Patent Publication Number: US-7905343-B2

Title: Self-propelled crushing machine

Description:
TECHNICAL FIELD 
     The present invention relates to a self-propelled crushing machine that finds utility in crushing an object to be crushed, e.g., concrete aggregate, fieldstone et cetera, at a job site. 
     BACKGROUND ART 
     Such a type of self-propelled crushing machine is constructed such that a hopper, a crusher, a belt conveyor et cetera are incorporated into a base carrier. This self-propelled crushing machine operates as follows. An object (to be crushed) is dumped into the hopper and crushed by the crusher and crushed pieces of the object are conveyed from the crusher to outside the crushing machine by means of the belt conveyor. 
     However, there are cases where these crushed object pieces include metallic materials (magnetic materials) such as concrete reinforcing steel bar, nails and wire. To cope with the situations, there is proposed a self-propelled crushing machine which employs a magnetic separator disposed over a belt conveyor so that magnetic materials are selectively removed from the crushed object during conveyance by the belt conveyor (see JP-A-2003-159546). 
     Referring to  FIGS. 8(   a ) and  8 ( b ), there is illustrated a magnetic separator  100  which is provided with a magnetic separator belt  103  which moves in a direction orthogonal to the travel direction of a conveyor belt  102  in a belt conveyor  101 . It is arranged such that a magnet  105  exerts magnetic force to a concrete reinforcing steel bar (magnetic material)  104  on the conveyor belt  102  through the magnetic separator belt  103 , whereby the concrete reinforcing steel bar  104  is attracted and adhered to the magnetic separator belt  103  and taken off of the conveyor belt  102 . 
     Incidentally, as shown in  FIG. 8(   a ), upon attraction and adhesion of a leading end  104   a  of the concrete reinforcing steel bar  104  to the magnetic separator belt  103 , the leading end  104   a  of the concrete reinforcing steel bar  104  is moved together with the magnetic separator belt  103  while on the other hand a trailing end  104   b  of the concrete reinforcing steel bar  104  is moved together with the conveyor belt  102 . 
     At time point T 1  (the moment at which the leading end  104   a  of the concrete reinforcing steel bar  104  has been attracted and adhered to the magnetic separator belt  103 ), the concrete reinforcing steel bar  104 , when viewed from the side of the conveyor belt  102 , is placed in a tilted position to form an acute angle a with the conveyor belt  102 , as illustrated in  FIG. 8(   a ). 
     At time point T 2  (the moment at which the trailing end  104   b  of the concrete reinforcing steel bar  104  has reached line L indicative of a leading end attraction/adhesion position at which the leading end  104   a  of the concrete reinforcing steel bar  104  is to be attracted and adhered to the magnetic separator belt  103 ), the concrete reinforcing steel bar  104 , when viewed from the side of the conveyor belt  102 , is placed in an upright position that forms a right angle with the conveyor belt  102 , as illustrated in  FIG. 8(   a ′). 
     Therefore, conventional self-propelled crushing machines may cause the problem that the trailing end  104   b  of the concrete reinforcing steel bar  104  will pierce into the conveyor belt  102  if the relationship in belt velocities between the conveyor belt  102  and the magnetic separator belt  103  is such that the concrete reinforcing steel bar  104  is still on the conveyor belt  102  as shown in  FIG. 8(   b ′) at time point T 2  at which the concrete reinforcing steel bar  104  is placed in an upright position as shown in  FIG. 8(   a ′). 
     The present invention is directed to overcoming the foregoing problem with the conventional technology. Accordingly, a primary object of the invention is to provide a self-propelled crushing machine capable of ensuring that, even when the object (to be crushed) contains a concrete reinforcing steel bar or other like material, it is prevented that the concrete reinforcing steel bar will pierce into the conveyor belt. 
     SUMMARY OF THE INVENTION 
     In order to accomplish the aforesaid object, the invention provides the following as one embodiment thereof. That is, the invention discloses a self-propelled crushing machine having a conveyor belt which travels carrying crushed pieces of an object crushed by a crusher and a magnetic separator belt which is disposed above the conveyor belt and which travels in a direction intersecting the travel direction of the conveyor belt, whereby magnetic material pieces of the crushed pieces of the object are taken off of the conveyor belt. The self-propelled crushing machine comprises: a conveyor belt drive means by which the conveyor belt is driven at a conveyor belt velocity in response to a given conveyor belt velocity instruction signal; a magnetic separator belt drive means by which the magnetic separator belt is driven at a magnetic separator belt velocity in response to a given magnetic separator belt velocity instruction signal; and a belt velocity instruction signal output means for providing a belt velocity instruction signal to the conveyor belt drive means and to the magnetic separator belt drive means, said belt velocity instruction signal being composed of a conveyor belt velocity instruction signal and a magnetic separator belt velocity instruction signal, said conveyor belt velocity instruction signal being provided to the conveyor belt drive means, and said magnetic separator belt velocity instruction signal being provided to the magnetic separator belt drive means, wherein if the conveyor belt velocity in response to a set conveyor belt velocity instruction signal is higher than the magnetic separator belt velocity in response to the magnetic separator belt velocity instruction signal, the belt velocity instruction signal output means makes a change in the aforesaid belt velocity instruction signal. 
     In accordance with the invention, even when crushed pieces of an object include a bar-shaped magnetic material (for example, a concrete reinforcing steel bar), the concrete reinforcing steel bar attracted and then adhered to the magnetic separator belt is taken off of the conveyor belt before the trailing end of the concrete reinforcing steel bar travels past a leading end attraction/adhesion position at which the leading end of the concrete reinforcing steel bar is to be attracted and then adhered to the magnetic separator belt, in other words, before the concrete reinforcing steel bar is placed in an upright position (as viewed from the side of the conveyor belt) to form right angles with the conveyor belt, thereby ensuring that it is prevented that the concrete reinforcing steel bar will pierce into the conveyor belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , comprised of  FIGS. 1(   a ) and  1 ( b ), shows a self-propelled crushing machine according to one embodiment of the invention wherein  FIG. 1(   a ) is a side view and FIG.  1 ( b ) is a plan view. 
         FIG. 2 , comprised of  FIGS. 2(   a ) and  2 ( b ), shows a belt conveyor and a magnetic separator that are mounted on the self-propelled crushing machine of the embodiment wherein  FIG. 2(   a ) is a side view and  FIG. 2(   b ) is a plan view. 
         FIG. 3 , comprised of  FIGS. 3(   a ) and  3 ( b ), is an enlarged view of section A of  FIG. 2(   a ) wherein  FIG. 3(   a ) illustrates the point of time at which the concrete reinforcing steel bar is attracted and adhered to a magnetic separator belt and  FIG. 3(   b ) is a cross-sectional view taken along line B-B of  FIG. 3(   a ). 
         FIG. 4 , comprised of  FIGS. 4(   a ) and  4 ( b ), is an enlarged view of section A of  FIG. 2(   a ) wherein  FIG. 4(   a ) illustrates the point of time at which the concrete reinforcing steel bar is taken off of a conveyor belt and  FIG. 4(   b ) is a cross-sectional view taken along line C-C of  FIG. 4(   a ). 
         FIG. 5  is a block diagram outlining the system configurations of a conveyor belt drive means, a magnetic separator belt drive means, and their control systems. 
         FIG. 6  is comprised of  FIGS. 6(   a ) and  6 ( b ) wherein  FIG. 6(   a ) is a conveyor belt velocity control map and  FIG. 6(   b ) is a magnetic separator belt velocity control map. 
         FIG. 7  is a flow chart illustrating the contents of processing of a belt velocity control program. 
         FIG. 8  shows diagrams for explaining a conventional technique. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the accompanying drawings, a description will be made about a concrete embodiment of a self-propelled crushing machine according to the invention. 
       FIGS. 1(   a ) and  1 ( b ) illustrate in side view and in plan view respectively a self-propelled crushing machine according to one embodiment of the invention. 
       FIGS. 2(   a ) and  2 ( b ) illustrate in side view and in plan view respectively a belt conveyor and a magnetic separator both mounted on the self-propelled crushing machine of the embodiment. 
     The self-propelled crushing machine  1  shown in  FIG. 1(   a ) is adapted to crush, at a job site, an object (to be crushed) (e.g., construction and demolition waste including concrete aggregate, industrial waste, fieldstone et cetera) into small pieces for the on-site production of small crushed pieces of the object having good reusability or transportability. 
     The self-propelled crushing machine  1  has a base carrier  2  equipped with a track-type undercarriage. A body frame  3  is fixedly mounted on the base carrier  2 . 
     An object-to-be-crushed feeder  4  is mounted in a front section of the body frame  3 . A crusher (jaw crusher)  5  is provided in the middle of the body frame  3 , and an engine compartment  6  is provided in a rear section of the body frame  3 . 
     The body frame  3  is provided, in its lower part, with a belt conveyor  7  which extends towards the back from a position under the crusher  5 . A console panel  8 , containing measuring instruments for monitoring the self-propelled crushing machine  1  and various control units for use in drive operations, is mounted in place in the body frame  3 . 
     As illustrated in  FIG. 1(   b ), the object-to-be-crushed feeder  4  is composed of a hopper  9  into which an object (to be crushed) is dumped and a feeder  10  by which the dumped object in the hopper  9  is conveyed towards the crusher  5 . 
     As illustrated in  FIGS. 1(   a ) and  1 ( b ), a magnetic separator  11  is disposed behind the engine compartment  6  so that it is located above the belt conveyor  7 . The magnetic separator  11  is supported in a hanging manner by a magnetic separator support frame  12  which is assembled onto the body frame  3 . 
     As shown in  FIGS. 2(   a ) and  2 ( b ), the belt conveyor  7  has: a conveyor frame  13  extending in a front/rear direction; an idler pulley  14  and a drive pulley  15  that are rotatably mounted respectively on the front and rear ends of the conveyor frame  13 ; a conveyor belt  16  mounted in a wound manner around the idler and drive pulleys  14  and  15 ; and a conveyor belt drive means  17  configured to drive the conveyor belt  16 . In addition, the belt conveyor  7  is constructed such that, when the conveyor belt  16  is brought into rotating motion driven by the conveyor belt drive means  17 , crushed pieces of the object, dropped from the crusher  5  (see  FIG. 1)  onto the conveyor belt  16 , are taken out to behind the self-propelled crushing machine  1 . 
     As shown in  FIGS. 3(   a ) and  3 ( b ), the magnetic separator  11  has: an idler pulley  21  and a drive pulley  22  that are rotatably mounted on a magnetic separator casing  20  at a given axial distance apart from each other in a direction orthogonal to the belt travel direction, Rc, of the conveyor belt  16 ; a magnetic separator belt  23  mounted in a wound manner around the idler and drive pulleys  21  and  22  so as to be disposed face to face with the conveyor belt  16 ; a magnet  24  firmly secured to the magnetic separator casing  20  through a fixing means (not shown) so as to be located between the idler pulley  21  and the drive pulley  22 ; and a magnetic separator belt drive means  25  for driving the magnetic separator belt  23 . In addition, the magnetic separator  11  is constructed such that, when the magnetic separator belt  23  is made to travel around the magnet  24  driven by the magnetic separator belt drive means  25 , the magnet  24  exerts its magnetic force to, for example, a concrete reinforcing steel bar (bar-shaped magnetic material)  26  on the conveyor belt  16  through the magnetic separator belt  23 , whereby the concrete reinforcing steel bar  26  on the conveyor belt  16  is attracted and adhered to the magnetic separator belt  23  and then taken off of the conveyor belt  16  by way of a concrete reinforcing steel bar discharge chute  27  attached to the side of the conveyor frame  13 . 
     Next, the configurations of the conveyor belt drive means  17 , the magnetic separator belt drive means  25 , and their control systems will be explained below with reference to the block diagram of  FIG. 5 . 
     The conveyor belt drive means  17  has: a conveyor hydraulic motor  32  for rotationally driving the drive pulley  15  upon supply of operating oil from a main hydraulic pump  31  driven by an engine  30  that serves as the power source of the self-propelled crushing machine  1 ; a control valve  33  for controlling the rate of flow of operating oil supplied from the main hydraulic pump  31  to the conveyor hydraulic motor  32  in response to a pilot pressure; and an electric proportional valve  35  for adjusting the pilot pressure provided by a pilot hydraulic pump  34  driven by the engine  30  to the control valve  33  in response to the control electric current. In addition, the conveyor belt drive means  17  is adapted to drive the conveyor belt  16  in order that the conveyor belt velocity may become responsive to the control current (which corresponds to the “conveyor belt velocity instruction signal” in the invention) supplied from a controller  36  to the electric proportional control valve  35 . 
     The magnetic separator belt drive means  25  has: a magnetic separator hydraulic motor  37  for rotationally driving the drive pulley  22  upon supply of operating oil from the main hydraulic pump  31 ; a control valve  38  for controlling the rate of flow of operating oil supplied from the main hydraulic pump  31  to the magnetic separator hydraulic motor  37  in response to the pilot pressure; and an electric proportional control valve  39  for regulating the pilot pressure provided by the pilot hydraulic pump  34  to the control valve  38  in response to the control current. The magnetic separator belt drive means  25  is adapted to drive the magnetic separator belt  23  in order that the magnetic separator belt velocity may become responsive to the control current (which corresponds to the “magnetic separator belt velocity instruction signal” in the invention) supplied from the controller  36  to the electric proportional control valve  39 . 
     The controller  36  is configured such that it has a microprocessor (MPU)  40  for executing arithmetic processing in accordance with the instruction of a program; a memory  41  (which corresponds to the “memory means” in the invention) for storage of programs, data, and other like information; an input interface  42  for conversion of input signals into signals for processing by the MPU  40 ; and an output interface  43  for controlling, based on the result of the arithmetic processing by the MPU  40 , the magnitude of control currents provided to each of the electric proportional control valves  35  and  39 . 
     Also, it should be noted that the configuration including the MPU  40  and the output interface  43  corresponds to the “belt velocity instruction signal outputting means” of the invention. 
     The console panel  8  includes a mode select switch  44  for selective switching between a concrete aggregate mode and a stone crush mode, and a conveyor belt velocity control dial  45  for manual adjustment of the belt velocity of the conveyor belt  16 . The mode select switch  44  and the conveyor belt velocity control dial  45  are each connected to the input interface  42  of the controller  36 . 
     In addition, the concrete aggregate mode is an operation mode which is intended for crushing a chunk of concrete mixed with concrete reinforcing steel bars or the like and whose operation conditions (such as crushing velocity) are set such that a chunk of concrete is crushed efficiently by the crusher  5 . The concrete aggregate mode corresponds to the “specific operation mode” of the invention. 
     The stone crush mode is an operation mode which is intended for crushing of fieldstone and whose operation conditions (such as crushing velocity) are set such that fieldstone is crushed efficiently by the crusher  5 . 
     In addition, by controlling the belt velocity of the conveyor belt  16  by means of the conveyor belt velocity control dial  45 , the operator is allowed to set any conveyor belt velocity depending on the properties of objects to be crushed. 
     The memory  41  of the controller  36  stores a conveyor belt velocity control map (shown in  FIG. 6(   a )) and a magnetic separator belt velocity control map (shown in  FIG. 6(   b )). Additionally, the memory  41  also stores a belt velocity control program prepared based on the algorism shown in the flow chart of  FIG. 7 . 
     The MPU  40  retrieves the belt velocity control program stored in the memory  41  and takes in signals from the mode select switch  44  and the conveyor belt velocity control dial  45  according to the instruction of the retrieved belt velocity control program. With reference to the conveyor belt velocity control map and to the magnetic separator belt velocity control map, both stored in the memory  41 , the MPU  40  performs arithmetic to calculate the value of the control current for supplying to each of the electric proportional control valves  35  and  39  and then transmits the control current value obtained by the arithmetic calculation to the output interface  43  as a set control current value. The output interface  43  provides control of the magnitude of the control current in order that the magnitude of the control current for supplying to each of the electric proportional control valves  35  and  39  may have a set control current value. 
     Next, with making reference to the flow chart shown in  FIG. 7 , the contents of processing of the belt velocity control program will be described. Also note that the upper case letter “S” stands for “step” in  FIG. 7 . In addition, the contents of the processing hereinafter described are repeatedly executed in a predetermined cycle time. 
     Contents of Processing in Step S 1   
     In Step S 1 , the MPU  40  determines whether or not the currently selected operation mode is the concrete aggregate mode, based on the switch select signal from the mode select switch  44 . 
     The process moves forward to Step S 2  if the MPU  40  determines that the concrete aggregate mode is being selected. 
     Contents of Processing in Step S 2   
     In Step S 2 , the MPU  40  reads a set control current value Ic 1  currently set in response to a dial manipulated variable signal Dc 1  from the conveyor belt velocity control dial  45 , and reads a set conveyor belt velocity Vc 1  corresponding to the set control current value Ic 1  based on the conveyor belt velocity control map of  FIG. 6(   a ) in the memory  41 . Then, the MPU  40  reads a set control current value Im 1  currently set, and reads a set magnetic separator belt velocity Vm 1  corresponding to the set control current value Im 1  based on the magnetic separator belt velocity control map of  FIG. 6(   b ) retrieved from the memory  41 . In the present embodiment, the magnetic separator belt velocity is fixed at a constant velocity. 
     Contents of Processing in Step S 3   
     In Step S 3 , the MPU  40  compares the set conveyor belt velocity Vc 1  and the set magnetic separator belt velocity Vm 1  obtained respectively from the conveyor belt velocity control map and the magnetic separator belt velocity control map. And, the MPU  40  determines whether or not the set magnetic separator belt velocity Vm 1 (=Vm(Im 1 )) is lower than the set conveyor belt velocity Vc 1 (=Vc(Ic 1 )), i.e., Vm 1 &lt;Vc 1 . 
     If the MPU  40  determines that the set magnetic separator belt velocity Vm 1  is lower than the set conveyor belt velocity Vc 1 , i.e., Vm 1 &lt;Vc 1 , the process moves forward to Step S 4 . Otherwise, the process moves forward to Step S 7 . 
     Contents of Processing in Steps  4 - 5   
     In Step S 4 , the MPU  40  reads a control current value Ic 2  from the conveyor belt velocity control map of  FIG. 6(   a ) and sets the read control current value Ic 2  as a set control current value Ic 2  for transmission to the output interface  43 . Here, the relationship between a conveyor belt velocity Vc 2  corresponding to the set control current value Ic 2  and the set magnetic separator belt velocity Vm 1  is that the former is lower than the latter, i.e., Vc 2 &lt;Vm 1 . 
     Subsequently, in Step S 5 , the MPU  40  transmits both the set control current value Ic 2  and the set control current value Im 1  to the output interface  43 , and the flow is terminated. 
     If, in Step S 1 , the MPU  40  determines, based on the switch select signal from the mode select switch  44 , that the currently-selected operation mode is not the concrete aggregate mode (in other words, if the MPU  40  determines that the currently-selected operation mode is the stone crush mode), then the processing of Step S 6  is carried out and the flow is terminated. 
     Contents of Processing in Step S 6   
     In Step S 6 , the MPU  40  takes in the dial manipulated variable signal Dc 1  from the conveyor belt velocity control dial  45  and, in addition, finds the control current value Ic 1  corresponding to the dial manipulated variable signal Dc 1  by making reference to the conveyor belt velocity control map of  FIG. 6(   a ). The MPU  40  sets the control current value Ic 1  thus found as the set control current value Ic 1  for transmission to the output interface  43  and then transmits it to the output interface  43 . 
     If, in Step S 3 , the MPU  40  determines that the set magnetic separator belt velocity Vm 1  is equal to or higher than the set conveyor belt velocity Vc 1 , i.e., Vm 1 ≧Vc 1, the processing of Step S 7  is carried out, and the flow is terminated. 
     Contents of Processing in Step S 7   
     In Step S 7 , the MPU  40  transmits both the set control current value Ic 1  and the set control current value Im 1  to the output interface  43 . 
     Upon execution of the processing of Step S 5  in the self-propelled crushing machine  1  of the present embodiment, the control current Ic 2  is fed from the output interface  43  to the electric proportional control valve  35  of the conveyor belt drive means  17 , while on the other hand the control current Im 1  is fed from the output interface  43  to the electric proportional control valve  39  of the magnetic separator belt drive means  25 . As a result, the conveyor belt  16  is driven at the belt velocity Vc 2  by the conveyor belt drive means  17 , while on the other hand the magnetic separator belt  23  is driven at the belt velocity Vm 1 (&gt;Vc 2 ) by the magnetic separator belt drive means  25 . 
     In addition, upon execution of the processing of Step S 7 , the control current Ic 1  is fed from the output interface  43  to the electric proportional control valve  35  of the conveyor belt drive means  17 , while on the other hand the control current Im 1  is fed from the output interface  43  to the electric proportional control valve  39  of the magnetic separator belt drive means  25 . As a result, the conveyor belt  16  is driven at the belt velocity Vc 1  by the conveyor belt drive means  17 , while on the other hand the magnetic separator belt  23  is driven at the belt velocity Vm 1 (&gt;Vc 1 ) by the magnetic separator belt drive means  25 . 
     That is, once the concrete aggregate mode is chosen by manipulation of the mode select switch  44 , the relationship in belt velocities between the conveyor belt  16  and the magnetic separator belt  23 , in which the belt velocity, Vm, of the magnetic separator belt  23  is higher than the belt velocity, Vc, of the conveyor belt  16 , is established, regardless of the conveyor belt velocity previously set by means of the conveyor belt velocity control dial  45 . 
     Referring now to  FIGS. 2 ,  3  and  4 , the following is a description of the operation of separation of the concrete reinforcing steel bar  26  by the magnetic separator  11  when the aforesaid belt velocity relationship of Vm&gt;Vc is established. 
     In the event that the concrete reinforcing steel bar  26  rides and travels on the conveyor belt  16  along the belt travel direction, Rc, of the conveyor belt  16  as shown in  FIG. 2(   b ) and the leading end  26   a  of the concrete reinforcing steel bar  26  is attracted and adhered to the magnetic separator belt  23  as shown in  FIGS. 3(   a ) and  3 ( b ), the leading end  26   a  of the concrete reinforcing steel bar  26  is shifted in the belt travel direction, Rm, of the magnetic separator belt  23  together with the magnetic separator belt  23 , whereas the trailing end  26   b  of the concrete reinforcing steel bar  26  is shifted in the belt travel direction, Rc, of the conveyor belt  16 , together with the conveyor belt  16 . 
     The position of the leading end  26   a  of the concrete reinforcing steel bar  26  attracted and adhered to the magnetic separator belt  23  is indicated by line L (alternate long and short dash line) in  FIG. 3(   a ). Line L represents a plane orthogonal to the belt travel direction, Rc, of the conveyor belt  16  and including the leading end  26   a.    
     At the moment that the leading end  26   a  of the concrete reinforcing steel bar  26  is attracted and adhered to the magnetic separator belt  23 , the concrete reinforcing steel bar  26 , as viewed from the side of the conveyor belt  16 , is placed in a tilted position to form an acute angle a with the conveyor belt  16  as shown in  FIG. 3(   a ). 
     At the time just before the concrete reinforcing steel bar  26  attracted and adhered to the magnetic separator belt  23  is taken off of the conveyor belt  16  as illustrated in  FIG. 4(   b ), the trailing end  26   b  of the concrete reinforcing steel bar  26  has not yet traveled past line L indicative of the leading end attraction/adhesion position at which the leading end  26   a  of the concrete reinforcing steel bar  26  is to be attracted and adhered to the magnetic separator belt  23 , as shown in  FIG. 4(   a ). At this point of time, the concrete reinforcing steel bar  26 , as viewed from the side of the conveyor belt  16 , is placed in a tilted position to form an acute angle α′(&gt;α) with the conveyor belt  16 , as illustrated in  FIG. 4(   a ). Therefore, the concrete reinforcing steel bar  26  in question is soon taken off of the conveyor belt  16 . 
     Therefore, this ensures that the concrete reinforcing steel bar  26  is prevented from piercing into the conveyor belt  16 . 
     Heretofore, the description has been made about the self-propelled crushing machine of the invention based on one embodiment thereof. It should however be noted that the invention is not necessarily limited to the particular configuration discussed in the one embodiment, and various changes and modifications may be accordingly made to the configuration without departing from the spirit and scope of the invention. 
     In the embodiment described herein, the concrete reinforcing steel bar  26  is taken off of the conveyor belt  16  before the trailing end  26   b  of the concrete reinforcing steel bar  26  travels past the leading end attraction/adhesion position L, whenever the relationship in belt velocities between the magnetic separator belt  23  and the conveyor belt  16  is that Vm (the belt velocity of the magnetic separator belt  23 ) is higher than Vc (the belt velocity of the conveyor belt  16 ), and there is shown an example in which, in order that the belt velocity relationship (Vm&gt;Vc) may be established, the belt velocities of the conveyor belt  16  and the belt velocity of the magnetic separator belt  23  are controlled. 
     However, there is the possibility that, depending on the conditions (e.g., the width dimension of the conveyor belt  16 , the distance between the conveyor belt  16  and the magnetic separator belt  23  and so on), the concrete reinforcing steel bar  26  may be taken off of the conveyor belt  16  before the trailing end  26   b  of the concrete reinforcing steel bar  26  travels past the leading end attraction/adhesion position L, even in conditions other than the belt velocity relationship (Vm&gt;Vc) used in the one embodiment (for example, in the belt velocity relationship of Vm=Vc or Vm&lt;Vc). 
     Therefore, it is conceivable to employ an embodiment in which the conveyor belt  16  and the magnetic separator belt  23  are controlled in their respective belt velocities so that there is established therebetween a belt velocity relationship (Vm=Vc or Vm&lt;Vc) in addition to the belt velocity relationship (Vm&gt;Vc) employed in the one embodiment. 
     To sum up, a relationship in belt velocities between the conveyor belt  16  and the magnetic separator belt  23  (in which relationship, before the trailing end  26   b  of the concrete reinforcing steel bar  26  travels past the leading end attraction/adhesion position L at which the leading end  26   a  of the concrete reinforcing steel bar  26  is to be attracted and adhered to the magnetic separator belt  23 , the concrete reinforcing steel bar  26  attracted and adhered to the magnetic separator belt  23  is taken off of the conveyor belt  16 ) is pre-stored in the memory  41  using a format that incorporates the belt velocity relationship into the velocity control map of the conveyor belt  16  and the velocity control map of the magnetic separator belt  23 . And, when the concrete aggregate mode is selected by manipulating the mode select switch  44 , both the belt velocity of the conveyor belt  16  and the belt velocity of the magnetic separator belt  23  are controlled based on the belt velocity relationship stored in the memory  41 , thereby to accomplish the operation and working effects described in the foregoing embodiment. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed crushing machine without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.