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Excessive breakage of stalk in the process of rape threshing has become the main reason for the entrainment loss and the increase of the whole power consumption. Taking the harvest rape stalks as the research object, this study aims to investigate the collision and crushing behavior between threshing nail tooth and rape stem, further to clarify the breakage mechanism of rape stems caused by the collision of threshing spike tooth on a self-made collision test-bed. A prescale film was used to measure the impact force between the rape stalks and spike tooth, according to the force and trajectory. A single factor and an orthogonal experiments were carried out, where the breakage rate of rape stalk as the index, and the length of rape stalk, feeding times, rotational speed of cylinder, and type of spike tooth as factors. An attempt was made to explore the collision form and collision force between the threshing nail tooth and the stem of rapeseed, thereby to figure out the main factors affecting the breakage rate of stalk. The results were as follows: The collision process between single spike tooth and rape stalk was a multiple high-speed instantaneous collision, where 89% of the collisions were multiple collisions, and only 11% had one collision, particularly that the collision times were strongly related to the position of impact point on the spike tooth. In the process of instantaneous multiple collisions, the collision force decreased with the number of collisions. In the case of test conditions, the single impact force was 13.25 N, which was less than the yield limit of radial compression in a rape stalk. The stalk collided only once cannot be broken. The breakage rate of stalk was positively related to the stalk length, feeding times, and rotational speed of cylinder. In three kinds of nail tooth, cutter surface, cylinder, and plane, there was the greatest influence of nail teeth formed on the cutter face on the stem breakage rate, whereas, there was the least influence of plane nail teeth on the stem breakage rate. In the experimental conditions, the crushing rates of the upper, middle and lower parts for the main stem were 84.4%, 91.1%, and 97.8%, respectively, after feeding the rape stem into the collision test-bed for 8 times, and the fragmentation rate for the lateral branches of the rape was 42.2%, indicating that the broken rate of main stem was much higher than that of lateral branch. The orthogonal test showed that, there was the greatest effect of the length of rape stalk on the breakage rate, followed by the rotational speed of cylinder, and the type of spike tooth, whereas, the effect of feeding times was the smallest within the scope of the selected parameters, where the stalk length was 100 mm, the roller speed was 500 r/min, the feeding times were 2 times, and the tooth shape was flat nail teeth, as well as the breakage rate of rape stalk was the lowest. The finding can provide a sound basis for the optimal design of rape threshing device. [ABSTRACT FROM AUTHOR]

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