Study of the Grinding Process by Friction of Cereal Grains in Stone Mills

Abstract

The grinding process via friction at the micro-scale in a mill with stones is considered a variable combination of contacts, with two-body (the asperities of lower millstone in direct contact with the asperities of upper millstone) and three-body (micro-particles of ground seeds trapped between the asperities of lower and upper stones of the mill) contacts. Three elements are described: (1) the mechanical contact of the asperities of the lower and upper millstones to predict pressures on asperities by modeling; (2) tests on a millstone sample covered with grinding particles; and (3) tests on a wafer sample formed by the millstones with the grinding particles between them. This paper highlights the combined effects of the micro-scale friction via individual measurements, using an analytical model to sum these effects and validating the model by performing several experiments. An efficiency grind by friction assumes the grain’s movement and interaction between the seeds and solid surfaces, and is highlighted through theoretical and experimental studies. Topography analysis of the surface of the millstones reveals the model of microscopic frictional force. Endpoint measurements (the traces of the surface topography evolution) enable model verification in the grinding process. Thus, the results obtained in the grinding process in the stone mills via friction have practical utility through research benefits. Therefore, they allow for the improvement of quality, reliability, flexible grinding, quality control of the flours, and uniformity degree (fineness/shredding).