Material selection processing, importance

Of more importance to us in the materials selection processes is the availability of data upon which to base om decisions. The nature of the data needed in the early stages differs greatly in its level of precision and breadth from that needed in later... 

In most materials selection processes, it is virtually impossible to make materials choices independent of the product shape. This includes not only the macroscopic, or bulk, shape of the object such as hammer or pressure relief valve, but also the internal or microscopic shape, such as a honeycomb structure or a continuous-fiber-reinforced composite. Shape is so important because in order to achieve it, the material must be subjected to a specific processing step. In Chapter 7, we saw how even simple objects made from a single-phase metal alloy could be formed by multiple processes such as casting or forging, and how these processing steps can affect the ultimate properties of the material. As illustrated in Figure 8.6, function dictates the choice of... 

From the preceding descriptions of erosive wear, we see that fracture toughness and hardness are important parameters in the materials selection process. There is some... 

Mechanical Properties of Candidate Materials. The mechanical properties of enamel and dentin were presented earlier in Table 5.14. We will use these values as the basis for our material selection process. Of these properties, compressive strength is the most important. The candidate material should have a compressive strength at least that of enamel, which is about 384 MPa. 

It is important to recognize that the unique combination of property reqnirements in this case stndy will complicate the materials selection process. In particnlar, the criterion of biocompatibility, while grouped with the other secondary criteria, is important enongh to completely reject a candidate material if it is not met. As a resnlt, we mnst farther recognize that experimentation will be a critical part of this materials selection process and that substantial testing will be required before materials can be deemed acceptable or not. 

One of the primary variables which influences the recoveries of volatile flavor and aroma chemicals during spray drying is the wall material. Utilization of spray dried flavors in food systems presents further constraints on the wall material selection process. Of the food grade polymers available to the manufacturer of spray dried flavorings (i.e., gum acacia, lipophilic starches, maltodextrins, corn syrup solids), no single wall material exhibits the ideal traits deemed necessary for this economically important process. 

Materials selection process can be depicted in terms of Figure 1.40. Materials selection involves many factors that have to be optimized for a particular application. The foremost consideration is the cost of the material and its applicability in the environmental conditions so that integrity can be maintained during the lifetime of the equipment. When the material of construction is metallic in nature, the chemical composition and the mechanical properties of the metal are significant. Some of the important mechanical properties are hardness, creep, fatigue, stiffness, compression, shear, impact, tensile strength and wear. 

The procedure we have discussed is not a cook book process. Prior plant experience should always be an important part of the materials selection process. Common sense plays a key role in evaluating candidate materials. Time should be taken to determine the leeway provided by ease of maintenance, repairability, and sparing. In some cases, these considerations require upgrading of the materials or fabrication procedures (e.g., PWHT). In other cases, it may make sense to recom-... 

Selection of fluoropolymers is an integral part of the overall material selection process. This implies that all the available materials such metals, ceramics, and plastics are considered candidates for an application. The end user then considers these materials against established criteria such as required life, mean time between inspection (MTBI), ease of fabrication, frequency of inspection, extent of maintenance and, of course, capital cost. More often than not it is the initial capital cost, rather than the life cycle cost of equipment, that affects the decision made during the material selection step. However, the most important piece of data is the corrosion resistance of a material in the medium under consideration over the life of the equipment. This information is available in a different format for plastics than for metals. A comparison is appropriate. 

A pavement is a set of superimposed layers of imported materials (selected, processed unbound and bound materials) that are placed on the natural soil for the creation of a road. A pavement is a complex structure that has to accomplish various functions different from each other. 

Cite three criteria that are important in the materials selection process. 

Elimelech 2004 Religa et al. 2013 Simon et al. 2013). However, the deterioration of membrane structures due to the acidic or alkaline solution can greatly shorten the membrane lifespan. The ability of the polymeric membrane to withstand an extreme pH condition will definitely determine the life expectancy of the membrane in certain applications. In addition, fouling control of polymeric membranes, through either operating condition adjustment or membrane material selection, is important in order for the wider employment of NF processes to become feasible. 

To solve a flow problem or characterize a given fluid, an instmment must be carefully selected. Many commercial viscometers are available with a variety of geometries for wide viscosity ranges and shear rates (10,21,49). Rarely is it necessary to constmct an instmment. However, in choosing a commercial viscometer a number of criteria must be considered. Of great importance is the nature of the material to be tested, its viscosity, its elasticity, the temperature dependence of its viscosity, and other variables. The degree of accuracy and precision required, and whether the measurements are for quaUty control or research, must be considered. The viscometer must be matched to the materials and processes of interest otherwise, the results may be misleading. 

Proper material selection for chemical and process equipment is one of the first important problems encountered by the designer. Among the many parameters that must be considered are structural strength specifications, heat resistance, corrosion resistance, physical properties, fabrication characteristics, composition and structure of material and cost. 

This book is designed as a handy desk reference covering fundamental engineering principles of project planning schemes and layout, corrosion principles and materials properties of engineering importance. It is intended as a general source of typical materials property data, useful for first pass materials selection in process design problems. 

Although the source of raw materials may not be at the plant site, it is an e.xtremcly important factor in the ultimate location of the plant. Process development work and economic studies will indicate the minimum standards for raw materials selection. When these standards have been determined, all possible sources of acceptable raw materials can be located and a detailed analysis can proceed. 

Material and process interaction and their effects on the performance of plastic products are important factors for the designer to understand. It can result in design limitations such as a selected material meeting performance requirements but not pro-cessible by the desired method of fabrication. Most of the limitations that are reviewed in this book can be corrected and do not effect the product performances when qualified people handle the limitations. However they are presented to reduce or eliminate potential problems. 

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