Injection molded parts

How does the type and level of tacticity of the polypropylene chain affect the degree of crystallinity of the solid polymer  

Which crystalline form of polypropylene exhibits the lowest free energy of crystallization Which form exhibits the highest  

Compare and contrast the slurry, gas phase, solution and liquid propylene polymerization methods, 

How do metallocene catalysts define the molecular weight distribution and tacticity of polypropylene  

Oriented polypropylene is used for clear films used as food wrap. What advantageous properties do the oriented films have over standard films How can a polymer that is, typically semicrystalline be transparent  

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Fabrication. Acetal resins are most commonly fabricated by injection mol ding. A homogeneous melt is essential for optimum appearance and for performance of injection molded parts. A screw compression ratio of no less than 3 1 is advised and the size of the injection molded shot should be 50 to 75% of the rated capacity (based on polystyrene) of the barrel. 

By the 1950s P/M parts were used in postage meters and home appHances. In the 1970s P/M superaHoys for aerospace appHcations were used, followed by steel P/M forgings. The 1980s opened the way for rapid soHdification processing, P/M tool steels, and metal injection molded parts. 

The injection mol ding process eliminates the restriction of straight-sided components required when parts are ejected from a die, and offers opportunities for external undercuts and threads. A wide variety of alloys can be processed, including alloy steels and stainless steels. Material properties of injection molded parts are available (32). 

Materials Standardsfor Metal Injection Molded Parts, Metal Powder Industries Federation, Princeton, N.J. 

Design Considerations for Injection Molded Parts (Parting lines, draft angles, wall thickness, fillets and radii, bosses, ribs, opening formations, shrinkage, gating, vents, potential knit lines)... 

What causes polypropylene injection molded parts to be susceptible to warpage upon cooling How can this issue be addressed during the manufacture of these parts ... 

Polyethylene terephthalate is most often extruded into films or fibers, or blow molded into bottles. Polybutylene terephthalate is primarily found in injection molded parts. Such parts are highly crystalline, which makes them opaque. Polybutylene terephthalate is often modified with glass fibers or impact modifiers. Table 24.1 contains applications by processing method and resin. 

Contents Introduction to Materials. Manufacturing Considerations for Injection Molded Parts. The Design Process and Material Selection. Structural Design Considerations. Prototyping and Experimental Stress Analysis. Assembly of Injection Molded Plastic Parts. Conversion Constants. 

A number of organic pigments can cause warping of certain thick-walled, large-area, non-axially symmetrical injection-molded parts such as bottle crates, where they act as nucleating agents for partially crystalline polymers. 

Figure 17.2 Applications of DuPonT BIOMAX hydrobiodegradable polyester -film, rigid containers, fibers, injection molded parts and paper coatings. Photograph reproduced by permission of DuPonT1...

Recently, the telecommunication industry has undergone rapid expansion, and a strong consumer trend towards smaller and lighter telecommunication devices, such as cellular phones and notebook computers, is indicated. Small connection sockets and chip carriers are micro-injection-molded parts requiring the high flowability, high mechanical properties and dimensional stability of LCPs. These merits are now thought to be another application field for LCPs in the electronics industry. 

As shown by Fig. 3.11 for an applied force, the creep strain is increasing at a decreasing rate with time because the elongation of the spring is approaching the force produced by the stress. The shape of the curve up to the maximum strain is due to the interaction of the viscosity and modulus. When the stress is removed at the maximum strain, the strain decreases exponentially until at an infinite time it will again be zero. The second half of this process is often modeled as creep recovery in extruded or injection-molded parts after they cool. The creep recovery usually results in undesirable dimensional changes observed in the cooled solid with time. 

Tobin, W.J., Troubleshooting Injection-Molded Parts, WJT Associates, Louisviiie, CO (1996)... 

Many of the contamination defects that typically occur in extrusion processes can also occur in injection-molded parts. The most obvious defects are caused by foreign material contamination, resin degradation, and surface defects known as splay. The next sections provide case studies where contamination caused defects in injection-molded parts. 

Splay is a common term for surface imperfections that occur on injection-molded parts. Like the term gels for films, splay can occur from several root causes. Many of the root causes originate from the plasticating system and are related to moisture in... 

Figure 11.27 Photographs for surface defects in an ABS injection-molded part a) surface photograph, and b) cross-sectional view showing a void just under the surface (photographs courtesy of James T. Seliskar of The Dow Chemical Company)...

Several case studies are presented in the next sections that show some common root causes of contamination in injection-molded parts. In these case studies, the problem is presented in a manner that the troubleshooter would encounter during a trial or information-gathering session. In each case study, the modifications required to fix the process are detailed along with supporting fundamental information. Two of the case studies used (ET) screws to eliminate the defects. ET screws and other high-performance screws will be discussed in Chapter 14. 

Injection-Molded Parts with Splay and Poor Resin Color Purge... 

Salamon, B.A., Koppi, K.A., and Little, J., Halo Surface Defects on Injection-Molded Parts, SPE ANTEC Tech. Papers, 44, 515 (1998)... 

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