... with good quality 4. Galvanized sheet frame Axial Flow Exhaust Fan 1. The outline border adopt advanced automatic process, more ... close, windproof, rainproof and dustproof.5. Newly punch forming fan blade, reasonable angel and reach the max air flow,low Noise ... test process: noise test, vibration test, concentric performance test, fan blade turning speed test, input air test and vehicle efficiency test ...