Plastics, as materials of construction

The use of plastics as materials of construction has expanded rapidly in recent years and now they compete with metals, glass, and wood in many applications (see Table 1). The chemical structure of plastics is complicated, but most of them are polymers, that is they consist of large numbers of small, identical groups of atoms joined together to form one chain-like molecule. 

A wide range of rubbers are available for successful use as materials of construction and are applied in areas such as handling inorganic salt solutions where metals are unsuitable. The use of rubber linings is widespread in equipment such as tanks, pipes, and drums and most other critical chemical equipment. However, their use is limited to moderate temperatures, and they are generally suitable for use in abrasive duties. Some of the more commonly used plastics are PVC, PTFE and polypropylene. 

Glass, carbon, stoneware, brick, rubber, plastics, and wood are common examples of nonmetals used as materials of construction. Many of the nonmetals... 

The characteristic brittleness of unsaturated polyester resins was overcome by reinforcement with silane-treated fiber glass. While over 750 thousand tons of these reinforced plastics are produced annually in the U.S., the emphasis in this chapter will be on room temperature-curable-filled unsaturated polyester mortars or concrete. As discussed in Chapters 1 and 7, these anaerobic polyester mortars are widely used as materials of construction.—... 

Plastics have continued to play an important role as material of construction for parts in key industries such as automotive, aerospace, medical devices, consumer, electronic, and others. Fabrication processes, such as injection molding, are capable of producing complex shape parts. In spite of this adhesion of plastic surfaces to other plastics, elastomers, metals, and ceramics are still required to produce parts with intricate design. 

Reinforced plastics form an important area of structural application of plastics since the modulus and strength of plastics can be increased significantly through reinforcement. In reinforced plastics, the polymer (popularly called the resin) forms the matrix and a filler (mostly used in the form of fibers, hut particles, for example glass spheres, are also used) provides the reinforcing effect. In view of then-distinctive nature and extensive use as materials of construction in load-hearing applications, a special focus has been on analysis of properties of reinforced plastics, especially those reinforced by continuous or discontinuous fibers, as well as their deformation, fi-acture, fatigue, and impact behaviors. 

Materials of Construction and Operational Stress. Before a centrifugal separation device is chosen, the corrosive characteristics of the Hquid and soHds as weU as the cleaning and saniti2ing solutions must be deterrnined. A wide variety of materials may be used. Most centrifuges are austenitic stainless steels however, many are made of ordinary steel, mbber or plastic coated steel. Monel, HasteUoy, titanium, duplex stainless steel, and others. The solvents present and of course the temperature environment must be considered in elastomers and plastics, including composites. 

A development of interest to the chemical industiy is the tubular precipitator of reinforced-plastic construction (Wanner, Gas Cleaning Plant after T1O2 Rotary Kilns, technical bulletin, Lurgi Corp., Frankfurt, Germany, 1971). Tubes made of polyvinyl chloride plastic are reinforced on the outside with polyester-fiber glass. The use of modern economical materials of construction to replace high-maintenance materials such as lead has been long awaited for corrosive applications. 

CoiTosion prevention is achieved by correct choice of material of construction, by physical means (e.g. paints or metallic, porcelain, plastic or enamel linings or coatings) or by chemical means (e.g. alloying or coating). Some metals, e.g. aluminium, are rendered passive by the formation of an inert protective film. Alternatively a metal to be protected may be linked electrically to a more easily corroded metal, e.g. magnesium, to serve as a sacrificial anode. 

The materials of construction, from the cupboard to the fan, should be inorganic and resistant to attack by perchloric acid. For the cupboard itself suitable materials include stainless steel of types, 316 or 317, solid epoxy resin, and rigid PVC. Stainless steel has been popular for this application as it is easy to form, weld, and polish. It is, however, attacked by the acid, which causes discoloration of the metal surface and the formation of iron(III) perchlorate, which can be explosive. Ductwork, separate from other extract systems, is usually made from stainless steel or plastic materials. Fire regulations may preclude the use of plastic ductwork or require it to be sheathed in an outer casing of metal or GRP. The fan casing and impeller can both be made of plastic. 

The materials of construction are usually stainless steel as well as specific other metals that will draw into wire, or crimp without cracking. The wire mesh types have been fabricated of some plastics such as Teflon , polypropylene, etc. however, the surface must be wettable by the liquid, or the efficiency will be poor, and performance data are needed to complete a good design. 

There are plastics that have equal or less than those of other materials of construction (metals, glass, or wood). In fact with certain additives such as graphite powder contraction can occur rather than the expected expansion with the application of heat. However many plastics typically have coefficients that are considerably higher than those of other materials of construction such as metals. This difference may amount to a factor of 10 to 30. Also available are plastics, particularly TS-RPs, with practically no change. 

Design problems with the other conventional materials of construction are usually solved with the aid of textbooks or handbooks that refer the reader to data sheets where the characteristics of a specific material are listed. However, products designed with plastics involve some special considerations when using these textbooks or handbooks as reviewed in Chapter 2. 

A compromise among properties, cost, and manufacturing process generally determines the material of construction. Selecting a plastic is very similar to selecting a metal. Even within one class, plastics differ because of varying formulations, just as steel compositions vary (tool steel, stainless steel, etc.). There are, of course, products for which no plastics is satisfactory, and the interests of the producer and consumer alike are best served by using some other material. 

Lead was one of the traditional materials of construction for chemical plant but has now, due to its price, been largely replaced by other materials, particularly plastics. It is a soft, ductile material, and is mainly used in the form of sheets (as linings) or pipe. It has a good resistance to acids, particularly sulphuric. 

The shell of a rotary dryer is usually constructed by welding rolled plate, thick enough for the transmission of the torque required to cause rotation, and to support its own weight and the weight of material in the dryer. The shell is usually supported on large tyres which run on wide rollers, as shown in Figure 16.10, and although mild steel is the usual material of construction, alloy steels are used, and if necessary the shell may be coated with a plastics material to avoid contamination of the product. 

Reactivity with Common Materials — This is limited to hazardous reactions with fuels and with common materials of construction such as metal, wood, plastics, cement, and glass. The nature of the hazard, such as severe corrosion or formation of a flammable gas, is described for specific chemicals in Chapter 4. 

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