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Metal Casting Technologies : June 2007
www.metals.rala.com.au 32 bstract: Large counter-gravity casting equipment (CGCE) has been developed, which is specially designed for the production of large-size, thin-walled, high-quality aluminum alloy parts. With a mold transportation system, the gigantic resin sand mold can easily be moved and filled in CGCE, and up to 2500kg casting can be produced with the equipment. PID algorithm associated with fuzzy control and digital assembled valve system was applied in CGCE, so the high pressure-tracing precision can be obtained. Meanwhile, we put forward some casting techniques under the condition of counter-gravity casting, such as gating system design, filling process parameter, etc. Compared to the castings produced under conventional gravity conditions, the castings under counter-gravity condition have generally higher soundness, higher tensile strengths and ductility. The equipment and the technology have been widely adopted by several users in China for the production of large-size thin-walled aluminum alloy castings with high property requirements. 1. INTRODUCTION The large-size or super large aluminum alloy components have been widely applied in aeronautics, astronautics and marine industries, with the development of design thinking about integration, light weight and high reliability of the parts. Counter-gravity casting offers the advantages of high quality, including high soundness, low shrinkage porosity, fine grains and high mechanical properties. The technologies have attracted increasing attention for many years throughout the world and have widely been applied to produce high quality aluminum alloy components [1-4]. However, present counter-gravity casting equipment is mainly designed for die-casting molds. Some difficult problems related to the hardware and process control technologies restrict the application of the technology in sand-mold casting. For example, the overall size of some important aluminum alloy parts is even up to 2500×2500×3000mm with the weight over two tons, but with a thickness of only 10mm. When these castings are formed by counter-gravity technology, many technical problems such as fluctuation of molten metal, riser tube gelation, shrinkage porosity formation, molds and cores assembly, etc, deteriorate the metallurgy quality of the castings. When large-size castings are formed in sand molds, the fitted molds weighing tens of tones have to be transferred to a working platform, which is a difficult problem in most foundry workshops. On the other hand, the preparation of eligible molten metal and mold-core assembly is lengthy and therefore to establish such equipment these hardware and manipulation problems need to be overcome. Counter-gravity casting method has many merits compared to other commercial methods. However, appropriate technology parameters have to be provided otherwise, the inherent merits could not be utilized properly. We have studied counter-gravity casting technologies for several years and put forward some principles for the design of casting processes, such as gating system design, filling rate option, feeding method, and so on, which are the key factors for the production of large-size aluminum alloy castings with high quality. The equipment and technologies developed in our laboratory have been applied in several foundry workshops for the production of thin-walled Al-alloy parts. Some parts weigh up to 2.5 tons, with the small thickness of less 5mm. Moreover, the castings formed by this equipment have perfect metallurgical and physical properties. 2. EQUIPMENT DEVELOPMENT The counter-gravity casting equipment developed by the present authors consists mainly of electric and pneumatic control system, controlling software and control algorithm. 2.1 Main part of equipment The main part of the equipment includes the pressure exerting unit, mold transportation unit, molten metal preparation unit and hydraulic pressure unit. The mold transportation and the pressure exerting units of CGCE are shown in Fig.1. The pressure exerting unit mainly consists of pressure-bearing can, locking ring and mid-dividing board. Working pressure of the pressure exerting unit can be as high as 0.25MPa, which meets the production desire of most aluminum alloy castings. The molten metal preparation unit is placed in the pressure exerting unit. The capability of crucible in molten metal preparation unit is up to 3000kg. The locking ring seals up pressure exerting Development of Counter-Gravity Dasting Equipment and Technology for Large-Size Aluminium Castings By Li Xinleia, Hao Qitangb, Jie Wanqic, College of Materials Science and Engineering, Northwestern Polytechnical, University, Xi'an 710072, China. email@example.com firstname.lastname@example.org, email@example.com. The following article has been provided in both English and Chinese by the authors.