or pressure system, along with the type of filters that will be utilized in the system Particle size is measured by using sieves that are made to standards set by the American Society of Testing Materials of the U.S Standards Institute The melting point of a material should be determined There are plastic materials that melt at low temperatures If these materials are conveyed

at a faster rate than necessary, they may slide against the walls of the conveying tubes or, more commonly, collect in a bend, and heat up by friction, which in turn will cause them to begin to melt, producing what is called angel hair This thin plastic will partially peel away from the wall as the pellet moves back toward the center of the air stream, leaving what appears to be a fine hair If enough of this occurs with other pellets in a particular area in a system, the angel hair will clog the system, thus preventing material from flowing

Materials that are abrasive may cause the conveying tubes to wear through quicldy Abrasive materials may have to be conveyed through- resistant material or at a lower rate than other materials

Very few plastics have a corrosive characteristic that may contain acids and erode tubing An acid content test can be conducted by determining their p H factor A p H of 7 is neutral Any reading below 7 is an indication of acid A p H reading above 7 would indicate that the material is alkaline Powdered materials with strong acid indications will have to be conveyed through special pneumatic systems in order to prevent any corrosion from taking place within the system

Control feeding devices to the hopper of primary equipment (injection molding, extrusion, etc.) is important to provide products that meet performance requirements at the lowest cost Equipment manufacturers have increased the feeding accuracy using different devices such as microprocessor blender/mixer controllers Also materials are being reduced in size with more uniformity to significantly improve uniformity in melt Processors can use blenders and other devices mounted on hoppers that target for precise and even distribution of materials

Hoppers are receptacles on the machines which direct the plastic materials (pellets, granules, flakes, etc.) being fed into the plasticators The hopper can be fitted with devices to perform different functions

As an example they can be fitted with a hinged or tightly fitted sliding cover and a magnetic screen for protection against moisture pick-up and metal ingress It is usually advisable to install a hopper drier, especially when processing certain materials such as hygroscopic plastics, regrind, and colors 3s2, 3s3 It can be of value in limiting material handling, as wcll as removing moisture

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18 Auxiliary equipment 557

There arc different equipment designs used for dispensing, metering, and mixing that use volume and the more popular/useful/cost saving gravimctcr/wcight blenders located over the feed hopper Included can bc motor-driven augers and vibrators as wcH as air-driven valves to process materials such as flakes, powders, granular material, liquids, and pellets

Plastic usage for a given process should be measured so as to determine how much plastic should be loaded into the hopper The hopper should hold enough plastic for possibly 1/2 to 1 hour's production This action

is taken so as to prevent storage in the hopper for any length of time

Processing TPs when compared to TS plastics is relatively easy Free- flowing TS molding compounds in pellet forms based on plastics such

as phenolic, melamine, or urea can be metered from a hopper just like TP pellets However doughy-bulk TS polyester and vinyl ester compounds, such as bulk molding compound (BMC), require force- feeding There are basically two ways of feeding these materials to the plastication unit, namely, the batchwise stuffer screw or continuous screw stuffer techniques These types of materials are principally used in injection molding machines

Different methods for handling and moving molded products are used The type employed depends on factors such as the fabricating equipment being used, size and shape of products, setting up for secondary operations, quantity of products, system for warehousing, and system for packaging and shipping to a customer Automating products/parts removal and other downstream operations reduces processing costs and increases profitability Automatic parts handling devices can be divided into two categories: the take-out with transfer mechanism or gravity systems that receive ejected parts from a mold and robots that perform machine tending and a variety of downstream handling tasks

Robots replicate in various degrees the actions of the human arm and hand When used for parts removal, they reach into the mold, grasp parts, remove parts and runners from the mold, and transfer them to the next stage of downstream operations For simple applications such

as machine tending, plastics processors use non-servo robots, in which positioning and speed are controlled mechanically and sequence of movement is determined by a robot controller For more complex downstream functions such as sophisticated parts orientation, secondary trimming, hot stamping, packaging, etc., they use full servo robots, in which position, speed, and sequence are computer-controlled with a feedback closed loop

Quick and cfficient approach is used to move and handle molds, dies, plasticators, and other parts of the production line equipment To save

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valuable time and particularly machine downtime, quick changes with microprocessor control are used in certain plants replacing manual mold changes

Figure 18.3 is an extrusion line schematic drawing of tension control equipment for the unwinding substrate The arrows indicate the motions of the driven tension control rolls and idlers as well as the substratc, and the direction of outward pressure-on the rolls Figure 18.4 is what is called a flying splice on a double-station-unrolling stand where:

1 In the starting position, the substrate is fed into the coater from the old roll A over a bumper roll

2 The old roll A that will soon be fully unrolled is moved forward, and a new roll B moves onto the stand where the old roll was before

Adhesive is applied along roll B near the beginning of the substrate web The driving tings are moved, located below roll B, against the roll that starts revolving until it has reached the required surface speed

Roll B is moved forward until it contacts the bumper roll Since now both rolls A and B rotate, substrate from both rolls is bonded together

For a very short time, the double substrate layer is fed into the coater The moment the substrate from roll B has caught on, a cut-off knife immediately moves into position against the substratc In the mean- time, the driving rings arc removed away from roll B All the steps described under d must occur almost simultaneously, taking no more than a few seconds

Figure 1 8 3 Examples of tension control rollers in a film, sheet, or coating line

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F i g u r e 1 8 4 Example 3f roll-charge sea er, ce wir, der [ecurtes¥ of Black Cl~wson]

" T O R O L L -

CHANGE POSITION

&

A

" A " SPINDLE WiTH

L A Y ~ N ROLL

&

d

UT AND TRANSFER

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There are many hundreds of different winders and rolls used in extrusion film and sheet lines There are those used for adhesive bonding, ultrasonically sealing a decorative pattern, reducing wrinkles

of web using a herringbone idler roll, matted and unmated embossing rolls, dancer roll controlling web tension, turret wind-up reel change system, sheet roll stock winder with triple fixed shafts, blown film line going through control rolls and dual wind-up turrets, and so on

Throughputs of winders can be over 2,200 l b / h (1,000 k g / h ) Transfers from one roll to another can take less then a second Material speeds are

up to at least 2,200 f t / m i n in cast film lines; at least 999 f t / m i n in blown film lines Blown film lines may want to use reverse winding systems to allow coextruded films to be wound with a particular material as the inside or outside layer

Their weights can be very low to at least 16,000 lb Diameters are at least up to 60 in and widths at least up to 30 ft Some rolls require roundness and surface finishes to be within 0.00005 in (0.00127 ram) Many winders offer sophisticated features and are highly automated, but some are designed to answer the need for simplicity, versatility, and economy There are surface winders with gap-winding ability for processing tacky films such as EVAs (ethylene vinyl alcohols) and the metallocene plastics Information on these different types of rolls is provided in Table 18.1

Decorating

An important area in fabricating products is the finishing or decorating

of plastics It is usually performed during fabrication or can be performed after fabrication Included are many different methods of adding either decorative a n d / o r functional surface effects such as printed information to a plastic product Plastics, of course, arc unique

in that color and decorative effects can be added to plastics prior to and during manufacturing Pigments and dyes, for example, are compounded into the plastic before they arc processed so that color is part of a plastic product and can be continuous throughout the product or just on the surface

Plastic parts can be post-finished in a number of ways Film and sheet can be post-embossed with textures and letterpress, gravure, or silk screening can print them Rigid plastic molded parts can be painted or they can be given a metallic surface by such techniques as metallizing, barrel plating, or electroplating Another popular method is hot

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