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所谓拉缸就是指农用机动车气缸壁内表面出现微观的金属粘附、剥落、熔移和撕裂现象;活塞或活塞环把缸壁(或活塞表面)拉毛或拉成沟槽。实际上是活塞或活塞环与缸壁之间局部高温,使金属熔化产生粘着磨损的结果,而活塞与缸壁之间的油膜中断是产生拉缸的必要前提。 相似文献
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发动机拉缸的原因及预防1.拉缸的原因(1)活塞环开口间隙小.活塞环开口间隙过小时,发动机工作时受热膨胀,环的端部紧顶住定位销钉,其他部位与气缸壁紧压,这样就加剧了活塞环、环槽、缸壁的磨损,严重时折断活塞环,拉坏缸壁。(2)活塞销卡簧脱落。活塞销卡簧用... 相似文献
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拉缸是指沿活塞运动方向的气缸内壁上,因高温产生熔着磨损而出现的一些深浅不一的沟痕。气缸拉缸将造成活塞与气缸壁配合间隙增大,出现敲击声,密封性变差,窜机油,积炭增多,冲淡润滑油,严重时还会引起活塞卡在气缸内,使发动机不能运转。 一、气缸拉缸的原因 1.气缸壁与活塞环材质差。气缸壁的含金成份及硬度应与活塞环配套,如气缸镗磨后出现一块块、一条条斑痕,则易被活塞环拉毛,如 相似文献
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一、气缸孔纵向磨损的形成 1.摩擦磨损 在所有气缸磨损形式中,气缸孔在高温高压下的摩擦磨损是形成磨损的主要原因。 内燃机工作中,气缸中的高压气体通过活塞与缸壁、活塞环与环槽的间隙到达活塞环环背,使活塞环以很高的压力压向气缸壁,尤其是在第一环位置,其最高压力可达爆发压力的70%。例如三轮车常用的195柴油机,其第一环背压最高可达8.5MPa左右。由内燃机的工作过程可知,不论是在压缩冲程 相似文献
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引起缸套磨损的原因很多,通常有以下几点: 1.新的或大修后的发动机没有严格按照磨合规范进行磨合(试运转)就正式投入工作,从而使缸套早期磨损。 2.气缸表面几何形状和粗糙的影响,使缸壁的凸起点与活塞环、活塞接触,导致气缸早期磨损。 相似文献
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1.拉缸的特征
柴油机气缸因受高温高压气体的推动、爆震或活塞剧烈的摩擦都会使缸壁拉伤.并在汽缸壁上沿活塞运行的方向出现一条条深度不等的竖向沟槽和金属剥落杂质.从而影响柴油机正常工作.此现象称为拉缸。这是在无外来物的情况下,由于活塞环外表面与气缸表面滑动接触时.在极小的表面上产生很高的温度。 相似文献
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柴油机在工作中因操作不当等原因容易出现拉缸故障。柴油机拉缸,是指气缸壁上沿活塞运行的方向出现一条条深度不等的沟纹。这是在无外来物的情况下,由于活塞环外表面与气缸表面滑动接触时,在极小的表面上产生很高的温度,进而引发活塞与气缸壁之间烧熔、黏着,当烧熔、黏着所产生的热量散失后,在活塞环上产生碳化物。这种碳化物或烧熔、黏着生成物就象一把锋利的刀具,将气缸壁上的金属切去,从而形成一道道深浅不规则的沟槽。本文就柴油机拉缸故障产生的原因一一进行了科学分析,并逐一指出了排除的技巧和措施。 相似文献
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<正>活塞环未装入气缸前,其外径是大于气缸的内径的,活塞环被弹性压缩后安装在气缸内,在活塞环弹力的作用下,环外圆表面紧贴在缸壁上形成弹性密封。当活塞环随着活塞在气缸内作上下往复高速运动时,环与缸壁及环与环槽不停地摩擦而发生磨损,活塞环的磨损造成活塞环与活塞环槽、气缸壁密封不严,产生漏气和机油窜烧,使柴油机机油、燃油消耗量增加,功率下降,工作无力。磨损使活塞环无法满足工作要求而提前报废。活塞环的工作条件很差,在高温、高压和润滑不良 相似文献
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《Journal of Agricultural Engineering Research》1998,69(3):249-254
A model to represent the discolouration of dried powder of carrots as a function of temperature was developed. Two types of carrots, Asian and European, containing large amount of lycopene and β-carotene, respectively, were tested. The dried powder was stored under an atmosphere with O2and at three different temperatures, 5,20 and 35°C. The surface colour of the powder was monitored during storage by a Hunter colour ratioa/b. In the proposed model, the rate of oxidation was assumed to be represented by the product of the fraction of concentration of oxidized pigment at arbitrary time and a specific rate of oxidation of pigment. The rate parameters in the proposed model were calculated by fitting the experimental data with smooth curves by trial and error at the end of the induction period but before discolouration took place. The frequency constant and activation energy, expressing the temperature dependence of the rate parameters, were expressed by the Arrhenius relation. The simulation results of a Hunter colour ratioa/bof dried powder at 25°C showed good agreement with the experimental data, suggesting that the proposed model was effective for the prediction of discolouration of dried powder of both types of carrot. The use of the induction period in the manner described may enable the shelf life of dried powder to be predicted. 相似文献
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感官检验棉花的品级,这是农村常见的一种检测手段.它的一个主要特点就是存在不确定性.这是由于检验员的品级检验水平存在一定的差异,其中有很多因素制约着检验的结果.文章对影响感官检验结果的因素进行了系统的分析. 相似文献
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The fractional outflow rate of water from the rumen, measured as the rate of disappearance of the chromium complex of ethylenediamine tetra-acetic acid, was related to a number of dietary factors. A multiple regression equation was derived which expressed fractional outflow rate as a function of the intakes of dry matter, ash, acid-detergent fibre and crude protein.The data analysed consisted of 243 observations for sheep on 59 diets, including forage, concentrate and mixed diets. The ranges covered by the data were: fractional outflow rate 0.7–3.6 day?1; dry matter intake 560–1400g/day; ash 4–30%, acid-detergent fibre 7–41%, crude protein 5–26 % of dry matter; there were no observations for sheep of less than 34 kg liveweight.The equation accounted for 56·3 % of the total variance. Between-sheep variance could not be calculated for the whole of the data but was undoubtedly substantial since, for a sixth of the data, it was known to account for 38 % of the total variance. 相似文献
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从灾害经济学的角度探讨了城镇供水优化调度的必要性和可能性,认为在缺水不可避免的情况下,对供水进行优化调度可以减小缺水带来的损失,产生较好的减灾效益,特别是可以大大减小严重干旱的灾害效应。并根据水资源的特性,提出了缺水损失的计算模式以及优化调度的原则和方法。 相似文献