Abstract:
The system for measuring wear in a grinding mill has at least one bolt passing through the shell and a wear plate. The bolt has an elongated oblong-shaped bolt head extending through the wear plate, flush with a surface of the wear plate. The bolt head is exposed to a same abrasion as the wear plate. The bolt has a groove there along and a plurality of wire loops embedded in that groove. Each wire loop extends to a distinct point along the bolt head, such as to form a ruler along the bolt head. A mobile transmitter-receiver is mounted to the stem of the bolt and is connected to the wire loops. The mobile transmitter-receiver has electronic circuitry therein for detecting broken loop conditions and for transmitting these conditions to a remote receiver where the conditions are related to degrees of wear on the wear plate.

Description:
FIELD OF THE INVENTION 
     This invention pertains to a system for measuring wear in a grinding mill for grinding minerals, and more particularly, it pertains to a self-contained measurement and wireless communication device for measuring wear in a grinding mill without stopping the mill. 
     BACKGROUND OF THE INVENTION 
     Mining companies grind several thousand tons of ore rocks per days. Generally, the grinding mills used for this task consist of revolving drums which are lined with wear-resistant plates, to resist the abrasion of the ore rocks tumbling against their inside surfaces. These wear plates are replaced periodically when they reach a minimum thickness. 
     The stopping of one of these mills for inspection represents enormous losses in production time and high energy demand to start it up again. Therefore, there has been numerous efforts made in the past to shorten the inspection time or to reduce inspection frequency to a minimum. For examples; 
     U.S. Pat. No. 1,772,026 issued to C. O. Bartley on Aug. 5, 1930; discloses a measuring system which consists of one or more screws extending radially through the shell of the mill and into corresponding cavities in one of the wear plates. When the bolt can be inserted further than the bottom of the cavity without resistance, the liner is either broken or has worn to its minimum thickness, and in either cases replacement of the wear plates is in order. 
     JP Patent 354,035,464 issued to Kubota Ltd., on Mar. 15, 1979, discloses a system wherein the bolts retaining the wear plates have their heads flush with the exposed surfaces of the plates. As a wear plate gets thinner, the bolt heads holding it also wear down. When a bolt head is worn away completely, a spring under the nut of the bolt pulls the nut and the stem of the bolt outside the shell of the mill. The stem and nut fall into a bolt casing and hit a switch in that casing. The switch is connected to a buzzer or other warning device to inform maintenance personnel that a wear plate inside that mill is due for replacement. 
     Although the systems of the prior art deserve undeniable merits, these systems provide warning when a wear plate is no longer protecting the shell of the mill and the mill must be shut down. These failures can occur during a time of reduced personnel such as a night shift or a holiday. The repair of the mill during these emergency situations is generally done by reduced-size crews and consequently, the mill is unproductive for a longer period than if the repairs would have been carried out during a planned shutdown. 
     Therefore, there is a need in the industry for a monitoring device which can provide sufficient warning time so that repair work can be schedule ahead, and proper spare parts, tools, rigging and lifting equipment can be brought to the job site in preparation for the job. There is a need for a monitoring device which can provide sufficient warning time to ensure that the repair can be effected quickly, and that the mill can be put back in operation in the shortest possible delay. 
     SUMMARY OF THE INVENTION 
     In the present invention, however, there is provided a system for measuring wear to a fraction of an inch for example, and wherein the measurements are transmitted in a wireless mode to a remote receiver, without stopping the mill. 
     In one aspect of the present invention, there is provided a system for measuring wear in a grinding mill having a shell and at least one wear plate affixed to an inside surface of that shell. The system comprises at least one bolt passing through the shell and the wear plate. The bolt has a bolt head extending through the wear plate, flush with the exposed surface of the wear plate. The bolt head is exposed to a same abrasion as the wear plate, and has a length similar to the usable thickness of the wear plate. 
     The bolt also has a stem extending through the shell and through the wear plate, and has a groove extending along the stem and the bolt head. At least one wire loop is embedded in that groove. The wire loop extends to a distinct point along the bolt head. 
     The system also includes a self-contained mobile transmitter-receiver mounted to the stem of the bolt and connected to the wire loop. The mobile transmitter-receiver has electronic circuitry therein for detecting broken loop conditions in the wire loop. 
     The system also comprises a base transmitter-receiver mounted in a remote location relative to the mill, and a communication system in both the mobile transmitter-receiver and the base transmitter-receiver for transmitting the broken-loop condition to the base transmitter-receiver. The system for measuring wear also includes a computer or other microprocessor for interpreting and relating the broken loop condition to a thickness of the wear plate inside the mill. 
     The end of the wire loop can be placed at a specific depth along the bolt head, at a depth corresponding to a mid-life thickness of the wear plate for example. The measuring system can be interrogated periodically or continually until the wire loop is broken by abrasion, indicating a specific degree of wear inside the mill. The remaining life of the wear plate can be extrapolated from the operating time on the wear plate prior to the broken loop condition, and the depth of that broken loop. A scheduled shutdown can then be planned and effected at a time that causes minimum disruption to production schedules. 
     In another aspect of the present invention, there is provided a plurality of wire loops in a same bolt, and the ends of these loops are spaced apart from each other along the bolt head. An electric signal is sent through each loop and each signal is identifiable by a unique frequency, such that each loop, when broken, provides a unique broken loop condition, whereby wear on the bolt head is measurable incrementally. 
     In yet another aspect of the present invention, a plurality of bolts each having a plurality of wire loops embedded therein and a mobile transmitter-receiver mounted thereon are used to monitor wear at various locations inside the mill. 
     In yet a further aspect of the present invention, the bolt mentioned above is replaced by a longitudinal probe extending through the thickness of a wear plate. The probe has a plurality of wire loops embedded in a hole along its core. The end of the probe is exposed to wear and the wire loops therein are severed one by one at a same rate as a reduction in thickness of the wear plate in which it is mounted. 
     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the present invention is illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which: 
         FIG. 1  represents a side view of a grinding mill, having a plurality of wear-plate thickness detectors according to the preferred embodiment of the present invention thereon; 
         FIG. 2  is a partial cross-section view of a thickness-detector assembly, as seen substantially along line  2  in  FIG. 1 ; 
         FIG. 3  is a side view of the plate-retaining bolt and a schematic view of a self-contained mobile transmitter-receiver mounted to that bolt; 
         FIG. 4  is a cross-section view of the plate-retaining bolt as seen along line  4 — 4  in  FIG. 3 ; 
         FIG. 5  is a partially cut-away side view of a thickness-measuring probe which can be used as an equivalent for the bolt shown in  FIG. 3 ; 
         FIG. 6  is a cross-section through the probe shown in  FIG. 5 , as seen along line  6 — 6  in  FIG. 5 ; 
         FIGS. 7 ,  8  and  9  illustrate three different thickness-measuring circuits which can be mounted inside the bolt as shown in  FIG. 3 , or inside the probe as shown in  FIG. 5 , for measuring wear in a grinding mill. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will be described in details herein one specific embodiment of a system for measuring wear in a grinding mill for grinding minerals, or a cement plant. The present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiment illustrated and described. 
     Although efforts have been made to limit the use of precise dimensions and exact geometric qualifiers, some narrow expressions remain in this disclosure and are used for convenience only to provide a better understanding of the present invention. Such dimensions and shapes can vary from one model of grinding mill to the other. Therefore the dimensions and geometric expressions mentioned herein should not be considered as being absolute and limiting. 
     Referring to  FIG. 1 , a typical grinding mill  20  for grinding minerals is represented therein. It will be appreciated that the illustration in  FIG. 1  can also represent a cement mixing plant or other aggregate processing equipment, wherein the present invention would be applicable as well. 
     A partial cross-section through the shell  22  of the mill is shown in  FIG. 2 . The shell&#39;s inside surface is lined with wear-resistant plates  24 , which are retained to the shell  22  by plate-retaining bolts  26 . Each bolt  26  has a round stem  28  and a stretched oblong-shaped head portion  30  which extends flush with the inside surface of the wear plate  24  as illustrated. Each bolt  26  has a threaded stem  28  and a nut  32  mounted on that stem outside the shell  22 . A plurality of these bolts  26  and nut  32  retain a plurality of wear plates  24  to the shell  22  of the mill. 
     In the preferred thickness-detector assembly, each thickness-detector bolt  26 ′ has a longitudinal groove  34  therein. This groove  34  encloses a plurality of wire loops  36 , wherein each loop  36  extends to a specific point along the bolt head  30 , such as to define a ruler along the bolt head  30 . 
     A self-contained mobile transmitter-receiver  40  is mounted to the outside end of the bolt  26 ′ by means of a threaded coupling  42  mounted to the bolt stem  28 , as a locknut against the nut  32 . The mobile transmitter-receiver  40  provides power to the wire loops  36 , and monitors the response from each loop  36 . The response is either an unaltered signal or a lost signal, as in the case of a broken or short circuit. 
     The mobile transmitter-receiver  40  communicates in a wireless mode to a base transmitter-receiver  44 , which is mounted to a fixed structure  46  in vicinity of the mill  20 . The base transmitter-receiver  44  is connected by wires  48  to a computer  50 , through a RS-232 port for example. Although a fixed base transmitter-receiver  44  as been illustrated, it is also possible to use a handheld electronic device to carry out the same functions, or a base transmitter-receiver mounted inside a laptop computer, for example. 
     Referring now to  FIGS. 3 and 4 , the thickness-detector bolt  26 ′ and the mobile transmitter-receivers  40  will be explained in greater details. 
     The thickness-detector bolt  26 ′ has a plurality of wire loops  36  embedded in the groove  34  there along. The wire loops  36  are embedded in an epoxy  60  or a similar hardened resinous material to keep them in place inside the groove. The wire loops  36  extend to different points along the bolt head  30  of the thickness-detector bolt  26 ′, with the end of each loop being spaced from the other loop ends a specific distance, such as on a ruler, to provide useful information concerning the rate of wear on the wear plates supported by that bolt. 
     Preferably, the bolt head  30  is made of a material that is softer than the material of the wear plate  24 . As the wear plate  24  wears down, the bolt head  30  also wears down at the same rate as the wear plate  24 , and the wire loops  36  in that bolt head  30  are broken one by one when they become exposed at the end of the bolt head  30 . When a loop  36  is broken, a short-circuit or an open circuit can be detected in that loop  36 . The severing of each wire loop  36  provides an indication of the actual thickness of the wear plate  24  at that time. In the preferred embodiment, a large number of wire loops may be used to detect a wear rate to a fraction of an inch for example. 
     The self-contained mobile transmitter-receiver  40  is built to detect short-circuit to ground or open circuit conditions in each of the wire loops  36 . The mobile transmitter-receiver  40  comprises a printed circuit (not shown) and is operated by a battery  62 . In use, each wire loop  36  is interrogated by an electrical signal, preferably a square signal, having a unique frequency, to distinguish that loop from other loops. For that purpose, the mobile transmitter-receiver  40  also comprises, a micro-controller  64 , connected to both a multiplexer  66  and a decoder  68 , with the multiplexer  66  and the decoder  68  being also connected to respective ends of the wire loops  36 . Other means of distinguishing one loop from the others can also be used, such other decoding means may include circuitry to pass a current in each loop in sequence or at different time intervals for example. 
     The base transmitter-receiver  44  also contains a second micro-controller (not shown), which is substantially the same as the first-mentioned one. Both micro-controllers can transmit and receive information to and from each other in a wireless mode. 
     When more than one bolt-detector  26 ′ and more than one mobile transmitter-receiver  40  are used, all thickness-detector assemblies can be interrogated in sequence or at different time intervals or under different frequencies or by other unique identification codes. 
     In use, the interrogation of a single thickness-detector assembly  26 ′,  40  is initiated by the computer  50 . A first signal is sent to the mobile transmitter-receiver  40  which in turn sends signals to all wire loops  36 . The mobile transmitter-receiver  40  reads the condition of each loop  36  and sends this information to the base transmitter-receiver  44  in a wireless mode. The base transmitter-receiver  44  relays this information to the computer  50  wherein the information is interpreted and displayed on the computer screen as an indication of the actual thickness of a wear plate  24  inside the mill. When the thickness of the wear plate reaches a specific measurement, the mill can be scheduled for preventive maintenance and replacement of all the wear plates inside the mill. 
     The mobile transmitter-receiver  40  and the base transmitted-receiver  44  are explained herein by their functions rather than by their specific structure. The structure of these devices is known to those skilled in the art of communication devices, and therefore, it does not need further explanation. 
     Although a groove  34  in a thickness-detector bolt  26 ′ has been mentioned herein before, it will be appreciated that a hole  70  though the centre of the bolt  26 ′ or through the centre a rod-like probe  72  can also be used, as illustrated in  FIGS. 5 and 6 . As an example, the probe  72  has a threaded portion  74  that is mountable through the shell  22  of a mill and that is retained thereto by a locknut for example. Other equivalents would include similar probes extending through the thickness of a wear plate, and each having a mounting flange (not shown) or other fastening means for attachment thereof to the shell of a mill. 
     Referring to  FIGS. 7 ,  8  and  9 , other equivalents for the wire loops  36  are illustrated. In  FIG. 7 , the measuring portion of the circuit in the thickness-detector assembly comprises a series of independent insulated wires  80 , each extending to a different point along the bolt  26 ′ or probe  72 . As wear reaches one wire  80 , the insulation  82  is broken and the corresponding bare wire  86  is exposed to the grounded body  88  of the bolt or probe. A grounded signal on one of the wires  82  corresponds to a remaining thickness of the wear plate  24 . 
     In  FIG. 8 , a single loop  90  with resistors  92  mounted in parallel and at spaced intervals are inserted in the bolt  26 ′ or in a probe  72  and used to detect a degree of wear in a wear plate  24 . When a resistor  92  is destroyed from wear, an electric signal in the loop  90  is altered. This signal is interpreted to indicate the remaining length of the bolt  26 ′ or the probe  72 . 
     Similarly, a single loop  100  with capacitors  102  can be mounted inside the bolt  26 ′ or the probe  72  to generate a signal in the loop  100  that is representative of the total capacitance of the loop  100 . A variation in that electric signal indicates a different length of the circuit. 
     As to other manner of usage and operation of the present invention, the same should be apparent from the above description and accompanying drawings, and accordingly further discussion relative to the manner of usage and operation of the invention would be considered repetitious and is not provided. 
     While one embodiment of the thickness measurement system according to the present invention has been illustrated and described herein above, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention which is defined by the appended claims.