Reinforced plastics conventional

DynaWave equipment is typicaUy smaller than conventional equipment and is usuaUy made of fiber glass reinforced plastic (ERP) at considerable capital savings over conventional materials. DynaWave is now in use at a number of plants worldwide. 

A wide variety of thermoplastics have been used as the base for reinforced plastics. These include polypropylene, nylon, styrene-based materials, thermoplastic polyesters, acetal, polycarbonate, polysulphone, etc. The choice of a reinforced thermoplastic depends on a wide range of factors which includes the nature of the application, the service environment and costs. In many cases conventional thermoplastic processing techniques can be used to produce moulded articles (see Chapter 4). Some typical properties of fibre reinforced nylon are given in Table 3.2. 

Conventional machining operations are used preferably from the same plastic to be used in the product (Chapter 8, SECONDARY EQUIPMENT). Different casting techniques are used that provide low cost even though they are usually labor intensive. The casting of unfilled or filled/reinforced plastic used include TS polyurethane, epoxy, structural foam, and RTV silicone. Also used are die cast metals. 

A further difficulty with the basic materials is that they do not lend themselves readily to simple concepts and to simple comparisons. The matrix components are essentially the same plastics as those used for conventional reinforced plastic laminates. Epoxy plastics are more widely used than others, although phenolics and silicones give structures with higher temperature properties. Thermoset polyesters are used for many commercial structures in which cost is a problem and high temperatures do not prevail. 

Conventional polypropylene is an appropriate container material for cylindrical VRLA cells because the necessary contact force for the glass-mat separator is supplied by the winding and maintained by a tensile force in the cell wall. Regardless of the nominal voltage, and therefore the number of cells, prismatic VRLA batteries require a reinforced plastic for the container and the lid to provide an AGM contact force and to keep the active-material compressed [42-44]. 

The simplest typa of fixed bed is shown in Fig. 13.3-3 which is illustrative of a mudem large plnot for water purification. The vessel is of a conventional dished-end pressure construction with supports and an access manhole. Construction malaria Is for the vessel are umally mild steel with a lining of rubber or plastic. Susnless steel is sometimes used and smaller vessels are made of reinforced plastic. The depth of settled resin bed is seldom more then about 1 m but the vessel must allow freaboard of about another meter above the upper surface of resin for expansion during fluidization to clenn ntbhish out of the bed. 

A concept of a composite LH2 container has been developed in Canada where the outer shell is fabricated from fiber reinforced plastics. The tank volume is 60 m. Such vessels of which a first set has been manufactured already, are to be used for the transportation of smaller amounts of LH2 onboard conventional container ships, railway carriers, or as a storage medium near power or refueling stations [34, 35]. 

Polymer matrix composites (PMCs), or fiber-reinforced plastics (FRPs). provide a wide range of properties and behavior. Materials with discontinuous fibers are slightly stiffer than conventional unreinforced plastics, whereas the fully aligned continuous fiber systems can record exceptionally high specific properties (property divided by density), exeeeding those of competing materials such as steel and aluminum. There are a virtually infinite number of materials, and material formats that can be combined to form a composite material, as shown in Table 1. 

Braids Is used to give high strength three-dimensional (3-D) reinforcement, incorporating more than one type of fiber, if required. Conventional woven fabrics are limited to providing reinforcement at orthogonal orientations, but many reinforced plastics structures are loaded in non-orthogonal fashion. Woven fabrics are, therefore, not necessarily mechanically efficient. 

Table 10.1 Examples of the more conventional reinforced plastics... 

Outdoor use means exposure to several influences simultaneously ultraviolet light, fluctuating temperatures, wind and moisture. If the article is buried in the soil, there may be microbiological activity, but this will not usually be a problem with the materials used in conventional reinforced plastics. 

For such critical applications, moisture uptake at high humidities can lead to changes in physical properties that are vitally important, especially as service temperatures varying between -30°C and +110°C can be encountered. Much study has been devoted to this (e.g. Wright [32] and Eckstein [33]). Water diffuses into even the most resistant resin, especially if the surface is damaged by weathering. It both plasticizes and swells the resin and reduces the bond between it and the reinforcement. For conventional epoxy resins, for each 1 % water pickup, decreases by about 20°C [32,35]. Eckstein [33] examined 70 different epoxy resin formulations and found... 

A very important feature of PLCs has been already mentimied in Section 41.1.4 thermotropic PLCs are often processable with conventional processing equipment for thermoplastics— in fact, given the orientation of LC sequences, more easily than thermoplastics. It is this ease of orientatiOTi which is the reason for one more name for PLCs, already mentioned above, namely self-reinforcing plastics. 

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