As a key core component of cotton pickers, the spindle is prone to wear of the hook teeth. This research explores the wear characteristics of the spindle hook teeth of cotton pickers under different working areas. The sampled spindles were cut, the element composition and hardness of the spindle hook tooth coating and substrate were determined, the surface morphology of the spindle hook tooth was characterized, and its wear area and coating thickness were extracted. Results show that the main constituent elements of the coating and substrate are Cr and Fe, respectively, the hardness of the coating is about 1020 HV_0.1, and the hardness of the substrate is 470~840 HV_0.1. During the field operation, scratches appeared on the surface of the coating, the coating thickness layer gradually decreased, and the coating peeled off as the operating area increased. Afterward, scratches and oxidized particles appeared on the surface of the substrate, the wear rate accelerated, and the wear area gradually increased. The wear of the spindle hook teeth started to appear from the front and rear tooth tips up to the tooth edge, the back of the tooth, and the doffering edge, hence forming a long boot-shaped wear area.

The wear performance of the spindle hook teeth during fieldwork was compared, and the causes of the wear failure of the spindle hook teeth were analyzed. Samples of three kinds of spindle were obtained from the fixed installation position under continuous field operation conditions. The hardness, phase structure, elemental composition, and micromorphology of the spindle hook teeth were characterized using microhardness, X-ray diffractometer (XRD), energy spectrum analyzer (EDS), and scanning electron microscope (SEM) after cutting of the spindles. Results show that the coating hardness and element penetration zone of No.3 spindle hook tooth are the largest, and the surface coating phase structure of the three kinds of the spindle is mainly a body-centered cubic structure of Cr (211). Micro-crack and hole defects exist in the coating of all three kinds of the spindle. The thicknesses of the coating of No.1, No.2, and No.3 spindles are 74, 100, and 130 µm, respectively. During the field operation, the wear of the spindle hook tooth coating is caused by abrasive wear and fatigue wear, while the wear of the substrate is the result of the combined effect of abrasive wear and oxidation wear. Extracting the wear area and width of spindle hook teeth shows that the wear area of all three kinds of spindle hook teeth increases exponentially and the wear width changes linearly with the increase in the field operation area.

The spindle is a key core component of a cotton picker, and its operating parameters directly affect the quality of cotton harvesting. In this study, the spindle was selected as the research object. The kinematics and mechanics analysis of the cotton-picking process was conducted, the dynamic motion trajectory of the spindle was obtained, and the working parameters affecting the picking performance of the spindle were determined. A test bench for spindle picking performance was built; the spindle speed and feed speed were used as test factors; the seed cotton rejection rate, picking time, and picking force were used as evaluation indices for spindle picking performance; and a full-factor test was conducted. The range, variance, and regression analyses were conducted on the test results, and the results showed that spindle speed and feed speed had significant effects on seed cotton rejection rate, picking force, and picking time (p < 0.01). The primary and secondary order of factors affecting seed cotton rejection rate and picking time were spindle speed and feed speed, and the primary and secondary order of factors affecting picking force were feed and spindle speed. By comprehensively analyzing the influence of factors on the evaluation indices, the best combination was obtained as the spindle speed and feed speed of 4000 r/min and 1.8 m/s, respectively. The research results have theoretical research value and practical significance for revealing the picking law of spindles when rotating at a high speed and then realizing efficient cotton harvesting.

As the core component of the cotton picker, the structural characteristics of the spindle directly affect not only its picking performance but also different components of the cotton picker. Therefore, in order to reveal the influence of different angle parameters of hook teeth on the performance of the spindle and the optimal hook tooth angle parameters, this study analyzes the working principle of the picking mechanism of the cotton picker and establishes the force balance equation for the process of picking cotton from the spindle. By analyzing the structural characteristics of the spindle, the best section shape of the spindle head is the equilateral triangle section. The spindle with different angle parameters was made by a metal 3D printer, and the testbed for the dynamic picking performance of the spindle was constructed. The single-factor test was carried out with tooth groove angle before the tooth angle and tooth inclination angle as experimental factors, and the rejection rate of seed cotton, picking time, and picking force as evaluation indexes. The results showed that the tooth groove angle and the tooth inclination angle were negatively correlated with the rejection rate of seed cotton (P < 0.01), and the tooth inclination angle was positively correlated with the picking time (p < 0.01). Further analysis shows that in order to reduce the ejection rate of seed cotton and reduce the picking time, the selection range of the tooth inclination angle should be 55~65°, and the large the tooth groove angle should be selected. Finally, the optimum hook angle parameters are determined as follows: tooth groove angle is 70° before the tooth angle is 89°, and the tooth inclination angle is 65°. The results are of practical significance to optimize the structure of picking hook tooth to improve the picking performance of the spindle and high efficiency of the cotton picker.