Spring Thermal Stabilization via Sequential Stress Relief
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Solution Overview
Problem
High temperature pressure relief valve springs face challenges in maintaining consistent preload and stiffness due to thermal instability, leading to hysteresis and dimensional changes, which are critical for precise pressure regulation in applications like aerospace and industrial systems.
Innovation Solution
A method involving forming springs from materials like Inconel X750, followed by heat treatment, machining, and sequential stress relief heat treatments to ensure precise geometric control and stability, including grinding steps and compressive loading under extreme conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional heat treatment and single machining step are used, then manufacturing process is simple, but spring exhibits hysteresis and dimensional changes at high temperature
Solution Approach 1:
The manufacturing process is segmented into multiple distinct stages: initial heat treatment, first machining step, first stress relief heat treatment, second machining step, and second stress relief heat treatment. Each stage addresses specific requirements sequentially, allowing the spring to achieve both geometric precision and thermal stability without overwhelming complexity in a single step.
Solution Approach 2:
The first stress relief heat treatment is performed as a preliminary action before the second machining step. This preliminary stress relief prevents dimensional changes and hysteresis that would occur if machining were performed directly on the heat-treated spring, ensuring that subsequent machining maintains precision even after final heat treatment.
2Stability of the object's composition
If multiple stress relief heat treatments are applied, then thermal stability is improved, but manufacturing time increases
Solution Approach 1:
The manufacturing process employs periodic stress relief heat treatments interspersed with machining operations. Rather than applying all heat treatments sequentially without interruption, the process alternates between heat treatment, machining, and stress relief steps, allowing each treatment to stabilize the spring before the next operation begins, thereby achieving cumulative thermal stability without excessive total time.
Solution Approach 2:
The stress relief heat treatments utilize specific temperature and time parameters that are optimized to achieve maximum stabilization effect. By controlling the thermal parameters (temperature, duration, cooling rate) of each stress relief step, the process achieves enhanced thermal stability while minimizing the time required for each treatment cycle.
3Manufacturing precision
If precise geometric control is maintained through multiple machining steps, then spring faces parallelism is improved, but manufacturing cost increases
Solution Approach 1:
The first stress relief heat treatment is applied as a preliminary action between the first and second machining steps. This stress relief prevents dimensional changes and hysteresis that would otherwise require additional machining corrections, thereby maintaining spring faces parallelism and geometric precision while avoiding the need for expensive re-machining or scrap.
Solution Approach 2:
The sequential machining and heat treatment process incorporates feedback mechanisms where the results of each machining step inform the parameters of subsequent operations. By monitoring spring dimensions and geometry after each machining step, the process can adjust subsequent machining parameters to maintain precision without requiring excessive material removal or multiple corrective passes, thereby controlling manufacturing costs.
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 method ensures consistent spring performance with no hysteresis and maintains a constant pressure set-point throughout the spring's life, addressing thermal instability and dimensional control issues.
Implementation Method 1
subjecting the spring to a first stress relief heat treatment
Implementation Method 2
first stress relief heat treatment; second stress relief heat treatment step
Data Source
AI summary
A method for manufacturing a spring is disclosed that comprises: forming the spring from a material; heat treating the spring; performing a first machining step to the ends of the spring; subjecting the spring to a first stress relief heat treatment; performing a second machining step to the ends of the spring; and subjecting the spring to a second stress relief heat treatment step. A spring that is manufactured by this method is also described. This spring may then be used in a pressure relief valve, as well as in other assemblies.