Experimental research of stress state of feed in wedge-shaped workspace of pellet mill

The problem of experimental determination of contact stresses in all zones of the wedgeshaped workspace of a pellet mill is relevant for perfecting the feed pelleting process, which is accompanied by the intense nonproductive lateral extrusion of the semi-finished material beyond the working surfaces of the ring die and press roller. In order to realize the structural and parametric synthesis of the pressing mechanism of the pellet mill on the unifying mathematical model of the process, a multilevel verification of its adequacy is required. The stress state behavior of the feed layer in the wedge-shaped workspace is studied insufficiently, therefore it is important to correctly describe the stress state parameters since the indicators characterizing the efficiency of the process depend directly on them. The method for research of the stress state in the conditions of the open and closed wedge-shaped workspace is proposed. This method allows obtaining the contact stresses distribution in the tangential direction and along the generating lines of the cylindrical operating parts and also determination of the axial stresses in a feed layer. To apply the method, a laboratory facility is created and designs of force-measuring operating parts – the tensometric press roller and replaceable restrictive ring – are developed. Characteristics of change of the radial stresses in the wedge-shaped workspace at different operating modes of the pressing mechanism are obtained using the measured stresses normal to the roller surface. It is shown that contact stresses in the axial direction in the open wedge-shaped workspace are always distributed unevenly. This unevenness is eliminated by preventing lateral extrusion. According to the measured reactions from the restrictive rings, the resistance force of the lateral strain of the feed and respectively, the active force of the lateral extrusion are estimated. The high value of these forces confirms the significance of the lateral extrusion problem. Based on the results of the strain-gauge testing, the main theoretical regularities of the process are validated, and the necessity of the butt restriction of the wedge-shaped workspace by additional contact surfaces is justified. The latter contributes to the increase of throughput capacity and the decrease in energy consumption of the pellet mill.

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