Figure 1

 

Shown here is a brazing preform

of a hydraulic fitting and steel tube

material without physical contact, without a heat source, and without producing products of combustion.

Induction has no source ralated temperature limitaions and is applicableat energy levels of power densities much higher than those of any indirect electric of fuel-fired method.

When inducton heating is applied to a razing, soldering, or joining process, the following considerations must be reviewed to determine a practical approach to the application:

1. Parts to be brazed: material, size and weight, thickness, special characteristics (holes, corners, mass uniformity), production rate, and required temperature.

2. Power Supply: required kilowatts, frequency, water cooling requirements, and coil designs

3. Process considerations: smoke and fume removal, part quality and fit, cleanliness, fluxing and flux removal, alloy selection, and cost of operation/ savings

4. Material handling concepts: manual station, two-station operation, conveyorized/ in-line systems, rotary indexing, and rotary continuous

Parts to be Brazed

Brazing is a method of joining two similar of dissimilar metals or ceramics at teperatures abvove 480 degrees Fahrenheit with a suitable filler metal that becomes liquidous at a temperature less than the parent materials being joined. Soldering shares many of the same characteristics but is preformed at much lower temperatures. Welding differs from these practices as the parent materials and the filler metal must be melted to join the assembly.

Brazed assemblies and applications are common in everything from hand tools to abrasive cutters, jewlery, lighting, aerospace, and automotive industries. Each part has individual service considerations for joint strength, aesthetic appearances, and part quality, including resistance to corrosion, stress, and temperature or pressure cycling.

Power supply considerations

To determine the appropriate power supply for an application, the kilowatts required to achieve a production rate must be determined first.

The formula representing the kilowatts required is expressed as:

M x S.H. x Delta T/ 57= kW (at 100 percent efficiency)

where:

M= Mass to be heated in pounds per minute

S.H.= Specified heat of the material to be heated

Delta T= The change in temperature from ambient

 

(57 BTU/ Minute= 1kW)

For example, a hydraulic fitting and steel tube (As seen in figure 1 at top left of page) require a temperature of 1,300 degrees Fahrenheit for a silver brazing application. The production rate is six parts per minute, and the weight of the heated area is .25 pound. Therefore the equation is:

 

.25 (6) x .12 x 1,230/ 57= 3.88 kW (at 100 percent efficiency)

 

The efficiency of the application involves the following issues when applied to a general mass per kilowatt calculatiion:

1. Power supply conversion efficiency.

2. Induction work coil efficiency

3. Transmission losses to the coil

4. Thermal losses throughout the mass of the part being heated.

Conversion Efficiencies. Typical line-to-load conversion efficiencies of

(Continued on Next Page)

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