CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending International patent application PCT/SE2006/050500 filed on Nov. 22, 2006 which designates the United States and claims benefit under 35 U.S.C. §119 (e) of the U.S. Provisional Patent Application Ser. No. 60/739,494 filed on Nov. 25, 2005. All prior applications are herein incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention concerns a method and device to increase the head rope life for single conveyance friction hoists for deep shafts. 
       BACKGROUND OF THE INVENTION 
       [0003]    A friction mine hoist, which may be of the double or of the single conveyance type, may be characterized by a pulley with friction liners, or similar, grooved to the diameter of the head ropes. The conveyances (skip or cage) for a double friction hoist are carried by the head rope(s) with the head ropes laid over the pulley with a contact angle of about 180 degrees. The rope ends are secured to the conveyances. The friction between the head rope(s) and the friction liners allows for a certain difference in rope tension of the two sides of the pulley without the occurrence of rope slip. Balance/Tail rope(s) are attached under the conveyances to limit the difference in rope tension between the two sides of the pulley. Traditionally the mass per meter of the balance ropes has been dimensioned to be equal or nearly equal to the mass per meter of the head ropes. Thereby the safety margin before rope slip occurs is independent of the position in the shaft of the two conveyances. 
         [0004]    A single friction hoist is based on the same principle as a double friction hoist, but with the difference that one of the conveyances is replaced by a counterweight. The mass of the counterweight is normally selected to be equal to the conveyance mass plus 50% of the net load. Thereby the difference in rope tension between the two sides of the pulley at empty conveyance and normal net load will be the same. Friction mine hoists can be ground mounted with head sheaves in the head frame or tower mounted with or without deflection sheaves. 
         [0005]    The static load variations in the head ropes occur as a result of loading the conveyance at the lower stop level and then hoisting it to the unloading (dumping) level at the upper end of the shaft whereby the balance rope(s) add mass to the ascending conveyance side, so adding rope tension in the head rope(s). The load variations can either be expressed as differences in tension (MPa or psi) or as load variations in percent of the breaking load of the head rope(s). 
         [0006]    The life of the head ropes of a mine hoist of the friction hoist type depends on several factors such as:
       load distribution between the ropes in case of multi-rope arrangement   diameter ratio between the pulley and the ropes and between deflection sheaves or head sheaves and the ropes   the rope construction and wire tensile strength   the breaking strength of the rope   rope oscillations at loading and dumping (release) of the load   longitudinal and transverse rope oscillations   quasi stationary loads under acceleration and retardation   static load variations in particular near the rope ends (Static Load Range)       
 
         [0015]    Acceptable rope life is normally obtained for friction hoists in installations with hoisting distances up to 1400 to 1500 m by adopting applicable mine hoist regulations and good engineering practice. 
         [0016]    At hoisting distances in excess of 1400 to 1500 m using friction hoists, the Static Load Range (SLR) increases to be the dominating factor determining the head rope life. 
         [0000]    Thereby, the SLR i.e. the maximum static load variation at the rope ends in percent of the rope breaking strength determines the limit for the practical/economical maximum hoisting distance for friction hoists. The SLR can be expressed by using the following equation: 
         [0000]        SLR  (%)=( Nl +( z 2* q 2* H ))* g* 100/( z 1* B ) where       Nl=Net load (kg)   z 2 =the number of balance ropes   q 2 =the total mass of the balance ropes (kg/m)   H=the hoisting distance (m)   g=9.81 (m/s2)   z1=the number of head ropes   B=the breaking strength for the head ropes (N)         
       SUMMARY OF THE INVENTION 
       [0024]    The load variation caused by the mass of the balance ropes is dominating in friction hoists over large hoisting distances. The technical solution for reducing the static load variations for single conveyance friction hoists is to reduce the mass per meter of the balance ropes instead of the traditional practice to keep the mass equal or close to the mass per meter of the head ropes. 
         [0025]    An embodiment of the present invention provides an improvement to considerably reduce the Static Load Range (SLR) while maintaining required margin before rope slip. Thereby the hoisting distance and/or the net loads can be significantly increased, and the lifetime for the head ropes can be significantly increased. Alternative solutions for single conveyance friction hoists are not known. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Embodiments of the invention will now be described, byway of example only, with particular reference to the accompanying drawings in which: 
           [0027]      FIG. 1  shows a simplified diagram of a system comprising a friction mine hoist according to an embodiment of the invention. 
           [0028]      FIG. 2  shows a simplified diagram of a system comprising a friction mine hoist with an empty conveyance in the lowest position. 
           [0029]      FIG. 3  shows a simplified diagram of a system comprising a friction mine hoist with a loaded conveyance in the lowest position. 
           [0030]      FIG. 4  shows a simplified diagram of a system comprising a friction mine hoist with a loaded conveyance in the highest position. 
           [0031]      FIG. 5  shows a simplified diagram of a system comprising a friction mine hoist with an empty conveyance in the highest position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The following example illustrates the advantage of the solution of the invention: 
         [0033]    Good engineering practice is to limit the SLR to at least 11.5% of the breaking strength of the head ropes. Taking this value as criteria for acceptable load variation illustrates the advantage of the solution:
       Head ropes: 4×56 mm 2  of certain construction and breaking load   Static Load Range: 11.5%       
 
         [0036]    Conveyance mass: Equal to the net load 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Possible net load (kg) 
                   
               
             
          
           
               
                 Hoisting distance 
                   
                 Balance rope mass as 
               
               
                 (m) 
                 Rope balance 
                 per the invention 
               
               
                   
               
               
                 1 700 
                 28 538 
                 57 764 
               
               
                 1 800 
                 22 776 
                 45 275 
               
               
                 1 900 
                 17 018 
                 33 583 
               
               
                 2 000 
                 11 259 
                 22 129 
               
               
                   
               
             
          
         
       
     
         [0037]    Balance ropes are also known as tail ropes. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Required rope safety factor 
                   
               
             
          
           
               
                 Hoisting distance 
                   
                 Balance rope mass as 
               
               
                 (m) 
                 Rope balance 
                 per the invention 
               
               
                   
               
               
                 1 700 
                 6.99 
                 5.15 
               
               
                 1 800 
                 7.26 
                 5.60 
               
               
                 1 900 
                 7.54 
                 6.15 
               
               
                 2 000 
                 7.85 
                 6.80 
               
               
                   
               
             
          
         
       
     
         [0038]    Head ropes and conveyance mass as above 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 SLR (%) 
               
             
          
           
               
                 Hoisting distance 
                 Rope safety 
                   
                 Balance rope mass 
               
               
                 (m) 
                 factor 
                 Rope balance 
                 as per the invention 
               
               
                   
               
               
                 1500 
                 6.0 
                 12.17 
                 10.01 
               
               
                 1600 
                 6.0 
                 12.43 
                 10.41 
               
               
                 1700 
                 6.0 
                 12.70 
                 10.80 
               
               
                 1800 
                 6.0 
                 12.96 
                 11.19 
               
               
                 1900 
                 6.5 
                 12.57 
                 11.26 
               
               
                 2000 
                 7.0 
                 12.28 
                 11.38 
               
               
                   
               
             
          
         
       
     
         [0039]      FIG. 1  shows a friction mine hoist ( 6 ) in a deep shaft ( 8 ) in the ground ( 9 ), the shaft having at least two levels ( 7   a,    7   b ) for loading and unloading of ore, materials and personnel, the hoist comprising a pulley ( 1 ), a counterweight ( 2 ), a conveyance ( 3 ), head ropes ( 4 ) and balance ropes ( 5 ). 
         [0040]    The static rope tension acting on the head ropes, may for example be calculated at 4 critical points (A, B, C and D), and at four different times (t 1 , t 2 , t 3 , and t 4 ) which depend on the position of the conveyance and if the conveyance is unloaded or loaded, according to the following equations: 
         [0041]      FIG. 2 :
       When t=t 1  (unloaded conveyance in lowest position)         
         [0000]      At point  A: F=Sk*g    
         [0000]      At point  B: F=Sk*g    
         [0000]      At point  C: F =( Sk+Lv 1)* g    
         [0000]      At point  D: F =( Mv+Lv 2)* g          where   F=the calculated static rope tension (N)   Sk=Conveyance mass (kg)   g=9.81 m/s2   Mv=Counterweight mass (=Sk+0.5*Nl) where Nl=Net load (kg)   Lv 1 =the total mass of the head ropes (kg)   Lv 2 =the total mass of the balance ropes (kg)         
         [0050]    Due to the large hoisting distance the mass of the upper and bottom part of the rope loops, as well as the rope mass between the points A and B, can be neglected. 
         [0051]      FIG. 3 :
       When t=t 2  (loaded conveyance in lowest position)         
         [0000]      At point  A: F =( Sk+Nl )* g    
         [0000]      At point  B: F =( Sk+Nl )* g    
         [0000]      At point  C: F =( Sk+Nl+Lv 1)* g    
         [0000]      At point  D: F =( Mv+Lv 2)* g          where   Nl=Net load (kg)   Mv=Counterweight mass (kg)   Other definitions as described above at t 1 .         
         [0057]    Due to the large hoisting distance the mass of the upper and bottom part of the rope loops, as well as the rope mass between the points A and B, can be neglected. 
         [0058]      FIG. 4 :
       When t=t 3  (loaded conveyance in highest position)         
         [0000]      At point  A: F =( Sk+Nl+Lv 2)* g    
         [0000]      At point  B: F =( Mv+Lv 1)* g    
         [0000]      At point  C: F=Mv*g    
         [0000]      At point  D: F=Mv*g          Definitions as described above at t 1  and t 2 .         
         [0061]    Due to the large hoisting distance the mass of the upper and bottom part of the rope loops, as well as the rope mass between the points C and D, can be neglected. 
         [0062]      FIG. 5 :
       When t=t 4  (unloaded conveyance in highest position)         
         [0000]      At point  A: F =( Sk+Lv 2)* g          At point  B: F =( Mv+Lv 1)* g      At point  C: F=Mv*g      At point  D: F=Mv*g            
         [0067]    Definitions as described above at t 1  and t 2 . 
         [0068]    Due to the large hoisting distance the mass of the upper and bottom part of the rope loops, as well as the rope mass between the points C and D, can be neglected. 
         [0069]    According to the equations mentioned above the load tension variations in critical points (A, B, C and D) can be calculated according to the following equations: 
         [0000]      Point  A:  ( Sk+Nl+Lv 2)* g−Sk*g= ( Nl+Lv 2)* g    
         [0000]      Point  B:  ( Mv+Lv 1)* g−Sk*g =( Sk+ 0.5* Nl+Lv 1− Sk )* g= ( Lv 1+0.5* Nl )* g    
         [0000]      Point  C:  ( Sk+Nl+Lv 1)* g−Mv*g= ( Sk+Nl+Lv 1− Sk− 0.5* Nl )* g =( Lv 1+0.5* Nl )* g    
         [0000]      Point  D:  ( Mv+Lv 2)* g−Mv*g=Lv 2* g    
         [0070]    Minimum rope tension variation appears when the variation in point 
         [0071]    A is equal to variation in point B, thus 
         [0000]      ( Nl+Lv 2)* g =( Iv 1+0.5* Nl )* g=&gt;Lv 2= Lv 1−0.5* Nl          this will give the following variations:         
         [0000]      Point  A:  ( Nl+Lv 1−0.5* Nl )* g =( Lv 1+0.5* Nl )* g    
         [0000]      Point  B:  ( Lv 1+0.5* Nl )* g    
         [0000]      Point  C:  ( Lv 1+0.5* Nl )* g    
         [0000]      Point  D: Lv 2*g=( Lv 1−0.5* Nl )* g    
         [0073]    The optimum balance rope mass per meter is calculated with the following equation: 
         [0000]        q 2=( z 1* q 1* H− 0.5* Nl )/( z 2* H )       where   q 2  is the balance rope mass (kg/m)   z 1  is the number of head ropes   q 1  is the head rope mass (kg/m)   H is the hoisting distance (m)   z 2  is the number of balance ropes         
         [0080]    At optimum balance rope mass the SLR is reduced by the value defined by the following equation: 
         [0000]      Δ  SLR  (%)=0.5* Nl*g* 100/( z 1* B ) 
         [0081]    It should be noted that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims.
The invention relates to a device and system for underground transport of ore, material and people, which includes electrical and mechanical drive systems, a plurality of hoisting devices, head ropes and balance ropes. The mass per meter of the balance ropes is significantly smaller than the mass per meter of the head ropes.