... type: ACBlade material: stainless steelFeatures:1. negative pressure exhaust fan 2. big wind capacity, low noise. galvanized steel frame ... close, windproof, rainproof and dustproof.5. Newly punch forming fan blade, reasonable angel and reach the max. air flow, mini ... process: noise test, vibration test .concentric performance test, fan blade turning speed test, input air teat and vehicle efficiency test ...