Patent Publication Number: US-2015059183-A1

Title: Method of removing a bearing from a shaft

Description:
BACKGROUND OF THE INVENTION 
     The method described herein relates generally to bearing removal. More specifically, the method relates to cooling a shaft from the inside to remove a bearing, without causing damage to the bearing. 
     In a typical wind turbine gearbox repair, bearings are removed from shafts by heating the inner race of the bearing rapidly with a torch (e.g., an oxy-acethylene type torch). Bearings are often attached to shafts by an interference fit or heat shrink fit. The heating expands the inner race and temporarily turns the interference fit into a loose fit, thus allowing the removal of the bearing. This is common practice and was previously acceptable since the bearings were not being reused but simply scrapped and replaced by new ones. Many modern wind turbines have parts that can be refurbished and reused, so disposing of potentially reusable parts is wasteful and economically disadvantageous. 
     The use of any type of fuel gas torch device precludes the removed bearings from being reused since their metal&#39;s grain structure will most likely have been negatively affected. A bearing, such as a main shaft bearing in a wind turbine, is an expensive and robustly made part that could be reconditioned by the original equipment manufacturer (OEM) or a qualified shop for a fraction of the cost of a new part. Applying the commonly used removal processes as described above renders an otherwise perfectly good core useless. Furthermore, applying intense heat to localized areas will never achieve a uniform distribution and may make the use of a large bearing pulling device necessary. This approach harbors the risk of rolling a burr and scoring the softer surface of the shaft which now would have to be reconditioned as well. The currently known methods of removing a bearing from a shaft result in damage to, and the disposal of, the bearing and possibly the shaft. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an aspect of the present invention, a method of removing a part from a shaft is provided. The part is attached to the shaft with an interference fit. The method includes the steps of, inserting an expandable plug into the shaft, and adding coolant to an interior of the shaft. The coolant cools the shaft from the interior of the shaft to an exterior of the shaft. Another step removes the part from the shaft. The part is removed from the shaft without sustaining damage to either the part or the shaft, so that the part and the shaft may be refurbished or reused. 
     In another aspect of the present invention, a method of removing a bearing from a main shaft is provided. The bearing is attached to the main shaft with an interference fit, and both the bearing and main shaft are parts of a wind turbine. The method includes the steps of, inserting an expandable plug into the main shaft, and adding coolant to an interior of the main shaft. The coolant cools the main shaft from the interior of the main shaft to an exterior of the main shaft. A removing step removes the bearing from the main shaft. The bearing is removed from the main shaft by transforming the interference fit into a loose fit, and without sustaining damage to either the bearing or the main shaft, so that the bearing and the main shaft may be refurbished or reused. 
     In yet another aspect of the present invention, a method of removing a bearing from a main shaft is provided. The bearing is attached to the main shaft with an interference fit, and both the bearing and main shaft are parts of a wind turbine. The method includes the steps of, orienting the bearing and the main shaft substantially vertically, inserting an expandable plug into the main shaft, and adding coolant to an interior of the main shaft. The coolant cools the main shaft from the interior of the main shaft to an exterior of the shaft. Another step is used for removing the bearing from the main shaft. The bearing is removed from the main shaft by transforming the interference fit into a loose fit, and without sustaining damage to either the bearing or the main shaft, so that the bearing and the main shaft may be (or are) refurbished and/or reused. Additional steps may include monitoring a level of the coolant and adding additional coolant if the level of the coolant drops more than a predetermined amount, monitoring a temperature of the main shaft, or applying heat to the bearing, where the heat is applied at a level to avoid damage to the bearing. The coolant is at least one of liquid nitrogen, dry ice/acetone, dry ice/isopropanol alcohol, butyl acetate/dry ice, propyl amine/dry ice, ethyl ether/dry ice, ethyl acetate/LN2, n-butanol/LN2, hexane/LN2, acetone/LN2, toluene/LN2, or methanol/LN2. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective illustration of an exemplary wind turbine; 
         FIG. 2  is a partially cut-away perspective illustration of a portion of the wind turbine shown in  FIG. 1 ; 
         FIG. 3  illustrates a main shaft bearing mounted on the main shaft; 
         FIG. 4  illustrates a main shaft bearing and main shaft positioned for a removal method, according to an aspect of the present invention; and 
         FIG. 5  illustrates a flowchart for a method for removing a bearing from a shaft, according to an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more specific aspects/embodiments of the present invention will be described below. In an effort to provide a concise description of these aspects/embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with machine-related, system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. Additionally, it should be understood that references to “one embodiment”, “one aspect” or “an embodiment” or “an aspect” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments or aspects that also incorporate the recited features. 
       FIG. 1  is a perspective view of an exemplary wind turbine  10 . Wind turbine  10  described and illustrated herein is a wind generator for generating electrical power from wind energy. Wind turbine  10  described and illustrated herein includes a horizontal-axis configuration. In some known wind turbines, wind turbine  10  includes a vertical-axis configuration (not shown). Wind turbine  10  may be coupled to an electrical load (not shown), such as, but not limited to, a power grid (not shown), and may receive electrical power therefrom to drive operation of wind turbine  10  and/or its associated components and/or may supply electrical power generated by wind turbine  10 . Although only one wind turbine  10  is shown in  FIGS. 1-2 , in some embodiments a plurality of wind turbines  10  are grouped together, to form a “wind farm”. 
     Wind turbine  10  includes a nacelle  12 , and a rotor (generally designated by  14 ) coupled to body  12  for rotation with respect to body  12  about an axis of rotation  16 . In the exemplary embodiment, nacelle  12  is mounted on a tower  18 . The height of tower  18  is any suitable height enabling wind turbine  10  to function as described herein. Rotor  14  includes a hub  20  and a plurality of blades  22  (sometimes referred to as “airfoils”) extending radially outwardly from hub  20  for converting wind energy into rotational energy. Although rotor  14  is described and illustrated herein as having three blades  22 , rotor  14  may include any number of blades  22 . The blades are mounted to a hub flange  80  and each blade is pitched by pitch motor  24 . 
       FIG. 2  is a partially cut-away perspective view of a portion of the exemplary wind turbine  10 . Wind turbine  10  includes an electrical generator  26  coupled to rotor  14  for generating electrical power from the rotational energy generated by rotor  14 . Generator  26  is any suitable type of electrical generator, such as, but not limited to, a wound rotor induction or permanent magnet generator. Rotor  14  includes a low speed rotor shaft  28  (or main shaft) coupled to rotor hub  20  for rotation therewith. The main shaft  28  is typically supported by one or more main shaft bearings  50 . The bearing are mounted to bedplate  52 . Generator  26  is coupled to a high speed rotor shaft  30  such that rotation of rotor shaft  28  drives rotation of the generator rotor, and therefore operation of generator  26 . In the exemplary embodiment, high speed rotor shaft  30  is coupled to low speed shaft  28  through a gearbox  32 , although in other embodiments generator rotor shaft  30  is coupled directly to rotor shaft  28 . The rotation of rotor  14  drives the generator rotor to thereby generate variable frequency AC electrical power from rotation of rotor  14 . 
     In some embodiments, wind turbine  10  includes a brake system (not shown) for braking rotation of rotor  14 . Furthermore, in some embodiments, wind turbine  10  includes a yaw system  40  for rotating nacelle  12  about an axis of rotation  42  to change a yaw of rotor  14 . Yaw system  40  is coupled to and controlled by a control system(s)  44 . In some embodiments, wind turbine  10  includes anemometry  46  for measuring wind speed and/or wind direction. Anemometry  46  is coupled to control system(s)  44  for sending measurements to control system(s)  44  for processing thereof. In the exemplary embodiment, control system(s)  44  is mounted within nacelle  12 . Alternatively, one or more control systems  44  may be remote from nacelle  12  and/or other components of wind turbine  10 . Control system(s)  44  may be used for, but is not limited to, overall system monitoring and control including, for example, pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application, and/or fault monitoring. Alternative distributed or centralized control architectures may be used in some embodiments. 
       FIG. 3  illustrates a main shaft bearing  50  mounted on the main shaft  28  (shown in phantom). As mentioned previously, the main shaft bearing  50  is attached to the main shaft  28  with an interference fit. The bearing  50  is a robustly made part and it can be refurbished and reused. However, heating of the bearing  50  may adversely affect the metal&#39;s grain structure, and the heat removal method turns a reusable part into a scrap part. 
       FIG. 4  illustrates a main shaft bearing  50  and main shaft  28  positioned for a removal method, according to an aspect of the present invention. The main shaft  28  may be positioned up-right and suspended in a rack (not shown) to prevent it from tipping over. The large flange  51  is facing upwards. An expandable plug  410  is inserted into the through hole  429  of the main shaft  28  and positioned at a depth corresponding to the position of the bearing seat on the outside of the main-shaft  28 . The expandable plug  410  may be comprised of any suitable polymeric material, natural or synthetic material, or any other suitable insulating and expandable material. The expandable plug  410  can be inserted in a non-expanded state, and then inflated to seal the through hole  429 . 
     The area of the main shaft  28  to be cooled is indicated by numeral  430 . The upper part of the through hole  429  may then be filled with a coolant  420 , such as liquid Nitrogen (LN 2 ). The evaporating coolant  420  withdraws heat from the main shaft  28  from the inside out, thus causing it to shrink. A steady trickle of coolant  420  into the through hole  429  will keep the coolant level nearly to the top thereby maximizing the cooling effect. During the cooling process, the surface temperature of the main shaft  28  may be monitored. If a noticeable temperature drop has occurred, mild force onto the main bearing  50  housing in the downwards direction may be applied. Optionally, a heating blanket (not shown) may placed on or around the bearing  50  to keep the bearing  50  from cooling down as well, which would negate the cooling efforts. Once the proper heat differential has been reached, the bearing  50  will drop off the main shaft  28 . 
     The coolant  420  may be LN 2  and this coolant is sufficient to cool the main shaft in region  430 . However, LN 2  may suffer from the Leidenfrost effect, which is a phenomenon where liquid, in contact with a surface significantly hotter than the liquid&#39;s boiling point, produces an insulating vapor layer, that keeps the liquid from boiling rapidly. The Leidenfrost effect, when experienced by LN 2 , may extend the exposure time needed to obtain a desired temperature differential between the main shaft  28  in region  430  and the bearing  50 . Other coolants that may be less susceptible to the Leidenfrost effect may include mixes of dry ice (solid CO 2 ) and acetone or isopropanol alcohol. These mixes remain fluid during the cooling process and the fluid increases the heat transfer (or cooling) rate. Additional coolant mixes may also include butyl acetate/dry ice, propyl amine/dry ice, ethyl ether/dry ice, ethyl acetate/LN 2 , n-butanol/LN 2 , hexane/LN 2 , acetone/LN 2 , toluene/LN 2 , and methanol/LN 2 , or any other suitable coolant mixture. 
       FIG. 5  illustrates a flowchart for a method  500  for removing a bearing  50  (or a part) from a shaft  28 , according to an aspect of the present invention. The method  500  includes the steps of orienting (step  510 ) the part  50  and the shaft  28  substantially vertically. The shaft could be oriented in non-vertical directions, as long as the coolant  420  can be kept in the target region  430  within shaft  28 . Step  520  inserts an expandable plug  410  into the shaft  28 , and preferably into through hole  429 . The expandable plug  410  may be located at one end of region  430 . Step  530  adds coolant  420  to an interior of shaft  28 , and preferably into the through hole  429 . As mentioned previously, the coolant may be liquid nitrogen, dry ice/acetone, dry ice/isopropanol alcohol, or any other suitable coolant. The expandable plug  410  prevents the coolant from leaking past the expandable plug  410 . The coolant  420  cools the shaft  28 , specifically in region  430 , from the inside out (i.e., from the interior of the shaft  28  to the exterior or surface of shaft  28 ). 
     Step  540  monitors the level of the coolant  420 , as the coolant will evaporate over time. When too much of the coolant  420  evaporates or the coolant  420  level drops more than a predetermined amount, more coolant  420  can be added by repeating step  530 . The temperature of the shaft  28  or bearing seat can be monitored in step  550 . Optionally, the temperature of the bearing  50  may also be monitored. When a predetermined temperature differential between the shaft  28  and part  50  exists, the interference fit is changed to a loose fit, and the part  50  can be removed. Optionally, step  560  can be used to apply heat to the part or bearing  50 . This heat may be applied with a heating blanket or other mild heat source. The important thing is to avoid applying too much heat, so that damage to the bearing  50  is avoided. A final step  570  removes the bearing  50  (or part) from the shaft  28 , and this occurs when the interference fit has been transformed into a loose fit. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.