Flowmeter Braze Joint Stress Reduction via Thermal Expansion Bends
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Solution Overview
Problem
The brazing process in flowmeter manufacturing introduces stress due to differential cooling rates between flow tubes and anchor blocks, leading to potential cracks at braze joints, especially in dual loop sensors where components are small and require precise measurement of minimal flow rates.
Innovation Solution
A method involving the attachment of anchor blocks to a support block after allowing the flow tube and anchor block to cool and contract, using plug welding with bosses and apertures that ensure precise alignment and reduce axial loading, and incorporating thermal expansion bends and offset bends to accommodate expansion/contraction cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the flow tube is completely restrained by being brazed to the anchor block, then the flow tube is securely attached to the support structure, but large stresses develop at the tube-to-anchor braze joints during cooling, leading to cracks
Solution Approach 1:
The patent divides the attachment function into two separate stages: first, the flow tube is brazed to the anchor block to create a secure attachment; second, the anchor block is welded to the support block to provide additional structural support. This segmentation allows the brazed joint to form without the constraint of the support block, reducing thermal stress while maintaining strong attachment.
Solution Approach 2:
The patent performs the brazing operation before the welding operation. By completing the brazing of the flow tube to the anchor block first, the components are allowed to cool and contract freely during the brazing process without being constrained by the support block. The welding to the support block is performed as a preliminary support action that does not interfere with the thermal contraction of the brazed joint.
2Measurement precision
If dual loop single tube sensor is used to achieve continuous smooth surface for low flow rate measurement, then measurement precision is improved, but manufacturing complexity increases due to difficult brazing processes
Solution Approach 1:
The patent segments the manufacturing process into distinct brazing and welding operations, allowing each to be optimized independently. The brazing process creates the smooth continuous surface required for low flow rate measurement, while the welding process provides structural support without interfering with the smooth surface requirement.
Solution Approach 2:
The anchor block serves as an intermediary component between the flow tube and the support block. It allows the flow tube to be securely attached while maintaining a smooth continuous surface, and it provides a separate welding interface to the support block, decoupling the brazing and welding operations.
3Reliability
If components are allowed to cool and contract freely during brazing, then residual stress is reduced, but additional welding steps are required to secure the assembly
Solution Approach 1:
The patent segments the attachment function into brazing and welding operations. The brazing operation allows free contraction for stress reduction, while the subsequent welding operation provides the necessary structural securing. This segmentation accepts the additional step as a trade-off for significantly improved joint integrity.
Solution Approach 2:
The patent changes the attachment mechanism from a single brazing operation to a two-step process involving brazing followed by welding. This parameter change in the manufacturing process allows the components to cool and contract freely during brazing, reducing residual stress, while the welding step provides the necessary structural support.
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
This approach reduces residual stress at braze joints, minimizes the risk of cracks, and enhances the manufacturing process by allowing components to 'float' during the brazing cycle, resulting in a more robust and accurate flowmeter assembly.
Implementation Method 1
as the flow tube and anchor block cool, they do so at different rates, which causes large stresses at the tube-to-anchor braze joints
Implementation Method 2
allowing the flow tube and anchor block to cool and contract a predetermined degree after brazing
Data Source
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AI summary
A method for reducing flowmeter braze joint stress is provided. The method comprises the step of bending a flow tube (20) to create at least one thermal expansion bend (300, 302) thereon. The method comprises the step of aligning a flow tube (20) with at least one anchor block (30a, 30b). Additionally, the flow tube (20) is brazed to the at least one anchor block (30a, 30b) in another step, after which the flow tube (20) and the at least one anchor block (30a, 30b) are allowed to cool and contract a predetermined degree after brazing. The method additionally comprises the step of attaching the at least one anchor block (30a, 30b) to a support block (100) after the flow tube (20) has been attached to the at least one anchor block (30a, 30b) and attaching a manifold (90, 92) to each end of the flow tube (20).