2J2 SAFETY IN WINDING OPERATIONS. 



lowered. The detaching hook did its duty, the conveyance being 

 safely, suspended, and the occupants sustaining no casualties. 



Detaching hooks are not fitted to cages or skips running in 

 every vertical shaft, for various practical reasons. They are not 

 considered suitable for use in incline shafts on the Rand, although 

 in the case of another African gold field thev have been, and 

 possibly still are, used as a safeguard against the vagaries of the 

 native engine-drivers. In one " compound " shaft on the Rand 

 the " Humble " hook has been successfully adopted, in this case 

 necessarily fitted quite close up to bridle of the skip. 



There have been a few cases of detaching hooks failing 

 during the process of the vertical hoist, the assignable causes 

 being — {a) rocks falling and striking the wings of the internal 

 plates; (b) brittleness of the hooked end of these plates, which 

 might have been ])revented by more regular annealing. 



With respect to the process of annealing, the following table 

 may be quoted containing the recommendations of the American 

 Society for Testing Materials : — 



Range of Carbon Content, Range of Annealing 



per cent. Temperature, Degrees C. 



Less than 0.12 S75 to 925 



From o. 12 to 0.29 840 to 870 



0.30 to 0.49 815 to 840 



0.50 to 0.90 790 to 815 



From a pai)er recording the results of a series of experiments 

 carried out in the U.S. Naval Yard, Boston, presented by Messrs. 

 ^\'ebster and Patch, to the American Society of Mechanical 

 Engineers, in December, 1916, it is noted that iron for annealing 

 should l)e heated to about 950 degrees C, insead of 890 degrees, as 

 was the j)revious practice. Heating to this temperature and 

 cooling in air gives strong and better chain than heating to lower 

 tem])eratures, and higher tem]>eratures give no imp'-ovement. 

 The air should preferably be still, and there should be ])rotection 

 from rain or snow. 



These chain cable results are quite applicable in tiie case of 

 t-age or ski]) connection, whether safety-hook, draw-bar. bridle, or 

 link. 



It has been noted that the detaching hook is of no avail in 

 the case of an overwind at speed, and in this respect it is subject 

 to the same limitations of successful employment as other safety 

 devices which aim at avitomatically applying the brakes to the 

 (^Irums when the conveyance reaches the " danger zone." 



The necessary safety arrangements are evidently: — (a) the 

 requisite movements of the control or reversing levers so that 

 speed mav be reduced before ( h) the automatic ajiplication of the 

 brakes. It is now well known that compliance with (h) is ineffec- 

 tual unless (a) is also com])lied with previously and adequately. 



Tliere is no difficulty in complying with ib). This is done 



