Abstract:
An angle-based method and device to protect a grinding mill used for grinding material therein by rotating the drum so that the material adheres to the drum inner surface and rises therewith over a cascading angle from a gravity-balanced condition prior to detach by gravity from the inner surface and tumble into a cascading flow. The method is used for protecting the grinding mill from damages potentially resulting from the material agglomerating into a generally solidified lumped volume that could adhere to the inner surface and rotate with the latter more than the cascading angle to a fall angle wherein the lumped volume may detach from the drum inner surface and impact an impact position within the drum. The method includes the steps of assessing for the presence of material adhering to the inner surface upon rotation of the drum by more than the cascading angle; and initiating an action to stop the rotation of the drum upon determination of material adhering to the inner surface upon rotation of the drum beyond the cascading angle.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the general field of rotating machines and is particularly concerned with an angle-based protection device and method for protecting a rotating component part of a machine.  
         BACKGROUND OF THE INVENTION  
         [0002]    The prior art is replete with various types of machines having rotating components for industrial, domestic, recreational and other purposes. Because of particular physical phenomenons associated with rotating movements, rotating components part of various types of machines are subjected to particular operational parameters that may be potentially damaging especially when the rotating components reach critical angular values. The potential for subjecting rotating components to damaging conditions is sometimes compounded when the rotating components are used for imparting a rotational movement to material contained therein, such as for mixing, grinding or other purposes.  
           [0003]    So-called grinding mills constitute a typical example of a machine having a rotating component, namely a rotating drum that may be subjected to potentially damaging conditions upon operational parameters of the machine meeting pre-determined critical parameter conditions while the rotating drum reaches a critical angular value. Such grinding mills are used extensively for reducing lumps or large pieces of various kinds of material to smaller sizes.  
           [0004]    Conventional grinding mills commonly include a hollow cylindrical or frusto-conical shell or drum mounted for rotation about its longitudinal axis. The drum is typically rotatably arranged about two trunnions by two head portions positioned at opposite longitudinal ends of the drum.  
           [0005]    Typically, each conical head portion includes a plurality of segments bolted together to form a composite structure. Each head portion is also typically provided an inner annular flange and an outer annular flange for securing the head portions respectively to a trunnion and to the drum.  
           [0006]    Also, conventional grinding mills are typically provided with a gear wheel forming part of the gear mechanism that drives the grinding mill. The gear wheel commonly includes a plurality of segmental rim portions that are bolted together to form an annular rim. Gear teeth are cut into the rim and shaped for cooperation with one or more pinions. The annular rim is typically displaced radially outward of the drum by a rib. The rib is usually provided with a plurality of apertures through which bolts may pass to fasten the rib to the outer annular flange of the head portion and the flange of the drum.  
           [0007]    The gear wheel typically forms part of a large speed-reducing gear system intended to transmit the power from a prime mover to the grinding mill. The prime mover, in turn, typically includes an electrical prime mover such as synchronous electrical motors or the like having enhanced starting torque characteristics. In order to compensate for enhanced starting torque, the gear wheel typically has a relatively large diameter.  
           [0008]    Different diameters and lengths of shells or drums have been used heretofore, and they normally vary in proportion to the capacity of the mill. During rotation of the drum about its longitudinal axis, the material to be ground is carried up the side of the drum to subsequently fall to the bottom of the drum. The grinding occurs principally by attrition and impact within the grinding mill charge.  
           [0009]    In the case of ore, the normal function of the grinding mill is to reduce the size of the ore to particles within a fine sieve range for flotation. Grinding mills used for grinding ores or the like optionally use grinding mediums such as pebbles, steel balls, ceramic balls, or the like to assist in the comminuting process as the mill is rotated.  
           [0010]    In other circumstances, the ore may be self-grinding. The axial ends of the drum may be open, and the material to be comminuted may be continuously fed into the mill at one end with the comminuted product continuously emerging from the other end.  
           [0011]    In view of the abrasive character of the material being ground, the wear on the inside of the grinding mill has heretofore been a serious problem. Hence, in order to protect the drum from the grinding action and to thereby lengthen the life of the grinding mill, the drum is typically provided with a metal or rubber lining. For example, grinding mills have been lined with cast or wrought abrasion-resistant ferrous alloy liners and, in some cases, rubber or ceramic liners. Typically, these liners are segmented due to the weight and size considerations.  
           [0012]    Liner assemblies hence typically include a plurality of separate lining components that are usually retained tightly against the interior or the mill shell or drum by mechanical fastening components such as bolts. Some ores, such as taconite, are relatively highly abrasive. In order to maintain continuous operation of the grinding mill, it is necessary to provide a liner for the drum that is highly abrasion-resistant. The liner also should be tough enough to withstand the continuous impact of ore fragments.  
           [0013]    Liners inevitably become worn and, hence, no longer effective. In such situations, the liners are typically replaced at periodic intervals. Other types of maintenance and repair also periodically require the grinding mill to be run at speeds considerably slower than the normal running speed or even to stop the rotation movement of the drum altogether.  
           [0014]    As a result of mill shut-down over a period of time, the charge within the mill may “freeze” into a generally solidified, hardened or rigid lump. Upon the mill being rotated after a mill shut-down there exists the possibility that the solidified lump will be carried up the side of the drum by the rotation of the latter. In such instances, instead of tumbling in a cascading flow upon reaching the position wherein non-solidified charge would cascade, the mass may eventually detach itself from the inner wall of the drum and fall on an impacting location within the drum.  
           [0015]    This may prove to be detrimental to various components of the mill including the lining, heads and bearings thereof. Also, since gear wheels are typically constructed with great accuracy, they may also be subjected to deformation by the impact. As can be appreciated, when the lining is affected or when a tooth in a gear wheel is damaged, the liner and the wheel must be replaced. The cost of the occurrence of such events is very burdensome. Not only is the cost of material and repair involved extensive but the high capitalization costs of plants using large autogenous mills may be mobilized by extended non-productive down-time.  
           [0016]    A solidified mass falling from the mill inner wall upon rotation of the latter constitutes a typical example of a rotating component that may be subjected to potentially damaging conditions upon the rotating component reaching a critical angular value. Another example of angle-dependent potentially damaging conditions may result from the potential mismatch between actual load and designed torques.  
           [0017]    Indeed, as the mill is rotated to the cascade position wherein the charge starts to tumble, the torque required increases quite considerably as the charge is moved away from the gravity-balanced position on a large radius. Once the charge begins to tumble, the required load torque drops. If the developed motor torque matches the load torque plus the friction torque, then the rotation will be smooth and continuous.  
           [0018]    It would be desirable to provide an angle-based protection device for protecting rotating component and corresponding supporting component part of machines. More particularly, in some situations the rotating component defines a critical angular value about which an operational parameter of the machine may be used for predicting the occurrence of a potentially damaging condition for the machine. Also, sometimes the potentially damaging condition for the machine is concurrently more susceptible to happen upon the operational parameter meeting predetermined critical parameter conditions while the rotating component reaches a critical angular displacement value. In such situations, it would be desirable to provide an angle-based protection device for reducing the risk of such potentially damaging conditions occurring.  
           [0019]    As mentioned previously, it is some times desirable to run the grinding mill at speeds considerably slower than the normal running speed. Typical examples include for the purpose of assuring proper gear, bearing and shaft alignment when a mill is first being installed, also for inspecting and potentially replacing the mill liner when the mill is empty or to start the mill after it has been stopped with a full charge. This slow running is often referred to as “spotting”, “inching”, “barring” or “turning gear”.  
           [0020]    Heretofore, inching has been accomplished in several ways. One of the simplest mechanical device used for inching includes a cable sling arrangement attached to an overhead crane. The cable sling arrangement allows for selective mill rotation. However, such a prior art technique is not precise. Also, it requires continuous use of a crane. Furthermore, it is dangerous to personnel who may be installing or re-lining the mill as slings have a known tendency to break.  
           [0021]    Another way to provide for inching uses a low frequency power source to provide power to the stator windings of the typically used three-phase synchronous drive motors. The low frequency power source may be a direct current (DC) supply connected to an inching supplied bus for the motors through a series of electromechanical or static switches to produce stepped low frequency three-phase voltages. These switches are typically referred to as sequencing or commutating switches. The switches, however, are relatively costly.  
           [0022]    Inching has heretofore also been accomplished through the use of clutches, the clutches may be partially engaged to cause rotation of the mill at lower speeds. This partial clutch closure for long periods however generates considerable heat in the clutches and requires that the wet clutches be installed and provision made to dissipate the heat generated. Also, typically, an installation using wet clutches is more expensive than one using dry clutches.  
           [0023]    Yet, another way to provide for inching is to use a removable hydraulic motor that is placed to engage main mill pinion gear. The present invention is particularly well suited for use with such inching devices. However, it can be appreciated by those skilled in the art that the present invention has broader applications and be used in conjunction with other types of machinery for obtaining an angle-based protection device.  
         SUMMARY OF THE INVENTION  
         [0024]    Advantages of the present invention include that the proposed angle-based protection device and method is intended to prevent angle-based potentially damaging conditions from damaging rotating components. For example, the proposed angle-based protection device and method can be used for preventing a solidified mass within a conventional grinding mill from impacting the mill and damaging the latter upon rotation of the mill drum. The proposed device may also be used for preventing damages caused by actual load torque and designed torque mismatches or any other angle-based potentially damaging conditions.  
           [0025]    The proposed device may be readily installed on conventional machines such as conventional grinding mills, inching devices or the like, through a set of quick and ergonomic steps. The proposed device and method may also be easily retrofitted to existing machines without requiring undue work and with reduced risks of damaging the machines.  
           [0026]    The proposed method and device is intended to protect the machine with reduced interference to its operational parameters so as to provide a device having reduced risks of lowering the efficiency of the machine on which it is mounted. Also, the proposed method may be accomplished through the use of various types of devices including devices readily commercially available.  
           [0027]    Furthermore, the proposed device is designed so as to be manufacturable using conventional forms of manufacturing so as to provide an angle-based protection device that will be economically feasible, long-lasting and relatively trouble-free in operation.  
           [0028]    According to an aspect of the present invention, there is provided a method for protecting a grinding mill including a rotatable mill drum used for grinding material from damages potentially caused by a lumped volume of the material falling from a fall position within the mill drum and impacting an impact position within the mill drum upon rotation of the latter, the mill drum being coupled to a torque provider able to generate a driving torque for rotating the mill drum, the method includes the steps of:  
           [0029]    assessing the presence of a potentially damaging lumped volume of the material in the mill drum by evaluating if the material within the mill drum is tumbling in a cascading flow upon rotation of the mill drum;  
           [0030]    initiating an action for stopping the rotation of the mill drum upon determination that the material within the mill drum is not tumbling in the cascading flow.  
           [0031]    Preferably, the step of evaluating if the material within the mill drum is tumbling in a cascading flow upon rotation of the mill drum includes:  
           [0032]    estimating a cascading angular displacement range of the mill drum within which the material within the mill drum is expected to separate from an inner surface of the mill drum and tumble in a cascading flow upon rotation of the mill drum;  
           [0033]    evaluating if the material within the mill drum separates from the inner surface of the mill drum within the cascading angular range upon rotation of the mill drum.  
           [0034]    Preferably, the step of evaluating if the material within the mill drum separates from the inner surface of the mill drum within the cascading angular range upon rotation of the mill drum includes:  
           [0035]    using the torque provider for rotating the mill drum with the material contained therein;  
           [0036]    monitoring the value of the driving torque for the presence of a torque value indicating that the material has not separated from the inner surface of the drum mill when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range.  
           [0037]    Preferably, the step of monitoring the value of the driving torque for the presence of a torque value indicating that the material within the mill drum has not separated from the inner surface of the mill drum within the cascading angular displacement range includes evaluating if the driving torque reaches a predetermined torque threshold when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range.  
           [0038]    Alternatively, the step of monitoring the value of the driving torque for the presence of a torque value indicating that the material within the mill drum has not separated from the inner surface of the mill drum within the cascading angular displacement range includes evaluating if the driving torque continues to increase when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range.  
           [0039]    Preferably, the method further comprises the steps of:  
           [0040]    assessing for the presence of a residual lump of material having remained adhered to the inner surface of the mill drum beyond the cascading angular displacement range despite a complementary volume of material having separated from the inner surface of the mill drum;  
           [0041]    stopping the rotation of the mill drum upon assessing the presence of the residual lump of material.  
           [0042]    Preferably, the value of the driving torque is monitored for the presence of a torque value indicating the presence of the residual lump of material when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range, the driving torque being monitored until the mill drum rotates from the gravity-balanced condition by a predetermined safe angular displacement.  
           [0043]    Preferably, monitoring the value of the driving torque for the presence of a torque value indicating the presence of a residual lump of material when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range includes evaluating if the driving torque continues to increase when the mill drum has rotated from a gravity-balanced condition more than the cascading angular displacement range until the mill drum rotates from the gravity-balanced condition by the predetermined safe angular displacement.  
           [0044]    Preferably, the torque provider is an inching device including a hydraulic driving motor, or alternatively an electrical driving motor coupled to the grinding mill.  
           [0045]    According to another aspect of the present invention, there is provided a method for protecting a grinding mill, the grinding mill including a rotatable mill drum defining a drum inner surface and being coupled to a torque provider able to generate a driving torque for rotating the mill drum, the grinding mill being used for grinding material by rotating the mill drum so that the material adhering to the drum inner surface rises therewith over a cascading angular displacement range from a gravity-balanced condition prior to being detached by gravity from the drum inner surface and tumbling into a cascading flow, the method being used for protecting the grinding mill from damages potentially resulting from the material agglomerating into a generally solidified lumped volume that could adhere to the drum inner surface and rotate with the latter from the gravity-balanced condition more than the cascading angular displacement range to a fall angular displacement wherein the lumped volume may detach from the drum inner surface and impact an impact position within the mill drum, the method includes the steps of:  
           [0046]    assessing for the presence of material adhering to the drum inner surface upon rotation of the mill drum by more than the cascading angular displacement range from the gravity-balanced condition;  
           [0047]    initiating an action for stopping the rotation of the mill drum upon determination of material adhering to the drum inner surface upon rotation of the mill drum by more than the cascading angular displacement range from the gravity-balanced condition.  
           [0048]    Preferably, the method further comprises the steps of:  
           [0049]    continuing to evaluate if the driving torque continues to increase when the mill drum has rotated from the gravity-balanced condition more than the cascading angular displacement range until the mill drum rotates from the gravity-balanced condition by a predetermined safe angular displacement;  
           [0050]    initiating an action for stopping the inching of the mill drum if the value of the torque continues to increase when the mill drum has rotated from the gravity-balanced condition more than the cascading angular displacement range and less than the predetermined safe angular displacement.  
           [0051]    According to another aspect of the present invention, there is provided a device for protecting a grinding mill, the grinding mill including a rotatable mill drum defining a drum inner surface and being coupled to a torque provider able to generate a driving torque for rotating the mill drum, the grinding mill being used for grinding material by rotating the mill drum so that the material adhering to the drum inner surface rises therewith over a cascading angular displacement range from a gravity-balanced condition prior to being detached by gravity from the drum inner surface and tumbling into a cascading flow, the device being used for protecting the grinding mill from damages potentially resulting from the a generally solidified lumped volume of the mass having adhered to the drum inner surface that could rotate with the latter from the gravity-balanced condition more than the cascading angular displacement range to a fall angular displacement wherein the lumped volume may detach from the drum inner surface and impact an impact position within the mill drum, the device comprises:  
           [0052]    a parameter monitor operatively coupled to the grinding mill and the torque provider for monitoring the angular displacement of the mill drum from the gravity-balanced condition and the value of the driving torque;  
           [0053]    an evaluator operatively coupled to the parameter monitor for evaluating if the value of the torque continues to increase upon the mill drum rotating from the gravity-balanced condition by the cascading angular displacement range;  
           [0054]    an effectuator operatively coupled to the evaluator and the torque provider for initiating an action leading to the stopping of the rotation of the mill drum if the value of the torque continues to increase upon the mill drum rotating from the gravity-balanced condition by the cascading angular displacement range.  
           [0055]    Preferably, the parameter monitor includes a torque monitor operatively coupled to the torque provider for monitoring the value of the driving torque to assess the presence of a torque value indicating that the material has not separated from the inner surface of the mill drum when the mill drum has rotated from the gravity-balanced condition by more than the cascading angular displacement range.  
           [0056]    Preferably, the parameter monitor includes an angular displacement sensor operatively coupled to the grinding mill for assessing the angular displacement of the mill drum from the gravity-balanced condition.  
           [0057]    Preferably, the angular displacement sensor includes a rotation encoder operatively coupled to the grinding mill for converting an operational parameter of the grinding mill into an estimate of the angular displacement of the mill drum from the gravity-balanced condition.  
           [0058]    Preferably, the rotation encoder includes:  
           [0059]    a reference component mounted on a driving shaft of the torque provider for rotating with the latter;  
           [0060]    an inductive-type sensor mounted adjacent the reference component for monitoring the displacement of the reference component and inferring the angular displacement of the mill drum from the displacement of the reference component.  
           [0061]    Typically, the parameter monitor includes a torque sensor operatively coupled to the torque provider for assessing the value of the driving torque.  
           [0062]    Preferably, the torque provider is an hydraulic motor part of an inching device, the torque sensor including a pressure transducer operatively coupled to the hydraulic circuitry of the hydraulic motor for assessing the hydraulic pressure in the hydraulic circuitry of the hydraulic motor.  
           [0063]    According to a furthar aspect of the present invention, there is provided an angle-based protection device for protecting a rotating component part of a machine, the rotating component being coupled to a drive provider, the drive provider being able to generate a driving torque for driving the rotating component about a component rotation axis, the rotating component defining a critical angular displacement value about which an operational parameter of the machine may be used for predicting the occurrence of a potentially damaging condition for the machine, the potentially damaging condition for the machine being more susceptible to happen upon the operational parameter meeting predetermined critical parameter conditions while the rotating component reaches the critical angular displacement value, the device comprises:  
           [0064]    a parameter sensor operatively coupled to the machine for providing an evaluation of the operational parameter upon the rotating component reaching the critical angular displacement value;  
           [0065]    an effectuator operatively coupled to the parameter sensor for receiving the evaluation of the operational parameter and effectuating an action for reducing the risks of damaging the machine upon the operational parameter meeting the predetermined critical parameter conditions.  
           [0066]    Preferably, the rotating component is a rotating drum defining a drum peripheral wall, the drum peripheral wall defining a peripheral wall reference location;  
           [0067]    the parameter sensor includes:  
           [0068]    an angle evaluator for providing an evaluation of the angular displacement relationship between the peripheral wall reference location and the critical angular displacement value;  
           [0069]    a torque evaluator for evaluating the driving torque.  
           [0070]    Alternatively, the present invention concerns an angle-based protection method for protecting a rotating component part of a machine, the rotating component being coupled to a drive provider, the drive provider being able to generate a driving torque for driving the rotating component about a component rotation axis, the rotating component defining a critical angular displacement value about which an operational parameter of the machine may be used for predicting the occurrence of a potentially damaging condition for the machine, the potentially damaging condition for the machine being more susceptible to happen upon the operational parameter meeting predetermined critical parameter conditions while the rotating component reaches the critical angular displacement value, the method comprises the steps of:  
           [0071]    providing an evaluation of the operational parameter upon the rotating component reaching the critical angular displacement value;  
           [0072]    receiving the evaluation of the operational parameter and effectuating an action for reducing the risks of damaging the machine upon the operational parameter meeting the predetermined critical parameter conditions.  
           [0073]    Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, within appropriate reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0074]    An embodiment of the present invention will now be disclosed, by way of example, in reference to the following drawings in which:  
         [0075]    [0075]FIG. 1, in a partially broken schematic top plan view, illustrates the protection device in accordance with an embodiment of the present invention, the protection device being used with a conventional hydraulic inching device coupled to a conventional grinding mill;  
         [0076]    [0076]FIG. 2, in a transverse cross-sectional view of the drum part of the grinding mill shown in FIG. 1, illustrates, in a diagrammatic manner, an exemplary cascading and tumbling disposition of grinding media and material being ground thereby during the rotation of the mill in the direction of the arrow shown adjacent the Figure;  
         [0077]    [0077]FIG. 3, in a transverse cross-sectional view of the drum shown in FIG. 2, illustrates, in a diagrammatic manner, an exemplary disposition of the grinding material and media when the latter is idle in gravity-balanced condition;  
         [0078]    [0078]FIG. 4, in a transverse cross-sectional view of the drum shown in FIGS.  2 , and  3 , illustrates, in a diagrammatic manner, an exemplary disposition of the grinding material and media, fully solidified, is into an undesired position requiring more torque than the normal cascading operation;  
         [0079]    [0079]FIG. 5, in a transverse cross-sectional view of the drum shown in FIGS. 2, 3 and  4 , illustrates, in a diagrammatic manner, an exemplary disposition of the solidified lump falling from the inner surface of the drum during the rotation of the mill in the direction of the arrow shown in the Figure;  
         [0080]    [0080]FIG. 6, in a transverse cross-sectional view of the drum shown in FIGS. 2, 3,  4  and  5  illustrates, in a diagrammatic manner, an exemplary disposition of the grinding material and media having a partially solidified lower portion reaching an undesired position also requiring more torque than the normal cascading operation;  
         [0081]    [0081]FIG. 7, in a graph, illustrates the typical relationship between the required driving torque and the drum rotation angle upon initiation of an inching process starting when the load is within the drum in an idle condition and ending when the load tumbles in a cascading flow;  
         [0082]    [0082]FIG. 8, in a diagram, illustrates the typical relationship between the driving torque and the rotation of the drum starting when the load is within the drum in an idle condition, the load being either normal, partially solidified or fully solidified; and  
         [0083]    [0083]FIG. 9, in a schematic diagram, illustrates a sequence of steps part of an angle-based protection method in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0084]    With reference to the annexed drawings a preferred embodiments of the present invention will be herein described for indicative purpose and by no means as of limitation.  
         [0085]    Referring to FIG. 1, there is shown a protection device generally indicated by reference numeral  10  in accordance with an embodiment of the present invention. The protection device  10  is shown being used with a conventional grinding mill  12  and a conventional hydraulic inching device  14 . It should be understood that this type of installation merely represents one type of exemplary installation through which the concepts of the subject invention may be intended to be used and will allow those skilled in the art to more readily appreciate the general gist of the application for the proposed protection device. The protection device  10  may be used in other environments in conjunction with other types of machinery without departing from the overall intent or scope of the present invention.  
         [0086]    The grinding mill  12  includes a hollow mill drum  16  having a drum peripheral wall  18  defining the drum wall inner surface  20 . The mill drum  16  is rotatably arranged about two trunnions  22  by a pair of conical heads  24  positioned at opposite ends of the mill drum  16 . Each head  24  is provided with an inner annular flange  26  and an outer annular flange  28  for securing the head respectively to mill drum  16  and to an adjacent trunnion  22 .  
         [0087]    Preferably, the mill drum  16  defines a feed end area or face  29  and an opposed discharge end area or face  30 . The mill drum  16  is preferably generally horizontally journalled to the trunnions  22  so as to be rotatably driven about its longitudinal axis  32  and typically extends in a generally slightly tilted or sloped orientation from horizontal.  
         [0088]    The grinding mill  12  is typically further provided with a gear ring or wheel  34  forming part of the gear mechanism for driving the grinding mill  12 . The gear wheel  34  commonly includes a plurality of segmental rim portions that are bolted together to form an annular rim  36 . Cut into the rim  36  are teeth  38  cooperating with one or more pinions  40 . Typically, the annular rim  36  is placed radially outward of the drum of the mill drum  16  by a rib  42 .  
         [0089]    The rib  42  is usually provided with a plurality of rib apertures extending therethrough for allowing bolts  44  to fasten the rib  42  to the inner annular flange  26  of the head  24  and the flange of the mill drum  16 .  
         [0090]    A lining  46  is typically provided over the drum inner surface  20  to protect the latter from the grinding action and thereby lengthen the life of the grinding mill  12 . The lining  46  may take any suitable form such as an assembly of modular longitudinal lining sections or an assembly of elongated slabs  48  preferably having wedge-shaped ribs  49  or the like thereon. The slabs  48  are forcibly held in place with radially extending fasteners  50 . The lining  46  may be made out of any suitable material such as a suitable abrasive and impact resistant metal alloy or even elastomeric resin.  
         [0091]    The grinding mill  12  is mechanically coupled to a prime mover able to provide a driving torque for rotating the mill drum  16 . The prime mover typically includes an electrical-type of mover having enhanced starting torque characteristics. The prime mover typically includes an electric drive motor  52  enclosed in a drive motor housing.  
         [0092]    The driving motor  52  includes a motor driving shaft  54  typically operatively communicating with a gear reducer structure  56  enclosed within a reducer housing via a motor clutch  58  operatively coupled to a reducer input shaft  59 . A reducer output shaft  60  extends outwardly from the reducer  56 . The reducer output shaft  60 , or conventional pinion shaft, operatively communicates with the drive pinion gear  40 . The drive pinion gear  40 , in turn, is typically journalled in driving communication with bull or girth teeth  38  of the gear ring  34 . Although the gear reducer  56  is preferred, the driving motor shaft  54  could alternatively be directly coupled to the pinion shaft  60 .  
         [0093]    Typically, the prime mover may include a pair of motors generating several thousands of horsepower for applying a relatively large torque at relatively slow speeds. The gear ring  34  typically has a relatively large diameter in order to compensate for enhanced starting torque. Also, the reducer  56  provides an output torque to the reducer output shaft  60  at a greater value and lower speeds than that of the driving shaft  54 . The torque requirements will, of course, vary substantially between various mill installations and designs.  
         [0094]    In use, typically, the grinding mill  12  is charged with the ore, rock or other material to be ground through an opening within the feed end area  29 , preferably at the center thereof. As the ore, rock or other material is ground to the appropriate or desired size, it is discharged from the mill drum  16  through a similar discharge opening at the discharge end area  30 . Typically, the ground material passes through a chute-like area (not shown) for transport to subsequent processing stations. Typically, the mill drum  16  is rotated about its longitudinal axis  32  so that the material being ground is continuously tumbled within the mill drum  16  and thereby pulverizes or breaks itself to the necessary size. Optionally, water or other solids and/or liquids, such as conventional manganese balls or the like, may be added to the material.  
         [0095]    The grinding mill  12  is optionally releasably operatively coupled to the inching device  14  for allowing the grinding mill  12  to be run at speeds considerably slower than the normal running speed. The slow running of the grinding mill  12  often referred to as “spotting” or “inching” may be accomplished in several ways. Clutches may be used for coupling the prime mover through the grinding mill  12 . These clutches may be partially engaged to cause rotation of the grinding mill  12  at lower speeds. Alternatively, low frequency power sources may be used to provide power to the stator windings of three-phase synchronous drive motors. The lower frequency power source may be a direct current (DC) supply connected to an inching supplied bus for the motors through a series of electromechanical or static switches to produce stepped low frequency three-phase voltages.  
         [0096]    A third method for providing inching uses a removable hydraulic motor positioned so as to engage the reducer input shaft  59  or be mechanically coupled thereto. This third method of providing inching is illustrated in FIG. 1. The inching device  14  includes a hydraulic motor  62  combined with an inching brake assembly (not shown) which is typically a holding-type brake. Typically, the hydraulic motor  62  is a high-efficiency hydraulic motor coupled to a multistage planetary-type gear reducer  63 . Typically, the inching brake assembly includes spring applied hydraulic released brakes. However, the hydraulic motor  62  may be of any suitable type without departing from the scope of the present invention.  
         [0097]    The hydraulic motor  62  and its associated inching brake assembly are hydraulically coupled to an appropriate hydraulic pump and motor  64  through conventional hydraulic fluid lines  66 . Optionally, mix-proof quick-disconnect couplings  68  may be used for coupling the hydraulic fluid lines  66  to the casing of the hydraulic motor  62 . Typically, the brake assembly is mechanically biased to a braking condition and hydraulically actuated to a non-braking condition. The requisite hydraulic fluid lines  67  for the brake assembly are schematically shown in FIG. 1.  
         [0098]    The hydraulic motor  62  includes a hydraulic motor output shaft  70 . The hydraulic motor output shaft  70  is mechanically coupled to the reducer input shaft  59  through suitable coupling means such as a mounting hub  72  provided with hub teeth (not shown) for mechanical and directional engagement with shaft teeth (not shown) formed on the outer surface of the reducer input shaft  59 .  
         [0099]    Typically, the hydraulic motor  62  and corresponding brake assembly is mounted on a motor mounting bracket  74 .  
         [0100]    Again, it should be understood that any suitable type of inching device may be used without departing from the scope of the present invention.  
         [0101]    Referring now more specifically to FIG. 3, when the mill drum  16  is idle, the charge including the material to be ground and optionally solids/liquids as well as a grinding charge form a mass  76  at the bottom of the mill drum  16  having a somewhat irregular although generally horizontal top surface  78 . The height of the top surface  78  and, hence, the amount of loading respective to the cross-sectional area of the mill drum  16  will depend upon various operational parameters. Hence, the particular loading shown in FIGS.  2  to  6  is only shown by way of example and other loading configurations and volumes could be used without departing from the scope of the present invention.  
         [0102]    When a loaded grinding mill  12  is being inched, the rotation begins on the “rest”, “idle” or “gravity-balanced” position shown in FIG. 3. As the mill is rotated according to arrow  80  in FIG. 2, a leading portion of the load  82  in contact with the lining  46  is carried upwardly according to arrows  84  up to a so-called cascading angular displacement  86 . Since the grinding medium and subject material form a generally coherent mass, most of the load  82  will be moved by the rotation of the milling drum  16 . Optionally, wedge-shaped ribs  49  or other suitable topographically enhancing means facilitate the carrying of the grinding medium and subject material with the drum during rotation thereof so as to enable the tumbling/cascading of the grinding medium and subject material, thereby creating the grinding action.  
         [0103]    The material to be ground is carried up the side of the mill drum  16  to subsequently fall to the bottom of the drum  16  when the cascading displacement  86  is reached. The grinding occurs principally by attrition and impact within the grinding mill charge  82 .  
         [0104]    At the cascading angular displacement  86 , the resultant forces acting on the charge  82  including friction, coherent and centrifugal forces tending to carry the load  82  up the side of the milling drum  16  and the gravitational and flowing forces tending to force the load  82  towards the bottom of the milling drum  16  cause the inner portion  88  of load  82  to tumble downwardly. Since the load  82  is typically relatively fluent, the outer portion  88  of load  82  will typically tumble in a cascading flow assuming somewhat the direction and configuration shown in FIG. 2. The material being generally fluent, tumbling of the top surface  78  will cause elements within the load  82  to fall upon other elements so as to enhance the crushing operation of the mill and produce a somewhat turbulent movement of the mass.  
         [0105]    When a grinding mill  12  is being inched without a load or charge, for example to inspect the mill liners, the torque required is relatively constant and of a lesser value than required for normal running. However, when the grinding mill  12  is being inched, the required torque varies depending on the angular position of the leading edge of the load  82 , as well as on the quantity of charge  82  therein.  
         [0106]    Referring now more specifically to FIG. 7, there is shown that when a loaded mill is being inched with the rotation beginning from the idle position, the initial torque  90  required to begin rotation is relatively small. The initial torque  90  is typically required only to overcome friction and start the rotation of the milling drum  16 . The torque requirements then typically decrease slightly as indicated at  92  when static friction is partially overcome. The required torque then begins to increase as drum mill  16  rotates and raises the load  82 , with increasing mill angle α, which had settled at the bottom when the mill was stopped in the gravity-balanced position. The torque continues to increase as indicated at  94  since the load is rotated farther away from the bottom position it had when the mill drum  16  was stopped, as illustrated in FIG. 3.  
         [0107]    As the mill drum  16  is rotated or inched up by the cascading angular displacement  86  at which the charge  82  starts to tumble, the torque required increases quite considerably as the charge  82  is moved away from the gravity-balanced position on a large radius. Although shown in FIG. 2 as being typically about forty-five (45) degrees from the gravity-balanced position (shown in FIG. 3 with α=0 degree), the cascading angular displacement  86  forming the cascading angle α c  could vary to be other angular displacements depending on the type and the quantity of material being ground without departing from the scope of the present invention.  
         [0108]    When the load  82  within the mill drum  16  cascades, as shown in FIG. 2, the torque requirement slightly decreases such as shown at  96  untill a generally steady state or constant torque  98  is reached.  
         [0109]    Obviously, the sloped portion ramped portion  94  must reach the steady or constant level  98  before the maximum load  100  is reached. In other words, before the load  82  is expected to cascade.  
         [0110]    Depending on the gear ratios and the type of motors used, the ramped portion  94  may be associated with various time intervals after inching has started. In practice, as the load  82  in the milling drum  16  can be determined only with relatively poor accuracy before inching and, since the cascading angular displacement  86  varies, it is difficult to provide an accurate ramp reference prior to inching.  
         [0111]    [0111]FIG. 4 illustrates a situation wherein a fully solidified mass  102  has formed because of prolonged idling or other conditions. When such a condition occurs, the solidified mass  102  may be prevented from tumbling in a cascading flow at the cascading angular displacement  86  and remain attached to the lining  46 .  
         [0112]    In such situation, the mill  12  must be stopped from rotating and preferably held in that position to remedy to the potentially damaging situation otherwise a portion  104  or the totality of the solidified mass  102  may detach itself suddenly from the lining  46  at a somewhat remote location from the bottom of the grinding drum  16  and fall according to arrows  106  on the lining  46 , as shown in FIG. 5. The fall of a relatively heavy mass may cause serious damages to various components of the grinding mill  12  including the lining  46 , the driving gears and other important components.  
         [0113]    Accordingly, the torque requirements continue to increase past the cascading angular displacement  86  as the solidified mass  102  is moved even further away from the gravity-balanced position on the large radius of the lining  46 . Hence, instead of peaking at the cascading angular displacement  86  as designated by reference  100  in full lines, the required torque continues to increase as indicated at  108  due to the solidified mass  102 , as shown in dashed lines in FIG. 7. Obviously, the initial sections of the ramped line are somewhat similar to the situation wherein the mass  102  eventually tumbles in a cascading flow at the cascading angular displacement  86 .  
         [0114]    Alternatively, as shown in FIG. 6, the solidified mass  102   a  can represent only a bottom or lower portion of the load  82 . The solidified mass  102   a  will make the torque requirements to increase again after the constant torque  98  has been reached slightly following the start of the cascading on the non-solidified portion of the load  82 , as represented by the second ramped dotted line  112  of FIG. 7. This situation can occur either when the solidified mass  102   a  is a portion of the load  82  or when the fully solidified mass  102  has only partially detached from the drum lining  46  and a remaining portion still remains solidified and attached to the drum lining  46 . The partial detachment of the solidified mass  102  from the drum lining  46  is illustrated by the negative sloped dashed line at  110  in FIG. 7, followed by the dotted line  112 .  
         [0115]    The proposed method and device typically makes use of the relationship between the required torque and drum rotation to assess the presence of a solidified mass  102  that may potentially damage the grinding mill  12 , as schematically shown in the diagram of FIG. 9.  
         [0116]    In situations wherein the method is used in the context of a grinding mill such as hereinabove disclosed, the proposed method includes the steps of assessing for the presence of a potentially damaging lump volume of material  102  in the mill drum  16  by evaluating if the material within the mill drum  16  is tumbling in a cascading flow upon rotation of the mill drum  16 . The method further includes the step of initiating an action for stopping the rotation of the mill drum  16  upon determination that the material within the mill drum  16  is not tumbling in a cascading flow. More specifically, the step of evaluating if the material within the mill drum  16  is tumbling in a cascading flow upon rotation of the latter may include the steps of initially estimating a cascading angular displacement range  86  within which the material within the mill drum  16  is expected to separate from the inner surface  20  of the mill drum  16  and tumble in a cascading flow upon rotation of the mill drum  16  from a gravity-balanced condition. Once the cascading angular displacement range  86  has been estimated, the method includes the step of evaluating if the material within the mill drum  16  separates from the inner surface  20  of the mill drum  16  within the cascading angular displacement range  86  upon rotation of the mill drum  16  from a gravity-balanced position.  
         [0117]    It should be understood that although the material within the drum  16  is hereinafter disclosed as potentially separating from the inner surface  20  of the mill drum  16 , the description also applies to situation where the material separates from the lining  46  or any other covering material protecting the inner surface  20  of the mill drum  16 .  
         [0118]    In accordance with one aspect of the present invention, the step of evaluating if the material within the mill drum  16  separates from the inner surface  20  within the cascading angular displacement range  86  upon rotation of the mill drum  16  from the rest or gravity-balanced position includes using a torque provider (such as the primary drive motor  52  or the inching device  14 ) for rotating the mill drum  16  with the material contained therein. Once the mill drum  16  is rotating, the next step involves monitoring the value of the driving torque for the presence of a torque value indicating that the material has not separated from the inner surface  20  of the drum mill  16  when the mill drum  16  has rotated from the gravity-balanced position by more than the cascading angular displacement range  86 . It should be understood that the spectrum of the cascading angular displacement range  86  may vary depending on the accuracy of the determination of the angle, or angular displacement from the gravity-balanced position, at which the material within the mill drum  16  separates from the inner surface  20  or the required accuracy. In the example shown throughout the figures, the cascading angular displacement range  86  is shown as being relatively narrow and identified as a single point in the graph. It should, however, be understood that the width or spectrum of the cascading angular displacement range  86 , typically in the range of a few degrees or the like about a nominal cascading angle α c , may vary without departing from the scope of the present invention.  
         [0119]    Preferably, the step of monitoring the value of the driving torque for the presence of a torque value indicating that the material within the mill drum  16  has not separated from the inner surface  20  of the mill drum  16  within the cascading angular displacement range  86  includes evaluating if the driving torque continues to increase when the mill drum  16  has rotated by more than the cascading angular displacement range  86  from the gravity-balanced position. Alternatively, the step of monitoring the value of the driving torque for the presence of a torque indicating that the material has not separated from the inner surface  20  within the cascading angular displacement range  86  includes evaluating if the driving torque reaches a predetermined torque threshold when the mill drum  16  has rotated by more than the cascading angular displacement range  86  from the gravity-balanced condition.  
         [0120]    As mentioned previously, in some situations, a residual lump of material  102   a  may remain attached to the inner surface  20  despite the complementary volume of solidified material having separated from the latter. Hence, optionally, the method further includes the steps of assessing for the presence of a residual lump of material  102   a  having remained adhered to the inner surface  20  of the mill drum  16  after the latter has rotated by more than the cascading angular displacement range  86  from the gravity-balanced position despite the complementary volume of material having separated from the inner surface. The method optionally further includes the step of stopping the rotation of the mill drum  16  upon assessing the presence of a residual lump of material  102   a.    
         [0121]    Typically, when these optional steps are performed, the value of the driving torque is monitored for the presence of a torque value indicating the presence of the residual lump of material  102   a  when the mill drum  16  has rotated from the gravity-balanced position by more than the cascading angular displacement range  86 . Typically, the driving torque is monitored until the drum  16  rotates from the gravity-balanced position by a predetermined safe angular displacement, or safe angle α s , as shown in FIGS. 7 and 9. Typically, the predetermined safe angular displacement is established as being 360° or any other suitable value.  
         [0122]    Preferably, monitoring the value of the driving torque for the presence of a torque value indicating the presence of a residual lump of material  102   a  includes evaluating if the driving torque continues to increase when the drum  16  has rotated by more than the cascading angular displacement range  86  until the drum  16  angular displacement from gravity-balanced condition reaches the predetermined safe angular displacement α s .  
         [0123]    Optionally, the cascading angular displacement range  86  may be estimated by obtaining data on the value of the driving torque at various angular displacements of the drum  16  from the gravity-balanced position when the mill drum  16  is rotating and the material is tumbling in a cascading flow. In such instances, the cascading angular displacement range  86  is typically approximated to an angular displacement a of the mill drum  16  from gravity-balanced condition wherein the value of the driving torque is comparatively high relative to the value of the driving torque at other angular displacements of the mill drum  16 .  
         [0124]    Although the proposed method has hereinabove been disclosed in the specific context of a grinding mill wherein an evaluation of the potential risk of having solidified material  102  fall within a drum is important, the proposed method may be generalized to any suitable type of rotating component part of a machine wherein the rotating component defines a critical angular displacement value α c  about which an operational parameter of the machine may be used for predicting the occurrence of a potentially damaging condition for the machine. A potentially damaging condition for the machine being more susceptible to happen upon the operational parameter meeting predetermined critical parameter conditions while the rotating component reaches the critical angular displacement value α c . In such general terms, the method may be generalized comprising the steps of providing an evaluation of the operational parameter upon the rotating component reaching the critical angular displacement value α c  from gravity-balanced condition and receiving the evaluation of the operational parameter for effectuating an action in order to reduce the risks of damaging the machine upon the operational parameter meeting the predetermined critical parameter conditions.  
         [0125]    In a sub-set of situations, the rotating component is typically a rotating drum defining a drum peripheral wall, itself defining a reference position thereof. Typically, the rotating component is coupled to a drive provider able to generate a driving torque for driving the rotating component about a component rotation axis. In such situations, the step of providing an evaluation of the operational parameter may include providing an evaluation of the angular displacement relationship between the peripheral wall reference location from the gravity-balanced position and the critical angular displacement value α c  and the method further includes the steps of evaluating the driving torque.  
         [0126]    Referring now more specifically to FIGS. 1 and 8, there is shown an example of a grinding mill  12  having a device  10  in accordance with an embodiment of the present invention operatively coupled thereto. The device  10  includes a parameter monitor operatively coupled to the grinding mill  12  and to the torque provider for monitoring the angular displacement of the mill drum  16  and the value of the driving torque. The device  10  also includes an evaluator operatively coupled to the parameter monitor for evaluating if the value of the torque continues to increase upon the drum  16  rotating by more than the cascading angular displacement range  86  from the gravity-balanced position. The device  10  further includes an effectuator operatively coupled to the evaluator and to the torque provider for initiating an action leading to the stopping of the rotation of the mill drum  16  if the value of the torque continues to increase upon the drum  16  rotating by more than the cascading angular displacement range  86  from the gravity-balanced condition.  
         [0127]    Typically, the parameter monitor includes a torque monitor operatively coupled to the torque provider for monitoring the value of the driving torque so as to assess the presence of a torque value indicating that the material has not separated from the inner surface  20  of the mill drum  16  when the mill drum  16  has rotated by more than the cascading angular displacement range  86 . Also, the parameter monitor typically includes an angular displacement sensor operatively coupled to the grinding mill  12  for assessing the angular displacement of the mill drum  16  from the gravity-balanced position.  
         [0128]    In one embodiment of the invention, the angular displacement sensor includes a rotation encoder  116  operatively coupled to the grinding mill  12  for converting an operational parameter of the grinding mill  12  into an estimate of the angular-displacement of the mill drum  16  from the gravity-balanced position. Typically, although by no means exclusively, the rotation encoder  116  includes a reference component  118 , which could simply be the teeth of one of the gears mounted on the hydraulic motor output shaft  70  of the inching device  14 , mounted on a driving shaft of the torque provider for rotating the latter. It should be understood that the torque provider could take the form of the any drive motor such as the drive motor  62  of the inching device  14  or any other suitable torque provider, as long as the angular displacement sensor is operatively coupled to the torque provider. The rotation encoder  116  further includes an inductive-type sensor  120 , or an optical sensor, mounted adjacent the reference component  118  for monitoring the displacement of the reference component  118  and inferring the angular displacement of the mill drum  16  from the position of the reference component  118 . Furthermore, the rotation encoder  116  could also be a conventional quadrature-type encoder, or two regular encoders with a ninety (90) degree phase shift therebetween, for determining the rotational direction of the torque provider and the mill drum without departing from the scope of the present invention.  
         [0129]    In one embodiment of the invention, the parameter monitor includes a torque sensor operatively coupled to the torque provider for assessing the value of the driving torque. In situations wherein the torque provider is a hydraulic motor  62  part of the inching device  14 , the torque sensor includes a pressure transducer  122  operatively coupled to the hydraulic circuitry  66  or hydraulic fluid lines of the hydraulic motor  62  for assessing the hydraulic pressure in the hydraulic circuitry  66  of the hydraulic motor  62 . In FIGS. 1 and 8, two pressure transducers  122  are coupled to corresponding fluid lines  66  are shown since the motor  62  of the inching device  14  can be operated in either rotational direction, clockwise and counterclockwise. Optionally, both the rotation encoder  116  and the pressure transducer  122  are electrically or electronically coupled to a control unit  124  for enabling an intended user to customize the input data and its processing depending on specific operational parameters such as the type of grinding mill, the gear ratio and the like. Typically, the controller unit  124  is linked to a suitable display  126 , visual or other type of display, for interfacing with the intended user.  
         [0130]    Various actions may be taken either automatically by the controller unit  124  or through the interface  128 , such as a keypad or the like, of the intended user for stopping the rotation of the mill drum  16 , should the value of the torque continue to increase upon the mill drum  16  rotating by more than the cascading angular displacement range  86 . For example, the controller unit  124  may send a signal to the display unit  126  to inform the intended user of the condition or may automatically send a signal to the torque provider for stopping the latter.  
         [0131]    Alternatively, the torque sensor could be a load cell (not shown) mounted on the shaft  70  of the inching drive  14  without departing from the scope of the present invention.  
         [0132]    Similarly, the inching drive  14  could include an electric-type motor (not shown) coupled to an amperage sensor acting as a torque sensor without departing from the scope of the present invention.  
         [0133]    Also, the above described method for protecting the rotating drum of a grinding mill applies when the mill drum itself includes windings (not shown) so as to directly be the rotor of the driving motor. The rotor (not shown) is surrounded by the stator part of the preferably stepper-type motor so as to form a gearless type grinding mill. Accordingly, an external drum brake (not shown) is operatively coupled to the mill drum to enable stopping and holding the latter in any rotational position whenever required by the method.  
         [0134]    Although the present angle-based method and device for protecting a rotating component have been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that the present invention is not limited to the features of the embodiments described and illustrated herein, but includes all variations and modifications within the scope and spirit of the invention as hereinafter claimed.