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Because of the low impurity removal rate and high damage rate of the potato combine harvester during the working process, a new type of impurity removal device for the potato combine harvester was designed. The device was mainly composed of retaining plates, impurity removal rollers, smooth rollers, and a control system. To determine the best working parameters of the device, the rotational speed of the rollers, the distance between two rollers, and the inclination angle of the device were used as the test factors. The impurity removal rate and damage rate were employed as the evaluation indexes. Then, the single factor test and the second rotation orthogonal regression test were performed. The optimum combination after parameter optimization was determined to be as follows: rotational speed of the rollers was 113.4 r/min, the distance between the two rollers was 97.5 mm and the inclination angle of the device was 10.4°. The corresponding impurity removal rate was 95.12%, and the damage rate was 0.54%. The device can better meet the requirements of impurity removal operations. [ABSTRACT FROM AUTHOR]

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes. • Formation mechanisms of the quenching and tempering surface layer induced by machining processes were revealed. • Machined surface morphology affects preferred grain orientation preference and austenitization characteristics. • Microhardness of the surface layer induced by machining processes is mainly attributed to the dynamic Hall-Petch effect. [ABSTRACT FROM AUTHOR]