GEOTECHNICAL ENGINEERING & BLASTING: TRICONE ROTARY BLASTHOLE DRILLING

Figure 1: Elements of Rotary Bit (1)

Cones

Cones make up the cutting elements of the rock bit and are comprised of the following:

Tungsten Carbide Inserts - which are pressed into the softer steel material with interface fit to hold item in place.
Cone Thrust Button - made of a wear resistant material used to take axial bearing loads.
Outer Cone Shell - insert land's and cone grooves.
Cone Bore - internal ball and roller bearing races.

Tungsten Carbide Insert Rows:
A >>> Nose
B >>> Inner
C >>> Next to Gage
D >>> Gage
E >>> Gage Bevel

Figure 2: Elements of Cone

Lugs

Coupled in threes, by 120 degree to form the bit body and the pin connection, the lugs are machined to hold the nozzles and a journal-bearing surface.

Nozzles

Nozzles are used to create back-pressure in the bit to force air through the bearing airways and increase the "air-blast" force to remove and flush cuttings from the bottom of the hole. Too large of a nozzle will cause insufficient volumes of air to be delivered to the bearings, while too small of nozzle will increase the back-pressure above the compressor modulation setting. When the compressor's modulation setting is reached, it will then reduce it's volume output causing a decrease in air volume to the bit.

Figure 3: Elements of Rotary Bit (2)

Tungsten Carbide Inserts

Inserts are the actual physical elements that spall and break the rock. Inserts are made from tungsten carbide powder and a cobalt binder material, which is pressed into the designed shape then sintered. Depending on the application, the tungsten carbide inserts in a given bit will have a shape and physical properties best suited for the rock being drilled.

>>> Conical

Figure 4: Conical Insert

The conical insert is used primarily in medium/medium-hard rock.

>>> Chisel

Figure 5: Chisel Insert

The chisel insert is used in soft/medium-soft rock. It is the standard insert in soft bits.

>>> Ogive

Figure 6: Ogive Insert

The ogive insert is used in areas where aggressiveness of the conical insert is required with additional toughness.

>>> Super Scoop

Figure 7: Super Scoop Insert

The super scoop is used in very soft rock. With the patented offset tip, digging and gouging help in sticky material.

>>> Round Top

Figure 8: Round Top Insert

The ovoid or round top insert is used in the hardest formations. Its blunt geometry gives it the most fracture resistant design. The round top is the standard insert in hard bits.

>>> Trimmer

Figure 9: Trimmer Insert

The trimmer insert, used in soft to medium brittle rock formation, enhances the gage rows ability to cut the bore hole wall.

>>> Wedge Crested Chisel

Figure 10: Wedge Crested Chisel Insert

Wedge crested chisel insert are used exclusively on the gage rows of very soft to hard bits. This shape gives a fracture resistant insert that is much tougher than conical or regular chisel inserts on gage.

>>> Serrated Flat Top