12 1/4" FG615G , Tricone Rock Bit , Well Drilling Bit , Hard Formation , TCI Bit

RECOMMENDED DRILLING PARAMETERS FOR APPLICATION

ROLLER CONE BIT CONE DESIGN

In some formations, it is advantageous to design the cones and their configuration so that they do not rotate evenly but that they slip during rotation. This Cone slippage, as it is called, allows a rock bit to drill using a scraping action, as well as the normal grinding or crushing action.

Cone slippage can be designed into the bit in two ways. Since cones have two profiles: the inner and the outer cone profile, a cone removed from the bit and placed on a horizontal surface can take up two positions . It may either roll about the heel cone or the nose cone. When the cone is mounted on a journal it is forced to rotate around the centre of the bit. This “unnatural” turning motion forces the inner cone to scrape and the outer cone to gouge. Gouging and scraping help to break up the rock in a soft formation but are not so effective in harder formations, where teeth wear is excessive.

Cone slippage can also be attained by offsetting the axes of the cones. This is often used in soft formation bits . To achieve an offset the journals must be angled slightly away from the centre. Hard formation bits have little or no offset to minimise slippage and rely on grinding and crushing action alone.