Multi-Start Drill String Threads for Low Uncoupling Torque
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Solution Overview
Problem
In rotary drilling, the screw threads of extension rods become tightly jammed due to torque and shock loading, making it difficult and dangerous to disconnect them, and existing solutions for percussive drilling are not applicable to rotary drilling.
Innovation Solution
A drill string with multi-start threads, such as double-start or triple-start threads, is used to increase the thread lead and lead angle, reducing the uncoupling torque and allowing for easy disconnection by hand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional single-start threads are used in rotary drilling extension rods, then the thread coupling provides sufficient tightening capacity and structural strength, but the uncoupling torque becomes excessively high making disconnection difficult and dangerous
Solution Approach 1:
The patent changes the fundamental parameter of thread configuration from single-start to multi-start (double-start or triple-start). This parameter change increases the lead angle of the threads, which directly reduces the uncoupling torque required to disconnect the extension rods. The multi-start thread geometry transforms the threading mechanics while maintaining sufficient tightening capacity during drilling operations.
2Ease of operation
If manual striking is used to uncouple tightly jammed threads, then the extension rods can be disconnected, but the operator safety is compromised and the extension rods may be damaged
Solution Approach 1:
The multi-start thread design preemptively addresses the jamming problem by incorporating a geometric configuration that inherently reduces friction and contact pressure between mating threads. This preliminary structural anti-action prevents the severe jamming that would otherwise require dangerous manual striking, allowing safe manual disconnection without compromising operator safety or rod integrity.
3Productivity
If conventional thread designs are used, then the drilling system maintains structural integrity under torque and shock loading, but the drilling efficiency is reduced due to difficulty in disconnecting rods
Solution Approach 1:
By changing the thread parameter from single-start to multi-start configuration, the patent achieves both maintained structural integrity during drilling and significantly reduced disconnection time. The increased lead angle of multi-start threads reduces the frictional engagement while maintaining sufficient mechanical strength to withstand drilling loads, thereby improving overall drilling efficiency.
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3B
AI summary
A drill string (400) for rotary drilling of underground mining machines comprising: a first elongate drill string member (100) having a main section (101) and a male end (102); a second elongate drill string member (100) having a main section (101) and a female end (103); the male end (102) and the female end (103) have respective threads to provide a thread coupling (401) between the male end (102) and the female end (103), the thread coupling (401) enables the male end (102) to be secured inside the female end (103) such that the male end (102) and the female end (103) overlap axially; wherein a thread lead (L2) of the respective threads of the male end (102) and the female end (103) is greater than a diameter (DM ; DFI ) of the male end (102) and the female end (103)