An experimental study of heat transfer in aluminum castings during water quenching

The influence of quenching orientation and agitation conditions on heat transfer of aluminum alloys during water quenching was experimentally investigated with a test casting. The results indicate that heat transfer in water quenching of casting aluminum alloy consists of film boiling, nucleate boiling and convection stages. The highest heat transfer coefficients (HTC) are observed in the nucleate boiling, while the lowest is in the convective cooling stage. The heat transfer coefficients on the horizontal surfaces facing down during quenching are lower than those of other surfaces regardless whether the water is agitated or not. Agitation enhances heat transfer process especially when castings are at high temperatures and heat transfer process is in the film boiling stage.     

Influence of Rewetting Behavior on the Distortion of Bearing Races

Immersion quenching in evaporable fluids like oil, polymer solutions, or water is a widely used technique in heat treatment shops because this technique provides higher heat transfer coefficients than the most alternative gas quenching techniques. The disadvantages of immersion quenching in evaporating fluids are the complex heat transfer mechanisms which consist of the three phases, film boiling, nucleate boiling, and convection. Especially the transition from film to nucleate boiling—the rewetting of the sample surface—is a complex process which leads to a strong position dependence of the heat transfer coefficient of the cooled work pieces. In particular, immersion quenching of thin-walled rings can result in large changes of ovality with comparable high scattering. To understand these results, two series of experiments were performed. Rings were quenched in oil in a special quenching tank and the rewetting behavior was documented. Furthermore, bearing races were quenched in a standard tank. Before and after heat treatment, these rings were measured by a coordinate measuring system and the distortion was determined. The investigations have clearly shown that the vapor film can have an important influence on distortion generation during oil quenching. The resulting distortion can principally be explained by the observed rewetting behavior.     

包晶合金定向凝固过程中的对流效应及带状组织形成机制Ⅱ.理论分析

本文分别利用纯扩散模型、溶质边界层对流模型和强对流Scheil方程对包晶合金定向凝固过程中的带状组织.宏观偏析的形成规律以及对流效应进行系统研究,详细讨论了对流对包晶合金定向凝固过程中带状组织和宏观偏析的影响规律.与Fe-Ni包晶合金定向凝固实验结果进行对比发现,对流强度参数λ在1.7至2之间时溶质边界层对流模型预测结...     

Passivation degradation of Alloy 800 on nucleate boiling surface

In this work, the passivation degradation of Alloy 800 on nucleate boiling surface was studied by using polarisation curve, electrochemical impedance spectroscopy and secondary ion mass spectrometry. Experimental results indicated that boiling bubble would significantly degrade the passive film, as indicated by a decreased pitting potential and increased passive current density. Under boiling condition, the mass transfer of electrolyte is accelerated and the temperature of Alloy 800 was increased, as a result, the cathodic reaction and the dissolution rate of the passive film were increased. The passive film was Cr-depleted but Ni- and Fe-enriched, and the decreased Cr content in the passive film led to a degraded passive film.     

Effect of Steam Temperature on the Corrosion of Metals under Heat-Transfer Conditions*

Abstract

Previous workers have shown that the corrosion rate of metals in acid media is frequently much greater under heat-transfer conditions than it is under simple immersion conditions. In the work described here it has been found that the rate of corrosion of a metallic heating surface is critically dependent upon the temperature of the heating surface in relation to the boiling point of the liquid heated. Experiments have been made with copper and stainless steel heat-transfer surfaces over the temperature range 75°-140° in acetic and sulphuric acids. It was found that there was a pronounced increase in the corrosion rate when. the temperature of the heat-transfer surface was held atapproximately the boiling point of the liquid being heated. At this temperature the corrosion rate was some five times that of the corrosion rates at higher and lower temperatures.     

包晶合金定向凝固过程中的对流效应及带状组织形成机制Ⅰ.实验结果

利用电阻加热和感应加热Bridgman定向凝固系统对非小平面包晶系模型合金Fe-Ni合金进行系统的定向凝固实验研究,探索2种常规定向凝固条件下对流对包晶合金定向凝固过程中带状组织和宏观偏析的影响规律.发现在高G/V定向凝固过程中,对流使包晶合金定向凝固过程中轴向和径向形成严重的宏观偏析,从而使组织演化异常复杂且难以达到...     

Thermal flow simulation and visualisation of PAG quenchants in cooling evaluation equipment with twin stir

Abstract

In this research, the formation and movement of bubbles in boiling film during quenching process was investigated with high speed video camera and particle image velocimetry (PIV) technology as the visualisation method. Cooling curves of surface temperature during quenching of a silver cylinder were measured and the heat transfer coefficients between quenchant and quenching parts were identified. The cooling ability of the coolant used for the quenching technology was evaluated relative to the quality the machine part. As for this paper, the cooling capacity of the PAG quenchants (polyalkylene glycol solutions) was evaluated. In addition, the heat transfer behaviour in the quenching process is clarified with regard to the generation and the destruction of the thermal flow and collapse of the steam film by using the PIV method of visualisation. The effect of mechanical stirring of the quenchant on the steam film and heat transfer is also studied.     

Development and application of computer simulation code COSMAP on induction heat treatment process

Abstract

Induction heating reduces energy consumption, contributes to the protection of the environment, and improves productivity. This paper describes the development and application of computer simulation of induction heat treatment considered with coupling of temperature field and magnetic field. In this paper, the developed simulation code COSMAP is introduced as a CAE software system for considering the design of induction heat treatment process. It covers all aspects of heat treatment simulation, from magnetic and electrical to thermal states, phase transformation, residual stresses including as well all metallurgical phenomena.     

The testing of corrosion inhibitors for central heating systems

Modern inhibitor formations for protecting central heating systems against corrosion and scaling are complex blends of chemicals, which often act synergistically. They need to protect the mixed metal system for upwards of 20 years. It is, therefore, important to be able to assess the long-term performance of an inhibitor within a reasonable time period. The present approach is to carry out initially short-term electrochemical studies on a variety of metals at 80°C. Longer-term testing is then carried out using both electrochemical and weight-loss measurements, usually under conditions of thermal cycling. The polarisation resistance of several metals can be measured simultaneously, either in a coupled or uncoupled state, using a multiple offset zero-resistance ammeter technique. Possible adverse effects due to nucleate boiling on boiler surfaces are investigated by subjecting specimens to heat flux of 25 W cm⁻². Other factors which have been taken into account are the water quality, over- and under-dilution with inhibitor and degree of aeration. The paper describes the development of a non-toxic nitrite free inhibitor based on molybdate-borate-phosphate-carboxylate.     

高频感应钎焊中电源频率的优化选择

在高频感应钎焊的过程中，要获得良好的钎焊接头，必须要根据接头材料的物理性能选择合适频率的高频电源，采用计算机数值分析手段建立了感应加热电源及其频率范围的选择数值分析模型。研究表明，数值解析法可以作为高频感应钎焊感应加热设备设计的重要方法。在对高频电源电流频率等参数的选择时，利用数值解析模型所得到的解析近似解进行频率选择比传统经验公式更精确。因为后者由平面电磁波在导电媒质中的传播特性导出，更适合于板状结构感应加热时频率的选择。而对于管状或其它复杂形状，利用数值解析解可以较好地对高频电源的频率进行优化选择。     

Analysis of acoustic characteristics for plasma arc cutting

Abstract

The sound emitted during plasma arc cutting is closely related to the cutting conditions including cutting speed, arc current, operating gas flowrate, torch standoff height, nozzle shape, etc., and it therefore contains useful information for the evaluation of the plasma arc cutting process. The present work investigates the characteristics of the sound emitted during plasma arc cutting under various cutting conditions, using fast Fourier transformation and probability statistical analyses. An acoustic model of plasma arc cutting, having two jet sound sources, is proposed to interpret this sound. The sensitive frequency band of the cutting sound and the relationship between the cutting sound and the conditions are then revealed. It is shown that the cutting sound is a random signal readily affected by cutting conditions, and its energy is concentrated in the high frequency field and originates mainly from the mixing region of the first sound source and the mixing and transition regions of the second sound source. Experimental results also suggest the possibility of developing an acoustically based monitor system for this plasma arc process, and of reducing the acoustic exposure level, thereby improving working conditions.     

金字塔砂带磨损状态的声信号GA-BP识别方法

目的 金字塔砂带连续磨损会引发钝峰、材料去除能力差和产热多等问题,为避免砂带磨损造成加工效率持续降低和工件表面质量逐渐恶化,需提高金字塔砂带磨损预测能力。方法 在配有声音采集系统的力控机器人磨削系统中对钛合金工件进行了砂带磨损试验;基于Archard模型建立了金字塔砂带磨损模型,并对金字塔砂带磨损程度进行量化;然后利用短时傅里叶和小波包分解分析、提取砂带磨损相关的声音特征;基于声音信号特征建立GA-BP模型,并对金字塔砂带磨损状态进行预测。结果 Kr与R0规律相近,随着磨削速度的增大而略微增大。对磨削声音进行小波包分解,DD2频段的声音特征随磨削时间逐渐降低,相较于其他频段更具有规律性。提取DD2频段的声音信号特征建立GA-BP模型,并对金字塔砂带磨损状态进行预测。结果表明,决定系数(R²)大于0.8,平均绝对误差(MAE)小于0.04,平均偏差误差(MBE)在±0.002之间,均方误差(RMSE)小于0.05。结论 随着砂带的磨损,金字塔尖锐的胞体开始磨平,单颗胞体的局部压力逐渐减小,材料去除能力减弱,产生的微振荡越来越弱,高频信号的声音特征逐渐下降。通过DD2频段声音信号特征建立的GA-BP模型对金字塔砂带磨损状态进行预测,具有准确性和稳定性。     

Comparative study of cooling curves with JIS silver specimens and alloy 600 specimens in relation to additive effectiveness

Quenching- oil cooling curves obtained using a silver specimen (Japanese Industrial Standard K 2242) in-dicate three stages of cooling: vapor blanket, boiling, and convection. The temperatures at which the va-por blanket stage transfers to the boiling stage and the boiling stage transfers to the convection stage are referred to as the characteristic temperature (CT) and the convection- stage starting temperature (CSST), respectively. As the amounts of CT- improving additives are increased in increments of 1,2,3,6, 8, 10, and 12%, the CTs become higher, as clearly shown in the cooling curves obtained using a silver specimen. Likewise, as the amounts of CSST- improving additives are increased from 1 to 2 to 3%, the CSSTs become lower. These tendencies are similarly observed when using an Alloy 600 specimen, and both additives effectively improve cooling performance. However, in the case of 6,8,10, and 12% CT- im-proving additions, the differences among the additive concentrations are more pronounced in cooling curves obtained using the silver specimen than in those obtained using the Alloy 600 specimen. This can be attributed to the greater temperature sensitivity of the silver specimen thermocouple. In field quench-ing operations, such phenomena as insufficient hardness, inverse quench hardening, and unstable distor-tion can be remedied by additive treating. However, one must know what type of additive and how much to use. To this end, cooling curve measurement using silver specimens is useful.     

机电一体化感应加热设备的应用进展

随着感应热处理技术的不断发展,对感应热处理设备提出越来越高的要求.感应加热电源:可控硅中频电源、IGBT全固态中频、超音频电源、MOSFET全固态高频电源,以及机电一体化技术的出现都为感应热处理的发展打下了坚实基础.本文介绍了新型感应加热电源及自动化、高机械化程度的机床设计开发程序,以及典型的应用实例.为缩短与发达国家在感应热处理设备方面的差距,我国的感应热处理设备正向节能、高效、机械化、自动化发展,已开发出一系列先进的、多品种的机电一体化感应加热成套设备,克服了传统感应热处理设备许多缺陷,满足了大批量生产的要求.     

IFHTSE Global 21: heat treatment and surface engineering in the twenty-first century Part 15 – Progress in surface heat treatment using electron beam surface hardening

Abstract

By using high frequency beam deflection techniques it is possible to carry out highly productive electron beam (EB) surface treatment. As a result of comprehensive investigations about the influence of EB parameters on structure and properties of the material in connection with EB hardening of steels and cast irons over the last 25 years, very interesting industrial applications are available now. The paper deals with the state of the art in this field.     

Cooling Curve's Effect on Hardening Behavior of Steel

TO QUENCH HARDEN STEEL MATERIAL,it isrequired to give rapid quenching in the temperaturerange required of rapid quenching.On the other hand,quenching oil comprised of mineral oil as majorcomponent can be modified of its cooling curve byusing various additives.Thereby,we havequench-hardened some steel material each havingdifferent pattern of CCT curve,using quenching oilcomprised of mineral oil modified of coolingcharacteristics by dosing additives,and surveyedrelationship between ha…     

The mechanism of initial de-wetting and detachment of thin Au films on YSZ

Thin Au layers on single crystal Y₂O₃-doped ZrO₂ (YSZ) de-wet from the substrate during thermal annealing in the solid state, and form small crystalline particles. Voids in the film nucleate at the metal–ceramic interface, and then grow to form pinholes in the film. Thus void nucleation at the metal–ceramic interface was identified to be the mechanism for solid-state de-wetting, rather than grain boundary grooving at the free surface of the film. Eventually, complete de-wetting occurs via solid-state diffusion, driven by minimization of the surface and interface energies of the system. In parallel to the de-wetting process, bubbles form in the film, driven by compressive thermal stresses and by the pressure exerted by gas chemisorbed from the substrate.     

Influence of sulphide ions on corrosion resistance of special austenitic stainless steels in phosphoric acid

Abstract

The influence of sulphide ions on the corrosion resistance of some special stainless steels in 40 wt-% H₃PO₄ with 330 ppm SO^2?₄ and 1000 ppm Cl^? at 80°C has been investigated using electrochemical (polarisation curves) and spectroscopic (infrared, SIMS) techniques. The behaviour of ZI NCDU 25–20 and ZI CNDU 25–25 commonly used in the phosphoric acid industry is compared with that of ZI CN 25–20 to estimate the role of the alloying elements. The corrosive effect of sulphide ions is confirmed: they shift the corrosion potential to more negative values and increase the anodic current in the active and passive states. In order of increasing corrosion rate the three steels are ranked as follows: ZI CNDU 25–25, ZI NCDU 25–20, ZI CN 25–20. The corrosion products consist largely of magnetite in a more or less oxidised state with chromium and nickel substituted for iron. The film formed on the ZI CNDU 25–25 alloy is more protective because of the high chromium content of the mixed oxide and the effect of molybdenum. The film retards the diffusion of corrosive ions through to the metal andfacilitates the development of passivity. However, the presence of a sufficiently high concentration of sulphides in solution prevents the establishment of passivity.     

New thermogalvanic method determines the conditions which cause dezincification of admiralty brass in field service

A newly developed laboratory test method based on thermogalvanic currents realistically simulates the dezincification of admiraly brass in fresh or sea water. It is especially useful for studying the dezincification of brass heat exchanger tubes.The method uses an internally heated tube that is exposed to a test solution while being galvanically coupled to a relatively large colder piece of the same metal. The tube is thermally insulated in such a way that hot spots and boiling are induced on its surface. The temperature difference between the hot tube and the colder piece of metal produces a thermogalvanic action that results in current densities up to 0.16 mA cm^?2. The electrode potential of the heated tube is more negative than when the tube is cold. Under these conditions, dezincification of inhibited admiralty tube occurred within 72 h in fresh water and much sooner in a 0.5% solution of sodium chloride.Under these test conditions, two types of dezincification were noted, depending on the kind of boiling and the intensity of the associated thermogalvanic current produced on the surface of the tube; localized film boiling caused a plug-type dezincification with strong evidence for the redeposition of copper, whereas localized nucleate boiling causes a layer-type dezincification with strong evidence for dissolution of the zinc. Very low water velocities, high process side temperatures, low pH or presence of a water conditioning treatment resulting in non-scaling water, high solution conductivity, and the absence of waterside corrosion inhibitors are factors which lead to dezincification in field service.     

Chloride induced pitting initiation on 304L stainless steel in acidic sodium sulphate solutions

Abstract

The kinetics of pit initiation on 304L austenitic stainless steel in aqueous sodium sulphate solutions containing various concentrations of sodium chloride have been investigated by induction time measurements using the potentiostatic test method. Oxide films were grown on the surface of the steel by potentiostatic oxidation in the passive region. Pitting induction time has been found to be dependent on the oxide film thickness: the thicker the oxide film, the longer the induction time. Measurements at temperatures rangingfrom 20 to 80°C gave an apparent activation energy for pitting initiation of ~ 48·1 kJ mol^?1, which suggests that the mechanism of single ion transport through the film is the rate determining step.