Crushed Quartz Sand Research Articles

Characterization of powder flow behavior for additive manufacturing

The flow behavior of powders has an essential role in many industrial processes, including powder bed additive manufacturing. The characterization of the flow behavior is challenging, as different methods are available, and their suitability for an application in additive manufacturing is still controversial. In this study, six standardized methods (measurement of bulk density by ISO 60 and by ASTM B329, angle of repose by ISO 4324, discharge time by ISO 6186 and by ASTM B964–16, and Hausner Ratio by ASTM 7481–18), the rotating drum method (by GranuDrum) and powder rheometry (Anton Paar powder cell), were applied to five size fractions of a crushed quartz sand powder and compared. A statistical approach is proposed and discussed to correlate the obtained flowability indexes with the packing density of powder beds deposited layer-by-layer, and these correlations are compared between methods. Overall, the measurement of bulk density by ASTM B329 showed the best correlation with the powder bed density. Advanced methods such as the rotating drum method and powder rheometry did not demonstrate particularly good correlations, however they provided complementary information which can be useful to assess the dynamic behavior of powders. • Ten methods to characterize powder flowability for additive manufacturing are compared. • A statistical approach is proposed to correlate flowability indexes and packing density of powder beds. • The measurement of bulk density by ASTM B329 (Scott volumeter) shows the best correlations. • The rotating drum method and powder rheometry provide complementary information to standard tests.

Effect of Tempering Temperature on Microstructures and Wear Behavior of a 500 HB Grade Wear-Resistant Steel

The microstructure and wear behavior of a 500 Brinell hardness (HB) grade wear-resistant steel tempered at different temperatures were investigated in this study. The tempering microstructures and wear surface morphologies were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The relationship between mechanical properties and wear resistance was analyzed. The microstructure of the steel mainly consisted of tempered martensite and ferrite. Tempered troosite was obtained when the tempering temperature was over 280 °C. The hardness decreased constantly with the increase of tempering temperature. The same hardness was obtained when tempered at 260 °C and 300 °C, due to the interaction of Fe3C carbides and dislocations. The impact toughness increased first and reached a peak value when tempered at 260 °C. As the tempering temperature was over 260 °C, carbide precipitation would occur along the grain boundaries, which led to temper embrittlement. The best wear resistance was obtained when tempered at 200 °C. At the initiation of the wear test, surface hardness was considered to be the dominant influencing factor on wear resistance. The effect of surface hardness improvement on wear resistance was far greater than the impact toughness. With the wear time extending, the crushed quartz sand particles and the cut-down burs would be new abrasive particles which would cause further wear. Otherwise, the increasing contact temperature would soften the matrix and the adhesive wear turned out to be the dominant wear mechanism, which would result in severe wear.

Influence of activation of quartz grain surface on efficiency of the process of processing the quartz sand grains with fluoride technology

The influence of grinding the initial quartz sand on the degree of activation of the sand-grain surface during processing using a fluorinating reagent has been studied. Using the method of the synchronous thermal analysis, the technological parameters of producing ammonium hexafluorosilicate using mixtures of different fractions of sand at temperatures in the range of 25–400°C were examined. The investigation of intermediate phases, formed during the thermogravimetric experiment was carried out with the X-ray analysis. It was established that formation of ammonium hexafluorosilicate with crushed quartz sand occurs at temperatures of 30–40°C lower than the source conditions.

Performance of asphalt concrete with dolomite sand waste and bof steel slag aggregate

The rapid growth of traffic loads in Latvia increases the demands for asphalt carrying capacity on large motorways. The dolomite and sandstone that can be found in Latvia lacks the mechanical strength and for most of the large motorways the aggregates are imported from other countries causing increase of costs and growth of emissions from transportation. On the other hand, large amounts of Basic Oxygen Furnace (BOF) steel slag aggregates with good qualities are being produced in Latvia and put to waste. During the recent decades, the dolomite sand waste has also been accumulated and its quantity has reached a million of tons and is rapidly increasing. This huge quantity of technological waste needs to be recycled with max efficiency. The lack of experience in the use of steel slag and dolomite sand waste requires an accelerated evaluation of the asphalt performance-based characteristics. This paper presents the testing results of dense graded asphalt concrete AC 11 mixtures made of four types of aggregate: steel slag, dolomite sand waste, conventional imported dolomite aggregates and conventional local crushed quartz sand that were proportioned to develop a mixture that would satisfy the requirements of permanent deformation and stiffness. Analysis of the results showed that the mixes with steel slag and dolomite waste sand or unconventional aggregate combination with dolomite in coarse portion, crushed quartz sand in sand portion plus dolomite waste sand in sand and filler portions had high resistance to plastic deformations and fatigue failure. These mixes can fully satisfy and in some cases significantly overcome the requirements of local asphalt specifications for highly loaded motorways.

Performance Based Evaluation on the Use of Different Waste Materials in Asphalt

The dolomite and sandstone that can be found in Latvia, lacks the mechanical strength and for most of the large motorways the aggregates are imported from other countries causing increase of the costs and growth of emissions from transportation. On the other hand, large amounts of BOF steel slag aggregates with good qualities are being produced in Latvia and put to waste. During the recent decades, the dolomite sand waste has been accumulating and its quantity has reached a million of tons and is rapidly increasing. This huge quantity of technological waste needs to be recycled with maximum efficiency.The lack of experience on the use of steel slag and dolomite sand waste requires an accelerated evaluation of the asphalt performance-based characteristics. This paper presents the testing results of dense graded asphalt concrete AC 11 mixtures made of four types of aggregate: steel slag, dolomite sand waste, conventional imported dolomite aggregates and conventional local crushed quartz sand that were proportioned to develop a mixture that would satisfy the requirements of permanent deformation and stiffness. Analysis of the results showed that mixes with steel slag and dolomite waste sand or unconventional aggregate combination with dolomite in coarse portion, crushed quartz sand in sand portion and dolomite waste sand in sand and filler portions had high resistance to plastic deformations. These mixes can fully satisfy and in some cases significantly overcome the requirements of local asphalt specifications for highly loaded motorways.

Evaluation of sand grain crushing in the sand dollar Mellita tenuis (Echinoidea: Echinodermata)

Sand dollars in the genus Mellita have been postulated to use their teeth to crush sedi- ments comprised of quartz. If so, sand dollars may have a greater impact on nearshore siliciclastic environments than generally thought. The present study compared the size distributions of quartz grains in the guts and immediate habitat of the common sand dollar Mellita tenuis in summer and winter in Port Saint Joseph Bay, Florida. In both seasons, sand dollars had significantly greater fre- quencies of the smaller size classes of grains in their guts. The hypothesis that sand dollars crushed quartz sand grains with their teeth was evaluated using light microscopy. We compared the degree of angularity of ingested grains with those collected from surrounding sediments. Among 6 individu- als examined (3 in summer and 3 in winter), only half (2 in summer and 1 in winter) had guts contain- ing more angular grains than those in the surrounding sediments. A comparison of more angular grains isolated from sand dollar guts with artificially broken grains using scanning electron microscopy indicated that gut-derived grains lacked freshly broken surfaces. In a laboratory study, after 72 h of feeding upon quartz sediments with the smallest size classes (<250 µm) removed, sand dollar guts were full but contained only trace amounts of sediments <250 µm. We conclude that the smaller size classes of grains found in the guts of M. tenuis are not the result of grain breakage. Rather, grains are selected pre- or post-ingestion, perhaps to optimize the surface to volume ratio of particles so as to maximize ingestion of microbial films that coat sand grains.

The influence of a cone-in-cone insert on flow pattern and wall pressure in a full-scale silo

A silo insert is sometimes placed inside the hopper to improve the flow pattern of solids in a funnel flow silo. This paper describes a recent experimental investigation of the flow pattern and wall pressures observed during filling and emptying of a cylindrical silo with and without a cone-in-cone insert. The 2.5 m diameter silo had an 8 m high cylindrical section and a 44° conical hopper, and was filled with crushed quartz sand. The wall pressures were measured at ten chosen locations using pressure cells mounted on the wall. To investigate the solids flow pattern, markers were placed at fixed positions in the silo during filling and the residence time for each marker during discharge was observed. The flow pattern can be inferred from the residence time measurements for the markers and the surface profile observations during discharge. These tests show that a cone-in-cone insert can have a strong influence on both the flow pattern during discharge and the pressure acting on the silo wall and its industrial use should be considered cautiously and implemented with care.

Compression and strength of dense sand at high pressures and elevated temperatures

The paper examines the stress–strain behaviour of densely compacted sand tested at pressures up to 80 MPa in one-dimensional compression and 7.2 MPa confining pressure in triaxial tests. Tests were performed at temperatures up to 100 °C. The testing relates to a proposal by Atomic Energy of Canada Limited to fill containers of waste nuclear fuel with a crushed quartz sand to provide additional stiffness. No significant effects of temperature were encountered in either isotropic compression or triaxial shear.Key words: sand, compression, shear strength, temperature, pressure.

Sources of non-glacial, loess-size quartz silt and the origins of “desert loess”

Descriptions of peridesertic loess deposits and possible non-glacial origins for silt size quartz are reviewed, including direct release from weathered bedrock. Results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt-size fragments are identified. These fragments may then be entrained by aeolian or fluvial action. Results from fluvial comminution experiments indicate that high energy, mixed sediment fluvial systems may be very effective in generating quartz silt. Purely aeolian attrition is also seen as a major source of silt size and finer material. Results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and Pannonian Sands from Hungary. Field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as ‘desert loess’.

Scaling Bacterial Filtration Rates in Different Sized Porous Media

Aquifer sediments contain a wide distribution of particle sizes, but only a single collector diameter ( d ) can be used in a filtration equation. To establish a method for selecting a characteristic d when media are composed of different sized particles, we measured bacterial retention in columns packed with either crushed quartz sand (separated into three different size ranges) or borosilicate glass beads. The best methods for choosing d were those that produced nearly constant collision efficiencies (α's). Characteristic diameters included: d10 (10% of all particles were smaller), d90 (90% of all particles were smaller), d a (arithmetic mean), and d g (geometric mean), where all diameters were calculated using number, area, and volume size distributions. Bacterial α's decreased in proportion to the distance traveled in the packed bed, and were scaled by the number of bacteria-sediment collisions using a dimensionless collision number (ξ). These comparisons indicated that characteristic diameters based on the smaller particles ( d a and d g using number distributions, and d10 using a volume distribution) most accurately described bacterial transport in the different-sized porous media.

Elastic Wave Velocities in Granular Soils

Laboratory tests, using the resonant column method, were conducted to evaluate the longitudinal and shear wave velocities in specimens of Ottawa sand, crushed quartz sand, and crushed quartz silt. The variables considered were the confining pressure, and the moisture content, void ratio, and grain characteristics of the materials. The wave velocities for the sands varied with approximately the 1/4 power of the confining pressure. At a given confining pressure, the velocity varied almost linearly with void ratio. A diagram is included that shows these relationships over a range of void ratio from 0.3 to 1.3 and confining pressures between 500 psf and 6,000 psf. The effects of relative density, grain size, and gradation entered only through their effects on void ratio. The wave velocities in the quartz silts were found to be greatly dependent on time.