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the property of parts or units in machines, assemblies, mechanisms, apparatus, and other technical structures that permits them to be replaced or assembled without additional treatment while retaining all the requirements placed on the operation of the particular unit, machine mechanism, or structure as a whole. In a broader sense interchangeability is a complex concept that characterizes a trend in the development of modern technology. From this viewpoint it includes problems of design, technology, and operation of machines, devices, and the like.
Interchangeability is of very great significance for the national economy and is one of the most important prerequisites in organizing mass and large-scale production. Only when interchangeability is assured is it possible to have cooperation in production (on a scale embracing one country or even several countries) on the basis of fabricating parts and units for the same machines in different specialized enterprises. Complete interchangeability refers to interchangeability requiring the delivery from production shops to assembly shops of parts which are identical by rating with respect to purpose, design, and dimensions; these parts must meet quality and physical requirements completely and in form and dimensions conform to the operating locations in the mechanisms that the parts will occupy. For instance, such devices as electric lamps (socket diameters and screw thread), plugs, razor blades, screws, nuts, and roller bearings can only be used provided that interchangeability is complete. In some cases it is economically or technically advantageous to have a small amount of extra treatment for one of the mating parts in an assembly or to sort the parts first and install them according to grouping, without, however, all the manual operations of fitting into place or the selection of separate parts from a batch according to sizes; this is called partial interchangeability. It is used mainly when assembling machines and devices in plants and is seldom extended to spare parts.
One of the basic prerequisites of interchangeability is the achievement of dimensions of mating parts that are within the range of established tolerances. Standards have been developed in the USSR for a system of tolerances and fits for various mating parts of machines and instruments. Work is also being done on the international standardization of systems of tolerances and fits.
REFERENCESPriborostroenie i sredstva avtomatiki (reference guide). Under the general editorship of A. N. Gavrilov. Vol. 1: Vzaimozameniaemost’ i tekhnicheskie izmereniia. Moscow, 1963.
Metodika i praktika standartizatsii. Edited by V. V. Tkachenko. Moscow, 1965.
Iakushev, A. I. Osnovy vzaimozameniaemosti i tekhnicheskie izmereniia, 2nd ed. Moscow, 1968.