Gravity Casting

Abstract
Casting has been widely used as a fabrication technique due to its simplicity and economic advantages. Gravity casting is a type of casting technique that utilizes gravity to completely fill the mold with the molten material. The objective of this experiment is to perform gravity casting of polyester resin on plaster of Paris mold and evaluate the casted product using visual inspection. In this experiment, casted product was not successfully removed from the mold. It was also observed that the material obtained several defects such as voids, incomplete casting, inclusions and irregular surface. Possible sources of error in this experiment include the insufficient application of petroleum jelly on the mold, inappropriate viscosity of

Casting is applicable to metals, ceramics and polymers (Groover 2010). Another advantage of casting is that it has the ability to form intricate external and intricate shapes and patterns (Rao 2007). Casting also allows addition of alloying elements which helps further enhance the range of properties of the final product (Rajput 2007). Lastly, casting is economical and considered as the cheapest manufacturing process despite recent developments in other available manufacturing techniques (Rao 2007). One major disadvantage of casting is that it provides poor surface finish and poor dimensional accuracy due to shrinkage (Groover 2010). To address these problems, procedures like surface machining and proper mold design can be performed. Other disadvantages of casting includes high energy requirement, highly labor intensive process, bad working conditions in foundries due to extreme heat, dust, and fumes (Rao

In order to obtain high quality casted products, high cooling rate is highly recommended. However, the cooling rate must also be properly regulated because cooling rates that are too high could also cause entrapment of air in the casting which gives rise to high amounts of porosity (Davis 1993). The pouring of the molten material on the mold also affects the quality of the casted product. To achieve high quality cast products, the molten material must be able to flow into all of the regions in the mold, especially in the casting’s main cavity (Bilal n.d.) In addition, the rate at which the material is poured onto the mold is also crucial. High rate of pouring might cause turbulence but slow rate of pouring might also cause the material to solidify even before the mold has been fully filled with the material (Bilal n.d). The pouring temperature, defined as the initial temperature of the material before it is poured into the mold, must be higher than the solidification temperature of the said material (Bilal n.d.) Fluidity, which is defined as the capability of the material to flow into the mold before solidification also affect the quality of cast products since it plays a key role in the ability of the material to completely fill the regions of the mold before the material solidifies. Some of the factors that affect fluidity include: temperature, material composition, heat transfer to the environment and