Induction Annealing of Small Stainless Steel Tubes

Objective: A manufacturer from the metalworking industry is looking for a new method of metal annealing. The customer wants to review the advantages that induction heating technology provides. They also want to remove the use of torch and flame heating from their process.

For this annealing application, we have to heat a stainless steel tube. The measures of the tube are 1.25″ (3.175 cm) OD x 0.065″ (0.165 cm) wall. The heated length is 1″ (2.54 cm) on the tube end so the end can be formed over and closed.

The objectives of this application test for induction annealing are better heating times and better repeatability. Desired productivity rate is 200 – 300 parts per week, the cycle time between 7 – 10 seconds per part, and the max temperature must be 1950°F (~1065°C). We have to demonstrate how induction heating works and choose the right heating equipment for the application.

Industry: Foundries & Metalworking

Equipment: The suitable induction heating equipment is UltraHeat SM – 5kW Induction Heater.

Process: The first step of the test was to determine the process parameters and choose the proper power supply for the application. We made two tests with different settings of power. For the first one, we detuned power to 2 kW with a temperature 1900°F (~1038°C) and reached a heat cycle time of 30 seconds. On the second test, we worked with the full power of the machine of 5 kW and the same temperature. With these settings, we reduced the heat time to 10 seconds.

To confirm the correct temperature, we used a Dual Color IR pyrometer. The induction coil for the two tests was with four turns. With all of these precise setups, we successfully annealed the samples and achieved the customer requirements.

Benefits: The conclusion and recommendation for this application are to use an UltraHeat 5kW induction heating machine. With that power, we achieve good quality, repeatability, and temperature uniformity. Also, we increased the productivity rate with faster heat cycle times and improved energy efficiency.

Reference Info: Application Note 3463-7274

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