Efficient Induction Preheating for Medical Devices

Application: Preheat & Postheat 

Industry: Medical & Dental 

Application Objectives: A medical equipment manufacturer wants to research new energy efficient methods of preheating their products, while also improving the quality and reliability of their process. They need to heat stainless steel or Titanium tubes that are set on a wire. They need to be heated from 250 to 450ºC and for different lengths of time. This will happen under a vacuum, and in a clean room as this is part of a medical device manufacturing process. 

Equipment: UltraHeat S5 – SHT-2/400, UltraHeat S5 – SMT-5/200, UltraHeat S2 – SMT-2/200, 4 turns helical coil, 10 turns helical coil 

Materials: Stainless Steel, Titanium 

Key Parameters: 

• Heated length or zone: 220 mm 

• Max Temperature: 450°C 

• Min/Max Heat Cycle: 1 hour 

Process: 

Heating only the tube using a small 4-turn coil at high frequency presented some challenges, primarily due to the tube’s small diameter. This limitation resulted in low efficiency, as cooling outpaced the heating process. We attempted to address the issue by employing a higher power setting using a 5-kW power supply. However, the outcomes remained consistent with those observed with the high-frequency approach. 

After the initial attempts with a 5-kW power supply and high frequency, we explored an alternative approach by using a small copper tube, sufficiently large to encase the steel tube. Through thermal conductivity, heating the copper tube resulted in the concurrent heating of the smaller tubes. We achieved positive results using this method. With the 2-kW power supply and the 10 turns coil, we successfully heated the steel tube within 30 seconds. Notably, the process proved even more efficient at a higher frequency of 161 kHz compared to the initial 74 kHz, and the required temperature was reached in only 20 seconds.  

Results and Conclusions:  

In conclusion, while direct induction heating of the small steel tube presented some challenges, we found that employing a larger tube acting as a susceptor for indirect heating is a more effective solution. This approach allows the initial warming of the larger tube to conduct heat to the smaller one efficiently. We recommend using magnetic steel as the optimal material for the larger tube.  

Reference Info: AR 3464-8570 

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