Coatings also

Commercial Availability All of the many types of coaters and dryers discussed herein are commercially available from many different vendors. These vendors usually have pilot faciUties so that new coating and drying techniques can be easily tested. Contract coating companies, specialising only in coating, also exist. 

The thickness of the coating also affects permeability, and in general, there is a correlation between thickness and life. However, with relatively thick coatings as obtained with some modern materials such as epoxies the relationship is not so well established. There may be a limiting thickness above which either little additional protection is obtained or the increase in cohesive strength reduces its adhesive strength. Coatings should always be applied as closely as possible to the manufacturer s recommended thickness. 

Up to 750°C, the performance of all aluminium diffusion coatings is considered to be very good, but above this temperature the results appear to be dependent on the coating thickness, diffusion treatment and the specific service environment. Sprayed aluminium coatings can be used up to 900°C after diffusion treatment. Hot-dipped coatings also benefit from additional diffusion treatment, and omission of silicon from the coating alloy improves performance at the elevated temperatures. 

Aluminium coatings also provide a suitable key or pretreatment for subsequent coatings, e.g. aluminised steel provides a good base for vitreous enamel. 

The hot-dipped coatings are distinct from the others in having practical thickness limits and in possessing an inner layer of intermetallic compound, usually described as the alloy layer. The flow-melted electrodeposited coatings also have an alloy layer, which is somewhat thinner than that obtained in hot dipping. 

Heat- and light-separation coatings (also known as hot and cold mirrors) are important applications that separate the hot (infrared) from the cold (visible) radiation. The principle is shown schematically inFig. 16.2. The transmittance of a cold mirror is shown in Fig. 16.3a. This mirror is coated with a dielectric film reflecting more than 90% of the... 

The semi-fuse thus produced is waterproofed by passing through troughs of molten bitumen or by coating also with plastic.For higher grade safety fuse, a further countering of textile, such as cotton, is followed by a final varnish, which may be coloured for identification purposes. 

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