Patent Publication Number: US-7584917-B2

Title: Seal for coiled spring assembly

Description:
TECHNICAL FIELD 
   The present invention relates to a seal for a coiled spring assembly for pulverizing a solid fuel, and more particularly, to a spring stud seal for a coiled spring assembly of a mill for pulverizing a solid fuel, such as coal, for example, in a new utility unit application or a retrofit application in an existing utility unit. 
   BACKGROUND 
   Pulverizers are well known for the reduction of the particle size of solid fuel to allow for combustion of the solid fuel in a furnace. A pulverizer employs some combination of impact, attrition and crushing to reduce a solid fuel to a particular particle size. Several types of pulverizer mills can be employed for the pulverization of the solid fuel, for example, coal, to a particulate size appropriate for firing in a furnace. These can include ball-tube mills, impact mills, attrition mills, ball race mills, and ring roll or bowl mills. Most typically, however, bowl mills with integral classification equipment are employed for the pulverization of the solid fuel to allow for transport, drying and direct firing of the pulverized fuel entrained in an air stream. 
   Bowl mills have a grinding ring carried by a rotating bowl. Fixed position rollers are mounted on roller journal assemblies such that the roll face of the rollers are approximately parallel to the inside surface of the grinding ring and define a very small gap therebetween. Pressure for grinding is applied through springs or hydraulic cylinders on the roller journal to crush solid fuel caught between the roll face of the roller and the grinding ring. 
   An air stream is typically utilized for drying, classification, and transport of the solid fuel through the pulverizer. The air stream employed is typically a portion of the combustion air referred to as the primary air. The primary air is combustion air first directed through a preheater whereby the combustion air is heated with energy recovered from the flue gas of the furnace. A portion of the primary air is then ducted to the pulverizers. In a bowl mill, the primary air is drawn through beneath the bowl of the bowl mill and up past the roller journal assemblies to collect the pulverized solid fuel. The small particles of solid fuel become entrained in the primary air. The air stream containing the solid fuel then passes through a classifier into the outlet of the pulverizer. After passing through the exhauster, the pulverized fuel can be stored, or more typically, is transported to the furnace by the air stream for direct firing. 
   For example, U.S. Pat. No. 4,706,900 entitled “Retrofitable Coiled Spring System,” which issued on Nov. 17, 1987 and which is assigned to the same assignee as the present invention illustrates a prior art form of bowl mill using a coiled spring assembly for applying pressure on the roller journal to crush solid fuel caught between the roll face of the roller and the grinding ring. U.S. Pat. No. 4,706,900 discloses both the nature of the construction and the mode of operation of a bowl mill that is suitable for use for purposes of effecting the pulverization of the coal that is used to fuel a coal-fired steam generator. 
   The journal loading, which dictates the amount of grinding force that the grinding rolls exert on the coal, as mentioned above has been provided to date either through the use of hydraulic systems or through the use of mechanical springs. One such arrangement of mechanical springs can be found depicted, for example, in U.S. Pat. No. 4,706,900. In accord with a showing contained in this U.S. patent, each grinding roll is urged towards the surface of the grinding table by means of an adjustable spring. To this end, a suitable mechanical coiled spring that possesses desired design characteristics is selected; namely, a spring that is capable of urging the grinding roll toward the grinding table surface in such a manner that the grinding roll exerts a predetermined grinding force on the coal disposed on the table, when the coal is of a predetermined depth on the table. 
   Although the coiled spring assembly constructed in accordance with the teachings of U.S. Pat. No. 4,706,900 has demonstrated to be operative for the purpose for which it has been designed, a need still exists to improve the coiled spring assembly. More specifically, a spring extension cap is presently incorporated on bowl mill type journal spring assembly to cover a spring stud extending from the coiled spring assembly in order to seal the coiled spring assembly. By sealing the exposed end of the spring assembly that is exposed to atmospheric conditions, the extension cap eliminates a differential pressure across the spring assembly so that solid fuel dust, such as coal dust, for example, cannot flow into a bushing assembly having a bushing which allows the spring stud to extend therethrough and to translate axially with respect to the bushing assembly of the coiled spring assembly. 
   It is desirable to visually inspect an end of the spring stud to determine the amount of spring movement, which indicates relative journal and grinding roll movement. However, when a spring extension cap is in place, the end of the spring stud cannot be visually inspected without removing the extension cap. Therefore, the extension cap must be removed to monitor spring stud movement, which allows solid fuel coal (e.g., coal dust) to flow into the coiled assembly as a result of the differential pressure across the spring assembly and cause premature failure of the bushing or spring stud. 
   Therefore, there remains a need for an apparatus and method for sealing a coiled spring assembly, which facilitates inspection of an end of a spring stud extending therefrom to determine an amount of spring movement of the coiled spring assembly. 
   SUMMARY 
   According to the aspects illustrated herein, there is provided a mill for pulverizing a solid fuel. The mill includes: a substantially closed separator body; a grinding table rotatably mounted on a shaft in the separator body; a grinding roll rotable via a journal assembly disposed in the separator body, the journal assembly being supported so as to be pivotable and move the grinding roll into and out of engagement with solid fuel disposed on the grinding table; a coil spring assembly connected to the separator body and in communication with the journal assembly to apply a spring force to the grinding roll. The coil spring assembly includes: a preload stud having a first end in communication with the journal assembly and an opposite second end extending from the coil spring assembly and exposed outside of the separator body; a spring adjustment bolt and bearing assembly being fixed relative to the preload stud extending therethrough; and a seal being substantially cylindrical shaped and flexible at least along a central axis thereof, the seal having a first end operably secured to the spring adjustment bolt and bearing assembly and an opposite second end operably secured to the second end of the preload stud thereby sealing a bushing area corresponding to a portion of the preload stud surrounded by the spring adjustment bolt and bearing assembly from ground solid fuel dust and allowing movement of the preload stud at least along the central axis thereof to apply the spring force from the coil spring assembly to the grinding roll. 
   According to the other aspects illustrated herein, a mechanical coiled spring assembly for a pulverizing mill is disclosed. The mechanical coiled spring assembly includes: a preload stud having an exposed first end and an opposite second end; a first pressure spring seat at the second end of the preload stud, the first pressure spring seat configured to transmit a spring force to an external assembly; a stud bearing housing configured to house at least an intermediate portion of the preload stud, the stud bearing housing configured to be fixedly secured to a bowl mill; a second pressure spring seat having the preload stud slidably extending therethrough, the second pressure spring seat being translatable within the stud bearing housing along an axis defining the preload stud; a pressure spring generating the spring force to bias the first pressure spring seat away from the second pressure spring seat; a spring adjustment bolt and bearing assembly disposed within the stud bearing housing and having one end abutting the second pressure spring seat, the spring adjustment bolt and bearing assembly allows axial translation of the preload stud extending therethrough; a spring adjustment nut abutting an opposite side of the spring adjustment bolt and bearing assembly, the spring adjustment nut threadably engaged with threads on the first end of the preload stud; a mounting ring portion having the exposed first end of the preload stud extending therefrom; and a seal being substantially cylindrical shape and flexible at least along a central axis thereof, the seal having a first end sealably secured to the journal spring adjusting bolt and bearing assembly and an opposite second end sealably secured to the mounting ring portion. 
   According to yet the other aspects illustrated herein, a method of retrofitting a seal for a mechanical coiled spring assembly is disclosed. The method includes: removing an extension cap from a first end of the coil spring assembly to expose a first end of a preload stud and spring adjusting nut of the coil spring assembly; removing an existing seal from a journal spring adjusting bolt and bearing assembly of the coil spring assembly; installing a mounting ring over a portion of the exposed first end of the preload stud; installing a substantially cylindrical shaped seal being flexible at least along a central axis thereof over the spring adjustment bolt and bearing assembly, the spring adjusting nut and the mounting ring; sealably securing a first end of the seal to the spring adjustment bolt and bearing assembly; and sealably securing an opposite second end of the seal to the mounting ring. 
   The above described and other features are exemplified by the following figures and detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike: 
       FIG. 1  is a side elevational view partially in section of a pulverizer bowl mill equipped with a mechanical coiled spring assembly constructed in accordance with the prior art; 
       FIG. 2  is an enlarged cross-sectional view of the mechanical coiled spring assembly of the pulverizer bowl mill of  FIG. 1  constructed in accordance with the prior art; 
       FIG. 3  is an enlarged partial cross-sectional view of the mechanical coiled spring assembly of  FIG. 2  constructed in accordance with the prior art and with a cotter pin removed from an adjusting castle nut; and 
       FIG. 4  is an enlarged partial cross-sectional view of an exemplary embodiment of a mechanical coiled spring assembly having an exemplary seal allowing a spring stud to extend therethrough in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , a pulverizing bowl mill  10  constructed in accordance with the prior art is illustrated. As the nature of the construction and the mode of operation of pulverizing bowl mills are well-known to those skilled in the art, it is not deemed necessary, therefore, to set forth herein a detailed description of the pulverizing bowl mill  10  illustrated in  FIG. 1  of the drawing. Rather, it is deemed sufficient for purposes of obtaining an understanding of a pulverizing bowl mill  10 , which is equipped with a mechanical coiled spring journal loading system constructed in accordance with the present invention, that merely a description of the nature of the construction and the mode of operation of the components of the pulverizing bowl mill  10  with which the mechanical coiled spring journal loading system cooperates. For a more detailed description of the nature of the construction and the mode of operation of the components of the pulverizing bowl mill  10 , which are not described in detail herein, reference is made to the prior art, e.g., U.S. Pat. No. 3,465,971, which issued on Sep. 9, 1969 to J. F. Dalenberg et al., and/or U.S. Pat. No. 4,002,299, which issued on Jan. 11, 1977 to C. J. Skalka. 
   Still referring to  FIG. 1 , the pulverizing bowl mill  10  includes a substantially closed separator body  12 . A grinding table  14  is mounted on a shaft  16 , which in turn is operatively connected to a suitable drive mechanism (not shown) so as to be capable of being suitably driven thereby. With the aforesaid components arranged within the separator body  12  in the manner depicted in  FIG. 1  of the drawing, the grinding table  14  is designed to be driven in a clockwise direction. 
   A plurality of grinding rolls  18 , preferably three in number in accord with conventional practice, are suitably supported within the interior of the separator body  12  so as to be equidistantly spaced one from another around the circumference of the separator body  12 . In the interest of maintaining clarity of illustration in the drawing, only one grinding roll  18  is shown in  FIG. 1 . Each of the grinding rolls  18  is supported on a suitable shaft (not shown) of a journal assembly  19  for rotation relative thereto. The grinding rolls  18  are each suitably supported in a manner for movement relative to the upper surface, as viewed with reference to  FIG. 1 , of the grinding table  14 . To this end, each of the grinding rolls  18  has a mechanical coiled spring system  20 , cooperatively associated therewith via the journal assembly  19 . Each of the mechanical coiled spring systems  20  is operative to establish a mechanical spring loading on the corresponding grinding roll  18  to exert the requisite degree of force on the solid fuel disposed on the grinding table  14  for the desired purpose of pulverizing the solid fuel. 
   The solid fuel material, e.g., coal, which is pulverized in the bowl mill  10  is fed thereto through the use of any suitable conventional type of feeding means such as a belt feeder (not shown). Upon falling free of the belt feeder (not shown), the coal enters the bowl mill  10  from a coal supply means, generally designated by reference numeral  22 . The coal supply means  22  includes a suitably dimensioned duct  24  having one end thereof which extends outwardly of the separator body  12  and preferably terminates in a funnel-like member (not shown). The latter funnel-like member (not shown) is shaped to facilitate the collection of the coal particles leaving the belt feeder (not shown), and to guide the coal particles into the duct  24 . The other end  26  of the duct  24  of the coal supply means  22  is operative to effect the discharge of the coal onto the surface of the grinding table  14 . As shown in  FIG. 1 , the duct end  26  is supported within the separator body  12  such that the duct end  26  is coaxially aligned with the shaft  16 , and is located in spaced relation to an outlet  28  provided in a classifier  30 , through which the coal flows in the course of being fed onto the surface of the grinding table  14 . 
   A gas such as air is used to convey the finer ground coal from the grinding table  14  through the interior of the separator body  12  for discharge from the pulverizing bowl mill  10 . The air enters the separator body  12  through a suitable opening (not shown) provided therein for this purpose. The air flows to a plurality of annular spaces  32  from the aforesaid opening (not shown) in the separator body  12 . The plurality of annular spaces  32  are formed between the circumference of the grinding table  14  and the inner wall surface of the separator body  12 . The air upon exiting from the annular spaces  32  is deflected over the grinding table  14  by means of suitably positioned deflector means (not shown). One such form of deflector means (not shown), which is suitable for this purpose in the bowl mill  10  of  FIG. 1 , comprises the subject matter of U. S. Pat. No. 4,234,132, which issued on Nov. 18, 1980 to T. V. Maliszewski, Jr., and which is assigned to the same assignee as the present application. 
   While the air is flowing along the path described above, the coal disposed on the surface of the grinding table  14  is pulverized by the grinding rolls  18 . As the coal becomes pulverized, the particles are thrown outwardly by centrifugal force away from the center of the grinding table  14 . Upon reaching the peripheral circumferential area of the grinding table  14 , the coal particles are picked up by the air exiting from the annular spaces  32  and are carried along therewith. The combined flow of air and coal particles is thereafter captured by the deflector means (not shown). The deflector means causes the combined flow of air and coal particles to be deflected over the grinding table  14 . In the course of effecting a change in direction in the path of flow of this combined stream of air and coal particles to be deflected over the grinding table  14 , the heaviest coal particles, because they have more inertia, become separated from the airstream and fall back onto the grinding table  14  whereupon they undergo further pulverization. The lighter coal particles, on the other hand, because they have less inertia continue to be carried along in the airstream. 
   After leaving the influence of the aforesaid deflector means (not shown) the combined stream of air and remaining coal particles flow to the classifier  30 . The classifier  30 , in accord with conventional practice and well-known to those skilled in the art, further sorts the coal particles that remain in the airstream. Namely, those particles of pulverized coal, which are of the desired particle size, pass through the classifier  30  and along with the air are discharged from the bowl mill  10  through the outlets  34 . However, the coal particles having a size larger than desired are returned to the surface of the grinding table  14  whereupon they undergo further pulverization. Thereafter, these coal particles are subject to repetition of the process described above. That is, the particles are thrown radially outwardly of the grinding table  14 , are picked up by the air exiting from the annular spaces  32 , are carried along with the air to the deflector means (not shown), are deflected back over the grinding table  14  by the deflector means (not shown), the heavier particles drop back on the grinding table  14 , the lighter particles are carried along to the classifier  30 , those particles which are of the proper size pass through the classifier  30  and exit from the bowl mill  10  through the outlets  34 . 
   The amount of force that must be exerted by the grinding rolls  18  in order to effect the desired degree of pulverization of the coal will vary depending on a number of factors. In other words, the amount of force that the grinding rolls  18  must exert in order to accomplish the desired pulverization of the coal is principally a function of the amount, e.g., depth, of coal present on the grinding table  14 . In turn, the amount of coal which is disposed on the grinding table  14  is a function of the output rate at which the bowl mill  10  is being operated to produce pulverized coal. 
   The amount of grinding force which the grinding rolls  18  apply to the coal on the grinding table  14  is a function of the amount of force with which the grinding rolls  18  are biased into engagement with the coal on the table  14 . The grinding roll  18  is supported so as to be pivotable about a pivot pin  36  into and out of engagement with the coal disposed on the grinding table  14 . Although only one grinding roll  18  is shown in  FIG. 1  and although this discussion is directed to one grinding roll  18 , it is to be understood that the bowl mill  10  commonly is provided with a plurality of grinding rolls  18 , e.g., preferably three in number, and that this discussion is equally applicable to each of the plurality of grinding rolls  18 . 
   The grinding roll  18  is designed to be biased by a spring force into and out of engagement with the coal on the grinding table  14 . More specifically, the spring force applied to the grinding roll  18  is applied by the mechanical coiled spring system  20 . To this end, the bowl mill  10  embodies a plurality of new and improved mechanical coiled spring assemblies  200 , as partially illustrated in  FIG. 4 . That is, in accord with the best mode embodiment of the invention each of the three grinding rolls  18  with which the bowl mill  10  is provided has cooperatively associated therewith a new and improved mechanical coiled spring system  200 . However, inasmuch as the three mechanical coiled spring systems  200  are each identical in construction and in mode of operation, it has been deemed sufficient for purposes of obtaining an understanding thereof as well as in the interest of maintaining clarity of illustration in the drawing to show only one of the three mechanical coiled spring systems  200  in  FIG. 4 . 
   Turning now to consideration in further detail of the nature of the construction of the mechanical coiled spring system  200  of  FIG. 4 , general reference will be made first to  FIGS. 2 and 3  for this purpose in describing the conventional mechanical coiled spring system  20  of  FIG. 1 . As depicted therein, the mechanical coiled spring system  20  includes the following major components: a stud bearing housing  37 ; a spring preload stud  38 ; pressure springs  39  and  40 ; a spring housing  42 ; and an extension cap  44 . 
   Referring to  FIGS. 2 and 3 , the spring preload stud  38  is configured to extend substantially the entire length of the mechanical coiled spring system  20 . Moreover, a first end  46  of the spring preload stud  38  extends from one end of the mechanical coiled spring system  20  and is covered by the extension cap  44 . With the first end  46  of the spring preload stud  38  positioned within the mechanical coiled spring system  20  in the manner depicted in  FIG. 2 , the first end  46  of the spring preload stud  38  is designed to protrude outwardly of the mechanical coiled spring system  20  to be visually inspected when the extension cap  44  is removed. 
   The mounting as shown in  FIG. 2  of the spring preload stud  38  within the mechanical coiled spring system  20  is accomplished through the operation of the stud bearing housing  37 . The stud bearing housing  37  is positioned relative to the spring preload stud  38  so as to encircle a spring adjust bolt bushing  50  interposed between the outer surface of an intermediate portion of the spring preload stud  38  and the inner surface of the stud bearing housing  37 . The spring adjust bolt bushing  50  in turn is fastened to the journal opening cover  52  of the bowl mill  10  through the use of any suitable form of conventional fastening means such as threaded fasteners, one of which can be seen depicted at  54  in  FIG. 2 . 
   A second end  62  of the spring preload stud  38  is configured so as to receive a first pressure spring seat  64 . The first pressure spring seat  64  is designed to interact with the pressure springs  39  and  40  on one side and is configured with on an opposite side to interact with the journal head  70  of the bowl mill  10  (see  FIG. 1 ). 
   Still referring to  FIG. 2 , the pressure springs  40  and  41  are inner and outer coil springs, respectively, in which each encircle the spring preload stud  38 . In addition, one end of each of the pressure springs  40  and  41  abut against a second pressure spring seat  80  having at least one piston ring  81  (two shown in  FIG. 2 ). The second pressure spring seat  80  is configured having the spring preload stud  38  to extend therethrough and abut a first end  82  extending from a spring adjust bolt and bearing assembly  85 . A second opposite end  84  extending from the spring adjust bolt and bearing assembly  85  abuts a spring adjusting nut  86  threadably engaged with threads  87  on the second end  46  of the spring preload stud  38 . As illustrated in  FIG. 2 , for example, but is not limited thereto, the spring adjusting nut  86  is a castle nut having a cotter pin  88  extending therethrough and through the preload stud  38  to prevent axial translation relative to each another. The other end of the journal pressure springs  40  and  41  abut against the first pressure spring seat  64  as discussed above. 
   The journal pressure springs  40  and  41  are housed within the spring housing  42 . The stud bearing housing  37  is positioned intermediate the journal opening cover  52  and the right-hand end of the spring housing  42 , as illustrated in  FIG. 2 . Furthermore, the stud bearing housing  37  is preferably both pinned and fastened to the journal opening cover  52 . That is, by means of a dowel pin (not shown), the stud bearing housing  37  is pinned to the journal opening cover  52 , whereas through the use of any suitable form of conventional fastening means such as threaded fasteners, the stud bearing housing  37  is fastened to the journal opening cover  52 . Any suitable form of conventional fastening means can also be used for purposes of securing the right-hand end, as viewed with reference to  FIG. 2 , of the spring housing  42  to the stud bearing housing  37  such as threaded fasteners (not shown). 
   As best seen with reference to  FIG. 2 , the spring adjustment bolt and bearing assembly  85  is associated with the spring adjust bolt bushing  50 . The spring adjustment bolt and bearing assembly  85  is threadably engaged with the spring adjust bolt bushing  50  allowing translation of the spring adjustment bolt and bearing assembly  85  relative to the spring adjust bolt bushing  50  fixed to the journal opening cover  52 . In this manner, the spring adjustment bolt and bearing assembly  85  can position the second pressure spring seat  80  which will in turn translate the first spring seat  64 , via connection to springs  40  and  41 , to provide a desired pivotal movement of the journal assembly  19  ( FIG. 1 ). Namely, rotation of the spring adjustment bolt and bearing assembly  85  is transmitted to the second pressure spring seat  80  and therethrough to the journal pressure springs  40  and  41  whereby as the grinding roll  18  wears, engagement is maintained as required between the spring stud insert  64  and the journal head insert  68  (see  FIG. 1 ). That is, as the grinding roll  18  wears the journal pressure springs  40  and  41  must be made to move closer to the journal head  70 . 
   A spring bolt locknut  94  is threadably engaged with corresponding threads on a first outside diameter  96  of the spring adjustment bolt and bearing assembly  85  to prevent further translation thereof once the desired position is selected. More specifically, the spring bolt locknut  94  is suitably located relative to the journal opening cover  52  so as to be in abutting engagement therewith. 
   As best understood with reference to  FIGS. 2 and 3 , an O-ring  98  is cooperatively associated with the spring bolt locknut  94 . Finally, the spring bolt locknut  94  and the other components associated therewith which have been enumerated above are all housed within the stud extension cap  44 . 
   Referring to  FIG. 3  in particular, the spring adjustment bolt and bearing assembly  85  includes a spring adjustment bolt  100  having the threaded first outside diameter  96  and a second outside diameter  102  smaller than the first outside diameter  96 . The second outside diameter  102  is not threaded and corresponds to a terminal end of the spring adjustment bolt  100  abutting the locknut  86 . A third outside diameter  104  smaller than the first outside diameter and larger than the second diameter  102  is interposed therebetween and defines a shoulder between the first and second outside diameters  96 ,  102  of the spring adjustment bolt  100 . The spring bolt locknut  94  is threadably engaged with corresponding threads  106  on the first outside diameter  96  of the spring adjustment bolt  100  to axially lock the spring adjustment bolt and bearing assembly  85  with respect to the spring adjust bolt bushing  50  fixed to the journal opening cover  52  and prevent further translation thereof once the desired axial position is selected. An inside diameter defining the spring adjustment bolt  100  includes a bushing  108  impregnated with a plurality of spaced apart long-wearing seals  110  (seven shown in  FIG. 2 ) along an axial length defining an inside diameter of the bushing  108 . The bushing  108  is made of bronze impregnated with long-wearing graphite as the seals  110  forming a seal with the spring preload stud  38  while allowing the spring preload stud  38  to be axially translatable therethrough. 
     FIG. 4  illustrates an exemplary embodiment of a seal assembly  300  for a mechanical coiled spring assembly  200  which allows visually inspection of the first end  46  of the preload stud  38  at all times, including during operation of a bowl mill to which it is associated while maintaining a positive seal at the end of the coil spring assembly  200 , in accordance with the present invention. In particular, it will be recognized that  FIG. 4  is a partial cross-sectional view of  FIG. 3  with the O-ring  98 , cotter pin  88  and extension cap  44  removed from the mechanical coiled spring assembly  200  of  FIG. 4 . 
     FIG. 4  illustrates the seal assembly  300  including a seal  344  which is substantially cylindrical shaped and flexible at least along a central axis thereof and corresponding to an axis defined by the preload stud  38 . The seal  344  includes a first end  346  operably secured to the spring adjustment bolt and bearing assembly  85  and an opposite second end  348  operably secured to the second end  46  of the preload stud  38  thereby sealing the bushing  108  corresponding to a portion of the preload stud  38  surrounded by the spring adjustment bolt and bearing assembly  85  from ground solid fuel dust and allowing movement of the preload stud  38  at least along the central axis thereof to apply the spring force from the coil spring assembly  200  to the grinding roll  18  ( FIG. 1 ). As described with reference to  FIGS. 2 and 3  above, the spring adjustment nut  86  abuts the spring adjustment bolt  100  of the spring adjustment and bearing assembly  85  by being threadably engaged with threads  87  on the second end  46  of the preload stud  38  extending therethrough. The second end  348  of the seal  344  is mounted to a mounting ring portion  350  having the second end  46  of the preload stud  38  extending therefrom. 
   In an exemplary embodiment as illustrated in  FIG. 4 , the mounting ring portion  350  is an independent mounting ring  352  slidably disposed over a portion of the exposed second end  46  of the preload stud  38 . Further, the mounting ring  352  is configured having an outside diameter substantially the same as an outside diameter corresponding to the third outside diameter  104  of the spring adjustment bolt and bearing assembly  85  to which the seal  344  is secured. In alternative exemplary embodiments, the mounting ring portion  350  may be integral with the spring adjusting nut  86 . For example, the spring adjusting nut  86  may include the flats of the nut configured having a cylindrical outside diameter to circumferentially clamp the second end  348  of the seal  344  thereto. 
   The seal assembly  300  further includes a nut  354  threadably engaged on corresponding threads  87  on a remaining portion of the exposed second end  46  of the preload stud  38  abutting the mounting ring  352  to secure the mounting ring  352  to the preload stud  38 . In exemplary embodiments, the nut  354  is a hex jam nut installed on the corresponding threads  87  on end  46  of the exposed spring preload stud  38 . 
   In exemplary embodiments of the seal assembly  300 , the seal  344  is flexible allowing relative motion of the preload stud  38  in axial, radial and angular directions, while exposing a terminal end of end  46  of the preload stud  38  and maintaining a positive seal to prevent solid fuel dust (e.g., coal dust) as a result of pulverization from entering a bushing area corresponding to the bushing  108  and a portion of the preload stud  38  surrounded thereby. In an exemplary embodiment as illustrated in  FIG. 4 , the positive seal is maintained using a bellows type seal  344  with a clamp circumferentially around each of the first and second ends  346 ,  348  of the seal  348 . The bellows seal  344  allows for a high amount of relative motion (e.g., axial, radial, and angular) between the spring preload stud  38  and the remainder of the coil spring assembly  200  while still providing a positive seal. In the prior art, internal lip type seals have been used to seal against the spring stud, but the internal lip type seals experienced excessive wear and were not capable of withstanding the relative motion of the spring preload stud and coil spring assembly. 
   It will be recognized, by those skilled in the pertinent art that the above described bellows seal  344  may be configured for different sizes and types of journal spring assemblies, both existing and new, but the same design concept will be consistent. In exemplary embodiments, the bellows seal  344  is made of a polymer such as nitrile or neoprene as well as plastics or other suitable sealing materials (e.g., rubber, a reinforced rubber, silicon, plastic, or any other suitably flexible material). Any suitable natural rubber or synthetic polymer may be employed; neoprene rubber, polyurethanes, styrene/butadiene rubbers, nitrile elastomers, and silicone resins might be mentioned as typical, but the selection of a suitable material for any given application will be evident to those skilled in the art. In addition to providing the requisite flexibility, resiliency and durability under the variety of conditions to which the seal might be exposed, the material from which the seal is formed must be capable of forming a seal with the preload stud and spring bolt and bearing assembly, both composed of metal. For example, one exemplary embodiment of a bellows type seal is comprised of a nylon reinforced neoprene rubber. Although a clamp has been described above to maintain such a seal with respect to the preload stud and spring bolt and bearing assembly, the seal may be promoted by the use of an adhesive, a bonding agent, a chemical surface activator, or the like (the choice of which will also be evident to those skilled in the art), as well as by roughening of the surface of the component to which the rubber is to be bonded (e.g., by sand-blasting or the equivalent), or by other means. 
   Referring to  FIGS. 3 and 4 , it will be recognized by those skilled in the pertinent art that mechanical coiled spring assembly  200  of  FIG. 4  may be obtained by retrofitting the mechanical coiled spring assembly  20  of  FIG. 3  while maintaining as many original parts as possible. More specifically, it will be noticed that in order to retrofit the mechanical coiled spring assembly  20  of  FIG. 3 , the extension cap  44  and O-ring  98  are first removed. 
   In particular still referring to  FIGS. 3 and 4 , a method of retrofitting a seal for a mechanical coiled spring assembly first includes removing the extension cap  44  from a first end of the coil spring assembly to expose the first end  46  of the preload stud  38  and spring adjusting nut  86  of the coil spring assembly. Next, the existing O-ring seal  98  is removed from the spring adjusting bolt and bearing assembly  85 . 
   The mounting ring  352  is then installed over a portion of the exposed first end  46  of the preload stud  38  and the substantially cylindrical shaped and flexible seal  344  is installed over the spring adjustment bolt and bearing assembly  85 , the spring adjusting nut  86  and the mounting ring  352 . The seal  344  is flexible at least along a central axis thereof. In exemplary embodiments as discussed above, the seal is a bellows type seal, as illustrated in  FIG. 4 , and is thus flexible allowing relative motion of the preload stud  38  in axial, radial and angular directions with respect to the remaining spring coil assembly, while maintaining a positive seal. 
   Referring to  FIG. 4 , the first end  346  of the seal  344  is sealably secured to the third outside diameter  104  of the spring adjustment bolt  100 . The opposite second end  348  of the seal  344  is sealably secured to the mounting ring  352 . As discussed, a bellows clamp is used at each of the ends  346 ,  348  for sealable securement with the third outside diameter  104  of the spring adjustment bolt  100  and the mounting ring  352 , respectively. The exemplary method further includes threadably engaging the nut  354  on corresponding threads  87  on a remaining portion of the exposed first end  46  of the preload stud  38  to secure the mounting ring  352  to the preload stud  38 . 
   There will now be set forth a description of the mode of operation of the mechanical coiled spring system  200 , which forms the subject matter of the present invention, in the context of the operation of the bowl mill  10  of  FIG. 1 . For this purpose, reference will be had in particular to  FIGS. 1 and 4 . The mechanical coiled spring system  200  of  FIG. 4  is suitably mounted on the exterior wall surface of the separator body  12 , and in particular on the journal opening cover  52  of  FIG. 1  in a same manner that the coil spring system  20  of  FIGS. 1-3 . Within the mechanical coiled spring system  200 , the journal pressure springs  40  and  41 , as has been described in detail hereinbefore is suitably supported for expansion and contraction therewithin. However, a single spring or more than two springs (e.g., may or may not be concentric with one another) or other biasing member other than a mechanical coiled spring is contemplated in alternative exemplary embodiments. Cooperatively associated with the journal pressure springs  40  and  41  is the spring stud insert  64 , which projects outwardly of the mechanical coiled spring system  200 . The spring stud insert  64  engages the journal head insert  68 , which is suitably affixed to the journal head  70 . The journal head  70  in turn comprises a portion of the support means for the grinding roll  18 . In a manner well-known to those skilled in the spring biasing art, the journal pressure springs  40  and  41  through the spring stud insert  64  exert a spring biasing force on the journal head insert  68  and thereby to the journal head  70 . 
   Accordingly, the engagement of the spring stud insert  64  with the journal head insert  68  and thereby the journal head  70  is a function of the force being exerted by the journal pressure springs  40  and  41 . In turn, the extent to which the spring stud insert  64  is biased into engagement with the journal head insert  68  and thereby with the journal head  70  by the journal pressure springs  40  and  41  determines the extent to which the grinding roll  18  is spring biased into engagement with the coal on the grinding table  14 , and concomitantly the amount of grinding force being applied to the coal by the grinding roll  18 . 
   By way of exemplification and referring to  FIG. 1 , as the coal builds up on the grinding table  14 , i.e., under the grinding roll  18 , the journal head  70  rotates in a counterclockwise direction about the pivot pin  36  which results in an increase in the spring force that is exerted by the mechanical coiled spring system  20 . Conversely, when the grinding roll  18  and/or grinding table  14  wears, the journal head  70  rotates in a clockwise direction about the pivot pin  36  which results in a decrease in the spring force that is exerted by the mechanical coiled spring system  200 . However, unlike the conventional mechanical spring system illustrated in  FIGS. 1-3  in which the extension cap  44  must be removed to allow inspection of the first end  46  of the preload stud  38  to determine the amount of spring movement indicative of movement of the journal head  70  and grinding roll  18 , the seal assembly  300  of  FIG. 4  allows visual inspection of first end  46  of the preload stud  38  to determine the amount of spring movement indicative of movement of the journal head  70  and grinding roll  18 . 
   The seal assembly  300  of  FIG. 4 , in accordance with exemplary embodiments of the present invention, allows visual inspection of an end of the preload stud exposed to atmospheric pressure without having to remove a cap for visual inspection thereof and maintains a positive seal across the coil spring assembly to effectively eliminate a differential pressure while allowing the preload stud to translate at least along a central axis thereof with respect to the fixed coiled spring assembly. In this manner, the end of the preload stud may be monitored at all times and solid fuel dust, such as coal dust, for example, can be effectively prevented from penetrating into the assembly. Lastly, exemplary embodiments of the seal assembly in accordance with the present invention permit the mechanical coiled spring assembly  200  of  FIG. 4  to be obtained by retrofitting the mechanical coiled spring assembly  20  of  FIGS. 2 and 3  while maintaining as many original parts as possible. 
   While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.