Qhov saum npoo ntawm lub qhov rooj hluav taws thiab lub qhov rooj yuav tsum tsis muaj qhov pom tseeb concave convex, khawb thiab lwm yam tsis xws luag. Cov txheej txheem phosphating, electrostatic txau thiab qhov kub thiab txias qhov cub curing ua rau saum npoo ruaj khov, thiab muaj zog tiv taus huab cua thiab corrosion. Raws li qhov sib txawv ntawm qhov hluav taws kub ntawm qhov rooj hluav taws, lawv qhov hluav taws kub tuaj yeem muab faib ua peb qib: A, B thiab c.