Boring Apparatus with Eccentric Pilot Bit for Hard Rock Drilling
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Solution Overview
Problem
Drill bits face challenges in efficiently and effectively drilling through hard subterranean materials, as existing technologies struggle to manage the rotational resistance and impact necessary for crushing such materials.
Innovation Solution
The apparatus includes a bit with a pilot bit and rolling elements between radial cam surfaces, allowing for differential rotation and axial movement to generate a percussive force, utilizing an eccentric conical surface or chiseled surface on the pilot bit for enhanced torque and friction, and a retainer to maintain the pilot bit's position, facilitating efficient drilling through subterranean rock formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a pilot bit is used to engage hard subterranean material, then the drilling effectiveness on hard formations is improved, but the rotational resistance and torque required increase significantly
Solution Approach 1:
The patent inverts the conventional drilling approach by having the pilot bit (smaller diameter) rotate at a higher speed than the main bit (larger diameter). This differential rotation creates a camming action where the pilot bit's engagement with hard formations generates forward thrust through axial movement rather than relying solely on rotational torque, thereby reducing the rotational resistance burden on the main driving system.
Solution Approach 2:
The patent introduces dynamic differential rotation between the pilot bit and main bit, allowing them to rotate at different speeds. The pilot bit rotates faster than the main bit, creating a relative motion that engages the cam surfaces. This dynamic configuration enables the system to adapt to varying formation hardness, generating percussive forces that reduce rotational resistance requirements while maintaining drilling effectiveness on hard formations.
2Force
If radial cam surfaces are used to convert rotational motion to axial movement, then percussive force generation is improved, but the device complexity increases
Solution Approach 1:
The pilot bit structure serves multiple functions: it acts as both a cutting tool for engaging hard formations and as a cam mechanism for generating axial percussive forces. The radial cam surfaces are integrated directly into the pilot bit and main bit bodies, eliminating the need for separate cam mechanisms. This multi-functionality reduces device complexity while maintaining effective percussive force generation.
Solution Approach 2:
The pilot bit is positioned within the central cavity of the main bit, creating a nested configuration. The pilot bit's smaller diameter allows it to fit inside the main bit structure, with both bits sharing a common rotational axis. This nested arrangement compactly integrates the differential rotation mechanism and cam surface interaction within the overall bit structure, minimizing additional complexity while enabling percussive force generation.
3Force
If an eccentric conical surface is used on the pilot bit, then torque and friction engagement are improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent employs an asymmetric eccentric conical surface on the pilot bit, where the cone's apex is offset from the pilot bit's central axis. This asymmetric geometry creates varying engagement characteristics during rotation, enhancing torque transmission and frictional engagement with the hard formation. The eccentric configuration allows the cutting edges to engage material at different radial positions, improving mechanical engagement without requiring extremely tight manufacturing tolerances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances drilling efficiency by generating a percussive force that effectively crushes and chisels through hard materials, increasing the longevity of the drill bits and improving drilling speed and accuracy.
Implementation Method 1
a first radial cam surface within the bit adapted for contact with a second radial cam surface on the pilot bit, wherein rotation of the bit relative to the pilot bit causes the first radial cam surface to engage the second radial cam surface so that a hammering force is generated in an axial direction
Implementation Method 2
one or more rolling elements disposed between and in contact with the first radial cam surface and the second radial cam surface
Implementation Method 3
The engaging surface of the pilot bit may include an eccentric conical surface or a chiseled surface
Data Source
Figure 1
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AI summary
A boring apparatus includes an upper member and a bit body configured to rotate relative to a pilot bit. A first end of the upper member is connected to a workstring. An inner cavity of the upper member includes a first radial cam surface. A first end of the bit body is connected to a second end of the upper member such that the bit body rotates with the upper member. A second end of the bit body includes a working face. The pilot bit includes a first end disposed within the inner cavity of the upper member, and includes a second radial cam surface configured to cooperate with the first radial cam surface to deliver a hammering force. The pilot bit extends through a central bore of the bit body, and includes an engaging surface on its second end configured to engage a formation surrounding the wellbore.