Dip Brazing and Aluminum Dip Brazing

Heat treating uses strictly controlled temperature modulation to enhance certain desirable characteristics in metals, such as hardness and durability. There are five unique heat treatments:

Each of these five processes alters the fundamental crystalline structure of the metal to improve specific properties such as toughness or ductility.

Learn more about the full range of heat-treating products available with Ajax Electric.

What Is Dip Brazing?

What if there was a way to simultaneously weld all the joints in a component simultaneously, or to weld parts in inaccessible sections after assembly?  Dip brazing is a process that allows simultaneous joining of multiple joints with different material thicknesses.  

A component that is being dip brazed first gets flux applied that will help keep the filler metal in place while being immersed in the brazing salt bath.  Minimum time in the bath is achieved by first pre-heating the components to right below the filler metal melting point.  Since the flux is soluble in the salt bath, as the filler metal starts melting, the flux dissolves away allowing the alloy filler metal to run into the joint spaces and bonds as a result of capillary action, bonding the pieces.

In aluminum dip brazing, the filler is made of aluminum and silicon. The assembly is pre-heated to 1,025°F to ensure uniform temperature in dissimilar thicknesses and then dipped in a saltwater brazing flux at 1,095°F, which quickly and evenly heats all of the components and melts the filler alloy bonding the pieces.

Dip Brazing Applications and Materials

Dip brazing can be used on a variety of metals including steel, copper, brass, and bronze which are often brazed with copper phosphorus silver alloys. To prevent distortion during aluminum dip brazing, it is advised to use stainless steel, Inconel, or nickel constructions. Dip brazing is a cost-effective option for parts assembly and large brazing furnaces allow for mass production of items such as electronic devices, medical equipment, and fixtures for the military.

To ensure success, it is important to use an alloy that is capable of withstanding 1100°F heat to avoid damage to the assembly. Aluminum is very well-suited for the brazing process and provides reliable, high quality results. Assembly design is also a crucial consideration as it can affect heat transfer ability, filler flow, if a fixture is needed, length of braze, and assembly procedure.  

Aluminum dip brazing is particularly excellent in applications such as chassis, aircraft parts, enclosures, heat-exchangers, and air-cooled applications.

Dip Brazing Process

  1. Assembly Preparation: It is necessary to remove grease, oil, oxides, and scale to ensure that the alloy wets the surface of the component parts.
  2. Application of Flux:  Apply flux by spraying, dipping, or brushing the components before, during, or after the assembly.  Stop-off bases having graphite bases are used to prevent flow of brazing metal into undesirable places such as tapped holes.
  3. Brazing Filler Metal:  Various Brazing metals in the form of wire, washers, shims, sheets, past, are available and need to contact all metals being joined.
  4. Fixturing: With brazing you can put as much work as can fit into the furnace, so fixtures using rods, hooks, or baskets are preferred.   
  5. Preheat: Heat up the components to just below the filter metal’s melting point so that time in the furnace is reduced to a minimum allowing more work to be treated.  Heating components this way also allows uniform heating of different thicknesses of metal while maintaining minimal distortion.
  6. Brazing: Remove from pre-heat and immerse in Dip Brazing Furnace for 30 seconds to 3 mins.  Brazing alloy flows through the joint by capillary action.
  7. Quench: Often, parts must be air-cooled to a lower temperature, prior to quenching, to prevent distortion.   
  8. Cleaning: Flux must be removed from the components after Quenching is complete by chemical cleaning.

Benefits of Dip Brazing and Aluminum Dip Brazing

Some of the advantages of dip brazing include:

  • Low tooling cost. The dip brazing process uses little to no special tooling equipment. Using common fixtures allows for inexpensive configuration changes.
  • Improved strength. Aluminum dip brazing creates sturdy, leak-proof, EMI shielded joints. 
  • Less chance of product distortion. Dip brazing heats metals uniformly allowing for less risk of distortion compared to welding. 
  • Higher quality at a lower cost. The superior results of dip brazing are achieved through a cost-effective process that allows many parts to be brazed at the same time. 
  • Superior conductivity. Aluminum dip brazing creates joints with better conductivity compared to adhesive or mechanically attached assemblies.
  • Uniform and timely. Because all joints of a component can be brazed simultaneously, the process produces components quickly and evenly. 

Aluminum dip brazing offers all the benefits above, plus:

  • Conductivity. Conductive to wall transitions from thin to thick.
  • Efficiency. Secondary machining operations can be minimized or excluded entirely with proper design tolerances.
  • Vertical Braze Joints. When brazing occurs in a salt bath furnace, it is possible to achieve vertical braze joints with capillary action of braze joints.
  • Ease of Assembly. In complicated assemblies, having inaccessible joints is a looming issue, but one dip brazing operation can most easily remedy this.

Considerations in Dip Brazing

  • Pre-Heat: Pre-heating components helps reduce distortion and allows for more brazing to happen inside the furnace, as the furnace will not have to bring parts up to proper temp.
  • Design: Proper cost-effective dip brazing starts with the design of the components.
    • Filler Metal: Grooves, holes, or recesses help guide the filler metal where it needs to go once melted.
    • Fixturing: With the proper design you can fixture the component without additional metal or parts that will get in the way and need to be heated with the work.
    • Submergible: With fixturing and small light-weight circuit boards, floating parts could become an issue if not thought of in advance.  
  • Maintenance: To eliminate chance of pitting in welds, poor brazing, or freezing of the pot a proper maintenance schedule must be upheld.
    • Sludge: The removal of any particulates should be done every two weeks with the proper tooling.
    • Fumes: Some brazing fluxes cause caustic fumes, so it is recommended to add exhaust systems and/or only add flux to the pot at the end of the day.
    • Flux: Keeping up with the removal of left-over flux must be diligent, as the flux solidifies around the edges of the pot your work area is effectively reduced.

Aluminum Dip Brazing Furnaces and Equipment from Ajax Electric

Ajax Electric manufactures both manual and automatic dip furnaces with temperatures ranging from 1,050°F to 1,150°F and with features including removable seal tiles and electrodes, air-cooled transformers, automatic heating, and prewired cubicles with interlocking breakers. 

Ajax Electric has been the trusted provider of quality dip brazing and heat treatment equipment for 60 years. Our company prides itself on delivering quality products and excellent customer service. Request a quote today to get started on your aluminum dip brazing solution.

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