冲床球头连杆螺旋传动失效原因浅析

为适应不同的模具,冲床设计有装模高度调节机构,通常该机构采用螺旋传动方式。螺旋传动偶尔会出现螺杆和螺母无法旋转的情况,导致传动失效。本文对球头连杆螺旋传动失效原因进行分析,指出改进方向及措施。     

某发动机轴承失效原因分析

在对某发动机工作过程中轴承失效的基本特征进行综合分析的基础上,确定了轴承失效属早期发生的疲劳剥落导致的最终失效,轴承早期疲劳剥落与滚棒上沿晶断裂特征有关.对滚棒非正常的沿晶脆性断裂进行了热处理模拟和金相组织以及断口分析,结果表明,掉块主断面上典型的沿晶断裂特征与该滚棒在热处理时局部接触900℃以上的高温有关.     

硬质合金螺旋孔棒材尺寸精度控制与标准探讨

硬质合金螺旋孔棒材是一类尺寸精度要求高、成型难度大而具有高附加值的产品,属于粉末冶金行业重点研究的对象。本文从螺旋孔棒的螺距、同心度、孔径、孔间距等关键指标出发,探讨了螺旋孔棒的尺寸及公差标准,分析了螺旋孔棒尺寸精度的影响因素,进行了提高螺旋孔棒尺寸精度的工艺研究。研究结果说明:模具固化工艺制备的螺旋孔棒比电动调节工艺的内外螺距一致性更好;挤压速度对螺距的影响比挤压压力更大;内孔位置度以同心度表征比孔偏离更科学;孔间距的稳定性与力学平衡相关;通过对芯杆座的改进,三螺旋孔棒的孔夹角精度达到120°±4°。     

桑车20MnCr5钢主动轴螺旋齿断裂分析

某大众试验车行驶8．6万公里后其主动轴螺旋齿断裂。采用宏观检验、金相分析、化学成分分析、应力测试等手段对失效件取样分析，结果表明，螺旋齿断裂是由于轴向定位松动，造成齿轮局部受力集中，在疲劳源基础上发展成裂纹，裂纹进一步扩展导致断裂。     

基于Simufact的螺旋棒压缩成形数值仿真

针对螺旋棒外形复杂、成形难等,分析了6061铝合金细长棒压缩成形原理,运用Simufact建立了压缩成形数值仿真模型,对不同加热温度、压缩速度下螺旋棒的等效应力及等效应变和不同成形阶段它们的分布进行了仿真分析。结果表明,随着加热温度增加,等效应力及等效应变都逐渐减小;随着压缩速度增加,等效应力及等效应变都逐渐增加;在铝合金螺旋棒不同压缩成形阶段,等效应力及等效应变分布位置不同。     

CPE机组荒管螺旋道的成因分析与控制

松棒后的荒管螺旋道是CPE顶管机组生产时的控制难点。分析CPE机组松棒机松棒后荒管螺旋道的形成机理,研究装备存在的问题及其对螺旋道的影响,并提出改进措施。分析认为:提高拉杆外管套的刚性并增大耐磨接触面,提高轧辊装配就位于转鼓上的定位精度,可有效解决荒管与轧辊之间的包络面小于70%的问题,消除松棒后荒管螺旋道,提高荒管质量,减轻工人的劳动强度,提升换辊效率。     

矫直松棒

采用经改进的二辊式和六辊式矫直机进行矫直松棒,松棒后管子的内外径尺寸精确,椭圆度小,内外表面螺旋道轻微。介绍了矫直松棒工艺和松棒机的规格、机型选择以及松棒后管子的性能等。     

发动机低压Ⅰ级涡轮叶片榫头断裂分析与预防

发动机低压Ⅰ级涡轮叶片榫头R处根部发生断裂。经宏微观检查、跨棒距测量、榫头应力计算及模拟疲劳试验分析,对叶片断裂性质及原因进行综合分析,结果表明:叶片断裂性质为多源线性疲劳断裂;渗铝工艺中,由于榫头防护不妥,榫头被渗铝层污染,榫头跨棒距超差,降低了叶片抗疲劳性能,最终导致叶片发生疲劳断裂失效。对渗铝层厚度在0.03 mm以内且跨棒距合格的叶片,通过对叶片榫头严格监控,增加跨棒距测量,渗铝层工艺采用严格的防护手段保护,可有效避免类似故障。     

热处理对H13型钢的力学性能影响

对未经处理和热处理后H13钢芯棒进行扫描电镜、金相及力学性能分析,研究其在不用热处理条件下的力学性能的变化规律。结果表明,未经过热处理的芯棒表面较热处理后出现了失效现象,产生了热疲劳裂纹和机械磨损裂纹。未经热处理芯棒心部有碳化物析出,马氏体的回复引起基体硬度下降,芯棒的边缘冲击韧度较高,过早出现热裂纹及深裂纹导致芯棒失效。     

游星齿轮轴承失效分析

某发动机用游星齿轮轴承在工作过程中发生失效,保持架断裂,滚棒、滚道磨损.本文对失效保持架、滚棒、中间齿轮轴进行了断口形貌观察、金相组织及硬度检测、化学成分分析等工作.分析结果表明,保持架的断裂性质为疲劳断裂,滚道的损伤性质为接触疲劳.游星齿轮轴承的失效主要与轴承组件中应力不均匀、局部应力过大有关.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.