1. Technical Field
The present invention relates to methods of manufacturing impellers for centrifugal fans, and to centrifugal fans as well.
2. Description of the Related Art
Device downsizing and performance upgrading of electronic equipment in recent years have entailed demands for the scaling down of cooling fans installed in such electronic devices. As one among such attempts, a centrifugal fan in which the impeller has been reduced in diameter, and the individual vanes constituting the impeller have been thinned and arranged at a denser spacing has been proposed.
Meanwhile, inasmuch as centrifugal-fan impellers have traditionally been manufactured by injection molding, various techniques for enhancing the quality of the manufactured product have been developed. Examples of such techniques include a method in which in advance of infusing a mold with thermoplastic resin, the mold is evacuated, as well as a method in which excessive exhausting of gases during the molding operation is prevented by sufficiently drying the thermoplastic material beforehand and then melting it. Another example utilizes highly fluid liquid crystal polymers as base materials to make it possible to mold impellers having longer vanes.
Nevertheless, to proceed to make the vanes thinner is to make it impossible to mold an impeller stably by traditional methods. In particular, designing the individual vanes of a centrifugal fan to be both thinned and elongated in order to improve the fan's performance would make it impossible to charge the inside of the mold sufficiently with thermoplastic resin.
Centrifugal-fan impellers are sometimes furnished with a ring section that links the tips of the vanes. The objective in such configurations is to enhance the impeller rigidity by tying the vane tips together. The ring section is vital to implementations in which an impeller is axially extensive and its vanes are thin. For ultra-miniature centrifugal fans (e.g., centrifugal fans whose outer diameter is 25 mm or less), however, if an impeller having a ring section is to be injection molded, the flow of thermoplastic resin inside the mold would be restrained such that the ring-forming portion of the mold could not be charged sufficiently with the resin. Or, even if it could be thus charged, then meld lines would form in the ring area, deteriorating the strength of the ring section. Such phenomena are detrimental to throughput during production, and invite increases in post-manufacturing breakage.