▁to ▁get ▁it ▁out ▁of ▁the ▁piece . ▁They ▁are ▁most ▁commonly ▁used ▁in ▁sand ▁casting , ▁but ▁are ▁also ▁used ▁in ▁die ▁casting ▁and ▁injection ▁m ould ing . ▁ ▁For ▁example , ▁cores ▁define ▁multiple ▁pass ages ▁inside ▁cast ▁engine ▁blocks . ▁One ▁model ▁of ▁G M ▁V - 8 ▁engine ▁requires ▁ 5 ▁dry - s and ▁cores ▁for ▁every ▁casting . ▁ ▁Material s ▁required ▁to ▁make ▁cores ▁Core ▁sand ▁Bent on ite ▁cl ay ▁Pul ver ized ▁coal ▁Res in ▁oil ▁ ▁Adv antages ▁and ▁dis adv antages ▁C ores ▁are ▁useful ▁for ▁features ▁that ▁cannot ▁toler ate ▁draft ▁or ▁to ▁provide ▁detail ▁that ▁cannot ▁otherwise ▁be ▁integrated ▁into ▁a ▁core - less ▁casting ▁or ▁m old . ▁ ▁The ▁main ▁dis adv antage ▁is ▁the ▁additional ▁cost ▁to ▁incorpor ate ▁cores . ▁ ▁Re quire ments ▁There ▁are ▁seven ▁requirements ▁for ▁cores : ▁ ▁Green ▁strength : ▁In ▁the ▁green ▁condition , ▁there ▁must ▁be ▁ade qu ate ▁strength ▁for ▁handling ▁In ▁the ▁hard ened ▁state , ▁it ▁must ▁be ▁strong ▁enough ▁to ▁handle ▁the ▁forces ▁of ▁casting ; ▁therefore , ▁the ▁compression ▁strength ▁should ▁be ▁ 1 0 0 ▁to ▁ 3 0 0 ▁p si ▁( 0 . 6 9 ▁to ▁ 2 . 0 7 ▁M Pa ). ▁P erme ability ▁must ▁be ▁very ▁high ▁to ▁allow ▁for ▁the ▁escape ▁of ▁g ases . ▁Fri ability : ▁As ▁the ▁casting ▁or ▁m old ing ▁co ols , ▁the ▁core ▁must ▁be ▁weak ▁enough ▁to