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A magnetic separator is a device that uses a magnet to pull magnetic material out of a mixture so it can be removed or collected. The same principle serves two different jobs: in process and food lines it removes ferrous contaminants (nails, rust, scale, bolts) from dry or liquid product, and in the laboratory a magnetic rack pulls magnetic beads, with their bound target, to the tube wall so the liquid can be taken off. This page is general information about equipment, not advice for a specific plant, product or protocol.
Short answer
A magnetic separator attracts ferromagnetic material out of a flow or a liquid. Industrial designs (overband, drum, plate, grate, hump, trap) are chosen by product form, temperature and cleaning method. Laboratory racks hold tubes or plates against magnets so labelled beads collect on the wall. Neither type removes non-ferrous metals; those need a different principle such as an eddy current separator.
Definition and scope
Eriez, a manufacturer of separation equipment, describes separators as removing “ferrous material such as nails, rust, scale, bolts, welding rod and other contaminants from dry or liquid products” (Eriez feature article, 2021). In the laboratory sense, Thermo Fisher describes its DynaMag racks as quickly pulling Dynabeads-bound target to the tube wall so that liquid can be removed. Both rest on the same physics, attraction of magnetic material to a magnet, but the purpose differs: the process separator discards or catches unwanted metal, while the lab rack captures a wanted target attached to a bead.
How a magnetic separator works in practice
Process and conveyor equipment
Goudsmit Magnetics describes an overband magnet as self-cleaning, continuously drawing ferrous parts out of a material flow, and states that iron removal efficiency “ranges from 70 to 90%” depending on design, product flow and placement. For drum separators it says the product flow falls over the shell while the magnet attracts ferromagnetic particles, and cleats carry the captured metal outside the magnetic field.
Eriez notes that separators perform best when the contamination is presented to the surface of the magnet, which is why a thin burden depth matters. Plate magnets used on chutes and belts are cleaned manually by swinging them away, so flow must be stopped. Drums, pulleys and suspended magnets, by contrast, “can provide for continuous automatic removal of tramp metal without stopping the flow.”
Laboratory racks
In bead-based workflows the magnetic particles bind the target, the tube sits in the rack, the beads move to the wall, and the supernatant is removed. Thermo Fisher lists DynaMag racks by tube format: DynaMag-2 (10 µL to 2 mL, 16 microfuge tubes), DynaMag-5 (1 to 5 mL, up to 8 tubes), DynaMag-15 (1 to 15 mL, 4 tubes), DynaMag-50 (5 to 50 mL, 2 tubes), DynaMag-Spin (10 µL to 1.5 mL, 6 tubes) and DynaMag-96 for plates. Thermo labels these “For Research Use Only. Not for use in diagnostic procedures.”
Types of magnetic separator
Every row below traces to the named manufacturer page, read 2026-11-08.
| Type | What the source says | Source |
|---|---|---|
| Overband magnet | Hangs above a belt; permanent (ferrite or neodymium) or electromagnet; self-cleaning; continuous removal of iron or steel from high volumes | Goudsmit |
| Drum separator | Product falls over the shell; cleats carry captured metal out of the field; described as almost maintenance-free | Goudsmit |
| Magnetic head pulley | Listed among belt-conveyor magnetic separators; pulleys can remove tramp metal without stopping flow | Goudsmit; Eriez |
| Plate magnet | For chutes and belts; cleaned manually by swinging away, flow must stop | Eriez |
| Grate magnet | Tubes (1 inch in the example given) arranged in a grid for dry, free-flowing product; damp product may not flow through | Eriez |
| Hump magnet | Two plates, used in pneumatic lines | Eriez |
| Magnetic trap | Grate or plate type for liquids and slurries | Eriez |
| Eddy current separator | Targets non-ferrous metals (aluminium, copper, zinc, gold, silver, magnesium); a different principle from magnet attraction | Goudsmit |
| Laboratory magnetic rack | Pulls bead-bound target to the tube wall so liquid can be removed; formats from 96-well plates to 50 mL tubes | Thermo Fisher |
Where it matters for labs, plants and supply decisions
Eriez lists the factors that shape which process separator fits an application. Use them as a specification checklist when talking to a supplier, which Eriez itself advises doing “as early in the decision cycle as possible”:
- Product form: dry free-flowing, damp or sticky, or liquid and slurry (grate, plate, hump and trap designs suit different forms).
- Magnet material: ceramic (ferrite) suits relatively large ferrous pieces; rare earth magnets (neodymium-iron-boron, samarium-cobalt) are described as more than 10 times the strength of ceramic and can remove very fine or weakly magnetic contamination such as rust, scale and work-hardened stainless steel; alnico is seldom used but may suit temperatures above 400°F (204°C).
- Temperature: permanent magnets lose strength when hot, and some of that loss is irreversible, so ambient and clean-in-place temperatures should be stated when specifying.
- Burden depth: thinner product layers expose contamination to the magnet surface.
- Cleaning method: manual (flow stops) or self-cleaning (continuous).
- Strength comparison: pull tests, gauss readings and product simulations are used, but competing products are hard to compare because their magnetic circuits differ.
In laboratories the relevant matches are tube format and volume range against the rack’s listed capacity. Racks are one of several ways to separate material at the bench; for separation by sedimentation see what a centrifuge is, and for other bench equipment explainers see what a sonicator is and what a cuvette is.
Common misunderstandings
- “A magnet removes all metal.” It attracts ferromagnetic material only. Aluminium, copper and similar non-ferrous metals need an eddy current separator, which works on a different principle (Goudsmit).
- “A separator removes 100% of the iron.” Goudsmit’s own range for an overband is 70 to 90%, depending on design, product flow and placement.
- “Stronger is always better.” Eriez says ceramic magnets are best for relatively large ferrous pieces, while rare earth magnets target fine or weakly magnetic contamination; the right strength depends on what must be caught.
- “Magnets keep their strength.” Permanent magnets lose strength when hot, and some loss does not recover (Eriez).
- “A lab rack is a purification kit.” A rack only holds the tubes against magnets; the beads and reagents are separate products, and Thermo marks its racks for research use only.
FAQ
What is a magnetic separator used for?
Industrial units remove ferrous contaminants such as nails, rust, scale and bolts from dry or liquid product (Eriez). Lab racks collect magnetic beads and their bound target at the tube wall (Thermo Fisher).
What is the difference between an overband and a drum separator?
An overband magnet hangs above a conveyor belt and continuously lifts ferrous parts from the material flow. A drum separator has the product fall over a magnetic shell, with cleats carrying captured metal outside the field (Goudsmit).
Can a magnetic separator remove aluminium or copper?
No. Those are non-ferrous; Goudsmit describes eddy current separators as the equipment aimed at aluminium, copper, zinc, gold, silver and magnesium.
Do magnetic separators need to be stopped for cleaning?
It depends on the type. Eriez says plate magnets are cleaned manually with flow stopped, while drums, pulleys and suspended magnets can remove tramp metal automatically without stopping the flow.
What does a laboratory magnetic rack do?
It holds tubes or plates beside magnets so bead-bound target is pulled to the wall and liquid can be removed. Thermo Fisher lists formats from 96-well plates to 50 mL tubes.
Sources
- Goudsmit Magnetics, belt conveyor magnetic separators: goudsmitmagnetics.com/en-us/products/belt-conveyor-magnetic-separators (read 2026-11-08).
- Eriez, “How to Choose and Use the Best Metal Separators and Detectors for Your Food Application” (2021): eriez.com/Documents/Feature-Articles/Eriez-Choose-and-Use-Magnetic-Separators-FoodQuality-Feature-Article.pdf (read 2026-11-08).
- Thermo Fisher Scientific, DynaMag magnets: thermofisher.com/magnets (read 2026-11-08).
