Industrial treatment processes for recycling of green foundry sands

Abstract

Three treatment processes for the reclamation of green moulding sands coming out from a cast iron foundry located in Northern Italy are considered in this study. A wet mechanical treatment, a dry mechanical treatment and a dry mechanical plus heat treatment are compared to evaluate the efficiency of each process and to point out the best regeneration solution for the recycling of reclaimed sand in foundry operations. The inflow and the outflow samples of each process were characterised by means of particle size analysis and the determination of silica, loss on ignition, acid request, oolitic and some metals contents. A final evaluation of the three processes was performed taking into account the obtained quality of recovered silica sand and the economical aspects; the wet mechanical and the dry mechanical plus thermal treatments are most effective for the recovery of green moulding sands coming out from the considered foundry plant for cold box core production.     

Effect of niobium on electrical properties of Sr0.8Bi2.3(Ta1-xNbx)2O9+ thin films processed by sol–gel method

Abstract

Polycrystalline SBTN ferroelectric thin films were prepared by the sol–gel method with various Nb mole ratioson Pt/SiO₂/Si(100) substrates. The films were annealed at different temperatures and characterised in terms of phase and microstructure. A relatively well saturated hysteresis pattern was obtained at x=0.2 in Sr_0.8Bi_2.3(Ta_1-xNb_x)₂O_9+ thin films. At an applied voltage of 5 V, the dielectric constant ε _r and dissipation factor tan δ of a typical Sr_0.8Bi_2.3(Ta_1-xNb_x)₂O_9+ thin film (x=0.2) were about 236.2 and 0.034. Measured remanent polarisation 2P _r and coercive field E _c were 4.28 µC cm², and 38.88 kV cm¹ respectively. No fatigue was observed up to 6×10¹⁰ switching cycles at 5 V and the normalised polarisation reduced by a factor of only 4%.     

Evaluation of green compressive strength of clay bonded moulding sand mix: neural network and neuro-fuzzy based approaches

Abstract

An attempt has been made to develop neural network and neuro-fuzzy based models to predict the green compressive strength of clay bonded moulding sand mixtures and to analyse the properties of the mixed sand. Data for the models were generated following standard experimental procedure in the sand laboratory. Process parameters such as clay content, moisture, coal dust and mulling time were varied. The collected data were used in developing these models. The predicted green compressive strengths by neural network and neuro-fuzzy based models have been found to be in good agreement with the experimental values. Furthermore, it has been observed from the results that the predicted values from the neuro-fuzzy model are more accurate than those predicted from the neural network model.     

Recycling of steel plant mill scale via iron ore pelletisation process

Abstract

Mill scale is an iron oxide waste generated during steelmaking, casting and rolling. Total generation of mill scale at JSWSL is around 150 t/day and contains 60–70%FeO and 30–35%Fe₂O₃. To recover the iron, the mill scale must be smelted in a blast furnace or other reduction furnace; however, it is usually too fine to use without previous agglomeration such as via pellet or sinter mix. JSWSL operates a 4·2 Mtpa pellet plant to produce pellets for Corex and BF ironmaking units. The aim of this study is to determine the effect of mill scale on pellet properties. Detailed laboratory basket trials were conducted using up to 40% of mill scale in the pellet mix. The addition of mill scale up to 10% is considered to provide the optimum balance of chemical, physical and metallurgical properties of the pellet.     

GREEN函数在滚动轴承故障诊断中的应用

通过不同工况滚动轴承振动信号的时序分析，发现其GREEN函数Gj的曲线都是衰减的或收敛的，且衰减速度取决于滚动轴承的运转状态、本文提出的一种新的参数G10可以定量反映其收敛速度。作为滚动轴承的故障诊断指标．参数C10比Kv和NRSS更有效。     

Bulk high hardness Al90Ce2Mn8 alloy prepared by powder metallurgy

Abstract

Using powder metallurgy, bulk high strength Al₉₀Ce₂Mn₈ alloy 25 mm in diameter by 10 mm with near nil porosity has been obtained under certain pressing and heating conditions. The conditions for the best mechanical properties are a pressing temperature of 753-793 K, a pressing time of 30 min, and pressing stress of 1·2 GPa. The compression strength reaches 895 MPa with a hardness of 26 HRC when the alloy is pressed at 753 K. The strength increase is attributed to second phase strengthening and fine grain strengthening.     

Foaming during reduction of iron oxide in molten slag

Abstract

Coal based direct liquid ironmaking processes, also known as smelting reduction (SR) processes, are now receiving serious consideration in the industry. However, although several processes have reached pilot plant trials, only one, namely Corex, has been commercialised. In all SR processes, most of the iron oxide is reduced in the molten slag phase and foaming is an important phenomenon. Better understanding of the foaming behaviour will result in design of a more efficient and economic reactor. Accordingly, some basic studies on the foaming behaviour of some typical SR process slags have been undertaken in this work. Experimental data on foaming in a 50 kW capacity plasma reactor are discussed in this paper. The data generated are analysed in terms of foaming index, which is equal to the residence time or travelling time of the gas in the foam layer. The influence of FeO percentage in the slag, slag basicity, crucible surface area, initial slag height, and CaF₂addition in the slag on foaming has been studied.     

Experimental investigation and numerical analysis of compaction behaviour of moulding sand

Abstract

The compaction behaviour of green sand was studied to assess the applicability of the Cooper–Eaton equation under conditions close to those of real foundry operations. The results indicate that the Cooper–Eaton equation describes the behaviour reasonably well, allowing prediction of the pressure required to achieve sand moulds of reasonable density. A corresponding distinct element method numerical simulation was also attempted. The study contributes useful information to the understanding of green sand compaction. It is clear that spherical sand is preferable to improve filling behaviour and that the gap between mould wall and pattern must be sufficiently large to avoid prevent weak sand compaction.     

Direct reduced iron production using cold bonded carbon bearing pellets Part 1 – Laboratory metallisation

Abstract

A new cold bonding technology for producing coal bearing composite pellets was developed. Alumina cement was used as binder, which gave high mechanical strength to the pellet even at elevated temperatures. Laboratory test results showed that the metallisation rate of the pellets was high owing to the intimate contact of the particulates of coal and the iron ore in the pellet. The developed cold bonding method can also be used to recycle electric arc furnace (EAF) dust, from which valuable zinc and lead can also be recovered.     

Cold bonded ore–coal composite pellets for sponge ironmaking Part 1 Laboratory scale development

Abstract

There is a need for the development of efficient industrial processes to use iron ore fines of high grade. Attention is particularly drawn to rotary kiln sponge ironmaking technology using lump iron ore, where productivity is low and energy consumption high compared with gas based processes. Fundamental studies carried out elsewhere indicate that the reduction of lump iron is accelerated if a limited amount of carbonaceous material is incorporated in the agglomerate of iron ore fines. Based on these considerations, cold bonded ore–coal composite pellets have been developed for sponge ironmaking in a rotary kiln. These composite pellets were tested in the laboratory and found to reduce very quickly, compared with lump iron ore. Composite pellets were also tested in an 8 t/day rotary kiln sponge iron plant giving enhanced productivity and lower coal consumption, and these results will be presented in Part 2 of this paper (next issue).