Is your magnet losing strength?

The failure you can’t see

Everything else in your plant announces its problems. Bearings scream, belts squeal, motors run hot, seals leak on the floor. A magnetic separator does none of it. A magnet that’s lost a third of its strength looks exactly like the day it shipped — same stainless shine, same everything — and it will sit in your product stream catching less and less until the metal it missed turns up somewhere expensive. A crusher. A roller mill. A reject bin that’s suddenly busy. A customer.

So don’t look at the magnet — look downstream. Metal-detector rejects creeping up. Wear metal in product that used to run clean. A grate that used to come out furry with tramp metal now coming out nearly bare, while nothing about your incoming material changed. Any of those, and the magnet goes to the top of the suspect list.

What weakens a magnet

Left alone on a shelf, a permanent magnet loses about 1% of its strength in a hundred years. Magnets don’t get to live on shelves:

How to pull test

A pull test measures the force it takes to pull a standardized steel test piece straight off the magnet face with a calibrated scale. It’s the simplest reliable way to trend a magnet’s health — if you hold the method steady:

• Clean and inspect the face first. Buildup chokes the reading and hides housing damage.
• Pick a test piece and never change it. Sphere or plate, matched to the magnet type — and then the same one, every test, forever. Swapping pieces can move the numbers double digits and turns your trend line into fiction.
• Test the middle of the working face. Edges and ends don’t tell you what the magnet does where the product actually runs.
• Pull smooth and straight, and log the breakaway force. Safety glasses on — when the piece lets go, it lets go all at once.
• Pull three or four times and average. Consistency is the whole point; one pull proves nothing.
• Write everything down — magnet, location, test piece, spacer, date, readings. This year’s number only means something standing next to last year’s.

Pull test vs gauss meter

You’ll hear both terms, and they answer different questions. A gauss meter reads magnetic field intensity at a point on the surface — the number that specifies a magnet’s design, and the one some food-safety standards want for validating separators. A pull test reads actual holding force on actual steel — less abstract, easy to repeat on a catwalk, and ideal for tracking a magnet against its own history. There is no fixed conversion between ounces of pull and gauss, so stop looking for one. The practical program: gauss to specify and validate, pull tests to verify and trend — same method, same test piece, every single time.

Replace or keep?

• Holding its baseline: keep it, clean it on schedule, retest next cycle.
• Down, but less than 20% from baseline: watch it — shorten the retest interval and hunt for a cause you can remove: heat, impact, housing damage.
• More than 20% below baseline, or sliding 15–20% inside a year: replace it — without debate anywhere the magnet is a critical control point. Permanent strength loss is exactly that. It is not coming back.
• Cracked, swollen or corroded housing: replace it regardless of what it pulls. In food or pharma duty, a compromised housing is its own contamination story.

Frequently asked questions

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