Coating process of multi-material composite sand mold 3D printing

Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.

Shape characterization of sand particles based on digital image processing technology

To characterize the shape of sand particles for concrete,a new method is proposed based on digital image processing(known as the DIP method).By analyzing sand particles projection,the length,width and thickness of sand were measured to characterize particle form.The area and perimeter were measured to characterize particle angularity.The results of the DIP method and Vernier caliper were compared to examine the accuracy of the DIP method.The sample size test was conducted to show the statistical significance of shape results measured by the DIP method.The practicality of the DIP method was verified by instance analysis.The results show that aspect ratios and roundness measured by the DIP method are equal to ones by the Vernier caliper.Results by DIP are dependent on the sand particle number,and at least 350 particles should be measured to represent the overall shape property of sand.The results show that the DIP method is able to distinguish the differences in the shape of sand particles.It achieves the direct measurement of sand particle thickness,and the characterization results of sand aspect ratios and roundness are accurate,statistically significant and practical.Therefore,the DIP method is suitable for sand particle shape characterization.

Influence of core sand properties on flow dynamics of core shooting process based on experiment and multiphase simulation

The influence of core sand properties on flow dynamics was investigated synchronously with various core sands, transparent core-box and high-speed camera. To confirm whether the core shooting process has significant turbulence, the flow pattern of sand particles in the shooting head and core box was reproduced with colored core sands. By incorporating the kinetic theory of granular flow(KTGF), kinetic-frictional constitutive correlation and turbulence model, a two-fluid model(TFM) was established to study the flow dynamics of the core shooting process. Two-fluid model(TFM) simulations were then performed and a areasonable agreement was achieved between the simulation and experimental results. Based on the experimental and simulation results, the effects of turbulence, sand density, sand diameter and binder ratio were analyzed in terms of filling process, sand volume fraction(αs) and sand velocity(Vs).

Effect of Vibrational Modes on Sand Pressure and Pattern Deformation in the EPC Process

During the EPC (expendable pattern casting) process, one of the essential requirements is to prevent pattern distortion duringsand filling and compaction. A new method which vibrates the system in a two-dimensional circular mode has been appliedto the EPC process. The molding properties of unbonded sand obtained by this new vibration mode are investigated andcompared with those in the one-dimensional vertical mode. For adequate compaction of sand. the circular vibration mode ismore effective than the vertical mode. Sand became more fluidized by the circular vibration and the particle pressure coefficientwas close to unity The particle pressure coefficient, which is defined as the ratio of horizontal to vertical sand pressure, isresponsible for the effectiveness of sand filling.

A Numerical Model of Coastal Processes of Sand Beaches Based on Long-Term Wave Series

A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable.

Modeling of Deposition Process of Particulate Organic Matter (POM) with Sand on Vegetated Area in a River

The transport and deposition of particulate organic matter (POM) in river streams has recently received much attention as one of important ecological processes in rivers. We focused on interacted behaviors of sand particles in bed load and POM in vegetated area on sand bars. The purpose of this study is to clarify the characteristics of deposition of POM with bed load on sandbars with the riparian vegetation. A basic experiment on POM transport and deposition with vegetation is conducted in a laboratory flume. It demonstrates that several issues still remain to be future investigated. In particular, the shear due to the bed roughness in the vegetated area and the transport and deposition process of sand particles and POM are required to be described by the proper modeling which will be introduced into a simulation model of various fluvial processes. The main results of this study are that ripples are formed by bed load in riparian vegetation and POM deposition is promoted by ripple behavior. Based on these results, the POM deposition with ripples in vegetated area is described by a conceptual model which will affect various aspects in ecosystem management based on fluvial processes.

Data-driven casting defect prediction model for sand casting based on random forest classification algorithm

The complex sand-casting process combined with the interactions between process parameters makes it difficult to control the casting quality,resulting in a high scrap rate.A strategy based on a data-driven model was proposed to reduce casting defects and improve production efficiency,which includes the random forest(RF)classification model,the feature importance analysis,and the process parameters optimization with Monte Carlo simulation.The collected data includes four types of defects and corresponding process parameters were used to construct the RF model.Classification results show a recall rate above 90% for all categories.The Gini Index was used to assess the importance of the process parameters in the formation of various defects in the RF model.Finally,the classification model was applied to different production conditions for quality prediction.In the case of process parameters optimization for gas porosity defects,this model serves as an experimental process in the Monte Carlo method to estimate a better temperature distribution.The prediction model,when applied to the factory,greatly improved the efficiency of defect detection.Results show that the scrap rate decreased from 10.16% to 6.68%.

Simulating the effect of wind erosion on aeolian desertification process of Horqin sandy land and its significance on material cycle:a wind tunnel study

Samples from the Horqin sandy land were exposed to a series of wind velocities,and sink particles were collected at the end of the diffusion section of a wind tunnel.Grain sizes of collected samples show great variation because of the granularity difference of the surface samples.The original samples show lower average content of SiO_(2) and higher average content of Al _(2)O_(3),Fe_(2)O_(3),MgO,CaO,Na_(2)O,and K_(2)O than collected samples.Compared with other dust source areas in China,the Horqin sandy land had higher content of Zr,Ba,SiO_(2),Al_(2)O_(3) and K_(2)O.Compared with the average upper continental crust(UCC)composition,surface samples were rich in the content of Y,Zr,Nb,Ba,La,Nd.Geochemistry characteristics of fine grain components of the Horqin sandy land differ from those from other dust source regions,because fine-grained particles in the Horqin sandy land were mostly derived from various local deposits formed in its unique depositional environments influenced by several tectonic activities.

Mineral Processing of Silica Sand in Hanout Area/South of Jordan

White sandstone samples from Hanout area of Late Cambrian-Early Ordovician sandstone in south of Jordan were studied and assessed as a source of glass sand. Upgrading the sand included removing or reducing the content of the contaminant oxides and the heavy minerals. The aim of this research was to achieve this upgrading by examining the best-suited and cost-effective processing method(s) with sufficient product recovery. Following the initial sample characterisation at “bench scale”, a pilot study was performed. A high-grade Glass Sand product of 500 - 125 μm size fraction was produced by wet screening, attrition scrubbing and the separation of heavy minerals using spirals. The high quality Glass Sand product compared well with Grade-A of the British Standard for glass sand. Due to the relatively low level of impurities in the raw material, a substantial silica sand recovery was produced with a high silica grade. The silica sand product was capable to be used in the high quality glass industry and in many other applications where pure silica is required. The mass flowrate of the feeds and the products in the spiral was calculated for the bulk sample as well as the amount of water required operating the process.

Migration process of ammonium ion in saturated silty sand and sandy loam

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Cosworth Process──前景广阔的铝合金成型新工艺

论述了CosworthProcess的可持续发展的优势;对该工艺的特点进行了描述;对该工艺在我国的未来发展方向作了展望。

一种铝合金精确成型工艺——Cosworth Process

介绍了一种用于高强、高致密度铝合金铸件生产的新型铝合金铸造工艺——Ｃｏｓｗ ｏｒｔｈ Ｐｒｏｃｅｓｓ，并对该工艺的参数作了简要概括；同时，对该法在我国的应用前景作了展望。

Understanding the Interactions between Climate Change,Landscape Evolution,Surface Processes and Tectonics in the Earth System:What Can the Studies of Chinese Deserts Contribute?

Due to large deserts on Earth surface a thorough understanding of climate change, landscape evolution and geomorphological processes having occurred in deserts is crucial for Earth System Science. The landscapes in deserts are, however, diverse and different over the globe with regard to their geomorphological nature, human activities and geological histories. In the last decades a great number of efforts have been put to the investigation of the initial timing of the occurrence of arid climate, e. g. in northwestern China. Silty sediments in the downwind directions have been used to deduce the histories of deserts. In general, there is a lack of knowledge about processes and landscapes in Chinese drylands between the initial Miocene silt sedimentation at desert margins and the late Quaternary multiple occurrences of wetter climate with assumed large lakes in many of the deserts in northern China. The geomorphological concept of three primary triggering factors, i.e., the sediment supply, sediment availability and transport capacity of wind, and additionally the underground geology need to be fully considered for a better understanding of the environmental histories of sand seas which should not be viewed as equivalent for deserts because sand seas cover between 〈 1% and ca. 45% of the desert areas in various continents dependent on a complex interaction between various processes of both exogenous and endogenous origins.

A new low-cost method of reclaiming mixed foundry waste sand based on wet-thermal composite reclamation

A lot of mixed clay-resin waste sand from large-scale iron foundries is discharged every day; so mixed waste sand reclamation in low cost and high quality has a great realistic significance. In the study to investigate the possibility of reusing two types of waste foundry sands, resin bonded sand and clay bonded sand which came from a Chinese casting factory, a new low-cost reclamation method of the mixed foundry waste sand based on the wet-thermal composite reclamation was proposed. The waste resin bonded sand was first reclaimed by a thermal method and the waste clay bonded sand was reclaimed by a wet method. Then, hot thermal reclaimed sand and the dehydrated wet reclaimed sand were mixed in certain proportions so that the hot thermal reclaimed sand dried the wet reclaimed sand leaving some water. The thermal reclamation efficiency of the waste resin bonded sand was researched at different heat levels. The optimized wet reclamation process of the waste clay bonded sand was achieved by investigating the effects of wet reclamation times, sand-water ratio and pH value on the reclaimed sand characteristics. The composite reclamation cost also was calculated. The research results showed that the properties of the mixed reclaimed sand can satisfy the application requirements of foundries; in which the temperature of the thermal reclamation waste resin bonded sand needs to be about 800 oC, the number of cycles of wet reclamation waste clay bonded sand should reach four to five, the optimal sand-water ratio of wet reclamation is around 1:1.5, and the pH value should be adjusted by adding acid. The mass ratio of hot thermal reclaimed sand to dehydrated wet reclaimed sand is about 1:2.5, and the composite reclaimed sand cost is around 100 yuan RMB per ton.

Microscopic sand production simulation and visual sanding pattern description in weakly consolidated sandstone reservoirs

To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and predict sand cavity shape.The microstructure model is a particle-objective model,which focuses on the random sedimentation of every sand grain.In the microstructure,every particle has its own size,sphericity and inclination angle.It is used to simulate the actual structure of cemented granular materials,which considers the heterogeneity and randomness of reservoir properties,provides the initial status for subsequent sanding simulation.With the particle detachment criteria,the microscopic simulation of sanding can be visually implemented to investigate the pattern and cavity shapes caused by sand production.The results indicate that sanding always starts initially from the borehole border,and then extends along the weakly consolidated plane,showing obvious characteristic of randomness.Three typical microscopic sanding patterns,concerning pore liquefaction,pseudo wormhole and continuous collapse,are proposed to illustrate the sanding mechanism in weakly consolidated reservoirs.The nonuniformity of sanding performance depends on the heterogeneous distribution of reservoir properties,such as rock strength and particle size.Finally,the three sanding patterns are verified by visually experimental work.The proposed integrated methodology is capable of predicting and describing the sanding cavity shape of an oil well after long-term sanding production,and providing the focus objective of future sand control measure.

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

In this paper the Expendable Pattern Casting with dry sand Vacuum(EPC-V) process is used to manufacture iron matrix composites with tungsten carbide particle.Microstructures of the composites layers were analyzed.The abrasive wear resistance of the composites layers were tested and compared with that of high chromium cast iron.The results show that the iron matrix composites with tungsten carbide particle have high hardness.The abrasive wear resistance of composites with tungsten carbide particle is higher than that of high chromium cast iron.The properties of the matrix materials have been improved remarkably.

Evolution of windblown sand flux and dune field——Trans-scale modeling and simulation

Windblown sand flux and dune field evolving toward the oasis have been a common ecological and environmental threat confronted by many countries.Meanwhile,it is also a kind of complex dynamical process involving multiple temporal and spatial scales which is still out of accurate description through current field observations.Available models and reliable quantitative simulations are of significant value to predict the spreading rate of desertification and provide an optimal design for sand prevention.This paper presents a 'triple-jump' method to realize quantitative simulations to the formation and evolution of an aeolian dune field from an arbitrary initial configuration.Simulated results achieve a satisfactory agreement with observations qualitatively and quantitatively,which also reveal the characteristics and dynamical behaviors of dunes and dune field.Such a paradigm is of a good level of generality,which provides an exploratory probe into the subject of multi-scale physics.

Variability of Sand Mobility Surrounding Cylinder Object Freely Resting on the Seabed under the Action of Typhoon

In sandy sediments, scour and fill is the key process contributed to mine burial. The scour processes surrounding the cylinder mines freely resting on the sandy seabed under the 12-hr combined action of tidal currents and wind-generated waves, especially over typhoon events are numerically simulated using the DRAMBUIE model. The East China Sea is a good case study due to the dominant impact of summer typhoon events on sediment transport and scour. The numerical results show that the scour depth generally increases with time under the combined current and wave stresses exerted on the seabed, while the depth of the scour pit depends on infill once the currents subside. There is a positive relationship between the scour depth and the bottom orbital velocity after experiencing 12-hr wave action including storm waves, while the relation is not linear. The experimental results also display an elevated trend for scour depth with the increase of orbital velocity. The numerical results reveal a surprising phenomenon: the mobility of sand altering with the increasing bed shear stress larger than the certain threshold, which is also manifested as the curves of scour depth with the different grain size might cross each other. For laboratory experiments, the variability of sand mobility does not occur, likely because typhoon storm waves cannot be reproduced in the flume. More numerical tests indicate that the intersection will be triggered by the division of critical Shields parameter. The preliminary analysis suggests that the phenomenon never documented is likely generated from the error of empirical formulae.

Spatial heterogeneity of soil water content in the reversion process of desertification in arid areas

Sandy soils in arid,rain-fed environments have low and limited water content,which is a principal factor limiting vegetation development,and a key constraint controlling the structure and functions of the ecological systems in arid areas.The spatial heterogeneity of soil water content is a major soil property,and a focus of soil science and hydrology.On the southern edge of the Tengger Desert,sample plots were selected from mobile sand dunes in desertified lands that had been enclosed for 5,15 and 25 years,respectively.This study explored the dynamic and spatial heterogeneity of soil water content in these different layers of soil that were also in the reversion process of desertification.The results showed that the soil water content of the mobile sand dunes was highest when in the initial stages of the reversion process of desertification,while the soil water content in the 0-20 cm,20-40 cm and 40-60 cm layers of soil was 1.769%,3.011%,and 2.967% respectively,presenting a restoring tendency after 25 years of enclosure.There were significant differences,as a whole,in the soil water content among different restoration stages and different soil layers,respectively.Changes in soil water content,in different soil layers,at different restoration stages,exhibited exponential or spherical patterns.The spatial distribution of soil water content exhibited a mosaic patch pattern with obvious spatial heterogeneity.The ratio of the heterogeneity of spatial autocorrelation to gross spatial heterogeneity was greater than 50%.The gross spatial heterogeneity of the 0-20 cm layer of soil improved gradually,while those of the 20-40 cm and 40-60 cm layers improved initially,then weakened in the reversion process of desertification.This study revealed that restoration with sand-binding vegetation reduced soil water content,and increased its spatial heterogeneity in arid areas.However,after 25 years of vegetation-soil system restoration,the soil water content started to increase and its spatial heterogeneity started to weaken.These results will further benefit the understanding of the ecological mechanism between soil water and sand-binding vegetation.

Evolution of crescent-shaped sand dune under the influence of injected sand flux:scaling law and wind tunnel experiment

This paper studies the evolution of crescent-shaped dune under the influence of injected flux. A scaling law and a wind tunnel experiment are carried out for comparison. The experiment incorporates a novel image processing algorithm to recover the evolutionary process. The theoretical and experimental results agree well in the middle stage of dune evolution, but deviate from each other in the initial and final stages, suggesting that the crescent-shaped dune evolution is intrinsically scale-variant and that the crescent shape breaks down under unsaturated condition.