Abstract:
An improved cartridge-type bearing seal includes removably connected stator and rotor sections. The stator section supports a distribution ring that divides an internal annular volume into radially outside and inside portions. The ring has a sufficient number of tangentially oriented ducts to permit fluid communication between the outside and inside portions. With this structure, when pressurized purge fluid is supplied to the outside portion, the fluid flows through the ducts, to induce a desired tangential fluid flow within the inside portion. This in turn causes circumferentially uniform fluid pressure in the annular volume that resides between the rotating shaft and the bearing housing, and the pressurized fluid traverses a flow path out of the bearing. This circumferentially uniform fluid pressure, by itself or in combination with a flexible lip, prevents contaminant ingress between the rotating shaft and the bearing housing. Because the structure that creates the tangential fluid flow is part of the removable cartridge, this bearing seal eliminates the need to machine or drill a tangentially oriented passage in the bearing housing. One embodiment adds a secondary ring adjacent the distribution ring, to reduce the need to precision machine the inside dimension of the bearing cap. These structural components render the circumferential purge fluid feature even more readily available, for a wider range of spindles.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an improved cartridge-type bearing seal for a machine tool spindle. 
       BACKGROUND OF THE INVENTION 
       [0002]    The assignee of the present invention, Setco Sales Company, owns U.S. Pat. Nos. 5,727,095, 5,980,115 and 6,217,219 B1, all of which are entitled “Bearing Seal With Uniform Fluid Purge,” and directed to a unique bearing seal which has proved tremendously successful in increasing the reliability of spindles. Setco sells this patented bearing seal under the trademark AIRSHIELD. These Setco patents are incorporated herein by reference, in their entireties. 
         [0003]    According to one aspect of the prior invention, as disclosed in the three above-cited patents, the bearing seal includes an annular cap located at a first end of a bearing housing, where a shaft exits therefrom. The cap has an internal surface which defines an annular internal volume, and a passage formed therethrough which tangentially intersects the annular volume. This structure allows pressurized purge fluid to be supplied to the annular volume via the passage, to create a circumferentially uniform fluid pressure within the annular volume. This circumferentially uniform pressure prevents ingress of contaminant materials within the bearing. 
         [0004]    This prior invention has significantly increased spindle reliability, by reducing downtime caused by failed bearing seals. Such downtime can have critical adverse effects on overall spindle efficiency and throughput. 
         [0005]    These prior patents disclose several embodiments for achieving the critical benefits of this prior invention. Moreover, these prior patents expressly suggest that the benefits of that prior invention can be obtained in retrofit situations, where an in-place spindle with a failed bearing seal requires the retrofitting of a new bearing seal. These prior patents suggested some general details of how such a retrofitted bearing seal could be achieved. However, those prior patents did not disclose or suggest a specific structure for achieving the benefits of the prior invention with a wide variety of spindles of various size and shape. 
         [0006]    For these reasons, Setco developed a second generation version of this type of bearing seal, i.e. a bearing seal with circumferentially uniform fluid pressure, which achieved certain advantages by using an annular cartridge having connectable stator and rotor sections. This second generation bearing seal was the subject of Setco&#39;s U.S. Pat. No. 7,090,220, entitled “Cartridge-Type Bearing Seal For Machine Tool Spindle,” which is expressly incorporated by reference herein, in its entirety. This cartridge type bearing seal facilitated the retrofitting of bearing seals on in-place spindles, readily accommodated various sizes and shapes of spindles, and did so in a simple and cost-effective manner. This second generation bearing seal also increased the availability, for a wide range of bearing seals, of the uniform air purge feature that was achieved with the original invention. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to still further increase the availability, for various bearing seals, of the uniform air purge feature of the original invention, and to do so in a relatively cost-effective manner. 
         [0008]    The present invention achieves these objectives by modifying the prior annular cartridge to include a distribution ring that induces tangential flow of pressurized purge fluid, to cause circumferentially uniform fluid pressure. By equipping the removable cartridge with the structure that causes this tangential flow, and hence the circumferentially uniform fluid pressure, the present invention eliminates the prior need to drill a tangentially oriented hole in the bearing cap. Such holes can be difficult to drill. 
         [0009]    With the present invention, rather than drilling a tangentially oriented hole in the bearing cap, the user needs only to drill a radially oriented hole. When pressurized purge fluid is supplied to the hole and directed into an internal annular volume that surrounds the shaft, the distribution ring induces the desired tangential flow. This tangential flow, and the resultant circumferentially uniform fluid pressure, continues along a fluid flow path that traverses the annular space between the rotor and stator sections of the cartridge, and eventually out of the cartridge. This is similar to the original invention. 
         [0010]    According to one preferred embodiment of the invention, an annular cartridge includes two removably connected sections, a stator section and a rotor section, and a distribution ring located on the inboard side of the stator section. The distribution ring is located adjacent an internal passage formed in the bearing housing, through which pressurized purge fluid is received. At the location where the distribution ring occupies the internal annular volume, the ring defines inside and outside portions of the annular volume. The distribution ring includes at least one, and preferably four, substantially tangentially oriented slots, or ducts. Each of the ducts provides a fluid connection from the outside portion to the inside portion so that pressurized purge fluid can flow therethrough. Each duct is curved along its length, with an outer section oriented generally radially and an internal section oriented substantially tangential to the axis. The number, sizing and spacing of the ducts may vary, depending on the dimensions of the particular spindle. 
         [0011]    The internal passage that is formed in the bearing housing is preferably located in a bearing cap. The internal passage may be drilled radially into the bearing cap, so as to terminate at the annular volume, and particularly at the outside part of the annular volume that is located radially outside of the distribution ring. Compared to the prior cartridge-type bearing seal, which required a tangentially oriented internal passage, the present structure does not require any particular orientation for the internal passage, so long as it terminates at the outside portion of the internal volume. Tangential drilling is no longer required because this structure incorporates into the cartridge the structure needed, namely, the ducts formed in the distribution ring, to induce the desired tangential flow of pressurized purge fluid. Because the distribution ring induces the desired tangential flow, rather than the internal passage, the internal passage in the bearing housing does not have to be formed via a tangential drilling step, a drilling step that can be difficult to perform. 
         [0012]    Additionally, the cartridge cooperates with, and if desired may actually include as an integral component thereof, a secondary ring located adjacent the distribution ring, just inboard thereof. This secondary ring is machined to provide a close gap between its radially internal surface and the rotating shaft. This close gap isolates the internal bearing. By incorporating this isolating structure into the cartridge, or at least by not requiring the bearing cap to have the isolating structure, this aspect of the invention eliminates the need to machine the bearing cap to a tight tolerance to provide this close gap. This secondary ring is a smaller component that is relatively easy to machine compared to the bearing cap. Thus, this secondary ring facilitates the setting of this clearance gap. Also, the secondary ring helps to affirmatively fix the distribution ring at the desired axial position. 
         [0013]    With this invention applicant has moved the tangential flow-inducing structure into the cartridge itself, to eliminate the need to drill a tangentially oriented passage in the bearing housing. Several other advantages flow from this structural change. 
         [0014]    These and other features of the invention will be more readily understood in the context of the following drawings and the detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a cartridge-type bearing seal constructed according to a first preferred embodiment of the invention. 
           [0016]      FIG. 2  is a longitudinal cross sectional view of the cartridge-type bearing seal of  FIG. 1 , but mounted on a spindle. 
           [0017]      FIG. 3  is an enlarged longitudinal cross-sectional view of the cartridge-type bearing seal shown in  FIG. 1 . 
           [0018]      FIG. 4  is a transverse view of the cartridge-type bearing seal of  FIG. 1  and a corresponding bearing cap, to show the orientation of the ducts in the distribution ring and the internal passage in the bearing cap. 
           [0019]      FIG. 5  is a longitudinal cross sectional view, similar to  FIG. 2 , of a cartridge bearing seal constructed according to a second preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  shows a cartridge-type bearing seal constructed in accordance with a first preferred embodiment of the invention. The cartridge-type bearing seal of this invention makes the inventive bearing seal of Setco&#39;s prior patents more readily available to a wider variety of spindle structures. And this inventive cartridge bearing seal is particularly suitable for retrofitting in-place spindles. 
         [0021]      FIG. 1  shows that the bearing seal of this invention comprises an annular cartridge  10  with interconnected first and second sections  12  and  14 , respectively. The first section  12  is a stator section, and it is fixedly mounted to a stator  16  ( FIG. 2 ), while second section  14  is a rotor section which is fixedly mounted to a rotor  18  ( FIG. 2 ). A distribution ring  15  is located adjacent the first section  12 , and preferably formed of rubber and adhered to the first section  12 , to essentially become a part thereof The distribution ring  15  includes a plurality of substantially tangentially oriented ducts  17 . In this context, substantially tangentially oriented also includes a purely tangential orientation. 
         [0022]      FIG. 2  shows that the rotor  18  is rotatable relative to the stator  16 , about an axis  19  when driven by a drive motor (not shown). The stator section  12  is piloted into a circular recess formed within stator  16 , and which is defined by an axially oriented surface  20  and a radially oriented surface  22 , which are parallel to and perpendicular to axis  19 , respectively. An O-ring  24  resides within a recess  25  formed within an exterior surface of the stator section  12 . The surfaces  20  and  22  form part of the stator  16  located at one end of a stator housing. When the first section  12  is mounted in place on the stator  16 , in a press fit condition, the first section  12  remains fixed relative to the axis  19 . That is, the first section  12  effectively becomes part of the stator  16 . In the context of this application, the terms rotor and stator are generally used interchangeably with the terms shaft and housing. That is because the rotor  19  rotates, via a shaft, and it rotates relative to a stator, or stationary housing. 
         [0023]    The second section  14  mounts to the rotor  18  in such as way that it effectively becomes a part of the rotor  18 , because the rotor  18  and the rotor section  14  rotate together about axis  19  during operation. The rotor section  14  may mount to the rotor  18  via any suitable connection or securement, such as, for instance via a press fit along axially directed surface  26  formed along the outer surface of the rotor surface  18 , or via a set screw arrangement. An O-ring  30  resides within a recess  31  formed along the radial inner edge of the rotor section  14 . 
         [0024]    The stator section  12  is rigidly mounted to the stator  16 , while the rotor section  14  is rigidly mounted to the rotor  18 . At the same time, the stator section  12  and the rotor section  14  are releasably connected to define an annular cartridge  10 , in a manner which permits relative rotation of rotor section  14  relative to the stator section  12  about axis  19 . The first section  12  and second sections  14  are preferably constructed in a manner which allows a snap fit interconnection of these two components, by applying axially directed force to both of the sections  12 ,  14  in order to snap them together, as described in the previously mentioned &#39;220 patent. 
         [0025]      FIG. 2  also shows an annular end cap  32  which forms part of the structure of the stator  16 . Preferably, the end cap  32  is removably connectable to the rest of the stator  16 , at the end of the bearing housing, via bolts (not shown). The cap  32  is machined so as to provide a clearance gap between its innermost radial end  33  and the rotor  18 , to isolate the internal bearings  35 . The end cap  32  includes an internal passage, or passageway  34 . This passageway  34  has an internal end that terminates at an internal annular volume  36  which circumferentially surrounds the rotor  18 . This annular volume  36  includes a relatively large annular volume located adjacent the end cap  32 , and a relatively thin annular volume located closer to the rotor section  14 . From an innermost part of the annular volume  36  (the right side in  FIG. 2 ) to an outermost part (the left side in  FIG. 2 ), within the cartridge  10 , the annular volume  36  defines an outbound flow path for pressurized purge fluid. The flow path is annular in shape along its axial length with no non-annular discontinuities along its axial length. 
         [0026]      FIG. 3  shows that the cartridge  10  generally has an outer or exterior surface  38  and an inner or interior surface  40 . The interior surface  40  is located adjacent to and forms an outer boundary for the internal annular volume  36 . Just radially outside of the annular volume  36 , the cartridge  10  includes a seal  42  affixed to the stator section  12 , of the type disclosed in the prior patents cited above. The circumferential seal  42  includes a circumferential lip  44  which engages the rotor section  14  when the rotor  18  is not rotating relative to the stator  16 . When the rotor  18  is rotating relative to stator  16  about axis  19 , and with pressurized purge fluid supplied to the annular volume  36 , the lip  44  flexes away from the rotor section  14  to allow purge fluid to flow radially outwardly, in a circumferentially uniform manner, along a path defined by the open space between the stator section  12  and rotor section  14 . Reference numeral  47  generally designates the axial distance between the stator section  12  and the rotor section  14 , when these two sections are snap fitted together. 
         [0027]      FIG. 3  also shows a circumferential collar  48  extending around the exterior of the stator section  12 . This collar  48  includes an outer axially extending section  50  and a radially inwardly extending section  52 . Preferably, the stator section  12  is made of a relatively flexible material, such as 1018 or 1020 steel. Alternatively, stator section  12  may be made of stainless steel, carbon steel or any other suitable material which is sufficiently durable and sufficiently flexible to achieve the purposes previously described. Preferably, the stator section  14  is made of  4145  hardstock steel, and it is machined to the desired shape via a series of machining steps which may be done on the same machine. 
         [0028]    When snap fitted together, the stator and rotor sections  12  and  14  define the outermost part of the fluid flow path At this part of the structure, i.e. radially outside of the lip  44 , this fluid flow path traverses an annular space residing between the stator section  12  and the rotor section  14 , and eventually beyond the outer surface  38  of the cartridge  10 . This flow path is the same as that described in detail in the above-cited &#39;220 patent. 
         [0029]      FIG. 4  shows the locations of the ducts  17  with respect to the axis  19  of the structure.  FIG. 4  also shows that each of the ducts  17  has an outer section  17   a  that is oriented primarily radially, and an inner section  17   b  that is oriented substantially tangentially. Each duct  17  curves somewhat along its length, to accommodate these two different orientations.  FIG. 4  also shows that the internal passage  34 , through which pressurized purge fluid is supplied, may be oriented radially with respect to the axis  19 . This radial orientation facilitates drilling. 
         [0030]    As shown best in  FIG. 2 , where the internal passageway  34  terminates within the cap  32  the distribution ring  15  defines an outside portion  36   a  and inside portion  36   b  of the internal annular volume  36 . Nonetheless, the substantially tangentially oriented ducts  17  place the outside portion  36   a  in fluid communication with the inside portion  36   b . Thus, when pressurized purge fluid is supplied from a pressure fluid supply source  39  to the internal passageway  34 , it first flows into the outside portion  36   a . Thereafter, the pressurized fluid moves radially inwardly through the ducts  17  of the distribution ring  15 , to the inside portion  36   b . As this occurs, the ducts  17  cause the pressurized purge fluid to flow tangentially. This induced tangential flow causes circumferential flow within inside portion  36   b , and also a circumferentially uniform fluid pressure within the annular volume  36 . This circumferentially uniform fluid pressure is maintained as the purge fluid axially traverses the flow path toward an outer surface  38  of the cartridge. The pressure fluid supply source  39  may be any device or structure that creates the desire fluid flow conditions. 
         [0031]    For ease in molding the ducts  17  into the ring  15 , the ducts  17  are preferably located adjacent the inboard surface of the distribution ring  15 . Nonetheless, the ducts  17  could be located anywhere along the axial dimension of the distribution ring  15 , or could even extend along the entire axial dimension of the distribution ring  15 . The ducts  17  can be made by molding, or by drilling, or any other suitable fashion. The ducts  17  of  FIG. 1  have a transverse shape that is rectangular in cross-section, although other transverse cross-sections would also be suitable, such as circular, which would occur if the ducts  17  were formed by drilling. 
         [0032]      FIG. 5  shows a second preferred embodiment of the cartridge-type seal of the this invention. More particularly, this second embodiment uses a secondary ring  51  located adjacent the distribution ring  15 . The secondary ring  51  protects the inboard surface of the distribution ring  15 . Also, it is sized to extend toward the shaft  18  so as to have a small clearance gap therebetween. With this structure, the secondary ring  51  serves the purpose of providing the needed small clearance gap to isolate the internal bearing  35  of the bearing housing from the seal structure. By using this secondary ring  51  to set this clearance gap and to isolate the internal bearing  35 , it is no longer necessary for the radially internal surface  33  of the bearing cap  32  itself to be machined so as to provide this desired close gap. Thus, this embodiment eliminates the need to machine a close clearance between the cap  32  and the shaft  18 . Still further, the secondary ring  51  and the distribution ring  15  could be connected together, or even formed as a single piece. 
         [0033]    In use, to retrofit an existing spindle which has a failed bearing seal, an operator selects a cartridge  10  of desired shape. This means that the stator section  12  is sized to be fixedly mounted to the stator of the existing spindle  16 , while the section  14  is sized to be mounted to the rotor  18 . If absolutely necessary, in situations where the stator  16  and the rotor  18  are not a standard size, it would be possible to machine these structures to obtain a desired size and shape to which a stator section  12  and the rotor section  14  of known dimension may be mounted. Alternatively, the stator and rotor sections  12  and  14  can be made to a specific size that is needed. Prior to mounting the stator section  12 , the end cap  32  is mounted to an end of the spindle housing. Depending on the circumstances, the end cap  32  and the stator section  12  may be supplied separately, or together, to facilitate and streamline the sizing of these components. Once the cap  32  has been mounted on the spindle housing, according to a preferred sequence of operation, the cartridge  10  is mounted to the cap  32 . This occurs by press fitting the stator section  12  into the recess defined by the surfaces of the cap  32 . In this manner, the rotor section  14  remains connected to the stator section  12 , so that the cartridge  10  is attached to the cap  32  as a single unit. This connection of the cartridge  10  to the cap  32  may occur either before or after the cap  32  is mounted to the end of the spindle housing, depending upon the particular circumstances. 
         [0034]    The rotor  18  is then moved in an axial direction, preferably toward the spindle housing, to press fit the rotor section  14  onto the rotor  18 . To achieve a desired axially position of the rotor section  14  relative to the stator section  12 , shims (not shown) are temporarily located in the outer radial end of the fluid flow passage. The rotor  18  is slowly rotated relative to the spindle housing and the shims are successively inserted or removed in order to orient the rotor section  14  in a desired position relative to the stator section  12 , and preferably in a manner which is circumferentially uniform about the spindle axis  19 . In the desired position, via this process, the stator section  12  and the rotor section  14  will be axially spaced away from each other during operation so that there is no surface to surface contact during rotation of the rotor  18 . Preferably, when the sections  12  and  14  of the cartridge  10  are connected via a snap fit, there is some amount of axial play, or axial tolerance. But when mounted, that play essentially becomes a clearance between the collar  48  and the rotor section  14 . Applicant has learned that an axial play dimension of about 0.5 mm has proved suitable for most purposes, although this dimension may vary depending upon the circumstances. 
         [0035]    A fluid pressure source  39  is operatively connected to the end cap  32 , to supply pressurized purge fluid to the passageway  34  which terminates at the outside portion  36   a  of the annular volume  36 . The substantially tangentially oriented ducts  17  induce tangential flow as the purge fluid moves to the inside portion  36   b . This generates circumferentially uniform flow of purge fluid in the annular volume  36 , and also circumferentially uniform fluid pressure, which is maintained as the purge fluid first flows axially along the shaft  18 , and then flows radially outwardly from the cartridge  10  via the space which resides between the two interconnected sections  12  and  14 . This flow path traverses the lip  44 , which flexes away from the rotor section  14  during rotation of the rotor  18  relative to the stator  16 , when pressurized purge fluid is applied to the volume  36 . Eventually, the purge fluid moves beyond the outer surface  38  of the cartridge  10 . 
         [0036]    Applicant previously learned that the supplying of circumferentially uniform purge fluid to the annular volume surrounding a rotating shaft could be used to achieve significant advantages in preventing contaminant ingress into the bearing seals of a spindle. The details and embodiments of that prior invention are described and shown in the four U.S. patents described above. With this invention the applicant has achieved another advance in applying the prior invention to a broader range of spindles, and has done so in a cost-effective manner. 
         [0037]    Thus, while embodiments of the invention has been described, it will be readily apparent to one of skill in the art that variations in these embodiments may be made without departing from the principles of the invention, the scope of which is defined by the appended claims.