The power of magnetic waves is evident to any Boy Scout with a compass. A Dutch firm is applying amplified magnetic force to the task of peeling an onion.

Rare earth isn’t just a rock band; it’s also a group of 17 chemical elements, some with notable magnetic properties critical for permanent magnet alloys for cordless tool motors and computer hard drives. A group of Dutch engineers recently harnessed the power of rare earth magnets to manipulate the motion of onions as they are peeled, replacing mechanical motion with the frictionless force of permanent super magnets.

Founded in 1959, Dofra Foodtec bv fabricates a line of machinery for washing, slicing and adding value to mushrooms, peppers, potatoes and other crops. The company’s latest innovation is a magnetic-driven onion peeling wheel, with both a mechanical and magnetic peeler. With the device, operators position onions in a metal cup, where they are oriented toward a peeling knife. But instead of relying on springs, friction drive belts and metal clamps, the new machine utilizes a double-horizontal, magnetic-driven holder to secure and rotate the onions as they are cut and peeled. The result is less product damage and waste, fewer parts and greater throughput, primarily because six instead of four onions rotate on the wheel. The higher capacity is possible because of a reduction in machine components, resulting in more operating space.

The new peeler is the culmination of a three-year development project headed by John de Groot, CEO and, since 2001, co-owner of Dofra. De Groot earned an undergraduate degree in computer science at the Poly Technical School for the Sciences in Venlo, the Netherlands.

FE: Had you used permanent super magnets previously?

De Groot: To a limited degree, though never in as comprehensive a manner as with the onion peeler. We actually were able to get some patents for the technology, which was a little bit of a surprise to me. We still have a conventional onion peeler in our portfolio, but since the new machine was introduced, no one has placed an order for it. Everyone wants to buy the new machine, even though it costs more.

FE: What precipitated the redesign?

De Groot: Many of our customers are onion processors. It’s a big crop worldwide and transcends different cultures. We all are huge onion eaters, in both whole and chopped forms and as a dry or powdered ingredient. It’s a common ingredient in soups and all sorts of dishes.

There are perhaps 10 OEMs of onion peeling machines worldwide, including ourselves. We were evaluating the conventional machines and asking customers what they did and didn’t like about them. The waste stream is a source of pollution that processors must address with frequent cleaning, and that requires downtime. Peelers typically operate 24 hours a day, seven days a week until the work is completed. Normally, the machines rely on springs and belts to move and control the onions, and those components are subjected to stretching and failure. From the customers’ perspective, failure always occurs at the worst possible time for production.

We conducted several brainstorming sessions where we asked ourselves how we might remove the belts and springs and deliver a machine that is more cleanable and requires less maintenance. An early design involved gear-toothed wheels that would convey the onions, but that would have exacerbated the sanitary issue. Next, we considered electromagnetics, but that would require electrical wiring that would pose problems during washdown. Finally, we considered permanent magnets, which are superior from a sustainability standpoint because they require less water and chemicals to clean and don’t consume any electricity. The magnets are not subject to friction and wear and don’t suffer any loss of their magnetic field unless they are heated to above 80˚C (176˚F). Even if an application requires operating at very high temperatures, specialty permanent magnets are available, though they are more costly.

FE: What were the key challenges in the R&D process?
De Groot: The power of every magnet, the Gauss value, has a distinct curve, including a part close to the middle that is almost linear. That is the part of the curve we were interested in, the range where there is a linear relationship between magnetic strength and distance to the opposite magnetic pole. Unfortunately, you cannot ask a supplier of permanent magnets, “Give me the curve of your magnet.” They don’t know. We had to buy a small testing machine and measure the curves for about 25 different super magnets. That was a critical first step in devising a system that incorporates 48 large magnets and about 200 small ones to control the precise movements of the onions through the magnetic field.

Three years ago, virtually all rare earth mines outside of China had closed because of declining prices. The only place to source desirable magnets for our machine was China, and it took 12 weeks for suppliers there to deliver them. Now, prices for rare earth are up dramatically and everyone is digging again, but securing the various rare earth magnets stretched out our timeline.


FE: How many design iterations did you build?

De Groot: We built two prototypes. With the first, we left the machine running through the night. When we returned in the morning, the sheet metal had bent because of the constantly moving magnetic force in the machine. We started off with 2 to3mm-thick metal and gradually increased the thickness. The final design uses 8mm-thick stainless steel.<br><br>
The magnetic force is tremendous. If your finger were to get stuck between two of the larger magnets during assembly, you would risk serious injury. We calculate the power to be 860kg (1,892 lbs.).

FE: What type of control architecture does the peeler use?

De Groot: You can control a machine with a PLC or by mechanical means. Early on, we chose mechanical controls because we have many customers in remote areas, where technical support doesn’t exist. Peeling raw onions adds a lot of value, and our philosophy was to provide a system that the farmer can repair himself, if something breaks down. Some of our customers don’t have e-mail; if they were to see a machine with electronic controls, they would freak out.<br>

FE: How did you determine a six-onion peeling wheel was optimum?

De Groot: In principle, the more the merrier. Conventional peelers have about 600 parts and handle four onions; ours has around 150 components and handles six. We wanted a cleanable design in a machine with the same footprint as a mechanical peeler. That makes it easy to replace old peeling machines with this unit.

FE: Given product variability, are changeovers necessary as size varies?

De Groot: Other machines require range adjustments, and if the variance within a batch exceeds 1 in., loss during peeling increases drastically. With the magnetic peeling wheel, variances of about 2 ½ to 5 ½ inches are handled without adjustment. The upper limit will be higher in the next generation because we have some Spanish customers. Their onions are like small footballs.

FE: Is a fully automatic peeling system on the horizon?

De Groot: We’re working on an automatic onion aligning system at the moment. It will automatically detect if alignment is within specified parameters, then feed onions into the peeler, eliminating operator involvement.


FE: How many people were involved in the R&D effort?

De Groot: The project team typically involved five to seven individuals, including three engineers who worked on it from the beginning. Two of the engineers were recent graduates, and they had very fresh ideas. In fact, one of them came up with the idea of using rare earth magnets. The third engineer has worked for years with onion processors, and his understanding of the customers’ needs and operating conditions was invaluable in guiding the project from feasibility work to the finished machine. I served as the project manager.

FE: When did the new machine make its commercial debut?

De Groot: We introduced it in May at the United Fresh Produce Association’s expo in New Orleans. We’re very proud that our first order came from Steve Gill, whose company is the US trendsetter. No OEMs had sold him any equipment before: Gill’s Onions designed and built all its own machines. When he saw the magnetic-driven peeling wheel, Mr. Gill said, “It’s a dream machine. Can I have three?”