Formation of Chromium-Containing Molten Salt Phase during Roasting of Chromite Ore with Sodium and Potassium Hydroxides

Chromium has a wide range of applications including metals and alloys manufacturing, pigments, corrosion resistance coatings and leather tanning. The production of chromium chemicals is based on the oxidative alkali roasting of chromite ores, which leads to the formation of water-soluble alkali chromates. Previous investigations reported that when chromite is roasted with soda-ash, a molten salt containing chromium, which is mainly composed of sodium carbonate and sodium chromate (Na2CO3-Na2CrO4 binary mixture), forms under typical roasting conditions. The physical properties of the liquid phase, which are dependent on the temperature, charge and gangue compositions, play an important role on the oxidation reaction and may limit the chromate recovery by hindering the oxygen transport to the reaction interface. This investigation focuses on the alkali roasting of chromite ore at 1,000 oC using NaOH and KOH, followed by water leaching. The influence of the alkali ratio on the chromium extraction yield is analysed, and the results obtained with both hydroxides are compared. Sample characterisation and thermodynamic analysis, including phase diagrams, equilibrium calculations and computation of liquidus curves, are combined with the purpose of studying the formation of the molten salt phase under different roasting conditions and its effect on the final chromium recovery.

A Review on Strategic Positioning of Bottleneck around the Customer Order Decoupling Point and Issues on Production Planning in Supply Chain

The decoupling point separates part of the supply chain oriented towards customer orders from the part based on forecast planning. This paper focuses on identification of bottlenecks and their positioning with respect to customer order decoupling point (CODP) in supply chain continuum. The research is based on a conceptual model that separates engineer to order (ETO), make to order (MTO), assemble to order (ATO) and make to stock (MTS) by a decoupling point. The important feature of this paper is that supply, demand and operational constraints are allocated in specific part of the supply chain, making it more versatile. Shifting bottleneck concepts, including impact of bottleneck position and issues concerning production and capacity planning, are studied extensively to stabilize the supply chain and reduce its complexity.

Slag Formation – Thermodynamic Aspects and Experimental Observations

Slags have a central role in pyro-metallurgical processes. They bind impurity compounds and absorb reaction products like oxides and sulfides. Functional slags are made by adding lime, magnesia, fluorspar, bauxite, calcium aluminate or other compounds into the reactor vessel where they form the slag together with the targeted reaction products. Additionally, refractory materials of the vessel tend to dissolve into the slag and thus influence its properties. Converter process for steelmaking is a rapid process and slag formation is extremely essential to ensure slag’s metallurgical functions and to avoid harmful reactions with the refractory materials. In this contribution, the progress of understanding the phenomena controlling slag formation and means to promote it were shortly reviewed. Thermodynamic constraints in slag formation were examined and the influence of fluxing additions was experimentally stated. Prefabricated “self-fluxing” lime was tested in industrial scale and proved to be a potential slag forming agent. Slag formation in secondary metallurgy and reduction of slag with aluminum dross or granules were experienced, and the effect on desulfurization and steel cleanliness was discussed.

Investigation on Effect of Machining Parameters of End Milling on Surface Finish and Temperature Using Taguchi Technique

Machining of alloy materials at high cutting speeds produces high temperatures in the cutting zone, which affects the surface quality. Thus, developing a model for estimating the cutting parameters and optimizing this model to minimize the surface roughness and cutting temperatures becomes utmost important to avoid any damage to the quality surface. This paper presents the development of new models and optimizing these models of machining parameters to minimize the surface roughness and cutting temperature in end milling process by Taguchi method with the statistical approach. Two objectives have been considered, minimum arithmetic mean roughness (Ra) and cutting temperature. Due to the complexity of this machining optimization problem, a single objective Taguchi method has been applied to resolve the problem, and the results have been analyzed.

A Slag Management Toolset for Determining Optimal Coal Gasification Temperatures

Gasifier operation is an intricate process because of the complex relationship between slag chemistry and temperature, limitations of feedstock materials, and operational preference. High gasification temperatures increase refractory degradation, while low gasification temperatures can lead to slag buildup on the gasifier sidewall or exit, either of which are problematic during operation. Maximizing refractory service life and gasifier performance require finding an optimized operating temperature range which is a function of the coal slag chemistry and viscosity. Gasifier operators typically use a slag’s viscosity-temperature relationship and/or ash-fusion fluid temperature to determine the gasification temperature range. NETL has built a slag management toolset to determine the optimal temperature range for gasification of a carbon feedstock. This toolset is based on a viscosity database containing experimental data, and a number of models used to predict slag viscosity as a function of composition and temperature. Gasifier users typically have no scientific basis for selecting an operational temperature range for gasification, instead using experience to select operational conditions. The use of the toolset presented in this paper provides a basis for estimating or modifying carbon feedstock slags generated from ash impurities in carbon feedstock.

An Experimental and Numerical Study on Orthogonal Machining of Ti–6Al–4V Alloy

In this work experimental and numerical result of high speed orthogonal machining of Ti-6AL-4V titanium alloy is presented. High speed orthogonal turning is carried in a lathe using uncoated carbide inserts under dry cutting conditions. Experimental study is carried out by focusing on the measurement of cutting force and cutting temperature. The experimentation is supplemented by simulations from 2D finite element model (FEM) using Third Wave AdvantEdge software. The measured cutting forces and temperature are compared with FEA results. The major factors affecting the machinability of titanium alloy such as spindle speed, feed and cutting tool rake angles are investigated. Numerical results agree with the experimental results at higher speeds and feed levels. These results can be used for further study in high speed turning of titanium alloys.

Multi-Objective Optimization of HAZ Characteristics for Submerged Arc Welding of Micro-Alloyed High Strength Pipeline Steel using GRA-PCA Approach

In any type of welding, its heat affected zone (HAZ) is the most critical section where the probability of hydrogen or solidification cracking is prominent. Continuous efforts are being applied by researchers and welders to minimize HAZ and its alterations. For the same purpose, by varying the factors of submerged arc welding (SAW) process which directly influences the heat input and cooling rate of the weld, experiments are carried out on the plates of micro-alloyed high strength pipeline steel. Voltage, welding speed, contact tube to work distance, wire feed rate and preheating temperature are taken as process variables. The experiments are designed according to the central composite rotatable design approach of response surface methodology (RSM). Multi-objective optimization of HAZ characteristics (HAZ area and its hardness) is carried out using grey relational analysis (GRA). To un-correlate the correlated characteristics of HAZ, principal component analysis (PCA) approach is coupled with GRA. The results of the confirmatory test have shown an improvement of 28.51 % and 5.94 % in area and hardness value of HAZ respectively at optimal setting combination of SAW process parameters.

Analysis of Shrinkage Characteristics of Aluminium Silicon Alloy

Analysis of shrinkage characteristics of Aluminium-Silicon alloy was studied theoretically and experimentally. The Aluminium alloys considered in the study are A413 (LM6), A360 (LM9) and A380 (LM24). Extensive literature survey has suggested that cavity filling and solidification process are two most critical aspects to produce high quality casting components. A statistical model of parameters and response to understand the influence of parameters on shrinkage and casting yield studies has been presented. Experiments were conducted in foundry in industrial environment to produce commercially treated aluminium alloy castings in sand mould. Alloy was found to be most significant factor influencing shrinkage. The yield of casting was improved using insulating and exothermic sleeves. Solidification time of exothermic riser was 10 % more than insulated riser. Thus, in order to produce radiographic quality casting a theoretical and experimental method is presented so that number of trials in foundry is reduced which leads to increased reliability and productivity. Study also shows that by using sleeves considerable metal is saved, energy saving during melting, improved quality, reduced cost and increased capacity of plant can be achieved.