1. Water-to-air exchanger: Exchanging the heat to a dry or evaporative radiator-style cooler

2. Water to water exchanger: Exchanging the heat to a plant or city water source.

3. Refrigeration exchange: Exchanging the heat to a refrigerator compressor-condenser unit.

Depending on the kilowatt size, duty cycle, and installation, one of these methods should be sufficient, and it should be chosen based on the existing availability of a plant cooling source.

Process Considerations

The choice of brazing or joining of any two or more parts necessitates good part design maintain a repeatable process. The joint tolerances within the braze area should be maintained with close proximity from part to part to avoid poor alloy flow or dissimilar characteristics in heating the assembly.

The ultimate goal is to reduce the variables to a minimum to obtain a repeatable assembly process. The induction system will provide a repeatable method to heat the assembly but cannot compensate for large variances in a part's design.

The assemblies must be clean and free of metal burrs, grease, machine lubricants, and rust inhibitors. These materials will burn off the assembly and, in some cases, prohibit proper flow of the alloy.

Alloys can be dispensed by a wound preform, paste, wirefeed, or any combination of the three. In most cases using induction heating, the alloy is prepositioned in the work area via a split preform ring.

Flux is required to act as a "getter" and clean the area before the alloy becomes liquidous. Whether the application is high-temperature brazing or low-tempertature soldering, flux is required in any oxidizing environment to prevent surface oxidation on the material at an elevated temperature.

In some cases of atmosphere brazing within a contained environment, hydrogen may be used in combination with other inert gases to create an active environment that will provide a "scrub" and brighten the metal while preventing oxidation allowing alloy to flow.

Fume extraction is recommended when brazing to remove vapors caused by flux activation, residual burn off of coatings, or rust inhibitors still on the part at heating.

Material Handling Concepts

Once adequate power has been selected to achieve the temperature and anticipated rate of the application, the next step is to determine the method of material handling that is both cost-effective and operator friendly (See figure 5 on previous page).

The most conventional approach is a manual brazing station in which the operator is responsible for loading and unloading the assembly. A manual station can incorporate pneumatic lift/lower mechanisms to assist the operator in positioning the parts within the coil.

Other methods include shuttle tables to free the work area or adjustable tables to accommodate a variety of assemblies that may be brazed at the same station. To increase throughput or capacity of a work cell, two or more parts can be brazed simultaneously, depending on how much time is required to assemble the parts versus how long it takes to braze all of the parts.

In cases in which the assembly time is equal to the heat cycle, a two-station non simultaneous operation of two independent brazing coils may be an option to maximize the duty cycle of the power supply. As the operator loads and unloads the first station, the second is heating and vice versa.

If the production requirements of the application require additional automation to increase throughput, rotary or in-line processing may be an acceptable alternative. The most common approaches in automation are through rotary indexing and a continuous rotary dial which allows the assemblies to index or pass through an induction coil.

Rotary indexing allows the operator to load and unload the assemblies away from the brazing station and is usually coupled with a lift mechanism at the brazing station. As the dial indexes, the workpeice is lifted by a pneumatic cylinder into the coil and heat is applied. Once the heat cycle has ended, the cylinder releases, allowing clearance to index to a cooling station before unloading.

A continuous rotary system uses a conveyor or "open-ended" work coil, allowing the part to pass progressively through the inductor without interruption.

Whether using a rotary indexing or continuous rotary dial, the equipment paces the throughput of the operation, guaranteeing continuous work flow through the work cell.

Rotation or puddling of the alloy through mechanical drives or vibration equipment enhances the alloy flow. In manual or automatic systems, companion equipment for for alignment or rotation may be necessary to enhance the alloy flow or remove flux from within the liquidous braze medium. This reduces the potential of voids within the joint by breaking the mechanical surface tension in the joint before it solidifies.

In addition, air cooling, misting, or water cooling of the part can be added to cool the assembly and remove fluxes before the parts discharge from the equipment.

Conclusion

Induction heating offers repeatability when brazing, soldering and joining. As in many manufacturing systems, the proper selection of equipment, combined with good manufacturing processes can lead to safe long-term, trouble-free operation.