Each casting is characterized by its quality, both surface and volume defects. These
defects are strongly influenced by the casting process. Gravity casting is one of the
processes that is usually used for larger castings, and in some cases for relatively
small. This casting technique takes place in single use and permanent moulds. In
single use moulds, sand with the addition of clay and water is most often used so called
the bentonite sand mixture, which is formed before casting and after casting, is
demolished. Casting system in gravity castings consists of a funnel, runner, gates and
the casting itself.
The mass ratios and placement of the individual components drastically affect final
casting, as it affects the melt velocity and the way casting cavity is filled during casting.
The consequences are various oxides in the casting, as well as surface and volume
defect, especially porosity.
To make this so, we poured plate – shaped casting in three different ways with three
repetitions. The pattern was a tile with a length of 10 cm, a width of 3 cm and a height
of 1 cm, which was made of wood. Other elements of the casting system with different
cross-sections and lengths were also made of the same material. In doing so, it is very
important to take into account the draft angle, which allows us to remove the
components of the pattern from the mold. Due to the size of the casting, we also added
two feeders to the far end of the casting to avoid the formation of porosity and its impact
on the quality of the casting.
The casting was sent for X-ray, a bending test and analysis of fracture surfaces were
performed. Our theory is most confirmed by the analysis of fracture surfaces, which
tells us that a casting cast with a non-pressure casting system has the fewest defects.
|
