Induction Heating: An Amazing Twist of Technology

What Is Induction Heating?

Induction heating relies on the existence of eddy currents discovered by Léon Foucault in . Briefly, when a changing magnetic field passes through any conductive object, current flow is induced in the object. That current flow creates a secondary electric field in the conductor. The secondary electric field, in turn, produces another flow of current which is known as the eddy current, so named because it flows in a circular pattern, much like water can swirl in a slow-moving stream when it encounters an obstacle. The push-pull between these fields—literally, the kinetic energy caused by electrons being shuttled back and forth—produces heat in the conductor.

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This use of eddy currents can not only cook a meal; it can melt steel and other metals.

Induction Heating Applications

Induction heating is used to manufacture end items as diverse as bulldozers, spacecraft, faucets and sealing plastic lids on pharmaceutical bottles. The fundamental design of an induction heating device uses a coil of wire and an AC current to induce a changing magnetic field in the item to be heated—the work piece. The coil can measure only a few centimeters in diameter, or any other dimension suited to the job at hand.

The work piece is placed inside the magnetic field generated by the coil, but not in contact with it, then heated to the desired level by the eddy currents. Depending upon the material being heated, temperatures as high as 2,200° F (1,200° C) can be achieved.

Induction heating is clean, requiring no fossil fuels. Parts exposed to induction heating simply heat up, so there’s no cleanup afterward and no worry about contamination of the work piece. It’s also fast. For example, manufacturers of pipes and tubular channels use induction heating to weld a seam along the longitudinal dimension of pipes passing by at high speed on a conveyor.

A few other processes that use induction heating include: 

• Induction hardening and tempering, which alters the physical characteristics of materials to meet the needs of various applications.
• Induction melting can be used to melt any ferrous or non-ferrous metal, including nuclear material and various alloys used in medicine and dentistry.
• Metal and carbon fiber materials can be bonded together by heating them, thereby curing adhesives placed between two surfaces.
• Soldering, brazing and welding are all natural applications for induction heating where precise temperature control and accurately confining heat to the desired area is important.

Induction Heating Solves Real Problems

The so-called Tylenol Murders took place in Chicago during when someone, never identified, laced Tylenol bottles with cyanide. The subsequent events led to a nationwide recall of Tylenol products. The poisoning also forced the entire over-the-counter pharmaceutical industry to package their products in tamper-proof containers.

The aluminum foil that’s commonly used to seal OTC drugs is part of the industry’s solution, and it uses induction heating. The process begins by placing the foil, which is electrically conductive, into the cap. The cap is screwed down, then the entire package is placed inside an induction heating coil. As the foil heats up, adhesives around its edge adhere it to the lip of the bottle.

Designers of induction cap sealing equipment must take several factors into account. The induction heater’s physical dimensions need to be tailored to the containers to be sealed. The electromagnetic field needs a depth suitable for heating the foil. The heating should take place as quickly as possible for productivity reasons. The efficiency of the induction heater needs to achieve a specific performance level.

These and other design constraints can be reduced dramatically when the wire used to make the coil is custom-manufactured. New England Wire Technology, a long-time supplier to the induction heating market, provides wire specially made to solve such design problems.

For instance, NEWT can supply round, square and rectangular conductors. Their exact size can be tailored specifically for the AC current and frequency to be used. And, because the efficiency can be optimized in the wire itself, the induction cap sealer design engineer has much greater flexibility in choosing the spacing, shape and size of the sealing head. In fact, that same flexibility benefits designers of any induction heating device.

The Case for Litz Wire

Induction heaters can run on AC power ranging from a few Hertz to 500 kHz and higher. The frequency chosen determines the heat’s penetration depth, with lower frequencies penetrating deeper. Frequencies for induction heaters are chosen at design time according to the particular work to be accomplished. For instance, an application that calls for hardening and a deep penetration uses low frequency. Another application that calls only for surface heating would use high frequency.

Higher frequencies passing through a wire cause the skin effect where much of the current flow travels along the outside of the wire, increasing its AC resistance and creating unwanted heat. Using NEWT’s unique Litz wire to build the coil virtually eliminates the skin effect, making the coil more efficient and allowing for more modest, lower cost power supply designs. (Read more about Litz wire).

Still, Challenges Do Arise

Because induction heating is used in so many applications, converting a customer’s design needs into a suitable Litz wire product involves many factors. According to NEWT engineers, “Almost every induction heating project takes on aspects of a custom job. While building wire and cable to customer specs seems simple, the number of variables that go into a solid design can be numerous.”

For instance, the wire size can be adjusted for the AC frequency to avoid skin effect and other losses in the coil. Then, the total number of conductors in the Litz wire can be chosen to accommodate the maximum current flow. Conductors that make up the Litz wire are insulated using a film that needs to accommodate certain temperatures. Case in point: an induction coil used to heat a large vat of steel has to work in a much hotter environment than one used to seal aspirin bottles. Likewise, the outer insulation needs to protect the high voltages often used, as well as environmental conditions.

Custom Design Services to the Rescue

Bio: Dr. Girish Dahake is Ambrell’s Senior Vice President, Global Applications. He has over 25 years of induction experience and leads a worldwide team of induction application experts at Ambrell’s applications laboratories. He holds patents, has authored numerous papers, and frequently presents at professional conferences on topics such as nanoparticle heating, heat staking and general induction heating. Dr. Dahake holds a Ph.D. in Mechanical and Aerospace Engineering from the University of Rochester.

Induction Heating: Benefits and Applications for Manufacturing

Induction heating isn’t a new technology, yet it still isn’t widely known and adopted within the manufacturing industry. To learn more about this technology, we met with Dr. Girish Dahake of Ambrell to discuss the basics of induction heating and its impact on the industry.

Q: Can you explain how induction heating works?

A: Induction heating uses magnetic fields to transfer energy. An induction machine creates an alternating current that flows through the induction heating coils and creates a magnetic field around the copper coils. This magnetic field and the alternating current create eddy currents in metal parts.

Basic knowledge of electricity: if you can get a current flowing in a part, it produces heat. So, induction heating relies on the transfer of that electric energy through the magnetic field to the part to create that heat. Compared to other forms of heating metal, induction is unique because it doesn’t require a transfer medium. It’s actually similar to the energy that we get from the sun. That’s the magical aspect of induction.

Q: What are the benefits of induction heating?

A: The biggest benefit of induction is that it’s very selective in its heating. So, it can heat a small section of a part without having to heat the entire part, and that only requires a minimal amount of energy. This makes the whole induction heating process very efficient. 

Another benefit of induction is that it’s extremely repeatable and reliable. Once you set up an induction process, it won’t suddenly stop working. Induction works repeatedly day after day, year after year, which is beneficial to manufacturing engineers because they don’t have to spend time fixing and debugging induction machines just to make them work. 

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Induction is also easily controlled. If somebody wants to heat a part to degrees but no more, induction is able to get up to that degrees and stay there. That kind of control is important in medical applications, aerospace applications, etc. to ensure parts are properly made and safe. 

All of these benefits combined make induction extremely efficient. Not only regarding energy consumption, but also in cost per part. Companies want to make their parts cheaper. Induction is one of the cheapest ways to make parts for production.

Q: While we’re on the topic of energy efficiency, can you describe some of the green benefits of induction heating?

A: Compared to heating methods that use fossil fuels, where something is burned to create heat, induction’s input is electrical energy. So, it’s not producing any combustible gases, flames, or smoke. With induction we don’t produce any residue, which makes it a green technology. And since nothing is being burned, this also makes induction heating safer. There are no dangerous fuels to transport and store, and no harmful UV radiation is being produced.

Q: With all these great benefits, why isn’t everyone using induction heating?

A: The biggest challenge in the industry is companies’ inability to change from the method they’re using to heat parts. To change their process is a big challenge. If somebody needs to create a new process, it’s easy to choose induction because there’s so many advantages. But if you already have all your infrastructure and operations around another heating method, then it’s hard to get rid of all that and go to induction unless you have an extremely pressing reason. Typically, with new installations, induction is the easy choice, but with existing installations companies have to make a commitment to get rid of their current heating method.

Q: What other options is induction heating competing with?

A: Fire is still the predominant heating method in the industry today, so a lot of installations that were set up decades ago use flame. Flame is one of the most common methods to heat parts because it’s easy to see, easy to implement, and everyone is familiar with it.

Other installations include ovens and furnaces. In those kinds of installations, the entire part gets heated. Usually, parts are heated to join two pieces together. So, before they’re joined, they have to be held in place. Now the holding fixture also ends up going into the oven or furnace and getting heated, which leads to more energy consumption.

So, for heating methods competing with induction, there’s open flame, ovens and furnaces, and then there’s also lasers. Lasers are used to cut metals; their cost makes them impractical to use for generalized heating. So, these are the main competing heating methods in the industry.

Q: How is induction heating different from these options?

A: One main difference is safety. Induction heating is safer because, unlike other heating methods, you’re not burning anything. Another difference is that induction is efficient. With other heating options, a lot of the heat escapes and is used inefficiently. With induction these things are a non-issue because the heat is going directly from the induction source into the part. There’s no heat in the air. So, induction is very efficient compared to these other forms of heating. 

Another difference is control. A lot of applications require parts to be heated at an extremely fast pace but only to a certain level. Induction can quickly heat a part to your desired temperature and then stop there, which is very difficult to do with the competing technologies.

Q: What are some applications that are a good fit for induction?

A: There are so many good applications for induction. One that everyone is probably familiar with is the aluminum foil seals on plastic bottles. Those are all sealed with induction heating. Another application is refurbishing turbine blades in aircraft engines. Induction heating is used to preheat the blades to help rebuild them. There’s a limited window of time for this process to be completed, so the speed of induction heating allows the turbine blades to be quickly refurbished.   

Induction heating is also used in a number of different electric vehicle applications, such as manufacturing rotors and fuses. For headlights and taillights, induction is used to heat metal inserts that are pushed into the light’s plastic encasing to anchor it to the frame of the car. A lot of electric vehicle battery manufacturing processes also use induction heating.

One particularly unique application that interests me is in the medical field there are researchers using induction heating to kill cancer and tumor cells in the human body. Which is a very different application of induction that involves injecting small particles into the tumor or cancerous cells and then heating them to kill off the circulation in those cells. So that is very exciting and as it comes to fruition in the marketplace, I think humanity will benefit a lot from this type of research.

Q: Are there any limitations or constraints to induction heating?

A: One of my toughest jobs is to say “no” to induction applications, but there are certain cases where other forms of heating are better suited. For example, induction is not a good fit for metal cutting. Lasers are a very good fit. Even though induction might be able to do it, it's not the right fit for that process. Everything has to be evaluated on a case-by-case basis to determine if induction is the right fit.

Ambrell does have an applications lab where we can experiment for customers and try to eliminate some of that risk when incorporating a new product/process. We know induction heating helps cut costs, doesn’t release emissions, and is a safe and efficient technology. Now we’re trying to get that knowledge out to the industry.

Q: What does the future look like for induction heating in the manufacturing industry?

A: I believe more and more companies are going to implement induction in their manufacturing processes whenever they need heat. Making parts with induction costs less, and induction’s capabilities are so far ahead of other heating methods. Most of the time people are just not aware of the advantages of induction. I think the more people find out about it, the more it will become a no-brainer. When people say, “I have this decision point should I buy an oven or an induction machine?”. They’re going to go for induction because it’s safer, more efficient, and better for the environment. 

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If you are interested in finding out more about induction heating, reach out to Ambrell to learn about their induction heating solutions. Or if you’d like to meet with them face-to-face, attend SOUTHTEC and find Ambrell at booth #733.