Secrets of a Successful Furnace Brazing Process

Secrets of a Successful Furnace Brazing Process

brazing furnace

Steel parts going in to brazing furnace

What is the difference between Soldering, Brazing, and welding?

Welding refers to the process of creating a metallurgical bond between two components by way of using high energy to melt the base components (and sometimes a filler material), forming a mixed alloy of the two base parts.

Soldering is the process of joining two components by way of melting a filler material to act as a “glue” between the parts to be joined. The “glue” is another metallic compound that has a lower melting point than the metals to be joined. At the precise temperature just above the melting point of the filler material and below that of the base materials, the filler material will flow into the voids between the carefully positioned base parts by way of a process called capillary action. When the joined assembly is removed from the heat, the filler material will solidify into a durable, airtight, joint.

Similar to a soldering process, brazing takes place at higher temperatures, typically over 450°C in order to create a joint with more strength using stronger filler materials.

Brazing can be accomplished via handheld or fixed torch in the open air, but in order to achieve the best possible brazed joint you need to remove as much oxygen as possible. This is where furnace brazing comes into play. Brazing furnaces displace the oxygen surrounding the work environment to allow for the ideal brazing conditions.

What is the difference between Furnace Brazing and Continuous Belt Furnace Brazing?

Furnace brazing typically refers to the vacuum furnace batch-type brazing process. This involves a large “oven” where entire batches of parts are loaded into the furnace at one time. The furnace door is then closed, and the furnace is evacuated of all air then heated to the desired brazing temperature. After the braze is complete the batch is then cooled so that the furnace can be reloaded with new parts and the process repeated. As you would expect, this type of process is time and energy intensive and is only justified when the base materials are highly reactive to oxygen, resulting in an oxide layer that will prevent a successful braze.

 Furnace brazing process at Automatic Machine Products

Abbott Dissociated Ammonia brazing furnace preparing to run brass refrigeration valves at Automatic Machine Products

Continuous belt furnace brazing refers to open ended furnaces that have a belt which continuously cycles through the heat and cooling zones and then returns to the loading area to receive a new load of parts to be brazed. With this style of furnace, parts can be loaded and unloaded indefinitely until the entire order is complete. Although continuous furnaces do not operate in a vacuum, the gaseous atmospheres fed into them replace the oxygen with certain type of non-reactive gases in order to prevent oxidation of the heated components. This is what is referred to as an atmosphere controlled continuous belt-fed brazing furnace. Continuous belt-fed furnaces are a much more cost effective option if the materials can be be brazed outside of vacuum.

What kind of atmosphere does my brazing project require?

Depending on the base part materials, a brazing method will be selected. There are a number of standard atmospheres which can be employed. Inert atmospheres of Hydrogen and Dissociated Ammonia are two common and cost effective choices to reduce or eliminate oxidation during the brazing process, as well as producing a clean and bright finished product. Inert atmospheres are required to reduce or eliminate common brazing problems such as oxidation, scaling and Carbon buildup (soot). Experienced brazing providers will analyze your brazing requirements and recommend the appropriate brazing environment for your project.

  • Dissociated Ammonia

Dissociated Ammonia is a mixture of Hydrogen and Nitrogen, which is usually created by thermal cracking of Ammonia in a gas generator. It is especially suited for copper and brass in order to remove oxidation of the joint without the use of flux.

  • Exothermic (Hydrogen)

Hydrogen atmospheres reduce surface oxides particularly on steel in order to improve the wetting properties of the material surface, creating better flow of the filler material.

Whatever the atmosphere, maintaining the proper mixture of gases is critical to a successful braze. A quality brazing supplier will have fine control of the input gases either by manual valved control, or a state-of-the-art electronic flow control solution such as this ExoFlex exothermic gas generator model installed at Automatic Machine Products, in Taunton, MA.

Atmosphere Engineering's Exothermic gas generator

An ExoFlex exothermic gas generator from Atmosphere Engineering which is used at Automatic Machine Products

How do I choose a quality brazing supplier?

Your brazing supplier should have extensive experience with various materials, temperatures, and filler materials and have multiple furnace types in order to accommodate a wide variety of brazing projects. Knowledgeable engineers can recommend the proper gap between components to be brazed, which is critical in creating the highest joint strength.

Automatic Machine Products has been creating the highest quality brazed assemblies for well over 80 years during our almost 100 years in service. Contact sales@ampcomp.com for more information and a free sample for your next brazing project.