T I P S containing a liquid or gas as a heating or cooling medium. Leakage from any joint would allow the liquid or gas to escape, and prevent the unit from functioning properly. These advantages, economy, strength and leak tightness are inherent in the brazing process.ContentsThe Many Uses of Brazing .3The Nature of the Brazing Process .41: Good Fit and Proper Clearance .52: Cleaning the Metals .63: Fluxing the Parts .64: Assemble for Brazing .75: Brazing the Assembly .86: Cleaning the Brazed Joint .10Some Things to Consider .10Three Common Joints.11Disassembling Brazed Joints .12Safety in Brazing .13Product ChartsBrazing Alloys .14Brazing Flux .19Solders .20Soldering Fluxes .22Quick Reference Chart .23工程焊工队伍包活QQ851596387 ，我的网友们有活不要把我忘记了哟！54The Nature of the Brazing ProcessWe can define brazing as the joining of metals through the use of a heat and a filler metal. In this process the melting temperature of the brazing filler metal is above 840 F (450 C), but in all cases below the melting point of the metals being joined. The brazing process consists of the broad heating of the base metals to the point where the filler metal, applied to the joint area, will be melted and drawn by capillary action through the entire joint. After cooling, the brazed joint constitutes a strong metallurgical bond between the filler metal and the two base metals.Two outstanding characteristics of a brazed joint are its high strength, and the low heat at which it is made. A properly made brazed joint will generally be stronger than the metals being joined. And the temperature at which the joint is made is much lower than the melting temperature of the metals being joined.A brazed joint “makes itself, ” in the sense that capillary action, rather than operator manipulation, is responsible for flowing the filler metal completely through the joint. But even a properly designed joint can turn out imperfectly unless you follow correct brazing procedures. These procedures can be described as six basic steps.1: Good Fit and Proper ClearanceThe best clearance between the two metal parts being brazed is a close one usually .001” to .003” , and generally not more than .005” . If the clearance is smaller than .001” , there may be no room for the molten filler metal to flow through the joint. And if the clearance is wider than .005” or .006” , capillary action is less effective and the filler metal may fail to fill the joint completely.In the fabrication of HVAC equipment, achieving the proper clearance for brazed joints is seldom a problem. The design of the joint is predetermined its almost always a “cup” design, in which one tube is inserted into the expanded end of another tube. As long as you start with tubing thats round and manufactured to the correct dimensions, you can anticipate no clearance problems.However, you do have to give some care to the preparation of the tubes for brazing. For example, if youre brazing a tube to a fitting, youll generally start by cutting the tube to the length you want. Make sure its cut square, by using a sawing vise or tube cutter, and remove the burrs. Slide the tube end into the fitting and check that it has the proper close fit an easy slip fit.The majority of brazed joints HVAC units are copper-to- copper joints. That means you dont have to worry about the “coefficients of expansion” of the base metals as the two copper parts will expand at the same rate. However, if youre brazing joints of dissimilar metals (copper to steel) you have to take into consideration the different expansion rates. You know A well brazed joint begins with a proper fit between components, .001” .003” of clearance.工程焊工队伍包活QQ851596387 ，我的网友们有活不要把我忘记了哟！76that non-ferrous metals (copper, brass) expand more during heating than ferrous ones (steel, stainless steel). So, be sure to adjust the initial joint clearance accordingly. Where heating will reduce the clearance, for example brazing a copper tube to a steel header, start with a relatively loose fit (approx. .010”). Wh