of elevator steel hlua scrapping standard Cov ntsiab lus tseem ceeb ntawm kev tsim hluav taws xob hauv of elevator thiab chav tshuab Cov cuab yeej kev nyab xeeb yuav pib thaum lub elevator hnyav dhau Dab tsi yog qhov yuav tsum tau ua ntawm lub qhov rooj of elevator? Of elevator lubrication thiab kev ua haujlwm yuav tsum tau ua rau cov roj lubricating Ntau cov lus nug kom nkag siab los ntawm cov neeg siv elevator