Injection molding products

Blow-molded products represent the biggest use of HDPE resins, at around 40%. Packaging appHcations account for by far the greatest share of this market. These include such products as botties (especially for milk, juice, and soap), housewares, toys, pails, dmms, and tanks. Expected aimual average growth rates for these appHcations are about 5—6%. Injection-molding products are the second largest appHcation, with approximately 20% of the HDPE market. These products include housewares, toys, food containers, pails, crates, and cases. 

Injection-Molded Products. Numerous housings, electrical enclosures, and cabinets are injection-molded from rigid PVC. These take advantage of PVC s outstanding UL flammabiUty ratings and easy mol ding into thin-waHed parts. PVC has developed melt flow capabiUties to the point where it competes with essentially any other flame-retarded engineering thermoplastic and molds easier than most. 

Fig. 2-62 Example of directional shrinkage in an injection molded product.

Generally, the more discussed and technically reviewed residual stresses are in injection molded products. It usually occurs because melt in the cavity next to the cavity is cold and does not properly flow. Cause could be the melt and/or the cavity surface was cold. Their presence can often be detected by... 

Many injection molded products will influence the final product s performance, dimensions, and other characteristics. The mold includes the cavity shape, gating, parting line, vents, undercuts, ribs, hinges, and so on (Table 3-17). The mold designer must take all these factors into account to eliminate problems. At times, to provide the best design... 

These cutting operations are usually used only for machined prototypes, or very low volume production of simple shapes. High speed routing is sometimes used for slotting or gate removal on injection molded products. Standard end mills (two-flute), cir-... 

Injection molding is a common process that we use to convert polymer granules to solid objects. Unlike the products made by continuous extrusion processes, discussed in Chapter 11, products made by injection molding are discrete objects, produced in individual mold cavities. We encounter injection molded products of all sorts in our daily lives, ranging from combs, bottle caps, and ballpoint pens to car steering wheels, camera bodies, and the keys on our computers. 

We will illustrate the wide range of injection molding products and process variations by discussing a few key examples. 

Injection molding is one of the most widespread methods used to make polymer products. A cursory look around our homes, schools, work places or cars suffices to find an abundance of injection molded products. One of the reasons that this conversion method is so popular is that it enables us to create complex shapes in a single fabrication process. 

Polyesters exhibit excellent high temperature strength and electrical properties making them a good choice for many demanding applications. They also are physiologically inert allowing them to be used in food contact applications. The two common polyesters, polyethylene terephthalate and polybutylene terephthalate, are both used in injection molded products. Polyethylene terephthalate is often used in both extrusion and blow molded processes also. 

Pigment powders continue to be used in thick-walled articles, such as extruded sheets, or hollow objects, or in injection-molded products although color concentrates are beginning to be more important even in these areas. 

Typical HDPE—blow-molded products bottles, cans, trays, drums, tanks, and pails injection-molded products housewares, toys, food containers, cases, pails, and crates films, pipes, bags, conduit, wire and cable coating, foam, insulation for coaxial and communication cables... 

While other organic esters are commercially available, namely cellulose butyrate and cellulose propionate, by far the most widely used is cellulose acetate, which is available as plastics, in films, sheets, fibers, and lacquers. Cellulose acetate is used in the manufacture of display packaging and as extruded film for decorative signs, and to coat a variety of fibers. Injected molded products include toothbrush handles, combs, and brushes. It is also used in lacquers and protective coatings for metal, glass, and paper. Cellulose acetate films are used in reverse osmosis to purify blood, fruit juices, and brackish water. Some eyeglass frames are... 

Analysis of the processes of polymerization revealed that the production volume of the ABS resin increases by shortening the processing time with a shorter reaction time, an increase in the rubber content of latex, a decrease in the rubber content of the final ABS injection molding products and extrusion products, or an increase in the total solid content of latex (9). 

Chlorinated vinyl chloride-based compositions composed from chlorinated poly(ethylene) and MMBS are suitable for injection molding products with good heat resistance, impact strength, mold-ability, and surface properties (20). 

Injection-molding products are the second largest application with approximately 20% of the HDPE market. These products includes housewares, toys, food containers, pails, crates, and cases... 

F. P. T. Baaijens, Calculation of Residual Stresses in Injection Molded Products, Rheol. Acta, 30, 284 (1991). 

There are far too many applications for injection molded products to thoroughly cover here. However, a few examples will help provide an idea of some of the important mold design and machining considerations. 

Even though it is possible to produce a seemingly countless number of products using conventional injection molding techniques, variations to this process open up even more opportunities. This section will cover some of the injection molding variations that are used to improve the properties, increase the production efficiency, and expand the usefulness of injection molded products. 

Kimura et al. [107] made a light resistant formulation of a block E-P copolymer by extruding it at 220 °C with Mg(OH)2, and 2-hydroxy-4-octoxybenzophenone. The injection molded product (at 800 kg cm pressure) shows fire retardation also due to MgO filler and the benzophenone derivative is an efficient UV absorber. 

Includes molded thermoplastics, and automotive and nonautomotive reaction injection molded products. 

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