Abstract:
A method of protecting coal mill journals from abrasive wear due to impingement of coal fines includes the steps of fabricating and attaching a mild steel liner form to the journal and welding wear plates to the liner form. Welding the plates to the form can occur before and/or after the form is attached to the journal. The liner form is made up of plates providing only flat exterior surfaces.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to the protection of coal mill journals from abrasive wear due to the impingement of coal fines carried by an air stream flowing through the coal mill and more particularly to a method and apparatus for of protecting a coal mill journal comprising the steps of attaching a liner form made up of flat surfaces to the journal and covering the flat surfaces with high hardness wear plates.  
       BACKGROUND  
       [0002]     Classifier type coal mills utilize pressure rollers which rotate over the holding surface of a rotating bowl onto which lump coal is fed so as to be crushed by interaction between the rollers and the bowl surface. The rollers are supported by journals having spring suspension systems. The journals and the suspension systems are subject to harsh abrasive wear as a result of the impingement of milled coal carried into contact with the journal and suspension system components by a stream of air which flows upwardly through the mill to perform a classifier function.  
         [0003]     In this environment coal mill journals and suspension components wear away in a relatively uneven fashion to create rough outer surfaces and eventually to weaken the structural components to the point where they must be replaced.  
         [0004]     In the past it has been common to protect the journal and associated components by welding custom cut wear plates to the eroded surfaces of the journal and suspension housings. Because each journal housing wears in a somewhat different fashion, liner wear plates have to be cut and fit in a laborious fashion. The attachment process is made more difficult by the fact that most journal housing surfaces are curved whereas the wear plates are cut from larger plates which are entirely flat. In many cases, the journal is so severely worn that insufficient material remains to level off the surface without further weakening it. The result is high expense in the process of attaching the wear materials and, in many cases, premature replacement of journal components.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention facilitates the protection of coal mill journals and associated suspension housings with high hardness wear materials by providing a liner form which essentially covers a journal to the extent needed to intercept impinging milled coal carried in an airstream and provides further advantage in offering exclusively flat contiguous outer surfaces to which high hardness wear plates are readily attached by processes such as welding. The liner form preferably has peripheral edges which are contoured to conform to the external configuration of the journal; for example, the partial enclosure defined by an illustrative liner form has a flat front surface with an arcuate cut-out which conforms to the cylindrical surface of a journal housing so as to permit the liner form to be attached such as by welding to the journal housing.  
         [0006]     In accordance with the present invention, the wear materials may be attached to the liner form before or after it is installed on the journal, the overall result of protecting the journal and suspension components from excessive wear being achieved in either case. Once the journal liner form is installed, the wear plates on it may be replaced several times either individually or in groups.  
         [0007]     In accordance with the preferred form of the invention, the liner form is made of flat half-inch mild steel plates welded together to create a form with all flat major surfaces. This simple design allows for the easy creation and attachment of flat wear plate components made, for example, from SA1750CR chromium carbide. Other equivalent materials include cast alloys, and ceramics with alumina filler. It has been found that the journal liner structure of the present invention not only protects the journal from wear but adds to its overall structural strength as well. It has also been found that the liner of the present invention may be installed over previously repaired areas even though such areas present highly irregular exterior surfaces.  
         [0008]     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0010]      FIG. 1  is a cross sectional perspective view of a representative coal mill embodying one form of the invention.  
         [0011]      FIG. 2  is a front view of a journal liner constructed in accordance with the present invention.  
         [0012]      FIG. 3  is a side view of the journal liner of  FIG. 2 .  
         [0013]      FIG. 4  is a perspective view with a portion of the wear plate liner broken away, of the liner form of  FIG. 2   
         [0014]      FIG. 5  is a side view of an installed journal liner from the coal mill of  FIG. 1 .  
         [0015]      FIG. 6  is a cross section of a weld area showing how a wear plate is welded to the liner form of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0016]     Referring to  FIG. 2 , a representative coal mill/classifier as shown comprises a large steel cylindrical housing  10  within which a pulverizer bowl  12  is mounted for rotation about a vertical axis. The bowl  12  receives lump coal through a loading chute  14  and a feed pipe  16 . A vane wheel  18  is attached to the bowl  12  around the outer periphery thereof and rotates with the bowl about the vertical axis. A surrounding structure  20  and a stationary deflector  21  control air flow in a known manner. Tapered rollers  22  are mounted within the mill  10  so as to crush the lump coal fed to the bowl  12  as the bowl rotates about the vertical axis. The contact surfaces of the rollers  22  rotate on axles  21  extending through journal housings  24  into a radially enlarged portion  26  of the housing  10 . Compression spring type suspension units  28  are mounted to the housing portion  26  above and in parallel to the journal axes and are mechanically engaged with radial arms  25  to permit the rollers  22  and journal assemblies associated therewith to pivot about an axis defined by mechanism  29  shown in  FIG. 5 . This allows the rollers  22  to lift off the contact surface of the bowl  12  to accommodate particularly large or hard lumps of coal or other foreign objects which may come between the surfaces of the rollers  22  and the bowl  12 . At the same time the compression springs in the suspension units  28  urge the rollers  22  into firm contact with the bowl thereby to efficiently perform the crushing action.  
         [0017]     The operation of the rollers  22  and the vane wheel  18  is such as to create an upward flowing air stream within the housing  10  which, as will be apparent for those knowledgeable about coal mill/classifiers, carries the coal fines upwardly to and through discharge chutes  30  which feed one or more combustion chambers for turbine boilers. This upward flow of coal fines is instrumental in eroding unprotected surfaces of the journal housing  24  and suspension arms connected between the journal housing  24  and the inner end of the suspension mechanisms  28 .  
         [0018]     To deal with this problem, the present invention employs generally triangular mild steel liner forms  32  mounted on the journals  24  to protect the radial suspension arm  25  and journal surfaces from erosion due to impingement by the upwardly flowing coal fines. As shown in  FIGS. 2-5  the mild steel forms  32  are constructed entirely of flat plates which are cut to the desired shape and size and welded together along the edges. Each liner form comprises a flat front plate  34 , side plates  36  and  38 , a top plate  40  and a lower front plate  42  having an arcuate cut out  43  which matches the radius of the journal housing  24  so as to sit in close abutting relationship thereover when installed as shown in  FIGS. 1 and 5 . The back of the liner form  32  is open but preferably has side and bottom flanges of approximately one-inch depth as shown by the dotted lines in  FIG. 2 , together with back straps  48  and  50  welded across the side flanges for rigidity as shown.  
         [0019]     High hardness chromium steel wear plates  52  are attached such as by welding to the flat exterior surfaces of the liner form  32  as shown in  FIGS. 2-5 . The attachment procedure and mechanism may take various forms; for example if the wear plates  52  are welded to the mild steel form  32  before the form is installed on the journal housing  24 , it i possible to weld them to the form from the inside. This is achieved by burning one or more holes in the liner form neatly under each of the wear plates  52  and then welding the form to the plate from the inside. It is more likely, however, that the wear plates  52  are welded to the form  32  from the outside so as to create greater latitude with respect to when the wear plates  52  are attached as well as to permit the wear plates  52  to be replaced from time to time over the life of the journal protecting form  32 . In short, attachment of the plates  52  to the form  32  after mounting the form on the journal is the preferred mode.  
         [0020]     To this end a hole is burned in the wear plate  52  as shown in  FIG. 6  and a weld  54  is formed to attach the wear plate  52  to the liner form  32 . Thereafter a hardened steel plug  56  is set in place to protect the weld. The plug  56  may be carefully shaped and simply hammered into place.  
         [0021]     Whether or not the wear plates  52  are attached before or after installation, it is necessary to seat the liner form  32  on the journal housing  24  so that the arcuate cut out  43  rests on and conforms to the curvature of the journal housing  24 . Thereafter a linear weld is applied along the seam between the cut out  43  and the journal housing  24 . The open back of the liner form  32  is of no consequence since any coal fines which may find there way in and through the back of the form have insufficient kinetic energy to create a significant erosion when contacting the unprotected metal of the journal housing  24  and/or the suspension arm. The liner form of the high hardness wear plates fully protects not only the critical upper surface of the journal housing  24  but the entirety of the radial suspension arm which lies within the liner form.  
         [0022]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.