Trapezoid

A profile, not a block

A trapezoid is not a rectangle with a corner missing. It is a profile with an included angle, and that angle is what the part is bought for: it fills a seat that is not rectangular, usually a wedge-shaped gap or a curved housing where a square block would leave a void at one end.

Because it is a profile, the drawing has to carry more than overall size. Top width, bottom width, height and thickness describe the outline; the angle describes the relationship between the two parallel sides, and a part quoted on the four dimensions alone has not yet said which trapezoid it is.

The taper is a die question before it is a dimension

Any pressed part has to come out of its die, and a taper is where that matters most. Whether the angle sits along the pressing direction or across it changes the tooling, and it changes what the part can hold on the two angled faces. This is why the angle belongs on the drawing as a dimension with a direction, not as a note.

Where an angle cannot be released by the die, the honest options are a different geometry, a cut part, or a segmented arrangement — not a tolerance concession. It is better to establish that before the drawing is issued than to discover it at tooling.

Why this one is wet-pressed ferrite here

The route currently worked for this geometry is wet-pressed ferrite. Wet pressing compacts a slurry at 30–40 % water content and drains that water during the press, which is what lets the particles align as the part is formed; that is the difference that matters where the flux per unit volume has to carry a narrow or awkward profile.

Ferrite also removes two problems at once. It needs no coating, so the angled faces are delivered as they are rather than plated, and it tolerates the ordinary environment without an additional process. The material systems listed further down this page are the ones that carry this geometry; a route that is not listed says the route is not confirmed for it — not that a trapezoid cannot be made another way.

Which face does the work

Most trapezoidal magnets are magnetized through the thickness, with one pole on the large face and one on the small one, and the two angled sides are then only fit surfaces. Some are magnetized across the profile instead, so that the flux crosses the narrow dimension and the angled faces become the working ones. The two readings produce different parts from the same outline, which is why the pole direction has to be drawn rather than inferred from the shape.

What follows is a question the outline cannot answer: which of the four sides the assembly seats against. That side carries the tolerance that matters, and the other three carry a general band.

A profile is also an assembly risk

A permanent magnet is brittle, and a trapezoid has two included corners that act as stress raisers on a part that will be pressed or bonded into a seat. Where the assembly pushes the profile into a wedge, the load goes through the narrow end first. That is a handling and fixture question rather than a magnetic one, and it is worth stating when the part is quoted, because the answer can move the tolerance on the angle.

What to send for a trapezoid review

• Top width, bottom width, height and thickness, with the angle and which side it is measured between.
• The pole direction, with N and S, and the face the assembly seats against.
• The seat the part goes into, and whether it is pressed, bonded or clamped there.
• The flux or field the circuit needs, the operating temperature, and the annual quantity.

The table further down this page lists the parameters a trapezoid drawing has to settle before the part can be quoted.