SmCo ring magnets - parallel to the axis
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1Read the three dimensions and the magnetisation
Rings are described by the outer diameter A, the inner diameter B and the height C. The magnetisation runs parallel to the axis, so the poles sit on the two flat annular faces and the ring works through its face, not through the inner or outer rim.
A shaft passing through the hole will therefore not be gripped by the ring; the hole is a fastening feature, not a magnetic one.
2Start from the hole and the seat
Choose the inner diameter first, because it has to clear whatever passes through it, and the outer diameter second. Leave clearance rather than aiming for a tight fit: SmCo is the most brittle of the common magnet materials and a forced fit cracks the ring instead of seating it.
Since the magnets are supplied bare, there is no plating thickness to allow for, so the stated hole is the hole you get.
3Never clamp it like a steel washer
- Always use a large washer that spreads the load across the flat face.
- Use a cylindrical or pan head screw. The hole is straight through, so a countersunk head wedges against the edge and splits the ring.
- Tighten by hand and use a thread locking compound for vibration instead of more torque.
- Where possible, bond the ring rather than clamping it at all.
4Buy it for the working conditions
These rings fall in the 201 to 350 °C band, with working temperatures around 300 °C, and they resist corrosion, which is why we supply them without surface treatment. Their force also changes very little with temperature, roughly 0.03 % per degree against roughly 0.11 % per degree for neodymium.
That combination is why SmCo rings end up in hot rotating assemblies, sensors and instruments rather than in ordinary fixings.
5Check whether you really need SmCo
A samarium ring costs many times more than the neodymium equivalent and considerably more than a ferrite one. If your assembly stays below 80 °C, a neodymium ring will do the same job far more cheaply; if the force requirement is modest and the temperature high, a ferrite ring may be enough.
Tip: If you cannot find the dimensions you need among the stocked rings, tell us the outer diameter, the hole, the height and the working temperature. Custom SmCo pieces can be quoted, and for a rotor or a sensor assembly that is often a better route than compromising on a dimension.
Related categories to the SmCo ring magnets category
- SmCo cylinders
- SmCo blocks
- SmCo cylinders by diameter
- SmCo cylinders by height
- Neodymium ring magnets
- Neodymium rings by inner diameter
- Ferrite ring magnets
- Magnets with holes
- Heat-resistant magnets
- Neodymium 201 to 350 °C
- Ferrite 201 to 350 °C
- All samarium magnets
- All magnets
Frequently asked questions about SmCo ring magnets
On the two flat annular faces. These rings are magnetised parallel to the axis, so the field runs through the height and the magnet works through its face. The inner and outer rims are magnetically neutral, which means a shaft passing through the hole is not gripped by the ring.
No. The hole runs straight through and is not countersunk, so a tapered head wedges against the edge and splits the magnet. Use a cylindrical or pan head screw with a large washer that spreads the load across the flat face, tighten by hand only, and where possible bond the ring instead of clamping it.
SmCo resists corrosion, so it is supplied bare. Besides the durability, this helps with fit: there is no plating thickness or plating tolerance to allow for, so the stated inner and outer diameters are the real ones, which matters when the ring goes into a machined seat.
These rings fall in the 201 to 350 °C band, with working temperatures around 300 °C, and their force changes by roughly 0.03 % per degree compared with roughly 0.11 % for neodymium. The exact maximum working temperature is listed in the parameters of each product.
Custom SmCo pieces can be quoted on enquiry. Send us the outer diameter, the inner diameter, the height and the working temperature of the assembly, and we will tell you what is feasible. For a rotor or a sensor, a custom ring is often a better answer than compromising on a dimension.
An SmCo ring gives you a fastening hole in a magnet that keeps working at around 300 °C and does not corrode, which is why we supply it without any surface treatment. The rings are magnetised parallel to the axis, so they work through the flat face, and because there is no plating, the stated hole and outer diameter are the real ones when you machine the seat. Dimensions outside the stocked range can be quoted as custom pieces.
