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 how to reduce

overall cost per joint while maintaining joint quality.

by STANLEY ZINN, Induction Heating Consultants • June 2011

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With regard to production cost, the sudden rise in the world price of silver has caused considerable rethinking with regard to brazing operations. Where other joining techniques are feasible (spot welding, arc welding, shrink fitting) alternatives must be explored and parts re­designed, if necessary, to utilize less expensive processes. However, within the realm of joint quality, other alloys, if they have acceptable properties, should be considered.

Particular attention should be paid to alloys with a lower silver content.

As a typical example, Governale Bros., Brooklyn, New York, has been induction brazing heavy malleable steel headers to copper bearing steel tubes for the manufacture of baseboard radiators and convectors (Fig. 2). Since the company used rings of 45 percent silver, alloy cost became a major concern. It was decided, therefore, to explore the possibility of using a brass brazing alloy for this operation.

Figure 2

Brass or bronze alloys have higher melting points than silver-bearing combinations. Accordingly, their flow point temperatures then approach that of the steel parts they are joining. Since a well designed joint will place the alloy where it will heat by conduction from the parts, the possibility exists of melting steel assembly components in trying to use a brass alloy.

In this instance, however, the header casting provided sufficient heat sink to permit balanced heating. Using a 50-kW, 10-kHz Cycle-Dyne generator, the three convector tubes are brazed to the casting with an 80-second heat cycle. Alloy cost savings achieved by switching to brass have averaged 90 percent per joint or more than $3.00 per radiator. As an additional benefit, the sluggish flow characteristics of the new alloy have reduced leaders to less than 1 percent of production, versus 14-15 percent with silver.

Large assemblies are not the only products that can achieve cost savings with

induction. Where production warrants, induction heating, due to its "fixed time" processing, is easily automated. This "flame spreader" (Fig. 3), assembly line for a manufacturer of gas hot water heaters provides a multi-part assembly system that can be handled by a single operator.

The assembly is composed of two stampings, two screw machine parts and three

alloy rings. The parts are assembled and fluxed right on the processing conveyor, with individual fixtures providing relative locations for accurate assembly. The parts proceed from the assembly station continuously through a channel type induction coil. The 10-kW induction generator, operating a 450-kHz produces 1800 parts per hour with an automatic stripper removing parts from the conveyor at the exit end.

In a similar installation, for an automotive manufacturer, carburetor fast idle cam assemblies are brazed at a rate of 1600 parts per hour. This system was initially designed to incorporate an automatic flux applicator. When installed, the spray heads fluxing should remove an additional manual function from the assembly line.

At present, automatic part removal from the conveyor deposits brazed assemblies automatically in the first of a series of baths. These are designed to remove the brazing flux and apply a rust inhibitor to the components.

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Figure 3