电动机轴电流引发的故障及对策探讨

在电动机中电动机轴电流经常引发故障,由于生产原因,电机不能立即停运,只能采取紧急措施,用轴流风机对电机进行通风降温,电机驱动端轴承温度有所下降。为此文章对电动机轴电流引发的故障及对策进行探讨。     

无卡轴旋切机的结构、使用和维护

介绍了简易无卡轴旋切机的结构、传动装置及使用要求,分析了旋切单板的质量缺陷及旋切机故障原因,给出了故障排除方法。     

纵向输送机报废承载轮及轴的改造和利用

大兴安岭林管局西林吉林业局贮木场在1987年“5.6”火灾后新建了四条单曳引索式原木输送机,当年底投入使用。其中三条输送机的承载轮与轴是直接滑动配合,生产实践表明,这种结构虽然构造简单,但故障多、维修费用高,承载轮与轴的磨损严重,使用寿命低。1989年夏季在停产检修输送机时,发现这三条输送机已有1/3的承载轮内孔和     

门式取料机受料皮带机驱动装置的改造

秦皇岛港煤四期工程门式取料机受料皮带机的减速机原来采用的是FLENDERB2DH-08型,经过两年的使用,其一级轴齿轮频繁断齿,轴也折断多次,最严重时三天就要对其更换一次,严重地影响了生产。通过对其分析与计算,确定故障主要由三方面原因造成。①原来的一级轴齿轮模数偏小,齿根抗折断能力不够。②原来使用的制动器制动力矩太大,制动时对轴制动扭矩达到250N·m,按公式估算出的轴径应为70mm以上,而原来的轴直径只有50mm,所以需要选用较小型号的制动器,并相应改小制动轮。③原来使用的液力偶合器为日本神冈公司的FC1.2D型,通过对其性能曲线进…     

无卡轴旋切机常见故障及排除

国产无卡轴旋切机自８０年代中期投入实际应用以来，由于其最小旋切直径由则Φ１００ｍｍ左右降低到Φ４０ｎｍ左右，所以大大提高了木材的利用率。因此，其应用越来越多，已成为胶合板厂必备的设备．经过多年的生产实践，笔者总结了该机常见的故障及排除方法，现介绍如下，以供同行参考．１摩擦辊推力不足 发生这一故障时，首先要检查系统压力是否合适。对于 ＢＱ１８２０无卡轴旋切机，其系统溢流阀压力一般应调至３．５ＭＰａ，摩擦辊减压阀压力一般调至３ＭＰａ（当旋切木芯材质较软时，可适当减压）。在调节溢流阀或减压阀时，看压力表…     

斯堪尼亚汽车变速箱润滑转子油泵监视仪表的安装

斯堪尼亚汽车离合器壳中,设有一个为付变速箱润滑的转子油泵。在车辆运行中,因故障而导致其泵轴折断及转子碎裂的情况均有所发生,而驾驶人员往往不能马上察觉。由于该泵的损坏,付变速箱得不到充分润滑,常常会造成     

卧式加工中心Z轴故障处理

通过对THK46100卧式加工中心的实践学习,从所加工产品的实际出发,分析Z轴故障原因及处理方法。将详细的理论分析同实践操作相结合,给出了消除反向间隙的方法。对研究工作给出认识和评价,对主要结论加以概括,并展望了丝杠丝母传动型设备的维护保养工作。     

长龄装载机变速箱动力档故障判断

长龄装载机变速箱动力档故障判断（３５０００９）福州人造板厂蒋文生（１５００３０）哈尔滨电力学校马立滨长龄装载机采用的是平行轴常啮合液压换档的变速箱，设有三个前进档和三个后退档，属于定轴式动力换档形式。这种变速箱的优点是传动齿轮是常啮合的，齿轮的使用寿...     

介绍一种自制的联轴器

吉林省八家子林业局贮木场,在1967年安装原木纵向输送机时,主动轮轴与中间传动轴的联接采用了牙嵌联轴器。从十多年的使用经验看,牙嵌联轴器安装不方便,接触面磨损快,传动系统零部件故障多,维修费用高。为更换这种联轴器,1982年自制了球面滚子联轴器(笔者取名),代替牙嵌联轴器。     

日本汽车柴油机缸套穴蚀的研究

日本产柴油车具有使用性能好、结构紧凑等优点，但随着柴油机强化指标的不断提高，带来了发动机气缸套穴蚀的问题。一般汽车行驶１５万ｋｍ～２０万ｋｍ，便出现缸套穴蚀，甚至漏水，故障日渐突出。穴蚀部位一般发生在气缸中上部，垂直于活塞销轴方向的一侧或两侧（靠近挺...     

Fractography of shear failure surface of softwood decayed by brown-rot fungus

In order to investigate shear failure surface of decayed wood, wood pieces of ezomatsu (Picea jezoensis) were exposed to brown-rot fungus (Fomitopsis palustris), and standard shear test in radial plane was conducted. The failure surfaces were examined by scanning electron microscopy and surface roughness measurements were also conducted. Transwall failure that the crack elongated parallel to the tracheid axis was observed in the earlywood region through all phases of decay. Intrawall failure principally occurred in the latewood region on the early phase of decay. When decay progressed considerably, transwall failure that the crack elongated perpendicularly to the tracheid axis occurred. And transwall failure was also dominant failure morphology in the latewood region. Fragments of tracheids which were partly peeled out from S₂ layers were observed in some specimens. Size and appearance frequency of fragments of tracheid were smaller and lower when decay progressed. Arithmetic average roughness, which was the index of fragment size and appearance frequency, had positive correlation to shear strength ratio. Especially, line surface roughness of radial direction, which was measured across the radial files of tracheid, had the highest correlation to the shear strength ratio. The surface roughness would be a good indicator to evaluate the decay degree.     

地轴极移变化与全球气候变迁规律对森林的影响

根据地轴极移变动理论,通过对地轴极移规律的了解,描绘出全球气候变化对森林变化的发生发展规律,从而预测今后森林变化,提出对应森林变化的对策。     

Location of the neutral axis in wood beams: A preliminary study

Abstract

It is commonly accepted in the analysis of wood beams that the neutral axis coincides with the beam's centroid. However, wood is not an isotropic material, has different elastic properties in the tangential, radial and longitudinal directions, and is non-homogeneous, as it contains characteristics such as knots. Therefore, there is need for an analysis of the neutral axis for anisotropic, non-homogeneous materials, such as wood, to predict deformations and strains. Specifically, digital imaging correlation, a non-contact technique to measure deformation of an object's surface, is used to examine how knots influence neutral axis location. Output from digital imaging correlation software provides a clear image of the location of the neutral axis. The neutral axis in a clear wood beam remains close to the centroidal axis throughout loading, while the location of a knot determines the size of the compression and tension zones as well as the location of the neutral axis.     

Evaluation of a modified Iosipescu shear test method for determining the shear properties of clear wood

A modified Iosipescu shear test method is proposed as an alternative for measuring the shear properties of clear wood. The method adopts four-point asymmetric loading procedure in the Iosipescu shear test but with the loading positions shifted to the neutral axis of the specimen. The original V-notched specimen is replaced by a combination of polyvinyl chloride blocks at two ends and a bow-tie-shaped wood specimen in the middle to provide a better stress pattern at failure. The measured shear strength and shear moduli are compared with results from compression test and off-axis tension test. Finite element analysis is also carried out to study the stress distribution in the wood specimen. Results show that the new shear test setup can provide close-to pure shear stress state in the specimen yielding better estimates of the shear properties of wood. The shear strength obtained by the new test setup is slightly lower than that from the off-axis tensile test which is probably due to the relatively thick specimen chosen in this study.     

Evaluation of the section modulus for tree-stem cross sections of irregular shape

The effect of section modulus, as estimated for tree stems of irregular cross section with hollow trunks, on windthrow resistance is discussed. The sample trees were 12 aged poplar trees growing along the roadside in Sapporo. Binarized bitmap images of photographs of the crosscut surface of the sample tree stems were used to calculate numerical solutions for section moduli. The error for image resolution was simulated to less than 1% under the condition in which the image was divided into more than 400 pixels. The coefficient of variation in section modulus concerning six neutral axis directions in a horizontal plane was 11%–14%. The reduction in section modulus caused by decay or hollow trunk was 36%–56% of the full cross section. The effect of section modulus on critical wind velocity was found to be considerable. The critical wind velocity calculated for some of the sample trees was less than 40m/s, and these trees were considered to be in danger of bending failure of the stems.     

Shear behaviour of laminated Douglas fir veneer

The rolling shear and longitudinal shear behaviour of laminated Douglas fir veneers was studied using specimens with 15 layers of 2.5 mm veneers. The rolling shear specimens were constructed such that the 3 central veneers were cross-plies with grain angle oriented perpendicular to the long axis of the specimen. The other layers were orthogonal to the cross-plies. The longitudinal shear specimens had a LVL lay-up with the exception of a reinforcement layer of fiber-glass attached to the bottom face veneer. The fiber-glass layer prevented specimens from failing in bending/tension mode and ensured longitudinal shear failures. Specimens were subjected to static and cyclic loads in a “flatwise” three point bending configuration. It was found that the rolling shear failure mode exhibited a higher fatigue resistance than the longitudinal shear failure mode. A damage model that took the stress history into account was calibrated to the experimental data of each specimen type. Good agreement between model predictions and experimental results were obtained for both failure modes. Received 5 November 1997     

Effect of fatigue and annual rings’ orientation on mechanical properties of wood under cross-grain uniaxial compression

The mechanics of fresh wood with and without a fatigue pre-treatment that mimics a mechanical pulping process was experimentally studied. The mechanical properties of Norway spruce samples under compression are considered with the macroscopic stress–strain data and from local strain properties via digital image correlation technique. The results highlight the effects of the orientation of the wood annual rings compared to the loading direction and of the pre-fatigue. The wood presents a low yield point when the annual rings are tilted compared to the load axis, but the Young’s modulus and yield stress are higher when the annual rings are either parallel or perpendicular to the load direction. In the last case, buckling of softest layers occurs. The fatigue treatment makes the wood less stiff as deduced from the decreases of Young’s modulus and yield stress, whatever the orientation of annual rings. Secondly, it creates a thin and localized softened layer.     

1860-1937 年广州城市空间格局与形态演变分析

晚清至民国时期是中国历史上的重要转折期,此时期广州的城市规划与建设共同促进了其向现代城市的转型。通过对1860—1937年(第二次鸦片战争至全面抗战前夕)广州城市规划建设的重要事件、历史文献等进行梳理,探讨广州城市格局与形态的演变过程及特征,并从城市组团、道路系统、中心轴线、公共绿地4个方面进行深入阐述。最终得出这一时期广州市城市形态发展变迁规律:在保留了原有城市核心及山水结构的基础上,广州城在拆城墙后逐渐向东、南方向发展,形成了兼具统领性、开放性、高效性的现代城市空间结构,奠定了此后的城市形态与发展格局。     

Process of absorption and desorption of water in a wood board,with 3-dimensional transport beyond the FSP

Summary The process of absorption of water in a piece of solid wood, as well as the following stage of desorption is studied, when the water content is beyond the fiber saturation point. A model based on a numerical method with finite differences is built and successfully tested. This model takes into account a 3-dimensional transport of water controlled by diffusion, with three principal axes of diffusion and three various principal diffusivities. The model is able to predict the kinetics of absorption or desorption when the three principal diffusivities are known, as well as the operational conditions.Symbols C (i, j, k) Concentration at the position of the coordinates i, j, k and at the time t - CN (i, j, k) Concentration at the same position, at the time t + t - C_s Moisture content at the surface - D_L Longitudinal diffusivity - D_T Tangential diffusivity - D_R Radial diffusivity - L Increment of space along the longitudinal axis - T Increment of space along the tangential axis - R Increment of space along the radial axis - t Increment of time - EMC or C_eq Moisture concentration at equilibrium - K Factor of evaporation (cm/s) - L, T, R Dimensions of the board along the longitudinal, tangential, radial directions, respectively - M_L Dimensionless number for the longitudinal axis - M_T Dimensionless number for the tangential axis - M_R Dimensionless number for the radial axis - Th Thickness of a sheet (in Eq. 15)     

论包装装潢马口铁在冲压制品中的工艺问题

本文对马口铁在冲压制品中的特点、基本分类及生产工艺做了比较详细的论述;并对生产过程中常出现的缺陷及原因进行了分析。