340 



STEEL HEAD FRAMES AND COAL TIPPLES. 



CHAP. X. 



rope itself, and the friction of the rope on the sheave and drum and of the skip or cage in the 

 guides. 



With round ropes the hoisting drum for deep mines is commonly made conical, the small 

 diameter being used when the load is at the bottom of the shaft. Flat ropes are wound on a reel, 



5heave 



^Sheave 



FIG. 3. 



so that the small diameter is used when the load is at the bottom of the shaft, the diameter of 

 the reel increasing as the rope is wound up. The required height of the head frame depends 

 upon (i) the room required for screening, crushing and handling the coal or ore; (2) the speed 

 of hoisting with rapid hoisting it is necessary to have a height from the landing to the sheaves 



-"Shesve 



r Ho/'s tin (f Drum 



FIG. 5. 



of from two to three times the height of the cage or skip or a full revolution of the drum to prevent 

 over winding, and (3) the desired location of the hoisting engine. ' With a given height of head 

 frame h, the distance d. Figs, i to 5, depends upon the diameter of the sheave, the diameter of 

 the rope, and whether the rope is round or flat. The sheave should be as large as can conveniently 



