Difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing

We examined the difference in the detection limits of flaws in the depths of multi-layered and continuous aluminum plates using low-frequency eddy current testing. The detection limits were measured by using a magneto-resistive sensor. Comparing the frequency of an applied magnetic field, the detection limit at 50 Hz is deeper than that at 1 kHz. Comparing the sample structure, the detection limit in the multi-layered samples is deeper than that in the continuous samples. These results are likely due to the differences in the skin depth and conductivity of the sample.     

提高冷轧板表面质量的工艺研究

通过对唐钢酸轧-罩退-平整-重卷各生产线关键技术的优化和生产实践的摸索,降低酸轧工序的板面残留物、减少罩退工艺粘结缺陷、优化平整、分卷工序工艺参数,实现生产线高产、高质量、低耗的目的。     

A study on horizontal stud welding by using steel stud for flat welding

ABSTRACT

In recent years, manufacturing sites have strongly requested for the steel stud with large diameter to be welded in the horizontal position, which is difficult because of gravity. In this study, the steel stud of 19 mm in diameter was welded horizontally to the mild steel plate by using ferrule for usage in flat position. As results two kinds of weld defect were observed; lack of fusion and blowhole. The former occurred in the welding condition of too small or too large heat input, and the latter did in the range of longer arc time. Therefore, the suitable welding condition could be found in the large current and shorter arc time. When the areal ratio of weld defect to the cross section of stud was lower than 10 percent, the welded joint had enough statical strength.     

提高6082-T6铝合金扁棒材力学性能的试验研究

针对6082-T6铝合金扁棒材力学性能较低不能满足用户使用要求,开展了调整其化学成分和生产工艺参数的试验研究。制定了内控的各元素含量范围;生产工艺中控制:铸锭均匀化温度565℃~575℃,保温8 h,出炉后强风+水雾联合冷却;挤压系数11.4;淬火温度540℃,时效温度(175±5)℃,保温10 h。生产出了力学性能较高的符合用户要求的扁棒材。     

Method for sizing of 3-D surface breaking flaws by leakage flux

A method is proposed for sizing of 3-D surface breaking flaws with complex profiles. The method can be used for either magnetic materials or conductive materials when a magnetic field or electric current are distributed homogeneously inside the sample. The distribution of the intensity of the leakage magnetic field or electric field has to be measured at a constant distance above the surface of the sample in a direction perpendicular to the long axis of the flaw. The method is based on a dipole model of the flaw which predicts the intensity of the leakage field and on minimisation of the error between the measured distribution of the intensity of the leakage field and the corresponding theoretical distribution which changes with the size of the flaw. Computations are made for sizing of flaws with different shapes and sizes while it is assumed that the density of the charge at the walls of the flaw can vary. It is shown that the method allows fast distinguishing of the shape of a particular flaw where the sample contains several flaws with different shapes and the sizes of these flaws are known. Fast determination of the size of a particular flaw is achieved when the sample contains flaws with the same shape and different but known sizes. Also, the size of the flaw and the density of the charge at the walls of the flaw could be computed precisely, independently of the initial approximation of the minimisation procedure, when the shape of the flaw is known. The speed of the minimisation process increases with the decrease of the measurement distance from the surface of the flaw. Experimental requirements for precise flaw sizing are discussed.     

Finite element modelling of the scattering of ultrasonic waves by isolated flaws

A two-dimensional finite element model with absorbing boundary conditions has been developed to investigate the scattering of ultrasonic waves in infinite isotropic solids. The model is capable of showing a complex mode-conversion, when a short duration sinusoidal pulse interacts with a flaw. The emphasis is on narrow crack-like defects, cylindrical and spherical holes of size equal to the wavelength of the incident wave. The results, which are presented in the form of snapshots and scattering cross-sections, assist in understanding wave–flaw interaction, especially mode-conversion of the incident field and optimizing the ultrasonic NDT.     

Experimental evaluation of electromagnetic-thermal non-destructive inspection by eddy current thermography in square aluminum plates

The performance of electromagnetic-thermal non-destructive inspection is investigated experimentally by eddy current thermography. The experiments concerned the detection of the crack in ten square aluminum plates at various positions and orientations. For the excitation are employed two circular coils with an outer diameter either smaller or comparable to the plate side. Crack detection is based not only on the thermograms, but on data processing techniques as well. Despite the fact that the performance of the infrared camera used is relatively low and the exciting frequency was only 50 Hz, the coil with small section detected effectively the nine cracks out of the ten while the coil with large section detected effectively seven out of ten.     

铝合金扁管补助弯曲工艺数值模拟及实验

针对扁管辊弯基本成形方法 直接成方成形过程中纵向拉应力过大的问题,提出了侧壁补助弯曲的解决方案。并以三点弯曲理论为基础建立数学模型,对辊弯过程进行有限元分析,得到一组较优的成形参数,并进行实验验证。结果表明,侧壁补助弯曲的成形方法能基本解决条料成形过程中纵向应力过大的问题;提高了成形质量,简化了成形工艺,降低了生产成本。     

A study on the cross-sectional profile of flat rolled wire

In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the cross-sectional profile. Also, the theoretical results are compared with the experimental data. It has been found that the numerical method is able to predict the lateral spread, the width of contact area, and the curvature radius in all ranges of the reduction in height with a good accuracy, while the other methods exhibit a reasonable accuracy only for a limited range of height reduction. All results of the methods show that with increasing the reduction in height, the lateral spread and width of contact area are increased and the curvature radius is decreased. The appropriate ranges of height reductions for each method are recommended.     

钢包渣洗脱硫剂的试验研究与应用

为了研究微合金化钢因硫含量超标而导致成品钢材出现裂纹等质量问题,以船板钢C36-1为研究对象,通过采用多因素多水平正交回归的试验方法进行了钢包渣洗脱硫剂的组分设计研究,根据实验室基础试验数据建立了脱硫剂的组分设计模型。结果表明,当脱硫剂中w(CaO)=42%~55%时对脱硫率的影响较为明显。w(Al₂O₃)<35%以下、w(CaC₂)=12%较为合适。经工业生产试验验证,脱硫剂的组分最终确定为w(CaO)=42%~55%、w(Al₂O₃)=30%~35%、w(CaC₂)=8%~12%、w(CaF₂)=8%~10%。该脱硫剂的工业平均脱硫率达到了80.93%。新型脱硫剂的使用稳定控制了船板钢钢液中硫质量分数至0.010%以下,铸坯裂纹判废率降低了85%左右,满足了企业对该类钢种控硫的工艺需求,增加了企业的经济效益。     

磁脉冲冲孔试验研究

磁脉冲冲孔是一种高能率成形方式,特别适合于薄板加工.采用试验的方法,在3种不同成形方式下,研究放电电压对冲孔成形性能的影响.研究结果表明：冲孔所需最小成形电压随着板料厚度的增加而增加;对于同一厚度的铝板,当电压大于最小冲孔电压时,电压越大,断面质量越好;在3种成形方式中,板坯上下放置弹性传压介质的成形方式毛刺区域最小,断面质量最佳,但所需能量最大.     

FEM study on the influence of air gap and specimen thickness on the detectability of flaw in the yoke method

The yoke method is usually used as a magnetic testing method of welds. In this paper, we study the influences of the air gap between the magnetic pole and the specimen surface on the average magnetic flux density passing through the specimen, and the specimen thickness on the leakage magnetic flux density from a flaw using finite element method (FEM). When the air gap increases the average magnetic flux density at the center of the specimen length decreases. We can estimate the intensity of the magnetic field on the specimen surface by extrapolating the magnetic flux density in space to that at lift-off being zero. Moreover, the maximum leakage magnetic flux density from a flaw decreases with increase in the specimen thickness even if the average magnetic flux density passing through the specimen is the same.     

A study on the analytical modeling for warm hydro-mechanical deep drawing of lightweight materials

The warm hydroforming process has become an emerging technology in recent years to reduce the weight of automotive body structure and minimize the number of process steps. In this study, analytical models were developed to investigate the effects of process conditions such as temperature, hydraulic pressure, blank holder force and forming speed. The analytical model under hydro-mechanical deep drawing (HMD) condition was developed based on experimental results in the literatures. FE models were also developed to validate the analytic models. Then, the analytic model was validated through comparisons with both existing experimental results and FE results. The analytical model provided rapid and reasonably accurate results for the design of warm hydroforming process. Based on this analytic model, several parametric studies were performed regarding to the temperature, hydraulic pressure, blank holder force, and punch speed conditions. It was demonstrated that the process windows for a successful part forming could be rapidly predicted with a reasonable accuracy by the analytic model compared to lengthy and costly thermo-mechanical FEA or experimental trial and error.     

分子识别技术分离提纯钯的工艺实验

采用分子识别材料SuperLig^ò2从含铂钯的溶液中选择性分离钯,钯吸附率大于99%,吸附、洗脱过程钯的直收率为95.87%,总收率为98.04%;得到的洗脱液氧化处理后生成钯沉淀,再经水合肼还原即可得到纯度为99.99%的钯粉。与传统的沉淀分离工艺相比,分子识别技术的生产流程短、铂不容易分散、操作方便、三废量少。     

超声波冲击破碎粗粒度金刚石的实验研究

利用超声波冲击方法控制金刚石的微破碎,实验中采用圆锥形和楔形两种不同刃口形状工具进行冲击破碎实验,观察不同参数下所获得的金刚石形貌,实验结果表明:利用楔形刃口形状工具冲击单颗金刚石,可以控制金刚石的破碎大小;并且在同一实验参数下,四边形顶面的金刚石破碎程度比六边形顶面的金刚石破碎程度大;通过调节合适的超声波冲击参数,利用楔形刃口工具可以使粗粒度金刚石按照不同形式刃口进行破碎。     

Change of the equilibrium state of ferromagnetic MnBi by high magnetic fields

Differential thermal analysis was carried out for ferromagnetic material MnBi in the temperature range 300-773 K in magnetic fields up to 45 T to investigate the effect of high magnetic fields on its decomposition process and corresponding phase diagram. The decomposition temperature T_t (MnBi → Mn_1.08Bi + liquid Bi) increases from 632 K (at a zero field) to 714 K by applying a magnetic field of 45 T. Furthermore, the magnetocaloric effect of MnBi is observed in 11.5-45 T in the vicinity of 689 K, showing that a field-induced composition process occurs. The obtained results show that the equilibrium state of MnBi can be controlled by a high magnetic field.     

Generation of ferromagnetic micro- and nanoparticles by laser and mechanical milling methods

The generation of micro- and nanoparticles using laser cutting of steel strips of the thickness of 0.2–0.6 mm and the separation of particles according to their size were studied. Under optimal cutting conditions (laser power, gas pressure before the nozzle), the cutting quality is good when a small amount of fully oxidized erosion products at the cut edge of a slit is obtained. The study showed that the cascade filter system can be used to separate the particles up to nanometer dimensions. The simulation of the gas flow can be used to create optimal conditions for collecting generated particles of the required dimensions. The modelling data confirmed that small particles from the liquid metal state in the cut slit are generated most effectively using nozzles forming ring flows. The larger particles modification with aluminium and zinc by milling was performed.     

管板材SGMF工艺传压介质的物理性能试验

固体颗粒介质成形工艺(SGMF)是采用固体颗粒代替刚性凸模(或凹模)的作用,对板材、管材等毛坯进行拉深、胀形的半模成形工艺。该工艺不同于传统的软模成形的重要区别是,其采用固体颗粒作为传力介质改变而导致成形规律与众不同。深入探索固体颗粒介质的物理特性,是实现应用该工艺进行实际生产的重要理论依据。文章通过试验,分析了不同粒径GM固体颗粒介质高压下的基本物理性能,得出GM颗粒介质体积压缩率曲线,并给出幂指函数本构关系方程;得出了GM颗粒之间及GM颗粒与板材之间在不同压力状态下的摩擦系数曲线;分析得到GM颗粒介质在轴线方向和底面上的压力传递规律,并给出了数学描述。     

Experimental and numerical characterisation of heat flow during flame cutting of thick steel plates

Temperatures measurements during flame cutting of a thick steel plate and measurements of the extension of the fusion and heat affected zones and Vickers hardness after cutting have been performed. Additionally, a 3-D thermal model for simulation of flame-cutting has been developed. For the sake of simplicity, the model depends only on two parameters: (i) the heat density within the flame, and (ii) the heat transfer coefficient within the air gap that forms behind the cut. The results show that the model is able to properly reproduce the measured temperature curves and the heat affected zone with an input power in the same range of those reported in the literature. A process efficiency of 26.5% is found in the steady state regime of flame-cutting.     

Numerical and experimental study on in-plane bending of microchannel aluminum flat tube

Microchannel aluminum flat tubes have attracted more and more attention in recent years, especially in ACR (air conditioning and refrigeration) industry. Rotary-draw bending is a versatile and precise method in forming of tubes. Compared with traditional out-of-plane bending method, in-plane bending can cause different forming defects. During the process, wall thinning, sectional distortion, wrinkling, and channel shape degradation are the main defects that affect tube quality in industrial applications. In this paper, an experimental apparatus for flat tube in-plane bending is manufactured, and experiments are performed to examine the forming quality of tubes. Considering the characteristics of the bending process, based on the LS-DYNA software environment, a 3D elastic–plastic finite element model is established and validated by experiment. Using the validated FE model, the forming quality of microchannel flat tube bending process is evaluated quantitively. Furthermore, the influence mechanism of process parameters, such as bending radius, tool–tube clearance, and channel diameter, has been revealed. The results indicate that the degradation of the tube channels is relatively small under common process conditions; bending radius is the main factor which influences the forming quality of the flat tube; the tool–tube clearance mainly affects the wrinkling of the flat tubes; channel diameter has little effect on the formability of tube.