Cov pwm khov no yog tom qab nrog cov khoom siv roj los yog pwm ntxuav, uas tiv thaiv kom tus casting ntawm cov pwm thiab ntev mus pwm lub neej. Txhua lub xuab zeb lossis hlau cores ces muab ntsia thiab pwm kaw lawm. Cov hlau no tau muab nchuav rau hauv pwm. Tsis ntev tom qab kev sib zog lawm cov pwm yog qhib thiab tshem tawm casting kom txo tau cov kua kub kua muag. Cov txheej txheem no yog pib tag nrho dua, tab sis tsis muaj qhov yuav tsum tau ua ntej vim hais tias lub tshav kub los ntawm cov casting yav dhau los yog txaus thiab lub zog txheej yuav tsum kav ntau castings. Vim hais tias txoj kev no feem ntau yog ua tiav rau ntawm cov khoom siv khiav ua haujlwm loj-siv cov khoom siv cuab yeej siv los npog cov pwm, hliv cov hlau, thiab tshem tawm cov casting.
Cov hlau yog raug ntim ntawm qhov ntsuas kub qis tshaj plaws kom txo tau cov kab nrib pleb thiab porosity.Lub ncuav kub hnyav tuaj yeem khwv tau zoo heev nyob ntawm cov khoom siv casting; piv txwv li zinc alloys yog nyob rau ntawm 370 ° C (698 ° F), thaum Grey hlau yog poured ntawm kwv yees li 1,370 ° C (2,500 ° F).