METHODS OF HOISTING. 



341 



be used, as the larger the sheave the longer the life of the hoisting rope. The inertia of a large, 

 heavy ^tn ,i\. , however, with rapid hoisting may kink the rope and cause excessive wear. The 

 Ix-mling stresses in flat ropes for a sheave of given diameter are less than in round ropes having 

 equul strength, but the life of flat ropes is less than for round ropes. Flat ropes are wound on 

 reels which are at all times in line with the head frame sheave, while round ropes are wound 

 on a drum so that the horizontal angle between the center line of the sheave and the cable is 

 continually changing. The distance, d, for flat ropes can then be less than for round ropes. 



J60-0 



h- .................... ' 



FIG. 6. GILBERTON STEEL HEAD FRAME. 



Hoisting from mine shafts is commonly done in two compartments of the shaft at the same 

 time, the unloaded skip or cage descending as the loaded skip or cage ascends. This is known as 

 hoisting in balance or counterbalance. There is a considerable saving in power in hoisting in 

 balance. To hoist in balance it is necessary to take ore from one level with both skips unless the 

 Whiting system is used. When a round rope winds off the drum it makes an angle with the 

 groove in the sheave on the head frame and the friction increases the tension in the cable and 

 also reduces its life. To reduce the friction and wear the hoisting engines are placed at a con- 

 siderable distance back from the head frame. 



The head frame may be placed so that the sheaves are parallel, as in Figs. I to 4, or so that 

 the sheaves are in tandem, as in Figs. 5 and 6. With the latter method it is necessary to place 

 the hoisting engine farther from the shaft than where the sheaves are in parallel. Where the 

 hoisting engine is placed well back from the shaft it becomes necessary to support the hoisting 

 rope on idlers, as shown in Fig. 6. Where mines have three compartment shafts, ore is commonly 

 hoisted from but two compartments, the third compartment being used for pumps, pipes, etc. 

 This arrangement makes it necessary to place the head sheaves so that they will not be sym- 

 metrical with the center line, bringing heavier working stresses on one side of the head frame 

 than on the other side. 



Hoisting from Deep Mines. In deep mines the rope in the mine becomes a large part of 

 the load and various methods have been used to counterbalance the weight of the rope. Four 

 methods for obviating the difficulty just mentioned have been used: (i) the Koepe system; 

 (2) the Whiting system; (3) modifications of (i) and (2), and (4) by the use of a taper rope. These 

 methods are described in the author's "The Design of Mine Structures." 



HOISTING ROPES. Round hoisting ropes are commonly made of six strands, each of 

 which is formed by twisting nineteen wires together, the strands being wound around a hemp 



