Patent Publication Number: US-6220818-B1

Title: Blower wheel assembly with steel hub, and method of making same

Description:
This is a continuation-in-part of application Ser. No. 09/316,658, filed May 21, 1999, which is a continuation-in-part of application Ser. No. 08/954,937, filed Oct. 21, 1997 now 5,934,876. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a blower wheel assembly and methods of manufacturing the same. In particular, the invention includes a blower wheel assembly with a hub attached to a backplate of the blower wheel assembly. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 shows a prior art centrifugal blower wheel assembly  10  which includes a backplate  12 , a hub  14 , and a plurality of blades  16 . The hub  14  and the blades  16  are attached to the backplate  12 , which is typically a separate part. The blades  16  are secured to a ring  17 ; alternatively, the blades may be formed as a single piece, known as a bladestrip. The assembly  10  is used by attaching it to a rotational mechanism (not shown) via the hub  14  by means of a shaft (not shown). Rotation of the shaft causes rotation of the hub  14 , backplate  12  and blades  16 , thereby providing air flow. The connection between the backplate  12  and the hub  14  therefore is required to transmit the rotational torque of the shaft. 
     The maximum torque the hub  14  can withstand before coming loose with respect to the backplate  12  is termed the holding torque. The holding torque is a function of the way in which the hub is attached to the backplate. In addition, the holding torque can decrease over time as use changes the strength of that attachment. If the holding torque is exceeded, the hub becomes loose and will spin independently of the backplate  12 , resulting in a catastrophic failure of the blower wheel assembly. 
     FIGS. 2A-2C illustrate details of a prior art hub and backplate configuration. The hub  14  has a concentric rim or lip  18  protruding from a front surface  19  of the hub  14 . The lip  18  is designed to be placed in a hole  20  of the backplate  12  as illustrated in FIG.  2 C. The hub  14  has a back surface  22  through which a hole  24  extends in order to receive a shaft (not shown) or other member for rotation. A threaded set screw hole  26  is provided along a radius of the hub. A set screw (not shown) can be threaded in the hole  26  to allow for the assembly  10  to be fixed with respect to the shaft within the hole  24 . 
     The hub  14  is attached to the backplate  12  by forcing back (via stamping, for example) the rim or lip  18  while the rim or lip  18  extends through the hole  20  of the backplate  12 , thereby crimping the rim or lip  18  against the backplate  12  and holding the hub  14  thereto. In some circumstances, however, the holding torque for this type of arrangement is either insufficient or inconsistent, and therefore undesirable. 
     The backplate  12 , the hub  14 , and the blades  16  are all typically made of steel, which provides for high strength, low cost, and ease of manufacture. 
     An objective of the invention is to provide a blower wheel assembly with a hub that is more strongly attached to the backplate, that can be used over a wide range of temperatures, and that is inexpensive to manufacture. 
     SUMMARY OF THE INVENTION 
     The invention includes a blower wheel assembly and method characterized by a steel hub with protruding lugs that mate with a corresponding array of holes in a backplate of the assembly. The lugs are riveted or otherwise deformed to upset the lug material, thereby permanently and securely attaching the hub to the backplate. The lugs may be formed on the hub by a machining process. The holes in the backplate may have stress relief portions to avoid stress concentrations in corners of the holes. 
     According to one aspect of the invention, a blower wheel assembly includes a backplate with an array of hub mounting holes therein; a plurality of blades attached to the backplate; and a steel hub attached to the backplate, the steel hub having one or more lugs corresponding to the array of holes, the lugs being formed by a machining process. 
     According to another aspect of the invention, a method of manufacturing a blower wheel assembly includes forming a steel hub having one or more machined lugs; and attaching the steel hub to a backplate which has an array of hub mounting holes corresponding to the one or more lugs, wherein the attaching includes inserting the lugs in the hub mounting holes and deforming the lugs to lock the hub in place. 
     According to yet another aspect of the invention, a blower wheel assembly includes a backplate with an array of hub mounting holes therein, each hub mounting hole having a stress relief portion; a plurality of blades attached to the backplate; and a hub attached to the backplate, the hub having one or more lugs corresponding to the array of holes. 
     According to another aspect of the invention, a blower wheel assembly includes a backplate with a central hole therein. The back plate includes a front surface and a rear surface. A plurality of blades is attached to the backplate and a hub is attached to the backplate. The hub is formed by a piece of tubing shaped into the hub by a tube end forming machine. 
     According to yet another aspect of the invention, a method of manufacturing a blower wheel assembly includes the steps of cutting a tubing piece from a tubing material to a desired length to form a hub, the tubing having a first hole extending therethrough, forming the hub from the tubing piece using a tube end forming machine, the hub having a front tubular portion connected to a rear tubular portion by a flange portion, attaching a plurality of blades to a backplate, and attaching the hub to the backplate which has a central hole therein, wherein the attaching of the hub includes inserting the front tubular portion into the central hole in the back plate and deforming the front tubular portion against the backplate and holding the hub thereto via, for example, stamping. 
     According to yet another aspect of the invention, a blower wheel assembly includes a backplate with an array of tab receiving holes therein. The back plate includes a front surface and a rear surface. A plurality of blades are attached to the backplate. Additionally, a hub is attached to the backplate. The hub includes one or more tabs corresponding to the array of tab receiving holes. 
     According to another aspect of the invention, a method of manufacturing a blower wheel assembly includes forming a hub out of sheet metal having one or more tabs, and attaching the hub to a backplate which has an array of tab receiving holes corresponding to the one or more tabs, wherein the attaching includes inserting the tabs in the tab receiving holes and flattening the tabs against the back plate to lock the hub in place. 
     According to still yet another aspect of the invention, a blower wheel assembly includes a backplate with an array of tab receiving holes therein. The back plate includes a front surface and a rear surface. A plurality of blades are attached to the backplate. Additionally, a hub is attached to the backplate. The hub includes a front surface and a back surface, a central hole therethrough and a tubular portion extending from the front surface of the hub and surrounding the central hole. The tubular portion and the central hole are adapted to receive a shaft. The tubular portion is adapted to be press fitted onto the shaft. The hub includes one or more tabs corresponding to the array of tab receiving holes. 
     To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the annexed drawings: 
     FIG. 1 is a perspective view of a prior art blower wheel assembly; 
     FIG. 2A is an end view of a prior art hub for a blower wheel assembly; 
     FIG. 2B is a sectional view along section A—A of FIG. 2A; 
     FIG. 2C is a sectional view showing the prior art hub attached to a backplate; 
     FIG. 3A is an end view of a prior art aluminum hub with protrusions; 
     FIG. 3B is a sectional view of the prior art aluminum hub; 
     FIG. 3C is a side view of the prior art aluminum hub attached to a backplate; 
     FIG. 4A is a side view showing the metal grains in the vicinity of a protrusion formed by machining; 
     FIG. 4B is a side view showing the metal grains in the vicinity of a protrusion formed by cold heading; 
     FIG. 5A is a side view of a hub of the present invention; 
     FIG. 5B is a plan view of the hub of FIG. 5A; 
     FIG. 5C is an exploded perspective view of a blower wheel assembly of the present invention; 
     FIG. 6 is a flow chart showing the steps in the preferred method of manufacturing the hub of the present invention; 
     FIG. 7 is a side view showing a cold-heading process; 
     FIG. 8A is a flow chart showing the steps of a method of assembling a blower wheel assembly according to the present invention; 
     FIG. 8B is an exploded perspective view of the parts of the blower wheel assembly which are assembled by the method of FIG. 8A; 
     FIG. 9A is a flow chart showing the steps of an alternative method of assembling a blower wheel assembly according to the present invention; 
     FIG. 9B is an exploded perspective view of the parts of the blower wheel assembly which are assembled by the method of FIG. 9A; 
     FIG. 10A is a plan view of an alternate embodiment blower wheel assembly of the present invention; 
     FIGS. 10B and 10C are bottom and side views, respectively, of a hub for use in the blower wheel assembly of FIG. 10A; 
     FIG. 10D is a plan view of a hub mounting hole of the blower wheel assembly of FIG. 10A, showing details of the stress relief portions of the hole; 
     FIG. 10E is a bottom view of an alternate embodiment hub of the present invention. 
     FIG. 11A is a side perspective view of a piece of tubing used in an alternate embodiment hub of the present invention; 
     FIG. 11B is a side view of an alternate embodiment hub and an alternate embodiment backplate in accordance with the present invention; 
     FIG. 11C is a side view of the alternate embodiment hub inserted through a hole in the alternate embodiment backplate where the back plate is shown as a cross-sectional view in accordance with the present invention; 
     FIG. 11D is a side view rotated 90° from FIG. 11C illustrating the alternate embodiment hub attached to the alternate embodiment backplate where the hub is shown as a cross-sectional view in accordance with the present invention; 
     FIG. 12 is a flow chart showing the steps of a method of assembling an alternate embodiment hub and backplate assembly according to the present invention; 
     FIG. 13A is a plan view of another alternate embodiment hub of the present invention; 
     FIG. 13B is a side cross-sectional view of the alternate embodiment hub of FIG. 13A in accordance with the present invention; 
     FIG. 13C is a plan view of another alternate embodiment backplate in accordance with the present invention; 
     FIG. 13D is a side cross-sectional view of the alternate embodiment hub of FIGS. 13A-13B attached to the alternate embodiment backplate of FIG. 13C in accordance with the present invention; and 
     FIG. 14 is a flow chart showing the steps of a method of assembling the alternate embodiment hub and backplate assembly illustrated in FIGS. 13A-13D in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 3A-3C show a prior art aluminum hub  34  for accommodating a backplate  32 . The prior art aluminum hub  34  has six radial protrusions  36  (also called lugs or pips) extending from a front surface  38  of the hub  34 . The protrusions  36  are formed on the hub  34  by cold extrusion. A hole  40  extends through the hub  34  to receive a shaft for rotation (not shown), similar to the way in which the hole  24  extends through the hub  14  in the prior art blower wheel assembly of FIGS. 2A-2C. Besides the lugs  36  there is a central protrusion  42  extending from the front surface  38 . The backplate  32  has a central hole  44  to receive the central protrusion  42  and an array of holes  46  for receiving the lugs  36 . The hub  34  is attached to the backplate  32  by first engaging the lugs  36  and the central protrusion  42  of the hub  34  in the corresponding holes  44  and  46  of the backplate  32 . Then, while a back surface  48  of the hub  34  is held in place, the lugs  36  are struck with sufficient force to cause them to deform, flattening them such that they no longer can be pulled back through the holes  46 . This securely attaches the hub  34  to the backplate  32 . The engagement of the lugs  36  in the array of holes  46  of the backplate  32  provides for increased strength in the attachment of the aluminum hub  34  to the backplate  32  for a blower wheel assembly using this prior art design. 
     However, difficulties have been discovered in evaluating the prior art aluminum hub  34 . Use of an aluminum hub involves a joining of dissimilar metals, since the backplate  32  is made of steel. Steel and aluminum have different coefficients of thermal expansion, so the hub  34  and the backplate  32  endure stresses at the attachment points when the blower wheel assembly undergoes a change of temperature. This difference in coefficients of thermal expansion is particularly a problem when the blower wheel assembly is to be used in an environment subjected to wide swings of temperature, such as in a furnace or air conditioner. In such applications it is common for the blower wheel assembly to be subjected to changes from ambient temperature to 450° F. within one minute. Because the shaft which extends through the hole  40  is made of steel, thermal gradient cycling results in a long term reliability problem of the hub coming loose with respect to the shaft. Additionally, because the set screw is made of steel, thermal gradient cycling leads to loosening of the set screw, thereby causing the shaft to rotate independently of the hub and the rest of the blower wheel assembly. 
     Joining of the dissimilar metals aluminum and steel can also lead to galvanic corrosion in the hub. 
     Further, the relative malleability of aluminum when compared to steel results in difficulties in securing the shaft by use of the set screw mating with the threaded hole in the hub. Since the steel set screw is harder than the aluminum hub, the screw can strip the threads of the hole unless care is taken to avoid overtightening. The above-mentioned difficulties all but rule out use of blower wheel assemblies with aluminum hubs for applications with large thermal gradients. Consequently, the prior art aluminum hub  34  is undesirable in blower wheel assemblies. 
     Despite the difficulties inherent in the prior art aluminum hub  34 , the malleability of aluminum has the advantage of being relatively easy to manufacture into a desired shape. In contrast, a steel hub with lugs is relatively difficult to manufacture. Several possible methods of manufacturing a steel hub with lugs, such as die casting or using a powdered metal process, turn out to have undesirable features. 
     Die-casting suffers from expensive tooling costs. In addition, the material that can be die cast is limited to zinc, aluminum, magnesium, and copper alloys. Die cast zinc is weaker than steel. Tooling wear is greater with die casting and piece price is higher than with steel, partly due to secondary operations such as sprue trimming and tumbling that would be necessary. Porosity may be an issue due to air entrapment in the mold cavity, resulting in a weaker part. 
     Powdered metal processes have the disadvantage that the metal produced is porous. This leads the lugs to have structural weaknesses at the preferred height/width ratio, making the lugs fragile and difficult to manufacture. These problems with manufacturability would result in a high rejection rate of hubs made by powdered metal processes. The problems can be alleviated to some extent by adding a second material (e.g., copper) to fill the gaps in the steel structure. However, this addition of a second material increases costs. 
     By contrast, it has been found that making lugs on a steel hub  54  by a cold-heading process (also known as cold upsetting or cold forging) provides cost and performance advantages over other methods of manufacture. Cold-heading does not require expensive tooling. In addition, the steel hub of an exemplary design may be manufactured in a cycle time of approximately two seconds by cold heading, as opposed to the approximately ten seconds required to machine a hub of similar dimensions. Further, the cold-headed process provides increased durability over the powdered metal processes (for substantial height/width ratios). 
     The steel hub  54  in accordance with the present invention is shown in FIGS. 5A-5C. It has a plurality of lugs  56  extending from a front surface  58 . In a manner similar to the prior art hubs, the hub  54  has a hole  60  extending therethrough to receive and engage a shaft (not shown). A threaded hole  61  is also provided for a set screw (not shown) that can fix the shaft to the blower assembly. The hub  54  is affixed to a backplate  62 , as illustrated in FIG. 5C, which is similar in design to the backplate  32  in that the backplate  62  has a central hole  63  for accommodating the shaft and an array of holes  64  for mating with the lugs  56 . 
     The assembly method for fixing the hub  54  to the backplate  62  involves first engaging the lugs  56  with the corresponding holes  64  of the backplate  62 . Then, while a back surface  65  of the hub  54  is held in place, the lugs  56  are struck with sufficient force to cause them to deform such that they no longer fit through the holes  64  of the backplate  62 . The process of striking the lugs  56  is termed “impacting”, “riveting”, or “upsetting”, depending on the method of the striking. 
     Four lugs  56  are shown in the preferred embodiment illustrated in FIGS. 5A and 5B, although a greater or lesser number of lugs  56  may be used. A hub with four lugs  56 , however, is preferred because of its relative symmetry and because it has been found to provide sufficient attachment strength for the blower wheel assembly. The use of fewer lugs than the prior art aluminum hub  34  provides the advantage of reduced cost of manufacture. 
     The lugs  56  may be formed into a variety of shapes. Cylindrical lugs, such as the lugs  36  employed in the prior art hub  34  (FIG. 2B) may be employed. Noncylindrical lugs, however, such as those shown in FIGS. 5A and 5B, have been found to be satisfactory. The lugs  56  have a height  66  which is approximately equal to their width  68  in the radial direction. The ratio of the width  68  to the height  66  may be in a broad range which is dependent on the characteristics of the material being worked. An exemplary range would be approximately 0.5:1 to approximately 2:1, with the ratio being preferably greater than approximately 0.8:1. However, a ratio that is too small can result in lugs that are prone to breaking off, thereby making the hub  54  more difficult to manufacture. The lugs  56  have a length  70  in a radial direction that is preferably approximately twice the width  68  of the lugs. This increased thickness in the radial direction provides greater strength in the direction of hub rotation and thus results in increased strength against radial stresses between the hub  54  and the backplate  62 . The lugs  56  having a shape such as that shown in FIGS. 5A and 5B will preferably be used with backplate holes  64  that are elliptical or slotted, but holes that are round or have other shapes may be used as well. 
     The hub  54  preferably has a basically square cross-section with flattened comers  72 . It will be appreciated, however, that the hub  54  may have a round or other shaped cross-section. A hub of any shape having one or more cold-headed protrusions for engaging a backplate is contemplated as falling within the scope of the present invention. 
     The method  200  of manufacturing of the steel hub  54  is illustrated in FIG.  6  and begins with cutting a length of steel wire at step  202  to a desired length. The hub  54  preferably is formed according to the disclosed method from lengths of 0.875″ diameter steel wire, although the method is by no means limited as to the size or cross-sectional shape of the steel wire. The length of steel wire is then rammed (impacted with a shaping punch having a recess of a given shape) to form the wire into a slug having a desired cross-sectional shape, at step  204 . 
     After ramming, the slug is then cold-headed to form the lugs  56  on the front surface  58 , at step  206 . This cold-heading process, illustrated in FIG. 7, consists of four substeps. A typical slug  90  is secured in a container or tray  92  which moves the slug  90  relative to a heading punch  94  in a direction  95 . The front surface  58  of the slug  90  faces the punch  94 . The punch  94  has an array of recesses (not shown) at four locations in the direction  95 , the recesses at each of the locations corresponding to the shape of the slug  90  and the positions where the lugs  56  are to be formed. As the slug  90  reaches each of the locations in the direction  95 , the container or tray  92  is stopped, and the punch  94  is engaged with great force in a direction  96  parallel to the axis of the slug  90 . The resulting impact between the punch  94  and the slug  90  causes the steel of the slug  90  to be compressed with such force that the metal of the slug  90  flows into the recesses of the punch  94 , thereby forming the lugs  56 . The punch  94  is preferably designed to impact four slugs simultaneously, with four impacts on a single slug  90  needed to form the lugs  56  of the hub  54 . However, the punch  94  may alternatively be designed to impact a greater or lesser number of slugs, with the impacting of multiple slugs not necessarily being simultaneous. In addition, cold-heading processes may be designed to be accomplished in greater than or less than four impacts. 
     After the cold-heading step  206 , the method  200  of manufacturing the hub  54  includes boring the hole  60  for the shaft at step  208 , and boring and tapping the set screw hole  61  at step  210 . 
     Turning to FIGS. 8A and 8B, a method  220  of manufacturing a blower wheel assembly of the present invention is shown. The initially individual blades  16  are cut to size at step  222 . Then one end  98  of each of the blades  16  is attached to the ring  17  at step  224 . The other ends  104  of the blades  16  are placed in holes or slots  100  in a backplate  102  at step  226 . After the lugs  56  of the hub  54  are inserted in the array of holes  46  near the center of the backplate  102  at step  228 , the hub  54  and blades  16  are preferably attached in a single step  230  of riveting the lugs  56  (deforming the lugs by impacting with high-frequency hammers) and riveting or bending the protruding ends  104  of the blades  16 . An example of a method of attaching individual blades of a blower wheel assembly through holes in a backplate is provided in U.S. Pat. No. 3,262,637, entitled INDIVIDUAL BLADE MOUNTINGS IN A BLOWER WHEEL, which is incorporated in its entirety herein by reference. Alternatively, the lugs  56  of the hub  54  may be attached to the backplate  102  by staking. 
     Another method  240  of manufacturing a blower wheel assembly according to the present invention is shown in FIGS. 9A and 9B. Initially a strip is cut from sheet metal at step  242 , the strip of metal (not shown) is stamped at step  244  to form blades, and then the strip is wrapped at step  246  to form a cylindrical bladestrip  110 . This method of forming a plurality of blades for a blower assembly as a single piece is demonstrated in U.S. Pat. No. 2,242,586, entitled METHOD OF MAKING BLOWERS, and in U.S. Pat. No. 3,711,914, entitled METHOD FOR ASSEMBLING CENTRIFUGAL BLOWERS, both of which are incorporated in their entireties herein by reference. The bladestrip  110  is then placed in an annular depression  112  near the perimeter of a backplate  114  and a ring  17  placed atop the bladestrip  114 , at step  248 . Thereafter, the bladestrip  110  is attached to the backplate  114  and the ring  17  by crimping at step  250 . An example of a crimped bladestrip is shown in FIG.  2 C. After the bladestrip  110  is attached to the backplate  114 , the lugs  56  of the hub  54  are placed in the array of holes  46  in the backplate  114 , and the hub  54  is attached to the backplate  114  by riveting, upsetting or otherwise deforming the lugs  56  at step  252 . 
     Machining of steel hubs with lugs involves use of relatively expensive machines which require large capital outlays, and may be time-consuming when compared to other methods. 
     Further, it has been noted that manufacturing steel hubs with lugs by machining possibly introduces structural weaknesses in the vicinity of the lugs. As illustrated in FIG. 4A, machining involves removing material, leaving the metal grains straight, breaking the grain flow and thereby creating a weakness at a junction  50  where a lug would be joined to the rest of the hub. This is in contrast to the continuous metal grains in a hub where the lugs are cold-headed, such as shown in FIG.  4 B. With continuous metal grains following the outline of the hub the cold-headed hub is considered to have greater strength than a machined hub. 
     Nonetheless, machining offers advantages as well. Machining offers the advantage over cold heading of lower additional cost per part produced; even taking into account the large capital outlays required, machining may have lower cost per unit over the long term. In addition, lugs produced by machining do not share the below-described disadvantage of porosity and resulting weakness that occurs in lugs made by powdered metal processes. 
     Further, though lugs produced by machining have a theoretical potential to be weaker than lugs made by cold heading, hubs with lugs produced by machining have been found to have adequate strength in actual practice. 
     Referring now to FIG. 10A, an alternate embodiment blower wheel assembly  410  is shown. The blower wheel assembly  410  has many features in common with the blower wheel assemblies described above, details of which are omitted for the sake of brevity. 
     The assembly  410  includes a backplate  414  having an array of hub mounting holes  416 , and a central hole  418 . Blades or a bladestrip  420  are mounted onto and are connected to the backplate  414  along the perimeter of the backplate  414 . 
     A hub  430  (FIGS. 10B and 10C) is connected to the backplate  414  as part of the assembly  410 . The hub  430  has lugs  432  protruding from a body  434 , the lugs  432  being of a size and shape such that they are able to pass through the hub mounting holes  416 . Preferably the lugs have a cross-section substantially similar to that of the hub mounting holes. 
     The body  434  has a shaft mounting hole  438  therein for receiving a shaft (not shown). A mechanism is included for coupling the shaft to the hub  430 . An exemplary mechanism is the set screw mechanism described above. 
     The lugs  432  each have sharp comers  440 . As shown best in FIG. 10D, the hub mounting holes have stress relief portions, such as stress relief holes  444 , in their comers which correspond to the sharp comers  440  of the lugs  432 . The stress relief holes  444  may be formed, for example, by drilling or punching. 
     The stress relief portions serve to avoid stress concentrations at those corresponding comers. The stress concentrations may cause cracking at the comers which may result in failure of the assembly. 
     The stress relief holes may be larger or smaller than as shown in FIG. 10D, and may be so small as to make them barely visible. 
     It will be appreciated that the stress relief portions may take many forms, such as circular or other-shaped holes, or other mechanisms that remove the sharp comers of the hub mounting holes and/or prevent contact between the hub mounting holes and the sharp comers of the lugs. 
     It will further be appreciated that the hub body may have a shape other than a circular cross section, for example having a square cross section. The cross-sectional shape of the hub body may affect the shape of the resulting lugs. 
     The lugs for the hub shown in FIGS. 10B and 10C may be formed by a machining process. A cylindrical hub may be cut from steel wire having a circular cross section. Then, material may be milled or otherwise removed along flat faces  448  on the hub. This removal of material leaves the lugs  432  protruding from the hub body  434 . Thereafter, the shaft mounting hole  438  may be bored in the hub  430 . 
     Connection of the hub  430  to the backplate  414  is similar to the process described above with respect to another embodiment—the lugs  432  are inserted through the hub mounting holes  416 , and then the ends of the lugs are deformed (flattened against the backplate  414 ) to secure the hub  430  to the backplate. 
     It will be appreciated that a greater of lesser number of lugs may be formed by, for example, changing the number of milling or material removing steps. For ease of manufacture, the removal of material steps preferably include sweeping across the hub, passing through the axis of the shaft mounting hole, with a swath wider than the diameter of the shaft mounting hole. Thus preferably the hub has an even number of lugs, although it will be appreciated that hubs with an odd number of lugs may also be formed with appropriate modifications to the above method. 
     Although the hub is described as being a steel hub with the lugs formed by machining, it will be appreciated that other materials and methods of manufacture may be used. 
     Referring to FIG. 10E, an alternate embodiment machined hub  430 ′ is shown. The hub  430 ′ has lugs  432 ′ which have rounded comers  440 ′. The rounded corners  440 ′ may reduce the amount of stress transmitted to the backplate in the vicinity of the comers of the hub mounting holes in the backplate. The rounded comers may be formed by machining or by other methods. 
     FIGS. 11A-11D illustrate details of an alternate embodiment of a hub and a backplate configuration. FIG. 11A illustrates a piece of tubing  450 , for example, annealed carbon steel tubing, cut to a length that is appropriate for forming a hub. The tubing  450  already includes a hole  462  extending through the tubing  450 , thus eliminating the need to machine a hole for receiving a shaft (not shown). It should be appreciated that although steel tubing is preferred, any type of metal or other type of tubing could be used to carry out the present invention. The tubing  450  is formed into a hub  450 ′, as illustrated in FIG. 11B, by a tube end forming machine or the like. It should be appreciated that use of the tubing  450  to form the hub  450 ′ eliminates the need for expensive machining processes, and further has the advantage of reduced material costs, since none of the tubing  450  is remove in the formation of the hub  450 ′. 
     The hub  450 ′ includes a shorter front tubular portion  452  connected to a longer rear tubular portion  460  by a flange portion  454 . The flange portion  454  has an outer peripheral circumference larger that the outer peripheral circumference of the front tubular portion  452  and the rear tubular portion  460 . The flange portion  454  includes a front surface  456  and a rear surface  458 . The outer peripheral circumference of the front tubular portion  452  is dimensioned to be received by a central hole  472  of a backplate  470 , as illustrated in FIG.  11 B. The backplate  470  includes a front surface  474  and a rear surface  476 . The hub  450 ′ includes the first hole  462  extending through the rear tubular portion  460  to a second hole  464  in the front tubular portion  452 . The first hole  462  connects to the second hole  464  at a location where the flange portion  454  connects the rear tubular portion  460  to the front tubular portion  452 . Preferably, the dimension of the second hole  464  is dictated by the tube end forming machine and has a diameter greater than the first hole  462 . The front tubular portion  452  is designed to have peripheral walls that are both thinner and shorter than the peripheral walls of the rear tubular portion  460 , such that the front tubular portion  452  is adapted to be deformed (e.g., stamped or crimped). The larger diameter of the second hole  464  with respect to the first hole  462 , the location of the connection between the second hole  464  to the first hole  462 , and the length of the first tubular portion  452  with respect to the second tubular portion  460 , all add to the malleability of the first tubular portion  452 . The first hole  462  is adapted to receive a shaft (not shown) or other member for rotation where the rear portion member  460  will be press fitted onto the shaft, thus eliminating the need to provide a threaded set screw hole and a set screw threaded in the screw hole, as described in the previous embodiments. 
     Referring now to FIGS. 11C and 11D, as previously stated the front tubular portion  452  is dimensioned to be received by the hole  472  of the backplate  470 . The hub  450 ′ is attached to the backplate  470  by inserting the front tubular portion  452  through the hole  472  of the backplate  470 , until the front surface  456  of the flange portion  454  is flush with the rear surface  476  of the backplate  470 , and forcing back (via stamping, for example) the front tubular portion  452  thereby crimping the front tubular portion  452  against the backplate  470  and holding the hub  450 ′ thereto. 
     A method  500  of manufacturing the alternate hub and backplate configuration of FIGS. 11A-D is illustrated in FIG. 12, and begins with the cutting of tubing, such as steel tubing material. The piece of tubing  450  having the desired length is cut for forming the hub  450 ′, in step  510 . In step  520 , the tubing piece  450  is formed into a hub  450 ′ by a tube end forming machine. For example, the tubing  450  is fixed and a die (not shown) consecutively strikes the tubing  450  to incrementally transform the tubing  450  into the hub  450 ′. Therefore the tube end forming machine is analogous to cold-heading discussed supra in that no material is removed in the forming process. That is, the tubing material is displaced or relocated (to form the flange  454 ) by consecutive hits with progressive tools using high tonnage. Consequently, the hub  450 ′ is inexpensive and rugged, and can be manufactured in a well-controlled manner. 
     The front tubing portion  452  is then inserted into the central hole  472  of the backplate  470 , until the front surface  456  of the flange portion  454  is flush with the rear surface  476  of the backplate  470 , in step  530 . In step  540 , the front tubing portion  452  is then deformed or otherwise forced back against the front surface  474  of the back plate via, for example, stamping, thereby crimping the front tubular portion  452  against the backplate  470  and securing the hub  450 ′ to the backplate  470 . The shaft (not shown) is then inserted through the first hole  462  of the rear tubular portion  460  and the rear tubular portion  460  is press fitted onto the shaft, in step  550 . The press fit preferably is achieved in the following manner. The inner diameter of the first hole  462  is slightly smaller than the outer diameter of the shaft (for example, by a couple thousandths of an inch or more). By forcing the shaft into the first hole  462 , a tight interference fit is achieved without use of a set screw. Such arrangements work well in blower wheel applications where the blower wheel would not normally be removed for service or replacement. The hub and backplate configuration can then be integrated into the blower wheel assembly process described supra in conjunction with FIGS. 8B and 9B, respectively. 
     Another alternate embodiment of a hub and a backplate configuration is illustrated in FIGS. 13A-13D. FIG.  13 A and FIG. 13B illustrate a hub  600  formed from a piece of sheet metal. One or more holes  602  are punched around an annular ring  615  at a top surface  608  of the hub  600  forming one or more tabs  605  extending from a bottom surface  612  of the hub  600 . Six tabs  605  are shown in the preferred embodiment illustrated in FIGS. 13A and 13B, although a greater or lesser number of tabs  605  may be used A central hole  610  is punched through the center of the hub  600  extending from the top surface  608  to the bottom surface  612 . Although the central hole  610  is generally D-shaped, the central hole could take on a variety of different shapes (e.g, a circle, hexagon, pentagon, square etc.). It should be appreciated that use of sheet metal to form the hub  600  not only eliminates the need for expensive machining processes, but is relatively inexpensive due to the low cost of the sheet metal material. The hub  600  includes a tubular portion  625  extending from the top surface  608  of the hub  600  and a generally flat portion  620 . The tubular portion  625  is formed by stamping through the central hole  610  with progressive tooling using a stamping press or the like. The tubular portion  625  and the central hole  610  are adapted to receive a shaft or rotation device (not shown). The tubular portion  625  can be press fitted onto the shaft eliminating the need to provide a threaded set screw hole and a set screw threaded in the screw hole, as described in the previous embodiments. 
     FIG. 13C illustrates a backplate  630  that can be used with the hub  600 . The back plate  630  includes an array of tab receiving holes  635  located around an annular ring  645 . The tab receiving holes  635  are adapted to receive one or more tabs  605  from the hub  600 . The tab receiving holes  635  can be formed by punching holes  635  through a top surface  632  to a back surface  638  of the backplate  630  or vice-versa. The back plate  630  also includes a central hole  640  adapted to allow a shaft (not shown) to pass therethrough. FIG. 13D illustrates the attachment of the hub  600  to the backplate  630 . The bottom surface  612  of the hub  600  is placed in juxtaposition with the top surface  632  of the back plate  630  with the tabs  605  passing through the tab receiving holes  635 . The tabs  605  are then flattened out against the bottom surface  638  of the backplate  630  attaching the hub  600  to the backplate  630 . 
     A method  650  of manufacturing the alternate hub and backplate configuration of FIGS. 13A-D is illustrated in FIG.  14 . The method begins with the cutting of the sheet metal material to the proper size for forming the hub  600  and punching central hole  610  through the sheet metal piece, in step  660 . In step  670 , one or more holes  602  is punched through the sheet metal around the inner annular ring  615  to form one or more tabs  605  extending from the bottom surface  612  of the hub  600 . In step  680 , the tubular portion  625  is formed from the sheet metal piece by stamping through the central hole  610  using progressive tooling. 
     In an alternative embodiment of the present invention, steps  660  and  680  may be combined into a single step. In step  690 , an array of tab receiving holes  635  are punched through the top surface  632  to the bottom surface  638  of the back plate  630  around the inner annular ring  645 . The one or more tabs  605  extending from the bottom surface  612  of the hub  600  are then inserted through the array of tab receiving holes  635  on the back plate  600 , and flattened against the back surface  638  of the back plate  600 . In step  710 , the shaft (not shown) is inserted into central hole  610  in the tubular portion  625  and the tubular portion  625  is press fitted onto the shaft (not shown). The hub and backplate configuration can then be integrated into the blower wheel assembly process as described supra in conjunction with FIGS. 8B or  9 B, respectively. 
     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified finction of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.