Patent Publication Number: US-2009218429-A1

Title: Hard elements for the autogenous wear protection of roller surfaces

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to hard bodies for partial insertion into recesses in the surface of rollers of roller presses for pressure comminution of granular stock material, whereby in operation of the roller press the interstices between the hard bodies, which protrude outwardly, are filled with compressed fine-grained stock material. 
     In roller presses granular brittle grinding stock is fed into the nip, by which the two pivotable oppositely rotatable rollers are separated from each other, and is subjected to pressure comminution there. Also known is the so called high pressure comminution in a nip of a high pressure roller, also called a roller press, in which individual particles of the grinding stock, which is fed into the nip by friction, are being mutually comminuted in a bed of grinding stock, i.e., in a material fill compressed between both roller surfaces, with application of high pressure. Here the roller surfaces are subject to high wear. At least the following requirements are being demanded from those roller surfaces: 
     They must have a high wear resistance, being able to be manufactured in a cost-saving way, having good feeding characteristics for the stock to be comminuted and if necessary be able to be repaired by the operator at least partially. 
     It is known to improve wear resistance of the roller surfaces of roller presses by incorporating into the roller surface a plurality of premanufactured hard bodies, like e.g. powder metallurgical manufactured pin shaped nap bolts, into corresponding tapped blind holes of the roller surface, e.g. DEL-A 41 32 474 FIG. 6 and EP-B-0 578 239. 
     Thereby the nap bolts, which stand within the radial tapped blind holes, protrude outwardly from the roller surface with such a height that during operation of the roller press the interstices between the nap bolts remain filled with the compressed fine-grained stock material, which forms an autogenous wear protection for the roller surfaces and due to its roughness comprises a good feeding characteristic. This well known roller surface armoring has proved of value in the interparticle comminution practice, especially of ore material. Because in the embodiment of DE-A-41 32 474 FIG. 5 bushing shaped pieces, which do not protrude, but which are flush with the roller surface, are incorporated in the roller body, this kind of roller surface is not covered by the afore-mentioned grid armoring. 
     In the grid armoring the pin shaped nap bolts sit tightly in their tapped blind holes. Should an exchange of individual nap bolts become necessary, the disassembly of the nap bolts may become difficult, especially when these tapped blind holes are partially broken out. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of supplying the afore-mentioned grid armorings of roller press rollers hard bodies, which are able to be manufactured in a cost-saving way and which primarily are easy to disassemble out of their roller body recesses even in a damaged condition for the purpose of repairing the roller. 
     The hard bodies according to the invention, namely the premanufactured normally powder metallurgical made, e.g., pin shaped respectively cylindrical hard metal nap bolts comprise a central recess, which starting from the radial inner end of the hard body extends at least partially over the hard body height. This central recess is dimensioned such that it does not weaken the hard body, but in any case contributes to cost reduction during manufacture of the premanufactured hard bodies by material saving. The more important advantage of the central recess in the premanufactured hard body is that the central recess is being exploited for disassembly of the hard body being stuck in a corresponding roller body recess, even if it should be partially broken out, by introducing an appropriate tool and/or a pressure medium like pressure oil, compressed air etc. through a central duct opening or a central duct bore to pull or push out and therewith disassembling the hard body. 
     In this way damaged parts of roller surfaces of roller presses furnished with grid armoring may be repaired with comparatively low effort. 
     According to a further feature of the invention the premanufactured, especially powder metallurgical made hard metal bodies, may be embodied in such a way that the central recess starting from the radial inner end extending partially over the hard body height has a greater diameter than the adjoining central recess extending to the radial outer end of the hard body, whereby at the junction leading from the radial inner end having a greater diameter to the radial outer end having a smaller diameter a step is embodied, which is suited for an attack of an appropriate tool for the disassembly of a hard body by pulling it out from its roller recess. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and its further features and advantages are being explained in more detail in the following sketched embodiment examples. 
       It is shown in: 
         FIG. 1 : a vertical cut of cylindrical hard body with a central recess introduced into a bore of a roller mantle in a first embodiment; 
         FIG. 2 : a corresponding hard body in a second embodiment, and 
         FIG. 3 : a corresponding hard body in a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a premanufactured cylindrical, especially from sintered hard metal powder metallurgical made hard body  10 , which is introduced into a corresponding bore of the roller mantle  11 , for instance pasted in, and having such a height respective length, that it protrudes outwardly from the surface of the roller mantle  11 , so that an afore-mentioned grid armoring comes about by an arrangement of a plurality of such hard bodies on the surface of a roller mantle  11  of the rollers of a roller press. 
     In the embodiment of  FIG. 1  the premanufactured hard body  10  comprises a premanufactured central recess  12 , which starting from the radial inner end of the hard body extends over the complete height or length of the hard body, that means the central recess is a duct opening. If during operation of the roller press for pressure comminution of granular material there becomes a partial or total damage of the hard body  10 , then the duct opening  12  after cleansing from stock material serves for simplified disassembly of the hard body, by introducing into the duct opening  12  an appropriate tool and/or a pressure medium like pressure oil, compressed air etc. for pulling out/pushing out the hard body  10 . 
     In the embodiment of  FIG. 2  the central duct opening of the hard body  10   a  is embodied in such a way that the central recess  13  starting from the radial inner end of the hard body extending partially over the hard body height has a greater diameter than the diameter of the central recess  14  at the radial outer end of the hard body, whereby at the junction leading from the radial inner end having a greater diameter to the radial outer end having a smaller diameter a step  15  is embodied, which is suited for engagement by an appropriate tool for the disassembly of a hard body  10   a  from its roller boring. Also in this solution before disassembly of the hard bodies  10   a  from the roller press the adjoining recesses  13  and  14  are cleaned out of processed grinding stock. 
     According to the embodiment in  FIG. 3  in the hard body  10   b  in its original form, the central recess extending from the radial inner end of the hard body  10   b  is not embodied in a continuous way, but initially closed facing towards to the top. Here in case of a disassembly of the hard body  10   b , above is formed into it from outside to inside, denoted with a dashed line, with an appropriate tool, by which the disassembly also of this type of the hard body  10   b  can be carried out. 
     To minimize mechanical stress concentrations with a risk of cleft or crack formation in the roller mantle in the operation of the roller press in all embodiments of the hard bodies their radial inner end like the roller body recesses at their deepest area may comprise approximate the curved shape of a semi-spherical calotte  16 . 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.