Key Questions to Ask When Ordering electromagnetic induction heater

Monthly Inquiry: We intend to utilize induction heating for composite metallic materials before diffusion bonding. Are there any potential issues regarding high noise levels? Have you identified specific frequencies that tend to be noisier? If yes, what strategies can help mitigate noise levels?

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Response: In most induction heating scenarios, the noise produced is typically low and does not reach levels of concern. However, there are exceptions to this. Generally, lower frequencies result in increased coil current, which can enhance electromagnetic forces and amplify coil vibrations. For instance, systems that operate at line frequency (60 Hz) are likely to generate more industrial noise than those operating at higher ranges like 3 kHz or 30 kHz. Furthermore, systems with higher kilowatt outputs, such as 500 kW, may create more noise than those with lower outputs, such as 100 kW.

When we discuss audible noise, two primary factors affect its impact on humans: intensity and discomfort level. For example, low-frequency noise (e.g., 50-60 Hz) may be louder but often less bothersome to the human ear than a quieter, higher-frequency noise (e.g., 1 kHz).

Here are the four principal sources of noise during induction heating:

• Power supply noise: Various power supplies are available for induction heating. Combinations of power and frequency, particularly those using single-module inverters, can range from line frequency to several hundred kHz with power levels exceeding kW, even at 800 kHz. The design advancements in modern semiconductor-based power sources often produce negligible noise.
• Vibration noise from copper coil turns: Induction coils can be constructed as either open-wound or encased in refractory materials. The open-wound approach, though simpler for repair, requires proper securing to minimize noise from vibrations. Conversely, encased coils enhance durability and significantly reduce unwanted noise due to vibrations.
• Noises from workpiece vibrations or resonance: Loose components can vibrate and generate noise; thus, the geometry of the workpiece must be assessed. Application of pressure in certain diffusion bonding scenarios can help reduce these vibrations. Particularly thin-walled tubular components may resonate at specific frequencies, causing notable noise, which should factor into frequency selection during heating.
• Noise from power cables, buses, and fixtures: While the risk of incorrect design in these components is minimal, any related concerns should be addressed with the help of an induction heating expert.

Additional discussions regarding these concerns can be found in Ref.1.

Interested in discovering more about electromagnetic induction heater? Reach out to us today for an expert consultation!

Dr. Valery Rudnev, FASM
Director, Science & Technology
Inductoheat Inc
www.inductoheat.com

Reference

1. V. Rudnev, D. Loveless, and R. Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, .

Starting in July, the Professor Induction column began a new series titled Induction Heating: Everything You Wanted to Know, But Were Afraid to Ask. This series aims to address common questions related to various aspects of induction heating and heat treatment. Questions may be submitted to Dr. Rudnev anonymously unless permission is granted to reveal the sender's identity.

Creating an induction heater can be an enjoyable project. I started with a small induction heater and soon wanted a more powerful version. A compact unit can be built in approximately 2 hours, while larger units will require additional time. These heaters are quite practical for camping, as they can easily be powered by a 12V car battery.

My largest induction heater was made from a microwave oven transformer. After removing the secondary coil, I substituted it with enough #12 solid copper wire to achieve 12V to 15V DC. I've managed to salvage around 15 MOTs, each featuring 100 turns on the primary coil. The math for the secondary coil running on 120VAC equates to about .833 VAC per turn.

I haven't dabbled with flat induction coils yet, but the minimum must be around 2 uH. Purchasing a resistor, capacitor, inductor, and meter costs about $35 online to test the coils. It's critical for the choke coil to be robust enough to avoid saturation; otherwise, it will stop functioning at a specific power range and suddenly spike current, causing mosfets to fail. Minimizing internal resistance in the mosfets will prevent overheating.

For my setup, skip the transformers for operation on a car battery. My smaller induction heater can heat a 1/4" steel rod to red hot within approximately 3 minutes, while a larger unit achieves the same in only 7 seconds. Note that a higher wattage isn't necessary for cooking, as food can burn before it cooks properly.

All my induction heaters utilize a similar circuit design, except for larger power supplies and bigger L2 choke coils for higher capacity units. If you opt for smaller gauge wire instead of #10, the skin effect permeability will increase, diminishing circuit efficiency. My induction heat is significantly lower than the wattage of the power supply, as illustrated in the accompanying images.

Ensure caps are arranged in a box configuration, akin to a Rail Gun cap bank, allowing for rapid charge and discharge. Start by constructing the small unit with six yellow caps. I prefer using insulated Romex solid copper wiring, and it's crucial to use insulated wire; contact with metal can cause oscillation failures, leading to mosfet explosions.

A small circuit can be built for around $15, with a larger circuit incurring extra costs for a 100A bridge rectifier and meter. I often salvage used components from old TVs and computers. You can find 10 mosfets online for about $6 with free shipping from China.

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