Temporary protectives

The related 2-/-butyl derivative has also been prepared and used to advantage as a temporary protective group for the stereogenic center of amino acids during alkylations. ... 

Even today, msting of industrial plant and material is accepted by some as an inevitable operating expense. There is no necessity for this attitude, however, as the petroleum industry has evolved effective, easily applied temporary protectives against corrosion, which are well suited to the conditions met in practice. 

The development of products in these categories has been guided by known market demands and many manufacturers have made use of established specifications for temporary protectives. 

The distinction between a simple part and a complex assembly is an important factor in selecting a temporary protective. The solvent-containing protectives may not be suited to treating assemblies, because ... 

Vapor phase inhibitors These are used for the temporary protection of new plant in transit or prior to commissioning. Volatile corrosion inhibitors such as cyclohexylamine derivatives are used. The plant must be sealed or contained to prevent rapid loss of the inhibitor. Sachets of these materials are placed in packing cases. Papers impregnated with them are available for wrapping steel items. These inhibitors are used primarily to protect steel. 

The main function of most lubricants is to reduce friction and wear between moving surfaces and to abstract heat. They also have to remove debris from the contact area, e.g. combustion products in an engine cylinder, swarf in metal-cutting operations. Sometimes they have to protect the lubricated or adjacent parts against corrosion, but this is not a prime function of most lubricants. On the other hand, many lubricants do contain corrosion inhibitors and some lubricating oils, greases, mineral fluids and compounds are specially formulated to prevent the corrosion of machinery or machine parts, particularly when these components are in storage or transit. These temporary protectives are described in Section 17.3. 

For protection of engineering parts against fretting corrosion, on electrical cables and on printing cylinders. Temporary protection allied with lubrication is provided by immersion deposits of copper on steel wire. 

A characteristic of the group (a) of resins is that they air-dry solely by solvent evaporation and remain permanently solvent soluble. This fact, combined with the need to use strong solvents, makes brush application very difficult, but sprayed coats can be applied at intervals of one hour. A full vinyl system such as (o) possesses excellent chemical and water resistance. Many members of group (o) have very poor adhesion to metal, and have therefore been exploited as strip lacquers for temporary protection. Excellent adhesion is, however, obtained by initial application of an etching primer the best known of such primers comprises polyvinyl butyral, zinc tetroxy-chromate and phosphoric acid. 

There are many temporary protectives on the market and it would be impracticable to describe them individually. However, they may be classified according to the type of film formed, i.e. soft film, hard film and oil film the soft film may be further sub-divided into solvent-deposited thin film, hot-dip thick film, smearing and slushing types. All these types are removable with common petroleum solvents. There are also strippable types based on plastics (deposited by hot dipping or from solvents) or rubber latex (deposited from emulsions) these do not adhere to the metal surfaces and are removed by peeling. In addition there are volatile corrosion inhibitors (V.C.I.) consisting of substances, the vapour from which inhibits corrosion of ferrous metals. 

The types of temporary protectives in general use are given in Table 16.5. 

Temporary protectives against corrosion should be used only where removal is subsequently necessary for the fitting or the working of surfaces to which they are applied. 

Stroud, E. G. and Vernon, W. H. J., J. Appl. Chem., 2, 173 (1952)t Temporary Protection of Metal Surfaces Against Corrosion (During Transport and Storage), BS 1 133 Section 6 1965 (also deals extensively with testing)... 

Surface cleaning as a preparation for coatings is discussed in Sections 11.1 and 11.2. It is important to control degreasing baths to prevent accumulation of water and formation of corrosive products which will contaminate the atmosphere as well as the objects being degreased. In the case of tri-chlorethylene, stabilisers are added to prevent formation of hydrochloric acid Exclusion of dust is beneficial, and may necessitate filtering the air or use of a temporary protective. 

Copper alloys are particularly prone to attack by long-chain fatty acids which are often present in sealing compositions, temporary protectives and as trace additives in many plastics under acid conditions ester plasticisers may saponify in the presence of copper giving rapid corrosion of the copper and accelerating degradation of the polymer. 

A large amount of perishable food now travels by air. Since the cargo holds of airliners are not pressurized, the problem may be one of temporary protection against low temperatures, rather than of keeping the product cold. 

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