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AbstractThis investigation was carried out to identify the major factors and their degree of influence on the dimensional accuracy of spheroidal-graphite iron castings produced in chemically- bonded sand moulds. Test castings were poured into furan-resin-bonded zircon sand and silica sand moulds and sodium silicate/ CO2 bonded silica sand moulds. A comparison of casting sizes with those of the mould cavity into which they were poured showed considerable scatter and overlap. From these data the size that each casting would have had, had it solidified without graphite formation, was calculated and found to depend on mould cavity size for each type of mould. By isolating the differences in casting size due to graphite it was possible to identify the influencing factors. Thus castings poured into furan-resin-bonded zircon sand have the highest contraction and their size depends primarily on the amount of graphite present. The dimensions of castings poured into silica sand moulds show more variation and depend not only on the amount of graphite present and the structure of the metal but also on the thermal expansion of the silica sand moulds. 相似文献
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《International Journal of Cast Metals Research》2013,26(1):28-36
AbstractThe present work was undertaken in hypereutectic ductile irons, to simultaneously study cooling curves, specimen contraction curves, microstructures and shrinkage tendencies as a function of inoculant selection and mould rigidity. Specific equipment was developed for simultaneous recording of cooling and contraction curves. The highest level of both concentrated and total shrinkage was recorded on the green sand mould system, where a much higher level of the initial eutectic expansion was observed, as compared to furan resin moulds. It was found that the Ca,Ce,S,O–FeSi inoculation gives the highest nodule count and a unique wide distribution of nodules sizes (large and small size nodules, in a peculiar ratio), as well as lower tendency to shrinkage formation. Also, the strongest graphitising effect before the start of eutectic solidification and more prolonged graphitising throughout the end of eutectic freezing characterise were observed with this complex inoculant system in addition to its peculiar action on minimising the shrinkage tendency of ductile irons. 相似文献
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建立变壁厚回字形结构多材质复合铸型,首先,通过对A356铝合金在多材质复合铸型的充型、凝固过程模拟仿真,获得多材质复合铸型铸件充型时间和温度场结果,锆英砂与石英砂、铬铁矿砂与石英砂过渡处凝固时间呈阶梯状递减;且锆英砂与石英砂过渡处及铬铁矿砂与石英砂过渡处铸件凝固时间更短,金属液凝固速度更快。其次,采用电子背散射衍射(EBSD)分析、电子显微探针(EPMA)分析对石英砂、铬铁矿砂、锆英砂复合铸型在重力铸造下A356铝合金铸件断口进行分析并进行抗拉强度测试。结果表明:在相同壁厚时,铬铁矿砂、锆英砂型铸件的晶粒尺寸细小,Al、Mg、Si等元素分布均匀、力学性能提高,断口呈现韧性断裂的特征;同时随着壁厚减小,同种材质砂型铸件晶粒细化、元素分布均匀、力学性能提高,断口呈韧性断裂特征。 相似文献
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Yin-Chun Cheng Chih-Kuang Lin An-Hung Tan Shih-Yuan Hsu Sheng-Long Lee 《Journal of Materials Engineering and Performance》2012,21(9):1873-1878
This study investigates the mechanical properties of Al-7Si-0.3Mg (A356) alloy affected by the spinning deformation processing (SDP). The cast structure of the A356 alloy becomes elongated with increasing reduction in thickness. This leads to reduction of casting defects, and refines and distributes the eutectic silicon phase throughout the Al-matrix. The hardness tends to reach a steady value due to the uniformity of the microstructure with the reduction in thickness. The SDP leads to a re-arrangement in the eutectic region, which forces the propagation of cracks through the ductile ??-Al phase. The tensile strength and elongation increases accordingly. The improvement on tensile strength and elongation produces the best quality index for A356 alloy. 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):260-264
AbstractThe frozen mould which is produced by refrigerating the mixture of sand and water has the possibility to improve both the casting cost and the poor working environments such as noise, vibration and dust. The transition of mechanical properties of the frozen mould when it was transforming into thawed and dried states was examined. The compressive strength of the standard frozen mould consisting of only sand and water dramatically decreased when it was thawed and the strength was not recovered by drying. In contrast, the frozen mould produced by substituting colloidal silica solution for water showed some compressive strength even in thawed state and the strength was elevated by subsequent drying. The reusability of the sand mixture with colloidal silica solution was also evaluated. The compressive strengths did not deteriorate with any reclamation. The above results prove that the frozen mould with colloidal silica solution has an excellent industrial potential. 相似文献
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462Q气缸体水套砂芯制芯工艺及热芯盒设计 总被引:8,自引:3,他引:5
选用酚醛树脂砂热芯盒法制作462Q气缸体水套砂芯,以国产ZZ8612射芯机作优先选用机型设计热芯盒,合理选择射砂方向及垂直分盒,确保细窄部位成型及砂芯的整体质量;热芯盒采用一个静模、两个动模,加之动模合理的顶芯机构,从而在ZZ8612射芯机上实现了一盒两芯的设计方案;采用成型冷却模,保证结构强度较低的该水套砂芯在冷却硬化过程中不变型或将变形量减小到最低限度。 相似文献
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以挤压铸造A356.2铝合金发动机悬置支架为研究对象,对支架铸态组织、不同固溶时效热处理后的显微组织与力学性能,以及内部缺陷进行了分析研究。结果表明,挤压铸造A356.2铝合金铸态组织由α-Al相和Al-Si共晶组成,晶粒尺寸约为148μm,二次枝晶间距约为20μm;经固溶时效处理后,共晶Si一部分溶入α-Al相中,一部分以粒状、球状形式分布在α-Al晶界;固溶时间、时效温度和时效时间对A356.2合金的力学性能有一定影响。试样经过535℃×6h固溶+8min水淬+170℃×6h时效处理后,抗拉强度为340.5MPa,屈服强度为274.5MPa,伸长率为10%,满足支架整体力学性能要求。 相似文献
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ABSTRACTInvestigations were carried out to use Granulated Blast furnace (GBF) slag as mould material for either full or partial replacement of existing silica sand in foundry industry. Nishiyama process was adopted for evaluating the same. A series of sand tests were carried out on sand and slag individually and also combinations of these two. Three types of moulds were made with sand, slag individually and combination of these two. Both laboratory and industrial castings of ferrous and non ferrous materials were performed. Results of mould permeability, compression and shear strength of GBF slag reveal that is a suitable candidate for either partial or full replacement of molding sand. During casting of both laboratory and industrial, neither fuse, dripping nor collapse of the mould walls was observed; this is true for both ferrous and non ferrous castings. Castings with good surface finish, no surface defects and porosity were made by slag moulds. 相似文献
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Recent studies revealed that in eutectic to slightly hypereutectic grey irons (CE = 4.3%-4.5%) the presence of austenite dendrites provides an opportunity to improve the cast iron properties, as a high number of eutectic cells are "reinforced" by austenite dendrites. An iron powder addition proved to be important by promoting dendritic austenite in hypereutectic irons, but was accompanied by adverse effect on the characteristics of potential nuclei for graphite. The purpose of the present paper is to investigate the solidification pattern of these irons. Chill wedges with different cooling moduli (CM = 0.11 - 0.43 cm) were poured in resin bonded sand and metal moulds.Relative clear / mottled / total chill measurement criteria were applied. Iron powder additions led to a higher chill tendency, while single inoculation showed the strongest graphitizing effect. The various double treatments show an intermediate position, but the inoculant added after iron powder appears to be the most effective in reducing base iron chill tendency, for all cooling moduli and chill evaluation parameters. This performance reflects the improved properties of (Mn,X)S polygonal compounds as nucleation sites for graphite, especially in resin bonded sand mould castings. Both austenite and graphite nucleation benefit from a double addition of iron powder + inoculant,with positive effect on the final structure and chill tendency. 相似文献
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Laurentiu Nastac Shian Jia Mihaela N. Nastac Robert Wood 《International Journal of Cast Metals Research》2013,26(4):194-201
Modelling of gas evolution during sand-mould castings is one of the most important technical and environmental issues facing the metal casting industry. The current effort focused on developing the capability of numerically predicting the gas evolution for the furan binder-silica sand system. Specifically, the decomposition of furan was experimentally analyzed and then predicted based upon the work developed in the current project. This methodology can be easily implemented into existing commercial casting codes. A parametric study was also performed for steel 4340 and aluminium A356 cylinders (D100 × H200 m) and bars (H50 mm × W50 mm × L250 mm) cast into silica sand moulds (furan binder) of 50-mm mould wall thickness to investigate the effects of superheat and heating/cooling conditions of the mould on the gas evolution. Such information would enable more technically and environmentally friendly decisions to be made concerning the process design used to make a given casting. 相似文献
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Experimental work has been undertaken to study the effects of polystyrene pattern material on the mechanical properties and microstructures of cast aluminium alloys. This paper reports results obtained using Al—Si 7% (LM25) alloy. Rectangular tensile test-pieces of various thickness were cast at different pouring temperatures into standard resin-bonded sand moulds. The experiments were then repeated with polystyrene patterns placed into the sand mould cavities. A direct comparison of the effects of polystyrene pattern material on the properties of the cast test-pieces with those obtained under identical conditions by a standard sand casting method has thus been obtained. Ultimate tensile strength, elongation, Vickers hardness, porosity volume, and dendrite arm spacing (DAS) values relating to both methods were evaluated for a range of casting section thickness (4–16 mm) and pouring temperature (690–780 °C). The microstructural differences observed between the test pieces obtained, with and without polystyrene patterns, were verified by the changes in the solidification cooling curves recorded simultaneously for both methods.The results obtained show that an expanded polystyrene pattern contained within a sand mould, under the experimental conditions used, does not have an adverse effect on the as-cast mechanical properties of LM25 alloy. On the contrary, the presence of polystyrene in the sand moulds resulted in higher rather than lower tensile properties. These findings have been supported by microstructural observations which reveal finer microstructures and lower volumes of porosity in the test pieces produced with the use of polystyrene, rather than in the absence of it. These observations are further supported by the evidence obtained from the cooling curves which reveal that the presence of polystyrene in the sand mould results in a faster casting cooling rate compared with that when no polystyrene is present. 相似文献
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Semisolid slurry of A356 aluminum alloy was prepared by self-inoculation method, and the microstructure and solidification behavior during rheo-diecasting process were investigated. The results indicate that the semisolid slurry of A356 aluminum alloy can be prepared by self-inoculation method at 600 °C. Primary α-Al particles with fine and spherical morphologies are uniformly distributed when the isothermal holding time of slurry is 3 min. Liquid phase segregation occurs during rheo-diecasting process of semisolid slurry and the primary particles(α1) show obvious plastic deformation in the area of high stress and low cooling rate. A small amount of dendrites resulting from the relatively low temperature of the shot chamber at the initial stage of secondary solidification are fragmented as they pass through the in-gate during the mould filling process. The amount of dendrite fragments decreases with the increase of filling distance. During the solidification process of the remaining liquid, the nucleation rate of secondary particles(α2) increases with the increase of cooling rate, and the content of Si in secondary particles(α2) are larger than primary particles(α1). With the increase of cooling rate, the content of Si in secondary particles(α2) gradually increases. The morphologies of eutectic Si in different parts of die casting are noticeably different. The low cooling rate in the first filling positions leads to coarse eutectic structures, while the high cooling rate in the post filling positions promotes small and compact eutectic structures. 相似文献
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In this study, the microstructure and corrosion behaviour of rheocast and gravity-cast A356 aluminium alloys were examined and compared. Scanning Kelvin probe force microscopy (SKPFM) results proved that large potential differences between iron-containing intermetallics and the α-Al matrix were responsible for the initiation of the attack at the intermetallics/α-Al interfaces. For longer immersion times, corrosion attack proceeded through the eutectic areas. Semisolid processing refined the eutectic silicon and iron-intermetallics and reduced the potential difference between secondary phases and the matrix. This resulted in improved pitting corrosion resistance of the rheocast A356 aluminium alloy. 相似文献