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CAB Maintenance Tips |
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Checking
the Braze at the Furnace Exit |
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A good method for checking this particular failure mode is running a steel rule between the airway and the extrusion. Check both sides of the coil. Generally the bottom part of the coil will be the most troublesome. Loose fins will move while brazed fins will not. This method is only a guide and you should section a part regularly to check the brazing. Check the fillet along the width of the fin. Possible causes of this problem could be: Insufficient flux loading Your flux loading should be around 15%. You could increase it to 25%, but no higher. Excessive flux will shorten the life of the muffle and furnace belt. Check the part after it exits the drying oven. The part should be homogeneously covered with flux. Obviously, areas that are not covered will not braze. Adjust the fluxer sprayers and the blow-off. Temperature Send the tracker through to check the temperature profile. Remember to put some of the probes in the region where there are heavy blocks that might be acting as a heat sink. The product should reach at least 600°C (1112°F). Reduce belt speed or increase temperature to remedy. Alloy Check that both sides of the airway are cladded. Try to hand braze something to it without using a filler. If you don't have any success the material probably is not cladded. Flux Check that the flux is not contaminated. Flux should be mixed with de-ionized water. A good soft water will also work. If a contaminant is found, drain the water and mix a fresh batch of flux slurry. Try and find what is contaminating the flux up-stream of the fluxer, such as the washer and/or the flux mixing process. For more information on CAB Brazing, check out http://www.secowarwick.com/aluminumbrazing.html The latest design, materials and equipment specifications should be obtained from the company before any reliance is placed on the enclosed since changes may occur due to product improvement. | Go to Part 3 Burnt Extrusions | |
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