Frequently Asked Questions

The Technical Services team at Lucas Milhaupt has compiled the most frequently asked questions about brazing and answered them below. The Lucas Milhaupt blog contains more detailed answers to the most common brazing challenges and questions.

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  What is brazing?

The American Welding Society (AWS) defines brazing as a group of joining processes that coalesce materials by heating them to the brazing temperature and using a filler metal (solder) with a liquidus above 840°F (450°C) and below the solidus of the base metals.

  What is soldering?

Soldering is the process of joining two base materials by heating them with a filler metal with a liquidus below 840°F (450°C) and below the solidus of the base metals. 

  What is the difference between brazing and soldering?

The primary difference between brazing and soldering is the temperature of liquidus: below 840°F (450°C).

  How does brazing work?

Brazing creates a metallurgical bond between the filler metal and the surfaces being joined. Heat is applied to the base metals and the filler metal is brought into contact with the heated parts. When the filler metal melts it is drawn through the joint by capillary action. 

  What is flux?

Flux is a chemical compound that is applied and shields the joint surface from air and prevents oxide formation. Although flux will dissolve and absorb oxides, the metals that are being joined should be properly cleaned prior to brazing. 

  How can flux be cleaned off?

The easiest way to clean flux off the brazed joint is to quench and soak the assembly in hot water. HCl (up to 25%) can be added to the water for stubborn flux residue. Special cleaners may also be purchased if needed.

  How can you reconstitute flux?

Water can be used to thin water-based flux. Usually distilled or de-ionized water is used for this purpose.

  What is the strength of a brazed joint?

The strength of a brazed joint depends on several different factors. These being: the base metals being joined, joint clearance, filler metal used. Joint strength varies with use of different base metals and filler metals. Joint strength also depends on the gap between the two metals being joined. When the gap is increased the joint strength decreases. Often times, under the correct conditions, the braze joint strength will be equal to or greater than the strength of the base metals.

  What is Handy One®?

Handy One® is a flux cored product that simplifies the brazing process. Handy One® is a brazing alloy in strip form rolled around a measured amount of powdered flux. As the part is heated the flux is released providing protection from oxidization. It is available in multiple filler metals and flux combinations to join virtually all common metals. 

  What alloy is recommended for brazing copper to copper joints?

In most cases, when brazing copper to copper in air conditioning and refrigeration service, one of our Sil Fos alloys would be recommended. The phosphorous in the alloys allow the Sil Fos group to be self fluxing when brazing copper to copper which eliminates the use of a separate flux.

  How is brazing used in HVAC/R?

For many years, brazing has been the principal metal joining method used to fabricate heating, air conditioning and refrigeration equipment. Today, a typical HVAC unit may contain hundreds of brazed joints.
Brazing is used to join copper tubing to return bends, copper tubes to headers and fins, and tube bundles to shells. Brazing joins both similar and dissimilar metals, thin and thick sections, and metals of widely differing melting temperatures.
Brazing is so universally used in this industry because it's economical, easy to do and because it produces strong, leak tight joints. Leak tightness is especially critical in HVAC units because these are all closed systems; 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.

  What is the nature of the brazing process?

We 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. 

  How do you disassemble brazed joints?

At some time you may find it necessary to disassemble a braze joint. The procedure to accomplish this is a simple one. You first flux the joint area completely. Fluxing will help the filler metal to flow at virtually its original flow point, and it will also keep the parts clean for rebrazing. After fluxing, heat the joint evenly to slightly higher than the melting temperature of the filler metal. At this point, the two components can be easily separated. Later on, you can rebraze the assembly by following the same six steps, however it's generally necessary to apply some additional brazing filler metal when you're rebrazing a disassembled joint to compensate for the filler metal lost in disassembly.


  How do you braze safely?

There are two primary safety concerns when brazing. The two sources of hazard to brazing operators are chemical fumes, and the heat and rays of the torch flame. Read this blog about Oxy-acetylene Torch Safety for more detailed instructions.

  How do you get rid of fumes when brazing?

Ventilate confined areas, using fans, exhaust hoods or respirators if necessary. Clean all base metals to remove surface contaminants that may create fumes when the metals are heated. Use flux (where required) in sufficient quantity to prevent oxidation during the heating cycle. Heat broadly, and heat only the base metals – not the filler metal. Remove any toxic coatings and be careful not to overheat assemblies.

  What is the best safety protection for torch brazing?

Operators should wear gloves to protect hands against heat. Shaded goggles or fixed glass shields protect operators against eye fatigue and vision damage. For a detailed discussion of safety factors, consult the National Standards Z49.1 "Safety in Welding and Cutting" published by the American Welding Society (AWS). For more detail on how to braze with a torch safely, read this blog: Oxy-acetylene Torch Safety. 

  What filler metals should I use?

Please reference our Alloy Selection Guide Download for finding the filler metal suitable for your current project. 


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