Temporary materials, useful life

Because of their favourable cost-performance ratio, polyvinyl chloride (PVC) coated polyester (PET) fabric is the most common basic material used. It can be applied over the whole spectrum from small temporary to wide-span structures. With a top-coat that protects the PVC from soiling and early ageing, a life-span of up to 20-25 years can be obtained. PVC-PET composites are joined by high-frequency or hot wedge welding. With flame-retardant additives to the PVC coating, fire class B1 can be achieved. 

The useful life of a polymer has to be defined for conservation. Feller developed a rule of thumb for classifying materials by their photochemical stability, a useful tool that should inform aU stages in the conservation process, from planning to use (Table 2.4). In most fields, it is expected that a conservation treatment will have to be reversed in the future. For instance, picture varnishes have traditionally been replaced every 80-120 years and stained glass window installations every 2-300 years. It is likely that a material used for temporary fixing may never be entirely removed (Section 1.3). It is therefore necessary that even these have long-term stabihty. 

Variations in a produet s material properties, serviee loads, environment and use typieally lead to random failures over the most protraeted period of the produet s expeeted life-eyele. During the eonditions of use, environmental and serviee variations give rise to temporary overloads or transients eausing failures, although some failures are also eaused by human related events sueh as installation and operation errors rather than by any intrinsie property of the produet s eomponents (Klit et al., 1993). Variability, therefore, is also the souree of unreliability in a produet (Carter, 1997). However, it is evident that if produet reliability is determined during the design proeess, subsequent manufaeturing, assembly and delivery of the system will eertainly not improve upon this inherent reliability level (Kapur and Lamberson, 1977). 

They are extensively used for temporary cementation of crowns and as temporary filling materials because of their therapeutic action. It is claimed that when strengthened some can be used for permanent cementation or as an intermediate restoration, that is a restoration that has a life somewhat greater than a temporary filling material. 

Many cosmetics manufacturers have used the lower phthalates (diethyl phthalate, dimethyl and dibutyl phthalates) for many years as solvents and diluents in perfumes. On the whole, the cosmetic industry is able to innovate guickly because cosmetic products have a relatively short life cycle this provides short to medium-term opportunities to formulate out the problem ingredients in the next version of the product. Raw materials come at different costs and to reformulate-out chemicals of concern may result in a temporary increase in material cost. However, as more companies switch to alternatives, economies of scale are realised and the price will fall. ... 

Oils, greases or temporary corrosion preventives should not be used to prevent corrosion of coated components in storage, because such materials will decrease the wear life. 

Construction workers can t do their job without electricity. However, constant activity at a construction site makes it a particularly hazardous environment. Extension cords, temporary wiring panels, water hoses, materials laying around, and constant use of electric tools, make it extremely important that you are careful around electricity. Your life may depend on it. 

---