Rock Drill Bit Transition Angle Reduces Stress Concentration
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Solution Overview
Problem
Conventional down-the-hole percussive drilling assemblies experience reduced lifespan due to high stress concentrations in the bit head-shank transition area, particularly in blind-bore drill bits where flushing holes intersect, leading to early bit failure.
Innovation Solution
A rock drill bit design featuring a bit head-shank transition angle greater than 100 degrees, optionally with a conical surface and recesses in the transition area, and a closed central bore that functions as part of the hammer's working chamber, reducing stress and enhancing strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the bit head-shank transition angle is 90 degrees (conventional design), then the structure is simple and manufacturing is easy, but the stress concentration in the transition area increases leading to reduced bit lifespan
Solution Approach 1:
The patent changes the geometric parameter of the bit head-shank transition angle from the conventional 90 degrees to an obtuse angle between 100-160 degrees. This parameter modification redistributes the stress distribution in the transition area, reducing stress concentration and preventing early bit failure while maintaining structural simplicity
Solution Approach 2:
The patent introduces a conical surface with a semi-vertical angle of 10-30 degrees in the bit head-shank transition area. This curved geometric feature smoothly transitions the stress flow from the head to the shank, eliminating sharp corners that cause stress concentration and significantly extending bit service life
2Productivity
If flushing holes are positioned in the bit head-shank transition area, then debris removal efficiency is improved, but stress concentration increases causing early bit failure
Solution Approach 1:
The patent positions flushing holes specifically in the bit head region away from the transition area, creating different functional zones: the head region handles debris removal while the transition area with its obtuse angle and conical surface handles stress distribution. This spatial separation allows both high productivity and reliability
3Device complexity
If the central bore is blind or closed at the axially forward end, then the bit structure is simplified, but stress in the transition area increases due to flushing hole intersection
Solution Approach 1:
The patent segments the internal bore structure into two distinct zones: a blind central bore in the head region for structural simplicity, and a transition zone with obtuse angles and conical surfaces that redirects stress flows. This segmentation allows the blind bore design to be maintained while eliminating stress concentration through the transition area geometry modification
Data Source
AI summary
The present disclosure relates to a rock drill bit for a percussive drilling hammer positioned at the cutting end of a hammer. The drill bit includes a head, an elongated shank connected to the head at a front end of the bit, a head-shank transition area where the head connects to the shank, an anvil at the rear end of the shank for receiving the impact of the piston, a plurality of buttons provided at the front face of the head configured to engage the material to be crushed in the intended direction of drilling, and a plurality of flushing passages extending through the head and having at least one opening at the front face of the head. An angle formed between the head and the shank at the head-shank transition area is greater than 100 degrees.