Good Grindability Research Articles

Grinding of Australian and Brazilian Iron Ore Fines for Low-Carbon Production of High-Quality Oxidised Pellets

Oxidised pellets have become an indispensable high-quality charge for blast furnaces. Nevertheless, high-quality pellet feeds are becoming scarcer and scarcer. To broaden the range of sources of pellet feeds and reduce the production cost of pellets, more steel mills are predicted to use coarse iron ore fines with a relatively low iron grade and low impurities for the preparation of desirable pellet feeds through a typical wet grinding–settling–filtering process. In this work, the grinding, settling and filtering behaviour of Brazilian and Australian iron ore fines are studied and compared, with the aim of discovering the internal relationship between the mineralogical characteristics of different iron ore types and their grinding–settling–filtering performance. Additionally, the effects of ore blending on pellet preparation were investigated. The results show that, usually, the higher the hardness of the iron ore, the more grinding energy is required. Australian and Brazilian ore fines exhibit good grindability, with a Bond work index of about 10–15 kW·h/t. Furthermore, ore blending can reduce grinding energy consumption and improve settling and filtration rates, and the addition of finely ground Australian ores improves the balling performance of pellet mixtures. At the same bentonite content, the ball drop strength of the three blends with added Australian ore is significantly higher than that of the base blend, and the fired pellets obtained from Blend 1, Blend 2 and Blend 3 blends exhibit good metallurgical properties.

Feasibility Analysis of Biomass Hydrochar Blended Coal Injection for Blast Furnace

It is critical for the iron and steel industry to achieve green transformation and development by effectively utilizing abundant biomass resources in blast furnace ironmaking. In this paper, four types of typical biomass were carbonized and upgraded using the hydrothermal carbonization (HTC) method, and the metallurgical performance of the prepared hydrochar for blast furnace injection was systematically tested. The results show that HTC treatment could remove volatile matter and dissolved mineral elements in biomass so that the hydrochar had the characteristics of high fixed carbon and low ash and alkali metal content. Moreover, the hydrochar had good grindability and excellent combustion performance, which meet the requirements of blast furnace injection. Finally, the metallurgical performance of blended coal and wood chip hydrochar was examined. It was observed that when the ratio of hydrochar was less than 15%, it would not affect the blast furnace injection, and the potential safety hazard caused by the explosive hydrochar could be resolved by mixing hydrochar with anthracite. The application of hydrochar in blast furnace injection could not only alleviate the current energy shortage situation, but also be of great significance to realize the “carbon peak” of the steel industry.

Ternesite-calcium sulfoaluminate cement: Preparation and hydration

Ternesite-calcium sulfoaluminate (TCSA) cement exhibits excellent properties. However, it is hard for sulfoaluminate (C4A3$) and ternesite (C5S2$) to coexist in the clinker. In this study, phosphogypsum (PG) was used for producing TCSA cement clinker. The joint effects of P2O5 and F in PG as well as the CaSO4 content in raw meals on the coexistence of C4A3$ and C5S2$ were investigated. The grindability and morphology of TCSA cement clinker were characterized. By the comparison with belite-calcium sulfoaluminate (BCSA) cement, the hydration and properties of TCSA cement were investigated. Results shows that the coexistence of C4A3$ and C5S2$ is achieved under the joint effects of P2O5, F and a sufficient amount of CaSO4. TCSA cement clinker could be prepared at 1125–1200 °C for 15–30 min and the clinker exhibits a good grindability. Ternesite in TCSA cement clinker presents a rodlike or granular shape Compared with BCSA cement, due to higher hydration rate of C4A3$, the setting time of TCSA cement is shorter and early compressive strength is higher. Due to the hydration of C5S2$, TCSA cement exhibits a higher late age compressive strength.

Торрефикация — ресурсосберегающее направление термохимической переработки биомассы

Significant scales in which biomass accumulates have prompted specialists to search ways of efficiently using its energy potential at the background of the crisis of non-renewable energy sources. One of such ways is torrefaction – thermochemical pyrolysis of biomass by subjecting it to slow heating and holding at a temperature of 200–300°C to obtain a solid carbon-containing product. Investigations carried out in the biomass torrefaction field are reviewed and analyzed. Biomass properties and various ways of processing it for use as power-generating fuel are considered. The properties of non-torrefied and torrefied pellets are compared. The latter, in comparison with the source ones, feature an increased heating value, low hygroscopicity, sufficient bulk density, and good grindability. The main torrefaction technologies and types of torrefaction reactors are considered. A mathematical model of a wood waste torrefaction plant was developed in the Aspen Plus software environment. The study results have revealed the effect the specific heat admission to the torrefaction reactor and the initial moisture content in the material have on the process operating parameters: the mass fraction of carbon transferred into solid torrefaction products and the pyrolysis gas specific yield, composition, heating value, and temperature. The possibility to arrange autonomous heating of the reactor using the chemical heat of pyrolysis gas has been shown. The reactor heating requires 44% of the gas waste from the torrefaction process; the other 56% can be used as an energy source in related technologies. The obtained results can be used in studying and designing the reactor and torrefaction plant.

The Grindability of Biochars from Agroforestry Biomass Prepared under Different Torrefied Conditions

The torrefaction experiments of four biomass including agricultural biomass (corn straw (CS) and wheat straw (WS)) and forestry biomass (polar wood (PW) and cedar wood (CW)) were carried out in a fixed bed reactor at torrefaction temperature of 200-300°C and holding time of 10-60min, the effects of torrefaction temperature and holding time on biochar grindability based on the component analysis and the particle size distribution of ground biomass and biochars. The obtained results indicated that the mass fraction of ground biochar with particle size less than 150 μm increases with increasing torrefaction temperature, and the mass fraction of ground biochar with particle size less than 150 μm achieves 100%. The larger the λC, the better the grindability of biochar. The correlation between the grindability of the woody biochar and the λC is not as good as that of the straw biochar. The grindability of corn straw biochar and cedar wood biochar is improved with the increase of holding time at the same torrefaction temperature, however, the grindability of wheat straw biochar and polar wood biochar gets a little change, which can keep good grindability at higher torrefaction temperature large than 275°C.

Ground calcium carbonate (GCC) from the Barre de Ghomrassene in Southeast Tunisia: a suitable raw material for paint industry

The main scope of the present work is to investigate the potential of using ground calcium carbonate (GCC) from the Barre de Ghomrassene (BDG) in Southeast Tunisia in paint industry. In order to evaluate the performance of the material and the formulated paint films, representative raw specimens of main deposits of naturel GCCs in the Mediterranean basin and Middle East countries such as extra-white limestone from the Abiod Formation (Feriana region in West-Central Tunisia), Asigedigi Formation (Nigde Group, South Central Turkey), and Samalut Formation (Elminea, South Cairo, Egypt) were considered. Samples were ground to specific surface of about 3000 cm2/g and were subjected to detailed characterization including chemical and mineral composition, physical, and chromaticity characteristics. Results show that the GCC from the lower part of the Barre de Ghomrassene is, in most, dark and grainstone in texture, which limit its use in paint and coating application. Elsewhere, it is marked by high purity degree (generally more than 97% calcite); high lightness (more than 86.5, 95.2 in average) with relatively low chromaticity (a* < 3.3, b* < 9.1); low oil intake (17.4 g/100 GCC); very low electrolyte levels; good pH buffering (close to 9); accepted ranges of density and abrasion (2.65–2.7 and 10–18, respectively); good grindability; low levels of harmful components such as MgO, SiO2, Fe2O3, and acid insoluble residue (less than 0.1% each); and improved rheological properties. The BDG seems to be a suitable filler for paint when mixed with water, styrene acrylic, and common additives. The formulated paint films meet all standard requirements, in that they have very good opacity, matt visual dualgloss 20/60°, high luminescence (L* = 96.4), suitable hardness (145 s), good adhesion (B5), and sufficient impact resistance (1.5 kg m). The performances of these films are analogous to those based on Abiod and Samalut formations (natural carbonate), but they are slightly less lighter than those based on Asigedigi Formation (metamorphic carbonate). Hence, the studied GCC can be used to substitute them in particular for local GCCs from the Abiod Formation, which are limited and over exploited.

The effect of torrefaction on oil palm empty fruit bunch properties using microwave irradiation

In this study, torrefaction via microwave irradiation was introduced towards oil palm empty fruit bunches (EFB) samples. The samples was fed into the alumina type crucible inside the microwave with the power input limit at 385W. Experimental was carried in non-oxidative atmosphere at 50 ml/min continous flow of nitrogen gas into the torrefaction system. The effects of main parameters from temperature, residence time were studied towards mass yield, energy yield, proximate analysis and hydrophobicity percentage Result revealed the increased of energy value up to 22.4MJ/kg for torrefied samples, whereby from proximate analysis mark the increased of fixed carbon percentage whilst volatile matter decreased. Torrefaction products also shows the ability of reducing of moisture uptake up to 60%, which is prudent the good grindability.

Microgrinding characteristics of Zr-based bulk metallic glasses

The microgrinding experiments of Zr-based bulk metallic glasses (Zr-based BMGs) were conducted by using a JX-1A ultraprecision grinding lathe. The grinding force ratio, surface roughness, and material removal mechanism in microgrinding for Zr-based BMGs were investigated. The experimental results indicated that the grinding force ratio was 1.74~4.12. The microgrinding force and surface roughness value decreased with the increase of the spindle speed. The microgrinding force increased with the increase of the grinding depth, and the surface roughness value decreased first with the grinding depth increasing from 2 to 6 μm and then increased with the grinding depth increasing from 6 to 10 μm. The microgrinding force and surface roughness value increased with the increase of workpiece feed rate. On the basis of simple single-factor tests, the modified empirical mathematical model of the microgrinding surface roughness for Zr-based BMG was established, and the theoretical model of microgrinding force for Zr-based BMGs was verified. The best surface quality can be obtained when the grinding depth was 6 μm, the spindle speed was 6 × 104 r/min, and the workpiece feed rate was 20 μm. The microcracks and microholes were observed on the grinding surface generated by using diamond abrasive grinding tool. CBN abrasive 500# grinding tool with 0.9-mm diameter was considered to have better grinding performance. Compared with traditional crystal materials, Zr-based BMGs had good grindability. No light emission was observed in these experiments by daylight.

Grindability, grading and wettability of recycled plaster

The changes of grindability, grading and wettability of recycled plaster(R-P)and the mechanisms of these changes were studied by using vickers hardness, particle size distribution(PSD), scanning electron microscope (SEM) and nitrogen adsorption porosimetry to reveal that R-P was obviously different from plaster of Paris(POP). At the same milling time, R-P had the characteristics of high specific surface area, fine particle diameter and uneven size distribution compared with POP, so R-P possessed both good grindability and poor grading. The water absorption, dissolution rate and mass loss in dry-wet cycle of the hardened recycled gypsum(hardened RG) increased, while the water saturated strength and dry-wet cycle strength decreased significantly compared with the hardened virgin gypsum(hardened VG). Therefore, poor wettability could be seen in R-P. The analyses indicated that the changes of grindability and grading could be attributed to the reduction in hardness and the increase in the porosity of hardened RG and that the poor wettability of R-P was caused by the increase of large pores and the changes of microstructure of hardened RG.

A grindability model for grinding aids and their impact on cement properties

This paper describes the grindability of four kinds of grinding aids – triethanolamine (TEA), propylene glycol (PG), calcium lignosulfonate (CLS) and sodium tripolyphosphate (STPP) – and their impact on cement properties. Experiments were carried out on cement samples to determine the specific surface area and sieve residue, on cement paste to determine the normal consistency, setting time and heat release, and on cement mortar to assess the compressive and flexural strength. The results showed that the increment of specific surface area (ΔS) at 30 min and decrement of 30 μm sieve residue (Δη) for the four kinds of grinding aids showed an exponential function with an increase in dosage. TEA, CLS and STPP showed good grindability to cement clinker, while PG even showed some negative grindability. Through the chemical action of the grinding aids and their impact on particle size distribution of the cement samples, TEA and PG were found to accelerate the heat release rate, while CLS and STPP delayed it. TEA enhanced early mortar strength. CLS increased both the early and late mortar strength. STPP showed no remarkable impact on mortar strength while PG was found to decrease the mortar strength.

An overview of oil palm biomass torrefaction: Effects of temperature and residence time

Biomass is characterized as high moisture content, low bulk and energy density, possesses hygroscopic behaviour and poor grindability material as compared to the superior coal. A thermal treatment called torrefaction is a heating of biomass in a temperature range between 200°C to 300°C under inert atmosphere in order to upgrade biomass properties. Torrefied biomass has many similar characteristics to coal such as low moisture content, high bulk and energy density, hydrophobic and good grindability. This paper reviews the effects of oil palm biomass torrefaction in terms of temperature and residence time. This is because comprehensive studies on torrefaction parameters need to be carried out since different parameters might affect the chemical and physical characteristic of the torrefied product. Hence, this paper aims to discuss the effects of different torrefaction temperature and residence time towards physicochemical characteristic, mass and energy yield as well as calorific value of torrefied oil palm biomass.

Evaluation of Grinding Performance of Unsaturated Polyester Resin

Polyester resins are unsaturated resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Polyester resins are being used in different mechanical and other industrial or household items. It also helps making Fibreglass Reinforced Plastics (FRP). Grinding of this unsaturated polyester resin is often needed, and hence, suitable process conditions are to be chosen to achieve desired grindability. In the present paper, grinding performance of unsaturated polyester resin with or without applying grinding fluid using an alumina wheel has been explored. Experimental observation shows fairly good grindability of this resin with alumina grinding wheel under wet condition and with less in feed in dry condition.

Exploring Grindability of Titanium Grade 1 Using Silicon Carbide Wheel

Titanium and its alloys are being increasingly used in aerospace engineering, corrosive fluid pumps, heat exchangers, sea vehicles, etc. However, it is quite difficult to grind for its high chemical reactivity, high strength, high hardenability and low thermal conductivity causing high grinding temperature, wheel loading, wheel material removal, grit wear, etc. Therefore, selection of wheel, wheel speed and fluid for grinding of titanium is important to achieve desirable surface quality. Formation of a stiff air layer is a major constrain restricting the fluid enter the grinding zone. Optimization of a method of grinding fluid application is essential to control thermal problems from interaction of the wheel grains with the work surface. Adopting an appropriate fluid delivery system may enhance grindability of titanium alloy and can reduce environmental pollution. In the present experimental work, surface roughness, grinding forces and grinding chips are observed under the condition of dry, and wet using a compound nozzle. Surface grinding of titanium Grade 1 alloy is done with the use of silicon carbide wheel. It is found out that grinding under wet with compound nozzle fluid delivery system exhibits fairly good grindability.

Co-firing based on biomass torrefaction in a pulverized coal boiler with aim of 100% fuel switching

Torrefied biomass has several benefits, such as higher energy density, good grindability, higher flowability and uniformity. The process of torrefaction moves the chemical and physical properties of raw biomass close to that of bituminous coal, which allows co-utilization with high substitution ratios of biomass in the existing coal-fired boilers without major modifications. In this study, a torrefaction based co-firing system was proposed and studied. Devolatilization and char oxidize kinetics of the torrefied biomass have been investigated experimentally. CFD modeling of co-firing with varying substitutions of torrefied biomass in a pulverized coal boiler have been carried out. To figure out the boiler performance when co-firing torrefied biomass, five different cases were involved and simulated, coal only, 25% biomass, 50% biomass, 75% biomass, and 100% biomass on thermal basis, respectively. The results showed torrefaction is able to provide a technical option for high substitution ratios of biomass in the co-firing system. The case-study pulverized coal boiler could be fired 100% torrefied biomass without obvious decreasing of the boiler efficiency and fluctuation of boiler load. More positively, the net CO2 and the NOx emissions significantly reduced with increasing of biomass substitutions in the co-firing system.

Reusing pretreated desulfurization slag to improve clinkerization and clinker grindability for energy conservation in cement manufacture

The purpose of this study was to combine the physical pretreatments of grinding, sieving, and magnetic-separation processes to reclaim iron-rich materials from the desulfurization slag, and to use the remainder for cement clinker production. The iron-rich materials can be separated out efficiently by grinding for 30 min and sieving with a 0.3 mm mesh. The non-magnetic fraction of the particles smaller than 0.3 mm was in the majority, and proved to be suitable for use as a cement raw material. The raw mixes prepared with a pretreated desulfurization slag had a relatively high reactivity, and the temperature at which alite forms was significantly reduced during the clinkerization process. The clinkers produced with 10% desulfurization slag had a high level of alite and good grindability. Generally, the improvements in clinkerization and clinker grindability are beneficial to energy conservation in cement manufacture.

Processing and characterization of plasma-sprayed ceramic coatings on steel substrate: Part II. On coating performance

This investigation envisages the performance evaluation of a series of plasma-sprayed coatings from a few inexpensive powders, namely, alumina, plasma dissociated zircon (PDZ), zircon sand, and zircon-20 wt pct calcia. The hardness and adhesion (bond) strength of the coatings have been evaluated. All coatings offer an attractive thermal fatigue property. An added layer of yttria between the top and bond coats improves the thermal fatigue resistance appreciably. The wear performance of these coatings has also been evaluated using a “pin-on-disc” type wear testing setup. The Indian alumina coating offers a superior wear resistance and thermal fatigue property compared to an imported alumina coating. The coatings based on zirconia-silica offer an attractive thermal fatigue resistance along with an acceptable wear resistance. The latter improves considerably upon annealing of the coatings because of the removal of the residual stresses accumulated during deposition. Among these zirconia-silica-based coatings, the zircon-20 wt pct calcia is the most promising. The finishability of these coatings has been studied using a surface grinding setup equipped with a diamond wheel. The cutting forces and the surface roughness of the ground surface have been measured. The coatings have been found to possess a reasonably good grindability.

Synthesis of carbon/EMD composite from carbon-suspended sulfuric acid and manganese sulfate bath

A study has been made of the electrodeposition of MnO 2 on a titanium anode from a carbon or carbon/MnO 2 composite suspended in a H 2SO 2-MnSO 4 bath. Electrolytic manganese dioxide (EMD) containing acetylene black or vapour-grown carbon fibre shows excellent alkaline battery performance ad good grindability. Nevertheless, passivation of the titanium anode sometimes occurs during electrolysis at a current density of 1 A dm −2. This problem is successfully resolved without loss of battery performance, by using carbon/δ-MnO 2 as suspension particles. Apart from producing EMDs with good grindability and excellent battery performance, this bath has several other advantages, namely: easy maintenance of the dispersion; good reproducibility; low anode potential during electrolysis, and higher carbon content. It is proposed that a close relationship exists between battery performance and the surface characteristics of EMDs such as BET surface area and pore size.

STORA ASP 30

Abstract STORA ASP 30 is a high hardenability tungsten-molybdenum alloyed high-speed steel with high cobalt content. It is recommended for cutting tools for hard-to-machine material and high cutting speeds. It has excellent wear resistance, toughness, hot hardness and resistance to tempering. The excellent size stability and good grindability of ASP 30 make it very suitable for tools with a complicated shape. This datasheet provides information on composition, physical properties, microstructure, hardness, and elasticity. It also includes information on forming, heat treating, and machining. Filing Code: TS-338. Producer or source: Stora Kopparberg, Special Steels Division.

STORA ASP 23

Abstract STORA ASP 23 high-speed tool steel offers very good abrasion resistance and resistance to softening at elevated temperatures. The excellent size stability and good grindability of this steel make it highly suitable for tools of complicated shape, such as hobs, broaches and threading dies. The high combination of wear resistance, tensile properties and toughness make ASP 23 suitable also for cold-work tools. This datasheet provides information on composition, physical properties, and elasticity. It also includes information on forming, heat treating, and machining. Filing Code: TS-334. Producer or source: Stora Kopparberg, Special Steels Division.

High-speed steels with low carbide inhomogeneity

1. Two concentrations of tungsten are characteristic for high-speed steel containing no more than 1.7–1.9% V and possessing good grindability. a) at 7–8% W — high red hardness and secondary hardness values and a lower carbide inhomogeneity are assured; but sensitivity to overheating is preserved; b) at 12–13% W — the fine grain is maintained, but the steel displays a somewhat higher carbide inhomogeneity than the steel with 7–8% W. 2. The sensitivity of 7–8% W steel to overheating may be reduced by addition of 0.1–0.2% Ti, or 0.01–0.02%N, or 0.7–1% Ni. The above additions increase the strength and diminish the amount of residual austenite. 3. In order to reduce carbide inhomogeneity it is possible to decrease the contents of chromium in steel to 2.8–3%. This causes the strength to increase and the quantity of residual austenite to diminish. A drop in chromium contents to below 2.2–2.5% prevents the dissolution of complex tungsten carbides and reduces considerably the secondary hardness. 4. For tools with a thin cutting edge (tape, reamers, broaches, and so on) it is recommended to use steel R12 containing 0.8–9% C, 12–13% W, 2.8–3% Cr, 1.5–1.9% V, and 0.3–0.6% Ni (quenching from 1235–1255°C in oil or in hot media and triple tempering at 560–570°C). 5. For instruments designed for machining of hard (up to HB 200) materials under moderate cutting conditions, and which must have a low carbide inhomogeneity, it is recommended to use steel R7T (0.75–0.83% C, 7.6–8.2% W, 2.7–3.2% Cr, 1.2–1.5%V, 0.1–0.2% Ti, 0.4–0.8% Ni), or steel R7 into which nitrogen should be introduced instead of titanium (quenching from 1200–1220°C in oil or in hot media, tempering at 540–550°C, three times 1 hour each).