发动机维修中的几种简单方法

随着建筑机械的不断发展,对外交流的日益广泛,进口发动机的检修已是建筑单位机械维修中的重点和难点,怎样在检修中做到既简单可靠又确保发动机的技术指标呢?本文讨论工地上实用的调整气门间隙、供油时间、检测轴瓦间隙的简单办法。1　发动机气门间隙的调整调整气门间隙通常采用逐缸调整或二次调整的办法,但如果发动机上没有刻度和记号,往往造成误差(尤其是二次调整),使发动机进气不足、排气不净,降低发动机功率和最大扭矩。维修上海英格索兰Ｐ600空压机时,日产ＢＦ6Ｌ913Ｃ发动机进、排气门间隙只有015ｍｍ,发动机上无任何刻度标记,若气门重…     

农机的检修与保养

<正>一、调整和换位法用增减垫片、调整螺钉、松紧螺母等方法来弥补零件的磨损。例如:用增减垫片的方法来调整已磨损的锥形磙子轴承的间隙、用螺钉来调整气门间隙、用调整螺母来调整离合器间隙等。将已磨损的零件部位,调换一个方向或位置,也就是利用未磨损的部位继续工作。例如,将拖拉机驱动轮轮胎左右调换使用;履带拖拉机驱动链轮齿单边磨损后,左右互换使用等。     

蒲石河抽水蓄能电站导叶间隙调整及影响因素分析

导叶间隙是保证导叶灵活转动和水轮机停机时漏水量大小的重要依据,包括端面间隙和立面间隙。结合蒲石河抽水蓄能电站的水轮机活动导叶端面间隙与立面间隙的调整工艺,分析影响端面间隙与立面间隙的因素,以及在装配过程中应注意的问题。结果表明,通过合理调整导叶间隙,确保了安装质量,节约了工期,各项数据符合标准及设计要求。     

探讨水稻插秧机的技术调整及使用

<正>水稻插秧机的技术调整比较复杂,主是三部分:一是插秧工作部分的调整,二是整机性能的调整,三是插秧机的操作使用。一、插秧工作部分的调整1、秧针与导轨插口侧面的标准间隙为l.3-1.7毫米,当间隙不对时,稍微松开导轨调节手柄,左右调整导轨,并使左右的间隙相同。2、秧针和苗箱侧面的标准间隙为1.5-5毫米,当间隙不对时,应松开苗秧支架和苗箱移动滑杆的紧固螺栓。通过左右移动苗箱进行调整,并使左右两端的间隙一致。     

试论水稻插秧机的技术调整及使用方法

<正>一、插秧工作部分的调整1、调整导轨插口间隙一般而言,水稻插秧机在正常作业的情况下,其导轨插口的侧面间隙在1.3到1.7毫米之间,一旦导轨两侧插口间隙不对称,就会对实际插秧作业质量造成影响。为此,要求作业人员适时调整手柄,确保两侧导轨间隙一致,从而保证插秧作业质量。2、调整秧针和苗箱侧面间隙水稻插秧机实际运行中,其秧针和苗箱的侧面间隙应控制在1.5毫米到5毫米之间。一旦秧针与苗箱之间的间隙超出     

KND系统数控铣床圆度误差补偿的实现

为了提升数控铣床的加工精度,利用球杆仪对数控铣床的圆度误差进行了测量。根据测量的结果,针对性的对影响机床较大反向跃冲、反向间隙、伺服不匹配等误差进行了参数补偿,通过补偿,该机床的圆度误差下降了76.7%,机床的精度有了明显的提高,取得了较理想的效果。     

630MW汽轮机可倾瓦轴承温度高原因分析及处理

某厂630MW汽轮机运行过程中,3号轴承出现了温度高故障。本文介绍了故障现象,结合各方面因素的分析及揭瓦检查,发现该轴承顶部间隙偏小、右侧下瓦块载荷过重。通过调整轴承顶部间隙及轴承调整垫块厚度等措施,解决了轴承温度高的问题,从而保障了机组的安全运行。     

读“发动机气门的可调性分析与快速调整方法”

发动机检查和调整气门间隙的关键是在曲轴转角位置确定后,准确地找到可以调整的气门,并将气门间隙高速到符合规定的要求.整个调整过程允许重复,但不可遗漏.     

等效间隙的近似计算及误差分析

等效间隙是静压支承理论分析和计算中的一个重要参数。本文对静压支承间隙液阻的等效间隙近似计算进行了详尽的误差分析,并提出了一种更为精确的近似计算方法,这种计算方法可以满足各种偏心率工况下的静压支承的工程计算,具有较强的实用价值。     

时域反射法测量膨胀土含水量试验研究

 通过对探管式TDR仪现场测量膨胀土含水量误差来源的分析,认为膨胀土的黏性以及土体收缩时产生的土与管壁之间的间隙是主要影响因素。在此基础上设计了3种类型的室内试验进行定量分析。试验结果表明：由于膨胀土的黏性大,土中结合水含量高、介电常数小,因此TDR仪测得的体积含水量q 比烘干法得到的qw低,但两者之间具有良好的对应关系,可通过线性拟合获得满意的标定效果;由土体收缩产生的间隙分为环管壁间隙和径向间隙两种,环管壁间隙对含水量测量影响较大,只要存在1 mm的间隙,可导致低估40%的体积含水量,且误差随含水量的增加而增大,而径向间隙对测量结果影响较小,在试验尺寸范围内,最大误差不超过5%,产生这种结果的原因是TDR探头测量敏感度随测量距离增大而迅速衰减。最后通过现场实测数据对试验结果进行验证并提出改进措施。     

Automated assessment of vertical clearance on highways scanned using mobile LiDAR technology

Assessing vertical clearance at bridges is a preliminary step in most routine bridge inspections. This information is critical when assessing the structural integrity of bridges. Furthermore, clearance information at bridges and other overhead assets on a highway network is also extremely important when routing oversized vehicles on a highway network. Efficient clearance assessment makes critical information readily available to asset owners. As a result, asset owners and transportation agencies are able to address concerns in a timely manner, which would help them avoid prohibitive maintenance costs sustained in case of collisions. Unfortunately, manual clearance assessment using conventional surveying tools is unsafe, time consuming, labour intensive. To overcome these challenges, this paper proposes a novel algorithm whereby mobile LiDAR data could be used to efficiently assess clearance at overhead objects on highways. The proposed algorithm first detects and classifies all overhead objects on a highway segment. The clearance is then assessed at each of those objects and minimum clearance is identified. Detection involves voxel-based segmentation of the point cloud followed by a nearest-neighbour search to locate overhead structures. After detecting the structures and identifying their locations, points representing the same object are clustered and classify into bridges and non-bridges. Furthermore, an estimate of the clearance at each object is also obtained. For objects of long span such as bridges, detailed clearance assessment is performed. The developed algorithm was tested on three highway segments in Alberta, Canada including a 242 km highway corridor. Testing revealed that the method was successful in detecting and classifying all overhead structures at an accuracy level of 97.8% and 96.2%, respectively. The algorithm was also successful in accurately measuring the clearance at those structures with the differences in measurement between ground truth data and the extracted results ranging between 0.03 and 0.47%.     

旋挖灌注桩清孔技术现状及在重庆地区适用性探讨

该文列举了国内旋挖成孔后常用的几种清孔方式,并对其施工原理、适用条件和优缺点进行了分析,结合重庆地区高填方抛填块石土场地的特点,对各类清孔技术在重庆地区的适应性进行探讨分析,并提出一种适用于抛填块石场地的高压风-破碎清孔法的新思路,供业界同行参考。     

浅析挖掘机工作装置轴与轴套的配合及设计问题

对挖掘机工作装置轴与轴套的配合在使用状况中的影响进行定性的分析,提出可能出现的问题及影响因素。对轴与轴套的间隙设计计算实例进行详细说明,在设计计算上考虑8种影响配合间隙的因素,并与同行业的其它代表性产品作类比分析,给出轴与轴套配合间隙选取值的范围。对轴套与焊接套的过盈量选取作了定性分析,并给出过盈量选取值的一般原则。对于设计轴和轴套需要注意的问题作详细的阐述,特别是对轴和轴套的材质、表面硬度以及表面粗糙度给出选取的原则,并对形位公差等级的选取加以详细说明。     

基于Kent法的PE燃气管道风险评价指标体系

基于Kent评分法,建立了PE燃气管道的风险评价指标体系。     

Online energy-based error indicator for the assessment of numerical and experimental errors in a hybrid simulation

Hybrid simulation is an effective structural test technique combining the numerical simulation of substructures with predictable behavior, and experimental testing of complex components that are difficult to model. Consequently, hybrid simulation is prone to both numerical and experimental errors. In this paper, the dominant sources of numerical and experimental errors that can contaminate the results of a hybrid simulation are examined. It is shown that linearized analytical stability and accuracy limits for algorithms and test procedures used in a hybrid simulation may fail to adequately predict the results due to errors and nonlinearities of actual tests. An alternative approach based on monitoring the energy balance of the structural system is proposed to capture the effects of both experimental and numerical errors. This method extends an existing experimental error indicator to also account for (a) errors resulting from modification of experimental measurements by iterative corrections in numerical integrators or other signal correction procedures, and (b) numerical errors in the integration algorithm including equilibrium errors and kinematic relations between displacement, velocity and acceleration. The effectiveness of the proposed energy error indicator in predicting severity of errors is demonstrated through numerical and experimental simulations using various integration procedures.     

Methodological issues of using observational human data in lung dosimetry models for particulates.

INTRODUCTION: The use of human data to calibrate and validate a physiologically based pharmacokinetic (PBPK) model has the clear advantage of pertaining to the species of interest, namely humans. A challenge in using these data is their often sparse, heterogeneous nature, which may require special methods. Approaches for evaluating sources of variability and uncertainty in a human lung dosimetry model are described in this study. METHODS: A multivariate optimization procedure was used to fit a dosimetry model to data of 131 U.S. coal miners. These data include workplace exposures and end-of-life particle burdens in the lungs and hilar lymph nodes. Uncertainty in model structure was investigated by fitting various model forms for particle clearance and sequestration of particles in the lung interstitium. A sensitivity analysis was performed to determine which model parameters had the most influence on model output. Distributions of clearance parameters were estimated by fitting the model to each individual's data, and this information was used to predict inter-individual differences in lung particle burdens at given exposures. The influence of smoking history, race and pulmonary fibrosis on the individual's estimated clearance parameters was also evaluated. RESULTS: The model structure that provided the best fit to these coal miner data includes a first-order interstitialization process and no dose-dependent decline in alveolar clearance. The parameter that had the largest influence on model output is fractional deposition. Race and fibrosis severity category were statistically significant predictors of individual's estimated alveolar clearance rate coefficients (P < 0.03 and P < 0.01-0.06, respectively), but smoking history (ever, never) was not (P < 0.4). Adjustments for these group differences provided some improvement in the dosimetry model fit (up to 25% reduction in the mean squared error), although unexplained inter-individual differences made up the largest source of variability. Lung burdens were inversely associated with the miners' estimated clearance parameters, e.g. individuals with slower estimated clearance had higher observed lung burdens. CONCLUSIONS: The methods described in this study were used to examine issues of uncertainty in the model structure and variability of the miners' estimated clearance parameters. Estimated individual clearance had a large influence on predicted lung burden, which would also affect disease risk. These findings are useful for risk assessment, by providing estimates of the distribution of lung burdens expected under given exposure conditions.     

能量的局部误差估计和直接积分法的时步自适应算法

本文研究了直接积分法中时间离散引起的位移和速度局部误差，区分了动力系统的能量，能量的局部误差和位移、速度局部误差的能量三者的关系。提出将系统能量的局部误差作为后验误差估计指标。该误差估计指标的物理意义明确，不仅考虑了位移局部误差而且还考虑了速度局部误差对能量局部误差的影响。本文还给出了相应的时间步长自适应调节算法，并在算例中实现了时间步长的自适调节计算，同时验证了本文误差估计的精确性和可靠性     

Modelling the dynamics of design error induced rework in construction

Rework that is experienced in construction projects is often caused by errors made during the design process. Factors that contribute to design errors are identified and used to design and develop a systems dynamics model, which is used to simulate a number of practical scenarios that can be used to reduce design errors and rework. The model presented in this paper can enable design and project managers to understand better the process of design documentation and how design errors occur in construction projects.     

考虑测量误差的路堤工程位移反分析

由于测量误差的存在,使反分析参数的可靠性降低。本文分析了路堤工程测量误差的来源以及确定方法,以及采用极大似然法导出了包含协方差矩阵的最小化目标函数表达式,并推导了测斜仪的协方差矩阵。将最小化目标函数值作为遗传算法的适应度值可以优化土性参数。给出一个实例,得出考虑测斜仪误差比未考虑测斜仪误差的计算结果更符合实际情况。     

大跨径外倾式拱桥钢箱拱肋拼装误差影响

分析了大跨径拱桥空间钢箱拱肋的施工特点。利用几何方法推导了空间钢箱拱肋节段拼装误差在拱肋最大悬臂端的累积规律：对首座大跨径曲线梁非对称外倾式拱桥——南宁大桥拱肋拼装进行了算例分析,分析了节段拼装线位移误差和角位移误差对最终拼装精度的不同影响,说明了拼装过程中对角位移误差进行精确控制的必要性。本文方法具有一般性,对类似工程有借鉴意义。