Chill Cast Microstructure
Anotec’s proprietary process assures consistent weight, greater density, less flake graphite grain boundary, and lower chemical segregation.
Porosity & Inclusions
Anotec’s method of chill casting in a static mold yields tubular anodes that are superior in every way to centrifugal-cast tubular anodes.
On the inside, it becomes clear to see (using radiography). Significantly less gas porosity and no slag inclusions.
The corrosion resistance of high silicon cast iron is attributed to the development of a thin passive barrier film of hydrated silicon dioxide on the metal surface. This film develops with time due to the dissolution of iron from the metal matrix leaving behind silicon which hydrates due to the presence of moisture.
Due to the fine grain size with spheroidal graphite and more uniform composition, chill cast high silicon cast iron has better corrosion resistance than a sand cast high silicon cast iron.
Please click here for in-depth findings from an anode life case study in sea water.
- Grain Size
Small grain size improves mechanical properties (tensile strength and toughness). Smaller grains tend to a more uniform structure and benefit the development of a hydrated silicon barrier film on high silicon iron anodes.
Structures that are more uniform, consistently tend to corrode more evenly across the exposed surfaces and waste less rapidly. As a result, homogeneous structures are more desirable.
- Carbon Form
Flake-type graphite is characteristic of grey iron and is associated with brittle behavior and macroscopic differences in free energy, expressed as minute differences in potential (carbon is noble). Spheroidized carbon results in superior mechanical properties and corrosion resistance, in comparison to flake-type structures.
- Grain Orientation
Chilled zones will exhibit a columnar grain structure with dendrite arms oriented perpendicular (radial for solid stick and tubular anodes) to the heat extraction surface. Comparatively, higher rates of cooling promote finer-grained structures. Slow-cooling structures tend to be more equiaxed, random, and coarser.
- Volumetric Flaws
Shrinkage porosity is an obvious mechanical detriment and, if presented to a sufficient degree, may be considered a casting defect. The presence of volumetric flaws may serve to disrupt the formation of desirable, continuous, hydrated silicon oxide film complexes. As well, volumetric flaws will act as corridors or passages in to the matrix promoting non-uniform anode consumption.