Interface microstructure of diffusion bonded austenitic stainless steel and medium carbon steel couple

Abstract

In the present study, an austenitic stainless steel and medium carbon steel were diffusion bonded. The effect of bonding temperature on microstructural changes and shear strength across the joint region was investigated by optical and scanning electron microscopy, energy dispersive spectroscopy and microhardness measurements. The results showed that the best joint free from microcrack and micovoids was obtained at 900°C with maximum shear strength of 475 MPa.     

Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

Adhesion Improvement of Powder Coating on Medium Density Fibreboard (MDF) by Thermal Pre-treatment

In the powder coating of non-conventional substrates such as engineered wood, natural fibre composites or synthetic polymers, several technological problems must be resolved which result from the substantial differences between such coating substrates and metallic ones. Unlike metals, non-conventional carrier materials show low temperature stability, much rougher and more irregular surface texture, large dependence of their dimensional stability on the moisture content of the surrounding environment and significantly less electrical conductivity. Hence, when powder technology is transferred from coating metals to coating fiberboards, for example, the surfaces of the boards need to be engineered in order to provide ideal adhesion for the coating layer. One major problem is the lack of electrical conductivity. Since the powder coatings are preferably applied using electrostatic spraying equipment, sufficient electrical conductivity of the surface is a major requirement and the correct moisture content plays an important role as well. In the present study, a pre-heating process was used to improve the powder application during powder coating of medium density fibreboards (MDFs). Electrical resistance, treatment temperature and moisture content were systematically studied to better understand the complex physical mechanisms leading to an improvement in powder application by such a pre-heating process. To this end, a new sophisticated procedure was developed to measure the electrical resistance (surface and core resistance) during pre-heating. The results show, that the electrical resistance of MDF is influenced by board temperature and moisture content. Moreover, it is confirmed that pre-heating proves to be an efficient method to improve the powder application onto non-conventional substrates.     

上海卷烟厂污水治理

上海卷烟厂选用一套日处理能力为1920m3(80m3/h)的生活、生产污(废)水二级生化处理装置处理污水。针对运行过程中产生的污染负荷增大、沉淀池沉淀区深度不足、污水中含有不能降解的纤维及影响中水回用问题,采取了相应的改进措施:①改厌氧池为缺氧池;②在沉淀池内增设斜板以弥补沉淀区深度不足的缺陷;③在二级生化处理后再增加过滤装置并进行投药杀菌。改进后,大大改善了出水水质,达到了接近零排放的环保要求,并且扩大了中水回用范围。实践证明,根据污水水质特点所选用的二级生化处理较为经济,能达到较好的治理效果。     

Estimation of resistance of filter media used for Prefil Footprinter tests of liquid aluminium alloys

Abstract

During the pressure filtration of molten metals, an essential parameter is the resistance of the filter medium, which is relevant to the calculation of flow velocity, pressure loss and distribution, and drag forces. The resistance has significant influences on the filtration behaviour and structure of the residual cake of inclusions retained on the filter. The Prefil Footprinter, a portable pressure filtration instrument, is usually used to determine the quality of molten aluminium alloys. To date, however, no data on the resistance of the filter medium used have been reported. The present work is an attempt to estimate the resistance. Experiments are described and analyses of flow behaviour are presented. Values of the medium resistance of the filters are determined and reported for the first time.     

Improved thermal modelling of SNF shipping cask drying process using analytical and statistical approaches

Abstract

Before being back filled with an inert gas and as preparation for shipment, a spent nuclear fuel shipping cask must usually be vacuum dried. This process results in an increase in the spent fuel temperature, due to the degradation of heat transport by the cover gas. The drying process is typically modelled by a thermal conduction set to zero in all the shipping cask free spaces. However, this approach does not take into account heat transfers that occur in a rarefied medium and, therefore, may be extremely conservative. A first analysis was performed in order to spot the cask areas whose thermal behaviour is modified by the drying process. This analysis involved the calculation of the Knudsen number, defined as the molecular mean free path to a representative length scale, for all the free spaces. The only area impacted by the drying process appeared to be the mechanical gap between the fuel basket and the shielding materials. During the drying process, the Knudsen number is actually large enough within the gap to consider the gas as a non-continuous medium. Results and methods coming from the microfluidics area were therefore used to develop a modelling, which is based on a double approach. First, an analytical approach was used. This approach consists in adding to the Fourier equation a new equation accounting for the thermodynamical non-equilibrium within the gap (Maxwell–Smoluchowski temperature jump). A thermal model, suitable to calculate heat transfers at pressures as low as 1 mbar, was developed. A second model, based on a statistical approach, was then developed. This model involves the Direct Simulation Monte Carlo method, a reference method used for microfluidics calculations. Computer simulations were performed and led to a good agreement with the results obtained by the analytical approach.     

Metal flow behaviour of wide flat bar in the spreading extrusion process

Abstract

To examine metal flow behaviour experimentally in the spreading extrusion process, a round billet is spread by means of a spread ring and extruded through a die opening wider than the internal diameter of the container. In spreading extrusion, the extrusion load is reduced by about 30% in comparison with basic extrusion. However, the metal flow balance in spreading extrusion worsens, because of the high frictional force generated at the interface of the billet and spread ring during the filling process. When the profile is wide or when spread ring height is low, the geometry of the plastic deformation zone on the die face changes from an ellipse into a figure of eight at the wide zone at both ends of the die opening. As a result, the metal flow balance markedly worsens, due to an increase in the size of the plastic deformation zone and frictional resistance acting on the spread ring wall.     

Effect of atomisation medium on sintering properties of austenitic stainless steel by eliminating influence of particle shape and particle size

Abstract

Gas and water atomised 316L stainless steel powders with similar powder morphology and particle size were injection moulded and sintered. The results show that compacts prepared from the gas atomised powder exhibit higher density and tensile strength, whereas those prepared from the water atomised powder exhibit higher elongation, finer grain size and superior corrosion resistance. Chemical analysis shows that the water atomised powder has a higher Si and O content, and microstructural analysis of the sintered compacts reveals that SiO₂ particles disperse as a second phase in the compacts prepared from the atomised powder, which accounts for the property behaviour. Due to the presence of SiO₂, the porosity increases, whereas the pore coarsening and grain growth are inhibited. Besides, SiO₂ particles can also improve the passivation effect of stainless steel, and hence increase the corrosion resistance.     

Simple model for consolidation of metal matrix coated SiC fibre composites

Abstract

A simple approach to modelling the consolidation of matrix coated fibre composites is presented. It employs an existing porous material constitutive model for monolithic materials. It is argued that in the consolidation of metal coated SiC fibres, the deformation primarily occurs in an outer layer of the fibre coating, and the internal core remains undeformed, largely because of the generally hydrostatic compressive loading, and because of the incompressible nature of the material in creep. The consolidation process is therefore not vastly different to that occurs for monolithic metal fibres, and similar equations can therefore be used for the composite consolidation. The constitutive equations have been implemented into general purpose non-linear finite element software within a large deformation formulation by means of two different user subroutines, one providing a general implementation, and the other a cpu time efficient approach. The manufacture and testing of SiC continuous fibre, Ti-6Al-4V metal matrix composite specimens is described and the results of the tests compared with the model calculations, showing that good agreement can be achieved with a simple model. The dependence of volume fraction of fibres and temperature can be introduced empirically through the specification of just two material constants. The model is therefore useful in the development of consolidation processes.