Resins case studies

Figure 13.12 Schematic of the channel depths for the original and modified screws for the PS resin case study...

In the second case study, variation tree analysis and the events and causal factors chart/root cause analysis method are applied to an incident in a resin plant. This case study illustrates the application of retrospective analysis methods to identify the imderlying causes of an incident and to prescribe remedial actions. This approach is one of the recommended strategies in the overall error management framework described in Chapter 8. 

This case study involved medical diagnostic parts manufactured from PC resin, which were beginning to break too easily. To determine the cause of the failure, a good sample was submitted for comparison to a cracked part. Two possible causes for the failures were postulated. These include brittleness due to an excess level of filler, or the presence of voids due to insufficient drying of the resin prior to molding. 

In the following sections, the instrumental features of direct mass spectrometry based techniques (DI-MS, DE-MS and DTMS) are presented, followed by a discussion of some mass spectra of standard compounds and reference materials. Finally, a series of case studies related to the presence of resinous materials in archaeological findings and works of art are reported and discussed. 

The following sections discuss in detail the Py-GC/MS of proteinaceous materials, oils and fats, and then briefly plant and animal resins, polysaccharide materials, and beeswax. Particular attention is given to the application of this analytical technique to characterise samples from works of art. At the end of the chapter four case studies are presented. 

For a specific resin, the shear stress at the interface depends on the temperature of the interface, pressure, and the sliding velocity, it also depends on resin type, additives and additive levels, and the rheological properties of the resin. Stresses at the interface and the coefficients of friction for numerous resins have been published previously from two sources, and the data can be found in the references [15-31]. Additional stress data are provided in Appendix A4 and in several of the case studies in Chapter 12. 

Several of the most commonly used resins were studied at a screw and barrel temperature of 35 °C. As previously discussed, this temperature condition is comparable to the conditions in the feed casing or Section 1. This is just the start of solids conveying as conveying continues into Section 2 where the inside barrel wall temperatures are considerably higher. In order to visualize the contrast between the six different polymers tested, the solids conveying rates as a function of discharge pressure for these select resins are presented in Fig. 5.14. 

Figure 9.1 Shear viscosity for the PE resin used in the scale-up case study...

The root cause of dark color streaks in gray-colored parts can sometimes be more difficult to determine since both poorly dispersed pigments and resin degradation products can be the source. In these cases, removing the color masterbatch from the process and operating with just the natural resin will allow the root cause to be identified. That Is, If the dark color streaks still occur in the product after the color masterbatch is removed, then the source of the problem is related to resin degradation. Two case studies are shown in Section 11.12 to illustrate these defects. 

Figure 11.16 Photographs of crosslinked gels in an LDPE resin film for the case study of Section 11.10.1...

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. 

Extrusion processes are often rate limited by motor power or torque, discharge temperature, or the melting capacity of the screw. Other root causes associated with the design of the screw can limit rates as shown in previous sections. The problems, however, are typically associated with other defects such as flow surging or resin degradation. Chapters 11 and 12 discuss process defects associated with resin degradation and flow surging, respectively. Rate limitations due to inadequate motor power and torque are common problems for commercial plants. Two case studies are presented in the next sections that show rate limitations due to the lack of torque and motor power. 

Blow-molding processes consists of five main operations plastication of the resin, formation of the parison, inflation of the parison, solidification of the part, and removal of the part from the tooling. The best process economics will occur with a part optimized for weight and a minimum cycle time. In order to have a minimum cycle time, the cooling operation must be the rate-limiting step. For the case study... 

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