How can you use drill BITS for rock?

Why can roller cone bits drill through rocks?

 

The reason why the roller cone bit can drill through the rock is mainly due to its special rock-breaking method. The roller cone bit is driven by a rotary pressurization mechanism at the bottom of the well so that the roller cone is in contact with the rock rolls and revolves around the centre of the bit at the same time. Under the action of the static load of the axial pressure and the dynamic load when the cone is rolling, the teeth on the cone break the rock in the form of chiselling, pressing, shearing and scraping.

The rock-crushing efficiency of the roller cone bit is high, and it is suitable for drilling into hard rock formations. The rock crushing method is active crushing and passive impact crushing. This composite rock-crushing method makes the roller cone bit have a better rock-breaking effect.

How does the roller cone bit realize the composite rock crushing method of active crushing and passive impact crushing?

 

1) The composite rock-breaking method of the roller cone bit is realized through its special structural design.

 

When the roller cone bit comes into contact with the rock, it is first pressed into the rock by the sharp part of the carbide teeth on the roller cone, which is called active crushing. Then, as the cone rolls, the teeth continue to roll and scrape the rock, which is known as passive impact crushing. This combined rock-crushing method of active crushing and passive impact crushing enables the roller cone bit to crush rocks more effectively.

 

2) The crushing mechanism of the roller cone bit mainly includes two modes: rotation and impact.

 

Rotation means that under the action of the rotary pressurization mechanism, the cone in contact with the rock produces self-rotation and revolution sliding, forming high-frequency shear crushing or impact crushing to crush the rock. The impact is to periodically change the axial pressure through the roller cone bit during the drilling process, so that the teeth rush to the rock at a high speed, resulting in impact crushing. This composite rock breaking method enables the roller cone bit to break hard rock more effectively.

 

The steps to drill rock with a roller bit are as follows:

 

1. When drilling, the drill bit and its cones rotate around the axis of the drill bit, and the teeth of the cones rotate around their own axis at the same time due to the resistance of the formation rock, and the teeth contact the bottom of the well alternately with single and double teeth.

2. When the cone contacts the bottom of the well from single teeth to double teeth, the centre of the cone drops from the highest position to the lowest position; when the cone contacts the bottom of the well from double teeth to single teeth again, the centre of the cone rises from the lowest position to the highest Location.

3. With such repeated movements, the cone shaft centre rises and falls periodically, causing the drill bit to vibrate longitudinally, and the amplitude is the vertical displacement of the wheel centre.

4. During each longitudinal vibration, the upward movement of the axis will compress the lower drill string to accumulate elastic energy, and the downward movement of the axis will make the lower drill string elastically elongate and release the elastic energy.

5. When the roller cone bit breaks rock at the bottom of the well, the force exerted by the teeth on the rock includes not only the static load generated by drilling pressure but also the dynamic load generated by the teeth rushing to the rock at a high speed due to longitudinal vibration. The former causes the teeth to crush the rock, which is called crushing action; the latter causes the teeth to impact and break the rock, which is called the impact action.

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