Blast fan
A blast fan includes: a tubular frame having a first opening and a second opening to pass airflow through between the first opening and the second opening. The first opening has a first reverse tapered portion expanding from inside to outside of the frame, and the first reverse tapered portion has a surface having first convex portions projecting to the inside of the frame.
1. A blast fan comprising:
a blade configured to rotate integrally with a motor;
a tubular frame having a first opening and a second opening to pass airflow through between the first opening and the second opening, the first opening being a discharge port during a normal rotation of the blade in which the airflow passes through the tubular frame from the second opening to the first opening and a suction port during a reverse rotation of the blade in which the airflow passes through the tubular frame from the first opening to the second opening, the second opening being a suction port during the normal rotation of the blade and a discharge port during the reverse rotation of the blade; and
a base member for installing the motor located at a position close to the first opening with respect to the second opening, the position being in a space inside the tubular frame, both the base member and the motor being fixed to the tubular frame, wherein:
the first opening has a first reverse tapered portion expanding from inside to outside of the tubular frame,
the first reverse tapered portion has a surface having first convex portions projecting to the inside of the tubular frame,
a maximum diameter of the first reverse tapered portion is at an outermost end of the first opening in a direction of the airflow during the normal rotation,
the second opening has a second reverse tapered portion expanding from inside to outside of the tubular frame,
the second reverse tapered portion has a surface having second convex portions projecting to the inside of the tubular frame, and
there are fewer second convex portions than first convex portions.
2. The blast fan according to claim 1 , wherein
the first reverse tapered portion is longer than the second reverse tapered portion.
3. The blast fan according to claim 1 , wherein the first convex portions are spaced in an axial direction of the tubular frame, and the first convex portions are provided to a whole circumference of the tubular frame.
4. The blast fan according to claim 1 , wherein the second convex portions are spaced in an axial direction of the tubular frame, and the second convex portions are provided to a whole circumference of the tubular frame.
5. The blast fan according to claim 1 , wherein the first convex portions are spaced in an axial direction of the tubular frame, and the first convex portions are provided to a whole circumference of the first opening, and
the second convex portions are spaced in the axial direction, and the second convex portions are provided to a whole circumference of the second opening.