Thread Pitch Optimization for Percussive Drilling Tool Joints
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Solution Overview
Problem
Threaded joints in percussive drilling tools experience bending forces from stress waves, leading to fatigue and eventual breakage due to high stress levels.
Innovation Solution
A novel design for the female portion of the threaded joint, featuring a mounting sleeve with a specific internal thread configuration, including a cylindrical threaded section, thread clearance section, and guiding section, optimized with a pitch length between 12.8-14.5 mm, and specific ratios of section lengths and diameters to reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the diameter of the male thread is increased to reduce stress in the threaded joint, then the stress in the threaded joint decreases, but the female part becomes weaker and more likely to break
Solution Approach 1:
The patent applies parameter changes by optimizing the pitch length to a specific range (12.8-14.5 mm) and adjusting the ratio of section lengths and diameters. This resolves the contradiction by finding optimal parameter values that balance stress reduction in the joint with maintaining sufficient strength in the female part, avoiding the need to simply increase male thread diameter which would weaken the female part.
Solution Approach 2:
The patent divides the mounting sleeve into distinct sections with different functions: a threaded section for stress distribution, a thread clearance section for stress reduction, and a guiding section for alignment. Each section has optimized dimensions that contribute to the overall solution, allowing different parts of the female portion to have different local qualities that collectively resolve the stress-strength contradiction.
2Productivity
If the diameter of the male thread is increased to improve performance, then the performance of the percussive drilling tool improves, but the female part becomes more likely to break
Solution Approach 1:
The patent resolves this contradiction by changing the parameters of the female portion geometry, specifically the pitch length (12.8-14.5 mm) and the ratio (L1+L2+D2)/L4 > 6.2. These parameter changes allow the system to achieve improved performance through optimized stress distribution without compromising the reliability of the female part.
Solution Approach 2:
The mounting sleeve is segmented into functionally distinct sections: threaded section (length L1), thread clearance section (length L2), and guiding section (length L3). This segmentation allows each section to perform its specific function optimally, with the threaded section engaging the male thread, the clearance section providing stress relief, and the guiding section ensuring proper alignment, thereby improving overall reliability without sacrificing performance.
Data Source
AI summary
A female portion arranged to form part of a thread joint for a percussive drilling tool includes a mounting sleeve, wherein the mounting sleeve has at least one substantially cylindrical internally threaded section having a length, L1, a thread entrance located towards an axial end and a thread exit located towards the axial inner wall. The threaded section has a thread form including crests, roots, contact flanks, and non-contact flanks, a pitch length, L4, located between two axially neighboring crests and an inner diameter, D2 disposed radially between the roots. A thread clearance section is positioned between the axial inner wall and the thread exit and has a length L2 and a diameter D1. A guiding section is positioned between the thread entrance and the axial end of the sleeve and has a length, L3. The pitch length, L4, is between 12.8-14.5 mm.