A tramp metal detector finds stray metal in the material on the belt and reacts (alarm, marker, or belt stop) so someone can pull the item out by hand. A magnetic separator does the opposite job: it lifts ferrous tramp off the belt on its own, continuously, with no belt stop and no manual step. So the short answer is that a detector tells you metal is there while a magnet takes it away, and plenty of sites run both. Which one your conveyor needs depends on the kind of tramp you actually get, how deep the material sits on the belt, your belt speed, and how much a belt stop costs you in lost production.
We supply, install and service both: our own tramp metal detector, and magnetic separators through our separation and detection range. Here’s how we walk a site through the choice.
What does a tramp metal detector actually do?
A tramp metal detector (TMD) is a coil arrangement the belt passes through, usually a frame around or under the belt. When metal moves through the field, the detector picks up the disturbance and responds. Depending on how it is set up, the response can be an alarm and light, a paint or flag marker on the belt so the spot is easy to find, or a belt stop so the item can be removed before it travels any further.
The key point is that a detector removes nothing itself. It is a sensor with a warning attached. Its value is catching what a magnet cannot: metal buried deep in the burden, items too heavy to lift, and non-magnetic or weakly-magnetic tramp such as manganese steel digger teeth, stainless offcuts, or worn bar and chain. Those are exactly the items that wreck a crusher, a sizer or a mill, so a detector earns its place as the backstop. Most sites want ferrous metal caught first, and many detectors also pick up non-ferrous and manganese steel at lower sensitivity. The smallest piece you genuinely need to catch is what sets the sensitivity.
What does a magnetic separator do differently?
A magnetic separator is a magnet suspended over or across the belt that pulls ferrous tramp straight out of the material stream. There are two common types. A fixed suspended magnet holds the caught metal against its face until someone cleans it off. A self-cleaning belt magnet has its own belt running across the magnet face, so it carries the caught metal off to the side and discharges it into a bin, on its own, without anyone stopping the conveyor.
The trade-off is what a magnet can and cannot do. It only catches ferrous metal, and only what it can physically pull out of the burden. It will not touch manganese teeth or stainless, and a heavy item bedded deep in a thick material layer may sit below its reach. But for the everyday drip of loose bolts, plate, weld offcuts and broken ferrous parts, a magnet clears them continuously with no interruption to the belt.
Which does my conveyor need?
They protect the same things: crushers, sizers, mills, and the belt itself. The classic loss event is a digger tooth or a length of bar going through a crusher, or a sharp item slitting a belt, either of which can cost far more than the equipment that would have caught it.
Because the two do different jobs, the answer for many conveyors is that they are complementary rather than rivals (more on running both below). If you can only fit or fund one, the choice comes down to your material and your risk. A magnet alone suits sites where the tramp is almost all loose ferrous metal near the surface of a modest burden. A detector alone suits sites where the real danger is non-magnetic or deeply buried items, or where a magnet is impractical, accepting that catching one means stopping the belt.
What affects how well a detector works?
A few site conditions matter more than the brochure:
- Steel-cord belts and metal splices. A steel-cord belt or a belt joined with metal clips looks like tramp to a detector, because it is metal moving through the coil. This has to be accounted for in the selection and setup so the belt itself does not trigger constant false alarms. Fabric belts are generally the simpler case. This is one of the first questions we ask, and the usual cause of false trips (see why a metal detector keeps false tripping).
- Burden depth against sensitivity. The deeper the material sits on the belt, the further a small item can be from the coil, which works against fine detection. There is a genuine trade-off between how small a piece you want to catch and how deep and fast the material is moving. A number here depends on the burden depth and belt speed, so we do not quote one blind.
- The smallest tramp size you need to catch. Pushing for very small items raises sensitivity, which raises the false-alarm rate and the nuisance-stop count. It is worth being honest about the smallest piece that actually matters for your downstream gear rather than setting the finest sensitivity by default.
What affects how well a magnet works?
For a magnet, the deciding factors are physical:
- Reach into the burden. A magnet's pull falls off quickly with distance, so a deep material bed and a big lump size both push tramp out of range. Thick burdens and large lumps are where magnets start to miss things a detector would still catch.
- Self-cleaning or manual clean. A self-cleaning unit discharges on its own and suits high-tramp or hard-to-access spots. A fixed magnet is simpler and cheaper but needs someone to clear it, and a magnet packed with old tramp stops working.
- Position on the conveyor. A magnet over the head pulley catches material as it thins and throws off the belt, while a mid-belt suspended unit reaches down into a running burden. The right spot depends on the transfer layout and how the material presents.
Can I have both?
Yes, and on higher-risk conveyors it is the sensible layout: a magnet removing the bulk of ferrous tramp continuously, and a detector downstream catching what the magnet cannot. The two do not fight each other. The magnet keeps the belt running by clearing the easy stuff without a stop, and the detector reserves its belt stops for the genuine problem items. Whether the extra cost of both is justified comes back to what a single item through your crusher would cost you.
How is each one serviced?
The two need different care, and both belong on a schedule.
A detector needs periodic sensitivity checks. We run a known metal test piece through on the belt to prove it still triggers at its coarse and fine settings, because a detector that has quietly drifted or failed gives false confidence, which is worse than none. This test-piece check is part of our routine service; see conveyor metal detector service.
A magnet is a mechanical inspection: the suspension and mounting, the condition of the magnet face, and on a self-cleaning unit the cleaning belt, its tracking and drive. A self-cleaning magnet has moving parts that wear, so it is not a fit-and-forget item.
What do you need to know to recommend one?
Before we quote a detector we survey the conveyor, because the answer depends on real numbers, not a guess. The questions we ask are:
- Belt width, idler spacing, conveyor angle, and belt speed.
- Whether it is a steel-cord belt, and whether the belt has metal splices or clips (both change the setup).
- The tramp catch size you want, meaning the smallest item that has to be caught.
- Maximum burden depth, maximum lump size, and the material's bulk density.
Our detector kit comes with a stainless steel enclosure. Those factors decide whether a detector protects your gear or spends the shift missing tramp and crying wolf. A magnet selection runs on similar numbers, with reach into the burden and tramp volume front of mind.
Frequently asked questions
Does a tramp metal detector remove the metal?
No. It detects and reacts (alarm, marker, or belt stop), and someone removes the item. A magnetic separator is the one that removes metal on its own.
Will a magnet catch digger teeth?
Often not. Manganese steel teeth are only weakly magnetic, and a magnet may not lift them, especially if they are bedded deep. That is a classic case for a detector as the backstop.
Do I need to stop the belt every time?
With a detector, catching an item usually means a stop so it can be removed by hand. A magnet avoids that for ferrous tramp by removing it continuously, which is much of why sites run both.