Lab on Casting

In this lab we saw the basic elements of the casting process. The casting process was studied by first preparing Styrofoam patterns. The Styrofoam patterns are burned out by the molten bronze when poured. Some of these patterns had different characteristics that would test different principles that should be followed when designing a part to be made by casting. Some of these characteristics were thin areas, sharp corners, and long parts with small gates and runners. The other patterns were made at random. Each pattern had a gate and runner system also made of Styrofoam.

Once the patterns were assembled they were placed in metal containers and packed with sand. The sand was mixed to have a small amount of moisture to allow the sand to be packed. If there is too much moisture in the sand it could damage the finished parts. Care was taken to not break the gates and runners leading to the patterns. To aid in the pouring of the metal each container was packed to have a funnel shape in the sand that tapered toward the opening of the gate. Once the packing was finished we waited for the bronze ingots to melt and reach a temperature of 1000-1200 F.

The bronze was melted in a furnace in a container called a cupola. The cupola was lifted with a winch and used to pour the molten bronze into the molds. Once the molds were filled with the molten bronze they were alowed to cool for a few minutes while the metal solidified. The containers were then tipped over to separate the sand from the finished parts. The parts were further cooled in a bucket of water once separated from the majority of the sand.

Measurements were taken of the Styrofoam before they were packed in sand and after they had cooled. These measurements can be seen below:

Object..................................Styrofoam Dimensions......................After Metal has Cooled

Large Balls..........................Diameter of 1.42"...............................1.39"

Small Balls..........................Diameter of 1.00"............................... 0.95"

Heart..................................w=5.9",h=5.82".................................w=5.7", h=5.3"

Square Thing........………..Bottom=1.9" x 1.9" x 1.9"……..Bottom=1.89" x1.88"x

……………………………………………………………….………..not measurable

...........................................Top=1.9" x1.9" x 1"……………….Top=not measurable

"h" with Thin Section ........h=2.28" wt=1.08.............................h=2.26" wt=1.10"

......................................….ht=.59" hb=.59"............................ht=.59" hb=.657"

......................................….web=.14" wb=.95"........................web=.14" wb=1.06"

All of the patterns turned out better than expected except for the "square thing" which was poured to fast and the metal splashed away the sand at the top of the pattern. This is why there were no good measurements of the top or the height of the bottom section. For most of the parts the dimensions were smaller after the parts had cooled. This shrinking was expected and has to be calculated into molds when production parts are produced in industry. Some of the parts that had larger dimensions after cooling could be related to the sand not being packed tight around the pattern. The finished parts also had the pocketed surface finish similar to the Styrofoam that was used.

The damaging characteristics that were made into the patterns turned out as expected for most of the patterns. The parts that had sharp corners were slightly rounded when finished. The long patterns with small gates and runners were not completely filled with metal. And the pattern with the thin section did not crack in the cooling stage as it was thought that it would.