Fabricating products common processes

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

The compounded rubber stock will be further processed for use. The process could be injection or transfer molding into a hot mold where it is cured. Tire curing bladders are made in this fashion. Extrusion of the rubber stock is used to make hose or tire treads and sidewalls. Another common process is calendaring, in which a fabric is passed through rolls where rubber is squeezed into the fabric to make fabric-reinforced rubber sheets for roofing membranes or body plies for tires. The actual construction of the final product can be quite complex. For example, a tire contains many different rubber components some of which are cord or fabric reinforced. All of... 

Another type of rubber that is used frequently is thermoplastic rubber. Components are fabricated in a process that is similar to that used for common hard plastics, such as polyethylene or polystyrene, but the final product is an elastic material with properties otherwise equivalent to those of thermoset rubbers. No chemical reactions are involved in the processing of a thermoplastic rubber. The fabrication process consists of heating the rubber compound until it liquefies, injecting the liquid into a mold, cooling the mold, and finally removing the closure from the mold. The process is reversible. Closures can be remelted and remolded into different shapes or sizes as desired. 

Because of their strong chemical bonds, bulk ceramics are most efficiently fabricated by means of densification of powders. The fabrication process involves two main stages (1) consolidation of the powder to form a porous, shaped article (the green body), also referred to as forming, and (2) heating of the shaped powder form to produce a dense article, referred to as firing or sintering. The final product commonly consists of a relatively dense polycrystal with some residual porosity (Fig. 1). The microstructure, which... 

Hand Lay-uplSpray up Spray up and open contact molding (hand lay-up) in one-sided molds is one of the cheapest and most common process for making fiber composite products. Typical products are boat hulls and decks, truck cabs and fenders. In a typical open mold application, the mold is first waxed and sprayed with gel coat and cured in a heated oven at about 49°C. In the spray up process, after the gel coat is cured, catalyzed resin (usually polyester or vinyl ester at 500-1,000 cP viscosity) is sprayed into the mold, along with chopped fiber. A secondary spray up layer imbeds the core between the laminates (sandwich construction). Then it is cured, cooled, and removed from the reusable mold. In hand layup processing, continuous fiber strand mat and other fabrics such as woven roving are manually placed in the mold. Each ply is sprayed with catalyzed resin (1,000-1,500 cP) and the resin is worked into the fiber with brush rollers to wet-out and compact the laminate. 

The reader should consider the individual plastic supplier as an excellent source of information on fabricating and finishing processes for specific types of plastic materials. Generally, this information is readily available because the plastic resin producers benefit by providing the most complete and up-to-date information on how their materials can reliably and economically produce commercial products. Because of the tremendous number of plastic materials available, their many forms, and the possible finishing and fabrication processes, it would be difficult to include comprehensive information covering all product possibilities in this chapter. Thus, this chapter is a guide that will help direct the reader to more complete information if required and provide sufficient information for most common complications. 

Application of flax fibre in textiles cover both the clothing and non-clothing sectors. Flax is a well-known textile raw material used for exclusive and healthy clothing, woven and knitted. The non-clothing textile sector covers mainly table, bed linen and curtain fabrics. Some textiles may need fire retardant treatment. Fortunately cellulosic fibres, contrary to common belief, are quite safe in this respect as compared to other polymers (Figs. 2.7 and 2.8). Flax production and processing is the source of valuable by-products such as seeds, shive and waste fibres. 

Up to 2000 chemicals are used in textile processing, many of them known to be harmful to human (and animal) health. Some of these chemicals evaporate, some are dissolved in treatment water which is discharged to our envirorunent, and some are residual in the fabric, to be brought into our homes (where, with use, tiny bits abrade and you ingest or otherwise breathe them in). A whole list of the most commonly used chemicals in fabric production are linked to human health problems that vary from annoying to profound. 

Texturing. The final step in olefin fiber production is texturing the method depends primarily on the appHcation. For carpet and upholstery, the fiber is usually bulked, a procedure in which fiber is deformed by hot air or steam jet turbulence in a no22le and deposited on a moving screen to cool. The fiber takes on a three-dimensional crimp that aids in developing bulk and coverage in the final fabric. Stuffer box crimping, a process in which heated tow is overfed into a restricted oudet box, imparts a two-dimensional sawtooth crimp commonly found in olefin staple used in carded nonwovens and upholstery yams. 

Sheet Drying. At a water content of ca 1.2—1.9 parts of water per part of fiber, additional water removal by mechanical means is not feasible and evaporative drying must be employed. This is at best an efficient but cosdy process and often is the production botdeneck of papermaking. The dryer section most commonly consists of a series of steam-heated cylinders. Alternate sides of the wet paper are exposed to the hot surface as the sheet passes from cylinder to cylinder. In most cases, except for heavy board, the sheet is held closely against the surface of the dryers by fabrics of carefuUy controUed permeabiHty to steam and air. Heat is transferred from the hot cylinder to the wet sheet, and water evaporates. The water vapor is removed by way of elaborate air systems. Most dryer sections are covered with hoods for coUection and handling of the air, and heat recovery is practiced in cold climates. The final moisture content of the dry sheet usually is 4—10 wt %. 

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

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