Casting Lab

Objective:

To become familiar with the basic procedure followed during a casting process. The type of process to be explored is a lost-foam type of casting procedure utilizing bronze, and styrofoam patterns which are packed in sand. When the material is poured, the styrofoam melts out and allows the material to fill the cavity in the sand (the mold).

Procedure:

Several different shapes were made from styrofoam and hot-melt glue. Some were purposely selected because it was thought that they represented patterns which could not be successfully cast with this type of process. This was done in hopes of being able to predict the results before the casting was done. Once the patterns had been assembled, initial dimensions were taken in crucial sections of the pattern. The patterns were then buried in slightly moist sand which was packed around the patterns in a piece of stove pipe. The moist sand is what will be used to form the mold of the pattern once the styrofoam burns out as the bronze is poured. It should be noted at this time that the sand was only slightly moistened, so that it retained the shape of the pattern once it was burned out. If the sand is too moist, it will cause the molten bronze to splatter possibly causing injury to those around. The stove pipes containing the molds were positioned in the sand of the casting pit.

The bronze ingots, which is the material that was being poured, were heated in the crucible until they melted and reached a temperature of 2200 F. Once the material was at temperature the molds were filled, trying to make sure that the mold was completely filled in a single pour. This is done to ensure that a complete part is formed. If the mold is not filled in a single pour, the pattern burns out prematurely and a less than desirable part is formed containing voids and imperfections where the two layers meet. Once the parts had been poured and allowed to cool slightly, they were removed from the stove pipes and the sand was knocked off to allow for inspection.

Recorded Data:

Dimensions of the different objects cast in lab.

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"

............................................Top=1.9" x1.9" x 1"...............................not measured

"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"

The micrographs of the material structure contained within the bronze cast parts which were sliced for examination are as follows: (not yet posted)

Conclusion:

The results of the lab were surprising. The surface texture of the parts is as it was expected to be. It is rough due primarily to the texture of the pattern material that was used. I was surprised to see that even those parts which were made intentionally to fail, also came out looking good. It is readily apparent that the quality of the surface texture can be directly attributed to the quality of the pattern material used. Those parts which were not poured in a single pour, did in fact have imperfections where the two separate layers met. The only dimensional changes that took place were very slight. This could be a result of experimental error introduced because of the way that the measurements were taken, or due to the actual process. Either way, the results were better than expected.