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Analysis of the Working Principle of the Insert Tricone Bit

Analysis of the Working Principle of the Insert Tricone Bit

The insert tricone roller bit is under the effect of the weight on bit and the rotation of the drill string. After the teeth are crushed, they also eat into the rock, and at the same time, there is a corresponding sliding to shear the rock.


In oil drilling, the roller cone bit can adapt to the drilling of various formations and is one of the main rock breaking tools. The movement of the toothed tricone roller bit at the bottom of the well determines the movement of the cones and the teeth, which directly determines the crushing effect of the teeth on the formation rock.


Therefore, before understanding how the drill bit works to break rock, it is important to understand the movement of the drill bit at the bottom of the hole. The motion state and stress state of the roller cone bit when it works at the bottom of the hole are quite complicated.


A lot of work has been done on the working principle of the roller cone bit, whether in theoretical or experimental research, and these research results provide the basis for the design and use of the bit.


Ⅰ. Analysis of the working principle of the insert three-cone bit


1. The revolution of the drill bit: The movement of the drill bit cone rotating in a clockwise direction around the axis of the drill bit is referred to as the revolution of the drill bit. The speed at which the drill bit revolves is the rotation speed of the turntable or the downhole power drilling tool.


When the drill bit revolves, the cone rotates around the axis of the drill bit. The linear speed of each row of teeth on the cone rotating around the axis of the drill bit is different, and the linear speed of the outer teeth is larger.


2. Rotation of the drill bit: When the drill bit rotates, looking in the direction from the bottom plane of the cone to the tip of the cone, the counterclockwise rotation of the cone bit around its own axis is called rotation.


The rotation of the cones is the result of the reaction of the rock to the crushing action of the teeth.


3. Factors affecting the rotation speed of the cone: revolution speed, bit structure, tooth surface structure, drilling parameters and rock properties, etc.


In general, the rotation speed of the roller cone is faster than the revolution speed of the roller cone bit. The ratio of the rotation speed of the cone to the revolution speed of the drill bit is called the wheel-to-head ratio, and the value of the wheel-to-head ratio is generally between 1--1.5.


Compared with the general mechanical sliding bearing, the sliding bearing system of the insert tricone roller bit has special characteristics in the bearing structure, the load it bears, the working environment of the bearing and the relative speed between the sliding pairs.


The radial circular runout at the drill tip should be within 0.02mm after the tool of the insert tricone drill bit is clamped. For the machining method of workpiece rotation, the deviation between the workpiece rotation center and the tool center line should be within 0.02mm.


The tool holder overhang should be as short as possible to enhance its mounting rigidity. The cutting fluid should be selected reasonably to reduce the friction and heat dissipation conditions during drilling.


Drilling is generally used for rough machining. The main function of cutting fluid is to improve the life of the drill bit, that is, to have better cooling performance. Usually, emulsified oil aqueous solution is used, which has large heat capacity, high thermal conductivity and good cooling performance.


If the drilling roughness and accuracy are required, the three-cone drill bit should use the cutting oil mainly for lubrication. For example, when machining aluminum alloy workpieces, it is appropriate to use the mixed oil of engine oil and kerosene.


When it rolls at the bottom of the well, the teeth on it will sequentially impact and press into the formation, and this effect can crush a part of the rock at the bottom of the well.


At the same time, relying on the sliding of the tri-cone bit makes the shearing effect weaken the remaining rocks between the teeth, so that all the rocks at the bottom of the well are broken and the wellbore can be extended.

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