Watching a 3/4″ square steel bar turn cherry red in 2 seconds can be a little intimidating to someone new to induction heating. But the fundamentals are actually quite simple.
Voltage will be induced when any conductive object is placed in a changing magnetic field (Faraday’s Law). The resulting electric currents are called eddy currents and generate Joule heating.
Efficiency
When a coil of metal (inductor) is placed near conductive material such as a piece of steel, electricity will pass through it and induce voltage into that material based on Faraday’s law. The induced voltage causes current flows, either isolated eddy currents within the workpiece or circulating currents based on transformer action. The energy from those current flows is converted to heat, and the workpiece gets hot.
Induction heating is an extremely efficient process, up to 50% more so than traditional resistance, flame, or oven methods. The process is also safe, clean, and non-contact, eliminating fire hazards and air pollutants.
The induction coil heater produces precise, contactless heat directly to the product being processed, with no heat loss to surrounding areas. This allows for fast, highly controlled heating with tight control of the process to improve productivity and quality.
Coil design and frequency selection are key factors in an induction system’s efficiency, impacting both process time and power requirements. The optimum induction coil design matches the application with the correct electromagnetic field, ensuring that the workpiece is efficiently heated and that a consistent temperature pattern is achieved throughout the product.
Many applications involve parts being moved relative to the induction coil with conveyors, turntables, or robots. A well-designed induction system will incorporate the motion into the heating cycle without losing heating efficiency or damaging the part. Frequency selection will depend on the application, with higher frequencies often used for brazing, soldering, and annealing where surface heating is required, while lower frequencies are better suited for applications that require thorough, through-heating to the core, like die and forging.
The type of metal also impacts induction heating efficiency, with copper requiring less power to heat than steel. Additionally, the resistivity of the metal also plays a role, with high-resistivity materials such as steel requiring more power to heat than low-resistivity metals such as aluminum or copper. The depth of the “skin effect” produced by the magnetic field also influences heating efficiency, with shallower skin effects requiring lower frequencies and deeper skin effects requiring higher frequencies.
Precision
Unlike combustion-based heating methods that produce open flames and radiant heat, induction technology utilizes an electromagnetic field to transfer energy directly to the workpiece. When a conductive material, like metal or plastic, is placed in the electromagnetic field, a voltage will be induced, and current will flow. The power generated by the coil is then used to heat the material.
Variation of current, voltage, and frequency through the induction coil allows for fine-tuned engineered heating for precise applications like case hardening, tempering, annealing, and wire hardening. This precision enables manufacturing processes to run with reduced cycle times, resulting in higher productivity and better product quality.
The versatility and adaptability of induction heating provide a wide range of industrial applications, especially for the plastics and petrochemical industries. Induction heating can be tailored to a variety of materials and sizes, and it can easily be integrated into existing production setups. This translates into high process efficiency and quality, improved throughput, and optimized energy utilization.
For example, induction is often employed for fast and efficient anti-icing of aircraft parts during flight to prevent the formation of ice on critical surfaces. The quick heating of the surface of the part reduces time spent on maintenance and improves operational safety.
Precise temperature control and uniform heating also make induction an ideal choice for sterilization or pasteurization of food and beverage products. Rapid heating speeds up liquid product processing, leading to shorter shelf life and more reliable results. This ensures that the food and beverage industry complies with stringent health regulations.
Induction heating also eliminates the risk of fire hazards or explosions. It is a safe and clean method of heating that can be employed in a wide range of industries that handle flammable materials, operate in confined spaces, or prioritize worker safety. This makes induction an ideal alternative to traditional open flame and resistive heating technologies.
Cleanliness
Induction coil heaters provide a clean, efficient, and non-contact form of heating. They produce no flames or hot surfaces and are easily cleaned up after work, saving you time and effort. This also makes induction safer, especially when used in areas with flammable materials or dangerous chemicals.
The power supply converts AC line power into high-frequency alternating current, which it sends through the induction coil. This creates a magnetic field that produces eddy currents that heat the workpiece when exposed to a conductive metal. The coil is cooled by water and the power supply, which has several internal components that also require cooling to perform correctly.
With the help of solid-state power supplies, induction coils are consistent and repeatable. This allows for stable and highly accurate heating, as the pattern of energy produced is the same each time the coil is turned on, and the same part is presented to it. This makes it ideal for jobs like soldering or brazing, which require repeatable results to be successful.
Unlike radiant heating solutions, induction is a clean process. There are no open flames, no smoke, or hot surfaces to contaminate the area around the work. This also reduces maintenance costs and downtime because there is no need to change the gas tanks, clean out burned-out flames, or turn off the heat when work is finished.
Coils can also be easily integrated into automation systems, allowing for higher part production without manual operation. This saves labor, time, and money and improves efficiency.
The longevity of an induction coil depends on how well it is maintained. A poorly maintained coil could be damaged by improper handling, poor installation, and other factors. It is important to keep the coil protected from other objects that could touch it and ensure it is never dropped or knocked off a work bench. Induction coils are fairly expensive, so a little care can extend their life span and minimize repair costs. For instance, using a coax saver to protect the coils from damage from being pulled into or out of the power supply adapter is a good idea.
Safety
Induction heating produces very high power density in a relatively small area, making it possible to heat a workpiece without contact. It also delivers the energy in a very short interaction time, which helps minimize thermal distortion of the part and damage from slag, hot spots, or other unwanted effects. Additionally, the magnetic field generated by the coil is only confined within the workpiece and does not affect surrounding areas. This allows for the safe handling of hazardous materials, such as toxic chemicals or radioactive materials.
With conventional conductive heaters, environmental and material losses—such as convection, radiation, or contact loss—consume considerable energy. However, induction heating is non-contact, so there are no energy losses from contact or IR.
The technology works by using a changing magnetic field to induce a flow of currents in the conductor. These induced currents, known as eddy currents, produce their own electric fields that interact with each other and generate heat. This process does not require direct contact with the workpiece, enabling manufacturers to work with a wide range of sensitive conductive materials, such as reactive metals, specialty alloys, and silicon.
This is important for applications such as induction hardening of steel parts and brazing or soldering for joining metal components. The ability to selectively confine the flow of currents to a specific area of the workpiece is also beneficial for processes that require a low-wear surface on the parts, such as welding and annealing.
Additionally, induction systems can be integrated into automated production lines for precise control, monitoring, and data logging. This further enhances efficiency, repeatability, and quality assurance.
Precise temperature control is crucial for sterilization or pasteurization of liquid products, like milk and other food and beverage ingredients. Induction systems provide a fast and effective means to kill harmful microorganisms while preserving the product’s nutritional value and sensory attributes.
A properly designed induction coil is key to ensuring that the process is efficient and effective. The size of the coil and its position relative to the workpiece must be optimal for the application, taking into account a variety of factors, including the frequency of the induction system (typically in the range of a few kHz to 500 kHz) and the part’s geometry.