Thread Bottom Curvature for Percussive Drill String Fatigue Resistance
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Solution Overview
Problem
Thread joints in drill string components for percussive rock drilling face high instantaneous loads and hostile environments, leading to loosening and fatigue fractures, which reduces their working life and requires improved resistance to loads and production at low cost.
Innovation Solution
The thread groove features a thread bottom with at least three part-circular surface portions of increasing radii, which reduces tension concentrations and allows for even tension distribution, making it economically producible and enhancing resistance to fatigue fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional trapezoidal threads with linear or evenly curved thread bottoms are used, then the thread joint can be produced at low cost with simple manufacturing, but tension concentrations occur in the root area leading to reduced fatigue resistance and shorter working life
Solution Approach 1:
The thread bottom is designed with multiple part-circular surface portions having increasing radii instead of linear or single-curve configurations. This curvature progression smoothly distributes tension concentrations across the root area, significantly improving fatigue resistance while remaining manufacturable with conventional methods
Solution Approach 2:
Different sections of the thread bottom have different curvature radii optimized for their specific functions: smaller radii near the thread flanks for stress distribution, and progressively larger radii toward the intermediate portion for tension relief. This localized optimization improves fatigue resistance without requiring complete redesign of the entire thread structure
2Reliability
If the thread bottom uses complex curved configurations to reduce tension concentrations, then fatigue resistance improves, but manufacturing complexity and cost increase
Solution Approach 1:
By using part-circular arcs instead of complex polynomial curves or irregular shapes, the thread bottom maintains geometric simplicity that is easy to manufacture with conventional machining methods while still achieving the stress-distributing benefits of curved configurations
Solution Approach 2:
The invention varies the radius parameter systematically across different surface portions of the thread bottom, creating a progressive curvature pattern that is both effective for tension distribution and simple to define for manufacturing purposes
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 design extends tension distribution over a larger area, reducing maximal tension and improving resistance to fatigue fractures, while allowing for easier induction of compressive stresses through shot peening, thus enhancing the working life and reliability of the thread joint.
Implementation Method 1
the surface portions with part-circular shape have increasing radiuses, as seen from each thread flank to an intermediate surface portion of the thread bottom... tension concentrations occurring in a most sensitive region of the thread, namely in connection to the root area of the pressure flank, will be widened and be levelled out
Implementation Method 2
allowing for easier induction of compressive stresses through shot peening
Data Source
Figure 1a~1f
Figure 2~3
Figure 4a~4b
AI summary
A device in an drill string component for percussive rock drilling including a thread for threading together with another drill string component being provided with a complementary thread, wherein the thread includes a thread groove (9) formed by two thread flanks (10, 11), whereof one in operation forms a pressure flank, and an intermediate thread bottom (12), and wherein the thread groove (9) has an essentially equally shaped sectional form along its axial extension. The thread bottom (12) exhibits at least three surface portions (Y1, Y2, YC) with part-circular shape, as seen in an axial section, and said surface portions (Y1, Y2, Y3) with part -circular shape have increasing radiuses, as seen from each thread flank to an intermediate surface portion of the thread bottom. The invention also relates to a thread joint and a drill string component.