At present there is no method to relate quantitative measurements of porosity as collected on random metallographic cross sections to the maximum shrinkage pore
size that might exist in the gage section of a tensile bar.
* more gas pores exist than shrinkage pore clusters.
Cluster analysis was performed on the samples to measure gas and shrinkage pores, and pore size and density were used in conjunction with the aspect and area to perimeter ratios to determine that the shrinkage pores are consistently irregular as compared to gas pores.
Oxide and other forms of nonmetallic contamination influence shrinkage pore
Thin section and SEM observations revealed that the conglomerate reservoir pore types mainly consist of intraparticle dissolution pores (Figures 6(a), 6(d), and 6(e)) and interparticle dissolution pores (Figures 6(a), 6(b), and 6(d)), with some mud shrinkage pores
Due to the pressure of compressed gas, it is also required that no shrinkage pores
and no serious porosities form in castings.
For example, simulated time/temperature profiles can predict the formation of isolated hot spots where late solidification might lead to shrinkage pores
The drawbacks to having too small a riser are mainly associated with defects in the casting, either due to insufficient feeding of liquid to compensate for solidification shrinkage, or shrinkage pores
because the solidification front is not uniform.
This helps refine the shrinkage pores
, which gives rise to improved mechanical properties with greater repeatability.
* the decrease in pore density is due to a decrease in the number of shrinkage pores
Its formation is attributed to two factors: shrinkage, coupled with a lack of interdendritic feeding during mushy zone solidification (shrinkage pores
), and the evolution of hydrogen (H) gas bubbles due to a sudden decrease in H solubility during solidification (gas pores).
In a paper presented at the Novi conference, Jack Dorcic of IIT Research Institute notes that squeeze casting also permits filling of heavy sections, minimizing hot spots and shrinkage pores
. Because of the relatively low melt temperature, certain alloys with wide freezing ranges can be cast, with tensile properties comparable to forgings but using less pressure.