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FILLERCALC~The Experimental Development of a Simple Formula to Predict the Optimum Cladding Thickness (or Percentage) for Header Plates Used in the Manufacture of Radiators and Charge Air Coolers
Published May 20, 2007 by Institution of Mechanical Engineers in United Kingdom
The amount of braze filler metal available for fillet formation will depend on a large number of factors, including 1) nominal cladding percentage; 2) tolerance on that percentage; 3) overall thickness of header plate; 4) proportion of header plate lost to tube holes; 5) geometry and orientation of tube holes; 6) cladding alloy composition; 7) core alloy temper and structure; 8) brazing cycle; 9) flowability of filter; 10) fluxing and other factors.
Too much braze filler can lead to problems with excess run-off and/or erosion of tubes and fins, whereas too little braze filler can lead to poor or incomplete tube to header fillets and need for expensive post-braze repair.
The initial study investigated the relationship between residual volume of filler metal after punching of tube holes and the size of resultant fillets between tube and header plate. This was done using unclad extruded tubes of two standard sizes, with different tube hole spacing but no fins. A standard header plate dimension was used.
The header plate materials were 3003 clad on one side with 4045 in nominal cladding percentages of 5% and 10%. Material from the same batch was rolled to different thicknesses of 2.5 mm and 1.5 mm. The cladding thicknesses on each were measured microscopically before punching.
The average fillet dimensions were measured under the microscope after brazing under standardized conditions.
In the initial study brazing was carried out with tube major axis vertical, with measurement of any gravitational effect on filler metal flow and the fillet size at top and bottom.
The initial study did not purport to answer all questions, but it did enable the development of a calculation tool to predict the size of the fillets (average, top and bottom) simply by entering the tube dimensions and number, the header plate parameters and the fin height.
The study indicated areas of useful further research, such as the influence of filler alloy silicon content, geometry of tube-holes and brazing cycle and a future phase of the study will look at these areas.