The process of air classification of substandard sands is discussed. It is demonstrated that via an optimum selection of separation boundaries for classifying equipment it is possible to obtain sand, whose granulometric composition meets the state standard requirements. A mathematical model is developed, which makes it possible to optimize the operating parameters of air classifiers and to obtain a maximum output of finished product. Examples of industrial use of air classifiers are given, which confirm the expediency of using air classification of sands in the glass industry.