FOR A GAS MOVING DEVICE

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates generally to an improved blade attachment member for a gas moving device, and more particularly, to a heat expansion joint of the blade attachment member which is exposed to thermal transients.

Description of the Related Art

[0002] Mechanical devices used to move fluids, such as gases, are known in the art. Exemplary mechanical devices include fans and blowers having a rotating arrangement of blades or vanes which, upon annular rotation, create a flow of fluid, i.e. gas. There are numerous applications for such fans and blowers including climate control, vehicle and machinery cooling systems, ventilation, fume extraction, drying, etc.

[0003] Common types of fans and blowers (as used herein, the term "fan" includes "blowers" unless otherwise specified) are axial, centrifugal and mixed-flow varieties. Axial fans intake and discharge gases (such as air) parallel to the rotational axis of the blades, which is coaxial with the rotatable drive shaft about which the blades rotate. An exemplary axial fan includes a ceiling fan. Centrifugal fans intake gases (such as air) parallel to the rotational axis of the blades and discharge air radially across the rotational plane of the blades, where the rotational plane is perpendicular to the rotational axis of the blades. Centrifugal fans are typically used in exhaust ventilation systems such as a home furnace or other industrial exhaust applications. Mixed-flow fans intake and discharge air parallel to the rotational axis of the blades, but between the intake and discharge the air traverses radially. Mixed-flow fans are used in industrial ventilation applications where higher pressures are desired within the same cylindrical boundary of the duct carrying the air. In any event, any fan includes an impeller operably attached to a rotatable member, such as a shaft, axle, or hub, where the rotatable member may be driven by a drive source to form a driven rotatable member.

[0004] The impeller for axial and centrifugal fans includes a connecting structure extending between the blades and the rotatable member about which the blades rotate and are operably attached. Such connecting structure is referred to as an attachment member. A conventional attachment member comprises a center plate (also referred to as a back plate in some instances), one end of which operably attaches to a rotatable member (such as by way of a shaft flange, for example) either welded or using fasteners, such as bolts, while the other end of the center plate attaches to the blades. The center plate includes a minimum thickness or varying thickness profile to maintain the integrity of the connection between shaft and the blades during rotation of the shaft. Fasteners used may include high tolerance fasteners, an example of which is a locational fit bolt. A locational fit bolt is known as a "body -bound" or "stripper" bolt with a high tolerance shank and a hole reamed to a high-tolerance. The resulting fit highly controls the relative location of the mating parts. Fastener bore holes are included in each of the shaft flange and the center plate to accommodate the fasteners to secure the center plate, and therefore the impeller, to the shaft flange. In this conventional design, the shaft flange is sufficiently sized to accommodate a single pitch circle of bolts to attach to the center plate. FIG. 3 shows a partial section view of a centrifugal fan as described above according to the prior art. A separate hub may also be used to connect the impeller to the shaft. The hub may be shrunk or secured by setscrews onto the shaft.

[0005] In specific applications, mechanical fans operate in a an environment in which the fan is exposed to thermal transients. Transient thermal analysis determines temperatures and other thermal quantities that vary over time. Thermal transients are generally considered as instantaneous (such as when a damper is opened), but may occur over a longer period of time. Thermal transients are sometimes referred to as rapid thermal transients. The thermal transients include increases or decreases in temperature, i.e. from a low temperature to a high temperature or from a high temperature to a low temperature. During a thermal transient associated with an increasing temperature, the structure of the conventional impeller rapidly increases in temperature due to the impeller's large surface area relative to its mass. In contrast, the shaft has a relatively small surface area to mass ratio, and accordingly the temperature increase of the shaft is much slower. A temperature differential between the impeller and the shaft will exist for several hours until both stabilize at an operating or transient gas temperature. A peak temperature differential will occur at some point during the thermal transient. The temperature differential results in uneven thermal growth of the impeller as compared to the shaft. In this instance, the impeller is increasing in diameter but is restrained at the shaft connection to the much cooler shaft. Radial forces resisting the impeller growth develop in the center plate between the outer portions of the impeller (near the blades) and the connection at the inner portion of the impeller (near the shaft). The connection of the inner portion of the center plate to the shaft is sometimes referred to as the impeller-to-shaft connection.

[0006] For fans exposed to high temperatures and/or thermal transients, the prior art design often exhibits stress levels extending beyond the yield strength and even beyond the tensile strength of the bolts and the bolt bore holes If the impeller is welded to the shaft, the thickness of the connection and the weld may be a concern and may require other parts of the design to be thicker. In a welded impeller-to-shaft connection using a separate hub, a transfer of thermal forces would occur that may cause the impeller-to-shaft connection to expand and potentially become loose (which thereby requires a significantly higher interference fit which increases costs, time an labor). Even below the yield strength and tensile strength limits, fatigue loading associated with starting and stopping or speed changes may demand a lower allowable design stress limit. The conventional solution to stress reduction is to increase the size and number of bolts. However, the prior art design has a minimal and limited area to place these fasteners. Depending upon the number of bolts required, the shaft flange may need to be made larger to increase the diameter of the pitch circle or to add a second pitch circle of bolts. Due to the practical, cost-effective limits of shaft design, if the necessary number of bolts is very high, the addition of a separate hub with a large flange, shrunk on to a shaft having no flange may be necessary. Additionally, or separately, the thickness of the center plate or shaft flange may be increased to withstand the increased stresses associated with high temperature and/or high heat transient conditions.

[0007] These solutions all require increases in material and increases in labor to implement as described below:

1. The additional mass, particularly of a separate installed hub, will have a significant secondary consequence of lowered rotor natural frequencies and thereby will require a larger shaft diameter. The material of a larger flange or hub must also be accounted for as well.

2. A larger flange integral to the shaft necessitates a significant increase in the raw material outer diameter in the area of the flange which must subsequently be machined away.

3. In order to insure the impeller maintains concentricity with the shaft, the bolt holes are usually body-bound requiring precise reaming of the shaft and impeller together as an assembly to ensure no mismatch between the holes and minimal to no clearance between the bolt body outer diameter and the shaft or impeller hole inner diameter. Each additional hole requires setup and machining/reaming time, plus another specialized fastener.

4. Transfer of thermal expansion forces into and through a separate hub shrunk or secured by setscrews onto the shaft will cause the fit between the hub and shaft to loosen. This requires either a higher interference fit or specialized means to prevent loss of contact of the setscrews (or make use of setscrews impracticable). Higher interference fits make removal of the hub potentially impossible without causing damage and run the risk of getting stuck in the wrong position during installation.

[0008] Given these reasons, various advantages may be gained by pursuing a solution that that does not require significant increases in mass or increases in the number of fasteners. Accordingly, there is need for an impeller-to-shaft connection which is less stiff than the conventional design to reduce the stresses occurring during a thermal transient at the location of operable attachment of the impeller to the rotatable member. It is desired that a portion of the attachment member extending between the blade and the location of operable attachment of the impeller to the rotatable member (where the portion is remote from the location of operable attachment) remains deformable or expandable in a thermal transient environment. It is further desired to actually reduce the thickness of the impeller-to-shaft connection to decrease the mass without increasing the number of fasteners.

SUMMARY OF THE INVENTION

[0009] Particular embodiments of the present invention include methods and apparatus for reducing stresses on a gas moving device. Particular embodiments of the present invention include a gas moving device including a fan or blower for directing a gas, said gas moving device comprising: a driven rotatable member having a rotational axis; a plurality of blades arranged radially outward the rotational axis and configured to rotate about the rotational axis of the driven rotatable member, each of the plurality of blades being operably attached to the rotatable driven member by an attachment member, the attachment member comprising: an inner portion proximal said driven rotatable member; an outer portion distal said driven rotatable member; and a stress-reducing expansion joint extending between said outer portion and said inner portion, at least a portion of said expansion joint being non- planar with respect to each of said inner portion and said outer portion. [0010] Particular embodiments of the present invention include an impeller configured for attachment to a driven rotatable member having a rotational axis to be used with a gas moving device, said impeller comprising: a plurality of blades arranged radially outward the rotational axis and configured to rotate about the rotational axis of the driven rotatable member, each of the plurality of blades being operably attached to the rotatable driven member by an attachment member, the attachment member comprising: an inner portion proximal said driven rotatable member; an outer portion distal said driven rotatable member; and a stress-reducing expansion joint extending between said outer portion and said inner portion, at least a portion of said expansion joint being non-planar with respect to each of said inner portion and said outer portion.

[0011] Particular embodiments of the present invention include methods of moving a gas using a gas moving device that include the steps of providing a driven rotatable member having a rotational axis, providing a plurality of blades arranged radially outward the rotational axis and configured to rotate about the rotational axis of the driven rotatable member, each of the plurality of blades being operably attached to the rotatable driven member by an attachment member, the attachment member comprising: an inner portion proximal said driven rotatable member; an outer portion distal said driven rotatable member; and a stress-reducing expansion joint extending between said outer portion and said inner portion, at least a portion of said expansion joint being non-planar with respect to each of said inner portion and said outer portion, rotating the driven rotatable member such that the plurality of blades rotate around the rotational axis, the plurality of blades concurrently discharging gas away from the blades and receiving new gas as the blades rotate; and receiving a change in heat, whereby the expandable joint deforms due to a change in temperature.

[0012] The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a perspective view of a centrifugal fan assembly according the present invention. [0014] FIG. 2 is a front view of the centrifugal fan assembly shown in Fig. 1 including a partial section view of the impeller according to a first embodiment.

[0015] FIG. 3 is a front view of a centrifugal fan assembly including a partial section view of the impeller according to the prior art.

[0016] FIG. 4A is a partial front view of a center plate for use with an impeller according to a second embodiment.

[0017] FIG. 4B is a partial front view of a center plate for use with an impeller according to a third embodiment.

[0018] FIG. 4C is a partial front view of a center plate for use with an impeller according to a fourth embodiment.

[0019] FIG. 4D is a partial front view of a center plate for use with an impeller according to a fifth embodiment.

[0020] FIG. 5 is an enlarged perspective section view of the impeller-to-shaft connection as shown in Fig. 2.

[0021] FIG. 6 is a perspective view of a centrifugal fan assembly as shown in Fig. 1 including a scroll-shaped fan casing.

[0022] FIG. 7 is a front view of an axial fan assembly shown including a partial section view of the shaft according to another embodiment.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0023] Particular embodiments of the present invention provide methods and apparatus for retaining the concentricity of an attachment member with a driven rotatable member during rotation of the driven rotatable member while maintaining the tuned natural frequencies of the same. In particular embodiments, such methods and apparatus inhibit the plastic (permanent) deformation of the fasteners or the fastener bore holes at the connection of the attachment member to the driven rotatable member.

[0024] Such methods may comprise methods for reducing stresses on a gas moving device, which may comprise a variety of steps. In particular embodiments, such methods include the steps of providing a driven rotatable member having a rotational axis; providing a plurality of blades arranged radially outward the rotational axis and configured to rotate about the rotational axis of the driven rotatable member, each of the plurality of blades being operably attached to the rotatable driven member by an attachment member, the attachment member comprising: an inner portion proximal said driven rotatable member; an outer portion distal said driven rotatable member; and a stress-reducing expansion joint extending between said outer portion and said inner portion, at least a portion of said expansion joint being non-planar with respect to each of said inner portion and said outer portion; rotating the driven rotatable member such that the plurality of blades rotate around the rotational axis, the plurality of blades concurrently discharging gas away from the blades and receiving new gas as the blades rotate; and receiving a change in heat, whereby the expandable joint deforms due to a change in temperature.

[0025] In the above described method, the change in heat may be received with the new gas, the new gas being received from a gas source. Additionally, the change may be received by convection or radiation heat transfer, and may be received from a heat source. The expandable joint may expand or contract depending the heat transfer or thermal transient.

[0026] It has been found that the magnitude of force transmitted through the attachment member to the connection of the attachment member to the driven rotatable member is strictly a function of the stiffness of the rotatable driven member. In the prior art design of a centrifugal fan assembly illustrated in FIG. 3, all force transmission occurs through a homogenous flat plate 21 wherein the stiffness is defined predominantly by the modulus of elasticity and the thickness. These forces cause localized stress increases in the impeller-to- shaft connection. During a thermal transient where the temperature is increasing, the stresses in the impeller-to-shaft connection can reach levels where plastic (permanent) deformation of the fasteners or the fastener bore holes occur. This may result in the impeller no longer being concentric to the shaft and ultimately failure of the impeller-to-shaft connection.

[0027] Further steps of such methods may include the step of injecting an influx of heated gas from a heat source to the gas moving device. Gas moving devices may operate in a high temperature environment and/or be exposed to thermal transients. It has been found that once a thermal transient reaches approximately 100-150 degrees Fahrenheit, the prior art design shown in FIG. 3 would need to be bolstered by increasing the mass of the design or including additional fasteners. Once the temperature achieves 200-250 degrees Fahrenheit, the prior art design would begin to exhibit overstress issues. Thermal transients may be well above 250 degrees Fahrenheit. As previously stated, thermal transients are generally considered as instantaneous (such as when a damper is opened), but even if the temperature change occurs over an hour, or a potentially longer period of time, the effect of the transient continues to require assessment and features to mitigate it. Therefore, the present invention is applicable to both situations, i.e. when the thermal transient is instantaneous and when the thermal transient occurs over a longer period of time.

[0028] Further steps of such methods may include the step of providing a attachment member comprising an inner portion proximal the driven rotatable member, an outer portion distal the driven rotatable member and an expansion joint extending between the outer portion and the inner portion, the expansion joint being non-planar with respect to at least one of the inner portion and the outer portion. Providing the expansion joint being non-planar with respect to the inner portion, the outer portion or both introduces the additional parameters of shape, depth and angle in addition to the modulus of elasticity and thickness which reduces the radial stiffness of the attachment member.

[0029] The above described methods may be used with the following apparatus in a number or specific embodiments.

[0030] Gas moving devices for directing a gas can be used for many different applications including climate control, vehicle and machinery cooling systems, ventilation, fume extraction, drying, etc. Such devices may be referred to as air flowing devices, air circulating devices or air moving devices. Exemplary devices include fans. More specifically, these fans may be described as centrifugal or axial which refers to the direction of the flow imparted by the fan as previously discussed.

[0031] A driven rotatable member having a rotational axis a drives the rotation of the gas moving device. The rotational axis can be concentric with the driven rotatable member. Examples of driven rotatable members may include shafts. The driven rotatable member may also be a hub. The hub may attach to another driven member or drive source. However, it is contemplated that the driven rotatable member may have a cross section other than a circle. Such additional cross sectional shapes may include square, rectangular, triangular, elliptical or some other type of polygonal or curvilinear configuration.

[0032] The gas moving device includes a plurality of blades arranged radially out the rotational axis and is configured to rotate about the rotational axis the least one rotating member for directing the gas. Typically, the plurality of blades are also known as vanes, airfoils or wings. These blades can have many types of configurations depending on the specific application. For example, the blades may be forward curved, backward curved or have any type of configuration to produce an aerodynamic effect.

[0033] An attachment member operatively connects the driven rotatable member to the plurality of blades. The attachment member may be in the form of a plate which extends radially from the driven rotatable member and is sometimes referred to as a center plate or back plate, which may be annular. However, the center pate or back plate may have other geometric shapes which are not round. Additionally, the attachment member does not have to be plate-like in structure. For example, the attachment member may include a plurality of separate members where each extends radially from the shaft not in the form of an annulus. The combination of the attachment member and the plurality of blades is also known as an impeller.

[0034] The attachment member includes an inner portion, an outer portion and an expansion joint extending between the inner portion and the outer portion. The inner portion of the attachment member operatively connects to the driven rotatable member or shaft. If fasteners are used for this connection, the driven rotatable member may include a connecting structure or flange, hereinafter referred to as a shaft flange. The shaft flange may be integral with the driven rotatable member, i.e. it can be a one-piece construction. Of course the shaft flange can be separate from the driven rotatable member and may be heat shrunk to the driven rotatable member. Shaft flange extends radially outward from the driven rotatable member and includes a plurality of openings for accommodating fasteners. The openings may be circumferentially spaced around the shaft flange, and the shaft flange may be concentric. Alternatively, the openings may be spaced in any number of patterns on the shaft flange for securing the shaft flange to the inner portion of the attachment member. Since the inner portion is secured to the shaft flange, the inner portion itself may be a flange and is sometimes referred to as an impeller flange. The inner portion includes a plurality of openings corresponding to the plurality of openings in the shaft flange. In other words, the respective plurality of openings axially align to allow a fastener, such as a bolt, to pass therethrough. It is contemplated that the respective plurality of openings may be holes, slots, bores or some other type of openings known in the art for accommodating fasteners.

[0035] An optional separate connecting structure or hub ring may be connected to the shaft flange and the rotatable attachment member to further secure the same. The hub ring, if used, would also include a plurality of openings corresponding to the respective plurality of openings in the shaft flange and in the inner portion to accommodate a fastener. The combination of the shaft flange and the hub ring is sometimes referred to as a hub assembly. When attaching the attachment member to the shaft flange, the inner portion is inserted or sandwiched between the shaft flange and the hub ring such that the respective plurality of openings are axially aligned to allow fasteners to pass therethrough.

[0036] The use of bolts may be desired when the rotatable attachment member, the shaft flange and the optional hub ring comprise dissimilar materials. Rather than using fasteners to secure the rotatable attachment member to the hub assembly, another option may be the use of welding. In this instance, the respective plurality of holes described above would be unnecessary as the rotatable attachment member, the shaft flange and optionally the hub ring would be welded together. Welding would be an option if the rotatable attachment member, the shaft flange and optionally the hub ring all comprised the same material, although the welding of dissimilar materials is also possible. Additionally, shaft flange may not be necessary as the rotatable attachment member may be directly welded to the driven rotatable member or shaft.

[0037] Attachment member also includes an outer portion which operatively connects to the plurality of blades in any known manner such as by welding or by fasteners, for example.

[0038] A stress-reducing expansion joint extends between the inner portion and the outer portion of the attachment member. At least a portion of the expansion joint is non-planar (out-of-plane) with respect to each of the inner portion and the outer portion. The expansion joint reduces stresses occurring at the inner portion and the shaft flange (or the driven rotatable member if no shaft flange exists) during rotation of the driven rotatable member during a thermal transient. The connection of the inner portion of the attachment member to either the driven rotatable member or the shaft flange is sometimes referred to as the impeller-to-shaft connection. The reduction in the stresses occurring at this connection will be described in more detail later in the application.

[0039] The expansion member extending between the inner portion and the outer portion may comprise any number of orientations where at least a portion of the expansion joint is non-planar with respect to each of the inner portion and the outer portion. It may also be described in such a way where the expansion member is non-planar with respect to each of the inner portion and the outer portion as the attachment member extends radially outward from the driven rotatable member. It could also be stated that attachment member extends radially outward of the driven rotatable member or shaft along a non-planar path. Additionally, the inner portion and the outer portion of the attachment member may be co- planar (and parallel) or the inner portion and the outer portion may be parallel but not co- planar. In the scenario where the inner portion and the outer portion are co-planar (and parallel) and the expansion member is non-planar with respect to both the inner portion and the outer portion, this may be referred to as a staggered configuration. In the scenario where the inner portion and the outer portion are parallel but not co-planar and the expansion member is non-planar with respect to either the inner portion, the outer portion or both, this may be referred to as an offset configuration.

[0040] The expansion joint may be angled or inclined between the inner portion and the outer portion. This configuration can also be described in a two-dimensional plane having an x-axis and a y-axis, where the driven rotatable member includes an axis about which it rotates which is co-linear with the y-axis. The inner portion and the outer portion of the attachment member would be parallel and possibly co-linear to the x-axis depending on whether the configuration was staggered or offset. If the expansion joint is angled or inclined between the inner portion and the outer portion, the expansion joint would include a vector component in the x-axis direction and a vector component in the y-axis direction in the two-dimensional plane. The expansion joint may include any orientation in which the expansion joint includes a vector component in the y-axis direction in the two-dimensional plane. Stated another way, the expansion joint is non-linear with respect either the inner portion, the outer portion or both in the two-dimensional plane. The expansion joint may also include multiple sections, where at least one section of the expansion joint includes a vector component in the y-axis direction in the two-dimensional plane. Therefore, it is possible for one section of the expansion joint to be parallel to either the inner portion, the outer portion or both as long as at least another section of the expansion joint includes a vector component in the y-axis direction in the two-dimensional plane. Recited another way, at least one section of the expansion joint is non-linear with respect either the inner portion, the outer portion or both in the two-dimensional plane. Stated yet another way, the expansion member may follow any non-linear path between the inner portion and the outer portion in the two-dimensional plane. This non-linear path may be referred to as a stepped path. The stepped path may be generally V-shaped, U-shaped, Z-shaped, for example. It is also contemplated that the non-linear path may comprise curvilinear or wave-like sections. For example, a wave-like configuration that connects the inner portion to the outer portion may be sinusoidal or parabolic. [0041] The expansion joint may be manufactured by known methods such as forming or welding where multiple plates are spliced together to form a sheet of sufficient size. The expansion joint is not limited by any specific dimensions except that it should not detrimentally affect gas flow via blockage.

[0042] The following description refers to several preferred embodiments of a new inventive design as compared to the prior art design. Analysis was conducted on one of the new inventive designs and compared to the prior art design as detailed later in this application. The testing concluded that the inventive design far outperformed the prior art design in reducing stresses during the thermal transient. The specific preferred embodiments will now be described below.

[0043] With reference to FIG. 1, a perspective view of a centrifugal fan assembly 10 is shown. The centrifugal fan assembly 10 includes a drive shaft 12 having a shaft flange 14 near the midpoint of the shaft 12. The centrifugal fan assembly 10 also includes a blade housing 16 for housing fan blades 18. A scroll-shaped fan casing 19 encloses the blade housing 16 as shown in FIG. 6. The fan casing 19 includes an inlet 17 and an outlet 21 for expelling the gas perpendicularly from the shaft 12. Fan blades 18 are mounted to a fan plate or center plate 20 at an outer portion 22 of the center plate 20 as seen in FIG. 2 (and hidden from view in FIG. 1). A drive motor 23 is attached to one end of the shaft.

[0044] The center plate 20 comprises two concentric portions (the outer portion 22 and an inner portion 24) and a expansion joint 26 therebetween. The expansion joint 26 is non- planar with respect to both the inner portion 24 and the outer portion 22. The inner portion 24 is proximal the shaft 12 and distal the fan blades 18. On the other hand, the outer portion 22 is proximal the fan blades 18 and distal the shaft 12.

[0045] The centrifugal fan assembly 10 includes a hub assembly 30 for securing the center plate 20 to the shaft 12. The hub assembly 30 comprises the shaft flange 14 and an opposing hub ring 32. The shaft flange 14 is integral with the shaft 12 while the opposing hub ring 32 is separate from the shaft 12. The center plate 20 attaches to the hub assembly 30 by inserting the inner portion 24 between the shaft flange 14 and the hub ring 32 as further described below and as shown in FIG. 5.

[0046] Shaft flange 14 includes a plurality of holes 34 each having an axis circumferentially spaced around the shaft flange 14. Similarly, a plurality of holes 36 each having an axis is also positioned circumferentially around hub ring 32. Lastly, another plurality of holes 38 each having an axis is circumferentially spaced around the inner portion 24 of center plate 20. When attaching the center plate 20 to the hub assembly 30, the inner portion 24 is inserted between the shaft flange 14 and the hub ring 32 such that the plurality of holes 34, 36 and 38 are axially aligned to allow fasteners 39 to pass therethrough. FIG. 5 shows an enlarged perspective section view of this impeller-to-shaft attachment. Various embodiments of the non-planar relationship between the inner portion 24, the outer portion 22 and the expansion joint 26 will now be described.

[0047] With reference to FIG. 2, the center plate 20 extends radially away from shaft 12 on different planes, where the inner portion 24, the outer portion 22 or both are non-planar with respect to the expansion joint 26. Additionally, the inner portion 24 is non-planar from the outer portion 22. That is, in the partial section view shown in FIG. 2 showing a plane having an x-axis and a y-axis (hereinafter the xy plane), the inner portion 24 and the outer portion 22 are parallel but not co-linear. This configuration where the inner portion 24 and the outer portion 22 are parallel but not co-linear in the xy plane can also be described as an offset configuration. The expansion joint 26 is angled or inclined between the inner portion 24 and the outer portion 22. Therefore, the expansion joint 26 is non-linear with respect to both the inner portion 24 and the outer portion 22 in the xy plane. Stated another way, the expansion joint 26 includes a y-axis vector component parallel to the y-axis as shown in FIG. 2.

[0048] Referring to FIG. 4A, another offset configuration is shown where the inner portion 24 and the outer portion 22 are parallel but not co-linear in the xy plane in the partial front view presented. In this embodiment, however, an expansion joint 126 is substantially perpendicular to both the inner portion 24 and the outer portion 22. Again, the expansion joint 126 is non-linear with respect to both the inner portion 24 and the outer portion 22 in the xy plane. Stated another way, the expansion joint 126 only includes a y-axis vector component parallel to the y-axis in the xy plane. A hole 38 for accommodating a fastener is shown in the inner portion 24.

[0049] Another example of a staggered configuration between the inner portion 24 and the outer portion 22 is shown in FIG. 4B. This configuration may be referred to as a Z- shaped configuration. In this embodiment, an expansion joint 326 includes a first angled or inclined member 228, a second angled or inclined member 230 and a third angled or inclined member 232. The first angled member 228 and the third angled member 232 are substantially parallel to one another in the xy plane, and the second angled member 230 connects the first angled member 328 and the third angled member 332. The first angled member 328 and the second angled member 330 connect at a first spine 334. The second angled member 330 and the third angled member 332 connect at a second spine 336. Although the first angled member 328 and the third angled member 332 are substantially parallel to each other, it is contemplated that such members may not be parallel. Again, the first angled member 328, the second angled member 330 and the third angled member 332 are non-linear with respect to both the inner portion 24 and the outer portion 24 in the xy plane. Stated another way, the first angled member 228 and the second angled member 230 both include a y-axis vector component parallel to the y-axis in the xy plane as shown in FIG. 4B. A hole 38 for accommodating a fastener is shown in the inner portion 24.

[0050] Still another non-linear relationship between the inner portion 24 and the outer portion 22 is shown in FIG. 4C in the xy plane. In the partial front view shown in FIG. 4C, the inner portion 24 and the outer portion 22 are co-linear (and parallel) in the xy plane, i.e. a staggered configuration is displayed. An expansion joint 326 includes a V-shaped configuration with a first angled or inclined member 328 and a second angled or inclined member 330 meeting at a spine 332. Both the first angled member 328 and the second angled member 330 are non-linear with respect to both the inner portion 24 and the outer portion 22 in the xy plane. Stated another way, the first angled member 328 and the second angled member 330 both include a y-axis vector component parallel to the y-axis in the xy plane as shown in FIG. 4C. A hole 38 for accommodating a fastener is shown in the inner portion 24.

[0051] With respect to FIG. 4D, still another embodiment of a staggered configuration between the inner portion 24 and the outer portion 22 is shown. An expansion joint 426 includes a U-shaped configuration including a first member 428, a second member 430 and a third member 432. The first member 428 connects to and is substantially perpendicular to the inner portion 24 and the third member 432 connects to and is substantially perpendicular to the outer portion 22. The second member 430 connects the first member 428 and the third member 432 as shown in FIG. 4D. The second member 430 is parallel to, but not co-linear with, the inner portion 24 and the outer portion 22 in the xy plane. Thus, second member 430 is perpendicular to both first member 428 and third member 432. In this embodiment, the first member 428 and the third member 432 are non-linear with respect to both the inner portion 24 and the outer portion 22 in the xy plane. Stated another way, the first member 428 and the third member 432 both include a y-axis vector component parallel to the y-axis in the xy plane as shown in FIG. 4D. A hole 38 for accommodating a fastener is shown in the inner portion 24.

[0052] Although the above described specific embodiments may be used with new equipment (i.e. new impeller and shaft designs), a number of the specific embodiments may be used as retrofit devices for existing equipment (i.e. existing impeller and shaft designs). For example, the staggered embodiments shown in FIGS. 4B, 4C and 4D can be retrofit to existing equipment since the respective inner portions and outer portions are co-linear (and parallel) and would attach to the shaft flange without any offset as is done in the prior art design of FIG. 2.

[0053] The previous embodiments illustrated in FIGS. 1-6 have been applicable to centrifugal fans. However, it is contemplated that the present invention may be used with axial and mixed flow fans. FIG. 7 displays an axial fan having blades 18 which direct air parallel to the shaft 12 (i.e. in the direction of the arrow shown). A center plate 20 is the same center plate as described above with respect to FIG. 2, and includes the inner portion 24, the outer portion 22 and the expansion joint 26. The axial fan in FIG. 7 also includes the same shaft flange 14, hub ring 32 and fasteners 39 as shown in FIG. 2.

[0054] A finite element analysis was conducted on the prior art centrifugal fan assembly shown in FIG. 3 and the inventive centrifugal fan assembly shown in FIG. 2 to evaluate the differences in their mechanical performance. All of the impeller materials for both designs were identical. Similarly, the bolts used in both designs were also identical material. The shaft material for both designs was also the same and the clamping disc material was identical as well. The mechanical performance between the two designs was evaluated based on the stress levels in the results and based on the ability of the impeller-to-shaft connection to remain deformable or expandable through a flue gas thermal transient.

[0055] The prior art fan assembly and the inventive fan assembly were analyzed at 900 rpm under a normal operating temperature of 350 degrees Fahrenheit. A thermal transient or excursion (increase in the flue gas temperature) was introduced instantaneously to 650 degrees Fahrenheit constituting a rise in temperature of 300 degrees Fahrenheit. The thermal transient or excursion was limited to 30 minutes. The peak temperature differentials occurred at approximately 1,800 seconds after the start of the thermal transient.

[0056] Stresses and deflection were calculated at critical components of the prior art design and the inventive design. The maximum principle stress at the bore holes of the shaft flange was found to be approximately 25% less in the inventive design than the prior art design. The maximum principle stress at the bore holes of the inner portion (impeller flange) was found to be approximately 72% less in the inventive design than the prior art design. The maximum principle stress of the bolt shank was found to be approximately 48% less in the inventive design than in the prior art design. The maximum principle stress in the bolt head was found to be approximately 42% less in the inventive design than in the prior art design. Lastly, the radial to centerline stiffness of the center plate in the inventive design was found to be approximately 76% less in the inventive design than in the prior art design. Thus, the inventive design has approximately ¼ the stiffness of the prior art design.

[0057] The prior art design was found to be not workable due to a stress level above yield in the fasteners. The inventive design provided a reduction in stress of at least 42% in the fasteners which made the design workable. In other words, the testing conducted shows that the stress around the bore holes has been reduced and moved away from the bore holes and closer to the expansion joint which is able to absorb these stresses. It has been found that the stress levels remain in the deformable or expandable range for the material in the inventive design and at these low levels, low cycle fatigue will not be an issue.

[0058] In comparing the prior art design and the inventive design, it has been found that the magnitude of force transmitted through the center plate to the shaft connection is strictly a function of the stiffness of the center plate. In the prior art design, all of the force transmission occurred through the homogenous flat center plate wherein the stiffness is defined predominantly by the modulus of elasticity and the thickness. In the inventive design, the expansion joint of the center plate introduces to the center plate stiffness the additional parameters of shape, depth and angle in addition to the modulus of elasticity and the thickness. The result of the latter is a center plate design that is significantly less stiff radially than the prior art design. It has been found that the inventive center plate configuration continues to perform its fundamental duties of keeping the impeller concentric to the shaft and allowing for properly tuned natural frequencies.

[0059] Although the above-described embodiments include an expansion joint located closer to the shaft than to the blades, it is contemplated that the expansion joint may be further away from or isolated from the shaft. Additionally, more than one expansion joint may be included as part of the center plate, where each additional expansion joint may extend radially further from the shaft than the previous expansion joint. [0060] The present invention may be utilized in association with any type of gas moving device having blade members for directing a gas where the rotary device is exposed to thermal transients. Centrifugal and axial fans may be more of the common applications for the present invention but it is contemplated that blowers are applicable as well. Some of the specific types fans which are exposed to thermal transients include induced draft fans, induced booster draft fans, gas recirculation fans, clinker cooler fans, raw mill fans, hot primary air fans, mill induced draft fans, kiln induced draft fans, furnace plug fans and preheater fans. Most of the above recited fans are used in the utility and cement industries, and there can be many additional specific names depending on the industry involved. Therefore, the above recited list is for exemplary purposes only and is not meant to be exhaustive.

[0061] The terms "comprising," "including," and "having," as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms "at least one" and "one or more" are used interchangeably. The term "single" shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as "two," are used when a specific number of things is intended. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (i.e., not required) feature of the invention. Ranges that are described as being "between a and b" are inclusive of the values for "a" and "b" unless otherwise specified.

[0062] While this invention has been described with reference to particular embodiments thereof, it shall be understood that such description is by way of illustration only and should not be construed as limiting the scope of the claimed invention. Accordingly, the scope and content of the invention are to be defined only by the terms of the following claims. Furthermore, it is understood that the features of any specific embodiment discussed herein may be combined with one or more features of any one or more embodiments otherwise discussed or contemplated herein unless otherwise stated.