1) txoj kev molding tsis yog zoo meej, feem ntau tshwm sim rau cov neeg pluag tsis zoo ntawm lub rooj sib txoos thiab cov khoom siv tua hluav taws tuag, thiab kev kho cov tshuab hluav taws xob thiab tshuab muaj teeb meem, ua rau kev tsis zoo ntawm lub rooj sib tham thiab kev tuag concave, qhov muag muag thiab uneven hardness. Qee lub sij hawm muaj cov kab nrib pleb thiab kab tawg.
Kev sib tsoo thiab polishing tsis yog nyob rau hauv qhov chaw, thiab qhov saum npoo roughness yog loj heev.
2) tsis muaj lubrication lossis lubrication, tab sis cov nyhuv tsis zoo.
