If you work in the recycling, mining, or waste processing industries, you've likely heard of eddy current separators. These machines play a key role in separating non-ferrous metals like aluminum and copper from bulk materials. They help improve product purity, increase recovery rates, and reduce labor costs.
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But not all eddy current separators perform the same. The results you achieve depend on how the machine is set up and used. In this guide, you'll learn about eddy current separators. Whether you're planning to purchase new equipment or looking to improve the performance of existing equipment, it's crucial to understand the core parameters that influence separation efficiency. Read this article and let us help you make informed operational decisions.
What is an Eddy Current Separator
An eddy current separator is a type of magnetic separator commonly used in recycling plants to separate metal cans or scrap from plastic, glass, or other non-metallic waste. It can separate non-ferrous metals from mixed material streams. It uses a rapidly rotating magnetic rotor to generate rapidly varying magnetic fields. These fields react with non-ferrous metals such as aluminum, copper, and brass, separating them from other materials. The machine does not touch or damage the material; it simply uses the principles of physics to quickly and accurately separate the metals.
But achieving optimal performance requires more than just starting it up. The effectiveness of an eddy current separator depends on several key settings, such as the rotor's rotation speed, the material's deposition depth, and the configuration of the internal magnets. In the following sections, we'll explain the five most important parameters you need to understand and adjust for optimal separation results.
Rotor Speed
The rotor is the heart of every eddy current separator. It spins inside the machine, generating a rapidly changing magnetic field that separates nonferrous metals from other materials. The rotor's speed is crucial to separation effectiveness.
Why Rotor Speed Matters
The higher the rotor speed, the faster the magnetic field changes. This is how "eddy currents" are generated in metals like aluminum, copper, or brass. These eddy currents create a repulsive force that lifts and ejects the metal from the material flow. If the rotor speed is too slow, this repulsive force may be too weak to effectively separate smaller or lighter metal fragments.
Finding the Right Speed
There's no one-size-fits-all speed. The optimal rotor speed depends on your material mix. Lighter metals, such as aluminum foil or crushed beverage cans, require higher rotor speeds to generate sufficient repulsive force. Heavier metal fragments may not require such high speeds.
Balance is Key
Excessive speed can also cause problems. It could throw material too far, disrupt the belt's trajectory, or increase wear on the machine. The goal is to find a balance, strong enough to separate, but not so strong that it wastes energy or stresses the system.
Belt Speed
The speed of the belt on your eddy current separator may seem simple, but it plays a major role in how well the machine sorts your materials. Getting this speed right helps make sure metals are thrown far enough and that everything stays on track during separation.
What Belt Speed Does
The belt carries your materials across the magnetic rotor. As the rotor spins underneath, it sends non-ferrous metals flying off in a different direction. But how fast that belt moves affects how long each piece of material is exposed to the magnetic field.
If the belt moves too slowly, materials might pile up or get stuck. If it moves too fast, lightweight metals might not get enough time to generate strong eddy currents. That means poor separation and more mixed material ending up where it shouldn't.
Matching Belt Speed to Rotor Speed
Your belt speed and rotor speed work together. A high-speed rotor often needs a faster belt to keep up with the magnetic force. But if the belt goes too fast compared to the rotor, you might lose control of your material flow.
A good starting point is to follow your separator's recommended belt speed range. Then test and adjust based on the material you're handling. If you notice too much carryover or poor separation, slow the belt slightly and observe the results.
Focus on Stability
What matters most is keeping material moving in a smooth, even layer. Sudden jumps or inconsistent flow will throw off the separation. Keep your belt speed steady and matched to your operation; it makes all the difference.
Burden Depth
Burden depth refers to how thick the layer of material is on the conveyor belt. It may not seem like a big deal, but it has a huge impact on how well your eddy current separator performs.
Why Burden Depth Matters
When the layer of material is too deep, lighter non-ferrous metals like aluminum and copper can get buried underneath heavier items. That means the magnetic field can't reach them properly-and they don't get separated. Instead, they pass through with the rest of the waste, which lowers your recovery rate.
A shallow burden depth gives each piece of material more exposure to the rotor's magnetic field. That means better separation and cleaner results.
Finding the Right Depth
There's no one-size-fits-all rule for burden depth. It depends on the type of material you're processing and the size of your separator. But as a general guideline, try to keep the burden thin, just a single layer, if possible.
If you're seeing poor separation or missing metals, check the feed system. You might need to slow down the infeed conveyor or use a vibrating feeder to help spread the material more evenly.
Keep It Consistent
What matters most is keeping the burden depth consistent. If the material comes in waves, thick in some places, thin in others, you'll get uneven separation. Aim for a steady, even flow. That gives your eddy current separator the best chance to do its job efficiently, every time.
Pole Configuration
Pole configuration refers to how the magnetic poles are arranged inside the rotor of your eddy current separator. It's one of the most important design factors, because it controls how the magnetic field is generated and how fast it changes.
What Are Magnetic Poles?
Inside the rotor, there's a ring of alternating north and south magnetic poles. As the rotor spins, these poles move past the non-ferrous metals on the belt. This movement creates eddy currents in those metals, which push them away from the rotor.
The number of poles and how they're spaced affect how strong and how fast the magnetic field changes.
Fewer Poles vs. More Poles
If your separator has fewer poles, the magnetic field goes deeper into the material. That helps eject larger or thicker metal pieces like heavy aluminum castings.
If it has more poles, the field switches faster. That's better for throwing out smaller, lighter particles, like shredded copper wire or thin foil.
The trick is choosing the right configuration for your material. If you're mostly handling light metals, a high-pole rotor gives you more accuracy. For heavier pieces, fewer poles may give better results.
Match Your Setup
Your material type, rotor speed, and pole configuration all work together. If you're not getting the separation you expect, the pole setup might be off for your needs. Talk to your equipment supplier, or test a few different rotors, to find the best fit for your application.
Magnet Material and Rotor Design
The type of magnet and how the rotor is built both play a big role in how well your eddy current separator performs. These two features control how strong the repelling force is and how precisely metals are thrown from the belt.
Why Magnet Material Matters
Most eddy current separators use rare-earth magnets, especially neodymium. These magnets are small but very powerful. Their strength helps create fast-changing magnetic fields, which is what you need to push non-ferrous metals like aluminum, copper, or brass away from the conveyor.
Weaker magnets, like ceramic, are sometimes used for lower-cost or lower-performance applications. But if you're separating fine particles or need longer throw distances, neodymium is the better choice.
Rotor Design Basics
The rotor sits inside the drum and spins at a very high speed. It's usually made of a non-conductive shell with magnets placed around it in a circular pattern. The faster it spins, the faster the magnetic field switches polarity. That's what creates the eddy currents in the metals on your belt.
Some rotors are designed with air cooling or special balancing to prevent overheating or wear. If you're running heavy loads or operating nonstop, a durable and well-balanced rotor makes a big difference.
Think Long Term
Choosing the right magnet material and rotor design depends on your workload and material type. If you're unsure, always ask about magnet grade, rotor speed, and how long the components are expected to last. It'll help you make better decisions-not just now, but down the line too.
Maintenance and Safety Best Practices for Eddy Current Separators
To keep your eddy current separator working at its best, regular maintenance and safety checks are key. It's not just about keeping the machine running; it's also about protecting your team and equipment from unexpected issues.
Stick to a Routine Maintenance Schedule
You should inspect the rotor and belt regularly. Look for signs of wear, misalignment, or unusual noise. Clean the magnetic rotor area to prevent the buildup of dust or debris, which can affect performance. Don't forget to check belt tension and tracking; it matters more than you think.
Monitor Bearings and Motor Health
If you hear grinding, notice excess heat, or see increased vibration, stop and investigate. Bearings and motors are core components. Replacing them early can save you a bigger repair later.
Train Your Operators
Make sure everyone who runs the machine knows how to start, stop, and monitor it properly. When people understand how it works, they're more likely to spot small problems before they grow.
Follow Safety Lockout Procedures
Never perform maintenance while the machine is powered. Always use lockout/tagout protocols. Safety first, it's the rule that saves lives.
Taking a few extra minutes each day can help you avoid costly downtime. And when your separator runs smoothly, your entire line does too.
Eddy Current Separator Buying Guide
Buying the right eddy current separator is crucial for your operation. To make an informed choice, first understand your materials and processing needs.
Ask yourself the following questions
What metals will you be separating?
How much material will you process daily?
What particle size will you be processing?
Next, consider the following key characteristics
Rotor speed and magnetic pole configuration-these influence sorting accuracy.
Are you interested in learning more about Eddy Current Separator Plants? Contact us today to secure an expert consultation!
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Everything You Need To Know To Find The Best Carton Packing Machine10 Things to Consider When Buying Shea butter tea seed oil extraction machine 6YL-128Belt width and speed-these are critical to throughput.
Magnet type and strength-these influence sorting capacity and durability.
Also, check the supplier's reputation. Good support and service mean fewer headaches down the road.
If you're looking for high-quality Eddy Current Separators, Great Magtech is your ideal choice. As an industry-leading, specialized manufacturer, they offer advanced sorting technology and a wide range of equipment models to meet diverse processing needs. Whether you're recycling non-ferrous metals like aluminum and copper or sorting complex industrial scrap, Great Magtech equipment guarantees efficient and stable performance. Choosing Great Magtech not only gives you high-quality products but also professional after-sales service and technical support, helping your production line achieve higher recovery rates and lower operating costs.
Conclusion
Eddy current separators are essential for efficiently recovering non-ferrous metals such as aluminum, copper, and brass in recycling and waste processing operations. Their performance depends on several key parameters, including rotor speed, belt speed, burden depth, pole configuration, and magnet type. Proper adjustment and maintenance of these factors can significantly improve separation accuracy, material purity, and overall productivity. When selecting equipment, it's important to consider your material type, particle size, and processing volume. Partnering with a reputable manufacturer like Great Magtech ensures you receive high-performance machines backed by expert technical support and reliable after-sales service.
Recycling plants around the world rely on Eddy Current Separators to separate and recover non-ferrous metals. The technology utilises high strength magnetic forces to repel and eject non-ferrous metals in many different forms including aluminium beverage cans, car frag, and foils.
The large UK-based metal recycler, the Bird Group, developed the world’s first Eddy Current Separator in . The significance of the development resulted in the Bird Group receiving the Prince of Wales’ Award for Technology and Innovation and the Tomorrow’s World Award to Technological Development and Innovation. The technology would change the landscape of metal recycling, enabling easier and more efficient recovery and separation of valuable non-ferrous metals such as aluminium and copper. In the following decade, Eddy Current Separator technology evolved with many different suppliers offering their own designs with varying separation abilities.
- Technical product information: Eddy Current Separators
Successfully separating non-ferrous metals with an Eddy Current Separator depends on a number of critical criteria. In this technical review, we assess five key design characteristics with the aim of dispelling some myths about the Eddy Current Separator. These include:
- The rotational speed of the magnetic rotor;
- The speed of the feed belt;
- The length of the feed belt;
- The necessity of pre-removing ferrous metal;
- The relative magnetic strength of the rotor;
Rotor Speed
An Eddy Current Separator consists of a magnetic rotor with alternating magnetic poles (north/south) rotating inside a slower rotating non-metallic shell. A rubber feed belt, rotating at the same speed as the non-metallic shell, conveys material into the rapidly rotating magnetic field generated by the rotor where non-ferrous-metals become induced by magnetically-driven eddy currents. The eddy currents generate an electric current in the non-ferrous metal particle, which then produces its own magnetic field. This magnetic field reacts with the magnetic field of the rotor, resulting in a repulsive effect that enables the displacement and, therefore, separation of the non-ferrous metal.
This separation is in accordance with two laws:
- Faraday’s Law of induction, where electrical currents are induced when conductors enter a rotating magnetic field (e.g. non-ferrous metals such as aluminium);
- Lenz’s Law, where the induced eddy currents create a magnetic field that opposes the magnetic field that created it. This results in the repulsion of a conductor away from the magnetic source;
In theory, an increase in the number of polarity changes per second would have a positive effect on the separation efficiency (i.e. more flux change generating a greater reactive magnetic field in the non-ferrous metal). However, investigative tests show that as the rotor speed increases (thus increasing the rate of change of polarity) the actual displacement or thrown distance of a non-ferrous metal particle reaches a peak. After reaching a peak, the displacement of the non-ferrous metal particle displacement is sustained or indeed falls, significantly for some smaller particles.
Investigations into the relationship between the magnetic rotor speed and the throw distance of a non-ferrous metal particle identified that the amount of repulsive energy induced into a non-ferrous metal particle is proportional to the dwell time in the field. If this dwell time is too short, then there is less induced energy and, therefore, a reduction in the displacement or throw of non-ferrous metal particle.
Additional considerations include maintenance and wear. With an increased rotor speed there is a higher wear factor on key components such as bearings.
In practice, there is an optimum rotational speed for every magnetic rotor design to produce the best level of non-ferrous metal displacement for each application. This is commonly between 2,000 and 5,000 RPM. The perception that increased rotor speed always produces a higher level of non-ferrous metal separator is misguided.
- Eddy Current Separator Technical Overview by Prof Neil Rowson (Video on YouTube)
Belt Speed
The belt of an Eddy Current Separator conveys material into the rotating magnetic field of the head pulley rotor. The speed of the belt determines the burden depth on the conveyor, the dwell time in the magnetic field, and the trajectory of the material when leaving the belt.
Burden Depth
Optimum separation requires a uniformly thin, monolayer of material. A two-stage feed system produces the ideal feed characteristics. Initially, a vibratory feeder evenly spreads feed material across the whole tray width (which is slightly narrower than the belt width of the Eddy Current Separator). The material feeds onto the faster moving ECS belt, further spreading the material into a single particle depth. Such a burden depth reduces the risk of non-ferrous metal particles colliding with non-metallic materials and, thus, reducing the separation efficiency.
Dwell Time
The belt speed dictates the dwell time of a particle in the rotating magnetic field. A longer dwell time allows more energy induction into the non-ferrous metal particle. In fact, aluminium held in the rotating magnetic field gets exceptionally hot and anneals. An extremely high belt speed often transfers the material too quickly through the magnetic field, reducing the separation effect.
Material Trajectory
The belt speed of any conveyor creates a trajectory of material as it leaves the belt. In operation, higher belt speeds produce longer projections of conveyed material away from the head pulley. Successfully separating non-ferrous metals on an Eddy Current Separator requires an understanding of all the forces imparted on the particles, including the belt speed.
The forces on a non-ferrous metal particle on entering the rotating magnetic field of the Eddy Current Separator include:
- Eddy Current repulsion from the Magnetic Rotor;
- Conveyor propulsion (proportional to the belt speed);
- Gravity;
These three forces combine to produce a Resultant Force that determines the trajectory of the non-ferrous metal particle.
Forces B and C will affect all the material on the conveyor belt, with the Eddy Current repulsion (i.e. force A) only generating a reaction in any non-ferrous metal particle. Therefore, if the size, shape, and weight of all the particles on the conveyor were the same and there was no Magnetic Rotor, the throw trajectory would be the same. Adding in the Eddy Current repulsion changes the trajectory of the non-ferrous particle, propelling it in an upward direction away from the magnetic rotor.
During the commissioning of an Eddy Current Separator, technicians commonly initially run non-metallic material over the unit to check the material trajectory for positioning of the splitter. The addition of the non-ferrous metal fraction enables a comparison of the two trajectories and the optimum setting of the splitter. The splitter enables the separation of the non-metallic and non-ferrous metal constituents.
However, if Force B (the forward force from the feed belt) is increased and all the other forces remain constant, the resultant force vector flattens to a point where the trajectories of the non-ferrous metal particle and non-metallic material cross or are nearly the same. At this point, the limited difference in trajectories prevents a decent separation.
As Eddy Current Separators have different designs of magnetic rotor and the variety of shapes, sizes and characteristics of non-ferrous metal particles is extensive, there is not one belt speed that suits all. The application and installation determines the optimum belt speed.
Feed Belt Length
The length of the conveyor belt of an Eddy Current Separator ranges considerably and there are claims that longer belts improve the level of separation. The function of the belt and the interaction with the other parts of the separation system determines the belt length.
The belt simply transports the material into the rotating magnetic field or ‘separation zone’. For optimum separation, the material must be settled and, ideally, still on the conveyor belt before entering the ‘separation zone’. A long belt provides an extended dwell time for the material to settle.
However, when the material feeds onto the belt via a Vibratory Feeder the particles settle quicker. The action of the Vibratory Feeder evenly spreads the material across the width of the tray before dropping gently onto the moving belt. Regulating the vibration frequency controls the flow rate of the material. With careful adjustment, a monolayer of material flows evenly off the end of the tray onto the faster moving belt. This further splays the material. In practice, including a Vibratory Feeder eliminates the need for a long Eddy Current Separator belt.
For some specialist applications, direct feed of the material from a Vibratory Feeder (with a non-metallic tray or tray tip) directly into the ‘separation zone’ may even negate the need for any belt. However, the belt also functions as a cleaning device, transporting any attracted magnetic material out of the product stream and away from the shell of the Eddy Current Separator rotor.
Ferrous Metal Removal
Despite the Eddy Current Separator being a separation system based on magnetic principles, there is often confusion regarding the separation of ferrous metals.
In essence, an Eddy Current Separator has a belt and two pulleys, of which one is magnetic. Due to the laws of physics, the magnetic head pulley (or Rotor) attracts ferrous metal. Therefore, the system would separate ferrous magnetic metals from non-magnetic materials. However, there are some limitations.
Concentric Rotors
Eddy Current Separators with Concentric Magnetic Rotors have a magnetic rotor with the same gap between the magnets and the outer non-magnetic shell for the whole circumference. The high-strength of the magnetic rotor (constructed with neodymium rare earth magnets), holds any ferrous metal, making discharge from the belt difficult. Also, due to the high-speed rotating magnetic field, undischarged ferrous metal remains on top of the belt at the bottom point of the magnetic rotor. Due to the constant rotating and changing magnetic field, the metal vibrates and gets very hot. Subsequently, when the conveyor belt stops, the hot ferrous metal could burn through the belt and onto the surface of the non-metallic shell. Over time, this ferrous metal wears away on the surface of the non-metallic shell, creating holes. Attracted ferrous metals pass through the holes and attach to the magnets of the rotor, ultimately causing failure.
Eccentric Rotors
The Eccentric Magnetic Rotor design has a smaller rotor mounted in the top quadrant of the non-metallic shell. Therefore, attracted magnetic material moves through a diminishing magnetic field to a point where it falls away from the belt. This ferrous metal often discharges into the non-metallic fraction.
Best Practice
Optimum metal recovery and separation requires a multi-staged approach with specific materials recovered at different stages. Overband Magnets, Pulley Magnets and Drum Magnets preferentially and successfully recover saleable ferrous metals prior to the Eddy Current Separator. This enables a non-obstructive separation and recovery of non-ferrous metals on the Eddy Current Separator.
Rotor Magnetic Strength
The laws of Faraday and Lenz suggest that the strongest rotating magnetic field would produce a greater repulsive effect. However, in operation this is not the case.
An Eddy Current Separator rotor is constructed from a number of strong permanent magnets (neodymium rare earth or ceramic ferrite) attached to a steel carrier. The dimensions of the permanent magnet (both in length around the rotor and thickness) dictate the throw of magnetic field.
- Longer and thicker magnets produce deeper magnetic fields;
- Shorter and thinner magnets produce shallow intense magnetic fields;
Irrespective of whether the magnet is long or short, the maximum magnetic intensity is on the pole (surface) of the magnet mounted on the carrier of the magnetic rotor. One key design parameter focuses on minimising the distance between the magnet pole and the surface of the belt for there is a significant reduction in magnetic field at distance. This distance is influenced by four variables:
- Carbon fibre wrap: The magnets sit on the rotor’s magnet carrier, which rotates independently inside the non-magnetic shell. Carbon fibre tape, wrapped around the rotor, securely hold the magnets to the carrier;
- The Air Gap: The air gap between the surface of the carbon fibre tape and inside of the shell must be sufficient to ensure no contact, even when the rotor is spinning at high speeds and there may be a small degree of flexing;
- Shell Thickness: Due to the arduous working environments of the recycling industry, the thickness of the shell must be sufficient to withstand wear;
- Belt Thickness: This also applies to the belt thickness, with some applications requiring thicker and more robust feed belt designs.
The combination of the carbon fibre tape, the air gap between the outer shell, the thickness of the shell and the thickness of the belt means that there are several millimetres between the point of maximum magnetic strength (on the pole of the magnet) and the surface of the belt. Once these parameters are set, the next step is to consider the expected performance of rotors with short or long magnets.
Short magnets produce a shallow but intense magnetic field. However, the magnetic intensity is far lower on the surface of the belt than on the pole of the magnet. In contrast, longer magnets throw a deeper magnetic field. In practice this means a magnetic rotor with short and exceptionally strong neodymium rare earth magnets may produce a weaker magnetic field than one constructed from longer standard strength ferrite magnets at the point of separation (i.e. on the surface of the belt).
The effect of a shallow or deep magnetic field makes classifying a magnetic rotor as being ‘strong’ or ‘weak’ is totally dependent on where the measurement to support that description is taken. For example:
In operation the application dictates the selection of magnetic rotor design. Applications where the non-ferrous particle is large (e.g. an aluminium can) and the aim is to project a magnetic field projected into the centre of that particle for maximum separation effect, are more suited to rotors with a deep magnetic field produced by longer magnets. The separation of small non-ferrous metal particles (e.g. as found in plastics) is better achieved using a rotor with a shallow magnetic field with shorter magnets.
Understanding these principles is vitally important when considering a design and type of Eddy Current Separator to suit a specific application. Simply being advised that the actual strength of the magnetic field is the ‘strongest on the market’ will not determine if that Eddy Current Separator Rotor design offers the optimum level of separation.
Selecting an Eddy Current Separator
Understanding the application is key to selecting the optimum non-ferrous metal separator. Our engineers consider the following:
Material
- Particle size range (typically between 3mm and 50mm)
- Material
- Non-ferrous metal particles
- Shape of non-ferrous metal particles (e.g. angular, wire, spherical, etc)
- Moisture level of the feed
- Separation objective
Installation
- Feed conveyor width
- Capacity feeding to the separator including burden depth on feed conveyor
For additional information on Eddy Current Separator or other metal separators such as the Stainless Steel Separator and Overband Magnets, please contact us on:
: Gordon Kerr at
Via the website
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