Blower motor is reversed. Use of a pressure gauge or flowmeter is suggested. Proper rotation is that at which the highest flow is indicated.
The goal in some cases is precise uals. Once the machine is operating, the op- adherence to a control point. In other cases, erator methodically targets one change at a maintaining the temperature within compar- time to achieve maximum injection molding atively small range is all that is necessary efficiency.
This problem-solving ume, 3 a reduction of demolding time, and approach fits into the overall PC and fabri- 4 a shortening of transit time if additional cating interface. Such systems injection molding plant is influenced by consist mostly of control chains and circuitry 1 increased capital cost, 2 reduced per- that are often coupled in their functions, as sonnel costs due to fewer personnel required, well as the corresponding exchange of data. With automation, new the purpose of cost reduction by monitoring goals can be met through plant flexibility, quality and establishing high line efficiency, such as 1 improved delivery consistency, in addition to the reduction of raw mate- 2 greatest possible preparedness for meet- rial consumption and labor costs.
A control ing delivery dates, 3 large range of products, system contributes in different ways, partic- and 4 short job processing time. There are ularly in controlling the flow of plastic melt. Work environment changes oc- provement. The solutions, when intro- the injection molding machine, and 4 the ac- duced into practice, served first of all to cident risk situation. An evaluation of the uti- improve the product line in different manu- lization efficiency serves for assessing the cri- facturing plants.
However, initially these sys- teria that cannot be quantified in monetary tems established themselves in only relatively terms. An established utilization efficiency small niches of the commercial market. Later value can be taken as a decision aid, which in many more came aboard. The 1 production-cost reduction, 2 short job more you pay attention to details, the fewer processing time, 3 low expenditure on hassles you will get from the process.
If a pro- setup, 4 greatest possible preparedness cess has been running well, it will continue for meeting delivery dates, 5 large product running well unless a change occurs. Correct range, and 6 improved delivery consistency. That may In order to utilize the advantages of flexi- not be an easy task, but understanding your bly automated injection molding cells, a con- equipment, material, environment, and peo- siderably larger capital investment is nec- ple can make it possible.
This increases the investment risk, so that the Fine Tuning question of the profitability of such systems becomes more urgent. The IMM stops only in achieving high quality zero defects , 3 the event of a malfunction or if it is man- increasing productivity, and 4 minimizing ually interrupted. Machinery and mecha- cost. It does this in several ways, basically by nisms are self-controlled so that manual in- enabling the molder to fine-tune all the re- put is not necessary during operation.
The lationships that exist among the many ma- continuing development of more sophisti- chine settings and properties of the plastic cated processing equipment in turn allows melt. These systems, when properly used, the development of more integrated process- readily adapt to enhanced processing capa- ing equipment.
This action results in many bilities. Establishing the to manufacturing information by supervisors initial settings during startup can be inher- and management, and 5 process control and ently complex and time-consuming. Regard- process management. However, it Automation level The automation level is is evident that self-regulation of injection the degree to which a process operates au- molding can be effective only when the de- tomatically. The choice of level must take sign of the product and the mold are opti- into account the ability of the system to di- mized with the correct processing conditions.
Therefore, the efficient utilization of microprocessor control systems depends Automated vision Vision automation on the success of utilizing correct and opti- provides a means to achieve automatic mum programs with knowledgeable people equipment operation by adaptive part re- Chap. On the horizon is the potential for moval. It provides the capability of detecting fuzzy control to provide an important aid to a variety of part problems or defects by optimizing process control performance.
As critical part inspection. A semiautomatic machine will perform a complete cycle of programmed molding func- Molding Operations tions automatically and then stop. It will then require an operator to start another cycle The following modes of operations typify manually. Manual Automatic It is an operation in which each function A machine operating automatically will and the timing of each function is controlled perform a molding cycle where programmed manually by an operator.
As equipment to fabricate products namely the reviewed throughout this book, performance injection molding machine Chap. They usually require raw materials, Secondary additives, spare parts, molds, tools, molded products, and so on to be stored and handled After fabricating primary molded prod- safely and economically.
Various systems are ucts, secondary operations may be required available to meet different needs in ware- to produce the final finished product. These housing. They can implement schemes for operations can occur online or offline. They integrating the inward and outward flow of include any one or a combination of opera- goods, order picking and transportation, fac- tions such as the following: annealing to re- tory administration, and process control for lieve or remove residual stresses and strains , warehousing.
The type of There are basically three types of proces- operation to be used depends on the type of sor: captive, custom, and proprietary. As an example, decorating or bonding certain plastics is easy, while others require special surface treatments for those purposes Chap. Capfive Captive processors, also called captive fab- Purchasing and Handling Plastics ricators, are in-house facilities of companies that have acquired plastics processing equip- On the average, raw materials and their ment to make parts they need for the prod- handling services incur at least half of the uct they manufacture.
For example, a electri- costs in plastic injection molding. Wages, util- cal connector manufacturer may acquire an ities, overhead, and capital equipment costs IMM to produce connectors. All costs are important to Generally speaking, these manufacturers evaluate and justify. Nevertheless, economy product or process. Some manufacturers that and rationality are worthy aims when pur- run their own plastics fabricating lines will chasing equipment Chap.
The vendor may be a possible design minimum wall thicknesses of custom processor or have a captive operation products, do not overpack in cavity, etc. A problem with some ensure that material conforms to the required captive operations is that they do not keep up specification s. Action is usually required to with new developments, some of which may check materials received. They process plastics into products , honing loo , EDM , inspection or components used in other industries.
For tools loo , and so on. Custom processors typically have moldmaking and related programs is growing a close relationship with the companies for rapidly. As the industry continues to review whom they work.
They may be involved to the labor pool and come up short, and as un- varying degrees in the design of the product dergraduate institutions fight over a shrink- and the mold, they may have a voice in ma- ing market, education-and-industry partner- terial selection, and in general they assume ing is increasing in urgency.
As an example, responsibility for the work they turn out. They have little involvement in put able program that, in conjunction with the business of their customers. In effect, they other area schools, has provided local indus- just sell machine time. Proprietary Processor Certifications A proprietary operation is one where the processor makes a product for sale directly to National skills certification programs by the public or to other companies.
It usually different organizations are in existence has its own trade name. Action by the different organizations Training Programs continues to provide methods of improving these programs. Their ef- the plastics industries. The examination in- fective programs are based on well-planned cludes basic process control; prevention and services that involve properly supervised on- corrective action on primary and secondary the-job training and classroom instruction.
Manufacturing Corp. Skokie, IL. With new de- ricating many different plastic materials into velopments in equipment and materials, the many different products. Figures and processor is required to keep up to date and provide a summary of the interrela- determine when changes are to be made, tions of plastics, processing, and products taking advantage of the continuing new de- The different processes each have their velopments.
Factors such as energy conser- area of capabilities, at times competing. A technical duct growth. Long-fiber mate- cesses without the prohibitive economic bur- rials such as bulk molding compounds have den of trial-and-error innovation and process been used for about half a century using optimization. A gain in one area can com- economic and legal concerns Chaps. Cost problems are particularly acute other factors. However, with people work- when the technology that will be employed ing smarter, using the F A L L 0 approach is not fully understood and much of the Fig.
Because thermoplastic materials consist of individual molecules, properties of thermoplastics are largely influenced by molecular weight. For instance, increasing the molecular weight of a thermoplastic material increases its tensile strength, impact strength, and fatigue strength ability of a material to withstand constant stress.
Instead, many properties of thermosetting plastics are determined by adding different types and amounts of fillers and reinforcements, such as glass fibers. Thermoplastics may be grouped according to the arrangement of their molecules. Highly aligned molecules arrange themselves more compactly, resulting in a stronger plastic.
For example, molecules in nylon are highly aligned, making this thermoplastic extremely strong. The degree of alignment of the molecules also determines how transparent a plastic is.
Thermoplastics with highly aligned molecules scatter light, which makes these plastics appear opaque. Thermoplastics with semialigned molecules scatter some light, which makes most of these plastics appear translucent. Thermoplastics with random amorphous molecular arrangement do not scatter light and are clear.
Amorphous thermoplastics are used to make optical lenses, windshields, and other clear products. Air, heat, and molds are used to shape the plastic during its formation. Plastic is an increasingly popular manufacturing material because it is relatively durable, inexpensive, and versatile. Many different processes are used to make plastic products, and in each process, the plastic resin must be softened or sufficiently liquefied to be shaped. A Forming Thermoplastics How Thermoplastics are Formed Thermoplastics are plastics that can be hardened and melted more than once.
In the calendering process, continuous plastic sheets are formed by forcing hot plastic between successive sets of heated rollers. Injection molding uses a screw to push plastic through a heated tube into a mold. Extrusion is a continuous process that heats plastic pellets in a long barrel. A screw pushes the heated plastic through a die opening to form objects such as garden hose and piping.
In thermoforming a hot plastic sheet is draped over a mold and a vacuum draws the plastic down into the mold. Blow molding forms containers from soft, hollow plastic tubes that have a mold fitted around the outside. The tube is heated, and air injected into the heated tube expands the plastic against the walls of the mold. Although some processes are used to manufacture both thermoplastics and thermosetting plastics, certain processes are specific to forming thermoplastics.
For more information, see the Casting and Expansion Processes section of this article. The mold is then opened and the plastic cast removed.
Thermoplastic items made by injection molding include toys, combs, car grills, and various containers. A2 Extrusion Plastic Pellets and Extrusion Early in the manufacturing process, small pellets of nylon a synthetic resin are stirred and melted. Once melted, the blue plastic mixture will be forced into the desired shape in a process called extrusion. Extrusion is a continuous process, as opposed to all other plastic production processes, which start over at the beginning of the process after each new part is removed from the mold.
In the extrusion process, plastic pellets are first heated in a long barrel. In a manner similar to that of a pasta-making or sausage-stuffing machine, a rotating screw then forces the heated plastic through a die device used for forming material opening of the desired shape.
As the continuous plastic form emerges from the die opening, it is cooled and solidified, and the continuous plastic form is then cut to the desired length. Melted thermoplastic forced through extremely fine die holes can be cooled and woven into fabrics for clothes, curtains, and carpets.
A3 Blow Molding Blow molding is used to form bottles and other containers from soft, hollow thermoplastic tubes. First a mold is fitted around the outside of the softened thermoplastic tube, and then the tube is heated. Next, air is blown into the softened tube similar to inflating a balloon , which forces the outside of the softened tube to conform to the inside walls of the mold.
Once the plastic cools, the mold is opened and the newly molded container is removed. Blow molding is used to make many plastic containers, including soft-drink bottles, jars, detergent bottles, and storage drums. A4 Blow Film Extrusion Blow film extrusion is the process used to make plastic garbage bags and continuous sheets. This process works by extruding a hollow, sealed-end thermoplastic tube through a die opening. As the flattened plastic tube emerges from the die opening, air is blown inside the hollow tube to stretch and thin the tube like a balloon being inflated to the desired size and wall thickness.
The plastic is then air-cooled and pulled away on take-up rollers to a heat-sealing operation. The heat-sealer cuts and seals one end of the thinned, flattened thermoplastic tube, creating various bag lengths for products such as plastic grocery and garbage bags.
For sheeting flat film , the thinned plastic tube is slit along one side and opened to form a continuous sheet. The air inflates the plastic tube like a balloon, until a bag with the desired shape, size, and wall thickness is formed. A5 Calendering The calendering process forms continuous plastic sheets that are used to make flooring, wall siding, tape, and other products.
These plastic sheets are made by forcing hot thermoplastic resin between heated rollers called calenders. A series of secondary calenders further thins the plastic sheets.
Paper, cloth, and other plastics may be pressed between layers of calendered plastic to make items such as credit cards, playing cards, and wallpaper. Products made from thermoformed sheets include trays, signs, briefcase shells, refrigerator door liners, and packages.
In a vacuum-forming process, hot thermoplastic sheets are draped over a mold. Air is removed from between the mold and the hot plastic, which creates a vacuum that draws the plastic into the cavities of the mold. When the plastic cools, the molded product is removed.
In the pressure-forming process, compressed air is used to drive a hot plastic sheet into the cavities and depressions of a concave, or female, mold.
Vent holes in the bottom of the mold allow trapped air to escape. B Forming Thermosetting Plastics Thermosetting plastics are manufactured by several methods that use heat or pressure to induce polymer molecules to bond, or cross-link, into typically hard and durable products.
How Thermosetting Plastics are Formed Thermosetting plastics are plastics that cannot be remelted once they have hardened. Compression molding forms thermosetting plastic objects in a steel mold. When heat and pressure are applied, the softened plastic squeezes into all parts of the mold to form the desired shape. Laminating binds layers of materials together in a plastic matrix. The layers are fused when heated plates melt the plastic and squeeze the material together.
First, thermosetting resin is placed into a steel mold. The application of heat and pressure, which accelerate cross-linking of the resin, softens the material and squeezes it into all parts of the mold to form the desired shape.
Once the material has cooled and hardened, the newly formed object is removed from the mold. This process creates hard, heat-resistant plastic products, including dinnerware, telephones, television set frames, and electrical parts.
B2 Laminating The laminating process binds layers of materials, such as textiles and paper, together in a plastic matrix. This process is similar to the process of joining sheets of wood to make plywood. Resin-impregnated layers of textiles or paper are stacked on hot plates, then squeezed and fused together by heat and pressure, which causes the polymer molecules to cross-link. The best-known laminate trade name is Formica, which is a product consisting of resin-impregnated layers of paper with decorative patterns such as wood grain, marble, and colored designs.
Formica is often used as a surface finish for furniture, and kitchen and bathroom countertops. Thermosetting resins known as melamine and phenolic resins form the plastic matrix for Formica and other laminates.
Electric circuit boards are also laminated from resin-impregnated paper, fabric, and glass fibers. B3 Reaction Injection Molding RIM Strong, sizable, and durable plastic products such as automobile body panels, skis, and business machine housings are formed by reaction injection molding. In this process, liquid thermosetting resin is combined with a curing agent a chemical that causes the polymer molecules to cross-link and injected into a mold.
Most products made by reaction injection molding are made from polyurethane. How Both Types of Plastics are Formed Both types of plastic, thermoplastics and thermosetting plastics, can be formed through casting and expansion processes. Casting forms plastic objects in a mold. After the plastic is poured in the mold, additives mixed into the plastic cause the resin to harden. Expansion processes inject gases into the plastic melt, creating a foam plastic from the tiny bubbles trapped inside.
Styrofoam contains a chemical that produces gas as it is heated. As the styrofoam cools and hardens, tiny bubbles left inside the material from the gas create a foam plastic. C1 Casting The casting process is similar to that of molding plaster or cement. Fluid thermosetting or thermoplastic resin is poured into a mold, and additives cause the resin to solidify. Photographic film is made by pouring a fluid solution of resin onto a highly polished metal belt.
A thin plastic film remains as the solution evaporates. The casting process is also used to make furniture parts, tabletops, sinks, and acrylic window sheets. As the resin cools, tiny bubbles of gas are trapped inside, forming a cellular plastic structure.
This process is used to make foam products such as cushions, pillows, sponges, egg cartons, and polystyrene cups. Foam plastics can be classified according to their bubble, or cell, structure. Sponges and carpet pads are examples of open-celled foam plastics, in which the bubbles are interconnected.
Flotation devices are examples of closed-celled foam plastics, in which the bubbles are sealed like tiny balloons. Foam plastics can also be classified by density ratio of plastic to cells , by the type of plastic resin used, and by flexibility rigid or flexible foam.
For example, rigid, closed-celled polyurethane plastics make excellent insulation for refrigerators and freezers. These plastics have a spectrum of properties that are derived from their chemical compositions. As a result, manufactured plastics can be used in applications ranging from contact lenses to jet body components. A Thermoplastics Thermoplastic materials are in high demand because they can be repeatedly softened and remolded.
The most commonly manufactured thermoplastics are presented in this section in order of decreasing volume of production. Polyethylene, with the chemical formula [-CH2-CH2-]n where n denotes that the chemical formula inside the brackets repeats itself to form the plastic molecule is made in low- and high-density forms.
Low-density polyethylene LDPE has a density ranging from 0. The molecules of LDPE have a carbon backbone with side groups of four to six carbon atoms attached randomly along the main backbone. LDPE is the most widely used of all plastics, because it is inexpensive, flexible, extremely tough, and chemical-resistant.
LDPE is molded into bottles, garment bags, frozen food packages, and plastic toys. High-density polyethylene HDPE has a density that ranges from 0. Its molecules have an extremely long carbon backbone with no side groups. As a result, these molecules align into more compact arrangements, accounting for the higher density of HDPE. HDPE is stiffer, stronger, and less translucent than low-density polyethylene. HDPE is formed into grocery bags, car fuel tanks, packaging, and piping.
PVC is the most widely used of the amorphous plastics. PVC is lightweight, durable, and waterproof. Chlorine atoms bonded to the carbon backbone of its molecules give PVC its hard and flame-resistant properties. In its rigid form, PVC is weather-resistant and is extruded into pipe, house siding, and gutters.
Rigid PVC is also blow molded into clear bottles and is used to form other consumer products, including compact discs and computer casings. PVC can be softened with certain chemicals. This softened form of PVC is used to make shrink-wrap, food packaging, rainwear, shoe soles, shampoo containers, floor tile, gloves, upholstery, and other products. Most softened PVC plastic products are manufactured by extrusion, injection molding, or casting.
Because the most common form of polypropylene has the methyl groups all on one side of the carbon backbone, polypropylene molecules tend to be highly aligned and compact, giving this thermoplastic the properties of durability and chemical resistance.
Many polypropylene products, such as rope, fiber, luggage, carpet, and packaging film, are formed by injection molding. The random attachment of benzene prevents the molecules from becoming highly aligned. As a result, polystyrene is an amorphous, transparent, and somewhat brittle plastic. Polystyrene is widely used because of its rigidity and superior insulation properties. Polystyrene can undergo all thermoplastic processes to form products such as toys, utensils, display boxes, model aircraft kits, and ballpoint pen barrels.
Plastic bottle manufacturers generally use one of four types of plastic to create bottles. Typically, the plastic bottles used to hold potable water and other drinks are made from polyethylene terephthalate PET , because the material is both strong and light. Polyethylene PE in its high-density form is used for making rigid plastic bottles such as detergent bottles and in its low-density form for making squeeze bottles. Polypropylene PP is used for pill bottles and the like.
Polycarbonate PC is used for refillable water bottles and similar reusable containers. To understand the manufacturing process, it is helpful to first examine the compositions of the materials they're made from. You can also learn more about how glass bottles are made and types of glass bottles in our other guides. We'll be examining how each material affects the bottle manufacturing process below.
Polyethylene Terephthalate is a thermoplastic polymer that can be either opaque or transparent, depending on the exact material composition. As with most plastics, PET is produced from petroleum hydrocarbons, through a reaction between ethylene glycol and terephthalic acid. Polymerization itself can be a complicated process and accounts for many of the inconsistencies between one batch of manufactured PET and another. Typically, two kinds of impurities are produced during polymerization: diethylene glycol and acetaldehyde.
Although diethylene glycol is generally not produced in high enough amounts to affect PET, acetaldehyde can not only be produced during polymerization but also during the bottle manufacturing process.
A large amount of acetaldehyde in PET used for bottle manufacturing can give the beverage inside an odd taste. Once the plastic itself has been manufactured, the PET bottle manufacturing process can begin.
To ensure that the plastic is appropriate for use, numerous tests are done post-manufacturing to check that the bottles are impermeable by carbon dioxide which is important for bottles that carry soda. Other factors, such as transparency, gloss, shatter resistance, thickness, and pressure resistance, are also carefully monitored.
For more information about PET, please see our polyester resins article. Another thermoplastic, polyethylene is used for manufacturing blow-molded milk and water jugs, detergent bottles, ketchup bottles, spray bottles , and other products. LDPE was one of the first plastics to be blow molded and today it is still used for making squeezable bottles, as it has high ductility compared with HDPE, but lower strength.
HDPE is used for many forms of pourable bottles. The material in its natural form is usually white or black and becomes translucent when thinned to the dimensions of milk bottles and the like.
Suppliers can adjust formulation to increase tear strength, transparency, formability, printability, or other parameters. Polyethylene is composed of a single monomer, ethylene, making it a homopolymer. Polyethylene is more expensive than polypropylene — the cheapest of the thermoplastics — though the two share many applications. For more information about HDPE, please see our polyethylene resins article. Polypropylene resin is a usually opaque, low-density polymer with excellent thermoforming and injection molding characteristics.
For bottles , It competes primarily against polyethylene and can be made transparent for see-through applications, while polyethylene can only be made translucent, as in milk jugs, for example. Polypropylene cannot match the optical clarity of polymers such as polycarbonate, but it does quite well.
Its low viscosity at melt temperatures makes it well suited to extrusion and molding applications, including blow molding.
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