Patent Grant
7264446
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.
An object of the present invention, brought about in order to resolve the problems discussed above, is to make available a method of manufacturing, by injection molding and at high throughput, impellers for micro-diameter centrifugal fans—in particular, impellers whose axial length has been extended in order to improve the impeller's characteristics.
In the present invention, in order to heighten throughput in the injection-molding manufacture of ultra-miniature impellers for centrifugal fans, the thickness of the ring section is secured, and at the same time a fixed or greater axial length for the ring section is secured. In this way securing the dimensions of the ring facilitates the flow of the thermoplastic resin in the area of the mold interior that corresponds to the ring.
The causative factor behind deterioration in the strength of the ring section in ultra-miniature impellers originates in insufficiency in the flow of thermoplastic resin into the ring-forming portion of the mold, which makes it likely that meld lines will form. In the present invention, the thickness and length of the ring section are rendered fixed dimensions or greater in order to avert this problem. Doing so keeps meld lines from forming within the ring-forming portion of the mold to enhance the strength and durability of the ring section, even in impeller molding implementations in which the gate is positioned in the end of the mold opposite the ring section. In a further aspect of the present invention, the formation of meld lines is also held in check by increasing the vane thickness in the area in which the vanes connect to the ring section.
Such improvement is particularly pronounced in implementations in which thermotropic liquid-crystal polymers are employed as the base material-implementations that are especially vulnerable to strength deterioration where the polymer melds.
When an ultra-miniature impeller as described above is to be molded in an injection mold, in addition to sufficiently drying the thermoplastic resin base material beforehand, the inside of the mold must be evacuated during the molding operation. The evacuation port is advantageously provided along the rim of the vanes, in the end of the mold opposite its gate. For example, the port can be provided in the lateral surface of the cavity that corresponds to the ring section, or in the vicinity of the borderline between the ring section and the vane tips.
In order to make the flow of thermoplastic resin inside the ring-forming portion of the mold more definite and reliable, the resin may be forced out through the evacuation port and then cut off.
As another means of enhancing the strength of the ring section, a ring-shaped element formed from metal or other suitable material may be placed into a position inside in the mold equivalent to the ring section and then the thermoplastic resin infused into the mold. Exploiting such an insert-molding technique also contributes to enhancing the strength of the ring section of an ultra-miniature impeller.
From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.
Reference is made to
The centrifugal fan 1 is an electromotive fan utilized in order to air-cool electronic parts in the interior of electrical products and electronic devices (portable articles in particular). The centrifugal fan 1 is equipped with: an impeller 2 that by rotating generates a flow of air; a motor 3 for rotating the impeller 2; and a housing 4 for housing the impeller 2 and the motor 3, and that controls the flow of air generated by the rotation of the impeller 2, sending the air outside the fan.
The impeller 2 is approximately round-cylindrical in external form, and is furnished with: a plurality of vanes 21 for generating a flow of air; a connector section 22 for linking together and anchoring the motor-ward ends of the plurality of vanes 21, and being the impeller end that connects to the motor 3; and an approximately round cylindrical reinforcing ring 23, fixed to the vane ends on the side of the plurality of vanes 21 that is opposite the connector section 22, that reinforces the linkage of the vanes 21. The plural vanes 21, the connector section 22, and the reinforcing ring 23 are molded unitarily from a thermoplastic resin.
As shown in
The housing 4 is, as shown in
In a centrifugal fan 1 having the configuration just described, when the impeller 2 spins, air flows into the space 90 through the air inlet 41 and flows out from between the plurality of vanes 21, traveling along the inner surface 49 of the housing 4, and is sent out through the venting port 42.
Herein, the outer diameter 2r of the impeller 2 (r being the radius) illustrated in
In the impeller 2, by the relation 2≦fL/r being satisfied the point of maximum flow speed of the air flowing out from between the plurality of vanes 21 is put in the vicinity of midway between the two ends of the vanes 21. The flow volume of air is increased as a result, enabling the generation of a highly efficient flow of air. At the same time, by fL/r≦20 being satisfied, vibration is held down even at rotating speeds of more than 10,000 rpm, (for example, 20,000 rpm). The configuration is thus favorable to revving the fan at high rpm, whereby the flow volume and static pressure of the air can be heightened all the more.
Reference is now made to
The mold 6 comprises: a first plate 61, to which a nozzle 91 of the injection-molding machine connects; a second plate 62 in contact with the left side of the first plate 61; a third plate 63 that is located on the leftmost side of the mold; two side blocks 64 in between the second plate 62 and the third plate 63, located above and below to enclose the cylindrical side of the impeller 2 being molded; and a core 65 inserted into the approximately round cylindrical space flanked by the two side blocks 64.
A flowpath 611 through which thermoplastic resin ejected through the nozzle 91 passes is formed in the first plate 61; the gate 612 in the end of the flowpath 611 corresponds to the center of the connector section 22 of the impeller 2. (The center of the impeller connector section 22 is actually where a hole is formed, through which the motor 3 is connected after molding—c.f.
The third plate 63 has an opening through which the core 65 is inserted/removed, and the right-side surface of the plate corresponds to the end face of the reinforcing ring 23, which is the rim of the opening in the impeller 2. In a position corresponding to the corner between the end face and lateral surface (a position pointing to the cylindrical surface) of the reinforcing ring 23—in particular, in a position that is between the third plate 63 and one of the side blocks 64 and is in one of the flutes 651—an evacuation port 631 is formed as a slight breach. The evacuation port 631 is connected to an evacuation passage 632 formed between the third plate 63 and the side block 64. The evacuation passage 632 is connected to an evacuating pump in the injection-molding machine. Along the opening for the core 65 in the third plate 63, grooves corresponding to the core's gill-like regions 652 are formed so that the core 65 can be extracted following an injection molding operation. Thus in this configuration, the flutes 651 in the core 65, which correspond to the vanes 21, are tangent to the inner-side surface of the side blocks 64; and twin walls of the grooves formed in the third-plate 63 opening through which the core 65 is introduced define projections that (where they correspond to the end faces of the vanes 21) close off the flutes 651.
Once the mold 6 has been set into the injection-molding machine, the evacuating pump is run to evacuate the mold 6 interior space—that is, the mold cavity—through the evacuation passage 632 to put the cavity into a vacuum state (step S2). Meanwhile, a pellet of thermoplastic source material, having been dried beforehand by heating the material 2.5 to 3 hours at 140-165° C. inside a drier under a reduced-pressure environment or under a predetermined gas environment, is fed from a hopper into the injection-molding machine, without prolonged contact with external air. Within a screw cylinder in the molding machine the thermoplastic resin is melted by heating it up to 250-330° C. using a heater. The mold 6 is maintained at 70-90° C. by means of a separate heater. It should be understood that an injection-molding machine in which pre-drying of the pellet is unnecessary may be employed.
Once the above-described preparations have been finished, the molten resin is ejected through the nozzle 91, directed into the flowpath 611, and the resin flows heading from the first plate 61 to the third plate 63—in particular, heading from a location corresponding to the connector section 22 of the impeller 2, to a location corresponding to the reinforcing ring 23—whereby the cavity interior is filled with resin (step S3). Gas evolving from the resin at the same time that the resin is flowing into the cavity is forced through the evacuation port 631 and exhausted from the cavity via the evacuation passage 632. It will be appreciated that because the infused resin swiftly fills the cavity interior and thereafter hardens rapidly, the mold temperature is adjusted in advance to be 70-90° C. when the resin is being injected.
Utilized as the source material are thermoplastic resins whose principal component is a thermotropic liquid-crystal polymer (here indicating that half or more of the weight is a thermotropic liquid-crystal polymer, and including instances in which the resin is exclusively a thermotropic liquid-crystal polymer), which are resins that excel in fluidity, and have high post-setting strength and outstanding mechanical properties. Specifically, a fully aromatic polyester liquid-crystal polymer to which on the order of 20 weight % fibrous matter such as glass or carbon fiber has been added—a material typified by polyphenylene sulfide (PPS) or Vectra® into which fiberglass has been mixed—is utilized. Furthermore, materials in which PPS and Vectra® are intermixed, or in which other resin(s) are mixed into a thermotropic liquid-crystal polymer, may be utilized.
Notwithstanding that each of the vanes 21 is of slender form, by the exhausting of gases in the cavity interior through the evacuation port 631 formed in a region that corresponds to one end of the plural vanes 21, and by the infusing of molten resin through the gate 612 formed in a region that corresponds to where the other end of the plural vanes 21 is (that is, a region that is associated with the other end), the cavity is appropriately filled with resin to form the vanes 21 in their entirety. Moreover, the reinforcing ring 23, which is molded in parallel with the vanes 21, is formed by the corresponding space inside the mold becoming appropriately filled with resin. It should be understood that, as long as the resin flows for the most part unidirectionally inside the space 651 for the vanes 21, the gate 612 may be formed in another region of the mold 6 that corresponds to where the other end of the plurality of the vanes 21 is—for example, in a region that corresponds to the outer-side surface of the connector section 22 of the impeller 2.
After the resin has cooled and set, the molded impeller 2 is taken out of the mold 6 (step S4). Initially, the core 65 is extracted from the third plate 63 and the side blocks 64.
After the core 65 has been extracted the two side blocks 64 are parted slightly, and then by pushing out the connector section 22 of the impeller 2 with a shoving member 613 provided in the vicinity of the flowpath 611 in the first plate 61, the impeller 2 is completely separated from and taken out of the mold 6. In the impeller 2 after having been withdrawn, in a place corresponding to the gate 612, a hole into which a rotor yoke 31 component of the motor 3 fits is formed (c.f.
Reference is now made to
The description turns now to
In utilizing the mold 6 depicted in
In an implementation in which an impeller is molded in this manner, when the thermoplastic resin melds in the reinforcing ring 23 portion of the cavity, the resin in the vicinity of the meld lines flows fully, improving the joint strength along the meld lines.
In an implementation of a mold 6 configured as shown in
Next, the results of actually molding impellers 2 as explained in the foregoing and testing the strength of their reinforcing rings 23 will be described. Table 1 is a tabulation setting forth three types (Characterizations 1 to 3) of injection-molded impeller 2 conformations. The units of length in Table 1 are millimeters. In the test, Vectra® was utilized as the thermoplastic resin, and samples in which, as depicted in
In the “Ring strength” column in Table 1, “x” indicates that in taking the impellers 2 out of the mold 6 following the injection-molding operation, there was a 70% or greater likelihood that fracturing in the reinforcing rings 23 would occur, while “∘” indicates that there was a less than 10% likelihood. It may be ascertained from the table that with Characterizations 2 and 3, in which the reinforcing rings 23 were made longer, although the thicknesses of the rings were not increased, the reinforcing ring 23 strength was sufficient.
In addition, impellers as shown in FIGS. 11B and 11C—of a form in which part of the reinforcing ring 23 jutted out from the vanes 21, and of a form in which the reinforcing ring 23 was connected to the end face of the vanes 21—were fabricated under Characterization 3 in Table 1. In these implementations as well, the incidence of fracturing in the reinforcing ring in taking the impeller out of the mold was less than 10%, and thus strength in the reinforcing rings was secured.
Here, by having the length of the projecting portion 23b, which from the ends of the vanes 21 juts out paralleling the center axis 10, of reinforcing rings 23 in the
In molding applications in which articles of extremely slender conformation are injection-molded, as is the case with the vanes of impellers 2 of the present invention, thermotropic liquid-crystal polymers of long flow length are often employed as the molded material. Thermotropic liquid-crystal polymers during molding exhibit strong anisotropy in terms of the resin flow direction, such that degradation in strength along meld lines is serious. Utilizing the present invention, however, averts compromised strength along meld lines that form in the reinforcing ring, to enable high-strength impellers to be produced.
Next, referring to
With the exception of being furnished with the impeller 2a depicted in
In the impeller 2a, as indicated in 14, along each of the plural vanes 21a the thickness ft2 of the region (called “ring joint” hereinafter) 211 connected to the reinforcing ring 23 is thicker than the thickness dimension of the rest of the vane 21a, wherein each vane 21a gradually diminishes in thickness as the dimension parts away from the reinforcing ring 23. Thus the minimum thickness ft1 is in the verges 212 at the inner-peripheral side of the vanes 21a, (with the roundness attendant on rounding off the vane edges not being deemed thickness).
The process flow in manufacturing the impeller 2a by injection molding is the same as the flow, set forth in
Next, the results of molding impellers 2a and testing the strength of their reinforcing rings 23 will be described. Table 2 is a tabulation setting forth two types (Characterizations 4 and 5) of injection-molded impeller 2a conformations, and as a comparative example, entered together with these characterizations is the impeller 2 conformation of Characterization 1 set forth in Table 1. In the test, Vectra® was utilized as the thermoplastic resin, and samples in which, in the same way as is the case with the vanes 21 and reinforcing ring 23 depicted in
In the “Ring strength” column in Table 2, like in Table 1, “x” indicates that in taking the impellers 2a out of the mold 6 following the injection-molding operation, there was a 70% or greater likelihood that fracturing in the reinforcing ring would occur, while “∘” indicates that there was a less than 10% likelihood. The units of length in Table 2 are also millimeters.
From the results of the test it may be ascertained that with the impellers 2a of Characterizations 4 and 5, in which the thickness of the vanes 21a gradually diminishes the further away from the reinforcing ring 23 the measurement is (that is, the characterizations in which ft1 is smaller than ft2), the reinforcing rings 23 had sufficient strength.
Although methods of manufacturing centrifugal fans and impellers involving modes of embodying the present invention have been explained in the foregoing, in that various modifications of the present invention are possible, the invention is not limited to the embodiments described above.
For example, in the foregoing embodiments, examples were set forth in which prior to the injection molding operation the cavity in the mold 6 was evacuated to bring it into a vacuum state, but the evacuation may be carried out in parallel, for the most part, with the molding operation. Additional examples are that in the third side plate 63 a minute evacuation port may be formed to carry the evacuation out through a position corresponding to the end face of the reinforcing ring 23, and that the minute evacuation port may be formed in the base of the recess 641 corresponding to the reinforcing ring 23.
In any of the examples of
In the implementation illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-101994 | Mar 2004 | JP | national |
| 2005-032495 | Feb 2005 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2652190 | Meltzer et al. | Sep 1953 | A |
| 3201032 | Gelbard | Aug 1965 | A |
| 3257071 | Harris | Jun 1966 | A |
| 3306529 | Nelson | Feb 1967 | A |
| 3536416 | Glucksman | Oct 1970 | A |
| 6095752 | Gronier et al. | Aug 2000 | A |
| 6893220 | Eaton et al. | May 2005 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20050220613 A1 | Oct 2005 | US |
