Excerpt from the January-March 2014 International Journal of Advanced Engineering Technology article by Raghwendra Banchhor, S.K. Ganguly.
Among the industrial activities, sand casting remains one of the most complex and indefinite processes. Due to the specific relationship between casting defects and green sand properties, it is imperative to control many green sand characteristics that influence casting quality. The traditional trial-and-error method based on know-how and experience has many disadvantages. These include being nonsystematic, time-consuming, error-prone, and require long durations of experimentation. There is a need to replace this traditional approach to produce higher quality casting products within reasonable periods making better use of statistics, artificial intelligence knowledge acquisition neural networks, and data mining tools.
This paper extensively reviews published research on the green sand casting process. The riser design, gating system, molding sand, oxidation and deformation of casting during heat treatment, and machining allowance effects on the economical manufacturing of quality castings were reviewed. Determining the optimal process parameter setting will significantly improve the mold yield, output ratio of metal, shorten manufacturing period, save energy and resource, reduce pollution, and improve competitiveness.
The term "Green sand casting" refers to an object solidified in green sand mold. Green sand molds are prepared with mixtures of silica sand, bonding clay, and water. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a green sand casting process. Although there are many new advanced technologies for metal casting, green sand casting remains one of the most widely used casting processes today. This popularity is due to the low cost of raw materials, a wide variety of castings concerning size and composition, and the possibility of recycling the molding sand.
The sand casting process is one of the most versatile manufacturing processes because it is used for most metals and alloys with high melting temperatures such as iron, copper, and nickel. The sand casting process consists of pouring molten metal into a sand mold, allowing the metal to solidify, and then breaking away the sand mold to remove a casting product. The casting product can then be machined to remove surface imperfections or add new features using standard machining methods such as grinding, turning, milling, and polishing. The sand used in the sand casting process is typically bonded with bentonite and water to mold the sand. The used sand can be recycled many times by adding new material to the return sand during reconditioning.
With the fast development of the car and machine-building industry, the casting consuming areas called for steady higher productivity. The basic process stages of the mechanical molding and casting process are similar to the manual sand casting process. However, the technical development was so rapid and profound that the character of the sand casting process changed radically. The first mechanized molding lines consisted of sand slingers or jolt-squeeze devices that compacted the sand in the flasks. Subsequent mold handling was mechanical using cranes, hoists, and straps. After core setting, the copes and drags were coupled using guide pins and clamped for closer accuracy. The molds were manually pushed off on a roller conveyor for casting and cooling. The molding lines can achieve a molding rate of 90 to 100 sand molds per hour.
In 1962, Dansk Industri Syndikat A/S invented a flaskless molding process by using vertically parted and poured molds. Today molding lines can achieve a molding rate of 550 sand molds per hour and requires only one monitoring operator. The maximum mismatch of two mold halves is 0.1 mm. Cores need to be set with a core mask instead of by hand and must hang in the mold instead of being set on a parting surface.
Castings are high-tech products that integrate materials, metallurgy, casting, heat treatment, welding, and measurement. Although some new casting technologies prosper, such as lost foam casting and die casting, green sand casting technology is still the most important and popularly used method for mass production of small and medium weight casting. While foundry engineers have access to an overwhelming amount of experimental work carried out over the last hundred years, many results contradict each other. Inapplicable to real-life casting, most foundries still take several weeks to develop a casting, rejection levels are high, and the yields are sub-optimal. Therefore realization of efficient and economical manufacture of casting is significant on the road to modernization.
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