Choosing Materials for Instrument Manufacture: IMPORTANCE OF CORRECT CHOICE FOR SENSITIVE MECHANISMS

Probably the most popular view concerning corrosion is that its promotion is largely the result of atmospheric conditions and oxidation. Only too frequently is the fact ignored that treatments and processes are often a major cause of trouble developing. Again, the degree of corrosion which may cause trouble is quite relative and in many large and heavy equipments slight corrosion may in no way impair efficiency. On the other hand, in light electrical apparatus, particularly that concerned with the telecommunications industry and with accurate sensitive instruments, trouble can be caused by a very slight degree of corrosion which may not be readily visible. It is, of course, common practice to attempt to seal hermetically delicate equipment to prevent oxidation and corrosion occurring due to polluted atmospheres and relatively high humidity. Even so, no matter how effectively an instrument or equipment may be sealed hermetically, the absence of corrosion will, to a very great extent, depend upon the purity of the materials used, the processes to which the parts have been subjected, the standard of finish and the nature of the protective coatings. In this article it is proposed to discuss some aspects of the care required to prevent contamination of components and the standards of quality which must be imposed upon the materials used. This is necessary to ensure the absence of deleterious substances which, in the presence of moisture and with the possibility of a d.c. leak developing, may cause a degree of corrosion sufficient to cause breakdown or sufficient contact resistance to impair the functioning of the equipment.