Figure 29-7. A bit which has been operated in a "balled up" condition. 



abrasive wear causes reduced resistance of the teeth to chippage and breakage. 

 The elimination of the hardfacing from the teeth, particularly in hard formations, 

 will reduce chippage and breakage. 



Figure 29-6 shows a bit with severely chipped and upset teeth. This type 

 of wear is not unusual because it follows the pattern of the normal way that bits 

 dull on hard formations (limestone or dolomite) under heavy weights. As the 

 bit dulls, the case-hardened surface of the teeth wears and chips away and 

 exposes the tough core to the formation. When teeth are dulled in this manner, 

 the driller may apply more weight to maintain drilling rate and cause upsetting 

 of teeth. This type of wear is quite often erroneously interpreted as being the 

 result of improper heat treatment. Improved performance can be obtained by 

 selecting a harder formation bit type. The harder types are usually available 

 with non-hardfaced teeth. 



647 



