Table 2. Mechanical Properties of the Gravity-Filled Green Sand at Various Compactability Levels
Compactability (%)
30 33 35
Compaction in Focus
In this study, a green sand system was tested at three target compactabil- ities (Figs. 3-4). Major green proper- ties were obtained and their inherent variability reported.
One of the most fundamen- tal tasks of green sand control is monitoring sand temper. The moisture must be varied to produce the target compactability. The more clay, carbonaceous and dead materi- als contained in the sand, the more moisture required to produce a given compactability. Moisture cannot be used as a control because the mois- ture requirement varies, but insuf- ficient or excessive moisture levels must be avoided. Moisture control is difficult because as the sand compo- sition changes, the amount of mois- ture needed to produce the target compactability also changes. After testing in this study, the grav-
ity and aerated sand systems showed no differences in mold hardness, permeability, green compression and splitting strengths at the various com- pactability levels. In other words, the basic green property tests could not detect differences among compactabil- ity levels between the sand systems. High compactability levels (35%- 50%) in conventional green sand sys- tems help avoid dry sand defects such as inclusions, erosion, cuts and washes. For the green sand samples tested, the lower the compactability, the higher the friability (Fig. 5). Friability tests showed it was greater in the gravity- filled green sand. Te modified cone jolt test was
used to compare the gravity and aeration-filled green sand samples in ultimate strength, stiffness and toughness (Tables 1-2). Te low com- pactability level showed lower stiffness and toughness, regardless of the green sand fill system used.
September 2013 MODERN CASTING | 33
Ultimate Strength (# Jolts)
7 8
10
Stiffness (Jolts/in.)
143 171 219
Toughness (Jolt*in.)
0.22 0.31 0.39
Table 3. Mechanical Properties of the Aeration-Filled Green Sand at Various Compactability Levels
Compactability (%)
30 33 35
Ultimate Strength (# Jolts)
10 15 18
Stiffness (Jolts/in.)
148 201 233
Toughness (Jolt*in.)
0.30 0.44 0.56
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