## Tendency towards defects

Clay-bonded sands have a tendency to develop sand expansion defects, such as scabbing, rat tails, veining and grooves.

According to eq. 1, this tendency towards defects can be expressed as the quotient of compressive stress and wet tensile strength:

eg.1:$Fehlerneigung\ F = \frac{DS\ \frac{N}{cm^2}}{\sigma_n\ \frac{N}{cm^2}}$

Both parameters are determined during mold sand testing. They are combined in the scabbing time diagram (Fig. 1).