Induction Heating Consultant

Induction Heating

Stanley Zinn

Stanley Zinn • Induction Consultants • Tel: 585-737-8824
15307 Strathearn Drive, Unit 11202, Delray Beach FL 33446 •
email address

Stanley Zinn

When Induction Brazing Saves on Energy, Labor and Alloys  View as PDF

Some typical applications are discussed here to illustrate haw to reduce

overall cost per joint while maintaining joint quality.

by STANLEY ZINN, Induction Heating Consultants • June 2011

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The ultimate in labor savings of course, is the robot-operated system. Induction heating, which can be tailored to match available machine index lines, lends itself readily to integration in modern automated systems. Figures 4 thru 7 show the brazing station on a robot operated line producing office copier rolls. Here, the brazing and cleaning operations had to be performed "in line" with the robot-fed machining operations.

The rolls are heavy copper tube approximately 3 inches in diameter. They have

stainless steel hubs brazed in each end.

Production requirements of 60 parts per hour were met with an off line transfer system which lifts two parts at a time from the pallets on the conveyor and places them on a walking beam handling system. The beam transfers the parts to a work station where the ends are fluxed, the brazing rings inserted and the hubs placed in position.

Design of this operation was based upon the fact that the automated machining

operations could maintain lose tolerance fits between the tube and hub components.

Initially it was thought the part would have to be held in a vertical plane so that the molten alloy would not run unevenly in the joint. However, this would have necessitated doing one joint at a time, then turning the roll end for end to complete the opposite joint. The double handling would have made the job cost prohibitive.

By maintaining .002- .003-inch clearance between the hubs and the roll, the part can be held horizontally. Capillary action draws the alloy evenly through the joint, and 85 per-cent coverage of the joint area, by the alloy, is achieved.

In the next index position, an American Induction 40-kW, 1-kHz induction generator brazes two assemblies (four hubs) at a time. In this instance, two matching heat stations, each with a two-position coil, index into each side of the assembly to perform all brazing operations simultaneously.

Figure 6: Brazing station on a robot-operated line making office copier rolls. Brazing and cleaning are done in-line.

It is interesting to note that though the tube is a heavy mass of low resistivity copper, the high power input capability of the induction heater can perform this function with a minimum of heat conducted down the tube.

The coils are designed to place most of the heat in the low resistivity copper tube. A smaller Field is generated in the stainless steel hub which, with conduction from the copper, comes to brazing temperature at the same time as the tube. The same machine then automatically washes the parts internally before replacing them on the pallet, at the next conveyor station.

With regard to energy costs, direct conversion of electrical power to heat at the joint is, today, considerably more cost efficient than that produced by gas flame. Restricting the heat to the joint area, the induction heater draws only sufficient power to heat the localized area for proper alloy flow.

Though induction processes are capital intensive (initial equipment cost is normally higher than that for an equivalent gas-fired unit), present gas costs are rising. Natural gas conversion efficiencies of 8-10 percent on operating installations are normal. Equivalent typical electric costs of .03 cents/kW hour coupled with line to load efficiencies of 55-65 percent have made operating costs highly competitive.

In any brazing process, the basics—
1. Part cleanliness
2. Proper fit for good capillary action
3. Balanced heat placement —

must be employed for structural integrity of the joint.

Within these constraints, analysis of the process can lead to the use of induction as a cost effective brazing tool.

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Fig 4: "Flame spreader" assembly line has a multi-part system that can be handled by the operator.
Figure 5: Copper sheet is induction-brazed to 100 small tubes, and simultaneously, to the housing of marine coolers.
Figure 7: Heavy malleable steel headers are brazed to copper bearing steel tubes for a manufacturer of radiators