Qhov tshwm sim uas qhov ntim thiab qhov loj ntawm cov kua alloy txuas ntxiv txo qis thaum lub sij hawm txias thiab solidification txheej txheem hu ua contraction (shrinkage). Shrinkage yog cov cuab yeej ntawm lub cev ntawm cov hlau casting nws tus kheej, thiab nws yog lub hauv paus ua rau ntau yam tsis xws luag (shrinkage kab noj hniav, shrinkage porosity, sab hauv kev nyuaj siab, deformation thiab tawg, thiab lwm yam) nyob rau hauv lub casting. Cov kua alloy mus dhau peb theem los ntawm kev nchuav rau hauv kab noj hniav kom txias mus rau chav sov:
1. Kua shrinkage: lub shrinkage los ntawm qhov txias ntawm lub pouring kub mus rau lub liquidus kub uas crystallization pib.
2. Solidification shrinkage: lub shrinkage los ntawm qhov kub thiab txias ntawm qhov pib ntawm crystallization mus rau lub solidus kub uas lub crystallization tiav.
3. Solid state shrinkage: lub shrinkage los ntawm qhov kub thiab txias uas lub crystallization tiav mus rau chav tsev kub.
Cov kua shrinkage thiab solidification shrinkage ntawm cov hlau yog manifested raws li lub ntim txo ntawm cov alloy, uas yog feem ntau qhia los ntawm lub ntim shrinkage tus nqi. Lawv yog cov laj thawj tseem ceeb rau qhov shrinkage kab noj hniav thiab shrinkage defects ntawm casting. Txawm hais tias lub zog-lub xeev shrinkage ntawm cov hlau kuj yog ib qho kev hloov pauv, nws tsuas yog ua rau muaj kev hloov pauv ntawm qhov ntev ntawm qhov casting. Yog li ntawd, nws yog feem ntau qhia los ntawm linear shrinkage tus nqi. Cov khoom hauv lub xeev shrinkage yog lub hauv paus ua rau tsis xws luag xws li kev ntxhov siab sab hauv, deformation thiab tawg hauv castings.
Cov tshuaj muaj pes tsawg leeg ntawm cov alloy, pouring kub, pwm tej yam kev mob thiab casting qauv yog lub ntsiab yam tseem ceeb cuam tshuam rau alloy shrinkage. Cov duab, qhov loj me thiab cov txheej txheem ntawm cov casting yog txawv, thiab qhov tseeb shrinkage kuj txawv.
Tsis tas li ntawd, qhov tsis sib xws ntawm cov tshuaj muaj pes tsawg leeg ntawm txhua feem hauv cov txheej txheem txias cov kua alloy rau hauv cov casting, uas yog, kev sib cais, kev nqus roj thiab oxidation muaj qhov cuam tshuam tsis zoo rau kev ua haujlwm casting.