均衡凝固技术在精密铸造三通件上的应用

熔模铸造不锈钢三通铸件生产时,由于冒口与热节之间距离较远,导致两者之间的补缩通道堵塞,产生缩松缺陷。为消除此缺陷,运用均衡凝固技术对其进行工艺改进,在偏离热节的位置设置浇冒口。利用模拟软件对改进后工艺进行模拟分析。结果表明,新设置的冒口与产生缩松的热节之间补缩通道畅通,铸件中的缩松消失。     

降低干式缸体渗漏率的工艺措施

针对干式六缸体渗漏缺陷问题进行分析,探究了缸体铸件渗漏产生的原因。通过在热节处采取放置内冷铁、涂刷碲粉涂料及产品结构优化等一些列工艺措施后,热节处缩松缺陷大大降低,该缸体的渗漏率由22%降低到的5%。这为公司开发干式缸体解决渗漏问题积累了经验,同时对解决缸盖渗漏问题也有一定参考价值。     

碲粉涂料的副作用及其防止

我厂生产的6105Q缸盖由于在涡流室、螺栓孔等较厚的地方出现缩松漏水,曾一度报废惊人,后于1981年下半年使用了碲粉涂料工艺。经过几年来的生产实践证明,碲粉涂料确实具有消除缩松、疏松缺陷,使铸件厚壁部分组织致密等功能,在某些地方完全可以代替冷铁。但我们也发现有促进白口,产生针孔等副作用。     

应用均衡凝固理论设计灰铁圆轮铸件的浇注系统

出口欧洲的灰铁铸件圆轮,采用传统顺序凝固理论,正对热节开设冒口补缩的铸造工艺,铸件在补缩的冒口颈处产生缩松缺陷,废品率80%,而且铸件的硬度不均匀,不能满足客户对铸件硬度范围的技术要求。按照均衡凝固理论重新设计浇注系统,冒口不开设在铸件的几何热节处,冒口颈的设计为短薄宽的形式,加大浇口的总截面实现快浇,缩松缺陷得到解决,同时解决了铸件硬度不均匀的问题。生产实践表明,利用均衡凝固理论设计圆轮类铸件的浇注系统工艺,不仅能够解决缩松问题,而且能够使得铸件的硬度更加均匀。     

解决铸件缩松的方法

1 缩松产生的原因①铸件产生缩松的根本原因是“热不平衡”所致.缩松的位置,产生在铸件的厚大中心部位、几何热节处、不同壁厚的交接处和浇口根、冒口根的人为热节处.这些地方都因热量过多最后凝固,得不到充分补缩而产生缩松,严重时产生集中性缩孔.②铸造工艺设计不合理,人为地制造热节而产生缩松缺陷.     

轴瓦体铸铁件的数值模拟和铸造工艺优化

根据轴瓦体铸铁件的结构特点,对轴瓦体进行铸造工艺设计。在铸件一侧设计浇注系统,在铸件顶部设计了冒口来实现对壳体进行补缩。用CAD软件建立了铸件的三维模型,运用ViewCast模拟软件对轴瓦体进行凝固过程模拟,发现在铸件顶部及热节处存在缩孔缩松等缺陷。根据数值模拟结果并结合理论分析,通过改用保温冒口的方法改进了铸造工艺方案。结果表明,只在热节处出现少量的缩松,铸件的缺陷已经消失。     

碲涂料铸渗工艺

碲是一种非金属材料、它是强烈的反石墨化元素,原子序数为52,比重6.25,熔点452℃,汽化温度1390℃,液化热4.27千卡/克原子,汽化热11千卡/克原子。碲涂料已逐步在我国铸造生产中推广使用。在铸造生产中,与碲涂料层相邻的铸铁件表面会形成较薄一层白口或麻口层。某些铸件需要有较硬的外壳(例如轧辊)而另一些铸件在工作状态下要经受水、油、气的压力,由于铸件内部产生缩松通道,这些工作介质会渗漏出来,那么致密的白口或麻口层就会阻碍它们的渗出。厚度在13～15mm以下的灰铸铁件,调整碲涂料中碲的含量可以使白口层、麻口层、细     

旋流器铸钢件的数值模拟和铸造工艺优化

根据旋流器铸钢件的结构特点,对旋流器进行铸造工艺设计。在铸件一侧设计浇注系统,在铸件顶部设计了冒口来实现对壳体进行补缩。用CAD软件建立了铸件的三维模型,运用ViewCast模拟软件对旋流器进行凝固过程模拟,发现在铸件顶部及热节处存在缩孔、缩松等缺陷。根据数值模拟结果并结合理论分析,通过改用保温冒口、增加冷铁的方法修改铸造工艺方案。结果表明,只在热节处出现少量的缩松,铸件的缺陷已经完全消失,从而获得了优化的工艺。     

冷铁在我厂球铁件上的应用

球墨铸铁易产生缩松、缩孔缺陷,过去沿用铸钢工艺,靠加大冒口来进行补缩,结果不但使铸件收得率大大降低,而且还很难完全消除缩孔、缩松缺陷。我厂根据球铁凝固特性,通过生产实践,掌握了冒口和冷铁相结合的造型工艺,提高了球铁件的质量和铸件收得率。一、使用冷铁目的1.由于冷铁的激冷作用,可以调整铸件各部位的冷却速度,使易产生缩松、缩孔的热节处加快冷却,从而消除缩孔、缩松缺陷,得到致密的优质铸件,并可用小冒口或无冒口铸造。2.大断面球铁的冷却凝固时间较长,由于孕育衰退造成球墨畸变产生球化不良、用冷铁后,加     

一种解决垂直线铸件缩松的工艺方法

利用MAGMA凝固模拟软件预测垂直造型线铸件热节部位和缩松缺陷,模拟结果表明凝固后期形成的孤立热节是产生缩松的主要原因.采用顺序凝固原则可以解决部分缩松问题,但不能解决所有补缩问题.通过优化铸造工艺,改变内浇口位置并重新模拟,发现孤立热节得到了消除,试验结果与模拟吻合,缩松问题得到了彻底解决,利用凝固模拟优化冒口成功提...     

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).     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

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.