Rock Breaking Mechanism of Roller Bits

A. Roller motion

1. Revolution: when the cone drill rotates clockwise around the central axis of the pile, the rotary movement made by the cone drill around the axis of the cylinder drill is called "revolution of the cone". The speed is equal to that of the power head and drill tool.

2. Rotation: The roller rotates counterclockwise about its axis. This rotation is called "rotation." The speed depends on the revolution speed, namely the drill tool speed. The roller spins much faster than it rotates.

3. Sliding: the roller bit with the overtop, shifting shaft, and multi-cone cone types also produces the sliding of the tooth relative to the rock surface while the roller rolls along the bottom of the hole, forming the shear fracture.

In order to adapt to the needs of breaking different rocks, the bit should be made to slide when working. The slide of the bit is the roll of the roller. In general, the bit has a large slip when drilling in soft formation. When drilling in hard and highly abrasive formations, the bit slip should be minimized to avoid rapid tooth wear.

4. Longitudinal vibration: when the roller rotates, the contact between the teeth and the bottom of the hole is carried out alternately by single and double teeth. When the single tooth touches the ground, the center of the roller is in a high position, and when the two teeth touch the ground, it is in a low position. This causes the wheel center to rise and fall continuously, that is, the roller longitudinal vibration. The longitudinal vibration of the roller makes the whole bit move up and down along the axis, and the amplitude is related to the structure and lithology of the bit, such as tooth height and tooth distance. In addition, the uneven bottom of the hole will also cause longitudinal vibration.

B. Rotational speed and bit weight

The rock breaking state of rocks with different hardness is different, and the impact of bit weight and rotation speed on it is also different. Therefore, the factors of lithology and rock breaking time should be taken into account in the speed and rotation speed of the bit.

1. Soft formation, small abrasive, mainly cutting, easy to drill, generally adopt high speed, low bit pressure, too much bit pressure is easy to produce mud bag.

2. In medium and hard rock formations, the bit produces a combination of shear, impact, and crushing, generally using medium speed and medium to high bit pressure.

3. The difficulty of crushing hard rock is increased, and the abrasive property is also higher. The drill teeth are constantly blunted during drilling, and the contact area between the drill teeth and the rock is increasing, which increases the difficulty and slows down the footage. If the speed is too fast, the drill teeth have not sufficiently broken the rock, and the rock is separated, causing the depth of rock breaking to decrease. That is, the surface is broken, or fatigue is broken. Therefore, limited by the time of rock breaking, in order to avoid the rapid wear of drill teeth, hard rock is mainly crushed, and impact broken. Generally, high bit pressure and low speed are used to ensure that the contact time of drill teeth is greater than the time needed for rock breaking and the bulk crushing is formed.

Drilling in fractured rock or at the bottom of the hole is not normal. It is easy to produce skipping, so the bit pressure should be appropriately reduced to avoid breaking the drill teeth. In addition, the weight applied should be within the cone bit bearing range.

The rotary drilling rig is different from the oil drilling rig only when the final hole bearing layer of human rock, usually the uniaxial compressive strength of more than 60 MPa, will be used to drill the core of human rock. Therefore, the rotary drilling rig is only for medium-hard or hard rock, and it is recommended that the output be of medium speed and medium bit weight.

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