Judge an industrial magnetic separator on field strength at the working distance, capture performance under your real burden, and build details that survive dust and heat. A pole-face gauss number proves almost nothing. Measure the field 50 mm and 100 mm off the surface at operating temperature, run a seeded test with marked tramp metal, inspect the frame, bearings and wear liners, and demand the magnet grade with its temperature rating. Quality is a set of checkable facts.

Key Takeaways

✔ Field at the gap decides capture, not the headline gauss figure ✔ Magnet grade and temperature rating decide what the field is after two years ✔ Seeded capture tests settle arguments datasheets can't ✔ Frame stiffness, bearing access and face liners separate good units from cheap ones ✔ The spares list is an honest statement of what the maker expects to fail

Summary Table

Definition

An industrial magnetic separator is a machine that projects a magnetic field across a material stream and holds ferrous contamination against a surface — a magnet face, a drum shell, a self-cleaning belt — while the cleaned material passes. The quality question is narrower than it looks: not "how strong is the magnet" but "how much field arrives at the metal, at your burden depth, at your feed temperature, for how many years." Everything in the evaluation follows from that restatement. The Magnetic Separators range spans several machine classes, and each must be judged against its own duty.

Working Principle

The gap between magnet and burden is where the field has to work — and where datasheets go quiet.

A magnetic circuit — ferrite, NdFeB or SmCo blocks arranged against a steel pole system — projects field across an air gap into the burden. Ferrous pieces experience force toward the pole; the machine then either holds them for manual cleaning or carries them out of the field zone on a cleated self-cleaning belt. Drum and roller designs rotate the circuit inside a stainless shell, so captured metal travels with the shell and releases where the field ends.

Two physics details drive most disappointments. Field falls off roughly with the inverse square of distance, so doubling the gap can leave a quarter of the capture force. And heat demagnetises: NdFeB loses about 0.1% of remanence per degree, with steeper loss past the grade's rated ceiling. Both effects compound quietly. The machine that tested strong on the workshop floor can be weak on a hot line over a Crushing discharge with a deep burden.

Benefits

A properly evaluated separator pays back in three ways. Downstream protection: a nut or bucket tooth reaching a crusher or belt scale costs far more than the magnet that stops it. Product quality: iron contamination in shipped concentrate triggers claims, and assay trending catches the drift before the customer does. And predictability — a unit specified with the right grade and gap runs for years without anyone thinking about it, which is exactly what a good wear part should do.

Applications

Tramp iron removal over conveyors is the classic duty, handled by suspension magnets and the Electromagnetic Overband Separator class for deep burdens. Continuous duty uses a Magnetic Drum at conveyor head pulleys or a Magnetic Roller inline on dry granular flows. Where the stream has already been scalped by Screening, the separator sees a cleaner, coarser burden and capture improves for the same field. Non-magnetic but conductive contaminants need a different physics entirely — that's the territory of Electrostatic Separators.

Material Comparison

Read the table as a system, not a ranking. NdFeB at 180 °C continuous may deliver less field than ferrite in the same housing. The grade only matters alongside the temperature it will actually see.

Application Comparison

For deep, continuous burdens the Self-Cleaning Electromagnetic Separator removes manual cleaning from the operator's shift entirely.

Industry Application Matrix

Selection Guide

Work the five inputs in order. First the stream: temperature, burden depth, moisture, and what the tramp iron actually looks like — pieces from your own plant, not catalog assumptions. Second the machine position: over a belt, at a head pulley, inline. Third the cleaning expectation: manual, self-cleaning, or unattended. Fourth the field requirement, calculated from gap and burden rather than quoted from habit. Fifth the operating reality — who adjusts it, who greases it, and what happens when the belt tracks off at 3 a.m.

A unit that survives this list is usually the right unit. The Magnetic section arranges the range by duty rather than by size, which speeds up the first two inputs.

Procurement Guide

Put five requests to every supplier, in writing. A field-versus-distance curve for the actual model at operating temperature. The magnet grade, temperature rating and coating spec. An agreed capture-test protocol with seeded metal sizes from your plant. The wear-part list — Magnetic Separation Spares — with lead times and prices. And a reference installation on comparable duty.

Then watch the answers. Field figures without distance, grades without temperature ratings, and capture percentages without feed conditions are all numbers that can't be checked. Magnetic Drums & Rollers supplied against a written curve are comparable; machines supplied against flyers are not.

Failure Analysis

Shell thickness, grade and block spacing decide both the field and how long it survives.

Maintenance Guide

Measure the field annually at fixed reference points and log the readings — trend beats any single number. Grease the bearings on schedule and keep the cooling paths clear on electromagnetic units. Inspect wear liners quarterly on heavy tramp duties. On self-cleaning units, track belt tension and idler alignment, because tracking problems compound quietly until the belt fouls the frame. And keep the critical spares on site: a liner or bearing set costs little, while a day of downtime at a head pulley rarely does.

Case Study

Customer Type: Iron ore processing plant, conveyor protection duty Ore Type: Tramp steel from primary crushing, mixed shapes and masses Operating Conditions: 1400 mm belt, 350 mm burden, feed at 70 °C, continuous operation Problem: Frequent crusher damage despite a separator rated at 12,000 gauss on its datasheet Solution: Field survey showed only 900 gauss at the actual working gap once temperature and distance were accounted for; unit replaced with a correctly projected circuit and the suspension height was re-set against the measured burden Result: Tramp-related crusher stoppages effectively eliminated over the following year; iron-in-product assays held flat across four quarters

FAQ

Is a higher gauss rating always better? No. Capture happens at the working distance, and a tighter circuit can outperform a bigger number. High gauss with poor projection wastes strength inside the housing. Match the field to burden depth and belt speed first.

How do I test capture performance myself? Run a seeded trial. Mark representative tramp pieces, introduce them upstream at your real bed depth and speed, then count what the separator holds. Three burden depths, flat and round pieces both, and you'll know more than any brochure told you.

Why does my separator weaken on hot feed? The magnet grade is losing remanence with temperature. NdFeB grades lose roughly 0.1% per degree, faster past their rated ceiling. Check the grade's temperature rating against the actual feed temperature, not ambient.

What should be in the wear-part list? Liners, belts and take-up hardware for self-cleaning units, bearings and seals for drums, and for electromagnetic units the coil service kit. A maker who stocks these knows what fails; ask for lead times, not just part numbers.

How often should field strength be checked? Annually at fixed reference points, and after any impact or coil repair. Log the trend. Gradual decline is normal; a sharp drop means heat, shock or corrosion, all of which get worse if ignored.

Can one separator protect the whole plant? Rarely. Burden depth and position decide capture, so protection usually means a primary unit over the main feed conveyor plus drums or rollers at critical points. Design the coverage from the flowsheet, not from a single purchase.

Are electromagnetic units better than permanent ones? Only where you need adjustability or very deep burdens. Electromagnets cost more to run and need cooling, but their field can be controlled. For most tramp duty a well-specified permanent circuit is simpler and cheaper over life.

What's the most common specification mistake? Quoting and buying on pole-face gauss. It measures the magnet, not the duty. Insist on the field-versus-distance curve and the capture protocol, and the mistake disappears from the process.

Conclusion

Evaluating a magnetic separator is a checklist, not a negotiation. Field at the gap, at temperature. A capture test you designed. Build details you can see with your own eyes. Spares that admit what wears. Suppliers who answer those requests in writing have already told you how they engineer; the rest have told you how they sell.

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• Electromagnetic Overband Separator

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