Other Molding Processes

Thermoformed products are used in various outdoor and commercial applications which require tough products that have a large surface area. Typically, these products do not have close dimensional tolerances. Such applications include ornamental pool liners, dumpster lids, panels for portable sanitation facilities, and agricultural feed troughs. These products, which are not required in very large numbers, could not be produced economically by other molding processes,... 

With the pressures in the mixing head at between 1,500 to 3,000 psi (10.3 to 20.6 MPa), the in-mold pressures are significantly lower than in many of the other molding processes. When comparing a typical RIM in-mold pressure of 50 to 150 psi (0.4 to 1.1 MPa) with the 5000 to 30,000 psi (34.5 to 206.7 MPa) required for thermoplastic injection molding (Chapter 4), it becomes apparent why RIM is particularly suitable for larger parts. Automotive bumpers are routinely produced on RIM presses with 100 to 150 tons of clamping force, while comparable injection molded parts require presses of 3500 tons or more. 

The reinforcement can be predesigned to meet performance shape requirements. The molder uses the prepreg in a compression mold or other molding process that will allow the required temperature (low to high) and pressure (low to high) conditions to be met, based on how the resin was compounded. With proper storage condition of temperature [at least about 21°C (70°F)], their shelf life can be controlled lasting at least 6 months. 

OTHER MOLDING PROCESSES 14.8.1 Reaction Injection Molding... 

Other mold-based SCP processes that have been iavestigated iaclude utilization of sulfite waste Hquor by I aecilomyces varioti conversion of carob bean waste yg Jispergillus niger com- and pea-processiag wastes by Giotrichium sp. and coffee-processiag wastes by Trichoderma har anum (62). However, none of these processes is practiced commercially. 

Vibr toiy Consolidation. Powders are vibrated in a mold or other container in which they will be sintered, or in a metal container that will be used for extmsion or other metalworking process (31). Vibratory consoHdation produces packings of UO2 particles up to 95% of theoretical density. 

Polymer-matrix materials include a wide range of specific materials. Perhaps the most commonly used polymer is epoxy. Other polymers include vinyl ester and polyester. Polymers can be either of the thermoset type, where cross-linking of polymer chains is irreversible, or of the thermoplastic type, where cross-linking does not take place but the matrix only hardens and can be softened and hardened repeatedly. For example, thermoplastics can be heated and reheated, as is essential to any injection-molding process. In contrast, thermosets do not melt upon reheating, so they cannot be injection molded. Polyimides have a higher temperature limit than epoxies (650°F versus 250°F or 350°F) (343°C versus 121°C or 177°C), but are much more brittle and considerably harder to process. 

A snap joint is economical in two respects it allows the structural member to be molded simultaneously with the molded product, and it allows rationalizing the assembly, compared with such other joining processes as screws. Table 3-4 provides a comparison of its advantages and disadvantages. Some examples of the various types and their design considerations are shown in Figs. 3-23 to 3-25. 

Many product designs are inherently limited by the economics of the process that must be used to make them. For example, to date TSs are not blow molded, and they have limited extrusion possibilities. Many hollow products, particularly very large ones, may be produced more economically by the rotational process than by blow molding. The need for a low quantity of products may eliminate certain molding processes and indicate the use of casting or others. 

One channel is made by KOH etching (in the framework of the above-mentioned technology steps), the other by a molding process using an PDMS mold and an epoxy cast. 

Describe both the extrusion blow molding and injection blow molding processes. Why would one method be chosen over the other ... 

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