Blade for a low-noise industrial axial fan, industrial axial fan and process for manufacturing a blade of an industrial axial fan

An industrial axial fan, comprising:

• a hub rotatable about a rotation axis;
• and
• a plurality of blades coupled to the hub, each blade comprising:
• an airfoil, extending along a blade axis and having a leading edge, a trailing edge a root side, a tip side, an intrados and an extrados;
• and a rod, having a first end connected to the airfoil at an insertion point through the root side and a second end protruding from the airfoil for coupling to a hub;
• wherein the root side has a rounded contour with a concave stretch adjacent to the leading edge and a convex stretch adjacent to the trailing edge;
• wherein a root end of the leading edge protrudes with respect to the insertion point toward the second end of the rod in a direction parallel to the blade axis;
• wherein the airfoil forms a lobe at a junction between the trailing edge and the root side and the lobe extends in the direction parallel to lade axis toward the second end of the rod more than with respect to the root end of the leading edge;
• wherein the airfoil is extruded or pultruded and wherein the leading edge is rectilinear and parallel to the blade axis;
• and
• wherein the concave stretch of the root side of each blade is circular with a first radius equal to an outer radius of the hub and the convex stretch is circular with a second radius smaller than the first radius.

A process for manufacturing a blade of an industrial axial fan comprising the following steps:

• by extrusion or pultrusion, forming a section bar extending along an axis and having an airfoil section with a leading edge, an intrados and an extrados;
• cutting the section bar transversely to the axis so as to define a tip side and a root side having a rounded contour with a concave stretch adjacent to the leading edge and a convex stretch;
• and
• inserting a first end of a rod at an insertion point through the root side in the concave stretch;
• wherein cutting comprises shaping the root side so that a root end of the leading edge protrudes with respect to the insertion point toward the second end of the rod in a direction parallel to the axis and so that the airfoil forms a lobe that extends in the direction parallel to the axis toward the second end of the rod more than the root end of the leading edge;
• and
• wherein the section bar comprises a hollow first portion and a second portion in the form of a lamina, wherein the first portion and the second portion extend longitudinally adjacent to each other and wherein the first portion defines the leading edge.