Preparation of coated sand for selective laser sintering and optimization of baking process of sand moulds

A cold method was used to prepare coated sand for application in the selective laser sintering(SLS)process.Tensile strength,loss on ignition,gas evolution,and accuracy of the SLS samples were tested and analyzed,and the baking process was thoroughly investigated.Compared with coated sand prepared by the hot method,the cold method yields a more uniform and complete resin film on the sand's surface,resulting in enhanced tensile strength and accuracy.Additionally,the cold method requires a lower binder content to meet the same strength requirements,thereby minimizing gas evolution,reducing porosity defects,and ultimately improving casting quality.The coated sand samples prepared through the cold method exhibit superior accuracy,with a size error of within±0.4 mm.In contrast,the coated sand samples prepared by the hot method display a lower accuracy,with an average negative error of 2.1993 mm.The highest tensile strength could be attained by controlling the baking temperature within a suitable range(180-190°C),which can effectively reduce the generation of gas,thus contributing to improved overall performance.

Effects of laser energy density on forming accuracy and tensile strength of selective laser sintering resin coated sands

Baozhu sand particles with size between 75 μm and 150 μm were coated by resin with the ratio of 1.5 wt.% of sands. Laser sintering experiments were carried out to investigate the effects of laser energy density(E = P/v), with different laser power(P) and scanning velocity(v), on the dimensional accuracy and tensile strength of sintered parts. The experimental results indicate that with the constant scanning velocity, the tensile strength of sintered samples increases with an increase in laser energy density; while the dimensional accuracy apparently decreases when the laser energy density is larger than 0.032 J·mm-2. When the laser energy density is 0.024 J·mm-2, the tensile strength shows no obvious change; but when the laser energy density is larger than 0.024 J·mm-2, the sample strength is featured by the initial increase and subsequent decrease with simultaneous increase of both laser power and scanning velocity. In this study, the optimal energy density range for laser sintering is 0.024-0.032 J·mm-2. Moreover, samples with the best tensile strength and dimensional accuracy can be obtained when P = 30-40 W and v = 1.5-2.0 m·s-1. Using the optimized laser energy density, laser power and scanning speed, a complex coated sand mould with clear contour and excellent forming accuracy has been successfully fabricated.

Influence of resin flow on shrinkage of additive manufacturing coated sand molds

Coated sands are used extensively for additive manufacturing sand molds in the metal casting process, and the packing structure changes caused by the resin flow promote the shrinkage and deformation of the part. During the coated sand heating, the resin on the surface flowing to the contact points of the particles forms the resin neck and causes particles to pack close to each other. In this work, the diameters of the coated ceramsite sand before and after heating were measured based on in-situ experimental observations with image measuring apparatus and blue laser, to obtain the relationship between resin coating thickness and the particle diameter. The particle packing model was established to describe the particles' achievement of a stable state one by one. A re-packing simulation was then performed after reducing the particle diameter according to the resin coating thickness, to obtain the shrinkage ratios at different particle size distributions. It was found that the resin coating thickness increased from 0.8 to 2.3 μm as the particle diameter increased from 107 to 500 μm, for the coated ceramsite sand with the resin content of 2 wt.%; the shrinkage ratio decreased first and then increased as the particle diameter increased. The experimental minimum shrinkage ratio was 3.28%, and the corresponding particle diameter was 300-375 μm, while the minimum shrinkage ratio obtained by simulation was 3.43%, and the corresponding particle diameter was 214-300 μm. After mixing the five groups proportionally, the shrinkage ratios of the simulation and experiment dropped to 2.81% and 3.04%, respectively, indicating the best results.

Carbon coated sand filtration

The goal of this work is to determine the removal efficiency of pathogen by using carbon coated sand filter.For the bacterial research,serial dilution and agar plate methods are used,E.coli is used as bacterial indicator and the experiments are operated under four different conditions:different HRTs,different sand:bran ratios,different carbon sources and different sand types.As a result the treatment efficiency of bacteria is too much less than the slow sand filtration.It’s not suitable for bacteria removal.Although its treatment efficiency is less than the advanced methods,it is a low-tech system which can be easily built up and it is very economic.

Freeze-Thaw Effect on Coarse Sand Coated Interface between FRP and Concrete

This paper examines the effect of freezing and thawing on the coarse sand coating chosen to achieve the composition of FRP and concrete in FRP-concrete composite deck. Push-out test specimens with dimensions of 100 × 100 × 450 mm were subjected to repeated freeze-thaw cycles under wet conditions ranging from -18℃± 2℃ to 4℃ ± 2℃. The failure strength of the interface and the deformation of FRP at failure exhibited by the specimens that experienced 300 freezing-thawing cycles showed a difference of merely 5% compared to those of the specimens that were not subjected to freeze-thaw. This indicates that coarse sand coating is not affected by freezing-thawing cycles and the FRP-concrete composite deck owns sufficient applicability in terms of durability against freezing-thawing.

Adsorption of Fluoride from Water Using Aluminum Coated Sand: Kinetics, Equilibrium, Effect of pH, and Coexisting Ions

An aluminum coated sand (AlCS) was evaluated as a metal oxide adsorbent for adsorption and removal of fluoride from water using a low-cost adsorbent with potential application in continuous flow adsorber systems. Surface characterization of the AlCS sorbent was performed using TEM, SEM/EDX, XRD and BET. The AlCS sorbent contained mostly amorphous aluminum oxides based on adsorbent characterization results. Favorable adsorption of fluoride onto the AlCS sorbent occurred according to the Langmuir and Freundlich adsorption equations, while physical adsorption of fluoride onto the AlCS sorbent was observed based on results from the Dubinin-Radushkevich equation. Fluoride adsorption onto the AlCS sorbent followed pseudo-second order kinetics, while surface charge analysis indicated a pHPZC of 7.1 for the AlCS sorbent. Effective fluoride removal occurred over a broad pH range from 3 to 11 with a maximum fluoride removal observed at pH 4 to 5. The effect of co-existing ions in water resulted in a decrease in fluoride uptake in the presence of bicarbonate, while resulting in an increase in fluoride uptake in the presence of calcium. The AlCS sorbent was a low-cost and sustainable adsorbent for effective adsorption and rapid removal of fluoride from water within an hour.

Hydraulic and mechanical properties of wax-coated sands

Wax-coated sands are a new category of synthetic soils, which are gradually becoming a reliable construction material. Because of their valuable drainage ability and mechanical properties, wax coated sandy soils are specifically applicable to pavement construction of horseracing tracks and sport fields. Although the mechanical and hydraulic properties of these synthetic soils are well-proven, there is still a lack of studies on how the soil samples behave differently when mixing with different wax fractions. Adding the wax affects permeability and compressibility of pure sand. Intensity of influences is a function of weight percentage of wax that has been added, and other physical and environmental factors. The effects of wax content on hydraulic properties(permeability), and mechanical properties(stress strain behavior, compressibility) of sandy soils based on a series of experimental efforts were investigated. Obtained experimental results infer that increasing the amount of wax up to 6% causes an about 50% increase in permeability, mainly because of the significant effect of wax in lowering the friction along with covering and filling the angular parts of particles' surfaces and forming rounded particles. In addition, wax-coated sands show a 20% to 60% decrease in confined compression modulus compared to non wax-coated sands.

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.

Wear behavior of high velocity arc sprayed 3Cr13 steel coating in oil containing sand

To improve the wear resistance of the machine components serving in desert areas, the 3Cr13 stainless steel coating was produced by the high velocity arc spraying technique. The microstructure and phase constitute of the coating were analyzed by SEM and XRD. The effects of sand content on the friction and wear behaviors of the coating under the lubrication of oil containing sand were investigated on a ball-on-disk tester. SEM was used to reveal the wear mechanisms of the coating. The results show that the wear volume increases with increasing the sand content in the oil, and the sprayed coating exhibits better triobological properties compared with the 1045 steel. The predominant wear mechanisms of the sprayed coating are micro-cutting, brittle fracture and delamination.

Sand-wear resistance of brush electroplated nanocomposite coating in oil and its application to remanufacturing

Sand-wear resistance of nano scale alumina particle reinforced nickel matrix composite coating （n-Al2O3/Ni） prepared by brush electroplating technique was investigated via wear tests in sand-contaminated oil lubricant, comparing with that of AISI1045 steel and brush electroplated Ni coating. Effects of testing load, sand content and sand size on worn volume of the three materials, and also coating surface roughness on worn volume of the brush electroplated coatings were accessed. Results show that the worn volume of all the three materials increases with increasing of testing load, sand content and sand size. In the same conditions, n-Al2O3/Ni composite coating has the smallest worn volume while AISI1045 steel has the largest because of the n-Al2O3 particle effects. As to n-Al2O3/Ni and Ni coatings, the surface-polished coatings have obviously lower worn volume than the as-plated coatings. The brush electroplated n-Al2O3/Ni composite coating was employed to remanufacture the sand-worn bearing seats of a heavy vehicle and good results were gained.

不同支撑剂组合方式下页岩导流能力实验评价

为了深入了解多粒径支撑剂组合条件下页岩储层导流能力的大小,依据达西定律,采用API支撑剂实验装置,评价分析不同支撑剂质量比例、粒径、铺砂浓度、类型、流体类型、岩性等对导流能力的影响。实验结果表明:随着闭合压力增加,各种支撑剂组合方式下的导流能力都有很大程度下降;相同条件下,铺砂浓度与导流能力呈正相关关系,覆膜砂的导流能力高于石英砂,清水条件下的导流能力高于破胶液,硬度高的页岩储层导流能力高于硬度低的页岩储层;70/140目陶粒+40/70目覆膜砂+30/50目覆膜砂支撑剂组合,在质量比为1∶6∶3时导流能力最优;在高闭合压力下,70/140目陶粒+40/70目覆膜砂+30/50目覆膜砂组合的导流能力,略高于70/140目陶粒+30/50目覆膜砂+20/40目覆膜砂支撑剂组合。可见,对于较软地层采用覆膜砂组合支撑剂,更有利于长期保持较高的导流能力;压裂液选用时更要注重压裂液配方的低伤害性,以提高导流能力。

涂膜、腻子膜打磨性测定仪校准方法的研究

研究建立了涂膜、腻子膜打磨性测定仪的校准方法。通过对生产厂家和用户的调研,参考相关的国家标准和校准规范,提出一种采用电子秒表、钢直尺、电子天平作为校准设备,校准涂膜、腻子膜打磨性测定仪的摩擦速度示值误差、摩擦行程、打磨头质量、附加砝码质量的方法。选择代表性的涂膜、腻子膜打磨性测定仪,依据该校准方法对计量特性进行实验验证,验证结果符合指标要求。该方法促进了涂膜、腻子膜打磨性测定仪量值溯源的标准化和规范化,推动其校准规范的制定。

内河水沙冲蚀条件下港口钢构件涂层损伤劣化的图像识别方法

为探究内河港口码头钢构件在水沙冲蚀条件下防腐涂层的损伤劣化规律,通过自制的水沙加速冲蚀磨损装置开展不同冲蚀条件下涂层材料损伤劣化的试验研究,基于图像识别技术对冲蚀损伤后的涂层表面形貌进行数字化和二值化特征提取,设定区分像素孔隙的灰度阈值,用以定量分析涂层表面破坏形式和损伤劣化面积。结果表明:当来流角度呈45°时,涂层损伤劣化最严重且表面凹坑比和划痕比大致相同,涂层损伤劣化面积随来流速度的增大呈指数扩大趋势;当含沙量低于45 kg/m^(3)时,含沙量的增大对涂层损伤劣化有促进作用,但当超过45 kg/m^(3)后反而降低了涂层损伤劣化速率,实现了在无损情况下对内河水沙冲蚀条件下钢构件涂层的损伤劣化规律分析。

复杂内腔铝合金件液态模锻试验研究

目的为拓宽液态模锻技术的应用范围,实现具有复杂内腔结构件的高性能短流程成形制造,开展了使用砂芯的液态模锻技术试验研究。方法以具有复杂内腔的新能源汽车铝合金空气弹簧顶座为对象,利用广州和德装备制造公司生产的卧式液态模锻机,对比研究不同砂芯、涂料及液锻加压制度对黏砂缺陷的影响作用。结果普通砂芯在液锻中容易被压溃或产生黏砂缺陷;在苏铸砂芯的基础上自行配制HDSC01液锻砂芯,配合HDCoating03专用涂料,采用阶梯加压方法进行液态模锻,所得液锻件内表面光洁无黏砂、尺寸精确。结论液态模锻可以使用砂芯进行复杂内腔结构件的高性能精密成形,但工艺控制不当,容易出现黏砂缺陷。阶梯加压、使用专用砂芯和专用涂料是防止黏砂的有效途径。

基于沥青砂涂层设计的沥青混凝土路面抗紫外光老化性能分析

针对沥青路面光老化问题,参照含砂雾封层技术原理,基于沥青抗紫外光添加剂最优组合,制备含砂沥青涂层,开展不同级配和厚度的沥青砂涂层试验研究,通过沥青混凝土高低温性能试验和抗滑性能试验分析含砂涂层设计下沥青混凝土路面抗光老化性能,结果表明:涂层设计下沥青路面老化前后抗滑性能降低,但是相比于无涂层时老化后降低幅度变小且仍满足规范要求,在不考虑抗滑损失的情况下,可选择使用;老化后高低温路用性能试验说明增加路表面密实度可以提高抗光老化能力,但是涂层厚度不宜过厚,以基本完全填充混凝土表面空隙最好,建议理论厚度2 mm,要重点考虑细料涂层的级配设计,适当提高沥青砂中较大粒径的比例对封层设计效果会更好。

直升机旋翼前缘弹性耐砂蚀涂料的制备和性能研究

为提高直升机旋翼前缘的耐砂石侵蚀能力,采用弹性树脂作为基料树脂,碳化硅、聚四氟乙烯粉料为耐磨填料,制备了弹性耐砂蚀涂料的A组分,采用弹性固化剂作为耐砂蚀涂料的B组分。重点讨论了不同基料树脂、固化剂、n(—NCO)∶n(—OH)、耐磨填料以及耐磨填料的用量对弹性耐砂蚀涂料性能的影响。结果表明:所制备的弹性耐砂蚀涂料的耐磨损失为10 mg,拉伸强度达到26.3 MPa,断裂伸长率为278%,同时还具有优异的耐砂蚀性,能满足直升机旋翼前缘不锈钢件的防护要求。

汽车发动机缸体内腔质量影响因素分析及工艺控制

随着汽车轻量化的发展,发动机缸体壁厚要求越来越薄。针对水套内腔质量的影响因素进行了分析和工艺改善;介绍了烧结陶瓷砂、纤维素和铬尖晶石用于硅砂制芯添加对砂芯高温和常温特性以及产品质量的影响;指出涂料的热暴、热膨胀和烧结性对产品内腔质量影响以及涂料粉料的作用机理;运用射砂模拟技术对砂芯致密性进行了分析和质量改善。

选区激光烧结技术在复杂流道砂芯中的应用

介绍了选区激光烧结技术生产复杂流道砂芯的整套工艺流程,通过合适的选区激光烧结砂芯结构设计、成形制造工艺及覆膜砂原材料的选择,制造出了结构复杂的整体流道砂芯。原材料采用抗拉强度更高的覆膜宝珠砂、合理的砂芯定位支撑面和砂芯排气通道等措施,更能满足复杂薄壁流道砂芯的实际铸造需求,通过实际生产验证,利用选区激光烧结技术整体制造了复杂流道砂芯,生产的铸件尺寸精度达到CT8级,采用100/200目的覆膜砂原材料,流道表面粗糙度可达Ra 6.9~10μm。

磷酸盐干态覆膜砂结块现象的改善措施研究

结块现象是磷酸盐干态覆膜砂在保存中遇到的问题之一,难以使覆膜砂保持散砂状态,从而严重影响了覆膜砂的流动性,阻碍了无机覆膜砂的应用。通过向干态覆膜砂里加入偶联剂和干燥剂以改善结块问题,结果表明:将偶联剂处理前、后的两种干态覆膜砂以质量比为1∶1混合均匀,再加入占覆膜砂质量分数为1/200的硅胶干燥剂,能有效改善覆膜砂结块问题,结块率下降65%左右,射砂成形所得试样的抗拉强度达到1.5 MPa以上。