... zinc coat2.Aluminum magnesium alloy hub, light weight, high strength and good tensile3. Stainless steel blade, bearing ... inspection process: noise inspection, vibration test, concentricperformance test, fan blade rotation test, wind capacity test and the efficiencytest7 ... ventilating and cooling fan1.circulation fan 2.cone fan3.drop hammer fan 4. roof fan 1250mm low noise cooling and ventilation fan