120装载机履带节以铸代锻的研究

介绍了用ZC-42CrMo材质，以精密铸造的方法，代替通常使用的50Mn材质、锻造方法生产的120立爪装载机履带总成的履带节的研制和应用情况。结果表明，该方法不仅满足履带节力学性能及使用性能要求，而且生产成本显著降低。     

Hot mold casting process of ancient East India and Bangladesh

Ancient casting process for production of brass or bronze utensils and icons were made in hot molds using clay molded investment casting or piece mold process, as presumed by archaeologists. Piece mold process is still traditionally practiced in many parts of Eastern India and Bangladesh along with investment casting process. Incidentally, Bengal artisans are more accustomed to piece mold process unlike tribal artisans who practiced investment casting process. This piece mold casting process has been reconstructed to get the idea of metal characteristics in order to investigate ancient casting process of Bengal and Bangladesh. The characterization of ancient archaeo-metal products come to a type of cast Cu-Sn-Zn-Pb type quaternary alloy produced by a slow freezing process. Though these alloys physically differ from the traditional cast alloy of binary Cu-Zn type brass, the physical characteristics are similar to the binary cast alloy character. This investigation throws light on the similarity of the production processes by which ancient artisans probably produced cast metal products.     

Effect of particle size variations of gypsum bonded investment powders on metallurgical quality of investment castings

Abstract

In the present work, the effect of particle size distribution parameters of investment powder on the metallurgical characteristics of castings produced by flask mould investment casting process was investigated. The main aim of this study is to establish the relationships between the casting quality and investment powder characteristics. For this purpose, models for tensile, density and surface roughness specimens were prepared in accordance with the standards and these models were moulded by gypsum bonded investment powders. Specimens of sterling silver (92·5Ag–7·5Cu alloy) were subsequently cast into these moulds by centrifugal casting process. After the completion of solidification process, the specimens were tested and results were analysed. The preliminary results illustrate that fineness of investment powders play an important role in determining the metallurgical quality of castings produced by investment casting process.     

Mechanical properties and microstructures of AlSi7 alloy cast in sand and in polystyrene-containing sand moulds

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.     

K465涡轮导向器熔模铸造工艺研究

涡轮导向器是在研某型号航天发动机的关键部件,采用K465铸造高温合金无余量整体熔模铸造而成。该部件由内锥、内环、叶片、外环和法兰五位一体构成,整体呈复杂框架结构,其叶片最薄处仅为0.7mm,且壁厚相差悬殊,铸造凝固过程易产生疏松、裂纹等缺陷,试制工艺难度很大。设计采用了蜡模分体压制,组合夹具精确定位,蜡模拼装组合成型的工艺方案,使叶片的一致性和尺寸精度得到了保证,获得了导向器熔模铸造用整体蜡模;通过浇注系统、铸造工艺的优化,解决了试制过程中出现的疏松和开裂问题,保证了铸件的冶金质量,研制出了合格的导向器铸件。     

Contraction of Investment Cast H13 Tool Steel Real Time Measurement

This paper presents the results of an investigation into the dimensional changes and variability of investment cast H13 tool steel. An experimental apparatus has been developed to measure the dimensional changes during the casting process. Investigating the dynamics of mould expansion and alloy contraction during investment casting, it has been possible to determine in greater detail the contributions of the cast alloy and the mould to the final contraction of unconstrained castings. Contraction and dimensional variability of the final cast product is defined and experimental estimations of the contributions of each stage of investment casting are made. A technique for combining the variability of sequential stages is discussed. The measured contraction appears to be non-uniform and dependent on the position along the casting.     

Development of permanent-mold cast TiAl automotive valves

This paper presents the results of an EMTEC funded project to develop low-cost TiAl automotive valves. The alloy studied was Ti-47Al-2Nb-1.75Cr (at %). Over 800 valves were cast, using several variations of the permanent-mold process, in a multi-cavity steel mold. Applying pressure during solidification improved the casting fill. However, none of the permanent-mold casting methods produced pore free as-cast valves. The as-cast microstructures of valves produced by permanent-mold casting were much finer than investment castings of similar section sizes. Of the permanent-mold casting methods, the injection cast method exhibited the finest as-cast structure showing a potential for a new high output method for producing fine-grained TiAl components. Room temperature tensile properties of the permanent-mold material were superior to those of investment castings with a similar microstructure. Two sets of valves were road tested for a total of 50000 km with average 2% fuel savings and no valve damage. There is a need to overcome few challenges before this technology can be implemented in the automotive industry.     

Evaluation of crucible and investment materials for lost wax investment casting of Ti and NiTi alloys

Abstract

The aim of this study is to assess the suitability of selected commercial ceramic crucibles for the investment casting of Ti6Al4V and NiTi alloys for jewellery purposes. A commercial vacuum tilt casting machine and a centrifugal casting machine were employed to cast the alloys in cold copper moulds or in refractory investment shells. The form filling of the shell and the crucible and investment reactions were assessed by microstructural investigation, chemical analysis and hardness profiles of the as cast items as a function of shell temperature. The reaction of the alloys strongly depended on the alloy, the crucible material, the coating of the crucibles and the temperature of the ceramic shell. Optimum results were achieved with yttria and yttria coated Al titanate crucibles for Ti6Al4V and NiTi alloys respectively. Improvement of the materials and process costs is necessary to allow the competitive casting of jewellery made from titanium alloys.     

Heat transfer and solidification analysis in the mould region of a horizontal copper alloy billet continuous caster

Abstract

Mathematical modelling has been widely used as a powerful tool for process design and optimisation of the continuous casting process. A three-dimensional heat transfer model was developed to simulate heat transfer and solidification in a horizontal billet continuous casting system. In this model, the air gap formation and its effect on heat extraction from the billet was also modelled and considered. The developed model was run to simulate the heat transfer and solidification for an industrial billet casting machine. The predicted temperature distribution within the mould and billet was compared with those measured on an industrial caster and good agreement was obtained. Parametric studies were carried out to evaluate the effects of different parameters on the temperature distribution and solidification profile within the cast brass billet. Finally, the secondary dendrite arm spacing (SDAS) was determined experimentally and a semi-empirical correlation between measured SDAS and corresponding calculated cooling rate was proposed for continuously cast brass billet.     

Microstructure and Mechanical Properties of Mg–RE–TM Cast Alloys Containing Long Period Stacking Ordered Phases: A Review

Casting magnesium alloys hold the greatest share of magnesium application products due to their short processing period, low cost and near net shape forming. Compared with conventional commercial magnesium alloys or other Mg–RE-based alloys, the novel Mg–RE–TM cast alloys with long period stacking ordered(LPSO) phases usually possess a higher strength and are promising candidates for aluminum alloy applications. Up to now, two ways: alloying design and casting process control(including subsequent heat treatments), have been predominantly employed to further improve the mechanical properties of these alloys. Alloying with other elements or ceramic particles could alter the solidifi cation pattern of alloys, change the morphology of LPSO phases and refi ne the microstructures. Diff erent casting techniques(conventional casting, rapidly solidifi cation, directional solidifi cation, etc.) introduce various microstructure characteristics, such as dendritic structure, nanocrystalline, metastable phase, anisotropy. Further heat treatments could activate the transformation of various LPSO structures and precipitation of diverse precipitates. All these evolutions exert great impacts on the mechanical properties of the LPSO-containing alloys. However, the underlying mechanisms still remain a subject of debate. Therefore, this review mainly provides the state of the art of the casting magnesium alloys research and the accompanying challenges and summarizes some topics that merit future investigation for developing high-performance Mg–RE–TM cast alloys.     

大直径铸钢套筒的离心铸造研究

主要介绍了卧式离心铸造大直径铸钢套筒的方法。讨论了降低套筒气孔和铸造裂纹的工艺措施，离心铸造铸钢套筒具有组织致密、均匀、工艺出口率高和铸件加工量少等特点，生产成本比普通静态铸造降低20%以上，用作铝箔轧机的出口端卷筒，获得了较好的效果。     

固液混合铸造高铬铸铁的热变形性能研究

采用一种新的材料制备技术-固液混合铸造工艺制备了高铬铸铁合金坯料,对合金进行了高温热压试验,并对热压过程和合金组织进行了观察和分析。研究结果表明,固液混合铸造的高铬铸铁合金相对于普通铸造合金的热变形性能得到明显提高,累计墩粗变形比可达到34%以上,固液混合铸造工艺对高铬铸铁合金组织的改善是提高材料热变形性能的主要原因。     

微精密铸造工艺研究进展

三维复杂形状的金属微构件的微细加工一直是微机械研究的重点和热点，近年来涌现出许多的加工工艺，比较而言，微精密铸造工艺在高效制备三维复杂形状的微构件方面具有十分独到的优势。文中从微精密铸造工艺、合金、铸型材料及相关理论等几个方面综述了国外基于熔模铸造的微精密铸造工艺的发展现状，并讨论了现有微精密铸造工艺的不足，提出了微精密铸造工艺的发展方向，同时，对作者在金属型微精密铸造工艺方面的研究作了简要的介绍。     

Heat transfer and solidification microstructure evolution of continuously cast steel by non-steady physical simulation

The heat transfer and solidification microstructure evolution during continuous casting were experimentally studied in this work. A new approach to physically simulate the steel solidification behavior during continuous casting was developed. Six steel grades with different solidification mode were introduced to elucidate the carbon equivalent dependent mold heat flux, prior austenite grain size and secondary dendrite arm spacing. It is found that the non-steady mold heat fluxes in the experiment against time for all steel grades are comparative to that versus distance in practical continuous casting. Due to the occurrence of L→L+δ→δ+γ→γ transformation with the largest amount of volume contraction in hypo-peritectic steel, it shows the lowest mold heat flux among these six steel grades. It is also demonstrated from the solidification microstructure results that the prior austenite grain size and secondary dendrite arm spacing in the physical simulation are in good agreement with those in continuously cast strand. In addition, the steel with a higher temperature for the onset of δ→γ transformation reveals the larger prior austenite grains resulted from the higher grains growth rate in the post solidification process.     

Casting of aluminum-copper based alloy by controled difusion solidiication

A quaternary alloy(Al-5.0Cu-0.35Mn-0.25Ti, wt.%), having a similar chemical component with ZL205A, was prepared using a controlled diffusion solidification(CDS) process and a conventional casting process. The effect of the casting process on microstructure and hardness was investigated. The grain morphology and casting defects of the alloy prepared via the conventional casting and CDS were observed and compared at various pouring temperatures. Results show that the CDS process can alleviate the hot tearing defects and reduce the density of porosity, while getting rid of the riser that is generally used for feeding during conventional casting. Structure observations show that the grain morphology of the conventional cast alloy is mainly dendritic, and the grain size decreases when the pouring temperature is decreased, while the CDS cast alloy consists of a large number of spherical grains, which can decrease the thermal cracking tendency and segregation defect, and enhance the hardness of the alloy.     

Investigation of carbon contamination in lost foam castings of low carbon steel

Lost foam casting(LFC) process is a special casting method in which polymeric foam patterns with refractory coatings are utilized as a mould component. In this work, four types of foam: expandable polyethylene(EPE), expandable polypropylene(EPP) and expandable polystyrene(EPS) foams with two different densities were employed as pattern materials. LFC and conventional green sand mould casting methods were used to cast a low carbon steel, A216 Grade WCB. Both casting processes were carried out at 1,580 °C. Chemical analysis results showed that the carbon contamination level was high and was influenced by pattern type. Metallographic investigations revealed a significant increase in the percentage of pearlite phase in all LFC samples. Densities of manufactured samples were calculated in order to evaluate porosity of the products. It was determined that the densities of the LFC samples were lower than the green sand mould cast reference sample(RS). Vickers hardness tests were also carried out and increments in hardness values with increased carbon content was observed.     

Variation of microstructure and mechanical property of slurry die cast Al-Si-Mg-Fe alloy

Semi-solid metal processing technologies have been intensively studied in recent years. Gas Induced Semi-Solid (GISS) is a slurry preparation technique for producing non-dendritic or globular structures for cast alloys. In the present study, GISS technique was used in conjunction with conventional die cast process for casting Al–Si–Mg–Fe alloy. The shape of die cast specimen was designed as a simple flat plate. The variation of microstructures and tensile properties of specimens from different locations of cast plates was studied. The results show that the specimens from bottom location, near the gate section and the middle location of cast plates are stronger and more ductility than those from the top location. The microstructural examination reveals that the specimens from top location of cast plates contain more defects, such as shrinkage pores than those from the other locations. These defects are resulted in lower strength and ductility of the cast product.     

ZL114A铝合金铸件力学性能的计算机预测

为保证大型铝合金铸件的质量,本研究采用数值模拟方法对其力学性能进行了预测。试验中测定了对应于不同冷却速度的铸件各部位微观组织中的枝晶二次臂间距(DAS)和孔隙率(fv),通过数学回归推导得它们与力学性能关系的数学模型,从而在浇注前即可预测铸件的力学性能。铸件的计算机预测结果与实际浇注结果一致。     

Valid mould and process design to cast tensile and fatigue test bars in tilt pour casting process

Abstract

Tilt pour gravity casting technology is increasingly being used for shape casting various components with aluminium alloys. The ASTM B108/B108M-08 standard exists for a metal mould to evaluate the mechanical properties of castings made by gravity permanent mould process, yet there is no standard mould for the tilt pour process. We have designed, developed, tested and validated a standard mould to cast tensile and fatigue test bars in a tilt pour casting process. The new mould has demonstrated abilities to cast sound castings of A356·2 aluminium alloy, and the uniaxial tensile properties were superior to those obtained from conventional direct pour gravity casting process.     

挤压在镁合金金属型铸造中的应用

在金属型铸造中采用局部挤压方式,可防止铸件内部缩孔、疏松缺陷的出现,获得的内部组织致密,晶粒细小,具有较高的强度和硬度。此法不失为称补金属型铸件缺陷的一种较佳工艺手段。