Soldering

SOLDERING, the joining of two or more pieces of metal by means of a layer of a more fusible metal, which, solidifying between the surfaces to be joined, firmly connects them. The surfaces to be soldered are first cleaned mechanically and fitted together; after this, to avoid the formation during soldering of oxides, soot, and the like, they are covered with special substances, so-called "fluxes" or "fusible metals"; the metals used for soldering are called "solders". Depending on their melting point, the latter are divided into soft and hard solders. The composition of fluxes and solders varies. For soft solders, fluxes containing a large proportion of zinc chloride are used, while for hard solders, borax (melting point = 740°) is the flux. Soft solders always contain lead and tin in various proportions, most often in a ratio of 1 part tin to 2 parts lead (tin and sheet metal work) or 2 parts tin to 3 parts lead (for soldering lead), or 1 part tin to 3 parts lead (for casting gas and water-pipe systems). Hard solders, which contain alloys of the most diverse metals (copper, zinc, silver, brass, aluminum, etc.), rarely contain lead. Soldering is performed: with soft solders using a soldering iron and a soldering lamp (gas, kerosene, alcohol); with hard solders by heating in furnaces equipped with blowers; for small work, instead of furnaces, a soldering tube (fever) is used, into which the worker blows, directing air through the narrow end onto the flame. Soldering is practiced both by solderers who are constantly engaged in this work and by workers in many other professions, for whom soldering is a component part of their work; these include roofers, sheet metal workers, jewelers, engravers, and others. The harmful aspects of the work of solderers and related professions include: 1. The release of gases and vapors from the fluxes, which irritate the respiratory tract; these include hydrogen chloride and zinc or tin chloride vapors, which have a sharp irritating effect (arsenic may also be present, leading to the formation of arsine). Cases of serious damage from the action of these vapors are rare; the three very serious cases reported by Koelsch in 1924 deserve attention, two of which had a fatal outcome (in one case, burns of the respiratory tract with subsequent necrosis and sepsis, in the second, bronchopneumonia). 2. The possible release of lead vapors. This danger, however, is relatively small, since when working with soft solders, which contain lead, the heating temperature is unlikely to reach the point where lead vapors (more accurately, smoke) are formed, and in hard solders lead is not often present. Therefore, the danger of lead poisoning in these professions is relatively small. In the collection "Borba so svintsom kak promyshlennym yadom" (Struggle Against Lead as an Industrial Poison) (1930) of the Leningrad Institute of Labor Hygiene, which presents characteristics of solderers on various works, it is stated that they have constant contact with lead; as for the release of lead into the air, in the overwhelming majority of cases it was not found during investigations; only in the battery production, where during soldering of tanks a hydrogen flame (1000°) is used, 0.9 mg/m³ of lead was found. During soldering with a voltaic arc (soldering of batteries in the same production), the release of lead vapors (smoke) undoubtedly occurs to a much greater extent; on the filters of respirators worn by workers, 0.3-0.4 mg of lead was retained in an hour, but it must be borne in mind that a significant part of the finest lead colloid suspension was not retained by a cotton filter. Among these solderers, 4 cases of lead poisoning were registered at the "Krasnaya Iskra" plant (Leningrad) from 1926-1928. The last point, soldering with a flame at a very high temperature, is of special importance for work on lead coating, which is very widespread in a number of industries; German and English authors usually include "lead coaters" (Legge-Goadby, Froboese) among "solderers", who cover lead on the entire surfaces of large objects (boilers, barrels, tanks, etc.) or on smaller parts. Here the work is usually performed using a hydrogen or acetylene flame, and at such a high temperature lead evaporates - the formation of lead smoke, which is a colloid suspension of lead oxide in a state of strong dispersion (particles less than 0.5 µm). Froboese, using specially constructed apparatus, determined the amount of lead released into the air during homogeneous (continuous) lead coating and found it to be from 0.07 to 2.33 mg/m³. The danger of lead poisoning for this type of worker is much higher than for those working on ordinary soldering, which is confirmed by statistical data: in England from 1900-1909, 95 cases of poisoning were registered among solderers, and they occur mainly among homogeneous lead coaters. The data on mass examination of solderers in Germany in 1925 by Engel are interesting: signs of lead action were found: among those working exclusively or predominantly on homogeneous lead coating (93 people) - in 44%, among those engaged in this work along with other work (213 people) - in 29%, among those working on small-scale lead coating (125 people) - in 3%, on other soldering work (175 people) - in 4%. Engel considers that among solderers, cases of serious lead poisoning are rare. Closely related to solderers in terms of working conditions are tinsmiths (see Tinning). - Prevention: admission to work of flux completely free of arsenic. To remove flux vapors, zinc chloride, and the like - ventilation installations at workplaces where soldering is performed; these works must be performed in general in properly equipped and isolated from other rooms. For work on homogeneous lead coating, where it is difficult or impossible to install ventilation devices, and generally for work at high temperatures (hydrogen, acetylene flame) - masks with a supply of fresh air. Personal hygiene of workers: special clothing, washbasins, etc. Periodic medical control.