Incomplete Thread Design for Burr-Free Steel Pipe Joints
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Solution Overview
Problem
Conventional threaded joints for steel pipes in oil country tubular goods (OCTG) face challenges in efficiently removing burrs from the beveled portion during thread cutting, which can cause galling and are difficult to completely remove without scratching the metal seal or complete thread, leading to inefficiencies and risks in the manufacturing process.
Innovation Solution
The threaded joint design features an incomplete thread at the start of cutting with a specific angle and height, allowing for the efficient removal of burrs by cutting off the top portion under the same feed conditions as thread cutting, preventing galling and ensuring no damage to the metal seal or complete thread.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional thread cutting is used to form tapered male threads on steel pipes, then threads are formed efficiently, but burrs develop on the incomplete thread portion at the start of cutting which are difficult to remove without scratching the metal seal or complete thread
Solution Approach 1:
The patent applies preliminary action by forming a beveled portion at the start of thread cutting before the complete thread portion. This beveled portion serves as a preliminary structure that prevents burr formation on the incomplete thread. The beveled portion is created during the initial stage of thread cutting, and its specific geometry (with a smaller major diameter than the complete thread) ensures that burrs do not develop in a way that would scratch the metal seal or complete thread during subsequent operations.
2Manufacturing precision
If manual deburring is performed to remove burrs from the beveled portion, then burrs can be removed, but the process is time-consuming and may scratch the metal seal or complete thread
Solution Approach 1:
The patent applies self-service by designing the beveled portion geometry such that the thread cutting tool itself removes the burrs during the normal thread cutting process. The specific angle and dimensions of the beveled portion cause the cutting tool to automatically clean up burrs as it forms the threads, eliminating the need for separate manual deburring operations. The incomplete thread portion is designed to work with the cutting tool to achieve self-deburring.
3Reliability
If the beveled portion is designed with optimal angle and height, then burrs are prevented from causing galling, but the thread cutting process becomes more complex
Solution Approach 1:
The patent applies local quality by creating a beveled portion with specific geometric properties only at the start of the thread (the incomplete thread portion), while the rest of the thread maintains standard geometry. The beveled portion has a smaller major diameter and specific angle characteristics localized to where burrs would form, without affecting the overall thread design. This localized modification prevents galling while maintaining standard thread specifications for the majority of the threaded portion.
Data Source
AI summary
A threaded joint for steel pipes comprises a pin having male threads and a box having female threads which engage with the male threads. An incomplete thread is formed at the start of the male threads and the incomplete thread has a portion in which the angle θ formed between its crest face and its flank on the side facing a complete thread is an obtuse angle and in which the thread height h from the base of the flank is at least 0.2 mm.