Casting Lab

Objective:

To be familiarized with the process of sand casting.

Procedure:

The process was lost styrofoam casting. The sytrofoam was cut into various shapes to model the part to be cast.
Some of the molds were created long to show the effect of the cooling flow of the material. The metal was projected to stop short of the end of the mold. Some of the parts did not have any radii molded at their corners. This was done to determine the effects of the cooling process. It was projected that the mold would have cracks or deformed edges. Each mold consisted of a runner and spru. The runners were generally kept very short to provide the flow needed to reach all the cavities of the mold. If the runners were too long the metal would cool in them and cause the mold to be partial filled. The sprus were generally of the same dimensions. It was desired to have a spru large enough to provide easy access to pour into. Some of the mold included a riser. The riser was too allow for the shrinkage of the metal as it cooled. Based on this, the risers were created with a volume greater than that of the part. The riser could not cool quicker than the part less it defeats its own purpose. The molds were than put into stove pipes which were too provide a rigid support for the sand. The molds were placed on a layer of tightly compacted sand which provided a barrier or insulation from the environment. Sand was then packed around the molds as tightly as could be with out destroying the features of the mold. The top layer of sand was funneled into the spru to provide a path for the liquid metal. The metal was heated to a temperature between 1000 and 1200 degrees F in a gas furnace. The metal was then poured and cooled and the parts were removed.

The parts looked better than we expected. Most of the parts were completely filled. The heart was a surprise in that it was very smooth and the part was far from being completely filled. The smoothness was a result of the surface finish of the part and the filling was a function of the length and curvature of the flow. Most of the parts had a rough surface finish. This could have been attributed to the compaction of the sand and the surface of the molds. None of the parts showed any major problems with the cavitation of the sand. The part with sharp edges instead of radii came out with some radii formed on its own. All of the castings had some shrinkage to their dimensions, so none of the risers were deemed efficient. The risers may have helped the letters form because one spru fed all of the letters.

Dimensional Results:

Part Styrofoam Dimensions Cast Dimensions

Chain of Small Balls Dia. = 1.00" Dia. = 0.95"

Chain of Large Balls Dia. = 1.42" Dia. = 1.39"

Heart W = 54.9" W = 5.7"

H = 5.82" H = 5.3"

"H" H = 2.28" H = 2.26"

Wt = 1.08" Wt = 1.10"

Ht = 0.59" Ht = 0.59"

Hb = 0.59" Hb = 0.675"

Web = 0.14" Web = 0.14"

Wb = 0.95" Wb = 1.06"

Square Bottom- sides = 1.9" Bottom- 1.89" x 1.88"

Top- sides = 1.9" x 1.9" x 1.0" Top- not measurable