Plastic Product Material and Process Selection Handbook Part 17 potx

544 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. Pelletizer Die With these die-faced pelletizers the extrudate is cut on or near the die face by high-speed knives. There are different designs used that include: An extruder pumps melt through a straining head into the die. It passes through round holes in its die plate where a wet atmosphere exists. Upon exiting the plate, a spinning knife blade cuts the extru- date into pellets. The pellet/water slurry is pumped into a dryer where the pellets separate from the water. Water is reclaimed for repeat use. 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. Throughput rates are at least up to 50,000 lb/h (22,700 kg/h). Smaller units are economical to operate as low as 500 lb/h (227 kg/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 lb/h (45 to 590 kg/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 and/or water quenched, followed with drying if water is involved. Throughput is up to at least 15,000 lb/h (6810 kg/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. 17 9 Mold and die tooling 545 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 and/or 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 multi- manifold 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 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 and/or 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. 17 9 Mold and die tooling 547 ::: :.: ::.~_ ~.~ 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 per- formance 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 ~ ZZZ2 2 - 2 ; ~;222;2 2Z.Z.Z.;.2. .DD?L. 22 22.Z 2.222 Z.2222 222~ 222-2L~_ TZ ;[ 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. 336 548 Plastic Product Material and Process Selection Handbook 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 world- wide 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. 17 9 Mold and die tooling 549 Table 17~4 Rapid prototyping processes Manufacturer 3D Systems Inc., Valencia, CA, U.S.A. CMET, Japan SONY-Japan Synth- etic Rubber, Tokyo, Japan SPARX, Molndal, .~eden Stratasys Inc., Minneapolis, WI, U.S.A. Light Sculpting Inc., Milwaukee, WI, U.S.A. Mitsui Engr' & Shipbuilding Ltd., Tokyo, Japan Process name Stereo litho- graphy Appar- atus (SLA) Solid Object UV Plotter ( SOUP ) Solid Creater Hot Plot Fused Deposit- ion Modelling (FDM) LSI COLAMM Material & structure generation Photopolymer system; point-by-point irradiation with a HeCd resp. an argon ion laser Photopolymer system; point-by-point irradiation with an argon ion laser Photopolymer system; point-by-point irradiation 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 Photopolymer system; point-by-point irradiation with a HeCd laser 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, 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 552 Plastic Product Material and Process Selection Handbook 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 and/or 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, ultra- sonic 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 18 9 Auxiliary equipment 553 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. [...]... designed to cut plastic that eliminate or reduce the heating problem Some plastic materials machine much 568 Plastic Product Material and Process Selection Handbook easier and faster than others due to their physical and mechanical properties Generally, a high melting point, inherent lubricity, and good hardness and rigidity are factors that improve machinability Laser cutting is a fast growing process The...554 Plastic Product Material and Process Selection Handbook 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... 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... 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 558 Plastic Product Material and Process Selection Handbook 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... such as LDPE, HDPE, UHMWPE, and so on (Chapter 2) Smarter Plastic Another example of many developments is the new plastics being created by chemical engineering researchers at Rcnsselacr Polytechnic Institute, Troy, NY The target is to improve medical care and other 572 Plastic Product Material and Process Selection Handbook Table 19.1 Comparison of theoretically possible and actual experimental values... the plastic industry, with continual growth materialwise, processwise, and productwisc 53, 65,475 REFERENCES 1 Rosato, D V., Plastics Mechanical Engineering Design Handbook, Elsevier, 2003 2 Rosato, D V., Designing with Plastics, Kluwer, 2001 3 Rosato, D V., Injection Molding Handbook, 3rd Ed., Kluwer, 2000 4 Rosato, D V., Designing with Reinforced Composites, Hanser, 1997 5 Rosato, D V., 'Materials Selection. .. PVC, PC, etc.) cutting 566 Plastic Product Material and Process Selection Handbook characteristic will change, depending on the fillers and reinforcements used (Chapter 1) Elastic recovery occurs in plastics both during and after machining requiring provisions to be made in the tool geometry for sufficient clearance to allow for it This is due to the expansion of any compressed material due to elastic... 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. .. 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 556 Plastic Product Material and Process Selection Handbook airflow in a system, whether it is a vacuum or pressure system,... early 1990s for the high-speed bonding of thermoplastic parts, and has been used to assemble millions of telephones, etc The University licenses the technology to others for use in a wide range of commercial applications UMass-Lowell will also 574 Plastic Product Material and ProcessSelection Handbook commit resources to further develop the technology and incorporate it into the school's curriculum . 554 Plastic Product Material and Process Selection Handbook Material /product handling _ _ _ _ Z __~.__~Z Z.~ Z~ 7 ~ ~._Z _Z ~_~ J_._ Z Design of the raw material and fabricated product handling. product. 336 548 Plastic Product Material and Process Selection Handbook The technology of RT and RP provides a quick way timewise between design creativity ideas and the fabricated product. More. production line equipment. To save 558 Plastic Product Material and Process Selection Handbook valuable time and particularly machine downtime, quick changes with microprocessor control are used in