Brazing Stack Assembly Using Pyrolytic Graphite for Faster Heat Transfer
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Solution Overview
Problem
Brazing cycle times for large stacks of parts are excessively long due to low thermal diffusivity of interleaved material layers, particularly in coldplate technologies, which can take up to 12 hours or more.
Innovation Solution
Replace interleaved material layers in large stacks with pyrolytic graphite (PG) sheets, which have a high thermal diffusivity of about 500 mm2/s or more, to enhance heat transfer and reduce cycle times by increasing effective thermal diffusivity by up to 3 times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional interleaved material layers are used in large stacks of braze parts, then the structural integrity and assembly are maintained, but the thermal diffusivity is low causing excessively long brazing cycle times (up to 12 hours or more)
Solution Approach 1:
The patent changes the thermal diffusivity parameter of the interleaved material by replacing traditional materials with pyrolytic graphite, which has superior thermal conductivity. This parameter change enables faster heat penetration through the stack, reducing cycle time from 12+ hours to significantly shorter durations while maintaining the structural function of the interleaved layers.
Solution Approach 2:
The patent employs pyrolytic graphite as a composite material solution, combining carbon layers with specific orientations to create an interleaved structure that provides both mechanical support and enhanced thermal transfer. This composite approach allows the material to serve dual functions: maintaining stack integrity during brazing while dramatically improving heat conduction to reduce cycle time.
2Loss of time
If pyrolytic graphite is interposed between pairs of braze parts, then effective thermal diffusivity increases by about 3.0 times, but additional materials and process steps are required
Solution Approach 1:
Pyrolytic graphite sheets serve as intermediary materials placed between pairs of braze parts in the stack. These intermediaries facilitate rapid thermal energy transfer across the interfaces between parts, acting as thermal conduits that penetrate the stack quickly and uniformly, thereby reducing the overall brazing cycle time despite the added material complexity.
3Productivity
If multiple pairs of braze parts are stacked together for efficient use of braze volume, then productivity is improved, but heat penetration to the center of the stack becomes slower due to low thermal diffusivity
Solution Approach 1:
The patent segments the thermal path by inserting pyrolytic graphite sheets at strategic positions between pairs of braze parts throughout the stack. This segmentation creates multiple high-speed thermal conduits that divide and distribute heat rapidly throughout the stack, allowing the center regions to reach brazing temperature faster while maintaining the ability to process multiple parts simultaneously in one batch.
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
PG significantly reduces brazing cycle times by facilitating faster heat conduction to the center of the stack, allowing multiple parts to be brazed together efficiently.
Implementation Method 1
interposing pyrolytic graphite (PG) between the first pair of the braze parts and the second pair of the braze parts in the stack and heating the first and second pairs of the braze parts to a brazing temperature
Implementation Method 2
the PG increases an effective thermal diffusivity of the stack and correspondingly reduces a cycle time required to braze the braze parts
Implementation Method 3
The filler metal flows into the gap between close-fitting parts by capillary action
Implementation Method 4
melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal
Data Source
AI summary
A method of decreasing a cycle time of a brazing process is provided. The method includes arranging each of first and second pairs of braze parts together, each of the first and second pairs of the braze parts having braze material interposed between the braze parts, stacking the first and second pairs of the braze parts to form a stack, interposing pyrolytic graphite (PG) between the first pair of the braze parts and the second pair of the braze parts in the stack and heating the first and second pairs of the braze parts to a brazing temperature to braze the braze parts of each of the first and second pairs of the braze parts together.