What Is A Tricone Bit?

A tricone bit is a mechanical drill bit located in the bottom hole assembly. The bit cuts away the surface of the rock being drilled through rotation and mechanical friction caused by the teeth of the bit. Tricone bits are designed to take the energy of the rotating drill string and the supply of mud and to apply this force to deepen the well.

How Does It Work?

A tricone bit is a rock drilling tool found in the mining and well drilling industries. The bits consist of three rotating, cone shaped heads equipped with several rows of concentric teeth. The heads are inclined at an angle of approximately 45° and arranged around the bit body with their apexes facing inwards towards each other. Each head is fitted with a bearing to ensure smooth rotation. The tricone bit is typically fitted onto the end of a drill string and rotated against the drill face, thereby causing the teeth on the heads to shear away material from the face and advance the drill hole.

Mill tooth tricone bits are used in soft rock formations. The protruding teeth are widely spaced to prevent getting clogged with material as they cut through the surface material. Tungsten carbide insert (TCI) tricone bits are used for medium and hard rock formations. These bits are designed with smaller teeth, which are more closely arranged together. Drill speeds are higher when the rock face is harder and TCI can withstand the heat generated from these conditions. Mud is pumped down the drill string and out through the tricone bit to keep the bit clean from cuttings and to move these cuttings back to the surface.

Design Concept

This particular bit was developed by engineers from the Sharp-Hughes Tool Company in 1933 using the company's two cone bits as a base design. The original two cone bit design featured a pair of opposed rotating cones fitted with rows of teeth. When rotated against a rock face on the end of a drill string, the dual axis rotational friction on the head teeth abraded the rock material to form a hole. The tricone bit followed the design concept fairly closely with the exception of the addition of a third bit head. This configuration proved to be far more efficient, thereby drilling faster and with less wear to the individual bit heads.

The basic concept which underpins the efficiency of rotating cone drill bits is the dual axis action of the bit. When drilling, the bit body turns around its own axis while the heads themselves revolve around theirs at an angle to the body axis. This multi-axis action is a particularly effective cutting mechanism, thus making the tricone bit a common choice for deep drilling operations. The design is also cost effective because the three drill heads improve the bits wear to drill advancement ratio.

ricone bits consist of a cylindrical bit body equipped with three head mounting points arranged in a cloverleaf pattern around its circumference. The bit heads are cone shaped and equipped with integral bearings which ensure smooth rotation under heavy loads. The heads are attached to the bit body at an angle of approximately 45° with their apex points facing in towards the center of the body. Each head is equipped with several concentric rows of hardened teeth which form the bearing or cutting points of the bit.

There are two basic bit head tooth designs used on the tricone bit: mill and insert. The mill tooth has a flat wedge shaped profile while the insert type is a rounded cone shape. When rotated under pressure against the rock face, the teeth cause a crush type of failure of the material causing a layer of rock to be sheared away at each rotation of the bit. Although bit heads can be refurbished when worn, the heads are generally discarded once the teeth become worn or broken.

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