Patent Application
20070154313
The present invention relates generally to molded impellers, and more particularly to a molded impeller having a locating insert therein.
Prior art pump impeller assemblies include an over-molded knurled insert for retaining and locating the impeller on a driveshaft. The insert includes internal threads that mate with external threads on the driveshaft and serve to locate the impeller relative to the driveshaft. It is important that the insert be properly positioned on the shaft because it locates the impeller, and such positioning, if incorrect, may reduce seal life, increase vibration and cause fluid leakage. However, prior art inserts, and the threads therein, do not satisfactorily locate the impeller on the driveshaft. This may be due in part to the difficulty of exactly controlling the location of thread surfaces. Moreover, the threads may not satisfactorily locate the impeller during molding of the impeller. The latter problem can cause eccentricity or “wobble” of the impeller during operation, necessitating a secondary machining operation or other measure to prevent contact of the impeller inlet with the pump housing. Such added manufacturing operations add to the cost of the impeller. In some cases a secondary seal ring must be added between the impeller and the housing, which again adds cost. Accordingly, an improved insert for the impeller is needed.
In one aspect, an impeller assembly comprises a molded impeller and an insert within the impeller. The insert includes an unthreaded sleeve and a shoulder adjacent the sleeve for locating the impeller and the insert.
In another aspect, a method of forming an impeller assembly in a mold comprises placing an insert over a positioning pin of the mold, the pin engaging a shoulder and a sleeve of the insert. Other steps include injecting a material into the mold for forming an impeller of the assembly and removing the positioning pin from the insert.
In still another aspect, the insert is mounted within the impeller for transmitting force to the impeller. The insert includes an outer surface and a plurality of protrusions extending outward from the outer surface and engaging portions of the impeller. The protrusions are sized and shaped to inhibit withdrawal of the insert from the impeller and for transmitting only radial force to the impeller so that substantially no axial force is transmitted to the impeller by the insert.
Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring to
Referring to
The insert 17 of this embodiment is cylindrical in shape, an outer surface of the sleeve including a plurality of ribs 33 (or protrusions) extending therefrom. Broadly, the ribs engage portions of the impeller. The ribs 33 are sized and shaped to inhibit withdrawal of the insert from the impeller 13 and for transmitting only radial force to the impeller so that substantially no axial force is transmitted to the impeller by the insert. Each rib 33 of one embodiment includes an axially symmetric surface, e.g. surfaces 33a of
The axial force caused by prior art inserts is undesirable because they may contribute to withdrawal of the insert 17 from the impeller 13, especially where a relatively large force is transmitted through the insert. In one example, the drive shaft forces the insert and impeller to go from 0 to 3600 RPM in 150 milliseconds. Such force causes a “cycling force” on the drive mechanism. In the prior art where the outer surface includes angled knurling on the outer surface, the angled knurling may cause an axial, rather than a purely radial force. In this embodiment, the ribs or protrusions are said to be “square” with the impeller so that all or substantially all the driving torque is torsional or radial and there is no or an insignificant amount of axial force that may damage the assembly.
In one embodiment of a suitable method for making the assembly, the insert 17 is placed over a positioning pin 45 of a portion 46 of an injection mold 47 prior to injection molding. The positioning pin 45 engages the sleeve 39 and the shoulder 41. The positioning pin 45 is sized to fit snugly in the sleeve 39 so that the sleeve and shoulder 41 are precisely located and temporarily fixed relative to the positioning pin. The positioning pin 45 is likewise precisely located relative to the other portions of the mold 47. The material that will form the impeller 13 is injected into the die and around the insert 17.
After the material solidifies, the formed impeller 13 is fixed to the insert 17. Because the insert 17 cannot move relative to the pin, and because the impeller 13 becomes fixed to the insert during molding, the potential for “float” during molding is eliminated.
Thereafter, the impeller assembly may be installed inside a pump housing, such as the housing 51 shown in
The insert 17 of this embodiment is also advantageous for at least some of the following reasons. The sleeve 39 of the insert 17 accurately locates the insert during molding (e.g., injection molding). The arrangement reduces the tolerance build-up or “stack”. The pin of the mold is precisely located against the sleeve 39 of the insert 17. In particular, the shoulder 41 forms the reference plane P off of which the other features of the assembly 11 are formed. Because the pin of the mold is shaped like the driveshaft, the impeller assembly 11 fits precisely on the shaft. The sleeve 39 also serves as an inspection feature for incoming part inspection. For example, the reference plane P can be used to check the location of other features during inspection. Moreover, the sleeve 39 eliminates the need to thread the insert 17 onto and off of the pin prior to and after the molding process. The sleeve 39 only needs to be slipped over the pin, which makes production quicker and cheaper.
The alignment of the impeller-shaft assembly 11 is controlled by the fit of the sleeve 39 of the insert 17 with respect to the shaft extension. In particular, the internal diameter of the sleeve 39 controls concentricity and thus controls eccentricity or “wobble”, especially at the outer edges of the impeller, and the shoulder 41 controls perpendicularity. Accordingly, the size and shape of the sleeve 39 is tightly controlled, e.g., the diameter is controlled to within about 0.001 inches or even about 0.0006 inches.
By tightly controlling alignment, the insert 17 eliminates the need to machine the impeller, in particular the inlet 27 and more generally the outer diameter of the impeller. Such machining has been done in the past to prevent contact of the inlet with the housing at gap G. The insert 17 also allows the gap G to be minimized because there is no eccentricity, i.e., the impeller axis will be substantially coaxial with that of the insert and the driveshaft. Therefore, the insert 17 also may eliminate the need to add a seal between the impeller and the housing, e.g., where the gap G was too large around prior art impeller assemblies. The insert 17 also extends the life of the seals 53, 55. By controlling concentricity and thus “wobble” of the impeller, the seals are not worn as quickly. Note that in the prior art where the impeller would move radially relative to the housing, the seals were stressed on each rotation. In this embodiment, the insert, impeller and housing are all co-axial, the insert and impeller rotating concentrically without wobble. In this way, there is reduced or no radial movement of the impeller within the housing so that rotation of the impeller does not stress or wear any seals (e.g., seals 53, 55) between the impeller and the housing.
The insert 17 and impeller 13 may be formed of a variety of materials. In one embodiment, the impeller 13 is made of a molded plastic, and the insert 17 is made of a metal, e.g., brass, powder metal or steel. The metal may be chosen based on the material of the driveshaft DS, for example.
When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. For example, the impeller is suitably formed over the insert by over-molding, but other methods of forming the impeller are contemplated. The insert may have many other configurations within the scope of the invention. For example, the nose of the insert need not extend into the hub, its shape may be other than cylindrical, and the bore could be open at both ends. These are merely some examples of possible changes to the constructions described above. Also, the various constructions need not necessarily have all the various advantages listed herein.
