Improving the operational durability of tangential-rotary picks for rock cutting with central spraying and hydrodynamic rotation.

This article presents a proposal for a new solution of tangential-rotary picks intended for mining, especially hard rocks with roadheaders. The design of these picks is characterized by many innovative solutions aimed at significantly increasing their service life. The method to achieve this goal is to provide effective central spraying of the ring tip picks, crown picks, or similar types of picks while using the spray water to cause the picks to rotate as they contact the rock being mined. An important element of the work is to conduct extensive simulation studies using FEM to determine the stress distribution in the pick shank subjected to external load from cutting. The new design of the tangential-rotary pick is equipped with a reinforcing sleeve, in which a state of compressive stress is induced. This enables a significant improvement in the fatigue strength of the pick shanks. The conducted FEM comparative tests confirm the accuracy of the adopted design assumptions. They also determine the beneficial value of the tension nut torque, which tightens the reinforcing sleeve located on the pick shank.

Electrical Conduction Mechanism and Dielectric Properties of Spherical Shaped Fe3O4 Nanoparticles Synthesized by Co-Precipitation Method.

On the basis of dielectric measurements performed in a wide temperature range (173⁻373 K), a comprehensive analysis of the dielectric and electrical properties of magnetite nanoparticles electrical conduction mechanism of compressed spherical shaped Fe3O4 nanoparticles was proposed. The electrical conductivity of Fe3O4 nanoparticles was related to two different mechanisms (correlated barrier hopping and non-overlapping small polaron tunneling mechanisms); the transition between them was smooth. Additionally, role of grains and grain boundaries with charge carrier mobility and with observed hopping mechanism was described in detail. It has been confirmed that conductivity dispersion (as a function of frequencies) is closely related to both the long-range mobility (conduction mechanism associated with grain boundaries) and to the short-range mobility (conduction mechanism associated with grains). Calculated electron mobility increases with temperature, which is related to the decreasing value of hopping energy for the tunneling of small polarons. The opposite scenario was observed for the value of electron hopping energy.