Patent Publication Number: US-2018050343-A1

Title: Reduction gear for a stirred mill, and corresponding mill and use

Description:
The invention relates to a reduction gear for driving a stirred mill, of the type comprising: 
     a reduction gear housing, 
     an input shaft suitable for being connected to a drive motor, 
     a reduction stage arranged in the reduction gear housing, and 
     an output shaft, which extends along an output axis (Y-Y), which is suitable for being connected to a stirred mill element and which is suitable for being driven by the reduction stage. 
     Stirred mills are known in the state of the art comprising a stirred milling element and a mill housing. Stirred mills of the known type also comprise a reduction gear and a motor for driving the stirred milling element. 
     The stirred milling element is generally guided by a radial bearing and an axial bearing arranged on the mill housing. The milling element is connected by an elastic coupling to the output shaft of the reduction gear such that the output shaft of the reduction gear is stressed only by the rotational force. 
     Optionally, the distal end of the milling element is mounted on a radial bearing arranged in the mill housing. 
     The solutions of the state of the art do not make it possible to transmit a high power, given that the applied forces become too substantial to be reacted by the bearings of the mill housing. Furthermore, the known stirred mills are complicated to assemble. 
     The invention aims to design a reduction gear for driving a stirred mill that allows substantial milling forces to be reacted for given dimensions of the mill. Furthermore, the invention aims to propose a reduction gear for driving a stirred mill that allows more cost-effective assembly of the stirred milling element. The reduction gear must in particular be suitable for stirred mills with very high powers, in particular greater than 746 kW (1000 HP). 
     To that end, the invention relates to a reduction gear for driving a stirred mill as defined above, characterized in that the output shaft comprises a proximal axial side, associated with the reduction stage, and a distal axial side, opposite the proximal axial side and intended to be fastened to the stirred mill element, and in that the reduction gear comprises an axial stop, which is suitable for axially guiding the output shaft and which is suitable for limiting an axial movement of the output shaft in a direction oriented from the proximal axial side toward the distal axial side. 
     According to specific embodiments, the reduction gear according to the invention may include one or more of the following features: 
     the axial stop is either an axial bearing, in particular hydrostatic or hydrodynamic, or a thrust bearing with rolling elements; 
     the reduction gear housing comprises an outlet wall defining an outlet opening that is traversed by the output shaft, the reduction gear comprises a radial output bearing, in particular a radial rolling bearing, arranged in the outlet opening, and the output shaft is guided relative to the outlet wall by the radial outlet wall; 
     the axial stop is arranged axially between the reduction stage and the outlet wall, in particular in which the axial stop bears on the outlet wall; 
     the output shaft comprises a fastening flange suitable for fastening the stirred milling element; 
     the reduction stage comprises a planet reduction gear, and this planet reduction gear is provided with:
         a planet carrier,   a crown,   a sun gear, and   planet gears,   in particular the output shaft is fastened to the planet carrier and/or the input shaft is fastened to the sun gear; and       

     the reduction stage comprises at least one simple parallel gear train, in particular with cylindrical sprockets. 
     The invention also relates to a stirred mill of the type comprising: 
     a mill housing, 
     a stirred milling element, 
     a drive reduction gear of the milling element, characterized in that the drive reduction gear is a reduction gear as defined above, and in that the stirred milling element is fastened to the output shaft by a fastening coupler. 
     The stirred mill may include one or more of the following features: 
     the milling element is guided and maintained relative to the mill housing completely via the drive reduction gear; 
     the milling element is kept cantilevered by the reduction gear relative to the mill housing and/or the milling element comprises a free end that is spaced away from the mill housing; 
     all of the forces acting on the stirred milling element, and in particular all of the milling forces, are reacted only by the axial stop, and optionally by the radial bearing. 
     The invention also relates to the use of a reduction gear as defined above or a mill as defined above, comprising the step: 
     reacting all of the forces acting on the stirred milling element, and in particular all of the milling forces, in particular during milling at a nominal power of the mill, by the axial stop, and optionally by the radial bearing. 
    
    
     
       The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which: 
         FIG. 1  is a schematic view of a stirred mill according to the invention; and 
         FIG. 2  is an enlarged schematic sectional view of part of the stirred mill of  FIG. 1 . 
     
    
    
     Hereinafter, unless otherwise indicated, the expressions “axially” and “radially” will be used relative to the axis of the element to which they refer. 
       FIG. 1  shows a stirred mill according to the invention, designated by general reference  2 . 
     The stirred mill  2  comprises a mill housing  4 , a stirred milling element  6 , a drive support  8 , and a drive device  10  of the milling element  6 . 
     The drive device  10  is provided with a drive motor  12  and a reduction gear  14 . The drive device  10  is suitable for rotating the milling element  6 , via the drive motor  12  and the reduction gear  14 . The drive motor  12  is an electric motor in particular having a nominal power above 746 kW (1000 HP). 
     The mill housing  4  is provided with a bottom wall  16 , a side wall  18 , which is for example cylindrical, in particular with a circular section, and a ceiling wall  20 . The drive support  8  is arranged on the ceiling wall  20  and serves as a spacer between the mill housing  4  and the reduction gear  14 . The drive support  8  for example comprises a frustoconical support wall  24  and two fastening flanges. Alternatively, the drive support  8  is omitted. In this case, the mill housing  4  is adjacent to the reduction gear housing  40 . 
     The ceiling wall  20  defines a housing opening  22  through which the milling element  6  extends inside the mill housing  4 . 
     The milling element  6  extends along a milling axis X-X, arranged vertically. The milling element  6  comprises a milling shaft  26 , extending along the milling axis X-X, and at least one milling member  28 , for example a milling helix. The milling member  28  can also comprise milling discs or milling fingers extending perpendicular to the milling axis X-X. 
     The milling shaft  26  is provided with a fastening flange  30 , which forms an axial connecting end of the milling member  6 . Furthermore, the milling element  6  comprises a free axial end  31 . This axial end  31  is spaced away from the milling housing  4  and is not supported by a radial bearing arranged in the mill housing  4 . More particularly, the axial end  31  is arranged away from the bottom wall  16 . The milling element  6  is kept cantilevered by the reduction gear  14  relative to the mill housing  4 . 
     The reduction gear  14  is provided with a reduction gear case  40 , an input shaft  42 , a reduction stage  44  and an output shaft  46 . 
     The reduction gear  14  is suitable for transmitting a rotation of the input shaft  42  to the output shaft  46 . The output rotation speed is lower than the input rotation speed. 
     The reduction gear case  40  comprises an inlet wall  50 , associated with the input shaft  42 , an outlet wall  52 , associated with the output shaft  46 , and a connecting wall  54  connecting the inlet wall  50  to the outlet wall  52 . The connecting wall  54  is generally cylindrical, in particular with a circular section. The inlet wall  50  defines an inlet opening  56 . The outlet wall  52  defines an outlet opening  58  that is traversed by the outlet wall  46 . 
     The output shaft  46  extends along an output axis Y-Y and the input shaft  42  extends along an input shaft Z-Z. These two axes Y-Y and Z-Z are coaxial. 
     The reduction gear  14  also comprises a radial output bearing  60 , which is for example a radial rolling bearing. The output shaft  46  is radially guided relative to the outlet wall  52  by the radial output bearing  60 . The radial output bearing  60  is arranged in the outlet opening  58 . 
     The radial output bearing  60  is for example a rolling bearing with cylindrical rolling elements. 
     The output shaft  46  comprises a proximal axial side, associated with the reduction stage  44 . The proximal axial side is formed by a support flange  62 . The output shaft  46  comprises a distal axial side, associated with the milling element  6 . The distal axial side is formed by a fastening flange  64 . 
     The reduction gear  14  is provided with an axial stop  66 , which is suitable for axially guiding the output shaft  46  and which is suitable for limiting an axial movement of the output shaft  46  relative to the reduction gear case  40  along the output axis Y-Y in a direction oriented from the proximal axial side toward the distal axial side. The axial stop  66  axially guides the output shaft  46  and limits the axial movement of the output shaft  46  relative to the reduction gear case  40  along the output axis Y-Y in the direction oriented from the proximal axial side toward the distal axial side. To that end, the support flange  62  bears on the axial stop  66  and the axial stop  66  is supported by the outlet wall  52 . 
     The axial stop  66  is therefore arranged axially between the support flange  62  and the outlet wall  52 . The axial stop  66  bears on the outlet wall  52 . 
     The axial stop  66  is a bearing with hydrostatic pads or a bearing with hydrodynamic pads. These bearings can withstand very substantial forces. Alternatively, the axial stop  66  is a thrust bearing with rolling elements, for example rollers or beads. 
     Thus, all of the forces acting on the milling element  6 , and in particular all of the milling forces generated by the milling process, are transmitted to the output shaft  46  and reacted by the outlet wall  52 . 
     In particular, all of the radial forces generated by the milling process and applied on the milling element  6  are transmitted to the output shaft  46  and are reacted by the radial output bearing  60  on the outlet wall  52 . 
     The torque generated by the milling process, applied on the milling element  6  and acting around an axis perpendicular to the milling axis X-X or the output axis Y-Y, is transmitted to the output shaft  46  and is transmitted by the axial stop  66  onto the outlet wall  52 . 
     The weight of the milling element  6  and acting vertically downward is also reacted in full by the axial stop  66 . The milling element  6  is suspended by the output shaft  46  from the axial stop  66 . 
     All of the axial forces generated by the milling process and applied on the milling element  6  are transmitted to the output shaft  46  and are reacted by the axial stop  66  on the outlet wall  52 . 
     The fastening flange  64  of the output shaft  46  is fastened to the fastening flange  30  of the stirred milling element  6 , both axially and radially. The stirred mill comprises a fastening coupler  69  of the output shaft  46  to the milling element. This fastening coupler  69  is rigid, i.e., does not allow the output shaft  46  to move relative to the milling element  6  during the milling operation. The fastening coupler  69  therefore has no degree of freedom. In the present case, the fastening coupler  69  comprises the fastening flange  64  of the output shaft  46  is fastened to the fastening flange  30  of the stirred milling element  6 . 
     The reduction stage  44  comprises a planet reduction stage  70  that is provided with a planet carrier  72 , a crown  74 , a sun gear  76  and planet wheels  78 . 
     The output shaft  46  is fastened in rotation to the planet carrier  72 , in particular is secured in rotation and translation relative to the planet carrier  72 . More particularly, the output shaft  46  is secured to the support flange  62 , which is secured to the planet carrier  72 . Preferably, the support flange  62  and/or the planet carrier  72  and/or the output shaft  46  are integral or in a single piece. The crown  74  is fastened to the reduction gear housing  40  and is for example secured to the connecting wall  54 . 
     The input shaft  42  is fastened to the sun gear  76 , in particular these two elements being integral or in a single piece. 
     The drive motor  12  comprises a driveshaft  80 , with motor axis A-A and a motor housing  82 . The motor shaft  80  is connected to the input shaft  42  via a coupler  84 . The coupler  84  is suitable for transmitting a rotation from the motor shaft  80  to the input shaft  42  while allowing a radial and/or angular misalignment between the input shaft Z-Z and the motor axis A-A. The minimum allowed radial misalignment is for example 5 mm. The minimum allowed angular misalignment between the input shaft Z-Z and the motor axis A-A is for example 1°. 
     The reduction gear housing  40  and the mill housing  4  are separate and separable elements and are not manufactured in a single piece or integrally. 
     As shown in  FIG. 1 , the mill element  6  is guided relative to the mill housing  4  only via the drive reduction gear  14  and more particularly only by the radial bearing  60  and the outlet wall  52 . 
     The fastening coupler  69  is situated axially between the milling shaft  26  and the radial output bearing  60 . Furthermore, the fastening coupler  69  is situated axially between the milling shaft  26  and the axial stop  66 . 
     No other radial or axial bearing supporting the milling element  6  is arranged on the milling element  6 . 
     During the operation of the stirred mill  2 , the milling shaft  26  is rotated via the motor  12  and the reduction gear  14 . The radial, axial and torque milling forces acting on the milling element  6 , in particular during the operation of the mill at nominal power, are transmitted in full by the fastening coupler  69  and are reacted only by the radial bearing  60  and by the axial stop  66  and are transmitted only by the reduction gear housing  40  to the mill housing  4 , optionally via the drive support  8 . 
     According to the invention, the reduction gear or the mill is used to react all of the forces acting on the stirred milling element, and in particular all of the milling forces, in particular during milling at a nominal power of the mill, by the axial stop  66 , and optionally by the radial bearing  60 . 
     The structure of the mill and the reduction gear described above makes it possible to react very substantial milling forces for given dimensions. The total height of the structure is also small owing to the integration of the axial stop into the reduction gear. This also leads to a simple and compact assembly for a given milling and transmission force. 
     Alternatively, the reduction gear does not include only one planet reduction stage  70 , but rather, the input shaft  42  is connected to an additional planet reduction stage including an input shaft  42  that is connected to the shaft  80 . The reduction gear may also comprise three or four planet reduction stages mounted in a cascade. 
     Alternatively, the reduction gear does not comprise a planet reduction stage, but one or several reduction stages made up of simple parallel gear trains, in particular with cylindrical sprockets. 
     Alternatively, the reduction gear may be made up of a combination of planet reduction stages and simple parallel gear trains.