Insimbi empunga, esetshenziswa kabanzi ukukhiqiza ukusakaza ngokwezifiso ngokusakazwa kwesihlabathi esiluhlaza, ukubunjwa kwegobolondo noma ezinye izinqubo zokuphonsa isihlabathi esomile, inobulukhuni obuvumelanayo bomshini we-CNC. Insimbi empunga, noma insimbi empunga, iwuhlobo lwensimbi ekhonjiwe ene-graphite microstructure. Iqanjwe ngombala ompunga we-fracture eyakhayo. Insimbi empunga isetshenziselwa izindlu lapho ukuqina kwengxenye kubaluleke kakhulu kunamandla ayo aqinile, njengamabhulokhi amasilinda enjini evuthayo, izindlu zamaphampu, imizimba yamavalvu, amabhokisi kagesi, izisindo zokubala nezinsimbi zokuhlobisa. I-Gray cast iron's high thermal conductivity kanye nomthamo wekhanda othize kuvame ukusetshenziselwa ukwenza i-cast iron cookware nama-disc brake rotor. Ukwakheka kwamakhemikhali okujwayelekile ukuze uthole i-graphitic microstructure yi-carbon engu-2.5 kuya ku-4.0% kanye ne-silicon engu-1 kuya ku-3%. I-graphite ingase ithathe u-6 kuya ku-10% wevolumu yensimbi empunga. I-silicon ibalulekile ekwenzeni insimbi empunga ngokuphambene nensimbi emhlophe, ngoba i-silicon iyisici sokuzinzisa i-graphite ku-cast iron, okusho ukuthi isiza i-alloy ukukhiqiza i-graphite esikhundleni se-iron carbides; ku-3% i-silicon cishe ayikho ikhabhoni ebanjwe ekuhlanganisweni kwamakhemikhali nensimbi. I-graphite ithatha isimo se-flake enezinhlangothi ezintathu. Ngezilinganiso ezimbili, njengoba indawo epholile izovela ngaphansi kwesibonakhulu, ama-graphite flakes avela njengemigqa emihle. I-iron empunga futhi inamandla amahle kakhulu wokumanzisa futhi yingakho isetshenziswa kakhulu njengesisekelo sokunyuswa kwamathuluzi omshini.