Investigation of Steel Roller–Material Interaction Based on Frictional Properties of Round Bales

In order to provide a theoretical basis for the monitoring and control of the formation process of round bales, the friction test platform for the rolling formation of round bales was built to study the interaction between steel roll and material in the forming process. The results showed that the torque value of the steel roller at the lowest position (No. 2 steel roll) in the bale chamber was closely related to the forming process of the round bale. According to the change of the torque value, the forming process can be divided into an initial stage, straw core formation stage, compression stage and bale-forming stage. The change of torque value can be used for monitoring the forming process of round bales. During the forming process, materials were subject to sliding friction and rolling friction. From the initial stage to the forming stage, the friction of materials gradually changed from sliding friction to rolling friction, and the surface contacted between the material and the steel roll gradually changed to line contact. The interaction model of steel roll and material was established and verified; the model showed that the maximum error between the theoretical value and the experimental value of the forming density is 13.24% and the minimum error is 0.75%. The forming density of round bales was positively correlated with the mass of material fed per second and negatively correlated with the volume of the bale-forming chamber. The forming density of round bales can be expressed by the tangential force per unit length of No. 2 steel roll under the condition that the moisture content of material, the mass of material fed per second and the volume of the baling chamber were fixed. The model provides a theoretical basis for monitoring and controlling the forming process of round bales.