Neodymium Block Magnets 40x20x10 mm

A 40x20x10 mm neodymium block magnet is a rectangular bar of sintered Neodymium (NdFeB), forty millimetres along, twenty across and ten through, ground on the faces that do the work and plated to keep water off an alloy that rusts. This is what a shop buys after a small disc has already been tried and the object being held turned out to have weight and a habit of sliding, since the long face gives the joint somewhere to sit and the ten millimetres gives the flux a route that is not straight through the air

On a block of this size the coating is the decision people get wrong rather than the grade, because a bar this heavy is handled, dropped and slid across benches. Nickel-copper-nickel is what most of them leave with, and the table compares it against the three alternatives we quote, with the thickness each is laid down at and the job it suits. Zinc is cheaper and duller and will not forgive a damp corner. Black epoxy goes on thicker than either and is what a block destined for a gate, a boat hatch or an outside corner should be ordered in. Passivation is a film a micron or two and is meant for a sample that stays in a tray.

 

Where blocks of this shape and size are used. On a machining table a temporary clamp is often nothing more than one of these laid on top of the plate being milled, and the forty millimetres of length gives an operator something to pry against when it comes off. Timber box lids and cabinet doors close over a pair sunk into a rebate so nothing shows when the joinery is shut. A van fitment keeps a crate behind a steel lip with two of them, and an exhibition crew fixes a panel to a steel frame with four because the wall has to come down again on Sunday.

Ten millimetres is thick enough that the block gives up little of its field into a plate a few millimetres deep, and thin enough that the surface still does the work. A block holds best with its long axis across the load rather than along it, because the poles sit on the broad faces and the steel behind has to carry the flux from one to the other, and charging through the ten millimetres is standard. A design that wants the poles on the short ends is a different drawing rather than a different magnet.

Tolerance holds to about ±0.1 mm on all three dimensions once ground, the corners are chamfered so the plating is not lifted when the block is slid across a table top, and material is N42 as standard with N52 for a job that has run out of room.

If the drawing has settled on a 40x20x10 mm neodymium block magnet, send the quantity, the coating you want and what the block will pull against, and we will confirm grade and magnetising before quoting. Other sizes are cut and ground to drawing.

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