Abstract:
A relief spring stop bolt assembly for shallow bowl coal pulverizing mills and a method of using the same to smooth operation of such a pulverizer during low load operation is described. The subject relief spring stop bolt assembly is sized to be used with or for “retrofit” within existing journal space and existing journal opening cover space of a shallow bowl mill to effectively smooth rough operating conditions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to solid fuel pulverizers, and more specifically, to a relief spring stop bolt assembly for shallow bowl coal pulverizing mills. 
     BACKGROUND OF THE INVENTION 
     Solid fossil fuels such as coal often are ground in order to render the solid fossil fuel suitable for certain applications. Grinding the solid fossil fuel can be accomplished using a device referred to by those skilled in the art as a pulverizer. One type of pulverizer suited for grinding is referred to as a “bowl mill pulverizer”. This type of pulverizer obtains its name by virtue of the fact that the pulverization that takes place therein is effected on a grinding surface that in configuration bears a resemblance to a bowl. In general, a bowl mill pulverizer comprises a body portion on which a grinding table is mounted for rotation. Grinding rollers mounted on suitably supported journals interact with the grinding table to effect the grinding of material interposed therebetween. After being pulverized, the particles of material are thrown outwardly by centrifugal force, whereby the particles are fed into a stream of warm air and blown into other devices for separation by particle size. 
     Grinding rollers are urged toward the grinding table against the fossil fuel being ground by a spring assembly. The force that this exerts may be manually adjusted. The greater the force, the finer the particle size of the fossil fuels being ground. 
     Coal pulverizers operating under low load conditions when there isn&#39;t enough coal feed to develop a stable coal bed causes rough operation. Rough operation causes high bending stresses to be placed on a main vertical shaft of the pulverizer, which can result in its failure. These stresses are also high enough that many component failures have been attributed to such rough operation. Relief spring assemblies have been used in the past on deep bowl mills to reduce such stresses at times of rough operation. However, such spring, assembly arrangements are not possible on shallow bowl mills due to the very small space available working within existing journal and journal opening cover spaces. 
     It is important that any solution to this existing rough operation issue is capable of implementation within existing journal and journal opening cover spaces due to the expense of otherwise replacing such equipment. Accordingly, any solution must be able to be used with or “retrofitted” to fit within existing journal space and existing journal opening cover space of a shallow bowl mill. 
     SUMMARY OF THE INVENTION 
     The present invention is a relief spring stop bolt assembly for shallow bowl mills used in fossil fuel pulverization. The subject relief spring stop bolt assembly is used with or for “retrofit” within existing journal space and existing journal opening cover space of a shallow bowl mill. The relief spring stop bolt assembly is spring loaded to be solid under the full pivoting weight of the journal assembly, while providing approximately one quarter of an inch of travel to dampen or ease the journal assembly&#39;s downward travel as it comes down on the stop bolt. This spring load feature of the subject stop bolt assembly also assists the journal as it first starts to lift off the stop bolt. By easing the journal assembly&#39;s downward travel and assisting the journal as it first starts to lift off the stop bolt, the pulverizer&#39;s operation is smoothed out or less rough under low load conditions when there isn&#39;t enough fossil fuel, such as coal, feed to develop a stable fuel bed or coal bed. 
     The present relief spring stop bolt assembly, which works with existing commercial journals and journal opening covers, comprises an adjustable threaded stationary section. The adjustable threaded stationary section may be turned clockwise in or counterclockwise out to adjust the “ring to roll” distance or setting. The ring to roll setting dictates the distance between an associated grinding table and the journal roll when there is no fuel or coal in the mill. A nose section of the relief spring stop bolt assembly contacts the journal when there is no coal in the mill. The spring used in the assembly is either a coil spring or spring discs to allow the bolt to be solid under the gravity load of the journal assembly and to allow proper ring to roll setting without the risk of the spring flexing too much and allowing the journal to hit the grinding table. The spring portion of the assembly must also be strong enough to provide sufficient dampening or easing for loads over ten tons and sufficient spring assist for the journal in order to smooth out low load operation thereof. The selected spring must have a useful operating life in the millions of cycles. 
     The present relief spring stop bolt assembly likewise comprises a bolt bushing to provide protection to the assembly from dust and debris and to allow for lubrication of the stop bolt spring. 
     Accordingly, the present disclosure provides for a pulverizer stop bolt assembly comprising a stop bolt with a spring mechanism solidly immobile for adjustment to prevent a pulverizer journal assembly from contacting a grinding surface of the pulverizer upon bearing a gravity load of the journal assembly, and a spring in the spring mechanism strong enough to provide significant load dampening and ample spring assist to smooth out low load operation of a shallow bowl mill-type pulverizer. 
     The present disclosure also provides a method of smoothing pulverizer operation during low load use comprising fixing to a pulverizer housing a stop bolt with a spring mechanism solidly immobile for adjustment to prevent a pulverizer journal assembly from contacting a grinding surface of the pulverizer upon bearing a gravity load of the journal assembly, and using a spring in the spring mechanism strong enough to provide significant load dampening and ample spring assist to smooth out low load operation of a shallow bowl mill-type pulverizer. 
     Likewise, the present disclosure provides a method of replacing a pulverizer stop bolt assembly for smoother operation during low load use comprising removing screws from a stop bolt assembly, removing the stop bolt assembly from a pulverizer housing, inserting a relief spring stop bolt assembly into the pulverizer housing, and tightening screws to fix the relief spring stop bolt assembly to the pulverizer housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, partial, side cross-sectional view of a pulverizer including a prior art stop bolt assembly. 
         FIG. 2  is a schematic, enlarged side cross-sectional view of the prior art stop bolt assembly of  FIG. 1 . 
         FIG. 3  is a schematic, enlarged side cross-sectional view of the journal stop bolt assembly of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , is a shallow bowl mill-type pulverizer  10  that includes a pulverizer housing  12  with an interior area  14  having a grinding table  16  situated therein. Grinding table  16  provides a grinding surface  18  for a material, such as a fossil fuel, such as coal, to be pulverized. In one embodiment, the grinding table  16  is mounted on a shaft (not shown) operatively connected to a gearbox drive mechanism (not shown) so as to be capable of driven rotation within the pulverizer housing  12 . A journal assembly  20  is pivotally mounted on a pivot shaft  22  that is secured to the pulverizer housing  12 . For ease of illustration, only one journal assembly  20  and associated spring assembly  24  are shown and described, but the invention is not limited in this regard, and in other embodiments, the pulverizer  10  may comprise two, three, or more journal assemblies  20  and associated pressure spring assemblies  24 , which may be evenly distributed about the grinding surface  18 . 
     The journal assembly  20  carries a grinding roll  26  rotatably mounted thereon and positions the grinding roll to define a gap G 1  between the grinding roll  26  and the grinding surface  18 . The gap G 1  varies when the journal assembly  20  pivots on the pivot shaft  22 . The journal assembly  20  includes a journal stop flange  28  and an associated stop bolt  30  in the pulverizer housing  12  to limit the pivoting motion of the journal assembly  20  toward the grinding surface  18 , thus setting a minimum size for the gap G 1 . As known in the art, selecting the minimum size for gap G 1  contributes to determining the particle size distribution of the pulverized material produced in the pulverizer  10 . 
     The journal assembly  20  also includes a journal head  32 , and the journal assembly  20  and the spring assembly  24  are mounted on the pulverizer housing  12  so that the journal head  32  can engage the spring seat  34  when the journal assembly  20  pivots away from the grinding surface  18 , e.g., in response to the introduction of granule material between the grinding surface  18  and the grinding roll  26 . Optionally, the journal assembly  20  and the spring assembly  24  may be configured so that there is a gap G 2  between the journal head  32  and the spring seat  34 . The gap G 2  is at a maximum when the journal assembly pivots fully forward, i.e., when the gap G 1  is at a minimum. The maximum gap G 2  can be adjusted by advancing or retracting the support bolt  36  of spring assembly  24 . When the journal assembly  20  pivots sufficiently to close the gap G 2 , the journal head  32  engages the spring seat  34  and the spring assembly  24  imposes a spring force upon the journal head  32 . The journal assembly  20  then conveys the spring force onto the granule material to be pulverized via the grinding roll  26 . The more that the granule material causes the journal assembly  20  to pivot away from the grinding surface  18 , the more the springs  38  of spring assembly  24  are compressed and the greater the spring force that is imposed on the journal head  32 . 
     As noted previously, the journal assembly  20  includes a journal stop flange  28  and an associated stop bolt  30  in the pulverizer housing  12  to limit the pivoting motion of the journal assembly  20  toward the grinding surface  18 , thus setting a minimum size for the gap G 1 . As best illustrated in  FIG. 2  is an enlarged, detailed illustration of the stop flange  28  and associated prior art stop bolt  30  of  FIG. 1 . Stop bolt  30  is one component of the prior art stop bolt assembly  40 . Stop bolt assembly  40  includes a housing  42  positioned in the pulverizer housing  12  and fixed into place with threaded screws  42 . Stop bolt  30  extends from exterior surface  44  of pulverizer housing  12  and from interior surface  46  of pulverizer housing  12  through a channel  48  formed through housing  42 . A portion of exterior surface  50  of stop bolt  30  has threading  52  for fixed positioning of stop bolt  30  within housing  42  thereby setting gap G 1 . 
     Illustrated in  FIG. 3  is the subject relief spring stop bolt assembly  300  of the present disclosure. Relief spring stop bolt assembly  300  is sized to readily replace stop bolt assembly  40  illustrated in  FIG. 2 . As such, stop bolt assembly  40  is removed from pulverizer housing  12  by counterclockwise rotation of threaded screws  42  for removal thereof. Upon removal of threaded screws  42 , housing  42  is removed from an interior seating area  12   a  in pulverizer housing  12 . Once housing  42  is removed from interior seating area  12   a  in pulverizer housing  12 , relief spring stop bolt assembly  300  is placed in interior seating area  12   a  in pulverizer housing  12 . Accordingly, the subject relief spring stop bolt assembly  300  may be installed in a new pulverizer housing  12  as new equipment or may be installed as just described in a used pulverizer housing  12  as a “retrofit” to replace stop bolt assembly  40 . 
     As illustrated in  FIG. 3 , relief spring stop bolt assembly  300  comprises a housing  302  that comprises fixative screws  304 , an elongated head portion  306 , an O-ring channel  308 , and an O-ring  310 . Relief spring stop bolt assembly  300  also comprises stop bolt  312  with nose surface  314  opposite an adjustment end  316 . Proximal to adjustment end  316  is threaded area  318  on exterior surface  320  of stop bolt  312 . Between nose surface  314  and adjustment end  316  is spring  322 . Spring  322  comprises either a coil spring or spring discs selected to allow the stop bolt  312  to go solid under the gravity load of the journal assembly  20  to allow proper ring to roll adjustment without the risk of the spring  322  flexing too much and allowing the journal assembly  20  to hit the grinding surface  18 . At the same time, the spring  322  must be strong enough to provide significant dampening and ample spring assist to smooth out low load operation of the pulverizer  10 . Due to extreme size limitations, strength requirements and durability requirements, spring  322  preferably comprises a disc spring, such as a Belleville disc spring. 
     As noted above, stop bolt  312  goes solid under the gravity load of the journal assembly  20  to allow proper ring to roll adjustment without the risk of the spring  322  flexing too much and allowing the journal assembly  20  to hit the grinding surface  18 . To accomplish these requirements, stop bolt  312  has a number of specialized features. Nose surface  314  forms free end  324  of contact portion  326 . Contact portion  326  includes opposite nose surface  314 , an elongated arm  328 . Elongated arm  328  of contact portion  326  extends through a center area  330  of spring  322  for positioning within a slot  332  of base portion  334 . Elongated arm  328  has an oversized aperture  336  therethrough. A pin member  338  extends through oversized aperture  336  into base portion  334  to moveably interlock contact portion  326  to base portion  334 . When no weight is on contact portion  326 , spring  322  holds elongated arm  328  away from bottom  340  of slot  332  so pin member  338  is in contact with a base side  342  of oversized aperture  336 . When the journal assembly  20  comes to rest on nose surface  314  of contact portion  326 , stop bolt  312  goes solid by free end  344  of elongated arm  328  abutting bottom  340  of slot  332  so pin member  338  is in contact with a nose side  346  of oversized aperture  336 . Also under such conditions, spring  322  is compressed between wall  354  of contact portion  326  and a hardened thrust washer  356  in groove  358  on free ends  360  of base portion  334 . As the weight of journal assembly  20  moves from stop bolt  312 , spring  322  provides ample spring force assist to smooth out low load operation of the pulverizer  10 . The spring force assist of spring  322  moves elongated arm  328  of contact portion  326  away from bottom  340  of slot  332  so pin member  338  is again in contact with base side  342  of oversized aperture  336 . According to the mechanism just described, the stop bolt  312  goes solid under the gravity load of the journal assembly  20  to allow proper ring to roll adjustment without the risk of the spring  322  flexing too much and allowing the journal assembly  20  to hit the grinding surface  18 . At the same time, spring  322  is strong enough to provide significant dampening and ample spring assist to smooth out low load operation of the pulverizer  10 . At the same time, the subject relief spring stop bolt assembly  300  meets the extreme size limitations, strength requirements and durability requirements, for use or retrofit with shallow bowl mill-type pulverizers  10 . 
     As noted above, relief spring stop bolt assembly  300  comprises a housing  302  that comprises fixative screws  304 , an elongated head portion  306 , an O-ring channel  308 , and an O-ring  310 . Elongated head portion  306  extends a distance beyond surface  12   b  of pulverizer housing  12  so as to accommodate movement of stop bolt  312  by spring  322  therein, O-ring channel  308 , and an O-ring  310 . O-ring  310  abuts side  348  of contact portion  326  of stop bolt  312  to form a seal  350  therearound. Seal  350  serves to keep dust, dirt and debris away from the mechanical features of stop bolt  312  and serves to maintain a lubricant or grease on spring  322 . A grease port  352  with closure cap  352   a  may be provided through pulverizer housing  12  into housing  302  for lubricant supply and maintenance. 
     A method of smoothing shallow bowl mill-type pulverizer  10  operation during low load use comprises using a relief spring stop bolt assembly  300  that is solid under a gravity load of journal assembly  20  and provides spring assist upon a change in the gravity load. As such, the subject relief spring stop bolt assembly  300  allows for proper ring to roll adjustment without the risk of the spring  322  flexing too much to allow the journal assembly  20  to hit the grinding surface  18 . At the same time, the relief spring stop bolt assembly  300 , with spring  322 , is strong enough to provide significant dampening and ample spring assist to smooth out low load operation of the shallow bowl mill-type pulverizer  10 . 
     A method of replacing a pulverizer stop bolt assembly for smoother operation during low load use comprises removing screws  42  from stop bolt assembly  40 , removing stop bolt assembly  40  from pulverizer housing  12 , inserting the subject relief spring stop bolt assembly  300  into pulverizer housing  12  and tightening screws  304  into pulverizer housing  12 . 
     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.