Process Optimization And Defects Prevention Of Railway Steel Casting With Green Moulding Clay Sand

The process for railway steel casting with green moulding clay sand has manyadvantages including high efficiency, low cost, continuous production and being easy toimplement mechanization and automation. But there are some key technical problems foractual application such as requirement of high-quality raw materials and precise control ofmolding sand properties, being prone to creating blowhole, scab, crack and other castingdefects. To produce qualified castings, every aspect of the casting process is needed to beanalysed carefully and controlled strictly. So we should ensure the quality of raw materials,develop reasonable recipes of green moulding clay sand and process of sand mixing, makea simulation and optimization on the casting process with some simulation softwares toreduce or avoid the casting defects and propose effective solutions based on macro andmicro analysis of all kinds of casting defects. The goal of this paper is to produce highquality steel castings in low cost with process of green moulding clay sand, which is ofgreat theoretical and practical significance.Based on systematic sand tests, this paper developed reasonable recipes of facing andbacking sand which met the requirement of production. The optimized facing sand recipewas “100%new sand+(8.0-8.5%) bentonite+(0.3-0.5%) starch additives+(3.0-3.6%)water” and the corresponding molding sand properties were degree of ramming51-54%,permeability440-450, green strength85-95kPa, hot wet tensile strength4.1-4.5kPa,shatter index70-72%and surface stability index97.0-97.5%. And the optimized backingsand recipe was “100%reconditioned sand+(0.2-0.3%) bentonite+(0.1-0.3%) starchadditives+(3.3-3.6%) water” and the corresponding molding sand properties were degreeof ramming55-60%, permeability200-210, green strength90-95kPa, hot wet tensilestrength3.8-4.5kPa, shatter index72-75%and surface stability index97.5-98.0%. Bothrecipes had passed the verification of mass production.The Procast software bought by cooperative plant was effectively used to simulatethe mold filling and solidification process of the original casting process of No.17coupleryokes and No.16coupler knuckles, and the location of erosion, slag inclusions, burning-on, blowhole, shrinkage cavity and porosity and hot tearing were predicted. Based on thesimulation results, the optimized casting process design was obtained. The calculatedresults of the optimized design had less defects than those of the original one, so theoptimized casting process design had been served as the process of trial production.There existed some key casting defects such as cracks during the process of trialproduction. The category and feature of the defects and the causes were analyzed in detail,besides, some effective solutions were proposed from several aspects and the final castingprocesses of yokes and knuckles had been obtained. The products of yokes and knucklesproduced by the final casting processes also passed all levels of identifications and thequality test items all met the standard, that was to say, the plant had the capacity of massproduction of No.17coupler yokes and No.16coupler knuckles. There was no obvioussurface defects in the products during mass production and the existing crack defectscould be successfully processed and controlled. So the mass production could be operatedcontinuously and effectively. This paper has well done the research objectives and tasks.