BRAZING & SOLDERING TODAY What Matters Most in Vacuum Aluminum Brazing Featured are the process types, benefits, parts, fundamentals, and characteristics Vacuum aluminum brazing is a careful balance of time, temperature, and vacuum level. These parameters are controlled to maintain the fundamental brazing success parameters — load the parts, heat the parts, get the braze joints clean, melt the braze filler, and get the parts out. This is done in a specific work environment, utilizing sophisticated controls to ensure fast pumping, low parts per million (PPM) of oxygen, and exceptional temperature uniformity combined in one synergistically designed vacuum furnace system. As detailed in the below text, vacuum aluminum brazing is described along with braze joint fundamentals, furnace characteristics, and maintenance tips. Introduction Brazing Definition The American Welding Society defines brazing as follows (Ref. 1): “A group of welding processes that produces coalescence of materials by heating them to the brazing temperature in the presence of a filler metal having a 50 FEBRUARY 2014 liquidus above 840°F (450°C) and below the solidus of the base metal. The filler metal is distributed between the closely fitted faying surfaces of the joint by capillary action.” The solidus is the highest temperature at which the metal is completely solid; the temperature at which melting starts. The liquidus is the lowest temperature at which the metal is completely liquid; the temperature at which solidification starts. Fig. 1 — Vacuum-aluminum-brazed radiator. (Photo courtesy of API Tech.) Types of Aluminum Brazing Aluminum brazing can be done with or without flux, and includes many different methods for creating the bond. In flux brazing, the flux flows into the joint and is displaced by the liquidus BY CRAIG MOLLER AND JIM GRANN filler metal entering the joint to remove oxides on the part to create a strong, solid braze. Flux comes in several different forms — paste, liquid, or powder. Some brazing rods are coated with flux or have a flux core to apply necessary flux during the brazing process. Flux brazing processes include torch brazing (manual and automatic), induction, salt CRAIG MOLLER (craig.moller@ipsenusa.com) is the chief engineer and JIM GRANN is a senior technical manager for Ipsen, Inc., Cherry Valley, Ill. Based on paper presented at IBSC 2012, 5th International Brazing and Soldering Conference, April 22–25, 2012, Las Vegas, Nev.
Welding Journal | February 2014
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