An axial fan , comprising: a hub configured to be driven by motor to rotate about a fan rotational axis ; a band that surrounds the rotational axis and is concentric with the hub, the band including a cylindrical portion that extends in parallel to the fan rotational axis , a lip portion that extends in at an angle to the fan rotational axis , and a curved intermediate portion that connects one end of the cylindrical portion to one end of the lip portion ; blades that protrude radially from the hub , each blade comprising a root that is connected to the hub and a tip that is connected to a hub-facing surface of the cylindrical portion ; and a structurally-reinforcing rib that protrudes from the hub-facing surface of the cylindrical portion , the rib disposed between respective tips of an adjacent pair of the blades , wherein a circumferential dimension of the rib is at least 40 percent of a distance along the hub-facing surface between the respective tips of the blades of the adjacent pair of the blades , wherein the hub , the blades and the band are formed as a single piece; wherein the rib comprises a plurality of ribs , each rib being disposed between a pair of adjacent blades such that a single rib is disposed between the blades of a given pair of adjacent blades , wherein a distance between the fan rotational axis and the band is constant for every location along a line that extends about the circumferences of the band , where the line is disposed on the hub-facing surface of the band at the band trailing end , wherein the line does not intersect with the rib , characterized in that the rib extends onto the curved intermediate portion , and in that a radial dimension of the band is non-uniform along the line , wherein the radial dimension of the band has a maximum value at locations corresponding to a rib . a hub configured to be driven by motor to rotate about a fan rotational axis ; a band that surrounds the rotational axis and is concentric with the hub, the band including a cylindrical portion that extends in parallel to the fan rotational axis , a lip portion that extends in at an angle to the fan rotational axis , and a curved intermediate portion that connects one end of the cylindrical portion to one end of the lip portion ; blades that protrude radially from the hub , each blade comprising a root that is connected to the hub and a tip that is connected to a hub-facing surface of the cylindrical portion ; and a structurally-reinforcing rib that protrudes from the hub-facing surface of the cylindrical portion , the rib disposed between respective tips of an adjacent pair of the blades , wherein a circumferential dimension of the rib is at least 40 percent of a distance along the hub-facing surface between the respective tips of the blades of the adjacent pair of the blades , wherein the hub , the blades and the band are formed as a single piece; wherein the rib comprises a plurality of ribs , each rib being disposed between a pair of adjacent blades such that a single rib is disposed between the blades of a given pair of adjacent blades , wherein a distance between the fan rotational axis and the band is constant for every location along a line that extends about the circumferences of the band , where the line is disposed on the hub-facing surface of the band at the band trailing end , wherein the line does not intersect with the rib , the rib extends onto the curved intermediate portion , and in that a radial dimension of the band is non-uniform along the line , wherein the radial dimension of the band has a maximum value at locations corresponding to a rib . <EOS>