Sheet metal fans and blowers
The scroll of a centrifugal fan or blower: the side plates, the band that wraps round the impeller and the cutoff plate, by the four-centre layout.
Centrifugal Fan Scroll
Centrifugal fan scroll and blower housing: the four-centre layout, side plates with the inlet, the band and the cutoff plate as DXF and a 1:1 template.
Which part to use
- The spiral casing of a centrifugal fan or blower: Centrifugal Fan Scroll.
How it is calculated
The spiral is four quarter circles struck from the corners of a square around the impeller axis, of side a quarter of the outlet: each quarter is one side larger in radius, and in one turn the spiral grows by exactly the outlet.
The band develops on the mean line, with the radius changes marked; the side plates cover the band from outside, and the front one carries the inlet hole. The result includes the 1:1 PDF template and the DXF for plasma or laser.
Frequently asked questions
- What clearance between the impeller and the scroll?
- 5% to 10% of the impeller diameter at the cutoff, the closest point, and the spiral moves away from there, one outlet per turn.
- How big should the outlet be?
- The area the fan needs, 1.5 to 2.5 times the impeller's discharge area by the book rule; its width is the casing's, and its height goes into the spiral as its opening.
- Can it be made in thin sheet?
- Yes: the band rolls stretch by stretch and the side plates are flat. In thin sheet the band closes against the side plates by spot welds, rivets or a folded flange.