Preheat magnetic steel strip with very even heating across the strip

PUBLISHED: 11 May 16

Test 4: Thermal image at end of 1.6 seconds heat cycle (static heat test) using the 5 kW power supply
Test 4: Thermal image at end of 1.6 seconds heat cycle (static heat test) using the 5 kW power supply

Inductively heat the magnetic steel strip at a rate equal to 6 meters/minute to 260°C (500 °F). For the customer's application, evenness of heating is critical, with a requested delta-T of +/- 5°C (255°C - 265°C; or 491°F - 509°F)

Materials Magnetic steel strip, 5" long / 0.02" thick, Spine .259" wide, legs are 0.0835" wide with approximately 0.050" space between each leg.

C-1010 mild steel

Test 1

Equipment
UPT S-2 Water Cooled Power Supply
HS-4 Heat Station
Helical coil
Power: 1.8 peak kW
Temperature: Spine at end of 1 seconds cycle - 500°F (260°C), legs end of cycle + seconds -400°F (204°C).
Frequency: 160 kHz
Time: 1 second cycle.

Process and Results: The purpose of initial tests is to better understand how the strip will heat, and in particular, how the 'fingers' heat in comparison to the spine. In this test, the spine temperature reached 500°F (260°C) and the fingers lagged. Delta T was noted to be approximately 100 °F (56°C).

Test 2

Equipment
UPT S-2 Water Cooled Power Supply
HS - 4 Heat Station
"Lab" Oval coil
Power: 1.89 peak kW
Temperature: Spine at the end of a 3 seconds cycle - 500°F (260°C), legs at end of the 3 second cycle - 440°F (227°C).
Frequency: 126 kHz
Time: Basic simulation of a conveyor coil heat pattern - allow 450 milliseconds for ramp time - total static cycle 3 seconds.
Process and Results: With this test, we change from a round coil to an oval coil. This allows us to focus heat differently into the 'fingers' versus the spine, in order to reduce the delta T. The delta T for the simulated conveyor coil test was improved - 60°F differential. Based on the improved results, we see that further decoupling away from the spine is needed, in order to ensure even heating, and to further reduce the delta-T.

Test 3

Equipment
UPT S-2 Water Cooled Power Supply
HS - 4 Heat Station
Oval 2 turns coil
Power: 1.84 peak kW
Temperature: Temperature on the spine at end of 3.3 second cycle 491°F (255°C), legs lagged 2 seconds behind and reached 472°F (244°C).
Frequency: 242 kHz
Time: 3.3 seconds needed using the 2 kW fully tuned to heat the 5" length of sample as noted above.
Process and Results: With this test, we decouple further away from the spine to further improve the evenness of heating. The coil was changed to a 2 turn coil with an opening 1.75". The delta-T has been further improved; however, due to the decoupling, our overall heating rate is below the customerís targeted rate.

Test 4

Equipment
UPT S-5 Water Cooled Power Supply
HS - 4 Heat Station
Oval 2 turns coil
Power: 4.61 peak kW
Temperature: Peak temperature on the spine at the end of a 1.6 seconds static heat cycle - 506°F (263°C), peak temperature on the legs - 494°F (257°C).
Frequency: 184 kHz
Time: 1.6 seconds used to heat the 5" strip to temperature as noted above.
Process and Results: In this test, we increase power to a 5 kW unit, and continue to use 2 turn coil that decouples from the spine of the strip, ensuring more even heating. A higher power induction system is needed since we are decoupled away from the spine of the part. With this test, we meet both the target heat rate and achieve the desired evenness of heating.

Results/Benefits:
Induction preheating provides:

  • Faster heating cycles
  • The process is safer than the flame heating
  • Technology without pollution, clean and safe

Ultraflex Power Technologies, USA
Tel: + 1 631 467 6814
Email: sales@ultraflexpower.com
Web: www.ultraflexpower.com

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