... 400mm, 450mm, 500mm, 600mm, 880mm Benefits: light weight, high revolving speed, strong corrosion resistance, high air exhausting efficiency, sturdy and durable ... is 0.45.It begins to revolve at the wind speed of 0.12m/s Roof Angle: applied in different roofing in ... surrouding, to make the workers more energetic and to increase the benefits of the company. B. Lower the users production costs. Because ...