Abstract:
HVLP (High Velocity Low Pressure) motor-driven fans and other types of fans, blowers and vacuums take advantage of different thermal and mechanical properties of dissimilar materials used in the motor-driven fans. The dissimilar materials include aluminum for a stacked arrangement of fan wheels and spacers, steel for a shaft that supports the fan wheels and spacers, and a polymeric adhesive. In some examples, the polymeric adhesive is trapped between the aluminum and steels parts. Compared to steel and aluminum, the adhesive has a relatively high coefficient of thermal expansion but relatively low strength such that thermal expansion of the adhesive exerts additional clamping pressure during startup and during high temperature operation. The additional clamping pressure reduces vibration and eliminates other causes of fan or motor failure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 62/350,922 filed on Jun. 16, 2016 by the present inventor and specifically incorporated herein by reference. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    This disclosure generally pertains to motor-driven fans and more specifically to means for minimizing vibration and strain. 
       BACKGROUND 
       [0003]    High-velocity low pressure fans, sometimes known as HVLP fans or turbines, typically comprise a multi-stage stacked series of fan wheels driven by a high speed motor. The term, “HVLP,” as used herein, refers to high-velocity low-pressure fans operating at 15,000 to over 30,000 rpm for compressing air to less than 15 psig, and delivering air up to 10 psig to a paint sprayer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a front cross-sectional view of an example motor-driven fan constructed in accordance with the teachings disclosed herein. 
           [0005]      FIG. 2  is a partially exploded front cross-sectional view of the motor-driven fan shown in  FIG. 1 . 
           [0006]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 1 . 
           [0007]      FIG. 4  is a view taken along line  4 - 4  of  FIG. 2 . 
           [0008]      FIG. 5  is a view similar to  FIG. 4  but showing another example shape of a thin shim or slightly raised surface adjacent to a recessed surface. 
           [0009]      FIG. 6  is a view similar to  FIGS. 4 and 5  but showing another example shape of a thin shim or slightly raised surface adjacent to a recessed surface. 
           [0010]      FIG. 7  is a view similar to  FIGS. 4-6  but showing another example shape of a thin shim or slightly raised surface adjacent to a recessed surface. 
           [0011]      FIG. 8  is a front cross-sectional view similar to  FIG. 1  but showing another example motor-driven fan constructed in accordance with the teachings disclosed herein. 
           [0012]      FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8 . 
           [0013]      FIG. 10  is a front cross-sectional view similar to  FIGS. 1 and 8  but showing another example motor-driven fan constructed in accordance with the teachings disclosed herein. 
           [0014]      FIG. 11  is a cross-sectional view taken along line  11 - 11  of  FIG. 10 . 
           [0015]      FIG. 12  is a front cross-sectional view similar to  FIGS. 1, 8 and 10  but showing another example motor-driven fan constructed in accordance with the teachings disclosed herein. 
           [0016]      FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 12 . 
           [0017]      FIG. 14  is an enlarged view of spacers and adjacent parts shown in  FIG. 1 . 
           [0018]      FIG. 15  is a cross-sectional view taken along line  15 - 15  of  FIG. 14 . 
           [0019]      FIG. 16  is a view similar to  FIG. 14  but showing the spacers clamped more tightly. 
           [0020]      FIG. 17  is a view similar to  FIG. 16  but showing the spacers clamped even more tightly. 
           [0021]      FIG. 18  is a bottom view of a fan wheel used in the example motor-driven fan shown in  FIG. 1 . 
           [0022]      FIG. 19  is a bottom view similar to  FIG. 18  but with the upstream disk omitted and four fan blades omitted. 
           [0023]      FIG. 20  is view taken along line  20 - 20  of  FIG. 19 . 
           [0024]      FIG. 21  is a view similar to  FIG. 20  but an exploded version of it with two fan disks. 
           [0025]      FIG. 22  is a front cross-sectional view similar to  FIG. 16  but with the addition of an adhesive. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIGS. 1-22  show an example motor-driven fan  10  and variations thereof. In some examples, motor-driven fan  10  comprises an inboard bracket  12  defining an air outlet  14 ; an outboard bracket  16 ; a stator  18  comprising a plurality of laminations  20 ; a screw  22  clamping stator  18  between inboard bracket  12  and outboard bracket  16 ; an armature rotor  24  comprising a steel shaft  26  being elongate in an axial direction  28 , a known commutator  30  supported by shaft  26 , and a set of windings  35  being electrically coupled to commutator  30 ; and a set of bearings  32  mounted to at least one of inboard bracket  12  and outboard bracket  16 . Bearings  32  provide shaft  26  with support in a radial direction  36  that is perpendicular to axial direction  28 . Bearings  32  also support shaft  26  in axial direction  28  so as to centrally position windings  35  proximate stator  18 . 
         [0027]    Motor-driven fan  10  also includes a fan housing  38  connected to inboard bracket  12 . Fan housing  38  (comprising one or more components) defines an air inlet  40  that is in fluid communication with outlet  14  of inboard bracket  12 . A plurality of aluminum fan wheels  42  and a plurality of aluminum spacers  44  are in an axially stacked arrangement within fan housing  38 . A threaded nut  46  fastens the plurality of fan wheels  42  and the plurality of spacers  44  to shaft  26 . As shaft  26  of armature  24  rotates fan wheels  42  at 15,000 to 30,000 rpm or more, fan wheels  42  force a current of air  48  from inlet  40  to outlet  14 . Stationary dividers  50  direct air  48  sequentially through fan wheels  42 . In some examples, dividers  50  include known stationary guide vanes that help direct air  48  in a more efficient flow pattern. Depending on the specific design and operation of motor-driven fan  10 , the air pressure at outlet  14  can be up to 15 psig. In vacuum applications, inlet  40  is at subatmospheric pressure. In the example illustrated in  FIG. 1 , motor-driven fan  10  is part of an HVLP system that delivers up to 10 psig to a paint sprayer  55 . A hose  57  connects outlet  14  in fluid communication with paint sprayer  55 . More information about paint sprayer  55  is found in U.S. Pat. No. 8,387,898; which is specifically incorporated herein by reference. 
         [0028]    The illustrated example of motor-driven fan  10  has what is sometimes referred to as a frameless or skeleton assembly. For the illustrated example, the frameless or skeleton assembly means that at least two screws  22  first go through outboard bracket  16  on top of stator laminations  20 , then through laminations  20 , and then a threaded end  52  of each screw  22  screws into a corresponding hole  54  in inboard bracket  12 . Screws  22  are tightened to securely clamp laminations  20  between brackets  12  and  16 . In examples where outboard bracket  16  is made of a glass-filled thermoset plastic (e.g., thermoset polyester glass-filled bulk molding compound, sometimes known as BMC) and inboard bracket  12  is made of a die cast aluminum, tightening of screws  22  might crack outboard bracket  16  due to a combination of factors including the stack of laminations  20  being somewhat compressible, outboard bracket  16  being relatively brittle when made of BMC or certain other plastics, and inboard bracket  12  being relatively strong and rigid when made of die cast aluminum. 
         [0029]    The source of the cracking problem originates with the stack of laminations  20  being slightly compressible. Each sheet of lamination  20  is about 0.018 to 0.030 inches thick, whereby the thin individual sheets or laminations improve the magnetic quality of the stator&#39;s core. Each sheet of lamination can have small burrs that cumulatively contribute to the stator&#39;s overall height when the laminations are stacked and held together by staking, riveting, clipping and etc. When stator  18  is in an uninstalled position, as shown in  FIG. 2 , an axial stator face  56  of stator  18  is substantially planar. 
         [0030]    During subsequent assembly of the motor, additional compressive force exerted by screws  22  can flatten the burrs, thus laminated stator core  18  acts as a compressible structure. Under the compressive force of screws  22 , the lamination core  18  in its installed position ( FIGS. 1 and 3 ) becomes shorter in a localized area  58  where screws  22  are tightened but is taller in outlying areas  60  farther away from screws  22 . The outboard thermoset bracket  16  being weaker than the aluminum inboard bracket  12  will try to flex to match the compressed contour of the lamination core  18 . Although such flexure can maintain a beneficial axial load on screws  22 , the flexure can also cause the outboard thermoset bracket  16  to crack. 
         [0031]      FIGS. 1-13  illustrate various means for avoiding this problem. In the example shown in  FIGS. 1-3 , inboard bracket  12  has a protruding first axial surface  62  (e.g., first axial surface  62   a,    62   b,    62   c  or  62   d ) and a recessed second axial surface  64  (axial surfaces  62  and  64  are displaced out of coplanar alignment with each other). When screw  22  tightly clamps laminations  20  between brackets  12  and  16 , both surfaces  62  and  64  engage stator face  56  of stator core  18 . First axial surface  62  engages localized area  58 , and second axial surface  64  engages outlying area  60 . In some examples, but not necessarily in all examples, stator  18  is pressed more tightly against first axial surface  62  than against second axial surface  64 .  FIG. 3 , for instance, shows a first axial distance  66  between first axial surface  62  of inboard bracket  12  and a third axial surface  68  of outboard bracket  16  being less than a second axial distance  70  between second axial surface  64  of inboard bracket  12  and a fourth axial surface  72  of outboard bracket  16 . 
         [0032]    In some examples, it has been discovered that it works best when first axial surface  62  and second axial surface  64  are displaced out of coplanar alignment with each other by an offset axial distance  74  that is less than twice an axial thickness  76  of a single lamination  20 , wherein offset axial distance  74  equals second axial distance  70  minus first axial distance  66 . In examples where axial thickness  76  of each lamination  20  is between 0.018 and 0.030 inches thick, best results are attained when offset axial distance  74  is between 0.005 and 0.020 inches. Providing inboard bracket  12  with the desired offset axial distance  74  can be achieved by various means. Examples of such means include, but are not limited to, those shown in  FIGS. 4-7 . 
         [0033]      FIG. 4  shows first axial surface  62   a  being in a circular shape encircling hole  54 .  FIG. 5  shows first axial surface  62   b  in a C-shape partially encircling hole  54 .  FIG. 6  shows first axial surface  62   c  in a rectangular shape surrounding or adjacent to hole  54 .  FIG. 7  shows first axial surface  62   d  comprising multiple pads or bosses adjacent to hole  54 . 
         [0034]      FIGS. 8-13  show alternate designs for achieving similar results of the design shown in  FIGS. 1-3 . While first axial surface  62  of  FIGS. 1-3  is an integral, seamless protrusion of inboard bracket  12 , first axial surface  62  of  FIGS. 8 and 9  is provided by an annular shim  78  that provides similar results. In this example, annular shim  78  is considered a component part of inboard bracket  12 . 
         [0035]      FIGS. 10 and 11  show annular shim  78  being installed between outboard bracket  16  and laminations  20  to achieve results similar to those of  FIGS. 8 and 9 . In this example, annular shim  78  is considered a component part of outboard bracket  16 . Outboard bracket  16 , in this example, includes third axial surface  68  on annular shim  78  and also includes fourth axial surface  72 . Third axial surface  68  is adjacent to or at least partially encircles screw  22 . Third axial surface  68  and fourth axial surface  72  are displaced out of coplanar alignment with each other, and both engage stator  18 .  FIGS. 12 and 13  is similar to the design shown in  FIGS. 10 and 11 ; however,  FIGS. 12 and 13  show third axial surface  68  being a seamless, integral protrusion of outboard bracket  16 . 
         [0036]    It should be noted that the concept of using a shim or otherwise protruding axial surface adjacent to screw  22  can be applied to a variety of fan/motor designs. Examples of suitable designs include, but are not limited to, inboard bracket  12  being metal and outboard bracket  16  being plastic (as illustrated), inboard bracket  12  being plastic and outboard bracket  16  being metal, and both brackets  12  and  16  being plastic. 
         [0037]    Referring to  FIGS. 14-17 , the illustrated spacer design is meant to address a thermal expansion problem that can occur with HVLP motor-driven fans that have a combination of aluminum and steel parts. Motor-driven fan  10 , for instance, has spacers  44  and fan wheels  42  made of aluminum and shaft  26  made of steel. Aluminum has a relatively high coefficient of thermal expansion (e.g., a CTE of about 22×10 −6  m/mK), and steel has a lower CTE (e.g., about 12×10 −6  m/mK). 
         [0038]    Some HVLP motor-driven fans operate with very small exhaust orifices, often in the range of 0.125 to 0.375 inch effective exhaust orifice size range. At this small exhaust orifice size, these HVLP motor-driven fans can generate very high heat, as there is a very low volume of air flowing through the fan wheels to carry the heat away. Fan air temperatures can be in the range of 100-150 degree Celsius. At these high temperatures, the relatively high coefficient of thermal expansion (CTE) for aluminum spacers  44  and aluminum fan wheels  42  versus the lower coefficient of thermal expansion of steel shaft  26  can cause significant quality and reliability problems. 
         [0039]    When the motor-driven fan is assembled, a relatively high torque (typically 50-80 in-lbs or higher) is applied to nut  46  securing the whole fan/spacer/shaft assembly together. After the motor-driven fan has been running for a while (perhaps 10 minutes or several hours of continuous run), the rotating parts all become very hot. Because the CTE of the aluminum parts is higher than CTE of the steel shaft, the aluminum parts undergo greater expansion. Since the aluminum parts on shaft  26  are axially constrained between nut  46  and the inner race of inboard bearing  32 , the aluminum spacers are forced to expand radially while being more constrained axially. While the motor-driven fan is running, such expansion keeps all the parts tight and secure. 
         [0040]    However, a problem may arise when the rotating parts cool back down after the unit is turned off. The parts retract as they cool, so the aluminum spacers might become axially shorter than they were initially. Consequently, nut  46  and the other parts on shaft  26  might not be as secure as they were originally, so the next time the motor-driven fan is started, the parts might spin relative to shaft  26 . 
         [0041]    To overcome this problem, the axially resilient preload design of spacer  44 , shown in  FIGS. 14-17  includes a shallow counterbore  80  that helps accommodate the difference in thermal expansion of aluminum spacers  44  and fan wheel  42  with respect to steel shaft  26 . In some examples, counterbore  80  is about 0.002 to 0.005 inches deep (e.g., 0.003 inches deep, as indicated by dimension  82  of  FIG. 14 ). When nut  46  is tightened during assembly, counterbore  80  allows spacers  44  to resiliently flex slightly in axial direction  28  such that each fan wheel  42  remains securely supported at the spacer&#39;s outer periphery, thus providing better radial retention of fan wheels  42  and reducing the chance of radial slippage of fan wheel  42  relative to shaft  26 . 
         [0042]    More specifically, in some examples, each spacer  44  (e.g., a first spacer) of the plurality of spacers  44  has a first axial face  82  comprising a first recessed surface  84 , a first peripheral rim  86 , and a first step  88  extending in axial direction  28  (about 0.002 to 0.005 inches deep, as indicated by dimension  82 ) between first recessed surface  84  and first peripheral rim  86 . Nut  46 , when tightened, exerts a nut-clamping force  90  ( FIG. 16 ) that urges first recessed surface  84  and first peripheral rim  86  toward a substantially planar surface  92  of fan wheel  42 . 
         [0043]      FIG. 14  shows that when nut  46  is tightened just lightly to exert nut-clamping force  90  of minimal magnitude, only first peripheral rim  86  engages the fan wheel&#39;s planar surface  92  while spacer  44  experiences little if any axial deflection.  FIG. 16  shows that when nut  46  is tightened further to exert nut-clamping force  90  of moderate magnitude, still only first peripheral rim  86  engages the fan wheel&#39;s planar surface  92 , but spacer  44  undergoes appreciable axial deflection.  FIG. 17  shows that when nut  46  is tightened even further to exert nut-clamping force  90  of significantly higher magnitude, both first peripheral rim  86  and at least a portion of recessed surface  84  engage the fan wheel&#39;s planar surface  92 , whereby spacer  44  experiences even more axial deflection. The chosen degree of nut tightness may depend on the fan&#39;s specific design and operating conditions. In some examples, particularly under severe operating conditions (e.g., 15,000 to 30,000 rpm and up to 15 psig) nut  46  is fully tightened to resiliently compress spacers  44  as shown in  FIG. 17 . Of course, nut  46  can be fully tightened for any operating conditions if so desired. 
         [0044]    In some examples, as shown in  FIGS. 14, 16 and 17 , each fan wheel  42  is clamped between two opposing spacers  44  (e.g., a first spacer  44   a  and a second spacer  44   b ). Second spacer  44   b  has a second axial face  82   b  comprising a second recessed surface  84   b,  a second peripheral rim  86   b,  and a second step  88   b  extending in axial direction  28  between second recessed surface  84   b  and second peripheral rim  86   b.  Two spacers  44   a  and  44   b  in an opposing arrangement doubles the axial compressive distance to about 0.004 to 0.010 inches while the nut&#39;s exerted nut-clamping force  90  remains the same. In other words, a given nut-clamping force  90  provides twice the distance of compression when two spacers  44  are installed in an opposing arrangement. 
         [0045]    Referring to  FIGS. 18-21 , some examples of motor-driven fan  10  have a fan blade design that resists blade tip bending under extreme centrifugal force. In the illustrated example, fan wheel  42  comprises an upstream disk  94 , a downstream disk  96  and a plurality of curved fan blades  98  between the two disks  94  and  96 . Downstream disk  96  has a shaft hole  100  for aligning fan wheel  42  to shaft  26 . Upstream disk  94  has an air inlet hole  102  for receiving air  48  into fan wheel  42 . Fan blades  98  extend lengthwise between the fan blade&#39;s inner leading edge  104 , near air inlet hole  102 , and an outer trailing edge  106  near an outer diameter  108  of fan wheel  42 . 
         [0046]    In the illustrated example, fan blades  98  and disks  94  and  96  are all made of aluminum sheet metal. To hold fan blades  98  in place, a plurality of sheet metal tabs  110  on fan blades  98  extend into a matching plurality of tab openings  112  in disks  94  and  96 . After tabs  110  are inserted into their corresponding tab openings  112 , tabs  110  are staked or otherwise affixed to disks  94  and  96  to complete the assembly of fan wheel  42 . 
         [0047]    Without careful consideration to the design details of fan wheels  42 , problems may arise. For instance, due to the high speeds and temperatures of HVLP motor-driven fans, the fan blades between the two disks can become distorted during normal operation. Due to the fan blade&#39;s backward inclined orientation, the actual length of the fan blade might be roughly twice the radial distance between the inner diameter of air inlet hole  102  and the outer diameter  108  of disk  94 . So, if the radial distance between the radially outermost tab  110  and the outer diameter  108  of disk  94  is, for example, 0.100 inches, then the fan blade might have a 0.200 inch tail distance (i.e., two times 0.100 inches) extending in a generally unsupported cantilevered manner beyond the fan blade&#39;s outermost tab. 
         [0048]    Surprisingly, in some applications, centrifugal force is sufficient to bend the fan blade&#39;s tail section  114  radially outward. Tail section  114  is that portion of the fan blade that extends over a tail distance  116  generally unsupported between the fan blade&#39;s outermost tab  110  and the disk&#39;s outer diameter  108 . This effect or vane shape change is most likely to occur in high power multistage HVLP applications because of the high air temperatures resulting from the typically small exhaust orifice for these HVLP motor-driven fans. With rotational speeds of 20,000 to 40,000 rpm, the centrifugal force coupled with the high temperatures tends to bend the outer tip of the fan blades. As this happens the fan wheels become unbalanced, thereby causing excessive vibration and early motor/turbine failure. 
         [0049]    To overcome this problem, in some examples, it has been discovered that by decreasing tail distance  116  to no more than about 0.050 inches, blade deflection and resulting vibration is basically eliminated. Reducing tail distance  116  to zero, however, is not feasible because doing so would mean the radially outermost tab opening  112  would “break out” or be open to the disks&#39; outer diameter  108 , thus reducing the strength and integrity of the fan wheel. 
         [0050]    Although reducing tail distance  116  to 0.050 inches or less works well for certain sized motor-driven fans, a suitable value of tail distance  116  can depend on certain other physical dimensions, material properties, and operating conditions of the motor-driven fan. In some examples, tail distance  116  is less than three times a blade material thickness  118  of fan blade  98 . In addition, in some examples, tail distance  116  is such that a blade height  120  of fan blade  98  is at least five times greater than the fan blade&#39;s material thickness  118  and/or at least five times greater than tail distance  116 . 
         [0051]    With HVLP motor-driven fans, the differences in thermal expansion of aluminum and steel parts plus high inertial forces at startup can cause fan wheels  42  and spacers  44  to slip or shift relative to shaft  26  and nut  46 . Such slippage can lead to subsequent vibration and premature failure. However, with consideration of the relative tensile strengths and thermal expansion of steel, aluminum and some polymers, certain part geometries and a polymeric adhesive  122  can be used advantageously to overcome these problems. 
         [0052]    For instance, in some examples, adhesive  122  is applied to rotor  24 , as shown in  FIG. 22 . In this example, adhesive  122  has a coefficient of thermal expansion that is much greater than the steel of shaft  26  and the aluminum of spacers  44  and fan wheels  42 . Adhesive  122  also has a much lower yield tensile strength than that of steel and aluminum. These material properties in combination with certain physical features of spacers  44 , nut  46 , fan blades  42  and shaft  26  securely bond those pieces to each other. 
         [0053]    In the illustrated example, counterbore  80  in spacer  44  creates a cavity  124  ( FIGS. 14, 16 and 17 ) between the spacer&#39;s recessed surface  84  and the substantially planar surface  92  of the fan wheel&#39;s downstream disk  96 . With respect to radial direction  28 , cavity  124  is bound by the spacer&#39;s step  88  and either the outer diameter of shaft  26  ( FIGS. 14 and 16 ) or the area where the spacer&#39;s recess surface  84  might engage the fan wheel&#39;s disk  96  near shaft  26  ( FIG. 17 ). 
         [0054]    In the example where cavity  124  is filled with adhesive  122  and is bound by the outer diameter of shaft  26 , as shown in  FIGS. 14 and 16 , one or more interesting phenomena seem to occur. As rotor  24  heats up during operation, spacer  44  expands radially due to thermal expansion. Adhesive  122  within cavity  124  tries to expand even more due to adhesive  122  having a much higher coefficient of thermal expansion than that of the aluminum spacer  44 . Spacer  44 , however, has a much higher yield tensile strength and is sufficiently strong to restrict the attempted radial outward expansion of adhesive  122 . Thus, adhesive  124  being trapped within the confines of cavity  124  exerts pressure against its bounding surfaces, such as radial pressure against the outer diameter of shaft  26  and axial pressure between spacer  44  and disk  96 . This radial and axial pressure seems to provide a secure holding force between shaft  26  and its adjoining parts, spacer  44  and fan wheel  42 . In examples where adhesive  124  does not take a set within cavity  124 , it is speculated that the relatively fluid or gelatin adhesive  124  provides a dampening effect. 
         [0055]    In addition or alternatively, adhesive  124  is applied to nut  46 . In the example illustrated in  FIG. 22 , nut  46  comprises an integral flange  126  having an axial face  128  that includes a plurality of serrations  130 , which in turn define a plurality of grooves  132 . Partially coating grooves  132  with adhesive  122 , as shown in  FIG. 22 , and/or trapping some adhesive  122  between nut  46  made of steel and an abutting element  134  (e.g., a washer, a spacer, a disk, etc.) made of steel or aluminum with steel shaft  26  extending between nut  46  and element  126  results in thermal expansion possibly causing adhesive  122  to exert axial pressure against nut  46  and element  134 . In some examples, spacers  44  and disks  96  are made of an aluminum alloy having a coefficient of thermal expansion of about 22×10 −6  m/mK and a yield tensile strength of about 35,000 psi, shaft  26  and nut  46  are made of steel having a coefficient of thermal expansion of about 12×10 −6  m/mK and a yield tensile strength of at least 36,000 psi, and adhesive  122  is a LOCTITE 620 having a coefficient of thermal expansion of about 80×10 −6  m/mK and a shear or yield tensile strength of less than 4,000 psi. It should be noted that LOCTITE 620 is just one example of a suitable polymeric adhesive and other example adhesives are well within the scope of the invention. LOCTITE is a registered trademark of Henkel AG &amp; Co. KGaA of Dusseldorf, Germany. 
         [0056]    In some examples, adhesive  122  is disposed within a radial gap  136  between shaft  26  and spacer  44 , as shown in  FIG. 22 . This provides an even more securely bonded rotor assembly. To provide further bonding or radial restraining forces, some examples of fan  10  have adhesive  122  extending radially beyond peripheral rim  86  of spacer  44 . 
         [0057]    Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of the coverage of this patent application is not limited thereto. On the contrary, this patent application covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.