Roller Cone Bit Ball Plug Weld Residual Stress Reduction
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Solution Overview
Problem
Residual stress accumulation in the weld region of roller cone bit ball plug welds reduces the service load capacity and leads to structural failures such as cracks, which initiate at the root of the ball plug weld and propagate towards the head outer diameter and bearing pin.
Innovation Solution
The method involves forming an inner weld from a first material, such as nickel, and an outer weld from a second material with higher strength, or creating a void in the weld area to reduce residual stress, and applying heat treatment or ultrasonic vibrations to the barrier and perimeter area to increase service load capacity and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ball plug is secured to the head OD by welding, then the ball plug is retained in the ball way, but residual stress accumulates in the weld region reducing service load capacity
Solution Approach 1:
The patent applies heat treatment (stress relief annealing) to change the physical state of the weld region, reducing residual stress parameters while maintaining the welded retention structure. This thermal parameter change allows the weld region to achieve lower residual stress levels, thereby improving service load capacity while preserving ball plug retention functionality.
Solution Approach 2:
The patent employs a multi-layer weld structure with different materials (e.g., nickel-based alloy for the first layer, steel for the second layer) to create a composite weld system. This composite approach allows the softer first layer to reduce residual stress generation while the stronger second layer provides structural integrity, resolving the contradiction between retention reliability and service load capacity.
2Strength
If residual stress is reduced through heat treatment, then service load capacity increases, but additional processing time and complexity are required
Solution Approach 1:
The patent performs stress relief heat treatment as a preliminary or intermediate step during the manufacturing process, before final assembly and service. By addressing residual stress early in the production sequence, the method prevents stress accumulation that would otherwise require more complex corrective measures later, thereby improving service load capacity without significantly increasing overall processing complexity.
3Duration of action of stationary object
If a multi-layer weld structure is used to reduce residual stress, then service life increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies different material properties to different layers of the weld structure: the first layer uses a softer, more ductile material (nickel-based alloy) specifically designed to reduce residual stress, while the second layer uses a stronger material (steel) for structural support. This local differentiation of material quality allows each layer to perform its specific function optimally, extending service life while managing manufacturing precision requirements through clear functional differentiation.
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
The solution effectively reduces residual stress, enhancing the service load capacity and service life of the roller cone bit by mitigating crack initiation and propagation, thereby improving the structural integrity of the ball plug welds.
Implementation Method 1
applying heat treatment or ultrasonic vibrations to the barrier and perimeter area to increase service load capacity and service life
Implementation Method 2
applying heat treatment or ultrasonic vibrations to the barrier and perimeter area to increase service load capacity and service life
Data Source
Figure 1~4
Figure 2~3
AI summary
A roller cone bit comprising stress reduction means for reducing residual stress at the barrier (e.g., weld) (29) and the perimeter area (23) of the head (15) adjacent the outer diameter to increase the service load capacity and the service life of the roller cone bit. The stress reduction means comprises forming a barrier (29) at the perimeter area (23) to retain the ball plug (27) in the ball way (21) by forming a weld from a material selected from the group consisting of: nickel; nickel alloy; stainless steel; and Inconel.