Patent ID: 8793872

Claim:
A method for manufacturing a closed impeller, the method comprising: forming a frustum-shaped front plate having no grooves for positioning and that includes an annular plate with a shape of a cut off of a head section of a cone, and a disk-shaped base plate formed therebelow, upper surfaces of a plurality of unit impeller blade plates comprising a synthetic resin extending in radial directions which are formed as impeller blade tip surfaces, with sharp-pointed ridge-like protrusions comprising an acute upper end and a width less than a width of the impeller blade tip surface being integrally formed on the impeller blade tip surfaces; forming an inner surface of the front plate and the plurality of impeller blade tip surfaces, other than the sharp-pointed ridge-like protrusions, formed as parts of conical surfaces that have a high central portion and a height that decreases towards an outer periphery, the forming being implemented such that cone apex angles of two conical surfaces are equal to each other, with the front plate being placed on the impeller blade having the base plate attached thereto, and the sharp-pointed ridge-like protrusions and the inner surface of the front plate being brought into contact with each other; providing small vibrations at a level, at which the sharp-pointed ridge-like protrusions are completely melted and then, after the impeller blade tip surface in the location of root section of the sharp-pointed ridge-like protrusions has slightly melted, supplied energy of said vibration becomes insufficient and the resin does not melt anymore, while applying an appropriate pressurizing force between the front plate and the impeller blade having the base plate attached thereto; melting the sharp-pointed ridge-like protrusions; and fusing the front plate to the impeller blade tip surfaces.