Controlled Atmosphere Furnace Brazing for Cost-Effective Assembly

Controlled Atmosphere Furnace Brazing for Cost-Effective Assembly

Steel valves going into controlled atmosphere brazing furnace

Steel refrigeration valves going into controlled atmosphere brazing furnace at Automatic Machine Products

Manufacturers have a selection of options for joining metals: fasteners, adhesives, soldering, welding, and brazing. Fasteners are preferable when the product may have to be disassembled later. Adhesive and solder are fine when high strength or temperature resistance is not required. Welding and brazing produce permanent joints that resist leaks, vibrations, and shocks.

Brazing gets the nod over welding in many instances. First of all, unlike welding, brazing can successfully join dissimilar metals. It works extremely well in high-production projects. Also, brazing offers strong joints and works with thick and thin metals.

Brazing is not a new process. Archaeologists have dug up evidence showing that it dates back to at least ancient Egypt. And over the centuries since then, brazing has established its place in an industrialized world. 

Brazing lends itself to an array of materials including mild steel, stainless steel, cast iron, nickel, aluminum, copper, brass, and bronze. Even ceramics, magnesium, and titanium can be brazed. And its list of applications is extensive. Here’s a small sample:

  • Metal housings
  • Electro-mechanical assemblies  
  • Pipe fittings 
  • Plumbing fixtures
  • Automotive engine components
  • HVAC system components

The list of applications is almost endless, and there are several methods for achieving a high-quality braze. If a project calls for quantities, you should understand continuous controlled atmosphere brazing.

What is controlled atmosphere brazing? 

Steel valves entering continuous atmosphere controlled brazing furnace

High volumes of parts can be brazed with extreme consistency with continuously fed brazing furnaces.

Brazing manually with a torch in an open-air atmosphere can overheat, weaken and oxidize the base metal, resulting in weak joints and unsightly cosmetic appearance. When flux is used to prevent oxidation, residue and flux voids are always a possibility.

Controlled atmosphere furnace brazing prevents localized overheating and damage to the metal, allowing the filler material to melt correctly and flow into the joints—all without flux! And in some cases, the metal parts come out of the furnace looking shinier than when they went in. This brazing process is done in large quantities inside the “controlled atmosphere” of a furnace. There are two options for this process: inside a vacuum chamber with sealed doors and a continuous-belt furnace without doors.

The “batch-type” process involves loading parts into a large furnace and closing the doors. After a vacuum is created by removing the air, the furnace is heated to the brazing temperature. When the brazing process is complete, the parts are allowed to cool and then removed. New parts are loaded, and the next batch is brazed.

Companies have traditionally used the batch process when brazing base metals that are especially sensitive to oxidation. Oxides on the metal surface will not allow the brazing filler metals to bond with the base metal, so the vacuum created in the oven prevents any oxidation. Unfortunately, the process of loading, evacuation, heating, cooling and unloading is relatively slow and unsuitable for maintaining high-volume production. 

Continuous belt furnaces offer consistency and control throughout the brazing process

Basic Diagram of a Controlled Atmosphere Furnace Brazing line.

Basic Diagram of a Controlled Atmosphere Furnace Brazing line.

By comparison, the continuous belt furnace is open-ended with a long metallic-mesh belt that moves continuously through the heating chamber and cooling zones to the unloading area, returning to the loading area where more parts can be added and brazed. The belt’s speed can be adjusted to carry parts through the furnace at the optimum speed for their requirements. This continuous, non-stop flow of product into and out of the chamber dramatically increases the throughput.

Continuous belt furnaces do not operate in a vacuum. Instead, they are fed non-reactive gases to replace the oxygen and prevent oxidation of the heated parts. In other words, the atmosphere is carefully controlled rather than evacuated. These continuous belt-fed furnaces are efficient and effective, offering a less expensive option for any materials that can be brazed outside of a vacuum.

Determining which inert atmosphere is suitable for a brazing project

An exothermic hydrogen atmosphere reduces surface oxides, particularly on mild or low-carbon steel. It comprises small quantities of hydrogen (H2) and carbon monoxide (CO) and is the most commonly used inert gas in controlled atmosphere brazing. Exothermic hydrogen improves the wetting properties of the base material, resulting in a better flow of the filler material and a lower potential for soot.

Dissociated ammonia is a mixture of hydrogen and nitrogen typically created by the thermal cracking of ammonia in a gas generator. It is especially suited for brazing stainless steel or other nickel alloys. 

Why work with Automatic Machine Products?

Automatic Machine Products can be a one-stop-shop for your next project. We can produce precision machined parts, braze and anneal them if needed, and provide the assembly work, saving your company those internal labor costs and the extra handling expenses.

Starting with our design staff transforming your ideas into reality, we will employ state-of-the-art machine tools with up to 11-axis capabilities to manufacture your parts to your requirements within your time frame. If your parts need secondary machining operations, we can handle that, too.  

Making the components at AMP gives us first-hand knowledge of their design and total control of their quality. Because of that, any brazing and assembly operations will go much more smoothly. 

Of course, we can also modify your supplied parts to ensure a high-quality brazed part with continuous contact between components and an assembly that fits together perfectly. We are proficient at complex assemblies consisting of multiple materials in a single brazed assembly.

AMP’s brazing lines utilize fully automated atmosphere generators that are computer monitored to certify continuous gas quality. A refrigerated gas drying system ensures consistency and repeatability, while a solvent cleaning system safeguards against oxidation.

EXOFLex Exothermic gas generator

The ExoFlex Exothermic gas generator at Automatic Machine Products

One of two inert atmospheres -exothermic or dissociated ammonia-help to substantially reduce or eliminate oxidation, soot, scaling, and other common brazing defects during the brazing process. 

Keep in mind that we offer ISO 9001-2015 quality assurance on our precision machining services, and we test our brazing (including destructive testing) for strength and leak integrity. We use mass spectrometers that automatically detect even the smallest of leaks.

Because our brazing furnaces are running daily for our production needs, our lead times are usually better than most others.

Trust your furnace brazing, precision machining, heat treating, and assembly requirements to Automatic Machine Products. Contact or call us at 508-822-4226 for more information and receive a free sample for your next brazing project.