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学生搞不清楚麻花钻刃磨时几何角度之间的关系,导致麻花钻头的刃磨失败,最终使学生形成了麻花钻内容太难,麻花钻刃磨起来太麻烦的结论。用图示、口诀配合文字讲解的方式讲解标准麻花钻切削部分之间的关系,学生易于接受。 相似文献
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王宏立 《黑龙江八一农垦大学学报》2016,(4):93-97
以国产和西班牙产破茬刀为研究对象,采用试验方法对比考察了两种破茬刀的化学成分、微观组织和硬度,并利用球-盘摩擦磨损试验机对其摩擦磨损性能进行研究。结果表明:两种破茬刀成分相近,西班牙刀材质为优质硼钢,韧性好,国产刀材质为中碳优质锰钢。西班牙刀显微组织为针状马氏体,组织更加细密,洛氏硬度值为50 HRC,是国产刀的1.1倍。在干摩擦条件下,西班牙刀表面摩擦系数较小,为0.48~0.52;相同条件下,国产刀表面的磨损量是西班牙刀的2.5倍,西班牙刀具有更好的耐磨性。两种破茬刀的磨损机制均为磨粒磨损。 相似文献
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油麦兼用型精量宽幅免耕播种机仿形凿式开沟器研究 总被引:6,自引:0,他引:6
针对播种作业地表不平、播种机宽幅导致各行播深均匀性和稳定性差等问题,设计了一种基于仿形辊弹性形变、实现仿形功能的凿式播种开沟器。阐述了凿式播种开沟器仿形开沟工作原理,确定了凿式刃口曲线方程,构建了开沟器与土壤互作关系力学模型,阐明了仿形机构的弹性形变与仿形阻力及仿形量之间的关系。以凿式曲面刃口宽度、仿形辊直径、入土角、播深为试验因素,采用二次回归正交组合试验方法,利用高速数字化土槽平台,开展了各试验因素对播深稳定性影响试验。试验结果表明,刃口宽度12mm、仿形辊直径24mm、入土角22°时,播深稳定性较优。田间对比试验表明,在最优参数组合下,凿式开沟器的播深变异系数低于9%,地表平整度低于18.5mm,作业通过性好,其开沟性能优于翼铲式开沟器;田间播种试验表明,以4.8m工作幅宽、24行播种的油麦兼用型精量宽幅免耕播种机播种的油菜、小麦,单行苗数变异系数、各行苗数一致性变异系数均低于10%,小麦各行1m内平均苗数为35,春油菜各行1m内平均苗数为26,冬油菜各行1m内平均苗数为20,满足油菜、小麦精量播种及成苗率要求。 相似文献
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Effects of four tillage systems (direct drill, subsoiler, chisel plough and mouldboard plough) on the dynamics of Polygonum aviculare populations were studied over three growing seasons. Cumulative emergence on a weekly basis was determined. Cumulative emergence from two years of chisel ploughing was used to develop an emergence model for P. aviculare based on hydrothermal time. Results showed that direct drilling, which had the highest seed yields of winter cereal crops every season, was the unique soil management system that lowered P. aviculare populations because of effective weed emergence reduction. The model accurately described seedling emergence in different tillage systems, although it failed in direct drilling, probably due to very low numbers of emerged seedlings. To better control this weed, direct drilling may be the best tillage option, but if this cannot be implemented, the hydrothermal time model is a practical tool that can describe the relative proportions of emergence and assist in the timing for management operations of P. aviculare in different tillage systems. 相似文献
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目的比较涡轮机去骨拔除法(试验组)与凿骨劈冠法(对照组)在拔除中位和低位阻生智齿时的优劣.方法100例(200颗中/巾毛位阻生智齿)均采用自体左右对照,通过掷硬币随机抽样决定试验组和对照组.试验组采用涡轮机拔除法,对照组采用凿骨劈冠拔除法.对手术时间,以及术后疼痛、术后肿胀进行对比观察.结果对于低位阻生齿,涡轮机去骨拔除法手术时间短、术后疼痛及术后肿胀轻.对中位阻生智齿,涡轮机去骨拔除法的手术时间和术后疼痛及肿胀程度大于凿骨劈冠法.结论涡轮机去骨拔除法较凿骨劈冠法在拔除低位阻生齿时具有优势,凿骨劈冠法较涡轮机去骨拔除法在拔除中位阻生智齿时有优势. 相似文献
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The advantage of fall soil tillage by loosening with an experimental chisel implement to a depth of 40–42 cm compared with
moldboard plowing with a share plow to a depth of 25–27 cm is shown.
Original Russian Text ? V.I. Pyndak, V.F. Loboiko, V.N. Pavlenko, 2009, published in Doklady Rossiiskoi Akademii Sel’skokhozyaistvennykh
Nauk, 2009, No. 2, pp. 54–55. 相似文献
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Seed production of residual weed populations needs to be taken into account when estimating the long-term impact of low-input agronomic practices. The objective of this study was to measure the effects and interactions of crop, weed control, tillage practice and nutrient source on the seed production of the dominant residual weed species in a maize/soyabean rotation at two sites: Echinochloa crus-galli (L.) Beauv. on a Sainte-Rosalie clay and Chenopodium album L. on a Duravin clay loam. Seed production per unit area was estimated in each experimental unit. Weed seed production was greater under mechanical weed control compared with chemical weed control. In 1997, E. crus-galli seed production reached over 326 000 seeds m–2 in mechanical weed control treatments, but averaged less than 500 seeds m–2 in the chemical weed control treatments. Chenopodium album produced in the range of 766 000 and 73 000 seeds m–2 in mechanical and chemical weed control treatments respectively. Very few or no weed seeds were produced in soyabean under chemical control. Tillage intensity and nutrient source did not affect seed production of either weed species, with the exception that E. crus-galli produced more seeds in chisel than in mouldboard plough tillage in soyabean. Weed control method had more impact on seed production than tillage intensity and nutrient source in a maize/soyabean rotation. 相似文献
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