Flat-Round Tube-to-Header Joint for CuZnFe Heat Exchangers

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

CuproBraze™ heat exchangers with brazed tube-to-header joints are prone to leaks and premature failure due to thermal stress, poor tolerances, and the use of secondary filler materials that can cause environmental concerns.

Innovation Solution

A flat-round tube-to-header joint is created by shaping the tube end into a circular cross-section for a mechanical bond with a thicker header, reducing thermal stress and eliminating the need for secondary fillers, using internal and external sizing tools to form a strong, durable connection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a brazed tube-to-header joint is used, then the joint is relatively strong, but it is prone to leaks and premature failure due to thermal stress and requires precise process control

Engineering Contradiction:

Improvejoint strengthVSAvoidjoint reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent replaces the thermal brazing process with a mechanical expansion process. The tube end is mechanically expanded using a tool to create interference fit with the header opening, eliminating the need for thermal stress-induced brazing while achieving strong, reliable joints that resist thermal cycling fatigue

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the physical state and dimensions of the tube end through mechanical expansion. The tube end diameter is increased and its cross-sectional shape is modified to create an interference fit with the header opening, transforming the joining mechanism from thermal bonding to mechanical interlocking

Inventive Principle:

Principle #35Parameter changes

2Strength

If brazing process is used with secondary filler material, then the joint can be strengthened, but it introduces environmental concerns and additional thermal stress

Engineering Contradiction:

Improvejoint strengthVSAvoidenvironmental harm and thermal stress

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent removes the secondary filler material (such as leaded solder) from the joining process entirely. The mechanical expansion process achieves sufficient joint strength without requiring additional filler materials, thereby eliminating environmental hazards and associated thermal stress

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the potential harm of thermal stress from the brazing process into a benefit by using cold mechanical expansion. The room-temperature expansion process avoids thermal cycling that would otherwise damage the tube material and create premature failure points

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Adaptability or versatility

If oblong tubes are used with oblong header openings, then the design accommodates standard tube geometry, but the bonding process adds thermal stress that reduces tensile strength

Engineering Contradiction:

Improvetube-header compatibilityVSAvoidtensile strength

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The patent applies local quality change by modifying only the end portion of the tube where it joins the header. The tube end is expanded and reshaped locally to create an interference fit with the header opening, while the rest of the tube maintains its original oblong cross-section and compatibility with the heat exchanger core

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of forcing the oblong tube into a matching oblong opening and relying on brazing, the patent inverts the approach by expanding the tube end to a circular or rounded shape that creates interference fit with the header opening, achieving mechanical bonding without thermal stress

Inventive Principle:

Principle #13The other way round (Inversion)

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 flat-round joint significantly reduces premature failures, increases heat exchange capability, and eliminates environmental concerns associated with secondary fillers, while providing a stronger and more reliable bond than traditional brazed joints.

Implementation Method 1

creating a mechanical bond between a coolant tube having an oblong cross-section and a header

Methodology Applied

Scientific EffectInterference fit: Mechanical Fastener

Data Source

PatentUS8839846B2Mechanical joint for CuZnFe alloy heat exchanger and method

Publication Date: 2014.09.23 WESTINGHOUSE AIR BRAKE TECH CORP

AI summary

A method of creating a flat-round tube-to-header joint in a CuproBraze™ heat exchanger wherein the flat-round tube-to-header joint is disposed between a tube and a header having a generally circular opening having a first predetermined diameter formed on a first side thereof for receiving one end of a tube, and provides at least one generally circular end having a second predetermined diameter on the tube to fit into the generally circular opening of in the header. The method further provides a predetermined temper on at least one generally circular end which is at least sufficient to enable cold working of at least one generally circular end to prevent premature failures of the flat-round tube-to-header joint. The flat-round tube-to-header joint is formed by inserting one end of the tube into the first side of the header and forming the flat-round tube-to-header joint between one end of the tube and the header.