Mining tri-cone bit is one of the main tools for rock drilling and well drilling. It breaks rock through the double action of impact and shearing. It has both an impact on the teeth and the shear caused by the sliding of the cone. Therefore, the rock-breaking efficiency is the high, low operating cost. The lifespan and performance of the tri-cone bit will directly affect the quality, speed, and cost of drilling project, which is very important to the construction party. If the manufacturer wants to improve the rock-breaking efficiency of the tri-cone bit and prolong its service life, in addition to studying the material selection and heat treatment process, it can also start with research on the failure mode of tri-cone bit.

The common failure modes of mining tri-cone bits include bearing failure, cutting structure failure, cone shell wear, and gauge structure damage.

1. Bearing failure

Bearing failure is the main form of mining tri-cone bit failure. Common bearing failures are divided by failure location:

Ⅰ. Radial failure.

Excessive drilling pressure, fatigue peeling and wear of the bearing surface of the journal, and wear of the roller.

Ⅱ. Axial failure.

The thrust block is worn or broken, and the two stop surfaces are worn.

Ⅲ. Seal failure.

The wear of the palm tip causes contact wear between the seal ring and rock debris, the expansion of grease squeezes the seal ring, and the bearing is abnormally stressed and eccentrically loaded.

2. Cutting structure failure

The failure of the cutting structure is mainly the wear, chipping, and tooth loss of carbide. The specific failure forms are:

Ⅰ. A row of broken teeth.

The drill pipe rotates too high, and the linear velocity of a row of teeth is too high.

The tooth material is hard, the tooth shape is not suitable, and the tooth height is high.

The bending moment becomes bigger after the shell wears and the exposed height increases.

Ⅱ. Broken teeth in the inner row.

The drilling pressure is too high when the formation is hard.

There is a foreign object in the hole.

Tooth material is hard.

The tooth type is not suitable.

The tooth height is high.

Increase bending moment after shell wear.

The cone moves and fights.

Ⅲ. Loss teeth.

The interference amount of teeth and perforations are small.

Carbide pressure deviation.

The tooth hole roughness is poor.

Decrease in tooth fixing force after cone housing wear.

Ⅳ. Worn carbide.

Tooth material is soft.

The slag discharge is abnormal, and carbides are broken repeatedly.

The cone of the gears leads to flat grinding of carbide tops.

3. Shell wear and gauge structure damage

Ⅰ. Abrasion of the cone shell and core out.

The formation is highly abrasive.

The stratum is soft, the selection is not suitable, carbides enter the stratum, or after breaking or dropping the tooth, the shell directly contacts the rock to participate in the crushing, resulting in the cone shell wear.

Abnormal slag discharge caused by air compressor air volume, insufficient air pressure or unsuitable nozzle, etc.

Ⅱ. Abrasion of shirttail and backing.

The screw thread is biased upwards, resulting in eccentric wear of shirttail.

Abnormal slag discharge caused by insufficient air volume and air pressure of air compressor or improper nozzle, rock debris suspension leads to wear of shirttail and backing.

Abnormal slag discharge caused by inappropriate selection of drill pipe diameter.

The collapse of the hole and wear of shirttail group due to backward scratching of drill bit.

After use, most blunt drill bits have multiple failure modes at the same time, and it is difficult to determine the main form of failure and the early form of failure of a drill bit. Because failure in one part of the drill bit can cause failure in other parts. For example, bearing failure will lead to cones fighting, absenteeism, or jamming, which will lead to broken teeth or flat grinding of carbide, while bearing absenteeism will also make the cones lose the protection of the shirttail tip, which will also lead to the wear of the shirttail tip and backing. The broken teeth and wear of carbide will also cause uneven force on the gear and accelerate the failure of the bearing. The wear of shirttail tip will reduce the protection of the bearing sealing ring and accelerate the failure of the bearing.

For the above reasons, it is difficult to judge the failure mode of a blunt drill bit, especially on some foreign automatic drilling rigs, the use of the drill bit is relatively thorough, which often conceals the early failure mode of the drill bit. Therefore, in mine service, the following two points can be done to better find the early failure mode and major failure mode of the drill bit:

1. Check as many blunt drill bits as possible, and conduct a comparative analysis through the status of a large number of blunt drill bits.

2. Track the use process of drill bit, according to the average feed life of drill bit, gradually check, take photos, and record the state of the cutting structure, bearing, shirttail, and other parts in each stage.