There are many devices for determining the coefficients of external friction, but there are almost no devices for determining the coefficients of internal friction of bulk products. The paper considers the question of physical and mechanical characteristics of bulk materials - the coefficients of external and internal friction. The purpose of this study was to create a device for determining the friction characteristics of bulk materials and its approbation by determining the coefficients of static and dynamic friction of grain materials. The basic parameters of the installation to determine the friction characteristics of bulk materials were defined - static and dynamic, internal and external friction coefficients. The developed installation allows measurements of shear forces inside the bulk material. The relationship between the coefficient of static and dynamic friction in organic and inorganic bulk materials is revealed. Grain crops have a higher value of the dynamic coefficient of friction at a speed up to 0.215 m/s. The difference between the values of static and dynamic friction coefficients was not revealed in the specified speed range of legumes. Dynamics of change in the coefficient of friction for grain crops depending on speed is studied using the example of wheat, and for mineral materials - using the example of table salt. For a speed range of 0-0.215 m/s, the relative change in the coefficient of friction for grain crops has a polynomial regression model, for mineral materials it has a logarithmic.

The article highlights the issues related to the study of physical and mechanical characteristics of bulk materials, namely internal friction coefficients in static and dynamic modes. An innovative device of the carousel type for determining the frictional characteristics of bulk materials is described, which allows to implement the tasks of practical determination of dynamic coefficients of internal friction. Presented the program, methodology and results of research on the practical study of the internal friction coefficient of typical bulk products of agricultural production in the range of linear velocities of displacement of layers from 0 to 2.79 m/s, the reliability of which is not lower than 0.878.

The article is devoted to the study of the coefficients of external friction of grain agricultural products-friction in static and dynamic modes, as the most important physical and mechanical characteristics of bulk materials. The description of carousel laboratory unit, program, methodology and results of studies on the practical determination of the coefficients of external friction for typical agricultural grain products according to the materials typical of the working bodies of the production machines. As a result of the research, it was found that in the range of linear velocities from 0 to 1.75 m/s, there is a change in the friction coefficients, which has a nonlinear character.