Furnace Brazing

Brazing has often been overlooked by designers, possibly due to a poor historical image. The modern brazing process and materials are a far cry from this perception however - it has become an exceptional joining process that makes possible engineering assemblies with joint strengths that cannot be achieved by any other means. Furnace brazing allows the economic processing of large batches of components, whilst a protective atmosphere enables materials to be processed without discoloration.

Furnace Brazing is still one of the least appreciated manufacturing techniques with many engineers being unaware of its existence or its advantages as a method of joining two or more parts together. Kraftube uses furnace atmospheres that permit the brazing of multi-jointed components in mild steel and copper without the use of flux.

Typical Applications

The list of potential applications is substantial, however, the most common categories are:

Hydraulic Fittings
Heat Exchanges
Tube Manipulations
Machined Assemblies
Pressed Assemblies

Joint Design

Brazing relies on capillary action. Therefore, the joint design is crucial in the success of the brazing. An unbroken capillary path with gaps not exceeding 0.004" are required for most applications. Whenever possible, joints should be self-supporting or self-jigging as furnace jigs can be expensive, they may move in the heat during the process and they occupy furnace space adding to the unit costs.

Joint Strength

A correctly designed and brazed joint should produce a strength of joint that is in excess of the parent metal.

Advantages / Disadvantages of Furnace Brazing
Surface Condition

Components should be clean, free from fine metallic filings or shavings (see "swarf"), rust and excess grease before brazing. It should be noted that score marks, shot blasted or roughened areas in the region of the brazed joint will pull the braze filler metal away from the joint.

Post Braze Processes

Due to the high melting point of the braze material [1083C for Copper], most commonly used hardening and case hardening heat treatments can be carried out after brazing. Also, most plating processes take well on copper brazed components.

Main Advantages of Furnace Brazing

Distortion due to uniform heating and cooling is kept to a minimum.
Joint strengths greater than the parent metal are possible.
Parent metals are not fused or damaged.
Stresses are relived during brazing.
No surface deterioration takes place during the process.
Dissimilar metals can be brazed together.
Different metal thickness are permissible in brazed joints.
Multiple joints can be brazed at once.
Long and inaccessible joints can be filled successfully.
Complicated and delicate assemblies have been brazed which could not have been manufactured by any other route.
Skilled labor is not required to carry out the process.
Rapid reproducible results are obtainable.
Disadvantages of Furnace Brazing

Close fits are necessary to facilitate the capillary action.
Component parts will be annealed during the process.
Provision for location of the brazing material has to be allowed for in the design.