Abstract:
A steady bearing for supporting an end of an impeller shaft with respect to a mixer vessel wall, includes a downwardly projecting cylindrical hollow sleeve mounted to the end of the shaft and projecting away from the end of the shaft, an upwardly projecting bearing holder mounted to the bottom of the vessel wall and projecting upwardly inside part of the hollow portion of the sleeve, and a roller bearing assembly mounted in between the bearing holder and the sleeve.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention pertains generally to the field of mixing assemblies and related bearings. More particularly, the invention relates to steady bearings used to provide support to a mixer impeller shaft with respect to a mixer vessel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Industrial mixers are in wide use. In general, many of these mixers include a vessel that contains a material to be mixed or agitated. Projecting into the vessel is a shaft having radially extending impellers or paddles. Sometimes the shaft is supported from the top of the vessel and driven by a motor located at the top of the vessel. The shaft extends downwardly and in some instances simply has a free hanging lower end spaced apart from the bottom of the vessel. In the case of long shafts and shafts that extend all the way down to very near the bottom of the vessel, a so-called “steady bearing” is sometimes used. The steady bearing is an assembly that connects the rotating lower tip of the shaft to the bottom of the mixer vessel. Steady bearings are known that use an intermediate sliding friction bushing. 
         [0003]    One example of a steady bearing for the bottom tip of a mixer impeller shaft is a type of bearing that uses a sleeve-type bushing that has a frictional rotational sliding contact interposed between a rotating part connected to the bottom end of the shaft and a stationary part connected to the bottom of the vessel. 
         [0004]    A disadvantage of the sliding friction bushing type steady bearings can be that they often do not perform well when dry running. In some applications, it is desirable to have dry running performance so that the bearing can be operated while the vessel is being emptied. Also, these bushings may not perform well when exposed to cleaning solutions while mixing. Further, the materials that are used in the case of bushing type steady bearings may not be suitable for certain applications due to material contact, metallic wear, and/or inability to perform at certain temperatures. 
         [0005]    Accordingly, there is a need in the art for an improved steady bearing for use to support the free end of a mixer impeller shaft with respect to a vessel wall. 
       SUMMARY OF THE INVENTION 
       [0006]    Some embodiments of the present invention provide a steady bearing that is used to support the free end of a mixer impeller shaft with respect to a vessel wall. 
         [0007]    An embodiment of the present invention is a steady bearing for supporting an end of an impeller shaft with respect to a mixer vessel wall which includes a downwardly projecting cylindrical hollow sleeve mounted to the end of the shaft and projecting away from the end of the shaft, an upwardly projecting bearing holder mounted to the bottom of the vessel wall and projecting upwardly inside part of the hollow portion of the sleeve, and a roller bearing assembly mounted in between the bearing holder and the sleeve. 
         [0008]    Another embodiment discloses a steady bearing for supporting an end of an impeller shaft with respect to a mixer vessel wall, comprising a downwardly projecting cylindrical hollow outer bearing engaging means mounted to the end of the shaft and projecting away from the end of the shaft, an upwardly projecting inner bearing engaging means mounted to the bottom of the vessel wall and projecting upwardly inside part of the hollow portion of the outer bearing engaging means and a roller bearing assembly mounted in between the inner bearing engaging means and the outer bearing engaging means. 
         [0009]    Yet another embodiment provides a method of installing a steady bearing for supporting the end of an impeller shaft with respect to a mixer vessel wall, comprising mounting a pedestal to the vessel wall, with the pedestal having a bearing mounting portion having an aperture therethrough that is spaced apart from the vessel wall, inserting a central bearing holder through the aperture to project away from the vessel wall, mounting a downwardly projecting cylindrical hollow sleeve to the end of the shaft projecting away from the end of the shaft and towards the vessel wall, installing a roller bearing assembly onto the upwardly projecting bearing holder, and inserting the upwardly projecting bearing holder and the roller bearing assembly inside the cylindrical hollow sleeve, wherein each of the steps can be performed in any order. 
         [0010]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0011]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0012]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a cross-sectional view of a steady bearing according to a first preferred embodiment of the invention. 
           [0014]      FIG. 2  is a cross-sectional view of a steady bearing according to a second preferred embodiment. 
           [0015]      FIG. 3  is a top cross-sectional view of the steady bearing of  FIG. 2  taken through lines  3 - 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Some embodiments of the present invention provide a steady bearing that is used to support the free end of a mixer impeller shaft with respect to a vessel wall. Some preferred embodiments of the invention will now be described with respect to the drawing figures in which like reference numerals are referred to like parts throughout. 
         [0017]    Turning first to  FIG. 1 , a first embodiment is shown. The lower end of a shaft  12  is typically supported from above and essentially hangs into a mixer vessel. The shaft  12  is typically rotated by a motor (not shown) outside the mixer vessel, and typically has radially extending impellers or paddles (not shown) extending outwardly therefrom. 
         [0018]    In the example given, the lower end of the shaft  12  has a reduced diameter portion  14  that has a threaded mounting hole  16  projecting therein. A bolt  18  mounts a bearing sleeve  20  to the lower end of the shaft. The sleeve  20  also has a tapered lower end portion  28 , the significance of which is described further below. The bearing sleeve  20  has one or more vent holes  22  projecting therein below the bottom end of the shaft  12  which are discussed in more detail below. The sleeve  20 , in this example, has a reduced diameter portion  24  which has an inner diameter sized to go over the end diameter of the reduced diameter portion of the shaft  14 . Of course, the shaft may have a constant diameter across its lower portions  12  and  14 , and the portion  24  of the sleeve  20  rather than being a reduced diameter portion as in this example may have a larger diameter, based on whatever diameter is needed to mount securely to the bottom end of the shaft  12 . 
         [0019]    The bearing sleeve  20  also has, in this example, an increased diameter portion  24 . The increased diameter portion  24  has an inner diameter sized for sliding contact with a rotating element bearing  30 . In this example, the bearing assembly  30  has an outer race  32 , a plurality of balls  34 , and an inner race  36 . A cage (not shown) may be interposed between the races to maintain the balls  34  and evenly spaced circumferential alignment. 
         [0020]    The inner race  36  sits upon an upwardly projecting bearing holder element  40 . The bearing holder element  40  has a top portion  42  having a diameter sized to accept the inner diameter of the inner race  36 . A clip such as a C-shaped ring  44  can be provided to trap the inner race  36  between the clip  44  and a shoulder  46  on the bearing holder  40 . Although a snap ring  44  is shown, in some instances, a threaded knot may be tightened down around the top section  42 . The bearing holder  40  has a larger diameter post  48  projecting upward from a bottom plate  50 , also a part of the bearing holder  40 . The bearing holder  40  also has a central longitudinal bore  49  extending all the way therethrough from the bottom to the top. The plate  50  is mounted to a pedestal  60  by virtue of one or more pins  52  and attachment bolts  54 . The pin  52  is press fit into a hole in the lower portion  50 , and has a sliding fit with an accepting hole in the pedestal  60 . The pedestal  60  has an aperture  62  which is sized to permit at least the portions  48  and  42  of the bearing holder  40  to extend upward therethrough. The aperture  62  may also be sized to permit the sleeve  20  to be extended upward therethrough during installation if desired. 
         [0021]    The pedestal  60  has a generally horizontal mounting portion  64  and a plurality of legs  66 , in this example three legs  66  form a tripod. The legs  66  are fastened to the bottom of the mixing vessel  70  by respective pins  72  and bolts  74 . 
         [0022]    It will be appreciated that in this assembled configuration the sleeve  20  rotates together with the shaft, and the bearing assembly  30  provides radial restriction of the position of the sleeve  20 , due to its interaction with the bearing holder  40  which is held fixed during operation. The outer race  32  has a sliding contact with the inner surface of the sleeve  20 , so that axial up and down movement of the sleeve  20  with respect to the bearing holder  40  is accommodated by sliding. This is advantageous because in the case of temperature change the shaft  12  may elongate or contract, causing axial up and down movement of the sleeve  20 . Further, the flexing of the shaft and the intermediate position of the shaft may also cause some degree of axial movement of the sleeve  20 . An advantage of the arrangement shown in the figures is the ability to accommodate this axial movement through sliding, without putting any axial load on the bearing. That is, the bearing has only radial loads and is not subjected to any significant axial thrust load. 
         [0023]    In the illustrated embodiments, the bearing shown is a roller type bearing  30 . More specifically, in the example given, the roller bearing  30  is a ball type bearing utilizing balls  34 . A roller type ball bearing is preferred in the embodiments of this invention, but in other embodiments it can be any type of roller bearing that uses a rolling contact as opposed to the sliding bushing. 
         [0024]    The roller bearing  30  may be made from any of a wide variety of suitable materials. In some examples, the roller bearing  30  may be made of all steel. Steel has the advantages of operating to high temperature. However, in some applications, it is desirable to avoid the metallic particles that occur due to wear, or otherwise avoid the use of metal bearings. Other materials that can be used for the bearing include glass-filled Teflon, or alternatively PEEK. However, a disadvantage with some of these and similar non-metallic materials is that they may not be suitable for high temperature operation, such as for example operation in some applications greater than 400 degrees Fahrenheit. Therefore, in some embodiments the bearing races and/or roller elements are made from a ceramic material such as ceramic cured silicon nitride. In one preferred embodiment, the races are  440 C nickel coated material, the balls are ceramic cured silicon nitride, and the core is glass-filled Teflon. 
         [0025]    A benefit of using the pins  52  in combination with the bolts  54  is that the pins  52  absorb the radial loads and also provide accurate positioning without subjecting the bolts  54  to significant radial loads which may be undesirable or cause misalignment, or be loosened by vibration. 
         [0026]    One example of a preferred method of installing the arrangement shown in  FIG. 1  will now be described. In a first step, the shaft  12  is simply being suspended in the position shown from above, and the pedestal  60  remains mounted to the vessel wall  70 . At this initial stage, neither the sleeve  20 , the bearing  30  nor the bearing holder  40  are present. If the aperture  62  is sufficiently large as to allow the sleeve  20  to pass through, then the sleeve  20 , bearing  30 , and bearing holder  50  can be assembled substantially in the configuration shown, and slid under the horizontal portion  64  of the pedestal  60  and pushed upwardly through the aperture  62  into the final operating position. At this point, the bolt  18  can be affixed and the bolt  54  can be affixed with either one being affixed first. In situations where the outer diameter of the sleeve  20  is greater than the diameter of the aperture  62 , the shaft  12  can often be swung somewhat out of the way of the pedestal  60  if needed, and the sleeve  20  can be first mounted to the end of the shaft  12  using the bolt  18 . Then, the bearing holder  40  can be slid under the pedestal  60 , and its upwardly projecting shaft  42  and  48  can be projected through the aperture  62 , and the bearing holder  40  then mounted via the bolt  54  into the position shown. 
         [0027]    In either of the above installations, the taper  28  facilitates the sliding of the bearing  30  into the inner diameter of the sleeve  20 . This can be particularly advantageous in the case of ceramic or PEEK bearings, which can tend to be more brittle than metallic bearings. 
         [0028]    The combination of the vent  22  and the bore  49  provide for draining of material that can accumulate inside of the sleeve  20 . That is, as the vessel is emptied, the vent  22  allows an influx of air and the bore  49  allows drainage of material that would otherwise possibly be trapped inside the sleeve  20 . Further, drainage will occur through the gaps or spaces between the roller elements  34  of the roller bearing  30 . 
         [0029]    An advantage of this assembly method is that the pedestal  60  in these embodiments does not need to be removed from the bottom of the vessel  70 . Of course, in other embodiments, depending on the relative dimensions, it may be necessary to remove the pedestal  60 . Moreover, although an elevated pedestal  60  is shown, embodiments are possible where the bearing holder  40  is simply directly bolted to the bottom of the vessel  70  itself, and projects upward to support roller bearing  30  inside an outer bearing sleeve  20  otherwise in the manner as shown. 
         [0030]      FIGS. 2 and 3  depict a second embodiment with some design variations. Like reference numerals refer to corresponding parts with the variations in some parts. 
         [0031]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.