Down-the-hole drill drive coupling stress reduction
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Solution Overview
Problem
Conventional down-the-hole drill (DHD) hammers face issues with fatigue failure and costly manufacturing due to high elastic stress waves and aggressive sectional changes between the drill bit's head and shank, leading to localized burning and galling, as well as difficulties in removing the chuck and drill bit.
Innovation Solution
A down-the-hole drill hammer design featuring a cylindrical housing with a low-profile shank and a drive coupling that includes a plurality of lugs and a sleeve, which engages the drill bit, reducing stress and allowing for a larger torque moment arm and cross-sectional area, thereby minimizing contact pressures and eliminating the need for expensive forging processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional drill bits with integral alloy metal construction are used, then strength and durability are improved, but manufacturing cost increases due to expensive forging processes
Solution Approach 1:
The drill bit is divided into separate components: a bit head and a shank that can be manufactured independently and then assembled. This eliminates the need for expensive integral forging while maintaining the required strength through proper material selection and joining methods.
Solution Approach 2:
The invention changes the manufacturing parameters from traditional integral forging to a combination of machining and assembly processes. This allows for cost-effective production while maintaining structural integrity through optimized material properties and connection methods.
2Length of moving object
If conventional drill bits with elongated shank sections are used, then reach is improved, but fatigue failure increases due to high elastic stress waves
Solution Approach 1:
The shank section is designed with optimized local properties including increased cross-sectional area at critical stress points and modified geometry to reduce elastic stress wave amplitude. This localized optimization maintains reach while preventing fatigue failure.
Solution Approach 2:
The design incorporates stress-reducing features such as gradual transitions and reinforcement at critical locations to cushion against elastic stress waves before they can cause fatigue failure. This preventive approach maintains shank length while ensuring reliability.
3Area of moving object
If conventional drill bits with small torque transmission diameter are used, then compactness is improved, but contact pressure increases leading to localized burning and galling
Solution Approach 1:
The torque transmission interface is expanded from a small-diameter circular contact to a larger surface area through a stepped or flanged configuration. This dimensional change distributes the contact pressure over a larger area, preventing localized burning and galling while maintaining compact overall dimensions.
4Ease of operation
If conventional chuck threads are used with small torque forces, then ease of attachment is improved, but seizing occurs making removal difficult
Solution Approach 1:
The chuck attachment interface uses an asymmetric thread design with optimized engagement characteristics that allow easy attachment during normal operation but enable straightforward removal when needed. The asymmetric geometry prevents seizing by creating a mechanical advantage for both tightening and loosening operations.
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
The design reduces fatigue stress on the drill bit, prevents chuck seizing, and lowers manufacturing costs by using a low-profile shank and increased surface area for torque transmission, enhancing the durability and maintainability of the drill bit.
Implementation Method 1
a piston mounted within the housing along a longitudinal direction. The piston is configured to reciprocatively move within the housing along the longitudinal direction
Implementation Method 2
The drive coupling includes a bearing, a plurality of lugs and a sleeve. The lugs are configured to engage with corresponding lug ports on the drill bit shank
Implementation Method 3
Such impacts upon the back end of the shank section take place within the body of the main housing of the DHD hammer. Such impacts also makes the drill bit susceptible to elastic stress waves
Data Source
AI summary
A down-the-hole drill hammer is provided that includes a housing, a piston mounted within the housing, a drill bit mounted below the housing, and a drive coupling operatively engaged with the housing and drill bit. The drive coupling can be configured with a plurality of lugs circumferentially disposed about the drill bit and coupled with the casing for providing rotation thereof. Alternatively, the drive coupling can be configured with segmented lugs configured to circumscribe the drill bit, or as a cylindrical chuck formed out of arch-shaped chuck segments which radially assemble onto the shank of the drill bit.