Experimental Research on the Formation of the Third Body on the Friction Surface of Coal Cake Tamper Hammer Lifting Mechanism

Abstract

A tamping machine is the key equipment of large coking coal cake forming in the steelmaking industry, where the loose coal is compacted into a coal cake by the reciprocating movement of its tamping hammer. In the long-term friction process, the third particle attached to the surface of the friction pair of the hammer lifting mechanism often causes the tamping hammer to slip and wear the tamping hammer friction plate, resulting in an insufficient height of the hammer, uneven work of the tamping hammer, coal cake collapse and other problems. In order to avoid the adverse effect of the third body on the surface of the friction pair, this paper studies the formation of the third body on the friction surface of the lifting hammer mechanism of the coal cake tamper. The cam material (Q345B) of the hammer lifting mechanism and the copper-based powder-metallurgy composite material of the friction plate of the tamping hammer are prepared into the pin-disk friction test disk and pin, respectively. Based on the characteristics of the friction temperature variation in the pin-disk test, an equivalent accumulation method is proposed, that is, the wear state of several samples at different wear times is equivalent to characterize the wear condition of a sample at different stages during continuous wear, and the different stages of the third body formation process are obtained. By analyzing the change of the composition of the third body and the content proportion of each element on the surface of the bottom plate at different wear times, it is determined that Cu is the key index of the third body. The content of the Cu element is used to characterize the content of the third body on the surface of the disk sample, and the formation rule of the third body on the surface of the disk is inferred. Through an image processing method of color analysis, the distribution law of the third body on the whole disk is identified. The properties of the third-body material on the disk surface are obtained by analyzing the changes of hardness and morphology at each friction stage. The results show that with the increase of friction time, the content of Cu on the disk surface increases to 22% and then decreases to 15%. The microhardness of the friction surface reaches its highest at 7 min, which is 1.4 times that of the Q345B material. The maximum disk surface roughness is 0.452 µm. Finally, the formation process of the third body is summarized in three stages: formation, equilibrium and damage. Therefore, the frictional properties of the surface of the friction pair vary from weak to strong to weak with the formation characteristics of the third body.