高含水率玉米橡胶复合钉齿制备与脱粒性能试验

为降低高含水率果穗脱粒过程中的籽粒破碎率和未脱净率，以满足玉米籽粒直收技术对脱粒装置要求，改进设计了橡胶层与碳钢层复合结构的脱粒钉齿，自制丁腈橡胶、天然橡胶和三元乙丙橡胶作为复合钉齿的外层结构材料，并完成复合钉齿加工。采用台架试验方法研究不同外层材料的复合钉齿对玉米果穗脱粒性能（籽粒破碎率和未脱净率）和自身抗磨损性能（破损损失质量和表层组织磨损）的影响，脱粒试验表明：籽粒含水率范围为29.7%~30.5%、果穗喂入量为8~12kg/s时，丁腈橡胶、天然橡胶及三元乙丙橡胶复合钉齿和传统碳钢钉齿籽粒破碎率分别为4.85%~7.27%、3.77%~6.23%、2.92%~4.88%和6.90%~10.35%，未脱净率分别为0.41%~0.82%、0.35%~0.78%、0.30%~0.69%和0.24%~0.59%。磨损试验表明：由表层组织宏观磨损可见，丁腈橡胶层沟壑痕迹明显，且磨损破坏严重，三元乙丙橡胶层凹坑数量远少于天然橡胶层，两者均未导致破损失效；由SEM表层微观形貌可知，丁腈橡胶层裂纹缺陷数量最多，且组织不连续，天然橡胶层孔洞削弱组织间结合力，且易疲劳失效，三元乙丙橡胶层大部分组织相对完整连续，且具有较强抵抗外力作用。结果表明：在籽粒高含水率时，橡胶复合钉齿能显著提高玉米果穗脱粒性能，其中三元乙丙橡胶复合钉齿的脱粒与自身抗磨损的综合性能最佳，较传统碳钢钉齿籽粒破碎率降低了52.85%~57.68%，未脱净率与传统碳钢钉齿相近，能够满足玉米籽粒收获机脱粒质量评价技术规范要求。

Preparation and Threshing Performance Tests of Rubber Composite Nail Teeth under Maize with High Moisture Content

In order to meet the requirements of maize combine harvester for threshing device, the breakage rate and the non threshing rate of maize should be reduced in the threshing process of ear with high moisture content. The threshing nail teeth with composite structure of rubber and carbon steel layers were improved and designed. Besides NBR, NR and EPDM were self-made as the materials of outer structure of composite nail teeth. The effects of composite nail teeth in different outer materials on threshing performance of maize ears (the breakage rate and the non threshing rate of maize) and self anti-fraying performance (loss weight on damage and abrasion of surface tissue) were studied by bench tests. The results of threshing tests showed that when the moisture content of maize grain was 29.7%~30.5%, and the feed quantity of maize ear was 8~12kg/s, the breakage rates of maizes in NBR, NR, EPDM composite nail teeth and traditional carbon steel nail teeth were 4.85% to 7.27%, 3.77% to 6.23%, 2.92% to 4.88% and 6.90% to 10.35%, respectively, and the non threshing rates of maize were 0.41% to 0.82%, 0.35% to 0.78%, 0.30% to 0.69% and 0.24% to 0.59%, respectively. The results of abrasion tests showed that from the macroscopic abrasion of the surface, the gullies of the NBR layer were obvious and the abrasion of surface was serious, the number of pits in the EPDM layer was far less than that of the NR layer, neither of which led to the failure;from the microscopic morphology of the surface based on SEM, the number of cracks in the NBR layer was the most and the structure was discontinuous, and the holes in the NR layer weakened the combination between the tissues. Most of the structures of EPDM were relatively complete and continuous and had strong resistance to external forces. The comprehensive results showed that under the high moisture content of maize grain, rubber composite nail teeth could significantly improve the threshing performance of ear, among which EPDM composite nail teeth had the best comprehensive effects in threshing and self anti-fraying performance, the breakage rate of maize was 52.85%~57.68% lower than that of traditional carbon steel nail teeth, and the non threshing rate of maize was similar to that of traditional carbon steel nail teeth, meeting the requirements of technical specifications for threshing quality evaluation of maize harvester.