Sintering Speed Research Articles

Effect of TiO2 on the Sintering Behavior of Chromium-Bearing Vanadium–Titanium Magnetite

The sintering pot test was used to investigate the effect of TiO2 on the sintering behavior of chromium-bearing vanadium–titanium magnetite (CVTM) sinter. The main characterization methods of X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), and metallographic microscopy were employed. In this study, yield, tumbler index (TI), vertical sintering speed, productivity, reduction degradation index (RDI), and reduction index (RI) were tested and calculated. The yield first increases from 82.87% to 84.37% and then decreases to 83.65%, vertical sintering speed first increases from 17.00 mm·min−1 to 23.45 mm·min−1 and then decreases to 20.61 mm·min−1, and productivity first increases from 2.33 t·m−2·h−1 to 3.14 t·m−2·h−1 and then decreases to 2.69 t·m−2·h−1 with increasing TiO2 content. The TI increases from 45.81% to 52.09%, and RDI increases from 74.99% to 96.74%, while RI decreases from 67.92% to 47.15% with increasing TiO2 content.

Effect of characteristics of fine iron ores on the granulation behavior of concentrate in sintering granulation process

Concentrates have advantages of high ferrous grade, less harmful impurities and lower price. However, the small size and poor granulation behavior of concentrates could deteriorate the permeability of the sinter bed and reduce sinter productivity, thus making it difficult to use concentrates effectively. Therefore, in order to strengthen the granulation behavior of concentrates, granulation experiments were carried out and experiment samples made with one kind of concentrates and five kinds of fine iron ores were produced in this paper. Then, the effects of water absorbility and wettability of fine iron ores on granulation behavior of concentrates were investigated. Furthermore, optimized ore blending recipes were proposed to strengthen the granulation behavior of concentrates by sinter pot tests. Results show that the granulation behavior of concentrates was improved for the samples exhibiting high maximum capillary water and small contact angle in fine iron ores. Compared with the scheme of blending ores containing 15 mass% concentrate, the growth index of quasi-particles increased by 20.62% in the case of iron ore BR-2 replacing half of iron ore BR-1, the vertical sintering speed went up from 26.32 to 29.26 mm min−1, the productivity increased from 1.95 to 2.20 t m−2 h−1. The growth index of the quasi-particles increased by 30% when using iron ore AR-2 to replace half of iron ore AR-1. The vertical sintering speed and the productivity of sinter improved to 29.82 mm min−1 and 2.24 t m−2 h−1, respectively. The results help to improve the granulation behavior of concentrates by optimizing the blending ore recipes, based on the characteristics of fine iron ores, and thus use these concentrates more efficiently in the sintering process.

Effect of characteristics of coarse iron ores on the granulation behaviour of concentrates in the sintering process

ABSTRACTTo strengthen the granulation behaviour of concentrates and thereby improve the permeability of the sinter bed. In this paper, granulation experiments were conducted for the case of concentrates as adhesive powders, and five kinds of coarse ores were used as nuclei particles. Then, the effect of characteristics of coarse ores on the granulation behaviour of concentrates was investigated. Furthermore, optimised blending ore was explored to strengthen the granulation behaviour of concentrates by sinter pot tests. The results showed that the growth index had a positive correlation with the circularity degree but a negative correlation with the contact angle and water absorption of coarse ores. In addition, the granulation index increased by 30 % by optimising the blending ore when the sinter blending ore contained 15 mass% concentrate. The vertical sintering speed increased from 26.32 to 29.82 mm·min−1, the yield and productivity increased by two points percent and 14.87 %, respectively.

TRANSLUCENCY AND BIAXIAL FLEXURAL STRENGTH OF MONOLITHIC ZIRCONIA AS AFFECTED BY SINTERING SPEEDS

Statement of the problem: Approaches towards reducing fixed prosthetic restoration fabrication times include; (CAD/CAM) chair side systems in addition to rapid sintering cycles, which can be carried out in minutes rather than hours in order to deliver zirconia-based restorations in one visit .However, limited information is available regarding the effect of rapid sintering on properties of monolithic translucent zirconia.Aim of the study: The aim of this study was to evaluate the effect of changing the sintering speed (classic, speed and super speed cycles) on translucency and biaxial flexural strength of monolithic translucent zirconia before and after thermodynamic aging.Materials & Methods: 36 monolithic translucent zirconia discs (10mm diameter×0.8mm thickness) were CAD/CAM fabricated from translucent zirconia blocks(In Coris TZI) and randomly divided into three main groups (n=12 each) according to the sintering speed; group I: samples sintered by classic sintering cycle (sintering at 1510°C for 120 min holding time & 8 hours total cycle time), group II: speed sintering (sintering at 1540°C for 25 min holding time & 2 hours total cycle time) and group III: super speed sintering (sintering at 1580°C for 10 min holding time representing the total firing cycle). In each group, half of the samples were evaluated in the non-aged condition (subgroup1, n=6) while the other half were evaluated after thermodynamic aging (subgroup2, n=6) in a chewing simulator. Translucency parameter (TP) and contrast ratio (CR) were measured using a digital reflective spectrophotometer. Biaxial flexural strength (MPa) was tested using piston on three ball technique in a universal testing machine. Representative sample from each subgroup was analyzed by Scanning electron microscope. Statistical analysis was performed using Two-way ANOVA and Tukey’s post-hoc tests ( P ≤ 0.05).Results: Two-way ANOVA revealed that sintering speed and thermodynamic aging had a statistically significant effect on mean (TP), (CR).Either before or after aging, classic cycle showed the statistically significantly highest mean (TP) & lowest (CR) values. On the other hand, biaxial flexural strength was statistically significantly affected by the sintering speed only and not by thermodynamic aging; the super speed cycle registered the lowest mean biaxial flexural strength before and after thermodynamic aging.

Integrated assessment on the characteristics of straw-based fuels and their effects on iron ore sintering performance

Employing waste agricultural straw into iron ore sintering is a promising approach to realize efficient energy utilization and environmental protection. In this paper, the characteristics of four types of straw-based fuels including raw straw (RS), preformed straw (PS), straw char (SC) and preformed straw char (PSC) were assessed. The results indicate that RS and PS mainly consisted of volatile matters, which was pyrolyzed in the downstream of combustion zone. This property of RS and PS led to lower fuel utilization and then decreased the bed temperature for minerals melting. Recommended replacement percentage of RS and PS to coke breeze was restricted at 10%. Compared with RS and PS, SC had the advantage of improving fuel utilization and ensuring higher bed temperature. But SC showed considerably faster combustion speed than coke breeze, which accelerated sintering speed excessively when SC replacing coke breeze exceeded 20%, and the suitable replacement percentage of SC to coke breeze was 20%. PSC ingeniously integrated the advantages of PS and SC by joint preformation-carbonization process. Comparable sintering performance was achieved when improving the replacement percentage of PSC to coke breeze to 40%, and its capacity for reducing CO2, SOx and NOx emissions achieved 24.5%, 26.6%, and 28.2% respectively.

Effect of H2O(g) Content in Circulating Flue Gas on Iron Ore Sintering with Flue Gas Recirculation

The influence of H2O(g) content in circulating flue gas on sintering was studied by simulating the flue gas circulating sintering. The results show that the burning speed of solid fuel and the heat transfer rate during sintering process are improved when the H2O (g) content increases from 0 to 6%, which accelerates the sintering speed. However, when the H2O (g) content exceeds 6%, the over-wet zone in sinter bed is thickened, which deteriorates the permeability of sintering bed. In addition, the magnetite content in sinter increases, while the acicular calcium ferrite content decreases. Accordingly, the sinter yield and tumble index decrease with excessive H2O (g) content. To guarantee the yield and quality of sinter, the favourable H2O (g) content in circulating flue gas should be controlled to be less than 6%.

Influence of Laser Speed on Average Manufacturing Speed of Selective Laser Sintering

With the technology of Additive manufacturing (AM) still developing and more and more AM machines and technologies becoming available, it is very important to know accurate data about every machine to make the right choice for your product. This paper will focus on selective laser sintering (SLS) and more specifically the influence of the laser speed on the average manufacturing speed.

On the self-damping nature of densification in photonic sintering of nanoparticles.

Sintering of nanoparticle inks over large area-substrates is a key enabler for scalable fabrication of patterned and continuous films, with multiple emerging applications. The high speed and ambient condition operation of photonic sintering has elicited significant interest for this purpose. In this work, we experimentally characterize the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. It is shown that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. Further, high densification can be achieved even without nanoparticle melting. Electromagnetic Finite Element Analysis of photonic heating is coupled to an analytical sintering model, to examine the role of interparticle neck growth in photonic sintering. It is shown that photonic sintering is an inherently self-damping process, i.e., the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached. By accounting for this phenomenon, the developed coupled model better captures the experimentally observed sintering temperature and densification as compared to conventional photonic sintering models. Further, this model is used to uncover the reason behind the experimentally observed increase in densification with increasing weight ratio of smaller to larger nanoparticles.

Sintering behaviors and consolidation mechanism of high-chromium vanadium and titanium magnetite fines

To achieve high efficiency utilization of high-chromium vanadium–titanium magnetite (V–Ti–Cr) fines, an investigation of V–Ti–Cr fines was conducted using a sinter pot. The chemical composition, particle parameters, and granulation of V–Ti–Cr mixtures were analyzed, and the effects of sintering parameters on the sintering behaviors were investigated. The results indicated that the optimum quicklime dosage, mixture moisture, wetting time, and granulation time for V–Ti–Cr fines are 5wt%, 7.5wt%, 10 min, and 5–8 min, respectively. Meanwhile, the vertical sintering speed, yield, tumbler strength, and productivity gains were shown to be 21.28 mm/min, 60.50wt%, 58.26wt%, and 1.36 t·m−2·h−1, respectively. Furthermore, the consolidation mechanism of V–Ti–Cr fines was clarified, revealing that the consolidation of a V–Ti–Cr sinter requires an approximately 14vol% calcium ferrite liquid-state, an approximately 15vol% silicate liquid-state, a solid-state reaction, and the recrystallization of magnetite. Compared to an ordinary sinter, calcium ferrite content in a V–Ti–Cr sinter is lower, while the perovskite content is higher, possibly resulting in unsatisfactory sinter outcomes.

Characterization of semi-coke generated by coal-based direct reduction process of siderite

Solid wastes derived from metallurgical industries pose a significant threat to environment. The utilization and disposal of these solid wastes are the major concern in the world. Semi-coke generated in coal-based direct reduction process of iron ore is a by-product and its suitable utilization is not available so far. In order to handle it properly, the characteristics of this by-product were comprehensively investigated. A series of analysis methods were used to demonstrate its mineral compositions, petrography and physico-chemical properties. The results reveal that the semi-coke has poor washability. The fixed carbon content of semi-coke reaches 76.11% and the gross calorific value is 28.10 MJ/kg, both of which are similar to those of traditional sinter coke breeze. Also, semi-coke ash possesses lower content of SiO2, Al2O3, S and higher content of CaO and MgO, which could improve the strength of sinter ore when partially substituting for coke breeze in sintering. Semi-coke features well-development porous structure and higher reaction activity, which predicts that the sintering speed could be elevated to some extent when employing it as a partial replacement of coke breeze, so the studies further suggest that the potential adverse effect of the high reactivity on sintering process could be weakened by adequately coarsening the semi-coke’s particle size.

Rapid laser sintering of alkaline fuel cell substrates using integrating mirror

Nickel screens and foams are commonly used in alkaline fuel cell (AFC) as substrates to support electrodes. The methods used for fabrication of these substrates impact significantly on the viability, with the material and processing cost of nickel comprising almost one third of the total. Therefore, improvements to the manufacturing speed of substrates would increase affordability. Currently, state of the art commercial selective laser sintering systems are limited to a volumetric manufacturing speed of 1–3 mm3/s. This study describes a novel technique that multiplies the sintering speed of nickel AFC substrates. The novel technique is based on an integrating mirror, which creates a homogenized 60 mm wide and 0.3 mm long beam from a Nd:YAG laser, and a 0.8 mm thick nickel powder layer in a nitrogen environment. The influence of the nickel powder characteristics, and sintering parameters, as velocity, laser power, etc., and postsintering treatments of the samples on the mechanical properties of the substrates were studied. Based on experimental results, the sintering speed could be multiplied up to a factor of 150 compared to the standard laser sintering speed. Additionally, because structure of the substrate has a significant impact on cell performance, a case study was defined to present the performance and characteristics of the sintered substrates on AFCs. Laser sintered substrates show promise, exhibiting a small performance drop of less than 25 mV (about 7%) compared to the in-house standard.

Effect of Size Distribution of Coke Breeze on Sintering Performance

Coke breeze is added as fuel in sintering process. The size distribution of coke breeze is one of the important factors, which plays an important role in achieving proper sintering process. Therefore, the effects of size distribution of coke breeze on sintering performance are investigated. Experimental results show that, in practical production, we should adjust the size distribution of coke breeze according to the different production strategy (aimed for best strength or highest productivity, or others). For example, aimed for sinter with maximum tumble strength, the size distribution of coke breeze should be 57.20% of −1 mm, 25.63% of 1–3 mm, 11.17% of 3–5 mm, and 6.00% of +5 mm. Then the tumble strength of sinter increases about 1.48%, production yield increases about 1.7%. Similarly, aimed for sinter with maximum productivity, the size distribution of coke breeze should be 47.22% of −1 mm, 23.10% of 1–3 mm, 28.68% of 3–5 mm, and 1.00% of +5 mm. For this case, the productivity increases 0.1 t m−2 h−1, the sintering speed increases 0.7 mm min−1, and the production yield increases 0.4%. There are two reasons for that sinter B (optimized by maximum tumble strength) has better sintering performances, they are as follows: (i) the effect of coke breeze size on the sintering temperature profile and (ii) pores distribution. The research results of present work could give a scientific guide to reasonably utilize fuel resources in practical sintering process.

Speed and Accuracy of High Speed Sintering

High Speed Sintering is a novel powder based additive manufacturing process that retains the major benefits of Laser Sintering but eliminates some major drawbacks. The process uses inkjet print head and infrared lamps to fabricate parts layer by layer using polymer powder. The purpose of this research was to evaluate the speed and accuracy of High Speed Sintering by closely following a method published in the research paper of Rapid Prototyping Journal, entitled 'Speed and Accuracy Evaluation of Additive Manufacturing Machines'. This methodology involves the manufacturing of test parts defined in the paper analysis using the method provided, speed and accuracy of High Speed Sintering is assessed and then benchmarked against four other Additive Manufacturing processes. Based on a theoretical speed evaluation, results show that High Speed Sintering is able to achieved superior average manufacturing speed than the other specified Additive Manufacturing technologies.

Contribution to Study of the Sintering Mechanism

In all process based in powder and in particular in the rotational moulding process, the major physical phenomenon during the flow of the powders is the sintering and grains growth. The sintering is the formation of only one particle starting from two or many particles under the effect of the temperature and the forces of surface tension. We interest in this study in particular at the mechanism of Polyvinylidene fluoride (PVDF) sintering. The results of this study can enable us to maximize our knowledge about sintering mechanism and enable us to determine parameters such as the speed of sintering for the optimization of the process.

Synthesis, characterization, biocompatibility of hydroxyapatite–natural polymers nanocomposites for dentistry applications

Hydroxyapatite (HA), the main mineral component of bones and teeth, was synthesized by using the reaction between calcium nitrate tetrahydrate Ca(NO3)2∙4H2O and diammonium hydrogen phosphate (NH4)2HPO4 (DAHP) with a chemical precipitation method. The objective of this study is to utilize novel inorganic–organic nanocomposites for biomedical applications. HA is an inorganic component (75% w) and chitosan, alginate and albumin (Egg white) are organic components of nanocomposites (25% w). Nanocomposites were prepared in deionized water solutions, at room temperature, using a mechanical and magnetic stirrer for 48 h. The microstructure and morphology of sintered n-HAP were tested at different preheating temperature and laser sintering speed with scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).

Effect of CO<sub>2</sub> Pretreatment Operation Conditions on the Catalytic Performance and Structure of Ni-Co Bimetallic Catalyst

The performance of the Ni-Co bimetallic catalyst was significantly improved by a novel H2 and CO2 (HCD) pretreatment in the dry reforming of methane compared with traditional H2 pretreatment. The effects of the HCD pretreatment operating conditions, such as pretreatment time, temperature, gas feeding ratio, and gas flow rate, on the catalytic performance of Ni-Co bimetallic catalyst were investigated. The optimal pretreatment time, temperature, gas feeding ratio (CH4/CO2), and gas flow rate were 0.5-1 h, 780800 °C, 0:10, and 175-200 mL∙min-1, respectively. Biogas was simulated with CH4 and CO2 in a volume ratio of 1 and without any other diluted gas. The catalyst was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry (TG) coupled to differential scanning calorimetry (DSC). In a 511 h stability test under the optimized operating conditions, the catalyst pretreated with both H2 and CO2 exhibited excellent stability. The average conversions of CH4 and CO2, selectivities for H2 and CO, and volume ratio of H2/CO were 96%, 97%, 98%, 99%, and 0.98, respectively. The average carbon deposition rate over the Ni-Co bimetallic catalyst was only about 0.2 mg∙g-1∙h-1. The characterization results revealed that the sintering speed of the metal greatly decreased with testing time, and the metal particle will not greatly sinter with further testing time. The amount of deposited carbon on the catalyst gradually decreased and growth of filamentous carbon over the surface of the catalyst could be inhibited. 1325 Acta Phys. -Chim. Sin. 2014 Vol.30

Current Distribution Model and Control Principle of MgAlON Composites by Spark Plasma Sintering (SPS)

The current distribution had remarkable effect on the microstructure and properties of MgAlON composites in the process of spark plasma sintering (SPS). MgAlON composites, using alumina, magnesia and aluminum as starting materials, were prepared by SPS. Based on the current distribution method, the current distribution model on samples and single grain was established, and the basic electric current control principle was analyzed. It was found that the current conveyance by sample or single Al grain could be expressed by a formula including B and I.In the formula, B was the Al volume fraction and I was the total current. When the Al volume fraction was controlled within 12%, the current conveyance by sample increased significantly with the Al addition increasing. Meanwhile, the current conveyance by single Al grain decreased significantly. The sintering speed and properties of MgAlON composites by SPS would show a significantly change.

ВЛИЯНИЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИНА ИЗМЕНЕНИЕ МЕХАНИЧЕСКИХ СВОЙСТВ МЕТАЛЛОКЕРАМИЧЕСКОЙ КОМПОЗИЦИИ НА ОСНОВЕ ЖЕЛЕЗА

In this paper, the authors study the influence of the drawback temperature of metal-ceramics composites on their mechanical properties, if composites are produced using the iron-graphite powder method. The authors have studied the microstructure of the materials and the influence that the thermal treatment produces on their strength, plastic properties and toughness. The authors have also identified specific thermal treatment parameters aimed at the improvement of mechanical properties of parts of machines and mechanisms made of the above composites. The analysis of the authors’ findings is applied to find the ways of improving the mechanical properties of machine parts produced using powder metallurgy methods. The analysis of the microstructure confirms the presence of changes in the mechanical properties of materials, namely, their plastic properties and toughness. The combination of the most efficient sintering regime (using double pre-pressing) and subsequent thermal treatment in the form of hardening and tempering can improve the mechanical properties of machine parts. The authors performed experiments to identify the best sintering conditions and improve the mechanical properties of the Fe-C composition, including its tensile and flexural strength, as well as compressive and impact strength using the above process parameters and other data obtained from the reference literature. The authors have discovered that if the sintering speed and the shrinkage ratio are maximal and vary insignificantly at the temperature near the Ac3 value and slightly above it, the mechanical properties after sintering, for example, at 870 °C and 1100°C will differ slightly.

Hierarchical Intelligent Control System and Its Application to the Sintering Process

This paper presents a hierarchical intelligent control system (HICS) based on soft-sensing of burn-through point(BTP) and vertical sintering speed (VSS) for the sintering process, which has a two-level hierarchical configuration (intelligent control level and basic automation level), and is being used in an iron and steel plant. At the intelligent control level, first, BTP and VSS soft-sensing models are established, respectively. Next, the BTP mechanical control model and fuzzy controller are designed. The basic automation level contains a distributed control system (DCS), which performs process control including stable tracking control of the strand velocity; and a communication interface, which enables the intelligent controller and the DCS to exchange data on process information. The real-world application results show that the system not only sufficiently suppresses the fluctuation, but also effectively improve the utilization factor of the sintering machine and the quality and quantity of the sinters.

Reliability Studies of Tensile Strength for Parts Produced by Direct Metal Laser Sintering Using Weibull Analysis

A study was carried out to find the reliability of components manufactured by direct metal laser sintering (DMLS) for tensile strength. An orthogonal array of modified L8 experimental design using Taguchi’s experimental design techniques was developed and used. Test results were analysed using analysis of variance technique to identify the main process parameter that influences the tensile strength. It has been found that sintering speed had more influence on tensile strength as compared to other process parameters. Regression analysis shows that regression model for tensile strength is within the significance level and adequate within 90%. Detailed investigations on reliability using Weibull analysis shows that the distribution plot considered as a good Weibull design. Results show that the Weibull distribution method can be used for describing the distribution of failure times for tensile strength of DMLS components for functional applications.