New method to prepare iron particles with different morphologies: a way to get high green strength metal compacts

Abstract

Metaliron powders of well controlled size and morphology were synthesised by thermal decomposition under hydrogen of precipitated ferrous oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strengths of compacts were measured.

The precipitation of β-FeC₂O₄.2H₂O oxalate from ammonium oxalate gives rise to the formation of spherical particles by aggregation ofelongated grains. Thermal decomposition of this oxalate from 400 to 500°C under hydrogen permits metal iron particles with a rough surface to be obtained. Decomposition occurring above 500°C induces a smoothness of the particle surface. Metal particles synthesised at 500°C show both surface roughness and micrometer sized primary grains.This specific microstructure has allowed the highest value ofcompact green strength (31·7 MPa) to be obtained.

Acicular shaping of the β-FeC₂O₄.2H₂O particles precipitated from oxalic acid involves, after decomposition, an increase in the surface roughness and shape irregularity of the metal particles, owing to an entanglement of the elementary grains. An exceptional value (about 60 MPa) for the metal compact green strength was thus obtained for this type of powder.     

无线传感器网络的路由协议研究

无线传感器网络（WSNs）是计算机、通信和传感器3项技术相结合的产物，因其巨大的应用前景受到了越来越广泛的关注。介绍了WSNs的一些特点，指出传统路由协议不能有效应用于WSNs的路由协议；然后分类阐述了当前较为典型的路由协议．分析了它们的优缺点；对比分析了这些协议的特点；总结了路由协议设计应满足的要求、存在的挑战以及可能的研究方向。     

一种QoS保证的WMSNs实时路由协议

为了满足无线多媒体传感器网络(WMSNs)对数据的实时性要求,本文提出了一种QoS保证的WMSNs实时路由协议(WMSNRR).该协议在路由选择时,充分考虑两跳节点的转播速率及剩余能量等信息.同时,还采用了一种基于缓存队列长度和节点收发数据率的控制方法,区分业务进行拥塞控制.仿真结果表明,在节点非均匀分布的情况下,该协...     

Laser welding of copper–nickel alloys: a numerical and experimental analysis

Abstract

Melt run trials were carried out on Cu–Ni bars using a CO₂ laser source in order to analyse the effects of welding parameters (i.e. laser power, welding speed) on geometrical characteristics and on the microstructure of the bead. Experimental results were then used to determine the source parameters to be employed in a finite element model (FEM) of the welding process, with particular attention paid to the thermal field induced by the laser beam. A specific procedure, named 'automatic remeshing technique', was used in order to minimise the computation time. The aim was to create a reliable numerical model, suitable for the optimisation, in practical cases, of welding processes of these kinds of materials. A good correlation, in terms of predicted cooling rates, with the values calculated from SDAS measurements, was observed.     

Humping mechanisms present in high speed welding

Abstract

As welding speeds continually increase owing to automation and newer processes, a common defect that occurs is humping. Humping is the periodic occurrence of beadlike protuberances. The objective of the present investigation is to review current and previous researches that were made on humping, including both experimental and theoretical studies. It is found that humping can be classified into two distinct categories of formation: gouging region morphology and beaded cylinder morphology. Various theories that explain the two types of humping formation are examined. Experimental data compiled from many sources are presented to verify the models and explain the fundamental mechanisms of humping morphology. Humping prevention measures that can be applied directly to industrial fabrication are also included. The direct benefit is increased travel speeds that reduce production costs.     

铼钠克G-SPEED数控系统在当代模具及零部件加工中的应用

本文介绍了铼钠克G—SPEED开放式数控系统的功能、特点以及G—SPEED数控系统往现代模具及零部件加工中的应用方法与技巧。包括在CNC自动车床上的应用、在加工小心及磨床上的应用、在鞋揎机上的应用、在四轴及五轴加工、在高光加工上的应用。     

Italian translation,validation, and repeatability of Standard Patient Evaluation of Eye Dryness (SPEED) Questionnaire

PurposeThe assessment of symptoms of dry eye disease using a questionnaire is an effective and simple method of quantifying symptoms. The aim of this study was to translate the SPEED questionnaire and adapt it for the Italian language and verify the main psychometric performance of the translated version, including repeatability and agreement.MethodsThe SPEED questionnaire was translated into Italian following a standard methodology. The resulting questionnaire was administered to 206 adult participants in order to perform a validation analysis. A subgroup of 82 participants was retested after one week to give a repeatability and agreement assessment.ResultsInternal consistency showed an alpha of 0.852 (95% CI 0.818–0.881) and no unnecessary items. The factor analysis showed a saturation for three main factors related to (i) Dryness and Soreness, (ii) Fatigue, and (iii) Burning. Repeatability was high, with a CCC of 0.896 (95% CI 0.844–0.931). Agreement analysis showed no significant bias between sessions and an interval of agreement of 5 points for SPEED score.ConclusionThe translation and adaptation of the SPEED questionnaire for the Italian language have demonstrated good psychometric properties for the translated questionnaire, confirming and expanding the original psychometric characteristics. Consequently, the SPEED questionnaire could be used to measure the presence of symptoms of dry eye quantitatively.     

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract

Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool, are essential to increase the maximum welding speed. These conditions can be obtained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4–4·5 m min^?1 is achieved by setting the current ratio to a value ranging from 0·31 to 0·5.     

Sintering transformations in mixtures of austenitic and ferritic stainless steel powders

Abstract

The microstructural transformations and the dimensional evolution of green specimens obtained by pressing mixtures of austenitic and ferritic stainless steel powders have been investigated by sintering at 1120 and 1240°C. Dilatometry experiments show that the linear shrinkage is influenced by the amount of ferritic powder. Moreover, during sintering Ni diffuses into the ferritic grains causing austenite destabilisation and the formation of a mixed constituent, whose constitution has been investigated by means of EDXS and interpreted on the basis of the Schaeffler diagram. Sigma phase also forms during sintering of the duplex mixtures.     

Physical modelling of fluid flow in electric arc furnace caused by impinging gas jets

Abstract

The interaction of liquid steel and an inclined impinging oxygen jet in an electric arc furnace (EAF) is of interest both commercially and scientifically. The bath activity in the EAF may vary from a surface splash ejected to high elevation to intense subsurface mixing. The system is appropriately modelled using water and nitrogen with scaled flowrates. In previous work, the gas/liquid contact was investigated by use of a geometrically similar 1/3rd scale three-dimensional water model. The cavity formed by the jet contacting the liquid surface was characterised by four modal regimes. These regimes were seen to depend on the lance angle, the height of the lance and the jet flowrate. To investigate the evolutionary mechanisms of the cavity regimes, a two-dimensional water model study was undertaken. The two-dimensional water model was a rectangular viewing tank with an inner movable glass wall that allowed a very thin slice of the system to be obtained. The shape of the cavity formed on the water surface was seen clearly along with the expected cavity oscillations. High speed video footage of the two-dimensional system allowed the cavity oscillation to be directly observed. The gas-liquid interaction produced a wave that travelled along the surface of the cavity until it reached the cavity crest where it was torn from the liquid surface and dispersed in a splash. It is the regular progression of the wave's nodes and antinodes along the cavity surface that makes the cavity appear to oscillate. When the wave reaches the crest of the cavity, it will either fall back into the path of the gas jet or be projected as a splash depending on the verticality of the cavity surface. The two-dimensional work, along with the initial three-dimensional investigation, has shown that the troublesome splash in the EAF is caused by how the lance is positioned directionally or azimuthally. By changing the lance angle or height the deleterious splashing of molten metal may be prevented, ameliorated or controlled. The frequency of the wave production was determined from the high speed video footage. The cavity oscillation was found to be a function of the size of the cavity, the inclined height of the lance and the modal regime being produced. Alterations to the flow through the lance had only a moderate effect on the frequency of oscillation indicating that velocity was not the major influential factor.