Arc Shaped Magnets

overview

A flat magnet placed against a curved surface only touches at one point or one line. The rest of the gap is air. Air is a poor conductor of magnetic flux. An arc shaped magnet is ground to match the curve of your housing, shaft, or mating part. The result is full surface contact. This gives you three practical benefits. First, more magnetic flux enters the adjacent component because there is no air gap. Second, the magnet sits mechanically stable without rocking or sliding. Third, adhesive bonding is stronger because the glue joint is uniform across the entire curved face. For these reasons, arc shaped magnets are preferred in sensors, latches, and compact assemblies where every millimeter of magnetic force matters.

Sintered NdFeB is the strongest choice. It is used when you need high holding force or a strong magnetic field from a small curved magnet. Standard grades run from N35 to N52. Maximum working temperature depends on grade: N (80°C), M (100°C), H (120°C), SH (150°C), UH (180°C), EH (200°C), AH (220°C). NdFeB requires a coating because the raw material oxidizes easily. Nickel, zinc, epoxy, and gold are common.

SmCo (Sm2Co17) is chosen for high heat or harsh environments. It works up to 350°C depending on grade. It also resists corrosion without any coating. SmCo costs more than NdFeB, but in some high-temperature designs it is cheaper than using a high-temperature NdFeB grade like UH or EH. Typical SmCo grades include YXG-24, YXG-26, YXG-28, and YXG-30.

Ferrite (ceramic) is the low-cost option. It has much lower magnetic strength than NdFeB or SmCo, but it is inexpensive and does not need a coating for most indoor applications. Ferrite arc magnets are used in large, cost-sensitive products such as toy motors, low-power generators, and simple holding devices. Common grades are Y10, Y25, Y30, Y33, and Y35.

We start from a pressed block or a diametrically magnetized blank. We then grind the inner radius, outer radius, and arc angle using diamond tooling. This grinding step is what gives the magnet its precise curve. We hold tolerances from ±0.05mm to ±0.1mm depending on size. For multi-piece sets, we number each piece so you can assemble them in order around a circle. We also chamfer the edges to reduce chipping during handling. NdFeB is brittle, and a sharp edge can crack if it hits a hard surface. Chamfering is a small detail that saves rejections on your assembly line.

We can magnetize arc shaped magnets in several directions. Radial magnetization puts the poles on the inner and outer curved faces. This is common for sensors and couplings. Axial magnetization puts the poles on the flat top and bottom faces. This is used when the magnet is stacked or when the magnetic field must run parallel to the shaft. Diametrical magnetization puts the poles on opposite sides of the arc. This is less common but used in some rotary sensor designs. We also produce custom multi-pole patterns on arc shaped magnets for encoder rings.

Rotary sensors and encoders. A curved magnet is mounted on a shaft. A Hall-effect or magnetoresistive sensor reads the field from the side. The arc shape keeps the air gap small and consistent as the shaft turns.

Door catches and cabinet latches. Arc shaped magnets fit into curved plastic or metal housings. They hold doors, lids, or panels closed without a mechanical latch. The curved shape allows the magnet to sit flush inside the housing.

Magnetic couplings. Two hubs face each other. Each hub holds a set of arc shaped magnets. Torque passes from one shaft to the other through the housing wall. No seal is needed, so leaks are impossible. This is used in pumps, mixers, and chemical equipment.

Small motors and generators. Arc shaped magnets are used in fractional horsepower motors, toy motors, and low-speed generators. They are glued or clamped inside a cylindrical housing. Ferrite arc magnets are common in these cost-sensitive products.

Magnetic assemblies. Arc shaped magnets are often combined with steel pole pieces, shafts, or brackets. We can supply the magnet alone or work with your assembly team. We also produce matched sets for customers who build complete rings.

Consumer products and toys. Curved magnets appear in magnetic building sets, educational kits, and novelty items. The curve can be decorative or functional. We produce both.

We test magnetic properties on every production batch. We measure residual flux density (Br), intrinsic coercivity (Hcj), and maximum energy product (BH)max. Tests follow IEC 60404-5 or ASTM A977. We also check chemical composition using ICP-OES or XRF to confirm the alloy matches the grade. Dimensional inspection covers inner radius, outer radius, arc angle, thickness, and length. We inspect 100% of critical dimensions. For multi-piece sets, we verify that all pieces in a set have the same radius and angle so they fit together without gaps. We keep full traceability from raw material to finished magnet. Our quality system is certified to IATF 16949, ISO 9001, ISO 14001, and ISO 45001. Products comply with RoHS, REACH, and CP65. Packaging uses anti-magnetic shielding, foam, and export-grade cartons. Large assemblies ship with wooden spacers to prevent movement.

To quote an arc shaped magnet, we need the following: inner radius, outer radius, arc angle, thickness, and length. If you do not have a drawing, a sketch with these dimensions is enough. Tell us the material (NdFeB, SmCo, or ferrite), grade, coating, and magnetization direction. If you are not sure which material or grade to use, describe your application: operating temperature, required holding force or magnetic field strength, and whether corrosion is a concern. Our engineers will recommend the most cost-effective option. We also need to know the quantity and whether you need a one-time sample or ongoing production. For multi-piece ring assemblies, tell us how many pieces make a full circle. We will produce a matched set.

Sample policy: custom samples are available in 10 to 15 working days. Sample fee is refundable against a bulk order. Standard production lead time is 15 to 20 working days for simple arcs and 25 to 35 working days for complex geometries or new tooling.

Can you make an arc shaped magnet from a drawing? Yes. Send a PDF, DXF, or even a hand sketch with dimensions. We will confirm manufacturability and quote.

What is the smallest arc angle you can produce? We regularly produce arcs from 15° to 180°. Smaller angles are possible but may require a minimum order quantity because they are difficult to handle during grinding.

What is the largest arc you can make? We have produced arc shaped magnets with outer radii over 500mm. Large arcs are often used in wind turbines, large motors, and industrial couplings. Please contact us with your dimensions.

Do you offer SmCo arc magnets? Yes. SmCo is available in grades YXG-24 through YXG-30. It is recommended for temperatures above 150°C or where no coating is desired.

Can you supply a complete ring made of arc pieces? Yes. Tell us the number of pieces per ring and the tolerance for the assembled diameter. We will grind the pieces so they fit together with minimal gap.

What is the difference between arc shaped and arc segment? In our factory, arc shaped is a general term for any curved magnet. Arc segment usually means a curved magnet designed for a motor or generator rotor. We produce both. If you are unsure which one you need, send us your application details and we will advise.

How do you ship arc magnets? NdFeB arc magnets are shipped with anti-magnetic shielding to prevent damage to nearby electronics. SmCo and ferrite do not require the same level of shielding but are still packed with foam and sturdy cartons. For large orders, we use wooden crates.

What is the minimum order quantity? MOQ depends on material, size, and complexity. For simple ferrite arcs, MOQ can be a few hundred pieces. For custom NdFeB or SmCo arcs, MOQ may be lower because the material cost is higher. Contact us for a specific quote.

Get a Quote Today! Email: zb16@magnets-world.com. Phone/WhatsApp: +86 18119636123. Address: Room 201, No.15, Longxinli, Siming District, Xiamen, Fujian, China. We reply within 24 hours.