Improvement of mechanical properties and wear resistance of cotton picker spindle by electromagnetic treatment

Abstract: Cotton is one of the major crops in Xinjiang, China, and has a significant impact on Xinjiang's economic development and social stability. The mechanization degree of cotton harvest is increasing with the development of productive forces and the progress of science and technology. For part of the mission field of Xinjiang Production and Construction Corps, China, mechanized harvesting has been achieved 100%, and overall, it has reached above 85%. Spindles are the core component of cotton picker; a single cotton picker has about 2 500 spindles, and a spindle uniquely has the structure of 3 rows × 14 teeth. In order to facilitate the removal of cotton, the first 3 teeth have an angle of 30o with respect to the pole axis, and the remaining 11 hook teeth form an angle of 45o to ensure the cotton picking rate, whose performance directly determines operation efficiency and cotton quality of the cotton picker. Moreover, the substrate material of the spindle is low carbon alloy steel, on which a chromium coating is electroplated to increase the wear resistance. In the case of correct installation and good lubrication, the average life span of spindle was picking cotton of about 400 ha. The wear resistance of the surface coating seriously affects the running cost of the cotton picker. Therefore, to further improve the wear resistance of spindle has always been a scientific and technical issue. In order to improve the wear resistance of the spindle, we have proposed electromagnetic treatment method for surface modification of spindle (Case's spindle made by Case Corp., USA, Deere's spindle made by John Deere Corp., USA and Yeer's spindle made by Yeer Corp., China). The main objective of this study was to reveal the mechanical properties of the electromagnetic treated spindle, but not changing the spindle structure that has been existing in cotton picker. The result showed that the residual stress of the 3 types of spindles was decreased significantly after electromagnetic treatment, the residual stress of Case's and Yeer's spindle decreased by 60%, and that of Deere's spindle by about 50%. The main cause of residual stress decrease was that electromagnetic treatment can cause stress relaxation in the material, resulting in local inelastic deformation and stress redistribution, and improve the fatigue life. After electromagnetic treatment, the microhardness of the spindle's substrate material and the nanohardness of the electroplated chromium coatings did not change significantly, and the elastic modulus of the coating decreased. The ratio of elastic modulus to hardness of the 3 kinds of spindle surface coating was all over 21 before electromagnetic treatment. After electromagnetic treatment, the ratio value of Case's, Deere's and Yeer's spindle was 18, 17 and 20, respectively. The decrease of the ratio of elastic modulus to hardness will increase the elastic deformation, reduce the adhesion and wear, and improve the wear resistance. Through the scratch and wear test, the scratch depth of the spindle surface coating became smaller and the wear scar width decreased after electromagnetic treatment for all kinds of spindles. The wear scar width of Case's and Yeer's spindle decreased more significantly than Deere's spindle. Moreover, the wear scar width decreased with the increase of load in wear test, but the downtrend of wear scar width of Case's and Yeer's spindle was more obvious than Deere's spindle compared with that before electromagnetic treatment. By the comparison, the improved wear resistance of Case's spindle is the most notable after the electromagnetic treatment. Therefore, the Case's spindle of electromagnetic treatment is used to carry out the field test for cotton picking, which was to evaluate and verify wear resistance. The research results will be helpful for improving the wear resistance of spindle, which makes it possible to prolong the service life of spindle used, and has important social significance and remarkable economic benefits.