Multi-Thread Drill String Joints to Reduce Jamming and Cross-Threading
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Solution Overview
Problem
Existing thread designs in drill string components are prone to jamming, cross-threading, and wear, leading to reduced load capacity and reliability, particularly in high-torque and high-speed applications, due to inefficient use of material and unsymmetrical load distribution.
Innovation Solution
Drill string components with threads having leading ends oriented at an acute angle relative to the central axis, variable thread pitch, and a cylindrical thread root that circumscribes a frusta-cone, along with multiple threads to provide an abrupt transition to full thread depth and width, reducing interference fits and enhancing load efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional single-thread designs are used, then the structure is simple and easy to manufacture, but the load capacity is limited and wear resistance is poor
Solution Approach 1:
The patent divides a single thread into multiple separate threads (typically two threads) that are circumferentially spaced apart. Each thread acts as an independent load-bearing element, allowing the joint to distribute and bear higher loads. The multiple threads are formed on the same drill string component but function as separate engagement elements with the mating component, effectively segmenting the load distribution.
Solution Approach 2:
The patent combines multiple threads onto a single drill string component (both pin and box ends), merging their load-bearing functions into one unified joint structure. This allows the component to utilize the combined strength of multiple threads while maintaining a single integrated design, rather than requiring separate components for each thread.
2Reliability
If traditional thread designs are used, then the manufacturing process is straightforward, but jamming and cross-threading occur frequently
Solution Approach 1:
The patent introduces asymmetry in the thread geometry by orienting the threads at specific angles (e.g., 90 degrees circumferential spacing) and using non-standard pitch relationships between the multiple threads. This asymmetric configuration prevents symmetrical jamming and cross-threading that can occur with traditional single-thread designs, as the load paths and engagement points are distributed unevenly in a controlled manner.
Solution Approach 2:
The patent incorporates a thread start feature with a lead-in section that preliminary guides the mating threads into proper alignment before full engagement. This preliminary action prevents misalignment and cross-threading by ensuring the threads are correctly positioned before the full load is applied, reducing the risk of jamming during the making-up process.
3Strength
If material is used efficiently in traditional designs, then the component weight is controlled, but the thread depth and width are insufficient for high-load applications
Solution Approach 1:
The patent applies local quality by concentrating the increased thread depth and width only at the critical load-bearing regions where the multiple threads engage the mating component. The thread geometry is optimized locally at the engagement points to maximize load capacity, while the rest of the component maintains its original dimensions, thus minimizing overall weight increase.
Solution Approach 2:
The patent employs curved or tapered thread profiles rather than straight cylindrical threads, allowing the thread depth and width to vary smoothly along the engagement length. This curved geometry optimizes the distribution of contact stresses and maximizes the load-bearing capacity within the available material, providing better strength-to-weight ratio compared to uniform straight threads.
Data Source
AI summary
Drill string components having at least two threads extending around a body. The leading end of each thread can have a configuration having increased strength and resistance to jamming and cross-threading. In particular, the leading end of each thread can comprise a planar surface normal to the body. The leading end of each thread can provide an abrupt transition to full thread depth that helps reduce or eliminate cross-threading and can be oriented at an angle relative to the axis of the drill string component. Each thread can further provide at least one of a variable thread width and a variable thread pitch configured to create an axial progressive fit. Each thread can also provide a cylindrical thread root and a thread crest that circumscribes a frusta-cone over at least a portion of the axial length of the threads configured to create a radial progressive fit.